KR20240133652A - Polyimide-based film - Google Patents

Abstract

A laminated film comprising three or more layers of polyimide resin-containing layers,
A laminate (L) comprising two polyimide-based resin-containing layers that are positioned furthest from each other among the polyimide-based resin-containing layers constituting the above laminated film, and a layer positioned between the two polyimide-based resin-containing layers, is formed by the following formula (I):
AbsA/AbsB<4.00 (I)
[In formula (I), AbsA represents the absorbance of the laminate (L) at a wavelength of 465 nm, and AbsB represents the absorbance of the laminate (L) at a wavelength of 550 nm]
A laminated film that satisfies the requirements.

Description

Polyimide-based film {POLYIMIDE-BASED FILM}

The present invention relates to a laminated film comprising a polyimide-based resin-containing layer, particularly, a laminated film usable as a substrate material corresponding to a printed circuit board or antenna substrate for a high-frequency band, a laminated sheet comprising the laminated film, and a flexible printed circuit board.

Flexible printed circuit boards (hereinafter sometimes referred to as FPCs) are thin, lightweight, and flexible, and therefore allow for three-dimensional, high-density mounting, and are used in many electronic devices such as mobile phones and hard disks, contributing to their miniaturization and weight reduction. Conventionally, polyimide resins with excellent heat resistance, mechanical properties, and electrical insulation have been widely used in FPCs, and for example, a metal-clad laminate such as a copper-clad laminate (hereinafter sometimes referred to simply as CCL) used in FPCs, a laminate having a copper layer on one or both sides of a polyimide-based film, is known.

Recently, the fifth generation mobile communication system called 5G has been fully deployed (e.g., patent document 1), and polyimide films suitable for high-speed communication applications after 5G are being reviewed.

Japanese Patent Publication No. 2021-161285

Polyimide films used in FPCs may be subject to impact in the thickness direction of the film during processing, etc., and thus require a puncture strength that can withstand this. However, it is difficult to increase mechanical properties while controlling dielectric properties within an appropriate range. Therefore, there is a need to develop a polyimide film that has high puncture strength and can be used for high-speed communication applications after 5G.

An object of the present invention is to provide a polyimide-based laminated film having high puncture strength, a laminated sheet comprising the laminated film, and a flexible printed circuit board.

The inventors of the present invention have conducted extensive studies to solve the above-described problem and have found that the problem can be solved by controlling the absorbance of a polyimide-based resin-containing layer constituting a laminated film, thereby arriving at the present invention. That is, the present invention provides the following suitable embodiments.

[1] A laminated film comprising three or more layers of polyimide resin-containing layers,

Among the polyimide-based resin-containing layers constituting the above-mentioned laminated film, a laminate (L) comprising two polyimide-based resin-containing layers which are positioned furthest from each other and a layer positioned between the two polyimide-based resin-containing layers is formed by the following formula (I):

AbsA/AbsB<4.00 (I)

[In formula (I), AbsA represents the absorbance of the laminate (L) at a wavelength of 465 nm, and AbsB represents the absorbance of the laminate (L) at a wavelength of 550 nm]

A laminated film that satisfies the requirements.

[2] A laminated film comprising three or more layers of polyimide resin-containing layers,

Among the polyimide-based resin-containing layers constituting the above laminated film, a laminate (L) comprising two polyimide-based resin-containing layers which are positioned furthest from each other and a layer positioned between the two polyimide-based resin-containing layers is formed by the following formula (II):

AbsA-AbsB>0.016×T (II)

[In formula (II), AbsA represents the absorbance of the laminate (L) at a wavelength of 465 nm, AbsB represents the absorbance of the laminate (L) at a wavelength of 550 nm, and T represents the thickness (㎛) of the laminate (L)]

A laminated film that satisfies .

[3] A laminated film as described in [1] or [2], wherein the light transmittance of the laminate (L) at a wavelength of 600 nm is 60% or less.

[4] A laminated film according to any one of [1] to [3], wherein the thickness of the laminate (L) is 20 to 100 μm.

[5] At least one layer of polyimide-based resin-containing layer comprises a polyimide-based resin having a structural unit (A) derived from tetracarboxylic anhydride,

The above composition unit (A) is, formula (A1):

[In formula (A1), R ^a1 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom,

k represents an integer from 0 to 2]

A structural unit derived from tetracarboxylic anhydride represented by the formula (A1), and/or (A2):

[In formula (A2), R ^a2 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom, and l independently represents an integer from 0 to 3.]

A laminated film according to any one of [1] to [4], comprising a structural unit (A2) derived from tetracarboxylic anhydride represented by .

[6] At least one layer of polyimide-based resin-containing layer comprises a polyimide-based resin having a structural unit (B) derived from diamine,

The above composition unit (B) is, formula (B1):

[In formula (B1), R ^b1 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom,

W represents, independently of each other, a divalent linking group selected from the group consisting of -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -COO-, -OOC-, -SO-, -SO ₂ -, -S-, -CO-, -N(R ^c )-, and -CONH-, or a single bond (provided that m is 2 or more and at least one W is the divalent linking group), and R ^c represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom,

m represents an integer from 1 to 4,

q represents an integer from 0 to 4, independently of each other]

A laminated film according to any one of [1] to [5], comprising a structural unit (B1) derived from diamine represented by .

[7] The above laminate (L) includes a polyimide-based resin-containing layer (PI-2), a polyimide-based resin-containing layer (PI-1), and a polyimide-based resin-containing layer (PI-3) in this order, and the polyimide-based resin-containing layer (PI-1), the polyimide-based resin-containing layer (PI-2), and the polyimide-based resin-containing layer (PI-3) are, respectively, represented by Formula (A1):

[In formula (A1), R ^a1 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom,

k represents an integer from 0 to 2]

A structural unit derived from tetracarboxylic anhydride represented by the formula (A1), and/or (A2):

[In formula (A2), R ^a2 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom, and l independently represents an integer from 0 to 3.]

A laminated film according to any one of [1] to [6] above, comprising a polyimide-based resin having a structural unit (A2) derived from tetracarboxylic anhydride and a structural unit (B) derived from diamine.

[8] The laminate film described in [7] above, wherein the laminate (L) is a laminate (L1) composed of a polyimide-based resin-containing layer (PI-2), a polyimide-based resin-containing layer (PI-1), and a polyimide-based resin-containing layer (PI-3).

[9] The laminated film described in [8] above, wherein the thickness of the laminate (L1) is 20 to 100 μm, and further, the thicknesses of the polyimide-based resin-containing layer (PI-2) and the polyimide-based resin-containing layer (PI-3) are each 0.05 to 0.3 times the thickness of the polyimide-based resin-containing layer (PI-1).

[10] The above composition unit (B) is, formula (B1):

[In formula (B1), R ^b1 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom,

W represents, independently of each other, a divalent linking group selected from the group consisting of -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -COO-, -OOC-, -SO-, -SO ₂ -, -S-, -CO-, -N(R ^c )-, and -CONH-, or a single bond (provided that m is 2 or more and at least one W is the divalent linking group), and R ^c represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a hydrogen atom or a halogen atom,

m represents an integer from 1 to 4,

q represents an integer from 0 to 4, independently of each other]

A laminated film according to any one of [7] to [9], comprising a structural unit (B1) derived from diamine represented by .

[11] The polyimide resin contained in the polyimide resin-containing layer (PI-1) is formula (A3):

[In formula (A3), Z represents a divalent organic group,

R ^a3 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group or an aryloxy group which may have a halogen atom,

s represents an integer from 0 to 3, independently of each other]

A laminated film according to any one of [7] to [10], further comprising a structural unit (A3) derived from tetracarboxylic anhydride containing an ester bond represented by the following formula:

[12] The above composition unit (B) is, formula (B2):

[In formula (B2), R ^b2 independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group or aryloxy group which may have a halogen atom,

p represents an integer from 0 to 4]

A laminated film according to any one of [7] to [11], comprising a structural unit (B2) derived from a diamine containing a biphenyl skeleton represented by .

[13] A laminated film according to any one of [1] to [12], wherein the dielectric constant at 10 GHz is 0.0040 or less.

[14] A laminated sheet comprising a metal layer on one or both sides of the laminated film described in any one of [1] to [13] above.

[15] A flexible printed circuit board comprising the laminated sheet described in [14] above.

According to the present invention, it is possible to provide a polyimide-based laminated film having high puncture strength, a laminated sheet including the laminated film, and a flexible printed circuit board.

Fig. 1 is a schematic cross-sectional view showing an example of the layer configuration of the laminated film of the present invention.
Fig. 2 is a schematic cross-sectional view showing an example of the layer configuration of the laminated film of the present invention.

Hereinafter, embodiments of the present invention will be described in detail. In addition, the scope of the present invention is not limited to the embodiments described herein, and various changes can be made within a range that does not impair the spirit of the present invention.

[Laminated film]

The laminated film of the present invention comprises three or more polyimide-based resin-containing layers, and a laminate (L) comprising two polyimide-based resin-containing layers which are positioned furthest from each other among all polyimide-based resin-containing layers constituting the laminated film, and all layers positioned between the two polyimide-based resin-containing layers, wherein the laminated film is composed of the following formula (1):

AbsA/AbsB<4.00 (I)

[In formula (I), AbsA represents the absorbance of the laminate (L) at a wavelength of 465 nm, and AbsB represents the absorbance of the laminate (L) at a wavelength of 550 nm]

And/or, the following formula (II):

AbsA-AbsB>0.016×T (II)

[In formula (II), AbsA represents the absorbance of the laminate (L) at a wavelength of 465 nm, AbsB represents the absorbance of the laminate (L) at a wavelength of 550 nm, and T represents the thickness (㎛) of the laminate (L)]

Satisfies .

In the present invention, the polyimide-based resin-containing layer means a layer configured including a polyimide-based resin (hereinafter also referred to as PI-based resin), and the laminated film of the present invention contains three or more PI-based resin-containing layers. The laminated film of the present invention may be configured only with three or more PI-based resin-containing layers, and may further include, in addition to the PI-based resin-containing layers, other layers other than the PI-based resin-containing layers. Examples of the other layers include an adhesive layer for bonding PI-based resin-containing layers to each other, or a pressure-sensitive adhesive layer for bonding the PI-based resin-containing layer to a metal layer (e.g., a metal foil layer). The laminated film of the present invention, which is suitable for use as a printed circuit board or the like, is usually configured only with three or more PI-based resin-containing layers, or with three or more PI-based resin-containing layers and an adhesive layer for bonding them, and in one suitable embodiment, the laminated film of the present invention is configured only with three or more PI-based resin-containing layers, more preferably three layers.

In the above formula (I) or formula (II), the laminate (L), which serves as a reference for calculating each absorbance and thickness, is composed of two polyimide-based resin-containing layers which are positioned the furthest from each other among all polyimide-based resin-containing layers constituting the laminated film, and all layers positioned between the two polyimide-based resin-containing layers. Specifically, explaining based on the layer configuration shown in FIGS. 1 and 2, for example, as shown in FIG. 1, when the laminated film (1) is composed of three adjacent PI-based resin-containing layers (11), PI-based resin-containing layers (12), and PI-based resin-containing layers (13), the laminate (L) is composed of the three adjacent PI-based resin-containing layers (11), PI-based resin-containing layers (12), and PI-based resin-containing layers (13). In such a laminated film, the laminated film (1) is composed of the laminate (L). In addition, for example, as shown in Fig. 2, when the laminated film (1) is configured to include three PI-based resin-containing layers (11), PI-based resin-containing layers (12), and PI-based resin-containing layers (13) that are bonded to each other via an adhesive layer (14), the laminated body (L) is configured by two PI-based resin-containing layers (11) and PI-based resin-containing layers (13) that are positionally furthest from each other among all the PI-based resin-containing layers (11), PI-based resin-containing layers (12), and PI-based resin-containing layers (13) that constitute the laminated film (1), and a PI-based resin-containing layer (12) and two adhesive layers (14) that are positioned between the two PI-based resin-containing layers. In such a laminated film, the laminated film (1) is configured as the laminated body (L). In one embodiment of the present invention, the laminated film of the present invention is configured as the laminated body (L). In addition, the laminated film (1) shown in FIG. 1 and FIG. 2 can be laminated on a metal foil layer (21) to form a laminated sheet (2), respectively.

In one embodiment of the present invention, the laminated film of the present invention satisfies the above formula (1). That is, in the laminated film of the embodiment, the ratio (AbsA / AbsB) of the absorbance (AbsA) of the laminate (L) at a wavelength of 465 nm and the absorbance (AbsB) of the laminate (L) at a wavelength of 550 nm is less than 4.00. The laminated film of the present invention satisfying formula (I) has a high puncture strength. Furthermore, when formula (I) is satisfied, a laminated film having excellent dielectric properties and a low dielectric constant (hereinafter sometimes referred to as Df) and a low relative permittivity (hereinafter sometimes referred to as Dk) can be obtained. Thereby, the laminated film of the present invention can be a polyimide-based laminated film suitable for high-speed communication applications such as 5G, which require low transmission loss even in a high-frequency band that transmits high-frequency signals. The reason why such an effect is obtained is not necessarily clear, but can be inferred as follows. It is thought that the absorbance of the laminate (L) changes depending on the degree of crystallization or orientation of the PI resin in each PI resin-containing layer constituting the laminate (L), the presence or absence of branching of the resin, the amount of branching, and, further, when the PI resin-containing layers in the laminate (L) are in close contact with each other, the interaction between the PI resins constituting the adjacent PI resin layers at the interface, etc. In particular, the absorbance in the range of a wavelength of 465 nm to 550 nm reflects the intermolecular interaction of the PI resins in each PI resin-containing layer constituting the laminate (L), and in particular, the absorbance of an aromatic polyimide containing an aromatic tetracarboxylic acid compound and an aromatic diamine, particularly a wholly aromatic polyimide, is thought to be affected by the intermolecular charge transfer transition due to the interaction between polymer chains. In a laminate (L) including a PI-based resin-containing layer in which the interaction between such resin molecules is strengthened and the intermolecular distance is close to form a higher-order structure, the absorption band in the absorption spectrum of the laminate (L) becomes broad, and the end of the absorption band shifts to the long-wavelength side, so that the absorbance in the wavelength band of 465 nm to 550 nm increases overall, and since AbsB, which is on the long-wavelength side, increases more than AbsA, the value of AbsA/AbsB tends to decrease to a certain extent. Therefore, in a laminate (L) having a value of AbsA/AbsB of less than 4.00, it can be considered that the intermolecular interaction of the PI-based resin included in the PI-based resin-containing layer constituting it is strengthened, so that the distance between the resin molecules becomes close, thereby forming a higher-order structure in which the crystallinity and molecular orientation of the PI-based resin are appropriately increased. It is presumed that when each PI-based resin-containing layer is formed of a PI-based resin having a higher-order structure with an appropriately high degree of crystallinity or molecular orientation, the strength against an impact applied in the thickness direction of the PI-based resin-containing layer is improved, and the puncture strength of the laminated film including it is improved. In addition, since the PI-based resin can reduce the loss of electric energy due to rotational movement of polar groups in the PI-based resin, etc. by having a higher-order structure with an appropriate degree of crystallinity or orientation, it is presumed that Df is lowered and the dielectric properties are improved. In addition, even when the PI-based resin has an optimal branched structure, since the interaction between resin molecules becomes strong, the value of AbsA/AbsB of the laminate (L) tends to decrease to a certain extent, and the strengthening of the interaction between resin molecules can bring about an improvement in the puncture strength or a reduction in Df. In addition, between the PI-based resin-containing layers, since the PI-based resins of each resin layer are entangled with each other and the interaction becomes stronger, the end of the absorption band of the laminate (L) shifts to the long wavelength side, so that the value of AbsA/AbsB tends to decrease to a certain extent, and this also makes it possible to increase the puncture strength or reduce Df. Since the laminated film of the present invention is configured to include a plurality of PI-based resin-containing layers, it is thought that maintaining the AbsA/AbsB value of the laminate (L) including all of the PI-based resin-containing layers within a specific range, that is, controlling it to less than 4.00, leads to an improvement in the puncture strength of the laminated film or a reduction in Df.

The value of AbsA/AbsB of the laminate (L) is preferably 3.90 or less, more preferably 3.80 or less, still more preferably 3.70 or less, particularly preferably 3.60 or less, and is usually 1.80 or more, preferably 2.00 or more, more preferably 2.20 or more, still more preferably 2.50 or more, particularly preferably 2.80 or more. When the value of AbsA/AbsB is less than or equal to the upper limit described above, the interaction between the PI resin molecules contained in each PI resin-containing layer constituting the laminate (L) becomes stronger, so that the puncture strength of the laminated film can be increased. When the value of AbsA/AbsB is equal to or more than the lower limit described above, the flexibility of the laminated film can be increased. From the viewpoint of obtaining an even higher puncture strength, the value of AbsA/AbsB of the laminate (L) is preferably 2.96 or more, and may be 3.10 or more as the case may be. When a laminated film has high puncture strength, the impact resistance in the thickness direction of the film increases. This improves the handling properties of the laminated film during processing, and is advantageous in that it is difficult for defects to occur during operations such as when using it as a printed circuit board.

In another embodiment of the present invention, the laminated film of the present invention satisfies the above formula (II). As described above, the absorbance in the range of a wavelength of 465 nm to 550 nm is considered to reflect the intermolecular interaction of the PI resin in each PI resin-containing layer constituting the laminate (L), and in a laminate (L) including a PI resin-containing layer in which the intermolecular interaction is strong and the intermolecular distance is close to form a higher-order structure, the absorption band of the laminate (L) becomes broad and the end of the absorption band tends to shift to the long wavelength side. In an absorption spectrum exhibiting such behavior, since the absorbance in the wavelength band of a wavelength of 465 nm to 550 nm increases overall, the difference between the absorbance (AbsA) of the laminate (L) at a wavelength of 465 nm and the absorbance (AbsB) of the laminate (L) at a wavelength of 550 nm increases to a certain extent. When the thickness is the same, since, in general, the higher the absorbance, the higher the density of the higher-order structure, in a laminate (L) satisfying formula (II) that determines the difference between AbsA and AbsB in relation to the thickness, it can be considered that the PI-based resin constituting it forms a higher-order structure with a high density. Therefore, in a laminate (L) satisfying formula (II), the strength against an impact applied in the thickness direction of the PI-based resin-containing layer increases, so that the puncture strength of a laminate film including it is improved, or since the loss of electric energy due to the rotational motion of the polar group in the PI-based resin, etc. can be reduced, it can be considered that Df is lowered and the dielectric properties are improved. In addition, in a case where the laminate (L) satisfies formula (II), as in the laminate (L) satisfying formula (I), it can be considered that the PI-based resin has an optimal branched structure, or that the PI-based resins of each resin layer are entangled with each other between the PI-based resin-containing layers, thereby bringing about an improvement in the puncture strength or a reduction in Df.

In one embodiment of the present invention, the difference between the value of the left-hand side (AbsA-AbsB) and the value of the right-hand side (0.016 × T) in formula (II) is preferably 0.10 or more, more preferably 0.15 or more, more preferably 0.20 or more, still more preferably 0.25 or more, and particularly preferably 0.30 or more. In other words, the value of the left-hand side is preferably 0.10 or more, more preferably 0.15 or more, more preferably 0.20 or more, still more preferably 0.25 or more, and particularly preferably 0.30 or more larger than the value of the right-hand side. When the difference between the value of the left-hand side and the value of the right-hand side in formula (II) is equal to or larger than the lower limit described above, it becomes easy to cause interaction between the PI resin molecules included in each PI resin-containing layer constituting the laminate (L), thereby making it possible to improve the puncture strength of the laminated film or reduce Df. The upper limit of the difference between the values on the left side and the right side is not particularly limited, but is usually 1.0 or less, and from the viewpoint of increasing the flexibility of the laminated film, it is preferably 0.80 or less, more preferably 0.70 or less.

The value of the left side in formula (II) varies depending on the thickness of the laminate (L), but in one embodiment of the present invention, it is preferably 0.80 or more, more preferably 0.90 or more, and even more preferably 1.00 or more. When the difference between AbsA and AbsB is equal to or greater than the lower limit, it becomes easy to satisfy formula (II), and as a result of the strong interaction between the PI resin molecules constituting the laminate (L), an improvement in the puncture strength of the laminated film or a reduction effect of Df can be expected. The value of the left side in formula (II) is usually 2.0 or less, and from the viewpoint of increasing the flexibility of the laminated film, it is preferably 1.5 or less.

The present invention is directed to a laminated film satisfying either one of formula (I) or formula (II), but in one embodiment of the present invention, it is preferable that the laminated film of the present invention satisfies formula (I) and formula (II). A laminated film satisfying formula (I) or formula (II) has high puncture strength or dielectric properties as described above, but a laminated film satisfying both formulas (I) and (II) can easily realize even higher puncture strength or dielectric properties.

In one embodiment of the present invention, the absorbance (AbsA) of the laminate (L) at a wavelength of 465 nm is preferably 1.10 or more, more preferably 1.20 or more, further preferably 1.40 or more, and further preferably 2.50 or less, more preferably 2.20 or less, further preferably 2.00 or less. When AbsA is within the above range, it becomes easy to satisfy formula (I) and/or formula (II), and the interaction between the PI resin molecules contained in each PI resin-containing layer constituting the laminate (L) becomes stronger, whereby an improvement in the puncture strength of the laminated film or a reduction effect in Df can be expected, and furthermore, the flexibility of the laminated film can be increased.

In one embodiment of the present invention, the absorbance (AbsB) of the laminate (L) at a wavelength of 550 nm is preferably 0.30 or more, more preferably 0.40 or more, further preferably 0.45 or more, and may be more than 0.48 or 0.50 or more depending on the case, and further preferably 1.20 or less, more preferably 1.10 or less, further preferably 1.00 or less. When AbsB is within the above range, it becomes easy to satisfy formula (I) and/or formula (II), and the interaction between the PI resin molecules contained in each PI resin-containing layer constituting the laminate (L) becomes stronger, whereby an improvement in the puncture strength of the laminated film or a reduction effect in Df can be expected, and furthermore, the flexibility of the laminated film can be increased. From the viewpoint of obtaining an even higher puncture strength, AbsB may be 0.60 or less or 0.55 or less depending on the case.

The absorbances AbsA and AbsB in formulas (I) and (II) can be measured using, for example, an ultraviolet-visible-near-infrared spectrophotometer. Specifically, for example, they can be measured by the method described in the Examples described below. In addition, the thickness (T) of the laminate (L) in formula (II) can be obtained by, for example, measuring the cross-section of the laminate portion to be measured using a laser microscope or a thickness gauge, and specifically, for example, they can be measured by the method described in the Examples described below. Hereinafter, the same applies to the measurement of the thickness of each layer constituting the laminated film, laminated sheet, etc.

In the present invention, the thickness (T) of the laminate (L) can be appropriately determined depending on the configuration or application of the laminate film. In one embodiment of the present invention, the thickness of the laminate (L) is preferably 20 µm or more, more preferably 30 µm or more, and may be, for example, 35 µm or more or 40 µm or more, and further preferably 100 µm or less, more preferably 90 µm or less, and may be, for example, 85 µm or less or 80 µm or less. When the thickness of the laminate (L) is equal to or greater than the lower limit described above, it is easy to secure the required puncture strength and bending resistance in the laminate film. In addition, when the thickness of the laminate (L) is within the above range, since the Df is reduced and the puncture strength, bending resistance and flexibility can be improved, it is possible to obtain a laminate film having a well-balanced puncture strength suitable for a flexible printed circuit board and dielectric properties suitable for high-speed communication applications such as 5G.

In one embodiment of the present invention, from the viewpoint of improving the puncture strength or dielectric properties, it is preferable that AbsA and AbsB are each within the ranges of the upper and lower limits described above, and further, it is preferable that the thickness of AbsA and/or AbsB and the laminate (L) are each within the ranges described above.

The values of formula (I) and formula (II) can both be controlled by appropriately adjusting the types and configurations of the constituent units constituting the PI resin contained in each PI resin-containing layer of the laminate (L), the molecular weight of the PI resin, the configuration and combinations of the PI resin-containing layers in the laminate (L), the thickness of the laminate (L), and/or the manufacturing method, such as the coating conditions and imidization conditions in film formation. For example, based on preferable aspects advantageous to the improvement of the puncture strength described later or the reduction of Df, such as the preferable constituent units of the PI resin described later and their contents, the solvent included in the preferable PI resin precursor solution described later, the preferable imidization conditions described later, etc., the degree of crystallinity, orientation or branched structure of the PI resin constituting each PI resin-containing layer, the thickness of each PI resin-containing layer, the interaction between adjacent PI resin-containing layers, etc., can be controlled, thereby adjusting the absorbance of the laminate (L) in the specific wavelength band. In particular, by performing the drying conditions or temperature elevation conditions of the coating film in imidization according to the conditions for imidization described later, the absorbance of the laminate (L) in the wavelength range of 465 nm to 550 nm can be adjusted to control so as to satisfy Formula (I) and/or Formula (II). In addition to the imidization conditions, if the PI resin is not overly rigid and has a flexible structure with a certain degree of freedom, it is easy to cause orientation or branching of the resin during heating during imidization, so the absorbance of the specific wavelength band tends to have a relationship that satisfies formula (I) and/or formula (II).

In the present invention, the absorbance of the laminate (L) at a wavelength of 600 nm is preferably 0.20 or more, more preferably 0.25 or more, and even more preferably 0.30 or more. When the absorbance of the laminate (L) at a wavelength of 600 nm is equal to or greater than the lower limit described above, the crystallinity or molecular orientation of the PI resin in the PI resin-containing layer constituting the laminated film tends to increase, or the interaction of the resin molecules between the resin layers tends to increase, so that the puncture strength of the laminated film can be effectively increased. In addition, when the absorbance at a wavelength of 600 nm is equal to or greater than the lower limit described above, since the dielectric properties tend to improve, a laminated film having an excellent balance of dielectric properties and puncture strength can be obtained. The upper limit of the absorbance at 600 nm of the laminate (L) is usually 1.0 or less, and from the viewpoint of further increasing the stabbing intensity, it is preferably 0.80 or less, more preferably 0.70 or less, even more preferably 0.60 or less, and in some cases, it may be 0.48 or less or 0.40 or less.

The absorbance at 600 nm can be measured using an ultraviolet-visible-near-infrared spectrophotometer, similar to AbsA and AbsB.

In the present invention, the light transmittance of the laminate (L) at a wavelength of 600 nm is preferably 60% or less, more preferably 55% or less, and even more preferably 50% or less. When the light transmittance of the laminate (L) at a wavelength of 600 nm is equal to or less than the upper limit described above, the crystallinity or molecular orientation of the PI resin in the PI resin-containing layer constituting the laminated film tends to increase, or the interaction of the resin molecules between the resin layers tends to increase, so that the puncture strength of the laminated film can be effectively increased. In addition, when the light transmittance at a wavelength of 600 nm is equal to or less than the upper limit described above, since the dielectric properties tend to improve, a laminated film having an excellent balance of dielectric properties and puncture strength can be obtained. The lower limit of the light transmittance at 600 nm of the laminate (L) is not particularly limited, but from the viewpoint of further increasing the puncture strength, it is preferably 10% or more, more preferably 20% or more, even more preferably 30% or more, and in some cases, it may be 34% or more.

In the present invention, the light transmittance at a wavelength of 600 nm is calculated from the absorbance of the laminate (L) at 600 nm using the following formula:

Absorbance = -log(light transmittance)

It is calculated based on .

In the present invention, the absorption coefficient of the laminate (L) at a wavelength of 600 nm is preferably 4.0×10 ^-3 µm ^-1 or higher, more preferably 4.5×10 ^-3 µm ^-1 or higher, still more preferably 5.0×10 ^-3 µm ^-1 or higher, and particularly preferably 5.5×10 ^-3 µm ^-1 or higher. When the absorption coefficient of the laminate (L) at a wavelength of 600 nm is equal to or higher than the lower limit described above, the crystallinity or molecular orientation of the PI resin in the PI resin-containing layer constituting the laminated film tends to increase, or the interaction of the resin molecules between the resin layers tends to increase, so that the puncture strength of the laminated film can be effectively increased. In addition, since the dielectric properties tend to improve, a laminated film having an excellent balance of dielectric properties and puncture strength can be obtained. From the viewpoint of further increasing the piercing strength, the upper limit of the absorption coefficient at 600 nm of the laminate (L) is preferably 1.2×10 ^-2 µm ^-1 or less, more preferably 1.1×10 ^-2 µm ^-1 or less, even more preferably 1.0×10 ^-2 µm ^-1 or less, and in some cases may be 9.7×10 ^-3 µm ^-1 or less, 9.5×10 ^-3 µm ^-1 or less, or 8.7×10 ^-3 µm ^-1 or less.

In the present invention, the absorption coefficient at a wavelength of 600 nm is calculated from the absorbance of the laminate (L) at 600 nm using the following formula:

Absorption coefficient = absorbance / thickness of laminate (L) (μm)

It is calculated based on .

Hereinafter, a description will be given of a suitable configuration for controlling the absorbance in the range of wavelengths 465 nm to 550 nm in the laminate (L) to satisfy formula (I) and/or formula (II), thereby obtaining a laminate film having a high puncture strength, particularly preferably a laminate film having high puncture strength and dielectric properties suitable for high-speed communication applications such as 5G.

In addition, in this specification, dielectric properties mean dielectric properties such as Df and Dk, and increasing or improving the dielectric properties means decreasing Df and/or Dk. In addition, thermal properties may include CTE, glass transition temperature (hereinafter sometimes referred to as Tg), degree of thermal denaturation or deterioration, and increasing or improving thermal properties means, for example, decreasing CTE, increasing Tg, and/or decreasing thermal denaturation or deterioration.

In one embodiment of the present invention, a laminate (L) constituting a laminated film includes a polyimide-based resin-containing layer (PI-2), a polyimide-based resin-containing layer (PI-1), and a polyimide-based resin-containing layer (PI-3) in this order (hereinafter, the polyimide-based resin-containing layer (PI-1), the polyimide-based resin-containing layer (PI-2), and the polyimide-based resin-containing layer (PI-3) may be simply referred to as layer (PI-1), layer (PI-2), and layer (PI-3), respectively). For example, when this aspect is explained with reference to FIGS. 1 and 2, the PI-based resin-containing layer (11) corresponds to layer (PI-2), the PI-based resin-containing layer (12) corresponds to layer (PI-1), and the PI-based resin-containing layer (13) corresponds to layer (PI-3). In the present invention, the laminate (L) may include layers other than the layer (PI-1), the layer (PI-2), and the layer (PI-3) (hereinafter, sometimes referred to as other layers), but since the value of formula (I) in the laminate (L) can be easily controlled within a desired range, and even higher puncture strength and dielectric properties can be realized, it is preferable that the laminate is formed of the layers (PI-2), the layer (PI-1), and the layer (PI-3) which are adjacent to each other in this order, and the laminated film of the present invention is preferably formed only of the laminate (L) formed of the layers (PI-2), the layer (PI-1), and the layer (PI-3). In addition, examples of the layers other than the layer (PI-1), the layer (PI-2), and the layer (PI-3) include a pressure-sensitive adhesive layer formed of a polymer material such as an acrylic resin other than a PI resin, which is positioned between the layer (PI-2) and the layer (PI-1) and/or between the layer (PI-1) and the layer (PI-3). When layers other than the layer (PI-1), the layer (PI-2), and the layer (PI-3) are included, it is preferable that the other layers have a configuration that does not affect the absorbance or thickness when the laminate (L) is assumed to be composed of the layer (PI-2), the layer (PI-1), and the layer (PI-3) excluding the other layers, and specifically, the film thickness is preferably 1 µm or less, or the laminate is transparent. Hereinafter, a laminate (L) including the layer (PI-2), the layer (PI-1), and the layer (PI-3) in this order and formed so that these layers are adjacent to each other is sometimes described as a laminate (L1). The laminate (L1) is a suitable embodiment of the laminate (L), and unless otherwise specifically described, matters described as the laminate (L) are also suitable for the laminate (L1).

When the laminate (L) is a laminate (L1), the thickness can be appropriately determined depending on the configuration or application of the laminate film, but in one embodiment of the present invention, it is preferably 20 to 100 μm. When the thickness of the laminate (L1) is within the above range, the laminate film can have mechanical properties such as high puncture strength and flexibility suitable for flexible printed circuit boards, etc. In addition, since the Df of the laminate film can be reduced and the puncture strength can be improved, a laminate film having a well-balanced mechanical properties suitable for flexible printed circuit boards and dielectric properties suitable for high-speed communication applications such as 5G can be obtained. The thickness of the laminate (L1) is more preferably 25 μm or more, further preferably 30 μm or more, further preferably 35 μm or more, particularly preferably 40 μm or more, more preferably 90 μm or less, more preferably 85 μm or less, particularly preferably 80 μm or less.

In one embodiment of the present invention, the thicknesses of the layer (PI-2) and the layer (PI-3) are preferably 0.05 to 0.3 times the thickness of the layer (PI-1), respectively. When the thicknesses of the three layers in the laminate (L1) are in the above relationship, the laminated film can have mechanical properties such as high puncture strength and flexibility suitable for a flexible printed circuit board. In addition, since the Df of the laminated film can be reduced while the puncture strength can be improved, a laminated film having a well-balanced mechanical properties suitable for a flexible printed circuit board and dielectric properties suitable for high-speed communication applications such as 5G can be obtained. In particular, when the thickness of the laminate (L1) is 20 to 100 μm, and further, the thicknesses of the layer (PI-2) and the layer (PI-3) are 0.05 to 0.3 times the thickness of the layer (PI-1), the effect of the present invention can be more easily obtained. The thickness of the layer (PI-2) and the layer (PI-3) is preferably 0.08 times or more, more preferably 0.10 times or more, particularly preferably 0.12 times or more, and more preferably 0.25 times or less, more preferably 0.23 times or less, particularly preferably 0.20 times or less, relative to the thickness of the layer (PI-1), respectively.

In one embodiment of the present invention, the thickness of each PI-based resin-containing layer included in the laminate (L) is usually in the range of 0.5 to 100 μm, and may be appropriately determined depending on the function or use of each PI-based resin-containing layer. For example, in one embodiment of the present invention, the thickness of the layer (PI-1) is usually 5 μm or more, preferably 10 μm or more, more preferably 15 μm or more, more preferably 20 μm or more, and further preferably 60 μm or less, more preferably 55 μm or less, and further preferably 50 μm or less. In addition, the thicknesses of the layer (PI-2) and the layer (PI-3) are usually 0.5 μm or more, preferably 1 μm or more, more preferably 2 μm or more, more preferably 3 μm or more, and further preferably 4 μm or more, and further preferably 20 μm or less, more preferably 15 μm or less, more preferably 10 μm or less, and further preferably 8.5 μm or less. The thickness of layer (PI-2) and the thickness of layer (PI-3) may be the same or different from each other, but from the viewpoint of suppressing warping of the laminated film, preferably, one value is within a range of ±25% of the other value, more preferably, within a range of ±20%.

In the laminate (L) or the laminate (L1), it is preferable that at least one of the PI-based resin-containing layers containing at least three layers is a non-thermoplastic modified polyimide-based resin-containing layer (hereinafter, sometimes referred to as an mPI layer). The mPI layer is generally a PI-based resin-containing layer that is the main layer in a laminated film for use as a flexible printed circuit board. Furthermore, it is preferable that at least one layer, and preferably at least two layers, of the PI-based resin-containing layers containing at least three layers is a thermoplastic polyimide-based resin-containing layer (hereinafter, sometimes referred to as a TPI layer). The TPI layer is a layer that can also function as an adhesive layer that adheres the laminated film to a metal layer (for example, a metal foil layer such as copper foil), and is preferably positioned as the outermost layer in the laminated film that can come into contact with the metal layer, and the arrangement of the PI-based resin-containing layers containing three or more layers is preferably provided in this order: a TPI layer, an mPI layer, and a TPI layer. Therefore, in the laminate (L1), the layer (PI-1) is preferably an mPI layer, and the layers (PI-2) and (PI-3) are preferably TPI layers, respectively. When the laminate (L) or the laminate (L1) has such a layer configuration, improved thermal properties can be secured in the mPI layer, so that thermal denaturation or deterioration can be suppressed, and dimensional stability of the laminated film can be secured, and the adhesion to a metal layer (for example, a metal foil layer such as copper foil) can be improved by the TPI layer. In addition, by selecting the molecular structure of the PI resin in the mPI layer or the TPI layer, and controlling the imidization conditions, etc. in the production of the laminated film, the absorbance in the laminate (L), or the absorbance and thickness, can be controlled within a specific range (i.e., so as to satisfy formula (I) and/or formula (II)), a laminated film having excellent puncture strength and dielectric properties can be obtained.

When the laminate (L) includes multiple TPI layers or mPI layers, the configurations of the multiple included TPI layers or mPI layers may be the same or different. Furthermore, in the laminate (L1), the configurations of the layer (PI-1), the layer (PI-2), and the layer (PI-3) are usually different, but the configurations of the layer (PI-2) and the layer (PI-3) may be the same or different.

<PI resin>

In the laminated film of the present invention, the PI resin constituting each PI resin-containing layer can use any PI resin known in the art, as long as the PI resin-containing layer can be formed so that the absorbance in the range of 465 nm to 550 nm in the laminate (L) becomes the specific relationship described above. In the laminated film of the present invention, the PI resin constituting the PI resin-containing layer is a resin containing a repeating structural unit containing an imide group, and may contain a repeating structural unit containing both an imide group and an amide group.

In addition, in the present invention, a "non-thermoplastic" polyimide means a polyimide having a storage elastic modulus of 1.0×10 ⁹ Pa or more at 40°C and a storage elastic modulus of 1.0×10 ⁸ Pa or more at 300°C as measured using a dynamic viscoelasticity measuring device (DMA), and a "thermoplastic" polyimide means a polyimide having a storage elastic modulus of 1.0×10 ⁹ Pa or more at 40°C and a storage elastic modulus of less than 1.0×10 ⁸ Pa at 300°C.

In the present invention, the PI resin constituting each PI resin-containing layer preferably contains a structural unit (A) derived from tetracarboxylic anhydride and a structural unit (B) derived from diamine from the viewpoint of improving the puncture strength and dielectric properties of the laminated film. Furthermore, in the present invention, the “derived structural unit” means a “derived structural unit,” and for example, the “structural unit (A) derived from tetracarboxylic anhydride” means a “structural unit (A) derived from tetracarboxylic anhydride.” Furthermore, “the PI resin-containing layer contains the structural unit (A)” means that “the PI resin constituting the PI resin-containing layer contains the structural unit (A),” and the same applies to other structural units.

(Constituent unit derived from tetracarboxylic anhydride (A))

The structural unit (A) derived from tetracarboxylic anhydride (hereinafter, sometimes simply referred to as structural unit (A)) is, for example, formula (1):

[In formula (1), Y represents a tetravalent organic group]

It is preferable that the structural unit be derived from tetracarboxylic anhydride represented by .

In formula (1), Y independently represents a tetravalent organic group, preferably a tetravalent organic group having 4 to 40 carbon atoms, and more preferably a tetravalent organic group having 4 to 40 carbon atoms and having a cyclic structure. Examples of the cyclic structure include an alicyclic ring, an aromatic ring, and a heterocyclic ring structure. In the organic group, a hydrogen atom in the organic group may be replaced by a halogen atom, a hydrocarbon group, an alkoxy group, or a halogenated hydrocarbon group, and in that case, the carbon number of these groups is preferably 1 to 8. In the present invention, the PI resin may contain multiple types of Y, and the multiple types of Y may be the same as or different from each other. As Y, a group or structure represented by formulae (31) to (40); Examples thereof include groups in which hydrogen atoms in the groups represented by formulae (31) to (40) are substituted with a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a fluoro group, a chloro group or a trifluoromethyl group; tetravalent C1 to C8 chain hydrocarbon groups, etc.

[In formulas (31) to (33), R ¹⁹ to R ²⁶ and R ^23' to R ^26' independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and the hydrogen atoms included in R ¹⁹ to R ²⁶ and R ^23' to R ^26' may be independently substituted with a halogen atom,

V ¹ and V ² are, independently of each other, a single bond (except when e+d=1), -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, -S-, -CO-, -N(R ^j )-, or formula (a):

(In formula (a), R ²⁷ to R ³⁰ independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms,

D represents, independently of each other, a single bond, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ ,

i represents an integer from 1 to 3,

* indicates a combined hand)

Indicates,

R ^j represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with a hydrogen atom or a halogen atom,

e and d represent, independently of each other, integers from 0 to 2 (but e+d is not 0),

f represents an integer from 0 to 3,

g and h, independently of each other, represent integers from 0 to 4,

In equation (39), Z represents a divalent organic group,

R ^a3 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group or an aryloxy group which may have a halogen atom,

s represents an integer from 0 to 3, independently of each other,

In formula (40), R ^a2 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom,

l represents an integer from 0 to 3, independently of each other,

* indicates a combined hand]

In the present invention, from the viewpoint of improving the puncture strength, dielectric properties, thermal properties, etc. of the laminated film, the PI resin constituting each PI resin layer preferably contains, as Y in formula (1), at least one structure selected from the group consisting of structures represented by formulas (31), (32), (33), (39), and (40), more preferably at least one structure selected from the group consisting of structures containing a benzene skeleton, and even more preferably at least one structure selected from the group consisting of structures represented by formulas (32), (39), and (40).

In formulas (31) to (33), R ¹⁹ to R ²⁶ and R ^23' to R ^26' are, independently of each other, preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and even more preferably a hydrogen atom.

In formula (31), V ¹ and V ² independently represent preferably a single bond (except when e+d=1), -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ - or -CO-, and more preferably a single bond (except when e+d=1), -O-, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -.

In formula (31), e and d independently represent preferably 0 or 1 (provided that e+d is not 0). In addition, e+d preferably represents 1. In addition, in formula (31), when e is 0, it represents that the two benzene rings are not bonded as V ¹ , and when d is 0, it represents that the two benzene rings are not bonded as V ² .

In equations (32) and (33), f preferably represents 0 or 1, more preferably 0.

In equation (33), g and h independently represent an integer of preferably 0 to 2, more preferably 0 or 1. In addition, g+h preferably represents an integer of 0 to 2. In addition, when f is 1 or more, a plurality of g and h may be the same or different, independently of each other.

In formula (a), R ²⁷ to R ³⁰ independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, more preferably a hydrogen atom. i is preferably 1 or 2, and when i is 2 or more, a plurality of Ds and R ²⁷ to R ³⁰ independently may be the same or different.

In formula (39), Z preferably represents a divalent organic group having 4 to 40 carbon atoms, more preferably a divalent organic group having 4 to 40 carbon atoms having a cyclic structure, even more preferably a divalent organic group having 4 to 40 carbon atoms having an aromatic ring, and particularly preferably a divalent organic group having formulas (z1), (z2) and (z3):

[In formulas (z1) to (z3), R ^z11 to R ^z14 independently represent a hydrogen atom or a monovalent hydrocarbon group which may have a halogen atom, R ^z2 independently represents a monovalent hydrocarbon group which may have a halogen atom, n represents an integer from 1 to 4, j independently represents an integer from 0 to 3, and * represents a bond.]

It represents a divalent organic group selected from the group consisting of, and more preferably, it represents a divalent organic group represented by formula (z1).

In formula (z1), R ^z11 to R ^z14 independently represent, preferably, a hydrogen atom, an alkyl group which may have a halogen atom, more preferably a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, more preferably a hydrogen atom, or an alkyl group having 1 to 3 carbon atoms which may have a halogen atom, and particularly preferably a hydrogen atom. In the benzene ring having R ^z11 to R ^z14 in formula (z1), at least one of R ^z11 to R ^z14 may be a monovalent hydrocarbon group which may have a halogen atom, but it is particularly preferable that R ^z11 to R ^z14 are all hydrogen atoms.

In formula (z1), n is preferably an integer of 1 to 3, more preferably 1 or 2, and particularly preferably 2.

In formula (z2), R ^z2 independently represents an alkyl group which may preferably have a halogen atom, more preferably an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, and even more preferably an alkyl group having 1 to 3 carbon atoms which may have a halogen atom.

In equation (z2), j is preferably 0 or 1, independently of one another, more preferably 0, and even more preferably, all j are 0.

In formula (39), R ^a3 preferably represents, independently of one another, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

The hydrogen atoms contained in R ^a3 may be independently substituted with halogen atoms, and among these, R ^a3 independently represents an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms.

In equation (39), s preferably represents an integer of 0 to 2, independently of each other, more preferably 0 or 1.

In formula (40), R ^a2 preferably represents, independently of one another, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

The hydrogen atoms contained in R ^a2 may be independently substituted with halogen atoms, and among these, as R ^a2 , an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, can be exemplified.

In equation (40), l preferably represents an integer of 0 to 2, more preferably 0 or 1, independently of each other.

Specific examples of the structures represented by formulas (31) to (33), (39), and (40) include structures represented by formulas (41) to (56). In addition, in these formulas, * represents a bond.

In one embodiment of the present invention, when the PI resin constituting the PI resin-containing layer includes at least one selected from the group consisting of structures represented by formulas (31) to (33), formula (39), and formula (40) as Y in formula (1), the proportion of the structural unit derived from tetracarboxylic anhydride represented by at least one selected from the group consisting of structures represented by formulas (31) to (33), formula (39), and formula (40), particularly the proportion of the structural unit derived from tetracarboxylic anhydride represented by at least one selected from the group consisting of structures represented by formulas (32), formula (39), and formula (40) as Y in formula (1) is preferably 30 mol% or more, more preferably 50 mol% or more, further preferably 70 mol% or more, particularly preferably 90 mol% or more, relative to the total amount of the structural unit (A), and preferably It is 100 mol% or less. When the ratio is within the above range, it is advantageous in improving the puncture strength and dielectric properties of the laminated film.

The ratio of the above-mentioned constituent units can be measured, for example, using ¹ H-NMR, or can be calculated from the introduction ratio of raw materials. Hereinafter, the same applies to the calculation of the ratio of the constituent units of PI resin. In addition, in this specification, the "total amount" of the constituent units indicates the amount of the unit when the constituent unit is composed of one unit, and indicates the sum of the units when the constituent unit is composed of two or more units.

<Composition Unit (A1) and Composition Unit (A2)>

In one embodiment of the present invention, the PI resin constituting at least one PI resin-containing layer comprises a constituent unit (A), and the constituent unit (A) is represented by formula (A1):

[In formula (A1), R ^a1 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom,

k represents an integer from 0 to 2]

A structural unit (A1) derived from tetracarboxylic anhydride represented by formula (A2): (hereinafter, sometimes abbreviated simply as structural unit (A1)), and/or

[In formula (A2), R ^a2 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom, and l independently represents an integer from 0 to 3.]

It is preferable to include a structural unit (A2) derived from tetracarboxylic anhydride represented by (hereinafter, it is sometimes simply referred to as structural unit (A2)).

When the PI resin contains the constituent unit (A) and the constituent unit (A1) and/or the constituent unit (A2), it becomes easy to control the absorbance of the PI resin-containing layer or laminate (L) containing the PI resin within a desired range in a specific wavelength band, so that the puncture strength and dielectric properties of the laminated film can be improved. In addition, since the CTE of the laminated film tends to decrease, improvement in the dimensional stability of the laminated film can be expected.

From the viewpoint of improving the puncture strength, dielectric properties or CTE, etc., in formulas (A1) and (A2), R ^a1 and R ^a2 are preferably, independently of each other, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms.

Examples of alkyl groups having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 2-methyl-butyl group, a 3-methyl-butyl group, a 2-ethyl-propyl group, and an n-hexyl group.

Examples of alkoxy groups having 1 to 6 carbon atoms include a methoxy group, an ethoxy group, a propyloxy group, an isopropyloxy group, an n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group, and a cyclohexyloxy group.

Examples of aryl groups having 6 to 12 carbon atoms include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a biphenyl group.

The hydrogen atoms contained in R ^a1 and R ^a2 may be independently substituted with halogen atoms, and examples of the halogen atoms include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among these, R ^a1 and R ^a2 are preferably, independently, an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms.

The bonding positions of the two carboxylic anhydrides bonded to the benzene ring in formula (A1) are not particularly limited, but from the viewpoint of improving the puncture strength, dielectric properties, CTE, etc., the 1,2-position and the 4,5-position are preferable, or the 1,2-position and the 3,4-position, and the 1,2-position and the 4,5-position are more preferable. k is preferably 0 or 1, and more preferably 0.

The bonding positions of the two carboxylic anhydrides bonded to the benzene rings constituting the biphenyl skeleton in formula (A2) are not particularly limited, and may be independently 3,4- or 2,3- based on the single bond bonding the two benzene rings, and from the viewpoint of improving the puncture strength, dielectric properties, CTE, etc., it is preferable that it is 3,4-.

In formula (A2), l is independently an integer of preferably 0 to 2, more preferably 0 or 1, and even more preferably 0.

In a preferred embodiment of the present invention, formula (A1) is formula (A1-1):

is a structural unit (A1-1) represented by. In addition, in another suitable embodiment of the present invention, formula (A2) is represented by formula (A2-1):

The constituent unit (A2-1) is represented by . When the PI resin contains the constituent unit (A1-1) and/or the constituent unit (A2-1) as the constituent unit (A), the absorbance in the PI resin-containing layer or laminate (L) containing the PI resin becomes easy to control within a desired range in a specific wavelength band, which is advantageous in improving the puncture strength or dielectric properties of the laminated film. In addition, since the CTE of the laminated film tends to decrease, improvement in the dimensional stability of the laminated film can be expected.

In one embodiment of the present invention, it is preferable that the PI resin-containing layer constituting the laminated film includes any one or more of the following configurations.

· In all PI-based resin-containing layers of the laminated film, the PI-based resin contains at least one of the constituent unit (A1) and the constituent unit (A2);

· In all PI-based resin-containing layers in the laminated film, each PI-based resin contains a constituent unit (A1);

· At least one PI-based resin-containing layer of the laminated film, preferably a TPI layer, wherein the PI-based resin comprises a constituent unit (A1) and a constituent unit (A2);

· In at least one PI-based resin-containing layer of the laminated film, preferably in the TPI layer, the PI-based resin comprises the constituent unit (A1) and the constituent unit (A2), and further, in at least one other PI-based resin-containing layer, preferably in the mPI layer, the PI-based resin comprises the constituent unit (A1) and/or the constituent unit (A2).

· In at least one PI-based resin-containing layer of the laminated film, preferably a TPI layer, the PI-based resin contains the constituent unit (A1) and the constituent unit (A2), and further, in at least one other PI-based resin-containing layer, preferably an mPI layer, the PI-based resin contains the constituent unit (A1) but substantially does not contain the constituent unit (A2).

In addition, in this specification, “substantially does not include” means that the total amount of all constituent units constituting the PI resin is 0.5 mol% or less. The same applies to other constituent units, unless otherwise specifically stated.

In one embodiment of the present invention, when the PI resin contains the structural unit (A1) and/or the structural unit (A2), the content thereof is preferably 10 mol% or more, more preferably 15 mol% or more, more preferably 20 mol% or more, particularly preferably 25% or more, and particularly preferably 30 mol% or more, based on the total amount of the structural unit (A), and further preferably 90 mol% or less, more preferably 85 mol% or less, more preferably 80 mol% or less, particularly preferably 75 mol% or less, and particularly preferably 70 mol% or less. When the contents of the structural unit (A1) and the structural unit (A2) are each in the above range, it becomes easy to control the absorbance of the PI resin-containing layer or laminate (L) containing the PI resin within a desired range in a specific wavelength band, which is advantageous in improving the puncture strength and dielectric properties of the laminated film. In addition, since the CTE of the laminated film tends to decrease, improvement in the dimensional stability of the laminated film can be expected.

In addition, in one embodiment of the present invention, when the PI resin contains the structural unit (A1) and the structural unit (A2), the content ratio (molar ratio, (A1):(A2)) is preferably 10:90 to 90:10, more preferably 20:80 to 80:20, and even more preferably 25:75 to 50:50. When the content ratio of the structural unit (A1) and the structural unit (A2) is within the above range, the effects of the present invention expected by the PI resin having the structural unit (A1) and/or the structural unit (A2) are easily obtained, and furthermore, the effects can be further enhanced.

<Composition Unit (A3)>

In one embodiment of the present invention, the PI resin contained in at least one PI resin-containing layer constituting the laminated film of the present invention is, as a constituent unit (A), formula (A3):

[In formula (A3), Z represents a divalent organic group,

R ^a3 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group or an aryloxy group which may have a halogen atom,

s represents an integer from 0 to 3, independently of each other]

It may contain a structural unit (A3) derived from a tetracarboxylic anhydride containing an ester bond represented by (hereinafter, simply referred to as structural unit (A3)).

When the PI resin contains the constituent unit (A3) as the constituent unit (A), it becomes easy to control the absorbance of the PI resin-containing layer or laminate (L) containing the PI resin within a desired range in a specific wavelength band, which can be advantageous in improving the puncture strength or dielectric properties of the laminated film. In addition, since the CTE of the laminated film tends to decrease, improvement in the dimensional stability of the laminated film can be expected. In addition, since the puncture strength and dielectric properties can be improved even at a relatively low imidization temperature (for example, 360°C or less), even when the PI resin precursor film is thermally imidized in a laminated configuration with a metal layer (for example, a metal foil layer such as copper foil), deterioration of the surface of the metal layer can be suppressed, and a laminated sheet having high puncture strength and excellent high-frequency properties can be obtained.

As R ^a3 in formula (A3), the same groups as those exemplified as R ^a3 in formula (39) described above can be mentioned, and the suitable modes are also the same.

In formula (A3), s independently represents preferably 0 or 1, more preferably 0.

As Z in formula (A3), the same divalent organic group as that exemplified as Z in formula (39) described above can be exemplified, and the suitable mode is also the same.

In a preferred embodiment of the present invention, formula (A3) is preferably a structural unit (A3-1) represented by formula (A3-1) or a structural unit (A3-2) represented by formula (A3-2).

If the PI resin constituting at least one PI resin-containing layer constituting the laminated film contains, as the constituent unit (A), the constituent unit (A3-1) and/or the constituent unit (A3-2), the absorbance in the PI resin-containing layer or laminate (L) containing the PI resin can be easily controlled within a desired range in a specific wavelength band, which can be advantageous in improving the puncture strength or dielectric properties of the laminated film. In addition, since the CTE of the laminated film tends to decrease, improvement in the dimensional stability of the laminated film can be expected. In addition, since the puncture strength and dielectric properties can be improved even at a relatively low imidization temperature (for example, 360°C or lower), even when the PI resin precursor coating film is thermally imidized in a laminated configuration with a metal layer (for example, a metal foil layer such as copper foil), deterioration of the surface of the metal layer can be suppressed, and a laminated sheet having high puncture strength and excellent high-frequency properties can be obtained.

In one embodiment of the present invention, when the PI resin constituting at least one PI-based resin-containing layer, preferably the mPI layer, contains a structural unit (A3) as the structural unit (A), particularly the structural unit (A3-1) and/or the structural unit (A3-2), the PI-based resin can have a flexible structure with a certain degree of freedom without being excessively rigid, so that a branched structure can be easily formed by heating during imidization, and the puncture strength of the laminated film can be further improved. In addition, the Df of the laminated film tends to be further reduced, and the CTE tends to be reduced, so that the dimensional stability of the laminated film tends to be improved.

In one embodiment of the present invention, when the PI resin contains the structural unit (A3), the content thereof is preferably 3 mol% or more, more preferably 5 mol% or more, further preferably 7 mol% or more, even more preferably 10 mol% or more, particularly preferably 20 mol% or more, particularly more preferably 30 mol% or more, and particularly more preferably 40 mol% or more, and further preferably 80 mol% or less, more preferably 70 mol% or less, further preferably 65 mol% or less, and particularly preferably 60 mol% or less. When the content of the structural unit (A3) is within the above range, the effects of the present invention expected by the PI resin having the structural unit (A3) can be easily obtained, and furthermore, the effects can be further enhanced.

In another embodiment of the present invention, the content of the structural unit (A3) in the structural unit (A) of the PI-based resin, particularly at least the PI-based resin contained in the PI-based resin-containing layer (PI-1), may be preferably 45 mol% or less (0 to 45 mol%) relative to the total amount of the structural unit (A). That is, in this embodiment, the structural unit (A) of the PI-based resin may or may not contain the structural unit (A3), and when it contains the structural unit (A3), the amount is preferably 45 mol% or less. In addition, the content of the structural unit (A3) is more preferably 35 mol% or less, further preferably 25 mol% or less, further preferably 15 mol% or less, particularly preferably 5 mol% or less, and particularly more preferably 1 mol% or less, relative to the total amount of the structural unit (A), and the lower limit may be 0 mol%. When the content of the constituent unit (A3) in the PI resin, particularly the constituent unit (A3-1) and/or the constituent unit (A3-2), is below the upper limit, the CTE of the laminated film tends to decrease, and improvement in the dimensional stability of the laminated film can be expected.

In one embodiment of the present invention, in at least one PI-based resin-containing layer constituting the laminated film, preferably a TPI layer, the PI-based resin preferably contains a structural unit (A1) and a structural unit (A2), and further, in at least one other PI-based resin-containing layer, preferably an mPI layer, the PI-based resin preferably contains at least two kinds of structural units selected from the structural unit (A1), the structural unit (A2) and the structural unit (A3), more preferably containing the structural unit (A1) and the structural unit (A2) and/or the structural unit (A3), and even more preferably containing the structural unit (A1) and the structural unit (A3). When the PI-based resin-containing layer, for example, an mPI layer, contains the structural unit (A1) and the structural unit (A3), the structural unit (A2) may not substantially be included.

In a preferred embodiment of the present invention, in the laminate (L1), it is preferred that in at least one, and preferably both, of the layer (PI-2) and the layer (PI-3), the PI-based resin comprises a structural unit (A1) and a structural unit (A2). Furthermore, in the laminate (L1), it is preferred that in the layer (PI-1), the PI-based resin comprises at least two kinds of structural units selected from the structural unit (A1), the structural unit (A2) and the structural unit (A3), more preferably comprises the structural unit (A1) and the structural unit (A2) and/or the structural unit (A3), and even more preferably comprises the structural unit (A1) and the structural unit (A3). When the layer (PI-1) comprises the structural unit (A1) and the structural unit (A3), it need not substantially comprise the structural unit (A2).

<Composition Unit (A4)>

In one embodiment of the present invention, the PI resin may contain, as a constituent unit (A), a constituent unit (A4) derived from tetracarboxylic anhydride other than the constituent unit (A1), the constituent unit (A2), and the constituent unit (A3) (hereinafter, the term may be simply abbreviated as the constituent unit (A4)).

In addition, in the present specification, “a structural unit (A4) derived from tetracarboxylic anhydride other than the structural unit (A1), the structural unit (A2), and the structural unit (A3)” means a structural unit derived from tetracarboxylic anhydride that does not correspond to any of the structural units (A1), (A2), and (A3), and “content of the structural unit (A4)” means the total amount of the structural units (A4) when there are multiple structural units (A4).

In one embodiment of the present invention, as the structural unit (A4), for example, Y in formula (1) is a structural unit derived from tetracarboxylic anhydride represented by formula (31), formulas (33) to (38). From the viewpoint of improving the puncture strength or dielectric properties of the laminated film, preferably, Y in formula (1) is a structural unit derived from tetracarboxylic anhydride represented by formula (42), formulas (44) to (49), or formula (53), more preferably, Y in formula (1) is a structural unit derived from tetracarboxylic anhydride represented by formula (42), formula (46), formula (49), or formula (53).

In one embodiment of the present invention, when the PI resin includes a structural unit (A4), the content thereof may be, for example, 0.01 to 55 mol%, or 0.01 to 40 mol%, based on the total amount of the structural unit (A), preferably 40 mol% or less, more preferably 35 mol% or less, even more preferably 30 mol% or less, and particularly preferably 25 mol% or less, and furthermore, usually 0.01 mol% or more, preferably 10 mol% or more.

(Diamine derived structural unit (B))

The PI resin constituting each PI resin-containing layer usually contains a constituent unit (B) derived from diamine (hereinafter, sometimes abbreviated simply as constituent unit (B)). The constituent unit (B) is, for example, represented by formula (2):

[In formula (2), X represents a divalent organic group]

It is preferable that the structural unit is a diamine-derived unit represented by .

In formula (2), X represents a divalent organic group, and preferably a divalent organic group having 2 to 100 carbon atoms. Examples of the divalent organic group include a divalent aromatic group, a divalent aliphatic group, and the like, and examples of the divalent aliphatic group include a divalent acyclic aliphatic group or a divalent cyclic aliphatic group. Among these, from the viewpoint of improving the puncture strength or dielectric properties of the laminated film, a divalent cyclic aliphatic group and a divalent aromatic group are preferable, and a divalent aromatic group is more preferable. In the divalent organic group, a hydrogen atom in the organic group may be replaced by a halogen atom, a hydrocarbon group, an alkoxy group, or a halogenated hydrocarbon group, and in such a case, the carbon number of these groups is preferably 1 to 8. In addition, in the present specification, a divalent aromatic group is a divalent organic group having an aromatic group, and may include an aliphatic group or other substituents in part of its structure. In addition, a divalent aliphatic group is a divalent organic group having an aliphatic group, and may include other substituents in part of its structure, but does not include an aromatic group.

In one embodiment of the present invention, the PI resin may include a plurality of types of X, and the plurality of types of X may be the same or different from each other. As X in formula (2), examples thereof include groups (structures) represented by formulas (60) to (65); groups in which a hydrogen atom in a group represented by formulas (60) to (65) is substituted with a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a fluoro group, a chloro group or a trifluoromethyl group.

[In formula (60) and formula (61), R ^a and R ^b independently represent a halogen atom, or an alkyl group, an alkoxy group, an aryl group or an aryloxy group which may have a halogen atom, and the hydrogen atoms included in R ^a and R ^b may independently be substituted with a halogen atom,

W represents, independently of each other, a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -COO-, -OOC-, -SO-, -SO ₂ -, -S-, -CO-, -N(R ^c )- or -CONH-, and R ^c represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a hydrogen atom or a halogen atom,

t' represents an integer from 0 to 4, u represents an integer from 0 to 4, n represents an integer from 0 to 4,

In formula (62), ring A represents a cycloalkane ring having 3 to 8 carbon atoms,

R ^d represents an alkyl group having 1 to 20 carbon atoms,

r is an integer greater than or equal to 0 and less than or equal to (the number of carbon atoms in ring A - 2),

S1 and S2, independently of each other, represent integers from 0 to 20,

In equations (60) to (65), * indicates a bond.]

Other examples of X in formula (2) include divalent acyclic aliphatic groups, such as straight-chain or branched-chain alkylene groups, such as ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, propylene, 1,2-butanediyl, 1,3-butanediyl, 1,12-dodecanediyl, 2-methyl-1,2-propanediyl, and 2-methyl-1,3-propanediyl. In the divalent acyclic aliphatic group, a hydrogen atom may be replaced by a halogen atom, and a carbon atom may be replaced by a heteroatom, such as an oxygen atom, a nitrogen atom, or the like.

Among these, from the viewpoint of improving the puncture strength or dielectric properties of the laminated film, the PI resin in the present invention preferably contains structures represented by formulas (60) and (61) as X in formula (2), and more preferably contains a structure represented by formula (60).

In formulas (60) and (61), the bond of each benzene ring or each cyclohexane ring may be bonded at any of the ortho-position, the meta-position, the para-position, the α-position, the β-position, or the γ-position, based on -W- or the single bond connecting each benzene ring or each cyclohexane ring, and from the viewpoint of improving the puncture strength or dielectric properties of the laminated film, it is preferably bonded at the meta-position or the para-position, or the β-position or the γ-position, more preferably the para-position or the γ-position. When the amino group directly connected to the benzene ring and the divalent linking group -W- are at the meta-position, the flexibility of the polyimide molecular chain tends to improve.

In formulas (60) and (61), R ^a and R ^b are, independently of each other, preferably a halogen atom, or an alkyl group, an alkoxy group or an aryl group which may have a halogen atom, more preferably a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above. The hydrogen atoms contained in R ^a and R ^b may be independently substituted with a halogen atom, and examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. It is preferred that R ^a and R ^b are, independently of each other, an alkyl group having 1 to 6 carbon atoms or a fluorinated alkyl group having 1 to 6 carbon atoms, and from the viewpoint of adhesion to a metal layer or the like, an alkyl group having 1 to 6 carbon atoms that does not contain fluorine is more preferred, an alkyl group having 1 to 3 carbon atoms that does not contain fluorine is even more preferred, and a methyl group is particularly preferred.

In equations (60) and (61), t' and u are, independently of each other, preferably integers of 0 to 2, more preferably 0 or 1.

In formulas (60) and (61), W is, independently of one another, preferably a single bond, -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, -S-, -COO-, -OOC- or -CO-, more preferably a single bond, -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -COO-, -OOC- or -CO-, even more preferably a single bond, -O-, -CH ₂ - or -C(CH ₃ ) ₂ -, and particularly preferably -O- or -C(CH ₃ ) ₂ -.

In formulas (60) and (61), n is preferably an integer from 0 to 3, more preferably from 1 to 3. When n is 2 or more, a plurality of W, R ^a , and t' may be the same or different, and the positions of the bonds of each benzene ring based on -W- may also be the same or different.

In the case where the PI resin in the present invention includes two or more structures represented by either formula (60) or formula (61) as X in formula (2), W, n, R ^a , R ^b , t' and u in one formula (60) and formula (61) may be independently the same as or different from W, n, R ^a , R ^b , t' and u in the other formula (60) and formula (61).

In formula (62), examples of the cycloalkane ring having 3 to 8 carbon atoms represented by ring A include a cyclopropane ring, a cyclobutane ring, a cyclopentane ring, a cyclohexane ring, a cycloheptane ring, and a cyclooctane ring, and preferably a cycloalkane ring having 4 to 6 carbon atoms. In ring A, each bond may or may not be adjacent to each other. For example, when ring A is a cyclohexane ring, two bonds may be in a positional relationship at the α-position, β-position, or γ-position, and preferably they may be in a positional relationship at the β-position or γ-position.

In formula (62), R ^d is preferably an alkyl group having 1 to 10 carbon atoms. In formula (62), r is preferably 0 or more, and preferably 4 or less. In formula (62), S1 and S2 are each independently preferably 0 or more, more preferably 2 or more, and preferably 15 or less.

As specific examples of the structures represented by formulas (60) to (62), for example, structures represented by formulas (71) to (92) can be cited. In addition, in these formulas, * represents a bond.

In one embodiment of the present invention, when the PI resin constituting the PI resin-containing layer contains at least one diamine-derived structural unit represented by formulas (60) and (61) as X in formula (2), the proportion of the diamine-derived structural unit represented by formulas (60) and (61) in X in formula (2) is preferably 30 mol% or more, more preferably more than 50 mol%, further preferably 70 mol% or more, particularly preferably 90 mol% or more, and preferably 100 mol% or less, with respect to the total amount of the structural unit (B). When the proportion of the diamine-derived structural unit represented by formulas (60) and (61) in X in formula (2) is within the above range, the absorbance of the PI resin-containing layer or laminate (L) including the PI resin can be easily controlled within a desired range in a specific wavelength band, whereby the puncture strength and dielectric properties of the laminated film can be enhanced. In addition, since the CTE of the laminated film tends to decrease, improvement in the dimensional stability of the laminated film can be expected.

<Composition Unit (B1)>

In one embodiment of the present invention, at least one PI-based resin-containing layer comprises a PI-based resin having a diamine-derived structural unit (B), wherein the structural unit (B) is represented by formula (B1):

[In formula (B1), R ^b1 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom,

W represents, independently of each other, a divalent linking group selected from the group consisting of -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -COO-, -OOC-, -SO-, -SO ₂ -, -S-, -CO-, -N(R ^c )-, and -CONH-, or a single bond (provided that m is 2 or more and at least one W is the divalent linking group), and R ^c represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a hydrogen atom or a halogen atom,

m represents an integer from 1 to 4,

q represents an integer from 0 to 4, independently of each other]

It is preferable to include a diamine-derived structural unit (B1) represented by (hereinafter, simply, it may be abbreviated as structural unit (B1)).

When the PI resin contains the constituent unit (B1) as the constituent unit (B), it becomes easy to control the absorbance of the PI resin-containing layer or laminate (L) containing the PI resin within a desired range in a specific wavelength band, so that the puncture strength and dielectric properties of the laminated film can be improved. In addition, since the CTE can be reduced, improvement in the dimensional stability of the laminated film can be expected, and it can also contribute to improvement in the adhesion to the metal layer. In addition, since the puncture strength and dielectric properties of the obtained laminated film can be improved even at a relatively low imidization temperature (for example, 360°C or lower), even when the PI resin precursor coating film is thermally imidized in a laminated configuration with a metal layer (for example, a metal foil layer such as copper foil), deterioration of the surface of the metal layer can be suppressed, so that a laminated sheet having high puncture strength and excellent high-frequency characteristics can be obtained.

As R ^b1 in formula (B1), the same groups as those exemplified as R ^a and R ^b in formula (60) described above can be exemplified. q in formula (B1) is, independently of each other, preferably an integer of 0 to 2, more preferably 0 or 1. Furthermore, m in formula (B1) is, from the viewpoint of improving the puncture strength, dielectric properties, CTE, etc. of the laminated film, preferably an integer of 1 to 3, more preferably 2 or 3. In formula (b2), a plurality of W, R ^b2 , and q may be the same as or different from each other, and the positions of -W- with respect to -NH ₂ of each benzene ring may be the same or different.

In formula (B1), -W- may be independently bonded to any of the ortho _- position, the meta-position, the para-position, or the α-position, the β-position, or the γ-position, respectively, with respect to -NH2 of each benzene ring, and preferably can be bonded to the meta-position or the para-position, or the β-position or the γ-position, more preferably the para-position or the γ-position. When m is 2 or more, in the benzene ring to which two Ws are bonded, the bonding positions of the two Ws may be a relationship of the ortho-position, the meta-position, or the para-position, or a relationship of the α-position, the β-position, or the γ-position, and preferably a relationship of the meta-position or the para-position, or a relationship of the β-position or the γ-position.

As specific examples of the structure represented by formula (B1), for example, structures represented by formulas (B1-1) to (B1-6) can be mentioned.

In formulas (B1-1) to (B1-6), R ^b1 and q are defined in the same manner as R ^b1 and q in formula (B1), and W ¹ to W ⁶ independently represent a divalent linking group selected from the group consisting of -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -COO-, -OOC-, -SO-, -SO ₂ -, -S-, -CO-, -N(R ^c )-, and -CONH-, and R ^c represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a hydrogen atom or a halogen atom. In addition, in formula (B1-4), a compound having the same structure as formula (B1-3) is defined as a compound of formula (B1-3).

As R ^b1 and q in formulas (B1-1) to (B1-6), the same embodiments as those exemplified as R ^b1 and q in formula (B1) are exemplified, and suitable embodiments are also the same.

In formulas (B1-1) to (B1-6), W ¹ to W ⁶ are preferably, independently of one another, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -COO-, -OOC-, -SO ₂ -, -S-, -CO- or -CONH-. W ¹ in formula (B1-1) is preferably -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -SO ₂ -, -S- or -CO-. W ² , W ⁴ and W ⁶ in formulas (B1-2), (B1-4) and (B1-6) are each preferably -O-. In formula (B1-3), W ³ is preferably -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -SO ₂ -, -CO- or -CONH-, and in formula (B1-5), W ⁵ is preferably -C(CH ₃ ) ₂ -, -O-, -SO ₂ - or -CO-.

In one embodiment of the present invention, the PI resin constituting at least one PI resin-containing layer in the laminated film of the present invention preferably contains, as a structural unit (B), a diamine-derived structural unit in which m in formula (B1) is 1 or 2, for example, the structural unit (B1-1) and/or the structural unit (B1-2). As the diamine-derived structural unit in which m is 2, it is preferable to contain, for example, the structural unit (B1-2). When such a structural unit is contained, it becomes easy to control the absorbance of the PI resin-containing layer or laminate (L) containing the PI resin within a desired range in a specific wavelength band, so that the puncture strength and dielectric properties of the laminated film can be improved. In addition, since the CTE of the laminated film tends to decrease, improvement in the dimensional stability of the laminated film can be expected. In addition, the inclusion of these structural units can also contribute to improvement in the adhesion between the laminated film and the metal layer.

In another embodiment of the present invention, the PI resin constituting at least one PI resin-containing layer constituting the laminated film of the present invention preferably contains, as a structural unit (B), a diamine-derived structural unit in which m is 3 or 4, for example, the structural units (B1-3) to (B1-6) above, and more preferably contains a diamine-derived structural unit in which m is 3. As the diamine-derived structural unit in which m is 3, it is preferable to contain, for example, the structural unit (B1-5) above. When such a structural unit is contained, it becomes easy to control the absorbance of the PI resin-containing layer or laminate (L) containing the PI resin within a desired range in a specific wavelength band, and thus the puncture strength and dielectric properties of the laminated film can be improved. In addition, since the CTE of the laminated film tends to decrease, improvement in the dimensional stability of the laminated film can be expected. In addition, the inclusion of these structural units can also contribute to improvement in the adhesion between the laminated film and the metal layer.

In one embodiment of the present invention, the constituent unit (B1) is preferably a constituent unit (B1-2), and the constituent unit (B1-2) is more preferably a constituent unit represented by formula (B1-2') and/or formula (B1-2'').

R ^b1 , W ² , and q in formula (B1-2') and formula (B1-2'') are defined identically to R ^b1 , W ² , and q in formula (B1-2).

In one embodiment of the present invention, it is preferable that the constituent unit represented by formula (B1-2') or formula (B1-2'') is a constituent unit represented by formula (B1-2'a) or formula (B1-2''a), respectively.

As a structural unit (B), if the above structural unit is included, it becomes easy to control the absorbance of the PI resin-containing layer or laminate (L) including the PI resin within a desired range in a specific wavelength band, so that the puncture strength and dielectric properties of the laminated film can be improved. In addition, since the CTE of the laminated film tends to decrease, improvement in the dimensional stability of the laminated film can be expected. In addition, inclusion of these structural units can also contribute to improvement in the adhesion between the laminated film and the metal layer.

In another embodiment of the present invention, the constituent unit (B1) is preferably a constituent unit (B1-5), and the constituent unit (B1-5) is more preferably a constituent unit represented by formula (B1-5a).

As a constituent unit (B), if the above constituent unit is included, it becomes easy to control the absorbance in the PI resin-containing layer or laminate (L) including the PI resin within a desired range, which is advantageous in improving the puncture strength or dielectric properties of the laminated film, reducing the CTE, etc.

In one embodiment of the present invention, when the PI system resin constituting the PI system resin-containing layer includes a structural unit (B1), the content thereof is preferably 3 mol% or more, more preferably 5 mol% or more, more preferably 7 mol% or more, further preferably 10 mol% or more, particularly preferably 20 mol% or more, particularly more preferably 30 mol% or more, and particularly more preferably 40 mol% or more, relative to the total amount of the structural unit (B). When the content of the structural unit (B1) is equal to or greater than the above lower limit, it becomes easy to control the absorbance of the laminate (L) within a desired range in a specific wavelength band, which is advantageous in improving the puncture strength or dielectric properties of the laminated film, reducing the CTE, and the like. In addition, since the adhesion with the metal layer tends to increase when the total amount of the structural unit (B1) increases, from this viewpoint, the content of the structural unit (B1) may be, for example, 50 mol% or more, 60 mol% or more, or 70 mol% or more relative to the total amount of the structural unit (B). The content of the constituent unit (B1) is preferably 99 mol% or less, more preferably 95 mol% or less, and even more preferably 90 mol% or less, relative to the total amount of the constituent unit (B).

<Composition Unit (B2)>

In one embodiment of the present invention, a PI resin constituting at least one PI resin-containing layer in the laminated film of the present invention is, as a constituent unit (B), represented by formula (B2):

[In formula (B2), R ^b2 independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group or aryloxy group which may have a halogen atom,

p represents an integer from 0 to 4]

It is preferable that the structural unit (B2) derived from a diamine containing a biphenyl skeleton represented by (hereinafter, sometimes simply abbreviated as the structural unit (B2)) be included. When the structural unit (B) includes the above-mentioned structural unit (B2), the PI resin is not excessively rigid and can have a flexible structure with a certain degree of freedom, so that it is easy to form a branched structure by heating during imidization, and further, since the orientation tends to be high, it becomes easy to obtain the desired absorbance of the PI resin-containing layer or laminate (L) including the PI resin in a specific wavelength band, which is advantageous in improving the puncture strength and dielectric properties of the laminated film, reducing CTE, etc.

In formula (B2), R ^b2 preferably, independently of one another, represents a halogen atom, or an alkyl group, an alkoxy group or an aryl group which may have a halogen atom, and more preferably represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above. The hydrogen atoms contained in R ^b2 may be independently substituted with a halogen atom, and examples of the halogen atoms include the same ones as those described above. R ^b2 is preferably, independently of one another, an alkyl group having 1 to 6 carbon atoms or a fluorinated alkyl group having 1 to 6 carbon atoms. Additionally, from the viewpoint of adhesion to a metal layer or the like, it is more preferably an alkyl group having 1 to 6 carbon atoms that does not contain fluorine, is further preferably an alkyl group having 1 to 3 carbon atoms that does not contain fluorine, and is particularly preferably a methyl group.

In formula (B2), p is, independently of each other, preferably an integer from 0 to 2, more preferably 0 or 1.

In formula (B2), the -NH ₂ group bonded to each benzene ring may be bonded to any of the ortho-position, the meta-position, the para-position, the α-position, the β-position, or the γ-position, based on the single bond connecting each benzene ring, and from the viewpoint of improving the dielectric properties of the laminated film, the puncture strength, or the reduction of the CTE, it is preferably bonded to the meta-position or the para-position, or the β-position or the γ-position, and more preferably to the para-position or the γ-position.

In a preferred embodiment of the present invention, formula (B2) is formula (B2'):

It is preferable that the PI resin constituting at least one PI resin-containing layer include a PI resin having, as a constituent unit (B), a constituent unit (B2), particularly a diamine-derived constituent unit represented by formula (B2'), so that the PI resin is not excessively rigid and can have a flexible structure with a certain degree of freedom, so that it is easy to form a branched structure by heating during imidization, and furthermore, since the orientation tends to increase, it becomes easy to obtain the desired absorbance of the PI resin-containing layer or laminate (L) including the PI resin in a specific wavelength band, which is advantageous in improving the puncture strength or dielectric properties of the laminated film, reducing CTE, etc. In addition, since the above effect is obtained even at a relatively low imidization temperature (e.g., 360°C or less), even when a laminated sheet is manufactured by thermally imidizing a PI-based resin precursor coating film in a laminated configuration with a metal layer (e.g., a metal foil layer such as copper foil), deterioration of the surface of the metal layer is suppressed, and a laminated sheet having high puncture strength and excellent high-frequency characteristics can be obtained.

In one embodiment of the present invention, when the PI resin contains the structural unit (B2), the content thereof is preferably 1 mol% or more, more preferably 5 mol% or more, further preferably 10 mol% or more, relative to the total amount of the structural unit (B), and may also be, for example, 30 mol% or more, 35 mol% or more, 40 mol% or more, or 50 mol% or more. When the content of the structural unit (B2) is equal to or greater than the above lower limit, it becomes easy to control the absorbance of the PI resin-containing layer or laminate (L) containing the PI resin within a desired range in a specific wavelength band, which is advantageous in improving the puncture strength or dielectric properties of the laminated film, reducing the CTE, and the like. In addition, the structural unit (B1) is preferably 95 mol% or less, more preferably 92 mol% or less, further preferably 90 mol% or less, further preferably 80 mol% or less, and particularly preferably 70 mol% or less, relative to the total amount of the structural unit (B).

In one embodiment of the present invention, when the PI resin constituting the PI resin-containing layer includes the structural unit (B1) and the structural unit (B2), their total content is preferably 30 mol% or more, more preferably 40 mol% or more, more preferably 60 mol% or more, particularly preferably 70 mol% or more, particularly more preferably 80 mol% or more, particularly more preferably 90 mol% or more, particularly more preferably 95 mol% or more, and preferably 100 mol% or less. When the total content of the structural unit (B1) and the structural unit (B2) is equal to or greater than the lower limit described above, the effects of the present invention expected by the PI resin having the structural unit (B1) and the structural unit (B2) are easily obtained, and furthermore, the effects can be further enhanced.

In addition, in one embodiment of the present invention, when the PI resin contains the structural unit (B1) and the structural unit (B2), the content ratio (molar ratio, (B1):(B2)) is preferably 95:5 to 5:95, more preferably 92:8 to 8:92, more preferably 90:10 to 10:90, still more preferably 80:20 to 20:80, and particularly preferably 75:25 to 50:50. When the content ratio of the structural unit (B1) and the structural unit (B2) is within the above range, the effects of the present invention expected by the PI resin having the structural unit (B1) and the structural unit (B2) can be easily obtained, and furthermore, the effects can be further enhanced.

<Composition Unit (B3)>

In one embodiment of the present invention, the structural unit (B) may include a diamine-derived structural unit (B3) (hereinafter, sometimes simply referred to as structural unit (B3)) other than the structural unit (B1) and the structural unit (B2). As the structural unit (B3), for example, a diamine-derived structural unit in which m in formula (B1) is 0, a diamine-derived structural unit in which X in formula (2) is represented by formulas (61) to (64), etc., and among these, a diamine-derived structural unit in which X in formula (2) is represented by formula (74) (a structural unit derived from p-phenylenediamine) is preferable. In the present specification, "a diamine-derived structural unit (B3) other than the structural unit (B1) and the structural unit (B2)" means a diamine-derived structural unit that is different from either the structural unit (B1) or the structural unit (B2).

In one embodiment of the present invention, when the structural unit (B) includes the structural unit (B3), the content of the structural unit (B3) is preferably 25 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, and usually 0.01 mol% or more, relative to the total amount of the structural unit (B).

In one embodiment of the present invention, it is preferable that the PI resin-containing layer constituting the laminated film includes any one or more of the following configurations.

· In all PI-based resin-containing layers in the laminated film, the PI-based resin contains at least one of the constituent unit (B1) and the constituent unit (B2);

· In all PI-based resin-containing layers in the laminated film, the PI-based resin contains a constituent unit (B1);

· In at least one PI-based resin-containing layer of the laminated film, the PI-based resin includes a constituent unit (B1) and a constituent unit (B2);

· In all PI-based resin-containing layers in the laminated film, the PI-based resin includes a constituent unit (B1) and a constituent unit (B2).

In one embodiment of the present invention, in at least three PI-based resin-containing layers constituting the laminated film, preferably in the mPI layer and the TPI layer, it is preferable that the PI-based resin contains, as the structural unit (A), a structural unit (A1) and/or a structural unit (A2), and a structural unit (B). Furthermore, it is preferable that in at least three PI-based resin-containing layers constituting the laminated film, preferably in the mPI layer and the TPI layer, the PI-based resin contains, as the structural unit (A), a structural unit (A1) and/or a structural unit (A2), and as the structural unit (B1), preferably a structural unit (B1) and a structural unit (B2).

In a preferred embodiment of the present invention, the PI resin contained in at least one PI-based resin-containing layer, preferably an mPI layer, constituting the laminated film comprises, as a structural unit (A), at least two kinds of structural units selected from the structural unit (A1), the structural unit (A2) and the structural unit (A3) (preferably the structural unit (A1) and the structural unit (A2) and/or the structural unit (A3)), and the PI resin contained in at least one, preferably at least two, PI-based resin-containing layers, preferably the TPI layer, comprises, as a structural unit (A), the structural unit (A1) and the structural unit (A2), and further, the PI resins constituting all of the layers each comprise a structural unit (B), preferably a structural unit (B1), more preferably a structural unit (B1) and a structural unit (B2).

In one embodiment of the present invention, the layers (PI-1) to (PI-3) in the laminate (L1) each contain a structural unit (A1) and/or a structural unit (A2) and a structural unit (B). Additionally, in one preferred embodiment of the present invention, in the layers (PI-2) and (PI-3) in the laminate (L1), the PI-based resin contains the structural unit (A1), the structural unit (A2) and the structural unit (B), and in the layer (PI-1), the PI-based resin contains the structural unit (A1), the structural unit (A2) and/or the structural unit (A3) and the structural unit (B). Furthermore, in any of the layers (PI-1) to (PI-3) in the above embodiment, as the structural unit (B), preferably the structural unit (B1) is contained, more preferably the structural unit (B1) and the structural unit (B2).

When the mPI layer, the TPI layer, the layer (PI-1), the layer (PI-2), and the layer (PI-3) are each configured by combining the above-described structural units, the PI-based resin of each layer can have a flexible structure with a certain degree of freedom without being excessively rigid, so it is easy to form a branched structure by heating during imidization, and further, the orientation tends to be high. In addition, the interaction between two adjacent layers can be enhanced. Therefore, the desired absorbance of the laminate (L) or laminate (L1) configured by these layers can be obtained in a specific wavelength band, so that the above-described respective effects of the present invention expected by the PI-based resin having the respective structural units can be easily obtained, and furthermore, the effects can be further enhanced.

<Floor (PI-1)>

In one embodiment of the present invention, the PI resin constituting the layer (PI-1) contains, as the structural unit (A), a structural unit (A1) and/or a structural unit (A2), preferably contains at least two kinds of structural units selected from the structural unit (A1), the structural unit (A2) and the structural unit (A3), more preferably contains the structural unit (A1) and the structural unit (A2) and/or the structural unit (A3), and more preferably contains the structural unit (A1) and the structural unit (A3). When the layer (PI-1) contains these structural units, the content of the structural unit (A1) is preferably 20 mol% or more, more preferably 30 mol% or more, more preferably 35 mol% or more, particularly preferably 40 mol% or more, based on the total amount of the structural unit (A), and is preferably 80 mol% or less, more preferably 75 mol% or less, more preferably 70 mol% or less, and particularly preferably 65 mol% or less. The content of the structural unit (A2) is preferably 20 mol% or more, more preferably 30 mol% or more, more preferably 35 mol% or more, particularly preferably 40 mol% or more, and is preferably 80 mol% or less, more preferably 75 mol% or less, more preferably 70 mol% or less, and particularly preferably 65 mol% or less, relative to the total amount of the structural unit (A). In addition, the content of the structural unit (A3) is preferably 3 mol% or more, more preferably 5 mol% or more, more preferably 7 mol% or more, further preferably 10 mol% or more, particularly preferably 20 mol% or more, particularly more preferably 30 mol% or more, particularly more preferably 35 mol% or more, particularly more preferably 40 mol% or more, and is preferably 75 mol% or less, more preferably 70 mol% or less, more preferably 65 mol% or less, and particularly preferably 60 mol% or less. In addition, in another embodiment, the content of the structural unit (A3) is preferably 45 mol% or less, more preferably 35 mol% or less, more preferably 25 mol% or less, even more preferably 15 mol% or less, particularly preferably 5 mol% or less, and particularly more preferably 1 mol% or less, and the lower limit may be 0 mol%.

When the contents of the constituent unit (A1), the constituent unit (A2), and/or the constituent unit (A3) are each within the above range, the PI resin can have a flexible structure with a certain degree of freedom without being excessively rigid, so that it is easy to form a branched structure by heating during imidization, and further, the orientation tends to be high. Thereby, it becomes easy to control the absorbance in the layer (PI-1) within a desired range, and a laminated film having excellent puncture strength, dielectric properties, and thermal properties can be obtained.

Meanwhile, in another embodiment of the present invention, the content of the structural unit (A2) in the PI resin constituting the layer (PI-1) is preferably less than 30 mol%, more preferably not more than 25 mol%, further preferably not more than 20 mol%, and particularly preferably not more than 10 mol%, based on the total amount of the structural unit (A). In one embodiment of the present invention, the layer (PI-1) may not substantially contain the structural unit (A2), and the lower limit of the content of the structural unit (A2) can be 0 mol%.

In one embodiment of the present invention, the PI-based resin constituting the layer (PI-1) preferably includes a constituent unit (B1) as the constituent unit (B). As the constituent unit (B1), it is preferable to include a constituent unit (B1-2) and a constituent unit (B1-5), more preferably a constituent unit (B1-2), and even more preferably a constituent unit (B1-2''). The content of the constituent unit (B1) in the PI resin constituting the layer (PI-1) is preferably 3 mol% or more, more preferably 5 mol% or more, further preferably 7 mol% or more, even more preferably 10 mol% or more, particularly preferably 20 mol% or more, particularly more preferably 30 mol% or more, particularly more preferably 35 mol% or more, particularly preferably 40 mol% or more, and is preferably 80 mol% or less, more preferably 75 mol% or less, more preferably 70 mol% or less, and particularly preferably 65 mol% or less, based on the total amount of the constituent unit (B). In addition, the PI resin constituting the layer (PI-1) preferably further includes a constituent unit (B2) as the constituent unit (B), the content of which is preferably 10 mol% or more, more preferably 20 mol% or more, more preferably 30 mol% or more or more than 30 mol%, further preferably 35 mol% or more, particularly preferably 40 mol% or more, and preferably 75 mol% or less, more preferably 70 mol% or less, more preferably 65 mol% or less, particularly preferably 60 mol% or less, based on the total amount of the constituent unit (B).

When the content of the constituent unit (B1) and/or the constituent unit (B2) is within the above range, the PI resin is not excessively rigid and can have a flexible structure with a certain degree of freedom, so that it is easy to form a branched structure by heating during imidization, and further, the orientation tends to be high. Thereby, the puncture strength of the layer (PI-1) can be improved or the Df can be reduced, and furthermore, the CTE can be effectively reduced, so that a laminated film having excellent puncture strength, dielectric properties, and thermal properties can be obtained.

<Floor (PI-2) and Floor (PI-3)>

In one embodiment of the present invention, the PI-based resin constituting the layer (PI-2) and the layer (PI-3) each contains a constituent unit (A1) as the constituent unit (A), and preferably contains a constituent unit (A1) and a constituent unit (A2). When these constituent units are contained, the content of the constituent unit (A1) is preferably 10 mol% or more, more preferably 15 mol% or more, more preferably 20 mol% or more, and preferably 80 mol% or less, more preferably 70 mol% or less, and further preferably 60 mol% or less, based on the total amount of the constituent unit (A). In addition, the content of the constituent unit (A2) is preferably 20 mol% or more, more preferably 30 mol% or more, more preferably 40 mol% or more, and particularly preferably 50 mol% or more, and preferably 90 mol% or less, more preferably 85 mol% or less, more preferably 80 mol% or less, and particularly preferably 75 mol% or less, based on the total amount of the constituent unit (A).

When the content of the constituent unit (A1) and/or the constituent unit (A2) is within the above range, the PI resin can have a flexible structure with a certain degree of freedom without being excessively rigid, so that it is easy to form a branched structure by heating during imidization, and further, the orientation tends to be high. Thereby, the puncture strength of the layer (PI-2) and the layer (PI-3) can be improved or the Df can be reduced, and furthermore, the CTE can be effectively reduced, so that a laminated film having excellent puncture strength, dielectric properties and thermal properties can be obtained. In addition, an effect of improving the adhesion with a metal layer can be expected.

In one embodiment of the present invention, the PI resin constituting the layer (PI-2) and the layer (PI-3) preferably does not substantially contain the structural unit (A3). The content of the structural unit (A3) in these layers is preferably 10 mol% or less, more preferably 8 mol% or less, even more preferably 5 mol% or less, and particularly preferably 1 mol% or less, based on the total amount of the structural unit (A). In one embodiment of the present invention, the layer (PI-2) and the layer (PI-3) do not substantially contain the structural unit (A3), and the lower limit of the content of the structural unit (A3) can be 0 mol%.

In one embodiment of the present invention, the PI-based resin constituting the layer (PI-2) and the layer (PI-3) preferably contains a structural unit (B1) as the structural unit (B). As the structural unit (B1), it is preferable to contain a structural unit (B1-2), and it is more preferable to contain a structural unit (B1-2') that increases the flexibility of the PI-based resin. The content of the structural unit (B1) in the PI-based resin constituting these layers is preferably 20 mol% or more, more preferably 30 mol% or more, further preferably 35 mol% or more, particularly preferably 40 mol% or more, and is preferably 80 mol% or less, more preferably 75 mol% or less, more preferably 70 mol% or less, and particularly preferably 65 mol% or less, relative to the total amount of the structural units (B). In addition, as the structural unit (B), it is preferable to further include a structural unit (B2), and the content thereof is preferably 1 mol% or more, more preferably 5 mol% or more, even more preferably 10 mol% or more, and for example, 20 mol% or more, 30 mol% or more, or more than 30 mol%, and further may be 40 mol% or more, and is preferably 80 mol% or less, more preferably 70 mol% or less, more preferably 65 mol% or less, and particularly preferably 60 mol% or less.

In the PI resin constituting the layer (PI-2) and the layer (PI-3), if the contents of the constituent unit (B1) and/or the constituent unit (B2) are each within the above range, the PI resin can have a flexible structure with a certain degree of freedom without being excessively rigid, so that it is easy to form a branched structure by heating during imidization, and further, the orientation tends to be high. Thereby, the puncture strength of the layer (PI-2) and the layer (PI-3) can be improved or the Df can be reduced, and the CTE can also be effectively reduced, so that a laminated film having even better puncture strength, dielectric properties, and thermal properties can be obtained. In addition, an effect of improving the adhesion to a metal layer can be expected.

The various physical properties (molecular weight, glass transition temperature, etc.) of the PI resin comprising the above-mentioned structural unit (A) and/or structural unit (B) may be appropriately determined based on, for example, the following suitable ranges, depending on the role or purpose of each PI resin-containing layer in the laminated film.

In one embodiment of the present invention, the PI resin constituting each PI resin-containing layer may contain a halogen atom, preferably a fluorine atom, which can be introduced by, for example, the above-mentioned halogen atom substituent. When the PI resin contains a fluorine atom, the dielectric constant of the resulting PI resin-containing layer is easily reduced, which leads to improvement in the dielectric properties of the laminated film. Preferred fluorine-containing substituents for containing fluorine atoms in the PI resin include, for example, a fluoro group and a trifluoromethyl group.

In addition, in another embodiment of the present invention, the PI-based resin preferably does not contain fluorine atoms from the viewpoint of enhancing the adhesion of the obtained PI-based resin-containing layer to the metal layer. Therefore, for example, the PI-based resin-containing layer in contact with the metal layer, preferably the TPI layer, and particularly the PI-based resin constituting the layer (PI-2) and the layer (PI-3) in the laminate (L1), preferably does not contain fluorine atoms. In addition, since the PI-based resin tends to weaken the interaction between molecular chains when it contains fluorine atoms, the Df of the PI-based film tends to decrease when the PI-based resin does not contain fluorine atoms.

When the PI resin contains halogen atoms, the content of halogen atoms, particularly fluorine atoms, in the PI resin is preferably 0.1 to 35 mass%, more preferably 0.1 to 30 mass%, further preferably 0.1 to 20 mass%, and particularly preferably 0.1 to 10 mass%, based on the mass of the PI resin. When the content of halogen atoms is equal to or greater than the lower limit described above, the heat resistance and dielectric properties of the resulting PI resin-containing layer tend to increase, which leads to improvement in the dielectric properties and thermal properties of the laminated film. When the content of halogen atoms is equal to or less than the upper limit described above, it is advantageous in terms of cost, it is easy to reduce CTE, and furthermore, synthesis of the PI resin becomes easy.

In one embodiment of the present invention, the imidization ratio of the PI resin is preferably 90% or more, more preferably 93% or more, further preferably 95% or more, and usually 100% or less. From the viewpoint of improving the puncture strength, dielectric properties and thermal properties of the laminated film, it is preferable that the imidization ratio is equal to or more than the lower limit above. The imidization ratio represents the ratio of the molar amount of the imide bond in the PI resin to twice the molar amount of the structural unit derived from the tetracarboxylic acid compound in the PI resin. Furthermore, when the PI resin contains a tricarboxylic acid compound, the ratio of the molar amount of the imide bond in the PI resin to the sum of twice the molar amount of the structural unit derived from the tetracarboxylic acid compound in the PI resin and the molar amount of the structural unit derived from the tricarboxylic acid compound is represented. Furthermore, the imidization ratio can be obtained by the IR method, the NMR method, or the like.

In one embodiment of the present invention, the weight average molecular weight (Mw) of the PI resin in terms of polystyrene is preferably 5000 or more, more preferably 10000 or more, further preferably 15000 or more, and particularly preferably 20000 or more, from the viewpoint of increasing the puncture strength. Furthermore, from the viewpoint of the ease of production of the varnish or the film-forming property, it is preferably 1200000 or less, more preferably 1000000 or less, further preferably 800000 or less, and particularly preferably 700000 or less. For example, the Mw of the mPI layer, particularly, the layer (PI-1) in the laminate (L1), is preferably 5000 to 800000, more preferably 10000 to 700000. In addition, the Mw of the TPI layer, particularly the layer (PI-2) and the layer (PI-3) in the laminate (L1), is preferably 10,000 to 1,000,000, and more preferably 20,000 to 900,000.

In one embodiment of the present invention, the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the PI resin of the present invention is, from the viewpoint of the puncture strength and adhesion to the metal layer, preferably 1.1 or more, more preferably 1.3 or more, more preferably 1.5 or more, particularly preferably 1.7 or more, and preferably 15 or less, more preferably 12 or less, more preferably 11 or less, and particularly preferably 10 or less. For example, the Mw/Mn of the mPI layer, particularly, the layer (PI-1) in the laminate (L1), is preferably 1.1 to 15, more preferably 1.5 to 10. In addition, the Mw/Mn of the TPI layer, particularly, the layer (PI-2) and the layer (PI-3) in the laminate (L1), are each preferably 1.1 to 15, more preferably 1.5 to 10. In addition, Mw and Mn can be obtained by measuring gel permeation chromatography (hereinafter sometimes referred to as GPC) and converting to standard polystyrene.

In one embodiment of the present invention, the Tg of the PI resin is preferably 350°C or less, more preferably 330°C or less, further preferably 310°C or less, and particularly preferably 300°C or less, from the viewpoint of improving the puncture strength of the obtained laminated film or reducing Df. Furthermore, the Tg of the PI resin is preferably 200°C or more, more preferably 205°C or more, further preferably 210°C or more, and particularly preferably 220°C or more, from the viewpoint of increasing the puncture strength of the laminated film, reducing Df, or improving the thermal properties. When the PI-based resin-containing layer includes an mPI layer and a TPI layer, the Tg of the PI-based resin constituting the mPI layer is preferably 350°C or less, more preferably 330°C or less, more preferably 310°C or less, and particularly preferably 295°C or less, and preferably 220°C or more, more preferably 230°C or more, more preferably 250°C or more, further preferably 260°C or more, and particularly preferably 270°C or more. When the Tg of the PI-based resin constituting the mPI layer is in the above range, the puncture strength of the laminated film can be increased, and furthermore, the dielectric properties and thermal properties can be increased. The Tg of the PI-based resin constituting the TPI layer is preferably 310°C or less, more preferably 300°C or less, more preferably 290°C or less, further preferably 270°C or less, and particularly preferably 250°C or less, and preferably 200°C or more, more preferably 210°C or more, more preferably 220°C or more, and particularly preferably 230°C or more. When the Tg of the PI resin constituting the TPI layer is in the above range, the puncture strength of the laminated film can be increased, and in addition to reducing Df and improving thermal properties, the adhesion to the metal layer can be increased. The Tg of the PI resin can be measured by dynamic viscoelasticity measurement. For example, it can be calculated based on the peak of the tanδ curve, which is the ratio of the values of the storage modulus (E') and the loss modulus (E''), obtained using a dynamic viscoelasticity measuring device.

In one embodiment including an mPI layer and a TPI layer as the PI-based resin-containing layer, when the Tg of the PI-based resin constituting the mPI layer is within the above range, preferably 250 to 330°C, and further, when the Tg of the PI-based resin constituting the TPI layer is within the above range, preferably 220 to 300°C, each PI-based resin tends to easily form a desirable higher-order structure in which rotational motion is suppressed. Therefore, in the case of the embodiment, each PI-based resin-containing layer can be formed by a PI-based resin having a higher-order structure that maintains high orientation, and it can be thought that the strength against an impact applied in the thickness direction of the PI-based resin-containing layer increases, thereby improving the puncture strength of the laminated film. In addition, since it is presumed that the rotation of polar groups in each PI-based resin is suppressed, and the loss of electrical energy as thermal motion is reduced, it can be thought that a laminated film with low Df is obtained by using a PI-based resin having a Tg within the above range. In addition, by using such a PI resin, even if the imidization temperature is a low temperature of, for example, 360°C or lower, the puncture strength and dielectric properties of the resulting laminated film can be improved, so that even when a PI resin precursor coating film is thermally imidized in a laminated configuration with a metal layer (for example, a metal foil layer such as copper foil), deterioration of the surface of the metal foil can be suppressed, and a laminated sheet (CCL) having both high puncture strength and excellent high-frequency characteristics can be obtained.

The Tg of the PI resin can be adjusted by appropriately adjusting the types of constituent units constituting the PI resin, their composition, the molecular weight of the PI resin, the manufacturing method, and especially the imidization conditions, and for example, by adjusting it within the range described as a preferred embodiment in this specification, it can be adjusted within the above range.

(Method for manufacturing laminated film)

The laminated film of the present invention can be manufactured by a method including, for example, a step of reacting tetracarboxylic anhydride and diamine, each appropriately selected according to the composition of the PI resin constituting each PI resin-containing layer included in the laminated film, to obtain a PI resin precursor, and a step of imidizing the obtained PI resin precursor.

In one embodiment of the present invention, each PI resin-containing layer constituting the laminated film comprises, for example,

· A method of applying a solution of a PI resin precursor corresponding to a support substrate, drying it, and then imidizing it on the support substrate, or

· A method of applying a solution of a PI resin precursor corresponding to a support substrate, drying the solution, peeling the dried film from the support substrate, and then imidizing the peeled dry film.

It can be prepared by the following methods.

In addition, the laminated film of the present invention is a multilayer film including multiple layers of PI-based resin-containing layers, and as an aspect of the manufacturing method thereof, for example,

· A method of applying and drying a solution of a corresponding PI resin precursor to a support substrate repeatedly several times, and then performing imidization, or

· A method of applying and drying a solution of PI resin precursor corresponding to each layer simultaneously in a multilayered state by multilayer extrusion, and then performing imidization.

You can hear the back.

<Preparation of PI resin precursor>

As the tetracarboxylic acid anhydride used in the synthesis of the PI resin precursor, examples thereof include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic acid dianhydride; and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic acid dianhydride. The tetracarboxylic acid compounds may be used alone or in combination of two or more. In addition to the dianhydride, the tetracarboxylic acid compound may be a tetracarboxylic acid compound analogue such as an acid chloride compound.

As the tetracarboxylic acid compound, examples thereof include tetracarboxylic anhydride represented by formula (A1), tetracarboxylic anhydride represented by formula (A2), and tetracarboxylic anhydride represented by formula (A3), and a tetracarboxylic acid compound known in the art can be appropriately selected and used.

Examples of such tetracarboxylic acid compounds include pyromellitic anhydride (hereinafter sometimes referred to as PMDA), 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride (hereinafter sometimes referred to as BPADA), 1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (hereinafter sometimes referred to as BPDA), 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (hereinafter sometimes referred to as 6FDA), 4,4'-oxydiphthalic dianhydride (hereinafter sometimes referred to as ODPA), 2,2',3,3'-, 2,3,3',4'- or 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,3',3,4'-Biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, p-phenylenebis(trimellitic acid monoester dianhydride) (hereinafter sometimes referred to as TAHQ), esterified product of trimellitic anhydride and 2,2',3,3',5,5'-hexamethyl-4,4'-biphenol (hereinafter sometimes referred to as TMPBP), 4,4'-bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-ylcarbonyloxy)biphenyl (hereinafter sometimes referred to as BP-TME), 2,3',3,4'-diphenylethertetracarboxylic dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, 3,3'',4,4''-p-terphenyltetracarboxylic acid Dicarboxylic acid dianhydride, 2,3,3'',4''-p-terphenyltetracarboxylic acid dianhydride, 2,2'',3,3''-p-terphenyltetracarboxylic acid dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,2,7,8-, 1,2,6,7-phenanthrene-tetracarboxylic acid dianhydride, 1,2,9,10-Phenanthrene-tetracarboxylic dianhydride, 2,2-Bis(3,4-dicarboxyphenyl)tetrafluoropropane dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride (hereinafter sometimes referred to as HPMDA), 2,3,5,6-cyclohexanetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, 4,4'-Bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (hereinafter sometimes referred to as CBDA), Norbornane-2-spiro-α'-spiro-2''-norbornane-5,5',6,6'-tetracarboxylic anhydride, p-phenylenebis(trimellitate anhydride), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-Tetrachloronaphthalene-2,3,6,7-tetracarboxylic dianhydride, 1,4,5,8-Tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 1,4,5,8-Tetrachloronaphthalene-2,3,6,7-tetracarboxylic dianhydride, 2,3,8,9-Perylene-tetracarboxylic dianhydride, 3,4,9,10-Perylene-tetracarboxylic dianhydride, 4,5,10,11-Perylene-tetracarboxylic dianhydride, 5,6,11,12-Perylene-tetracarboxylic dianhydride, Pyrazine-2,3,5,6-tetracarboxylic dianhydride, Pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, Examples thereof include thiophene-2,3,4,5-tetracarboxylic acid dianhydride, bis(2,3-dicarboxyphenyl)sulfone dianhydride, and bis(3,4-dicarboxyphenyl)sulfone dianhydride. Among these, from the viewpoints of improving the puncture strength of the resulting laminated film and reducing Df or CTE, it is preferable to use a combination of BPDA, PMDA, TAHQ, and/or BP-TME. These tetracarboxylic acid compounds can be used alone or in combination of two or more.

As the diamine compound used in the synthesis of the PI resin precursor, for example, aliphatic diamines, aromatic diamines, and mixtures thereof can be mentioned. In addition, in the present embodiment, "aromatic diamine" refers to a diamine having an aromatic ring, and may include an aliphatic group or other substituents in part of its structure. The aromatic ring may be a single ring or a condensed ring, and examples thereof include, but are not limited to, a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring. Of these, a benzene ring is preferable. In addition, "aliphatic diamine" refers to a diamine having an aliphatic group, and may include other substituents in part of its structure, but does not have an aromatic ring.

As the diamine compound, examples thereof include a diamine represented by formula (B1), a diamine represented by formula (B2), a diamine represented by formula (2), etc., and a diamine compound known in the relevant field can be appropriately selected and used.

Examples of such diamine compounds include 1,4-diaminocyclohexane, 4,4'-diamino-2,2'-dimethylbiphenyl (hereinafter sometimes referred to as m-Tb), 4,4'-diamino-3,3'-dimethylbiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl (hereinafter sometimes referred to as TFMB), 4,4'-diaminodiphenyl ether, 1,3-bis(3-aminophenoxy)benzene (hereinafter sometimes referred to as 1,3-APB), 1,4-bis(4-aminophenoxy)benzene (hereinafter sometimes referred to as TPE-Q), 1,3-bis(4-aminophenoxy)benzene (hereinafter sometimes referred to as TPE-R), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (hereinafter sometimes referred to as BAPP), 2,2'-Dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxy-4,4'-diaminobiphenyl, 2,2-bis-[4-(3-aminophenoxy)phenyl]propane, bis[4-(4-aminophenoxy)]biphenyl, bis[4-(3-aminophenoxy)]biphenyl, bis[1-(4-aminophenoxy)]biphenyl, bis[1-(3-aminophenoxy)]biphenyl, bis[4-(4-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(4-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)]benzophenone, bis[4-(3-aminophenoxy)]benzophenone, 2,2-Bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis-[4-(3-aminophenoxy)phenyl]hexafluoropropane, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 4,4'-methylenedianiline, 3,3'-methylenedianiline, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 3,3-diaminodiphenylether, 3,4'-diaminodiphenylether, benzidine, 3,3'-Diaminobiphenyl, 3,3'-dimethoxybenzidine, 4,4''-diamino-p-terphenyl, 3,3''-diamino-p-terphenyl, m-phenylenediamine, p-phenylenediamine (hereinafter sometimes referred to as p-PDA), resorcinol-bis(3-aminophenyl)ether, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisaniline, 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisaniline, bis(p-aminocyclohexyl)methane, bis(p-β-amino-tert-butylphenyl)ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-Diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino-tert-butyl)toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, piperazine, 4,4'-diamino-2,2'-bis(trifluoromethyl)bicyclohexane, 4,4'-diaminodicyclohexylmethane, 4,4''-diamino-p-terphenyl, bis(4-aminophenyl)terephthalate, 1,4-bis(4-aminophenoxy)-2,5-di-tert-butylbenzene, 4,4'-(1,3-phenylenediisopropylidene)bisaniline, 1,4-Bis[2-(4-aminophenyl)-2-propyl]benzene, 2,4-diamino-3,5-diethyltoluene, 2,6-diamino-3,5-diethyltoluene, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-(hexafluoropropylidene)dianiline, 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,2-diaminopropane, 1,2-diaminobutane, 1,3-diaminobutane, 2-methyl-1,2-diaminopropane, 2-methyl-1,3-diaminopropane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, norbornanediamine, 2'-Methoxy-4,4'-diaminobenzanilide, 4,4'-diaminobenzanilide, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 4,4'-diaminodiphenylsulfide, 3,3'-diaminodiphenylsulfide, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 2,5-diamino-1,3,4-oxadiazole, bis[4,4'-(4-aminophenoxy)]benzanilide, bis[4,4'-(3-aminophenoxy)]benzanilide, Examples thereof include 2,6-diaminopyridine, 2,5-diaminopyridine, etc. Among these, from the viewpoints of improving the puncture strength of the resulting laminated film, reducing Df or CTE, etc., it is preferable to use a combination of m-Tb, BAPP, TPE-Q, and TPE-R. The diamine compounds can be used singly or in combination of two or more.

In addition, the PI resin precursor may be obtained by further reacting, in addition to the tetracarboxylic acid compound used in the synthesis of the PI resin precursor, other tetracarboxylic acids, dicarboxylic acids, and tricarboxylic acids and their anhydrides and derivatives, within a range that does not damage the various physical properties of the obtained PI film.

As other tetracarboxylic acids, an anhydride addition product of the above tetracarboxylic acid compound can be mentioned.

As the dicarboxylic acid compound, aromatic dicarboxylic acid, aliphatic dicarboxylic acid, and flexible acid chloride compounds and acid anhydrides thereof may be mentioned, and two or more types may be used in combination. Specific examples include terephthalic acid; isophthalic acid; naphthalenedicarboxylic acid; 4,4'-biphenyldicarboxylic acid; 3,3'-biphenyldicarboxylic acid; dicarboxylic acid compounds of chain hydrocarbons having 8 or fewer carbon atoms, and compounds in which two benzoic acids are linked by a single bond, -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, or a phenylene group, and acid chloride compounds thereof.

Examples of the tricarboxylic acid compound include aromatic tricarboxylic acid, aliphatic tricarboxylic acid, and their flexible acid chloride compounds, acid anhydrides, etc., and two or more types may be used in combination. Specific examples include anhydride of 1,2,4-benzenetricarboxylic acid; 2,3,6-naphthalenetricarboxylic acid-2,3-anhydride; and compounds in which phthalic anhydride and benzoic acid are linked by a single bond, -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, or a phenylene group.

In the production of a PI-based resin precursor, the amounts of a diamine compound, a tetracarboxylic acid compound, a dicarboxylic acid compound, and a tricarboxylic acid compound can be appropriately selected depending on the ratio of each constituent unit of the desired PI-based resin precursor.

In the present invention, the total number of moles of diamine compound used per 1 mole of the total amount of tetracarboxylic acid compounds is defined as the amine ratio. In a suitable embodiment of the present invention, the amine ratio is preferably 0.90 mole or more, and preferably 0.999 mole or less, per 1 mole of the total amount of tetracarboxylic acid compounds. In addition, in another embodiment, the amine ratio is preferably 1.001 mole or more, and preferably 1.10 mole or less, per 1 mole of the total amount of tetracarboxylic acid compounds.

In one embodiment of the present invention, when the amine ratio is 1 or less, the amine ratio is preferably 0.90 mol or more and 0.999 mol or less, more preferably 0.95 mol or more and 0.997 mol or less, and even more preferably 0.97 mol or more and 0.995 mol or less.

In one embodiment of the present invention, when the amine ratio is 1 or more, the amine ratio is preferably 1.001 mol or more and 1.10 mol or less, more preferably 1.002 mol or more and 1.06 mol or less, and even more preferably 1.003 mol or more and 1.05 mol or less.

When the amine ratio is close to 1.0 mol, the molecular weight tends to increase rapidly during synthesis, and when it is significantly away from 1.0 mol, the molecular weight of the obtained PI resin tends to decrease. When the molecular weight increases rapidly, it tends to grow unevenly in the synthetic mass, and the properties of the PI resin obtained from the PI resin precursor tend to be difficult to stabilize. On the other hand, when the molecular weight is excessively low, the mechanical properties tend to decrease.

The reaction temperature of the diamine compound and the tetracarboxylic acid compound is preferably 50°C or lower, more preferably 40°C or lower, and even more preferably 30°C or lower. In addition, the reaction temperature of the diamine compound and the tetracarboxylic acid compound is preferably 5°C or higher, more preferably 10°C or higher, and even more preferably 15°C or higher. When the reaction temperature is within the above range, the effects of the present invention can be easily obtained, and furthermore, the reaction speed tends to be increased and the polymerization time can be shortened. The reaction time is not particularly limited, and may be, for example, about 0.5 to 36 hours, preferably 1 to 24 hours.

The reaction of a diamine compound and a tetracarboxylic acid compound is preferably carried out in a solvent. The solvent is not particularly limited as long as it does not affect the reaction, and examples thereof include alcohol solvents such as water, methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, 1-methoxy-2-propanol, 2-butoxyethanol, and propylene glycol monomethyl ether; phenol solvents such as phenol and cresol; ester solvents such as ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, propylene glycol methyl ether acetate, and ethyl lactate; lactone solvents such as γ-butyrolactone (hereinafter sometimes referred to as GBL) and γ-valerolactone; ketone solvents such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, 2-heptanone, and methyl isobutyl ketone; Examples thereof include aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; alicyclic hydrocarbon solvents such as ethylcyclohexane; aromatic hydrocarbon solvents such as toluene and xylene; nitrile solvents such as acetonitrile; ether solvents such as tetrahydrofuran and dimethoxyethane; chlorine-containing solvents such as chloroform and chlorobenzene; amide solvents such as N,N-dimethylacetamide (hereinafter sometimes referred to as DMAc) and N,N-dimethylformamide (hereinafter sometimes referred to as DMF); sulfur-containing solvents such as dimethylsulfone, dimethyl sulfoxide, and sulfolane; carbonate solvents such as ethylene carbonate and propylene carbonate; pyrrolidone solvents such as N-methylpyrrolidone (hereinafter sometimes referred to as NMP); and combinations thereof. Among these, from the viewpoint of solubility, phenol solvents, lactone solvents, amide solvents, pyrrolidone solvents, and more preferably amide solvents can be suitably used.

In one embodiment of the present invention, the boiling point of the solvent used in the reaction between the diamine compound and the tetracarboxylic acid compound is preferably suitable for the imidization conditions for controlling the absorbance in the range of 465 nm to 550 nm in the laminate (L) to a desired range so as to satisfy formula (I) and/or formula (II), and is preferably 230°C or less, more preferably 200°C or less, further preferably 180°C or less, and preferably 100°C or more, more preferably 120°C or more.

The reaction of a diamine compound and a tetracarboxylic acid compound may be carried out, if necessary, under an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere or under conditions of reduced pressure, and is preferably carried out under an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere, in a strictly controlled dehydration solvent while stirring.

The obtained PI resin precursor may be isolated by a conventional method, but may be used as a PI resin precursor solution by appropriately diluting the reaction solution containing the PI resin precursor obtained by synthesizing the PI resin precursor without isolation with a solvent as necessary.

<Coating of polyimide resin precursor solution>

The coating process of the PI-based resin precursor solution is a process of forming a coating film by coating the PI-based resin precursor solution containing the PI-based resin precursor and a solvent on a supporting substrate.

The solvent included in the PI-based resin precursor solution may be exemplified as a solvent used in the reaction of a diamine compound and a tetracarboxylic acid compound in the production of a PI-based resin precursor, and is preferably a lactone-based solvent, an amide-based solvent, a pyrrolidone-based solvent, and more preferably an amide-based solvent. Furthermore, in one embodiment of the present invention, the boiling point of the solvent included in the PI-based resin precursor solution is preferably suitable for the imidization conditions for controlling the absorbance in the range of 465 nm to 550 nm in the laminate (L) to a desired range so as to satisfy formula (I) and/or formula (II), and is preferably 230°C or less, more preferably 200°C or less, further preferably 180°C or less, particularly preferably 170°C or less, and is preferably 100°C or more, more preferably 120°C or more.

The content of the PI resin precursor included in the PI resin precursor solution is preferably 8 mass% or more, more preferably 10 mass% or more, further preferably 12 mass% or more, particularly preferably 13 mass% or more, based on the total amount of the PI resin precursor solution, and is preferably 30 mass% or less, more preferably 25 mass% or less, further preferably 23 mass% or less, particularly preferably 20 mass% or less. When the content of the PI resin precursor is within the above range, the processability at the time of film formation is excellent.

A coating film of a PI-based resin precursor solution can be formed by coating a PI-based resin precursor solution on a supporting substrate by a known coating method or application method. Known coating methods include, for example, a wire bar coating method, a reverse coating method, a roll coating method such as gravure coating, a die coating method, a comma coating method, a lip coating method, a spin coating method, a screen printing coating method, a fountain coating method, a dipping method, a spray method, a curtain coating method, a slot coating method, a flow forming method, and the like. A coating film of a multiple-layer PI-based resin precursor solution may be formed by coating a PI-based resin precursor solution on a supporting substrate one layer at a time or in multiple portions, or a laminated coating film of a multiple-layer PI-based resin precursor solution may be formed at the same time. As a method for forming a coating film of a multiple layer at the same time, for example, a coextrusion processing method, a multilayer curtain coating method, and the like can be employed.

Examples of the supporting substrate include a metal plate (e.g., copper plate) such as a metal foil (e.g., copper foil), a SUS plate such as a SUS foil or a SUS belt, a glass substrate, a PET film, a PEN film, a PI resin film other than the PI resin-containing layer in the present invention, a polyamide resin film, and the like. Among these, from the viewpoint of excellent heat resistance, a copper plate, a SUS plate, a glass substrate, a PET film, a PEN film, etc. are preferably mentioned, and from the viewpoints of adhesion and cost, a copper plate, a SUS plate, a glass substrate or a PET film, etc. are more preferably mentioned. In one embodiment of the present invention, the metal constituting the metal plate includes, for example, aluminum, copper, iron, nickel, chromium, titanium, tantalum, stainless steel, and alloys thereof. Among these, the metal foil is preferably a copper foil, a copper alloy foil, an SUS foil, an aluminum foil, etc., and from the viewpoints of conductivity and metal workability, a copper foil or a copper alloy foil is more preferable, and a copper foil is particularly preferable. By using a metal layer (e.g., metal foil, etc.) as a supporting substrate, a resin film can also be formed directly on the metal layer.

<Imidization process>

The imidization process is a process of imidizing a PI resin precursor coated on a substrate, for example, by heat treatment at 200°C or higher and 500°C or lower.

In a preferred embodiment of the present invention, the imidization process is preferably a process in which, prior to imidization of the PI-based resin precursor, a PI-based resin precursor solution coated on a support substrate is dried by heating (sometimes referred to as pre-drying) at a relatively low temperature of, for example, less than 300°C, preferably 60°C or more and 200°C or less, more preferably 80°C or more and 150°C or less, and the resulting dried PI-based resin precursor film is imidized by heat treatment at 200°C or more and 500°C or less.

In one embodiment of the present invention, the imidization process preferably includes a step of pre-drying a PI-based resin precursor coated on a support substrate, then relatively rapidly heating from a low temperature (referred to as a first temperature) to a high temperature (referred to as a second temperature), and maintaining the temperature at the high temperature. By rapidly heating at a relatively high speed, preferably rapidly, to proceed with imidization, and then reaching a high temperature and maintaining the temperature at the high temperature for a predetermined time to complete imidization, the absorbance in the range of 465 nm to 550 nm in the laminate (L) is adjusted to the specific range, making it easy to control so as to satisfy formula (I) and/or formula (II). Furthermore, from the viewpoint of obtaining a smooth film or reducing Df, it is preferable to perform heating in steps as described above.

In one embodiment of the present invention, the first temperature is preferably 20°C or more and 50°C or less, more preferably 25°C or more and 35°C or less, and the second temperature is preferably 220°C or more and 450°C or less, more preferably 250°C or more and 400°C or less, even more preferably 300°C or more and 380°C or less, and particularly preferably 330°C or more and 360°C or less. By appropriately selecting the constituent units of the PI resin, even if imidization is performed at a relatively low temperature of, for example, about 360°C, the resulting PI resin-containing layer or laminated film can exhibit sufficiently high puncture strength, or Df can be reduced. In addition, when the imidization temperature is 360°C or less, even when copper foil is used as a supporting substrate, since thermal deterioration of the copper foil can be suppressed, it is easy to obtain a laminated sheet having excellent high-frequency characteristics. In addition, from the viewpoint of sufficiently improving the imidization rate, improving the puncture strength, or reducing Df, the imidization temperature is preferably 200°C or higher, more preferably 210°C or higher, and even more preferably 220°C or higher.

In one embodiment of the present invention, the temperature increase from the first temperature to the second temperature may be performed at a single-stage temperature increase rate, or may be performed at a multi-stage temperature increase rate of two or more stages. In one embodiment of the present invention, when the temperature increase from the first temperature to the second temperature is performed in one stage, the temperature increase rate is preferably 3.5°C/min or more, more preferably 5°C/min or more, still more preferably 7°C/min or more, particularly preferably 10°C/min or more, and is preferably 25°C/min or less, more preferably 20°C/min or less, still more preferably 18°C/min or less, particularly preferably 15°C/min or less. Furthermore, in one embodiment of the present invention, when the temperature increase from the first temperature to the second temperature is performed in two or more stages, the temperature increase rate is preferably such that the temperature increase rate of the first stage is 3.5°C/min or more, and it is preferable that the second and subsequent stages are faster than the first stage. For example, when the heating from the first temperature to the second temperature is performed in two stages, the heating rate of the second stage is preferably 1.2 times or more, more preferably 1.5 times or more, even more preferably 1.8 times or more, and is usually 10 times or less. For example, when the heating from the first temperature to the second temperature is performed in two stages, the heating rate of the first stage is preferably 1°C/min or more, more preferably 2°C/min or more, still more preferably 3°C/min or more, particularly preferably 3.5°C/min or more, and is preferably 18°C/min or less, more preferably 15°C/min or less, particularly preferably 12°C/min or less. In addition, the temperature rising rate of the second stage is preferably 3°C/min or more, more preferably 5°C/min or more, further preferably 8°C/min or more, and in some cases may be, for example, 10°C/min or more, and preferably 35°C/min or less, more preferably 30°C/min or less, further preferably 25°C/min or less. In the case where the temperature rising from the first temperature to the second temperature is performed in two stages, for example, the temperature rising to a temperature intermediate between the first temperature and the second temperature can be performed at the temperature rising rate of the first stage, and the temperature rising from the intermediate temperature to the second temperature can be performed at the temperature rising rate of the second stage. By employing such a heating rate, the orientation of the PI resin increases, the PI resin becomes more likely to form a higher-order structure, or the PI resin becomes more likely to form branching, making it easy to adjust the absorbance in the range of 465 nm to 550 nm in the laminate (L) to the specific range, making it easy to control so as to satisfy formula (I) and/or formula (II).

In one embodiment of the present invention, the heating time from the first temperature to the second temperature can be appropriately selected depending on these temperatures or the heating rate, and is preferably 5 hours or less, more preferably 3 hours or less, further preferably 2 hours or less, particularly preferably 1 hour or less, and in some cases may be 50 minutes or less, and further preferably 10 minutes or more, more preferably 15 minutes or more, and further preferably 20 minutes or more. When the heating time from the first temperature to the second temperature is in the above range, it is easy to adjust the absorbance in the range of 465 nm to 550 nm in the laminate (L) to the above specific range, and it is easy to control so as to satisfy formula (I) and/or formula (II).

In one embodiment of the present invention, the retention time at the second temperature is preferably 1 minute or more, more preferably 3 minutes or more, and preferably 30 minutes or less, more preferably 20 minutes or less, and even more preferably 10 minutes or less. When the heating rate from the first temperature to the second temperature is within the above range, and further, the retention time at the second temperature is within the above range, the orientation of the PI-based resin is increased, the PI-based resin is more likely to form a higher-order structure, the PI-based resin is more likely to form branching, and so on, thereby making it easy to adjust the absorbance in the range of 465 nm to 550 nm in the laminate (L) to the above specific range, making it easy to control so as to satisfy formula (I) and/or formula (II).

After imidization, a laminated film can be obtained by peeling off the laminated coating formed on the support substrate from the substrate. In one embodiment of the present invention, when the support substrate is a metal foil (e.g., copper foil), a laminated sheet in which the laminated film is laminated on the metal foil can be obtained without peeling off the coating from the metal foil.

(Properties of laminated film)

In one embodiment of the present invention, the content of the PI resin in each PI resin-containing layer constituting the laminated film is preferably 60 mass% or more, more preferably 70 mass% or more, further preferably 80 mass% or more, and particularly preferably 90 mass% or more, based on the mass of the PI resin-containing layer. In addition, the upper limit of the content of the PI resin is not particularly limited, and may be, for example, 100 mass% or less, 99 mass% or less, or 95 mass% or less based on the mass of the PI resin-containing layer. When the content of the PI resin is within the above range, a laminated film having improved puncture strength, dielectric properties, and thermal properties can be obtained.

In the laminated film of the present invention, each PI-based resin-containing layer may contain a filler, if necessary. Examples of the filler include metal oxide particles such as silica and alumina, inorganic salts such as calcium carbonate, polymer particles such as fluororesin and cycloolefin polymer, and the like. The filler may be used alone or in combination of two or more. When a filler is contained, the content thereof is preferably 50 mass% or less, more preferably 40 mass% or less, further preferably 30 mass% or less, and preferably 0.01 mass% or more, relative to the mass of the PI-based resin-containing layer.

In addition, in one embodiment of the present invention, each PI-based resin-containing layer constituting the laminated film of the present invention may contain additives as necessary. Examples of the additives include antioxidants, flame retardants, crosslinking agents, surfactants, compatibilizers, imidization catalysts, weathering agents, lubricants, antiblocking agents, antistatic agents, antifogging agents, anti-dropping agents, pigments, etc. The additives may be used singly or in combination of two or more. The content of various additives may be appropriately selected within a range that does not impair the effects of the present invention, and when various additives are included, the total content is preferably 7 mass% or less, more preferably 5 mass% or less, further preferably 4 mass% or less, particularly preferably 1 mass% or less, and preferably 0.001 mass% or more, relative to the mass of each PI-based resin-containing layer.

In one embodiment of the present invention, the coefficient of linear expansion (CTE) of the laminated film is preferably less than 45 ppm/K, more preferably less than 40 ppm/K, more preferably less than 35 ppm/K, and even more preferably less than 32 ppm/K. When the CTE of the laminated film is equal to or less than the upper limit described above, excellent thermal properties and high dimensional stability can be expected. In addition, the CTE of the laminated film is preferably 0 ppm/K or more, more preferably 5 ppm/K or more, more preferably 8 ppm/K or more, and particularly preferably 10 ppm/K or more. When the CTE of the laminated film is within the above range, the CTE of the metal layer (particularly, a metal foil layer such as copper foil) and the PI-based resin-containing layer of the laminated film become close to each other, so that the effect of suppressing peeling of the laminated film from the metal layer is obtained. In addition, the CTE can be measured by, for example, a thermomechanical analyzer (hereinafter sometimes referred to as "TMA"), and is obtained by the method described in the Examples.

In printed circuits, transmission loss is required to be small. Transmission loss is expressed as the sum of dielectric loss, which is the loss caused by the electric field generated in the dielectric, and conductor loss, which is the loss caused by the current flowing through the conductor. And, it is known that the dielectric loss is approximately proportional to the index E, which is expressed by equation (i).

E=Df×(Dk) ^1/2 (i)

[In formula (i), Df represents the dielectric constant and Dk represents the dielectric constant]

In the high-frequency range used in FPCs for high-speed communications such as 5G, dielectric loss tends to increase, so materials that can suppress dielectric loss by having a small value of the above index E are particularly demanded.

Meanwhile, high-frequency signals concentrate current on the polar surfaces of the conductor. Therefore, conductor loss is related to the dielectric properties of the dielectric in contact, and is known to be approximately proportional to (Dk) ^1/2 .

Since the laminated film of the present invention has small Df and Dk, and thus also has small dielectric loss index E and conductor loss, transmission loss can be reduced in a circuit including the laminated film.

In one embodiment of the present invention, the index E of the dielectric loss of the laminated film at 10 GHz is preferably 0.0080 or less, more preferably 0.0075 or less, further preferably 0.0070 or less, still more preferably 0.0065 or less, particularly preferably 0.0060 or less, and most preferably 0.0058 or less. Since the smaller the index E, the lower the transmission loss of an electronic circuit including the laminated film, the lower the lower limit of the index E is not particularly limited, and may be, for example, 0 or more.

In one embodiment of the present invention, the Df of the laminated film at 10 GHz is preferably 0.0040 or less, more preferably 0.0035 or less, further preferably 0.0033 or less, particularly preferably 0.0032 or less, and most preferably 0.0030 or less, from the viewpoint of reducing the transmission loss of an electronic circuit when the laminated film is included in the electronic circuit. Since the smaller the Df, the lower the transmission loss of an electronic circuit including the laminated film, the lower the lower limit of the Df is not particularly limited, and may be, for example, 0 or more.

In one embodiment of the present invention, the Dk of the laminated film at 10 GHz is preferably 3.500 or less, more preferably 3.450 or less, and even more preferably 3.400 or less.

Df and Dk of the laminated film can be measured using a vector network analyzer and a resonator, for example, by the method described in the examples.

The laminated film of the present invention may be subjected to surface treatment such as corona discharge treatment, plasma treatment, or ozone treatment by a method commonly employed industrially.

The puncture strength of the laminated film of the present invention is preferably 2.0 N or more, more preferably 3.0 N or more, more preferably 5.0 N or more, particularly preferably 8.0 N or more, particularly preferably 9.0 N or more, and particularly more preferably 10.0 N or more. In other words, the puncture strength per unit thickness of the laminated film of the present invention is preferably 0.05 N/μm or more, more preferably 0.07 N/μm or more, more preferably 0.10 N/μm or more, still more preferably 0.12 N/μm or more, particularly preferably 0.18 N/μm or more, and particularly more preferably 0.22 N/μm or more. When the puncture strength of the laminated film is equal to or greater than the lower limit described above, breakage when the film is subjected to an impact in the thickness direction can be effectively suppressed. The upper limit of the puncture strength of the laminated film is not limited, and may be, for example, 30 N or less. The puncture strength can be measured using a small tabletop tester in accordance with JIS Z 1707 under an environment of a temperature of 23°C and a relative humidity of 50%. Specifically, it can be measured by, for example, the method described in the examples described below.

Since the laminated film of the present invention has high puncture strength, it can be suitably used as a substrate material corresponding to a printed circuit board or an antenna substrate. In addition, since the laminated film of the present invention has low Df, it can realize low transmission loss even in a high-frequency band transmitting a high-frequency signal, and is therefore particularly suitable as a substrate material corresponding to a printed circuit board or an antenna substrate for high-speed communication such as 5G.

〔Laminated sheet〕

Since the laminated film of the present invention has a sufficiently high puncture strength while being capable of reducing Df, it can be suitably used for forming a metal-clad laminate used in FPC. Accordingly, the present invention includes a laminated sheet including the laminated film of the present invention and a metal layer. In one embodiment of the present invention, the laminated sheet of the present invention may include the metal layer on only one side of the laminated film of the present invention or on both sides.

In one embodiment of the present invention, as the metal constituting the metal layer, examples thereof include aluminum, copper, iron, nickel, chromium, titanium, tantalum, stainless steel, and alloys thereof. Among these, the metal layer is preferably a copper layer, a copper alloy layer, a SUS layer, an aluminum layer, etc., and from the viewpoint of conductivity and metal workability, a copper layer or a copper alloy layer is more preferable, and a copper layer is particularly preferable. Furthermore, from the viewpoint of metal workability, it is preferable that the metal layer is a metal foil layer. Examples of the metal constituting the metal foil layer include the metals described above. Among these, the metal foil layer is preferably a copper foil layer, a copper alloy foil layer, a SUS foil layer, an aluminum foil layer, etc., and from the viewpoint of conductivity and metal workability, a copper foil layer or a copper alloy foil layer is more preferable, and a copper foil layer is particularly preferable. The metal layer may be manufactured by, for example, an electrolytic casting method such as an electroplating method or a plastic working method such as rolling, or a commercially available product may be used. When the metal layer is a metal foil, a surface treatment layer may be provided by electroplating on at least one surface of the metal foil, and examples of the surface treatment layer include a roughening layer, a rust-preventive layer, and further, if necessary, an alloy layer provided between the surface of the metal foil and the roughening layer, a chromate layer or a silane coupling agent layer provided on the surface of the rust-preventive layer, etc. When the metal layer is a copper foil, an electrolytic copper foil or a rolled copper foil can be used, and it is preferable that the metal layer has a roughening layer made of copper, zinc, titanium, tungsten, molybdenum, nickel, cobalt, iron, or two or more of these elements, and/or a rust-preventive layer made of zinc, tin, nickel, cobalt, chromium, molybdenum, or two or more of these elements. From the viewpoint of uniformly forming a harmony layer, it is additionally desirable to form an alloy layer of copper and at least one element selected from molybdenum, zinc, tungsten, nickel, cobalt, and iron on the surface of the copper foil.

In one embodiment of the present invention, the thickness of the metal layer, particularly the metal layer such as a copper foil layer, is preferably 1 µm or more, more preferably 5 µm or more, and further, from the viewpoint of facilitating miniaturization of the circuit and facilitating improvement of bending resistance, is preferably 100 µm or less, more preferably 50 µm or less, even more preferably 30 µm or less, and particularly preferably 20 µm or less. The thickness of the metal layer, particularly the metal foil layer such as a copper foil layer, can be measured using a thickness gauge or the like. Furthermore, when a laminated film includes a metal layer, particularly a metal layer such as a copper foil layer, on both surfaces of the laminated film, the thickness of each metal foil layer, particularly each copper foil layer, may be the same or different from each other.

The laminated sheet of the present invention may include other layers, such as a functional layer, in addition to the laminated film and metal layer of the present invention, particularly the metal foil layer (copper foil layer, etc.). Examples of the functional layer include an adhesive layer, etc. The functional layer may be used alone or in combination of two or more.

In one embodiment of the present invention, the laminated sheet of the present invention may be a metal-clad laminate composed of a laminated film comprising a metal layer and three or more PI-based resin-containing layers, or may be a metal-clad laminate composed of a laminated film comprising a metal layer, three or more PI-based resin-containing layers, and an adhesive layer. However, from the viewpoints of heat resistance, dimensional stability, and weight reduction, it is preferable that the metal-clad laminate not include an adhesive layer.

In addition, since the laminated film of the present invention can be formed at a relatively low imidization temperature, even when a laminated sheet having a copper foil as a metal layer is manufactured by performing thermal imidization of a PI-based resin precursor coating film on a copper foil, it is possible to realize a sufficiently high puncture strength or low Df while suppressing deterioration of the surface of the copper foil. Therefore, the laminated sheet of the present invention has excellent high-frequency characteristics even if it does not include an adhesive layer.

In addition, in one embodiment of the present invention, the laminated film and the metal layer, particularly the metal foil layer (copper foil layer, etc.) of the present invention may be in direct contact, or a functional layer may be inserted between the laminated film and the metal layer, particularly the metal foil layer (copper foil layer, etc.), and they may be in contact with each other via the functional layer. However, from the viewpoint of improving the puncture strength or thermal properties, it is preferable that the laminated film and the metal layer, particularly the metal foil layer (copper foil layer, etc.) are in direct contact.

<Method for manufacturing laminated sheets>

The laminated sheet of the present invention is, for example, produced by the following processes:

A process for coating a PI resin precursor solution onto a metal layer, and

For example, a process of forming a laminated film of the present invention on a metal layer by imidizing a PI resin precursor through heat treatment at 200°C or higher and 500°C or lower.

It can be manufactured by a method including:

In the above manufacturing method, the description of each process in the manufacturing method of the laminated film of the present invention described above is suitable, and the suitable aspects, etc. are also the same.

The laminated sheet of the present invention may also be manufactured by a method other than the above-described method, for example, a method of coating and drying a PI-based resin precursor solution on a support substrate other than a metal layer (e.g., metal foil) included in the laminated sheet, thereby obtaining a dried film of the PI-based resin precursor, peeling the dried film of the PI-based resin precursor from the substrate, and bonding the peeled dry film of the PI-based resin precursor to a metal layer. As a method of bonding the dried film of the PI-based resin precursor and the metal foil, a method using a press, a lamination method using a hot roll, or the like may be employed, and in the bonding step, imidization of the PI-based resin precursor may be performed simultaneously. However, since the laminated film of the present invention can be formed at a relatively low imidization temperature, even if a laminated sheet in which the metal layer is copper is manufactured by performing thermal imidization of the PI-based resin precursor coating film on copper foil, high puncture strength and low Df can be realized while suppressing deterioration of the surface of the copper foil. Therefore, the laminated sheet of the present invention has excellent high-frequency characteristics even if it is manufactured without going through the above-described bonding process.

In addition, the laminated sheet of the present invention may be manufactured by a method of bonding a metal layer to a resin film by heat pressing or heat lamination, as described in the section of (Method for Manufacturing Laminated Film), after manufacturing the resin film, or by a method of providing a metal layer (metal plating layer) on the surface of the laminated film by performing metal plating on the surface of the laminated film. From the viewpoint of the conductivity of the laminated sheet, the metal plating layer is preferably a copper plating layer or a copper alloy plating layer, and a copper plating layer is more preferable.

(Flexible Printed Circuit Board)

The laminated film of the present invention can be suitably used as an FPC substrate material because it has excellent puncture strength. In addition, since the laminated film of the present invention can have a low Df, it can reduce the transmission loss of an electric circuit formed by including the laminated film. In addition, since the laminated film of the present invention has a low CTE and excellent thermal properties, it can be suitably used as an FPC substrate material, particularly an FPC substrate material for high-speed communication applications such as 5G. Therefore, the present invention also includes a flexible printed circuit board comprising the laminated film or laminated sheet of the present invention.

[Example]

Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

The abbreviations used in the examples and comparative examples represent the following compounds.

BPDA: 3,3',4,4'-Biphenyltetracarboxylic dianhydride

BP-TME: 4,4'-Bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-ylcarbonyloxy)biphenyl

PMDA: Pyromellitic anhydride

m-Tb: 4,4'-diamino-2,2'-dimethylbiphenyl

TPE-Q: 1,4-Bis(4-aminophenoxy)benzene

TPER: 1,3-Bis(4-aminophenoxy)benzene

1. Preparation of polyimide resin precursor solution

(1) Polyimide resin precursor solution 1

48.61 g (228.9 mmol) of m-Tb and 66.92 g (228.9 mmol) of TPE-Q were dissolved in 1598 g of DMAc, 118.22 g (221.2 mmol) of BP-TME was added, and the mixture was stirred at 20°C for 1 hour under a nitrogen atmosphere. Thereafter, 48.25 g (221.2 mmol) of PMDA was added, and the mixture was stirred at 20°C for 3 hours under a nitrogen atmosphere to obtain PI-based resin precursor solution 1. The molar ratio of the diamine monomer to the acid dianhydride monomer used (amine ratio) was 1.04.

(2) Polyimide resin precursor solution 2

After dissolving 9.87 g (46.5 mmol) of m-Tb and 122.35 g (418.5 mmol) of TPE-R in 1890 g of DMAc, 30.26 g (138.7 mmol) of PMDA and 95.25 g (323.7 mmol) of BPDA were sequentially added, and the mixture was stirred at 20°C for 3 hours under a nitrogen atmosphere to obtain PI-based resin precursor solution 2. The molar ratio of the diamine monomer to the acid dianhydride monomer used (amine ratio) was 1.01.

(3) Polyimide resin precursor solution 3

44.34 g (208.8 mmol) of m-Tb and 61.06 g (208.8 mmol) of TPE-R were dissolved in 1598 g of DMAc, and then 85.39 g (290.2 mmol) of BPDA and 27.13 g (124.4 mmol) of PMDA were sequentially added, and the mixture was stirred at 20°C for 3 hours under a nitrogen atmosphere to obtain PI-based resin precursor solution 3. The molar ratio of the diamine monomer to the acid dianhydride monomer used (amine ratio) was 1.01.

(4) Polyimide resin precursor solution 4

57.72 g (271.9 mmol) of m-Tb and 8.83 g (30.2 mmol) of TPE-Q were dissolved in 810 g of DMAc, and then 32.53 g (149.1 mmol) of PMDA and 43.87 g (149.1 mmol) of BPDA were added, and the mixture was stirred at 20°C for 3 hours under a nitrogen atmosphere to obtain PI-based resin precursor solution 4. The molar ratio of the diamine monomer to the acid dianhydride monomer used was 1.01.

<Measurement of storage elastic modulus>

The storage elastic modulus of the PI resin contained in the above PI resin precursor solutions 1 to 4 was obtained by measuring a PI resin film produced by the following method.

Each PI-based resin precursor solution was flexibly molded onto a glass substrate to a dry thickness of 30 μm to form a coating film of the PI-based resin precursor solution. The coating film was heated at 120°C for 30 minutes, and the obtained film was peeled off from the glass substrate, and then fixed to a metal frame. The film fixed to the metal frame was maintained at 320°C for 5 minutes in an atmosphere with an oxygen concentration of 1%, thereby obtaining a PI-based resin film.

The storage modulus (E') was obtained by measuring the dynamic viscoelasticity measuring device (DVA-220, IT Instrumentation and Control Co., Ltd.) under the following samples and conditions.

Test piece: Rectangular body with a length of 40 mm, a width of 5 mm, and a thickness of 30 μm

Experimental mode: single frequency, constant temperature ramp

Experimental Format: Tensile

Length between sample grips: 15mm

Measurement start temperature: room temperature to 342℃

Heating rate: 5℃/min

Frequency: 10Hz

Static/dynamic stress ratio: 1.8

As a result of measurement by the above method, the PI resin film formed from the PI resin precursor solution 1 has a storage elastic modulus of 2.3×10 ⁹ Pa at 40°C and a storage elastic modulus of 2.8×10 ⁸ Pa at 300°C, the PI resin film formed from the PI resin precursor solution 2 has a storage elastic modulus of 2.4×10 ⁹ Pa at 40°C and a storage elastic modulus of 1.1×10 ⁷ Pa at 300°C, the PI resin film formed from the PI resin precursor solution 3 has a storage elastic modulus of 2.3×10 ⁹ Pa at 40°C and a storage elastic modulus of 1.2×10 ⁷ Pa at 300°C, and the PI resin film formed from the PI resin precursor solution 4 has a storage elastic modulus of 7.5×10 ⁹ Pa at 40°C and a storage elastic modulus of 300°C. It was 4.8×10 ⁸ Pa.

2. Production of laminated film

(1) Example 1

On the roughened surface side (surface roughness; Rz = 0.6 μm) of an electrolytic copper foil (thickness: 12 μm), the PI-based resin precursor solution 2/PI-based resin precursor solution 1/PI-based resin precursor solution 2 prepared above were simultaneously coated as upper/middle/lower layers so that the dry thicknesses were 7.0 μm/37.1 μm/6.0 μm, respectively, to form a laminate of the coating films of the PI-based resin precursor solutions. Next, the laminate of the coating films was dried by heating at 100°C for 10 minutes, and then the laminate composed of the copper foil and the PI-based resin precursor was fixed to a metal frame. In an atmosphere with an oxygen concentration of 1%, the temperature was increased from 30°C to 360°C over 30 minutes, and then maintained at 360°C for 5 minutes. A laminated film having a copper foil composed of the obtained PI-based resin-containing layer and copper foil was immersed in a large amount of a 40 mass% ferric chloride aqueous solution at room temperature for 10 minutes, and then the ferric chloride aqueous solution was washed with purified water. After confirming with the naked eye that no copper remains, it was dried at 80°C for 1 hour, and a laminated film (1) composed of three PI-based resin-containing layers (corresponding to a laminate (L)) was obtained. The thickness of the laminated film 1 was 50.1 μm.

(2) Example 2

Except that the upper/middle/lower layers were coated with a dry thickness of 7.1 µm/37.8 µm/6.1 µm, respectively, in the same manner as in Example 1, a laminate of a coating film of a PI-based resin precursor solution was formed. Next, the laminate of the coating film was dried by heating at 100°C for 10 minutes, and then the laminate composed of the copper foil and the PI-based resin precursor was fixed to a metal frame. In an atmosphere having an oxygen concentration of 1%, the temperature was increased from 30°C to 200°C over 20 minutes, then further increased from 200°C to 360°C over 10 minutes, and then heated and maintained at 360°C for 5 minutes. The laminate film having the obtained PI-based resin-containing layer and the copper foil composed of the copper foil was immersed in a large amount of a 40 mass% ferric chloride aqueous solution at room temperature for 10 minutes, and then the ferric chloride aqueous solution was washed with purified water. After confirming with the naked eye that there was no copper residue, the film was dried at 80°C for 1 hour to obtain a laminated film 2 composed of three PI resin-containing layers (equivalent to the laminate (L)). The thickness of the laminated film 2 was 51.0 μm.

(3) Example 3

On the roughened surface side (surface roughness; Rz = 0.6 μm) of an electrolytic copper foil (thickness: 12 μm), the PI-based resin precursor solution 3/PI-based resin precursor solution 1/PI-based resin precursor solution 3 prepared above were simultaneously coated as upper layer/middle layer/lower layer so that the dry thicknesses were 6.6 μm/36.8 μm/7.3 μm, respectively, to form a laminate of the coating films of the PI-based resin precursor solutions. Next, the laminate of the coating films was dried by heating at 100°C for 10 minutes, and then the laminate composed of the copper foil and the PI-based resin precursor was fixed to a metal frame. In an atmosphere having an oxygen concentration of 1%, the temperature was increased from 30°C to 200°C over 40 minutes, then further increased from 200°C to 360°C over 20 minutes, and then heated and maintained at 360°C for 5 minutes. The laminated film having the obtained PI-based resin-containing layer and the copper foil was immersed in a large amount of a 40 mass% ferric chloride aqueous solution at room temperature for 10 minutes, and then the ferric chloride aqueous solution was washed with purified water. After confirming with the naked eye that no copper remains, it was dried at 80°C for 1 hour to obtain a laminated film 3 comprising three PI-based resin-containing layers (corresponding to the laminate (L)). The thickness of the laminated film 3 was 50.7 μm.

(4) Example 4

Except that the upper/middle/lower layers were coated with a dry thickness of 6.4 µm/35.5 µm/7.0 µm, respectively, in the same manner as Example 3, a laminate of a coating film of a PI-based resin precursor solution was formed. The laminate of the coating film was dried by heating at 100°C for 10 minutes, and then the laminate composed of the copper foil and the PI-based resin precursor was fixed to a metal frame. In an atmosphere having an oxygen concentration of 1%, the temperature was increased from 30°C to 200°C over 52 minutes, then further increased from 200°C to 360°C over 8 minutes, and then heated and maintained at 360°C for 5 minutes. The laminate film having the obtained PI-based resin-containing layer and the copper foil composed of the copper foil was immersed in a large amount of a 40 mass% ferric chloride aqueous solution at room temperature for 10 minutes, and then the ferric chloride aqueous solution was washed with purified water. After confirming with the naked eye that there was no copper residue, the film was dried at 80°C for 1 hour to obtain a laminated film 4 composed of three PI resin-containing layers (corresponding to the laminate (L)). The thickness of the laminated film 4 was 48.9 μm.

(5) Example 5

Except that the upper/middle/lower layers were coated with a dry thickness of 6.6 ㎛/36.6 ㎛/7.3 ㎛, respectively, in the same manner as Example 3 to form a laminate of a coating film of a PI-based resin precursor solution. The laminate of the coating film was dried by heating at 100°C for 10 minutes, and then the laminate composed of the copper foil and the PI-based resin precursor was fixed to a metal frame. In an atmosphere having an oxygen concentration of 1%, the temperature was increased from 30°C to 200°C over 20 minutes, then further increased from 200°C to 360°C over 10 minutes, and then heated and maintained at 360°C for 5 minutes. The laminate film having the obtained PI-based resin-containing layer and the copper foil composed of the copper foil was immersed in a large amount of a 40 mass% ferric chloride aqueous solution at room temperature for 10 minutes, and then the ferric chloride aqueous solution was washed with purified water. After confirming with the naked eye that there was no copper residue, the film was dried at 80°C for 1 hour to obtain a laminated film 5 composed of three PI resin-containing layers (equivalent to the laminate (L)). The thickness of the laminated film 5 was 50.5 μm.

(6) Comparative Example 1

Except that the upper/middle/lower layers were coated with a dry thickness of 7.1 µm/37.8 µm/6.1 µm, respectively, in the same manner as in Example 1, a laminate of a coating film of a PI-based resin precursor solution was formed. The laminate of the coating film was dried by heating at 100°C for 10 minutes, and then the laminate composed of the copper foil and the PI-based resin precursor was fixed to a metal frame. In an atmosphere having an oxygen concentration of 1%, the temperature was increased from 30°C to 160°C over 40 minutes, then further increased from 160°C to 320°C over 20 minutes, and then heated and maintained at 320°C for 5 minutes. The laminate film having the obtained PI-based resin-containing layer and the copper foil composed of the copper foil was immersed in a large amount of a 40 mass% ferric chloride aqueous solution at room temperature for 10 minutes, and then the ferric chloride aqueous solution was washed with purified water. Thereafter, after confirming with the naked eye that there was no copper residue, the film was dried at 80°C for 1 hour to obtain a laminated film 6 composed of three PI-based resin-containing layers (corresponding to the laminate (L)). The thickness of the laminated film 6 was 51.0 μm.

(7) Example 6

A PI-based resin precursor solution 2 was applied to the roughened surface side (surface roughness; Rz = 0.6 μm) of an electrolytic copper foil (thickness: 12 μm) so as to have a dry thickness of 5.0 μm to obtain a coating film. The coating film was dried by heating at 120°C for 10 minutes, and a PI-based resin precursor solution 4 was applied onto the dried coating film so as to have a dry thickness of 36.0 μm to obtain a two-layer laminated coating film. The two-layer laminated coating film was dried by heating at 120°C for 30 minutes, and PI-based resin precursor solution 2 was applied onto the dried two-layer laminated coating film so as to have a dry thickness of 5.0 μm to obtain a three-layer laminated coating film. After drying the three-layer laminated coating film by heating at 120°C for 30 minutes, the laminate composed of the copper foil and the PI-based resin precursor was fixed to a metal frame. In an atmosphere having an oxygen concentration of 1%, the temperature was increased from 30°C to 200°C over 20 minutes, then further increased from 200°C to 360°C over 10 minutes, and then heated and maintained at 360°C for 5 minutes. The laminated film having the obtained PI-based resin-containing layer and the copper foil was immersed in a large amount of a 40 mass% ferric chloride aqueous solution at room temperature for 10 minutes, and then the ferric chloride aqueous solution was washed with pure water. After confirming with the naked eye that no copper remains, it was dried at 80°C for 1 hour to obtain a laminated film 7 composed of three PI-based resin-containing layers (corresponding to the laminate (L)). The thickness of the laminated film 7 was 46.0 μm.

Regarding the laminated films 1 to 7 obtained in the examples and comparative examples, measurements and evaluations were performed. The measurement and evaluation methods are described below.

<Measurement of film thickness>

From each of the laminated films 1 to 7 obtained in the examples and comparative examples, an arbitrary portion of 5 mm × 5 mm was cut out, and the samples for film thickness measurement were prepared by embedding them in resin. In the prepared sample for film thickness measurement, a measurement cross-section was prepared by cutting with a microtome, and the thickness of each of the three PI-based resin-containing layers and the thickness of the laminated film (total thickness (T) of the three layers: equivalent to the thickness of the laminate (L)) were measured under the following conditions using a laser microscope.

Device: LEXT OLS4100, manufactured by Olympus Corporation

Observation magnification: 100x

<Measurement of Df and Dk>

From the laminated films 1 to 7 obtained in the examples and comparative examples, measurement samples of 50 mm x 50 mm were cut out, respectively, and Df and Dk were measured under the following conditions. In addition, the measurements were performed after the measurement samples were conditioned at 23°C/50% RH for 24 hours.

Device: Compact USB Vector Network Analyzer (Product Name: MS46122B) manufactured by Anritsu Corporation

(주)에이티제 Joint Resonator (TE Mode 10GHz Type)

Measurement frequency: 10GHz

Measurement atmosphere: 23℃/50% RH

<Evaluation of indicator E of genetic loss>

The dielectric loss index E of the laminated films 1 to 7 obtained in the examples and comparative examples was calculated based on the following formula.

E=Df×(Dk) ^1/2 (i)

Df: genetic tangent

Dk : dielectric constant

<Measurement of coefficient of thermal expansion (CTE)>

The CTE of the laminated films 1 to 7 obtained in the examples and comparative examples was measured using a thermomechanical analyzer TMA under the following conditions, and the CTE at 50°C to 100°C was calculated.

Device: TMA/SS7100, manufactured by Hitachi High-Tech Sciences Co., Ltd.

Load: 50.0mN

Temperature program: Rising temperature from 20℃ to 130℃ at a rate of 5℃/min.

Test piece: length 40mm, width 5mm

<Measurement of stabbing intensity>

The puncture strength of the laminated films 1 to 7 obtained in the examples and comparative examples was measured in an environment of a temperature of 23°C and a relative humidity of 50%, in accordance with JIS Z 1707, using a small tabletop tester EZ-LX manufactured by Shimadzu Corporation. Specifically, a test piece having a width of 50 mm and a length of 50 mm was used, and a test was conducted under the conditions of a load cell of 50 N and a test speed of 200 mm/min, a pressurizer of a semicircular needle having a diameter of Φ2.5 mm and a tip shape of 0.5 mm, and the displacement at the breaking point was measured, and the maximum load at that time was taken as the puncture strength.

<Measurement of absorbance>

The absorbance of laminated films 1 to 7 obtained in Examples and Comparative Examples at wavelengths of 465 nm, 550 nm, and 600 nm was measured using an ultraviolet-visible-near-infrared spectrophotometer UV-3600 (manufactured by Shimadzu Corporation). The measurement conditions were as follows.

(Measurement conditions)

Attachment: Integrating Sphere ISR-3100

Background Measurements: Wait

<Light transmittance at 600 nm>

From the absorbance at a wavelength of 600 nm obtained above, the light transmittance at a wavelength of 600 nm was calculated based on the following formula.

Absorbance = -log(light transmittance)

The results of each of the above measurements are shown in Table 1. In Table 1, the numbers listed in the column for “Type of PI resin precursor” indicate the numbers of the PI resin precursor solutions used.

As shown in Table 1, the laminated films obtained in Examples 1 to 6 were confirmed to have sufficiently high puncture strength compared to the laminated film of Comparative Example 1. In addition, the laminated films obtained in Examples 1 to 6 were confirmed to have lower Df and lower dielectric loss index E compared to the laminated film of Comparative Example 1.

1: Laminated film
2: Laminated sheet
11: Polyimide resin-containing layer 1 (equivalent to layer (PI-2))
12: Polyimide resin-containing layer 2 (equivalent to layer (PI-1))
13: Polyimide resin-containing layer 3 (equivalent to layer (PI-3))
14: Adhesive layer
21: Metal foil layer

Claims (15)

A laminated film comprising three or more layers of polyimide resin-containing layers,
A laminate (L) comprising two polyimide-based resin-containing layers that are positioned furthest from each other among the polyimide-based resin-containing layers constituting the above laminated film, and a layer positioned between the two polyimide-based resin-containing layers, is formed by the following formula (I):
AbsA/AbsB<4.00 (I)
[In formula (I), AbsA represents the absorbance of the laminate (L) at a wavelength of 465 nm, and AbsB represents the absorbance of the laminate (L) at a wavelength of 550 nm]
A laminated film that satisfies the requirements. A laminated film comprising three or more layers of polyimide resin-containing layers,
Among the polyimide-based resin-containing layers constituting the above laminated film, a laminate (L) comprising two polyimide-based resin-containing layers which are positioned furthest from each other and a layer positioned between the two polyimide-based resin-containing layers is formed by the following formula (II):
AbsA-AbsB>0.016×T (II)
[In formula (II), AbsA represents the absorbance of the laminate (L) at a wavelength of 465 nm, AbsB represents the absorbance of the laminate (L) at a wavelength of 550 nm, and T represents the thickness (㎛) of the laminate (L)]
A laminated film that satisfies . In claim 1 or 2,
A laminated film having a light transmittance of 600 nm at a wavelength of the above laminate (L) of 60% or less. In claim 1 or 2,
A laminated film having a thickness of the above laminate (L) of 20 to 100 μm. In claim 1 or 2,
At least one layer of the polyimide-based resin-containing layer comprises a polyimide-based resin having a structural unit (A) derived from tetracarboxylic anhydride,
The above composition unit (A) is, formula (A1):

[In formula (A1), R ^a1 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom,
k represents an integer from 0 to 2]
A structural unit derived from tetracarboxylic anhydride represented by the formula (A1), and/or (A2):

[In formula (A2), R ^a2 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom, and l independently represents an integer from 0 to 3.]
A laminated film comprising a structural unit (A2) derived from tetracarboxylic anhydride represented by . In claim 1 or 2,
At least one layer of polyimide-based resin-containing layer comprises a polyimide-based resin having a structural unit (B) derived from diamine,
The above composition unit (B) is, formula (B1):

[In formula (B1), R ^b1 independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group or aryloxy group which may have a halogen atom,
W represents, independently of each other, a divalent linking group selected from the group consisting of -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -COO-, -OOC-, -SO-, -SO ₂ -, -S-, -CO-, -N(R ^c )-, and -CONH-, or a single bond (provided that m is 2 or more and at least one W is the divalent linking group), and R ^c represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom,
m represents an integer from 1 to 4,
q represents an integer from 0 to 4, independently of each other]
A laminated film comprising a structural unit (B1) derived from diamine represented by . In claim 1 or 2,
The above laminate (L) includes a polyimide-based resin-containing layer (PI-2), a polyimide-based resin-containing layer (PI-1), and a polyimide-based resin-containing layer (PI-3) in this order, and the polyimide-based resin-containing layer (PI-1), the polyimide-based resin-containing layer (PI-2), and the polyimide-based resin-containing layer (PI-3) are each represented by Formula (A1):

[In formula (A1), R ^a1 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom,
k represents an integer from 0 to 2]
A structural unit derived from tetracarboxylic anhydride represented by the formula (A1), and/or (A2):

[In formula (A2), R ^a2 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom, and l independently represents an integer from 0 to 3.]
A laminated film comprising a polyimide-based resin having a structural unit (A2) derived from tetracarboxylic anhydride and a structural unit (B) derived from diamine. In paragraph 7,
The above laminate (L) is a laminate film, which is a laminate (L1) composed of a polyimide-based resin-containing layer (PI-2), a polyimide-based resin-containing layer (PI-1), and a polyimide-based resin-containing layer (PI-3). In Article 8,
A laminated film, wherein the thickness of the laminate (L1) is 20 to 100 μm, and further, the thicknesses of the polyimide-based resin-containing layer (PI-2) and the polyimide-based resin-containing layer (PI-3) are each 0.05 to 0.3 times the thickness of the polyimide-based resin-containing layer (PI-1). In paragraph 7,
The above composition unit (B) is, formula (B1):

[In formula (B1), R ^b1 independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group or aryloxy group which may have a halogen atom,
W represents, independently of each other, a divalent linking group selected from the group consisting of -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -COO-, -OOC-, -SO-, -SO ₂ -, -S-, -CO-, -N(R ^c )-, and -CONH-, or a single bond (provided that m is 2 or more and at least one W is the divalent linking group), and R ^c represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a hydrogen atom or a halogen atom,
m represents an integer from 1 to 4,
q represents an integer from 0 to 4, independently of each other]
A laminated film comprising a structural unit (B1) derived from diamine represented by . In paragraph 7,
The polyimide resin contained in the above polyimide resin-containing layer (PI-1) is formula (A3):

[In formula (A3), Z represents a divalent organic group,
R ^a3 independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group or an aryloxy group which may have a halogen atom,
s represents an integer from 0 to 3, independently of each other]
A laminated film further comprising a structural unit (A3) derived from tetracarboxylic anhydride containing an ester bond represented by the following formula: In paragraph 7,
The above composition unit (B) is, formula (B2):

[In formula (B2), R ^b2 independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group or aryloxy group which may have a halogen atom,
p represents an integer from 0 to 4]
A laminated film comprising a structural unit (B2) derived from a diamine containing a biphenyl skeleton represented by . In claim 1 or 2,
A laminated film having a dielectric constant of 0.0040 or less at 10 GHz. A laminated sheet comprising a metal layer on one or both sides of the laminated film described in claim 1 or claim 2. A flexible printed circuit board comprising the laminated sheet described in claim 14.