JP7120819B2 - Laminate of polyimide film and flexible glass - Google Patents

Description

The present invention relates to a laminate of polyimide film and flexible glass.

In recent years, bendable flexible devices such as flexible displays and devices with curved surfaces such as organic EL lighting and organic EL displays have been developed. In such devices, instead of a rigid substrate, a laminate of a bendable film made of a polymer material and flexible glass is used as a substrate for forming a surface protective layer, a color filter, a touch panel, a thin film transistor (TFT), and the like. is being considered.

For example, Patent Document 1 describes a flexible glass substrate in which a glass substrate is bonded to a film substrate made of a polymer material from the viewpoint of compatibility between gas and water vapor barrier properties and flexibility, and reduction in thickness. there is Polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polyethersulfone, polyimide, epoxy resin, phenol resin, melamine resin, polyurethane, polyurea, polyethylene, polypropylene, nylon resin, polyvinyl chloride, acrylic resin, Various resins such as polystyrene, acrylonitrile butadiene styrene resin, acrylonitrile styrene resin, polyvinylidene chloride, etc. are mentioned.

Japanese Patent No. 4565670

In recent years, the demand for flexible substrates has been increasing more and more. The surface is required to be smooth so that the organic EL light-emitting layer can be formed without defects. However, Cited Document 1 does not describe or suggest these problems or how to use a film having a specific configuration to solve them. However, it has been difficult to obtain a flexible substrate having excellent optical properties and surface smoothness.

｛式中、式中、Ｘ_１は４価の有機基であり、Ｙ_１は２価の有機基であり、ｍは正の整数である。ｍは、特に限定されず、例えば、２～１５０の整数でよい。｝
で表される構造単位を含む、項目１～３のいずれか一項に記載の積層体。
［５］
上記ポリイミドフィルムは、下記式（２）：

｛式中、Ｘ_２は４価の有機基であり、Ｙ_２は２価の有機基であり、Ｘ_２はＸ_１と同一であっても異なってもよく、Ｙ_２はＹ_１と同一であっても異なってもよく、ｎ_１は２～１５０の整数であり、そしてＲ_１及びＲ_２は、それぞれ独立に、水素原子又は１価の有機基である｝
で表される構造単位を更に含む、項目４に記載の積層体。
［６］
上記（１）において、Ｘ_１が、下記式（Ａ１）～（Ａ４）からなる群から選択される四価の有機基の少なくとも１種であり、及び／又はＹ_１が、下記式（Ｂ１）～（Ｂ５）からなる群から選択される二価の有機基の少なくとも１種である、項目４に記載の積層体。

［７］
Ｘ_１が式（Ａ１）である、項目６に記載の積層体。
［８］
Ｘ_１が式（Ａ２）である、項目６に記載の積層体。
［９］
Ｘ_１が式（Ａ３）である、項目６に記載の積層体。
［１０］
Ｘ_１が式（Ａ４）である、項目６に記載の積層体。
［１１］
Ｙ_１が式（Ｂ１）である、項目６～１０のいずれか一項に記載の積層体。
［１２］
Ｙ_１が式（Ｂ２）である、項目６～１０のいずれか一項に記載の積層体。
［１３］
Ｙ_１が式（Ｂ３）である、項目６～１０のいずれか一項に記載の積層体。
［１４］
Ｙ_１が式（Ｂ４）である、項目６～１０のいずれか一項に記載の積層体。
［１５］
Ｙ_１が式（Ｂ５）である、項目６～１０のいずれか一項に記載の積層体。
［１６］
２層の上記ポリイミドフィルムの間に１層の上記フレキシブルガラスが積層された、項目１～１５のいずれか一項に記載の積層体。
［１７］
項目１～１６のいずれか一項に記載の積層体を有する、フレキシブルデバイス。 The inventors of the present application have made intensive studies to solve the above problems. As a result, a polyimide film having a specific yellowness index (YI) and flexible glass are laminated, and the arithmetic mean roughness of at least one surface of the laminate ( The inventors have found that the above problems can be solved by setting Ra) within a specific range, and have completed the present invention. That is, the present invention is as follows.
[1]
at least one layer of polyimide film;
A laminate in which at least one layer of flexible glass is laminated,
A laminate, wherein the polyimide film has a yellowness index (YI) of 5 or less, and an arithmetic average roughness (Ra) of at least one surface of the laminate of 1.5 nm or less.
[2]
The laminate according to item 1, wherein the polyimide film has a haze of 1% or less.
[3]
3. The laminate according to item 1 or 2, wherein the polyimide film has a thickness of 2 μm or more and 100 μm or less, and the flexible glass has a thickness of 30 μm or more and 200 μm or less.
[4]
The polyimide film has the following formula (1):

{wherein X ₁ is a tetravalent organic group, Y ₁ is a divalent organic group, and m is a positive integer. m is not particularly limited, and may be an integer from 2 to 150, for example. }
4. The laminate according to any one of items 1 to 3, comprising a structural unit represented by
[5]
The polyimide film has the following formula (2):

{wherein X ₂ is a tetravalent organic group, Y ₂ is a divalent organic group, X ₂ may be the same as or different from X ₁ , and Y ₂ is the same as Y ₁ ; may be different, n ₁ is an integer of 2 to 150, and R ₁ and R ₂ are each independently a hydrogen atom or a monovalent organic group}
5. The laminate according to item 4, further comprising a structural unit represented by:
[6]
In (1) above, X ₁ is at least one tetravalent organic group selected from the group consisting of the following formulas (A1) to (A4), and/or Y ₁ is the following formula (B1) 5. The laminate according to item 4, which is at least one divalent organic group selected from the group consisting of (B5).

[7]
7. The laminate according to item ₆ , wherein X1 is formula (A1).
[8]
The laminate according to item ₆ , wherein X1 is formula (A2).
[9]
The laminate according to item ₆ , wherein X1 is formula (A3).
[10]
The laminate according to item ₆ , wherein X1 is formula (A4).
[11]
11. The laminate according to any one of items 6 to 10, wherein Y ₁ is formula (B1).
[12]
11. The laminate according to any one of items 6 to 10, wherein Y ₁ is the formula (B2).
[13]
11. The laminate according to any one of items 6 to 10, wherein Y ₁ is the formula (B3).
[14]
11. The laminate according to any one of items 6 to 10, wherein Y ₁ is the formula (B4).
[15]
11. The laminate according to any one of items 6 to 10, wherein Y ₁ is the formula (B5).
[16]
16. The laminate according to any one of items 1 to 15, wherein one layer of the flexible glass is laminated between two layers of the polyimide film.
[17]
A flexible device comprising the laminate according to any one of items 1-16.

ADVANTAGE OF THE INVENTION According to this invention, the flexible substrate excellent in heat resistance and an optical characteristic can be provided, having a high barrier property. It should be noted that the above description should not be considered as disclosing all embodiments of the invention or all advantages associated with the invention. Further embodiments of the invention and its advantages will become apparent with reference to the following description and drawings.

An embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail below for the purpose of illustrating, but the present invention is not limited to the present embodiment. In the specification of the present application, the upper limit and lower limit of each numerical range can be arbitrarily combined.

《Laminate》
The laminate of this embodiment has a structure in which at least one layer of polyimide film and at least one layer of flexible glass are laminated. The number of laminated layers of the polyimide film and the flexible glass and the order thereof are not limited. At least one side of the laminate of the present embodiment is preferably a polyimide film. For example, it may have a structure in which one layer of polyimide film and one layer of flexible glass are laminated. From the viewpoint of slipperiness when it is formed, it may have a structure in which one layer of flexible glass is laminated between two layers of polyimide films.

At least one surface of the laminate of the present embodiment has an arithmetic mean roughness (Ra) of 1.5 nm or less, preferably 1.0 nm or less. When Ra is 1.5 nm or less, the optical properties are excellent. Although the lower limit of Ra is not limited, for example, when it is 0.5 nm or more, the slipperiness is improved, and it is possible to prevent the winding deviation when the laminate is rolled, so that the handleability is excellent. Depending on the laminate structure of the laminate, the "one side" may be the surface of the polyimide film or the surface of the flexible glass. Preferably, from the viewpoint of slipperiness, the surface having an Ra of 1.5 nm or less is the surface of the polyimide film.

The thickness of the laminate of the present embodiment, that is, the thickness of the laminate as a whole including the polyimide film and the flexible glass is not limited, but from the viewpoint of strength, it is preferably 32 μm or more, more preferably 60 μm or more, and flexibility from the point of view, it is preferably 300 μm or less, more preferably 180 μm or less.

<Polyimide film>
In the laminate of the present embodiment, a polyimide film having a yellowness index (YI) adjusted to 5 or less is used as a film base material to be laminated with flexible glass. In addition, a polyimide film is a film containing a polyimide as a main component. In the present specification, the film "containing polyimide as a main component" means that the film contains 50% by mass or more of polyimide based on the total mass of the film. The polyimide film preferably contains 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more of polyimide based on the total mass of the film. In addition, the polyimide film may optionally further contain additives.

Although not limited to theory, the reason for using the polyimide film is as follows. Conventionally, polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) have been studied as film substrates. Although PET and PEN are advantageous in terms of manufacturing cost, they are inferior in bending resistance, and when the radius of curvature is small or when bending is repeated, bending traces, cracks, and breaks are likely to occur. Also, PET and PEN have a glass transition point (Tg) of about 100° C. to 150° C. and are inferior in heat resistance. Furthermore, since PET and PEN have a retardation (Rth) of about 400 nm to 1000 nm, birefringence occurs when bent or when viewed through polarized sunglasses, resulting in iridescent stripes on the surface of the laminate. A pattern (the so-called "rainbow unevenness phenomenon") occurs. Therefore, it has been found that it is difficult to satisfy the recent demands for flexible substrates. On the other hand, when polycarbonate (PC) and cycloolefin polymer (COP) are used as the film substrate, Rth is about 20 nm or less, so the rainbow unevenness phenomenon can be reduced. However, PC and COP have a Tg of about 130° C. to 160° C., and are also insufficient in heat resistance. Polyethersulfone (PES) as a film substrate has a Tg of about 230° C. and an Rth of about 10 nm. proved difficult. In this regard, polyimide (PI) generally has a high Tg and excellent heat resistance, as well as excellent heat radiation resistance, low temperature resistance, and chemical resistance. considered adopting. However, as a result of intensive studies by the inventors, it was found that the optical properties of the resulting laminate were not always sufficient by simply using polyimide, and further creative ideas were required. Therefore, the inventors of the present application have succeeded in meeting the requirements for the optical properties of the laminate by adjusting the YI of the polyimide film to 5 or less. YI of the polyimide film is preferably 3.0 or less, more preferably 2.5 or less, and still more preferably 2.0 or less.

The haze of the polyimide film in the present embodiment is preferably 1% or less, more preferably 0.9% or less, from the viewpoint of transparency.

In the present embodiment, the thickness of the polyimide film is not limited, but is preferably 2 μm or more, more preferably 10 μm or more from the viewpoint of strength, and preferably 100 μm or less, more preferably 80 μm or less from the viewpoint of flexibility.

In the present embodiment, the retardation (Rth) of the polyimide film is preferably 200 nm or less, more preferably 50 nm or less when converted to a thickness of 15 μm, from the viewpoint of preventing iridescent unevenness. From the viewpoint of heat resistance, the glass transition point (Tg) of polyimide is preferably 200° C. or higher, more preferably 250° C. or higher.

In the present embodiment, the structure of the polyimide constituting the polyimide film is the four represented by the following formulas (A1) to (A4) from the viewpoint of ensuring transparency by balancing aromaticity and aliphaticity. It is preferred to have at least one valent organic group.

In the present embodiment, the structure of the polyimide constituting the polyimide film is, in addition to or as an alternative to the organic groups represented by the above formulas (A1) to (A4), balanced aromaticity and aliphaticity and transparent From the viewpoint of ensuring the properties, it is preferable to have at least one divalent organic group represented by the following formulas (B1) to (B5).

Although not wishing to be bound by theory, by introducing the structure represented by the formula (A2), (A3) or (B5) into the polyimide, the molar ratio of the structural units of the aromatic group is relatively increased. If it is lowered, it is considered that the π-π stacking phenomenon is suppressed, making it easier to ensure the transparency of the film.

Although not wishing to be bound by theory, the introduction of the structures represented by formulas (A1) or (B1) to (B4) into the polyimide causes steric hindrance groups such as sulfonyl groups or fluoroalkyl groups to form polyimides. It is conceivable that the formation of a complex is suppressed, and it becomes easier to ensure transparency.

｛式中、式中、Ｘ_１は４価の有機基であり、Ｙ_１は２価の有機基であり、ｍは正の整数である。ｍは、特に限定されず、例えば、２～１５０の整数でよい。｝
で表される構造単位を有することが好ましい。
また、ポリイミドフィルムは、式（１）で表される構造に加え、下記式（２）：

｛式中、Ｘ_２は４価の有機基であり、Ｙ_２は２価の有機基であり、Ｘ_２はＸ_１と同一であっても異なってもよく、Ｙ_２はＹ_１と同一であっても異なってもよく、ｎ_１は２～１５０の整数であり、そしてＲ_１及びＲ_２は、それぞれ独立に、水素原子又は１価の有機基である｝
で表される構造単位を有することができる。 The polyimide film of this embodiment has the following formula (1):

{wherein X ₁ is a tetravalent organic group, Y ₁ is a divalent organic group, and m is a positive integer. m is not particularly limited, and may be an integer from 2 to 150, for example. }
It is preferable to have a structural unit represented by
Further, the polyimide film has the following formula (2) in addition to the structure represented by formula (1):

{wherein X ₂ is a tetravalent organic group, Y ₂ is a divalent organic group, X ₂ may be the same as or different from X ₁ , and Y ₂ is the same as Y ₁ ; may be different, n ₁ is an integer of 2 to 150, and R ₁ and R ₂ are each independently a hydrogen atom or a monovalent organic group}
It can have a structural unit represented by

The imidization rate of the polyimide film is preferably 40% or more, preferably 50% or more,
60% or more is preferred, 70% or more is preferred, 80% or more is preferred, 90% or more is preferred, 95% or more is preferred, and 100% is most preferred. The imidization rate means the mole fraction of the structural unit represented by formula (1) based on the total number of moles of the structural units represented by formula (1) and formula (2) in the polyimide film. For example, the imidization rate can be calculated by FT-IR measurement. Since the aromatic ring does not change before and after imidization, the imidization rate can be determined from the intensity of the absorption peak characteristic to the C—N bond of the imide group near 1375 cm ⁻¹ based on the absorption peak of the aromatic ring near 1480 cm ⁻¹ . First, FT-IR measurement is performed on the polyimide film to be measured. Next, the film is heat-treated at, for example, 300 to 350° C. for 1 to 3 hours, and then FT-IR is measured. Assuming that the imidization rate after the heat treatment is 100%, the imidization rate can be calculated from the ratio of the peak intensity after the heat treatment and the peak intensity of the object to be measured.

In general formula (1), the tetravalent organic group X ₁ may be at least one tetravalent organic group selected from the group consisting of formulas (A1) to (A4), and the divalent organic group Y ₁ may be at least one divalent organic group selected from the group consisting of formulas (B1) to (B5). In general formula (2), the tetravalent organic group X ₂ may be the same as or different from X ₁ , and at least one of the tetravalent organic groups represented by formulas (A1) to (A4) OK. The divalent organic group Y ₂ may be the same as or different from Y ₁ and may be at least one divalent organic group represented by formulas (B1) to (B5). In addition, in general formula (2), the tetravalent organic group X ₂ preferably has at least one acid group, such as —COOH, for subsequent imidization. Specifically, the general formula ( In 2), at least one of R ₁ and R ₂ can be a hydrogen atom.

The polyimide film in the present embodiment preferably contains γ-butyrolactone in an amount of 0.01% by mass or more and 20% by mass or less. The content of γ-butyrolactone is 0.01% by mass or more from the viewpoint of suppressing yellowing of the film and obtaining a colorless and transparent film, and 20% by mass or less from the viewpoint of suppressing film stacking. be. γ-Butyrolactone in the polyimide film can be derived from the solvent of polyamic acid varnish, which is a polyimide precursor.

<Flexible glass>
The thickness of the flexible glass used in the present embodiment is preferably 30 μm or more, more preferably 50 μm or more from the viewpoint of mechanical strength, and preferably 200 μm or less, more preferably 100 μm or less from the viewpoint of flexibility. .
The type of glass is not limited, but examples thereof include alkaline earth aluminoborosilicates, alkaline earth aluminosilicates, alkali aluminophosphosilicates, and alkali aluminosilicates. The glass may be chemically strengthened glass or non-strengthened glass.

<<Method for manufacturing laminate>>
Examples of the method for producing the laminate of the present embodiment include methods such as the following methods (1) and (2) in which a polyimide film is formed directly on flexible glass, and after forming a polyimide film, on flexible glass. and the following methods (3) and (4) of laminating the same.
(1) A method comprising coating a flexible glass substrate with polyamic acid varnish, which is a polyimide precursor, and imidizing it by heating to form a polyimide film.
(2) Heating a polyamic acid varnish that is a polyimide precursor to imidize it to obtain a polyimide varnish containing a polyimide and a solvent; drying to form a polyimide film.
(3) Coating a polyamic acid varnish, which is a polyimide precursor, on an arbitrary support; imidizing it by heating to form a polyimide film; and peeling the polyimide film from the support later laminating onto a flexible glass substrate, or peeling the support after laminating the polyimide film onto a flexible glass substrate.
(4) Heating a polyamic acid varnish, which is a polyimide precursor, to imidize it to obtain a polyimide varnish containing a polyimide and a solvent; drying the solvent to form a polyimide film; peeling the polyimide film from the support and then laminating it onto a flexible glass substrate; or laminating the polyimide film onto a flexible glass substrate and then laminating the support. exfoliating the body.

<Production of polyamic acid varnish>
Polyamic acid varnish, which is a polyimide precursor, contains (a) polyamic acid, (b) solvent, and optionally (c) additives.

(a) Polyamic Acids Polyamic acids can be used as polyimide precursors and thus possess an amide moiety (--NHCO--) along with an acid group that can be subjected to an imidization reaction, such as --COOH. You can

Polyamic acid is at least one tetravalent organic group selected from the group consisting of the above formulas (A1) to (A4), and / or a divalent group selected from the group consisting of formulas (B1) to (B5) It is preferred to have at least one organic group of This introduces these structures into the resulting polyimide.

｛式中、Ｘ_２は４価の有機基であり、Ｙ_２は２価の有機基であり、Ｘ_２はＸ_１と同一であっても異なってもよく、Ｙ_２はＹ_１と同一であっても異なってもよく、ｎ_１は２～１５０の整数であり、そしてＲ_１及びＲ_２は、それぞれ独立に、水素原子又は１価の有機基である｝
で表される構造単位を有することができる。 In the polyamic acid, at least one tetravalent organic group selected from the group consisting of formulas (A1) to (A4) and a divalent organic group selected from the group consisting of formulas (B1) to (B5) At least one of may be bonded through -NHCO-, for example, polyamic acid has the following general formula (2):

{wherein X ₂ is a tetravalent organic group, Y ₂ is a divalent organic group, X ₂ may be the same as or different from X ₁ , and Y ₂ is the same as Y ₁ ; may be different, n ₁ is an integer of 2 to 150, and R ₁ and R ₂ are each independently a hydrogen atom or a monovalent organic group}
It can have a structural unit represented by

In general formula (2), the tetravalent organic group X ₂ may be at least one of the tetravalent organic groups represented by formulas (A1) to (A4), and the divalent organic group Y ₂ may be represented by the formula At least one divalent organic group represented by (B1) to (B5) may be used. In addition, the tetravalent organic group X ₂ preferably has at least _one acid group, such as —COOH, for subsequent imidization. At least one of ₂ can be a hydrogen atom.

In general, the polyimide precursor polyamic acid is a copolymer of a dianhydride with _two X groups and a diamine with _two Y groups. In that case, the tetravalent organic groups represented by formulas (A1) to (A4) are derived from acid dianhydrides, and the divalent organic groups represented by formulas (B1) to (B5) are diamines. can be derived from
Further, a varnish containing (a) a polyamic acid having a structural unit represented by the general formula (2) and (b) a solvent is converted to a polyimide having a structural unit represented by the general formula (1). A method for producing a polyimide including steps is also an aspect of the present invention.

For example, the tetravalent organic group represented by formula (A1) is derived from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (abbreviation: 6FDA) and represented by formula (A2). The tetravalent organic group is derived from 1,2,4,5-cyclohexanetetracarboxylic dianhydride (abbreviation: HPMDA) or the like, and the tetravalent organic group represented by formula (A3) is bicyclo[ 2.2.2] is derived from oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (abbreviation: BTA) and the like.

For example, the divalent organic group represented by formula (B1) is derived from 3,3′-diaminodiphenylsulfone (abbreviation: 3-DAS) and the like, and the divalent organic group represented by formula (B2) is derived from 4,4′-diaminodiphenylsulfone (abbreviation: 4-DAS) and the like, and the divalent organic group represented by formula (B3) is 2,2′-bis(trifluoromethyl)benzidine ( Abbreviated name: TFMB) or the like, the divalent organic group represented by formula (B4) is derived from 2,2-bis(4-aminophenyl)hexafluoropropane (abbreviation: 6F diamine) or the like, and The divalent organic group represented by the formula (B5) is derived from 1,4-cyclohexanediamine (trans isomer, cis isomer, or cis-, trans-mixture) (abbreviation: CyHex).

(b) Solvent As a solvent, a known solvent capable of dissolving polyamic acid or polyimide may be used. Among known solvents, ester group, ether group, ketone group, hydroxyl group, hydroxy group, Solvents containing at least one selected from the group consisting of sulfone groups and sulfinyl groups are preferred.

Solvents having an ester group include ester solvents such as methyl acetate, ethyl acetate, butyl acetate, and dimethyl carbonate.
Solvents having a cyclic ester group include lactone solvents such as γ-butyrolactone (GBL), δ-valerolactone, ε-caprolactone, γ-crotonolactone, γ-hexanolactone, α-methyl-γ-butyrolactone. , γ-valerolactone, α-acetyl-γ-butyrolactone, δ-hexanolactone and the like.
Solvents having an ether group include tetrahydrofuran, dioxane, dibutyl ether, and the like.
Solvents having a ketone group include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone.
Solvents having a hydroxyl group include phenolic solvents such as m-cresol.
Solvents having a sulfone group include methylsulfone, ethylphenylsulfone, diethylsulfone, diphenylsulfone, sulfolane, bisphenol S, sorapson, dapsone, bisphenol A polysulfone, and sulfolane.
Solvents having a sulfinyl group include sulfoxide solvents such as N,N-dimethylsulfoxide (DMSO).
Among these, GBL is preferable from the viewpoints of suppression of yellowing of the polyimide film, imidization at a relatively low temperature of about 220° C. or less, and imidization in the air.
In addition to the solvents listed above, amide solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc) and the like are used. can do.

(c) Additives The polyamic acid varnish may optionally contain additives. Additives include, for example, leveling agents, dispersants, or surfactants for improving coatability of the film, surfactants or adhesion aids for adjusting the peelability or adhesiveness of the film from the support, Flame retardant for imparting flame retardancy to the film, inorganic particles other than silica such as strontium carbonate for adjusting the retardation of the film, organic compounds such as polystyrene, polyvinylnaphthalene, polymethyl methacrylate, cellulose triacetate, and fluorene derivatives, Antioxidants, UV inhibitors, light stabilizers, plasticizers, waxes, fillers, pigments, dyes, foaming agents, antifoaming agents, dehydrating agents, antistatic agents, antibacterial agents, antifungal agents and the like may be used.
Additives added to the varnish may remain in the polyimide film.

A method for producing a polyamic acid varnish includes dissolving the diamine and dianhydride described above in (b) a solvent to produce (a) a polyamic acid as a polyimide precursor. The (c) additive may be added to the reaction solvent during or after the formation of the polyamic acid. The (c) additive added to the reaction solvent can be contained in the polyimide film as it is. The obtained reaction solvent can be used as it is as a polyamic acid varnish, or can be replaced with another solvent.

<Imidation>
The imidization conditions are not particularly limited, but for example, the reaction temperature may be 0° C. to 180° C., the reaction time may be 3 to 72 hours, and the reaction atmosphere may be an inert atmosphere such as argon or nitrogen. If desired, a solvent that is azeotropic with water, such as toluene, may be added to the polyamic acid varnish to facilitate removal of the water generated during the dehydration reaction of the polyamic acid.

〈Coating〉
The coating process can be carried out using various coating apparatuses depending on the application of the film, and for example, known coating methods such as spin coating, slit coating, slot die coating and blade coating may be used. .

Any support in the coating step, when used, includes, for example, an alkali glass substrate, a non-alkali glass substrate (Eagle XG (registered trademark), manufactured by Corning), and metals such as copper substrates, aluminum substrates, and SUS substrates. Substrate, or plastic film such as Upilex (registered trademark) film (manufactured by Ube Industries), Kapton (registered trademark) film (manufactured by Toray DuPont), polycarbonate film, PET film, etc., or copper foil, aluminum foil, SUS foil, etc. It may be a metal foil such as
Alternatively, as described above, polyamic acid varnish or polyimide varnish may be directly applied onto a flexible glass substrate to form a polyimide film.

〈Drying〉
In the drying step, the solvent is dried from the polyamic acid varnish or the polyimide varnish at a temperature of, for example, 150 to 350° C. to form a polyimide film. Although not wishing to be bound by theory, when the drying process is carried out in an inert gas atmosphere such as nitrogen gas, there is a tendency to obtain a colorless and transparent polyimide film regardless of the type of solvent contained in the polyamic acid varnish. be. On the other hand, when the solvent contained in the polyamic acid varnish is γ-butyrolactone (GBL), it is preferable to carry out the drying step in the air from the viewpoint of economy and colorless transparency of the film.

〈Stretching〉
When the polyimide film is individually produced and then laminated with the flexible glass, the resulting polyimide film may be stretched to thin the film before lamination with the flexible glass. For example, in order to obtain a film having a thickness of less than 10 μm, it can be produced by stretching a polyimide film having a thickness of 10 μm or more. The stretching treatment may be uniaxial stretching or biaxial stretching. In the case of biaxial stretching, simultaneous biaxial stretching or sequential biaxial stretching may be used.

《Laminate》
When polyamic acid varnish or polyimide varnish is directly coated on a flexible glass substrate to form a polyimide film, it can be used as a laminate as it is.
When the polyimide film is laminated on the flexible glass, the polyimide film and the flexible glass can be adhered with a sheet adhesive to form a laminate.

《Flexible Device》
The flexible device of this embodiment has the laminate of this embodiment. Preferably, a flexible display can be manufactured using the laminate of the present embodiment. Flexible displays include organic EL displays such as bottom emission flexible organic EL displays and top emission flexible organic EL displays; or flexible liquid crystal displays. When the laminate of the present embodiment is used in a flexible device, the flexible device is provided with a light source, and the light from the light source passes through the laminate of the present embodiment and is output to the outside of the flexible device. is preferred. When the laminate of the present embodiment is used for a flexible device, the laminate may be arranged so that the polyimide film is arranged closer to the light source than the flexible glass, and the flexible glass is arranged closer to the light source than the polyimide film. Laminates may be arranged as follows.

In another embodiment, a functional layer may be provided on the surface of the polyimide film. The functional layer can be obtained by forming, for example, a transparent electrode layer on the surface of the polyimide film using a sputtering apparatus. When the laminate of the present embodiment has polyimide films on both sides, the transparent electrode layer may be formed on both sides of the laminate of the present embodiment. At this time, it is preferable to form at least one or more transparent electrode layers on each of the polyimide films on both sides of the laminate. In addition, between the transparent electrode layer and the polyimide film, an undercoat layer for imparting smoothness, a hard coat layer for imparting surface hardness, an index matching layer for improving visibility, and gas barrier properties are imparted. You may have other layers, such as a gas barrier layer for carrying out. A hard coat layer for imparting surface hardness and an index matching layer for improving visibility may be laminated on the transparent electrode layer and the polyimide film. The laminate of this embodiment is particularly suitable for use in touch panel materials such as transparent electrode films.

EXAMPLES Hereinafter, embodiments of the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples and Comparative Examples.

《Measurement and evaluation method》
<Yellowness index (YI) and haze>
Using a Konica Minolta spectrophotometer (CM3600A) and a D65 light source, the yellowness (YI value) and haze of the laminate were measured.
The obtained yellowness index (YI) and haze were ranked according to the following criteria.
(Yellowness index (YI) rank)
◯ (Good): YI of the cured film is 5 or less.
x (defective): YI of the cured film exceeds 5;
(Haze Rank)
A (very good): Haze is 1% or less.
◯ (Good): Haze is 1.5% or less and more than 1%.
x (defective): Haze exceeds 1.5%.

<Arithmetic mean roughness (Ra)>
Using a nanoscale hybrid microscope (VN8000, manufactured by Keyence Corporation), the measurement area (50 μm × 50 μm) of the film layer side of the laminate was scanned to measure the arithmetic mean roughness (Ra). When there was a difference in Ra between the front and back of the film, the rougher value was used as the evaluation value.
(Ra rank)
○ (Good): Arithmetic mean roughness of 1.5 nm or less.
x (defective): Arithmetic mean roughness exceeds 1.5 nm.

<Gas barrier property>
The water vapor transmission rate of the laminate was measured by the MOCON method, and the water vapor transmission coefficient [g·mm/m ² ·day] was calculated.
(Gas barrier property rank)
◯ (Good): Water vapor permeability coefficient is 1×10 ⁻³ or less.
× (defective): Water vapor permeability coefficient exceeds 1×10 ⁻³ .

<Heat resistance (Tg)>
Measurement of the glass transition temperature (Tg) of the film layer was performed by thermomechanical analysis. After partially incising the support base material, it was allowed to absorb moisture for 24 hours in an environment with a temperature of 23 ° C. and a humidity of 90% RH or more, and the polyimide film was peeled off. Used as a piece. After conditioning the test piece at a temperature of 23 ° C. and a humidity of 50% RH, using a measuring device (EXSTAR6000) manufactured by Seiko Instruments Inc., a tensile load of 49 mN, a temperature increase rate of 10 ° C./min and under a nitrogen stream (flow rate 100 ml/min), the elongation of the test piece was measured in the temperature range of 50 to 350°C. The inflection point of the obtained chart was taken as the glass transition temperature.
(Heat resistance rank)
◯ (Good): Tg is 250° C. or higher.
x (defective): Tg is less than 250°C.

<Retardation (Rth)>
Rth of the laminate is determined by measuring Δn at a wavelength of 589 nm using a phase difference measurement device (KOBRA-WR) manufactured by Oji Scientific Instruments Co., Ltd., and assuming that the refractive index of the glass is not anisotropic, the film is obtained by the following formula. Rth was calculated in terms of a layer thickness of 15 μm.
Rth=Δn×d
Δn = {(Nx + Ny)/2-Nz}
Here, Nx and Ny indicate the refractive index in the plane direction, and Nz indicates the refractive index in the thickness direction.
where d refers to the thickness of the film layer. In this measurement, Rth (nm) was calculated with d=15 μm.
(Rth rank)
A (very good): Rth is 50 nm or less.
◯ (Good): Rth is more than 50 nm and 200 nm or less.
x (defective): Rth exceeds 200 nm.

"raw materials"
<Tetracarboxylic dianhydride>
6FDA: 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (corresponding to A1)
HPMDA: Cyclohexane-1,2,4,5-tetracarboxylic dianhydride (corresponding to A2)
BTA: bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (corresponding to A3)
ODPA: oxydiphthalic dianhydride (corresponding to A4)
PMDA: pyromellitic anhydride

<Diamine>
3-DAS: 3,3′-diaminodiphenylsulfone (corresponding to B1)
4-DAS: 3,3'-diaminodiphenylsulfone (corresponding to B2)
TFMB: 2,2'-bis(trifluoromethyl)benzidine (corresponding to B3)
6F diamine: 2,2-bis(4-aminophenyl)hexafluoropropane (corresponding to B4)
CyHex: 1,4-cyclohexanediamine (corresponding to B5)

<Resin film>
PET film: Cosmoshine A4100 (registered trademark) (manufactured by Toyobo Co., Ltd.)
PEN film: Teonex (registered trademark) (manufactured by Teijin)

<<Synthesis example>>
Into a 500 mL separable flask equipped with a stirring bar, while introducing nitrogen gas, acid dianhydride and diamine were added in the presence of γ-butyrolactone solvent as shown in Table 1, then using an oil bath for 40 minutes. C. and stirred for 3 to 12 hours, the oil bath was removed and the temperature was returned to room temperature to obtain a polyamic acid solution (hereinafter also referred to as a polyamic acid varnish).

《Laminate》
In Examples 1 and 2, and Comparative Examples 1 and 6 to 8 , polyimide films were prepared by casting polyamic acid varnish using flexible glass as a support, followed by heating and drying. The flexible glass support and the prepared polyimide film were directly used as a laminate.
Comparative Example 2 is a single film layer.
In Comparative Examples 3 and 4, a sheet adhesive was used to laminate flexible glass and a resin film to form a laminate.

Claims (13)

at least one layer of polyimide film;
A laminate in which at least one layer of flexible glass is laminated,
The polyimide film has the following formula (1):

{wherein X ₁ is a tetravalent organic group, Y ₁ is a divalent organic group, and m is a positive integer. m is an integer from 2 to 150; }
contains a structural unit represented by
Y ₁ includes a divalent organic group represented by the following formula (B1) and a divalent organic group other than the following formula (B1),

A laminate, wherein the polyimide film has a yellowness index (YI) of 5 or less, and an arithmetic mean roughness (Ra) of at least one surface of the laminate of 1.5 nm or less. The laminate according to claim 1, wherein the divalent organic group other than the formula (B1) is at least one selected from divalent organic groups represented by the following formulas (B2) to (B5). .

3. The laminate according to claim 2, wherein the divalent organic group other than the formula (B1) is a divalent organic group represented by the formula (B2). The laminate according to any one of claims 1 to 3, wherein the polyimide film has a haze of 1% or less. The laminate according to any one of claims 1 to 4, wherein the polyimide film has a thickness of 2 µm or more and 100 µm or less, and the flexible glass has a thickness of 30 µm or more and 200 µm or less. The polyimide film has the following formula (2):

{wherein X ₂ is a tetravalent organic group, Y ₂ is a divalent organic group, X ₂ may be the same as or different from X ₁ , and Y ₂ is the same as Y ₁ ; may be different, n ₁ is an integer of 2 to 150, and R ₁ and R ₂ are each independently a hydrogen atom or a monovalent organic group}
The laminate according to any one of claims 1 to 5 , further comprising a structural unit represented by 7. The invention according to any one of claims 1 to 6, wherein in (1), X ₁ is at least one tetravalent organic group selected from the group consisting of formulas (A1) to (A4) below. laminate.

8. The laminate according to claim 7 _, wherein X1 is formula (A1). 8. The laminate according to claim 7 _, wherein X1 is formula (A2). 8. The laminate according to claim 7 _, wherein X1 is formula (A3). 8. The laminate according to claim 7 _, wherein X1 is formula (A4). The laminate according to any one of claims 1 to 11 , wherein one layer of said flexible glass is laminated between two layers of said polyimide film. A flexible device comprising the laminate according to any one of claims 1 to 12 .