JP7579649B2 - Resin composition for printed circuit boards and resin molded body - Google Patents

Description

The present invention relates to a resin composition and a resin molded body for printed circuit boards, in particular a resin composition and a resin molded body suitable as materials for printed circuit boards in electronic devices that use radio waves in the high frequency band.

Electronic devices such as information and communication devices are equipped with printed circuit boards on which electronic components are mounted and which function as electronic circuits. Printed circuit boards usually have a laminated structure including a metal layer on which a patterned circuit is formed and a substrate that supports the metal layer. Like printed circuit boards, printed wiring boards before electronic components are mounted also have the above-mentioned laminated structure. In this specification, printed circuit boards and printed wiring boards are simply referred to as "printed boards."

The substrate included in the printed circuit board is formed, for example, from a resin composition. From the viewpoints of insulation, water resistance, etc., it is preferable that the resin composition for forming the substrate contains a fluorine-containing polymer. For example, Patent Documents 1 and 2 exemplify printed circuit boards as an application of a resin composition in which a fluorine-containing polymer is mixed with an inorganic filler or a liquid crystal polymer. In the examples of Patent Documents 1 and 2, a fluorine-containing polymer containing a monomer unit derived from tetrafluoroethylene (TFE) is disclosed.

JP 2016-65217 A JP 2018-177931 A

In recent years, in the field of information and communications, the use of radio waves in the high frequency band has been considered in response to the increasing amount of information to be processed. For example, the fifth generation mobile communication system (5G) uses radio waves with a frequency of about 28 GHz. However, the higher the frequency of the radio waves used, the greater the signal transmission loss in the printed circuit board. With conventional resin compositions for printed circuit boards, it is difficult to sufficiently suppress the increase in signal transmission loss in the printed circuit board when radio waves in the high frequency band are used.

The present invention aims to provide a resin composition for printed circuit boards that is suitable for suppressing an increase in signal transmission loss in printed circuit boards, even when radio waves in the high frequency band are used.

［式（１）中、Ｒ_ff ¹～Ｒ_ff ⁴は各々独立に、フッ素原子、炭素数１～７のパーフルオロアルキル基、又は炭素数１～７のパーフルオロアルキルエーテル基を表す。Ｒ_ff ¹及びＲ_ff ²は、連結して環を形成してもよい。］ The present invention relates to
The present invention provides a resin composition for printed circuit boards, which comprises a fluorine-containing polymer having a structural unit (A) represented by the following formula (1):

[In formula (1), R _ff ¹ to R _ff ⁴ each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. R _ff ¹ and R _ff ² may be linked to form a ring.]

［式（１）中、Ｒ_ff ¹～Ｒ_ff ⁴は各々独立に、フッ素原子、炭素数１～７のパーフルオロアルキル基、又は炭素数１～７のパーフルオロアルキルエーテル基を表す。Ｒ_ff ¹及びＲ_ff ²は、連結して環を形成してもよい。］ Further, the present invention relates to
The present invention provides a resin molded article for printed circuit boards, which comprises a fluorine-containing polymer having a structural unit (A) represented by the following formula (1):

[In formula (1), R _ff ¹ to R _ff ⁴ each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. R _ff ¹ and R _ff ² may be linked to form a ring.]

The present invention provides a resin composition for printed circuit boards that is suitable for suppressing an increase in signal transmission loss in printed circuit boards, even when radio waves in the high frequency band are used.

The following describes an embodiment of the present invention, but the following description is not intended to limit the present invention to a specific embodiment.

[Resin composition for printed circuit boards]
The resin composition for printed circuit boards of this embodiment (hereinafter sometimes simply referred to as "resin composition") contains a fluoropolymer having a structural unit (A) represented by the following formula (1). The structural unit (A) is a structural unit suitable for lowering the relative dielectric constant of the resin composition in the high frequency band. The fluoropolymer containing the structural unit (A) also has the characteristic of being easily soluble in a solvent.

In formula (1), R _ff ¹ to R _ff ⁴ each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. R _ff ¹ and R _ff ² may be linked to form a ring. "Perfluoro" means that all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. In formula (1), the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5, more preferably 1 to 3, and even more preferably 1. The perfluoroalkyl group may be linear or branched. Examples of the perfluoroalkyl group include a trifluoromethyl group, a pentafluoroethyl group, and a heptafluoropropyl group.

In formula (1), the number of carbon atoms in the perfluoroalkyl ether group is preferably 1 to 5, and more preferably 1 to 3. The perfluoroalkyl ether group may be linear or branched. Examples of perfluoroalkyl ether groups include a perfluoromethoxymethyl group.

When R _ff ¹ and R _ff ² are linked to form a ring, the ring may be a 5-membered ring or a 6-membered ring. Examples of the ring include a perfluorotetrahydrofuran ring, a perfluorocyclopentane ring, and a perfluorocyclohexane ring.

Specific examples of the structural unit (A) include structural units represented by the following formulas (A1) to (A8).

Of the structural units represented by the above formulas (A1) to (A8), the structural unit (A) is preferably the structural unit (A2), that is, the structural unit represented by the following formula (2).

The structural unit (A) is derived from a compound represented by the following formula (3), for example: In formula (3), R _ff ¹ to R _ff ⁴ are the same as those in formula (1).

Specific examples of the compound represented by formula (3) above include compounds represented by formulas (M1) to (M8) below.

The fluorine-containing polymer may contain one or more types of structural unit (A). The fluorine-containing polymer contains, for example, the structural unit (A) as a main component. In this specification, "main component" means the structural unit contained most abundantly in the fluorine-containing polymer on a molar basis. The content of the structural unit (A) in the fluorine-containing polymer is, for example, 80 mol% or more, preferably 90 mol% or more, and more preferably 95 mol% or more. The fluorine-containing polymer is, for example, substantially composed of the structural unit (A). The content of the structural unit (A) in the fluorine-containing polymer may be 99 mol% or less.

The fluorine-containing polymer may contain, in addition to the structural unit (A), a structural unit (B) having at least one functional group (F) selected from the group consisting of a carbonyl-containing group, a hydroxyl group, an epoxy group, an isocyanate group, and a cyano group. The structural unit (B) is a structural unit suitable for improving the adhesiveness of the resin composition. A resin molded product formed from a resin composition having sufficient adhesiveness can be easily bonded to a metal layer of a printed circuit board.

The structural unit (B) is not particularly limited as long as it has the above-mentioned functional group (F). The structural unit (B) is derived, for example, from a compound having a carbon-carbon double bond and a functional group (F). The structural unit (B) preferably does not contain hydrogen atoms, but may contain hydrogen atoms. The hydrogen atoms bonded to the carbon atoms contained in the structural unit (B) may be substituted with fluorine atoms.

Examples of the carbonyl-containing group of the functional group (F) include an acid anhydride group, a carboxy group, an acid halide group, an alkoxycarbonyl group, and a carbonate group, and an acid anhydride group is preferred. From the viewpoint of improving the adhesiveness of the resin composition, the structural unit (B) preferably has at least one selected from the group consisting of an acid anhydride group, an epoxy group, an isocyanate group, and a cyano group, and more preferably has an acid anhydride group. When the structural unit (B) contains a cyano group, the fluorine-containing polymer can form a trimer via the cyano group. The trimer of the fluorine-containing polymer is suitable for improving the durability of a resin molded product formed from the resin composition.

The structural unit (B) may have a ring structure. The ring structure of the structural unit (B) may be monocyclic or polycyclic. The number of carbon atoms in the ring structure of the structural unit (B) is, for example, 4 to 10, and preferably 4 to 6. In the structural unit (B), the ring structure may have a functional group (F) as a substituent, or the ring structure itself may contain a functional group (F). The ring structure of the structural unit (B) is preferably an acid anhydride ring. The carbon atoms contained in the ring structure of the structural unit (B) may form the main chain of the fluorine-containing polymer.

Specific examples of the structural unit (B) containing an acid anhydride ring include a structural unit derived from itaconic anhydride, a structural unit derived from maleic anhydride, and a structural unit derived from 5-norbornene-2,3-dicarboxylic anhydride. That is, examples of compounds that form the structural unit (B) containing an acid anhydride ring include itaconic anhydride, maleic anhydride, and 5-norbornene-2,3-dicarboxylic anhydride.

Examples of the structural unit (B) containing a cyano group include structural units derived from vinyl ether compounds containing a cyano group. The vinyl ether compounds containing a cyano group may be fully fluorinated, and examples of such structural units include perfluoro(5-cyano-3-oxa-1-hexene), perfluoro(7-cyano-5-methyl-3,6-dioxa-1-heptene), perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene), and perfluoro(9-cyano-5-methyl-3,6-dioxa-1-octene). Examples include perfluoro-(10-cyano-5-methyl-3,6-dioxa-1-decene), perfluoro-(11-cyano-5,8-dimethyl-3,6,9-trioxa-1-undecene), and perfluoro(8-cyano-5-methyl-3,6-dioxa-1-nonene). A method for producing a vinyl ether compound containing a cyano group is described, for example, in U.S. Pat. No. 4,281,092.

The fluorine-containing polymer may contain one or more types of structural unit (B). The content of structural unit (B) in the fluorine-containing polymer is, for example, 20 mol % or less, preferably 10 mol % or less, and more preferably 5 mol % or less. The fluorine-containing polymer may not contain structural unit (B). The content of structural unit (B) may be 1 mol % or more. By adjusting the content of structural unit (B) in the fluorine-containing polymer to the range of 1 mol % to 20 mol %, there is a tendency to improve the adhesiveness of the resin composition while reducing the relative dielectric constant of the resin composition in the high frequency band.

The fluorine-containing polymer may further contain other structural units (C) other than the structural units (A) and (B). Examples of compounds that form the other structural units (C) include fluorine-containing olefin compounds such as tetrafluoroethylene and chlorotrifluoroethylene; perfluorovinyl ether compounds such as perfluoropropyl vinyl ether; and fluorine-containing compounds having two or more polymerizable double bonds and capable of cyclopolymerization, such as perfluoroallyl vinyl ether and perfluorobutenyl vinyl ether. However, from the viewpoint of the relative dielectric constant of the resin composition in the high frequency band, it is preferable that the fluorine-containing polymer does not contain other structural units (C).

The polymerization method for the fluorine-containing polymer is not particularly limited, and a general polymerization method such as radical polymerization can be used. The polymerization initiator for polymerizing the fluorine-containing polymer may be a perfluorinated compound.

The weight average molecular weight of the fluoropolymer is, for example, 50,000 to 1,000,000. The glass transition temperature (Tg) of the fluoropolymer is, for example, 100° C. to 140° C. In this specification, Tg means the midpoint glass transition temperature (T _mg ) determined in accordance with the provisions of JIS K7121:1987. The 1% weight loss temperature of the fluoropolymer is, for example, 220° C. or higher. In this specification, the 1% weight loss temperature means the temperature at which the weight of the fluoropolymer decreases by 1% from the weight before the start of measurement when the fluoropolymer is heated from room temperature (20° C.±15° C.) at a heating rate of 10° C./min in an air atmosphere using a thermogravimetric analyzer (TGA).

The melting point of the fluoropolymer is, for example, 100°C or higher and 330°C or lower, and preferably 120°C or higher and 300°C or lower. A fluoropolymer having a melting point of 100°C or higher and 330°C or lower is suitable for melt molding.

The content of the fluorine-containing polymer in the resin composition is, for example, 70 wt % or more, and preferably 90 wt % or more. The resin composition is, for example, substantially composed of a fluorine-containing polymer. When the resin composition contains a solvent described below, the content of the fluorine-containing polymer in the resin composition may be 10 wt % to 50 wt %, or may be 20 wt % to 40 wt %.

The resin composition may further contain other components other than the fluorine-containing polymer. Examples of the other components include hollow particles, a foaming agent, a porogen (pore-forming agent), and a solvent. The resin composition may contain, for example, at least one selected from the group consisting of a foaming agent and a porogen. The hollow particles may be suitable for reducing the relative dielectric constant of the resin composition in the high frequency band. The hollow particles may improve the mechanical properties or realize low linear expansion of a molded body formed from the resin composition. The hollow particles are preferably composed of an inorganic compound, and particularly preferably contain hollow silica particles. The hollow particles may be a mixture of hollow silica particles and other hollow particles, or may be composed of hollow silica particles alone.

The average particle size of the hollow particles is preferably in the range of 10 nm to 200 nm, and more preferably in the range of 50 nm to 120 nm. The average particle size of the hollow particles can be determined, for example, by the following method. First, the resin composition is observed with a transmission electron microscope (TEM). In the obtained electron microscope image, the area of a specific hollow particle is calculated by image processing. The diameter of a circle having the same area as the calculated area is regarded as the particle size (particle diameter) of the specific hollow particle. The particle sizes of an arbitrary number of hollow particles (at least 50 particles) are calculated, and the average of the calculated values is regarded as the average particle size of the hollow particles. The shape of the hollow particles is not particularly limited, and may be spherical, ellipsoidal, scaly, or fibrous.

The hollow particle content in the resin composition is not particularly limited, and is preferably in the range of 1 wt% to 90 wt%, more preferably in the range of 1 wt% to 80 wt%, even more preferably in the range of 5 wt% to 70 wt%, and may be 30 wt% to 70 wt%. In some cases, the hollow particle content in the resin composition may be 1 wt% to 30 wt%, 1 wt% to 25 wt%, or 5 wt% to 25 wt%. The hollow particle content in the resin composition can be calculated, for example, from the ratio of the area of the resin composition portion to the area of the hollow particle portion in the above electron microscope image.

The hollow particles are preferably uniformly dispersed in the resin composition, and are preferably dispersed in the form of primary particles without forming aggregates (i.e., secondary particles). From the viewpoint of dispersibility, it is preferable that the hollow particles have been subjected to a surface treatment, such as a hydrophobic treatment.

Examples of the foaming agent contained in the resin composition include known physical foaming agents and chemical foaming agents. When the resin composition contains a foaming agent, a resin molded body having a porous structure can be obtained by foaming the resin composition with the foaming agent.

The porogen is, for example, a solvent that causes reaction-induced phase separation during polymerization of the above-mentioned fluorine-containing polymer. By removing the porogen from the resin composition in which reaction-induced phase separation has occurred, a resin molded product having a porous structure can be obtained. Examples of the porogen include linear hydrocarbons and cyclic hydrocarbons. In particular, from the viewpoint of phase separation and removability, cyclic hydrocarbons, particularly polycyclic hydrocarbons, are preferably used. As the cyclic hydrocarbons, in particular, monoterpenes such as menthane, limonene, phellandrene, terpinolene, terpinene, cymene, and camphor; and polycyclic hydrocarbons such as norbornene, adamantane, and dicyclopentadiene are preferred.

The content of the foaming agent or porogen in the resin composition is determined according to the type of foaming agent, the type of porogen, the composition of the resin composition, etc., and is, for example, in the range of 1 wt% to 90 wt%.

The solvent contained in the resin composition is preferably one that dissolves or disperses the fluorine-containing polymer. Examples of the solvent include 1H-tridecafluorohexane (manufactured by Asahi Glass Co., Ltd., Asahiklin (registered trademark) AC2000), 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane (manufactured by Asahi Glass Co., Ltd., Asahiklin (registered trademark) AC6000), 1,1,2,2-tetrafluoro-1-(2,2,2-tri'"fluoroethoxy)ethane (manufactured by Asahi Glass Co., Ltd., Asahiklin (registered trademark) AE3000), dichloropentafluoropropane (manufactured by Asahi Glass Co., Ltd., Asahiklin (registered trademark) AK-225), 1,1,1,2,3,4,4,5, 5,5-Decafluoro-3-methoxy-2-(trifluoromethyl)pentane (manufactured by Asahi Glass Co., Ltd., Cytop (registered trademark) CT-solv100E), 1-methoxynonafluorobutane (manufactured by 3M Japan, Ltd., Novec (registered trademark) 7100), 1-ethoxynonafluorobutane (manufactured by 3M Japan, Ltd., Novec (registered trademark) 7200), perfluorohexyl methyl ether (manufactured by 3M Japan, Ltd., Novec (registered trademark) 7300), 1,1,1,2,3,3-hexafluoro-4-(1,1,2,3,3,3-hexafluoro (3M Japan, Novec (registered trademark) 7600), 2H,3H-perfluoropentane (Mitsui-Chemours Fluorochemicals, Vertrel (registered trademark) XF), 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanol, 4,4,5,5,6,6,7,7,8,8,9,9,9-tridecafluoro-1-nonanol, hexafluorobenzene, hexafluoro-2-propanol, 2,2,3,3,4,4,5,5-octafluoro-1-pentanol, 1H, Examples of the solvent include fluorine-containing compounds such as 1H,7H-dodecafluoro-1-heptanol, and other commercially available fluorine-based solvents (for example, Fluorinert (registered trademark) FC-770 and FC-72 manufactured by 3M Japan, and Cerefin (registered trademark) 1233Z manufactured by Central Glass Co., Ltd.). The resin composition may contain one or more of these solvents. From the viewpoint of the solubility of the components contained in the resin composition, the solvent is preferably hexafluorobenzene, perfluorohexyl methyl ether, or 2H,3H-perfluoropentane.

From the viewpoint of improving mechanical properties, the resin composition may contain liquid crystal polymers or inorganic fillers other than hollow particles. However, from the viewpoint of the relative dielectric constant of the resin composition in the high frequency band, it is preferable that the resin composition does not contain liquid crystal polymers or inorganic fillers other than hollow particles. In some cases, the resin composition may not contain hollow particles.

The resin composition of this embodiment has a relative dielectric constant of 2.40 or less at a frequency of 28 GHz. The relative dielectric constant of the resin composition at a frequency of 28 GHz is preferably 2.30 or less, more preferably 2.20 or less, even more preferably 2.15 or less, particularly preferably 2.10 or less, and particularly preferably 2.05 or less. The lower limit of the relative dielectric constant of the resin composition at a frequency of 28 GHz is not particularly limited, and is, for example, 1.50. The relative dielectric constant of the resin composition at a frequency of 28 GHz can be determined, for example, by the Fabry-Perot method or the cavity resonator method in accordance with the provisions of Japanese Industrial Standards (JIS) R1641:2007. In addition, when the resin composition contains a solvent, the relative dielectric constant should be measured after removing the solvent from the resin composition. In this specification, the relative dielectric constant means a value in an environment of 23°C ± 2°C and 60 ± 5% RH.

The transmission loss α of the dielectric is expressed by the following formula (i). Therefore, if the relative dielectric constant of the resin composition at a frequency of 28 GHz is 2.40 or less, even when radio waves in a high frequency band are used, there is a tendency that an increase in the transmission loss of signals in a printed circuit board can be sufficiently suppressed. In the following formula (i), K represents a proportional constant, f represents a frequency, εr represents a relative dielectric constant, and tan δ represents a dielectric tangent.

It is preferable that the resin composition has a low dielectric constant even in frequency bands higher than 28 GHz. As an example, the dielectric constant of the resin composition at a frequency of 75 GHz is preferably 2.40 or less, more preferably 2.30 or less, even more preferably 2.15 or less, particularly preferably 2.10 or less, and especially preferably 2.05 or less. The lower limit of the dielectric constant of the resin composition at a frequency of 75 GHz is not particularly limited, and is, for example, 1.50. The dielectric constant of the resin composition at a frequency of 75 GHz can be determined, for example, by the Fabry-Perot method or the cavity resonator method in accordance with the provisions of JIS R1660-1:2004.

It is preferable that the resin composition has a low dielectric tangent in the high frequency band. As can be seen from the above formula (i), the lower the dielectric tangent tan δ, the more likely it is that the increase in signal transmission loss in the printed circuit board can be suppressed, even when radio waves in the high frequency band are used. As an example, the dielectric tangent of the resin composition at a frequency of 28 GHz is preferably 0.001 or less, more preferably 0.0005 or less, and even more preferably 0.0003 or less. The lower limit of the dielectric tangent of the resin composition at a frequency of 28 GHz is not particularly limited, and is, for example, 0.0001. The dielectric tangent of the resin composition at a frequency of 28 GHz can be determined, for example, by the Fabry-Perot method or the cavity resonator method in accordance with the provisions of JIS R1641:2007.

It is preferable that the resin composition has a low dielectric tangent even in a frequency band higher than 28 GHz. As an example, the dielectric tangent of the resin composition at a frequency of 75 GHz is preferably 0.001 or less, more preferably 0.0005 or less, and even more preferably 0.0003 or less. The lower limit of the dielectric tangent of the resin composition at a frequency of 75 GHz is not particularly limited, and is, for example, 0.0001. The dielectric tangent of the resin composition at a frequency of 75 GHz can be determined, for example, by the Fabry-Perot method or the cavity resonator method in accordance with the provisions of JIS R1660-1:2004.

[Resin molded body for printed circuit boards]
The resin molded product for printed circuit boards of this embodiment (hereinafter, sometimes simply referred to as "resin molded product") is obtained by molding the above-mentioned resin composition. Therefore, the resin molded product contains the above-mentioned fluorine-containing polymer, i.e., a fluorine-containing polymer having the structural unit (A). The composition of the resin molded product is the same as the composition of the resin composition, except that it does not contain, for example, a foaming agent, a porogen, or a solvent.

Like the resin composition, the resin molded body tends to have a low relative dielectric constant at a frequency of 28 GHz. The relative dielectric constant of the resin molded body at a frequency of 28 GHz is, for example, 2.40 or less, preferably 2.30 or less, more preferably 2.20 or less, even more preferably 2.15 or less, particularly preferably 2.10 or less, and especially preferably 2.05 or less. The lower limit of the relative dielectric constant of the resin molded body at a frequency of 28 GHz is not particularly limited, and is, for example, 1.50. The relative dielectric constant of the resin molded body at a frequency of 28 GHz can be determined by the measurement method described above for the resin composition.

It is preferable that the resin molding has a low dielectric constant even in frequency bands higher than 28 GHz. As an example, the dielectric constant of the resin molding at a frequency of 75 GHz is preferably 2.40 or less, more preferably 2.30 or less, even more preferably 2.15 or less, particularly preferably 2.10 or less, and especially preferably 2.05 or less. The lower limit of the dielectric constant of the resin molding at a frequency of 75 GHz is not particularly limited, and is, for example, 1.50. The dielectric constant of the resin molding at a frequency of 75 GHz can be determined by the measurement method described above for the resin composition.

It is preferable that the resin molding has a low dielectric loss tangent in the high frequency band. As an example, the dielectric loss tangent of the resin molding at a frequency of 28 GHz is preferably 0.001 or less, more preferably 0.0005 or less, and even more preferably 0.0003 or less. The lower limit of the dielectric loss tangent of the resin molding at a frequency of 28 GHz is not particularly limited, and is, for example, 0.0001. The dielectric loss tangent of the resin molding at a frequency of 28 GHz can be determined by the measurement method described above for the resin composition.

It is preferable that the resin molding has a low dielectric loss tangent even in frequency bands higher than 28 GHz. As an example, the dielectric loss tangent of the resin molding at a frequency of 75 GHz is preferably 0.001 or less, more preferably 0.0005 or less, and even more preferably 0.0003 or less. The lower limit of the dielectric loss tangent of the resin molding at a frequency of 75 GHz is not particularly limited, and is, for example, 0.0001. The dielectric loss tangent of the resin molding at a frequency of 75 GHz can be determined by the measurement method described above for the resin composition.

The resin molded body preferably has a porous structure. The porous structure may be suitable for reducing the relative dielectric constant of the resin molded body in the high frequency band. The porous structure of the resin molded body may be due to hollow particles, may be formed by foaming the resin composition with a foaming agent, or may be formed by reaction-induced phase separation of the resin composition with a porogen. The porous structure of the resin molded body is preferably composed of pores that are independent of each other (independent pores), but may also include pores that are connected inside the resin molded body (connected pores).

The average diameter of the pores in the resin molded body is preferably in the range of 10 nm to 100 μm, more preferably in the range of 10 nm to 10 μm, and even more preferably in the range of 50 nm to 1 μm. The average diameter of the pores in the resin molded body can be determined, for example, as follows. First, the resin molded body is cut. The cut surface of the resin molded body is observed with a transmission electron microscope. In the obtained electron microscope image, the maximum diameter of the pores is calculated, and the calculated value is regarded as the diameter of that specific pore. The diameters of an arbitrary number of pores (at least 50 pores) are calculated, and the average of the calculated values is regarded as the average diameter of the pores.

The porosity of the resin molded body is, for example, 1% to 90%, or may be 1% to 80%, 5% to 70%, or 30% to 70%. The porosity of the resin molded body can be calculated from the volume V (cm ³ ), true specific gravity D (g/cm ³ ), and mass M (g) of the resin molded body by the formula: porosity (%) = {1 - M/(V x D)} x 100.

The resin molded body has, for example, a film shape. The film-shaped resin molded body is suitable as a base material for a printed circuit board. It is preferable that the film-shaped resin molded body has isotropy. The thickness of the film-shaped resin molded body is not particularly limited, and is, for example, 3 μm to 5 mm, preferably 5 μm to 800 μm, and more preferably 10 μm to 200 μm.

Molding methods for obtaining resin molded bodies include extrusion molding, press molding, and inflation molding. When the resin composition contains a solvent, the resin composition can be applied to any substrate and the resulting coating film can be dried to produce a resin molded body.

[Printed circuit board]
The printed circuit board of the present embodiment includes, for example, a substrate, a metal layer, and an insulating layer, and the metal layer is located between the substrate and the insulating layer. In the printed circuit board, at least one of the substrate and the insulating layer is typically the above-mentioned resin molded body. The insulating layer may be composed of a known solder resist instead of the resin molded body. For example, a pattern circuit is formed on the metal layer. The material of the metal layer is not particularly limited, but is preferably copper.

The printed circuit board may further include layers other than the substrate, metal layer, and insulating layer. Examples of materials for the other layers include glass, ceramics, and resin compositions other than the above-mentioned resin compositions. The other layers may be prepregs or coverlay films disposed on the insulating layer. The coverlay film is, for example, a polyimide film.

The printed circuit board can be produced, for example, by the following method. First, a metal film before forming a pattern circuit is formed on the above-mentioned resin molded body. The metal film can be produced, for example, by laminating a metal foil on the resin molded body and bonding them by thermocompression bonding or the like. The metal film may be produced by using a physical method such as sputtering, vapor deposition, or ion plating, or a chemical method such as electroless plating or electrolytic plating. Furthermore, the metal film can also be produced by applying a conductive ink to the resin molded body by a screen printing method, an inkjet method, or the like. In order to improve adhesion with the metal film, the resin molded body may be subjected to a surface treatment in advance. Examples of the surface treatment include plasma treatment, corona treatment, flame treatment, and itro treatment. Next, a pattern circuit is formed on the metal film by etching. This results in a laminate of the substrate (resin molded body) and the metal layer.

Next, a coating liquid containing the material for the insulating layer is applied onto the metal layer. When the resin composition contains a solvent, the resin composition can be used as is as the coating liquid. Examples of methods for applying the coating liquid include spraying, roll coating, spin coating, bar coating, gravure coating, microgravure coating, gravure offset, knife coating, kiss coating, die coating, fountain-meyer bar, and slot die coating. Next, the resulting coating film is dried to form an insulating layer. The coating film can be dried using an oven, a continuous drying furnace, or by irradiation with heat rays such as infrared rays. This allows a printed circuit board to be produced.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

Example 1
<Synthesis of poly(perfluoro-4-methyl-2-methylene-1,3-dioxolane)>
First, a reaction product was obtained by a dehydration condensation reaction of 2-chloro-1-propanol, 1-chloro-2-propanol, and methyl trifluoropyruvate. The reaction product was purified to obtain 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane. Next, fluorination treatment of 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane was carried out. 1,1,2-trichlorotrifluoroethane was used as a solvent for the fluorination treatment. In the fluorination treatment, first, nitrogen gas and fluorine gas were each flowed into the reaction tank at a constant flow rate. Under an atmosphere of nitrogen and fluorine, 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane was slowly added to the reaction tank. As a result, 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane was fluorinated. The obtained fluorinated product was distilled to obtain perfluoro-2,4-dimethyl-1,3-dioxolane-2-carboxylic acid. This was neutralized with an aqueous potassium hydroxide solution to obtain potassium perfluoro-2,4-dimethyl-2-carboxylate-1,3-dioxolane. This potassium salt was vacuum dried and further decomposed under an argon atmosphere to obtain perfluoro-4-methyl-2-methylene-1,3-dioxolane (PFMMD).

Next, perfluoro-4-methyl-2-methylene-1,3-dioxolane and perfluorobenzoyl peroxide were placed in a glass tube, which was degassed using a freeze/thaw vacuum machine. The glass tube was then filled with argon and heated for several hours. This caused the contents to solidify, yielding a transparent polymer. The polymer was a homopolymer of perfluoro-4-methyl-2-methylene-1,3-dioxolane (poly-PFMMD). Next, a sheet-shaped test specimen was made using this polymer.

Example 2
10.0 g of poly-PFMMD obtained in Example 1 and 3.0 g of hollow silica particles (average particle size 110 nm) were put into a simple kneader (Labo Plastomill manufactured by Toyo Kikai Co., Ltd.) and mixed at 230°C and 60 rpm for 30 minutes. As a result, 13.0 g of a milky white resin kneaded product was obtained. A sheet-shaped test piece was produced using this resin kneaded product.

Example 3
Perfluoro-4-methyl-2-methylene-1,3-dioxolane (PFMMD), perfluoropropyl vinyl ether (PFPVE) and perfluorobenzoyl peroxide obtained in Example 1 were placed in a glass tube, which was degassed using a freeze/thaw vacuum machine. The weight ratio of PFMMD to PFPVE (PFMMD/PFPVE) was 95/5. Next, argon was filled into the glass tube, and the tube was heated for several hours. This solidified the contents, and a transparent polymer was obtained. Next, a sheet-shaped test piece was prepared using this polymer.

(Comparative Example 1)
Perfluoropropyl vinyl ether and perfluorobenzoyl peroxide were placed in a glass tube and degassed using a freeze/thaw vacuum machine. The glass tube was then filled with argon and heated for several hours. This caused the contents to solidify, resulting in a transparent polymer. Sheet-shaped test specimens were then made using this polymer.

(Comparative Example 2)
Perfluorohexyl vinyl ether (PFOVE) and perfluorobenzoyl peroxide were placed in a glass tube and degassed using a freeze/thaw vacuum machine. The glass tube was then filled with argon and heated for several hours. This caused the contents to solidify, resulting in a transparent polymer. Sheet-shaped test specimens were then made using this polymer.

(Dielectric constant)
The dielectric constants of the test pieces of the examples and comparative examples at a frequency of 28 GHz and at a frequency of 75 GHz were measured using the Fabry-Perot method. For the test piece of Example 1, the dielectric loss tangent was also measured using the Fabry-Perot method. The results are shown in Table 1.

As can be seen from Table 1, the resin compositions of Examples 1 to 3, which contain a fluorinated polymer having structural unit (A), have a lower relative dielectric constant in the high frequency band compared to Comparative Examples 1 and 2. In light of the above formula (i), it can be said that the resin compositions of Examples 1 to 3 are suitable for suppressing an increase in signal transmission loss in a printed circuit board, even when radio waves in the high frequency band are used.

The resin composition and resin molded body of this embodiment are suitable as materials for printed circuit boards, particularly printed circuit boards used in electronic devices that use radio waves in the high frequency band.

Claims (18)

A resin composition for printed circuit boards comprising a fluorine-containing polymer having as a main component a structural unit (A) represented by the following formula (1):

[In formula (1), R _ff ¹ to R _ff ⁴ each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. R _ff ¹ and R _ff ² may be linked to form a ring.] The resin composition according to claim 1 , wherein the structural unit (A) is represented by the following formula (2):

The resin composition according to claim 1 or 2, wherein the fluorine-containing polymer contains a structural unit (B) having at least one functional group selected from the group consisting of a carbonyl-containing group, a hydroxyl group, an epoxy group, an isocyanate group, and a cyano group. The resin composition according to claim 3, wherein the structural unit (B) has at least one functional group selected from the group consisting of an acid anhydride group, an epoxy group, an isocyanate group, and a cyano group. The resin composition according to claim 3 or 4, wherein the structural unit (B) has an acid anhydride group. The resin composition according to any one of claims 3 to 5, wherein the structural unit (B) has a ring structure. The resin composition according to any one of claims 1 to 6, having a relative dielectric constant of 2.40 or less at a frequency of 28 GHz. The resin composition according to any one of claims 1 to 7, further comprising hollow particles. The resin composition according to claim 8, wherein the hollow particles are composed of an inorganic compound. The resin composition according to claim 8 or 9, wherein the hollow particles include hollow silica particles. The resin composition according to any one of claims 8 to 10, wherein the hollow particles have an average particle size of 50 nm or more and 120 nm or less. The resin composition according to any one of claims 8 to 11, wherein the hollow particle content is 1 wt% or more and 90 wt% or less. The resin composition according to any one of claims 1 to 12, wherein the melting point of the fluoropolymer is 100°C or higher and 330°C or lower. The resin composition according to any one of claims 1 to 13, further comprising a solvent that dissolves or disperses the fluorine-containing polymer. The resin composition according to any one of claims 1 to 14, further comprising at least one selected from the group consisting of a foaming agent and a porogen. A resin molded article for printed circuit boards, comprising a fluorine-containing polymer having as a main component a structural unit (A) represented by the following formula (1):

[In formula (1), R _ff ¹ to R _ff ⁴ each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. R _ff ¹ and R _ff ² may be linked to form a ring.] The resin molded body for printed circuit boards according to claim 16, which has a relative dielectric constant of 2.40 or less at a frequency of 28 GHz. The resin molded body according to claim 16 or 17, having a porous structure.