Curable resin composition, curable film, and laminated film

Abstract

The curable resin composition according to the present disclosure includes: (A) a rubber component; (B) a crosslinking component having an epoxy group; (C) a maleimide compound; and (D) a filler.

Description

Curable resin composition, curable film, and laminated film

[0001] This disclosure relates to a curable resin composition, a curable film, and a laminated film.

[0002] In recent years, with the increasing speed of signal transmission on printed circuit boards, the frequency of signals has also increased. Consequently, there is a growing demand for low dielectric properties (low dielectric constant, low dielectric loss tangent) in the high-frequency range for printed circuit boards. Furthermore, protective layers (coverlays) that cover the circuits of printed circuit boards, and interlayer adhesives in multilayer printed circuit boards, are required to have low dielectric properties in addition to adhesive properties to the substrate. As a resin composition that can produce a cured product with low dielectric properties, for example, Patent Document 1 proposes an adhesive composition containing a styrene-based elastomer.

[0003] Japanese Patent Publication No. 2018-150543

[0004] Interlayer adhesive compositions sometimes require high embedding properties to adequately embed circuits and other components in printed circuit boards. However, while adhesive compositions using elastomers tend to produce cured products with excellent dielectric properties, the large molecular weight of elastomers and their low fluidity tend to result in high melt viscosity of the adhesive composition. High melt viscosity of the adhesive composition makes it difficult to adequately embed circuits and other components in printed circuit boards.

[0005] This disclosure has been made in view of the above circumstances, and aims to provide a curable resin composition, a curable film, and a laminated film that can form a cured product with excellent dielectric properties and excellent embedding properties.

[0006] To solve the above problems, this disclosure provides the following curable resin composition, curable film, and laminated film.

[0007] [1] A curable resin composition comprising (A) a rubber component, (B) a crosslinking component having epoxy groups, (C) a maleimide compound, and (D) a filler. [2] The curable resin composition according to [1], wherein the (C) maleimide compound comprises at least one selected from the group consisting of aliphatic maleimide resins, aromatic maleimide resins, and maleimide resins having an indane skeleton. [3] The curable resin composition according to [1] or [2], wherein the content of the (C) maleimide compound is 5% by mass or more and 80% by mass or less, based on the total amount of the (A) rubber component, the (B) crosslinking component having epoxy groups, and the (C) maleimide compound being 100% by mass. [4] The curable resin composition according to any one of [1] to [3], wherein the content of the (A) rubber component is 15% by mass or more and 85% by mass or less, based on the total amount of the (A) rubber component, the (B) crosslinking component having epoxy groups, and the (C) maleimide compound being 100% by mass. [5] The curable resin composition according to any one of [1] to [4] above, wherein the content of the crosslinking component having epoxy groups (B) is 1% by mass or more and 20% by mass or less, based on 100% by mass of the total amount of the rubber component (A), the crosslinking component having epoxy groups (B), and the maleimide compound (C). [6] The curable resin composition according to any one of [1] to [5] above, wherein the filler (D) comprises a filler having at least one group selected from the group consisting of (meth)acryloyl group, vinyl group, epoxy group, phenyl group, and phenylamino group. [7] The curable resin composition according to any one of [1] to [6] above, further comprising a curing agent, wherein the content of the curing agent is 1% by mass or more and 10% by mass or less, based on 100% by mass of the total amount of the rubber component (A), the crosslinking component having epoxy groups (B), and the maleimide compound (C). [8] A curable film made from the curable resin composition according to any one of [1] to [7] above. [9] A laminated film comprising a base film and the curable film described in [8] provided on the base film.

[0008] According to this disclosure, it is possible to provide a curable resin composition, a curable film, and a laminated film that can form a cured product with excellent dielectric properties and excellent embedding properties.

[0009] Several embodiments of this disclosure are described in detail below. However, this disclosure is not limited to the embodiments described below.

[0010] In this specification, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages in this specification, the upper or lower limit of a numerical range in one stage may be replaced with the upper or lower limit of a numerical range in another stage. Also, in numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples. When referring to the amount of each component in a composition in this specification, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of those multiple substances present in the composition. "A or B" means that either A or B may be included, or both may be included. "Solid content" refers to the non-volatile content in a resin composition excluding volatile substances (water, solvents, etc.). That is, "solid content" refers to components other than solvents that remain without volatilizing during the drying of the resin composition described later, and includes components that are liquid, syrup-like, or waxy at room temperature (25°C). In this specification, for example, "(meth)acrylic acid" means "acrylic acid" and its corresponding "methacrylic acid," and the same applies to other similar terms.

[0011] [Curable Resin Composition] The curable resin composition according to this embodiment contains (A) a rubber component (hereinafter also referred to as "component (A)"), (B) a crosslinking component having an epoxy group (hereinafter also referred to as "component (B)"), (C) a maleimide compound (hereinafter also referred to as "component (C)"), and (D) a filler (hereinafter also referred to as "component (D)"). The curable resin composition according to this embodiment can be used for forming a protective layer (coverlay) that covers electrical circuits in printed wiring boards, as an interlayer adhesive in multilayer printed wiring boards, etc. According to the curable resin composition according to this embodiment, it is possible to form a cured product (protective layer and adhesive layer, etc.) with excellent dielectric properties, and it is possible to have excellent embedding properties for circuits, etc. in printed wiring boards. For this reason, the curable resin composition according to this embodiment can be suitably used for forming a protective layer and as an interlayer adhesive in printed wiring boards, and in particular, it can be suitably used as an interlayer adhesive because it can achieve a low coefficient of thermal expansion of the cured product. The following describes each component that may be included in the curable resin composition.

[0012] <(A) Rubber component> The (A) rubber component may include, for example, at least one rubber selected from the group consisting of acrylic rubber, isoprene rubber, butyl rubber, styrene-butadiene rubber, butadiene rubber, styrene-butylene styrene rubber, styrene-ethylene propylene styrene rubber, styrene-ethylene butylene styrene rubber, acrylonitrile butadiene rubber, silicone rubber, urethane rubber, chloroprene rubber, ethylene propylene rubber, fluororubber, sulfur rubber, epichlorohydrin rubber, and chlorinated butyl rubber. From the viewpoint of reducing the impact on insulation reliability due to moisture absorption, reducing the impact on connection reliability, and reducing damage to wiring, a rubber component with low gas permeability may be used. From this viewpoint, the (A) rubber component may include at least one selected from styrene-butadiene rubber, butadiene rubber, styrene-ethylene butylene styrene rubber, and butyl rubber. The (A) rubber component may include styrene-ethylene butylene styrene rubber.

[0013] Examples of commercially available acrylic rubber products include Nippon Zeon Co., Ltd.'s "Nipol AR Series" and Kuraray Co., Ltd.'s "Clarity Series."

[0014] Examples of commercially available isoprene rubber products include the "Nipol IR series" from Nippon Zeon Corporation.

[0015] Examples of commercially available butadiene rubber products include the "Nipol BR series" from Nippon Zeon Corporation.

[0016] Examples of commercially available acrylonitrile butadiene rubber include the "NBR series" from ENEOS Material Corporation (formerly the "JSR NBR series" from JSR Corporation).

[0017] Examples of commercially available silicone rubber products include Shin-Etsu Silicone Co., Ltd.'s "KMP series."

[0018] Examples of commercially available ethylene propylene rubber products include ENEOS Material Corporation's "EP Series" (formerly JSR Corporation's "JSR EP Series").

[0019] Examples of commercially available fluororubber products include Daikin Corporation's "Dai-L series."

[0020] Examples of commercially available epichlorohydrin rubber products include the "Hydrin series" from Nippon Zeon Co., Ltd.

[0021] (A) Rubber components can also be produced by synthesis. For example, acrylic rubber can be obtained by reacting (meth)acrylic acid, (meth)acrylic acid esters, aromatic vinyl compounds, vinyl cyanide compounds, etc.

[0022] (A) The rubber component may include rubber having crosslinking groups. Using rubber having crosslinking groups tends to improve the strength, heat resistance, and adhesion of the cured product. The crosslinking group can be any reactive group capable of carrying out a reaction that crosslinks the molecular chains of the rubber component (A). Examples include the reactive groups, acid anhydride groups, amino groups, hydroxyl groups, epoxy groups, and carboxyl groups found in the crosslinking component (B) described later.

[0023] (A) The rubber component may include rubber having at least one of an acid anhydride group or a carboxyl group as a crosslinking group. An example of rubber having an acid anhydride group is rubber partially modified with maleic anhydride. Rubber partially modified with maleic anhydride is a polymer containing constituent units derived from maleic anhydride. (A) The rubber component may include rubber partially modified with maleic anhydride. An example of a commercially available product of rubber partially modified with maleic anhydride is the styrene elastomer "Toughprene 912" manufactured by Asahi Kasei Corporation.

[0024] The rubber partially modified with maleic anhydride may also be a hydrogenated styrene elastomer partially modified with maleic anhydride. Hydrogenated styrene elastomers can also be expected to have effects such as improved connection reliability, improved insulation reliability, and improved weather resistance. Hydrogenated styrene elastomers are elastomers obtained by adding hydrogen to the unsaturated double bonds of a styrene elastomer having a soft segment containing unsaturated double bonds. Examples of commercially available hydrogenated styrene elastomers partially modified with maleic anhydride include "FG1901" and "FG1924GT" from Kraton Polymer Japan Co., Ltd., and "ToughTec M1911," "ToughTec M1913," and "ToughTec M1943" from Asahi Kasei Corporation. The hydrogenated styrene elastomer partially modified with maleic anhydride may also be a hydrogenated styreneethylenebutylene styrene elastomer partially modified with maleic anhydride.

[0025] (A) The weight-average molecular weight of the rubber component may be 20,000 to 200,000, 30,000 to 150,000, or 50,000 to 125,000, from the viewpoint of coating properties and embedding properties. Here, the weight-average molecular weight (Mw) refers to the standard polystyrene equivalent value determined by gel permeation chromatography (GPC).

[0026] (A) The content of the rubber component may be 15% by mass or more and 85% by mass or less, with the total amount of (A) the rubber component, (B) the crosslinked component having epoxy groups, and (C) the maleimide compound being 100% by mass, preferably 20% by mass or more and 85% by mass or less, more preferably 30% by mass or more and 85% by mass or less, even more preferably 35% by mass or more and 80% by mass or less, very preferably 40% by mass or more and 75% by mass or less, and particularly preferably 40% by mass or more and 70% by mass or less. When the content of (A) the rubber component is 35% by mass or more, the dielectric properties and adhesive properties tend to be particularly excellent. When the content of (A) the rubber component is 85% by mass or less, the resulting cured product tends to have particularly excellent properties in terms of connection reliability, insulation reliability, and heat resistance.

[0027] (A) The content of the rubber component is preferably 5% by mass or more and 50% by mass or less, with the nonvolatile component in the curable resin composition being 100% by mass, and may be 5% by mass or more and 40% by mass or less, may be more than 10% by mass and 35% by mass or less, may be more than 15% by mass and 30% by mass or less, may be more than 25% by mass and 50% by mass or less, and may be more than 25% by mass and 40% by mass or less. (A) When the content of the rubber component is 5% by mass or more, the adhesiveness, dielectric properties and compatibility tend to be particularly excellent. (A) When the content of the rubber component is 50% by mass or less, the resulting cured product tends to have particularly excellent properties in terms of fluidity, connection reliability, insulation reliability and heat resistance.

[0028] <(B) Crosslinking component having epoxy groups> (B) Crosslinking component having epoxy groups is a component that crosslinks during the curing reaction to form a crosslinked polymer. (B) Crosslinking component having epoxy groups is a component that does not fall under (A) rubber component. (B) Crosslinking component having epoxy groups is not particularly limited as long as it has epoxy groups in its molecule, and may be, for example, a general epoxy resin. The epoxy resin may be monofunctional, difunctional, or polyfunctional (trifunctional or more), and is not particularly limited, but from the viewpoint of obtaining better curability, a difunctional or polyfunctional epoxy resin may be used.

[0029] Examples of epoxy resins include bisphenol A type, bisphenol F type, phenol novolac type, naphthalene type, dicyclopentadiene type, and cresol novolac type epoxy resins. From the viewpoint of low tack, dielectric properties, and heat resistance, a naphthalene type or dicyclopentadiene type epoxy resin may be selected as the crosslinking component having epoxy groups, or a dicyclopentadiene type epoxy resin may be selected. These epoxy resins can be used individually or in combination of two or more types.

[0030] Combining rubber having maleic anhydride or carboxyl groups with a compound having epoxy groups (epoxy resin) tends to yield particularly excellent results in terms of heat resistance, low moisture permeability, and adhesion of the cured product. Improved heat resistance of the cured product can suppress deterioration of the cured product during heating processes such as nitrogen reflow.

[0031] (B) The weight-average molecular weight of the crosslinking component having epoxy groups may be, for example, 200 to 2000, but from the viewpoint of the fluidity of the resin composition, the dielectric properties of the cured product, and the coefficient of linear expansion of the cured product, it is preferably 200 to 1000, more preferably 250 to 800, even more preferably 300 to 550, and particularly preferably 350 to 450.

[0032] (B) The number average molecular weight of the crosslinking component having epoxy groups may be, for example, 100 to 1000, but from the viewpoint of the fluidity of the resin composition, the dielectric properties of the cured product, and the coefficient of linear expansion of the cured product, it is preferably 150 to 500, more preferably 200 to 400, and even more preferably 250 to 350.

[0033] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) mentioned above refer to standard polystyrene equivalent values ​​determined by gel permeation chromatography (GPC).

[0034] (B) The epoxy equivalent of the crosslinking component having an epoxy group may be, for example, 200 to 300 g / eq, but from the viewpoints of the fluidity of the resin composition, the dielectric properties of the cured product, and the linear expansion coefficient of the cured product, it may be 220 to 290 g / eq, 220 to 280 g / eq, 230 to 270 g / eq, or 240 to 260 g / eq.

[0035] (B) The content of the crosslinking component having an epoxy group is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 15% by mass or less, and still more preferably 5% by mass or more and 10% by mass or less, with the total amount of (A) the rubber component, (B) the crosslinking component having an epoxy group, and (C) the maleimide compound being 100% by mass. When the content of the crosslinking component having an epoxy group is 1% by mass or more, the curability tends to be excellent. When the content of the crosslinking component having an epoxy group is 20% by mass or less, the fluidity and dielectric properties tend to be excellent.

[0036] The curable resin composition may contain other crosslinking components other than the crosslinking component having an epoxy group (B) as long as the effects of the present disclosure are not significantly impaired. From the viewpoint of more sufficiently reducing the dielectric tangent of the cured product, the content of the other crosslinking component is preferably less than 10 parts by mass with respect to 100 parts by mass of the crosslinking component having an epoxy group (B).

[0037] <(C) Maleimide compound> (C) The maleimide compound is a compound that itself participates in the curing reaction, and can improve the heat resistance of the cured product while reducing the dielectric tangent. When the (C) maleimide compound is used, the decrease in the fluidity of the curable resin composition can be suppressed. Therefore, in the curable resin composition according to the present embodiment, by containing the (C) maleimide compound, excellent embedding properties can be obtained, and a cured product having excellent dielectric properties (low relative dielectric constant and low dielectric tangent) can be formed.

[0038] The maleimide compound according to this embodiment can be obtained, for example, by reacting a tetracarboxylic dianhydride (c1) (hereinafter also referred to as "component (c1)"), an amine (c2) (hereinafter also referred to as "component (c2)"), and maleic anhydride (c3) (hereinafter also referred to as "component (c3)"). Here, component (c2) may include a dimer amine. Component (C) may have multiple maleimide groups in its molecule. Component (C) may be a bismaleimide compound. Component (C) can be used alone or in combination of two or more.

[0039] (c1) As the tetracarboxylic dianhydride of component (c1), those known as raw materials for polyimide can be used. (c1) For example, pyromellitic anhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 1,3,3a,4,5,9b-hexahydro-5(tetrahydro-2,5-dioxo-3-furanyl)naphtho[1,2-c]furan-1,3-dione, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3, 3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride, 1,2,3,4-butanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, bicyclo[2.2.2]octo-7-ene- 2,3,5,6-tetracarboxylic dianhydride, bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)1,4-phenylene, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, 4,4'-(ethyn-1,2-diyl)diphthalic anhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, dicyclohexyl-3,4,3',4'-tetracarboxylate Examples include dianhydrides of fluorocarbon acid, 3,4'-oxydiphthalic anhydride, 3,4'-biphthalic anhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid dianhydride, 5,5'-bis-2-norbornene-5,5',6,6'-tetracarboxylic acid-5,5',6,6'-dianhydride, and 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride. Among these, pyromellitic anhydride and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride are preferred from the viewpoint of heat resistance and availability. Component (c1) can be used alone or in combination of two or more.

[0040] Component (c2) may contain a dimer amine. A dimer amine is a compound derived from a dimer acid, which is a dimer of an unsaturated fatty acid such as oleic acid, as described in, for example, Japanese Patent Application Publication No. 9-12712. By using a dimer amine as component (c2), the dielectric properties of the cured product can be lowered. In this embodiment, known dimer amines can be used without particular limitation. Preferably, the dimer amine contains at least one of the compounds represented by the following general formula (1) and the compounds represented by the following general formula (2).

[0041]

[0042] In equations (1) and (2), m, n, p, and q represent integers of 1 or more selected such that m+n = 6 to 17 and p+q = 8 to 19, respectively. The dashed lines indicate carbon-carbon single bonds or carbon-carbon double bonds. However, if the dashed line indicates a carbon-carbon double bond, equations (1) and (2) have a structure in which the number of hydrogen atoms bonded to each carbon atom constituting the carbon-carbon double bond is reduced by one from the number shown in equations (1) and (2).

[0043] The dimer amine may be the compound represented by the general formula (2) above, or more particularly, a compound represented by the following formula (3).

[0044] Examples of commercially available dimer amines include PRIAMINE 1075 and PRIAMINE 1074 (both manufactured by Croda Japan Co., Ltd.).

[0045] (c2) Component may contain other amines other than dimer amines (hereinafter also referred to as "second amines"). The second amine is an amine that does not fall under the category of dimer amines described above. The second amine may be a diamine or a triamine, or it may be a diamine. By using an alicyclic diamine as the second amine, the dielectric constant can be made lower. By using an aromatic diamine as the second amine, the elastic modulus, Tg, and CTE of the cured product are improved.

[0046] If the second amine is a diamine, examples of such diamines include 1,3-diaminopropane, norbornanediamine, 4,4'-methylenedianiline, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis[3-fluoro-4-aminophenyl]fluorene, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, bis(aminomethyl)norbornane, 4,4'-(hexafluoroisopropylidene)dianiline, 3(4),8(9)-bis(aminomethyl)tricyclo[5.2.1.0 ２，６Decane, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, isophoronediamine, 4,4'-methylenebis(cyclohexylamine), 4,4'-methylenebis(2-methylcyclohexylamine), 1,1-bis(4-aminophenyl)cyclohexane, 2,7-diaminofluorene, 4,4'-ethylenedianiline, 4,4'-methylenebis(2,6-diethylaniline), 4,4'-methylenebis(2-ethyl-6-methylaniline), 2,2-bis[4-(4-aminophenoxy)phenyl]propane, bis[4-(4-aminophenoxy)phenyl]methane, 4,4'-bis(4-aminophenoxy)biphenyl Examples include bis[4-(4-aminophenoxy)phenyl] ether, bis[4-(4-aminophenoxy)phenyl] ketone, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2'-dimethylbiphenyl-4,4'-diamine, (4,4'-diamino)diphenyl ether, (3,3'-diamino)diphenyl ether, paraphenylenediamine, orthophenylenediamine, metaphenylenediamine, 2,2'-dimethylbiphenyl-4,4'-diamine, bis[4-(3-aminophenoxy)phenyl] sulfone, and bis[4-(4-aminophenoxy)phenyl] sulfone. These can be used individually or in combination of two or more.

[0047] When the second amine is a triamine, examples of such triamines include tris(aminomethyl)amine, tris(2-aminoethyl)amine, tris(2-aminopropyl)amine, 2-(aminomethyl)-2-methyl-1,3-propanediamine, trimertriamine, 3,4,4'-triaminodiphenyl ether, 1,2,4-triaminobenzene, 1,3,5-triaminobenzene, 1,2,3-triaminobenzene, 1,3,5-triazine-2,4,6-triamine, 2,4,6-triaminopyrimidine, 1,3,5-tris(4-aminophenyl)benzene, and 1,3,5-tris(4-aminophenoxy)benzene. Among these, aliphatic amines and alicyclic amines are preferred from the viewpoint of photocurability, and norbornanediamine, isophoronediamine, and tris(2-aminoethyl)amine are more preferred. These can be used individually or in combination of two or more.

[0048] The second amine may contain either one of the diamines and triamines mentioned above, or both. Furthermore, the second amine may contain amines other than diamines and triamines.

[0049] (c2) In component (c2), the molar ratio of the second amine to the total amount of amine (moles of the second amine / (moles of dimer amine + moles of the second amine)) may be 0.70 or less, or 0.50 or less. If this ratio is 0.70 or less, the dielectric properties of the cured product can be made lower.

[0050] If the second amine contains a diamine, the molar ratio of the diamine in the second amine to the total amount of diamine in component (c2) (moles of diamine in the second amine / (moles of dimeramine + moles of diamine in the second amine)) may be 0.70 or less, or 0.50 or less. If this ratio is 0.70 or less, the dielectric properties of the cured product can be made lower.

[0051] Component (C) can be produced by various known methods. For example, first, components (c1) and (c2) are subjected to a polyaddition reaction at a temperature of about 60 to 120°C, preferably 70 to 90°C, for about 0.1 to 2 hours, preferably 0.1 to 1.0 hours. Next, the obtained polyaddition is subjected to an imidation reaction, i.e., a dehydration ring-closing reaction, at a temperature of about 80 to 250°C, preferably 100 to 200°C, for about 0.5 to 30 hours, preferably 0.5 to 10 hours. Subsequently, the dehydrated ring-closing product and component (c3) are subjected to a maleimidation reaction, i.e., a dehydration ring-closing reaction, at a temperature of about 60 to 250°C, preferably 80 to 200°C, for about 0.5 to 30 hours, preferably 0.5 to 10 hours, to obtain the desired component (C).

[0052] In the imidation reaction or maleimidation reaction, various known reaction catalysts, dehydrating agents, and organic solvents can be used.

[0053] Examples of reaction catalysts include aliphatic tertiary amines such as triethylamine, aromatic tertiary amines such as dimethylaniline, heterocyclic tertiary amines such as pyridine, picoline, and isoquinoline, and organic acids such as methanesulfonic acid and p-toluenesulfonic acid monohydrate. Examples of dehydrating agents include aliphatic acid anhydrides such as acetic anhydride and aromatic acid anhydrides such as benzoic anhydride.

[0054] Organic solvents used in the above reaction include, for example, aromatic hydrocarbons such as benzene, toluene, xylene, and mesitylene; alcoholic solvents such as methanol, ethanol, isopropyl alcohol, butanol, pentanol, hexanol, propanediol, and phenol; ketone solvents such as acetone, methyl isobutyl ketone, methyl ethyl ketone, pentanone, hexanone, cyclopentanone, cyclohexanone, isophorone, and acetophenone; ester solvents such as methyl cellsolve and ethyl cellsolve, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, butyl formate, and γ-butyrolactone; and ethylene glycol mono-n-butyl ether. Examples include glycol ether solvents such as ethylene glycol mono-iso-butyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-iso-butyl ether, triethylene glycol monoethyl ether, triethylene glycol mono-n-butyl ether, and tetraethylene glycol mono-n-butyl ether; and nitrogen-containing compounds such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide. Organic solvents can be used individually or in combination of two or more.

[0055] For the organic solvent used in the above reaction, it is preferable to use an organic solvent with a boiling point of 150 to 200°C. Examples of organic solvents with a boiling point of 150 to 200°C include 1,2,3,5-tetramethylbenzene (boiling point: 198°C), n-propylbenzene (boiling point: 160°C), 2-ethyltoluene (boiling point: 164°C), 3-ethyltoluene (boiling point: 158°C), 4-ethyl-m-xylene (boiling point: 186°C), 1,2,3-trimethylbenzene (hemimelitene, boiling point: 176°C), phenethole (ethoxybenzene) (boiling point: 173°C), cumene (boiling point: 152°C), and 1,2,4-trimethylbenzene. Examples include pseudocumene (boiling point: 169°C), 1,3,5-trimethylbenzene (mesitylene, boiling point: 165°C), anisole (boiling point: 154°C), butyl cellosolve (boiling point: 171°C), methyl carbitol (boiling point: 194°C), dipropylene glycol monomethyl ether (boiling point: 188°C), dipropylene glycol dimethyl ether (boiling point: 171°C), N,N-dimethylformamide (boiling point: 153°C), and N,N-dimethylacetamide (boiling point: 165°C). In addition, as organic solvents with a boiling point of 150 to 200°C, petroleum-based solvents such as solvent naphtha (boiling point: 150 to 185°C), which is a distillation component of naphtha, may be used. Specific examples of solvent naphtha include T-SOL100 (trade name, manufactured by ENEOS Corporation), Swazole 1000 (trade name, manufactured by Cosmo Matsuyama Oil Co., Ltd.), and Ipsol 100 (trade name, manufactured by Idemitsu Kosan Co., Ltd.).

[0056] Component (C) can be purified by various known methods, and its purity can be increased. For example, first, component (C) dissolved in an organic solvent and pure water are placed in a separatory funnel. Next, the separatory funnel is shaken and allowed to stand. After the aqueous layer and organic layer separate, only the organic layer is collected to purify component (C).

[0057] An example of the expected structure of component (C) produced by the above method is shown in the following general formula (4).

[0058] In general formula (4), each X independently represents a tetravalent organic group, each Y independently represents a divalent organic group, and a represents an integer of 1 or more. However, at least one of the multiple Ys represents a divalent organic group derived from the dimer amine described above. Furthermore, X and Y may be organic groups having an aliphatic group, an alicyclic structure, or an aromatic ring, and they may contain heteroatoms.

[0059] The molecular weight of component (C) can be controlled by the number of moles of component (c1) and component (c2), and the smaller the number of moles of component (c1) is compared to the number of moles of component (c2), the smaller the molecular weight can be. For the purpose of easily achieving the effects of this disclosure, the number of moles of component (c1) per mole of component (c2), i.e., [number of moles of component (c1)] / [number of moles of component (c2)] is usually in the range of 0.30 to 0.95, preferably 0.50 to 0.85.

[0060] (C) The molecular weight of component (C) is preferably 1,000 to 40,000 in weight-average molecular weight (Mw), more preferably 1,500 to 30,000, and even more preferably 1,800 to 28,000, or 2,000 to 27,000, from the viewpoint of solubility in solvents and heat resistance. When the weight-average molecular weight is 40,000 or less, solubility in organic solvents is good, and when it is 1,000 or more, a sufficient effect of improving heat resistance tends to be obtained. Mw can be measured by gel permeation chromatography (GPC) and converted using a calibration curve for standard polystyrene.

[0061] (C) As maleimide compounds, aliphatic maleimide resins (maleimide resins having an aliphatic skeleton), aromatic maleimide resins (maleimide resins having an aromatic skeleton), and maleimide resins having an indan skeleton are preferably used from the viewpoint of superior dielectric properties and embedding ability. More specifically as maleimide compounds, examples include compounds represented by the following formula (5), compounds represented by the following formula (6), compounds represented by the following formula (7), etc. These can be used individually or in combination of two or more.

[0062] In equation (5), t is an integer from 1 to 20, s is an integer from 1 to 10, R ３is an alkyl group having 1 to 10 carbon atoms, R ４ represents an alkyl group having 1 to 10 carbon atoms.

[0063] In the compound represented by formula (5), in formula (5), t is 1 to 15, s is 7, R ３ is an alkyl group having 6 carbon atoms, R ４ may be a compound in which is an alkyl group having 8 carbon atoms.

[0064] In formula (6), w represents an integer of 1 to 10.

[0065] In formula (7), R ５ is an alkyl group having 1 to 10 carbon atoms, an alkyloxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aryloxy group having 6 to 10 carbon atoms, an arylthio group having 6 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a halogen atom, a hydroxyl group or a mercapto group, and z1 represents an integer of 0 to 3. R ６ to R ８ each independently represents an alkyl group having 1 to 10 carbon atoms. R ９ each independently represents an alkyl group having 1 to 10 carbon atoms, an alkyloxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aryloxy group having 6 to 10 carbon atoms, an arylthio group having 6 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a halogen atom, a nitro group, a hydroxyl group or a mercapto group, z2 each independently represents an integer of 0 to 4, and z3 represents a number of 0.95 to 10.0.

[0066] In the above formula (7), a plurality of R ５ among themselves, a plurality of z1 among themselves, a plurality of R ９ among themselves, and a plurality of z2 among themselves may each be the same or each may be different. When z3 exceeds 1, a plurality of R ６ among themselves, a plurality of R ７ among themselves, and a plurality of R ８ among themselves may each be the same or each may be different.

[0067] R in the above formula (7) ９Examples of C1-C10 alkyl groups represented by include methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, nonyl, and decyl groups. These alkyl groups may be linear or branched. ９ Examples of alkyl groups included in the C1-C10 alkyloxy group and C1-C10 alkylthio group represented by the above include the same C1-C10 alkyl groups. ９ Examples of aryl groups having 6 to 10 carbon atoms represented by R include the phenyl group and the naphthyl group. ９ The aryl groups included in the aryloxy and arylthio groups having 6 to 10 carbon atoms, as represented by , are the same as the aryl groups having 6 to 10 carbon atoms mentioned above. ９ Examples of cycloalkyl groups having 3 to 10 carbon atoms represented by include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, and cyclodecyl groups. Among these, R ９ From the viewpoint of solvent solubility and ease of manufacture, the group is preferably an alkyl group having 1 to 4 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 10 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group.

[0068] In formula (7) above, z2 represents an integer from 0 to 4, and from the viewpoint of compatibility with other resins, dielectric properties, conductive adhesion, and ease of manufacture, z2 is preferably an integer from 0 to 3, and more preferably 0 or 2. When z2 is 1 or greater, the benzene ring and the N-substituted maleimide group have a twisted conformation, and solvent solubility tends to be further improved by suppressing intermolecular stacking. From the viewpoint of suppressing intermolecular stacking, when z2 is 1 or greater, R ９ The substitution position is preferably the ortho position relative to the N-substituted maleimide.

[0069] In formula (7) above, z3 is preferably 0.98 to 8.0, more preferably 1.0 to 7.0, and even more preferably 1.1 to 6.0, from the viewpoint of dielectric properties, conductive adhesion, solvent solubility, handling properties, and heat resistance. Note that z3 represents the average value of the number of structural units containing indan rings.

[0070] Examples of compounds represented by formula (5) include BMI-5000 (manufactured by DESIGNER MOLECULES Inc., trade name), and examples of compounds represented by formula (6) include MIR-3000-70MT (manufactured by Nippon Kayaku Co., Ltd., trade name).

[0071] The method for producing the compound represented by formula (7) is not particularly limited. The compound represented by formula (7) can be produced, for example, by the method described in the Japan Institute of Invention and Innovation Published Technical Report No. 2020-500211. According to the production method described in the Japan Institute of Invention and Innovation Published Technical Report No. 2020-500211, a bismaleimide compound containing an indane skeleton can be obtained.

[0072] (C) The content of the maleimide compound may be 5% to 80% by mass, 15% to 80% by mass, 20% to 65% by mass, or 25% to 60% by mass, based on the total amount of (A) rubber component, (B) crosslinking component having epoxy groups, and (C) maleimide compound as 100% by mass, from the viewpoint of dielectric properties, fluidity, insulation reliability, and heat resistance.

[0073] In a curable resin composition, the total content of (B) crosslinking component and (C) maleimide compound may be 5 to 85% by mass, preferably 15 to 85% by mass, more preferably 15 to 70% by mass, even more preferably 20 to 65% by mass, very preferably 25 to 60% by mass, particularly preferably 10 to 35% by mass, and extremely preferably 15 to 35% by mass. When the total content of (B) crosslinking component and (C) maleimide compound is 5% by mass or more, more sufficient curing is more easily obtained, and the cured product tends to have particularly excellent properties in terms of connection reliability, insulation reliability, and heat resistance. When the total content of (B) crosslinking component and (C) maleimide compound is 85% by mass or less, the rubber component and crosslinking component tend to mix well, and the cured product tends to have better properties in terms of adhesion and dielectric properties.

[0074] In a curable resin composition, the ratio of the content of (B) crosslinking component to the content of (C) maleimide compound (content of (B) crosslinking component / content of (C) maleimide compound) is preferably in the range of 0.01 to 1.0 by mass ratio, more preferably in the range of 0.03 to 0.7, and even more preferably in the range of 0.05 to 0.5. When the content ratio is within the above range, sufficient curing is more easily obtained, and the cured product tends to have particularly excellent properties in terms of dielectric properties, adhesion, insulation reliability, and heat resistance.

[0075] In a curable resin composition, the ratio of the content of (A) rubber component to the total content of (B) crosslinking component and (C) maleimide compound (content of (A) rubber component / total content of (B) crosslinking component and (C) maleimide compound) may be in the range of 0.18 to 5.5 by mass ratio, preferably in the range of 0.25 to 5.5, more preferably in the range of 0.43 to 5.5, even more preferably in the range of 0.54 to 4.0, very preferably in the range of 0.60 to 3.0, and particularly preferably in the range of 0.60 to 2.5. When the content ratio is within the above range, sufficient curing is more easily obtained, and the cured product tends to have particularly excellent properties in terms of dielectric properties, adhesion, insulation reliability, and heat resistance.

[0076] <(D) Filler> (D) Filler tends to reduce the coefficient of thermal expansion (CTE) of the cured product.

[0077] (D) Filler may be a filler produced by the deflagration method, a filler produced by the sol-gel method, or a filler produced by the flame melting method. (D) Filler may be a filler produced by the deflagration method or the flame melting method from the viewpoint of fluidity, and is preferably a filler produced by the deflagration method from the viewpoint of particle size and particle size distribution.

[0078] (D) The filler may be a filler having at least one group selected from the group consisting of (meth)acryloyl group, vinyl group, epoxy group, phenyl group, and phenylamino group. Having these groups tends to result in particularly excellent properties in terms of compatibility with the resin component at the filler interface, dispersibility of the filler, storage stability of the curable resin composition, coefficient of thermal expansion of the cured product, and adhesion of the cured product. Therefore, the curable resin composition can be more preferably used as an interlayer adhesive for multilayer printed circuit boards.

[0079] (D) The filler preferably includes a filler having at least one group selected from the group consisting of (meth)acryloyl groups, vinyl groups, epoxy groups, phenyl groups, and phenylamino groups, more preferably includes a filler having at least one group selected from the group consisting of (meth)acryloyl groups, epoxy groups, and phenylamino groups, and even more preferably includes a filler having an epoxy group.

[0080] (D) As for the filler, from the viewpoint of the coefficient of linear expansion and adhesion to low-polarity resin substrates, a filler having vinyl groups or epoxy groups is more preferred, and from the same viewpoint, a filler having epoxy groups is particularly preferred. Examples of low-polarity resin substrates include liquid crystal polymers.

[0081] (D) The filler may be a surface-treated filler. A surface-treated filler can be obtained by treating the surface of the filler with a surface treatment agent such as an organosilane compound. By treating the surface of the filler, it tends to have particularly excellent properties in terms of compatibility with the resin component at the filler interface, dispersibility of the filler, storage stability of the curable resin composition, coefficient of linear expansion of the cured product, and adhesion of the cured product. Therefore, by using a surface-treated filler as the (D) filler, the curable resin composition can be used more suitably as an interlayer adhesive for multilayer printed circuit boards. The surface treatment may be surface modification.

[0082] As a surface treatment filler, it is preferable to include a filler having at least one group selected from the group consisting of (meth)acryloyl groups, vinyl groups, epoxy groups, phenyl groups, and phenylamino groups, from the viewpoint of coefficient of linear expansion and adhesion, more preferably to include a filler having at least one group selected from the group consisting of vinyl groups, epoxy groups, and phenylamino groups, and even more preferably a filler having an epoxy group or a phenylamino group.

[0083] As a surface treatment filler, from the viewpoint of the coefficient of linear expansion and adhesion to low-polarity resin substrates, a filler having at least one group selected from the group consisting of (meth)acryloyl groups, vinyl groups, epoxy groups, phenyl groups, and phenylamino groups is more preferable, and from the same viewpoint, a filler having (meth)acryloyl groups, epoxy groups, or phenylamino groups is particularly preferred. Examples of low-polarity resin substrates include liquid crystal polymers.

[0084] When the above-mentioned surface treatment filler is used, the cured product of the curable resin composition tends to exhibit improved adhesion to materials constituting printed circuit boards, and in particular, improved adhesion to substrates having low-roughness or no-roughness surfaces. With conventional curable resin compositions, it was difficult to improve adhesion to, for example, no-roughness liquid crystal polymer films, but the cured product of a curable resin composition containing the above-mentioned surface treatment filler tends to achieve good adhesion to low-polarity resin substrates, such as no-roughness liquid crystal polymer films.

[0085] (D) As a filler, inorganic fillers may be used from the viewpoint of further reducing the coefficient of thermal expansion and improving the modulus of elasticity. Examples of inorganic fillers include those containing at least one inorganic substance selected from the group consisting of silica, alumina, titania, tantalum oxide, zirconia, silicon nitride, gallium oxide, boron nitride, barium titanate, barium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, lead titanate, lead zirconate titanate, lead lanthanum zirconate titanate, spinel, mullite, cordierite, talc, aluminum titanate, yttria-containing zirconia, barium sulfate, barium silicate, calcium carbonate, calcium sulfate, zinc oxide, and magnesium titanate. One type of inorganic filler may be used alone or in combination of two or more types. Among these, the inorganic filler may contain silica, alumina, titania, or boron nitride from the viewpoint of dispersibility and heat resistance of the cured product. The inorganic filler may contain silica from the viewpoint of dielectric properties.

[0086] (D) Organic fillers may be used as fillers. Organic fillers are generally particulate and disperse in organic solvents without dissolving. Also, organic fillers do not fall under (A) rubber components. Examples of organic fillers include liquid crystal polymers (LCP) and polytetrafluoroethylene (PTFE), etc. Organic fillers may be used individually or in combination of two or more types. Also, (D) fillers may be used in combination of one or more inorganic fillers and one or more organic fillers.

[0087] (D) The filler may be an inorganic filler surface-treated with silica, alumina, titania, or boron nitride, from the viewpoint of dispersibility and heat resistance. (D) The filler may be a surface-treated silica filler, from the viewpoint of linear expansion coefficient and adhesion.

[0088] As a surface treatment agent for inorganic fillers, organic silane compounds such as epoxy silane compounds, amino silane compounds, (meth)acrylic silane compounds, and vinyl silane compounds may be used from the viewpoint of coefficient of linear expansion and adhesion.

[0089] (D) The filler preferably contains at least one selected from the group consisting of silica modified with (meth)acryloyl groups, silica modified with epoxy groups, and silica modified with phenylamino groups, from the viewpoint of dielectric properties, embedding ability, coefficient of linear expansion, adhesion, dispersibility, and heat resistance.

[0090] Examples of organic silane compounds include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropylmethyldimethoxysilane, 3-phenylaminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, vinyltriacetoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, and Examples include lyltrimethoxysilane, diallyldimethylsilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltriethoxysilane, N-(1,3-dimethylbutylidene)-3-aminopropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, and 3-isocyanatetopropyltriethoxysilane.

[0091] From the viewpoint of achieving both the fluidity of the curable resin composition and a reduction in the coefficient of linear expansion of the cured product, the content of (D) filler may be 30 to 75% by mass, 30 to 70% by mass, 40 to 70% by mass, or 50 to 70% by mass, based on the total solid content of the curable resin composition. When the content of (D) filler is within the above range, it is possible to achieve both the fluidity of the curable resin composition and a reduction in the coefficient of linear expansion of the cured product.

[0092] (D) The average particle size of the filler may be 0.01 μm or more, 0.1 μm or more, or 0.2 μm or more, and may be 5.0 μm or less, 4.0 μm or less, 3.0 μm or less, 1.0 μm or less, or 0.8 μm or less, from the viewpoint of excellent dielectric properties, adhesion, and film appearance of the cured product. That is, the average particle size of the (D) filler may be 0.01 to 5.0 μm, 0.1 to 4.0 μm, 0.2 to 3.0 μm, 0.2 to 1.0 μm, or 0.2 to 0.8 μm. The average particle size of the (D) filler refers to the particle size with an integrated frequency of 50% in the particle size distribution determined by the laser diffraction / scattering method.

[0093] <(E) Curing Accelerator> The curable resin composition may further contain (E) a curing accelerator (hereinafter also referred to as "component (E)"). The (E) curing accelerator is a compound that functions as a catalyst for the curing reaction. The (E) curing accelerator may be selected from tertiary amines, imidazoles, organic acid metal salts, phosphorus compounds, Lewis acids, amine complex salts, and phosphines. Among these, imidazole may be used from the viewpoint of storage stability, curability, and dielectric properties of the cured product of the varnish of the curable resin composition. If the (A) rubber component includes rubber partially modified with maleic anhydride, an imidazole compatible with it may be selected. The imidazole may be 1-benzyl-2-phenylimidazole or 1-benzyl-2-methylimidazole.

[0094] In a curable resin composition, the content of (E) curing accelerator may be 0.1 to 10% by mass, where the total amount of (A) rubber component, (B) crosslinking component, and (C) maleimide compound is 100% by mass. When the content of (E) curing accelerator is 0.1% by mass or more, it tends to be easier to obtain sufficient curing. When the content of (E) curing accelerator is 10% by mass or less, it tends to improve heat resistance, dielectric properties, and storage stability of varnishes, films, etc. of the curable resin composition. From the above viewpoint, the content of (E) curing accelerator may be 0.1 to 7% by mass, 0.3 to 5% by mass, 0.3 to 3% by mass, or 0.5 to 2% by mass.

[0095] The curable resin composition may contain a curing agent, to the extent that it does not significantly impair the effects of the present disclosure. In this disclosure, (C) maleimide compounds are not included in the curing agent. Examples of curing agents include active ester curing agents, phenolic curing agents, acid anhydride curing agents, thiol curing agents, and the like.

[0096] From the viewpoint of suppressing the increase in the melt viscosity of the curable resin composition and further improving its embeddability, the content of the curing agent is preferably 1% by mass or more and 10% by mass or less, with the total amount of (A) rubber component, (B) crosslinking component having epoxy groups, and (C) maleimide compound being 100% by mass.

[0097] From the viewpoint of suppressing the increase in the melt viscosity of the curable resin composition and further improving its embeddability, the curing agent content is preferably 20 parts by mass or less, or 10 parts by mass or less, per 100 parts by mass of the (C) maleimide compound.

[0098] <Other Components> In addition to the components described above, the curable resin composition may further contain, as necessary, antioxidants, anti-yellowing agents, ultraviolet absorbers, visible light absorbers, colorants, plasticizers, stabilizers, fillers, flame retardants, leveling agents, etc., to the extent that they do not significantly impair the effects of the present disclosure.

[0099] In particular, the curable resin composition may contain at least one degradation inhibitor selected from the group consisting of antioxidants, heat stabilizers, light stabilizers, and hydrolysis inhibitors. Antioxidants suppress degradation due to oxidation. Antioxidants also impart sufficient heat resistance to the cured product at high temperatures. Heat stabilizers impart stability to the cured product at high temperatures. Examples of light stabilizers include ultraviolet absorbers that prevent degradation due to ultraviolet rays, light blocking agents that block light, and quenchers that have a quenching function that stabilizes organic materials by accepting light energy absorbed by organic materials. Hydrolysis inhibitors suppress degradation due to moisture. The degradation inhibitor may be at least one selected from the group consisting of antioxidants, heat stabilizers, and ultraviolet absorbers. As the degradation inhibitor, only one of the components exemplified above may be used, or two or more may be used in combination. Two or more degradation inhibitors may be used in combination to obtain a better effect.

[0100] The curable resin composition may be prepared as a resin varnish by dissolving or dispersing each of the above-mentioned components in an organic solvent. There are no particular restrictions on the organic solvent, but examples include aromatic hydrocarbons such as toluene, xylene, mesitylene, cumene, and p-cymene; cyclic ethers such as tetrahydrofuran and 1,4-dioxane; ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclohexanone, and 4-hydroxy-4-methyl-2-pentanone; esters such as methyl acetate, ethyl acetate, butyl acetate, methyl lactate, ethyl lactate, and γ-butyrolactone; carbonate esters such as ethylene carbonate and propylene carbonate; and amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone. From the viewpoint of solubility and boiling point, toluene or N,N-dimethylacetamide may be used. These organic solvents can be used individually or in combination of two or more. The concentration of solids (components other than organic solvents) in the resin varnish may be 20 to 80% by mass.

[0101] The mixing and kneading of the above resin varnishes can be carried out by appropriately combining conventional mixers, stirring machines, three-roll mixers, ball mills, and other dispersing machines.

[0102] [Curable Film and Laminated Film] The curable film according to this embodiment consists of the curable resin composition described above. The curable film can be easily manufactured, for example, by applying a resin varnish containing the curable resin composition to a base film and removing the solvent from the coating. According to this method, a laminated film comprising a base film and a curable film provided on the base film can be obtained.

[0103] The solvent is removed from the coating on the substrate film by drying at a temperature that does not cause the curable resin composition to harden, while ensuring sufficient solvent evaporation. Specifically, the coating is dried by heating at 60 to 180°C for 0.1 to 90 minutes. The preferred residual volatile content of the resulting curable film is 10% by mass or less. When the residual volatile content is 10% by mass or less, it is easier to suppress the formation of voids inside the cured product due to foaming caused by solvent evaporation during assembly heating. It is also easier to suppress contamination of surrounding materials or components by volatile components generated during heating.

[0104] There are no particular restrictions on the material of the base film, and examples include polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; polycarbonate, polyamide, polyimide, polyamide-imide, polyetherimide, polyether sulfide, polyether sulfone, polyether ketone, polyphenylene ether, polyphenylene sulfide, polyarylate, polysulfone, and liquid crystal polymers. Among these, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polypropylene, polycarbonate, polyamide, polyimide, polyamide-imide, polyphenylene ether, polyphenylene sulfide, polyarylate, and polysulfone are preferred from the viewpoint of flexibility and toughness.

[0105] The thickness of the base film may be appropriately varied depending on the desired flexibility, but it may be between 3 and 250 μm. Generally, a thickness of 3 μm or more provides sufficient film strength, while a thickness of 250 μm or less provides sufficient flexibility. From this viewpoint, the thickness may be between 5 and 200 μm, or between 7 and 150 μm. From the viewpoint of improving release properties from curable films, a base film treated with a release agent such as a silicone compound or a fluorine-containing compound may be used as needed.

[0106] If necessary, a protective film may be attached to the curable film to form a laminated film with a three-layer structure consisting of a base film, a curable film, and a protective film.

[0107] There are no particular restrictions on the material of the protective film, and examples include polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; and polyolefins such as polyethylene and polypropylene. Among these, polyesters such as polyethylene terephthalate and polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of flexibility and toughness. From the viewpoint of improving release from the curable film, a protective film treated with a release agent such as a silicone compound or a fluorine-containing compound may be used as needed.

[0108] The thickness of the protective film may be adjusted as appropriate depending on the desired flexibility, but it may be between 10 and 250 μm. Generally, a thickness of 10 μm or more provides sufficient film strength, while a thickness of 250 μm or less provides sufficient flexibility. From this perspective, the thickness may be between 15 and 200 μm, or between 20 and 150 μm.

[0109] The thickness of the curable film after drying is not particularly limited, but is usually between 5 and 1000 μm. When the thickness is 5 μm or more, the curable film or its cured product tends to have sufficient strength. When the thickness is 1000 μm or less, drying can be performed sufficiently, which tends to reduce the amount of residual solvent in the curable film.

[0110] Laminated films can be easily stored, for example, by winding them into a roll. Alternatively, laminated films can be stored in sheet form, cut to a suitable size from the roll.

[0111] The curable resin composition, curable film, and laminated film according to this embodiment are suitable for forming a protective layer (coverlay) that covers electrical circuits in printed circuit boards, and as an interlayer adhesive in multilayer printed circuit boards, and are particularly suitable as an interlayer adhesive.

[0112] [Printed Wiring Board] The printed wiring board in this embodiment includes a laminate formed from a metal part that forms an electrical circuit (conductor circuit) and a resin substrate as its constituent elements. The printed wiring board can be manufactured, for example, by conventionally known methods such as the subtractive method using a metal-clad laminate. The printed wiring board in this embodiment is a general term for so-called flexible circuit boards (FPCs), flat cables, and circuit boards for automated tape bonding (TAB), in which the conductor circuit formed by the metal part is covered partially or entirely with a coverlay film or screen printing ink, as needed.

[0113] The printed circuit board of this embodiment can have any laminated configuration that can be used as a printed circuit board. For example, it can be a printed circuit board having a base layer, an adhesive layer, a metal portion, and a protective layer.

[0114] Furthermore, if necessary, the above-mentioned printed circuit boards can be laminated in layers of two or more using interlayer adhesive to form a multilayer printed circuit board.

[0115] In the printed circuit board of this embodiment, any substrate that has been conventionally used as a substrate for printed circuit boards can be used as the substrate layer.

[0116] In the printed circuit board of this embodiment, any resin that has been conventionally used as a base material for printed circuit boards can be used as the base layer. Examples of resins for the base layer include polyester resin, polyamide resin, polyimide resin, polyamide-imide resin, liquid crystal polymer, polyphenylene sulfide, syndiotactic polystyrene, polyolefin resin, and fluorine-based resins such as polytetrafluoroethylene (PTFE).

[0117] The curable resin composition of this embodiment can be used for adhesive layers, protective layers, and interlayer adhesives in printed circuit boards. In particular, when these layers are formed using the curable resin composition of this embodiment, the improved fluidity results in excellent embeddability and moldability, and the layers formed using the curable resin composition themselves exhibit excellent low dielectric properties and a low coefficient of thermal expansion. The cured product of the curable resin composition of this embodiment tends to have excellent adhesion to materials constituting printed circuit boards, such as substrate layers and metal parts, especially to low-polarity substrates such as liquid crystal polymers, polyphenylene sulfide, syndiotactic polystyrene, polyolefin resins, and PTFE. Therefore, the curable resin composition of this embodiment is suitable as an interlayer adhesive for multilayer printed circuit boards. Furthermore, the curable resin composition of this embodiment is also suitable as a curable resin composition for use in coverlay films, laminates, resin-coated metal foils, and bonding sheets. In addition, since the curable resin composition of this embodiment contains (A) a rubber component, its cured product can be flexible. Therefore, the curable resin composition of this embodiment can be suitably used for forming protective layers and as an interlayer adhesive in flexible printed circuit boards.

[0118] In the printed circuit board of this embodiment, the metal portion is not particularly limited, but from the viewpoint of wiring formation, it may be copper. There are no particular restrictions on the material used to form the copper, and for example, electrolytic copper foil and rolled copper foil used in copper-clad laminates and printed circuit boards can be used. Examples of commercially available electrolytic copper foils include F0-WS-18 (manufactured by Furukawa Electric Co., Ltd., product name), NC-WS-20 (manufactured by Furukawa Electric Co., Ltd., product name), YGP-12 (manufactured by Nippon Electrolytic Co., Ltd., product name), GTS-18 (manufactured by Furukawa Electric Co., Ltd., product name), and F2-WS-12 (manufactured by Furukawa Electric Co., Ltd., product name), and F2-WS-18 (manufactured by Furukawa Electric Co., Ltd., product name). Examples of rolled copper foils include TPC foil (manufactured by JX Metals Corporation, product name), HA foil (manufactured by JX Metals Corporation, product name), HA-V2 foil (manufactured by JX Metals Corporation, product name), and C1100R (manufactured by Mitsui Sumitomo Metal Mining Copper Co., Ltd., product name). From the viewpoint of adhesion to the cured product of the curable resin composition of this embodiment, roughened copper foil may be used. From the viewpoint of folding resistance, rolled copper foil may be used. In addition, the metal portion may have a roughened surface formed by the roughening treatment. When using roughened copper foil, from the viewpoint of transmission loss, it is preferable that the roughening treatment of the copper foil be kept to a minimum, and it is preferable to use finely roughened copper foil. Examples of finely roughened copper foil include FV(FHG)-WS (FV-WS / FHG-WS, copper foil product, manufactured by Furukawa Electric Co., Ltd., trade name) and FZ-WS (copper foil product, manufactured by Furukawa Electric Co., Ltd., trade name).

[0119] Although embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above embodiments. For example, the curable resin composition described above can be used for purposes other than as a composition for forming a protective layer (coverlay) or as an interlayer adhesive, as follows: That is, the curable resin composition can be used as a primer layer for difficult-to-bond materials, an adhesive layer for low-dielectric materials with an adhesive layer, etc. The method of applying the curable resin composition is not particularly limited, and for example, application methods such as comma coater, bar coater, die coater, dipping, and spin coat can be used. Furthermore, the curable film described above can be used as a build-up film, a resin layer for resin-coated metal foil, a low-dielectric stretchable substrate, etc.

[0120] The present disclosure will be further described with reference to the following embodiments. However, the present disclosure is not limited to these embodiments.

[0121] (Examples 1-7 and Comparative Examples 1 and 2) <Preparation of Curable Resin Compositions> Each material shown in Tables 1 and 2 was mixed in the proportion of solids (unit: parts by mass) shown in the same table to prepare curable resin compositions. The curable resin compositions were then prepared by adding toluene as a solvent to obtain a solids content of 40% by mass. Details of each material are shown below.

[0122] (A) Rubber component FG1924: Maleic anhydride-modified styrene-ethylene-butylene-styrene elastomer (Kraton Polymer Japan Co., Ltd., product name "FG1924GT")

[0123] (B) Crosslinking component having epoxy groups HP7200L: Dicyclopentadiene type epoxy resin (manufactured by DIC Corporation, product name "EPICLON HP-7200L", epoxy equivalent: 247 g / eq, number average molecular weight: 288, weight average molecular weight: 401)

[0124] (C) Maleimide Compound Maleimide Resin 1 (Maleimide having the structure of formula (5) above, BMI-5000) Maleimide Resin 2 (Maleimide having the structure of formula (7) above, weight-average molecular weight (Mw): approximately 2100)

[0125] (D) Filler 5SE-CH1: Spherical silica modified with epoxy groups (average particle size: 0.5 μm, manufactured by Admatex Co., Ltd., cyclohexane solution) SC2050-KNK: Spherical silica modified with phenylamino groups (average particle size: 0.5 μm, manufactured by Admatex Co., Ltd., methyl ethyl ketone (MEK) solution)

[0126] (E) Curing accelerator 1B2PZ: 1-benzyl-2-phenylimidazole (manufactured by Shikoku Chemicals Co., Ltd.)

[0127] <Preparation of Laminated Film> A release-treated polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "Purex A3100", thickness 25 μm) was prepared as the base film. The above curable resin composition was applied to the release-treated surface of this PET film using a knife coater (manufactured by Yasui Seiki Co., Ltd., product name "SNC-350"). The coating was dried in a dryer (manufactured by Futaba Kagaku Co., Ltd., product name "MSO-80TPS") at 80°C for 15 minutes to form a curable film with a thickness of 30 μm. A release-treated PET film, the same as the base film, was attached to the formed curable film as a protective film with the release-treated surface facing the curable film side to obtain a laminated film.

[0128] [Measurement of Fluidity (Minimum Melt Viscosity)] The protective film was peeled off the laminated films of Examples 1 to 7 and Comparative Example 2, and the exposed curable films (two curable films) were laminated together using a vacuum pressure laminator (manufactured by Nikko Materials Co., Ltd., product name "V130") under the conditions of a pressure of 0.5 MPa, a temperature of 100°C, and a pressurizing time of 60 seconds. This operation (for the second and subsequent laminations, the base film was peeled off from one of the curable films to be laminated) was repeated until the curable film was 0.4 mm thick, and then the film was punched out to a diameter of 8 mm to prepare a sample. The base film was removed from the obtained sample, and the minimum melt viscosity of this curable film was measured using a viscoelasticity measuring device (manufactured by TA Instruments, product name "ARES-G2", heating rate: 3°C / min, temperature range: 30 to 200°C, load: 0.2 N, frequency: 1 Hz, strain: 1%).

[0129] [Measurement of Relative Permittivity (Dk) and Dielectric Loss Tangent (Df)] The obtained laminated film was heated at 180°C for 60 minutes to cure the curable film and form a cured film. The base film and protective film were removed from the cured film, and the cured film was cut to a size of 60 mm x 60 mm to obtain test specimens. Using these test specimens, the relative permittivity (Dk) and dielectric loss tangent (Df) were calculated using the SPDR (Split post dielectric resonator) method. A vector network analyzer E8364B (Keysight Technologies), CP531 (Kanto Electronics Applied Development Co., Ltd.), and CPMA-V2 (program) were used as measuring instruments, and measurements were performed under conditions of an ambient temperature of 25°C and a frequency of 10 GHz. The results are shown in Tables 1 and 2. In Comparative Example 1, the curable resin composition did not cure, so a cured film could not be formed.

[0130]

[0131]

Claims

1. A curable resin composition comprising (A) a rubber component, (B) a crosslinking component having an epoxy group, (C) a maleimide compound, and (D) a filler.

2. The curable resin composition according to claim 1, wherein the (C) maleimide compound comprises at least one selected from the group consisting of aliphatic maleimide resins, aromatic maleimide resins, and maleimide resins having an indane skeleton.

3. The curable resin composition according to claim 1, wherein the content of the (C) maleimide compound is 5% by mass or more and 80% by mass or less, based on the total amount of the (A) rubber component, the (B) crosslinked component having epoxy groups, and the (C) maleimide compound being 100% by mass.

4. The curable resin composition according to claim 1, wherein the content of the rubber component (A) is 15% by mass or more and 85% by mass or less, based on the total amount of the rubber component (A), the crosslinked component having epoxy groups (B), and the maleimide compound (C) being 100% by mass.

5. The curable resin composition according to claim 1, wherein the content of the crosslinking component having epoxy groups (B) is 1% by mass or more and 20% by mass or less, based on the total amount of the rubber component (A), the crosslinking component having epoxy groups (B), and the maleimide compound (C) being 100% by mass.

6. The curable resin composition according to claim 1, wherein the (D) filler comprises a filler having at least one group selected from the group consisting of (meth)acryloyl group, vinyl group, epoxy group, phenyl group, and phenylamino group.

7. The curable resin composition according to claim 1, further comprising a curing agent, wherein the content of the curing agent is 1% by mass or more and 10% by mass or less, based on 100% by mass of the total amount of the (A) rubber component, the (B) crosslinking component having epoxy groups, and the (C) maleimide compound.

8. A curable film comprising the curable resin composition according to any one of claims 1 to 7.

9. A laminated film comprising a base film and a curable film according to claim 8 provided on the base film.

Images