Curable resin composition, curable film, and layered film

Abstract

A curable resin composition according to one aspect of the present disclosure comprises (A) a rubber component, (B) a compound having an epoxy group, (C) a curing agent, (D) a curing accelerator, and (E) a filler, wherein the rubber component (A) comprises a modified styrene-based elastomer having a degree of modification with maleic anhydride of 1.8-10.0 mass%.

Description

Curable resin composition, curable film, and laminated film

[0001] The present disclosure relates to a curable resin composition, a curable film, and a laminate film.

[0002] In recent years, as the speed of transmission signals in printed wiring boards increases, the frequency of signals is also increasing. Accordingly, there is an increasing demand for printed wiring boards to have low dielectric properties (low dielectric constant, low dielectric loss tangent) in the high-frequency range. Furthermore, protective layers (coverlays) that cover circuits on printed wiring boards, interlayer adhesives in multilayer printed wiring boards, and the like are also required to have low dielectric properties in addition to adhesiveness to substrates, etc. Patent Document 1, for example, proposes an adhesive composition containing a styrene-based elastomer as a resin composition that can yield a cured product with low dielectric properties.

[0003] Japanese Patent Application Laid-Open No. 2018-150543

[0004] Adhesive compositions using the above-mentioned elastomers tend to easily give cured products with excellent dielectric properties, but when used as interlayer adhesives, etc., it may be necessary to sufficiently embed the circuits of printed wiring boards within the cured product.

[0005] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a curable resin composition, a curable film, and a laminate film that are excellent in embeddability.

[0006] In order to solve the above problems, the present disclosure provides the following curable resin composition, curable film, and laminate film.

[0007] [1] A curable resin composition comprising (A) a rubber component, (B) a compound having an epoxy group, (C) a curing agent, (D) a curing accelerator, and (E) a filler, wherein the (A) rubber component comprises a modified styrene-based elastomer having a maleic anhydride modification rate of 1.8 to 10.0 mass%. [2] The curable resin composition according to [1] above, which is used as an interlayer adhesive for multilayer printed wiring boards. [3] The curable resin composition according to [1] or [2] above, wherein the modified styrene-based elastomer has a weight-average molecular weight of 20,000 to 120,000. [4] The curable resin composition according to any one of [1] to [3] above, wherein the (B) compound having an epoxy group has a weight-average molecular weight of 200 to 1,000. [5] The curable resin composition according to any one of [1] to [4] above, wherein the content of the (D) curing accelerator is 0.1 to 10 parts by mass per 100 parts by mass of the total amount of the (A) rubber component, (B) compound having an epoxy group, and (C) curing agent. [6] The curable resin composition according to any one of [1] to [5] above, wherein the (E) filler comprises a surface-treated filler. [7] The curable resin composition according to [6] above, wherein the surface-treated filler comprises a filler having at least one group selected from the group consisting of an epoxy group, a vinyl group, and a phenylamino group. [8] A curable film comprising the curable resin composition according to any one of [1] to [7] above. [9] A laminate film comprising a substrate film and the curable film according to [8] above provided on the substrate film.

[0008] According to the present disclosure, it is possible to provide a curable resin composition, a curable film, and a laminate film that have excellent embeddability.

[0009] Hereinafter, several embodiments of the present disclosure will be described in detail, but the present disclosure is not limited to the following embodiments.

[0010] In this specification, numerical ranges indicated using "to" indicate ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range may be replaced with the upper or lower limit of another numerical range. Furthermore, in numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with a value shown in the Examples. When referring to the amount of each component in a composition in this specification, if multiple substances corresponding to each component are present in the composition, unless otherwise specified, this refers to the total amount of those multiple substances present in the composition. "A or B" may contain either A or B, or both. "Solid content" refers to the non-volatile content of a resin composition excluding volatile substances (water, solvent, etc.). In other words, "solid content" refers to components other than the solvent that remain without volatilizing during drying of the resin composition, as described below, and also 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 the present embodiment contains (A) a rubber component, (B) a compound having an epoxy group, (C) a curing agent, (D) a curing accelerator, and (E) a filler, and the (A) rubber component contains a modified styrene-based elastomer having a maleic anhydride modification rate of 1.8 to 10.0 mass %.

[0012] The curable resin composition according to this embodiment can be used for forming a protective layer (coverlay) that covers the electrical circuits in a printed wiring board, or as an interlayer adhesive in a multilayer printed wiring board. The curable resin composition according to this embodiment has adhesive properties with adherends, for example, with materials that constitute the printed wiring board, such as the metal parts and substrate of the printed wiring board. By using a modified styrene-based elastomer having a maleic anhydride modification rate of 1.8 to 10.0 mass% as the rubber component, the curable resin composition can sufficiently embed the circuits of the printed wiring board when used as an interlayer adhesive. Hereinafter, each component that can be contained in the curable resin composition will be described.

[0013] <(A) Rubber Component> The (A) rubber component contains a modified styrene-based elastomer having a maleic anhydride modification rate of 1.8 to 10.0 mass% (hereinafter referred to as "modified styrene-based elastomer (A1)"), which can enhance compatibility with other components (particularly the (B) compound having an epoxy group) and improve embeddability of the curable resin composition. The modified styrene-based elastomer (A1) has an acid anhydride group derived from maleic anhydride, which tends to easily improve the strength, heat resistance, and adhesion of the cured product.

[0014] The modified styrene elastomer (A1) can be produced by reacting a styrene elastomer with maleic anhydride, and has an acid anhydride group based on maleic anhydride in a side chain. The styrene elastomer may be a copolymer having structural units derived from a styrene compound and structural units derived from a conjugated diene compound.

[0015] Examples of styrene compounds include styrene, α-methylstyrene, p-methylstyrene, and p-tert-butylstyrene. Among these, from the viewpoints of availability and productivity, styrene, α-methylstyrene, and 4-methylstyrene are preferred, and styrene is more preferred.

[0016] Examples of conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 1,3-pentadiene (piperylene), 1-phenyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 3,4-dimethyl-1,3-hexadiene, and 4,5-diethyl-1,3-octadiene. Among these, 1,3-butadiene and isoprene are preferred from the viewpoints of availability and productivity.

[0017] The styrene elastomer may be a hydrogenated styrene elastomer in which at least a portion of the structural units derived from a conjugated diene compound are hydrogenated. Examples of hydrogenated styrene elastomers include hydrogenated products of styrene-butadiene-styrene block copolymers (styrene ethylene butylene styrene elastomers, SEBS) and hydrogenated products of styrene-isoprene-styrene block copolymers. Commercially available SEBS products include the Tuftec (registered trademark) H series manufactured by Asahi Kasei Corporation, the Septon (registered trademark) series manufactured by Kuraray Co., Ltd., and the Kraton (registered trademark) G Polymer series manufactured by Kraton Polymer Japan, Ltd.

[0018] The modification rate of maleic anhydride in the modified styrene-based elastomer (A1) may be 1.8% by mass or more, 1.9% by mass or more, or 2.0% by mass or more from the viewpoint of further improving compatibility with other components. The modification rate of maleic anhydride may be 9.0% by mass or less, 8.0% by mass or less, 7.0% by mass or less, or 6.0% by mass or less from the viewpoint of improving dielectric properties. The modification rate may be 1.8 to 9.0% by mass, 1.8 to 8.0% by mass, 1.9 to 7.0% by mass, or 2.0 to 6.0% by mass. The modification rate can be calculated using the acid value of the modified styrene-based elastomer.

[0019] From the viewpoint of further enhancing compatibility, the acid value of the modified styrene-based elastomer (A1) may be 20 to 120 mgKOH / g, 25 to 100 mgKOH / g, 30 to 90 mgKOH / g, or 35 to 80 mgKOH / g.

[0020] From the viewpoints of coating properties and circuit embedding properties, the weight average molecular weight (Mw) of the modified styrene-based elastomer (A1) may be 20,000 to 120,000, 30,000 to 110,000, 40,000 to 100,000, or 50,000 to 80,000. Mw refers to a value calculated in terms of standard polystyrene determined by gel permeation chromatography (GPC).

[0021] The content of the modified styrene-based elastomer (A1) is preferably 10 to 95% by mass, more preferably 15 to 90% by mass, and even more preferably 20 to 85% by mass, based on the total amount of the rubber component (A), the compound having an epoxy group (B), and the curing agent (C). When the content of (A1) is 10% by mass or more, embeddability tends to be superior. When the content of (A1) is 95% by mass or less, the resulting cured product tends to have particularly excellent properties in terms of adhesion, connection reliability, and insulation reliability. The content of (A1) in the cured product may be within the above range based on the mass of the cured product.

[0022] The rubber component (A) may further contain a modified styrene-based elastomer having a maleic anhydride modification rate of less than 1.8% by mass (hereinafter referred to as "modified styrene-based elastomer (A2)"). Commercially available examples of modified styrene-based elastomer (A2) include "FG1901" and "FG1924" from Kraton Polymer Japan Co., Ltd., and "Tuftec M1911," "Tuftec M1913," and "Tuftec M1943" from Asahi Kasei Corporation.

[0023] The rubber component (A) may further contain an unmodified rubber component that is not modified with maleic anhydride. Examples of unmodified rubber components include 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, vulcanized rubber, epichlorohydrin rubber, and chlorinated butyl rubber.

[0024] Commercially available acrylic rubber products include, for example, the "Nipol AR Series" from Zeon Corporation and the "Clarity Series" from Kuraray Co., Ltd. Commercially available isoprene rubber products include, for example, the "Nipol IR Series" from Zeon Corporation. Commercially available butadiene rubber products include, for example, the "Nipol BR Series" from Zeon Corporation. Commercially available acrylonitrile butadiene rubber products include, for example, the "NBR Series" from ENEOS Material Corporation. Commercially available silicone rubber products include, for example, the "KMP Series" from Shin-Etsu Silicones Co., Ltd. Commercially available ethylene propylene rubber products include, for example, the "EP Series" from ENEOS Material Corporation. Commercially available fluororubber products include, for example, the "Dai-El Series" from Daikin Corporation. Commercially available epichlorohydrin rubber products include, for example, the "Hydrin Series" from Zeon Corporation.

[0025] In the curable resin composition, the content of the (A) rubber component may be 50 to 95% by mass, 65 to 90% by mass, or 60 to 85% by mass, based on the total amount of the (A) rubber component, (B) the compound having an epoxy group, and (C) the curing agent. When the content of the (A) rubber component is 50% by mass or more, the rubber component tends to be more compatible with other components, and the resulting cured product tends to have excellent dielectric properties. When the content of the (A) rubber component is 95% by mass or less, the resulting cured product tends to have particularly excellent properties in terms of adhesion, connection reliability, insulation reliability, and heat resistance. The content of the (A) rubber component in the cured product may be within the above range, based on the mass of the cured product.

[0026] <(B) Compound Having Epoxy Group> The (B) compound having an epoxy group is not particularly limited as long as it has an epoxy group in the molecule, and can be, for example, a general epoxy resin. The epoxy resin may be any of monofunctional, bifunctional, and polyfunctional (trifunctional or higher) epoxy resins, and is not particularly limited, but from the viewpoint of obtaining better curability, a bifunctional or polyfunctional epoxy resin may be used.

[0027] Examples of epoxy resins include bisphenol A, bisphenol F, phenol novolac, naphthalene, dicyclopentadiene, and cresol novolac epoxy resins. From the viewpoints of low tack, dielectric properties, and heat resistance, a naphthalene or dicyclopentadiene epoxy resin may be selected as the compound (B) having an epoxy group, or a dicyclopentadiene epoxy resin may be selected. These epoxy resins may be used alone or in combination of two or more.

[0028] The combination of a rubber having a maleic anhydride group or a carboxy group with a compound having an epoxy group (epoxy resin) tends to provide particularly excellent effects in terms of heat resistance, low moisture permeability, and adhesiveness 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.

[0029] The weight average molecular weight (Mw) of the compound having an epoxy group (B) may be, for example, 200 to 2000. From the viewpoints of the fluidity of the resin composition and the dielectric properties 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.

[0030] The number average molecular weight (Mn) of the (B) compound having an epoxy group may be, for example, 100 to 1,000. From the viewpoints of the fluidity of the resin composition and the dielectric properties of the cured product, it is preferably 150 to 500, more preferably 200 to 400, even more preferably 250 to 350, and particularly preferably 250 to 300.

[0031] The above-mentioned Mw and Mn refer to values ​​calculated in terms of standard polystyrene determined by gel permeation chromatography (GPC).

[0032] The epoxy equivalent of the (B) compound having an epoxy group may be, for example, 200 to 330 g / eq. However, from the viewpoint of the fluidity of the resin composition and the dielectric properties of the cured product, it may be 220 to 310 g / eq, 220 to 290 g / eq, 220 to 270 g / eq, or 230 to 260 g / eq.

[0033] The curable resin composition may contain a component having a polymerizable functional group other than the compound having an epoxy group (B) within a range that does not significantly impair the effects of the present disclosure. From the viewpoint of further reducing the dielectric loss tangent of the cured product, the content of the component having a polymerizable functional group is preferably less than 10 parts by mass per 100 parts by mass of the compound having an epoxy group (B).

[0034] <(C) Curing Agent> The curing agent is a compound that itself participates in the curing reaction. Examples of the curing agent include ester-based curing agents and phenol-based curing agents. The ester-based curing agent can improve the heat resistance of the cured product while reducing the dielectric tangent of the cured product.

[0035] The ester-based curing agent is not particularly limited, but from the viewpoint of obtaining a better effect of improving heat resistance and reducing dielectric tangent, compounds having one or more highly reactive ester groups per molecule, such as phenol esters, esters containing a dicyclopentadiene structure, esters containing a naphthalene structure, thiophenol esters, N-hydroxyamine esters, and esters of heterocyclic hydroxy compounds, are preferably used. A compound containing a naphthalene structure may also be used as the ester-based curing agent. Examples of ester-based curing agents include "EPICLON HPC8000-65T," "EPICLON HPC8000-L-65MT," "EPICLON HPC8150-60T," "EPICLON HPC8150-62T," and "EPICLON HPC8150-65T" (all trade names manufactured by DIC Corporation). These may be used alone or in combination of two or more.

[0036] The phenolic curing agent is not particularly limited, and examples thereof include alkylphenol resins, phenol novolac resins, and resins having a phenolic hydroxyl group at the terminal. From the viewpoint of further improving the heat resistance of the cured product of the curable resin composition, the phenolic curing agent may be, for example, an alkylphenol resin, a phenol novolac resin, or an alkylphenol resin. From the viewpoint of further improving the heat resistance of the cured product of the curable resin composition and the adhesiveness of the cured product, the phenolic curing agent may be, for example, a resin having a phenolic hydroxyl group at the terminal. Phenol-based curing agents are available, for example, as "PR1501" (trade name manufactured by Resonac Co., Ltd.) and "FTC509" (trade name manufactured by Gun-ei Chemical Industry Co., Ltd.). These may be used alone or in combination of two or more.

[0037] In the curable resin composition, the total content of the (B) epoxy group-containing compound and the (C) curing agent may be 5 to 50 mass%, 10 to 45 mass%, or 15 to 40 mass%, based on the total amount of the (A) rubber component, the (B) epoxy group-containing compound, and the (C) curing agent. When the total content of the (B) epoxy group-containing compound and the (C) curing agent is 5 mass% or more, more sufficient curing is likely to be achieved, and the cured product tends to have particularly excellent properties in terms of adhesion, insulation reliability, and heat resistance. When the total content of the (B) epoxy group-containing compound and the (C) curing agent is 50 mass% or less, more sufficient elasticity is likely to be achieved, and the cured product tends to mix well with the rubber component.

[0038] <(D) Curing Accelerator> The (D) curing accelerator is a compound that functions as a catalyst for the curing reaction. The (D) curing accelerator may be selected from tertiary amines, imidazoles, organic acid metal salts, phosphorus-based compounds, Lewis acids, amine complex salts, and phosphines. Among these, imidazole may be used from the viewpoints of the storage stability and curability of the varnish of the curable resin composition, and the dielectric properties of the cured product. When the (A) rubber component contains rubber partially modified with maleic anhydride, an imidazole compatible with this may be selected. The imidazole may be 1-benzyl-2-methylimidazole.

[0039] In the curable resin composition, the content of the (D) curing accelerator may be 0.1 to 10 parts by mass relative to 100 parts by mass of the total amount of the (A) rubber component, (B) epoxy group-containing compound, and (C) curing agent. When the content of the (D) curing accelerator is 0.1 parts by mass or more, more sufficient curing tends to be easily achieved. When the content of the (D) curing accelerator is 10 parts by mass or less, the storage stability of the curable resin composition varnish, film, etc., and the heat resistance and dielectric properties of the cured product tend to be improved. From the above viewpoints, the content of the (D) curing accelerator may be 0.1 to 7 parts by mass, 0.2 to 5 parts by mass, or 0.3 to 3 parts by mass.

[0040] <(E) Filler> When the curable resin composition contains (E) filler, the coefficient of linear expansion (CTE) of the cured product tends to be reduced.

[0041] The filler (E) may be a filler having at least one group selected from the group consisting of a (meth)acryloyl group, a vinyl group, an epoxy group, and a phenylamino group. By having these groups, the filler tends to have particularly excellent properties in terms of compatibility with the resin component at the filler interface, filler dispersibility, storage stability of the curable resin composition, linear expansion coefficient of the cured product, and adhesiveness of the cured product. Therefore, the curable resin composition can be more suitably used as an interlayer adhesive for multilayer printed wiring boards.

[0042] From the viewpoints of the linear expansion coefficient and adhesiveness, the (E) filler preferably contains a filler having at least one group selected from the group consisting of a (meth)acryloyl group, a vinyl group, an epoxy group, and a phenylamino group, more preferably contains a filler having at least one group selected from the group consisting of a vinyl group, an epoxy group, and a phenylamino group, and even more preferably contains a filler having an epoxy group.

[0043] As the filler (E), from the viewpoints of the linear expansion coefficient and adhesion to a low-polarity resin substrate, a filler having a vinyl group or an epoxy group is more preferable, and from the same viewpoint, a filler having an epoxy group is particularly preferable. An example of a low-polarity resin substrate is a liquid crystal polymer.

[0044] The (E) filler may be a surface-treated filler. The surface-treated filler can be obtained by treating the surface of the filler with a surface treatment agent such as an organic silane compound. By treating the surface of the filler, the filler tends to have particularly excellent properties in terms of compatibility with the resin component at the filler interface, filler dispersibility, storage stability of the curable resin composition, linear expansion coefficient of the cured product, and adhesiveness of the cured product. Therefore, by using a surface-treated filler as the (E) filler, the curable resin composition can be more suitably used as an interlayer adhesive for multilayer printed wiring boards. The surface treatment may be surface modification.

[0045] From the viewpoints of linear expansion coefficient and adhesiveness, the surface-treated filler preferably contains a filler having at least one group selected from the group consisting of a (meth)acryloyl group, a vinyl group, an epoxy group, and a phenylamino group, more preferably contains a filler having at least one group selected from the group consisting of a vinyl group, an epoxy group, and a phenylamino group, and even more preferably contains a filler having an epoxy group.

[0046] As the surface-treated filler, from the viewpoints of the linear expansion coefficient and adhesion to a low-polarity resin substrate, a filler having a vinyl group or an epoxy group is more preferable, and from the same viewpoint, a filler having an epoxy group is particularly preferable. An example of a low-polarity resin substrate is a liquid crystal polymer.

[0047] When the above-mentioned surface-treated filler is used, the cured product of the curable resin composition tends to have improved adhesion to materials constituting printed wiring boards, etc., and in particular, tends to have improved adhesion to substrates having low-roughening or non-roughening surfaces. The cured product of the curable resin composition containing the above-mentioned surface-treated filler tends to have good adhesion to low-polarity resin substrates, for example, non-roughening liquid crystal polymer films.

[0048] From the viewpoint of achieving both the fluidity of the curable resin composition and a reduced linear expansion coefficient of the cured product, the content of the (E) filler may be 30 to 75 mass%, 30 to 70 mass%, 40 to 70 mass%, or 50 to 65 mass%, based on the total solid content of the curable resin composition. When the content of the (E) filler is within the above range, it is possible to achieve both the fluidity of the curable resin composition and a reduced linear expansion coefficient of the cured product.

[0049] From the viewpoint of achieving excellent dielectric properties, adhesiveness, and film appearance of the cured product, the average particle size of the (E) filler may be 0.01 μm or more, 0.1 μm or more, or 0.2 μm or more, or 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. The average particle size of the (E) filler means the particle size at a cumulative frequency of 50% in a particle size distribution determined by a laser diffraction / scattering method.

[0050] As the (E) filler, an inorganic filler may be used from the viewpoint of further reducing the linear expansion coefficient and improving the elastic modulus. Examples of inorganic fillers include fillers 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 titanate zirconate, lead lanthanum titanate zirconate, 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 two or more types may be used in combination. Among these, the inorganic filler may be an inorganic filler containing silica, alumina, titania, or boron nitride from the viewpoint of dispersibility and heat resistance of the cured product. The inorganic filler may be an inorganic filler containing silica from the viewpoint of dielectric properties.

[0051] As the (E) filler, an organic filler may be used. Examples of the organic filler include fillers made of liquid crystal polymer (LCP) and polytetrafluoroethylene (PTFE). One type of organic filler may be used alone, or two or more types may be used in combination. Furthermore, as the (E) filler, one or more types of inorganic fillers may be used in combination with one or more types of organic fillers.

[0052] The (E) filler may be an inorganic filler whose surface is treated with silica, alumina, titania, or boron nitride from the viewpoints of dispersibility and heat resistance, or may be an inorganic filler whose surface is treated with silica, alumina, or boron nitride from the viewpoints of linear expansion coefficient and adhesiveness. The (E) filler may be a surface-treated silica filler whose surface is treated with silica.

[0053] 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 viewpoints of linear expansion coefficient and adhesiveness.

[0054] Examples of the organic silane compound 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 arylsilane. and 3-isocyanatopropyltriethoxysilane, N-(1,3-dimethylbutylidene)-3-amino ...

[0055] <Other Components> In addition to the components described above, the curable resin composition may further contain, as necessary, an antioxidant, an anti-yellowing agent, an ultraviolet absorber, a visible light absorber, a colorant, a plasticizer, a stabilizer, a filler, a flame retardant, a leveling agent, or the like, within a range that does not significantly impair the effects of the present disclosure.

[0056] In particular, the curable resin composition may contain at least one anti-degradation agent selected from the group consisting of antioxidants, heat stabilizers, light stabilizers, and hydrolysis inhibitors. The antioxidant suppresses degradation due to oxidation. The antioxidant also imparts sufficient heat resistance at high temperatures to the cured product. The heat stabilizer imparts stability at high temperatures to the cured product. 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 accepts light energy absorbed by an organic material and stabilizes the organic material. The hydrolysis inhibitor suppresses degradation due to moisture. The anti-degradation agent may be at least one selected from the group consisting of antioxidants, heat stabilizers, and ultraviolet absorbers. As the anti-degradation agent, only one of the components exemplified above may be used, or two or more may be used in combination. To achieve better effects, two or more anti-degradation agents may be used in combination.

[0057] The curable resin composition may be prepared as a resin varnish in which the above-described components are dissolved or dispersed in an organic solvent. The organic solvent is not particularly limited, 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; carbonates such as ethylene carbonate and propylene carbonate; and amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone. From the viewpoints of solubility and boiling point, toluene or N,N-dimethylacetamide may be used. These organic solvents may be used alone or in combination of two or more. The concentration of solids (components other than the organic solvent) in the resin varnish may be 20 to 80% by mass.

[0058] The mixing and kneading of the resin varnish can be carried out by appropriately combining a conventional mixer, a dispersing machine such as a mortar and pestle, a three-roll mill, or a ball mill.

[0059] [Curable Film and Laminated Film] The curable film according to this embodiment is made of the curable resin composition described above. The curable film can be easily produced, for example, by applying a resin varnish containing the curable resin composition to a substrate film and removing the solvent from the coating. This method can produce a laminated film including a substrate film and a curable film provided on the substrate film.

[0060] The solvent is removed from the coating film on the substrate film by drying at a temperature that does not cure the curable resin composition and under conditions that allow the solvent to volatilize sufficiently. Specifically, the coating film is typically dried by heating at 60 to 180°C for 0.1 to 90 minutes. The resulting curable film preferably has a residual volatile content of 10% by mass or less. This residual volatile content of 10% by mass or less helps to prevent voids from remaining inside the cured product due to foaming caused by solvent evaporation during assembly and heating. It also helps to prevent contamination of surrounding materials or components caused by volatile components generated during heating.

[0061] The material of the substrate film is not particularly limited and includes, for example, polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; polycarbonate, polyamide, polyimide, polyamideimide, polyetherimide, polyethersulfide, polyethersulfone, polyetherketone, polyphenylene ether, polyphenylene sulfide, polyarylate, polysulfone, and liquid crystal polymers. Among these, from the viewpoint of flexibility and toughness, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polypropylene, polycarbonate, polyamide, polyimide, polyamideimide, polyphenylene ether, polyphenylene sulfide, polyarylate, and polysulfone are preferred.

[0062] The thickness of the substrate film may be varied as appropriate depending on the desired flexibility, but may be 3 to 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 the above viewpoints, the thickness may be 5 to 200 μm, 7 to 150 μm, or 10 to 100 μm. From the viewpoint of improving releasability from the curable film, a substrate film that has been subjected to a release treatment using a silicone compound, a fluorine-containing compound, or the like may be used as needed.

[0063] If necessary, a protective film may be attached onto the curable film to form a laminated film having a three-layer structure consisting of a base film, a curable film, and a protective film.

[0064] The material of the protective film is not particularly limited, and examples thereof 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 viewpoints of flexibility and toughness. From the viewpoint of improving releasability from the curable film, a protective film that has been subjected to a release treatment with a silicone compound, a fluorine-containing compound, or the like may be used as needed.

[0065] The thickness of the protective film may be varied depending on the desired flexibility, but may be 10 to 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 the above viewpoints, the thickness of the protective film may be 10 to 200 μm, 15 to 150 μm, or 20 to 100 μm.

[0066] The thickness of the curable film after drying is not particularly limited, but may typically be 5 to 1000 μm. When the thickness is 5 μm or more, the curable film or its cured product tends to easily obtain sufficient strength. When the thickness is 1000 μm or less, drying can be carried out sufficiently, and the amount of residual solvent in the curable film tends to be easily reduced.

[0067] The laminate film can be easily stored by, for example, winding it up in a roll, or it can be stored in the form of a sheet cut into a suitable size from the roll.

[0068] The curable resin composition, curable film, and laminate film according to the present embodiment are suitable for forming a protective layer (coverlay) that covers an electric circuit in a printed wiring board, and as an interlayer adhesive in a multilayer printed wiring board, and are particularly suitable as an interlayer adhesive.

[0069] [Printed Wiring Board] The printed wiring board in this embodiment includes, as a component, a laminate formed from a metal portion forming an electric circuit (conductor circuit) and a resin substrate. The printed wiring board can be manufactured by a conventionally known method such as a subtractive method using a metal-clad laminate, for example. The printed wiring board in this embodiment is a general term for so-called flexible circuit boards (FPCs), flat cables, circuit boards for tape automated bonding (TAB), etc., in which a conductor circuit formed by a metal portion is partially or entirely covered with a coverlay film, screen printing ink, etc., as necessary.

[0070] The printed wiring board of this embodiment may have any laminated structure that can be used as a printed wiring board, for example, a printed wiring board having a base layer, an adhesive layer, a metal portion, and a protective layer.

[0071] Furthermore, if necessary, two or more of the above printed wiring boards may be laminated using an interlayer adhesive to form a multilayer printed wiring board.

[0072] In the printed wiring board of this embodiment, any substrate that has conventionally been used as a substrate for printed wiring boards can be used as the substrate layer.

[0073] In the printed wiring board of this embodiment, any resin conventionally used as a substrate for printed wiring boards can be used as the base material layer, and examples of the resin for the base material layer include polyester resin, polyamide resin, polyimide resin, polyamide-imide resin, liquid crystal polymer, polyphenylene sulfide, syndiotactic polystyrene, polyolefin resin, and fluorine-based resins (e.g., polytetrafluoroethylene (PTFE)).

[0074] The curable resin composition of this embodiment can be used for adhesive layers, protective layers, and interlayer adhesives in printed wiring boards. In particular, when these layers are formed using the curable resin composition of this embodiment, they have excellent embeddability and moldability, and the layers formed using the curable resin composition themselves have excellent low dielectric properties and a low linear expansion coefficient. The cured product of the curable resin composition of this embodiment tends to have excellent adhesion to materials constituting printed wiring boards, such as substrate layers and metal parts, particularly 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 wiring boards. The curable resin composition of this embodiment is also suitable as a curable resin composition for use in coverlay films, laminates, resin-coated copper foils, and bonding sheets. Furthermore, since the curable resin composition of this embodiment contains a rubber component (A), the 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 for flexible printed wiring boards.

[0075] In the printed wiring board of this embodiment, the metal portion is not particularly limited, but may be copper from the viewpoint of wiring formability. The material forming the copper is not particularly limited, and for example, electrolytic copper foil and rolled copper foil used in copper-clad laminates and printed wiring boards, etc., can be used. 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 Denkai Co., Ltd., product name), GTS-18 (manufactured by Furukawa Electric Co., Ltd., product name), 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 Nippon Mining Corporation, product name), HA foil (manufactured by JX Nippon Mining Corporation, product name), HA-V2 foil (manufactured by JX Nippon Mining Corporation, product name), and C1100R (manufactured by Sumitomo Metal Mining Co., Ltd., product name). From the viewpoint of adhesion to the cured product of the curable resin composition of this embodiment, a copper foil that has been subjected to a roughening treatment may be used. From the viewpoint of folding endurance, a rolled copper foil may be used. Furthermore, the metal portion may have a roughened surface formed by a roughening treatment.

[0076] The present disclosure will be described in more detail with reference to the following examples, although the present disclosure is not limited to these examples.

[0077] [Curable Resin Composition] (Examples 1 to 4 and Comparative Examples 1 to 3) Each material shown in Table 1 was mixed at the solid content ratio (unit: parts by mass) shown in the same table to prepare a curable resin composition. Toluene was added as a solvent to prepare the curable resin composition so that the solid content was 40 mass%. Details of each material are shown below.

[0078] (A) Rubber Component Unmodified styrene-based elastomer: SEBS elastomer (Kraton Polymer Japan Co., Ltd., trade name "KRATON MD1653 MO", Mw: 65,000, maleic anhydride modification: not performed) Modified styrene-based elastomer (A1): maleic anhydride-modified SEBS elastomer (Synthesis Example 1, Mw: 69,000, maleic anhydride modification rate: 2.1% by mass) Modified styrene-based elastomer (A2): maleic anhydride-modified SEBS elastomer (Kraton Polymer Japan Co., Ltd., trade name "KRATON FG1924 GT", Mw: 127,000, maleic anhydride modification rate: 1.0% by mass)

[0079] Synthesis Example 1: 950 g of xylene, 100 g of hydrogenated styrene-based thermoplastic elastomer (Kraton Polymer Japan, product name "KRATON MD1653 MO"), and 17.0 g of maleic anhydride (Fujifilm Wako Pure Chemical Industries, Ltd.) were added to a 2 L flask equipped with a condenser, nitrogen inlet, thermocouple, and stirrer. The mixture was stirred at 80°C for 0.5 hours, followed by nitrogen bubbling at a flow rate of 0.5 cm3 / L for 1.0 hour. Next, 6.5 g of benzoyl peroxide (Fujifilm Wako Pure Chemical Industries, Ltd.) was added, and the mixture was stirred at 80°C for 6.0 hours while bubbling with nitrogen to carry out the reaction. Unreacted maleic anhydride was extracted from the reaction solution three times with isopropyl alcohol and concentrated. The concentrate was dried under vacuum at 70°C to obtain a modified styrene-based elastomer having succinic anhydride groups (maleic anhydride-modified SEBS elastomer).

[0080] (Acid Value) Approximately 1 g of modified styrene-based elastomer (A1) and 200 g of xylene were mixed at 80°C, to which 0.5 mL of distilled water was added, followed by stirring at reflux temperature for 1 hour to hydrolyze the succinic anhydride groups. The mixture was cooled to 80°C, a small amount of phenolphthalein was added, and then a 0.1 M potassium hydroxide (KOH)-containing ethanol solution was added dropwise for 30 seconds until the color did not disappear. The acid value (mg KOH / g) was measured from the amount of modified styrene-based elastomer and the amount of KOH added dropwise. The acid value of the modified styrene-based elastomer is a value derived from the two carboxy groups generated by hydrolysis of the succinic anhydride groups.

[0081] (Modification Ratio) The modification ratio of the modified styrene-based elastomer (A1) with maleic anhydride was calculated by inputting the acid value, the molecular weight of KOH, and the molecular weight of maleic anhydride into the following formula: Modification ratio (mass%) = [acid value (mg KOH / g) / molecular weight of KOH (mg / mol)] × 0.5 × molecular weight of maleic anhydride (g / mol) × 100 (%)

[0082] (B) Compound having an epoxy group HP7200L: dicyclopentadiene-type epoxy resin (manufactured by DIC Corporation, trade name "EPICLON HP-7200L", epoxy equivalent: 247 g / eq, Mn: 288, Mw: 401)

[0083] (C) Curing Agent HPC8150-62T: Ester-based curing agent (manufactured by DIC Corporation, trade name "EPICLON HPC8150-62T", an active ester compound containing a naphthalene structure, a toluene solution with a solids content of 62% by mass)

[0084] (D) Curing accelerator 1B2MZ: 1-benzyl-2-methylimidazole (manufactured by Shikoku Chemicals Corporation, trade name "1B2MZ")

[0085] (E) Filler SC2050-MB: Epoxy group-modified silica filler dispersion (manufactured by Admatechs Co., Ltd., product name "SC2050-MB", average particle size: 0.50 μm, solvent: MEK, solid content: 70% by mass)

[0086] [Laminate Film A] A release-treated polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., trade name "Purex A3100", thickness 25 μm) was prepared as a base film. The curable resin composition was applied to the release-treated surface of this PET film using a knife coater (manufactured by Yasui Seiki Co., Ltd., trade name "SNC-350"). The coating film was dried by heating at 80°C for 15 minutes in a dryer (manufactured by Futaba Scientific Co., Ltd., trade name "MSO-80TPS") to form a curable film with a thickness of 30 μm. A release-treated PET film identical to the base film was attached as a protective film to the formed curable film, with the release-treated surface facing the curable film, to obtain laminate film A. Note that the curable resin composition of Comparative Example 2 separated, and laminate film A could not be produced.

[0087] (Melt Viscosity) The base film and the protective film were removed from the laminate film A to leave only the curable film, and the minimum melt viscosity of this curable film was measured using a viscoelasticity measuring device (manufactured by TA Instruments, trade name "ARES-G2", heating rate: 3°C / min, temperature range: 30 to 200°C, load: 0.2 N, frequency: 1 Hz, strain: 1%).

[0088] (Adhesion) The protective film of laminate film A was peeled off, and an electrolytic copper foil (manufactured by Furukawa Electric Co., Ltd., product name "F2-WS-18", thickness 18 μm) (hereinafter also referred to as "VLP-Cu foil") having a roughened surface with a surface roughness Rz of 1.8 μm was superposed on the exposed curable film. At this time, the VLP-Cu foil was superposed on the curable film with the roughened surface facing the curable film. In this state, the VLP-Cu foil was laminated on the curable film using a vacuum pressure laminator (manufactured by Nikko Materials Co., Ltd., product name "V130") under conditions of a pressure of 0.5 MPa, a temperature of 100°C, and a pressure time of 1 minute. Next, the base film was peeled off, and the VLP-Cu foil was superposed on the exposed curable film with the roughened surface facing the curable film, and the VLP-Cu foil was laminated on the curable film under the above conditions. Thereafter, the film was heated at 180°C for 60 minutes in a dryer (manufactured by Futaba Scientific Co., Ltd., product name "MSO-80TPS") to obtain a laminate having a VLP-Cu foil, a cured film which is a cured product of the curable film, and the VLP-Cu foil.

[0089] A sample for measuring peel strength, measuring 100 mm in length and 5 mm in width, was cut out from the resulting laminate. One VLP-Cu foil surface of this sample was fixed to a glass plate with an epoxy adhesive (Huntsman Japan, product name "Araldite Rapid"). A 90-degree peel test was performed using an autograph (Shimadzu Corporation, product name "EZ-LX") at a pulling rate of 50 mm / min, in which the other VLP-Cu foil and the cured film were gripped with a jig and peeled from the VLP-Cu foil fixed to the glass plate.

[0090] [Laminate Film B] A release-treated polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., trade name "Purex A3100", thickness 25 μm) was prepared as a substrate film. The above-mentioned curable resin composition was applied to the release-treated surface of this PET film using a knife coater (manufactured by Yasui Seiki Co., Ltd., trade name "SNC-350"). The coating film was dried by heating at 80°C for 15 minutes in a dryer (manufactured by Futaba Scientific Co., Ltd., trade name "MSO-80TPS") to form a curable film with a thickness of 25 μm. A release-treated PET film identical to the base film was attached as a protective film to the formed curable film, with the release-treated surface facing the curable film, to obtain laminate film B. Note that the curable resin composition of Comparative Example 2 separated, and laminate film B could not be produced.

[0091] (Embeddability) A substrate was prepared in which a copper foil having a dot-shaped etching pattern with a copper residual ratio of 90%, a thickness of 12 μm, and a diameter of 0.26 mm was laminated on one side, and a copper foil having a grid-shaped etching pattern with a copper residual ratio of 20%, a thickness of 12 μm, and a width of 0.15 mm was laminated on the other side. The protective film of laminated film B was peeled off, and the exposed curable film was laminated on both sides of the substrate, and then laminated using a vacuum pressure laminator (V130) under conditions of a pressure of 0.5 MPa, a temperature of 100 ° C., and a pressure time of 1 minute. Next, the substrate film was peeled off, and VLP-Cu foil (manufactured by Furukawa Electric Co., Ltd., trade name "F2-WS-18", thickness: 18 μm) was further laminated on both sides of the curable film, and a small vacuum press (manufactured by Imoto Machinery Co., Ltd., trade name "IMC-18EE-A") was used to press, producing a double-sided copper clad laminate. The pressing conditions were a pressure of 3 MPa, a temperature increase from 30°C to 180°C at a rate of 3°C / min in a vacuum, and a holding time of 60 minutes at 180°C. The double-sided copper-clad laminate was put into a reflow process at 260°C three times, and the result was evaluated as "OK" if no peeling or lifting occurred on the surface, and as "NG" if peeling or lifting occurred.

[0092]

Claims

1. A curable resin composition comprising (A) a rubber component, (B) a compound having an epoxy group, (C) a curing agent, (D) a curing accelerator, and (E) a filler, wherein the (A) rubber component contains a modified styrene-based elastomer having a maleic anhydride modification rate of 1.8 to 10.0 mass%.

2. The curable resin composition according to claim 1, which is used as an interlayer adhesive for a multilayer printed wiring board.

3. The curable resin composition according to claim 1, wherein the weight average molecular weight of the modified styrene-based elastomer is 20,000 to 120,000.

4. The curable resin composition according to claim 1, wherein the compound having an epoxy group (B) has a weight average molecular weight of 200 to 1,000.

5. The curable resin composition according to claim 1, wherein the content of the (D) curing accelerator is 0.1 to 10 parts by mass per 100 parts by mass of the total amount of the (A) rubber component, the (B) compound having an epoxy group, and the (C) curing agent.

6. The curable resin composition according to claim 1, wherein the (E) filler comprises a surface-treated filler.

7. The curable resin composition according to claim 6, wherein the surface-treated filler comprises a filler having at least one group selected from the group consisting of an epoxy group, a vinyl group, and a phenylamino group.

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

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

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