JP2025012977A - Resin composition, resin sheet, laminate and circuit board material - Google Patents

Abstract

To provide a resin composition, a resin sheet, a laminate, and a circuit board material which have low dielectric characteristics and are excellent in dimensional stability.SOLUTION: The resin composition contains: at least one thermoplastic resin (A) selected from the group consisting of a styrenic thermoplastic elastomer, an olefinic thermoplastic elastomer, and an ethylenic polymer; a radical polymerizable compound (B); an epoxy compound (C); and a curing agent (D). The content of the thermoplastic resin (A) is 20 mass% or more based on the total mass of the resin composition. The sum of the contents of the epoxy compound (C) and the curing agent (D) is 4 mass% or more and 80 mass% or less based on the total mass of the resin composition.SELECTED DRAWING: None

Description

The present invention relates to a resin composition, a resin sheet, a laminate, and a circuit board material.

2. Description of the Related Art In recent years, as electric and electronic devices have become more powerful and functional, communication frequencies have become higher in order to improve communication speeds and the amount of information transmitted.
When a digital signal is transmitted through a circuit board, a portion of the transmitted digital signal is converted into heat within the circuit board, resulting in transmission loss. Since the amount of transmission loss is expressed as the product of the dielectric constant and the dielectric loss tangent, a material with a low dielectric constant and dielectric loss tangent, i.e., a component with low dielectric properties, is required to achieve low-loss communication. Since transmission signals in the high-frequency range in particular are more easily converted into heat, materials with even lower dielectric properties are in demand.
Furthermore, in the case of high-frequency circuit boards, like conventional ones, components are mounted and connections to other circuit boards are made through processes such as solder reflow and hot bar soldering, so the circuit board materials are also required to have heat resistance.

Materials with low dielectric properties include, for example, polyphenylene ether resin compositions containing epoxy compounds and cyanate compounds (see, for example, Patent Document 1), thermosetting resins such as maleimide resins (see, for example, Patent Document 2), and thermoplastic resins such as cyclic olefin resin compositions (see, for example, Patent Document 3).

JP 2010-059363 A JP 2012-255059 A International Publication No. 2006/095511

However, conventional thermosetting resins tend to have higher dielectric constants and dielectric loss tangents than thermoplastic resins, and it has been necessary to add large amounts of inorganic particles or the like to achieve low dielectric properties.
On the other hand, conventional thermoplastic resins have low dielectric properties but often lack good heat resistance.
Furthermore, when the above-mentioned materials are used as circuit board materials, they are laminated with a conductor such as copper foil, and therefore it is required that the linear thermal expansion coefficient be reduced to prevent peeling from the conductor or deformation.

Therefore, the present invention aims to provide a resin composition, a resin sheet, a laminate, and a circuit board material that have low dielectric properties and excellent dimensional stability.

As a result of intensive research conducted by the present inventors to solve the above problems, the present inventors have found that a resin composition containing at least one thermoplastic resin (A) selected from the group consisting of styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, ethylene-based polymers, and cyclic polyolefin resin copolymers, a radically polymerizable compound (B), an epoxy compound (C), and a curing agent (D), in which the content of the thermoplastic resin (A) is 20% by mass or more relative to the total mass of the resin composition, and the sum of the contents of the epoxy compound (C) and the curing agent (D) is 4% by mass or more and 80% by mass or less relative to the total mass of the resin composition, can achieve both low dielectric properties and excellent dimensional stability.

The gist of the present invention is as follows.
[1] A resin composition comprising at least one thermoplastic resin (A) selected from the group consisting of a styrene-based thermoplastic elastomer, an olefin-based thermoplastic elastomer, an ethylene-based polymer, and a cyclic polyolefin resin copolymer, a radical polymerizable compound (B), an epoxy compound (C), and a curing agent (D), wherein the content of the thermoplastic resin (A) is 20 mass% or more based on the total mass of the resin composition, and the sum of the contents of the epoxy compound (C) and the curing agent (D) is 4 mass% or more and 80 mass% or less based on the total mass of the resin composition.
[2] The resin composition according to [1], wherein the thermoplastic resin (A) comprises a styrene-based thermoplastic elastomer, and the styrene content of the styrene-based thermoplastic elastomer is 10% by mass or more and 70% by mass or less.
[3] The resin composition according to [1] or [2], wherein the thermoplastic resin (A) has a mass average molecular weight (Mw) of 30,000 or more.
[4] The resin composition according to any one of [1] to [3], wherein the content of the radical polymerizable compound (B) per 100 parts by mass of the thermoplastic resin (A) is 1 part by mass or more and 50 parts by mass or less.
[5] The resin composition according to any one of [1] to [4], comprising, as the epoxy compound (C), a polyfunctional epoxy compound having an epoxy equivalent of 1000 g/eq or less.
[6] The resin composition according to any one of [1] to [5], wherein the epoxy compound (C) contains a fluorine atom.
[7] The resin composition according to any one of [1] to [6], wherein the curing agent (D) is an acid anhydride curing agent and/or an active ester curing agent.
[8] The resin composition according to any one of [1] to [7], wherein the resin composition is heat-pressed at 200° C. and 2 MPa for 30 minutes to obtain a cured product having a linear thermal expansion coefficient of 190 ppm/K or less.
[9] A resin sheet comprising the resin composition according to any one of [1] to [8].
[10] A laminate comprising a release film on one or both surfaces of the resin sheet according to [9].
[11] A circuit board material comprising an insulating layer formed from a cured product of the resin composition according to any one of [1] to [8] and a conductor laminated thereon.

According to the present invention, it is possible to obtain a resin composition, a resin sheet, a laminate, and a circuit board material that have low dielectric properties and excellent dimensional stability.

An example of an embodiment of the present invention will be described in detail below, however, the present invention is not limited to the embodiment described below.
In the present invention, the term "film" conceptually includes a sheet, a film, and a tape.
Furthermore, when the term "panel" is used, such as an image display panel or a protective panel, it encompasses a plate, a sheet, and a film.

In the present invention, when it is described as "x to y" (x and y are arbitrary numbers), unless otherwise specified, it includes the meaning of "x or more and y or less", as well as the meaning of "preferably larger than x" or "preferably smaller than y".
In addition, when it is stated that the amount is "x or more" (where x is any number), it also means that the amount is "preferably greater than x" unless otherwise specified, and when it is stated that the amount is "y or less" (where y is any number), it also means that the amount is "preferably smaller than y" unless otherwise specified.
Furthermore, "x and/or y (x and y are optional configurations)" means at least one of x and y, and means three possibilities: x only, y only, and x and y.
In the present invention, "(meth)acrylic" refers to a comprehensive definition of acrylic and methacrylic, "(meth)acrylate" refers to a comprehensive definition of acrylate and methacrylate, and "(meth)acryloyl" refers to a comprehensive definition of acryloyl and methacryloyl.

<Resin Composition>
A resin composition according to one embodiment of the present invention (hereinafter also referred to as "the resin composition") contains at least one thermoplastic resin (A) selected from the group consisting of a styrene-based thermoplastic elastomer, an olefin-based thermoplastic elastomer, an ethylene-based polymer, and a cyclic polyolefin resin copolymer, a radically polymerizable compound (B), an epoxy compound (C), and a curing agent (D).
Each component of the resin composition will now be described.

1. Thermoplastic resin (A)
The thermoplastic resin (A) of the present resin composition is at least one selected from the group consisting of styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, ethylene-based polymers, and cyclic polyolefin resin copolymers.

Examples of the styrene-based thermoplastic elastomer include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), and hydrogenated versions of these, such as styrene-ethylene-butadiene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), and styrene-isobutylene-styrene block copolymer (SIBS).

The olefin-based thermoplastic elastomer contains a polyolefin (excluding cyclic polyolefins, which will be described later) as a hard segment, and a rubber component as a soft segment.
The olefin-based thermoplastic elastomer may be a mixture (polymer blend) of a polyolefin and a rubber component, a crosslinked product obtained by crosslinking a polyolefin with a rubber component, or a polymer obtained by polymerizing a polyolefin with a rubber component.
The polyolefin includes polypropylene, polyethylene, and the like.
Examples of the rubber component include diene rubbers such as isoprene rubber, butadiene rubber, butyl rubber, propylene-butadiene rubber, acrylonitrile-butadiene rubber, and acrylonitrile-isoprene rubber; ethylene-propylene non-conjugated diene rubber; and ethylene-butadiene copolymer rubber.

The ethylene polymer includes a homopolymer of ethylene and a copolymer of ethylene and another monomer.
The copolymer of ethylene and another monomer preferably contains ethylene as a main component. Here, "containing ethylene as a main component" means that the copolymer contains 50 mol % or more, preferably 60 mol % or more, of ethylene structural units.
The other monomer to be copolymerized with ethylene is not particularly limited as long as it is a monomer copolymerizable with ethylene.
Preferred examples of the ethylene polymer include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), polyethylene obtained by polymerization using a metallocene catalyst, etc. Among these, it is particularly preferable to use linear low density polyethylene (LLDPE) because of its high flexibility.

The cyclic polyolefin resin copolymer is a copolymer having an alicyclic structure, specifically, a copolymer having an alicyclic structure in the side chain of polyolefin.Preferable examples of the alicyclic structure include cycloalkane, bicycloalkane, polycyclic compound, etc. Among these, cycloalkane is preferred, and cyclohexane is more preferred.
The alicyclic structure is more preferably an alicyclic structure generated by hydrogenation of an aromatic ring contained in a hydrogenated aromatic vinyl polymer block unit described below.

The cyclic polyolefin resin copolymer preferably has a crystal melting peak temperature of less than 100°C.
The crystalline melting peak temperature of the cyclic polyolefin resin copolymer is preferably 50° C. or higher, more preferably 60° C. or higher, and even more preferably 65° C. or higher. The crystalline melting peak temperature of the cyclic polyolefin resin copolymer is preferably 90° C. or lower, and more preferably 85° C. or lower.
The crystalline melting peak temperature in the present invention is the temperature at which a crystalline melting peak is detected in differential scanning calorimetry (DSC) measured at a heating rate of 10° C./min. The cyclic polyolefin resin copolymer used in the present resin composition may have a crystalline melting peak at less than 100° C., and may have a crystalline melting peak at two points, for example, less than 100° C. and 100° C. or higher.

Examples of known cyclic polyolefins include hydrogenated ring-opening polymers having repeating units derived from monocyclic norbornene monomers or polycyclic norbornene monomers (e.g., International Publication Nos. WO 2012/046443 and WO 2012/033076). These cyclic polyolefins have an alicyclic structure in the polymer main chain, and either do not have a crystalline melting peak temperature below 100° C. or are amorphous.
On the other hand, the cyclic polyolefin resin copolymer of the present resin composition has an alicyclic structure in the polyolefin side chain, and therefore has a crystal melting peak temperature below 100°C.

The melt flow rate (MFR) of the cyclic polyolefin resin copolymer is not particularly limited, but is usually 0.1 g/10 min or more, and from the viewpoint of the molding method and the appearance of the molded product, it is preferably 0.5 g/10 min or more. The melt flow rate (MFR) is usually 200 g/10 min or less, and from the viewpoint of material strength, it is preferably 100 g/10 min or less, more preferably 90.0 g/10 min or less. By setting the MFR within the above range, compatibility with the thermoplastic resin described below is improved.
The MFR is determined according to ISO R1133 at a measurement temperature of 230° C. and a measurement load of 2.16 kg.

<Cyclic polyolefin (a)>
As the cyclic polyolefin resin copolymer used in the present resin composition, from the viewpoint of low dielectric properties, a cyclic polyolefin containing at least one type of hydrogenated aromatic vinyl polymer block unit and at least one type of hydrogenated conjugated diene polymer block unit (hereinafter also referred to as "cyclic polyolefin (a)"), or a modified product of the cyclic polyolefin (a) with at least one of an unsaturated carboxylic acid and an anhydride thereof is preferred.

For purposes of this invention, "block" refers to a polymeric segment of a copolymer that exhibits microphase separation from structurally or compositionally distinct polymeric segments of the copolymer. Microphase separation occurs due to the immiscibility of the polymeric segments in the block copolymer.
Microphase separation and block copolymers are extensively discussed in "Block Copolymers-Designer Soft Materials" on pages 32-38 of the February 1999 issue of PHYSICS TODAY.

Examples of the cyclic polyolefin (a) include a diblock copolymer consisting of a hydrogenated aromatic vinyl polymer block unit (hereinafter also referred to as "block A") and a hydrogenated conjugated diene polymer block unit (hereinafter also referred to as "block B"), a triblock copolymer containing two or more of at least one of block A and block B, a tetrablock copolymer, and a pentablock copolymer.
The cyclic polyolefin (a) preferably contains at least two blocks A, and suitable examples thereof include ABA type, ABAB type, and ABABA type.

The cyclic polyolefin (a) preferably contains a segment made of an aromatic vinyl polymer at each end. For this reason, the hydrogenated block copolymer of the resin composition preferably has at least two hydrogenated aromatic vinyl polymer block units (block A), and at least one hydrogenated conjugated diene polymer block unit (block B) between the two hydrogenated aromatic vinyl polymer block units (block A). From these viewpoints, the cyclic polyolefin (a) is more preferably an A-B-A type or an A-B-A-B-A type.

The content of the hydrogenated aromatic vinyl polymer block unit (block A) in the cyclic polyolefin (a) is preferably 30 to 99 mol %, more preferably 40 to 90 mol %, still more preferably 50 mol % or more, and even more preferably 60 mol % or more.
When the ratio of the hydrogenated aromatic vinyl polymer block unit (block A) is equal to or higher than the lower limit, the rigidity is not decreased and the heat resistance and the linear thermal expansion coefficient are also good. On the other hand, when the ratio is equal to or lower than the upper limit, the flexibility is good.

The content of the hydrogenated conjugated diene polymer block unit (block B) in the cyclic polyolefin (a) is preferably 1 to 70 mol %, more preferably 10 to 60 mol %, still more preferably 50 mol % or less, and even more preferably 40 mol % or less.
When the ratio of the hydrogenated conjugated diene polymer block unit (block B) is equal to or higher than the lower limit, the flexibility is good. On the other hand, when the ratio is equal to or lower than the upper limit, the rigidity is not decreased and the heat resistance and the linear thermal expansion coefficient are also good.

The hydrogenated aromatic vinyl polymer block unit and the hydrogenated conjugated diene polymer block unit constituting the cyclic polyolefin (a) can be obtained by hydrogenating a polymer block composed of an aromatic vinyl monomer and a conjugated diene monomer such as 1,3-butadiene, which will be described later in detail.
Also, the cyclic polyolefin (a) is preferably a block copolymer having no functional groups. The term "no functional groups" means that the block copolymer does not have any functional groups, i.e., does not have any groups containing atoms other than carbon and hydrogen atoms.

The monomers for forming the aromatic vinyl polymer block units and the conjugated diene polymer block units before hydrogenation are described below.

(Aromatic vinyl monomer)
The aromatic vinyl monomer serving as a raw material for the aromatic vinyl polymer block unit before hydrogenation is a monomer represented by the following general formula (1).

In the above general formula (1), R is hydrogen or an alkyl group, and Ar is a phenyl group, a halophenyl group, an alkylphenyl group, an alkylhalophenyl group, a naphthyl group, a pyridinyl group, or an anthracenyl group.

When R is an alkyl group, it preferably has 1 to 6 carbon atoms, and the alkyl group may be mono- or polysubstituted with functional groups such as halo, nitro, amino, hydroxy, cyano, carbonyl, and carboxyl groups.
Moreover, the above Ar is preferably a phenyl group or an alkylphenyl group, and more preferably a phenyl group.

Examples of aromatic vinyl monomers include styrene, α-methylstyrene, vinyltoluene (including all isomers, with p-vinyltoluene being particularly preferred), ethylstyrene, propylstyrene, butylstyrene, vinylbiphenyl, vinylnaphthalene, vinylanthracene (including all isomers), and mixtures thereof. Of these, styrene is preferred.

(Conjugated Diene Monomer)
The conjugated diene monomer serving as the raw material of the conjugated diene polymer block unit before hydrogenation is not particularly limited as long as it is a monomer having two conjugated double bonds.
Examples of conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2-methyl-1,3-pentadiene and similar compounds, and mixtures thereof. Of these, 1,3-butadiene is preferred.

When 1,3-butadiene is used as the conjugated diene monomer, its polymer, polybutadiene, contains 1,4-bond units ([-CH ₂ -CH=CH-CH ₂ -]) and 1,2-bond units ([-CH ₂ -CH(CH=CH ₂ )-]), and upon hydrogenation, the former gives a structure similar to the repeating units of polyethylene (ethylene structure), and the latter gives a structure similar to the repeating units obtained when 1-butene is polymerized (1-butene structure). Therefore, the hydrogenated conjugated diene polymer block in the present resin composition preferably contains at least one of an ethylene structure and a 1-butene structure.
Furthermore, when isoprene is used as the conjugated diene monomer, its polymer, polyisoprene, contains 1,4-bond units ([-CH ₂ -C(CH ₃ )=CH-CH ₂ -]), 3,4-bond units ([-CH ₂ -CH(C(CH ₃ )=CH ₂ )-]) and 1,2-bond units ([-CH ₂ -C(CH ₃ )(CH=CH ₂ )-]), and contains at least one of the three types of repeating units obtained by hydrogenation.

(Block structure)
The cyclic polyolefin (a) is preferably produced by hydrogenation of a multiblock copolymer such as a triblock copolymer, a tetrablock copolymer, a pentablock copolymer, etc., such as SBS, SBSB, SBSBS, SBSBSB, SIS, SISIS, and SISBS (where S is polystyrene, B is polybutadiene, and I is polyisoprene). The block may be a linear block or may be branched. When branched, the polymerization chain may be bonded at any position along the backbone of the copolymer. In addition to a linear block, the block may be a tapered block or a star block.

The block copolymer constituting the cyclic polyolefin (a) before hydrogenation may contain one or more additional block units other than the aromatic vinyl polymer block units and the conjugated diene polymer block units. For example, in the case of a triblock copolymer, these additional block units may be bonded to any position of the triblock polymer backbone.

A preferred example of the hydrogenated aromatic vinyl polymer block unit is hydrogenated polystyrene, and a preferred example of the hydrogenated conjugated diene polymer block unit is hydrogenated polybutadiene or hydrogenated polyisoprene, with hydrogenated polybutadiene being more preferred.
A preferred embodiment of the cyclic polyolefin (a) is a hydrogenated triblock or pentablock copolymer of styrene and butadiene, with a hydrogenated triblock copolymer being more preferred.

(Hydrogenation Level)
The cyclic polyolefin (a) is a polyolefin in which the aromatic rings derived from styrene and the like are hydrogenated in addition to the double bonds derived from conjugated dienes such as butadiene, and is substantially completely hydrogenated. Specifically, it refers to a polyolefin having the following hydrogenation levels:
The hydrogenation level of the hydrogenated aromatic vinyl polymer block unit is preferably 90% or more, more preferably 95% or more, further preferably 98% or more, and particularly preferably 99.5% or more.
The hydrogenation level of the hydrogenated conjugated diene polymer block unit is preferably 95% or more, more preferably 99% or more, and even more preferably 99.5% or more.
Such a high level of hydrogenation reduces dielectric loss and also provides good stiffness and heat resistance.
The hydrogenation level of the hydrogenated aromatic vinyl polymer block unit refers to the proportion of the aromatic vinyl polymer block unit saturated by hydrogenation, and the hydrogenation level of the hydrogenated conjugated diene polymer block unit refers to the proportion of the conjugated diene polymer block unit saturated by hydrogenation.
The hydrogenation level of each block unit is determined by proton NMR.

The cyclic polyolefin (a) may be used alone or in combination of two or more kinds.
As the cyclic polyolefin (a) in the present resin composition, commercially available products can be used, specifically, TEFABLOC (registered trademark) manufactured by Mitsubishi Chemical Corporation can be mentioned.

Among the above thermoplastic resins (A), from the viewpoints of low dielectric properties and ease of processing, styrene-based thermoplastic elastomers are preferred, and styrene-ethylene-butadiene-styrene block copolymers (SEBS) are more preferred.
In addition, among the thermoplastic resins (A) exemplified above, when a combination in which the thermoplastic resin (A) itself is difficult to react with the radical polymerizable compound (B) is selected, the thermoplastic resin (A) and the radical polymerizable compound (B) form an interpenetrating polymer network structure (hereinafter also referred to as a "semi-IPN structure"), which is considered to improve low dielectric properties and heat resistance. The semi-IPN structure is a structure in which the molecular chains of the thermoplastic resin (A) and the radical polymerizable compound (B) are partially and physically entangled with each other, rather than the thermoplastic resin (A) and the radical polymerizable compound (B) forming a chemical bond. By forming this semi-IPN structure, the crosslink density is pseudo-higher than that of the thermoplastic resin (A) alone, while maintaining the low dielectric properties of the thermoplastic resin (A). Therefore, it is considered that the elastic modulus is improved and the heat resistance is improved.
From this viewpoint, among the above thermoplastic resins (A), styrene-based thermoplastic elastomers are preferred, styrene-isobutylene-styrene block copolymers (SIBS) or styrene-ethylene-butadiene-styrene block copolymers (SEBS) are more preferred, and styrene-ethylene-butadiene-styrene block copolymers (SEBS) are even more preferred.

When a styrene-based thermoplastic elastomer is used as the thermoplastic resin (A), the styrene content in the styrene-based thermoplastic elastomer is preferably 10% by mass or more, more preferably 15% by mass or more. The upper limit of the styrene content is preferably 70% by mass or less, more preferably 65% by mass or less, even more preferably 60% by mass or less, even more preferably 50% by mass or less, and particularly preferably 40% by mass or less.
When the styrene content is within the above range, the thermoplastic resin (A) has a low dielectric tangent and an appropriate elastic modulus, so that low dielectric properties and heat resistance can be achieved at the same time, and handling properties are also good.

From the viewpoint of improving heat resistance and dimensional stability while maintaining low dielectric properties, it is preferable that the thermoplastic resin (A) contains at least one selected from the group consisting of a styrene-based thermoplastic elastomer, an olefin-based thermoplastic elastomer, and an ethylene-based polymer (hereinafter also referred to as (A1)), and a cyclic polyolefin resin copolymer (hereinafter also referred to as (A2)).
The reason why the heat resistance of the cured product of the resin composition is good is not clear, but it is thought that when a resin composition containing, as the thermoplastic resin (A), at least one thermoplastic resin (A1) selected from the group consisting of a styrene-based thermoplastic elastomer, an olefin-based thermoplastic elastomer, and an ethylene-based polymer, and a cyclic polyolefin resin copolymer (A2), is cured, the crosslinking density is artificially increased by the radical polymerizable compound (B) entangled with the (A1) and the cyclic polyolefin resin copolymer (A2), thereby improving the elastic modulus.
In addition, the reason why the dimensional stability of the cured product of the resin composition is improved is unclear, but the more alicyclic structures contained in the cured product, the lower the linear thermal expansion coefficient and the more the dimensional stability tends to be improved. Therefore, it is considered that the inclusion of the cyclic polyolefin resin copolymer (A2) as the thermoplastic resin (A) relatively increases the alicyclic structure compared to the case of using the thermoplastic resin (A1) alone.
Among the above-mentioned (A1), from the viewpoints of low dielectric properties and processability, styrene-based thermoplastic elastomers are preferred, and styrene-ethylene-butadiene-styrene block copolymers (SEBS) are more preferred.

The mass average molecular weight (Mw) of the thermoplastic resin (A) is preferably 30,000 or more, more preferably 40,000 or more, and even more preferably 50,000 or more from the viewpoint of preventing tackiness from occurring in the resulting resin sheet, while being preferably 300,000 or less, more preferably 250,000 or less, and even more preferably 200,000 or less from the viewpoint of handling properties during film formation.
In the present invention, the weight average molecular weight (Mw) is a value calculated as polystyrene by measuring by gel permeation chromatography.

The thermoplastic resin (A) may be modified by a known method. Examples of the modified product include a reaction product of the above-mentioned thermoplastic resin (A) with at least one of an unsaturated carboxylic acid and an acid anhydride.
By modifying the thermoplastic resin (A), the polarity of the polymer increases, and this is expected to improve adhesion to conductors such as copper foil.

Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, α-ethylacrylic acid, maleic acid, fumaric acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, itaconic acid, citraconic acid, crotonic acid, isocrotonic acid, and nadic acids. Of these, acrylic acid, maleic acid, and nadic acid are preferred.
Examples of the acid anhydride include the anhydrides of the above unsaturated carboxylic acids as well as maleic anhydride, citraconic anhydride, and nadic anhydrides, with maleic anhydride and nadic anhydride being preferred.
Examples of nadic acids include endo-cis-bicyclo[2.2.1]hept-2,3-dicarboxylic acid (nadic acid) and methyl-endo-cis-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid (methylnadic acid).
These may be used alone or in combination of two or more.

The content of the thermoplastic resin (A) in the resin composition is 20% by mass or more based on the total mass of the resin composition. By having the content of the thermoplastic resin (A) of 20% by mass or more, it is possible to obtain a cured product having excellent low dielectric properties and excellent handleability. From this viewpoint, the content is preferably 25% by mass or more, more preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and even more preferably 60% by mass or more. The upper limit of the content is not particularly limited, but from the viewpoint of improving dimensional stability, it is preferably 99% by mass or less, more preferably 97% by mass or less, even more preferably 95% by mass or less, even more preferably 90% by mass or less, even more preferably 80% by mass or less, particularly preferably 75% by mass or less, and most preferably 70% by mass or less.
In this specification, the total mass of the resin composition means the sum of the components constituting the resin composition excluding the solvent (G) described below.

When the thermoplastic resin (A) contains the thermoplastic resin (A1) and the cyclic polyolefin resin copolymer (A2), the mass ratio of the thermoplastic resin (A1) to the cyclic polyolefin resin copolymer (A2) is preferably (A2)/(A1) = 10/90 to 90/10, more preferably 15/85 to 80/20, and even more preferably 20/80 to 70/30. When the mass ratio is within the above range, the balance of the moldability, dielectric properties, and linear thermal expansion coefficient of the sheet cured product is good.

The storage modulus of the thermoplastic resin (A) at 25° C. is preferably 0.1 MPa or more, more preferably 1 MPa or more, even more preferably 5 MPa or more, and particularly preferably 10 MPa or more. The storage modulus is preferably 5000 MPa or less, more preferably 4000 MPa or less, more preferably 3000 MPa or less, even more preferably 2500 MPa or less, and even more preferably 2000 MPa or less, 1000 MPa or less, even more preferably less than 500 MPa, even more preferably less than 300 MPa, even more preferably less than 100 MPa, and even more preferably less than 50 MPa.
By setting the storage modulus below the upper limit, the present resin composition has good flexibility when cured, whereas by setting the storage modulus to equal to or greater than the lower limit, the present resin composition has good heat resistance and handleability when cured.

The storage modulus can be determined by forming the thermoplastic resin (A) into a sheet having a thickness of 300 μm to prepare a test piece, and measuring the dynamic viscoelasticity with a viscoelasticity spectrometer.

The density of the thermoplastic resin (A) is preferably 0.98 g/cm ³ or less, more preferably 0.95 g/cm ³ or less, and even more preferably 0.91 g/cm ³ or less. On the other hand, the lower limit of the density is not particularly limited, but is preferably 0.80 g/cm ³ or more.
When the density is equal to or less than the above value, the present resin composition has good flexibility when cured.

The density can be measured in accordance with ASTM D792 by forming the thermoplastic resin (A) into a sheet having a thickness of 300 μm into a test piece.

The dielectric loss tangent of the thermoplastic resin (A) is preferably less than 0.005 at 10 GHz, more preferably less than 0.003, even more preferably less than 0.002, and particularly preferably less than 0.001. On the other hand, the lower limit is not particularly limited as long as it is 0 or more.
The smaller the dielectric tangent, the smaller the dielectric loss, and therefore when the resin composition is used as a circuit board material, the transmission efficiency and speed of electric signals can be increased.

The dielectric tangent can be determined by forming the thermoplastic resin (A) into a sheet having a thickness of 300 μm into a test piece, and measuring it at a temperature of 23°C and a frequency of 10 GHz in accordance with JIS C2565:1992.

2. Radically polymerizable compound (B)
The radically polymerizable compound (B) in the present resin composition is a compound having two or more carbon-carbon double bonds in the molecule, and these may be used alone or in combination of two or more kinds.
The mass average molecular weight (Mw) of the radical polymerizable compound (B) is preferably 100 or more, and more preferably 120 or more. The mass average molecular weight (Mw) is preferably 4,000 or less, more preferably 3,000 or less, even more preferably 2,000 or less, even more preferably 1,000 or less, still more preferably 800 or less, and particularly preferably 600 or less.
When the mass average molecular weight (Mw) of the radical polymerizable compound (B) is within the above range, foaming due to decomposition of the radical polymerizable compound (B) during curing is suppressed, and the molecular chains of the hydrocarbon-based polymer compound (A), the radical polymerizable compound (B), and the epoxy compound (C) are easily entangled with each other, making it easy to artificially increase the crosslinking density, and therefore the heat resistance and dimensional stability of the obtained sheet cured product are improved.
In addition, when the crosslinking agent is not partially crosslinked or polymerized, the "mass average molecular weight (Mw) of the radically polymerizable compound (B)" means the molecular weight of the compound used as the radically polymerizable compound (B).

Examples of functional groups having a carbon-carbon double bond include vinyl groups, acryloyl groups, and methacryloyl groups. Among these, vinyl groups are preferred from the viewpoints of providing good compatibility with the thermoplastic resin (A) and reducing the dielectric tangent of the resulting cured sheet.

Examples of the bifunctional radically polymerizable compound (B) include bifunctional aromatic vinyl compounds such as divinylbenzene, divinylnaphthalene, and divinylbiphenyl; ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetrapropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, ethoxylated polypropylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, and neopentyl glycol. difunctional aliphatic (meth)acrylate compounds such as di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 2-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, glycerin di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, and ethoxylated 2-methyl-1,3-propanediol di(meth)acrylate; cyclohexane dimethanol di(meth)acrylate, ethoxylated cyclohexane dimethanol di(meth)acrylate, propoxylated cyclohexane dimethanol di(meth)acrylate, ethoxylated propoxylated cyclohexane dimethanol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, bifunctional alicyclic (meth)acrylate compounds such as bisphenol A di(meth)acrylate, ethoxylated tricyclodecane dimethanol di(meth)acrylate, propoxylated tricyclodecane dimethanol di(meth)acrylate, ethoxylated propoxylated tricyclodecane dimethanol di(meth)acrylate, ethoxylated hydrogenated bisphenol A di(meth)acrylate, propoxylated hydrogenated bisphenol A di(meth)acrylate, ethoxylated propoxylated hydrogenated bisphenol A di(meth)acrylate, ethoxylated hydrogenated bisphenol F di(meth)acrylate, propoxylated hydrogenated bisphenol F di(meth)acrylate, and ethoxylated propoxylated hydrogenated bisphenol F di(meth)acrylate; Bifunctional aromatic (meth)acrylate compounds such as ethoxylated bisphenol F di(meth)acrylate, propoxylated bisphenol F di(meth)acrylate, ethoxylated propoxylated bisphenol F di(meth)acrylate, ethoxylated bisphenol AF di(meth)acrylate, propoxylated bisphenol AF di(meth)acrylate, ethoxylated propoxylated bisphenol AF di(meth)acrylate, ethoxylated fluorene type di(meth)acrylate, propoxylated fluorene type di(meth)acrylate, and ethoxylated propoxylated fluorene type di(meth)acrylate; and bifunctional heterocyclic (meth)acrylate compounds such as ethoxylated isocyanuric acid di(meth)acrylate, propoxylated isocyanuric acid di(meth)acrylate, and ethoxylated propoxylated isocyanuric acid di(meth)acrylate.

Examples of trifunctional or higher radical polymerizable compounds (B) include triallyl cyanurate and triallyl isocyanurate compounds such as triallyl cyanurate and triallyl isocyanurate; trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, ethoxylated propoxylated trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, ethoxylated pentaerythritol tri(meth)acrylate, propoxylated pentaerythritol tri(meth)acrylate, and ethoxylated propoxylated pentaerythritol tri(meth)acrylate. , polyfunctional aliphatic (meth)acrylate compounds such as pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, propoxylated pentaerythritol tetra(meth)acrylate, ethoxylated propoxylated pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetraacrylate, and dipentaerythritol hexa(meth)acrylate; and polyfunctional heterocyclic (meth)acrylate compounds such as ethoxylated isocyanuric acid tri(meth)acrylate, propoxylated isocyanuric acid tri(meth)acrylate, and ethoxylated propoxylated isocyanuric acid tri(meth)acrylate.

Among the above, from the viewpoint of compatibility with the thermoplastic resin (A), bifunctional aromatic vinyl compounds and trialkenyl isocyanurate compounds are preferred, and from the viewpoint of low dielectric properties, divinylbenzene or trialkenyl isocyanurate compounds are more preferred.

The radical polymerizable compound (B) preferably has no polar functional group or has a small number of polar functional groups in the molecule. When the radical polymerizable compound (B) has a cyclic structure, it preferably has no polar functional group or has a small number of polar functional groups in the substituent.
When the amount of polar functional groups is small, the compatibility with the thermoplastic resin (A) becomes good, and the dielectric loss tangent of the obtained sheet cured product also becomes low.
The polar functional group means a functional group having a negative atom (e.g., nitrogen, oxygen, chlorine, fluorine, etc.) and having a net dipole. Examples of the functional group include an ester group, a carbonyl group, a carboxyl group, a hydroxyl group, an amide group, and an amino group.
When the radical polymerizable compound (B) has an ester group, the polar functional group equivalent of the radical polymerizable compound (B) (molecular weight of the radical polymerizable compound (B)/molecular weight of the polar functional group (total amount of the polar functional groups when there are a plurality of polar functional groups)) is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, still more preferably 5 or more, and even more preferably 6 or more.

The content of the radical polymerizable compound (B) in the present resin composition is preferably 1 part by mass or more and 50 parts by mass or less, more preferably 3 parts by mass or more and 30 parts by mass or less, even more preferably 5 parts by mass or more and 25 parts by mass or less, and even more preferably 10 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the thermoplastic resin (A).
When the content of the radical polymerizable compound (B) is within the above range, the compatibility with the thermoplastic resin (A) is good and it becomes easier to increase the crosslinking density in a pseudo manner, so that the heat resistance of the obtained cured product is good.

3. Epoxy compound (C)
The epoxy compound (C) in the resin composition is a compound having at least one epoxy group in one molecule. By including the epoxy compound (C), it is possible to obtain a resin composition having excellent dimensional stability.
The epoxy compound (C) may be in a solid or liquid form, and one or more kinds may be used in combination.

Although thermoplastic resins such as styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, and ethylene-based polymers are suitable as materials having low dielectric properties, when these materials are used as circuit board materials, there is a problem that the dimensional stability is insufficient for laminating with a conductor such as copper foil, etc. Therefore, there has been a demand for a material that combines low dielectric properties and dimensional stability at a higher level.
Under these circumstances, the present inventors conducted extensive research and found that the use of a predetermined amount of an epoxy compound (C) and a curing agent (D) described below improves dimensional stability while maintaining low dielectric properties, thereby completing the present invention.

The reason why the dimensional stability is improved by using the epoxy compound (C) is not clear, but it is thought that the cured product obtained by reacting the epoxy compound (C) with the curing agent (D) described later becomes a domain in the resin composition, forming a sea-island structure, thereby suppressing the linear expansion coefficient.
In addition, by including the epoxy compound (C), the thermoplastic resin (A) and the epoxy compound (C) form an interpenetrating polymer network structure (hereinafter also referred to as "semi-IPN structure"), which is thought to contribute to a reduction in the linear expansion coefficient. The semi-IPN structure is a structure in which the molecular chains of the thermoplastic resin (A) and the epoxy compound (C) are partially and physically entangled with each other, rather than the thermoplastic resin (A) and the epoxy compound (C) forming a chemical bond. By forming a semi-IPN structure with the thermoplastic resin (A), the crosslink density becomes relatively higher than when crosslinking is performed only with the radical polymerizable compound (B). Therefore, it is thought that the linear expansion coefficient is lowered and the dimensional stability is improved.

Examples of the epoxy compound (C) include monofunctional aliphatic epoxy compounds such as ethyl glycidyl ether, propyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, 1,2-epoxytetradecane, and lauryl glycidyl ether; monofunctional fluorine-containing epoxy compounds such as 2-(trifluoromethyl)oxirane and 2,2,3,3,4,4,5,5,5-nonafluoropentyloxirane; bifunctional fluorine-containing epoxy compounds such as 2,2'-(2,2,3,3,4,4,5,5-octafluorohexane-1,6-diyl)bis(oxirane); o-phenylphenol glycidyl ether, phenyl glycidyl ether, and 2-biphenylyl glycidyl ether. monofunctional aromatic epoxy compounds such as 4-t-butylphenyl glycidyl ether; aromatic epoxy compounds such as bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, bisphenol C type epoxy compounds, bisphenol AF type epoxy compounds, naphthalene type epoxy compounds, biphenyl type epoxy compounds, resorcinol type epoxy compounds, phenol novolac type epoxy compounds, and cresol novolac type epoxy compounds; ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, glycidyl ether, tripropylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, butanediol diglycidyl ether, polytetramethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, trimethylolpropane triglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, cyclohexane diglycidyl ether, dicyclopentadiene diglycidyl ether Examples include aliphatic epoxy compounds such as glycidyl ether, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, hexahydrophthalic acid diglycidyl ester, vinyl(3,4-cyclohexene) dioxide, 2-(3,4-epoxycyclohexyl)-5,1-spiro-(3,4-epoxycyclohexyl)-m-dioxane, and epoxidized polybutadiene, as well as polyfunctional epoxy compounds such as triglycidyl isocyanurate, heterocyclic epoxy compounds such as hydantoin-type epoxy compounds, halogenated epoxy compounds, glycidylamine-type epoxy compounds, epoxy group-containing rubber compounds, epoxy group-containing polyurethane compounds, and epoxy group-containing acrylic compounds.

Among these, from the viewpoint of enhancing dimensional stability, polyfunctional epoxy compounds are preferred, and among these, epoxy compounds containing two or more epoxy groups in one molecule are more preferred.
From the viewpoints of compatibility with the present resin composition and obtaining an appropriate hardness, epoxy compounds having a cyclic structure are preferred, and among these, aromatic epoxy compounds are preferred, and among these, bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AF type epoxy resins, biphenyl type epoxy resins, naphthalene type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, dicyclopentadiene type epoxy resins, trisphenol type epoxy resins, naphthol type epoxy resins, naphthylene ether type epoxy resins, anthracene type epoxy resins, tetraphenylethane type epoxy resins, and bixylenol type epoxy resins are particularly preferred.
From the viewpoint of improving low dielectric properties, epoxy compounds containing fluorine atoms are preferred, and fluorine-containing epoxy resins are more preferred. Among these, bisphenol AF type epoxy compounds are particularly preferred from the viewpoint of improving dimensional stability.

From the viewpoint of compatibility with the thermoplastic resin (A), the epoxy equivalent of the epoxy compound (C) is preferably 1000 g/eq or less, more preferably 700 g/eq or less, and even more preferably 500 g/eq or less. The lower limit is preferably 10 g/eq or more, and more preferably 50 g/eq or more, from the viewpoint of increasing the crosslink density of the cured product and suppressing the volatilization of the epoxy compound (C).

The content of the epoxy compound (C) is preferably 4 to 70 parts by mass, more preferably 4 to 50 parts by mass, and even more preferably 5 to 30 parts by mass, per 100 parts by mass of the thermoplastic resin (A). When the content of the epoxy compound (C) is within the above range, it is possible to reduce the linear thermal expansion coefficient while maintaining low dielectric properties.

The sum of the contents of the radical polymerizable compound (B) and the epoxy compound (C) is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, based on the total mass of the resin composition. By setting the sum of the contents of the radical polymerizable compound (B) and the epoxy compound (C) within the above range, a cured product having a low linear thermal expansion coefficient can be obtained. From the viewpoint of ensuring handleability, the upper limit of the content is preferably 98% by mass or less, more preferably 97% by mass or less, and even more preferably 96% by mass or less.

4. Curing agent (D)
The curing agent (D) refers to a substance that contributes to a crosslinking reaction and/or a chain extension reaction between epoxy groups of the epoxy compound (C).
Examples of the curing agent (D) used in the present resin composition include phenol-based curing agents, acid anhydride-based curing agents, active ester-based curing agents, amide-based curing agents, cationic curing agent compounds, etc. These may be used alone or in combination of two or more kinds.

Examples of the phenol-based curing agent include bisphenols such as bisphenol A, bisphenol F, bisphenol S, bisphenol B, bisphenol AD, bisphenol Z, tetrabromobisphenol A, biphenols such as 4,4'-biphenol and 3,3',5,5'-tetramethyl-4,4'-biphenol, catechol, resorcin, hydroquinone, dihydroxynaphthalenes, and compounds in which the hydrogen atoms bonded to the aromatic rings of these compounds are replaced with non-interfering substituents such as halogen groups, alkyl groups, aryl groups, ether groups, ester groups, and organic substituents containing hetero elements such as sulfur, phosphorus, and silicon, as well as novolaks and resols which are polycondensates of the above-mentioned phenols, monofunctional phenols such as phenol, cresol, and alkylphenols, and aldehydes.

Examples of the acid anhydride curing agent include methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylhimic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride, methylcyclohexene dicarboxylic anhydride, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, ethylene glycol bistrimellitate, glycerol tristrimellitate, dodecenyl succinic anhydride, polyazelaic anhydride, poly(ethyloctadecanedioic) anhydride, and the like.

The active ester curing agent is not particularly limited, but generally, a compound having two or more highly reactive ester groups in one molecule, such as phenol esters, thiophenol esters, N-hydroxyamine esters, polyarylates, and esters of heterocyclic hydroxy compounds, is preferred.
The above-mentioned active ester curing agent is preferably one obtained by a condensation reaction between a carboxylic acid compound and/or a thiocarboxylic acid compound and a hydroxy compound and/or a thiol compound. In particular, from the viewpoint of improving heat resistance, an active ester resin obtained from a carboxylic acid compound or its halide and a hydroxy compound is preferred, and an active ester resin obtained from a carboxylic acid compound or its halide and a phenol compound and/or a naphthol compound is more preferred.

Examples of the amide-based curing agent include dicyandiamide and its derivatives, polyamide resins, etc.

The cationic polymerization curing agent generates cations by heat or active energy ray irradiation, and examples thereof include aromatic onium salts, etc. Specific examples thereof include compounds consisting of an anion component such as SbF ₆ ^- , BF ₄ ^- , AsF ₆ ^- , PF ₆ ^- , CF ₃ SO ₃ , B(C ₆ F ₅ ) ₄ ^- and an aromatic cation component containing an atom such as iodine, sulfur, nitrogen, or phosphorus.

From the viewpoint of improving various properties such as heat resistance and adhesion, it is preferable that the curing agent (D) contains at least one curing agent selected from the group consisting of a phenol-based curing agent, an amine-based curing agent, an acid anhydride-based curing agent, and an active ester-based curing agent.
Among the above, acid anhydride-based curing agents and active ester-based curing agents are preferred from the viewpoints that no hydroxyl group is generated in the reaction product with the epoxy compound (C) and the low dielectric properties of the cured product are easily maintained.
In addition, when the resin composition contains the acid anhydride-based curing agent or the active ester-based curing agent, it is preferable to further contain a curing aid (F) described later together with the curing agent. By using the curing aid (F) in combination, the reaction of the epoxy compound (C) proceeds efficiently.

The sum of the contents of the epoxy compound (C) and the curing agent (D) is 4% by mass or more and 80% by mass or less based on the total mass of the resin composition. By having the sum of the contents of the epoxy compound (C) and the curing agent (D) in the above range, excellent adhesion can be obtained.
From the above viewpoints, the sum of the contents of the epoxy compound (C) and the curing agent (D) is preferably 4 to 70 mass%, more preferably 4.5 to 50 mass%, and further preferably 5 to 30 mass%, relative to the total mass of the resin composition.

The content of the curing agent (D) is preferably 30 to 500 parts by mass, more preferably 40 to 300 parts by mass, and even more preferably 50 to 200 parts by mass, per 100 parts by mass of the epoxy compound (C).

5. Organic peroxide (E)
The present resin composition may contain an organic peroxide (E) for the purpose of accelerating the curing reaction.
Examples of the organic peroxide include those belonging to the group of hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxy esters, and ketone peroxides.
Specifically, hydroperoxides such as cumene hydroperoxide and tert-butyl hydroperoxide; dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butyl peroxide), dialkyl peroxides such as 2,5-bis(tert-butylperoxy)-hexane and 2,5-dimethyl-3-hexyne; diacyl peroxides such as lauryl peroxide and benzoyl peroxide; tert-butylperoxy Examples of the peroxyester include acetate, tert-butyl peroxybenzoate, and tert-butyl peroxyisopropyl carbonate; and ketone peroxides such as cyclohexanone peroxide.

The content of the organic peroxide (E) in the present resin composition is preferably 0.01 parts by mass or more and 5 parts by mass or less, more preferably 0.05 parts by mass or more and 3 parts by mass or less, and even more preferably 0.1 parts by mass or more and 1 part by mass or less, per 100 parts by mass of the thermoplastic resin (A).
When the content of the organic peroxide (E) is within the above range, the curing reaction can be promoted while the dielectric properties of the cured product can be maintained at a low level.

6. Curing aid (F)
In addition to the above-mentioned components, the resin composition may further contain a curing aid (F) as an optional component.
Examples of the curing assistant include organic phosphine curing assistants, phosphonium salt curing assistants, tetraphenyl boron salt curing assistants, metal curing assistants, imidazole curing assistants, amine curing assistants, organic acid dihydrazide curing assistants, boron halide amine complex curing assistants, etc. These curing assistants may be used alone or in any combination and ratio of two or more.

Organic phosphine curing assistants, phosphonium salt curing assistants, tetraphenylboron salt curing assistants Among the organic phosphine curing assistants, phosphonium salt curing assistants, and tetraphenylboron salt curing assistants, compounds that can be used as curing assistants for the epoxy resin composition of the present invention include triphenylphosphine, diphenyl(p-tolyl)phosphine, tris(alkylphenyl)phosphine, tris(alkoxyphenyl)phosphine, tris(alkyl-alkoxyphenyl)phosphine, tris(dialkylphenyl)phosphine, tris(trialkylphenyl)phosphine, tris(tetraalkylphenyl)phosphine, tris(dialkoxyphenyl)phosphine, tris(trialkoxyphenyl)phosphine, tris Examples include organic phosphines such as (tetraalkoxyphenyl)phosphine, trialkylphosphine, dialkylarylphosphine, and alkyldiarylphosphine, or complexes of these organic phosphines with organic borons, and compounds obtained by adding these organic phosphines to quinone compounds such as maleic anhydride, 1,4-benzoquinone, 2,5-toluquinone, 1,4-naphthoquinone, 2,3-dimethylbenzoquinone, 2,6-dimethylbenzoquinone, 2,3-dimethoxy-5-methyl-1,4-benzoquinone, 2,3-dimethoxy-1,4-benzoquinone, and phenyl 1,4-benzoquinone, and compounds such as diazophenylmethane.

Metal-based curing aids are not particularly limited, and include organometallic complexes or organometallic salts of metals such as cobalt, copper, zinc, iron, nickel, manganese, and tin. Specific examples of organometallic complexes include organocobalt complexes such as cobalt(II) acetylacetonate and cobalt(III) acetylacetonate, organocopper complexes such as copper(II) acetylacetonate, organozinc complexes such as zinc(II) acetylacetonate, organoiron complexes such as iron(III) acetylacetonate, organonickel complexes such as nickel(II) acetylacetonate, and organomanganese complexes such as manganese(II) acetylacetonate.

Examples of the organic metal salt include zinc octoate, tin octoate, zinc naphthenate, cobalt naphthenate, tin stearate, and zinc stearate.
As the metal-based curing aid, from the viewpoints of curability and solvent solubility, cobalt(II) acetylacetonate, cobalt(III) acetylacetonate, zinc(II) acetylacetonate, zinc naphthenate, and iron(III) acetylacetonate are preferred, with cobalt(III) acetylacetonate and zinc naphthenate being particularly preferred.

Examples of imidazole-based curing aids include 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[ Examples of imidazole compounds include 2'-methylimidazolyl-(1')-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 2-methylimidazoline, and 2-phenylimidazoline, as well as adducts of imidazole compounds and epoxy resins.

Examples of amine-based curing aids include trialkylamines such as triethylamine and tributylamine; and amine compounds such as 4-dimethylaminopyridine, benzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, and 1,8-diazabicyclo(5,4,0)-undecene (hereinafter abbreviated as DBU).

From the viewpoint of the progress of the curing reaction, the content of the curing aid (F) in the resin composition is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.05% by mass or more, relative to 100 parts by mass of the epoxy compound (C), and is preferably 0.3% by mass or less, more preferably 0.2% by mass or less, and even more preferably 0.1% by mass or less.

7. Solvent (G)
The present resin composition may contain a solvent (G) if necessary for viscosity adjustment or the like.
The solvent (G) is not particularly limited as long as the components of the resin composition are uniformly dissolved. Examples of the solvent (G) include toluene, cyclohexane, tetrahydrofuran, xylene, and methyl ethyl ketone. The above-mentioned solvents may be used alone or in any combination and ratio of two or more. The boiling point of the solvent (G) is preferably 200° C. or less in order to reduce the amount of residual solvent.

From the viewpoint of film-forming properties, the content of the solvent (G) in the resin composition is preferably 100 parts by mass or more and 500 parts by mass or less, and more preferably 200 parts by mass or more and 400 parts by mass or less, per 100 parts by mass of the thermoplastic resin (A).

8. Other Components The present resin composition may contain, as components other than those described above, a thermoplastic elastomer other than the thermoplastic resin (A), a crosslinking agent (excluding the radically polymerizable compound (B) and the epoxy compound (C)), a monofunctional vinyl compound, an ultraviolet absorber, an antistatic agent, an antioxidant, a coupling agent, a plasticizer, a flame retardant, a colorant, a dispersant, an emulsifier, an elasticity reducing agent, a diluent, an antifoaming agent, an ion trapping agent, a thickener, a leveling agent, inorganic particles, organic particles, and the like.

Examples of the crosslinking agent include bismaleimide compounds and isocyanate compounds.

The resin composition may further contain a monofunctional vinyl monomer having one carbon-carbon double bond in the molecule, if necessary. By containing a monofunctional vinyl compound having one vinyl group, the molecular weight between crosslinking points of the crosslinking agent can be increased, which is preferable in that the degree of freedom of movement of the molecular chain is increased, making it easier to obtain a cured product with excellent flexibility.
Examples of monofunctional vinyl compounds include monofunctional aliphatic (meth)acrylate compounds such as ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, stearyl acrylate, and isostearyl acrylate.
The monofunctional aliphatic (meth)acrylate compound preferably has an alkyl group having 8 to 25 carbon atoms. The carbon number is more preferably 10 or more, more preferably 12 or more, and even more preferably 15 or more. The carbon number is more preferably 20 or less. Specifically, at least one selected from the group consisting of isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, and isostearyl acrylate is preferred, and isostearyl acrylate is more preferred. When the carbon number of the alkyl group is within the above range, the compatibility of the thermoplastic resin (A) and the radical polymerizable compound (B) during curing is good, the molecular chains are easily entangled with each other, and the crosslinking density is easily increased in a pseudo manner, so that the heat resistance of the obtained sheet cured product is good.
When a monofunctional vinyl compound is contained, the content thereof is preferably 0.5 to 50 parts by mass, and more preferably 1 to 25 parts by mass, based on 100 parts by mass of the thermoplastic resin (A).

Examples of inorganic particles include calcium carbonate, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, zinc oxide, magnesium oxide, calcium oxide, titanium oxide, aluminum oxide, zinc oxide, alumina, aluminum hydroxide, hydroxyapatite, silica, magnesium silicate, mica, talc, kaolin, clay, glass powder, asbestos powder, zeolite, and clay silicate.
Examples of the organic particles include (meth)acrylate-based resin particles, styrene-based resin particles, silicone-based resin particles, nylon-based resin particles, polyethylene-based resin particles, benzoguanamine-based resin particles, and urethane-based resin particles.
When inorganic particles or organic particles are contained, the content thereof is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and still more preferably 15 parts by mass or more, per 100 parts by mass of the thermoplastic resin (A).
On the other hand, the upper limit is preferably less than 380 parts by mass relative to 100 parts by mass of the thermoplastic resin (A), more preferably 350 parts by mass or less, even more preferably 300 parts by mass or less, particularly preferably 250 parts by mass or less, and even more preferably 80 parts by mass or less, more preferably 75 parts by mass or less, even more preferably 70 parts by mass or less, particularly preferably 50 parts by mass or less. When the content of inorganic particles or organic particles is equal to or more than the lower limit, the dielectric properties of the sheet cured product can be further reduced, and the linear thermal expansion coefficient of the sheet cured product can be reduced, so that peeling from the substrate is less likely to occur when used as a circuit board material. On the other hand, when the content of inorganic particles or organic particles is equal to or less than the upper limit, the moldability when the resin composition is shaped into a sheet is good.
In order to enhance dispersibility, the inorganic particles may be surface-treated with a surface treatment agent as necessary.

<Physical Properties of the Resin Composition>
The present resin composition can have the following physical properties.

The coefficient of linear thermal expansion (CTE) of the present resin composition after curing is preferably 190 ppm/° C. or less, more preferably 180 ppm/° C. or less, even more preferably 170 ppm/° C. or less, and even more preferably 150 ppm/° C. or less. There is no particular lower limit to the coefficient of linear thermal expansion, but from the viewpoint of preventing peeling from or deformation of the conductor when the present resin composition is used as a circuit board material, a coefficient of linear thermal expansion of 10 ppm/° C. or more is preferred.
The linear thermal expansion coefficient can be measured by thermomechanical analysis using a test piece obtained by heat pressing the resin composition at 200°C and 2 MPa for 30 minutes and using a cured product as a test piece according to JIS K7197 (2012). Specifically, using a thermal analyzer "TMA 841" (manufactured by Mettler Toledo), the sample shape is 5 mm wide x 16 mm long, and the measurement is started from 30°C, heated to 100°C at 5°C/min, cooled to 0°C once, and then heated again to 150°C. The dimensional change during the reheating process is measured, and the average value of the thermal expansion coefficient in the in-plane direction at 0 to 120°C is calculated based on the results.

The relative dielectric constant of the resin composition after curing is preferably equal to or less than 4, more preferably equal to or less than 3, and even more preferably equal to or less than 2.5. On the other hand, there is no particular lower limit to the relative dielectric constant, and it is sufficient if it is equal to or more than 1.
The dielectric loss tangent of the resin composition after curing is preferably 0.01 or less, more preferably 0.008 or less, and even more preferably 0.006 or less. On the other hand, the lower limit of the dielectric loss tangent is not particularly limited, and it is sufficient that it is 0 or more.
The above-mentioned relative dielectric constant and dielectric tangent were determined by measuring the cured product obtained by heat pressing the resin composition at 200° C. and 2 MPa for 30 minutes as a test piece at a temperature of 23° C. and a frequency of 10 GHz in accordance with JIS C2565:1992.

<Resin sheet>
A resin sheet according to one embodiment of the present invention (hereinafter also referred to as "the present resin sheet") is obtained by forming the present resin composition in an uncured state into a sheet shape.

The thickness of the resin sheet is preferably from 10 to 500 μm, more preferably from 50 to 400 μm, and even more preferably from 100 to 350 μm.
When the thickness of the resin sheet is equal to or greater than the lower limit, the sheet has good handleability. When the thickness is equal to or less than the upper limit, the sheet has good conformability to steps in a circuit board when the sheet is used as a circuit board material.

<Laminate>
In order to improve the handling properties of the present resin sheet, it is preferable to provide a release film on one or both surfaces to form a laminate.
The release film may be, for example, a resin film mainly composed of polyolefin such as polyethylene or polypropylene, polyester such as polyethylene terephthalate or polyethylene naphthalate, polyimide, polycarbonate, etc. The peel strength may be adjusted by applying a silicone resin release agent or the like to the surface of these films.
The thickness of the release film is preferably from 1 to 300 μm, more preferably from 5 to 200 μm, even more preferably from 10 to 150 μm, and even more preferably from 20 to 120 μm.
The surface of the release film that comes into contact with the resin sheet may be subjected to a matte treatment, a corona treatment, or an antistatic treatment.

The laminate may be wound around a core to form a wound body.
In the wound body according to one embodiment of the present invention, the length of the laminate is preferably 10 m or more, more preferably 20 m or more. By having a length of the laminate of 10 m or more, for example, when the resin sheet is used as a flexible laminate or a stretchable laminate, it is possible to continuously produce electronic components, and the continuous film forming property is excellent. The upper limit of the length is not particularly limited, but it is preferably 1000 m or less.
The material of the core is not particularly limited, but examples thereof include paper, resin-impregnated paper, acrylonitrile/butadiene/styrene copolymer (ABS resin), fiber-reinforced plastic (FRP), phenol resin, inorganic-containing resin, etc. An adhesive may be used for the core.

<Method of manufacturing resin sheet>
Hereinafter, a method for producing the present resin sheet will be described, but the method for producing the present resin sheet is not limited to the following method.

[First manufacturing method]
The first method for producing a resin sheet includes a coating liquid preparation step of preparing a coating liquid containing a resin composition, and a molding step of molding the coating liquid into a sheet.

(1) Coating Liquid Preparation Step In the coating liquid preparation step, the thermoplastic resin (A), the radically polymerizable compound (B), the epoxy compound (C), the curing agent (D), and optionally the organic peroxide (E), the curing aid (F), the solvent (G) and other components are stirred and mixed uniformly to obtain a coating liquid.
For mixing, a general mixing/stirring device such as a mixer, blender, three-roll kneader, ball mill, kneader, single-screw kneader or twin-screw kneader can be used, and heating may be performed during mixing, if necessary.

(2) Molding Step In the molding step, the coating liquid is molded into a sheet to obtain a resin sheet.
The coating liquid can be formed into a sheet by any known method. For example, the method may be a doctor blade method, a solvent casting method, or an extrusion film forming method. A preferred forming method includes a method including the following (2-1) coating step and (2-2) drying step.

(2-1) Coating Step In the coating step, a coating liquid is applied to the surface of a release film to form a coating film.
The coating method may be a common method such as a dip method, a spin coating method, a spray coating method, a blade method, etc. For coating, a coating device such as a spin coater, a slit coater, a die coater, a blade coater, a gravure coater, etc. can be used, and this makes it possible to uniformly form a coating film of a predetermined thickness on the release film.

(2-2) Drying Step In the drying step, the solvent is removed from the coating film formed above.
The drying temperature is not particularly limited, but is usually 10 to 150° C., preferably 25 to 120° C., and more preferably 30 to 110° C. When the drying temperature is equal to or lower than the upper limit, the crosslinking reaction of the radical polymerizable compound (B) in the coating film is suppressed. When the drying temperature is equal to or higher than the lower limit, foaming of the resin sheet is suppressed, and the solvent can be effectively removed, improving productivity.
The drying time can be appropriately adjusted depending on the state of the coating film, the drying environment, etc. The drying time is preferably 30 seconds or more, more preferably 1 minute or more, and even more preferably 2 minutes or more. On the other hand, the drying time is preferably 1 hour or less, more preferably 30 minutes or less, and even more preferably 15 minutes or less.
By setting the drying time to the above lower limit or more, the solvent can be sufficiently removed, whereas by setting the drying time to the above upper limit or less, the productivity can be improved and the production cost can be reduced.
The solvent in the resin composition can be removed by a known heating method such as using a hot plate, a hot air oven, an IR heating oven, a vacuum dryer, or a high-frequency heater.

In addition, from the viewpoint of preventing contamination of the resin sheet surface and ease of handling, a release film may be laminated on the resin sheet after the drying process.

[Second manufacturing method]
The second method for producing the resin sheet includes a film-forming step of extruding a resin composition onto a release film.

In the film-forming process, the thermoplastic resin (A), the radically polymerizable compound (B), the epoxy compound (C), the curing agent (D), and optionally the organic peroxide (E) and other components are kneaded in a single-screw or twin-screw extruder, and extruded onto a release film using an extruder or the like under temperature conditions that are equal to or higher than the melting point of the thermoplastic resin (A) and lower than the crosslinking temperature of the radically polymerizable compound (B) and the epoxy compound (C) to form a film. The method for extruding the resin composition is not particularly limited, but a more specific example is T-die molding.

The curing temperature of the present resin composition may be any temperature at which the thermoplastic resin (A) does not flow and at which the crosslinking reaction of the radical polymerizable compound (B) and the epoxy compound (C) proceeds. Specifically, the curing temperature is preferably 120 to 300°C, more preferably 140 to 250°C, and even more preferably 150 to 220°C.
The curing time of the present resin composition is not particularly limited, but is preferably from 10 minutes to 2 hours.

<Applications of resin composition and resin sheet>
Applications of the resin composition and resin sheet according to one embodiment of the present invention include, but are not limited to, copper foil laminates, stretchable boards, flexible printed boards, multilayer printed wiring boards, circuit board materials for electric and electronic devices such as capacitors, underfill materials, interchip fills for 3D-LSIs, insulating sheets, vibration damping materials, adhesives, solder resists, semiconductor encapsulants, hole filling resins, and component embedding resins.

The resin composition of the present invention can be made into a circuit board material by laminating it with a conductor. When used as a circuit board material for electric and electronic devices, the resin composition may be formed into a resin sheet before use. The thickness of the resin sheet is preferably 10 μm or more and 500 μm or less. The thickness of the conductor is preferably 0.2 μm or more and 70 μm or less.

The conductor can be a metal foil made of a conductive metal such as copper or aluminum, an alloy containing these metals, or a metal layer formed by plating or sputtering.

<Circuit board materials>
The circuit board material of the present invention can be produced, for example, by the following method.
After the resin sheet according to one embodiment of the present invention is placed on a conductor, the resin sheet is heat cured to form an insulating layer, on which a further conductor is layered, and the required number of such layers are stacked.
The curing temperature of the present resin sheet may be any temperature at which the thermoplastic resin (A) does not flow and at which the crosslinking reaction of the radical polymerizable compound (B) and the epoxy compound (C) proceeds. Specifically, the curing temperature of the present resin sheet is preferably 120 to 300°C, more preferably 140 to 250°C, and even more preferably 150°C to 220°C.
The curing time of the resin sheet is not particularly limited, but is preferably from 10 minutes to 2 hours.
The lamination of the resin sheet and the conductor may be performed by directly laminating the resin sheet with a conductive metal foil, by bonding the resin sheet and the conductive metal foil with an adhesive, by forming a conductive metal layer by plating or sputtering, or by a combination of these methods.
The method may also include a step of drilling holes in the insulating layer to form via holes, and a step of roughening the surface of the insulating layer.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following examples and comparative examples, various physical properties were measured by the following methods.

<Ingredients>
[Thermoplastic resin (A)]
a-1: styrene-ethylene-butadiene-styrene block copolymer (SEBS: Asahi Kasei Corporation, "Tuftec M1052"), styrene content 20% by mass, storage modulus (24°C) = 6.2 MPa, density = 0.890 g/ ^cm3

[Radically polymerizable compound (B)]
b-1: Triallyl isocyanurate (TAIC: manufactured by Shinryo Corporation), mass average molecular weight (Mw): 250

[Epoxy compound (C)]
c-1: bisphenol AF diglycidyl ether (manufactured by Mitsubishi Chemical Corporation, "YX7660"), epoxy equivalent: 237 g/eq
c-2: 1,6-hexanediol diglycidyl ether (manufactured by Mitsubishi Chemical Corporation, "YED216D"), epoxy equivalent: 116 g/eq.

[Curing agent (D)]
d-1: A mixture of 4-methylhexahydrophthalic anhydride and hexahydrophthalic anhydride

[Organic peroxide (E)]
e-1: α,α-di(tert-butylperoxyisopropyl)benzene (manufactured by NOF Corporation, "Perbutyl P")

[Curing aid (F)]
f-1: 2-ethyl-4-methylimidazole (Tokyo Chemical Industry Co., Ltd.)

[Solvent (G)]
f-1: Toluene (content > 99.0% by mass)

<Examples 1 to 4, Comparative Examples 1 to 3>
The raw materials were mixed in the ratio shown in Table 1, and the raw materials were completely dissolved by heating at about 80 ° C. to prepare a resin composition. The prepared resin composition was spread in a sheet shape on the release-treated surface of a 50 μm-thick release film (PET film manufactured by Mitsubishi Chemical Corporation) that had been subjected to a silicone release treatment so that the thickness after drying was 100 μm, and heated in an oven at 100 ° C. for 15 minutes to volatilize the solvent. A 50 μm-thick release film (PET film manufactured by Mitsubishi Chemical Corporation) that had been subjected to a silicone release treatment was laminated on the surface of the resin composition from which the solvent had been volatilized so that the release-treated surface was on the resin sheet side, and a resin sheet with a release film having a thickness of 100 μm was prepared.

<Evaluation>
The resin composition thus obtained was subjected to the following evaluations. The results are shown in Table 1.

(1) Dielectric Properties The resin sheets with release films produced in the Examples and Comparative Examples were held in a heat press at 200° C. for 30 minutes while applying a pressure of about 2 MPa to completely harden the resin sheets, and the release films on both sides were peeled off to obtain hardened resin compositions.
The in-plane dielectric constant and dielectric loss tangent of the cured product were measured in TE mode using a cavity resonator (manufactured by AET Co., Ltd.) and a network analyzer MS46 122B (manufactured by Anritsu Co., Ltd.) at a measurement frequency of 10 GHz.

(2) Coefficient of linear thermal expansion (CTE)
The resin sheets with release films produced in the examples and comparative examples were held in a heat press at 200°C for 30 minutes while applying a pressure of about 2 MPa to completely harden the resin sheets, and the release films on both sides were peeled off to obtain a cured resin composition.
The linear thermal expansion coefficient of the obtained cured product was measured by thermomechanical analysis according to a method in accordance with JIS K7197 (2012). Specifically, using a thermal analyzer "TMA 841" (manufactured by Mettler Toledo), the sample shape was 5 mm wide x 16 mm long, and the measurement was started from 30°C, heated to 100°C at 5°C/min, cooled to 0°C once, and then reheated to 150°C. The dimensional change during the reheating process was measured, and the average value of the thermal expansion coefficient in the in-plane direction from 0 to 120°C was calculated based on the results.

From Examples 1 to 6, it was confirmed that a resin composition containing a thermoplastic resin (A), a radical polymerizable compound (B), an epoxy compound (C) and a curing agent (D), in which the content of the thermoplastic resin (A) is 20% by mass or more relative to the total mass of the resin composition, and the sum of the contents of the epoxy compound (C) and the curing agent (D) is 4% by mass or more and 80% by mass or less relative to the total mass of the resin composition, has excellent low dielectric properties and dimensional stability. Furthermore, a comparison between Examples 1 and 3 showed that by using an epoxy compound containing a fluorine atom as the epoxy compound (C), low dielectric constant properties and dimensional stability can be achieved at a higher level.
On the other hand, Comparative Example 1, which did not contain the epoxy compound (C) and the curing agent (D), had a high linear thermal expansion coefficient and poor dimensional stability.
In Comparative Examples 2 and 3, the sum of the contents of the epoxy compound (C) and the curing agent (D) was less than 4 mass% relative to the total mass of the resin composition, and the linear thermal expansion coefficient was high and the dimensional stability was poor.

Claims (10)

A resin composition comprising at least one thermoplastic resin (A) selected from the group consisting of styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, ethylene-based polymers, and cyclic polyolefin resin copolymers, a radically polymerizable compound (B), an epoxy compound (C), and a curing agent (D), wherein the content of the thermoplastic resin (A) is 20% by mass or more relative to the total mass of the resin composition, and the sum of the contents of the epoxy compound (C) and the curing agent (D) is 4% by mass or more and 80% by mass or less relative to the total mass of the resin composition. The resin composition according to claim 1, wherein the thermoplastic resin (A) contains a styrene-based thermoplastic elastomer, and the styrene content of the styrene-based thermoplastic elastomer is 10% by mass or more and 70% by mass or less. The resin composition according to claim 1, wherein the thermoplastic resin (A) has a mass average molecular weight (Mw) of 30,000 or more. The resin composition according to claim 1, wherein the content of the radical polymerizable compound (B) per 100 parts by mass of the thermoplastic resin (A) is 1 part by mass or more and 50 parts by mass or less. The resin composition according to claim 1, wherein the epoxy compound (C) contains a multifunctional epoxy compound having an epoxy equivalent of 1000 g/eq or less. The resin composition according to claim 1, wherein the curing agent (D) includes an acid anhydride curing agent and/or an active ester curing agent. The resin composition according to claim 1, wherein the linear thermal expansion coefficient of the cured product obtained by heat pressing the resin composition at 200°C and 2 MPa for 30 minutes is 190 ppm/K or less. A resin sheet comprising the resin composition according to any one of claims 1 to 7. A laminate comprising a release film on one or both sides of the resin sheet according to claim 8. A circuit board material comprising an insulating layer formed from a cured product of the resin composition according to any one of claims 1 to 7 and a conductor laminated thereon.