Curable composition, cured product, prepreg, and metal-clad laminate

Abstract

This curable composition contains a graft-modified styrene elastomer graft-modified with an aromatic vinyl monomer, and an unsaturated compound having two or more radically polymerizable carbon-carbon unsaturated double bonds in one molecule. The aromatic vinyl monomer is a compound represented by general formula (1). In general formula (1), R1, R2, R3, R4, R5, and R6 each independently represent a hydrogen atom, a halogen atom, or a C1-6 alkyl group. However, at least one of R2, R3, R4, R5, and R6 represents a C1-6 alkyl group.　

Description

Curable compositions, cured products, prepregs, and metal-clad laminates

[0001] The present invention relates to curable compositions, cured products, prepregs, and metal-clad laminates.

[0002] In recent years, there has been a growing demand for high-speed transmission and reception of large amounts of data in communication devices such as smartphones and electronic devices such as next-generation televisions. Consequently, the frequency of electrical signals is increasing. Specifically, in the field of wireless communication, the use of high-frequency bands of 10 GHz or higher is being considered for the introduction of fifth-generation mobile communication systems.

[0003] However, as the frequency of the signals used increases, the quality of the output signal deteriorates, which can lead to misinterpretation of information, i.e., transmission loss increases. To reduce this transmission loss, there is a need for low-dielectric materials with low dielectric loss tangents as insulating materials for constructing the materials of wiring boards (substrate materials). For these reasons, it has been proposed to use styrene-based thermoplastic elastomers as modifiers to obtain low-dielectric materials that can be used in high-frequency bands. Specifically, a resin composition (curable composition) has been proposed that contains a modified polyphenylene ether whose terminals are modified with specific radical polymerizable functional groups as a base material, and that a specific styrene-based thermoplastic elastomer is blended in order to improve dielectric properties (see Patent Document 1).

[0004] Japanese Patent Publication No. 2023-001134

[0005] On the other hand, substrate materials are usually metal-clad laminates, which consist of a layer containing a cured product of a curable composition (insulating layer) and a metal layer such as a copper layer. Metal-clad laminates require heat resistance suitable for high-temperature processes such as solder reflow. Furthermore, if the thermal expansion coefficient of the insulating layer in the metal-clad laminate is large, the adhesion between the insulating layer and the metal layer may decrease during high-temperature processes. The technology described in Patent Document 1 alone makes it difficult to obtain a cured product that is excellent in heat resistance and low thermal expansion while reducing the dielectric loss tangent.

[0006] In view of the above, an object of the present invention is to provide a curable composition capable of forming a cured product excellent in heat resistance and low thermal expansion while reducing the dielectric loss tangent, and a cured product, a prepreg, and a metal-clad laminate produced using the curable composition.

[0007] <Aspects of the Present Invention> The present invention includes the following aspects.

[0008] [1] A curable composition comprising a graft-modified styrene-based elastomer graft-modified with an aromatic vinyl monomer and an unsaturated compound having two or more radical-polymerizable carbon-carbon unsaturated double bonds in one molecule, wherein the aromatic vinyl monomer is a compound represented by the following general formula (1).

[0009]

[0010] In the general formula (1), R １ , R ２ , R ３ , R ４ , R ５ and R ６ each independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms. However, at least one of R ２ , R ３ , R ４ , R ５ and R ６ represents an alkyl group having 1 to 6 carbon atoms.

[0011] [2] The curable composition according to [1] above, wherein the graft ratio of the aromatic vinyl monomer is 0.05% by weight or more and 30% by weight or less.

[0012] [3] The curable composition according to [1] or [2] above, wherein the unsaturated compound has two or more functional groups selected from the group consisting of a vinyl group, a vinylbenzyl group, a styryl group, a (meth)acryloyl group, a maleimide group, and an allyl group in one molecule.

[0013] [4] The curable composition according to any one of [1] to [3] above, wherein the amount of the graft-modified styrene-based elastomer is 1 part by weight or more and 50 parts by weight or less with respect to 100 parts by weight of the unsaturated compound.

[0014] [5] A cured product of any one of the curable compositions described in [1] to [4] above.

[0015] [6] A prepreg comprising a fiber sheet and a semi-cured product of any one of the curable compositions described in [1] to [4] above, which is impregnated into the fiber sheet.

[0016] [7] A metal-clad laminate having a cured prepreg as described in [6] above, and a metal layer disposed on at least one main surface of the cured prepreg.

[0017] According to the present invention, it is possible to provide a curable composition capable of forming a cured product with excellent heat resistance and low thermal expansion while reducing dielectric loss tangent, as well as a cured product, prepreg, and metal-clad laminate manufactured using the curable composition.

[0018] Preferred embodiments of the present invention will be described in detail below, but the present invention is not limited thereto. Furthermore, all academic and patent documents cited herein are incorporated herein by reference.

[0019] First, let's explain the terms used in this specification. "Constituent unit" refers to the repeating unit that makes up the polymer. "Aromatic vinyl monomer graft rate" refers to the percentage (in weight %) of constituent units derived from aromatic vinyl monomers bonded by graft polymerization relative to the total amount (100% by weight) of the styrene-based elastomer before graft modification. The method for measuring the aromatic vinyl monomer graft rate is the same as or similar to the method described in the examples below. "Weight-average molecular weight" refers to the weight-average molecular weight (Mw) on a standard polystyrene basis, measured by gel permeation chromatography. "Main surface of cured product" refers to the surface perpendicular to the thickness direction of the cured product (insulating layer).

[0020] "Semi-cured state" refers to a state in which the degree of hardening can be further increased by hardening treatment (e.g., heating, exposure, etc.). "Semi-cured material" refers to a substance in a semi-cured state.

[0021] "Alkyl groups having 1 to 6 carbon atoms" are linear or branched and unsubstituted. Examples of alkyl groups having 1 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, s-butyl group, isobutyl group, n-pentyl group, isopentyl group, n-hexyl group, and isohexyl group.

[0022] "Solid content" refers to the non-volatile components in a composition, such as components other than the solvent. "Total solid content" refers to the total amount of components in the composition excluding the solvent.

[0023] In the following, the compound name may be followed by "system" to refer to the compound and its derivatives collectively. Furthermore, when "system" is followed by a compound name to represent a polymer name, unless otherwise specified, it means that the repeating units of the polymer originate from the compound or its derivatives. Additionally, acrylates and methacrylates may be collectively referred to as "(meth)acrylate." Similarly, acryloyls and methacryloyls may be collectively referred to as "(meth)acryloyl."

[0024] Unless otherwise specified, the components and functional groups exemplified herein may be used individually or in combination of two or more.

[0025] <Curable Composition> The curable composition according to this embodiment (hereinafter sometimes referred to as the "specific curable composition") comprises a graft-modified styrene elastomer graft-modified with an aromatic vinyl monomer represented by the following general formula (1), and an unsaturated compound having two or more radically polymerizable carbon-carbon unsaturated double bonds in one molecule.

[0026]

[0027] In general formula (1), R １ , R ２ , R ３ , R ４ , R ５ and R ６ Each of these independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms. However, R ２ , R ３ , R ４ , R５ and R ６ At least one of them represents an alkyl group having 1 to 6 carbon atoms.

[0028] Hereinafter, the aromatic vinyl monomer represented by general formula (1) may be referred to as the "specific aromatic vinyl monomer." Furthermore, the graft-modified styrene elastomer that has been graft-modified with the specific aromatic vinyl monomer may be referred to as "component A." In addition, an unsaturated compound having two or more radically polymerizable carbon-carbon unsaturated double bonds in one molecule may be referred to as "component B."

[0029] The specific curable composition can form a cured product with excellent heat resistance and low thermal expansion while reducing the dielectric loss tangent. The reason for this is presumed to be as follows.

[0030] Component A in the specific curable composition is graft-modified with a specific aromatic vinyl monomer. This specific aromatic vinyl monomer does not have polar groups (for example, one or more functional groups selected from the group consisting of epoxy groups, glycidyl groups, amino groups, cyano groups, acid anhydride groups, hydroxyl groups, and carboxyl groups). Therefore, since component A has side chains without polar groups introduced by graft modification, moisture absorption, which causes an increase in dielectric loss tangent, can be suppressed. Thus, the cured product obtained using the specific curable composition can have its dielectric loss tangent reduced.

[0031] Furthermore, the specific aromatic vinyl monomer has at least one alkyl group with 1 to 6 carbon atoms bonded to the aromatic ring. Radicals are easily generated at the benzyl carbon of the alkyl group through resonance stabilization. Therefore, heating or exposure during the curing of the specific curable composition makes it easier for radicals to be generated at the benzyl carbon of the constituent units derived from the specific aromatic vinyl monomer. As a result, the carbon-carbon unsaturated double bond in component B and the benzyl carbon undergo a radical reaction, making it easier to form a crosslinked structure. Consequently, the cured product obtained using the specific curable composition has a relatively high crosslink density, resulting in excellent heat resistance and low thermal expansion.

[0032] Furthermore, the cured prepreg used as an insulating layer in metal-clad laminates has a relatively small coefficient of thermal expansion in the planar direction (hereinafter sometimes referred to as "CTExy") due to the presence of fiber sheets. On the other hand, the cured prepreg of a general type tends to expand easily in the thickness direction, resulting in a relatively large coefficient of thermal expansion in the thickness direction (hereinafter sometimes referred to as "CTEz"). In contrast, prepregs obtained using a specific curable composition have a relatively high crosslinking density, which allows for a reduction in CTEz as well.

[0033] In this embodiment, to obtain a cured product with superior heat resistance and low thermal expansion, R in general formula (1) １ As such, a hydrogen atom or a methyl group is preferred, and a hydrogen atom is more preferred. In this embodiment, in order to obtain a cured product with superior heat resistance and low thermal expansion, R in general formula (1) ２ , R ３ , R ４ , R ５ and R ６ Each of these is independently preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and more preferably a hydrogen atom or a methyl group.

[0034] In this embodiment, in order to obtain a cured product with even better heat resistance and low thermal expansion, R in general formula (1) ４ Preferably, an alkyl group having 1 to 4 carbon atoms is preferred, and a methyl group is more preferred. In this embodiment, in order to obtain a cured product with even better heat resistance and low thermal expansion, R in general formula (1) １ , R ２ , R ３ , R ５ and R ６ Both are hydrogen atoms, and R in general formula (1) ４ Preferably, R in general formula (1) is an alkyl group having 1 to 4 carbon atoms. １ , R ２ , R ３ , R ５ and R ６ Both are hydrogen atoms, and R in general formula (1) ４ It is more preferable that the group is a methyl group.

[0035] In this embodiment, in order to obtain a cured product with superior heat resistance and low thermal expansion while further reducing the dielectric loss tangent, the graft rate of the specific aromatic vinyl monomer is preferably 0.05% by weight or more and 30% by weight or less, more preferably 0.05% by weight or more and 25% by weight or less, even more preferably 0.05% by weight or more and 20% by weight or less, and may also be 0.10% by weight or more and 20% by weight or less, or 0.50% by weight or more and 15% by weight or less.

[0036] The specific curable composition may contain, as an optional component, components other than components A and B described above. Examples of components other than components A and B include unsaturated compounds having one radically polymerizable carbon-carbon unsaturated double bond per molecule (hereinafter sometimes referred to as "component C"), radical polymerization initiators (hereinafter sometimes referred to as "component D"), styrene-based elastomers other than component A (hereinafter sometimes referred to as "component E"), organic solvents, etc. Components A, B, C, D, and E can each be used individually or in combination of multiple components.

[0037] The form of the specific curable composition is not particularly limited. From the viewpoint of ease of handling, the specific curable composition is preferably a varnish-like composition containing an organic solvent. When the specific curable composition is a varnish-like composition containing an organic solvent, in order to suppress defects in the appearance of the resulting cured product, the solid content concentration of the specific curable composition is preferably 20% by weight or more and 70% by weight or less, and more preferably 20% by weight or more and 60% by weight or less. Furthermore, when the specific curable composition is a varnish-like composition containing an organic solvent, in order to suppress defects in the appearance of the resulting cured product, the total content of component A and component B is preferably 15% by weight or more and 100% by weight or less, and more preferably 20% by weight or more and 70% by weight or less, relative to the total solid content (100% by weight) of the specific curable composition.

[0038] The essential components (components A and B) and optional components included in the specific curable composition are described below. In the following, the styrene-based elastomer before graft modification may be referred to as the "core polymer."

[0039] [Component A] Examples of the core polymer constituting component A include a styrene-based elastomer having a polystyrene-based block containing structural units derived from styrene-based monomers and a block (elastomer block) containing structural units derived from monomers other than styrene-based monomers. The content of polystyrene-based blocks in the core polymer is not particularly limited, but for example, it is 15% by weight or more and 45% by weight or less based on the total amount of the core polymer (100% by weight).

[0040] The styrene monomers used to form the polystyrene block are not particularly limited. Suitable examples of styrene monomers include styrene, 4-methylstyrene, α-methylstyrene, 2,6-dimethylstyrene, 2,4-dimethylstyrene, α-methyl-4-methylstyrene, 2,4,6-trimethylstyrene, α-methyl-2,4-dimethylstyrene, 4-chlorostyrene, α-chloro-4-chlorostyrene, 2,4,6-trichlorostyrene, α-chloro-2,4-dichlorostyrene, 4-t-butylstyrene, and 4-chloromethylstyrene. Among these styrene monomers, one or more selected from the group consisting of styrene, α-methylstyrene, and 4-methylstyrene are preferred, and one or more selected from the group consisting of styrene and α-methylstyrene are more preferred from the viewpoint of cost reduction.

[0041] The monomers used to form the elastomer block are not particularly limited, and conventional monomers known for forming styrene-based elastomers can be used. However, monomers capable of forming an elastomer block with a graft polymerization starting point are preferred. Examples of graft polymerization starting points include tertiary carbon atoms.

[0042] The styrene-based elastomer that forms the core polymer may be a block copolymer, a random copolymer, or a hydrogenated version thereof. To obtain a cured product with a further reduction in dielectric loss tangent, the core polymer is preferably a block copolymer, and more preferably a hydrogenated block copolymer.

[0043] Furthermore, from the viewpoint of ease of graft polymerization, the stem polymer is preferably one or more selected from the group consisting of styrene-ethylene-propylene copolymer elastomer, styrene-ethylene-propylene-styrene copolymer elastomer, styrene-isoprene copolymer elastomer, styrene-isoprene-styrene copolymer elastomer, styrene-ethylene-butylene-styrene copolymer elastomer, styrene-ethylene-ethylene-propylene-styrene copolymer elastomer, and hydrogenated products thereof, with styrene-ethylene-propylene-styrene copolymer elastomer being more preferred.

[0044] Examples of specific aromatic vinyl monomers include 4-methylstyrene, 3-methylstyrene, 2-methylstyrene, α-methyl-4-methylstyrene, α-methyl-3-methylstyrene, α-methyl-2-methylstyrene, 2,3-dimethylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 2,6-dimethylstyrene, 3,5-dimethylstyrene, 3,4-dimethylstyrene, and 2,4,6-trimethylstyrene. To obtain a cured product with superior heat resistance and low thermal expansion, it is preferable that the specific aromatic vinyl monomer be one or more selected from the group consisting of 4-methylstyrene, 3-methylstyrene, and 2-methylstyrene, with 4-methylstyrene being more preferable.

[0045] Furthermore, in order to further reduce the dielectric loss tangent, it is preferable to use only specific aromatic vinyl monomers as monomers for graft-modifying the stem polymer to form component A. In other words, in order to further reduce the dielectric loss tangent, it is preferable that component A is graft-modified with only specific aromatic vinyl monomers.

[0046] The method for graft-modifying a styrene-based elastomer (stem polymer) (graft polymerization method) is not particularly limited, and known graft polymerization methods can be employed. A preferred graft polymerization method involves reacting the stem polymer with a specific aromatic vinyl monomer in the presence of a radical polymerization initiator, as described later. Methods for this reaction include melt-kneading using a kneader or extruder, or reacting in solution.

[0047] Examples of radical polymerization initiators that can be used when graft-modifying styrene-based elastomers (stem polymers) include 1,3-di(t-butylperoxyisopropyl)benzene, dicumyl peroxide, di-t-butyl peroxide, and benzoyl peroxide. These radical polymerization initiators can be used individually or in combination of two or more.

[0048] The amount of radical polymerization initiator used is not particularly limited as long as the graft modification reaction proceeds well, but it is preferably 0.01 parts by weight or more and 10 parts by weight or less, and more preferably 0.2 parts by weight or more and 5 parts by weight or less, per 100 parts by weight of styrene elastomer (stem polymer).

[0049] From the viewpoint of ease of processing of the cured product, the weight-average molecular weight of component A is preferably 20,000 to 85,000, more preferably 20,000 to 70,000, even more preferably 35,000 to 70,000, and still more preferably 40,000 to 60,000. The weight-average molecular weight of component A can be adjusted, for example, by changing at least one of the weight-average molecular weight of the stem polymer and the reaction conditions when graft-modifying the stem polymer (specifically, reaction temperature, reaction time, etc.).

[0050] To obtain a cured product with superior heat resistance and low thermal expansion while further reducing the dielectric loss tangent, the amount of component A is preferably 1 to 50 parts by weight, more preferably 2 to 50 parts by weight, even more preferably 3 to 50 parts by weight, or 5 to 45 parts by weight or 10 to 40 parts by weight, relative to 100 parts by weight of component B, as described later.

[0051] In order to suppress defects in the appearance of the resulting cured product, the amount of component A is preferably 45 parts by weight or less, more preferably 40 parts by weight or less, even more preferably 35 parts by weight or less, and even more preferably 30 parts by weight or less, relative to 100 parts by weight of component B, as described later.

[0052] [Component B] Component B is an unsaturated compound having two or more radically polymerizable carbon-carbon unsaturated double bonds in one molecule. For example, component B is a compound having two or more carbon-carbon unsaturated double bond-containing groups in one molecule. To enhance radical polymerizability, the carbon-carbon unsaturated double bond-containing group is preferably one or more functional groups selected from the group consisting of vinyl group, vinylbenzyl group, styryl group, (meth)acryloyl group, maleimide group, and allyl group.

[0053] Component B may be one or more selected from the group consisting of polymers with a weight-average molecular weight of 1,000 or more (hereinafter sometimes referred to as "component B1") and compounds with a molecular weight of less than 1,000 (hereinafter sometimes referred to as "component B2"). To obtain a cured product with superior heat resistance, it is preferable to use component B1 as component B. Furthermore, to obtain a cured product with superior heat resistance and low thermal expansion, it is preferable to use both component B1 and component B2 as component B.

[0054] (Component B1) Examples of component B1 include polymers containing the constituent unit represented by the following general formula (2), modified polyphenylene ether resins, etc.

[0055]

[0056] In general formula (2), Ar represents a divalent aryl group. Hereinafter, the constituent unit represented by general formula (2) may be referred to as "constituent unit (2)". Also, a polymer containing "constituent unit (2)" may be referred to as "polymer (2)". Examples of monomers for forming constituent unit (2) include divinylbenzene, divinylnaphthalene, and divinylanthracene. Polymer (2) may also have constituent units derived from monovinyl aromatic monomers in addition to constituent unit (2). Examples of monovinyl aromatic monomers include styrene, 4-methylstyrene, α-methylstyrene, dimethylstyrene, trimethylstyrene, t-butylstyrene, isopropenyltoluene, and vinylnaphthalene.

[0057] Modified polyphenylene ether resins, for example, have carbon-carbon unsaturated double bond-containing groups at the ends of their molecular chains. Polyphenylene ethers typically have hydroxyl groups bonded to aromatic rings at the ends of their molecular chains. Modified polyphenylene ether resins can be obtained by substituting the hydrogen atoms in these terminal hydroxyl groups with carbon-carbon unsaturated double bond-containing groups.

[0058] The carbon-carbon unsaturated double bond-containing group of the modified polyphenylene ether resin is preferably one or more selected from the group consisting of vinylbenzyl group, vinyl group, allyl group, and (meth)acryloyl group. When the carbon-carbon unsaturated double bond-containing group is a vinylbenzyl group, allyl group, or (meth)acryloyl group, the terminal hydroxyl group of the polyphenylene ether can be converted to a vinylbenzyloxy group, allyloxy group, or (meth)acryloyloxy group by conventional methods using the corresponding halogen. When the carbon-carbon unsaturated double bond-containing group is a vinyl group, methods for introducing the vinyl group include ether exchange reactions between a vinyl ether compound (specifically, alkyl vinyl ethers such as methyl vinyl ether) and the terminal hydroxyl group of the polyphenylene ether; vinylization reactions using vinyl ester compounds such as vinyl acetate; and methods for converting the terminal hydroxyl group of the polyphenylene ether to a vinyloxy group by adding acetylene to the terminal hydroxyl group.

[0059] Furthermore, commercially available modified polyphenylene ether resins can also be used. Specific examples of commercially available products include modified polyphenylene ether resins with vinyl benzyl groups at both ends, such as "OPE-2St-2200" and "OPE-2st-1200" manufactured by Mitsubishi Gas Chemical Co., Ltd.; and modified polyphenylene ether resins with methacryloyl groups at both ends, such as "Noryl SA9000" manufactured by SABIC Corporation.

[0060] In order to obtain a cured product with superior heat resistance and low thermal expansion while promoting the crosslinking reaction between component A and component B1, it is preferable that the carbon-carbon unsaturated double bond equivalent of component B1 be 100 g / eq or more and 1000 g / eq or less, and more preferably 500 g / eq or more and 900 g / eq or less.

[0061] To obtain a cured product with superior heat resistance and low thermal expansion while promoting the crosslinking reaction between component A and component B1, the weight-average molecular weight of component B1 is preferably 1,000 or more and 10,000 or less, more preferably 1,500 or more and 5,000 or less, and even more preferably 2,000 or more and 3,000 or less.

[0062] (Component B2) Examples of component B2 include maleimide compounds, divinylbenzene, triallyl cyanurate, triallyl isocyanurate, trimetharyl isocyanurate, trimethylolpropane tri(meth)acrylate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, triallyl trimellitate, diallyl phthalate, and N,N',N'',N'''-tetraallyl terephthalamide. Among these, one or more selected from the group consisting of maleimide compounds, divinylbenzene, triallyl cyanurate, triallyl isocyanurate, trimetharyl isocyanurate, and trimethylolpropane tri(meth)acrylate are preferred, and one or more selected from the group consisting of divinylbenzene and triallyl isocyanurate are more preferred.

[0063] When using a maleimide compound as component B2, the usable maleimide compound is not particularly limited as long as it has two or more maleimide groups in one molecule and a molecular weight of less than 1,000. Examples include 1,3-phenylenediamine bismaleimide, N,N'-ethylene bismaleimide, N,N'-(1,3-phenylene) bismaleimide, N,N'-[1,3-(4-methylphenylene)] bismaleimide, 3,3'-dimethyl-5,5'-diethyl-4,4'-diphenylmethane bismaleimide, and 1,2-bis[4 Examples include -(3-maleimidophenoxy)phenyl]ethane, 2,2-bis[4-(4-maleimidophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, bis[4-(4-maleimidophenoxy)phenyl] sulfide, bis[4-(3-maleimidophenoxy)phenyl] sulfoxide, 1,3-bis[4-(3-maleimidophenoxy)-α,α-dimethylbenzyl]benzene, and 1,3-bis[4-(3-maleimidophenoxy)-3,5-dimethyl-α,α-dimethylbenzyl]benzene.

[0064] Furthermore, as component B, a maleimide resin having two or more maleimide groups in one molecule and a weight-average molecular weight of 1,000 or more may be used. This maleimide resin is a type of component B1.

[0065] When using both component B1 and component B2 as component B, in order to obtain a cured product with superior heat resistance and low thermal expansion, the weight ratio of component B1 to component B2 (component B1 / component B2) is preferably 1.0 or more and 8.0 or less, more preferably 1.2 or more and 7.0 or less, and even more preferably 1.5 or more and 6.0 or less.

[0066] [Component C] Component C is an unsaturated compound having one radically polymerizable carbon-carbon unsaturated double bond per molecule. By including component C in the specific curable composition, the amount of residual double bonds after the curing reaction of the specific curable composition can be reduced. This results in a cured product with a further reduced dielectric loss tangent.

[0067] To further reduce the dielectric loss tangent of the resulting cured product, the carbon (C) component is preferably a compound with a molecular weight of less than 1,000. Examples of carbon (C) components with a molecular weight of less than 1,000 include acenaphthylene and indene, which may have substituents. To further reduce the dielectric loss tangent of the resulting cured product, acenaphthylene is preferred as the carbon (C) component.

[0068] To obtain a cured product that can further reduce the dielectric loss tangent, the amount of component C is preferably 5 to 50 parts by weight, more preferably 10 to 45 parts by weight, and even more preferably 15 to 40 parts by weight, per 100 parts by weight of component B.

[0069] [Component D] Any known radical polymerization initiator can be used as component D without any particular limitations. Preferred specific examples of component D are the same as the specific examples of radical polymerization initiators that can be used when graft-modifying styrene-based elastomers as described above. In addition, azo-based radical polymerization initiators such as 2,2'-azobis(N-butyl-2-methylpropionamide) can also be used as component D. Component D can be used alone or in a mixture of two or more types.

[0070] The amount of component D is not particularly limited as long as the specific curable composition can be radically polymerized by heating or exposure. To obtain a cured product with superior heat resistance, the amount of component D is preferably 0.1 parts by weight or more and 5 parts by weight or less, more preferably 0.3 parts by weight or more and 3 parts by weight or less, and even more preferably 0.5 parts by weight or more and 2 parts by weight or less, based on 100 parts by weight of the total of components A and B.

[0071] [Component E] Component E is a styrene-based elastomer other than component A. The cured product of a specific curable composition containing component E can further reduce the dielectric loss tangent. To obtain a cured product that can further reduce the dielectric loss tangent, it is preferable that component E be one or more selected from the group consisting of styrene-ethylene-propylene-styrene copolymer elastomer, styrene-ethylene-butylene-styrene copolymer elastomer, styrene-isobutylene-styrene copolymer elastomer, styrene-vinyl-polydiene-styrene copolymer elastomer, and hydrogenated products thereof. To further reduce the dielectric loss tangent, it is preferable that the content of styrene-derived constituent units in component E is 5% by weight or more and 40% by weight or less, more preferably 10% by weight or more and 30% by weight or less, even more preferably 10% by weight or more and 25% by weight or less, even more preferably 10% by weight or more and 20% by weight or less, and may also be 10% by weight or more and 15% by weight or less, based on the total amount of component E (100% by weight).

[0072] To obtain a cured product that can further reduce the dielectric loss tangent, it is preferable that the amount of component E is 1 part by weight or more and 25 parts by weight or less, relative to 100 parts by weight of the total of components A and B.

[0073] [Other Components] The specific curable composition may contain, as needed, components such as flame retardants, core-shell particles, inorganic fillers (e.g., silica), and organic solvents. These components (other components) may be used individually or in combination of two or more.

[0074] When using organic solvents as other components, suitable organic solvents include ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as pentane, cyclopentane, hexane, cyclohexane, octane, decane, and dodecane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; ether solvents such as diethyl ether, diisopropyl ether, and tetrahydrofuran; and halogenated hydrocarbon solvents such as methylene chloride, methyl chloroform, carbon tetrachloride, dichlorodifluoromethane, and perchloroethylene. Organic solvents can be used individually or in combination of two or more.

[0075] [Method for Manufacturing a Specific Curable Composition] The method for manufacturing a specific curable composition is not particularly limited as long as it can uniformly mix component A, component B, and any optional components used as needed. A preferred method for manufacturing a specific curable composition is to prepare the specific curable composition by mixing component A, component B, and any optional solid components used as needed in an organic solvent, while avoiding curing by heating and allowing for uniform mixing of component A, component B, and any optional solid components used as needed.

[0076] [Preferred Embodiments of Specific Curable Compositions] In order to form a cured product that further reduces dielectric loss tangent and exhibits even better heat resistance and low thermal expansion, the specific curable composition preferably satisfies the following condition 1, more preferably satisfies the following condition 2, and even more preferably satisfies the following condition 3. Condition 1: The specific aromatic vinyl monomer is one or more selected from the group consisting of 4-methylstyrene, 3-methylstyrene, and 2-methylstyrene. Condition 2: The composition satisfies the above condition 1, and the graft rate of the specific aromatic vinyl monomer is 0.05% by weight or more and 30% by weight or less. Condition 3: The composition satisfies the above condition 2, and the amount of component A is 1 part by weight or more and 50 parts by weight or less per 100 parts by weight of component B.

[0077] <Cured Products, Prepregs, and Metal-Clad Laminates> Next, the cured products, prepregs, and metal-clad laminates according to this embodiment will be described. The cured products, prepregs, and metal-clad laminates according to this embodiment are all manufactured using a specific curable composition. Therefore, the cured products, prepregs, and metal-clad laminates according to this embodiment all exhibit excellent heat resistance and low thermal expansion while reducing dielectric loss tangent. In the following description, explanations of content that overlaps with the specific curable composition described above may be omitted.

[0078] The cured product according to this embodiment is obtained by applying energy to the above-mentioned specific curable composition by methods such as heating or exposure. For example, a cured sheet is a cured product that can be suitably used as a substrate material. This cured sheet can be obtained, for example, by forming the cured product of the above-mentioned specific curable composition into a sheet using a solution casting method.

[0079] The cured product according to this embodiment preferably has a dielectric loss tangent of less than 0.0050, measured under conditions of 28 to 40 GHz. In particular, the cured product according to this embodiment preferably has a dielectric loss tangent of less than 0.0050, measured under conditions of 40 GHz. A cured product exhibiting such a dielectric loss tangent is suitable as a material for semiconductor package substrates for smartphones and the like.

[0080] The prepreg according to this embodiment consists of a fiber sheet and a semi-cured product of a specific curable composition impregnated into the fiber sheet. The prepreg according to this embodiment is suitably used as a substrate material. The prepreg according to this embodiment can be obtained, for example, by impregnating a fiber sheet such as glass cloth with a specific curable composition, and then curing the specific curable composition impregnated into the fiber sheet in a semi-cured state by methods such as heating or exposure.

[0081] The metal-clad laminate according to this embodiment comprises a cured prepreg (insulating layer) according to this embodiment and a metal layer disposed on at least one main surface of the cured prepreg (insulating layer). As the metal layer, for example, metal foil made from copper, stainless steel, nickel, aluminum, and alloys of these metals is used, with copper foil being preferred. Since the cured prepreg according to this embodiment has excellent low thermal expansion properties, the metal-clad laminate according to this embodiment has excellent adhesion between the insulating layer and the metal layer even during high-temperature processes.

[0082] The following describes examples of the present invention, but the present invention is not limited to these examples. First, the grafting rate of the aromatic vinyl monomer of component A and the method for measuring the weight-average molecular weight (Mw) of the styrene elastomer (more specifically, either component A or component E) will be described.

[0083] <Grafting rate of aromatic vinyl monomers> First, the graft-modified styrene elastomer to be measured was dissolved in methylene chloride to obtain a sample for grafting rate measurement. Next, a nuclear magnetic resonance spectrometer (Brker, Inc.) was used. １ Using the H resonance frequency (400 MHz), the obtained sample １ The 1H-NMR spectrum was measured. １In the 1H-NMR spectrum, the grafting rate of the aromatic vinyl monomer (4-methylstyrene) was calculated from the integral ratio of the peak originating from the methyl group of 4-methylstyrene with a chemical shift value of approximately 2.5 ppm and the peak originating from the methyl group of the elastomer block with a chemical shift value of approximately 1.25 ppm.

[0084] <Mw of Styrene Elastomers> First, the styrene elastomer to be measured was dissolved in toluene (reagent grade) manufactured by Wako Pure Chemical Industries, Ltd. to obtain a sample for Mw measurement. Next, Mw was measured using a gel permeation chromatograph analyzer (Tosoh Corporation "HLC-8220GPC", detector: differential refractive index detector "RI-8022", measurement column: TSKgel SuperHZM-N (5 tubes) and TSKgel SuperHZ-1000 (1 tube)) under the following conditions: ・Flow rate: 0.35 mL / min ・Column temperature: 40°C ・Sample injection volume: 0.01 mL ・Standard sample: Monodisperse polystyrene manufactured by Tosoh Corporation ・Data processing: Tosoh Corporation GPC data processing system

[0085] <Synthesis of Graft-Modified Styrene Elastomer> [Synthesis of Graft-Modified Styrene Elastomer A-1] 100 parts by weight of styrene-ethylene-propylene-styrene copolymer elastomer (Kuraray Co., Ltd., "SEPTON2002", Mw: 50,000, polystyrene block content: 30% by weight of the total amount of copolymer) was placed in the kneading section of a kneading test apparatus (Toyo Seiki Seisakusho Co., Ltd., "Laboplastmill 3S150"), and kneaded at 180°C for 2 minutes to melt the styrene-ethylene-propylene-styrene copolymer elastomer. Next, 0.1 parts by weight of 4-methylstyrene (Jiangsu Changqingshu New Materials Technology Co., Ltd., purity: 99% or higher) and 0.25 parts by weight of 1,3-di(t-butylperoxyisopropyl)benzene (NOF Co., Ltd., "Perbutyl P") were added to the kneading section and kneaded at 180°C for 3 minutes. Next, the contents of the kneading section were dissolved in toluene, and then reprecipitated in methanol to remove unreacted monomers. The precipitate was then dried under reduced pressure at 60°C for 12 hours to obtain graft-modified styrene elastomer A-1.

[0086] [Synthesis of Graft-Modified Styrene Elastomer A-2] 100 parts by weight of styrene-ethylene-propylene-styrene copolymer elastomer (SEPTON2002, manufactured by Kuraray Co., Ltd., Mw: 50,000, polystyrene block content: 30% by weight of the total amount of copolymer) was placed in the kneading section of a kneading test apparatus (Laboplastmill 3S150, manufactured by Toyo Seiki Seisakusho Co., Ltd.), and kneaded at 180°C for 2 minutes to melt the styrene-ethylene-propylene-styrene copolymer elastomer. Next, 5.0 parts by weight of 4-methylstyrene (manufactured by Jiangsu Changqingshu New Materials Technology Co., Ltd., purity: 99% or higher) and 0.25 parts by weight of 1,3-di(t-butylperoxyisopropyl)benzene (Perbutyl P, manufactured by NOF Corporation) were added to the kneading section, and kneaded at 180°C for 3 minutes. Next, the contents of the kneading section were dissolved in toluene, and then reprecipitated in methanol to remove unreacted monomers. The precipitate was then dried under reduced pressure at 60°C for 12 hours to obtain graft-modified styrene elastomer A-2.

[0087] [Synthesis of Graft-Modified Styrene Elastomer A-3] 100 parts by weight of styrene-ethylene-propylene-styrene copolymer elastomer (SEPTON2002, manufactured by Kuraray Co., Ltd., Mw: 50,000, polystyrene block content: 30% by weight of the total amount of copolymer) was placed in the kneading section of a kneading test apparatus (Laboplastmill 3S150, manufactured by Toyo Seiki Seisakusho Co., Ltd.), and kneaded at 180°C for 2 minutes to melt the styrene-ethylene-propylene-styrene copolymer elastomer. Next, 15.0 parts by weight of 4-methylstyrene (manufactured by Jiangsu Changqingshu New Materials Technology Co., Ltd., purity: 99% or higher) and 0.25 parts by weight of 1,3-di(t-butylperoxyisopropyl)benzene (Perbutyl P, manufactured by NOF Corporation) were added to the kneading section, and kneaded at 180°C for 3 minutes. Next, the contents of the kneading section were dissolved in toluene, and then reprecipitated in methanol to remove unreacted monomers. The precipitate was then dried under reduced pressure at 60°C for 12 hours to obtain graft-modified styrene elastomer A-3.

[0088] [Synthesis of Graft-Modified Styrene Elastomer A-4] 100 parts by weight of styrene-ethylene-propylene-styrene copolymer elastomer (SEPTON2002, manufactured by Kuraray Co., Ltd., Mw: 50,000, polystyrene block content: 30% by weight of the total amount of copolymer) was placed in the kneading section of a kneading test apparatus (Laboplastmill 3S150, manufactured by Toyo Seiki Seisakusho Co., Ltd.), and kneaded at 180°C for 2 minutes to melt the styrene-ethylene-propylene-styrene copolymer elastomer. Next, 25.0 parts by weight of 4-methylstyrene (manufactured by Jiangsu Changqingshu New Materials Technology Co., Ltd., purity: 99% or higher) and 0.50 parts by weight of 1,3-di(t-butylperoxyisopropyl)benzene (Perbutyl P, manufactured by NOF Corporation) were added to the kneading section, and kneaded at 180°C for 3 minutes. Next, the contents of the kneading section were dissolved in toluene, and then reprecipitated in methanol to remove unreacted monomers. The precipitate was then dried under reduced pressure at 60°C for 12 hours to obtain graft-modified styrene elastomer A-4.

[0089] [Synthesis of Graft-Modified Styrene Elastomer A-5] 100 parts by weight of styrene-ethylene-propylene-styrene copolymer elastomer (SEPTON2002, manufactured by Kuraray Co., Ltd., Mw: 50,000, polystyrene block content: 30% by weight of the total amount of copolymer) was placed in the kneading section of a kneading test apparatus (Laboplastmill 3S150, manufactured by Toyo Seiki Seisakusho Co., Ltd.), and kneaded at 200°C for 2 minutes to melt the styrene-ethylene-propylene-styrene copolymer elastomer. Next, 8.0 parts by weight of 4-methylstyrene (manufactured by Jiangsu Changqingshu New Materials Technology Co., Ltd., purity: 99% or higher) and 0.50 parts by weight of 1,3-di(t-butylperoxyisopropyl)benzene (Perbutyl P, manufactured by NOF Corporation) were added to the kneading section, and kneaded at 250°C for 18 minutes. Next, the contents of the kneading section were dissolved in toluene, and then reprecipitated in methanol to remove unreacted monomers. The precipitate was then dried under reduced pressure at 60°C for 12 hours to obtain graft-modified styrene elastomer A-5.

[0090] Table 1 shows the grafting ratio and Mw of aromatic vinyl monomers for the obtained graft-modified styrene-based elastomers A-1 to A-5.

[0091]

[0092] <Preparation of Components B to E and Other Components> In addition to the graft-modified styrene elastomers A-1 to A-5 described above, the following components B to E and other components were prepared as materials for preparing the curable compositions of the examples and comparative examples.

[0093] [Component B] For component B, the following B1 components (B1-1 to B1-4) and B2 components (B2-1 and B2-2) were prepared. • B1-1: Modified polyphenylene ether resin with methacryloyl groups at both ends (SABIC Corporation's "Noryl SA9000", Mw: 2,300, carbon-carbon unsaturated double bond equivalent: 850 g / eq) • B1-2: Modified polyphenylene ether resin with vinylbenzyl groups at both ends (Mitsubishi Gas Chemical Corporation's "OPE-2St-1200", Mw: 1,600, carbon-carbon unsaturated double bond equivalent: 660 g / eq) • B1-3: Maleimide resin (Nippon Kayaku Co., Ltd.'s "MIZ-001", Mw: 3,000) • B1-4: Polymer (2) (Nippon Steel Chemical & Material Corporation's "ODV-XET (X04)", Mw: 3,000) • B2-1: Triallyl isocyanurate (manufactured by Mitsubishi Chemical Corporation) • B2-2: Divinylbenzene

[0094] [Component C] The following C-1 was prepared as component C: ・C-1: Acenaphthylene

[0095] [Component D] The following D-1 and D-2 were prepared as component D: • D-1: 1,3-di(t-butylperoxyisopropyl)benzene (NOF Corporation's "Perbutyl P") • D-2: 2,2'-azobis(N-butyl-2-methylpropionamide) (Fujifilm Wako Pure Chemical Industries, Ltd.'s "VAm-110")

[0096] [Component E] The following E-1 to E-8 were prepared as component E: ・E-1: Styrene-ethylene-propylene-styrene copolymer elastomer (Kuraray Co., Ltd. "SEPTON2002") ・E-2: Styrene-ethylene-butylene-styrene copolymer elastomer (Kuraray Co., Ltd. "SEPTON8007L", styrene-derived component content: 30% by weight of the total copolymer, Mw: 95,000) ・E-3: Styrene-isobutylene-styrene copolymer elastomer (Kaneka Corporation "SIBS 103T", styrene-derived component content: 30% by weight of the total copolymer, Mw: 90,000) ・E-4: Styrene-ethylene-butylene-styrene copolymer elastomer (Kraton Inc. "Kraton 1726VS", Mw: 70,000) • E-5: A styrene-based elastomer formed by copolymerizing a polystyrene-based block with styrene and 4-methylstyrene (Kuraray Co., Ltd. "SEPTON V9461", styrene-derived component content: 30% by weight of the total copolymer, 4-methylstyrene-derived component content: 11% by weight of the total copolymer, Mw: 350,000) • E-6: A styrene-based elastomer formed by copolymerizing a polystyrene-based block with styrene and 4-methylstyrene (Kuraray Co., Ltd. "SEPTON V9475", styrene-derived component content: 30% by weight of the total copolymer, 4-methylstyrene-derived component content: 15% by weight of the total copolymer, Mw: 450,000) • E-7: Hydrogenated styrene-vinyl-polydiene-styrene copolymer elastomer (Kuraray Co., Ltd. "Hybral H7125F", styrene-derived structural unit content: 20% by weight of the total copolymer, Mw: 106,000) • E-8: Hydrogenated styrene-vinyl-polydiene-styrene copolymer elastomer (Kuraray Co., Ltd. "Hybral H7311F", styrene-derived structural unit content: 12% by weight of the total copolymer, Mw: 180,000)

[0097] [Other Components] The following inorganic fillers and organic solvents were prepared as other components: • Inorganic filler: Silica (Admatex "SC2300-SVJ", average particle size: 0.5 μm) • Organic solvent: Toluene

[0098] <Preparation of Curable Compositions> Each component in Tables 2 to 4 was blended in the amounts indicated in Tables 2 to 4 to obtain the curable compositions of Examples 1 to 29 and Comparative Examples 1 to 10. In Tables 2 to 4, the numerical values ​​in the columns for each component (A-1, B1-1, etc.) represent the amount of that component blended (in grams). In Tables 2 to 4, a "-" in the column for each component means that the component was not used.

[0099]

[0100]

[0101]

[0102] <Prepreg Preparation> Using the curable compositions obtained in each example and comparative example, prepregs were prepared according to the following method. Specifically, first, glass cloth (NE-1078, manufactured by Nitto Boseki Co., Ltd., size: 100 mm x 200 mm) was impregnated with the curable composition. Next, the glass cloth impregnated with the curable composition was passed between two fluororesin rolls arranged parallel to each other with a gap of 0.4 mm between them to remove excess curable composition. Then, the glass cloth impregnated with the curable composition was heated at 60°C for 100 minutes, then heated at 100°C for 10 minutes, and further heated at 120°C for 50 minutes to obtain a prepreg with a thickness of 80 μm.

[0103] <Preparation of Cured Sheets> Using the prepregs obtained in each example and comparative example, cured sheets were prepared according to the following method for measuring the coefficient of thermal expansion (CTExy and CTEz), glass transition temperature (Tg), and dielectric properties (dielectric loss tangent and relative permittivity). First, a predetermined number of prepregs were sandwiched between two fluororesin sheets (Nitto Denko Corporation's "Nitoflon," thickness: 50 μm). In this case, the number of prepregs was 2 when preparing a cured sheet for CTExy measurement, and 10 when preparing a cured sheet for CTEz measurement. In addition, when preparing cured sheets for Tg measurement and dielectric property measurement, the number of prepregs was 1 in both cases.

[0104] Next, the prepreg, sandwiched between two fluororesin sheets, was placed in a press machine at a press temperature of 100°C and a press pressure of 0.5 MPa(G). The press temperature was then increased at a heating rate of 3°C / min. When the press temperature reached 140°C, the press pressure was increased to 3.0 MPa(G). The press temperature was then increased to 200°C at a heating rate of 3°C / min. After the press temperature reached 200°C, the pressing was continued for 75 minutes at a press temperature of 200°C and a press pressure of 3.0 MPa(G) to obtain a cured sheet, which is the cured product of the prepreg.

[0105] <Preparation of Copper-Clad Laminates> Using the prepregs obtained in each example and comparative example, copper-clad laminates for heat resistance evaluation were prepared according to the following method. First, one prepreg sheet was sandwiched between two electrolytic copper foils (Fukuda Metal Foil & Powder Industry Co., Ltd. "CF-T49A-DS-HD2-18", thickness: 18 μm, laminate surface roughness Rz: 0.42 μm, laminate surface roughness Ra: 0.06 μm) on their laminated (matte) sides. Next, the prepreg sandwiched between the two electrolytic copper foils was set in a press machine at a press temperature of 100°C and a press pressure of 0.5 MPa (G), and the press temperature was increased at a heating rate of 3°C / min. When the press temperature reached 140°C, the press pressure was increased to 3.0 MPa (G). Then, the press temperature was increased to 200°C at a heating rate of 3°C / min. Then, after the press temperature reached 200°C, the pressing was continued for 75 minutes under the conditions of a press temperature of 200°C and a press pressure of 3.0 MPa(G) to obtain a copper-clad laminate having a cured prepreg and two copper layers (layers made of electrolytic copper foil) arranged on both main surfaces of the cured prepreg.

[0106] <Measurement Method and Evaluation Method> [Viscosity of Curable Compositions] The viscosity of each curable composition was measured using a B-type viscometer (Tokyo Keiki Co., Ltd. "B8L", rotor: No. 2, rotation speed: 30 rpm) in an atmosphere at a temperature of 30°C.

[0107] [Prepreg Appearance] Each prepreg was cut to a size of 100 mm x 200 mm to obtain samples for evaluating the appearance of the prepreg. The surface of the obtained samples was observed with an optical microscope, and the number of foreign matter with a diameter of 0.5 mm or more, which was caused by poor dispersion, was counted. If the number of foreign matter was less than 3, it was evaluated as "A (good appearance)", and if the number of foreign matter was 3 or more, it was evaluated as "B (poor appearance)".

[0108] [Coefficient of thermal expansion in the planar direction (CTExy)] CTExy was measured using a thermomechanical analyzer (NETZSCH "TMA4000SA") by the tensile load method. Specifically, each hardened sheet was cut to a size of 5 mm x 10 mm to obtain a sample for measurement. Then, using the above thermomechanical analyzer, the sample was heated to 300°C at a heating rate of 10°C / min under a nitrogen gas stream, then cooled to 20°C at a cooling rate of 20°C / min, and then heated again to 300°C at a rate of 10°C / min to obtain a thermomechanical analysis chart. Of the obtained thermomechanical analysis charts, the temperature at 40°C (T) during the second heating was used. １ The length of the sample in the longitudinal direction (L) １ ) and the temperature during the second heating cycle was 125°C (T ２ The length of the sample in the longitudinal direction (L) ２ ) was read. Then, the length in the longitudinal direction of the sample before analysis (L ０ ) and T １ , T ２ , L １ and L ２ Therefore, the formula "CTExy = (L ２ -L １ ) / {L ０ (T ２ -T １ CTExy was calculated according to the following:

[0109] [Coefficient of thermal expansion in the thickness direction (CTEz)] CTEz was measured using a thermomechanical analyzer (TMA8310, Rigaku Corporation) by the compression load method. Specifically, each hardened sheet was cut to a size of 5 mm x 5 mm (thickness: 0.8 mm) to obtain a sample for measurement. Then, using the above thermomechanical analyzer, the sample was heated to 300°C at a heating rate of 10°C / min under a nitrogen gas flow, then cooled to 25°C at a cooling rate of 8°C / min, and then heated again to 300°C at a rate of 10°C / min to obtain a thermomechanical analysis chart. Of the obtained thermomechanical analysis charts, the temperature at 50°C (T) during the second heating was used. ３ Sample thickness (L) ３ ) and the temperature during the second heating cycle was 100°C (T ４ Sample thickness (L) ４ ) was read. And the sample thickness (L) before analysis was read. ５ ) and T ３ , T ４ , L３ and L ４ Therefore, the formula "CTEz = (L ４ -L ３ ) / {L ５ (T ４ -T ３ The CTEz was determined according to the following criteria. If the CTEz was 70 ppm / K or less, it was evaluated as having "excellent low thermal expansion properties." On the other hand, if the CTEz exceeded 70 ppm / K, it was evaluated as "not having excellent low thermal expansion properties."

[0110] [Glass Transition Temperature (Tg)] The dynamic viscoelasticity of each cured sheet was measured under the following conditions in an air atmosphere using a dynamic viscoelasticity measuring device (TA Instruments "DMS8100"). A graph was created plotting the loss tangent (tanδ) against the measurement temperature. The peak temperature of the obtained graph (the peak temperature of tanδ) was defined as the glass transition temperature. • Width of the measurement sample: 5 mm • Distance between grips: 10 mm • Measurement temperature range: 25°C to 300°C • Heating rate: 5°C / min • Strain amplitude: 10 μm • Measurement frequency: 10 Hz

[0111] [Dielectric Loss Tangent and Relative Permittivity] First, the hardened sheet to be evaluated was cut to a size of 30 mm x 40 mm to obtain a test specimen. The obtained test specimen was left to stand for 24 hours in an atmosphere of 23°C and 50% relative humidity. Next, the dielectric loss tangent and relative permittivity of the test specimen after the 24-hour standing period were measured using a network analyzer (KEYSIGHT N5222B) and a split cylinder resonator (EM Lab CR-740). The measurement conditions were as follows: • Measurement frequency: 40 GHz • Temperature: 23°C • Relative humidity: 50%

[0112] If the measured dielectric loss tangent was less than 0.0040, it was evaluated as "the dielectric loss tangent has been reduced." On the other hand, if the measured dielectric loss tangent was 0.0040 or higher, it was evaluated as "the dielectric loss tangent has not been reduced."

[0113] [Heat Resistance] First, the copper-clad laminate to be evaluated was cut to a size of 50 mm x 50 mm to obtain test specimens. The obtained test specimens were left to stand for 24 hours in an atmosphere of 23°C and 50% relative humidity. Next, the test specimens that had stood for 24 hours were heated in a hot air oven at a temperature of 280°C for 1 hour. After heating, the test specimens were visually inspected for the presence or absence of blistering and peeling of the copper-clad laminate, and judged according to the following criteria: A: No blistering or peeling was observed. B: Blistering or peeling was observed in only one place. C: Other than A and B.

[0114] If the result was A or B, it was evaluated as having "excellent heat resistance." On the other hand, if the result was C, it was evaluated as having "poor heat resistance."

[0115] <Results> For Examples 1 to 29 and Comparative Examples 1 to 10, the viscosity of the curable composition, evaluation results of the prepreg appearance, CTExy, CTEz, Tg, dielectric loss tangent, relative permittivity, and heat resistance determination results are shown in Tables 5 to 7. In Tables 5 to 7, "viscosity" refers to the viscosity of the curable composition.

[0116]

[0117]

[0118]

[0119] The curable compositions used in Examples 1 to 29 contained a graft-modified styrene elastomer graft-modified with a specific aromatic vinyl monomer and an unsaturated compound having two or more radically polymerizable carbon-carbon unsaturated double bonds in one molecule. As shown in Tables 5 and 6, the CTEz in Examples 1 to 29 was 70 ppm / K or less. Therefore, the cured sheets of Examples 1 to 29 exhibited excellent low thermal expansion. In Examples 1 to 29, the measured dielectric loss tangent was less than 0.0040. Therefore, the cured sheets of Examples 1 to 29 were able to reduce the dielectric loss tangent. In Examples 1 to 29, the heat resistance evaluation result was A or B. Therefore, the copper-clad laminates of Examples 1 to 29 exhibited excellent heat resistance.

[0120] The curable compositions used in Comparative Examples 1 to 10 did not contain graft-modified styrene elastomers graft-modified with specific aromatic vinyl monomers. As shown in Table 7, in Comparative Example 7, the CTEz exceeded 70 ppm / K. Therefore, the cured sheet of Comparative Example 7 did not exhibit excellent low thermal expansion. In Comparative Examples 1 and 8 to 10, the measured dielectric loss tangent was 0.0040 or higher. Therefore, the cured sheets of Comparative Examples 1 and 8 to 10 failed to reduce the dielectric loss tangent. In Comparative Examples 2 to 6 and 8, the heat resistance evaluation result was C. Therefore, the copper-clad laminates of Comparative Examples 2 to 6 and 8 did not exhibit excellent heat resistance.

[0121] From the above results, it has been shown that, according to the present invention, it is possible to form a cured product that is excellent in heat resistance and low thermal expansion while reducing the dielectric loss tangent.

Claims

1. A curable composition comprising a graft-modified styrene-based elastomer graft-modified with an aromatic vinyl monomer and an unsaturated compound having two or more radical-polymerizable carbon-carbon unsaturated double bonds in one molecule, wherein the aromatic vinyl monomer is a compound represented by the following general formula (1). (In the general formula (1), R １ , R ２ , R ３ , R ４ , R ５ , and R ６ each independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms, provided that at least one of R ２ , R ３ , R ４ , R ５ , and R ６ represents an alkyl group having 1 to 6 carbon atoms.) 2. The curable composition according to claim 1, wherein the grafting rate of the aromatic vinyl monomer is 0.05% by weight or more and 30% by weight or less.

3. The curable composition according to claim 1, wherein the unsaturated compound has two or more functional groups selected from the group consisting of vinyl group, vinylbenzyl group, styryl group, (meth)acryloyl group, maleimide group, and allyl group in one molecule.

4. The curable composition according to claim 1, wherein the amount of the graft-modified styrene elastomer is 1 part by weight or more and 50 parts by weight or less per 100 parts by weight of the unsaturated compound.

5. A cured product of the curable composition according to any one of claims 1 to 4.

6. A prepreg comprising a fiber sheet and a semi-cured product of a curable composition according to any one of claims 1 to 4 impregnated into the fiber sheet.

7. A metal-clad laminate having a cured prepreg according to claim 6 and a metal layer disposed on at least one main surface of the cured prepreg.

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