Graft-modified styrenic elastomer and curable composition

Abstract

This graft-modified styrenic elastomer is graft-modified by an aromatic vinyl monomer having no polar group. In the graft-modified styrenic elastomer, the graft ratio of the aromatic vinyl monomer is 0.5 mass% or more. The graft ratio of the aromatic vinyl monomer is preferably 10.0 mass% or less. This curable composition contains a base material and the graft-modified styrenic elastomer. The base material preferably includes a poly(phenylene ether).

Description

Grafted styrene-based elastomer and curable composition

[0001] The present invention relates to a graft-modified styrene-based elastomer and a curable composition.

[0002] In recent years, in communication devices such as smartphones and electronic devices such as next-generation TVs, it has been required to transmit and receive large amounts of data at high speed. Along with this, the high-frequency of electrical signals has been progressing. Specifically, in the field of wireless communication, when introducing the fifth-generation mobile communication system, the use of a high-frequency band of 10 GHz or more is being considered.

[0003] However, as the frequency of the signal used increases, the quality of the output signal, which may cause misrecognition of information, deteriorates, that is, the transmission loss increases. For the purpose of reducing this transmission loss, a low-dielectric material with a low dielectric tangent is required as an insulating material for constructing the material of the wiring board (substrate material). Under such circumstances, in order to obtain a low-dielectric material used in a high-frequency band, it has been proposed to use a styrene-based thermoplastic elastomer as a modifier. Specifically, a resin composition has been proposed that contains a modified polyphenylene ether whose terminal is modified with a specific radically polymerizable functional group as a base material and is blended with a specific styrene-based thermoplastic elastomer for the purpose of improving dielectric properties (see Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2023-001134

[0005] However, even when a low-dielectric material is used as the material of the substrate, if a communication device or an electronic device incorporating the substrate is stored in a high-temperature environment such as inside a vehicle for a long time, the dielectric tangent of the substrate material increases, and it may be difficult to reduce the transmission loss. It is difficult to reduce the dielectric tangent after being exposed to a high-temperature environment for a long time (hereinafter, sometimes simply referred to as "dielectric tangent at high temperature") only by the technique described in Patent Document 1.

[0006] In view of the above, an object of the present invention is to provide a graft-modified styrene-based elastomer capable of reducing the dielectric tangent at high temperature, and a curable composition containing the graft-modified styrene-based elastomer.

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

[0008] [1] A graft-modified styrene elastomer that is graft-modified with an aromatic vinyl monomer, wherein the aromatic vinyl monomer does not have polar groups, and the grafting rate of the aromatic vinyl monomer is 0.5% by mass or more.

[0009] [2] The graft-modified styrene elastomer according to [1], wherein the graft rate of the aromatic vinyl monomer is 10.0% by mass or less.

[0010] [3] The graft-modified styrene elastomer according to [1] or [2], wherein the polar group is one or more selected from the group consisting of epoxy group, glycidyl group, amino group, cyano group, acid anhydride group, hydroxyl group and carboxyl group.

[0011] [4] The graft-modified styrene elastomer according to any one of [1] to [3], wherein the content of constituent units derived from polar group-containing monomers is 0.15% by mass or less with respect to the total amount of the graft-modified styrene elastomer.

[0012] [5] The graft-modified styrene elastomer according to any one of [1] to [4] above, wherein the dielectric loss tangent at 40 GHz after being left standing for 100 hours in an environment of 125°C is less than 0.0009.

[0013] [6] A curable composition comprising a base material and a graft-modified styrene elastomer according to any one of [1] to [5] above.

[0014] [7] The base material is the curable composition according to [6], comprising polyphenylene ether.

[0015] [8] A curable composition according to [6] or [7], used as a substrate material.

[0016] According to the present invention, it is possible to provide a graft-modified styrene-based elastomer that can reduce the dielectric loss tangent at high temperatures, and a curable composition containing the graft-modified styrene-based elastomer.

[0017] 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.

[0018] 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 mass%) of constituent units derived from aromatic vinyl monomers bonded by graft polymerization relative to the total amount (100% by mass) 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. "Number average molecular weight" refers to the number average molecular weight (Mn) on a standard polystyrene basis, measured by gel permeation chromatography. "Resin" refers to a polymer with a number average molecular weight of 10,000 or more.

[0019] Unless otherwise specified, the "main component" of a material refers to the component that is present in the largest quantity by mass.

[0020] In the following, the compound name may be followed by "system" to comprehensively refer to the compound and its derivatives. Also, 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 derivative. Furthermore, acrylic and methacrylic may be comprehensively referred to as "(meth)acrylic." Furthermore, acrylate and methacrylate may be comprehensively referred to as "(meth)acrylate." Furthermore, acryloyl and methacryloyl may be comprehensively referred to as "(meth)acryloyl."

[0021] Unless otherwise specified, the components and functional groups exemplified herein may be used individually or in combination of two or more.

[0022] <First Embodiment: Graft-Modified Styrene Elastomer> The graft-modified styrene elastomer according to the first embodiment of the present invention (hereinafter sometimes referred to as "graft-modified styrene elastomer A") is a graft-modified styrene elastomer that has been graft-modified with an aromatic vinyl monomer. The aromatic vinyl monomer does not have a polar group (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). Furthermore, in graft-modified styrene elastomer A, the grafting rate of the aromatic vinyl monomer is 0.5% by mass or more. Hereinafter, an aromatic vinyl monomer that does not have a polar group may simply be referred to as "aromatic vinyl monomer".

[0023] Graft-modified styrene elastomer A can reduce the dielectric loss tangent at high temperatures. The reason for this is presumed to be as follows.

[0024] Graft-modified styrene elastomer A is graft-modified with aromatic vinyl monomers, and since the grafting rate of aromatic vinyl monomers is 0.5% by mass or more, it tends to have high heat resistance. Furthermore, in graft-modified styrene elastomer A, the constituent units derived from aromatic vinyl monomers bonded by graft polymerization do not have polar groups, thus suppressing moisture absorption, which causes an increase in dielectric loss tangent. For these reasons, graft-modified styrene elastomer A can reduce the dielectric loss tangent at high temperatures of materials containing graft-modified styrene elastomer A. To further reduce the dielectric loss tangent at high temperatures, it is preferable that the constituent units derived from aromatic vinyl monomers bonded by graft polymerization do not have any epoxy groups, glycidyl groups, amino groups, cyano groups, acid anhydride groups, hydroxyl groups, or carboxyl groups.

[0025] In the first embodiment, in order to further reduce the dielectric loss tangent at high temperatures by improving heat resistance, the graft rate of aromatic vinyl monomers is preferably 0.6% by mass or more, more preferably 0.7% by mass or more, even more preferably 0.8% by mass or more, even more preferably 0.9% by mass or more, and may be 1.0% by mass or more, 1.1% by mass or more, or 1.2% by mass or more.

[0026] In the first embodiment, in order to further reduce the dielectric loss tangent at high temperatures by reducing the dielectric loss tangent before prolonged exposure to high-temperature environments, the graft rate of aromatic vinyl monomers is preferably 10.0% by mass or less, more preferably 9.0% by mass or less, even more preferably 8.5% by mass or less, and even more preferably 8.2% by mass or less.

[0027] To further reduce transmission loss in high-temperature environments, the dielectric loss tangent of graft-modified styrene-based elastomer A at 40 GHz after being left standing for 100 hours at a temperature of 125°C is preferably less than 0.0015, more preferably less than 0.0009, and even more preferably less than 0.0006. Hereinafter, the dielectric loss tangent at 40 GHz after being left standing for 100 hours at a temperature of 125°C may be referred to as the "specific high-temperature dielectric loss tangent." The method for measuring the specific high-temperature dielectric loss tangent is the same as or similar to the method used in the examples described later. The lower limit of the specific high-temperature dielectric loss tangent of graft-modified styrene-based elastomer A is not particularly limited, but for example, it is 0.0001 or higher.

[0028] The following describes the details of graft-modified styrene-based elastomer A. In the following, the styrene-based elastomer before graft modification may be referred to as the "core polymer."

[0029] Examples of the core polymer constituting the graft-modified styrene-based elastomer A include a styrene-based elastomer having a polystyrene-based block containing constituent units derived from styrene-based monomers and a block (elastomer block) containing constituent 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 mass or more and 45% by mass or less based on the total amount of the core polymer (100% by mass).

[0030] 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-tert-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.

[0031] 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.

[0032] As the styrene-based elastomer that will serve as the core polymer, from the viewpoint of ease of graft polymerization, 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 are preferred, one or more selected from the group consisting of styrene-ethylene-propylene-styrene copolymer elastomer and styrene-ethylene-butylene-styrene copolymer elastomer are more preferred, and styrene-ethylene-propylene-styrene copolymer elastomer is even more preferred.

[0033] The aromatic vinyl monomer used to form the graft-modified styrene-based elastomer A by graft-modifying the stem polymer is not particularly limited, as long as it does not have polar groups and is an aromatic vinyl monomer that can be bonded to the stem polymer by graft polymerization. Examples include styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, α-methylstyrene, 4-chlorostyrene, α-chlorostyrene, dichlorostyrene, 4-bromostyrene, dibromostyrene, 4-fluorostyrene, difluorostyrene, 1,2-divinylbenzene, 1,3-divinylbenzene, and 1,4-divinylbenzene. To further reduce the dielectric loss tangent at high temperatures, the aromatic vinyl monomer used to form the graft-modified styrene-based elastomer A is preferably one or more selected from the group consisting of styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, and α-methylstyrene, more preferably one or more selected from the group consisting of styrene, 2-methylstyrene, 3-methylstyrene, and 4-methylstyrene, and even more preferably one or more selected from the group consisting of styrene and 4-methylstyrene. To further reduce the dielectric loss tangent at high temperatures, it is preferable to use only aromatic vinyl monomers without polar groups as monomers for graft-modified styrene-based elastomer A by graft-modifying the stem polymer. In other words, to further reduce the dielectric loss tangent at high temperatures, it is preferable that graft-modified styrene-based elastomer A is graft-modified using only aromatic vinyl monomers without polar groups.

[0034] The method for graft-modifying styrene-based elastomers (stem polymers) (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 an aromatic vinyl monomer in the presence of a radical polymerization initiator. Methods for this reaction include melt-kneading using a kneader or extruder, or reacting in solution.

[0035] Examples of radical polymerization initiators that can be used when graft-modifying styrene-based elastomers (stem polymers) include methyl ethyl ketone peroxide, methyl acetacetate peroxide, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,2-bis(tert-butylperoxy)butane, 1,3-di(tert-butylperoxyisopropyl)benzene, permethane hydroperoxide, cumene hydroperoxide, dicumyl peroxide, di-tert-butyl peroxide, benzoyl peroxide, di(3-methyl-3-methoxybutyl)peroxydicarbonate, di-2-methoxybutyl peroxydicarbonate, tert-butyl peroxyoctate, tert-butyl peroxyisobutyrate, and di-tert-butyl peroxyisophthalate. The above radical polymerization initiators can be used individually or in combination of two or more.

[0036] 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 mass or more and 10 parts by mass or less, and more preferably 0.2 parts by mass or more and 5 parts by mass or less, per 100 parts by mass of styrene-based elastomer (core polymer).

[0037] Graft-modified styrene elastomer A may have constituent units derived from polar group-containing monomers, to the extent that it does not impede the expression of its effects. Examples of polar groups in polar group-containing monomers include one or more selected from the group consisting of epoxy groups, glycidyl groups, amino groups, cyano groups, acid anhydride groups, hydroxyl groups, and carboxyl groups. Constituent units derived from polar group-containing monomers may be formed by graft polymerization or incorporated into the stem polymer.

[0038] As the above polar group-containing monomer, a polar group-containing unsaturated compound having a polar group and an ethylenically unsaturated bond is preferred. Examples of polar group-containing unsaturated compounds include unsaturated group-containing epoxy compounds such as glycidyl (meth)acrylate, monoglycidyl maleate, diglycidyl maleate, monoglycidyl itaconic acid, monoglycidyl allylsuccinate, allylglycidyl ether, methacrylic glycidyl ether, 3,4-epoxy-1-butene, 3,4-epoxy-3-methyl-1-butene, and vinylcyclohexene monooxide; unsaturated amines such as allylamine, methallylamine, and 1-amino-4-pentene; cyano group-containing unsaturated compounds such as acrylonitrile; unsaturated group-containing acid anhydrides such as maleic anhydride, vinylsuccinic anhydride, and allylsuccinic anhydride; hydroxyl group-containing unsaturated compounds such as 2-hydroxyethyl (meth)acrylate, allyl alcohol, methallyl alcohol, and 1-butenyl alcohol; and unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, fumaric acid, itaconic acid, and crotonic acid.

[0039] When using aromatic vinyl monomers and polar group-containing unsaturated compounds in combination as monomers for graft modification of the stem polymer, the stem polymer can be graft modified with both aromatic vinyl monomers and polar group-containing unsaturated compounds, as seen in the graft-modified styrene-based elastomers used in Examples 3 to 5 and 9 described later.

[0040] To further reduce the dielectric loss tangent at high temperatures, the content of constituent units derived from polar group-containing monomers is preferably 0.20% by mass or less, more preferably 0.15% by mass or less, even more preferably 0.10% by mass or less, and may also be 0.09% by mass or less, 0.08% by mass or less, 0.07% by mass or less, 0.06% by mass or less, or 0.05% by mass or less, based on the total amount (100% by mass) of the graft-modified styrene-based elastomer A. To further reduce the dielectric loss tangent at high temperatures, it is preferable that the graft-modified styrene-based elastomer A does not contain constituent units derived from polar group-containing monomers. Hereinafter, the content of constituent units derived from polar group-containing monomers relative to the total amount (100% by mass) of the graft-modified styrene-based elastomer or styrene-based elastomer may be referred to as the "polar unit content". The method for measuring the polar unit content is the same as or similar to the method described in the examples below.

[0041] When using graft-modified styrene elastomer A as a substrate material, in order to improve the adhesion between the substrate material and the metal foil, the polarity unit content is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more.

[0042] To further reduce the dielectric loss tangent at high temperatures while improving handling ease, the number average molecular weight of graft-modified styrene-based elastomer A is preferably 10,000 to 150,000, and more preferably 50,000 to 100,000.

[0043] In order to further reduce the dielectric loss tangent at high temperatures, it is preferable that the graft-modified styrene-based elastomer A satisfies the following condition 1, more preferably satisfies the following condition 2, and even more preferably satisfies the following condition 3. Condition 1: The graft ratio of the aromatic vinyl monomer is 0.5% by mass or more and 9.0% by mass or less. Condition 2: The above condition 1 is satisfied, and the polar unit content rate is 0.15% by mass or less. Condition 3: The above condition 2 is satisfied, and the aromatic vinyl monomer for graft-modifying the base polymer to form the graft-modified styrene-based elastomer A is one or more selected from the group consisting of styrene, 2-methylstyrene, 3-methylstyrene, and 4-methylstyrene.

[0044] Since the graft-modified styrene-based elastomer A can reduce the dielectric loss tangent at high temperatures, it is suitable as a low-dielectric material used in the high-frequency band. When the graft-modified styrene-based elastomer A is used as a low-dielectric material, the graft-modified styrene-based elastomer A may be used alone or as a main component, or may be used as a modifier (additive for reducing the dielectric loss tangent at high temperatures) added to other materials (base materials). Hereinafter, a curable composition (curable composition according to the second embodiment of the present invention) using the graft-modified styrene-based elastomer A as a modifier will be described.

[0045] <Second Embodiment: Curable Composition> The curable composition according to the second embodiment of the present invention (hereinafter, may be referred to as "curable composition C") includes a base material and a graft-modified styrene-based elastomer A. Since the curable composition C contains the graft-modified styrene-based elastomer A, the dielectric loss tangent at high temperatures can be reduced. In the following description, the description of the content overlapping with the first embodiment may be omitted.

[0046] In the second embodiment, in order to further reduce the dielectric loss tangent at high temperatures, it is preferable that the amount of the graft-modified styrene-based elastomer A is 5 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the base material.

[0047] The base material is one or more selected from the group consisting of, for example, resins and curable compounds (compounds different from resins). Typical examples of curable compounds include radical polymerizable compounds and cationic polymerizable compounds. Radical polymerizable compounds will be described later. Examples of cationic polymerizable compounds include epoxy compounds, oxetane compounds, and vinyl ether compounds. The curable composition C may contain a curing agent depending on the type of base material.

[0048] When the base material contains both a resin and a curable compound, the amount of the curable compound is preferably 20 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the resin, from the viewpoint of the ease of curing of the curable composition C.

[0049] When the base material contains a resin, one or more resins selected from the group consisting of polyphenylene ether resins, polyolefin resins, and styrene-based elastomers (elastomers different from graft-modified styrene-based elastomer A) are preferred as the usable resin due to their good dielectric properties in the high-frequency range. When the base material contains only a resin, a resin having polymerizable groups (e.g., radical polymerizable groups, cationic polymerizable groups, etc.) is preferred as the resin.

[0050] To further reduce the dielectric loss tangent at high temperatures, the base material preferably contains polyphenylene ether. The polyphenylene ether may be a polyphenylene ether resin with a number average molecular weight of 10,000 or more, or a polyphenylene ether with a number average molecular weight of less than 10,000. From the viewpoint of ease of curing of curable composition C, a modified polyphenylene ether having a carbon-carbon unsaturated double bond-containing group is preferred as the polyphenylene ether. Polyphenylene ethers usually have hydroxyl groups bonded to aromatic rings at the ends of their molecular chains. A modified polyphenylene ether can be obtained by substituting the hydrogen atoms in these terminal hydroxyl groups with a carbon-carbon unsaturated double bond-containing group. Such a modified polyphenylene ether may be a modified polyphenylene ether resin with a number average molecular weight of 10,000 or more, or a modified polyphenylene ether with a number average molecular weight of less than 10,000. A modified polyphenylene ether with a number average molecular weight of less than 10,000 is a curable compound in that it has a carbon-carbon unsaturated double bond-containing group. The carbon-carbon unsaturated double bond-containing group is preferably one or more selected from the group consisting of vinylbenzyl group, vinyl group, allyl group, and (meth)acryloyl group.

[0051] The molecular weight of the modified polyphenylene ether is not particularly limited as long as the desired effect is not impaired. The molecular weight of the modified polyphenylene ether is preferably 1000 or more, and more preferably 2000 or more, as a number-average molecular weight (Mn).

[0052] The curable composition C may be a radical polymerizable composition. That is, the curable composition C may contain a radical polymerizable compound and a radical polymerization initiator. The radical polymerizable compound may be a monofunctional compound having one radical polymerizable group or a polyfunctional compound having two or more radical polymerizable groups, with polyfunctional compounds being preferred. The radical polymerizable group is not particularly limited, but is typically a carbon-carbon unsaturated double bond-containing group. Suitable examples of carbon-carbon unsaturated double bond-containing groups include alkenyl groups such as vinyl groups, allyl groups, and methallyl groups; (meth)acryloyl groups; and maleimide groups.

[0053] Suitable examples of radical polymerizable compounds include triallyl cyanurate, triallyl isocyanurate, trimethallyl isocyanurate, trimethylolpropane tri(meth)acrylate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, triallyl trimellitate, 1,3-phenylenediamine bismaleimide, p-quinone dioxime, p,p'-dibenzoylquinone dioxime, dipropargyl terephthalate, diallyl phthalate, and the like.

[0054] Any known radical polymerization initiator can be used without particular limitation as the radical polymerization initiator. Suitable specific examples of radical polymerization initiators are the same as the specific examples of radical polymerization initiators that can be used when graft-modifying styrene-based elastomers as described above. The above radical polymerization initiators can be used alone or in combination of two or more.

[0055] Inorganic fillers may be added to the curable composition C as needed. Examples of inorganic fillers include calcium carbonate, talc, clay, silica, magnesium carbonate, barium sulfate, titanium dioxide, alumina, montmorillonite, gypsum, glass flakes, glass fibers, milled glass fibers, carbon fibers, alumina fibers, silica-alumina fibers, aluminum borate whiskers, and potassium titanate fibers. Inorganic fillers may be used alone or in combination of two or more types.

[0056] The amount of these inorganic fillers used is not particularly limited, as long as the desired effect is not impaired. The amount of baseless filler used is preferably 10 parts by mass or more and 200 parts by mass or less, and more preferably 20 parts by mass or more and 100 parts by mass or less, per 100 parts by mass of base material.

[0057] The curable composition C may optionally contain various additives such as organic solvents, organic fillers, antioxidants, heat stabilizers, light stabilizers, flame retardants, lubricants, antistatic agents, colorants, rust inhibitors, crosslinking agents, foaming agents, fluorescent agents, surface smoothing agents, surface gloss improvers, and mold release improvers. These additives may be used individually or in combination of two or more.

[0058] A cured product is formed by curing the curable composition C described above using a curing method (radical polymerization, cationic polymerization, etc.) appropriate to the type of base material. Since the cured product of curable composition C is obtained using graft-modified styrene-based elastomer A, the dielectric loss tangent at high temperatures can be reduced and it has excellent heat resistance.

[0059] The cured product of curable composition C is suitably used as a substrate material. Preferred substrate materials include sheets made from the cured product of curable composition C, and prepregs consisting of a fiber sheet and the cured product of curable composition C impregnated into the fiber sheet. The method for forming the sheet made from the cured product of curable composition C is not particularly limited. If curable composition C is a varnish-like composition, for example, a sheet made from the cured product of curable composition C can be formed by a solution casting method. Furthermore, the prepreg can be formed, for example, by impregnating a fiber sheet such as glass cloth with a radically polymerizable curable composition C, and then curing the curable composition C impregnated into the fiber sheet by a curing method such as heating or exposure.

[0060] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0061] <Synthesis of Styrene Elastomers> [Synthesis of Styrene Elastomer A1] 100 parts by mass of styrene-ethylene-propylene-styrene copolymer elastomer (SEPTON2002, manufactured by Kuraray Co., Ltd., polystyrene block content: 30% by mass 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 parts by mass of 4-methylstyrene (manufactured by Jiangsu Changqingshu New Materials Technology Co., Ltd., purity: 99% or higher) and 0.5 parts by mass of 1,3-di(tert-butylperoxyisopropyl)benzene (Perbutyl P, manufactured by NOF Corporation) were added to the kneading section, and kneaded at 180°C for 3 minutes. Then, the contents of the kneading section were dissolved in toluene, and reprecipitation in methanol was performed to remove unreacted monomers. Next, the precipitate was dried under reduced pressure at 60°C for 12 hours to obtain styrene-based elastomer A1, which is a graft-modified styrene-based elastomer.

[0062] [Synthesis of Styrene Elastomer A2] Styrene elastomer A2, a graft-modified styrene elastomer, was obtained by the same method as the synthesis of styrene elastomer A1, except that the amount of 4-methylstyrene was 10 parts by mass per 100 parts by mass of styrene-ethylene-propylene-styrene copolymer elastomer.

[0063] [Synthesis of Styrene Elastomer A3] 100 parts by mass of styrene-ethylene-propylene-styrene copolymer elastomer (SEPTON2002, manufactured by Kuraray Co., Ltd., polystyrene block content: 30% by mass relative to 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 parts by mass of 4-methylstyrene (manufactured by Jiangsu Changqingshu New Materials Technology Co., Ltd., purity: 99% or higher), 0.15 parts by mass of glycidyl methacrylate, and 0.5 parts by mass of 1,3-di(tert-butylperoxyisopropyl)benzene (Perbutyl P, manufactured by NOF Corporation) were placed in 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 styrene-based elastomer A3, which is a graft-modified styrene-based elastomer.

[0064] [Synthesis of Styrene Elastomer A4] Styrene elastomer A4, a graft-modified styrene elastomer, was obtained by the same method as the synthesis of styrene elastomer A3, except that the amount of glycidyl methacrylate was 0.25 parts by mass per 100 parts by mass of styrene-ethylene-propylene-styrene copolymer elastomer.

[0065] [Synthesis of Styrene Elastomer A5] Styrene elastomer A5, a graft-modified styrene elastomer, was obtained by the same method as the synthesis of styrene elastomer A3, except that the amount of glycidyl methacrylate was 1.00 part by mass per 100 parts by mass of styrene-ethylene-propylene-styrene copolymer elastomer.

[0066] [Synthesis of Styrene Elastomer A6] Styrene elastomer A6, a graft-modified styrene elastomer, was obtained by the same method as the synthesis of styrene elastomer A1, except that the amount of 4-methylstyrene was 2.5 parts by mass per 100 parts by mass of styrene-ethylene-propylene-styrene copolymer elastomer.

[0067] [Synthesis of Styrene Elastomer A7] Styrene elastomer A7, a graft-modified styrene elastomer, was obtained by the same method as the synthesis of styrene elastomer A1, except that the amount of 4-methylstyrene was 12 parts by mass per 100 parts by mass of styrene-ethylene-propylene-styrene copolymer elastomer, and the amount of 1,3-di(tert-butylperoxyisopropyl)benzene was 0.75 parts by mass per 100 parts by mass of styrene-ethylene-propylene-styrene copolymer elastomer.

[0068] [Synthesis of Styrene Elastomer A8] Styrene elastomer A8, a graft-modified styrene elastomer, was obtained using the same method as the synthesis of styrene elastomer A1, except that 5 parts by mass of styrene were used instead of 5 parts by mass of 4-methylstyrene.

[0069] [Synthesis of Styrene Elastomer A9] Styrene elastomer A9, a graft-modified styrene elastomer, was obtained using the same method as the synthesis of styrene elastomer A3, except that 5 parts by mass of styrene were used instead of 5 parts by mass of 4-methylstyrene.

[0070] [Synthesis of Styrene Elastomer A10] Styrene elastomer A10, a graft-modified styrene elastomer, was obtained by the same method as the synthesis of styrene elastomer A1, except that 100 parts by mass of styrene-ethylene-butylene-styrene copolymer elastomer ("ToughTec H1052" manufactured by Asahi Kasei Corporation, polystyrene block content: 19% by mass relative to the total amount of copolymer) was used instead of 100 parts by mass of styrene-ethylene-propylene-styrene copolymer elastomer.

[0071] [Preparation of Styrene Elastomer B1] 100 parts by mass of styrene-ethylene-propylene-styrene copolymer elastomer (SEPTON2002, manufactured by Kuraray Co., Ltd., polystyrene block content: 30% by mass relative to 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 then kneaded at a temperature of 180°C for 5 minutes to melt the styrene-ethylene-propylene-styrene copolymer elastomer. Next, the kneaded styrene-ethylene-propylene-styrene copolymer elastomer was dissolved in toluene and then reprecipitated in methanol. The precipitate was then dried under reduced pressure at a temperature of 60°C for 12 hours to obtain styrene elastomer B1. The above procedure was performed to equalize the thermal history of styrene elastomers A1 to A10 and styrene elastomer B1.

[0072] [Synthesis of Styrene Elastomer B2] Styrene elastomer B2, a graft-modified styrene elastomer, was obtained by the same method as the synthesis of styrene elastomer A1, except that the amount of 4-methylstyrene was 0.5 parts by mass per 100 parts by mass of styrene-ethylene-propylene-styrene copolymer elastomer.

[0073] <Method for measuring the physical properties of styrene-based elastomers> The following describes the method for measuring the physical properties of styrene-based elastomers A1 to A10, B1 and B2.

[0074] [Graft rate of aromatic vinyl monomers] First, the styrene elastomer to be measured (any of styrene elastomers A1 to A10, B1, and B2) was dissolved in methylene chloride to obtain a sample for graft 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 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. For styrene-based elastomer B1, the content of aromatic vinyl monomer relative to the total amount of styrene-based elastomer B1 before dissolution in dimethyl chloride was calculated.

[0075] [Polar Unit Content] In accordance with JIS K7236, the glycidyl group content of the styrene-based elastomers to be measured (any of styrene-based elastomers A1 to A10, B1, and B2) was measured using a potentiometric automatic titrator (AT700, manufactured by Kyoto Electronics Manufacturing Co., Ltd.). Then, from the obtained glycidyl group content, the content of constituent units derived from glycidyl methacrylate, which is a polar group-containing monomer, relative to the total amount (100% by mass) of the styrene-based elastomer (polar unit content) was calculated.

[0076] <Preparation of Evaluation Films> The methods for preparing evaluation films for Examples 1 to 10, Comparative Example 1, and Comparative Example 2 will be described below.

[0077] [Example 1] Styrene elastomer A1 was dissolved in toluene to obtain a coating solution with a solid content concentration of 15% by mass. Next, the coating solution was applied to a fluororesin sheet (Nitto Denko "Nitoflon", 50 μm thick) and dried using a hot plate at a temperature of 60°C for 10 minutes, followed by drying at a temperature of 90°C for 10 minutes. Then, the dried coating film was dried under reduced pressure in a vacuum oven at 60°C for 12 hours, after which the fluororesin sheet was peeled off to obtain an evaluation film with a thickness of 150 μm (evaluation film for Example 1).

[0078] [Examples 2-10, Comparative Example 1 and Comparative Example 2] Evaluation films for Examples 2-10, Comparative Example 1 and Comparative Example 2 were obtained in the same manner as in Example 1, except that the styrene elastomers listed in Table 1 described later were used instead of styrene elastomer A1.

[0079] <Method for Measuring Dielectric Loss Tangent at High Temperature> First, a 30 mm x 40 mm specimen was obtained by cutting one of the films to be evaluated (either the evaluation films from Examples 1-10, Comparative Example 1, or Comparative Example 2). The obtained specimen was subjected to a heat resistance test by being left standing for 100 hours in an oven set at 125°C. Next, the specimen after the heat resistance test was left standing for 24 hours in an atmosphere at 23°C and 50% relative humidity. Then, the dielectric loss tangent of the specimen after the 24-hour standing period was 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%

[0080] If the measured value of the above dielectric loss tangent (dielectric loss tangent under specific high temperatures) was less than 0.0015, it was evaluated as "the dielectric loss tangent under high temperatures has been reduced." On the other hand, if the measured value of the above dielectric loss tangent (dielectric loss tangent under specific high temperatures) was 0.0015 or higher, it was evaluated as "the dielectric loss tangent under high temperatures has not been reduced."

[0081] <Results> Table 1 shows the type of styrene-based elastomer used, the graft rate of aromatic vinyl monomers, the polar unit content, and the measured values ​​of the dielectric loss tangent at high temperature (specifically, the dielectric loss tangent at a specific high temperature) for Examples 1 to 10, Comparative Example 1, and Comparative Example 2.

[0082]

[0083] As shown in Table 1, in Examples 1 to 10, the grafting rate of aromatic vinyl monomers was 0.5% by mass or more. In Examples 1 to 10, the dielectric loss tangent at high temperatures was less than 0.0015. Therefore, the films using the graft-modified styrene-based elastomers in Examples 1 to 10 were able to reduce the dielectric loss tangent at high temperatures.

[0084] As shown in Table 1, the grafting rate of aromatic vinyl monomers in Comparative Examples 1 and 2 was less than 0.5% by mass. As shown in Table 1, the dielectric loss tangent at high temperatures in Comparative Examples 1 and 2 was 0.0015 or higher. Therefore, the films using styrene-based elastomers in Comparative Examples 1 and 2 were unable to reduce the dielectric loss tangent at high temperatures.

[0085] The results above demonstrate that the present invention can provide a graft-modified styrene-based elastomer that can reduce the dielectric loss tangent at high temperatures.

[0086] <Preparation of Curable Compositions> Next, the methods for preparing the curable compositions of Example 11 and Comparative Example 3 will be described.

[0087] [Example 11] 18 g of styrene-based elastomer A1, 47 g of modified polyphenylene ether (SABIC "Noryl SA9000", number average molecular weight: 1,700, carbon-carbon unsaturated double bond-containing group equivalent: 850 g / eq, polyphenylene ether modified with methacryloyl groups at both ends), 20 g of triallyl isocyanurate (Mitsubishi Chemical Corporation), 0.9 g of 1,3-di(tert-butylperoxyisopropyl)benzene (NOF Corporation "Perbutyl P"), 30 g of silica (Admatex "SC2300-SVJ", average particle size: 0.5 μm), and 160 g of toluene were combined to obtain the curable composition of Example 11.

[0088] [Comparative Example 3] A curable composition of Comparative Example 3 was obtained using the same preparation method as in Example 11, except that 18 g of styrene-based elastomer B1 was used instead of 18 g of styrene-based elastomer A1.

[0089] <Prepreg Preparation> Using the curable compositions of Example 11 and Comparative Example 3, prepregs were obtained according to the following method. Specifically, first, a 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 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 the prepreg of Example 11 and the prepreg of Comparative Example 3, respectively. The thickness of the prepreg of Example 11 and the prepreg of Comparative Example 3 were both 80 μm.

[0090] <Preparation of Copper-Clad Laminates> Using the prepregs from Example 11 and Comparative Example 3, 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.

[0091] <Heat Resistance Evaluation of Copper-Clad Laminates> 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 for 1 hour at a temperature of 280°C using a hot air oven. After heating, the test specimens were visually inspected for the presence or absence of blistering and peeling of the copper-clad laminate. No blistering or peeling was observed in the copper-clad laminate obtained using the prepreg of Example 11. On the other hand, blistering and peeling were observed in the copper-clad laminate obtained using the prepreg of Comparative Example 3.

Claims

1. A graft-modified styrene elastomer that is graft-modified with an aromatic vinyl monomer, wherein the aromatic vinyl monomer does not have polar groups, and the grafting rate of the aromatic vinyl monomer is 0.5% by mass or more.

2. The graft-modified styrene elastomer according to claim 1, wherein the graft rate of the aromatic vinyl monomer is 10.0% by mass or less.

3. The graft-modified styrene elastomer according to claim 1, wherein the polar group is one or more selected from the group consisting of epoxy group, glycidyl group, amino group, cyano group, acid anhydride group, hydroxyl group, and carboxyl group.

4. The graft-modified styrene elastomer according to claim 1, wherein the content of constituent units derived from polar group-containing monomers is 0.15% by mass or less with respect to the total amount of the graft-modified styrene elastomer.

5. The graft-modified styrene-based elastomer according to claim 1, wherein the dielectric loss tangent at 40 GHz after being left standing for 100 hours in an environment at a temperature of 125°C is less than 0.0009.

6. A curable composition comprising a base material and a graft-modified styrene elastomer according to any one of claims 1 to 5.

7. The curable composition according to claim 6, wherein the base material comprises polyphenylene ether.

8. The curable composition according to claim 6, used as a substrate material.

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