Syndiotactic polystyrene low dielectric sheet molded body

Abstract

[Problem] To provide a sheet molded body that has excellent dielectric properties and solder heat resistance, and that also exhibits a low dimensional change rate (low thermal shrinkage) and a low linear expansion coefficient. [Solution] A sheet molded body containing a styrene-based polymer (A) having a syndiotactic structure, a fibrous filler (C), and a non-fibrous filler (D), wherein: the sheet molded body is unstretched and contains 1-50 parts by mass of the fibrous filler (C) with respect to 100 parts by mass of the styrene-based polymer (A) having a syndiotactic structure; and the relative permittivity of the sheet molded body in a frequency band of 10 GHz is 3 or less.

Description

Syndiotactic polystyrene low dielectric sheet molding

[0001] The present invention relates to an unstretched sheet-shaped article containing a syndiotactic polystyrene polymer having excellent dielectric properties, more specifically to an unstretched sheet-shaped article containing a syndiotactic polystyrene polymer and having excellent solder heat resistance, low thermal shrinkage, and low linear expansion.

[0002] In recent years, there has been active development of materials and applications for high-speed information communications such as 5G, and in order to improve information transmission speeds, plastic materials with low dielectric constants and dielectric loss tangents at high frequencies above 10 GHz are required. Among these, syndiotactic polystyrene (SPS) resin has excellent dielectric properties, and is therefore expected to be widely adopted in circuit boards that require high-frequency characteristics in applications such as printed wiring boards and flexible printed wiring boards.

[0003] Such circuit boards are often exposed to high-temperature environments during use and manufacturing, and therefore generally require high heat resistance and dimensional stability. Heat resistance here refers to the ability to withstand the heat treatment conditions (e.g., 260°C, 120 seconds) present in the soldering process that is included in the manufacturing of circuit boards and electronic components.

[0004] Patent Document 1 discloses a method for producing a release film made of a biaxially oriented plastic film, in which a film containing 80% by weight or more of a syndiotactic polystyrene resin is biaxially stretched and then heat-treated at a predetermined temperature. Patent Document 2 discloses a laminate for printed wiring boards, in which 99 to 5% by weight of a molding material for printed wiring boards made of a styrene polymer having a highly syndiotactic structure and polar groups is laminated with 1 to 95% by weight of glass cloth surface-treated with a coupling agent.

[0005] Patent No. 5896753 JP 7-142830 Publication

[0006] However, biaxial stretching, as described in Patent Document 1, requires enormous capital investment for stretching and heat treatment, making it difficult to meet the cost requirements for film production. Furthermore, although stretching improves the film's properties by orienting and crystallizing it, the strain generated during stretching is not fully alleviated, resulting in a large dimensional change rate when the film is reheated at high temperatures. This makes it difficult to apply this method to applications requiring high dimensional stability, such as circuit boards. The laminate with glass cloth described in Patent Document 2 contains a large amount of glass cloth, which significantly deteriorates the dielectric properties, in addition to SPS modified with polar groups, making it difficult to use as a high-frequency circuit board. Furthermore, there are issues with in-plane thickness variation in the sheet and adhesion to the glass cloth interface, making this a poorly feasible method.

[0007] In view of the above circumstances, an object of the present invention is to provide a sheet molded article that is excellent in dielectric properties and solder heat resistance, and further exhibits a low dimensional change rate (low thermal shrinkage) and a low coefficient of linear expansion.

[0008] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention. That is, the present invention relates to a sheet molded body as set forth in the following claims.

[0009] [1] A sheet molded body containing a styrene-based polymer (A) having a syndiotactic structure, a fibrous filler (C), and a non-fibrous filler (D), wherein the sheet molded body is an unstretched sheet molded body, and contains 1 to 50 parts by mass of the fibrous filler (C) per 100 parts by mass of the styrene-based polymer (A) having a syndiotactic structure, and the sheet molded body has a relative dielectric constant of 3 or less in a 10 GHz frequency band. [2] The sheet molded body according to [1], which contains 1 to 40 parts by mass of a rubber-like elastomer (B) per 100 parts by mass of the styrene-based polymer (A) having a syndiotactic structure. [3] The sheet molded body according to [1] or [2], wherein the fibrous filler (C) is glass fiber having a D50 average fiber length of 40 to 4,000 μm. [4] The sheet molded body according to any one of [1] to [3], wherein the non-fibrous filler (D) is a granular or spherical filler having a D50 average particle size of 0.1 to 45 μm. [5] The sheet molded body according to any one of [1] to [4], wherein the rubber-like elastomer (B) contains a styrene-based or olefin-based thermoplastic elastomer. [6] The sheet molded body according to any one of [1] to [5], wherein the linear expansion coefficients of the sheet molded body in the machine direction (MD) and the transverse direction (TD) are 10 to 80 ppm / °C, and the MD / TD ratio is in the range of 0.6 to 1.4. [7] The sheet molded body according to any one of [1] to [6], wherein the absolute value of the dimensional change rate when the sheet molded body is heat-treated at 150°C for 30 minutes is less than 0.4%.

[0010] The sheet molded article of the present invention has excellent dielectric properties and solder heat resistance, and further exhibits low dimensional change (low thermal shrinkage) and a low coefficient of linear expansion, making it possible to provide an excellent sheet molded article that can satisfy the signal speed and dimensional stability at high temperatures required for high-frequency circuit boards.

[0011] <Styrenic polymer (A) having a syndiotactic structure> In the present invention, the syndiotactic structure in the styrenic polymer having a syndiotactic structure as component (A) (hereinafter also referred to as "SPS" or "syndiotactic polystyrene" or component (A)) is a stereochemical structure in which phenyl groups, which are side chains, are alternately positioned in opposite directions relative to a main chain formed from carbon-carbon bonds, and the tacticity is quantified by nuclear magnetic resonance (C-NMR) using a carbon isotope. Tacticity measured by C-NMR can be expressed by the proportion of multiple consecutive structural units present, for example, dyads when there are two, triads when there are three, and pentads when there are five. In the present invention, the styrene polymer having a syndiotactic structure refers to polystyrene, poly(alkylstyrene), poly(halogenated styrene), poly(halogenated alkylstyrene), poly(alkoxystyrene), poly(vinyl benzoate ester), hydrogenated polymers thereof, mixtures thereof, or copolymers containing these as the main component, having a syndiotacticity of preferably 75 mol % or more, more preferably 85 mol % or more in racemic dyads, or preferably 30 mol % or more, more preferably 50 mol % or more in racemic pentads.

[0012] Here, examples of poly(alkylstyrenes) include poly(methylstyrene), poly(ethylstyrene), poly(isopropylstyrene), poly(tert-butylstyrene), poly(phenylstyrene), poly(vinylnaphthalene), and poly(vinylstyrene), while examples of poly(halogenated styrenes) include poly(chlorostyrene), poly(bromostyrene), and poly(fluorostyrene). Examples of poly(halogenated alkylstyrenes) include poly(chloromethylstyrene), and examples of poly(alkoxystyrenes) include poly(methoxystyrene), poly(ethoxystyrene), and the like.

[0013] Among these, particularly preferred styrene-based polymers include polystyrene, poly(p-methylstyrene), poly(m-methylstyrene), poly(p-tert-butylstyrene), poly(p-chlorostyrene), poly(m-chlorostyrene), poly(p-fluorostyrene), hydrogenated polystyrene, and copolymers containing these structural units.

[0014] The styrene-based polymer (A) having a syndiotactic structure may be a copolymer of styrene having a syndiotactic structure and another monomer. The content of styrene having a syndiotactic structure in component (A) is preferably 50% by mass or more. It is more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 100% by mass. A content of styrene having a syndiotactic structure of 50% by mass or more results in excellent dielectric properties, solder heat resistance, dimensional change rate, and linear expansion coefficient. In particular, it is preferable to keep the content of unsaturated nitrile group-containing monomers low, as this may result in a deterioration in the above-mentioned performance. Specifically, it is preferably 2% by mass or less, more preferably less than 2% by mass, even more preferably 1% by mass or less, and particularly preferably 0% by mass.

[0015] The styrene polymer (A) having a syndiotactic structure may be used alone or in a mixture of two or more styrene polymers. There are no particular restrictions on the composition ratio of the styrene copolymer, but the content of substituted styrene units is preferably in the range of 3 to 50 mol%. If this content is 3 mol% or more, modification is easy, and if it is 50 mol% or less, compatibility with other components can be maintained.

[0016] The molecular weight of the styrene polymer (A) having a syndiotactic structure is not particularly limited, but the weight-average molecular weight is preferably 10,000 or more, more preferably 50,000 or more, and even more preferably 100,000 or more. Furthermore, there are no restrictions on the width of the molecular weight distribution, and various types can be used. By setting the weight-average molecular weight to 10,000 or more, the thermal and mechanical properties of the resulting composition or molded article are not reduced and good ones can be obtained. The upper limit is not particularly limited, but is preferably 500,000 or less, more preferably 400,000 or less.

[0017] The styrene polymer (A) having such a syndiotactic structure can be produced, for example, by polymerizing a styrene monomer (a monomer corresponding to the above-mentioned styrene polymer) in an inert hydrocarbon solvent or in the absence of a solvent using a condensation product of a titanium compound, water, and trialkylaluminum as a catalyst (JP-A-62-187708). Poly(halogenated alkylstyrene) can be obtained by the method described in JP-A-1-46912, and hydrogenated polymers thereof can be obtained by the method described in JP-A-1-178505.

[0018] The syndiotactic styrene polymer (A) preferably has a melt flow rate (MFR) measured at a temperature of 300°C under a load of 1.2 kg of 1 to 60 g / 10 min, more preferably 2 to 40 g / 10 min, even more preferably 3 to 30 g / 10 min, and most preferably 4 to 20 g / 10 min. By setting the melt flow rate within the above range, a sheet having good physical properties can be obtained, and the thickness of the sheet can be made uniform.

[0019] Representative commercially available examples of the styrene-based polymer (A) having a syndiotactic structure used in the present invention include XAREC (registered trademark) 142ZE, XAREC (registered trademark) 300ZC, XAREC (registered trademark) 130ZC, and XAREC (registered trademark) 90ZC manufactured by Idemitsu Kosan Co., Ltd. Among these resins, only one type may be used alone, or two or more types may be used in combination.

[0020] The styrene-based polymer (A) having a syndiotactic structure may be unmodified with a compound having a polar group (hereinafter also referred to as the unmodified (A) component), or may be modified (hereinafter also referred to as the modified (A) component). The (A) component may be the unmodified (A) component alone, the modified (A) component alone, or a mixture of the unmodified (A) component and the modified (A) component. The unmodified (A) component alone or a mixture of the unmodified (A) component and the modified (A) component is preferred, and the unmodified (A) component alone is more preferred. The content of the (A) component in the sheet molding is the total amount of the unmodified (A) component and the modified (A) component. The modification amount in the modified (A) component is preferably more than 0.01% by mass, more preferably 0.1% by mass or more, and even more preferably 1.0% by mass or more. By modifying the styrene polymer (A) having a syndiotactic structure within the above range, the affinity between the unmodified (A) component and the fibrous filler (C) and non-fibrous filler (D) is improved.

[0021] The amount of modified component (A) is preferably in the range of 0.01 to 40% by mass, more preferably 0.05 to 30% by mass, based on the total amount of component (A). By setting this content at 0.01% by mass or more, the effect as a compatibilizer can be exerted. Furthermore, there is no need to include a large amount, and the mechanical properties and heat resistance of the composition are not adversely affected. Furthermore, by setting the content at 40% by mass or less, a decrease in dielectric properties can be prevented.

[0022] The compound having a polar group is not particularly limited, but examples thereof include maleic acid, phthalic acid, glycidyl (meth)acrylic acid, and their acid anhydrides or esters, as well as amines, etc. Examples of the modified (A) component include maleic anhydride-modified SPS, fumaric acid-modified SPS, glycidyl methacrylate-modified SPS, and amine-modified SPS.

[0023] <Rubber-like elastomer (B)> The rubber-like elastomer (B) (hereinafter also referred to as component (B)) is preferably added because it imparts appropriate flexibility and improves mechanical properties when winding the sheet, thereby suppressing cracking of the sheet. Examples of the rubber-like elastomer (B) component include a single polymer composed of polyolefin, polystyrene, or polyacrylate, or a composition composed of multiple copolymers containing these components. Specific examples of rubber-like elastomers include natural rubber, polybutadiene, polyisoprene, polyisobutylene, neoprene, polysulfide rubber, thiokol rubber, acrylic rubber, urethane rubber, silicone rubber, epichlorohydrin rubber, ethylene-propylene copolymer rubber (EPM), ethylene-propylene-diene copolymer rubber (EPDM), ethylene-α-olefin copolymer rubber, styrene-butadiene block copolymer (SBR), hydrogenated styrene-butadiene block copolymer (SEB, SEBC), styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer (SEBS), styrene-isoprene block copolymer (SIR), hydrogenated styrene-isoprene block copolymer (SEP), styrene-isoprene block copolymer (SIR), hydrogenated styrene-isoprene block copolymer (SEP), styrene-isoprene block copolymer (SBR), hydrogenated styrene-isoprene block copolymer (SEP), styrene-isoprene block copolymer (SBR), hydrogenated styrene-isoprene block copolymer (SEB), styrene-isoprene block copolymer (SBR), hydrogenated styrene-isoprene block copolymer (SEB), styrene-isoprene block copolymer (SBR), hydrogenated styrene-isoprene block copolymer (SEP ... Examples of the core-shell type particulate elastomer include styrene-isoprene block copolymer (SIS), hydrogenated styrene-isoprene-styrene block copolymer (SEPS), butadiene-acrylonitrile-styrene-core-shell rubber (ABS), methyl methacrylate-butadiene-styrene-core-shell rubber (MBS), methyl methacrylate-butyl acrylate-styrene-core-shell rubber (MAS), octyl acrylate-butadiene-styrene-core-shell rubber (MABS), alkyl acrylate-butadiene-acrylonitrile-styrene-core-shell rubber (AABS), butadiene-styrene-core-shell rubber (SBR), and siloxane-containing core-shell rubbers such as methyl methacrylate-butyl acrylate-siloxane, as well as modified rubbers thereof.

[0024] Among these, SEBS, SIR, SEP, SIS, SEPS, ethylene-α-olefin copolymer rubber, or modified rubbers thereof are particularly preferred. These rubbery elastomers can be used singly or in combination of two or more. From the viewpoint of the processing temperature when mixed with the styrene-based polymer (A) having a syndiotactic structure, a rubbery elastomer with high heat resistance is preferred. By mixing a rubbery elastomer in which unsaturated bonds are selectively or completely hydrogenated, gas generation during hot press processing can be suppressed, and the mechanical properties of the sheet-molded article can be maintained even when exposed to a high-temperature environment.

[0025] The rubber-like elastomer (B) preferably has a melt flow rate (MFR) of 0.1 to 40 g / 10 min, more preferably 1.0 to 20 g / 10 min, and even more preferably 1.5 to 14 g / 10 min, measured at a temperature of 230° C. and a load of 2.16 kg. By setting the melt flow rate within the above range, compatibility with the styrene-based polymer (A) having a syndiotactic structure is improved, and the thickness of the sheet can be made uniform.

[0026] When the rubber-like elastomer (B) is contained, its content is preferably 1 to 40 parts by mass relative to 100 parts by mass of the styrene copolymer (A) having a syndiotactic structure. It is more preferably 3 to 30 parts by mass, and even more preferably 5 to 25 parts by mass. By making the content of component (B) 1 part by mass or more, the flexibility of the sheet-molded body is improved, and the winding property on a roll is improved. In addition, the drilling processability in the subsequent process is improved. Furthermore, by making the content 40 parts by mass or less, the sheet-molded body is prevented from becoming too soft, sticking to the roll is prevented, and the heat resistance required for high-frequency circuit boards can be maintained.

[0027] It is also preferable that the rubber-like elastomer (B) contains a styrene-based thermoplastic elastomer. When the rubber-like elastomer (B) is a styrene-based thermoplastic elastomer, the styrene content is preferably 5 to 60% by mass. It is more preferably 8 to 50% by mass, even more preferably 10 to 40% by mass, and particularly preferably 15 to 32% by mass. By setting the styrene content to 5% by mass or more, the compatibility between the (A) component and the (B) component is improved, resulting in good mechanical properties. Furthermore, by setting the styrene content to 60% by mass or less, the elastic modulus of the (B) component does not become too high, thereby enhancing the stress relaxation effect and improving the flexibility of the sheet-molded body. Furthermore, the polarity of the sheet-molded body can be suppressed, thereby suppressing an increase in the dielectric constant.

[0028] <Fibrous Filler (C)> The fibrous filler (C) (hereinafter also referred to as component (C)) is a fibrous filler that can improve the linear expansion coefficient and dimensional change suppression effect in the direction parallel to the extrusion direction (MD) of the sheet molding. It is a necessary filler for the sheet molding of the present invention, which may retain some residual strain even in unstretched state. The fibrous filler (C) can be inorganic or organic. In the case of inorganic fibers, wollastonite (or whiskers) or glass fiber can be used, with glass fiber being particularly preferred in terms of dielectric properties. The content of the fibrous filler (C) is 1 to 50 parts by mass per 100 parts by mass of the styrene-based polymer (A) having a syndiotactic structure to achieve a balance between the target linear expansion coefficient, dimensional stability, impact resistance, and mechanical properties. The content is preferably 3 to 40 parts by mass, more preferably 5 to 30 parts by mass.

[0029] The fibrous filler (C) may be in any form, such as roving, surfacing mat, chopped strand mat, satin weave, lattice weave, plain weave, open plain weave, twill weave, or net, and may be of any type, such as alkali-rich glass (C glass) or alkali-free glass (E glass).

[0030] More preferably, glass containing a large amount of boric acid (D glass) or glass with an adjusted balance of silica and boric acid (NE glass) is used. ２ and B ２ O ３ Preferably, the material contains SiO ２ The preferred range of the content is 65.0 to 80.0 mass %, and in this case, B ２ O ３ The preferred range of the content is 15.0 to 30.0 mass %. ２ and B ２ O ３ Preferably, the material contains SiO ２ The preferred range of the content is 45.0 to 65.0 mass %, and in this case, B ２ O ３ The preferred range of the content is 10.0 to 25.0 mass %.

[0031] Glass fibers with circular or non-circular cross sections can be used as the fibrous filler (C). Glass fibers with non-circular cross sections include those that are approximately elliptical, approximately oval, or approximately cocoon-shaped in a cross section perpendicular to the fiber length, and in such cases, the flatness is preferably 1.5 to 8. Here, the flatness is the ratio of the major axis to the minor axis, where the length of the long side of the rectangle with the smallest area circumscribing the cross section perpendicular to the longitudinal direction of the glass fiber is the major axis and the length of the short side of the rectangle is the minor axis. The thickness of the glass fiber is not particularly limited, but the minor axis is approximately 1 to 20 μm and the major axis is approximately 2 to 100 μm. Glass fibers with circular cross sections preferably have a fiber diameter of 1 to 50 μm, more preferably 2 to 20 μm, and even more preferably 3 to 15 μm.

[0032] The D50 average fiber length of the fibrous filler (C) is preferably 40 μm to 4000 μm, more preferably 40 μm to 3200 μm, even more preferably 45 μm to 2000 μm, and most preferably 50 μm to 500 μm. If the D50 average fiber length is 40 μm or more, the surface area of ​​the fibrous filler (C) is sufficiently large, improving the adhesion at the interface between the matrix resin components (A) and (C), and improving the physical properties of the sheet molded body. Furthermore, by setting the length to 4000 μm or less, excessive rigidity during film formation of the sheet molded body can be prevented, and the occurrence of cracks observed during sheet winding can be suppressed. Furthermore, the occurrence of aggregates in the sheet molded body can be suppressed.

[0033] The fibrous filler (C) may or may not be surface-treated. When the fibrous filler (C) is surface-treated, examples of the coupling agent used for the surface treatment include a silane coupling agent and a titanium coupling agent. Among these, surface treatment with a silane coupling agent is particularly preferred from the viewpoint of compatibility with component (A). Specific examples of the silane coupling agent include triethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, β-(1,1-epoxycyclohexyl)ethyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxy ... Examples of suitable silanes include hydroxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltris(2-methoxyethoxy)silane, N-methyl-γ-aminopropyltrimethoxysilane, N-vinylbenzyl-γ-aminopropyltriethoxysilane, 3-ureidopropyltrimethoxysilane, 3-4,5-dihydroimidazolepropyltriethoxysilane, hexamethyldisilazane, N,N-bis(trimethylsilyl)urea, and 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine. Among these, aminosilanes and epoxysilanes such as γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane are preferred.

[0034] Specific examples of titanium-based coupling agents include isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, tetraisopropyl bis(dioctyl phosphite) titanate, tetraoctyl bis(ditridecyl phosphite) titanate, tetra(1,1-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, and bis(dioctyl pyrophosphate)oxyacetate. titanate, bis(dioctyl pyrophosphate)ethylene titanate, isopropyl trioctanoyl titanate, isopropyl dimethacryl isostearoyl titanate, isopropyl isostearoyl diacryl titanate, isopropyl tri(dioctyl phosphate)titanate, isopropyl tricumyl phenyl titanate, isopropyl tri(N-amidoethyl, aminoethyl)titanate, dicumyl phenyloxyacetate titanate, diisostearoyl ethylene titanate, etc. Among these, isopropyl tri(N-amidoethyl, aminoethyl)titanate is preferred.

[0035] The surface treatment method for the fibrous filler (C) using the coupling agent is not particularly limited. For example, it can be performed by a method appropriate for the shape of the fibrous filler (C), such as a sizing treatment in which an organic solvent solution or suspension of the coupling agent is applied to the fibrous filler (C) as a sizing agent, a dry mixing treatment using a Henschel mixer, super mixer, Loedige mixer, V-type blender, or the like, a spray method, an integral blend method, or a dry concentrate method. Among these, surface treatment by sizing treatment, dry mixing treatment, or a spray method is preferred. A film-forming substance for glass, for example, can be used in combination with the coupling agent. The film-forming substance is not particularly limited, and examples thereof include polyester-based, urethane-based, epoxy-based, acrylic-based, vinyl acetate-based, and polyether-based polymers.

[0036] A modified polymer may be used as a compatibilizer for the fibrous filler (C) in addition to the styrene polymer (A) having a syndiotactic structure. The compatibilizer is added for the purpose of improving the interfacial strength between the syndiotactic polystyrene polymer (A) and the fibrous filler (C) and non-fibrous filler (D).

[0037] Specific examples of the compatibilizer include modified polyphenylene ether polymers such as styrene-maleic anhydride copolymer (SMA), styrene-glycidyl methacrylate copolymer, terminal carboxylic acid-modified polystyrene, terminal epoxy-modified polystyrene, terminal oxazoline-modified polystyrene, terminal amine-modified polystyrene, sulfonated polystyrene, styrene-based ionomer, styrene-methyl methacrylate-graft polymer, (styrene-glycidyl methacrylate)-methyl methacrylate-graft copolymer, acid-modified acrylic-styrene-graft polymer, (styrene-glycidyl methacrylate)-styrene-graft polymer, polybutylene terephthalate-polystyrene-graft polymer, polyphenylene ether, (styrene-maleic anhydride)-polyphenylene ether-graft polymer, maleic anhydride-modified polyphenylene ether, fumaric acid-modified polyphenylene ether, glycidyl methacrylate-modified polyphenylene ether, and amine-modified polyphenylene ether. Among these, unmodified or modified polyphenylene ether is preferred, and maleic anhydride-modified polyphenylene ether and fumaric acid-modified polyphenylene ether are more preferred.

[0038] The modified polyphenylene ether can be obtained by modifying a known polyphenylene ether with a modifying agent, but is not limited to this method as long as it can be used for the purposes of the present invention. The polyphenylene ether is a known compound, and for this purpose, reference can be made to the specifications of U.S. Pat. Nos. 3,306,874, 3,306,875, 3,257,357, and 3,257,358. Polyphenylene ether is usually prepared by oxidative coupling reaction using di- or tri-substituted phenols in the presence of a copper amine complex catalyst. The copper amine complex can be derived from primary, secondary, or tertiary amines.

[0039] Examples of polyphenylene ethers include poly(2,3-dimethyl-6-ethyl-1,4-phenylene ether), poly(2-methyl-6-chloromethyl-1,4-phenylene ether), poly(2-methyl-6-hydroxyethyl-1,4-phenylene ether), poly(2-methyl-6-n-butyl-1,4-phenylene ether), poly(2-ethyl-6-isopropyl-1,4-phenylene ether), poly(2-ethyl-6-n-propyl-1,4-phenylene ether), poly(2,3,6-trimethyl-1,4-phenylene ether), poly[2-(4'-methylphenyl)-1,4-phenylene ether], poly(2-bromo-6-phenyl-1,4-phenylene ether), poly(2-methyl-6-phenyl-1,4-phenylene ether), poly(2-phenyl-1,4-phenylene ether), poly(2-chloro-1,4-phenylene ether), poly(2-methyl-1,4-phenylene ether), poly(2-chloro-6-ethyl-1,4-phenylene ether), poly(2-chloro-6-bromo-1,4-phenylene ether), poly(2,6-di-n-propyl-1,4-phenylene ether), poly(2-methyl-6-isopropyl-1,4-phenylene ether), poly(2-chloro-6-methyl-1,4-phenylene ether), poly(2-methyl-6-ethyl-1,4-phenylene ether), poly(2,6-dibromo-1,4-phenylene ether), poly(2,6-dichloro-1,4-phenylene ether), poly(2,6-diethyl-1,4-phenylene ether), and poly(2,6-dimethyl-1,4-phenylene ether).

[0040] For example, copolymers derived from two or more of the phenolic compounds used in the preparation of the polyphenylene ether can be used. Further examples include graft copolymers and block copolymers of vinyl aromatic compounds such as polystyrene with the polyphenylene ether. Poly(2,6-dimethyl-1,4-phenylene ether) is particularly preferred.

[0041] Modifiers used to modify polyphenylene ether include compounds having an ethylenic double bond and a polar group in the same molecule, such as maleic anhydride, maleic acid, fumaric acid, maleic acid esters, fumaric acid esters, maleimide and its N-substituted derivatives, maleates, fumarates, acrylic acid, acrylic acid esters, acrylic acid amides, acrylic acid salts, methacrylic acid, methacrylic acid esters, methacrylic acid amides, methacrylic acid salts, and glycidyl methacrylate. Of these, maleic anhydride, fumaric acid, and glycidyl methacrylate are particularly preferred. The above-mentioned various modifiers may be used alone or in combination of two or more.

[0042] Modified polyphenylene ether can be obtained, for example, by reacting the polyphenylene ether with a modifier in the presence of a solvent or other resin. There are no particular limitations on the modification method, and known methods can be used. Specific examples include a method of melt-kneading the polyphenylene ether at a temperature ranging from 150 to 350°C using a roll mill, Banbury mixer, extruder, or the like, and a method of heating the polyphenylene ether in a solvent such as benzene, toluene, or xylene. Furthermore, to facilitate the reaction, it is also effective to add a radical generator, such as benzoyl peroxide, di-tert-butyl peroxide, dicumyl peroxide, tert-butyl peroxybenzoate, azobisisobutyronitrile, azobisisovaleronitrile, or 2,3-diphenyl-2,3-dimethylbutane, to the reaction system. The melt-kneading method in the presence of a radical generator is particularly preferred.

[0043] The polar group content in the polyphenylene ether is desirably in the range of 0.01 to 20% by mass, preferably 0.05 to 10% by mass. If this content is less than 0.01% by mass, the effect as a compatibilizer is not fully exerted, and if it exceeds 20% by mass, the compatibility with the styrene-based polymer (A) having a syndiotactic structure decreases. The blending amount of the polyphenylene ether is 0.1 to 10% by mass, preferably 0.5 to 8% by mass, based on the total weight of the resin component. If it is less than 0.1% by mass, the effect as a compatibilizer may be insufficient. If it exceeds 20% by mass, the heat resistance of the composition may be significantly reduced.

[0044] [Non-fibrous filler (D)] The non-fibrous filler (D) (hereinafter also referred to as component (D)) is a non-fibrous filler that is expected to suppress the linear expansion coefficient and dimensional change in the direction parallel to the extrusion direction (MD) and the direction perpendicular to the extrusion direction (TD) of the sheet molding. As the non-fibrous filler (D), fillers of known shapes such as spherical, granular, and plate-like shapes can be used. Either inorganic or organic fillers are acceptable, but inorganic spherical, granular, or plate-like fillers are preferred, such as talc, carbon black, graphite, titanium dioxide, silica, mica, calcium carbonate, calcium sulfate, barium carbonate, magnesium carbonate, magnesium sulfate, barium sulfate, oxysulfate, tin oxide, alumina, kaolin, silicon carbide, metal powder, glass powder, glass flakes, and glass beads.

[0045] Among these inorganic fillers, silica is particularly preferred from the viewpoints of productivity, cost, and the dielectric properties of the filler itself, and amorphous silica or fused silica is more preferred. Amorphous silica has lower hardness than crystalline silica, and can suppress wear of machines and screws.

[0046] Fused silica is made by melting the raw material in a flame and then rapidly solidifying the volatilized gas. The resulting spherical shape is formed by surface tension, resulting in few sharp edges and no tendency for the filler itself to crumble, making it easy to form a stable shape.

[0047] The silica is preferably granular or spherical, more preferably spherical. The granular or spherical shape of the silica facilitates mixing when added to a molten resin. Furthermore, because the silica is stable regardless of the direction of force, the mechanical properties of the sheet molding are less likely to deteriorate, and the silica is less likely to break down and fall off from the sheet molding.

[0048] The D50 average particle size of the non-fibrous filler (D) is preferably 0.1 to 45 μm. It is more preferably 0.2 to 30 μm, and even more preferably 0.3 to 20 μm. By having a D50 average particle size of 0.1 μm or more, aggregation of the (D) components is suppressed, they do not become foreign matter in the sheet molding, and mechanical properties are not reduced. Furthermore, by having a D50 average particle size of 45 μm or less, the spacing between the (D) components does not become too narrow, and crack propagation at the interface when stress occurs can be suppressed. In addition, heat resistance can be maintained during the soldering process.

[0049] The content of the non-fibrous filler (D) is preferably 1 to 60 parts by mass relative to 100 parts by mass of the polystyrene-based polymer (A) having a syndiotactic structure. It is more preferably 3 to 50 parts by mass, and even more preferably 5 to 40 parts by mass. When it is 1 part by mass or more, the effects of the component (D) can be exhibited. Furthermore, by setting it to 60 parts by mass or less, the surface smoothness of the sheet molding is improved, making it easier to control the film thickness, and it is possible to suppress aggregation of the component (D) within the sheet molding and suppress deterioration of mechanical properties.

[0050] The above does not apply to hollow amorphous silica and fused silica. The use of hollow silica is expected to further reduce the dielectric constant. When hollow silica is used, the film thickness is preferably in the range of 0.5 to 2.0 μm, more preferably 0.5 to 1.5 μm, and even more preferably 0.5 to 1.2 μm. If the film thickness is too thin, the silica may crack during screw mixing in a twin-screw kneader, making it impossible to maintain its hollow shape. If the film thickness is too thick, the volume fraction of hollow spaces decreases, and the effect of reducing the dielectric constant may not be achieved. The D50 average particle size of the hollow silica is preferably in the range of 3 to 45 μm. If the particle size is less than 3 μm, the effect of reducing the dielectric constant cannot be expected, and if the particle size exceeds 45 μm, the mechanical properties of the sheet molding may be reduced.

[0051] The non-fibrous filler (D) may be either surface-treated or non-surface-treated. The surface treatment agent is not limited as long as it is a known agent, but by subjecting it to hydrophobic treatment with a silane-based or titanate-based coupling agent, the dispersion state in the styrene polymer (A) having a syndiotactic structure can be improved, leading to improvement in the mechanical properties of the sheet and suppressing the generation of aggregates.

[0052] There are no particular restrictions on the polymer used as the organic spherical, granular, or plate-like filler, but considering the processing temperature of the styrene-based resin (A) having a syndiotactic structure, if it is a crystalline resin, it is preferably one having a melting point of more than 280°C, more preferably more than 300°C. Furthermore, if it is an amorphous resin, it is preferably one having a glass transition temperature of more than 150°C, more preferably more than 180°C. By setting the melting point and glass transition temperature within the above ranges, the shape of the filler can be maintained even during processing into a sheet molded body, and the effect of suppressing the linear expansion coefficient of the sheet molded body can be exerted.

[0053] <Antioxidant (E)> From the viewpoint of processability, the sheet molding of the present invention may contain the following antioxidant (E) (hereinafter also referred to as component (E)). The antioxidant (E) in the present invention may be either a primary antioxidant that prevents oxidation by capturing generated radicals, or a secondary antioxidant that prevents oxidation by decomposing generated peroxides. Examples of primary antioxidants include phenolic antioxidants and amine-based antioxidants, while examples of secondary antioxidants include phosphorus-based antioxidants and sulfur-based antioxidants. The incorporation of these antioxidants alone or in combination can suppress the decrease in molecular weight of component (A) or (B) during the production of the SPS resin composition and can suppress the generation of gas originating from component (A) or (B) during the hot-pressing step in the production of the sheet molding.

[0054] Specific examples of the phenolic antioxidant include monophenolic antioxidants such as 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, 2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, 2,6-di-t-butyl-4-[4,6-bis(octylthio)-1,3,5-triazin-2-ylamino]phenol, and n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate. Further examples include bisphenol-based antioxidants such as 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol), N,N'-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl]hydrazine, N,N'-hexane-1,6-diylbis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionamide], and 3,9-bis[1,1-dimethyl-2-[β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane. Further examples include polymeric phenolic antioxidants such as 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], bis[3,3'-bis-(4'-hydroxy-3'-t-butylphenyl)butyric acid]glycol ester, 1,3,5-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)-sec-triazine-2,4,6-(1H,3H,5H)trione, and d-α-tocophenol.

[0055] Specific examples of amine-based antioxidants include alkyl-substituted diphenylamines.

[0056] Specific examples of phosphorus-based antioxidants include triphenyl phosphite, diphenyl isodecyl phosphite, phenyl diisodecyl phosphite, 4,4'-butylidene-bis(3-methyl-6-t-butylphenylditridecyl)phosphite, octadecyl phosphite, tris(nonylphenyl)phosphite, diisodecyl pentaerythritol diphosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-(3,5-di-t-butyl-4-hydroxybenzyl)-9,10- Examples thereof include dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-decyloxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene, tris(2,4-di-t-butylphenyl)phosphite, cyclic neopentanetetraylbis(2,4-di-t-butylphenyl)phosphite, cyclic neopentanetetraylbis(2,6-di-t-butyl-4-methylphenyl)phosphite, and 2,2'-methylenebis(4,6-di-t-butylphenyl)octyl phosphite.

[0057] Specific examples of sulfur-based antioxidants include dilauryl-3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate, pentaerythritol tetrakis(3-laurylthiopropionate), and 2-mercaptobenzimidazole.

[0058] From the viewpoint of improving the heat resistance of the sheet and suppressing thermal degradation during processing, primary antioxidants are preferred, and phenolic antioxidants are particularly preferred. The antioxidant preferably has a thermal decomposition temperature of 250°C or higher. A higher thermal decomposition temperature enhances the effect of improving the breakdown voltage at high temperatures. A thermal decomposition temperature that is too low is undesirable, as it tends to cause problems such as thermal decomposition of the antioxidant itself during melt extrusion, contaminating the process and discoloring the polymer yellow. From this viewpoint, the thermal decomposition temperature of the antioxidant is more preferably 280°C or higher, even more preferably 300°C or higher, and particularly preferably 320°C or higher. It is preferable that the antioxidant in the present invention is less susceptible to thermal decomposition, and a higher thermal decomposition temperature is preferable, but in reality, the upper limit is approximately 500°C or lower.

[0059] The melting point of the antioxidant is preferably 90°C or higher. If the melting point is too low, the antioxidant melts faster than the polymer during melt extrusion, which tends to cause the polymer to slip at the screw feed section of the extruder. This leads to problems such as unstable polymer supply and uneven thickness of the sheet. From this perspective, the melting point of the antioxidant is more preferably 120°C or higher, even more preferably 150°C or higher, and particularly preferably 200°C or higher. On the other hand, if the melting point of the antioxidant is too high, the antioxidant tends to melt less easily during melt extrusion, which tends to result in poor dispersion within the polymer. This leads to problems such as the antioxidant only exerting its effect locally. From this perspective, the melting point of the antioxidant is preferably 300°C or lower, more preferably 250°C or lower, even more preferably 220°C or lower, and particularly preferably 170°C or lower.

[0060] As the antioxidant, commercially available products can be used as they are. Preferred examples of commercially available products include pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (manufactured by Ciba Specialty Chemicals, Inc., trade name IRGANOX 1010), N,N'-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl]hydrazine (manufactured by Ciba Specialty Chemicals, Inc., trade name IRGANOX 1024), and N,N'-hexane-1,6-diylbis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionamide] (manufactured by Ciba Specialty Chemicals, Inc., trade name IRGANOX 1098).

[0061] The content of the antioxidant is preferably 0.1% by mass or more and 8% by mass or less, based on the mass of the polystyrene-based resin composition. By including the antioxidant in a content within the above range, the heat resistance and heat degradation resistance of the sheet can be improved. If the content of the antioxidant is too low, the effect of adding the antioxidant is insufficient, and the effect of improving the breakdown voltage tends to be low. From this perspective, the content of the antioxidant is more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and particularly preferably 0.5% by mass or more. On the other hand, if the content is too high, the antioxidant tends to easily aggregate in the sheet, which tends to increase defects caused by the antioxidant, and such defects deteriorate the mechanical properties of the sheet. From this perspective, the content of the antioxidant is more preferably 6% by mass or less, even more preferably 4% by mass or less, and particularly preferably 2% by mass or less.

[0062] The antioxidants may be used alone or in combination of two or more. When two or more types are used in combination, two or more primary antioxidants may be used, two or more secondary antioxidants may be used, or one or more primary antioxidants may be used in combination with one or more secondary antioxidants. For example, by using two antioxidants, a primary antioxidant and a secondary antioxidant in combination, it is expected that both primary and secondary oxidations can be prevented. In the present invention, the use of a primary antioxidant alone or two or more primary antioxidants is preferred from the viewpoint of achieving a higher effect of suppressing thermal degradation during processing. In particular, the use of a phenolic antioxidant alone or two or more phenolic antioxidants is preferred.

[0063] The sheet molding of the present invention may contain flame retardants, mold release agents, lubricants, viscosity reducers, hardeners, etc., other than those mentioned above. The flame retardants are not particularly limited, but suitable flame retardants include halogen-based flame retardants containing bromine, and organic or inorganic phosphates, phosphoric acid esters, and phosphorus copolymers. The flame retardants used may be liquid or solid, but from the viewpoint of long-term stability, it is preferable to use one that is solid at room temperature.

[0064] <Polystyrene-based resin composition> The polystyrene-based resin composition is a composition containing at least the aforementioned components (A), (C), and (D) in predetermined amounts, and further containing the aforementioned components (B) and (E) as necessary. The sheet molding of the present invention can be produced using the polystyrene-based resin composition. The polystyrene-based resin composition is preferably prepared by blending the aforementioned components in predetermined amounts, kneading, and pelletizing them.

[0065] <Sheet Molded Product> The sheet molded product of the present invention is an unstretched sheet molded product. Unstretched does not only mean that the sheet molded product is not completely stretched, but also that some residual strain may be present. Specifically, the stretching ratio in both the direction parallel to the extrusion direction of the sheet molded product (longitudinal direction, MD) and the direction perpendicular to the extrusion direction of the sheet molded product (transverse direction, TD) is preferably 1.3 or less, more preferably 1.2 or less, even more preferably 1.1 or less, and most preferably 1.0. By setting the stretching ratio within the above range, the dimensional change rate of the sheet molded product can be reduced (low thermal shrinkage).

[0066] The sheet molding of the present invention has a dielectric constant of 3 or less at a temperature of 23°C, a relative humidity of 50%, and a frequency of 10 GHz. Preferably, it is 2.8 or less, and more preferably, it is 2.7 or less. When the dielectric constant is 3 or less, the signal transmission speed is fast and dielectric loss can be reduced. The lower limit is not particularly limited, but industrially it may be 1.0 or more, or even 2.0 or more.

[0067] The dielectric loss tangent of the sheet molding of the present invention is preferably 0.002 or less at a temperature of 23°C, a relative humidity of 50%, and a frequency of 10 GHz. It is more preferably 0.0015 or less, and even more preferably 0.001 or less. When the dielectric loss tangent is 0.002 or less, the dielectric loss is suppressed, and the performance as a circuit board at high frequencies is improved. The lower limit is not particularly limited, but it may be 0.0001 or more, or even 0.0002 or more.

[0068] The linear expansion coefficients in the machine direction (MD) and transverse direction (TD) of the sheet molded article of the present invention are each preferably 10 to 80 ppm / ° C., more preferably 15 to 75 ppm / ° C., and even more preferably 20 to 70 ppm / ° C. The MD / TD ratio is preferably 0.6 to 1.4, more preferably 0.65 to 1.35, and even more preferably 0.7 to 1.3.

[0069] The sheet molding of the present invention preferably exhibits a dimensional change rate of less than 0.4% in each of the machine direction (MD) and the transverse direction (TD) when heat-treated at 150°C for 30 minutes, more preferably 0.3% or less, and even more preferably 0.2% or less.

[0070] The thickness of the sheet molded article of the present invention is preferably 10 μm to 2000 μm, more preferably 20 μm to 1000 μm, even more preferably 30 μm to 500 μm, and most preferably 50 μm to 350 μm. If the thickness is less than 10 μm, the sheet molded article becomes prone to cracking, while if it exceeds 2000 μm, the sheet may draw down due to its own weight when extruded as a sheet, or may suffer from partial shrinkage (sink marks), resulting in uneven thickness of the sheet.

[0071] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following examples, parts and percentages are expressed by mass unless otherwise specified.

[0072] (1) Raw materials used in the examples and comparative examples <Styrene polymer (A) having a syndiotactic structure> A1: XAREC (registered trademark) 130ZC (manufactured by Idemitsu Kosan Co., Ltd., 100% syndiotactic polystyrene by mass, MFR = 15 g / 10 min, measurement temperature: 300°C, load: 1.2 kg, not modified with a compound having a polar group) A2: XAREC (registered trademark) 90ZC (manufactured by Idemitsu Kosan Co., Ltd., 100% syndiotactic polystyrene by mass, MFR = 9 g / 10 min, measurement temperature: 300°C, load: 1.2 kg, not modified with a compound having a polar group)

[0073] <Rubber-like elastic body (B)> B1: Tuftec (registered trademark) H1062 (manufactured by Asahi Kasei Corporation, styrene ratio = 18 mass%, MFR = 4.5 g / 10 min, measurement temperature: 230°C, load: 2.16 kg) B2: Tuftec (registered trademark) H1041 (manufactured by Asahi Kasei Corporation, styrene ratio = 30 mass%, MFR = 5.0 g / 10 min, measurement temperature: 230°C, load: 2.16 kg) B3: Tuftec (registered trademark) H1517 (manufactured by Asahi Kasei Corporation, styrene ratio = 43 mass%, MFR = 3.0 g / 10 min, measurement temperature: 230°C, load: 2.16 kg) B4: Tuftec (registered trademark) H1521 (manufactured by Asahi Kasei Corporation, styrene ratio = 18 mass%, MFR = 15.0 g / 10 min, measurement temperature: 230 ° C, load: 2.16 kg)

[0074] <Fibrous filler (C)> C1: HDT09100T (manufactured by Tochu Corporation, fiber diameter (diameter): 9 μm, D50 average fiber length: 100 μm, D-glass) C2: EPH80M-01N (manufactured by Nippon Electric Glass Co., Ltd., fiber diameter (diameter): 10 μm, D50 average fiber length: 80 μm, E-glass) C3: EFH30-01 (manufactured by Central Glass Fiber Co., Ltd., fiber diameter (diameter): 11 μm, D50 average fiber length: 30 μm, E-glass) C4: ECS301HP-3-H (manufactured by Chongqing International Composite Materials Co., Ltd., fiber diameter (diameter): 10 μm, D50 average fiber length: 3000 μm, E-glass) C5: ChopVantage HP-3610 (manufactured by Nippon Electric Glass Co., Ltd., fiber diameter (diameter): 10 μm, D50 average fiber length: 4500 μm, E-glass)

[0075] <Non-fibrous filler (D)> D1: Silica particles: FB-3SDC (manufactured by Denka Company, Ltd., D50 average particle size: 3.1 μm) D2: Silica particles: FB-7SDC (manufactured by Denka Company, Ltd., D50 average particle size: 5.4 μm) D3: Silica particles: SFP-130MC (manufactured by Denka Company, Ltd., D50 average particle size: 0.6 μm) D4: Hollow glass beads: iM-30k (manufactured by 3M Japan Co., Ltd., D50 average particle size: 17 μm) D5: Calcium carbonate: Whiten P-30 (Shiraishi Calcium Industry Co., Ltd., D50 average particle size: 4.8 μm) D6: Magnesia: RF-98 (manufactured by Ube Material Industries, Ltd., D50 average particle size: 50 μm)

[0076] <Antioxidants (E)> E1: ANOX20 (manufactured by BASF Japan Ltd., pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] E2: PEP-36 (manufactured by ADEKA Corporation, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane)

[0077] <Method for producing polystyrene-based resin composition> A polystyrene-based resin composition (SPS resin composition) was produced to obtain the sheet molded article of the present invention. The various components (A) to (D) and (E) including SPS were blended and kneaded to obtain the composition.

[0078] More specifically, (A) to (D) and (E) were compounded by feeding them into a 36 mmφ unidirectional twin-screw extruder (resin temperature: 300°C) via the main or side feeder, respectively, and extruding them through a round die in the form of four φ4 mm strands. The strands were then cooled and solidified in a water-cooled bath and cut to obtain cylindrical pellets of the SPS resin composition.

[0079] <Method for Manufacturing Sheet Molded Article> Pellets of the SPS resin composition obtained by the above manufacturing method were placed in the hopper of a 20 mm diameter single-screw extruder (resin temperature: 300°C) and remelted. Then, they were extruded into a sheet form through a T-die. They were sandwiched between two rolls (temperature: 90°C) and compressed, cooled, and solidified. They were then wound onto an 80 mm diameter paper tube at a speed of 1 m / min to obtain a 300 μm thick unstretched SPS sheet. The windability of the sheet was evaluated as follows: no sticking to the chill roll and no thickness unevenness on the sheet surface (◯); sticking to the roll or thickness unevenness on the sheet surface (△); no sticking to the roll but thickness unevenness or minor cracks on the sheet surface (△△); and no winding due to sticking to the roll or cracks on the sheet surface (×). Hereinafter, the direction parallel to the extrusion direction of the sheet is defined as MD, and the direction perpendicular to the extrusion direction is defined as TD.

[0080] Heat Treatment and Humidity Conditioning Process: Heat treatment of the unstretched SPS sheet increases the crystallinity of component (A) contained in the SPS sheet and improves the solder heat resistance of the SPS sheet. The SPS sheet obtained by the above manufacturing method was sandwiched between a commercially available polyimide film (Ube Industries, Ltd., Upilex) and a silicone sheet and compressed and heated using a hydraulic hand press (vacuum, temperature: 200°C, time: 30 min, pressure: 2 MPa). The resulting heat-treated SPS sheet (hereinafter referred to as the sheet molded product) was subjected to humidity conditioning for 24 hours at 23°C and 50% RH to eliminate the effects of humidity and obtain a sample with minimal variation due to external factors. The appearance of the sheet molded product was observed and rated as follows: those with obvious surface swelling (△), those with no swelling but some uneven transfer due to gas generated by resin decomposition during heat pressing (△), and those with a clean glossy or uniformly matte surface (○).

[0081] To confirm whether crystallization of the sheet molded body was complete, a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Corporation) was used to perform evaluations in accordance with JIS K7121 (2012). More specifically, when 5 mg of the sheet molded body was packed into an aluminum pan and heated from room temperature at a rate of 20 °C / min, it was confirmed that no exothermic peak was observed in the temperature range of 100 to 220 °C, confirming that crystallization was complete due to the heat treatment during pressing. In the following paragraphs, physical property evaluations 1 to 4 were performed on the sheet molded body that had been subjected to heat treatment and humidity conditioning treatment.

[0082] To produce a biaxially stretched sheet, a 500 μm-thick unstretched SPS sheet was obtained by the same method as above, and then subjected to simultaneous biaxial stretching (temperature: 110°C, stretch ratio: 3.3 × 3.4 (MD × TD), stretching rate: 500% / min) and then relaxation heat treatment (temperature: 230°C, relaxation ratio: 0.95 × 0.95 (MD × TD)) in a thermal drying oven to obtain a biaxially stretched SPS sheet with a thickness of 50 μm.

[0083] <Evaluation Method> 1. Dielectric Properties The sheet molding was cut to prepare strip-shaped test pieces measuring 3 mm in MD direction and 80 mm in TD direction. The dielectric properties (relative dielectric constant: Dk / dielectric loss tangent: Df) of the test pieces at a frequency of 10 GHz were measured a total of five times under a test environment of 23 ° C. and 50% humidity, and the average value was calculated (in accordance with JIS C2565). As measuring devices, a network analyzer MS46122B manufactured by Anritsu Corporation and a cavity resonator manufactured by AET Corporation were used. A relative dielectric constant (Dk) of 3 or less was considered pass (○), and a value exceeding 3 was considered fail (×). A dielectric loss tangent (Df) of 0.002 or less was considered pass (○), and a value exceeding 0.002 was considered fail (×).

[0084] 2. Linear expansion coefficient (TMA) The sheet molding was cut and strip-shaped test pieces measuring 3 mm in width and 25 mm in length were prepared in the MD direction (test piece with the longitudinal direction being the MD direction) and the TD direction (test piece with the longitudinal direction being the TD direction). The linear expansion coefficient of each test piece in the MD and TD directions was measured five times, and the average value was calculated (in accordance with JIS K7197). The measurement was performed using a TMA7100 manufactured by Hitachi High-Tech Science Corporation under a load of 2 gf / mm. The measurement results were read in a temperature range of 23 ° C to 80 ° C, and a linear expansion coefficient of 10 ppm / ° C or more and 80 ppm / ° C or less in both the MD and TD directions was considered to be acceptable.

[0085] 3. Dimensional Change Rate The sheet molding was cut to prepare rectangular test pieces measuring 180 mm in the MD direction and 130 mm in the TD direction. On the surface of the test piece, straight lines were drawn to form a rectangle measuring 120 mm x 70 mm (MD x TD), parallel to the MD and TD directions, and intersecting at the midpoint. The lengths of the straight lines in the MD and TD directions of the test piece were measured. The test piece was then placed in a hot air circulating oven set at 150 ° C. for 30 minutes in a suspended state with one corner supported. The test piece was then removed from the oven and allowed to cool for 24 hours in an environment of 23 ° C. and 50% RH to remove the influence of moisture content. The lengths of the straight lines in the MD and TD directions were then measured, and the amount of change from the length measured before the 150 ° C. / 30-minute test was determined. The thermal shrinkage rate was calculated as the ratio of the change to the respective lengths before the test. A positive value for the thermal shrinkage rate indicates shrinkage. If the absolute value of the thermal shrinkage rate was less than 0.4%, it was judged as pass (◯), and if it was 0.4% or more, it was judged as fail (×).

[0086] 4. Solder Heat Resistance Test The sheet molded body was cut to prepare a test piece of 50 mm in MD x 50 mm in TD. The test sheet was then floated in a solder bath heated to 260 ° C for 120 seconds, and visually observed for the degree of deformation and appearance abnormalities such as swelling. A test sheet showing no deformation or appearance swelling was rated as (◎), a test sheet showing no significant deformation or appearance swelling was rated as pass (◯), a test sheet showing partial wrinkles was rated as pass (△), and a test sheet showing significant deformation or appearance abnormalities such as swelling was rated as fail (×).

[0087] Examples 1 to 23: Examples 1 to 12, which contain the prescribed amounts of components (A), (C), and (D), satisfy the required physical properties and exhibit excellent overall balance of performance. The results are shown in Tables 1 and 2.

[0088] (Comparative Examples 1 to 8) When the components (A), (C), and (D) were added in excess or insufficiently, some physical properties could not be satisfied, as in Comparative Examples 1 to 12, and the sheet molding lacked quality. The results are shown in Table 3.

[0089]

[0090]

[0091]

[0092] As is clear from the above explanation, according to the present invention, the sheet molded body described in the examples exhibits excellent properties in terms of dielectric properties, linear expansion coefficient, dimensional stability, and solder heat resistance, and is expected to be used in high-frequency circuit boards. Specifically, it is expected that the sheet molded body of the present invention can be used in electronic components and antenna components for communication devices that require 5G.

Claims

1. A sheet molded article containing a styrene-based polymer (A) having a syndiotactic structure, a fibrous filler (C), and a non-fibrous filler (D), The sheet molded body is an unstretched sheet molded body, The fibrous filler (C) is contained in an amount of 1 to 50 parts by mass per 100 parts by mass of the styrene-based polymer (A) having a syndiotactic structure, The sheet molding has a relative dielectric constant of 3 or less in a frequency band of 10 GHz.

2. 2. The sheet molding according to claim 1, comprising 1 to 40 parts by mass of a rubber-like elastic material (B) per 100 parts by mass of the styrene-based polymer (A) having a syndiotactic structure.

3. 3. The sheet molded body according to claim 1, wherein the fibrous filler (C) is glass fiber having a D50 average fiber length of 40 to 4000 μm.

4. 3. The sheet molding according to claim 1, wherein the non-fibrous filler (D) is a granular or spherical filler having a D50 average particle size of 0.1 to 45 μm.

5. 3. The sheet molding according to claim 2, wherein the rubber-like elastic material (B) contains a styrene-based or olefin-based thermoplastic elastomer.

6. The sheet molded body according to claim 1 or 2, wherein the linear expansion coefficient in the machine direction (MD) and the transverse direction (TD) of the sheet molded body is 10 to 80 ppm / °C, and the MD / TD ratio is in the range of 0.6 to 1.

4.

7. 3. The sheet molded body according to claim 1, wherein the absolute value of the dimensional change rate when the sheet molded body is heat-treated at 150°C for 30 minutes is less than 0.4%.