Resin composition for heat resistant resin foamed sheet

Abstract

To provide a resin composition for heat resistant resin foamed sheets which contains a styrene-based resin, a polyphenylene ether and a styrene-methacrylic acid copolymer, and by which a heat resistant resin foamed sheet having excellent heat resistance and impact resistance can be manufactured, and a heat resistant resin foamed sheet made of the resin composition for heat resistant resin foamed sheets.SOLUTION: A resin composition for heat resistant resin foamed sheets contains a styrene-based resin (A), a polyphenylene ether (B) and a styrene-methacrylic acid copolymer (C). When the total of the styrene-based resin (A), the polyphenylene ether (B) and the styrene-methacrylic acid copolymer (C) is 100 pts.mass, the resin composition for heat resistant resin foamed sheets contains the styrene-based resin (A) by 25 to 40 pts.mass, (B) polyphenylene ether by 51 to 75 pts.mass, and styrene-methacrylic acid copolymer (C) by 0 to 24 pts.mass.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a resin composition for a heat-resistant resin foam sheet, which contains a styrene-based resin, a polyphenylene ether, and a styrene-methacrylic acid copolymer. [Background technology]

[0002] Polystyrene-based resin foam sheets are lightweight, have excellent heat insulation properties, and have beautiful appearances, and are therefore widely used in food packaging applications, such as being processed into food trays, lunch box containers, instant noodle cup containers, etc. In recent years, with the widespread use of microwave ovens in food packaging applications, high heat resistance is required to withstand heating in microwave ovens, and for foam sheets of styrene-based resin compositions, materials that are capable of high expansion ratios and have excellent foaming properties are required. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2018-188537 [Patent Document 2] Patent Publication No. 2008-094919 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the styrene-based resin compositions containing a styrene-based resin and a polyphenylene ether-based resin disclosed in Patent Documents 1 and 2 have heat resistance, but have the drawback of insufficient impact resistance.

[0005] An object of the present invention is to provide a resin composition for heat-resistant resin foam sheets, which contains a styrene-based resin, polyphenylene ether, and a styrene-methacrylic acid copolymer and which can be used to produce heat-resistant resin foam sheets having excellent heat resistance and impact resistance, and a heat-resistant resin foam sheet characterized by comprising the resin composition for heat-resistant resin foam sheets. [Means for solving the problem]

[0006] (1) A resin composition for heat-resistant resin foam sheets containing a styrene-based resin (A), a polyphenylene ether (B), and a styrene-methacrylic acid copolymer (C), wherein the resin composition for heat-resistant resin foam sheets contains 25 to 40 parts by mass of the styrene-based resin (A), 51 to 75 parts by mass of the polyphenylene ether (B), and 0 to 24 parts by mass of the styrene-methacrylic acid copolymer (C), when the total amount of the styrene-based resin (A), the polyphenylene ether (B), and the styrene-methacrylic acid copolymer (C) is 100 parts by mass. (2) The resin composition for a heat-resistant resin foam sheet according to (1), wherein the styrene-based resin (A) is a rubber-modified styrene-based resin. (3) The resin composition for a heat-resistant resin foam sheet according to (2), wherein the rubber-modified styrene-based resin is high-impact polystyrene. (4) The resin composition for a heat-resistant resin foam sheet according to (3), wherein the rubber-like dispersed particles of the high impact polystyrene have a volume median particle size of 1.0 to 4.0 μm. (5) The resin composition for heat-resistant resin foam sheet according to (3) or (4), wherein the polybutadiene used in the high impact polystyrene has a 1,4-cis structure ratio of 90 mol % or more. (6) The resin composition for a heat-resistant resin foam sheet according to any one of (1) to (5), wherein the styrene-methacrylic acid copolymer (C) has a methacrylic acid content of 2 to 10 mass %. (7) A heat-resistant resin foam sheet comprising the resin composition for a heat-resistant resin foam sheet according to any one of (1) to (6). (8) A heat-resistant resin foam sheet comprising the resin composition for a heat-resistant resin foam sheet according to any one of (1) to (7) above and a styrene-methacrylic acid copolymer. Effect of the Invention

[0007] According to the present invention, there can be provided a resin composition for a heat-resistant resin foam sheet, which has excellent heat resistance and impact resistance and contains a styrene-based resin, polyphenylene ether, and a styrene-methacrylic acid copolymer, and a heat-resistant resin foam sheet, which is characterized by comprising the resin composition for a heat-resistant resin foam sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, embodiments of the present invention will be described. The features of the embodiments described below can be combined with each other. Also, each feature can be an invention independently.

[0009] [Styrene-based resin composition] A resin composition for a heat-resistant resin foam sheet according to one embodiment of the present invention contains a styrene-based resin (A), a polyphenylene ether (B), and a styrene-methacrylic acid copolymer (C).

[0010] When the total of the styrene-based resin (A), the polyphenylene ether (B) and the styrene-methacrylic acid copolymer (C) is taken as 100 parts by mass, the content of the styrene-based resin (A) is 25 to 40 parts by mass, and preferably 28 to 35 parts by mass. Specifically, for example, it may be within the range of any two values ​​among 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 and 40 parts by mass. In addition, the styrene-based resin (A) may be used in combination with various styrene-based resins (A), and when the styrene-based resin (A) is used in combination, the amount of the styrene-based resin (A) used means the total amount of the styrene-based resin (A) used in combination. When the content of the styrene-based resin (A) exceeds 40 parts by mass, the Vicat softening temperature (VST) of the resin composition for heat-resistant resin foam sheet decreases. When the content of the styrene-based resin (A) is less than 25 parts by mass, the Charpy strength of the resin composition for a heat-resistant resin foam sheet decreases.

[0011] When the total of the styrene-based resin (A), the polyphenylene ether (B) and the styrene-methacrylic acid copolymer (C) is taken as 100 parts by mass, the content of the polyphenylene ether (B) is 51 to 75 parts by mass, and preferably 51 to 70 parts by mass. Specifically, for example, it may be within the range of any two values ​​among 51, 52, 53, 54, 55, 60, 65, 70, 71, 72, 73, 74 and 75 parts by mass. Note that the polyphenylene ether (B) may be used in combination with various polyphenylene ethers (B), and when polyphenylene ethers (B) are used in combination, the amount of polyphenylene ether (B) used means the total amount of polyphenylene ethers (B) used in combination. When the content of the polyphenylene ether (B) exceeds 75 parts by mass, the extrudability of the resin composition for heat-resistant resin foam sheet decreases. When the content of the polyphenylene ether (B) is less than 51 parts by mass, the VST of the resin composition for a heat-resistant resin foam sheet decreases.

[0012] When the total of the styrene-based resin (A), the polyphenylene ether (B) and the styrene-methacrylic acid copolymer (C) is taken as 100 parts by mass, the content of the styrene-methacrylic acid copolymer (C) is 0 to 24 parts by mass, preferably 0 to 21 parts by mass. Specifically, for example, it may be within the range of any two values ​​among 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 and 24 parts by mass. In addition, the styrene-methacrylic acid copolymer (C) may be used in combination with various styrene-methacrylic acid copolymers (C), and when the styrene-methacrylic acid copolymer (C) is used in combination, the amount of the styrene-methacrylic acid copolymer (C) used means the total amount of the styrene-methacrylic acid copolymer (C) used in combination. When the content of the styrene-methacrylic acid copolymer (C) exceeds 25 parts by mass, the Charpy strength of the resin composition for a heat-resistant resin foam sheet decreases.

[0013] <Styrene-based resin (A)> The styrene-based resin (A) is obtained by radical polymerization of an aromatic vinyl compound monomer, and may be modified into rubber by adding a conjugated diene rubber-like polymer as necessary. The polymerization method may be a known method, such as bulk polymerization, two-stage bulk / suspension polymerization, or solution polymerization. The aromatic vinyl compound monomer is a monocyclic or polycyclic aromatic vinyl monomer, such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene, p-ethylstyrene, m-ethylstyrene, o-ethylstyrene, p-tert-butylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, 1,1-diphenylethylene, isopropenylbenzene (α-methylstyrene), isopropenyltoluene, isopropenylethylbenzene, and the like. The aromatic vinyl monomer may be used alone or in combination of two or more of styrene, isopropenylpropylbenzene, isopropenylbutylbenzene, isopropenylpentylbenzene, isopropenylhexylbenzene, isopropenyloctylbenzene, etc., and preferably styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene, p-ethylstyrene, m-ethylstyrene, o-ethylstyrene, p-tert-butylstyrene. The aromatic vinyl monomer may be used alone or in combination of two or more. The homopolymer of the styrene monomer is obtained by polymerizing a styrene monomer, which is an aromatic vinyl monomer. The homopolymer of the styrene monomer means a polymer of only a styrene monomer, and may be a copolymer of two or more styrene monomers.

[0014] The styrene resin (A) may be a rubber-modified styrene resin. The rubber-modified styrene resin is a product obtained by dissolving a rubber component in a styrene monomer and polymerizing it under stirring using a thermal polymerization or a polymerization initiator such as a peroxide, and the manufacturing process may be batch polymerization or continuous polymerization. As the rubber component, a homopolymer such as butadiene or isoprene, or a copolymer of butadiene and styrene or methyl methacrylate that can be copolymerized with butadiene, is used, and the molecular structure of the copolymer may be a random structure or a block structure, or may have a branched structure. In addition, such a rubber-modified styrene resin may be used in combination with polystyrene (GPPS) that does not contain a rubber component, for the purpose of adjusting the amount of rubber component, impact strength, and fluidity as a resin composition. The rubber-modified styrene resin may be high impact polystyrene (HIPS), styrene-butadiene copolymer, styrene-butadiene-styrene copolymer, styrene-ethylene-butylene-styrene copolymer, or methyl methacrylate-butadiene-styrene copolymer, and high impact polystyrene is particularly preferable. The rubbery polymer used for rubber modification of the styrene-based resin (A) may be a conjugated diene-based rubbery polymer. Examples of the conjugated diene-based rubbery polymer include polybutadiene, random or block copolymers of styrene-butadiene, polyisoprene, polychloroprene, random, block or graft copolymers of styrene-isoprene, ethylene-propylene rubber, ethylene-propylene-diene rubber, etc., and polybutadiene is particularly preferred. The polybutadiene may be a high cis type with a high cis-1,4 structure ratio or a low cis type with a low cis-1,4 structure ratio, but is preferably a high cis type with a high cis-1,4 structure ratio, and more preferably a 1,4-cis structure ratio of 90 mol% or more. In addition, these may be partially hydrogenated, and may be used alone or in combination of two or more types. In an embodiment, the styrene-based resin (A) does not include a styrene-methacrylic acid copolymer.

[0015] The content of the rubber-like polymer in 100 parts by mass of the rubber-modified styrene-based resin according to the present embodiment is preferably 4.0 to 15.0 parts by mass, more preferably 8.0 to 12.0 parts by mass, from the viewpoint of strength and rigidity. The content of the rubber-like polymer in this range is preferable because it provides a good balance between impact strength and rigidity. The content of the rubber-like polymer may be within any two of the following ranges: 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 parts by mass. When a rubber-like polymer is used in combination, the amount of the rubber-like polymer used means the total amount of the rubber-like polymers used in combination.

[0016] The content of the rubber-like polymer can be measured, for example, as follows. The sample is dissolved in chloroform, a certain amount of iodine monochloride / carbon tetrachloride solution is added, and the mixture is left in a dark place for approximately 1 hour. After that, a 15% by mass potassium iodide solution and 50 ml of pure water are added, and the excess iodine monochloride is titrated with a 0.1 N sodium thiosulfate / ethanol aqueous solution, and the amount of iodine monochloride added is calculated.

[0017] The rubber-like polymer in the rubber-modified styrene-based resin may be present as rubber-like dispersed particles. The volume median particle diameter of the rubber-like dispersed particles of the rubber-modified styrene-based resin may be 1.0 to 4.0 μm, and may be within any two values ​​of 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, and 4.0. When a rubber-like polymer is used in combination, the volume median particle diameter of the rubber-like polymer means the volume median particle diameter of the entire rubber-like polymer used in combination. If the volume median particle diameter is within the range of 1.0 to 4.0 μm, the heat resistance and impact resistance of the resin composition for heat-resistant resin foam sheet are improved.

[0018] The method of adjusting the particle size of the rubber-like dispersed particles includes adjusting the stirring speed in the phase inversion region of the rubber particles in the polymerization process, adjusting the amount of the chain transfer initiator in the raw material liquid, etc. The volume median particle size of the rubber-like dispersed particles is determined by dissolving the rubber-modified styrene resin in dimethylformamide and measuring it with a laser diffraction / scattering particle size distribution measuring device (LA-920: relative refractive index 120A000I manufactured by Horiba, Ltd.), and the volume median particle size of the present invention is the 50 volume % particle size of the volume-based particle size distribution curve.

[0019] The polymerization method of the styrene-based resin (A) may be a known styrene polymerization method such as bulk polymerization, solution polymerization, suspension polymerization, or emulsion polymerization. In terms of quality and productivity, bulk polymerization and solution polymerization are preferred, and continuous polymerization is preferred. As the solvent, for example, alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane can be used.

[0020] In the case of continuous polymerization, first, a known complete mixing tank type stirring tank or tower type reactor is used in the polymerization process, and the polymerization reaction is controlled by adjusting the polymerization temperature, etc., so as to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate. The polymer solution containing the polymer that has left the polymerization process is transferred to a devolatilization process, where unreacted monomers and polymerization solvent are removed. The devolatilization process is composed of a vacuum devolatilization tank equipped with a heater or a devolatilization extruder equipped with a vent. The molten polymer that has left the devolatilization process is transferred to a granulation process. In the granulation process, the molten resin is extruded in the form of strands from a multi-hole die, and processed into pellets by a cold cut method, an air hot cut method, or an underwater hot cut method.

[0021] During polymerization of the styrene-based resin (A), a polymerization initiator and a chain transfer agent can be used as necessary. As the polymerization initiator, a radical polymerization initiator is preferable, and examples of the polymerization initiator include peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(t-butylperoxy)butane, 2,2-di(4,4-di-t-butylperoxycyclohexyl)propane, and 1,1-di(t-amylperoxy)cyclohexane, hydroperoxides such as cumene hydroperoxide and t-butyl hydroperoxide, alkyl peroxides such as t-butyl peroxyacetate and t-amyl peroxy isononanoate, t-butyl cumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, and di-t-hexyl peroxide. Examples of the dialkyl peroxide include dialkyl peroxides such as t-butyl peroxyacetate, t-butyl peroxybenzoate, and t-butyl peroxyisopropyl monocarbonate; peroxyesters such as t-butyl peroxyisopropyl carbonate and polyether tetrakis(t-butyl peroxycarbonate); peroxycarbonates such as N,N'-azobis(cyclohexane-1-carbonitrile), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylvaleronitrile), and N,N'-azobis[2-(hydroxymethyl)propionitrile], and these may be used alone or in combination of two or more. Examples of the chain transfer agent include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, and terpinolene.

[0022] <Polyphenylene ether (B)> The polyphenylene ether (B) can be produced by the oxidative coupling of a phenol compound. The catalyst for the oxidative coupling reaction of polyphenylene ether is not particularly limited, but at least one of heavy metal compounds such as copper, manganese, and cobalt is used (see U.S. Patent Nos. 4,042,056, 3,306,874, and 3,306,875, etc.).

[0023] Specific examples of phenols include phenol, o-, m-, p-cresol, 2,6-, 2,5-, 2,4- or 3,5-dimethylphenol, 2-methyl-6-phenylphenol, 2,6-diphenylphenol, 2,6-diethylphenol, and 2-methyl-6-t-butylphenol. Two or more of the above phenolic compounds may be copolymerized, and two or more of the resulting homopolymers or copolymers may be mixed and used. Among the above phenolic compounds, 2,6-dimethylphenol is particularly suitable, and therefore, in the present invention, poly(2,6-dimethyl-1,4-phenylene) ether obtained by polymerizing this phenolic compound gives good results. The molecular weight of the polyphenylene ether in the present invention is not particularly limited, but preferably has an intrinsic viscosity of 0.3 dl / g or more (at 25°C in chloroform solvent), and more preferably has an intrinsic viscosity of 0.3 to 0.6 dl / g. Specifically, for example, it may be 0.3, 0.4, 0.5, or 0.6 dl / g, and may be within a range between any two of the numerical values ​​exemplified here. By setting it in such a range, a resin composition for a heat-resistant resin foam sheet having good mechanical strength can be obtained.

[0024] <Styrene-methacrylic acid copolymer (C)> The styrene-methacrylic acid copolymer (C) can be obtained by copolymerizing a styrene monomer and a methacrylic acid monomer by radical polymerization using heat or a peroxide catalyst. As the polymerization method, known styrene polymerization methods such as bulk polymerization, solution polymerization, and suspension polymerization can be used.

[0025] The content of methacrylic acid in the styrene-methacrylic acid copolymer (C) is preferably 2 to 10% by mass. Specifically, it may be, for example, 2, 3, 4, 5, 6, 7, 8, 9, or 10% by mass, and may be within a range between any two of the numerical values ​​exemplified here. The content of methacrylic acid can be adjusted by the concentration of methacrylic acid in the raw material liquid in the polymerization step.

[0026] The mass average molecular weight (Mw) of the styrene-methacrylic acid copolymer (C) of the present invention is preferably 160,000 or more. When Mw is 160,000 or more, a resin composition for a heat-resistant resin foam sheet having a good balance between strength and moldability can be obtained. The Mw of the styrene-methacrylic acid copolymer (C) can be adjusted by the reaction temperature and residence time in the polymerization step, the type and amount of polymerization initiator, the type and amount of chain transfer agent, the type and amount of solvent used during polymerization, etc.

[0027] The mass average molecular weight (Mw) of the styrene-methacrylic acid copolymer (C) can be calculated by the method for calculating the mass average molecular weight (Mw) of the styrene-based resin (A).

[0028] <Glass transition temperature (Tg)> From the viewpoints of heat resistance and moldability, the styrene-methacrylic acid copolymer (C) according to this embodiment has a glass transition temperature (Tg) of preferably 50 to 160° C., more preferably 80 to 130° C. The glass transition temperature (Tg) can be controlled, for example, by adjusting the mass average molecular weight of the monomer and copolymer constituting the homopolymer. The glass transition temperature (Tg) can be measured, for example, using an EXTER DSC6200 manufactured by SII Corporation, by raising the temperature from 20° C. at a rate of 10° C. / min.

[0029] <Other ingredients> To the resin composition of the present invention, other additives, for example, known additives such as reinforcing materials, flame retardants, dyes and pigments, coloring inhibitors, lubricants, antioxidants, antiaging agents, light stabilizers, antistatic agents, fillers, crystallization nucleating agents, and compatibilizers, and modifiers such as colorants such as titanium oxide and carbon black, can be added within the scope of the present invention. The method of adding these is not particularly limited, and they may be added by known methods. For example, a method of adding them in the raw material charging process, polymerization process, and finishing process during the production of the styrene-based resin (A), polyphenylene ether (B), and styrene-methacrylic acid copolymer (C), or a method of adding them in the process of mixing the resin composition using an extruder or molding machine can be applied.

[0030] <Method of producing resin composition> The method for mixing the resin composition of the present invention is not particularly limited, and known mixing techniques can be applied. For example, a homogeneous resin composition can be produced by mixing various raw materials in advance using a mixing device such as a mixer-type mixer, a V-type blender, and a tumbler-type mixer, and melt-kneading the mixture. The melt-kneading device is also not particularly limited, and examples thereof include a Banbury-type mixer, a kneader, a roll, a single-screw extruder, a special single-screw extruder, and a twin-screw extruder. Furthermore, there is also a method in which additives such as a flame retardant are added separately from the middle of a melt-kneading device such as an extruder.

[0031] The molding method for obtaining a molded article, film, sheet, or foam from the resin composition of the present invention is not particularly limited, and known molding methods such as extrusion molding methods such as calendar molding, blow molding, extrusion foam molding, profile extrusion molding, lamination molding, inflation molding, T-die film molding, sheet molding, vacuum molding, and pressure molding, and injection molding methods such as injection molding, RIM molding, and injection foam molding can be suitably used.

[0032] The resin composition of the present invention may be used by itself to form a first sheet, but a further styrene-based resin (second styrene-based resin) may be added to the resin composition of the present invention to form a second sheet, and in this case, a sheet excellent in heat resistance and impact resistance can also be obtained. The second styrene-based resin may be the same as or different from the styrene-based resin exemplified as the styrene-based resin (hereinafter referred to as the "first styrene-based resin") used in producing the resin composition of the present invention described above.

[0033] When forming the second sheet, the resin composition of the present invention and the second styrene-based resin may be melt-kneaded to prepare the second resin composition in advance, and the second sheet may be formed using the second resin composition, or the resin composition of the present invention and the second styrene-based resin may be directly put into a molding machine to form the second sheet. When the second resin composition is prepared in advance, the melt-kneading device is preferably used.

[0034] <How to evaluate heat resistance> The heat resistance can be evaluated by the Vicat softening temperature (VST) (heating rate 50°C / hr, test load 50N, in accordance with JIS K 7206). The VST of the resin composition (pellets) of the present invention is preferably 140°C or higher, and particularly preferably 143°C or higher.

[0035] <Strength evaluation method> The strength of the resin composition (pellet) of the present invention can be evaluated by Charpy impact strength (based on JIS K7111). The Charpy impact strength of the resin composition (pellet) of the present invention is 8 J / cm 2 More preferably, it is equal to or greater than this.

[0036] <Foam sheet> The heat-resistant resin foam sheet of the present invention is a foam of the above-mentioned resin composition for heat-resistant resin foam sheet.

[0037] [Method of manufacturing foam sheet] The method for producing the foamed sheet of the present invention is not particularly limited, and examples thereof include a method in which the above-mentioned styrene-based resin composition, a nucleating agent, and the like are supplied to an extruder, heated and melted, a foaming agent is added and kneaded, extrusion foaming is performed through a die attached to the tip of the extruder, and the obtained foamed sheet is wound up and recovered.

[0038] The foaming agent may be any commonly used one, including chemical foaming agents such as azodicarbonamide, dinitrosopentamethylenetetramine, hydrazoyldicarbonamide, and sodium bicarbonate, and physical foaming agents such as saturated aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane, ethers such as dimethyl ether, methyl chloride, carbon dioxide, and nitrogen.

[0039] Examples of the nucleating agent include talc, sodium hydrogen carbonate, ammonium hydrogen carbonate, calcium carbonate, clay, and citric acid. Among them, talc is preferable as the nucleating agent. The nucleating agent may be used alone or in combination of two or more. The amount of the nucleating agent to be added is preferably 0.01 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the styrene-based resin composition.

[0040] Examples of the die attached to the tip of the extruder include an annular die (circular die) having an annular opening, a T-die, etc. A specific embodiment when an annular die is used is, for example, a cylindrical foam extruded from the annular die is aligned along a cooling mandrel, and cut into two foam sheets by making slits in the axial direction of the cylindrical foam using cutters provided on both sides of the tip of the cooling mandrel.

[0041] There is no particular limitation on the method for controlling the thickness, expansion ratio, average cell diameter and closed cell ratio of the foamed sheet. For example, the expansion ratio increases by increasing the amount of the nucleating agent used. Also, the expansion ratio decreases by decreasing the amount of the foaming agent used. The thickness of the foamed sheet can be controlled by changing the amount and type of the foaming agent used. Also, the average cell diameter increases by decreasing the amount of the nucleating agent used. EXAMPLES

[0042] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these.

[0043] The materials used in the examples and comparative examples are as follows.

[0044] [Styrene-based resin (A)] (A-1) HIPS (polystyrene resin modified with polybutadiene rubber, high cis type, rubber polymer content of 10% by mass in 100% by mass of resin, volume median particle size of 1.8 μm) (A-2) HIPS (polystyrene resin modified with polybutadiene rubber, high cis type, rubber polymer content of 12% by mass in 100% by mass of resin, volume median particle size 4.7 μm) (A-3) HIPS (polystyrene resin modified with polybutadiene rubber, low cis type, rubber polymer content in 100% resin by mass 9.3% by mass, volume median particle diameter 2.7 μm)

[0045] [Polyphenylene ether (B)] (B-1) Product name: "IUPIACE PX100F" manufactured by Mitsubishi Engineering Plastics Corporation (intrinsic viscosity 0.36 dl / g)

[0046] [Styrene-methacrylic acid copolymer (C)] (C-1) Styrene-methacrylic acid copolymer (mass average molecular weight (Mw) 200,000, glass transition temperature (Tg) 122°C, methacrylic acid monomer 8% by mass) (C-2) Styrene-methacrylic acid copolymer (mass average molecular weight (Mw) 270,000, glass transition temperature (Tg) 113°C, methacrylic acid monomer 4% by mass)

[0047] (Examples 1 to 8, Comparative Examples 1 to 4) The components were premixed in the amounts shown in Tables 1 and 2 in a Henschel mixer (Mitsui Miike Chemical Co., Ltd., FM20B), fed to a twin-screw extruder (Toshiba Machine Co., Ltd., TEM26SS) to make strands, cooled with water, and then fed to a pelletizer to be pelletized. The main operating conditions were as follows: Cylinder temperature setting: 190℃ (transport area) - 280℃ (mixing - weighing area) Screw rotation speed: 400 rpm Extrusion speed: 320kg / h Resin temperature: 280~290℃

[0048] [Extrusion] The extrudability of the resin composition was evaluated based on whether or not problems such as venting up or strand breakage occurred during the process of producing pellets of the resin composition. The meanings of the symbols for extrudability in Tables 1 and 2 are as follows: Extrudability: ○(manufacturable) × (Problems such as bent-up and strand breakage occur. Production is not possible.)

[0049] [Charpy impact strength] Test pieces were prepared using an injection molding machine and measured according to JIS K7111. "-" in Table 2 means that measurement was not possible.

[0050] [Measurement of Vicat softening temperature (VST)] The Vicat softening temperature was measured in accordance with JIS K 7206 at a temperature rise rate of 50° C. / hr and a test load of 50 N. In Table 2, "-" means that the measurement was not possible.

[0051] [Table 1]

[0052] [Table 2]

[0053] It was found from the Examples in Table 1 that the resin compositions of the present invention are excellent in heat resistance and impact resistance. On the other hand, from the Comparative Examples in Table 2, it was found that the resin compositions not satisfying the requirements of the present invention were inferior in heat resistance and / or impact resistance, and the resin compositions with inferior extrudability were impossible to mold. [Industrial Applicability]

[0054] The foamed sheet produced from the resin composition of the present invention has high heat resistance and impact resistance and can therefore be advantageously used in applications such as food containers and packaging, office automation equipment, home appliance parts, and miscellaneous goods, and has industrial applicability.

Claims

1. A resin composition for heat-resistant foamed resin sheets containing a styrene resin (A), a polyphenylene ether (B), and a styrene-methacrylic acid copolymer (C), wherein, when the total amount of the styrene resin (A), the polyphenylene ether (B), and the styrene-methacrylic acid copolymer (C) is 100 parts by mass, the composition contains 25 to 40 parts by mass of the styrene resin (A), 51 to 75 parts by mass of the polyphenylene ether (B), and 0 to 24 parts by mass of the styrene-methacrylic acid copolymer (C).

2. The resin composition for heat-resistant foamed resin sheets according to claim 1, characterized in that the styrene resin (A) is a rubber-modified styrene resin.

3. The resin composition for heat-resistant foamed resin sheets according to claim 2, characterized in that the rubber-modified styrene resin is high-impact polystyrene.

4. The resin composition for heat-resistant foamed resin sheets according to claim 3, characterized in that the median particle size of the rubbery dispersed particles of the high-impact polystyrene is 1.0 to 4.0 μm.

5. The resin composition for heat-resistant foamed resin sheets according to claim 3, characterized in that the proportion of 1,4-cis structures of polybutadiene used in the high-impact polystyrene is 90 mol% or more.

6. A resin composition for a heat-resistant resin foam sheet according to any one of claims 1 to 5, characterized in that the methacrylic acid content in the styrene-methacrylic acid copolymer (C) is 2 to 10% by mass.

7. A heat-resistant resin foam sheet characterized by comprising the resin composition for heat-resistant resin foam sheets described in claim 1.

8. A heat-resistant resin foam sheet characterized by comprising the resin composition for heat-resistant resin foam sheets described in claim 1 and a styrene-methacrylic acid copolymer.