Thermoplastic resin composition and molded article

Abstract

A thermoplastic resin composition comprising a graft copolymer (A), a vinyl copolymer (B), and a metal component (C), wherein: an amount of the metal component (C) is 60 ppm or more relative to a total mass of the thermoplastic resin composition, the graft copolymer (A) is a graft polymer obtained by polymerizing 80 % by mass to 20 % by mass of a vinyl monomer mixture (m1) including at least one type of vinyl monomer in the presence of 20 % by mass to 80 % by mass of a rubbery polymer (a) including a polyorganosiloxane and an alkyl (meth)acrylate polymer, the vinyl copolymer (B) is a vinyl copolymer obtained by polymerizing a vinyl monomer mixture (m2) including an alkyl (meth)acrylate monomer, and the metal component (C) is an alkali metal.

Description

Thermoplastic resin compositions, molded products

[0001] The present invention relates to a thermoplastic resin composition and a molded article thereof. This application claims priority based on Japanese Patent Application No. 2021-059491, filed on March 31, 2021, the contents of which are incorporated herein by reference.

[0002] Improving the impact resistance of molded articles increases their industrial usefulness, such as by expanding the range of applications for the molded articles. Therefore, various methods have been proposed to improve the impact resistance of molded articles. Among these methods, a method of using a resin material that combines a rubbery polymer with a hard resin to increase the impact resistance of molded articles while retaining the properties inherent in the hard resin has already been commercialized. Examples of such resin materials include acrylonitrile-styrene-acrylic acid ester (ASA) resin, acrylonitrile-ethylene-α-olefin-styrene (AES) resin, and thermoplastic resin compositions in which these resins are further added to a hard resin.

[0003] The following, for example, has been proposed as a thermoplastic resin composition capable of producing molded articles excellent in weather resistance, impact resistance, and molded appearance: A thermoplastic resin composition containing a graft copolymer (A1) obtained by polymerizing an aromatic alkenyl compound and a vinyl cyanide compound onto a polyalkyl acrylate rubber, and a polymethyl methacrylate resin (B) (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2002-371167

[0005] The thermoplastic resin of Patent Document 1 sometimes causes thermal discoloration, which results in a difference in the color of the resulting molded product, depending on the molding temperature.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thermoplastic resin composition and a molded article thereof that are excellent in resistance to thermal discoloration (hereinafter referred to as "thermal discoloration resistance").

[0007] The present invention has the following aspects: [1] A thermoplastic resin composition comprising the following graft copolymer (A), the following vinyl copolymer (B), and the following metal component (C), wherein the content of the following metal component (C) is 60 ppm or more relative to the total mass of the thermoplastic resin composition. (A): A graft polymer obtained by polymerizing 80% by mass to 20% by mass of a vinyl monomer mixture (m1) containing one or more vinyl monomers in the presence of 20% by mass to 80% by mass of a rubber-like polymer (a) obtained from a polyorganosiloxane and an alkyl (meth)acrylate polymer (wherein the total of the rubber-like polymer (a) and the vinyl monomer mixture (m1) is 100% by mass). (B): A vinyl copolymer obtained by polymerizing a vinyl monomer mixture (m2) containing an alkyl (meth)acrylate monomer. (C): A metal component which is an alkali metal. [2] The thermoplastic resin composition according to [1], wherein the content of the metal component (C) is 100 ppm to 400 ppm relative to the total mass of the thermoplastic resin composition. [3] The thermoplastic resin composition according to [1] or [2], wherein the metal component (C) includes potassium. [4] The thermoplastic resin composition according to any one of [1] to [3], wherein the content of the graft polymer (A) is 20 to 80 parts by mass, relative to the total mass of the thermoplastic resin composition. [5] The thermoplastic resin composition according to any one of [1] to [4], wherein the content of the graft copolymer (A) is preferably 20 to 80 parts by mass, more preferably 30 to 70 parts by mass, and even more preferably 40 to 60 parts by mass, relative to the total mass of the thermoplastic resin composition. [6] The thermoplastic resin composition according to any one of [1] to [5], wherein the content of the metal component (C) is 60 ppm or more, preferably 100 ppm or more, more preferably 100 ppm to 700 ppm, and even more preferably 100 ppm to 400 ppm, relative to the total mass of the thermoplastic resin composition.[7] The polyorganosiloxane is preferably a polyorganosiloxane containing a vinyl polymerizable functional group (vinyl polymerizable functional group-containing polyorganosiloxane); a polyorganosiloxane having a vinyl polymerizable functional group-containing siloxane unit and a dimethylsiloxane unit is more preferred; a polyorganosiloxane having a vinyl polymerizable functional group-containing siloxane unit and a dimethylsiloxane unit, wherein the vinyl polymerizable functional group-containing siloxane unit is bonded to the dimethylsiloxane unit via a siloxane bond. The thermoplastic resin composition according to any one of [1] to [6]. [8] The rubbery polymer (a) is preferably a composite rubber obtained by combining the polyorganosiloxane and the alkyl(meth)acrylate polymer; more preferably a graft polymer having a polyorganosiloxane-derived structure as a trunk polymer and an alkyl(meth)acrylate polymer-derived structure as a branch polymer. [9] The thermoplastic resin composition according to any one of [1] to [8], wherein the rubbery polymer (a) is preferably crosslinked between side chains of the alkyl(meth)acrylate polymer.

[10] The thermoplastic resin composition according to any one of [1] to [9], wherein the proportion of the polyorganosiloxane relative to the total mass (100% by mass) of the polyorganosiloxane and the alkyl(meth)acrylate polymer is preferably 3% by mass or more but less than 24% by mass, more preferably 5% by mass or more but 20% by mass or less, and even more preferably 7% by mass or more but 15% by mass or less.

[11] The thermoplastic resin composition according to any one of [1] to

[10] , wherein the vinyl-based monomer mixture (m1) contains an aromatic vinyl compound, and the content of the aromatic vinyl compound is preferably 65% ​​by mass to 82% by mass, more preferably 73% by mass to 80% by mass, and even more preferably 75% by mass to 80% by mass, relative to the total mass (100% by mass) of the vinyl-based monomer mixture (m1).

[12] The thermoplastic resin composition according to any one of [1] to

[11] , wherein the vinyl-based monomer mixture (m1) contains a vinyl cyanide compound, and the content of the vinyl cyanide compound is preferably 18% by mass to 35% by mass, more preferably 20% by mass to 27% by mass, and even more preferably 20% by mass to 25% by mass, relative to the total mass (100% by mass) of the vinyl-based monomer mixture (m1).

[13] The thermoplastic resin composition according to any one of [1] to

[12] , wherein the metal component (C) preferably contains an alkali metal, preferably at least one selected from the group consisting of sodium and potassium.

[14] The thermoplastic resin composition according to any one of [1] to

[13] , wherein the thermal discoloration index Δb*, determined by the method described in the Examples below, is preferably 1.0 or less, more preferably 0.8 or less, and even more preferably 0.7 or less.

[15] The thermoplastic resin composition according to any one of [1] to

[14] , wherein the thermoplastic resin composition comprises a resin, the resin essentially consisting of a graft copolymer (A) and the following vinyl copolymer (B).

[16] The thermoplastic resin composition according to any one of [1] to

[14] , wherein the thermoplastic resin composition comprises a resin, the resin consisting of the graft copolymer (A) and the vinyl copolymer (B).

[16] A molded article formed from the thermoplastic resin composition according to any one of [1] to

[16] .

[17] A method for producing a rubbery polymer (a), comprising a step (radical polymerization step) of radically polymerizing a monomer component containing one or more alkyl (meth)acrylates in the presence of a latex-like polyorganosiloxane to obtain a copolymer latex.

[18] A method for producing the rubbery polymer (a) according to

[17] , comprising a step of polymerizing a siloxane mixture containing a dimethylsiloxane oligomer and a siloxane containing a vinyl polymerizable functional group in the presence of an emulsifier containing a metal component (C) to obtain the latex-like polyorganosiloxane.

[19] The method for producing the rubbery polymer (a) according to

[18] , wherein the amount of the emulsifier used is preferably 0.05 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, and even more preferably 0.3 to 2.0 parts by mass, per 100 parts by mass of the siloxane mixture.

[20] A method for producing a rubbery polymer (a) according to any one of

[17] to

[19] , wherein the metal component (C) preferably contains an alkali metal, and preferably contains at least one selected from the group consisting of sodium and potassium.

[21] A method for producing a graft copolymer (A), comprising a step of polymerizing a vinyl-based monomer mixture (m1) in the presence of the rubbery polymer (a) obtained by the method for producing a rubbery polymer (a) according to any one of

[17] to

[20] , to obtain a graft copolymer (A).

[22] A method for producing a thermoplastic resin composition, comprising a step of mixing the graft copolymer (A) obtained by the method for producing a graft copolymer (A) according to

[21] , a vinyl-based copolymer (B), and a metal component (C) to obtain a thermoplastic resin composition.

[0008] According to the present invention, it is possible to provide a thermoplastic resin composition having excellent resistance to heat discoloration and a molded article thereof.

[0009] The following definitions of terms apply throughout the present specification and claims. "(Meth)acrylate" means acrylate or methacrylate. "Molded article" means an article obtained by molding a thermoplastic resin composition. The symbol "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits.

[0010] [Thermoplastic Resin Composition] A thermoplastic resin composition according to one embodiment of the present invention comprises a graft copolymer (A), a vinyl copolymer (B), and a metal component (C). The thermoplastic resin composition of this embodiment may contain other thermoplastic resins and various additives, as necessary, within ranges that do not impair the effects of the present invention.

[0011] The graft copolymer (A) is obtained by polymerizing 80% to 20% by mass of a vinyl monomer mixture (m1) containing one or more vinyl monomers in the presence of 20% to 80% by mass of a rubber-like polymer (a) containing a polyorganosiloxane and an alkyl (meth)acrylate polymer. The vinyl copolymer (B) is obtained by polymerizing a vinyl monomer mixture (m2) containing an alkyl (meth)acrylate monomer. The metal component (C) is an alkali metal. Each component ((A) to (C), (m1), (m2), etc.) will be described below.

[0012] "Polyorganosiloxane" The polyorganosiloxane is not particularly limited, but is preferably a polyorganosiloxane containing a vinyl polymerizable functional group (a vinyl polymerizable functional group-containing polyorganosiloxane), and more preferably a polyorganosiloxane having a vinyl polymerizable functional group-containing siloxane unit and a dimethylsiloxane unit.

[0013] Examples of vinyl polymerizable functional groups include methacryloyloxyalkyl groups, acryloyloxyalkyl groups, vinyl groups, and vinyl-substituted phenyl groups. The number of carbon atoms in the alkyl groups in the methacryloyloxyalkyl groups and acryloyloxyalkyl groups may be, for example, 1 to 20. The vinyl polymerizable functional group-containing siloxane unit may have an organic group other than the vinyl polymerizable functional group. Examples of the other organic group include alkyl groups such as methyl groups, and phenyl groups.

[0014] The content of the vinyl polymerizable functional group-containing siloxane unit is preferably 0.3 mol% to 3 mol% relative to the total number of moles (100 mol%) of all units constituting the polyorganosiloxane. If the content of the vinyl polymerizable functional group-containing siloxane unit is within the above range, the polyorganosiloxane and the alkyl (meth)acrylate polymer are sufficiently compounded, and the polyorganosiloxane is less likely to bleed out on the surface of the molded article. Therefore, the color development is better and the impact resistance of the molded article is further improved.

[0015] As the polyorganosiloxane, since the color development property is further improved, the content of silicon atoms having three or more siloxane bonds is 0 mol% to 1 mol% relative to the total number of moles of all silicon atoms in the polyorganosiloxane (100 mol%). It is preferable.

[0016] A preferred embodiment of the polyorganosiloxane is a polyorganosiloxane comprising 0.3 mol% to 3 mol% of vinyl polymerizable functional group-containing siloxane units and 99.7 mol% to 97 mol% of dimethylsiloxane units (wherein the total of the vinyl polymerizable functional group-containing siloxane units and the dimethylsiloxane units is 100 mol%), and having a content of silicon atoms having three or more siloxane bonds of 1 mol% or less relative to the total number of moles of all silicon atoms.

[0017] The average particle size of the polyorganosiloxane is not particularly limited, but is preferably 400 nm or less, more preferably 150 nm or less, since this improves the color development of the molded article. The lower limit is preferably 20 nm or more. Here, the average particle size of the polyorganosiloxane is a value (mass average particle size) calculated from the particle size distribution obtained by measuring the mass-based particle size distribution using a dynamic light scattering particle size distribution measuring instrument.

[0018] "Method for Producing Polyorganosiloxane" Polyorganosiloxane can be obtained, for example, by polymerizing a siloxane mixture containing a dimethylsiloxane oligomer and a vinyl-polymerizable functional group-containing siloxane.

[0019] As the dimethylsiloxane oligomer, a dimethylsiloxane-based cyclic compound having three or more members is preferred, and a dimethylsiloxane-based cyclic compound having three to seven members is more preferred. Specific examples include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylcyclohexasiloxane. These dimethylsiloxane oligomers may be used alone or in combination of two or more.

[0020] The vinyl polymerizable functional group-containing siloxane is not particularly limited as long as it contains a vinyl polymerizable functional group and can bond to a dimethylsiloxane oligomer via a siloxane bond, but considering the reactivity with the dimethylsiloxane oligomer, an alkoxysilane compound containing a vinyl polymerizable functional group is preferred. Specific examples of the alkoxysilane compound containing a vinyl polymerizable functional group include methacryloyloxysiloxanes such as β-methacryloyloxyethyldimethoxymethylsilane, γ-methacryloyloxypropyldimethoxymethylsilane, γ-methacryloyloxypropylmethoxydimethylsilane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropylethoxydiethylsilane, γ-methacryloyloxypropyldiethoxymethylsilane, and δ-methacryloyloxybutyldiethoxymethylsilane; and vinylsiloxanes such as tetramethyltetravinylcyclotetrasiloxane and p-vinylphenyldimethoxymethylsilane. These vinyl polymerizable functional group-containing siloxanes may be used alone or in combination of two or more.

[0021] The method for polymerizing the siloxane mixture is not particularly limited, but emulsion polymerization is preferred. Emulsion polymerization of the siloxane mixture is typically carried out using an emulsifier, water, and an acid catalyst. Anionic emulsifiers are preferred. Specific examples include sodium alkylbenzenesulfonate, sodium lauryl sulfonate, and sodium polyoxyethylene nonylphenyl ether sulfate. Among these, sulfonic acid-based emulsifiers such as sodium alkylbenzenesulfonate and sodium lauryl sulfonate are preferred. These emulsifiers may be used alone or in combination of two or more. The amount of emulsifier used is preferably 0.05 to 5 parts by mass per 100 parts by mass of the siloxane mixture. Using an amount of emulsifier of 0.05 parts by mass or more facilitates stabilizing the dispersion state of the siloxane mixture and maintaining an emulsified state with a small particle size. On the other hand, using an amount of emulsifier of 5 parts by mass or less can suppress discoloration of the molded product caused by the emulsifier.

[0022] Examples of acid catalysts include organic acid catalysts such as sulfonic acids (e.g., aliphatic sulfonic acid, aliphatic-substituted benzenesulfonic acid, aliphatic-substituted naphthalenesulfonic acid, etc.); and inorganic acid catalysts such as mineral acids (e.g., sulfuric acid, hydrochloric acid, nitric acid, etc.). These acid catalysts may be used alone or in combination of two or more. Among these, aliphatic-substituted benzenesulfonic acid is preferred, and n-dodecylbenzenesulfonic acid is particularly preferred, due to its excellent stabilizing effect on the siloxane latex, as described below. Furthermore, the combined use of n-dodecylbenzenesulfonic acid and a mineral acid such as sulfuric acid can minimize the effect of the color of the emulsifier used in the production of polyorganosiloxane on the color of the molded product. The amount of acid catalyst added can be determined as appropriate, but is typically about 0.1 to 20 parts by weight per 100 parts by weight of the siloxane mixture.

[0023] The acid catalyst may be mixed with the siloxane mixture, emulsifier, and water at the same time they are mixed, or the siloxane mixture, emulsifier, and water may be mixed and emulsified to form a latex (siloxane latex), the siloxane latex may be microparticulated, and then mixed with the microparticulated siloxane latex. Since this makes it easier to control the particle size of the resulting polyorganosiloxane, it is preferable to microparticulate the siloxane latex and then mix the microparticulated siloxane latex with the acid catalyst. In particular, it is preferable to drop the microparticulated siloxane latex into an aqueous acid catalyst solution at a constant rate. When the acid catalyst is mixed with the siloxane mixture, emulsifier, and water at the same time, it is preferable to microparticulate the mixture after mixing.

[0024] Siloxane latex can be microparticulated using, for example, a homomixer or a homogenizer. A homomixer microparticulates the particles using shear force generated by high-speed rotation. A homogenizer microparticulates the particles using the jetting force of a high-pressure generator. Methods for mixing a siloxane mixture with an emulsifier, water, and an acid catalyst, and methods for mixing microparticulated siloxane latex with an acid catalyst include, for example, mixing by high-speed stirring and mixing using a high-pressure emulsifying device such as a homogenizer. Among these, the method using a homogenizer is preferred because it can narrow the particle size distribution of the polyorganosiloxane.

[0025] The polymerization temperature is preferably 50° C. or higher, more preferably 80° C. or higher. When the finely divided siloxane latex is added dropwise to an aqueous acid catalyst solution, the temperature of the aqueous acid catalyst solution is preferably 50° C. or higher, more preferably 80° C. or higher.

[0026] The polymerization time is preferably 2 hours or more, more preferably 5 hours or more, when the acid catalyst is mixed at the same time as the siloxane mixture, emulsifier, and water are mixed. On the other hand, when the finely divided siloxane latex and the acid catalyst are mixed, it is preferable to drop the finely divided siloxane latex into the aqueous acid catalyst solution and then hold the mixture for about 1 hour.

[0027] The polymerization can be terminated by cooling the reaction solution and then neutralizing it with an alkaline substance such as sodium hydroxide, potassium hydroxide, or sodium carbonate so that the pH of the reaction solution at 25°C is about 6 to 8.

[0028] As described above, a polyorganosiloxane latex is obtained. The average particle size of the polyorganosiloxane can be controlled by adjusting the composition of the siloxane mixture, the amount of acid catalyst used (the content of the acid catalyst in the acid catalyst aqueous solution), the polymerization temperature, etc. For example, the average particle size tends to increase as the amount of acid catalyst used decreases, and the average particle size tends to decrease as the polymerization temperature increases.

[0029] "Alkyl (meth)acrylate polymer" The alkyl (meth)acrylate polymer is a polymer having alkyl (meth)acrylate units. The alkyl (meth)acrylate polymer may further have units of a monomer (another monomer) other than the alkyl (meth)acrylate units.

[0030] The number of carbon atoms in the alkyl group of the alkyl (meth)acrylate may be, for example, 1 to 20. Examples of the alkyl (meth)acrylate include alkyl acrylate esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate; and alkyl methacrylate esters such as hexyl methacrylate, 2-ethylhexyl methacrylate, and n-lauryl methacrylate. These alkyl (meth)acrylates may be used alone or in combination of two or more. Of these, n-butyl acrylate is preferred in terms of further improving the impact resistance of molded articles.

[0031] The other monomer is not particularly limited as long as it is copolymerizable with alkyl(meth)acrylate, and examples thereof include aromatic vinyl compounds (e.g., styrene, α-methylstyrene, p-methylstyrene, etc.), vinyl cyanide compounds (e.g., acrylonitrile, methacrylonitrile, etc.), etc. These other monomers may be used alone or in combination of two or more.

[0032] In the alkyl (meth)acrylate polymer, the content of the alkyl (meth)acrylate unit is preferably 80% by mass to 100% by mass, and more preferably 90% by mass to 100% by mass, based on the total mass of all monomer units of the alkyl (meth)acrylate polymer.

[0033] The alkyl (meth)acrylate polymer is obtained by polymerizing a monomer component containing one or more alkyl (meth)acrylates. This monomer component may contain other monomers. The polymerization method of the monomer component is not particularly limited, and can be carried out according to a known method.

[0034] "Rubber polymer (a)" The rubber polymer (a) is a composite rubber formed by combining a polyorganosiloxane and an alkyl (meth)acrylate polymer. In this specification, the "composite rubber" may include one or more polymers, or may be a graft polymer having a trunk polymer and a branch polymer.

[0035] In the rubber-like polymer (a), the proportion of polyorganosiloxane relative to the total mass (100 mass%) of the polyorganosiloxane and the alkyl (meth)acrylate polymer is not particularly limited, but is preferably 3 mass% or more and less than 24 mass%. If the proportion of polyorganosiloxane in the rubber-like polymer (a) is within the above range, the impact resistance and color development of the resulting molded article will be better.

[0036] The rubbery polymer (a) is granular and exists in the granular form in the thermoplastic resin composition. The volume average particle diameter of the rubbery polymer (a) is not particularly limited, but is preferably 50 nm or more and less than 120 nm. If the volume average particle diameter of the rubbery polymer (a) is within the above range, the impact resistance and color development of the obtained molded article will be better. Here, the volume average particle diameter of the rubbery polymer (a) is a value calculated from the particle size distribution obtained by measuring the volume-based particle size distribution using a dynamic light scattering particle size distribution measuring instrument.

[0037] The proportion of particles having a particle diameter of more than 200 nm to all particles in the rubbery polymer (a) is preferably less than 5% by volume. That is, the rubbery polymer (a) preferably has a particle size distribution (volume basis) in which particles having a particle diameter of more than 200 nm account for less than 5% by volume of all particles. When the proportion of particles having a particle diameter of more than 200 nm is less than 5% by volume, the color development of the molded article is more excellent. The proportion of particles having a particle diameter of more than 200 nm is a value calculated from the particle size distribution obtained by measuring the volume-based particle size distribution of the rubbery polymer (a) using a dynamic light scattering particle size distribution analyzer.

[0038] "Method for producing rubbery polymer (a)" The method for producing the rubbery polymer (a) is not particularly limited, but includes hetero-aggregation or co-enlargement of a plurality of latexes each containing a polyorganosiloxane and an alkyl (meth) acrylate polymer; a method of polymerizing the monomer component that forms the other polymer in the presence of a latex containing either a polyorganosiloxane or an alkyl (meth) acrylate polymer to form a composite, and the like. Since the volume average particle diameter of the rubbery polymer (a) can be easily adjusted to be within the above-mentioned range, a method having a step of radically polymerizing a monomer component containing one or more alkyl (meth) acrylates in the presence of a latex-like polyorganosiloxane to obtain a copolymer latex (radical polymerization step) is preferred.

[0039] The radical polymerization step is a step of radically polymerizing a monomer component containing one or more alkyl (meth)acrylates in the presence of a latex-form polyorganosiloxane. The monomer component containing one or more alkyl (meth)acrylates may be added to the latex-form polyorganosiloxane all at once, continuously, or intermittently. The polymerization conditions may be, for example, 30°C to 95°C and 1 hour to 10 hours.

[0040] When radically polymerizing a monomer component containing one or more alkyl (meth)acrylates, a grafting agent or a crosslinking agent may be used as needed. Examples of grafting agents or crosslinking agents include allyl methacrylate, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, and 1,4-butylene glycol dimethacrylate. These may be used alone or in combination of two or more.

[0041] Radical polymerization typically uses a radical polymerization initiator and an emulsifier. Examples of radical polymerization initiators include peroxides, azo initiators, and redox initiators that combine an oxidizing agent and a reducing agent. Among these, redox initiators are preferred, and sulfoxylate initiators that combine ferrous sulfate, ethylenediaminetetraacetic acid disodium salt, sodium formaldehyde sulfoxylate, and hydroperoxide are particularly preferred.

[0042] The emulsifier is not particularly limited, but carboxylic acid salts such as sodium sarcosinate, potassium fatty acid, sodium fatty acid, dipotassium alkenyl succinate, and rosin acid soap are preferred because they provide excellent latex stability during radical polymerization and can increase the polymerization rate. Among these, dipotassium alkenyl succinate is preferred because it can suppress gas generation when the resulting graft copolymer (B) and a thermoplastic resin composition containing it are molded at high temperatures. Specific examples of dipotassium alkenyl succinate include dipotassium octadecenyl succinate, dipotassium heptadecenyl succinate, and dipotassium hexadecenyl succinate. These emulsifiers may be used alone or in combination of two or more.

[0043] "Vinyl Monomer Mixture (m1)" The vinyl monomer mixture (m1) may contain one or more vinyl monomers, but is preferably a monomer mixture containing an aromatic vinyl compound and a vinyl cyanide compound. It may also contain other monomers copolymerizable with these monomers, provided that the effects of the present invention are not impaired.

[0044] Examples of aromatic vinyl compounds include styrene, α-methylstyrene, o-, m-, or p-methylstyrene, vinylxylene, p-t-butylstyrene, and ethylstyrene. From the viewpoints of the flowability of the thermoplastic resin composition, the color development property of the molded article, and the impact resistance, styrene and α-methylstyrene are preferred. One type of aromatic vinyl compound may be used alone, or two or more types may be used in combination.

[0045] Examples of the vinyl cyanide compound include acrylonitrile, methacrylonitrile, etc. One type of vinyl cyanide compound may be used alone, or two or more types may be used in combination.

[0046] Examples of the other monomers include acrylic acid esters (methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, etc.), methacrylic acid esters (methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, etc.), maleimide monomers (N-cyclohexylmaleimide, N-phenylmaleimide, etc.), etc. One type of the other monomers may be used alone, or two or more types may be used in combination.

[0047] The ratio of each monomer component constituting the vinyl-based monomer mixture (m1) is not particularly limited, but the content of the aromatic vinyl compound relative to the total mass (100 mass%) of the vinyl-based monomer mixture (m1) is preferably 65 mass% to 82 mass%, more preferably 73 mass% to 80 mass%, and even more preferably 75 mass% to 80 mass%. If the content of the aromatic vinyl compound is within the above range, the impact resistance and color development of the molded article will be even more excellent.

[0048] Furthermore, the content of the vinyl cyanide compound relative to the total mass (100 mass%) of the vinyl monomer mixture (m1) is preferably 18 mass% to 35 mass%, more preferably 20 mass% to 27 mass%, and even more preferably 20 mass% to 25 mass%. When the content of the vinyl cyanide compound is within the above range, the impact resistance and color development of the molded article are further improved.

[0049] "Graft copolymer (A)" The graft copolymer (A) is a copolymer obtained by polymerizing a vinyl-based monomer mixture (m1) in the presence of a rubber-like polymer (a). In the case of the graft copolymer (A), it is difficult to specify how the vinyl-based monomer mixture (m1) is polymerized in the presence of the rubber-like polymer (a). In other words, there are circumstances (impossible or impractical circumstances) in which it is impossible or practical to directly specify the graft copolymer (A) by its structure or properties. Therefore, it is more appropriate to define the graft copolymer (A) as "obtained by polymerizing a vinyl-based monomer mixture (m1) in the presence of a rubber-like polymer (a)."

[0050] The mass ratio of the rubbery polymer (a) to the vinyl-based monomer mixture (m1) containing one or more vinyl-based monomers is preferably 20% to 80% by mass of the rubbery polymer (a) and 80% to 20% by mass of the one or more vinyl-based monomer mixture (m1), and more preferably 30% to 70% by mass of the rubbery polymer (a) and 70% to 30% by mass of the one or more vinyl-based monomer mixture (m1) (where the total of the rubbery polymer (a) and the one or more vinyl-based monomer mixture (m1) is 100% by mass). If the rubbery polymer (a) is less than 20% by mass, the impact resistance of the molded article will be poor, and if it exceeds 80% by mass, the color development of the molded article will be poor and the flowability of the thermoplastic resin composition will tend to be reduced.

[0051] "Method for Producing Graft Copolymer (A)" The graft copolymer (A) is obtained by polymerizing a vinyl-based monomer mixture (m1) in the presence of a rubber-like polymer (a). The polymerization method is not particularly limited, but emulsion polymerization is preferred because it allows for control so that the reaction proceeds stably. Specific examples include a method in which the vinyl-based monomer mixture (m1) is charged all at once to a latex of the rubber-like polymer (a) and then polymerized; a method in which a portion of the vinyl-based monomer mixture (m1) is first charged to a latex of the rubber-like polymer (a) and polymerized as needed, while the remainder is added dropwise to the polymerization system; and a method in which the entire amount of the vinyl-based monomer mixture (m1) is added dropwise to the latex of the rubber-like polymer (a) and polymerized as needed. These methods can be carried out in one or more stages. When carried out in two or more stages, it is also possible to vary the type and composition ratio of the monomers constituting the vinyl-based monomer mixture (m1) in each stage.

[0052] A radical polymerization initiator and an emulsifier are usually used in the emulsion polymerization. Examples of these radical polymerization initiators and emulsifiers include the radical polymerization initiators and emulsifiers exemplified above in the description of the production method for the rubbery polymer (a). During the polymerization, various known chain transfer agents may be added to control the molecular weight and graft ratio of the resulting graft copolymer (A). The polymerization conditions may be, for example, 30°C to 95°C and 1 hour to 10 hours.

[0053] The graft copolymer (A) obtained by emulsion polymerization is usually in the form of a latex. Methods for recovering the graft copolymer (A) from the latex of the graft copolymer (A) include, for example, a wet method in which the latex of the graft copolymer (A) is introduced into hot water in which a coagulant is dissolved to coagulate it into a slurry state; and a spray-dry method in which the latex of the graft copolymer (A) is sprayed into a heated atmosphere to recover the graft copolymer (A) semi-directly.

[0054] Coagulants used in the wet method include inorganic acids such as sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid; and metal salts such as calcium chloride, calcium acetate, and aluminum sulfate, and are selected depending on the emulsifier used in the polymerization. For example, when only a carboxylic acid soap such as a fatty acid soap or a rosin acid soap is used as the emulsifier, one or more of the above-mentioned coagulants can be used. Furthermore, when an emulsifier that exhibits stable emulsifying power even in the acidic range, such as sodium alkylbenzenesulfonate, is used as the emulsifier, a metal salt is preferred as the coagulant.

[0055] When a wet method is used, a graft copolymer (A) in a slurry state is obtained. Methods for obtaining a dry graft copolymer (A) from the slurry graft copolymer (A) include a method in which the remaining emulsifier residue is first dissolved in water and washed, and then the resulting slurry is dehydrated using a centrifuge or a press dehydrator, etc., and then dried using a flash dryer, etc.; and a method in which dehydration and drying are simultaneously performed using a compression dehydrator, extruder, etc. By such a method, a dry graft copolymer (A) in a powder or particulate state is obtained.

[0056] The washing conditions are not particularly limited, but washing is preferably performed under conditions such that the amount of emulsifier residue contained in 100% by mass of graft copolymer (A) after drying is in the range of 0.3% to 2% by mass. When the amount of emulsifier residue in graft copolymer (A) is 0.3% by mass or more, the fluidity of the resulting graft copolymer (A) and the thermoplastic resin composition containing it tends to be further improved. On the other hand, when the amount of emulsifier residue in graft copolymer (A) is 2% by mass or less, gas generation during high-temperature molding of the thermoplastic resin composition can be suppressed. The amount of emulsifier residue can be adjusted, for example, by the washing time. The drying temperature may be, for example, 50°C to 90°C. The volume average particle size and volume-based particle size distribution of the rubbery polymer (a) in the resulting graft copolymer (A) are the same as the volume average particle size and volume-based particle size distribution of the rubbery polymer (a) in the latex of the rubbery polymer (a) used to produce the graft copolymer (A). It is also possible to directly send the graft copolymer (A) discharged from the squeeze dehydrator or extruder to an extruder or molding machine for producing a resin composition, without recovering it, to form a molded article.

[0057] "Vinyl-based monomer mixture (m2)" The vinyl-based monomer mixture (m2) is a monomer mixture containing at least an alkyl(meth)acrylate-based monomer. In addition to the alkyl(meth)acrylate-based monomer, the vinyl-based monomer mixture (m2) may contain other monomers copolymerizable therewith, within a range that does not impair the effects of the present invention.

[0058] Examples of alkyl (meth)acrylate monomers include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, amyl methacrylate, isoamyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, phenyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate. As the alkyl (meth)acrylate monomer, alkyl (meth)acrylate monomers having a hydrocarbon group having 1 to 8 carbon atoms are preferred. At least one of methyl methacrylate and ethyl methacrylate is preferred, as this provides molded articles with even better heat resistance and impact resistance. The alkyl (meth)acrylate monomers may be used alone or in combination of two or more.

[0059] Examples of the other monomer include the aromatic vinyl compounds and vinyl cyanide compounds exemplified above in the description of the vinyl monomer mixture (m1). One type of the other monomer may be used alone, or two or more types may be used in combination.

[0060] The proportion of the alkyl(meth)acrylate monomer contained in the vinyl-based monomer mixture (m2) is not particularly limited, but is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, relative to the total mass (100% by mass) of the vinyl-based monomer mixture (m2). If the content of the alkyl(meth)acrylate monomer is within the above range, the impact resistance and color development of the molded article will be even more excellent.

[0061] "Vinyl Copolymer (B)" The vinyl copolymer (B) is a polymer obtained by polymerizing the vinyl monomer mixture (m2).

[0062] "Method for producing vinyl copolymer (B)" The vinyl copolymer (B) is a polymer of the vinyl monomer mixture (m2). The vinyl copolymer (B) contains at least units derived from an alkyl (meth)acrylate monomer.

[0063] The proportion of alkyl (meth)acrylate monomer-derived units contained in the vinyl copolymer (B) is not particularly limited, but is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, relative to the total mass (100% by mass) of the vinyl monomer mixture (m2). If the content of alkyl (meth)acrylate monomer-derived units is within the above range, the impact resistance and color development of the molded article will be even better.

[0064] The weight average molecular weight (Mw) of the vinyl copolymer (B) may be, for example, 5,000 to 500,000. The weight average molecular weight of the vinyl copolymer (B) is a value measured using gel permeation chromatography (GPC) in terms of standard polystyrene. The vinyl copolymer (B) may be used alone or in combination of two or more.

[0065] The vinyl copolymer (B) is obtained by polymerizing a vinyl monomer mixture (m2). The polymerization method of the vinyl monomer mixture (m2) is not particularly limited. Examples of the polymerization method include known polymerization methods (emulsion polymerization, suspension polymerization, solution polymerization, etc.). When the vinyl monomer mixture (m2) contains two or more types of monomers, the obtained vinyl copolymer (B) is typically a random copolymer in which units derived from these two or more types of monomers are randomly arranged.

[0066] Examples of methods for producing the vinyl copolymer (B) using emulsion polymerization include charging a vinyl monomer mixture (m2), an emulsifier, a polymerization initiator, and a chain transfer agent into a reactor, heating the mixture to polymerize, and obtaining an aqueous dispersion containing the vinyl copolymer (B), followed by recovering the vinyl copolymer (B) from the aqueous dispersion by precipitation. The emulsion polymerization conditions may be, for example, 30°C to 95°C and 1 hour to 10 hours. Examples of emulsifiers include conventional emulsion polymerization emulsifiers (potassium rosinate, sodium alkylbenzene sulfonate, etc.). Examples of polymerization initiators include organic and inorganic oxide initiators. Examples of chain transfer agents include mercaptans, α-methylstyrene dimer, and terpenes. The precipitation method can be the same as that used to recover the graft copolymer (A) from its latex.

[0067] Examples of methods for producing the vinyl copolymer (B) using suspension polymerization include a method in which a vinyl monomer mixture (m2), a suspending agent, a suspending aid, a polymerization initiator, and a chain transfer agent are charged into a reactor, heated to polymerize, and the resulting slurry is dehydrated and dried to recover the vinyl copolymer (B). The polymerization conditions for suspension polymerization may be, for example, 60°C to 150°C and 1 hour to 20 hours. Examples of suspending agents include tricalcium phosphite and polyvinyl alcohol. Examples of suspending aids include sodium alkylbenzene sulfonate. Examples of polymerization initiators include organic peroxides. Examples of chain transfer agents include mercaptans, α-methylstyrene dimer, and terpenes.

[0068] "Metal Component (C)" The metal component (C) is an alkali metal. Among the alkali metals, sodium (Na) and potassium (K) are preferred. The metal component (C) more preferably contains potassium. The metal component (C) may be derived from a compound containing a metal component used in the production of the graft copolymer (A) or the vinyl copolymer (B), or may be blended as a compound containing a metal component in the production of the thermoplastic resin composition described below.

[0069] "Other thermoplastic resins" Examples of other thermoplastic resins include polycarbonate, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyvinyl chloride, polystyrene, polyacetal, modified polyphenylene ether (modified PPE), ethylene-vinyl acetate copolymer, polyarylate, liquid crystal polyester, polyethylene, polypropylene, fluororesin, polyamide (nylon), and the like.

[0070] "Additives" Examples of additives include antioxidants, lubricants, processing aids, pigments, dyes, fillers, silicone oils, and paraffin oils.

[0071] "Content of each component" The content of the graft copolymer (A) in the thermoplastic resin composition is preferably 20 to 80 parts by mass, more preferably 30 to 70 parts by mass, and even more preferably 40 to 60 parts by mass, relative to the total mass (100 parts by mass) of the thermoplastic resin composition. When the content of the graft copolymer (A) is equal to or greater than the lower limit, the mechanical properties of the molded article are good. When the content of the graft copolymer (A) is equal to or less than the upper limit, the color development and molded appearance of the molded article are good.

[0072] The content of the metal component (C) in the thermoplastic resin composition is 60 ppm or more, preferably 100 ppm or more, more preferably 100 ppm to 700 ppm, and even more preferably 100 ppm to 400 ppm, relative to the total mass of the thermoplastic resin composition. If the content of the metal component (C) is less than 60 ppm, the effect of suppressing thermal discoloration cannot be obtained. If the content of the metal component (C) is 100 ppm or more, the effect of suppressing thermal discoloration is more excellent, and if it is less than 700 ppm, the appearance of the molded article is good. In this specification, the content of the metal component (C) is a value measured by the method described in the examples below. Specifically, the content of the metal component (C) is a value obtained by quantifying the metal component using a fluorescent X-ray device ("MagiX PRO" manufactured by Spectris Inc.) and measuring the content of the metal component (C) contained in the thermoplastic resin composition.

[0073] "Method for producing thermoplastic resin composition" The method for producing the thermoplastic resin composition is not particularly limited. For example, the graft copolymer (A), the vinyl copolymer (B), the metal component (C), and, if necessary, other components (other thermoplastic resins, additives) are mixed and dispersed using a V-type blender, a Henschel mixer, or the like, and the resulting mixture is melt-kneaded using a melt-kneading machine such as a screw extruder, a Banbury mixer, a pressure kneader, or a mixing roll, to produce a thermoplastic resin composition. After melt-kneading, the melt-kneaded mixture may be pelletized using a pelletizer, if necessary.

[0074] <Action and Effect> In the thermoplastic resin composition of the present embodiment described above, it contains a graft copolymer (A), a vinyl copolymer (B), and a metal component (C), and the content of the metal component (C) is 60 ppm or more with respect to the total mass of the thermoplastic resin composition, and the graft copolymer (A) is a rubber-like polymer (a) containing polyorganosiloxane and an alkyl (meth) acrylate polymer. In the presence of 20% by mass to 80% by mass of a vinyl monomer mixture (m1) containing one or more vinyl monomers. A graft polymer obtained by polymerizing 80% to 20% by mass, the vinyl copolymer (B) is a vinyl copolymer obtained by polymerizing a vinyl monomer mixture (m2) containing an alkyl (meth) acrylate monomer, and the metal component (C) is an alkali metal. Since it is a thermoplastic resin composition, a molded article having excellent heat discoloration resistance can be obtained.

[0075] [Molded Article] A molded article according to one embodiment of the present invention is made from the thermoplastic resin composition according to this embodiment. In other words, the molded article according to this embodiment is obtained by molding the thermoplastic resin composition according to this embodiment using a known molding method. Examples of molding methods include injection molding, press molding, extrusion molding, vacuum molding, and blow molding. Applications of the molded article include vehicle interior and exterior parts, office equipment, home appliances, and building materials, with vehicle exterior parts being preferred.

[0076] The molded article of the present embodiment described above uses the thermoplastic resin composition of the present embodiment, and therefore has excellent resistance to heat discoloration.

[0077] Specific examples are shown below. However, the present invention is not limited to these examples. In the following, "%" means "% by mass" and "parts" means "parts by mass." Various measurement and evaluation methods in the following examples and comparative examples are as follows.

[0078] <Evaluation of Thermal Discoloration> Pellets of the thermoplastic resin composition were molded using a 30-ton injection molding machine ("NEX30W-3E" manufactured by Nissei Plastic Industrial Co., Ltd.) under conditions of cylinder set temperatures of 230°C and 280°C and a mold temperature of 60°C, to obtain molded articles having a length of 80 mm, a width of 55 mm, and a thickness of 2 mm. For both the obtained molded articles at 230°C and 280°C, b*, which indicates the intensity of the color from blue to yellow, was measured using an ultraviolet-visible-near-infrared spectrophotometer ("V-670" manufactured by JASCO Corporation) using the SCE method, and the index of thermal discoloration Δb* was calculated using the following formula (1). The smaller Δb* is, the better the thermal discoloration is suppressed. Δb* = b* （２８０℃） -b* （２３０℃） (1) However, in the above formula (1), b* （２３０℃） is the b* value of the product molded at 230°C, b* （２８０℃） is the b* value of the product molded at 280°C.

[0079] <Evaluation of molded appearance> Pellets of the thermoplastic resin composition were molded into dumbbell test pieces used in the ISO 178 test using an 85-ton injection molding machine ("J85AD-110H" manufactured by The Japan Steel Works, Ltd.) under conditions of a cylinder set temperature of 280°C and a mold temperature of 60°C, and the resulting test pieces were visually inspected for the presence or absence of silver streaks. The evaluation criteria are as follows: A: No silver streaks observed B: Minor silver streaks observed in 1 to 2 places C: Silver streaks observed in 3 or more places

[0080] <Content of Metal Component> The metal components of the molded articles evaluated for thermal discoloration were quantified using a fluorescent X-ray analyzer ("MagiX PRO" manufactured by Spectris Inc.), and the concentrations of sodium (Na) and potassium (K) contained in the thermoplastic resin composition were measured.

[0081] <Polyorganosiloxane (s)> (Production of polyorganosiloxane (s-1)) 98 parts of octamethylcyclotetrasiloxane and 2 parts of γ-methacryloyloxypropyldimethoxymethylsilane were mixed to obtain 100 parts of a siloxane mixture. To this was added an aqueous solution of 0.67 parts of sodium dodecylbenzenesulfonate and 300 parts of ion-exchanged water, and the mixture was stirred at 10,000 rpm for 2 minutes using a homomixer. After stirring, the mixture was subjected to a homogenizer at 300 kg / cm. ２ The reaction mixture was passed twice at a pressure of 100 kJ / min, yielding a stable premixed organosiloxane latex. Separately, 10 parts of dodecylbenzenesulfonic acid and 90 parts of ion-exchanged water were charged into a reactor equipped with a reagent injection vessel, a cooling tube, a jacket heater, and a stirrer, to prepare a 10% aqueous solution of dodecylbenzenesulfonic acid (acid catalyst aqueous solution). With this acid catalyst aqueous solution heated to 85°C, the premixed organosiloxane latex was added dropwise over two hours. After completion of the dropwise addition, the temperature was maintained for three hours and then cooled to below 40°C. The reaction mixture was then neutralized to pH 7.0 with a 10% aqueous sodium hydroxide solution to yield a latex of polyorganosiloxane (s-1). A portion of the polyorganosiloxane (s-1) latex was dried at 180°C for 30 minutes, and the solids content was determined to be 18.2%. The average particle diameter by mass of particles dispersed in the latex was 30 nm.

[0082] <Graft Copolymer (A)> (Production of Graft Copolymer (A-1)) In a reactor equipped with a reagent injection vessel, a cooling tube, a jacket heater, and a stirrer, 6.0 parts of polyorganosiloxane (s-1) latex (solids equivalent), 0.5 parts of sodium alkyl diphenyl ether disulfonate were charged, and 190 parts of ion-exchanged water was added and mixed. Thereafter, a mixture consisting of 44.0 parts of n-butyl acrylate as a monomer constituting an alkyl (meth)acrylate rubber-like polymer (a-1), 0.2 parts of allyl methacrylate, 0.06 parts of 1,3-butylene glycol dimethacrylic acid diester, and 0.1 parts of t-butyl hydroperoxide was added. A nitrogen stream was passed through the reactor to replace the atmosphere with nitrogen, and the temperature was raised to 60 ° C. When the temperature inside the reactor reached 60°C, an aqueous solution prepared by dissolving 0.0001 parts of ferrous sulfate, 0.0003 parts of ethylenediaminetetraacetic acid disodium salt, and 0.2 parts of Rongalit in 10 parts of ion-exchanged water was added to initiate radical polymerization. The liquid temperature rose to 78°C due to polymerization of the alkyl(meth)acrylate component. This state was maintained for 1 hour, and polymerization was continued until no further heat of polymerization was observed, yielding a latex of composite rubber polymer (a-1). The volume average particle diameter of the alkyl(meth)acrylate rubber polymer (a-1) dispersed in the latex was 88 nm.

[0083] Next, after the liquid temperature inside the reactor had dropped to 60°C, an aqueous solution containing 0.3 parts of Rongalite dissolved in 10 parts of ion-exchanged water was added. A mixed solution containing 2.5 parts of acrylonitrile, 7.5 parts of styrene, and 0.05 parts of t-butyl hydroperoxide was then added dropwise over approximately 1 hour to allow polymerization. After the completion of the dropwise addition and the resulting mixture was held for 1 hour, an aqueous solution containing 0.0002 parts of ferrous sulfate, 0.0006 parts of ethylenediaminetetraacetic acid disodium salt, and 0.25 parts of Rongalite dissolved in 10 parts of ion-exchanged water was added dropwise over approximately 40 minutes to allow polymerization. After the completion of the dropwise addition and the mixture was held for 1 hour, the mixture was cooled to obtain a latex of graft copolymer (A-1). Next, 250 parts of an aqueous solution containing 2% calcium acetate was heated to 50°C and stirred. 100 parts of the latex of the graft copolymer (A-1) was slowly added dropwise to the aqueous calcium acetate solution to coagulate the mixture, which was then separated, washed, and dried to obtain a dry powder of the graft copolymer (A-1).

[0084] <Vinyl-based copolymer (B)> (Vinyl-based copolymer (B-1)) Polymethyl methacrylate "ACRYPET VH5" (manufactured by Mitsubishi Chemical Corporation, 98 parts of methyl methacrylate, 2 parts of methacrylic acid, mass average molecular weight (Mw) 7×10 ３ ) was used as the vinyl copolymer (B-1).

[0085] <Metal Component (C)> (Metal Component (C-1)) As a potassium-containing compound, an aqueous solution of dipotassium alkenyl succinate (trade name: Latemul ASK, manufactured by Kao Corporation) was used.

[0086] <Metal Component (C)> (Metal Component (C-2)) Anhydrous sodium pyrophosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as a compound containing sodium.

[0087] <Metal Component (C)> (Metal Component (C-3)) Sodium acetate trihydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as a compound containing sodium.

[0088] Example 1: 45 parts of graft copolymer (A-1), 55 parts of vinyl copolymer (B-1), 0.4 parts of metal component (C-1), 0.5 parts of ethylene bisstearylamide, 0.3 parts of Adeka STAB LA-36 (manufactured by ADEKA Corporation), 0.3 parts of Adeka STAB LA-63P (manufactured by ADEKA Corporation), and 5 parts of titanium oxide as a colorant were mixed using a Henschel mixer. The mixture was melt-kneaded at a cylinder temperature of 240°C using a 28mmφ vacuum-vented twin-screw extruder ("TEX-28V" manufactured by The Japan Steel Works, Ltd.), and pelletized using a pelletizer ("SH-type pelletizer" manufactured by Soken Co., Ltd.) to obtain a thermoplastic resin composition. Various molded articles were produced using the obtained thermoplastic resin composition, and thermal discoloration and molded appearance were evaluated. The amounts of the metal component (C), additives, and colorants are expressed as a percentage of the total mass (100 parts) of the graft copolymer (A) and the vinyl copolymer (B). The results are shown in Tables 1 and 2. In Table 1, the amount of the metal component (C) represents the amount of the compound containing the metal component (C).

[0089] [Examples 2 to 9, Comparative Examples 1 and 2] Thermoplastic resin compositions were prepared in the same manner as in Example 1, except that the formulations were changed to those shown in Tables 1 and 2. Various molded articles were produced and evaluated for thermal discoloration and molded appearance. The results are shown in Tables 1 and 2.

[0090]

[0091]

[0092] The molded articles obtained from the thermoplastic resin compositions of Examples 1 to 9 are excellent in heat discoloration resistance. Therefore, it can be seen that the use of the thermoplastic resin composition of the present invention allows for the production of molded articles with excellent heat discoloration resistance. Furthermore, the molded articles obtained from the thermoplastic resin compositions of Examples 1 to 3, 5, and 9 are also excellent in molded appearance. On the other hand, the molded articles obtained from the thermoplastic resin compositions of Comparative Examples 1 and 2 are poor in heat discoloration resistance.

[0093] Molded articles using the thermoplastic resin composition of the present invention are useful as interior and exterior vehicle parts, office equipment, home appliances, building materials, etc., and are particularly useful as exterior vehicle parts.

Claims

1. A thermoplastic resin composition comprising the following graft copolymer (A), the following vinyl copolymer (B), and the following metal component (C), wherein the content of the following metal component (C) is 60 ppm or more based on the total mass of the thermoplastic resin composition. (A): A graft polymer obtained by polymerizing a vinyl monomer mixture (m1) containing one or more vinyl monomers in the presence of 20% by mass to 80% by mass of a rubbery polymer (a) obtained from a polyorganosiloxane and an alkyl (meth) acrylate polymer, the vinyl monomer mixture (m1) being 80% by mass to 20% by mass (however, the total of the rubbery polymer (a) and the vinyl monomer mixture (m1) is 100% by mass). (B): A vinyl copolymer obtained by polymerizing a vinyl monomer mixture (m2) containing an alkyl (meth) acrylate monomer. (C): A metal component that is an alkali metal 2. The thermoplastic resin composition according to claim 1, wherein the content of the metal component (C) is 100 ppm to 400 ppm based on the total mass of the thermoplastic resin composition.

3. The thermoplastic resin composition according to claim 1 or 2, wherein the metal component (C) contains potassium.

4. The thermoplastic resin composition according to any one of claims 1 to 3, wherein the content of the graft polymer (A) is 20 parts by mass to 80 parts by mass based on the total mass of the thermoplastic resin composition.

5. A molded article formed from the thermoplastic resin composition according to any one of claims 1 to 4.