Monomer mixture, resin composition, and resin molded article

Abstract

To provide a resin composition and a monomer mixture for the resin composition, capable of yielding a resin molded article under good thermal moldability, the resin molded article ensuring high impact resistance while retaining the inherent excellent transparency, suppression of yellowing, and heat resistance of methacrylic resin.SOLUTION: A monomer mixture comprises a monomer composition (S1) including methyl methacrylate, rubber particles (a), a mercaptan-type chain transfer agent (b), and a peroxyester-type radical polymerization initiator (c), wherein the monomer mixture further contains a phosphorus compound (d). A resin composition is produced by polymerizing the monomer mixture. A resin molded article is produced by molding the resin composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition, a resin molded article, and a monomer mixture for obtaining the same, which simultaneously exhibit two effects: excellent heat resistance and impact resistance. [Background technology]

[0002] Methacrylic resins are excellent in transparency, resistance to yellowing, heat resistance, and weather resistance, and also have well-balanced performance in terms of resin properties such as mechanical strength, thermal properties, moldability, etc. Due to these excellent properties, methacrylic resins are used in many applications such as vehicle components, medical components, toys, liquid containers, optical components, signs, displays, decorative components, architectural components, and face plates of electronic devices. However, in these applications, it is required to impart impact resistance to the products.

[0003] A known technique for improving the impact resistance of methacrylic resin products is to incorporate rubber particles obtained by emulsion polymerization, etc. By using rubber particles, the impact resistance of the resin composition can be easily improved without requiring precise control of polymerization conditions. For example, Patent Document 1 describes a method for obtaining a highly impact-resistant methacrylic resin composition by melt-kneading a mixture of rubber particles with a high gel content and a methacrylic resin to form pellets, and then hot-press molding the pellets. Furthermore, Patent Document 2 discloses a resin composition in which a rubber (core-shell rubber) having a core-shell structure, which has a core made of crosslinked rubber and a shell that ensures compatibility and dispersibility with a (meth)acrylic polymer that forms a matrix, is blended with a (meth)acrylic resin.

[0004] On the other hand, in the above-mentioned applications, it is required to mold the methacrylic resin into a complex shape using a thermoforming method depending on the shape of the product. In the polymerization of (meth)acrylic acid esters, known mercaptan chain transfer agents are often used as chain transfer agents to improve the thermoformability of the resulting polymers. In addition, peroxyester polymerization initiators, rather than azo polymerization initiators, are often used as polymerization initiators to prevent foaming during thermoforming. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 241690 [Patent Document 2] Special Publication No. 62-21804 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the inventors have found through their investigations that when methyl methacrylate is polymerized using a mercaptan-based chain transfer agent and a peroxyester-based radical polymerization initiator together with rubber particles as disclosed in Patent Documents 1 and 2 in order to improve impact resistance and thermoformability, the heat resistance of the resulting resin composition and resin molded article is significantly reduced, and further, the transparency is also impaired. For this reason, in a methacrylic resin composition containing a mercaptan chain transfer agent and a peroxyester radical polymerization initiator together with rubber particles, it has been difficult to obtain a resin molded article that has the excellent heat resistance and transparency inherent to methacrylic resins while maintaining high impact resistance and good thermoformability.

[0007] Therefore, in view of the above circumstances, an object of the present invention is to provide a resin composition and a monomer mixture therefor that can provide a resin molded article with good thermoformability that ensures high impact resistance while also ensuring the excellent transparency, suppression of yellowing, and heat resistance that are inherent to methacrylic resins. [Means for solving the problem]

[0008] As a result of intensive research, the present inventors have found that by adding a phosphorus-based compound (d) to a monomer mixture containing methyl methacrylate, rubber particles (a), a mercaptan-based chain transfer agent (b), and a peroxyester-based radical polymerization initiator (c), a resin composition obtained by polymerizing the mixture can be molded into a resin molded article, which can achieve extremely unique results in that the resin molded article can suppress the problems of deterioration in heat resistance and transparency and yellowing while maintaining the high impact resistance due to the inclusion of the rubber particles (a). The present invention was achieved based on these findings and has the following gist.

[0009] [1] A monomer mixture comprising a monomer composition (S1) containing methyl methacrylate, rubber particles (a), a mercaptan chain transfer agent (b), and a peroxyester radical polymerization initiator (c), wherein the monomer mixture further contains a phosphorus-based compound (d).

[0010] [2] The monomer mixture according to [1], wherein the rubber particles (a) are contained in an amount of 1.0 parts by mass or more and 10.0 parts by mass or less per 100 parts by mass of the total mass of the monomer composition (S1).

[0011] [3] The monomer mixture according to [2], wherein the rubber particles (a) are contained in an amount of 1.0 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the total mass of the monomer composition (S1).

[0012] [4] The monomer mixture according to any one of [1] to [3], wherein the monomer composition (S1) contains methyl methacrylate as a main component.

[0013] [5] The monomer mixture according to [4], wherein the monomer composition (S1) contains 70 to 100% by mass of methyl methacrylate and 0 to 30% by mass of an acrylic acid ester, based on 100% by mass of the total mass of the monomer composition (S1).

[0014] [6] The monomer mixture according to any one of [1] to [5], wherein the rubber particles (a) have a multilayer structure.

[0015] [7] The monomer mixture according to any one of [1] to [6], wherein the mercaptan chain transfer agent (b) is contained in an amount of 0.01 part by mass or more and 1.0 part by mass or less per 100 parts by mass of the total mass of the monomer composition (S1).

[0016] [8] The monomer mixture according to any one of [1] to [7], wherein the mercaptan chain transfer agent (b) has 8 or more and 15 or less carbon atoms.

[0017] [9] The monomer mixture according to [8], wherein the mercaptan chain transfer agent (b) is n-octyl mercaptan and / or n-dodecyl mercaptan.

[0018]

[10] The monomer mixture according to any one of [1] to [9], wherein the peroxyester radical polymerization initiator (c) is contained in an amount of 0.1 part by mass or more and 1.0 part by mass or less per 100 parts by mass of the total mass of the monomer composition (S1).

[0019]

[11] The monomer mixture according to any one of [1] to

[10] , wherein the phosphorus compound (d) is contained in an amount of 0.005 parts by mass or more and 1.000 parts by mass or less per 100 parts by mass of the total mass of the monomer composition (S1).

[0020]

[12] The monomer mixture according to any one of [1] to

[11] , wherein the phosphorus-based compound (d) comprises one or more compounds selected from the group consisting of phosphate esters, phosphonate esters, phosphoric acid, phosphonic acid, phosphines, phosphorous acid, and phosphite esters.

[13] The monomer mixture according to

[12] , wherein the phosphorus-based compound (d) comprises one or more compounds selected from the group consisting of phosphate esters, phosphines, and phosphoric acids.

[14] The monomer mixture according to

[13] , wherein the phosphorus-based compound (d) contains a phosphate ester.

[15] The monomer mixture according to

[14] , wherein the phosphate ester is a monoalkyl phosphate ester and / or a dialkyl phosphate ester.

[16] The monomer mixture according to

[15] , wherein the phosphorus compound (d) is ethyl acid phosphate and / or 2-ethylhexyl acid phosphate.

[0021]

[17] A resin composition obtained by polymerizing the monomer mixture according to any one of [1] to

[16] .

[0022]

[18] A resin molded product obtained by molding the resin composition according to

[17] .

[19] A resin cast plate comprising the resin composition according to

[17] .

[20] An optical member obtained by molding the resin composition according to

[17] .

[21] A vehicle component obtained by molding the resin composition according to

[17] .

[22] A signboard formed by molding the resin composition according to

[17] .

[23] A resin plate for an amusement machine, obtained by molding the resin composition according to

[17] . [Effects of the Invention]

[0023] According to the present invention, even in a methacrylic resin composition that contains rubber particles (a) to improve impact resistance and also contains a mercaptan chain transfer agent (b) and a peroxyester radical polymerization initiator (c) to improve thermoformability, the inclusion of a phosphorus-based compound (d) can suppress deterioration in heat resistance and transparency.

[0024] Therefore, according to the present invention, it is possible to provide a resin composition and a monomer mixture therefor that can obtain a resin molded product with good thermoformability that ensures high impact resistance while also ensuring the excellent transparency, suppression of yellowing, and heat resistance that are inherent to methacrylic resins. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following. In this specification, a numerical range expressed using "to" means a range that includes the numerical values written before and after "to" as the lower and upper limits, and "A to B" means A or more and B or less. In this specification, "(meth)acrylate" means at least one selected from "acrylate" and "methacrylate", and "(meth)acrylic acid" means at least one selected from "acrylic acid" and "methacrylic acid". The same applies to "(meth)acrylic" and "(meth)acrylo". "Methacrylic resin" means at least one selected from "acrylic resin" and "methacrylic resin". In the present invention, the term "monomer" refers to an unpolymerized compound, and the term "repeating unit" refers to a unit derived from a monomer formed by polymerization of the monomer. The repeating unit may be a unit formed directly by a polymerization reaction, or may be a unit obtained by converting a part of the unit into a different structure by treating the polymer. In this specification, the term "resin composition obtained" means a resin composition obtained by polymerizing the monomer mixture of the present invention. In this specification, the term "resin molded article obtained" refers to a resin molded article obtained by molding the resin composition obtained in the present invention.

[0026] [1. Monomer mixture] The monomer mixture of the present invention contains, as essential components, a monomer composition (S1) described below, rubber particles (a), a mercaptan-based chain transfer agent (b), a peroxyester-based radical polymerization initiator (c), and a phosphorus-based compound (d).

[0027] [1-1. Monomer composition (S1)] The monomer composition (S1) is a composition containing methyl methacrylate. When the resin composition of the present invention contains the (meth)acrylic polymer (P) described below, the monomer composition (S1) is a composition containing a monomer that is a raw material of the (meth)acrylic polymer (P).

[0028] The content of methyl methacrylate in the monomer composition (S1) is not particularly limited, but from the viewpoint of improving the transparency and mechanical strength of the resulting resin molded product, it is preferable that the monomer composition (S1) contains methyl methacrylate as a main component, and the content of methyl methacrylate is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, relative to 100% by mass of the total mass of the monomer composition (S1), and may be 100% by mass.

[0029] The monomer composition (S1) may contain a monomer component other than methyl methacrylate that is copolymerizable with methyl methacrylate. That is, the monomer composition (S1) may be a monomer composition consisting of 50 to 100 mass % of methyl methacrylate and 0 to 50 mass % of a monomer other than methyl methacrylate that is copolymerizable therewith (hereinafter, may be referred to as a "copolymerizable monomer"), or a partial polymer thereof, or a mixture thereof. A preferred monomer composition (S1) comprises 90% by mass or more of methyl methacrylate and 10% by mass or less of at least one copolymerizable monomer.

[0030] The copolymerizable monomer other than methyl methacrylate constituting the monomer composition (S1) is not particularly limited as long as it is a monomer copolymerizable with methyl methacrylate. The copolymerizable monomer may be a monofunctional monomer having one radically polymerizable double bond in one molecule, or a polyfunctional monomer having two or more radically polymerizable double bonds in one molecule. From the viewpoint of achieving an excellent balance between fluidity, moldability, and thermal decomposition property of the resulting (meth)acrylic polymer (P), the copolymerizable monomer other than methyl methacrylate is preferably an acrylic acid ester.

[0031] When the monomer composition (S1) contains an acrylic acid ester as a copolymerizable monomer, it preferably contains, in 100 mass% of the monomer composition (S1), 50 mass% or more and less than 100 mass% of methyl methacrylate and more than 0 mass% and 50 mass% or less of the acrylic acid ester, more preferably 70 mass% or more and less than 100 mass% of methyl methacrylate and more than 0 mass% and 30 mass% or less of the acrylic acid ester, even more preferably 80 mass% or more and 99.9 mass% or less of methyl methacrylate and 0.1 mass% or more and 20 mass% or less of the acrylic acid ester, and particularly preferably 90 mass% or more and 99.5 mass% or less of methyl methacrylate and 0.5 mass% or more and 10 mass% or less of the acrylic acid ester.

[0032] Examples of acrylic acid esters include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, isobornyl acrylate, glycidyl acrylate, tetrahydrofurfuryl acrylate, norbornyl acrylate, adamantyl acrylate, dicyclopentenyl acrylate, dicyclopentanyl acrylate, 2-hydroxyethyl acrylate, and 2-hydroxypropyl acrylate. Preferred are methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate, and more preferred are methyl acrylate and ethyl acrylate. The acrylic acid esters may be used alone or in combination of two or more.

[0033] In the present invention, examples of copolymerizable monomers other than the above-mentioned acrylic esters that can be used in combination with methyl methacrylate include methacrylic esters other than methyl methacrylate, such as ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, benzyl methacrylate, and 2-hydroxypropyl methacrylate; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and itaconic acid; acid anhydrides such as maleic anhydride and itaconic anhydride; maleimide derivatives such as N-phenylmaleimide, N-cyclohexylmaleimide, and Nt-butylmaleimide; vinyl acetate, vinylidene chloride, or derivatives thereof; nitrogen-containing monomers such as (meth)acrylamide, (meth)acrylonitrile, diacetone(meth)acrylamide, and dimethylaminoethyl (meth)acrylate; epoxy group-containing monomers such as allyl glycidyl ether and glycidyl (meth)acrylate; and styrene-based monomers such as styrene and α-methylstyrene. As for these copolymerizable monomers other than acrylate esters, one type may be used alone, or two or more types may be used in combination.

[0034] When the monomer composition (S1) contains a copolymerizable monomer other than these acrylate esters, the content of the copolymerizable monomer other than the acrylate esters in 100% by mass of the monomer composition (S1) is preferably 40% by mass or less, particularly 0 to 30% by mass, from the viewpoint of the transparency and mechanical strength of the resulting resin molded product.

[0035] [1-2. Rubber particles (a)] The rubber particles (a) constituting the monomer mixture of the present invention contain a rubbery graft polymer having a crosslinked structure. Unlike a (meth)acrylic copolymer, the rubbery graft polymer having a crosslinked structure is a particulate rubber containing a core made of a rubber portion and a shell component having functions such as compatibility with the matrix. The core-shell rubber is used for the purpose of imparting impact resistance to the resin composition of the present invention and the resin molded article obtained by molding it.

[0036] The rubber particles (a) are not particularly limited as long as they contain a rubbery copolymer having a cross-linked structure obtained by at least one polymerization stage. The rubber particles (a) may be obtained by two-stage polymerization of a rubbery copolymer having a cross-linked structure and a graft copolymer, or by three-stage polymerization in which the first polymerization stage produces a hard copolymer mainly composed of methyl methacrylate. The rubber particles (a) may also be obtained by four or more polymerization stages in which hard copolymers and rubbery copolymers are alternately arranged and the final stage is a hard graft copolymer. The rubber particles (a) preferably have a structure of two or more layers, and more preferably have a structure of three or more layers.

[0037] Suitable examples of the rubber copolymer include commonly used diene rubber, acrylic rubber, silicone rubber, and silicone / acrylic composite rubber. Among these, acrylic rubber is preferred from the viewpoints of weather resistance and transparency. Furthermore, from the viewpoint of improving impact resistance, these rubber copolymers are preferably contained in an amount of 30 parts by mass or more, more preferably 60 parts by mass or more, per 100 parts by mass of the rubber particles (a) which are multistage copolymers.

[0038] Suitable acrylic rubbers include, for example, acrylate polymers having an alkyl group with 4 to 10 carbon atoms, such as butyl acrylate and 2-ethylhexyl acrylate, and copolymers of the acrylate esters with monomers copolymerizable with the acrylate esters.

[0039] Examples of the copolymerizable monomer include styrene-based monomers such as styrene and α-methylstyrene; methacrylic acid esters such as methyl methacrylate and ethyl methacrylate; acrylic acid esters having an alkyl group with 1 to 3 carbon atoms such as methyl acrylate and ethyl acrylate; vinyl cyanide compounds such as (meth)acrylonitrile; and polyfunctional polymerizable compounds having two or more ethylenically unsaturated bonds in the molecule such as ethylene glycol di(meth)acrylate, allyl (meth)acrylate, divinylbenzene, and 1,3-butylene (meth)acrylate. Among these, polyfunctional polymerizable compounds capable of forming a crosslinked structure are preferred. The copolymerizable monomer may be used alone or in combination of two or more kinds, but it is particularly preferable that the copolymer contains at least one kind of the polyfunctional polymerizable compound.

[0040] The amount of the polyfunctional polymerizable compound used is preferably 5 parts by mass or less, more preferably 0.01 to 3.00 parts by mass, per 100 parts by mass of the rubber copolymer. When the amount of the polyfunctional polymerizable compound used is 5 parts by mass or less, an appropriate crosslink density can be obtained in the rubber copolymer, and impact resistance can be improved.

[0041] The polymerization method and polymerization conditions for producing the rubber particles (a) are not particularly limited, and ordinary emulsion polymerization, soap-free emulsion polymerization, etc. can be used.

[0042] The method for measuring the average primary particle size of the rubber particles (a) is not particularly limited, and the average primary particle size can be measured by known methods such as dynamic light scattering, laser diffraction, centrifugal sedimentation, and capillary hydrodynamic flow fractionation (hereinafter referred to as "CHDF").

[0043] The average primary particle diameter of the rubber particles (a) is not particularly limited, but is preferably 50 nm or more, more preferably 100 nm or more, and even more preferably 200 nm or more. The average primary particle diameter of the rubber particles (a) is preferably 1000 nm or less, more preferably 700 nm or less, and even more preferably 500 nm or less. If the average primary particle diameter is 50 nm or more, the rubber functions well, and toughness and impact resistance can be effectively improved. If the average primary particle diameter is 1000 nm or less, the interparticle distance is reduced, resulting in good toughness and impact resistance. The above upper and lower limit values can be combined arbitrarily.

[0044] Commercially available rubber particles (a) can also be used. Examples of commercially available rubber particles (a) suitable for the present invention include XC-IMPACT MODIFIERS (manufactured by Mitsubishi Chemical UK Limited), Metablen W-450A, S-2001, Acrypet IR377, IR441, and IR491 (manufactured by Mitsubishi Chemical Corporation), and Kane Ace M-570 and FM-40 (manufactured by Kaneka Corporation).

[0045] The rubber particles (a) may be of one type, or two or more types having different compositions, structures or physical properties may be used.

[0046] The content of the rubber particles (a) constituting the monomer mixture of the present invention is not particularly limited. However, from the viewpoint of improving the impact resistance of the resulting resin molded article, the lower limit is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 2.0 parts by mass or more, per 100 parts by mass of the total mass of the monomer composition (S1). Furthermore, from the viewpoint of maintaining the elastic modulus of the resulting resin molded article, the upper limit is preferably 10.0 parts by mass or less, more preferably 8.0 parts by mass or less, and even more preferably 5.0 parts by mass or less. The above upper and lower limits can be arbitrarily combined. For example, the content of the rubber particles (a) is preferably 0.5 to 10.0 parts by mass, more preferably 1.0 to 10.0 parts by mass, more preferably 1.0 to 8.0 parts by mass, and particularly preferably 1.0 to 5.0 parts by mass, per 100 parts by mass of the monomer composition (S1).

[0047] [1-3. Mercaptan chain transfer agents (b)] The mercaptan chain transfer agent (b) constituting the monomer mixture of the present invention is preferably contained in the polymerization stage of the monomer composition (S1) containing methyl methacrylate, i.e., the mercaptan chain transfer agent (b) is preferably added in the polymerization stage of the monomer composition (S1).

[0048] The mercaptan chain transfer agent (b) can be selected from those typically used in radical polymerization, and is preferably a mercaptan chain transfer agent (b) such as an alkyl mercaptan having 2 to 20 carbon atoms, mercapto acids, thiophenol, or a mixture thereof. More preferably, it is a mercaptan chain transfer agent (b) such as an alkyl mercaptan having 8 to 15 carbon atoms, mercapto acids, thiophenol, or a mixture thereof, and even more preferably, it is a mercaptan with a short alkyl group chain length, such as n-octyl mercaptan or n-dodecyl mercaptan. These mercaptan chain transfer agents (b) may be used alone or in combination of two or more.

[0049] The content of the mercaptan chain transfer agent (b) is typically 0.001 parts by mass or more, preferably 0.005 parts by mass or more, and more preferably 0.01 parts by mass or more, relative to 100 parts by mass of the total mass of the monomer composition (S1) constituting the monomer mixture, from the viewpoint of maximizing impact resistance. On the other hand, the content of the mercaptan chain transfer agent (b) is typically 2.0 parts by mass or less, preferably 1.5 parts by mass or less, and more preferably 1.0 part by mass or less. If the mercaptan chain transfer agent (b) exceeds 2.0 parts by mass, a significant decrease in molecular weight is observed, resulting in a decrease in the elastic modulus. The above upper and lower limits can be combined arbitrarily. For example, the content of the mercaptan chain transfer agent (b) may be in the range of 0.001 to 2.0 parts by mass, 0.001 to 1.5 parts by mass, 0.005 to 1.5 parts by mass, 0.01 to 1.5 parts by mass, or 0.01 to 1.0 parts by mass relative to 100 parts by mass of the monomer composition (S1).

[0050] [1-4. Peroxyester radical polymerization initiator (c)] The peroxyester radical polymerization initiator (c) constituting the monomer mixture of the present invention is preferably contained in the polymerization stage of the monomer composition (S1) mainly composed of methyl methacrylate, i.e., the peroxyester radical polymerization initiator (c) is preferably added in the polymerization stage of the monomer composition (S1).

[0051] Examples of the peroxyester radical polymerization initiator (c) include (α,α'-bis-neodecanoylperoxy)diisopropylbenzene, cumylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, t-hexylperoxyneodecanoate, t-butylperoxyneodecanoate, t-hexylperoxypivalate, and t-butylperoxyneohexanoate. peroxy-2-ethylhexanoate, t-amylperoxy-2-ethylhexanoate, t-butylperoxypivalate, t-amylperoxypivalate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate t-butylperoxyisopropyl monocarbonate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxylaurate, 2,5-dimethyl-2,5-bis(m-toluoylperoxy)hexane, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, t-hexylperoxybenzoate, 2,5-dimethyl t-butyl-2,5-bis(benzoylperoxy)hexane, t-butyl peroxyacetate, t-butyl peroxy-m-toluoylbenzoate, t-butyl peroxybenzoate, bis-t-butylperoxyisophthalate, 2,4,4-trimethylpentylperoxy-phenoxyacetate, di-t-butylperoxyhexahydroterephthalate, di-t-butylperoxyazelate, di-t-butylperoxy-trimethyladipate, and the like. These may be used alone or in combination of two or more.

[0052] Particularly preferred among the above peroxy ester radical polymerization initiators (c) are those having a decomposition temperature in the range of 35 to 65°C to obtain a 10-hour half-life, and examples thereof include t-butyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, t-butyl peroxypivalate, t-amyl peroxypivalate, t-hexyl peroxypivalate, t-butyl peroxy-2-ethylhexanoate, and t-butyl peroxyisobutyrate.

[0053] The content of the peroxyester radical polymerization initiator (c) in the monomer mixture of the present invention is typically 0.05 parts by mass or more, preferably 0.075 parts by mass or more, and more preferably 0.1 parts by mass or more, per 100 parts by mass of the total mass of the monomer composition (S1) constituting the monomer mixture, from the viewpoint of ensuring sufficient polymerization. On the other hand, the content is typically 5.0 parts by mass or less, preferably 3.0 parts by mass or less, and more preferably 1.0 parts by mass or less. If the content of the peroxyester radical polymerization initiator (c) exceeds 5.0 parts by mass, it becomes difficult to control the polymerization. The above upper and lower limits can be arbitrarily combined. For example, the content of the peroxyester radical polymerization initiator (c) may be in the range of 0.05 to 5.0 parts by mass, 0.05 to 3.0 parts by mass, 0.075 to 3.0 parts by mass, 0.075 to 1.0 parts by mass, or 0.1 to 1.0 parts by mass, per 100 parts by mass of the total mass of the monomer composition (S1).

[0054] In the present invention, other polymerization initiators than the peroxyester radical polymerization initiator (c) can be used in combination, provided that the object of the present invention is not impaired. Examples of other polymerization initiators that can be used in combination include azo compounds such as 2,2'-azobis-(2,4-dimethylvaleronitrile) and azobisisobutyronitrile. When these azo-based polymerization initiators are used in combination, the amount used is preferably 0.05 to 5 parts by mass, particularly 0.1 to 1 part by mass, per 100 parts by mass of the total mass of the monomer composition (S1). Other polymerization initiators such as azo-based polymerization initiators may be added in advance to the monomer mixture of the present invention separately from the peroxyester-based radical polymerization initiator (c), and a part of the monomer composition (S1) may be polymerized by this polymerization initiator, thereby containing the syrup in the monomer mixture of the present invention.

[0055] [1-5. Phosphorus compounds (d)] The phosphorus-based compound (d) constituting the monomer mixture of the present invention may be, for example, at least one phosphorus-based compound (d) selected from phosphate esters, phosphonate esters, phosphoric acid, phosphonic acid, phosphine, phosphorous acid, and phosphite esters. From the viewpoint of providing the resulting resin composition and resin molded article with excellent heat resistance and transparency, as well as the effect of inhibiting yellowing, at least one compound selected from phosphate esters, phosphines, and phosphoric acid is more preferred, and phosphate esters are even more preferred. The phosphorus-based compound (d) is preferably contained in the polymerization stage of the monomer mixture mainly composed of methyl methacrylate. That is, it is preferably added in the polymerization stage of the monomer composition (S1).

[0056] The phosphoric acid ester is not particularly limited, but examples thereof include aliphatic phosphoric acid esters such as monoethyl phosphate, monobutyl phosphate, methyl acid phosphate, ethyl acid phosphate, 2-ethylhexyl acid phosphate, butyl acid phosphate, dibutyl phosphate, trimethyl phosphate, and triethyl phosphate; aromatic phosphoric acid esters such as triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl diphenyl phosphate, and 2-ethylhexyl diphenyl phosphate; and derivative compounds thereof, condensates thereof, phosphorus oxychloride and dihydric phenol compounds; and phenol (or aryl phosphate). Examples of suitable phosphate esters include reaction products with bis(2,3-dichlorophenyl)sulfonyl phosphate, such as aromatic condensed phosphate esters such as resorcinol bis-diphenyl phosphate, resorcinol bis-dixylenyl phosphate, and bisphenol A bis-diphenyl phosphate; and derivative compounds and condensates thereof; and halogen-containing phosphate esters such as tris(chloroethyl)phosphate, tris(chloropropyl)phosphate, tris(dichloropropyl)phosphate, tris(dibromopropyl)phosphate, bis(2,3-dibromopropyl)-2,3-dichloropropyl phosphate, and bis(chloropropyl)octyl phosphate; and derivative compounds and condensates thereof. These may be used alone or in combination of two or more.

[0057] Of these, from the viewpoint of the heat resistance and transparency of the resulting resin molded article, monoalkyl phosphate esters and dialkyl phosphate esters are preferred, and ethyl acid phosphate and 2-ethylhexyl acid phosphate are particularly preferred.

[0058] Examples of commercially available phosphate esters that can be used include "JAMP-2," "JAMP-4," "JAMP-8," "JAMP-12," "JP-501," "JP-502," "JP-504," "JP-504A," "JP-506H," "JP-508," "JP-512," "JP-513," "JP-518O," "JP-524R," "DBP," and "LB-58" manufactured by Johoku Chemical Co., Ltd., and "TMP," "TEP," "TPP," "TCP," "TXP," "CDP," "PX-110," "#41," "CR-733S," "CR-741," "PX-200," "DAIGUARD-400 / 580 / 610," "TMCPP," "CRP," "CR-900," "CR-504L," "CR-570," and "DAIGUARD-540" manufactured by Daihachi Chemical Industry Co., Ltd.

[0059] The phosphonate ester is not particularly limited, but examples thereof include dimethyl vinyl phosphonate, diethyl vinyl phosphonate, diphenyl vinyl phosphonate, diphenyl vinyl phosphine oxide, and the like, as well as derivative compounds thereof and condensates thereof. These may be used alone or in combination of two or more.

[0060] As the phosphonate ester, for example, commercially available products such as "V Series" manufactured by Katayama Chemical Industry Co., Ltd. and "Non-nen 73" manufactured by Marubishi Yuka Kogyo Co., Ltd. can be used.

[0061] The phosphine is not particularly limited, but examples thereof include trialkylphosphines such as tributylphosphine and trioctylphosphine; and phosphines having an aromatic ring such as triphenylphosphine. These may be used alone or in combination of two or more.

[0062] As the phosphine, for example, commercially available products such as "tributylphosphine" and "triphenylphosphine" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. can be used.

[0063] The phosphite ester is not particularly limited, but examples thereof include trialkyl phosphites such as triethyl phosphite and tributyl phosphite; and phosphites having an aromatic ring such as triphenyl phosphite. These may be used alone or in combination of two or more.

[0064] As the phosphite ester, for example, commercially available products such as "JP-302," "JP-304," and "JP-360" manufactured by Johoku Chemical Co., Ltd. can be used.

[0065] The details of the mechanism by which the monomer mixture of the present invention containing the phosphorus-based compound (d) exhibits the effects of improving heat resistance and transparency and suppressing yellowing are not clear, but it is thought to be as follows. When rubber particles (a), mercaptan chain transfer agent (b), and peroxyester radical polymerization initiator (c) coexist in a monomer mixture, their reaction produces polymerization inhibitors. These polymerization inhibitors suppress the polymerization of the monomer composition (S1), reducing the heat resistance of the resulting resin composition. Furthermore, the rubber particles (a) aggregate within the monomer mixture and resin composition, making the resulting resin composition non-uniform and resulting in reduced physical properties, including heat resistance. The phosphorus-based compound (d) promotes the polymerization of the monomer composition (S1) by reducing polymerization inhibitors generated by the reaction of the mercaptan-based chain transfer agent (b) and the peroxyester-based radical polymerization initiator (c). The phosphorus-based compound (d) also promotes the dispersion of the rubber particles (a) in the monomer mixture and the resin composition, thereby making the resulting resin composition uniform. This maintains the heat resistance of the resin composition. Furthermore, when the rubber particles (a), the mercaptan chain transfer agent (b), and the peroxyester radical polymerization initiator (c) coexist in the monomer mixture, the resin composition obtained by polymerization may have a yellowish color, impairing the transparency of the resin composition. In contrast, by adding the phosphorus compound (d), the yellowish color of the obtained resin composition is eliminated, and a colorless resin composition with excellent transparency can be obtained.

[0066] The content of the phosphorus-based compound (d) in the monomer mixture of the present invention is preferably 0.001 parts by mass or more, more preferably 0.0025 parts by mass or more, and even more preferably 0.005 parts by mass or more, relative to 100 parts by mass of the monomer composition (S1) constituting the monomer mixture, from the viewpoint of suppressing a decrease in the heat resistance and transparency of the resulting resin composition and resin molded article. On the other hand, the content of the phosphorus-based compound (d) is preferably 2.0 parts by mass or less, preferably 1.5 parts by mass or less, and even more preferably 1.0 part by mass or less. If the content of the phosphorus-based compound (d) exceeds 2.0 parts by mass, a decrease in the elastic modulus occurs. The upper and lower limits can be combined in any desired manner. For example, the content of the phosphorus-based compound (d) can be in the range of 0.001 to 2.0 parts by mass, 0.001 to 1.5 parts by mass, 0.0025 to 1.5 parts by mass, 0.005 to 1.5 parts by mass, or 0.005 to 1.0 part by mass relative to 100 parts by mass of the monomer composition (S1).

[0067] [1-6. Other additives] The monomer mixture of the present invention may further contain, as necessary, an additive selected from a mold release agent, a lubricant, a plasticizer, an antistatic agent, a light stabilizer, an ultraviolet absorber, a flame retardant, a flame retardant aid, a polymerization inhibitor, an antioxidant, a filler, a pigment, a dye, a silane coupling agent, a leveling agent, an antifoaming agent, and a fluorescent agent. These may be used alone or in any combination and ratio.

[0068] [2. Resin composition] The resin composition of the present invention is a resin composition obtained by polymerizing the monomer mixture of the present invention. The resin composition of the present invention contains the (meth)acrylic polymer (P) obtained from the monomer composition (S1) described above, and thus can provide a resin molded article having good transparency and mechanical properties.

[0069] [2-1. (Meth)acrylic polymer (P)] The (meth)acrylic polymer (P) constituting the resin composition of the present invention is a (meth)acrylic polymer (P) whose main component is a repeating unit derived from methyl methacrylate in the monomer composition (S1) (hereinafter, sometimes referred to as a "methyl methacrylate unit"). The (meth)acrylic polymer (P) preferably contains 50% by mass or more of methyl methacrylate units, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the total mass (100% by mass) of the (meth)acrylic polymer (P), and may be a 100% by mass homopolymer. The (meth)acrylic polymer (P) may also contain repeating units derived from the above-mentioned copolymerizable monomers (hereinafter, sometimes referred to as "copolymerizable monomer units"). That is, the (meth)acrylic polymer (P) may contain 50 to 100% by mass of methyl methacrylate units and 0 to 50% by mass of copolymerizable monomer units.

[0070] The copolymerizable monomers other than methyl methacrylate that form the copolymerizable monomer units are as described above as the copolymerizable monomers contained in the monomer composition (S1), and among them, acrylic acid esters are preferred for the same reasons as in the monomer composition (S1) described above.

[0071] When the (meth)acrylic polymer (P) contains a repeating unit derived from an acrylic ester (hereinafter, sometimes referred to as an "acrylic ester unit") as a copolymerizable monomer unit, the (meth)acrylic polymer (P) preferably contains 50% by mass or more and less than 100% by mass of methyl methacrylate units and more than 0% by mass and 50% by mass or less of acrylic ester units, more preferably 70% by mass or more and less than 100% by mass of methyl methacrylate units and more than 0% by mass and 30% by mass or less of acrylic ester units, even more preferably 80% by mass or more and 99.9% by mass or less of methyl methacrylate units and 0.1% by mass or more and 20% by mass or less of acrylic ester units, and particularly preferably 90% by mass or more and 99.5% by mass or less of methyl methacrylate units and 0.5% by mass or more and 10% by mass or less of acrylic ester units.

[0072] [3. Method for producing resin composition] One example of a method for obtaining the resin composition of the present invention is to add rubber particles (a), a mercaptan chain transfer agent (b), a peroxyester radical polymerization initiator (c), and a phosphorus-based compound (d) to a monomer composition (S1) containing methyl methacrylate to form a polymerizable composition (S2), which is then polymerized. That is, the polymerizable composition (S2) contains at least methyl methacrylate, rubber particles (a), a mercaptan chain transfer agent (b), a peroxyester radical polymerization initiator (c), and a phosphorus-based compound (d). The polymerizable composition (S2) is the monomer mixture of the present invention.

[0073] There are no particular limitations on the method for polymerizing the above-mentioned polymerizable composition (S2) to obtain a resin composition and producing a resin molded article containing the resin composition. Examples of the polymerization method for the polymerizable composition (S2) include bulk polymerization, suspension polymerization, emulsion polymerization, dispersion polymerization, etc. Among these, bulk polymerization is preferred from the viewpoint of productivity.

[0074] Specific examples of the bulk polymerization method include a method of obtaining a resin molded product by bulk polymerization using a known cast polymerization method, or a method of obtaining a resin molded product by molding a composition produced by bulk polymerization, etc. From the viewpoint of further improving the heat resistance of the resin molded product by increasing the molecular weight or introducing a crosslinked structure, it is preferable to use a method utilizing cast polymerization.

[0075] Examples of the cast polymerization method include a cell cast method and a continuous cast method.

[0076] In the cell casting method, when obtaining a resin molded product having a plate-like shape, a space formed by two opposing glass or metal plates (SUS plates) and a gasket such as a soft resin tube placed on the edges thereof is used as a mold, and a polymerizable composition (S2) or a polymerizable composition (S2) containing a syrup obtained by polymerizing a part of the monomer composition (S1) is poured into the mold. Next, the polymerization is completed by a heat polymerization treatment, and the resin molded product is removed from the mold.

[0077] In the continuous casting method, a space formed by two stainless steel endless belts running in the same direction at the same speed opposite to each other with a predetermined gap between them and gaskets such as soft resin tubes placed on both sides of the belts is used as a mold, and the polymerizable composition (S2) or the polymerizable composition (S2) containing a syrup obtained by polymerizing a part of the monomer composition (S1) is continuously poured into the mold from one end of the endless belts. Next, the polymerization is completed by a heat polymerization treatment, and resin molded bodies are continuously taken out from the other end of the endless belts.

[0078] According to the cast polymerization method, the gap between the voids in the mold can be appropriately adjusted by adjusting the thickness (diameter) of the gasket, thereby obtaining a resin molded product (cast resin plate) of a desired thickness.

[0079] The polymerization temperature for polymerizing the polymerizable composition (S2) is not particularly limited and can be appropriately determined by a person skilled in the art according to well-known techniques. Generally, the temperature is appropriately set within a range of preferably 40 to 180°C, more preferably 50 to 150°C, depending on the type of radical polymerization initiator used. Furthermore, the polymerizable composition (S2) can be polymerized under multi-stage temperature conditions as needed. The polymerization time can be appropriately determined depending on the progress of polymerization and curing.

[0080] [4. Resin molded body] The resin molded article of the present invention includes the resin composition of the present invention. By molding the resin composition, a resin molded article having high impact resistance, excellent heat resistance, and transparency can be obtained.

[0081] Examples of molding methods for resin compositions include press molding, injection molding, gas-assisted injection molding, welding molding, extrusion molding, blow molding, film molding, blow molding, multi-layer molding, and melt spinning. In this specification, the term "resin molded product" is not particularly limited as long as it is a molded product containing the resin composition, and may be a molded product consisting only of the resin composition. When the resin molded product is a molded product consisting only of the resin composition, the resin composition essentially corresponds to both the resin composition and the resin molded product.

[0082] The shape of the resin molded product of the present invention is not particularly limited, but examples thereof include granular pellets, plate-shaped resin molded products (resin plates), and sheet-shaped resin molded products (resin sheets). Among these, plate-shaped resin molded products (resin plates) are preferred. The thickness of the resin molded product can be adjusted to any thickness, from a thick plate to a thin film, as required, and can be, for example, 1 to 30 mm.

[0083] The uses of the resin molded article of the present invention are not particularly limited, and it can be used for many purposes such as vehicle components, medical components, toys, liquid containers, optical components, signs, displays, decorative components, architectural components, and face plates of electronic devices, and is particularly preferably used for light-transmitting components such as optical components, vehicle components, signs, and resin plates for game machines. [Example]

[0084] 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 examples. In the following examples and comparative examples, "%" and "ppm" mean "% by mass" and "ppm by mass" unless otherwise specified. Furthermore, "parts" means "parts by mass."

[0085] [Compound name] The names of the compounds used in the examples and comparative examples are as follows. MMA: Methyl methacrylate (Mitsubishi Chemical Corporation) Rubber particles (a1): XC-IMPACT MODIFIERS (manufactured by Mitsubishi Chemical UK Limited) (rubber particles with a three-layer structure, with an average primary particle diameter measured by CHDF of 270 to 290 nm) Mercaptan chain transfer agents (b1): n-Dodecyl mercaptan (n-DM) (Kao Corporation) Peroxyester radical polymerization initiator (c1): t-Hexyl peroxypivalate (HPP) (manufactured by Nippon Oil & Fats Co., Ltd.) Phosphorus compounds (d1): Ethyl acid phosphate (EAP) (phosphate ester: manufactured by Johoku Chemical Co., Ltd.) Phosphorus compounds (d2): 2-Ethylhexyl acid phosphate (EHAP) (phosphate ester: manufactured by Johoku Chemical Co., Ltd.) Phosphorus compounds (d3): Triphenylphosphine (TPP) (Phosphine: Fujifilm Wako Pure Chemical Industries, Ltd.) Phosphorus compounds (d4): Phosphoric acid (Phosphoric acid: Fujifilm Wako Pure Chemical Industries, Ltd.)

[0086] [Analysis of the concentration of methacrylate components in resin compositions] The concentrations of the components of the resin compositions produced in the Examples and Comparative Examples were calculated as follows. The obtained resin composition was finely crushed, and 0.2 g of the crushed resin composition was dissolved in 10 mL of acetone. Next, 1 mL of an internal standard solution was added to the obtained solution using a whole pipette. A 0.1% by volume methyl salicylate / acetone solution was used as the internal standard solution. Three types of test solutions with different concentrations were prepared by diluting the target standard reagent with acetone, and an internal standard solution was added to create a three-point calibration curve by GC-MS measurement. Using this, the concentration of the methacrylate component in the resin composition was quantified. The measurement conditions of GC-MS are shown below.

[0087] <GC-MS Measurement Conditions> Apparatus: GC HP6890 / MS HP5973 (manufactured by Agilent Technologies) Ionization method: EI (Electron Ionization) method Column: DB-WAX 60 m × 250 μm × 0.5 μm (manufactured by Agilent Technologies) Temperature rising conditions: 70°C (5 min) → 200°C (5 min) Rate = 10°C / min Inlet temperature: 220°C AUX temperature: 230°C Ion source temperature: 230°C Split ratio: 10:1 Flow rate: 2.0 mL / min Average linear velocity: 37 cm / sec Injection volume: 1 μL Measurement mode: SIM

[0088] [Heat Resistance Evaluation of Resin Moldings] As an index of the heat resistance of the resin moldings produced in the examples and comparative examples, the heat deflection temperature (denoted as "HDT" in Table 1) was used. The HDT was measured for test pieces (length 120 mm × width 12.7 mm × thickness 3 mm) made of resin moldings in accordance with JIS K7191.

[0089] [Optical Property Evaluation of Resin Moldings] <Transparency Evaluation of Resin Molding: Measurement of HAZE> The haze of the resin molded body was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., model name: NDH4000) in accordance with JIS K 7136. For the measurement, a test piece (square shape, length 50 mm × width 50 mm, thickness 3 mm) made of the resin molded body was used.

[0090] <Evaluation of yellowing prevention of resin molded products: Yellowness index (YI) measurement> The yellowness index (YI) of the resin molded product was measured using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd., model name: SE-7700) in accordance with ASTM D 1925. For the measurement, a test piece (square shape, length 50 mm × width 50 mm, thickness 3 mm) made of the resin molded product was used.

[0091] [Impact resistance evaluation of resin molded products] The impact resistance of the resin molded article was measured in accordance with JIS K7111-1 using a digital impact tester (manufactured by Toyo Seiki Co., Ltd., model name: DG-UB). For the measurement, a test piece (length 80 mm × width 10 mm × thickness 3 mm) made of the resin molded article was used.

[0092] [Example 1] 100 parts of MMA was fed into a reactor (polymerization vessel) equipped with a condenser, thermometer, and stirrer. Nitrogen gas was bubbled through the mixture while stirring, and heating was then initiated. When the internal temperature of the reactor reached 80°C, 0.12 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added as a radical polymerization initiator. The reactor was further heated to an internal temperature of 100°C and maintained at this temperature for 9 minutes. The reactor was then cooled to room temperature to obtain a syrup. The polymer concentration in the syrup was 20% by mass relative to the total mass of the syrup. To 100 parts of the resulting syrup, 3 parts of rubber particles (a1), 0.05 parts of n-DM, 0.01 parts of EAP, and 0.3 parts of HPP were added to obtain a monomer mixture. The resulting monomer mixture was poured into a space between two opposing SUS plates with a gap of 4.1 mm, which was created by placing soft resin gaskets on the ends of the SUS plates, and cured by heating at 80°C for 45 minutes and then at 130°C for 30 minutes to obtain a resin composition. The resulting resin composition was then cooled together with the SUS plate, and the SUS plate was removed to obtain a 3 mm thick plate-shaped resin molded product (resin cast plate). This resin molded product was a resin molded product consisting only of the resin composition, and corresponds to both a resin composition and a resin molded product. The evaluation results of the properties of the resulting resin molded product are shown in Table 1.

[0093] [Examples 2 to 4] Resin compositions and resin molded articles were produced in the same manner as in Example 1, except that the type of phosphorus-based compound (d) was changed as shown in Table 1. The evaluation results of the properties of the obtained resin molded articles are shown in Table 1.

[0094] [Comparative Example 1] Except for not using the phosphorus-based compound (d), a resin composition and a resin molded article were produced in the same manner as in Example 1. The evaluation results of the properties of the obtained resin molded article are shown in Table 1.

[0095] As shown in Table 1, the resin compositions produced in Examples 1 to 4 exhibited superior heat resistance and optical properties to those of Comparative Example 1.

[0096] [Reference example 1] Except for not using the rubber particles (a1) and the phosphorus-based compound (d), a resin composition and a resin molded product were produced in the same manner as in Example 1. The evaluation results of the properties of the obtained resin molded product are shown in Table 1.

[0097] As shown in Table 1, the resin compositions produced in Examples 1 to 4 had superior impact resistance compared to Reference Example 1, and also showed a significantly superior effect of improving heat resistance due to the inclusion of the phosphorus-based compound (d).

[0098] [Table 1] [Industrial Applicability]

[0099] According to the present invention, it is possible to obtain a resin composition and a resin molded article that have the excellent heat resistance and optical properties inherent to methacrylic resins while ensuring high impact resistance, and are therefore industrially useful.

Claims

1. A monomer mixture comprising a monomer composition (S1) containing methyl methacrylate, rubber particles (a), a mercaptan-based chain transfer agent (b), and a peroxyester-based radical polymerization initiator (c), wherein the monomer mixture further contains a phosphorus-based compound (d).

2. The monomer mixture according to claim 1, wherein the rubber particles (a) are contained in an amount of 1.0 part by mass or more and 10.0 parts by mass or less per 100 parts by mass of the total mass of the monomer composition (S1).

3. The monomer mixture according to claim 2, wherein the rubber particles (a) are contained in an amount of 1.0 part by mass or more and 5.0 parts by mass or less per 100 parts by mass of the total mass of the monomer composition (S1).

4. The monomer mixture according to claim 1, wherein the monomer composition (S1) is mainly composed of methyl methacrylate.

5. The monomer mixture according to claim 4, wherein the monomer composition (S1) contains 70 to 100% by mass of methyl methacrylate and 0 to 30% by mass of an acrylic acid ester, based on 100% by mass of the total mass of the monomer composition (S1).

6. The monomer mixture according to claim 1 , wherein the rubber particles (a) have a multi-layer structure.

7. The monomer mixture according to claim 1, wherein the mercaptan chain transfer agent (b) is contained in an amount of 0.01 parts by mass or more and 1.0 parts by mass or less per 100 parts by mass of the total mass of the monomer composition (S1).

8. 2. The monomer mixture according to claim 1, wherein the mercaptan chain transfer agent (b) has 8 or more and 15 or less carbon atoms.

9. 9. The monomer mixture according to claim 8, wherein the mercaptan chain transfer agent (b) is n-octyl mercaptan and / or n-dodecyl mercaptan.

10. 2. The monomer mixture according to claim 1, wherein the peroxyester-based radical polymerization initiator (c) is contained in an amount of 0.1 part by mass or more and 1.0 part by mass or less per 100 parts by mass of the total mass of the monomer composition (S1).

11. The monomer mixture according to claim 1, wherein the phosphorus-based compound (d) is contained in an amount of 0.005 parts by mass or more and 1.000 parts by mass or less per 100 parts by mass of the total mass of the monomer composition (S1).

12. 2. The monomer mixture according to claim 1, wherein the phosphorus-based compound (d) comprises one or more compounds selected from the group consisting of phosphate esters, phosphonate esters, phosphoric acid, phosphonic acid, phosphines, phosphorous acid, and phosphite esters.

13. The monomer mixture according to claim 12, wherein the phosphorus-based compound (d) comprises one or more compounds selected from the group consisting of phosphate esters, phosphines, and phosphoric acids.

14. The monomer mixture according to claim 13 , wherein the phosphorus-based compound (d) comprises a phosphate ester.

15. The monomer mixture according to claim 14, wherein the phosphate ester is a monoalkyl phosphate ester and / or a dialkyl phosphate ester.

16. The monomer mixture according to claim 15, wherein the phosphorus-based compound (d) is ethyl acid phosphate and / or 2-ethylhexyl acid phosphate.

17. A resin composition obtained by polymerizing the monomer mixture according to any one of claims 1 to 16.

18. A resin molded article obtained by molding the resin composition according to claim 17.

19. A resin cast plate comprising the resin composition according to claim 17.

20. An optical member obtained by molding the resin composition according to claim 17.

21. A vehicle component obtained by molding the resin composition according to claim 17.

22. A signboard formed by molding the resin composition according to claim 17.

23. A resin plate for a game machine, formed by molding the resin composition according to claim 17.

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