Monomer composition, methacrylic resin composition and resin molded body

Abstract

To provide a methacrylic resin composition that has excellent photostability and is less prone to yellowing while securing excellent heat resistance of methacrylic resin, a resin molding comprising the methacrylic resin composition, and a monomer composition that yields the methacrylic resin composition.SOLUTION: A monomer composition includes methyl methacrylic acid and a compound of at least either methyl pyruvic acid or methyl 2-methyl butyrate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a monomer composition, a methacrylic resin composition, and a resin molded article. This application claims priority based on Japanese Patent Application No. 2021-085291, filed on May 20, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Methacrylic resins have excellent transparency, heat resistance, and weather resistance, and also have well-balanced performance in terms of resin properties such as mechanical strength, thermal properties, moldability, etc. In particular, methacrylic resin plates made from methacrylic resins in the form of plates are used as translucent components for tanning beds, lighting equipment, skin therapy equipment, medical equipment, UV irradiation devices, animal and plant cultivation equipment, skylights, HID lamps, etc.

[0003] In the above applications, there has been a problem in that when methacrylic resin sheets are placed in an environment where they are exposed to UV rays from direct sunlight or UV lamps, etc., the methacrylic resin sheets develop a yellowish color (yellowing, yellowish tinge). Therefore, there has been a demand for methacrylic resins that do not develop a yellowish color even when exposed to UV rays for long periods of time, i.e., methacrylic resins with excellent light stability.

[0004] As a technique for improving the light stability of methacrylic resins, Patent Document 1 discloses methacrylic resins obtained by polymerizing a monomer such as methyl methacrylate in the presence of a hindered amine compound (HALS) having a specific structure, which is a type of light stabilizer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 55-139404 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the methacrylic resin described in Patent Document 1 has improved photostability as the amount of HALS added during polymerization increases, but has the problem of becoming colored because HALS itself is colored. Furthermore, as the amount of HALS added increases, the polymerization efficiency decreases and the amount of residual monomers in the methacrylic resin increases, which causes a problem of reducing the photostability of the methacrylic resin.

[0007] In view of the above circumstances, an object of the present invention is to provide a methacrylic resin composition that has excellent light stability and suppressed yellowing while maintaining the excellent heat resistance of methacrylic resins; a resin molded product containing the methacrylic resin composition; and a monomer composition for obtaining the methacrylic resin composition. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention has the following features. That is, the gist of the present invention is as follows.

[0009] [1] A monomer composition comprising methyl methacrylate and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate. [2] A monomer composition comprising methyl methacrylate and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, A monomer composition, wherein the total content of at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate is 5 ppm by mass or more relative to the total mass of the monomer composition. [3] A monomer composition comprising methyl methacrylate and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, [4] A monomer composition, wherein the total content of at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate is 50 ppm by mass or more relative to the total mass of the monomer composition. A monomer composition comprising methyl methacrylate and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, A monomer composition, wherein the total content of at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate is 100 ppm by mass or more relative to the total mass of the monomer composition. [5] The monomer composition according to any one of [1] to [4], further containing an acrylic acid ester. [6] The monomer composition according to [5], wherein the acrylic acid ester is at least one compound selected from the group consisting of methyl acrylate, n-ethyl acrylate, and n-butyl acrylate. [7] The monomer composition according to [5], wherein the acrylic acid ester is n-butyl acrylate. [8] The monomer composition according to any one of [1] to [7], further containing at least one compound selected from the group consisting of methyl isobutyrate and methyl propionate. [9] A methacrylic resin composition obtained by radical polymerization of a polymerizable composition (X2) containing the monomer composition according to any one of [1] to [8].

[10] A methacrylic resin composition comprising a methacrylic polymer (P) and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate.

[11] A methacrylic resin composition comprising a methacrylic polymer (P) and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, A methacrylic resin composition, wherein the total content of at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate is 5 ppm by mass or more relative to the total mass of the methacrylic resin composition.

[12] A methacrylic resin composition comprising a methacrylic polymer (P) and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, A methacrylic resin composition, wherein the total content of at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate is 50 mass ppm or more relative to the total mass of the methacrylic resin composition.

[13] A methacrylic resin composition comprising a methacrylic polymer (P) and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, Total content of at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate The amount of the methacrylic resin composition is 100 ppm by mass or more relative to the total mass of the methacrylic resin composition.

[14] The methacrylic resin composition according to any one of

[10] to

[13] , wherein the methacrylic polymer (P) contains 70 to 100 mass% of repeating units derived from methyl methacrylate and 0 to 30 mass% of repeating units derived from an acrylic ester.

[15] The methacrylic resin composition according to any one of

[10] to

[13] , wherein the methacrylic polymer (P) contains 50 to 100% by mass of repeating units derived from methyl methacrylate and 0 to 50% by mass of repeating units derived from styrene.

[16] A resin molded article comprising the methacrylic resin composition according to any one of [9] to

[15] .

[17] A method for producing a methacrylic resin composition, comprising a radical polymerization step of radically polymerizing a polymerizable composition (X2) containing the monomer composition according to any one of [1] to [8]. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a methacrylic resin composition that has excellent light stability and suppressed yellowing while maintaining the excellent heat resistance of methacrylic resins; a resin molded product containing the methacrylic resin composition; and a monomer composition for obtaining the methacrylic resin composition. DETAILED DESCRIPTION OF THE INVENTION

[0011] In this specification, "(meth)acrylate" means at least one selected from "acrylate" and "methacrylate," and "(meth)acrylic" means at least one selected from "methacrylic" and "acrylic." Furthermore, a "methacrylic polymer" may contain repeating units derived from an acrylic monomer in addition to repeating units derived from a methacrylic monomer. As used herein, 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 in which a portion of the unit is converted into a different structure by treating the polymer. In this specification, "% by mass" indicates the content of a specific component contained in a total amount of 100% by mass.

[0012] Unless otherwise specified, 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, UV refers to light having a wavelength range of 295 nm or more and 430 nm or less, that is, light that mainly includes light in the wavelength region of 380 nm or less.

[0013] <1. Monomer composition> The monomer composition according to the first embodiment of the present invention contains methyl methacrylate and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate. The monomer composition may also contain other components within the scope of not impairing the effects of the present invention.

[0014] <1-1. Methyl methacrylate> The monomer composition according to this embodiment contains methyl methacrylate, and thus can provide a methacrylic resin composition that has good light stability and is inhibited from yellowing.

[0015] The lower limit of the methyl methacrylate content relative to the total mass of the monomer composition according to this embodiment is not particularly limited, but is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 97% by mass or more. The upper limit of the methyl methacrylate content is typically 99.9995% by mass or less, and may be 99.9950% by mass or less, or 99.9900% by mass or less. Therefore, the methyl methacrylate content may be, for example, in the ranges of 85% by mass or more and 99.9995% by mass or less, 90% by mass or more and 99.9995% by mass or less, 95% by mass or more and 99.9950% by mass or less, and 97% by mass or more and 99.9900% by mass or less.

[0016] Furthermore, the total content of methyl methacrylate, methyl pyruvate, and methyl 2-methylbutyrate relative to the total mass of the monomer composition according to this embodiment is not particularly limited, and is usually 100 mass % or less.

[0017] <1-2. Methyl pyruvate and methyl 2-methylbutyrate> The monomer composition according to this embodiment contains at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, and thus can provide a methacrylic resin composition that has good photostability and is inhibited from yellowing.

[0018] The lower limit of the total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the monomer composition according to this embodiment is not particularly limited, but is usually 5 ppm by mass or more, preferably 50 ppm by mass or more, more preferably 100 ppm by mass or more, even more preferably 200 ppm by mass or more, and particularly preferably 300 ppm by mass or more, in terms of being able to provide a methacrylic resin composition with better photostability.

[0019] The upper limit of the total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the monomer composition according to this embodiment is not particularly limited, but is usually 50,000 ppm by mass or less, preferably 25,000 ppm by mass or less, more preferably 20,000 ppm by mass or less, even more preferably 15,000 ppm by mass or less, and particularly preferably 10,000 ppm by mass or less, so as not to impair the heat resistance of the methacrylic resin when the monomer composition is converted into a methacrylic resin composition.

[0020] The above-mentioned preferable upper and lower limits can be combined arbitrarily. Specifically, the total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the monomer composition according to this embodiment is preferably 5 ppm by mass or more and 50,000 ppm by mass or less, more preferably 50 ppm by mass or more and 25,000 ppm by mass or less, even more preferably 100 ppm by mass or more and 20,000 ppm by mass or less, particularly preferably 200 ppm by mass or more and 15,000 ppm by mass or less, and most preferably 300 ppm by mass or more and 10,000 ppm by mass or less.

[0021] <1-3. Other Monomers> The monomer composition according to this embodiment may contain, together with methyl methacrylate, a monomer other than methyl methacrylate. Examples of the monomer other than methyl methacrylate include the following monomers 1) to 16). The following monomers 1) to 16) may be used alone or in any combination and ratio of two or more.

[0022] 1) Methacrylate esters: For example, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, or benzyl methacrylate. 2) Acrylate esters: For example, methyl acrylate, ethyl acrylate, n-butyl acrylate, iso-butyl acrylate, tert-butyl acrylate, or 2-ethylhexyl acrylate. 3) Unsaturated carboxylic acids: For example, acrylic acid, methacrylic acid, maleic acid, or itaconic acid. 4) Unsaturated carboxylic acid anhydrides: For example, maleic anhydride or itaconic anhydride. 5) Maleimide: For example, N-phenylmaleimide, or N-cyclohexylmaleimide. 6) Hydroxy group-containing vinyl monomers: For example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, or 2-hydroxypropyl methacrylate. 7) Vinyl ester: For example, vinyl acetate or vinyl benzoate. 8) Vinyl chloride, vinylidene chloride, or their derivatives. 9) Nitrogen-containing vinyl monomers: For example, methacrylamide, or acrylonitrile. 10) Epoxy group-containing monomers: For example, glycidyl acrylate or glycidyl methacrylate. 11) Aromatic vinyl monomers: For example, styrene, or alpha-methylstyrene.

[0023] 12) Alkanediol di(meth)acrylate: For example, ethylene glycol di(meth)acrylate, 1,2-propylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, or 1,6-hexanediol di(meth)acrylate. 13) Polyoxyalkylene glycol di(meth)acrylate: For example, diethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, triethylene glycol (meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, or neopentyl glycol di(meth)acrylate. 14) Vinyl monomers having two or more ethylenically unsaturated bonds in the molecule: For example, divinylbenzene. 15) Unsaturated polyester prepolymers obtained from at least one polycarboxylic acid including an ethylenically unsaturated polycarboxylic acid and at least one diol. 16) Vinyl ester prepolymer obtained by acrylic modification of the epoxy group terminals.

[0024] Among these, the monomer is preferably at least one acrylic acid ester selected from the group consisting of methyl acrylate, ethyl acrylate, and n-butyl acrylate, and more preferably n-butyl acrylate, from the viewpoint of providing a methacrylic resin composition with an excellent balance of transparency, heat resistance, and moldability. The content of this acrylic acid ester is preferably 0% by mass or more and 30% by mass or less, based on the total mass of the monomer composition.

[0025] <1-4. Methyl isobutyrate and methyl propionate> The monomer composition according to this embodiment may further contain at least one compound selected from the group consisting of methyl isobutyrate and methyl propionate. By including the above compound in the monomer composition in addition to at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, it is possible to provide a methacrylic resin composition having better light stability and further suppressed yellowing. can.

[0026] The lower limit of the total content of methyl isobutyrate and methyl propionate relative to the total mass of the monomer composition according to this embodiment is preferably 20 ppm by mass or more, more preferably 100 ppm by mass or more, even more preferably 200 ppm by mass or more, particularly preferably 500 ppm by mass or more, and most preferably 1000 ppm by mass or more, in terms of being able to provide a methacrylic resin composition with better photostability.

[0027] The upper limit of the total content of methyl isobutyrate and methyl propionate relative to the total mass of the monomer composition according to the present embodiment is not particularly limited, but is usually 50,000 ppm by mass or less, preferably 25,000 ppm by mass or less, more preferably 10,000 ppm by mass or less, even more preferably 7,000 ppm by mass or less, and particularly preferably 5,000 ppm by mass or less, so as not to impair the heat resistance of the methacrylic resin when the monomer composition is converted into a methacrylic resin composition.

[0028] The above-mentioned preferable upper and lower limits can be combined arbitrarily. Specifically, the total content of methyl isobutyrate and methyl propionate may be in the ranges of 20 ppm by mass to 50,000 ppm by mass, 100 ppm by mass to 25,000 ppm by mass, 200 ppm by mass to 10,000 ppm by mass, 200 ppm by mass to 7,000 ppm by mass, 500 ppm by mass to 7,000 ppm by mass, and 1,000 ppm by mass to 5,000 ppm by mass. Among these, the total content of methyl isobutyrate and methyl propionate is more preferably 100 ppm by mass to 25,000 ppm by mass, and even more preferably 200 ppm by mass to 7,000 ppm by mass.

[0029] In addition, when the monomer composition contains at least one of methyl isobutyrate and methyl propionate, the total content of methyl isobutyrate, methyl propionate, methyl pyruvate, and methyl 2-methylbutyrate relative to the total mass of the monomer composition is preferably within the range of the total content of methyl pyruvate and methyl 2-methylbutyrate described above.

[0030] <1-5. Additives> In this embodiment, methyl pyruvate and methyl 2-methylbutyrate are believed to exhibit excellent photostability through a mechanism of action different from that of commonly known UV absorbers and radical scavengers (HALS). Therefore, at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate can be used in combination with an additive such as a UV absorber and HALS. By including at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate and the additive in a monomer composition, it becomes possible to provide a methacrylic resin composition or a resin molded article with improved photostability at a lower cost.

[0031] Examples of the additives include known additives such as release agents, lubricants, plasticizers, antioxidants, antistatic agents, light stabilizers other than methyl pyruvate and methyl 2-methylbutyrate, ultraviolet absorbers, flame retardants, flame retardant assistants, polymerization inhibitors, fillers, pigments, dyes, silane coupling agents, leveling agents, antifoaming agents, and fluorescent agents. The additives may be used alone or in any combination of two or more.

[0032] Furthermore, the monomer composition according to this embodiment may contain compounds that are inevitably mixed into methyl methacrylate, such as methacrolein and methanol.

[0033] <2. Polymerizable composition (X2)> The polymerizable composition (X2) according to the second embodiment of the present invention can be prepared by the method described later in the third embodiment of the present invention. This is one aspect of a raw material for obtaining a methacrylic resin composition according to the embodiment. The polymerizable composition (X2) according to this embodiment is, for example, a polymerizable composition (X2-1) containing the raw material composition (X1) described below, at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, and a known radical polymerization initiator; or a polymerizable composition (X2-2) containing the monomer composition according to the first embodiment of the present invention and a known radical polymerization initiator.

[0034] <2-1. Raw material composition (X1)> The raw material composition (X1) is a constituent of the polymerizable composition (X2-1) and is also a raw material component of the methacrylic polymer (P) contained in the methacrylic resin composition according to the third embodiment of the present invention. In the following description, the raw material composition (X1) used to produce the methacrylic polymer (P1) containing repeating units derived from methyl methacrylate (hereinafter also referred to as "MMA") (hereinafter also referred to as "MMA units") and repeating units derived from an acrylic ester (hereinafter also referred to as "acrylic ester units") will be mainly described. However, by replacing the acrylic ester with styrene, the raw material composition (X1) can also be used to produce the methacrylic polymer (P2) containing MMA units and repeating units derived from styrene (hereinafter also referred to as "styrene units"). In this case, the styrene content can be determined based on the styrene unit content described in <3-1. Methacrylic Polymer (P)>.

[0035] The raw material composition (X1) may be a composition containing only MMA or a composition containing the MMA and an acrylic ester. The acrylic ester may be the acrylic ester described in <1-3. Other Monomers> or a monomer similar to the acrylic ester described in <3-1. Methacrylic Polymer (P)>. The raw material composition (X1) containing MMA and an acrylic acid ester improves the photostability of the methacrylic resin composition, and can suppress the generation of a yellowish color and the decrease in photostability when a resin molded article containing the methacrylic resin composition is exposed to UV light for a long period of time.

[0036] The content of MMA in the raw material composition (X1) is not particularly limited, and since it can improve the photostability of the methacrylic resin composition, a content similar to the content of MMA units in the methacrylic polymer (P1) or methacrylic polymer (P2) described in <3-1. Methacrylic polymer (P)> can be suitably applied. However, in <3-1. Methacrylic polymer (P)>, "relative to the total mass of the methacrylic polymer (P1)" and "relative to the total mass of the methacrylic polymer (P2)" should be read as "relative to the total mass of the raw material composition (X1)."

[0037] The content of the acrylic acid ester (M2) in the raw material composition (X1) is not particularly limited, and since it can improve the photostability of the methacrylic resin composition, a content similar to that of the acrylic acid ester unit contained in the methacrylic polymer (P1) or methacrylic polymer (P2) described in <3-1. Methacrylic polymer (P)> can be suitably applied. However, in <3-1. Methacrylic polymer (P)>, "relative to the total mass of the methacrylic polymer (P1)" and "relative to the total mass of the methacrylic polymer (P2)" should be read as "relative to the total mass of the raw material composition (X1)." As the type of acrylic acid ester, from the viewpoint of excellent light stability of the methacrylic resin composition, the acrylic acid esters described in <1-3. Other monomers> or compounds similar to the acrylic acid esters described in <3-1. Methacrylic polymer (P)> can be used.

[0038] Furthermore, the raw material composition (X1) may contain a polymer containing MMA units in advance. Specifically, the raw material composition (X1) may contain a polymer (a) described below in advance. When the raw material composition (X1) contains the polymer (a), the polymerizable composition (X2-1) has a high viscosity. Since the resulting mixture becomes a liquid (called "syrup") having the above structure, the polymerization time can be shortened and productivity can be improved. Examples of methods for obtaining the above-mentioned syrup include a method of dissolving a polymer in the raw material composition (X1), and a method of adding a known radical polymerization initiator to the raw material composition (X1) and polymerizing a part of it.

[0039] When the polymerizable composition (X2-1) is a syrup, it may be a composition containing the following polymer (a) and monomer composition (m). Polymer (a): a polymer containing 70.0 mass% or more of MMA units and 30.0 mass% or less of the acrylic acid ester units, or a polymer containing 50.0 mass% or more of MMA units and 50.0 mass% or less of the styrene units, or a polymer consisting of 100 mass% MMA units, relative to the total mass of polymer (a). Monomer composition (m): a monomer composition containing 70.0 mass% or more of MMA and 30.0 mass% or less of an acrylic acid ester, or a monomer composition containing 50.0 mass% or more of MMA and 50.0 mass% or less of styrene, or a monomer composition consisting of 100 mass% of MMA, relative to the total mass of the monomer composition (m).

[0040] The content (unit: mass %) of the raw material composition (X1) contained in the polymerizable composition (X2-1) is not particularly limited, and can be in the range of 97.5 mass % or more and 99.99 mass % or less relative to the total mass of the polymerizable composition (X2-1).

[0041] <2-2. Monomer composition> The monomer composition constituting the polymerizable composition (X2-2) is the monomer composition according to the first embodiment of the present invention, and is a composition containing raw material components of the methacrylic polymer (P) contained in the methacrylic resin composition according to the third embodiment of the present invention.

[0042] The content of the monomer composition according to the first embodiment of the present invention relative to the total mass of the polymerizable composition (X2-2) is 60 mass % or more and less than 100 mass %. The polymerizable composition (X2-2) may also contain other monomers (also simply referred to as "other monomers") that are copolymerizable with the monomers in the monomer composition. When the polymerizable composition (X2-2) contains other monomers, the content of the other monomers is more than 0% by mass and less than 40% by mass, based on the total mass of the polymerizable composition (X2-2).

[0043] Examples of the other monomers include the monomers 1) to 16) listed above in <1-3. Other monomers>. The above monomers 1) to 16) can be used singly or in any combination of two or more kinds in any ratio.

[0044] Among the above monomers 1) to 16), a monomer selected from ethylene glycol dimethacrylate and neopentyl glycol dimethacrylate is preferred from the viewpoint of providing a methacrylic resin composition having an excellent balance between heat resistance and transparency.

[0045] <2-3. Radical polymerization initiator> Examples of radical polymerization initiators include known azo compounds such as 2,2'-azobis(isobutyronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile); known organic peroxides such as benzoyl peroxide and lauroyl peroxide; and the like. These can be used alone or in any combination and ratio of two or more. If necessary, known polymerization accelerators such as amines and mercaptans can be used in combination with the radical polymerization initiator.

[0046] The content of the radical polymerization initiator in the polymerizable composition (X2) is not particularly limited and can be appropriately determined by a person skilled in the art according to well-known techniques. Specifically, the content of the radical polymerization agent may be 0.005 parts by mass or more and 5 parts by mass or less, or 0.01 parts by mass or more and 1.0 parts by mass or less, relative to 100 parts by mass of the total mass of the polymerizable composition (X2).

[0047] <2-4. Additives> The polymerizable composition (X2) may contain, as necessary, an additive selected from a mold release agent, a heat stabilizer, a lubricant, a plasticizer, an antioxidant, an antistatic agent, a light stabilizer other than methyl pyruvate and methyl 2-methylbutyrate, an ultraviolet absorber, a flame retardant, a flame retardant aid, a polymerization inhibitor, a filler, a pigment, a dye, a silane coupling agent, a leveling agent, an antifoaming agent, a fluorescent agent, and a chain transfer agent.

[0048] <3. Methacrylic resin composition> A methacrylic resin composition according to a third embodiment of the present invention (hereinafter also simply referred to as "methacrylic resin composition") is a methacrylic resin composition containing at least a methacrylic polymer (P) and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate. The methacrylic resin composition according to this embodiment may be a composition obtained by radical polymerization of the polymerizable composition (X2) according to the second embodiment of the present invention. The methacrylic resin composition according to this embodiment contains the methacrylic polymer (P), and thus can provide a resin molded article with good transparency. By including at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, the methacrylic resin composition can provide a resin molded product that is inhibited from developing a yellowish color even when exposed to UV rays for a long period of time, and that also inhibits a decrease in photostability. The form of the methacrylic resin composition is not particularly limited, but it is usually a solid.

[0049] The content of the methacrylic polymer (P) relative to the total mass of the methacrylic resin composition is not particularly limited, but from the viewpoint of obtaining good heat resistance, it is usually 95% by mass or more, preferably 97.5% by mass or more, more preferably 98% by mass or more, and even more preferably 99.0% by mass or more. On the other hand, from the viewpoint of obtaining excellent light stability, this content is usually 99.9995% by mass or less, preferably 99.9950% by mass or less, 99.99% by mass or less, 99.9850% by mass or less, 99.98% by mass or less, 99.97% by mass or less, 99.95% by mass or less, or 99.90% by mass or less. The above upper and lower limits can be combined arbitrarily. For example, preferred ranges of the content of the methacrylic polymer (P) include 95% by mass or more and 99.9995% by mass or less, 95% by mass or more and 99.9950% by mass or less, 97.5% by mass or more and 99.99% by mass or less, 98% by mass or more and 99.9850% by mass or less, 99.0% by mass or more and 99.98% by mass or less, 99.0% by mass or more and 99.97% by mass or less, 99.0% by mass or more and 99.95% by mass or less, and 99.0% by mass or more and 99.90% by mass or less. When the methacrylic resin composition contains two or more types of methacrylic polymers (P), the above content is the total content of the two or more types of methacrylic polymers (P).

[0050] The total content of at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the methacrylic resin composition is not particularly limited. From the viewpoint of obtaining excellent photostability, the total content of at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the methacrylic resin composition is usually 5 ppm by mass or more, preferably 50 ppm by mass or more, more preferably 100 ppm by mass or more, even more preferably 150 ppm by mass or more, particularly preferably 200 ppm by mass or more, and most preferably 300 ppm by mass or more.

[0051] The upper limit of the total content of at least one compound of methyl pyruvate and methyl 2-methylbutyrate contained in the methacrylic resin composition according to this embodiment is not particularly limited, but from the viewpoint of improving the heat resistance of the resin molded product, it is usually 50,000 ppm by mass or less, preferably 25,000 ppm by mass or less, more preferably 20,000 ppm by mass or less, even more preferably 15,000 ppm by mass or less, and particularly preferably 10,000 ppm by mass or less. The above upper and lower limits can be arbitrarily combined. For example, preferred ranges for the total content of at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate include 5 mass ppm to 50,000 mass ppm, 50 mass ppm to 25,000 mass ppm, 100 mass ppm to 20,000 mass ppm, 150 mass ppm to 15,000 mass ppm, 200 mass ppm to 15,000 mass ppm, and 300 mass ppm to 10,000 mass ppm. Among these, the total content of at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate is more preferably 50 mass ppm to 25,000 mass ppm, and even more preferably 150 mass ppm to 15,000 mass ppm.

[0052] In this embodiment, at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate is believed to exhibit excellent photostability through a mechanism of action different from that of commonly known UV absorbers and radical scavengers (HALS). Therefore, at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate can also be used in combination with additives such as UV absorbers and HALS. By using at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate in combination with the additive, it is possible to provide a methacrylic resin composition and a resin molded article with improved photostability at a lower cost.

[0053] The methacrylic resin composition may contain components other than the methacrylic polymer (P) and at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate, as long as the effects of the present invention are obtained. For example, the methacrylic resin composition may contain an additive selected from a release agent, a heat stabilizer, an antioxidant, an ultraviolet absorber, and a light stabilizer other than methyl pyruvate and methyl 2-methylbutyrate.

[0054] <3-1. Methacrylic polymer (P)> The methacrylic polymer (P) is one of the components contained in the methacrylic resin composition according to this embodiment. By including the methacrylic polymer (P), the methacrylic resin composition can improve transparency and inhibit decomposition due to heat or light, thereby improving thermoformability, heat resistance, and mechanical strength. Furthermore, the inherent heat resistance of the methacrylic polymer (P) and the synergistic effect of at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate inhibit the generation of a yellowish tinge when exposed to UV light for a long period of time, making it possible to obtain a methacrylic resin molded article that is highly photostable and maintains heat resistance.

[0055] The methacrylic polymer (P) is preferably a copolymer containing MMA units and acrylic ester units (hereinafter also referred to as methacrylic polymer (P1)), or a copolymer containing MMA units and styrene units (hereinafter also referred to as methacrylic polymer (P2)). The arrangement of these copolymers is not particularly limited and may be, for example, a random copolymer, a block copolymer, or an alternating copolymer, but a random copolymer is preferred.

[0056] The repeating unit derived from the acrylate ester is a repeating unit derived from the acrylate ester having an alkyl group having 1 to 6 carbon atoms in the side chain. The monomer constituting this unit is not particularly limited as long as it is a monomer copolymerizable with MMA. For example, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, or Examples of suitable monomers include acrylic acid esters such as t-butyl acrylate. These monomers may be used alone, or two or more may be used in any combination and ratio. Among these monomers, at least one acrylic acid ester selected from the group consisting of methyl acrylate, n-ethyl acrylate, and n-butyl acrylate is preferred, and n-butyl acrylate is more preferred, from the viewpoint of suppressing the generation of a yellowish color when a resin molded article containing the methacrylic resin composition is exposed to UV light for a long period of time and ensuring high photostability.

[0057] The content of MMA units in the methacrylic polymer (P1) is not particularly limited, but from the viewpoint of improving heat resistance, it is preferably 70.0% by mass or more, more preferably 80.0% by mass or more, and even more preferably 90.0% by mass or more, based on the total mass of the methacrylic polymer (P1), and is usually 100% by mass or less.

[0058] The content of the acrylic ester units in the methacrylic polymer (P1) is not particularly limited, but from the viewpoint of improving heat resistance and light stability, it is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and usually 0% by mass or more. When the methacrylic polymer (P1) contains two or more types of acrylic ester units, the above content is the total content of the two or more types of acrylic ester units.

[0059] The content of MMA units in the methacrylic polymer (P2) is not particularly limited, but from the viewpoint of improving heat resistance, it is preferably 50.0 mass% or more, more preferably 60.0 mass% or more, and even more preferably 70.0 mass% or more, relative to the total mass of the methacrylic polymer (P2), and is usually 100 mass% or less.

[0060] The content of styrene units in the methacrylic polymer (P2) is not particularly limited, but from the viewpoint of improving transparency, it is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and is usually 0% by mass or more.

[0061] Furthermore, the methacrylic polymer (P) in this embodiment can contain a structural unit derived from a polyfunctional monomer containing two or more radically polymerizable functional groups in one molecule (hereinafter referred to as a "polyfunctional monomer unit"), within the range in which the effects of the invention can be obtained. The radically polymerizable functional group referred to here may be any group that has a carbon-carbon double bond and is radically polymerizable, and specific examples include a vinyl group, an allyl group, a (meth)acryloyl group, and a (meth)acryloyloxy group. In particular, a (meth)acryloyl group is preferred from the viewpoints of excellent storage stability of a compound having a radically polymerizable functional group and ease of controlling the polymerizability of the compound. Note that "(meth)acryloyl" refers to either or both of "acryloyl" and "methacryloyl." Note that the respective radically polymerizable functional groups in a monomer having two radically polymerizable functional groups may be the same or different. When the methacrylic polymer (P) contains a polyfunctional monomer unit, the solvent resistance, chemical resistance, and the like can be improved.

[0062] Examples of polyfunctional monomers include, but are not limited to, allyl methacrylate, allyl acrylate, ethylene glycol di(meth)acrylate, ethylene glycol tri(meth)acrylate, neopentyl glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate. Among these, the polyfunctional monomer is preferably one selected from ethylene glycol di(meth)acrylate and neopentyl glycol di(meth)acrylate, and more preferably ethylene glycol di(meth)acrylate, from the viewpoint of improving solvent resistance and chemical resistance.

[0063] Furthermore, in the methacrylic resin composition according to this embodiment, the weight-average molecular weight (Mw) of the methacrylic polymer (P) measured by gel permeation chromatography (GPC) is not particularly limited. The weight-average molecular weight (Mw) can be appropriately set depending on the intended use of the resin molded article. For example, it may be 10,000 or more, 100,000 or more, or 150,000 or more, or 1,000,000 or less, 2,000,000 or less, or 4,000,000 or less.

[0064] The weight-average molecular weight is a value measured by gel permeation chromatography using standard polystyrene as a standard sample. By appropriately increasing the weight-average molecular weight, it is possible to improve solvent resistance and chemical resistance. The weight average molecular weight (Mw) of the methacrylic polymer (P) can be controlled by adjusting the polymerization temperature, polymerization time, amount of polymerization initiator added, or the type and amount of series transfer agent added.

[0065] <3-2. Methyl pyruvate and methyl 2-methylbutyrate> At least one compound selected from methyl pyruvate and methyl 2-methylbutyrate is one of the components contained in the methacrylic resin composition according to this embodiment. By including at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate, the methacrylic resin composition can suppress the occurrence of a yellowish color when exposed to UV light for a long period of time. Furthermore, it is less expensive than conventional ultraviolet absorbers and can also suppress a decrease in photostability.

[0066] <3-3. Methyl isobutyrate and methyl propionate> The methacrylic resin composition according to this embodiment may further contain at least one compound selected from the group consisting of methyl isobutyrate and methyl propionate.

[0067] The lower limit of the total content of methyl isobutyrate and methyl propionate relative to the total mass of the methacrylic resin composition according to this embodiment is preferably 20 ppm by mass or more, more preferably 100 ppm by mass or more, even more preferably 200 ppm by mass or more, particularly preferably 500 ppm by mass or more, and most preferably 1,000 ppm by mass or more, in that a methacrylic resin composition having better photostability can be provided.

[0068] The upper limit of the total content of methyl isobutyrate and methyl propionate relative to the total mass of the methacrylic resin composition according to this embodiment is not particularly limited, but is usually 50,000 ppm by mass or less, preferably 25,000 ppm by mass or less, more preferably 10,000 ppm by mass or less, even more preferably 7,000 ppm by mass or less, and particularly preferably 5,000 ppm by mass or less, so as not to impair the heat resistance of the methacrylic resin.

[0069] The above-mentioned preferable upper and lower limits can be combined arbitrarily. Specifically, the total content of methyl isobutyrate and methyl propionate is 20 ppm by mass or more and 50,000 ppm by mass or less, 100 ppm by mass or more and 25,000 ppm by mass or less, 200 ppm by mass or more and 10,000 ppm by mass or less, 200 ppm by mass or more and 7,000 ppm by mass or less, The ranges of the total content of methyl isobutyrate and methyl propionate are preferably 100 ppm by mass or more and 25,000 ppm by mass or less, 500 ppm by mass or more and 7,000 ppm by mass or less, and 1,000 ppm by mass or more and 5,000 ppm by mass or less. Of these, the total content of methyl isobutyrate and methyl propionate is more preferably 100 ppm by mass or more and 25,000 ppm by mass or less, and even more preferably 200 ppm by mass or more and 7,000 ppm by mass or less.

[0070] In addition, when the methacrylic resin composition contains at least one compound selected from methyl isobutyrate and methyl propionate, the total content of methyl isobutyrate, methyl propionate, methyl pyruvate, and methyl 2-methylbutyrate relative to the total mass of the methacrylic resin composition is preferably within the range of the total content of methyl pyruvate and methyl 2-methylbutyrate described above.

[0071] <3-4. Properties of methacrylic resin compositions> The methacrylic resin composition according to this embodiment contains the methacrylic polymer (P) and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, and therefore has excellent light stability.

[0072] Specifically, when a test piece (50 mm x 50 mm square, 3 mm thick) made of a methacrylic resin composition is subjected to the UV exposure test described below, the yellowness index (YI) of the test piece measured in accordance with ASTM D1925 before the start of the UV exposure test and during the period from 200 hours after the start of the UV exposure test is 7.1 or less, preferably 6.0 or less, more preferably 4.5 or less, and even more preferably 4.0 or less. Additionally, the test piece preferably has a light transmittance of 15.0% or more at a wavelength of 295 nm, or a light transmittance of 35.0% or more at a wavelength of 315 nm. More preferably, the test piece has a light transmittance of 15.0% or more at a wavelength of 295 nm and a light transmittance of 35.0% or more at a wavelength of 315 nm. The light transmittance refers to the total light transmittance (Tt) in the thickness direction of the test piece measured using a haze meter (for example, "NDH4000" manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7361-1:1997.

[0073] (UV exposure test method) A test piece (50 mm long x 50 mm wide, 5 mm thick) made of a methacrylic resin composition was placed in the evaluation chamber of a Metal Weather ultra-accelerated light stability tester (e.g., "KU-R5CI-A" manufactured by Daipla Wintes Co., Ltd.) equipped with a metal halide lamp (e.g., "MW-60W" manufactured by Daipla Wintes Co., Ltd.) and a light cut filter (e.g., "KF-1" manufactured by Daipla Wintes Co., Ltd.), and the test piece was exposed to ultraviolet light (irradiation intensity 80 mW / cm) from the metal halide lamp under conditions of a temperature of 63°C and a humidity of 50 RH%. 2 ) is irradiated onto the test piece.

[0074] <4. Resin molded body> A resin molded article according to a fourth embodiment of the present invention (also simply referred to as a "resin molded article") is a resin molded article containing the methacrylic resin composition according to the third embodiment of the present invention. By molding this methacrylic resin composition, a resin molded article having excellent photostability can be obtained. In this specification, the term "resin molded article" is not particularly limited as long as it is a molded article containing the above-mentioned methacrylic resin composition, and a molded article consisting only of a methacrylic resin composition essentially corresponds to both a methacrylic resin composition and a resin molded article.

[0075] The shape of the resin molded body may be, for example, a plate-like resin molded body (resin plate) or a sheet-like resin molded body (resin sheet). The thickness of the resin molded body can be adjusted to any thickness as needed, from a thick plate to a thin film. For example, the thickness can be 1 mm or more and 30 mm or less.

[0076] The resin molded article has excellent light stability because it contains the above-mentioned methacrylic resin composition. Specifically, a test piece of the resin molded product (square, 50 mm long x 50 mm wide, 3 mm thick) exhibits excellent light stability, such that the yellowness index (YI) measured in accordance with ASTM D1925 from before the start of the UV exposure test to 200 hours after the start of the UV exposure test is 7.1 or less, preferably 6.0 or less, more preferably 4.5 or less, and even more preferably 4.0 or less. Additionally, the test piece preferably exhibits high light stability, such that the light transmittance at a wavelength of 295 nm is 15.0% or more, or the light transmittance at a wavelength of 315 nm is 35.0% or more. More preferably, the test piece has a light transmittance at a wavelength of 295 nm of 15.0% or more and a light transmittance at a wavelength of 315 nm of 35.0% or more. The light transmittance refers to the total light transmittance (Tt) in the thickness direction of the test piece measured using a haze meter (for example, "NDH4000" manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7361-1:1997.

[0077] <5. Method for producing methacrylic resin composition or resin molded product> The method for producing a methacrylic resin composition or a resin molded article containing the resin composition (hereinafter, the methacrylic resin composition and the resin molded article are also collectively referred to as "resin composition, etc.") is not particularly limited. A specific example of a method for producing a resin composition, etc., is a method including a radical polymerization step of radically polymerizing a polymerizable composition (X2) according to the second embodiment of the present invention, preferably a polymerizable composition (X2-2) containing the monomer composition according to the first embodiment of the present invention. The radical polymerization step may include a syrup preparation step of polymerizing a portion of the polymerizable composition (X2) to prepare a syrup, and a polymerization step of polymerizing a polymerizable component in the syrup. Note that "polymerizing a portion of the polymerizable composition (X2)" in the syrup preparation step refers to polymerization such that the content of the methacrylic polymer in the resulting syrup is 10% by mass or more and 80% by mass or less, preferably 10% by mass or more and 60% by mass or less, and more preferably 10% by mass or more and 40% by mass or less.

[0078] The polymerization temperature for polymerizing the polymerizable composition (X2) 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°C or higher and 180°C or lower, more preferably 50°C or higher and 150°C or lower, depending on the type of radical polymerization initiator used. Furthermore, the polymerizable composition (X2) 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.

[0079] Examples of the polymerization method for the polymerizable composition (X2) include bulk polymerization, suspension polymerization, emulsion polymerization, and dispersion polymerization, and among these, bulk polymerization is preferred from the viewpoint of productivity.

[0080] Specific examples of the method for producing the resin composition include a method of obtaining a resin composition by bulk polymerization using a known cast polymerization method such as a cell casting method or a continuous casting method, or a method of molding a composition produced by bulk polymerization by an extrusion molding method or an injection molding method to obtain a resin composition. From the viewpoint of further improving the heat resistance of the methacrylic resin composition by increasing the molecular weight or introducing a crosslinked structure, it is more preferable to employ a method using cast polymerization (cast polymerization).

[0081] As an example of the cast polymerization method, when obtaining a resin composition or the like having a plate-like form, a cell casting method can be used in which a space formed by two opposing glass plates or metal plates (SUS plates) and gaskets such as soft resin tubes placed on the edges of the plates is used as a mold, and the polymerizable composition (X2) or a syrup obtained by polymerizing a part of the polymerizable composition (X2) is injected into the mold, the polymerization is completed by a heat polymerization treatment, and the resin composition or the like is removed from the mold. Alternatively, a cell casting method can be used in which a resin composition or the like is formed by two stainless steel endless belts running opposite each other at the same speed and in the same direction with a predetermined gap therebetween and gaskets such as soft resin tubes placed on both sides of the belts. The formed space is used as a mold, and the polymerizable composition (X2) or a syrup obtained by polymerizing a part of the polymerizable composition (X2) is continuously poured into the mold from one end of the endless belt, and the polymerization is completed by a heat polymerization treatment, and the resin composition or the like is continuously taken out from the other end of the endless belt. The spacing of the gaps in the mold can be adjusted appropriately by adjusting the thickness (diameter) of the gasket to obtain a resin composition of the desired thickness. The thickness of the plate-shaped resin composition is usually set in the range of 1 mm or more and 30 mm or less.

[0082] <6.Applications> The uses of the above-mentioned methacrylic resin composition and resin molded product ("resin composition, etc.") are not particularly limited, but they are preferably used as light-transmitting members, particularly transparent members, for use in any of tanning beds, lighting equipment, skin therapy equipment, medical equipment, UV irradiation devices, animal and plant cultivation equipment, skylights, HID lamps, etc. More specifically, they are preferably used as light-collecting members, which are members intended to admit light and are used in any of tanning beds, skylights, etc., or light-transmitting members, which are members intended to transmit light and are used in any of lighting equipment, skin therapy equipment, medical equipment, UV irradiation devices, animal and plant cultivation equipment, HID lamps, etc.

[0083] <7. Action and Effects> The monomer composition according to the first embodiment of the present invention contains at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate. A methacrylic resin composition obtained by radical polymerization of a polymerizable composition (X2) containing the monomer composition has excellent heat resistance, excellent light stability, and suppressed yellowing. The reason why the monomer composition according to the first embodiment of the present invention contains at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, and thereby a methacrylic resin composition having excellent light stability and suppressed yellowing while ensuring excellent heat resistance, is presumed to be as follows.

[0084] In polymers containing units based on methyl methacrylate (methacrylic polymers), the main chain or side chain is cleaved by light to generate radical species, which usually cause yellowing of the methacrylic resin and a decrease in molecular weight, resulting in a decrease in mechanical strength.

[0085] However, it is believed that at least one of methyl pyruvate and methyl 2-methylbutyrate contained in the monomer composition according to the first embodiment of the present invention remains in the methacrylic resin composition, and that this at least one of methyl pyruvate and methyl 2-methylbutyrate functions as a radical scavenger, resulting in the methacrylic resin composition exhibiting excellent heat resistance and good light stability. [Example]

[0086] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. In the following, "parts" refers to "parts by mass."

[0087] The abbreviations and names of the compounds used in the examples and comparative examples are as follows. MMA: Methyl methacrylate (Mitsubishi Chemical Corporation) BA: n-butyl acrylate (Mitsubishi Chemical Corporation) Methyl isobutyrate (Tokyo Chemical Industry Co., Ltd.) Methyl propionate (Tokyo Chemical Industry Co., Ltd.) Methyl pyruvate (Tokyo Chemical Industry Co., Ltd.) Methyl 2-methylbutyrate (Tokyo Chemical Industry Co., Ltd.) LA-57: 1,2,3,4-butanetetracarboxylic acid tetrakis(2,2,6,6-tetramethyl-4-piperidinyl) (ADEKA Corporation) The MMA (manufactured by Mitsubishi Chemical Corporation) contained, relative to the total mass of MMA, methyl isobutyrate at a concentration of 260 ppm by mass, methyl propionate at a concentration of 8 ppm by mass, methyl pyruvate at a concentration of 8 ppm by mass, and methyl 2-methylbutyrate at a concentration of 8 ppm by mass.

[0088] [Measurement and evaluation methods] <Method for measuring the amount of target substance remaining in methacrylic resin> (1) Sample and test solution preparation procedure The resin molded bodies obtained in the Examples and Comparative Examples were finely crushed, and 0.2 g of the crushed resin was dissolved in 10 mL of acetone for pesticide residue testing (hereinafter simply referred to as "acetone"). After the resin was dissolved, 1 mL of internal standard solution was added using a volumetric pipette. A 0.1% by volume solution of methyl salicylate / acetone was used as the internal standard solution. Three test solutions with different concentrations were prepared by diluting the target standard reagent with acetone, and a three-point calibration curve was created using gas chromatography mass spectrometry (GC / MS) measurement, as described below, to quantify the concentration of each target substance in the sample. A 0.1% by volume solution of methyl salicylate / acetone was used as the internal standard solution.

[0089] (GC / MS measurement conditions) Equipment: GC HP6890 / MS HP5973 (Agilent) Ionization method: EI (Electron Ionization) method Column: DB-WAX 60m x 250µm x 0.5µm (Agilent) Temperature rise conditions: 70℃ (5 min) → 200℃ (5 min) Rate = 10℃ / min Inlet temperature: 220℃ AUX temperature: 230℃ Ion source temperature: 230℃ Split ratio: 10:1 Flow rate: 2.0mL / min Average linear velocity: 37cm / sec Injection volume: 1μL Measurement mode: SIM

[0090] <Heat resistance evaluation method> As an index of the heat resistance of the methacrylic resin compositions obtained in the Examples and Comparative Examples, the deflection temperature under load (hereinafter referred to as "HDT") (°C) was measured for test pieces (length 127 mm x width 12.7 mm x thickness 3 mm) of the resin molded products obtained in the Examples and Comparative Examples in accordance with JIS K 7191.

[0091] <Photostability (ΔYI)> A UV exposure test was conducted using a Metal Weather ultra-accelerated light stability tester (manufactured by Daipla Wintes Co., Ltd., model: MW-60W) equipped with a metal halide lamp (manufactured by Daipla Wintes Co., Ltd., model: KF-1) and a light cut filter (manufactured by Daipla Wintes Co., Ltd., model: KU-R5CI-A), and the change in yellowness index (ΔYI) from before the start of the UV exposure test to 200 hours after the start was measured according to the method described below.

[0092] Specifically, test pieces (square, 50 mm long x 50 mm wide, 5 mm thick) made of the methacrylic resin compositions obtained in the examples and comparative examples were placed in the evaluation chamber of the Metal Weather ultra-accelerated light stability tester. The irradiation intensity of the ultraviolet (UV) irradiated onto the test piece from the metal halide lamp is The irradiation intensity at wavelengths of 330 to 390 nm measured with a linear illuminance meter (Ushio Inc., model name: UIT-101) was 80 mW / cm 2 The evaluation room of the Metal Weather ultra-accelerated light stability tester was set to an environment of temperature 63°C and humidity 50 RH%, and ultraviolet light (irradiation intensity 80 mW / cm) from a metal halide lamp was applied. 2 ) was irradiated onto the test piece. As an index of light stability, the yellowness index (YI) of the test specimens was measured in accordance with ASTM D 1925 using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd., model name: SE-7700). One test specimen was measured before the start of the UV exposure test and one test specimen was measured 200 hours after the start of the test. Each test specimen was measured once, and the change in the measured value was taken as the change in yellowness index (ΔYI).

[0093] <Production of methacrylic resin composition> [Example 1] (1) Syrup production Methyl 2-methylbutyrate was added to a reactor (polymerization vessel) equipped with a condenser, thermometer, and stirrer at a concentration of 300 ppm. 98.0 parts of MMA and 2.0 parts of BA were then added. Nitrogen gas was bubbled through the mixture while stirring, and heating was initiated. When the reactor's internal temperature reached 80°C, 0.12 parts of 2,2'-azobis-(2,4-dimethylvaleronitrile) as a radical polymerization initiator and 0.075 parts of 1-dodecanethiol as a chain transfer agent were added. The reactor was further heated to 100°C and held for 9 minutes. The reactor was then cooled to room temperature to obtain a syrup. The polymer content in the syrup was 25% by mass based on the total mass of the syrup.

[0094] (2) Casting polymerization Polymerizable composition (X2) was obtained by adding 0.15 parts of t-hexyl peroxypivalade as a radical polymerization initiator to 100 parts of the syrup. The polymerizable composition (X2) was then poured into a 6.5 mm gap between two opposing SUS plates, with soft resin gaskets placed at the ends of the SUS plates. The mixture was heated at 80°C for 30 minutes and then at 130°C for 30 minutes to cure the polymerizable composition (X2) and obtain a methacrylic resin composition. The composition of the methacrylic resin composition is shown in Table 1. The (meth)acrylic resin composition and the SUS plates were then cooled, after which the SUS plates were removed to obtain a 5 mm-thick plate-shaped resin molded product. The evaluation results of the properties of the obtained resin molded product are shown in Table 1. In Table 1, "-" indicates that no measurement was performed.

[0095] [Example 2] (1) Syrup production Methyl 2-methylbutyrate was added to a reactor (polymerization vessel) equipped with a condenser, thermometer, and stirrer at a concentration of 300 ppm, and 100 parts of MMA was then added. 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) was added as a radical polymerization initiator. The reactor was further heated to 100°C and maintained at this temperature for 9 minutes. The reactor was then cooled to room temperature, yielding a syrup. The polymer content in the syrup was 20% by mass relative to the total mass of the syrup.

[0096] (2) Casting polymerization To 100 parts of the above syrup, 0.15 parts of t-hexyl peroxypivalade was added as a radical polymerization initiator to obtain a polymerizable composition (X2). Next, the polymerizable composition (X2) was poured into a space with a gap of 4.1 mm, which was created between two opposing SUS plates and had soft resin gaskets placed on the ends of the SUS plates, and heated at 80°C for 30 minutes, then at 130°C for 30 minutes, to harden the polymerizable composition (X2) and obtain a methacrylic resin composition. The composition of the methacrylic resin composition is shown in Table 1. The methacrylic resin composition was then cooled together with the SUS plate, and the SUS plate was then removed to obtain a 3 mm thick plate-shaped resin molded product. The evaluation results of the properties of the obtained resin molded product are shown in Table 1. In Table 1, "-" indicates that no measurement was performed.

[0097] [Examples 3 to 6] A methacrylic resin composition and a resin molded article were produced in the same manner as in Example 2, except that the composition of the monomer composition was changed as shown in Table 1. The composition of the obtained methacrylic resin composition is shown in Table 1. The evaluation results of the properties of the obtained resin molded article are also shown in Table 1.

[0098] [Comparative Examples 1 to 2] A methacrylic resin composition and a resin molded product were obtained in the same manner as in Example 1, except that the composition of the monomer composition was as shown in Table 1. The composition of the obtained methacrylic resin composition is shown in Table 1. The evaluation results of the properties of the obtained resin molded product are also shown in Table 1.

[0099] Comparative Example 3 A methacrylic resin composition and a resin molded product were obtained in the same manner as in Example 2, except that the composition of the monomer composition was as shown in Table 1. The composition of the obtained methacrylic resin composition is shown in Table 1. The evaluation results of the properties of the obtained resin molded product are also shown in Table 1.

[0100] [Table 1]

[0101] From the comparison between Example 1 and Comparative Example 1, it can be seen that the methacrylic polymer is a simple polymer derived from an acrylic acid ester. It was found that in a system containing a unit, the photostability can be improved by adding at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate. Comparison between Example 1 and Comparative Example 2 revealed that, as long as the methacrylic polymer contains at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, even in an embodiment in which the resin composition does not contain a hindered amine compound, better light stability can be achieved than in an embodiment in which the resin composition contains a hindered amine compound. A comparison of Examples 2 to 6 and Comparative Example 3 revealed that in a system in which the methacrylic polymer does not contain units derived from an acrylic acid ester, the photostability can be improved by adding at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate.

Claims

1. A monomer composition comprising methyl methacrylate and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate.

2. A monomer composition comprising methyl methacrylate and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, A monomer composition, wherein the total content of at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate is 5 ppm by mass or more based on the total mass of the monomer composition.

3. A monomer composition comprising methyl methacrylate and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, A monomer composition, wherein the total content of at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate is 50 ppm by mass or more relative to the total mass of the monomer composition.

4. A monomer composition comprising methyl methacrylate and at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate, A monomer composition, wherein the total content of at least one compound selected from the group consisting of methyl pyruvate and methyl 2-methylbutyrate is 100 ppm by mass or more based on the total mass of the monomer composition.

5. The monomer composition according to any one of claims 1 to 4, further comprising an acrylic acid ester.

6. 6. The monomer composition according to claim 5, wherein the acrylic ester is at least one compound selected from the group consisting of methyl acrylate, ethyl acrylate, and n-butyl acrylate.

7. 6. The monomer composition of claim 5, wherein the acrylic ester is n-butyl acrylate.

8. The monomer composition according to any one of claims 1 to 4, further comprising at least one compound selected from the group consisting of methyl isobutyrate and methyl propionate.

9. A methacrylic resin composition obtained by radical polymerization of a polymerizable composition (X2) containing the monomer composition according to any one of claims 1 to 4.

10. A method for producing a methacrylic resin composition, comprising: a radical polymerization step of radically polymerizing a polymerizable composition (X2) containing the monomer composition according to any one of claims 1 to 4.