Monomer composition, methacrylic resin composition and resin molding

Abstract

To provide a methacrylic resin composition which is excellent in light stability and suppresses yellow discoloration while guaranteeing excellent heat resistance of a methacrylic resin, a resin molding containing the methacrylic resin composition, and a monomer composition for obtaining the methacrylic resin composition.SOLUTION: A monomer composition contains methyl methacrylate, and methyl propionate, wherein a content of the methyl propionate is more than 200 mass ppm and 50,000 mass ppm or less with respect to the total mass of the monomer composition.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a monomer composition, a methacrylic resin composition, and a resin molded body. This application claims priority based on Japanese Patent Application No. 2021-085291 filed in Japan on May 20, 2021, and incorporates its content herein.

Background Art

[0002] Methacrylic resins are excellent in transparency, heat resistance, and weather resistance, and have balanced performance in resin physical properties such as mechanical strength, thermal properties, and molding processability. In particular, a methacrylic resin plate made of a methacrylic resin is used as a translucent member for any of a sunbed, lighting equipment, skin therapy equipment, medical equipment, UV irradiation device, equipment for growing animals and plants, skylight, and HID lamp.

[0003] In the above applications, when a methacrylic resin plate is installed in an environment exposed to UV such as direct sunlight or a UV lamp, the methacrylic resin plate has a problem that a yellow band (yellowing, yellowish color) occurs. Therefore, there has been a demand for a methacrylic resin that does not develop a yellow band even when exposed to UV for a long time, that is, a methacrylic resin having excellent light stability.

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

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the methacrylic resin described in Patent Document 1 had a problem in that, while its photostability improved with increasing amounts of HALS added during polymerization, it also became discolored because HALS itself is colored. Furthermore, increasing the amount of HALS added led to a decrease in polymerization efficiency and an increase in residual monomers in the methacrylic resin, which in turn reduced the photostability of the methacrylic resin.

[0007] In view of the above circumstances, the present invention aims to provide a methacrylic resin composition that has excellent light stability and suppresses yellowing while ensuring the excellent heat resistance of a methacrylic resin; a resin molded article containing the methacrylic resin composition; and a monomer composition for obtaining the methacrylic resin composition. [Means for solving the problem]

[0008] To solve the above problems, the present invention has the following features. In other words, the gist of the present invention is as follows.

[0009] [1] A monomer composition comprising methyl methacrylate and methyl propionate, A monomer composition in which the methyl propionate content is greater than 200 ppm by mass and less than or equal to 50,000 ppm by mass, based on the total mass of the monomer composition. [2] A monomer composition comprising methyl methacrylate and methyl propionate, A monomer composition having a methyl propionate content of 250 ppm by mass or more relative to the total mass of the monomer composition. [3] A monomer composition comprising methyl methacrylate and methyl propionate, A monomer composition having a methyl propionate content of 300 ppm by mass or more relative to the total mass of the monomer composition. [4] A monomer composition according to any one of [1] to [3], further containing an acrylic acid ester. [5] The monomer composition according to [4], 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. [6] The monomer composition according to [4], wherein the acrylic acid ester is n-butyl acrylate. [7] A monomer composition according to any one of [1] to [6], further comprising at least one compound selected from the group consisting of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate. [8] A monomer composition according to any one of [1] to [6], further comprising at least one compound selected from methyl isobutyrate and methyl 2-methylbutyrate. [9] A methacrylic resin composition obtained by radical polymerization of a polymerizable composition (X2) containing the monomer composition described in any of [1] to [8].

[10] A methacrylic resin composition comprising a methacrylic polymer (P) and methyl propionate, A methacrylic resin composition in which the methyl propionate content is 100 ppm by mass or more and 50,000 ppm by mass or less, based on the total mass of the methacrylic resin composition.

[11] A methacrylic resin composition comprising a methacrylic polymer (P) and methyl propionate, A methacrylic resin composition in which the methyl propionate content is 200 ppm by mass or more based on the total mass of the methacrylic resin composition.

[12] A methacrylic resin composition comprising a methacrylic polymer (P) and methyl propionate, A methacrylic resin composition having a methyl propionate content of 300 ppm by mass or more relative to the total mass of the methacrylic resin composition.

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

[10] to

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

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

[10] to

[12] , 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. 2].

[15] A resin molded body containing the methacrylic resin composition according to any one of [9] to

[14] .

[16] 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]. [Effect of the Invention]

[0010] According to the present invention, there can be provided a methacrylic resin composition having excellent heat resistance possessed by a methacrylic resin, excellent light stability, and suppressed yellowing; a resin molded body containing the methacrylic resin composition; and a monomer composition for obtaining the methacrylic resin composition. [Embodiments for Carrying out the Invention]

[0011] In the present specification, “(meth)acrylate” means at least one selected from “acrylate” and “methacrylate”, and “(meth)acrylic” means at least one selected from “methacrylic” and “acrylic”. Further, the “methacrylic polymer” may contain repeating units derived from an acrylic monomer in addition to repeating units derived from a methacrylic monomer. In this specification, "monomer" means an unpolymerized compound, and "repeating unit" means a unit derived from the monomer formed by polymerization of the monomer. The repeating unit may be a unit directly formed by a polymerization reaction, or a unit in which a part of the unit is converted into another structure by treating the polymer. In this specification, "mass %" indicates the content of a specific component contained in the total amount of 100 mass %.

[0012] Unless otherwise specified, the numerical range represented by "~" in this specification means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value, and "A~B" means A or more and B or less. In this specification, UV means light having a wavelength range of 295 nm or more and 430 nm or less, that is, light mainly including 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 methyl propionate. Also, other components may be contained as long as the effects of the present invention are not impaired.

[0014] <1-1. Methyl Methacrylate> By containing methyl methacrylate, the monomer composition according to this embodiment can provide a methacrylic resin composition having good light stability and suppressed 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 usually less than 99.98% by mass, and may be 99.975% by mass or less, or 99.97% by mass or less. Therefore, examples of methyl methacrylate content include the ranges of 85% by mass or more and less than 99.98% by mass, 90% by mass or more and less than 99.98% by mass, 95% by mass or more and 99.975% by mass or less, and 97% by mass or more and 99.97% by mass or less.

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

[0017] <1-2. Methyl propionate> The monomer composition according to this embodiment, by containing methyl propionate, can provide a methacrylic resin composition with good photostability and suppressed yellowing.

[0018] The lower limit of the methyl propionate content relative to the total mass of the monomer composition according to this embodiment is usually greater than 200 ppm by mass (i.e., excluding the range of 200 ppm by mass or less), preferably 220 ppm by mass or more, more preferably 250 ppm by mass or more, even more preferably 270 ppm by mass or more, and particularly preferably 300 ppm by mass or more, in order to provide a methacrylic resin composition with better photostability.

[0019] The upper limit of the methyl propionate content 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, in that the heat resistance of the methacrylic resin is not impaired when the monomer composition is converted to a methacrylic resin composition.

[0020] The preferred upper and lower limits mentioned above can be combined in any way. Specifically, the content of methyl propionate relative to the total mass of the monomer composition according to this embodiment is preferably more than 200 ppm by mass and 50,000 ppm by mass or less, more preferably 220 ppm by mass and 25,000 ppm by mass or less, even more preferably 250 ppm by mass and 20,000 ppm by mass or less, particularly preferably 270 ppm by mass and 15,000 ppm by mass or less, and most preferably 300 ppm by mass and 10,000 ppm by mass or less.

[0021] <1-3. Other Monomers> The monomer composition according to this embodiment may contain monomers other than methyl methacrylate in addition to methyl methacrylate. Examples of monomers other than methyl methacrylate include the monomers listed in 1) to 16) below. The monomers listed in 1) to 16) below can be used individually or in any ratio and combination of two or more.

[0022] 1) Methacrylic acid ester: 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) Hydroxyl 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 derivatives thereof. 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) Alkanediolic 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) An unsaturated polyester prepolymer obtained from at least one polycarboxylic acid containing an ethylenically unsaturated polycarboxylic acid and at least one diol. 16) A vinyl ester prepolymer obtained by modifying the terminals of epoxy groups with acrylic.

[0024] Of 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 having an excellent balance of transparency, heat resistance, and moldability of the methacrylic resin composition. Furthermore, 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, methyl 2-methylbutyrate, and methyl pyruvate> The monomer composition according to this embodiment may further contain at least one compound selected from the group consisting of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate, and it is particularly preferable that it further contains at least one compound from methyl isobutyrate and methyl 2-methylbutyrate. By including the above compound in addition to methyl propionate in the monomer composition, it is possible to provide a methacrylic resin composition with better photostability and more suppressed yellowing.

[0026] The lower limit of the total content of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate 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 1,000 ppm by mass or more, in order to provide a methacrylic resin composition with better photostability.

[0027] The upper limit of the total content of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate relative to the total mass of the monomer composition according to this embodiment is not particularly limited, but the monomer composition In order to ensure that the heat resistance of the methacrylic resin is not impaired when converted to a methacrylic resin composition, the concentration 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.

[0028] The preferred upper and lower limits mentioned above can be combined in any way. Specifically, the total content of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate can range from 20 ppm to 50,000 ppm by mass, 100 ppm to 25,000 ppm by mass, 200 ppm to 10,000 ppm by mass, 200 ppm to 7,000 ppm by mass, 500 ppm to 7,000 ppm by mass, and 1,000 ppm to 5,000 ppm by mass. Of these, the total content of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate is more preferably 100 ppm to 25,000 ppm by mass, and even more preferably 200 ppm to 7,000 ppm by mass.

[0029] Furthermore, if the monomer composition contains at least one compound selected from the group consisting of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate, it is preferable that the total content of methyl propionate, methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate relative to the total mass of the monomer composition is within the range of the methyl propionate content described above.

[0030] <1-5. Additives> In this embodiment, methyl propionate is thought to exhibit superior photostability through a mechanism of action different from that of generally known UV absorbers and radical scavengers (HALS). Therefore, methyl propionate can be used in combination with additives such as UV absorbers and HALS. By including methyl propionate and the additive in the monomer composition, it becomes possible to provide methacrylic resin compositions and resin molded articles with increased photostability at a lower cost.

[0031] Examples of known additives include mold release agents, lubricants, plasticizers, antioxidants, antistatic agents, light stabilizers other than methyl propionate, ultraviolet absorbers, flame retardants, flame retardant aids, polymerization inhibitors, fillers, pigments, dyes, silane coupling agents, leveling agents, defoaming agents, and fluorescent agents. These additives can be used individually or in any combination of two or more.

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

[0033] <2. Polymerizable composition (X2)> A polymerizable composition (X2) according to the second embodiment of the present invention is one form of a raw material for obtaining a methacrylic resin composition according to the third embodiment of the present invention, which will be described later. The polymerizable composition (X2) according to this embodiment is, for example, a polymerizable composition (X2-1) containing the raw material composition (X1) described later, methyl propionate, 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 component of the polymerizable composition (X2-1) and is a raw material for the methacrylic polymer (P) contained in the methacrylic resin composition according to the third embodiment of the present invention. It is also a component. In the following explanation, we will mainly describe the raw material composition (X1) used in the production of a 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 acrylic acid esters (hereinafter also referred to as "acrylic acid ester units") as the methacrylic polymer (P). However, by changing the acrylic acid ester to styrene, it can also be applied to the production of a 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 the same as the styrene unit content ratio described in <3-1. Methacrylic Polymer (P)>.

[0035] Examples of raw material compositions (X1) include compositions containing only MMA, and compositions containing the MMA and an acrylic acid ester. As the acrylic acid ester, monomers similar to those described in <1-3. Other Monomers> or <3-1. Methacrylic Polymers (P)> can be used. By including MMA and acrylic acid ester in the raw material composition (X1), the photostability of the methacrylic resin composition is improved, and the occurrence of yellowing 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 can be suppressed.

[0036] The proportion 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 proportion similar to the proportion of MMA units in the methacrylic polymer (P1) or methacrylic polymer (P2) described in <3-1. Methacrylic Polymer (P)> can be suitably applied. However, "relative to the total mass of methacrylic polymer (P1)" and "relative to the total mass of methacrylic polymer (P2)" in <3-1. Methacrylic Polymer (P)> shall be read as "relative to the total mass of raw material composition (X1)".

[0037] Furthermore, the content ratio of 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 ratio similar to the content ratio of acrylic acid ester units contained in the methacrylic polymer (P1) or methacrylic polymer (P2) described in <3-1. Methacrylic Polymer (P)> can be suitably applied. However, "relative to the total mass of methacrylic polymer (P1)" and "relative to the total mass of methacrylic polymer (P2)" in <3-1. Methacrylic Polymer (P)> shall be read as "relative to the total mass of raw material composition (X1)". As for 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 Polymers (P)> can be used.

[0038] Furthermore, the raw material composition (X1) may pre-contain a polymer containing MMA units. Specifically, the raw material composition (X1) may pre-contain polymer (a), which will be described later. By including polymer (a) in the raw material composition (X1), the polymerizable composition (X2-1) becomes a viscous liquid ("syrup"), thus shortening the polymerization time and improving productivity. Methods for obtaining the syrup described above include, for example, dissolving a polymer in a raw material composition (X1), or adding a known radical polymerization initiator to the raw material composition (X1) and polymerizing a portion of it.

[0039] When the polymerizable composition (X2-1) is a syrup, examples of compositions include the polymer (a) and monomer composition (m) described below. Polymer (a): 70.0% by mass or more of MMA units relative to the total mass of polymer (a) and the above A polymer containing 30.0% by mass or less of acrylic acid ester units, or a polymer containing 50.0% by mass or more of MMA units and 50.0% by mass or less of the styrene units, or a polymer consisting of 100% by mass of MMA units. Monomer composition (m): A monomer composition comprising 70.0% by mass or more of MMA and 30.0% by mass or less of acrylic acid ester, or a monomer composition comprising 50.0% by mass or more of MMA and 50.0% by mass or less of styrene, or a monomer composition consisting of 100% by mass of MMA.

[0040] The content (in 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% by mass or more and 99.99% by mass or less, relative to the total mass of the polymerizable composition (X2-1).

[0041] <2-2. Monomer Compositions> The monomer composition that is a component of the polymerizable composition (X2-2) is a monomer composition according to the first embodiment of the present invention, and is a composition that includes 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% by mass or more and less than 100% by mass. Furthermore, the polymerizable composition (X2-2) may also contain other monomers copolymerizable with the monomers in the monomer composition (also simply referred to as "other monomers"). If the polymerizable composition (X2-2) contains other monomers, the content of the other monomers is greater than 0% by mass and less than 40% by mass, relative to the total mass of the polymerizable composition (X2-2).

[0043] Other monomers include the monomers 1) to 16) listed in <1-3. Other Monomers> above. The monomers described in 1) to 16) above can be used individually or in any ratio and combination of two or more monomers.

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

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

[0046] The content of the radical polymerization initiator in the polymerizable composition (X2) is not particularly limited and can be appropriately determined by those skilled in the art in accordance with well-known technology. 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 part by mass or less, per 100 parts by mass of the total mass of the polymerizable composition (X2).

[0047] <2-4. Additives> The polymerizable composition (X2) may optionally contain a release agent, heat stabilizer, lubricant, plasticizer, antioxidant, antistatic agent, light stabilizer other than methyl propionate, UV absorber, flame retardant, flame retardant aid, polymerization inhibitor, filler, pigment, dye, silane coupling agent, leveling agent, and defoamer. It may contain additives selected from agents, fluorescent agents, and chain transfer agents, etc.

[0048] <3. Methacrylic resin composition> The methacrylic resin composition according to the 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 a predetermined amount of methyl propionate. 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, by containing a methacrylic polymer (P), can provide a resin molded article with good transparency. The methacrylic resin composition, by containing methyl propionate, can provide a resin molded article in which the occurrence of yellowing is suppressed even after prolonged exposure to UV light, and furthermore, the decrease in photostability is suppressed. Furthermore, 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 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 photostability, this content is usually 99.99% by mass or less, preferably 99.985% by mass or less, more preferably 99.98% by mass or less, even more preferably 99.975% by mass or less, especially preferably 99.97% by mass or less, particularly preferably 99.95% by mass or less, and most preferably 99.90% by mass or less. The above upper and lower limits can be combined arbitrarily. For example, preferred content of methacrylic polymer (P) includes the ranges of 95% to 99.99% by mass, 95% to 99.985% by mass, 97.5% to 99.98% by mass, 97.5% to 99.975% by mass, 98% to 99.97% by mass, 98% to 99.95% by mass, and 99.0% to 99.90% by mass. Note that if the methacrylic resin composition contains two or more types of methacrylic polymer (P), the above content refers to the total content of the two or more types of methacrylic polymer (P).

[0050] The content of methyl propionate relative to the total mass of the methacrylic resin composition is not particularly limited. From the viewpoint of obtaining excellent photostability, the content of methyl propionate is usually 100 ppm by mass or more, preferably 150 ppm by mass or more, more preferably 200 ppm by mass or more, even more preferably 250 ppm by mass or more, particularly preferably 300 ppm by mass or more, and most preferably 1,000 ppm by mass or more, relative to the total mass of the methacrylic resin composition.

[0051] The upper limit of the methyl propionate content in the methacrylic resin composition according to this embodiment is not particularly limited, but from the viewpoint of having good heat resistance of the resin molded article, 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 combined arbitrarily. For example, preferred methyl propionate content ranges include 100 ppm to 50,000 ppm, 150 ppm to 25,000 ppm, 200 ppm to 20,000 ppm, 250 ppm to 15,000 ppm, 300 ppm to 15,000 ppm, and 1,000 ppm to 10,000 ppm. Of these, the methyl propionate content is more preferably 150 ppm to 25,000 ppm, and even more preferably 250 ppm to 15,000 ppm.

[0052] In this embodiment, methyl propionate is thought to exhibit superior photostability through a mechanism of action different from that of generally known UV absorbers and radical scavenging agents (HALS). Therefore, methyl propionate can be used in combination with additives such as UV absorbers and HALS. By using methyl propionate in combination with these additives, it becomes possible to provide methacrylic resin compositions and resin molded articles with increased photostability at a lower cost.

[0053] The methacrylic resin composition may contain components other than the methacrylic polymer (P) and methyl propionate, to the extent that the effects of the present invention are obtained. For example, it may contain additives selected from mold release agents, heat stabilizers, antioxidants, ultraviolet absorbers, and light stabilizers other than methyl propionate.

[0054] <3-1. Methacrylic polymer (P)> The methacrylic polymer (P) is one of the components included in the methacrylic resin composition according to this embodiment. The methacrylic resin composition, by containing a methacrylic polymer (P), can improve transparency, suppress decomposition due to heat and light, and improve heat moldability, heat resistance, and mechanical strength. Furthermore, due to the synergistic effect of the heat resistance inherent in the methacrylic polymer (P) and methyl propionate, it is possible to obtain a methacrylic resin molded article that suppresses the occurrence of yellowing when exposed to UV light for a long time, has high photostability, and maintains heat resistance.

[0055] The methacrylic polymer (P) is preferably a copolymer containing MMA units and acrylic acid 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 acrylic acid ester is a repeating unit derived from an acrylic acid ester having an alkyl group with 1 to 6 carbon atoms in its side chain. The monomer constituting this unit is not particularly limited as long as it is a monomer copolymerizable with MMA. Examples include acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, or t-butyl acrylate. These may be used individually, or two or more may be used in any ratio and combination. Among these monomers, from the viewpoint of suppressing the occurrence of yellowing and ensuring high photostability when the resin molded article containing the methacrylic resin composition is exposed to UV for a long time, it is preferable that at least one acrylic acid ester selected from the group consisting of methyl acrylate, n-ethyl acrylate, and n-butyl acrylate is used, and more preferably n-butyl acrylate.

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

[0058] The content of acrylic acid ester units in the methacrylic polymer (P1) is not particularly limited, but from the viewpoint of good heat resistance and photostability, it should be 30% by mass or less. It is preferable that the content be 20% by mass or less, more preferably 10% by mass or less, and usually 0% by mass or more. If the methacrylic polymer (P1) contains two or more types of acrylic acid ester units, the above content ratio is the total content ratio of the two or more types of acrylic acid ester units.

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

[0060] The styrene unit content in the methacrylic polymer (P2) is not particularly limited, but from the viewpoint of good 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 usually 0% by mass or more.

[0061] Furthermore, the methacrylic polymer (P) in this embodiment may contain structural units derived from polyfunctional monomers containing two or more radical polymerizable functional groups in a single molecule (hereinafter referred to as "polyfunctional monomer units"), to the extent that the effects of the invention are obtained. The radical polymerizable functional group referred to herein can be any group having a carbon-carbon double bond and capable of radical polymerization. Specifically, examples include vinyl groups, allyl groups, (meth)acryloyl groups, and (meth)acryloyloxy groups. The (meth)acryloyl group is particularly preferred from the viewpoint of excellent storage stability of compounds having radical polymerizable functional groups and the ease with which the polymerizability of such compounds can be controlled. Note that "(meth)acryloyl" refers to either "acryloyl" or "methacryloyl," or both. Note that the radical polymerizable functional groups in a monomer having two radical polymerizable functional groups may be the same or different. The methacrylic polymer (P) can have improved solvent resistance or chemical resistance by containing polyfunctional monomer units.

[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. These may be used individually or in any ratio and combination. Of these, the polyfunctional monomer is more preferably selected from ethylene glycol di(meth)acrylate and neopentyl glycol di(meth)acrylate, and even more preferably ethylene glycol di(meth)acrylate, from the viewpoint of obtaining better 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), as 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 molded resin article. For example, it may be 10,000 or more, 100,000 or more, 150,000 or more, 1,000,000 or less, 2,000,000 or less, or 4,000,000 or less.

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

[0065] <3-2. Methyl propionate> Methyl propionate is one of the components contained in the methacrylic resin composition according to this embodiment. By containing methyl propionate, the methacrylic resin composition can suppress the occurrence of yellow discoloration when exposed to UV light for a long period of time. Furthermore, it is less expensive than conventional UV absorbers and can also suppress the decrease in photostability.

[0066] <3-3. Methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate> The methacrylic resin composition according to this embodiment may further contain at least one compound selected from the group consisting of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate, and it is particularly preferable that it further contains at least one compound from methyl isobutyrate and methyl 2-methylbutyrate.

[0067] The lower limit of the total content of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate 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 order to provide a methacrylic resin composition with better photostability.

[0068] The upper limit of the total content of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate 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, in that the heat resistance of the methacrylic resin is not impaired.

[0069] The preferred upper and lower limits mentioned above can be combined in any way. Specifically, the total content of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate can range from 20 ppm to 50,000 ppm by mass, 100 ppm to 25,000 ppm by mass, 200 ppm to 10,000 ppm by mass, 200 ppm to 7,000 ppm by mass, 500 ppm to 7,000 ppm by mass, and 1,000 ppm to 5,000 ppm by mass. Of these, the total content of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate is more preferably 100 ppm to 25,000 ppm by mass, and even more preferably 200 ppm to 7,000 ppm by mass.

[0070] Furthermore, if the methacrylic resin composition contains at least one compound selected from the group consisting of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate, it is preferable that the total content of methyl propionate, methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate relative to the total mass of the methacrylic resin composition is within the range of the methyl propionate content described above.

[0071] <3-4. Properties of methacrylic resin compositions> The methacrylic resin composition according to this embodiment contains the methacrylic polymer (P) and methyl propionate, and therefore exhibits excellent photostability.

[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 (YI) of the test piece, measured in accordance with ASTM D1925, obtained from before the start of the UV exposure test to 200 hours after the start of the UV exposure test, is 5.5 or less, preferably 5.0 or less, more preferably 4.5 or less, and even more preferably 4.0 or less. In addition, 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. Even 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. Note that light transmittance refers to the total light transmittance (Tt) in the thickness direction of the test specimen, 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 specimen made of a methacrylic resin composition (50 mm x 50 mm square, 5 mm thick) was placed in the evaluation chamber of a metal weather accelerated photostability 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.). Under conditions of 63°C and 50 RH%, the specimen was subjected to ultraviolet light from the metal halide lamp (irradiation intensity 80 mW / cm²). 2 The test specimen is irradiated with )

[0074] <4. Resin molded product> A resin molded article (also simply referred to as "resin molded article") according to the fourth embodiment of the present invention is a resin molded article containing a methacrylic resin composition according to the third embodiment of the present invention. By molding the 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 contains the above-mentioned methacrylic resin composition, and a molded article consisting only of a methacrylic resin composition is substantially equivalent to either a methacrylic resin composition or a resin molded article.

[0075] Examples of the shape of the resin molded body include a plate-shaped resin molded body (resin plate) or a sheet-shaped 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 between 1 mm and 30 mm.

[0076] Because the resin molded article contains the methacrylic resin composition described above, it exhibits excellent photostability. In other words, the resin molded test specimen (50 mm x 50 mm square, 3 mm thick) exhibits excellent photostability such that the yellowness (YI) measured in accordance with ASTM D1925, obtained from before the start of the UV exposure test to 200 hours after the start of the UV exposure test, is 5.5 or less, preferably 5.0 or less, more preferably 4.5 or less, and even more preferably 4.0 or less. In addition, the test specimen preferably exhibits high photostability 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 specimen 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. Note that light transmittance refers to the total light transmittance (Tt) in the thickness direction of the test specimen, 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 compositions or resin molded articles> There are no particular limitations on 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 collectively referred to as "resin composition, etc."). Specific production methods for resin composition, etc. include, for example, the second method of the present invention. A method is provided that includes a radical polymerization step of a polymerizable composition (X2) according to the embodiment of the present invention, preferably a polymerizable composition (X2-2) containing a 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 the polymerizable components in the syrup. In the syrup preparation step, "polymerizing a portion of the polymerizable composition (X2)" means polymerizing so 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 when polymerizing the polymerizable composition (X2) is not particularly limited and can be appropriately determined by those skilled in the art in accordance with well-known techniques. Typically, it is appropriately set in a range of preferably 40°C to 180°C, more preferably 50°C to 150°C, depending on the type of radical polymerization initiator used. Furthermore, the polymerizable composition (X2) can be polymerized under multiple temperature conditions as needed. The polymerization time can be appropriately determined according to the progress of polymerization curing.

[0079] Examples of polymerization methods for the polymerizable composition (X2) include bulk polymerization, suspension polymerization, emulsion polymerization, or dispersion polymerization. Among these, bulk polymerization is preferred in terms of productivity.

[0080] Furthermore, specific methods for producing resin compositions include, for example, obtaining resin compositions by bulk polymerization using known cast polymerization methods such as the cell casting method or the continuous casting method, or obtaining resin compositions by molding a composition produced by bulk polymerization using methods such as extrusion molding or injection molding. From the viewpoint of further improving the heat resistance of methacrylic resin compositions by increasing molecular weight and introducing cross-linked structures, it is more preferable to employ a method utilizing cast polymerization (injection polymerization).

[0081] As an example of a cast polymerization method, when obtaining a resin composition having a plate-like form, a cell cast method is used in which a space formed by two opposing glass plates or metal plates (SUS plates) and gaskets such as flexible resin tubes placed on their edges is used as a mold, a polymerizable composition (X2) or syrup polymerized with respect to a portion of the polymerizable composition (X2) is injected into the mold, polymerization is completed by heat polymerization treatment, and the resin composition is removed from the mold. Alternatively, a continuous cast method is used in which a space formed by two stainless steel endless belts traveling opposite each other in the same direction at the same speed with a predetermined distance between them and gaskets such as flexible resin tubes placed on both sides of the endless belts is used as a mold, a polymerizable composition (X2) or syrup polymerized with respect to a portion of the polymerizable composition (X2) is continuously injected into the mold from one end of the endless belts, polymerization is completed by heat polymerization treatment, and the resin composition is continuously removed from the other end of the endless belts. By appropriately adjusting the spacing of the voids in the mold using the gasket thickness (diameter), a resin composition of the desired thickness can be obtained. The thickness of the plate-shaped resin composition is usually set within the range of 1 mm to 30 mm.

[0082] <6.Applications> The uses of the methacrylic resin composition and resin molded articles described above ("resin composition, etc.") are not particularly limited, but they are preferably used as light-transmitting members, particularly transparent members, used in any of the following: tanning beds, lighting equipment, skin therapy equipment, medical equipment, UV irradiation devices, plant and animal cultivation equipment, skylights, and HID lamps. More specifically, they are preferably used as light-gathering members intended to allow light to enter, used in any of the following: tanning beds and skylights, or as light-transmitting members intended to allow light to pass through, used in any of the following: lighting equipment, skin therapy equipment, medical equipment, UV irradiation devices, plant and animal cultivation equipment, and HID lamps.

[0083] <7. Effects> The monomer composition according to the first embodiment of the present invention contains methyl propionate, and the 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 methyl propionate, thereby ensuring excellent heat resistance, while also providing a methacrylic resin composition with excellent light stability and suppressed yellowing, is presumed to be as follows.

[0084] Polymers containing units based on methyl methacrylate (methacrylic polymers) undergo cleavage of the main chain or side chains upon exposure to light, generating radical species. Typically, these generated radical species cause yellowing of methacrylic resins and a decrease in mechanical strength due to a reduction in molecular weight.

[0085] However, it is believed that the methyl propionate contained in the monomer composition according to the first embodiment of the present invention remains in the methacrylic resin composition, and that the methyl propionate functions as a radical scavenger. As a result, the methacrylic resin composition is expected to exhibit excellent heat resistance and good photostability. [Examples]

[0086] The features of the present invention will be further described below with reference to examples and comparative examples. The materials, amounts used, proportions, processing content, processing procedures, etc., shown in the following examples can be modified 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 addition, 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 (manufactured by Mitsubishi Chemical Corporation) • Methyl isobutyrate (manufactured by Tokyo Chemical Industry Co., Ltd.) Methyl propionate (manufactured by Tokyo Chemical Industry Co., Ltd.) • Methyl 2-methylbutyrate (manufactured by Tokyo Chemical Industry Co., Ltd.) Furthermore, the MMA (manufactured by Mitsubishi Chemical Corporation) contained 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, relative to the total mass of MMA.

[0088] [Measurement Methods and Evaluation Methods] <Method for measuring the remaining amount of target substance in methacrylic resin> (1) Procedure for preparing samples and test solutions 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 residual pesticide testing (hereinafter simply referred to as "acetone"). After the resin was dissolved, 1 mL of the internal standard solution was added using a volumetric pipette. A 0.1 vol% methyl salicylate / acetone solution was used as the internal standard solution. Three different concentrations of test solutions were prepared by diluting the target standard reagent with acetone, and a three-level calibration curve was created by gas chromatography-mass spectrometry (GC / MS) measurement described later, and the concentration of each target substance in the sample was quantified. A 0.1 vol% methyl salicylate / acetone solution was used as the internal standard solution.

[0089] (GC / MS measurement conditions) Equipment: GC HP6890 / MS HP5973 (manufactured by Agilent) Ionization method: EI (Electron Ionization) method Column: DB-WAX 60m x 250μm x 0.5μm (manufactured by Agilent) Heating conditions: 70°C (5 min) → 200°C (5 min) Rate = 10°C / 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] <Method for evaluating heat resistance> As an indicator of the heat resistance of the methacrylic resin compositions obtained in the examples and comparative examples, the temperature of deflection under load (hereinafter referred to as "HDT") (°C) was measured for test specimens (length 127 mm × width 12.7 mm × thickness 3 mm) of the resin molded articles 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 accelerated photostability tester (manufactured by Daipla Wintes Co., Ltd., model: KU-R5CI-A) equipped with a metal halide lamp (manufactured by Daipla Wintes Co., Ltd., model: MW-60W) and a light cut filter (manufactured by Daipla Wintes Co., Ltd., model: KF-1). The change in yellowness (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 (50 mm x 50 mm square, 5 mm thick) made from the methacrylic resin compositions obtained in the examples and comparative examples were placed in the evaluation chamber of the metal weather accelerated photostability tester. The irradiation intensity of ultraviolet (UV) light irradiated onto the test specimen from the metal halide lamp was 80 mW / cm² at wavelengths of 330-390 nm, as measured by an ultraviolet irradiometer (Ushio Inc., model: UIT-101). 2 The values ​​were corrected accordingly. The evaluation chamber of the metal weather accelerated photostability tester was set to an environment with a temperature of 63°C and a humidity of 50 RH, and ultraviolet light (irradiation intensity 80 mW / cm²) from a metal halide lamp was used. 2 The test specimen was irradiated with ). As an indicator of photostability, a spectrophotometer (manufactured by Nippon Denshoku Industries, Ltd., model name: SE-7700) was used to measure the yellowness (yellow index: YI) of the test specimens in accordance with ASTM D1925. One test specimen was measured before the start of the UV exposure test, and another test specimen was measured 200 hours after the start of the test. The change in the measured value was defined as the change in yellowness (ΔYI).

[0093] <Manufacturing of methacrylic resin compositions> [Example 1] (1) Manufacturing of syrup Methyl propionate was added at a concentration of 300 ppm to a reactor (polymerization vessel) equipped with a condenser, thermometer, and stirrer. Then, 100 parts of MMA were supplied, and after bubbling with nitrogen gas while stirring, heating was started. When the internal temperature of the reactor reached 80°C, 0.12 parts of 2,2'-azobis-(2,4-dimethylvaleronitrile) were added as a radical polymerization initiator. The reactor was then heated further until the internal temperature reached 100°C, and held for 9 minutes. The reactor was then cooled to room temperature to obtain the syrup. The polymer content in the syrup was 20% by mass relative to the total mass of the syrup.

[0094] (2) Cast polymerization To 100 parts of the above syrup, t-hexylperoxypiva is used as a radical polymerization initiator. 0.15 parts of lade were added 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 by placing a soft resin gasket at the edge of the SUS plates between two opposing SUS plates. The polymerizable composition (X2) was cured by heating at 80°C for 30 minutes, and then at 130°C for 30 minutes, to obtain a methacrylic resin composition. The composition of the methacrylic resin composition is shown in Table 1. Next, the methacrylic resin composition and the SUS plates were cooled, and then the SUS plates were removed to obtain a 3 mm thick plate-shaped resin molded body. The evaluation results of the properties of the obtained resin molded body are shown in Table 1. In Table 1, "-" means that no measurement was performed.

[0095] [Examples 2-5] Except for changing the monomer composition as shown in Table 1, a methacrylic resin composition and a resin molded article were produced in the same manner as in Example 1. The composition of the obtained methacrylic resin composition is shown in Table 1. The results of the property evaluation of the obtained resin molded article are shown in Table 1.

[0096] [Comparative Example 1] A methacrylic resin composition and a resin molded article were obtained in the same manner as in Example 1, except that the monomer composition was as shown in Table 1. The composition of the obtained methacrylic resin composition is shown in Table 1. The results of the property evaluation of the obtained resin molded article are shown in Table 1.

[0097] [Table 1]

[0098] From a comparison of Examples 1-5 and Comparative Example 1, it was found that the photostability can be improved by including a specific amount of methyl propionate in the methacrylic resin composition. Furthermore, a comparison of Examples 3-5 and Comparative Example 1 revealed that the photostability can be further improved by adding at least one compound selected from the group consisting of methyl isobutyrate, methyl 2-methylbutyrate, and methyl pyruvate to the methacrylic resin composition.

Claims

1. A monomer composition comprising methyl methacrylate, methyl propionate, methyl isobutyrate, and methyl 2-methylbutyrate, The content of methyl methacrylate is 90% by mass or more based on the total mass of the monomer composition, A monomer composition having a methyl propionate content of more than 200 ppm by mass and not more than 50,000 ppm by mass, based on the total mass of the monomer composition.

2. A monomer composition comprising methyl methacrylate, methyl propionate, methyl isobutyrate, and methyl 2-methylbutyrate, The content of methyl methacrylate is 90% by mass or more based on the total mass of the monomer composition, A monomer composition having a methyl propionate content of 250 ppm by mass or more based on the total mass of the monomer composition.

3. A monomer composition comprising methyl methacrylate, methyl propionate, methyl isobutyrate, and methyl 2-methylbutyrate, The content of methyl methacrylate is 90% by mass or more based on the total mass of the monomer composition, A monomer composition having a methyl propionate content of 300 ppm by mass or more based on the total mass of the monomer composition.

4. The monomer composition according to any one of claims 1 to 3, further comprising an acrylic acid ester.

5. 5. The monomer composition according to claim 4, wherein the acrylic ester is at least one compound selected from the group consisting of methyl acrylate, ethyl acrylate, and n-butyl acrylate.

6. 5. The monomer composition of claim 4, wherein the acrylic ester is n-butyl acrylate.

7. A monomer composition described in any one of claims 1 to 3, further containing methyl pyruvate.

8. 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 3.

9. A resin molded article comprising the methacrylic resin composition according to claim 8.

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 3.