Monomer composition, methacrylic resin composition, and resin molded body

Abstract

A monomer composition containing methyl methacrylate, and containing at least one compound of methyl acrylate and methyl 2-methylbutyrate.

Description

Technical Field

[0001] This 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 possess excellent transparency, heat resistance, and weather resistance, and exhibit a good balance of physical properties such as mechanical strength, thermal properties, and processability. In particular, methacrylic resin sheets can be manufactured into translucent components used in any of the following applications: tanning beds, lighting equipment, skin treatment equipment, medical equipment, UV irradiation devices, plant and animal cultivation equipment, skylights, and HID lamps.

[0003] In the aforementioned applications, when methacrylic resin boards are placed in environments exposed to direct sunlight, UV lamps, or other UV radiation, they tend to yellow (become tinged with yellow). Therefore, a methacrylic resin that does not yellow even after prolonged exposure to UV radiation, i.e., a methacrylic resin with excellent photostability, is required.

[0004] As a technology to improve the light stability of methacrylic resins, Patent Document 1 discloses a methacrylic resin that is polymerized from monomers such as methyl methacrylate in the presence of a hindered amine compound (HALS) with a specific structure, which acts as a light stabilizer. Existing technical documents Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 55-139404 Summary of the Invention The problem that the invention aims to solve

[0006] However, the methacrylic resin described in Patent Document 1 has improved light stability as the amount of HALS added during polymerization increases. On the other hand, since HALS itself is colored, it can lead to coloring. In addition, the increased addition of HALS leads to a decrease in polymerization efficiency, resulting in an increase in residual monomers in methacrylic resins and a decrease in the photostability of methacrylic resins.

[0007] In view of the above, the objective of the present invention is to provide: a methacrylic resin composition that, while ensuring the excellent heat resistance of the methacrylic resin, also exhibits excellent light stability and inhibits yellowing; a resin molded article comprising the methacrylic resin composition; and a monomer composition for obtaining the methacrylic resin composition. Technical solutions to the problem

[0008] To address the aforementioned issues, the present invention has the following features. Specifically, the main points of the present invention are as follows.

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

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

[11] A methacrylic resin composition comprising a methacrylic polymer (P) and at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate, wherein... The total content of at least one of the compounds, 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 methyl pyruvate and methyl 2-methylbutyrate, wherein... The total content of at least one of the compounds, methyl pyruvate and methyl 2-methylbutyrate, is 50 ppm by mass 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 methyl pyruvate and methyl 2-methylbutyrate, wherein... The total content of at least one of the compounds, methyl pyruvate and methyl 2-methylbutyrate, 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) comprises 70 to 100% by mass of repeating units from methyl methacrylate and 0 to 30% by mass of repeating units from acrylate.

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

[10] to

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

[16] A resin molded article comprising any one of the methacrylic resin compositions described in [9] to

[15] .

[17] A method for manufacturing a methacrylic resin composition, the method comprising a free radical polymerization step: subjecting a polymerizable composition (X2) containing any of the monomer compositions described in any one of [1] to [8] to free radical polymerization. Invention Effects

[0010] According to the present invention, it is possible to provide: a methacrylic resin composition that, while ensuring the excellent heat resistance of methacrylic resins, also exhibits excellent light stability and inhibits yellowing; a resin molded article comprising the methacrylic resin composition; and a monomer composition for obtaining the methacrylic resin composition. Detailed Implementation

[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, "methacrylic polymer" may include repeating units from acrylic monomers in addition to repeating units from methacrylic monomers. In this specification, "monomer" refers to an unpolymerized compound, and "repeating unit" refers to a unit derived from the monomer formed by polymerizing the monomer. Repeating units can be units formed directly through a polymerization reaction, or units formed by processing the polymer to transform a portion of the unit into a different structure. In this specification, "mass%" indicates the content of a specific ingredient in 100% of the total mass.

[0012] Unless otherwise specified, the numerical range indicated by “~” in this specification refers to the range of values ​​recorded before and after “~” as the lower and upper limits. “A~B” means above A and below B. In this specification, UV refers to light whose wavelength range mainly includes light above 295nm and below 430nm, that is, light in the wavelength region below 380nm.

[0013] <1. Monomer Composition> The monomer composition of the first embodiment of the present invention contains methyl methacrylate and at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate. Furthermore, other components may be included without impairing the effects of the present invention.

[0014] <1-1. Methyl methacrylate> The monomer composition of this embodiment, by containing methyl methacrylate, can provide a methacrylic resin composition with good light stability and inhibited yellowing.

[0015] While there is no particular limitation on the lower limit of the methyl methacrylate content relative to the total mass of the monomer composition of this embodiment, it is preferably 85% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and even more preferably 97% by mass or more. Furthermore, the upper limit of the methyl methacrylate content is generally 99.9995% by mass or less, and may also be 99.9950% by mass or less, or 99.9900% by mass or less. Therefore, examples of methyl methacrylate content include, for instance, 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] In addition, the total content of methyl methacrylate, methyl pyruvate and methyl 2-methylbutyrate is not particularly limited relative to the total mass of the monomer composition of this embodiment, and is generally 100% by mass or less.

[0017] <1-2. Methyl pyruvate and methyl 2-methylbutyrate> The monomer composition of this embodiment, by containing at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate, can provide a methacrylic resin composition with good light stability and inhibited 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 of this embodiment is not particularly limited, but from the perspective of providing a methacrylic resin composition with better photostability, it is generally 5 ppm by mass or more, preferably 50 ppm by mass or more, more preferably 100 ppm by mass or more, further preferably 200 ppm by mass or more, and particularly preferably 300 ppm by mass or more.

[0019] The upper limit of the total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the monomer composition of this embodiment is not particularly limited. However, when converting the monomer composition into a methacrylic resin composition, based on the perspective of not impairing the heat resistance of the methacrylic resin, it is generally 50,000 ppm by mass or less, preferably 25,000 ppm by mass or less, more preferably 20,000 ppm by mass or less, further preferably 15,000 ppm by mass or less, and particularly preferably 10,000 ppm by mass or less.

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

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

[0022] 1) Methacrylates: For example, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, or benzyl methacrylate. 2) Acrylates: For example, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl 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 anhydrides: For example, maleic anhydride or itaconic anhydride. 5) Maleimide: For example, N-phenylmaleimide or N-cyclohexylmaleimide. 6) Hydroxyl-containing vinyl monomers: For example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, or 2-hydroxypropyl methacrylate. 7) Ethylene 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) Monomers containing epoxy groups: For example, glycidyl acrylate or glycidyl methacrylate. 11) Aromatic vinyl monomers: For example, styrene or α-methylstyrene.

[0023] 12) Alkanediol di(meth)acrylate: For example, ethylene glycol di(meth)acrylate, 1,2-propanediol di(meth)acrylate, 1,3-butanediol 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 with two or more vinyl unsaturated bonds in their molecules: For example, divinylbenzene. 15) An unsaturated polyester prepolymer obtained from at least one polycarboxylic acid containing at least one olefinically unsaturated polycarboxylic acid and at least one diol. 16) Vinyl ester prepolymer obtained by modifying the epoxy group end with acrylic acid.

[0024] Among these, from the perspective of achieving an excellent balance of transparency, heat resistance, and formability in methacrylic resin compositions, the monomer is preferably at least one acrylate selected from methyl acrylate, ethyl acrylate, and n-butyl acrylate, more preferably n-butyl acrylate. Furthermore, the content of this acrylate relative to the total mass of the monomer composition is preferably 0% by mass or more and 30% by mass or less.

[0025] <1-4. Methyl isobutyrate and methyl propionate> The monomer composition of this embodiment may further contain at least one compound selected from methyl isobutyrate and methyl propionate. By containing the above-mentioned compounds in addition to methyl pyruvate and methyl 2-methylbutyrate, the monomer composition can provide a methacrylic resin composition with better photostability and suppressed yellowing.

[0026] From the perspective of providing a methacrylic resin composition with better photostability, the lower limit of the total content of methyl isobutyrate and methyl propionate relative to the total mass of the monomer composition of this embodiment is preferably 20 ppm by mass or more, more preferably 100 ppm by mass or more, further preferably 200 ppm by mass or more, particularly preferably 500 ppm by mass or more, and most preferably 1000 ppm by mass or more.

[0027] The upper limit of the total content of methyl isobutyrate and methyl propionate relative to the total mass of the monomer composition of this embodiment is not particularly limited, but based on the perspective of not impairing the heat resistance of the methacrylic resin when converting the monomer composition into a methacrylic resin composition, it is generally 50,000 ppm by mass or less, preferably 25,000 ppm by mass or less, more preferably 10,000 ppm by mass or less, further preferably 7,000 ppm by mass or less, and particularly preferably 5,000 ppm by mass or less.

[0028] The above-mentioned preferred upper and lower limits can be combined arbitrarily. Specifically, the total content of methyl isobutyrate and methyl propionate can be categorized as follows: 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; 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. Among 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.

[0029] It should be noted that 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 mentioned 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 commonly known UV absorbers and free radical scavengers (HALS). Therefore, at least one of the compounds selected from methyl pyruvate and methyl 2-methylbutyrate can also be used in combination with additives such as UV absorbers and HALS. By containing at least one of the compounds selected from methyl pyruvate and methyl 2-methylbutyrate and this additive, monomer compositions can provide methacrylic resin compositions and resin molded articles with increased photostability at a lower cost.

[0031] Examples of such additives include: mold release agents, lubricants, plasticizers, antioxidants, antistatic agents, light stabilizers other than methyl pyruvate and methyl 2-methylbutyrate, UV absorbers, flame retardants, flame retardant auxiliaries, polymerization inhibitors, fillers, pigments, dyes, silane coupling agents, leveling agents, defoamers, and fluorescent agents. These additives can be used alone or in combination of any two or more.

[0032] In addition, the monomer composition of this embodiment may contain compounds such as isobutylene aldehyde and methanol, which are inevitably mixed into methyl methacrylate.

[0033] <2. Polymerizable Composition (X2)> The polymerizable composition (X2) of the second embodiment of the present invention is one way of preparing the raw material for obtaining the methacrylic resin composition of the third embodiment of the present invention, which will be described later. The polymerizable composition (X2) of this embodiment is, for example, a polymerizable composition (X2-1) containing at least one compound selected from the raw material composition (X1) described later, methyl pyruvate, and methyl 2-methylbutyrate, and a known free radical polymerization initiator; or a polymerizable composition (X2-2) containing the monomer composition of the first embodiment of the present invention and a known free radical polymerization initiator.

[0034] <2-1. Raw material composition (X1)> The raw material composition (X1) is a constituent component of the polymerizable composition (X2-1) described above, and is also a raw material component of the methacrylic polymer (P) contained in the methacrylic resin composition of the third embodiment of the present invention. In the following description, the raw material composition (X1) used in the manufacture of the methacrylic polymer (P1) will be mainly described as the methacrylic polymer (P). This methacrylic polymer (P1) contains repeating units (hereinafter also referred to as "MMA units") from methyl methacrylate (hereinafter also referred to as "MMA units") and repeating units (hereinafter also referred to as "acrylate units") from acrylates. However, this method can also be applied to the manufacture of a methacrylic polymer (P2) containing MMA units and repeating units (hereinafter also referred to as "styrene units") from styrene by replacing the acrylate with styrene. 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 both the MMA and acrylates. The acrylates described above can be the same monomers as those described in <1-3. Other Monomers> or <3-1. Methacrylate Polymers (P)>. By including MMA and acrylate in the raw material composition (X1), the light stability of the methacrylic resin composition can be improved, and the yellowing and light stability reduction of the resin molded body containing the methacrylic resin composition can be suppressed when exposed to UV for a long time.

[0036] The proportion of MMA in the raw material composition (X1) is not particularly limited. Based on its ability to improve the light stability of the methacrylic resin composition, it is suitable to use the same proportion of MMA units as described in <3-1. Methacrylic Polymer (P)> in the methacrylic polymer (P1) or methacrylic polymer (P2). However, the terms "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)> are replaced with "relative to the total mass of the raw material composition (X1)".

[0037] Furthermore, the proportion of acrylate (M2) in the raw material composition (X1) is not particularly limited. Based on the ability to improve the light stability of the methacrylic resin composition, it is suitable to use the same proportion of acrylate units as those contained in the methacrylic polymer (P1) or methacrylic polymer (P2) described in <3-1. Methacrylic Polymer (P)>. However, the terms "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)> are replaced with "relative to the total mass of the raw material composition (X1)". As for the type of acrylate, from the perspective of the excellent light stability of methacrylic resin compositions, compounds that are the same as those described in <1-3. Other Monomers> or <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 the polymer (a) described later. By containing polymer (a) in the raw material composition (X1), the polymerizable composition (X2-1) becomes a viscous liquid (referred to as a "slurry"), thereby shortening the polymerization time and improving productivity. As an example of the above-mentioned method for obtaining the slurry, the following methods can be cited: dissolving the polymer in the raw material composition (X1), or adding a known free radical polymerization initiator to the raw material composition (X1) to partially polymerize it, etc.

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

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

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

[0042] The content of the monomer composition in the first embodiment of the present invention is 60% by mass or more and less than 100% by mass relative to the total mass of the polymeric composition (X2-2) described above. Additionally, the polymerizable composition (X2-2) may also contain other monomers (also referred to simply as "other monomers") capable of copolymerizing with the monomers in the monomer composition. When the polymerizable composition (X2-2) contains other monomers, the content of these 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 mentioned above include monomers 1) to 16) mentioned in <1-3. Other Monomers>. The monomers mentioned in 1) to 16) above can be used alone or in any ratio and combination of two or more.

[0044] Among the monomers 1) to 16) above, from the perspective of providing a methacrylic resin composition that can provide an excellent balance between heat resistance and transparency, monomers selected from ethylene glycol dimethacrylate and neopentyl glycol dimethacrylate are preferred.

[0045] <2-3. Free Radical Polymerization Initiators> Examples of free radical polymerization initiators include, for example, well-known azo compounds such as 2,2'-azobis(isobutyronitrile) and 2,2'-azobis(2,4-dimethylpentanonitrile); well-known organic peroxides such as benzoyl peroxide and lauroyl peroxide; etc. They can be used alone or in any ratio and combination of two or more. Furthermore, as needed, they can be used in conjunction with well-known polymerization promoters such as amines and thiols.

[0046] The content of the free radical polymerization initiator in the polymerizable composition (X2) is not particularly limited, and can be appropriately determined by those skilled in the art based on known techniques. Specifically, relative to 100 parts by mass of the total mass of the polymerizable composition (X2), the content of the free radical polymerization agent can 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.

[0047] <2-4. Additives> The polymeric composition (X2) may also contain, as needed, additives selected from mold release agents, heat stabilizers, lubricants, plasticizers, antioxidants, antistatic agents, light stabilizers other than methyl pyruvate and methyl 2-methylbutyrate, ultraviolet absorbers, flame retardants, flame retardant auxiliaries, polymerization inhibitors, fillers, pigments, dyes, silane coupling agents, leveling agents, defoamers, fluorescent agents, and chain transfer agents.

[0048] <3. Methacrylic Acid Resin Compositions> The methacrylic resin composition of 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 at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate. The methacrylic resin composition of this embodiment can be obtained by free radical polymerization of the polymerizable composition (X2) of the second embodiment of the present invention. The methacrylic resin composition of this embodiment, by containing a methacrylic polymer (P), can provide a resin molded article with good transparency. The methacrylic resin composition, by containing at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate, can provide a resin molded article that can suppress yellowing and further inhibit the reduction of photostability even when exposed to UV for a long time. In addition, there are no particular restrictions on the form of the methacrylic resin composition, but it is usually in solid form.

[0049] While there is no particular limitation on the content of the methacrylic polymer (P) relative to the total mass of the methacrylic resin composition, from the perspective of achieving good heat resistance, it is generally 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 perspective of obtaining excellent photostability, this content is generally 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-mentioned upper and lower limits can be combined arbitrarily. For example, preferred contents of the methacrylic polymer (P) include: 95% by mass or more and 99.9995% by mass, 95% by mass or more and 99.9950% by mass, 97.5% by mass or more and 99.99% by mass, 98% by mass or more and 99.9850% by mass, 99.0% by mass or more and 99.98% by mass, 99.0% by mass or more and 99.97% by mass, 99.0% by mass or more and 99.95% by mass, and 99.0% by mass or more and 99.90% by mass. It should be noted that when the methacrylic resin composition contains two or more methacrylic polymers (P), the above contents refer to the total content of the two or more methacrylic polymers (P).

[0050] The total content of at least one compound among methyl pyruvate and methyl 2-methylbutyrate is not particularly limited relative to the total mass of the methacrylate resin composition. From the perspective of obtaining excellent photostability, the total content of at least one compound among methyl pyruvate and methyl 2-methylbutyrate is generally 5 ppm by mass or more relative to the total mass of the methacrylate resin composition, preferably 50 ppm by mass or more, more preferably 100 ppm by mass or more, further 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 of the compounds, methyl pyruvate and methyl 2-methylbutyrate, contained in the methacrylic resin composition of this embodiment is not particularly limited, but from the perspective of improving the heat resistance of the resin molded article, it is generally 50,000 ppm by mass or less, preferably 25,000 ppm by mass or less, more preferably 20,000 ppm by mass or less, further preferably 15,000 ppm by mass or less, and particularly preferably 10,000 ppm by mass or less. The aforementioned upper and lower limits can be combined arbitrarily. For example, preferred total contents of at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate include: 5 ppm by mass or more and 50,000 ppm by mass or less; 50 ppm by mass or more and 25,000 ppm by mass or less; 100 ppm by mass or more and 20,000 ppm by mass or less; 150 ppm by mass or more and 15,000 ppm by mass or less; 200 ppm by mass or more and 15,000 ppm by mass or less; and 300 ppm by mass or more and 10,000 ppm by mass or less. Among these, the total contents of at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate are more preferably 50 ppm by mass or more and 25,000 ppm by mass or less, and even more preferably 150 ppm by mass or more and 15,000 ppm by mass or less.

[0052] In this embodiment, at least one of 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 free radical scavengers (HALS). Therefore, at least one of 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 of methyl pyruvate and methyl 2-methylbutyrate and this additive in combination, it is possible to provide methacrylic resin compositions and resin molded articles with increased photostability at a lower cost.

[0053] Within the scope of achieving the effects of the present invention, 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. For example, it may also contain additives selected from mold release agents, heat stabilizers, antioxidants, ultraviolet absorbers, and light stabilizers other than methyl pyruvate and methyl 2-methylbutyrate.

[0054] <3-1. Methacrylate polymers (P)> The methacrylic polymer (P) is one of the components contained in the methacrylic resin composition of this embodiment. The methacrylic resin composition, by containing a methacrylic polymer (P), can improve transparency while suppressing heat- and light-induced decomposition, resulting in good thermoforming properties, heat resistance, and mechanical strength. Furthermore, through the synergistic effect of the inherent heat resistance of the methacrylic polymer (P) and at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate, it is possible to obtain methacrylic resin molded articles that exhibit suppressed yellowing, high light stability, and maintained heat resistance when exposed to UV for extended periods.

[0055] The methacrylic polymer (P) is preferably a copolymer containing MMA units and acrylate 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, for example, they can be random copolymers, block copolymers or alternating copolymers, etc., but random copolymers are preferred.

[0056] The repeating unit derived from the aforementioned acrylate is a repeating unit derived from an alkyl group having 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 capable of copolymerizing with MMA. Examples include acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, or tert-butyl acrylate. These can be used individually or in any ratio and combination of two or more. Among these monomers, the resin molded article containing the methacrylic resin composition is preferably an acrylate selected from at least one of methyl acrylate, n-ethyl acrylate, and n-butyl acrylate, and more preferably n-butyl acrylate, from the perspective of suppressing yellowing during prolonged UV exposure and ensuring high photostability.

[0057] There is no particular limitation on the proportion of MMA units in the methacrylic polymer (P1). From the perspective of improving heat resistance, it is preferably 70.0% by mass or more, more preferably 80.0% by mass or more, more preferably 90.0% by mass or more, and usually less than 100% by mass, relative to the total mass of the methacrylic polymer (P1).

[0058] While there is no particular limitation on the proportion of acrylate units in the methacrylic polymer (P1), from the perspective of good 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. It should be noted that when the methacrylic polymer (P1) contains two or more acrylate units, the above-mentioned proportion refers to the total proportion of the two or more acrylate units.

[0059] While there is no particular limitation on the proportion of MMA units in the methacrylic polymer (P2), from the perspective of improving heat resistance, it is preferably 50.0% by mass or more, more preferably 60.0% by mass or more, and even more preferably 70.0% by mass or more, and usually 100% by mass or less, relative to the total mass of the methacrylic polymer (P2).

[0060] While there is no particular limitation on the proportion of styrene units in the methacrylic polymer (P2), from the perspective 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 usually 0% by mass or more.

[0061] Furthermore, the methacrylic polymer (P) in this embodiment may include structural units (hereinafter referred to as "multifunctional monomer units") derived from a multifunctional monomer containing two or more free radical polymerizable functional groups in a molecule, within the scope of achieving the effects of the invention. The term "radical polymerizable functional group" as used here refers to any group possessing a carbon-carbon double bond and capable of free radical polymerization. Specifically, examples include vinyl, allyl, (meth)acryloyl, and (meth)acryloyloxy groups. In particular, (meth)acryloyl is preferred from the perspective of excellent storage stability of compounds possessing free radical polymerizable functional groups and ease of controlling the polymerizability of the compound. It should be noted that "(meth)acryloyl" refers to one or both of "acryloyl" and "methacryloyl". It should also be noted that the free radical polymerizable functional groups in a monomer possessing two free radical polymerizable functional groups can be the same or different. Methacrylic acid polymers (P) can improve solvent resistance or chemical resistance by including multifunctional monomer units.

[0062] Examples of multifunctional monomers include allyl methacrylate, allyl acrylate, ethylene glycol di(meth)acrylate, ethylene glycol tri(meth)acrylate, neopentyl glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate, but are not particularly limited to these. These can be used alone or in any ratio and combination of two or more. Among these, from the perspective of improving solvent resistance and chemical resistance, multifunctional monomers are more preferably selected from ethylene glycol di(meth)acrylate and neopentyl glycol di(meth)acrylate, and even more preferably ethylene glycol di(meth)acrylate.

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

[0064] It should be noted that the weight-average molecular weight is the value determined using standard polystyrene as the standard sample and by gel permeation chromatography. Appropriately increasing the weight-average molecular weight can improve solvent resistance and chemical resistance. The weight-average molecular weight (Mw) of methacrylic acid polymers (P) can be controlled by adjusting the polymerization temperature, polymerization time, amount of polymerization initiator, or type and amount of chain transfer agent.

[0065] <3-2. Methyl pyruvate and methyl 2-methylbutyrate> At least one of methyl pyruvate and methyl 2-methylbutyrate is one of the components contained in the methacrylic resin composition of this embodiment. By containing at least one of methyl pyruvate and methyl 2-methylbutyrate, the methacrylic resin composition can suppress yellowing upon prolonged exposure to UV. Furthermore, it is inexpensive compared to existing UV absorbers and further suppresses the decrease in photostability.

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

[0067] Relative to the total mass of the methacrylic resin composition of this embodiment, from the perspective of providing a methacrylic resin composition with better photostability, the lower limit of the total content of methyl isobutyrate and methyl propionate is preferably 20 ppm by mass or more, more preferably 100 ppm by mass or more, further 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.

[0068] The upper limit of the total content of methyl isobutyrate and methyl propionate relative to the total mass of the methacrylic resin composition of this embodiment is not particularly limited, but from the perspective of not impairing the heat resistance of the methacrylic resin, it is generally 50,000 ppm by mass or less, preferably 25,000 ppm by mass or less, more preferably 10,000 ppm by mass or less, further preferably 7,000 ppm by mass or less, and particularly preferably 5,000 ppm by mass or less.

[0069] The above-mentioned preferred upper and lower limits can be combined arbitrarily. Specifically, the total content of methyl isobutyrate and methyl propionate can be categorized as follows: 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; 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. Among 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] It should be noted that when the methacrylic resin 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 methacrylic resin composition, is preferably within the range of the total content of methyl pyruvate and methyl 2-methylbutyrate mentioned above.

[0071] <3-4. Characteristics of Methacrylic Acid Resin Compositions> The methacrylic resin composition of this embodiment contains the above-mentioned methacrylic polymer (P) and at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate, thus exhibiting excellent photostability.

[0072] Specifically, when performing the UV exposure test as shown below on a test piece (square shape, 50mm x 50mm, 3mm thick) made of a methacrylic resin composition, the yellow chromaticity (YI) measured according to ASTM D1925 for the test piece 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. Furthermore, the test piece preferably has a light transmittance of 15.0% or more at a wavelength of 295nm or a light transmittance of 35.0% or more at a wavelength of 315nm. More preferably, the test piece has a light transmittance of 15.0% or more at a wavelength of 295nm and a light transmittance of 35.0% or more at a wavelength of 315nm. To clarify, light transmittance refers to the total light transmittance (Tt) in the thickness direction of a test piece, measured according to JIS K 7361-1:1997 using a haze meter (e.g., the "NDH4000" manufactured by Nippon Denshoku Kogyo Co., Ltd.).

[0073] (UV Exposure Test Method) In an evaluation chamber equipped with a Metal Weather accelerated photostability testing machine (e.g., DAIPLA WINTES "MW-60W") and a light cutoff filter (e.g., DAIPLA WINTES "KF-1"), a metal halide lamp (e.g., DAIPLA WINTES "MW-60W") and a light cutoff filter (e.g., DAIPLA WINTES "KF-1"), test specimens (50mm x 50mm square, 5mm thick) made of methacrylic resin composition were placed. Under conditions of 63°C and 50% RH, the ultraviolet light from the metal halide lamp (irradiation intensity 80mW / cm²) was applied. 2 Irradiate onto the test piece.

[0074] <4. Resin Molded Body> The resin molded body (also simply referred to as "resin molded body") of the fourth embodiment of the present invention is a resin molded body comprising the methacrylic resin composition of the third embodiment of the present invention. By molding the methacrylic resin composition, a resin molded body with excellent light stability can be obtained. In this specification, "resin molded body" refers to any molded body comprising the above-mentioned methacrylic resin composition, without particular limitation, except that a molded body composed of the methacrylic resin composition substantially belongs to either the methacrylic resin composition or the resin molded body.

[0075] The shape of the resin molded body can be, for example, 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, from a thick plate to a thin film, as needed. For example, it can be set to a thickness of 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. That is, the test piece of the resin molded body (a square shape of 50mm x 50mm, 3mm thick) exhibits excellent light stability, with a yellow chromaticity (YI) of 7.1 or less, preferably 6.0 or less, more preferably 4.5 or less, and even more preferably 4.0 or less, as measured according to ASTM D1925, from before the start of the UV exposure test to 200 hours after the start of the UV exposure test. Furthermore, the test piece preferably exhibits high light stability, with a light transmittance of 15.0% or more at a wavelength of 295nm or 35.0% or more at a wavelength of 315nm. More preferably, the test piece has a light transmittance of 15.0% or more at a wavelength of 295nm and a light transmittance of 35.0% or more at a wavelength of 315nm. It should be noted that light transmittance refers to the total light transmittance (Tt) in the thickness direction of the test piece, measured according to JIS K 7361-1:1997 using a haze meter (e.g., "NDH4000" manufactured by Nippon Denshoku Kogyo Co., Ltd.).

[0077] <5. Method for manufacturing methacrylic resin compositions or resin molded articles> There are no particular limitations on the method for manufacturing methacrylic resin compositions or resin molded articles containing such resin compositions (hereinafter collectively referred to as "resin compositions, etc."). As specific manufacturing methods for resin compositions, etc., examples include methods comprising a free radical polymerization step in which a polymerizable composition (X2) containing the polymerizable composition (X2) of the second embodiment of the present invention, preferably the monomer composition of the first embodiment of the present invention, is subjected to free radical polymerization. The free radical polymerization step may also include a slurry preparation step in which a portion of the polymerizable composition (X2) is polymerized to prepare a slurry, and a polymerization step in which the polymerizable components in the slurry are polymerized. It should be noted that "polymerizing a portion of the polymerizable composition (X2)" in the slurry preparation step means polymerizing such that the content of the methacrylic polymer in the obtained slurry 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] There is no particular limitation on the polymerization temperature when polymerizing the polymerizable composition (X2), and those skilled in the art can determine it appropriately based on known techniques. Generally, depending on the type of free radical polymerization initiator used, it is preferably set within a range of 40°C to 180°C, more preferably 50°C to 150°C. Furthermore, the polymerizable composition (X2) can be polymerized under multiple temperature conditions as needed. The polymerization time can be appropriately determined based on the degree of polymerization and curing.

[0079] Examples of polymerization methods for polymerizable compositions (X2) include bulk polymerization, suspension polymerization, emulsion polymerization, and dispersion polymerization. However, from a productivity perspective, bulk polymerization is preferred.

[0080] Furthermore, specific methods for manufacturing resin compositions include, for example, using known casting polymerization methods such as cell casting or continuous casting, obtaining resin compositions by bulk polymerization, or molding compositions manufactured by bulk polymerization using extrusion molding or injection molding. From the perspective of further improving the heat resistance of methacrylic resin compositions by increasing molecular weight and introducing cross-linked structures, the method of using casting polymerization (injection molding polymerization) is more preferred.

[0081] As a casting polymerization method, for example, the cell casting method can be cited. In this method, when a resin composition or the like has a plate-like shape, a space formed by two opposing glass or metal plates (SUS plates) and spacers such as soft resin tubes disposed at their edges is used as a mold. The polymerizable composition (X2) or a slurry formed by polymerizing a portion of the polymerizable composition (X2) is injected into the mold. Polymerization is completed by heating and polymerization treatment, and the resin composition or the like is removed from the mold. Alternatively, the continuous casting method can be cited. In this method, a space formed by two stainless steel annular belts traveling opposite each other at the same speed in the same direction at a predetermined interval and spacers such as soft resin tubes disposed at their two sides is used as a mold. The polymerizable composition (X2) or a slurry formed by polymerizing a portion of the polymerizable composition (X2) is continuously injected into the mold from one end of the annular belts. Polymerization is completed by heating and polymerization treatment, and the resin composition or the like is continuously removed from the other end of the annular belts. By appropriately adjusting the gap spacing of the mold using the thickness (diameter) of the shims, a resin composition of the desired thickness can be obtained. The thickness of plate-shaped resin compositions is typically set within the range of 1 mm to 30 mm.

[0082] <6. Uses> The uses of the aforementioned methacrylic resin compositions and resin molded articles (“resin compositions, etc.”) are not particularly limited, but they are preferably used as light-transmitting components, especially transparent components, in any of the following: tanning beds, lighting equipment, skin treatment equipment, medical equipment, UV irradiation devices, plant and animal cultivation equipment, skylights, and HID lamps. More specifically, they are preferably used as light-transmitting components, which are components used for the purpose of light transmission in any of the following: tanning beds and skylights, or preferably as light-transmitting components, which are components used for the purpose of light transmission in any of the following: lighting equipment, skin treatment equipment, medical equipment, UV irradiation devices, plant and animal cultivation equipment, and HID lamps.

[0083] <7. Effects> The monomer composition of the first embodiment of the present invention contains at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate, and the methacrylic resin composition obtained by free radical polymerization of the polymerizable composition (X2) containing the monomer composition ensures excellent heat resistance, excellent light stability, and inhibits yellowing. The monomer composition of the first embodiment of the present invention contains at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate, and obtains a methacrylic resin composition that ensures excellent heat resistance while exhibiting excellent light stability and inhibiting yellowing. The reason for this is speculated as follows.

[0084] When the main chain or side chains of polymers containing methyl methacrylate-based units (methacrylic polymers) break due to light, free radical species are generated. Furthermore, these generated free radical species typically lead to yellowing of methacrylic resins and a decrease in mechanical strength due to a reduction in molecular weight.

[0085] However, since at least one of the compounds, methyl pyruvate and methyl 2-methylbutyrate, contained in the monomer composition of the first embodiment of the present invention remains in the methacrylic resin composition, it is believed that at least one of the compounds, methyl pyruvate and methyl 2-methylbutyrate, acts as a free radical scavenger. As a result, the methacrylic resin composition is considered to exhibit excellent heat resistance and good light stability. Example

[0086] The features of the present invention will be described more specifically below with examples and comparative examples. The materials, amounts, proportions, processing contents, processing steps, etc., shown in the following examples can be appropriately modified without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited by the specific examples shown below. Furthermore, 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 shown below. • MMA: Methyl methacrylate (manufactured by Mitsubishi Chemical Corporation) ·BA: n-Butyl acrylate (manufactured by Mitsubishi Chemical Corporation) Methyl isobutyrate (manufactured by Tokyo Chemical Industry Co., Ltd.) Methyl propionate (manufactured by Tokyo Chemical Industry Co., Ltd.) Methyl pyruvate (manufactured by Tokyo Chemical Industry Co., Ltd.) ·Methyl 2-methylbutyrate (manufactured by Tokyo Chemical Industry Co., Ltd.) LA-57: Tetra(2,2,6,6-tetramethyl-4-piperidinyl) ester of 1,2,3,4-butanetetracarboxylic acid (manufactured by ADEKA). To clarify, MMA (manufactured by Mitsubishi Chemical Corporation) contains 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] [Determination and Evaluation Methods] <Method for Determination of Residual Content of Target Substances in Methacrylic Resins> (1) Sample and solution preparation steps The resin molded articles obtained in the examples and comparative examples were finely pulverized, and 0.2 g of the pulverized resin was dissolved in 10 mL of acetone for pesticide residue testing (hereinafter referred to as "acetone"). After the resin was dissolved, 1 mL of internal standard solution was added using a single-label pipette. The internal standard solution used was a 0.1 v / v methyl salicylate / acetone solution. Three test solutions of different concentrations were prepared by diluting the standard reagent of the target with acetone, and the concentrations of each target substance in the sample were quantified by gas chromatography-mass spectrometry (GC / MS) as described later to construct a three-point calibration curve. The internal standard solution used was a 0.1 v / v methyl salicylate / acetone solution.

[0089] (GC / MS determination conditions) Device: GC HP6890 / MS HP5973 (manufactured by Agilent Technologies) Ionization method: EI (Electron Ionization) method Chromatographic column: DB-WAX 60m × 250μm × 0.5μm (manufactured by Agilent Technologies) Heating conditions: 70℃ (5 min) → 200℃ (5 min) rate = 10℃ / min Injection port temperature: 220℃ AUX temperature: 230℃ Ion source temperature: 230℃ Flow split ratio: 10:1 Flow rate: 2.0 mL / min Average linear velocity: 37 cm / sec Injection volume: 1 μL Measurement mode: SIM

[0090] <Evaluation Methods for Heat Resistance> As an indicator of the heat resistance of the methacrylic resin compositions obtained in the examples and comparative examples, the load deformation temperature (hereinafter referred to as "HDT") (°C) of the test pieces (127 mm long × 12.7 mm wide × 3 mm thick) of the resin molded articles obtained in the examples and comparative examples was measured in accordance with JIS K7191.

[0091] <Photostability (ΔYI)> A Metal Weather ultra-accelerated photostability tester (DAIPLAWINTES model KU-R5CI-A) equipped with a metal halide lamp (DAIPLA WINTES model: MW-60W) and a light cutoff filter (DAIPLA WINTES model: KF-1) was used to conduct UV exposure tests. The change in yellow chromaticity (ΔYI) was measured from before the start of the UV exposure test to 200 hours after the start of the test, according to the method described below.

[0092] Specifically, in the evaluation chamber of the Metal Weather ultra-accelerated photostability tester, a test piece (50mm x 50mm square, 5mm thick) composed of the methacrylic resin composition obtained in the examples and comparative examples was set up. The ultraviolet (UV) irradiation intensity from the metal halide lamp illuminating the test piece was corrected to 80 mW / cm², measured using a UV illuminometer (manufactured by Ushio Electric Co., Ltd., model name: UIT-101) at wavelengths of 330–390 nm. 2 In the evaluation chamber of the Metal Weather ultra-accelerated photostability testing machine, the environment was set at 63°C and 50% RH, and the ultraviolet light from the metal halide lamp (irradiation intensity 80 mW / cm²) was applied. 2 Irradiate the above test piece. As an indicator of light stability, the yellow chromaticity (yellow index: YI) of the above test pieces was measured using a spectrophotometer (manufactured by Nippon Denshoku Kogyo Co., Ltd., model name: SE-7700) according to ASTM D1925. One test piece was measured before the start of the UV exposure test and another test piece was measured 200 hours after the start of the test. The change in this measured value was taken as the change in yellow chromaticity (ΔYI).

[0093] <Preparation of Methacrylic Resin Compositions> [Example 1] (1) Preparation of slurry 2-Methylbutyrate at a concentration of 300 ppm was added to a reactor (polymerization vessel) equipped with a condenser, thermometer, and stirrer. 98.0 parts of MMA and 2.0 parts of BA were then added, and the mixture was bubbled with nitrogen while stirring. Heating was then initiated. When the reactor internal temperature reached 80°C, 0.12 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) as a free radical polymerization initiator and 0.075 parts of 1-dodecylthiol as a chain transfer agent were added. The reactor internal temperature was further heated to 100°C and maintained for 9 minutes. The reactor internal temperature was then cooled to room temperature to obtain a slurry. The polymer content in the slurry was 25% by mass relative to the total mass of the slurry.

[0094] (2) Injection molding polymerization Adding 0.15 parts of tert-hexyl peroxypentanoate as a free radical polymerization initiator to 100 parts of the above slurry yields a polymerizable composition (X2). Next, the polymerizable composition (X2) is poured into a 6.5 mm gap space between two opposing SUS plates, with soft resin gaskets placed at the ends of the SUS plates. The mixture is heated at 80°C for 30 minutes, followed by heating 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. After cooling the (meth)acrylic resin composition along with the SUS plates, the SUS plates are removed, yielding a 5 mm thick sheet-like resin molded body. The performance evaluation results of the obtained resin molded body are shown in Table 1. Note that in Table 1, "-" indicates that no measurement was performed.

[0095] [Example 2] (1) Preparation of slurry 2-Methylbutyrate at a concentration of 300 ppm was added to a reactor (polymerization vessel) equipped with a condenser, thermometer, and stirrer, followed by the supply of 100 parts of MMA. Nitrogen gas was bubbled while stirring, and then heating was initiated. When the reactor internal temperature reached 80°C, 0.12 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) were added as a free radical polymerization initiator, and the reactor internal temperature was further heated to 100°C and maintained for 9 minutes. The reactor internal temperature was then cooled to room temperature to obtain a slurry. The polymer content in the slurry was 20% by mass relative to the total mass of the slurry.

[0096] (2) Injection molding polymerization Adding 0.15 parts of tert-hexyl peroxypentanoate as a free radical polymerization initiator to 100 parts of the above slurry yields a polymerizable composition (X2). Next, the polymerizable composition (X2) is poured into a 4.1 mm gap space between two opposing SUS plates, with soft resin gaskets placed at the ends of the SUS plates. The mixture is heated at 80°C for 30 minutes, followed by heating 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. After cooling the methacrylic resin composition along with the SUS plates, the SUS plates are removed, yielding a 3 mm thick sheet-like resin molded body. The performance evaluation results of the obtained resin molded body are shown in Table 1. Note that in Table 1, "-" indicates that no measurement was performed.

[0097] [Examples 3-6] Except for changing the composition of the monomer composition as described in Table 1, the methacrylic resin composition and the resin molded article were manufactured using the same method as in Example 2. The composition of the obtained methacrylic resin composition is shown in Table 1. The performance evaluation results of the obtained resin molded article are shown in Table 1.

[0098] [Comparative Examples 1-2] Except that the monomer composition was as described in Table 1, the methacrylic resin composition and the resin molded article were obtained using the same method as in Example 1. The composition of the obtained methacrylic resin composition is shown in Table 1. The performance evaluation results of the obtained resin molded article are shown in Table 1.

[0099] [Comparative Example 3] Except that the monomer composition was as described in Table 1, the methacrylic resin composition and the resin molded article were obtained using the same method as in Example 2. The composition of the obtained methacrylic resin composition is shown in Table 1. The performance evaluation results of the obtained resin molded article are shown in Table 1.

[0100] [Table 1]

[0101] As can be seen from the comparison between Example 1 and Comparative Example 1, in a system of methacrylic polymers containing units derived from acrylates, photostability can be improved by containing at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate. As can be seen from the comparison between Example 1 and Comparative Example 2, as long as the methacrylate polymer contains at least one of methyl pyruvate and methyl 2-methylbutyrate, even if the resin composition does not contain hindered amine compounds, it can achieve good photostability compared to the composition containing hindered amine compounds. As can be seen from the comparison between Examples 2-6 and Comparative Example 3, in a system where the methacrylic polymer does not contain units from acrylates, photostability can be improved by containing at least one compound selected from methyl pyruvate and methyl 2-methylbutyrate.

Claims

1. A monomer composition comprising methyl methacrylate, methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the monomer composition is 100 ppm by mass or more.

2. A monomer composition comprising methyl methacrylate, methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the monomer composition is 200 ppm by mass or more.

3. A monomer composition comprising methyl methacrylate, methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the monomer composition is 300 ppm by mass or more.

4. A monomer composition comprising methyl methacrylate, methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the monomer composition is more than 100 ppm by mass and less than 50,000 ppm by mass.

5. A monomer composition comprising methyl methacrylate, methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the monomer composition is more than 100 ppm by mass and less than 25,000 ppm by mass.

6. A monomer composition comprising methyl methacrylate, methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the monomer composition is more than 100 ppm by mass and less than 20,000 ppm by mass.

7. A monomer composition comprising methyl methacrylate, methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the monomer composition is more than 100 ppm by mass and less than 15,000 ppm by mass.

8. A monomer composition comprising methyl methacrylate, methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the monomer composition is more than 100 ppm by mass and less than 10,000 ppm by mass.

9. The monomer composition according to any one of claims 1 to 8, further comprising acrylate.

10. The monomer composition according to claim 9, wherein, The acrylate is at least one compound selected from methyl acrylate, ethyl acrylate, and butyl acrylate.

11. The monomer composition according to claim 9, wherein, The acrylate is n-butyl acrylate.

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

13. A methacrylic resin composition, which is formed by free radical polymerization of a polymerizable composition (X2) containing any one of the monomer compositions of claims 1 to 12.

14. A methacrylic resin composition comprising a methacrylic polymer (P), methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the methacrylic resin composition is 100 ppm by mass or more.

15. A methacrylic resin composition comprising a methacrylic polymer (P), methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the methacrylic resin composition is 150 ppm by mass or more.

16. A methacrylic resin composition comprising a methacrylic polymer (P), methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the methacrylic resin composition is 200 ppm by mass or more.

17. A methacrylic resin composition comprising a methacrylic polymer (P), methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the methacrylic resin composition is 300 ppm by mass or more.

18. A methacrylic resin composition comprising a methacrylic polymer (P), methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the methacrylic resin composition is more than 100 ppm by mass and less than 50,000 ppm by mass.

19. A methacrylic resin composition comprising a methacrylic polymer (P), methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the methacrylic resin composition is more than 100 ppm by mass and less than 25,000 ppm by mass.

20. A methacrylic resin composition comprising a methacrylic polymer (P), methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the methacrylic resin composition is more than 100 ppm by mass and less than 20,000 ppm by mass.

21. A methacrylic resin composition comprising a methacrylic polymer (P), methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the methacrylic resin composition is 100 ppm by mass or more and 15,000 ppm by mass or less.

22. A methacrylic resin composition comprising a methacrylic polymer (P), methyl pyruvate, and methyl 2-methylbutyrate, wherein, The total content of methyl pyruvate and methyl 2-methylbutyrate relative to the total mass of the methacrylic resin composition is 100 ppm by mass or more and 10,000 ppm by mass or less.

23. The methacrylic resin composition according to any one of claims 14 to 22, wherein, The methacrylate polymer (P) contains more than 50% by mass of repeating units derived from methyl methacrylate.

24. The methacrylic resin composition according to any one of claims 14 to 22, wherein, The methacrylate polymer (P) is a copolymer containing repeating units from methyl methacrylate and repeating units from acrylate, a copolymer containing repeating units from methyl methacrylate and repeating units from styrene, or a methyl methacrylate homopolymer.

25. The methacrylic resin composition according to any one of claims 14 to 22, wherein, The methacrylate polymer (P) comprises 70-100% by mass of repeating units derived from methyl methacrylate and 0-30% by mass of repeating units derived from acrylate.

26. The methacrylic resin composition according to any one of claims 14 to 22, wherein, The methacrylate polymer (P) comprises 50-100% by mass of repeating units derived from methyl methacrylate and 0-50% by mass of repeating units derived from styrene.

27. A resin molded article comprising the methacrylic resin composition according to any one of claims 13 to 26.

28. A method for manufacturing a methacrylic resin composition, the method comprising a free radical polymerization step: subjecting a polymerizable composition (X2) containing a monomer composition according to any one of claims 1 to 12 to free radical polymerization.

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