Methacrylic resin and method for producing same, methacrylic resin composition, and molded body

Abstract

The present disclosure provides a methacrylic resin and a method for producing same, the methacrylic resin having good heat resistance and thermal decomposition resistance (thermal stability), good mechanical properties such as rigidity and surface hardness, and good moldability. This methacrylic resin comprises a methacrylic copolymer (A) including 40%-99% by mass of a methyl methacrylate (MMA) unit, 1%-40% by mass of one or more isopropenyl aromatic compound units (UI), and 0%-30% by mass of one or more other units (UO). The methacrylic resin has a glass transition temperature (Tg) of 120°C or higher, and satisfies (Mw / Mn)A / (Mw / Mn)B ≤ 1.40. (Mw / Mn)A is a molecular weight distribution obtained by GPC analysis using an absorbance detector with a detection wavelength of 254 nm, and (Mw / Mn)B is a molecular weight distribution (Mw / Mn) obtained by GPC analysis using a differential refractometer.

Description

Methacrylic resin, its manufacturing method, methacrylic resin composition, and molded body

[0001] The present disclosure relates to a methacrylic resin, a method for producing the same, a methacrylic resin composition, and a molded article.

[0002] Methacrylic resins such as polymethyl methacrylate (PMMA) have excellent transparency, scratch resistance, and moldability, and are widely used as materials for optical components such as light guide plates and lenses; vehicle components (e.g., vehicle interior and exterior materials); and various components for buildings, household goods, office automation equipment, and lighting equipment. Methacrylic resins are required to have heat resistance and / or rigidity depending on the application. For example, vehicle interior materials such as vehicle cover members may be placed in positions where they are likely to be exposed to direct sunlight and heat up due to considerations such as the design of the vehicle interior and the visibility of instruments, and therefore require heat resistance. Vehicle exterior materials such as tail lamps and vehicle headlights require thinner resin components to reduce the vehicle's weight. However, thinning conventional methacrylic resins such as PMMA, which have insufficient heat resistance and rigidity, may result in distortion in high-temperature environments. Methacrylic resins used in such applications require heat resistance and rigidity.

[0003] Known methacrylic resins with improved heat resistance include methacrylic copolymers containing methyl methacrylate (MMA) units and isopropenyl aromatic compound units such as α-methylstyrene (αMSt) units. For example, Patent Document 1 discloses a method for producing a methacrylic copolymer by adding a polyfunctional organic peroxide having a 10-hour half-life temperature of 60 to 110°C as a polymerization initiator to a monomer mixture containing methyl methacrylate (MMA) and α-methylstyrene (αMSt) and bulk polymerizing the mixture (claim 1). Patent Document 2 discloses a method for producing a methacrylic copolymer by adding an organic peroxide and divinylbenzene as polymerization initiators to a monomer mixture containing methyl methacrylate (MMA) and α-methylstyrene (αMSt) and bulk polymerizing the mixture (claim 1, paragraph 0022, etc.).

[0004] Patent Documents 3 and 4 disclose methacrylic copolymers containing methyl methacrylate (MMA) units and α-methylstyrene (αMSt) units, in which the relationship between the peak top molecular weight or its logarithm determined by gel permeation chromatography (GPC) analysis using a differential refractive index detector and the peak top molecular weight or its logarithm determined by gel permeation chromatography (GPC) analysis using an absorbance detector with a detection wavelength of 254 nm is specified (claim 1 of Patent Document 3, claim 1 of Patent Document 4). The methacrylic copolymer disclosed in Patent Document 4 has a 1% thermal weight loss temperature of greater than 260°C when heated at a rate of 10°C / min under a nitrogen atmosphere (claim 1). Patent Documents 3 and 4 also disclose methods for producing methacrylic copolymers, which involve continuous bulk polymerization of a polymerization raw material containing a monomer mixture containing methyl methacrylate (MMA) and α-methylstyrene (αMSt) and a polymerization initiator, followed by removal of the remaining monomer mixture (claim 12 of Patent Document 3, claim 12 of Patent Document 4).

[0005] Japanese Patent Application Laid-Open No. 4-218515 Japanese Patent Application Laid-Open No. 4-328111 International Publication No. 2021 / 117903 International Publication No. 2022 / 196827

[0006] However, in general, methacrylic copolymers containing MMA units and isopropenyl aromatic compound units such as αMSt units tend to be difficult to control the copolymerization of the isopropenyl aromatic compound. Therefore, it tends to be difficult to stably produce methacrylic copolymers with a uniform composition, such as the content of isopropenyl aromatic compound units. Variations in the composition, such as the content of isopropenyl aromatic compound units, may lead to a decrease in heat resistance and mechanical properties such as rigidity and surface hardness.

[0007] In addition, methacrylic copolymers containing MMA units and isopropenyl aromatic compound units such as αMSt units tend to have a relatively low thermal decomposition temperature. Therefore, methacrylic resins containing this copolymer as a main component may suffer from thermal decomposition of the copolymer during heat-melting during resin production and molding, resulting in an increase in the amount of residual monomers in the resin and a decrease in heat resistance. Furthermore, if the resin is held in a heated and molten state for a long time during resin production and molding, the thermal decomposition of the methacrylic copolymer may cause foaming and other defects in appearance.

[0008] The present disclosure has been made in view of the above circumstances, and aims to provide a methacrylic resin having good heat resistance and thermal decomposition resistance (thermal stability), good mechanical properties such as rigidity and surface hardness, and good moldability, and a method for producing the same.

[0009] The present disclosure provides the following methacrylic resins [1] to

[14] , a method for producing the same, a methacrylic resin composition, and a molded article: [1] A methacrylic resin comprising a methacrylic copolymer (A) consisting of 40 to 99 mass% of methyl methacrylate (MMA) units, 1 to 40 mass% of one or more isopropenyl aromatic compound units (UI), and 0 to 30 mass% of one or more other units (UO), having a glass transition temperature of 120°C or higher and satisfying the following formula (1): (Mw / Mn) Ａ / (Mw / Mn) Ｂ ≦1.40 (1) (wherein, (Mw / Mn) A is the molecular weight distribution (Mw / Mn) determined by gel permeation chromatography (GPC) analysis using an absorbance detector with a detection wavelength of 254 nm, and (Mw / Mn) B is the molecular weight distribution (Mw / Mn) determined by gel permeation chromatography (GPC) analysis using a differential refractive index detector.

[0010] [2] The methacrylic resin of [1], wherein the total residual amount of raw material monomers of the methacrylic copolymer (A) is 0 to 1.00 mass%. [3] The methacrylic resin of [1] or [2], wherein the one or more isopropenyl aromatic compound units (UI) contain α-methylstyrene units. [4] The methacrylic resin of any of [1] to [3], wherein the methacrylic copolymer (A) contains, as the other units (UO), aromatic vinyl compound units other than isopropenyl aromatic compound units.

[0011] [5] The methacrylic resin according to any one of [1] to [4], further comprising 1 to 1,000 ppm of one or more organic disulfide compounds (D). [6] The methacrylic resin according to [5], wherein the one or more organic disulfide compounds (D) comprise di-tert-dodecyl disulfide (DDS) and / or dibenzyl disulfide (DBS).

[0012] [7] The methacrylic resin according to any one of [1] to [6], wherein a test piece obtained by molding the methacrylic resin and having a length of 80 mm, a width of 10 mm, and a thickness of 4 mm has a flexural modulus of 3000 MPa or more as measured in accordance with JIS K 7171. [8] The methacrylic resin according to any one of [1] to [7], wherein a square test piece obtained by molding the methacrylic resin and having a side length of 50 mm and a thickness of 3 mm has a Rockwell hardness of 85 or more as measured under M-scale conditions in accordance with JIS K 7202-2.

[0013] [9] A methacrylic resin composition comprising the methacrylic resin of any one of [1] to [8].

[10] A molded article comprising the methacrylic resin of any one of [1] to [8] or the methacrylic resin composition of [9].

[0014]

[11] A method for producing a methacrylic resin according to any one of [1] to [8], comprising: a step (S1) of preparing polymerization raw materials containing, as raw material monomers, 30 to 99 mass% of methyl methacrylate (MMA), 1 to 59 mass% of one or more isopropenyl aromatic compounds (I), and 0 to 49 mass% of one or more other monomers (O), and further containing a polymerization initiator; a step (S2) of polymerizing the polymerization raw materials under conditions where the polymerization conversion rate is 30 to 60 mass% to obtain a resin solution containing the methacrylic resin; and a step (S3) of volatilizing and removing at least a portion of the raw material monomers present in the resin solution in one or more steps to obtain the methacrylic resin, wherein 10 to 2000 ppm of one or more organic disulfide compounds (D) are added to at least one of the polymerization raw materials, the resin solution obtained after completion of step (S2), and the resin solution during step (S3).

[0015]

[12] The method for producing a methacrylic resin according to

[11] , wherein one or more organic disulfide compounds (D) are added to at least the polymerization raw materials among the polymerization raw materials, the resin solution obtained after completion of step (S2), and the resin solution during step (S3).

[13] The method for producing a methacrylic resin according to

[11] or

[12] , wherein step (S3) comprises a step of heating the resin solution at 190 to 250°C to volatilize raw material monomers present in the resin solution.

[14] The method for producing a methacrylic resin according to any of

[11] to

[13] , wherein step (S3) comprises a step of charging the resin solution into an extruder having one or more vents, volatilizing the raw material monomers present in the resin solution and discharging it through the vents, and extruding the methacrylic resin through a die of the extruder, wherein the temperature of the molten resin in the die is 230 to 260°C.

[0016] According to the present disclosure, it is possible to provide a methacrylic resin having good heat resistance and thermal decomposition resistance (thermal stability), good mechanical properties such as rigidity and surface hardness, and good moldability, and a method for producing the same.

[0017] In this specification, unless otherwise specified, a "unit" contained in a polymer is a repeating unit contained in the polymer, and is a monomer unit derived from a raw material monomer or a derived unit derived from one or more monomer units. In this specification, (meth)acrylic is a general term for acrylic and methacrylic, and the same applies to (meth)acrylonitrile, etc.

[0018] [Methacrylic Resin] The methacrylic resin of the present disclosure contains a methacrylic copolymer (A) consisting of 40 to 99% by mass of methyl methacrylate (MMA) units, 1 to 40% by mass of one or more isopropenyl aromatic compound units (UI), and 0 to 30% by mass of one or more other units (UO). The content of the methacrylic copolymer (A) in the methacrylic resin of the present disclosure is not particularly limited, but is preferably 97.0% by mass or more. The lower limit is more preferably 97.5% by mass, even more preferably 98.0% by mass, particularly preferably 98.5% by mass, and most preferably 99.0% by mass. The upper limit is 99.9999% by mass. The methacrylic resin of the present disclosure may further contain one or more optional components as necessary.

[0019] (Methacrylic Copolymer (A)) The content of methyl methacrylate (MMA) units in the methacrylic copolymer (A) is 40 to 99% by mass. The lower limit is preferably 45% by mass, more preferably 50% by mass, even more preferably 55% by mass, even more preferably 60% by mass, even more preferably 65% ​​by mass, particularly preferably 70% by mass, and most preferably 75% by mass. The upper limit is preferably 95% by mass, more preferably 90% by mass, and particularly preferably 85% by mass. The content of one or more isopropenyl aromatic compound units (UI) in the methacrylic copolymer (A) (unless otherwise specified, the total amount in the case of multiple types) is 1 to 40% by mass. The lower limit is preferably 5% by mass, more preferably 10% by mass, and particularly preferably 15% by mass. The upper limit is preferably 35% by mass, more preferably 30% by mass, particularly preferably 25% by mass, and most preferably 20% by mass.

[0020] The content of one or more other units (UO) in the methacrylic copolymer (A) (unless otherwise specified, the total amount when there are multiple units) is 0 to 30% by mass. The upper limit is preferably 25% by mass, more preferably 20% by mass, even more preferably 15% by mass, particularly preferably 10% by mass, and most preferably 5% by mass. In the methacrylic copolymer (A), the total of the content of MMA units, the content of one or more isopropenyl aromatic compound units (UI), and the content of one or more other units (UO) is 100% by mass.

[0021] If the content of the isopropenyl aromatic compound unit (UI) is less than the above lower limit, the heat resistance of the methacrylic copolymer (A) may be insufficient. If the content of the isopropenyl aromatic compound unit (UI) exceeds the above upper limit, the polymerizability (productivity), thermal decomposition resistance, and molding processability of the methacrylic copolymer (A) may be reduced. If the content of the isopropenyl aromatic compound unit (UI) exceeds the above upper limit, it becomes difficult to control the copolymerization of the isopropenyl aromatic compound (I), and it may be difficult to stably produce a methacrylic copolymer (A) having a uniform composition, such as the content of the isopropenyl aromatic compound unit (UI). Variations in the composition, such as the content of the isopropenyl aromatic compound unit (UI), may lead to a decrease in heat resistance and mechanical properties such as rigidity and surface hardness.

[0022] When the content of the MMA unit and the content of the isopropenyl aromatic compound unit (UI) are within the above ranges, the methacrylic copolymer (A) can have good transparency, heat resistance, thermal decomposition resistance, polymerizability (productivity), and moldability. Also, when the content of the MMA unit and the content of the isopropenyl aromatic compound unit (UI) are within the above ranges, the copolymerization of the isopropenyl aromatic compound (I) in the methacrylic copolymer (A) is relatively easy to control, and the methacrylic copolymer (A) having a uniform composition such as the content of the isopropenyl aromatic compound unit (UI) can be stably produced, and the methacrylic copolymer (A) having good heat resistance and mechanical properties such as rigidity and surface hardness can be stably produced.

[0023] The methacrylic copolymer (A) is obtained by copolymerizing methyl methacrylate (MMA), one or more isopropenyl aromatic compounds (I), and, if necessary, one or more other monomers (O). Examples of the isopropenyl aromatic compounds (I) include alkyl-substituted isopropenyl benzenes such as isopropenyl benzene (α-methylstyrene (αMSt)), isopropenyl naphthalene, isopropenyl toluene, isopropenyl ethyl benzene, isopropenyl propyl benzene, isopropenyl butyl benzene, isopropenyl pentyl benzene, isopropenyl hexyl benzene, and isopropenyloctyl benzene. From the viewpoint of ease of raw material availability, the one or more isopropenyl aromatic compounds (I) preferably contain one or more alkyl-substituted isopropenyl benzenes, and particularly preferably contain isopropenyl benzene (α-methylstyrene (αMSt)).

[0024] Examples of the other monomer (O) include vinyl monomers (V) having one polymerizable unsaturated bond per molecule other than methyl methacrylate (MMA) and the isopropenyl aromatic compound (I). Examples of the vinyl monomer (V) include (meth)acrylic acid esters other than MMA, such as methyl acrylate; (meth)acrylic acid alkyl esters such as ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; (meth)acrylic acid aryl esters such as phenyl (meth)acrylate; and (meth)acrylic acid cycloalkyl esters such as cyclohexyl (meth)acrylate and norbornenyl (meth)acrylate. Other examples of the vinyl monomer (V) include (meth)acrylic acid, (meth)acrylamide, and (meth)allylonitrile. Other examples of the vinyl monomer (V) include styrene (St); alkyl-substituted styrenes such as o-, m-, or p-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene, o-, m-, or p-ethylstyrene; and aromatic vinyl compounds other than the isopropenyl aromatic compound (I), such as 1,1-diphenylethylene. The methacrylic copolymer (A) may contain, for example, an aromatic vinyl compound unit (e.g., a styrene (St) unit) other than the isopropenyl aromatic compound unit (UI) as the other unit (UO).

[0025] The methacrylic copolymer (A) may contain one or more ring structure units (UR) as one or more other units (UO). Examples of other monomers (O) capable of introducing a ring structure into the main chain by a radical polymerization reaction include acid anhydrides such as maleic anhydride (Mah) and itaconic anhydride; N-alkylmaleimides such as N-methylmaleimide, N-ethylmaleimide, N-butylmaleimide, and N-cyclohexylmaleimide (ChMI); N-arylmaleimides such as N-phenylmaleimide, N-methylphenylmaleimide, and N-chlorophenylmaleimide; and cycloolefins such as norbornene, ethylidenenorbornene, dicyclopentadiene, and tetracyclododecene. Among these, maleic anhydride (Mah), N-cyclohexylmaleimide (ChMI), and N-phenylmaleimide are preferred. The content of the ring structural unit (UR) in the methacrylic copolymer (A) (the total amount when there are multiple types of ring structural units unless otherwise specified) is 0 to 30% by mass, with the upper limit being preferably 25% by mass, more preferably 20% by mass, even more preferably 15% by mass, particularly preferably 10% by mass, and most preferably 5% by mass.

[0026] (Organic Disulfide Compound (D)) The methacrylic resin of the present disclosure can contain one or more organic disulfide compounds (D) as an additive. The content of one or more organic disulfide compounds (D) in the methacrylic resin of the present disclosure (total amount in the case of multiple types, unless otherwise specified) is preferably 1 to 1,000 ppm. The lower limit is preferably 10 ppm, more preferably 50 ppm, even more preferably 80 ppm, even more preferably 100 ppm, even more preferably 150 ppm, particularly preferably 200 ppm, and most preferably 250 ppm. The upper limit is preferably 800 ppm, more preferably 750 ppm, even more preferably 700 ppm, even more preferably 650 ppm, even more preferably 600 ppm, particularly preferably 550 ppm, and most preferably 500 ppm.

[0027] As explained in the section "Problems to be Solved by the Invention," conventionally, methacrylic copolymers containing MMA units and isopropenyl aromatic compound units (UI), such as αMSt units, tend to have relatively low thermal decomposition temperatures. Therefore, methacrylic resins primarily containing this copolymer may suffer from thermal decomposition of the copolymer during heat-melting during resin production and molding, resulting in an increase in the amount of residual monomer in the resin and a decrease in heat resistance. Furthermore, if the resin is held in a heated, molten state for a long time during resin production and molding, thermal decomposition of the methacrylic copolymer may result in foaming and other defects in appearance.

[0028] In the methacrylic resin of the present disclosure containing an appropriate amount of organic disulfide compound (D), the presence of the appropriate amount of organic disulfide compound (D) effectively suppresses thermal decomposition of the methacrylic copolymer (A) during resin production. As a result, a methacrylic resin with a low residual monomer content and excellent heat resistance and thermal decomposition resistance (thermal stability) can be stably produced. Furthermore, the presence of an appropriate amount of organic disulfide compound (D) during resin production makes it relatively easy to control the copolymerization of the isopropenyl aromatic compound (I), allowing for the stable production of a methacrylic copolymer (A) with a uniform composition, such as the content of isopropenyl aromatic compound units (UI), and thus allowing for the stable production of a methacrylic copolymer (A) with good heat resistance and mechanical properties, such as rigidity and surface hardness.

[0029] The methacrylic resin of the present disclosure containing an appropriate amount of the organic disulfide compound (D) has excellent heat resistance and resistance to thermal decomposition (thermal stability) because the presence of the appropriate amount of the organic disulfide compound (D) effectively suppresses thermal decomposition of the methacrylic copolymer (A) even when heated and melted during molding or other processing after the resin is produced.

[0030] The methacrylic resin of the present disclosure, which contains an appropriate amount of organic disulfide compound (D), suppresses appearance defects such as foaming due to thermal decomposition of the methacrylic copolymer (A), even if the residence time in a heated and molten state is long during resin production, molding, etc. When the content of organic disulfide compound (D) in the methacrylic resin of the present disclosure is equal to or less than the above upper limit, discoloration such as yellowing and odors during resin production, molding, etc. can be suppressed. For the above reasons, the methacrylic resin of the present disclosure, a methacrylic resin composition containing the methacrylic resin of the present disclosure, and a molded article containing the methacrylic resin of the present disclosure can be excellent in heat resistance, thermal decomposition resistance (thermal stability), mechanical properties such as rigidity and surface hardness, moldability, appearance, etc.

[0031] The addition of an appropriate amount of one or more organic disulfide compounds (D) to the polymerization raw materials and / or intermediate products provides the above-described effects during resin production, and therefore the content of one or more organic disulfide compounds (D) in the final methacrylic resin of the present disclosure may be less than 1 ppm or even 0 ppm. Even if the content of one or more organic disulfide compounds (D) in the final methacrylic resin of the present disclosure is less than 1 ppm, the amount of residual monomer in the resin is reduced, and the methacrylic resin of the present disclosure, which has a uniform composition such as the content of isopropenyl aromatic compound units (UI) in the methacrylic copolymer (A), can have excellent heat resistance and thermal decomposition resistance, as well as mechanical properties such as rigidity and surface hardness.

[0032] Generally, isopropenyl aromatic compounds such as αMSt are known to have a low ceiling temperature, which is the temperature at which the polymerization reaction rate and the depolymerization reaction rate become equal. For example, the ceiling temperature of αMSt is 61°C. Generally, copolymers containing monomer units having a methyl group at the α-position, such as MMA units, and isopropenyl aromatic compound units tend to contain a certain amount of this chain, although the isopropenyl aromatic compound chain, in which repeating units of the isopropenyl aromatic compound are lined up, can be suppressed by polymerizing them at a temperature higher than the ceiling temperature of the isopropenyl aromatic compound. During resin production and molding, etc., when heated and melted, depolymerization-type decomposition originating from this isopropenyl aromatic compound chain occurs. Therefore, methacrylic copolymers containing MMA units and isopropenyl aromatic compound units (UI), such as αMSt units, tend to have a relatively low thermal decomposition temperature. When an appropriate amount of organic disulfide compound (D) is present during heating and melting during resin production, molding, or the like, it is presumed that thiyl radicals generated by cleavage of disulfide bonds stabilize alkyl radicals generated by depolymerization originating from isopropenyl aromatic compound chains, thereby significantly improving thermal decomposition resistance.

[0033] Examples of the organic disulfide compound (D) include diethyl disulfide, di-n-propyl disulfide, di-n-butyl disulfide, di-sec-butyl disulfide, di-tert-butyl disulfide, di-n-amyl disulfide, di-tert-amyl disulfide, di-tert-hexyl disulfide, di-n-octyl disulfide, di-tert-octyl disulfide, di-n-dodecyl disulfide, di-tert-dodecyl disulfide (DDS), di-n-stearin disulfide, ethyl-n-propyl disulfide, ethyl-tert-butyl disulfide, ethyl-sec-butyl disulfide, and n-propyl- Examples of suitable disulfide compounds include dialkyl disulfide compounds such as isopropyl disulfide; aromatic disulfide compounds such as diphenyl disulfide, dibenzyl disulfide (DBS), and di-p-tolyl disulfide; cyclic disulfide compounds such as ditrimethylene disulfide, ditetramethylene disulfide, and dicyclohexyl disulfide; amino group-containing disulfide compounds such as cystine and diaminodiphenyl disulfide; disulfides of carboxylic acids or derivatives thereof such as dithiodiclycolic acid, dithiodipropionic acid, and 2-ethylhexyl dithiodiclycolate; and unsaturated bond-containing disulfide compounds such as diallyl disulfide. Among these, dialkyl disulfide compounds and / or aromatic disulfide compounds are preferred. From the viewpoint of the disulfide bond cleavage temperature, di-tert-alkyl disulfides such as di-tert-dodecyl disulfide (DDS) are preferred as dialkyl disulfide compounds. The aromatic disulfide compound is preferably dibenzyl disulfide (DBS), etc. The timing of adding the organic disulfide compound (D) is not particularly limited, and may be before, during, or after the polymerization of the methacrylic copolymer (A).

[0034] (Organic Phosphorus Compound (P)) The methacrylic resin of the present disclosure may contain one or more organic phosphorus compounds (P) as an additive. It is believed that the organic phosphorus compound (P) can effectively suppress thermal discoloration resulting from decomposition products of the organic disulfide compound remaining in the methacrylic copolymer (A). The organic phosphorus compound (P) may be a compound having one or more phosphorus atom-containing organic groups (e.g., an organic group containing a P-C bond and / or a P-O-C bond). Specific examples include organic phosphorus compounds containing trivalent phosphorus, such as phosphites (also referred to as phosphites), phosphonites, and their hydrolysis products; organic phosphorus compounds containing pentavalent phosphorus, such as phosphate esters (also referred to as phosphates), oxidation products of the above phosphites, and oxidation products of the above phosphonites; and combinations thereof. Phosphites, phosphonites, and phosphates are preferably relatively bulky compounds having an aromatic ring, such as compounds having an aryl substituent and a pentaerythritol structure.

[0035] Examples of the phosphorous esters (phosphites) include monoesters, diesters, and triesters of phosphorous acid (for example, phenyl phosphite, diphenyl phosphite, and triphenyl phosphite), tris(2,4-di-t-butylphenyl)phosphite, tris(2,6-di-t-butylphenyl)phosphite, tris(2,4-di-t-butyl-5-methylphenyl)phosphite, bis(2,4-di-t-butyl-6-methylphenyl)ethyl phosphite, 2,2'-methylenebis(4,6-di- tert-butylphenyl)octyl phosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite, (6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenz[d,f][1,3,2]dioxaphosphepine, cyclic neopentanetetraylbis(2,6-di-tert-butyl-4-methylphenyl)phosphite, and hydrolysis products of these phosphites.

[0036] The phosphites may be commercially available phosphorus-based antioxidants. Specific examples include tris(2,4-di-t-butylphenyl)phosphite (e.g., "Irgafos 168" manufactured by BASF), tris[2-[[2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosphepin-6-yl]oxy]ethyl]amine (e.g., "Irgafos 12" manufactured by BASF), bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphite (e.g., "Irgafos 38" manufactured by BASF), 2,2'-methylenebis(4,6-di-tert-butylphenyl)octyl phosphite (e.g., "ADEKA STAB HP-10" manufactured by ADEKA), and cyclic neopentanetetraylbis(2,4-di-tert-butylphenyl)phosphite (e.g., "ADEKA STAB HP-10" manufactured by ADEKA). Examples of suitable phosphate binders include bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite ("ADEKA STAB PEP36" manufactured by ADEKA Corporation, etc.), bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite ("ADEKA STAB PEP36A" manufactured by ADEKA Corporation, etc.), cyclic neopentanetetraylbis(2,4-di-tert-butylphenyl phosphite ("ADEKA STAB PEP-8" manufactured by ADEKA Corporation, etc.), and 6-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-t-butyldibenz[d,f][1,3,2]dioxaphosphepine ("Sumilizer GP" manufactured by Sumitomo Chemical Co., Ltd., etc.).

[0037] Examples of phosphonites include tetrakis(2,4-di-tert-butylphenyl)4,4'-biphenylene diphosphonite, tetrakis(2,4-di-tert-butyl-5-methylphenyl)4,4'-biphenylene diphosphonite, and hydrolysis products of these phosphonites. Phosphonites may also be commercially available as phosphorus-based antioxidants. Specific examples include tetrakis(2,4-di-tert-butylphenyl)4,4'-biphenylene diphosphonite (e.g., "Hostanox P-EPQ" manufactured by Clariant) and tetrakis(2,4-di-t-butyl-5-methylphenyl)4,4'-biphenylene diphosphonite (e.g., "GSY P101" manufactured by Sakai Chemical Industry Co., Ltd.).

[0038] Examples of phosphoric acid esters (phosphates) include 2-ethylhexyl acid phosphate, isodecyl acid phosphate, oleyl acid phosphate, bis(2-ethylhexyl)hydrogen phosphate, ethylene bis(diphenyl phosphate), propylene bis(diphenyl phosphate), phenylene bis(diphenyl phosphate), naphthylene bis(ditoluyl phosphate), bisphenol A bis(diphenyl phosphate), 3,5-di-t-butyl-4-hydroxybenzyl phosphate diethyl ester, and hydrolysis products thereof.

[0039] The content of the organic phosphorus compound (P) in the methacrylic resin of the present disclosure (unless otherwise specified, the total amount when multiple types are used) is not particularly limited, and from the viewpoints of thermal decomposition resistance (thermal stability) and suppression of discoloration during heat melting, it is preferably 0.0001% by mass (1 ppm) to 1.0% by mass. The lower limit is more preferably 5 ppm, even more preferably 10 ppm, even more preferably 20 ppm, even more preferably 50 ppm, particularly preferably 80 ppm, and most preferably 100 ppm. The upper limit is more preferably 0.5% by mass, particularly preferably 0.2% by mass, and most preferably 0.1% by mass.

[0040] If the content of the organic phosphorus compound (P) is too low, the effect of suppressing discoloration during heat melting due to the addition of the organic phosphorus compound (P) may not be effectively obtained. If the content of the organic phosphorus compound (P) is too high, the organic phosphorus compound (P) may suppress the effect of the organic disulfide compound (D) in improving thermal decomposition resistance (thermal stability), and the organic phosphorus compound (P) may bleed out during molding of the methacrylic resin of the present disclosure. The timing of adding the organic phosphorus compound (P) is not particularly limited, and may be before, during, or after polymerization of the methacrylic copolymer (A).

[0041] In the methacrylic resin of the present disclosure, the molar ratio of the organic phosphorus compound (P) to the organic disulfide compound (D) (organic phosphorus compound (P) / organic disulfide compound (D) molar ratio) is not particularly limited, and from the viewpoint of effectively improving thermal decomposition resistance (thermal stability) and suppressing discoloration during heat melting, it is preferably 0.01 to 100. The lower limit of this molar ratio is more preferably 0.05, particularly preferably 0.1, and most preferably 1.0. The upper limit of this molar ratio is more preferably 50, particularly preferably 10.

[0042] (Lubricant (L)) The methacrylic resin of the present disclosure may contain one or more lubricants (L) as additives, if necessary. The methacrylic resin of the present disclosure containing one or more lubricants (L) may improve mold releasability during molding. Examples of the lubricant (L) include stearic acid, behenic acid, stearamidic acid, and methylene bisstearamide; waxes such as paraffin wax and ketone wax; fatty alcohols (preferably alcohols having 8 to 30 carbon atoms) such as octyl alcohol, cetyl alcohol, and stearyl alcohol; hydrogenated oils; and glycerin fatty acid esters (preferably glycerin carboxylic acid esters having 8 to 30 carbon atoms) such as hydroxystearic acid triglyceride, stearic acid monoglyceride, and stearic acid diglyceride. As the lubricant (L), a fatty alcohol and a glycerin fatty acid monoester may be used in combination. In this case, the aliphatic alcohol / glycerin fatty acid monoester mass ratio is preferably 2.5 / 1 to 3.5 / 1, more preferably 2.8 / 1 to 3.2 / 1. The content of the lubricant (L) in the methacrylic resin of the present disclosure (total amount if multiple types are used unless otherwise specified) is not particularly limited, and is preferably 1000 to 5000 ppm. The upper limit is more preferably 4500 ppm, particularly preferably 4000 ppm, and most preferably 3500 ppm. The timing of addition of the lubricant (L) is not particularly limited, and may be before, during, or after polymerization of the methacrylic copolymer (A).

[0043] (Additives Other Than the Above) The methacrylic resin of the present disclosure may optionally contain one or more additives other than the organic disulfide compound (D), the organic phosphorus compound (P), and the lubricant (L). Examples of such additives include crosslinked polymer particles, impact resistance agents, processing aids, light stabilizers, light diffusers, UV absorbers, colorants (organic dyes, inorganic dyes, pigments, etc.), non-phosphorus antioxidants, antistatic agents, plasticizers, surfactants, foaming agents, defoamers, and fillers. The content of additives other than the organic disulfide compound (D), the organic phosphorus compound (P), and the lubricant (L) in the methacrylic resin of the present disclosure (total amount if multiple additives are used, unless otherwise specified) is preferably 0 to 0.5% by mass. The upper limit is more preferably 0.2% by mass. Excessive additive content may result in poor appearance, such as a silvery finish, in the molded article. The timing of addition of the additives is not particularly limited and may be before, during, or after polymerization of the methacrylic copolymer (A).

[0044] (Total Amount of Residual Raw Material Monomers) In the methacrylic resin of the present disclosure, at least a portion of at least one of the raw material monomers of the methacrylic copolymer (A) (specifically, methyl methacrylate (MMA), one or more isopropenyl aromatic compounds (I), and, if necessary, one or more other monomers (O)) may remain unreacted. As described above, in the method for producing a methacrylic resin of the present disclosure, one or more organic disulfide compounds (D) can be added to the polymerization raw materials and / or intermediate products. According to this production method, thermal decomposition of the methacrylic copolymer (A) during resin production is effectively suppressed, and the amount of residual monomers in the resin is effectively reduced. As a result, a decrease in the heat resistance of the methacrylic resin due to the presence of residual monomers can be effectively suppressed. The use of a small amount of the organic disulfide compound (D) can effectively suppress thermal decomposition of the methacrylic copolymer (A), thereby suppressing discoloration, such as yellowing, of the methacrylic resin caused by the addition of the organic disulfide compound (D).

[0045] In the methacrylic resin of the present disclosure, the total residual amount of raw material monomers of the methacrylic copolymer (A) may be 0 to 1.00% by mass, and the upper limit of the total residual amount of raw material monomers is preferably 0.80% by mass, more preferably 0.75% by mass, even more preferably 0.70% by mass, even more preferably 0.65% by mass, still more preferably 0.60% by mass, particularly preferably 0.55% by mass, and most preferably 0.50% by mass.

[0046] The amount of methyl methacrylate (MMA) remaining in the methacrylic resin of the present disclosure is 0 to 1.00% by mass, with the upper limit being preferably 0.80% by mass, more preferably 0.70% by mass, even more preferably 0.60% by mass, even more preferably 0.50% by mass, even more preferably 0.40% by mass, even more preferably 0.30% by mass, particularly preferably 0.20% by mass, and most preferably 0.10% by mass.

[0047] The content of the isopropenyl aromatic compound (I) remaining in the methacrylic resin of the present disclosure (the total amount when multiple types are present) is 0 to 1.00 mass%, with the upper limit being preferably 0.80 mass%, more preferably 0.70 mass%, even more preferably 0.60 mass%, even more preferably 0.50 mass%, even more preferably 0.40 mass%, particularly preferably 0.30 mass%, and most preferably 0.20 mass%.

[0048] The content of the other monomer (O) remaining in the methacrylic resin of the present disclosure (the total amount when multiple types are present) is 0 to 1.00 mass%, with the upper limit being preferably 0.80 mass%, more preferably 0.70 mass%, even more preferably 0.60 mass%, even more preferably 0.50 mass%, even more preferably 0.40 mass%, even more preferably 0.30 mass%, particularly preferably 0.20 mass%, and most preferably 0.10 mass%.

[0049] In this specification, "weight average molecular weight (Mw Ａ " is the weight average molecular weight (Mw) determined by gel permeation chromatography (GPC) analysis using an absorbance detector with a detection wavelength of 254 nm. Ａ")" is the number average molecular weight (Mw) determined by gel permeation chromatography (GPC) analysis using an absorbance detector at a detection wavelength of 254 nm. (Mw / Mn) A is the molecular weight distribution (Mw / Mn) determined by gel permeation chromatography (GPC) analysis using an absorbance detector with a detection wavelength of 254 nm. B " is the weight average molecular weight (Mw) determined by gel permeation chromatography (GPC) analysis using a differential refractive index detector. " is the number average molecular weight (Mn B ") is the number average molecular weight (Mw) determined by gel permeation chromatography (GPC) analysis using a differential refractive index detector. (Mw / Mn) B is the molecular weight distribution (Mw / Mn) determined by gel permeation chromatography (GPC) analysis using a differential refractive index detector. Unless otherwise specified, in this specification, "weight average molecular weight (Mw)" refers to the weight average molecular weight converted into standard polymethyl methacrylate (PMMA). Similarly, "number average molecular weight (Mn)" refers to the number average molecular weight converted into standard polymethyl methacrylate (PMMA).

[0050] The weight average molecular weight (Mw Ｂ ) is not particularly limited and is preferably 50,000 to 150,000. The lower limit is more preferably 55,000, even more preferably 60,000, even more preferably 65,000, even more preferably 70,000, particularly preferably 75,000, and most preferably 80,000. The upper limit is more preferably 120,000, particularly preferably 100,000. When Mw is equal to or greater than the above lower limit, the methacrylic resin of the present disclosure tends to have excellent mechanical properties, and when Mw is equal to or less than the above upper limit, the methacrylic resin of the present disclosure tends to have excellent moldability.

[0051] Molecular weight distribution (Mw / Mn) of the methacrylic resin of the present disclosure Bis not particularly limited, but is preferably 1.5 to 2.5. The lower limit is more preferably 1.8, and the upper limit is more preferably 2.3. (Mw / Mn) B When the methacrylic resin of the present disclosure is equal to or greater than the lower limit, the methacrylic resin of the present disclosure tends to have excellent melt fluidity and molding processability, and when the methacrylic resin is equal to or less than the upper limit, the methacrylic resin of the present disclosure tends to have excellent mechanical properties such as impact resistance and toughness.

[0052] In the present disclosure, by adding an appropriate amount of one or more organic disulfide compounds (D) to the polymerization raw materials and / or intermediate products and adjusting the polymerization conditions as necessary, it is possible to satisfactorily control the copolymerization of the isopropenyl aromatic compound (I), and to stably produce a methacrylic resin in which the content of isopropenyl aromatic compound units (UI) in the methacrylic copolymer (A) contained in the methacrylic resin is uniform or nearly so, and the unit composition of the methacrylic copolymer (A) has little variation.

[0053] The methacrylic resin of the present disclosure satisfies the following formula (1): (Mw / Mn) Ａ / (Mw / Mn) Ｂ ≦1.40...(1) (Mw / Mn) Ａ / (Mw / Mn) Ｂ The upper limit is preferably 1.35, more preferably 1.30, even more preferably 1.25, even more preferably 1.20, particularly preferably 1.15, and most preferably 1.10. The lower limit is not particularly limited and is, for example, 1.00. The methacrylic copolymer (A) contained in the methacrylic resin of the present disclosure that satisfies the above formula (1) has a uniform or nearly uniform content of isopropenyl aromatic compound units (UI), which are structural units that absorb light at a wavelength of 254 nm, regardless of molecular weight, and has little variation in composition.

[0054] The glass transition temperature (Tg) of the methacrylic resin of the present disclosure is not particularly limited and is preferably 120°C or higher. The lower limit is more preferably 123°C, particularly preferably 125°C, and most preferably 130°C. The upper limit is not particularly limited and is, for example, 150°C. The higher the Tg, the higher the heat resistance of the methacrylic resin of the present disclosure, which is preferable. Molded articles containing the methacrylic resin of the present disclosure having a high Tg are less likely to undergo deformation and / or shrinkage due to heat, which is preferable. In this specification, the "glass transition temperature (Tg)" can be measured in accordance with JIS K7121 by the method described in the "Examples" section below.

[0055] As described above, the methacrylic resin of the present disclosure has excellent thermal decomposition resistance. Thermal decomposition resistance can be measured, for example, by the 1% thermal weight loss temperature measured by thermogravimetric analysis (TGA) under an inert gas atmosphere. The 1% thermal weight loss temperature of the methacrylic resin of the present disclosure can be, for example, 270°C or higher, 280°C or higher, 285°C or higher, or 290°C or higher. The upper limit of the 1% thermal weight loss temperature is not particularly limited and can be, for example, 320°C or 310°C. The 1% thermal weight loss temperature can be measured using a thermogravimetric analyzer and is the temperature at which the weight loss rate is 1% relative to 100% weight before heating. For example, thermogravimetric analysis (TGA) can be performed under conditions of heating from room temperature (20-25°C) to 500°C at a heating rate of 10°C / min in a nitrogen atmosphere to obtain a TG curve, and the 1% thermal weight loss temperature can be determined from this TG curve.

[0056] The methacrylic resin of the present disclosure can have excellent rigidity. The methacrylic resin of the present disclosure can have a flexural modulus of 3000 MPa or more, 3100 MPa or more, 3200 MPa or more, or 3300 MPa or more, measured in accordance with JIS K7171, of a test piece having a length of 80 mm, a width of 10 mm, and a thickness of 4 mm obtained by molding the methacrylic resin of the present disclosure. The upper limit of the flexural modulus is, for example, 4000 MPa. A molded article with a high flexural modulus has high rigidity even when thinned, and distortion and the like are suppressed. Therefore, a molded article with a high flexural modulus can be thinned.

[0057] The methacrylic resin of the present disclosure can have excellent heat resistance and rigidity even under load. A test piece having a length of 80 mm, a width of 10 mm, and a thickness of 4 mm obtained by molding the methacrylic resin of the present disclosure can have a deflection temperature under load (HDT) of 105°C or higher or 110°C or higher, as measured in accordance with JIS K7191, after conditioning in accordance with JIS K6712-2. The upper limit of HDT is, for example, 130°C or 125°C.

[0058] The methacrylic resin of the present disclosure can have excellent surface hardness. The methacrylic resin of the present disclosure can have a Rockwell hardness of 85 or more or 90 or more, measured under M-scale conditions in accordance with JIS K7202-2, of a square test piece having sides of 50 mm and a thickness of 3 mm obtained by molding the methacrylic resin of the present disclosure. The upper limit is not particularly limited, and is, for example, 120. Molded articles with high surface hardness are preferred because they have excellent scratch resistance.

[0059] The methacrylic resin of the present disclosure can have excellent molding processability. The melt flow rate (MFR) can be used as an index of molding processability. The MFR of the methacrylic resin of the present disclosure is preferably 1 to 20 g / 10 min from the viewpoint of stability in hot melt molding. The lower limit is more preferably 2 g / 10 min, particularly preferably 3 g / 10 min. The upper limit is more preferably 15 g / 10 min, particularly preferably 10 g / 10 min. Unless otherwise specified in this specification, the MFR of a methacrylic resin is a value measured in accordance with JIS K7210 using a melt indexer at a temperature of 230°C and a load of 3.8 kg.

[0060] [Method for Producing Methacrylic Resin] The methacrylic resin of the present disclosure can be produced by a known method. One embodiment of the method for producing a methacrylic resin of the present disclosure includes the steps of: (S1) preparing a polymerization raw material containing, as raw material monomers, 30 to 99% by mass of methyl methacrylate, 1 to 59% by mass of one or more isopropenyl aromatic compounds (I), and 0 to 49% by mass of one or more other monomers (O), and further containing a polymerization initiator; (S2) polymerizing the polymerization raw material under conditions of a polymerization conversion rate of 30 to 60% by mass to obtain a resin solution containing the methacrylic resin; and (S3) volatilizing and removing at least a portion of the raw material monomers present in the resin solution in one or more stages, preferably to obtain the methacrylic resin having a total remaining amount of raw material monomers of 0 to 1.00% by mass.

[0061] (Step (S1)) A polymerization raw material containing the above-mentioned multiple raw material monomers and a polymerization initiator is prepared. The content of MMA in the polymerization raw material is preferably 30 to 99 mass%, more preferably 45 to 95 mass%, and particularly preferably 50 to 87 mass%. The content of one or more isopropenyl aromatic compounds (I) in the polymerization raw material is preferably 1 to 59 mass%, more preferably 5 to 40 mass%, and more preferably 10 to 30 mass%. The content of one or more other monomers (O) in the polymerization raw material is preferably 0 to 49 mass%, more preferably 0 to 30 mass%, and particularly preferably 0 to 25 mass%.

[0062] As the polymerization initiator, one or more known radical polymerization initiators can be used. Specific examples include t-hexylperoxyisopropyl monocarbonate, t-hexylperoxy 2-ethylhexanoate, 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate, t-butylperoxypivalate, t-hexylperoxypivalate, t-butylperoxyneodecanoate, t-hexylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, 1,1-bis(t-hexylperoxy)cyclohexane, benzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, lauroyl peroxide, 2,2'-azobis(2-methylpropionitrile) (AIBN), 2,2'-azobis(2-methylbutyronitrile), and dimethyl 2,2'-azobis(2-methylpropionate). Among these, 2,2'-azobis(2-methylpropionitrile) (AIBN), t-hexylperoxy 2-ethylhexanoate, 1,1-bis(t-hexylperoxy)cyclohexane, and dimethyl 2,2'-azobis(2-methylpropionate) are preferred.

[0063] The polymerization raw materials may contain one or more chain transfer agents as needed. The chain transfer agent can be used for purposes such as adjusting the molecular weight of the methacrylic copolymer (A). Examples of chain transfer agents include alkyl mercaptans such as n-octyl mercaptan (n-OM), n-dodecyl mercaptan, t-dodecyl mercaptan, 1,4-butanedithiol, 1,6-hexanedithiol, ethylene glycol bisthiopropionate, butanediol bisthioglycolate, butanediol bisthiopropionate, hexanediol bisthioglycolate, hexanediol bisthiopropionate, trimethylolpropane tris-(β-thiopropionate), and pentaerythritol tetrakisthiopropionate; α-methylstyrene (αMSt) dimer; and terpinolene. Among these, monofunctional alkyl mercaptans such as n-octyl mercaptan (n-OM) and n-dodecyl mercaptan are preferred. The amount of chain transfer agent used (total amount when multiple types are used unless otherwise specified) is not particularly limited, and is preferably 0 to 1 part by mass per 100 parts by mass of the total amount of the multiple types of raw material monomers. The upper limit is more preferably 0.5 parts by mass, particularly preferably 0.4 parts by mass, and most preferably 0.3 parts by mass.

[0064] The polymerization raw materials may contain one or more additives other than those described above, as needed. The polymerization raw materials can be prepared by mixing multiple raw material monomers, one or more polymerization initiators, one or more chain transfer agents, and one or more additives, as needed, under an inert gas atmosphere such as nitrogen gas or in the presence of oxygen. The materials may be mixed all at once or in portions, and the blending procedure when mixed in portions is not particularly limited. The water content in the polymerization raw materials is preferably 0 to 1,000 ppm. The upper limit is more preferably 700 ppm, and particularly preferably 280 ppm. The polymerization raw materials can be dehydrated, as needed, by a known method. The dissolved oxygen content of the polymerization raw materials is preferably adjusted to 0 to 10 ppm by nitrogen purging or the like. The upper limit of the dissolved oxygen content is more preferably 5 ppm, particularly preferably 4 ppm, and most preferably 3 ppm.

[0065] (Step (S2)) Polymerization can be carried out by known methods, with bulk polymerization being preferred. For example, a continuous bulk polymerization method is preferred, in which the polymerization raw materials prepared in step (S1) are continuously supplied to a tank reactor, bulk polymerization is carried out in the tank reactor under conditions of a polymerization conversion rate of 30 to 60%, to obtain a resin solution containing a methacrylic resin, and the resulting resin solution is continuously withdrawn from the tank reactor. Polymerization is preferably carried out under an atmosphere of an inert gas such as nitrogen gas. The polymerization temperature is not particularly limited, and is preferably 110 to 160°C, more preferably 120 to 155°C, and particularly preferably 130 to 150°C. The average residence time in the tank reactor is not particularly limited, and is preferably 1.5 to 6 hours, more preferably 2 to 5.5 hours, and particularly preferably 2.5 to 5 hours. The average concentration of the radical polymerization initiator present in the liquid in the tank reactor is not particularly limited, and is preferably 1.0 x 10 －６ ~2.0 x 10 －５ The polymerization conversion rate is more preferably 35 to 58%, particularly preferably 35 to 55%, and most preferably 35 to 50%.

[0066] (Step (S3)) At least a portion of the unreacted raw material monomers present in the resin solution are removed by volatilization in one or more stages. Examples of volatilization methods include adiabatic flash evaporation, equilibrium flash evaporation, and combinations thereof, with adiabatic flash evaporation being preferred. The unreacted raw material monomers present in the resin solution can be removed by volatilization using a known method such as a heat exchanger, a vented extruder, or a combination thereof, with the combined use of a heat exchanger and a vented extruder being preferred. The heating temperature of the heat exchanger (also referred to as the set temperature of the heat exchanger, or heat exchanger temperature) is not particularly limited and is preferably 180 to 280°C. The lower limit is more preferably 190°C, particularly preferably 200°C, and most preferably 270°C, particularly preferably 260°C, and most preferably 250°C.

[0067] Examples of the extruder include a single-screw extruder, a twin-screw extruder, and a multi-screw extruder. The extruder has a resin inlet into which the resin solution is introduced, a cylinder with a built-in screw, and a die including a resin outlet for discharging the methacrylic resin obtained after step (S3), and may also have an additive supply port as needed. The number of vents included in the vented extruder is one or more, preferably multiple. The temperature of the molten resin in the die (also referred to as the die resin temperature) is not particularly limited, but is preferably 230 to 260°C. The lower limit is more preferably 235°C, particularly preferably 240°C. The upper limit is more preferably 255°C, particularly preferably 250°C.

[0068] When the heating temperature of the heat exchanger and the molten resin temperature in the die are within the above ranges, thermal decomposition of the methacrylic copolymer (A) is suppressed, and a methacrylic resin having excellent heat resistance and thermal decomposition resistance (thermal stability) can be produced. Furthermore, a methacrylic copolymer (A) having a uniform composition, such as the content of isopropenyl aromatic compound units (UI), can be stably produced, and a methacrylic copolymer (A) having good heat resistance and mechanical properties such as rigidity and surface hardness can be stably produced. The unreacted raw material monomer removed from the resin solution may be recovered and reused as the raw material monomer.

[0069] In the method for producing a methacrylic resin of the present disclosure, it is preferable to add one or more organic disulfide compounds (D) to at least one of the polymerization raw materials, the resin solution obtained after completion of step (S2), and the resin solution during step (S3). It is preferable to add one or more organic disulfide compounds (D) to at least the polymerization raw materials among the polymerization raw materials, the resin solution obtained after completion of step (S2), and the resin solution during step (S3). The amount of one or more organic disulfide compounds (D) added to the polymerization raw materials is preferably 10 to 2000 ppm. The lower limit is more preferably 20 ppm, even more preferably 30 ppm, even more preferably 50 ppm, even more preferably 80 ppm, particularly preferably 100 ppm, and most preferably 200 ppm. The upper limit is more preferably 1500 ppm, particularly preferably 1200 ppm, and most preferably 1000 ppm.

[0070] In the method for producing a methacrylic resin according to the present disclosure, one or more organic phosphorus compounds (P) can be added, as necessary, to at least one of the polymerization raw materials, the resin solution obtained after completion of step (S2), and the resin solution being produced during step (S3). The one or more organic phosphorus compounds (P) can be supplied, for example, through an additive supply port of the extruder.

[0071] In the method for producing a methacrylic resin according to the present disclosure, one or more lubricants (L) can be added to at least one of the polymerization raw materials, the resin solution obtained after the completion of step (S2), and the resin solution during step (S3), as needed. The one or more lubricants (L) can be supplied, for example, from an additive supply port of the extruder.

[0072] The methacrylic resin of the present disclosure obtained after step (S3) can be processed into a form suitable for use as a molding material, such as pellets or powder, by a known method.

[0073] As described above, according to the present disclosure, it is possible to provide a methacrylic resin having good heat resistance and thermal decomposition resistance (thermal stability), good mechanical properties such as rigidity and surface hardness, and good moldability, and a method for producing the same.

[0074] [Methacrylic Resin Composition] The methacrylic resin composition of the present disclosure can include the methacrylic resin of the present disclosure and one or more optional components. The methacrylic resin composition of the present disclosure can include one or more other polymers.Other polymers include methacrylic resins other than the above-described methacrylic resins of the present disclosure; polyolefin resins such as polyethylene, polypropylene, polybutene-1, poly-4-methylpentene-1, and polynorbornene; other styrene resins such as polystyrene, high impact polystyrene, methyl methacrylate-styrene copolymer (MS resin), styrene-maleic anhydride copolymer (SMA resin), styrene-maleic anhydride-methyl methacrylate copolymer (SMM resin), acrylonitrile-styrene copolymer (AS resin), acrylonitrile-butadiene-styrene (ABS) resin, acrylonitrile-ethylene-propylene-diene-styrene (AES) resin, acrylic-acrylonitrile-styrene (AAS) resin, acrylonitrile-chlorinated ethylene-styrene (ACS) resin, and methacrylic butadiene styrene (MBS) resin; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polyamide resins such as nylon 6, nylon 66, and polyamide elastomer. Examples of suitable methacrylic resins include methacrylic resins, polycarbonate resins, other thermoplastic resins such as polyphenylene sulfide, polyether ether ketone, polysulfone, polyphenylene oxide, polyimide, polyetherimide, polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyacetal, ethylene-vinyl acetate copolymer, phenoxy resins, and ethylene-based ionomers, thermosetting resins such as phenolic resins, melamine resins, silicone resins, and epoxy resins, polyurethane and chlorinated polyurethane resins, modified polyphenylene ether, silicone-modified resins, acrylic rubber, silicone rubber, acrylic rubber, silicone rubber, acrylic thermoplastic elastomers such as diblock copolymers and triblock copolymers of methyl methacrylate polymer block-n-butyl acrylate polymer block, styrene thermoplastic elastomers such as SEPS, SEBS, and SIS, and olefinic rubbers such as IR, EPR, and EPDM. The methacrylic resin composition of the present disclosure can contain one or more optional additives.The timing of adding the additives contained in the methacrylic resin composition of the present disclosure may be during or after the production of the methacrylic resin of the present disclosure.

[0075] [Molded Article] The molded article of the present disclosure may contain the above-described methacrylic resin of the present disclosure or the above-described methacrylic resin composition of the present disclosure. Molding can be performed by known molding methods such as injection molding, compression molding, extrusion molding, and vacuum molding. Examples of molded articles include planar objects with single-layer or laminated structures such as films, sheets, and plates; any three-dimensional structures, and the like. The molded article may also be a laminate or composite containing a layer or member made of the methacrylic resin of the present disclosure or the methacrylic resin composition of the present disclosure and a layer or member made of other resins or various materials other than resins. Generally, the terms "film," "sheet," or "plate" are used for thin film molded articles depending on the thickness, but there are no clear definitions of these terms, and no clear distinction is made between them.

[0076] [Applications] The methacrylic resin of the present disclosure can be used for any application. The methacrylic resin of the present disclosure has excellent heat resistance and thermal decomposition resistance (thermal stability), and is characterized by suppressed discoloration such as yellowing, making it suitable for optical components; components for electronic devices such as mobile phones and personal computers; and components for transportation equipment such as vehicles (automobiles, etc.). Examples of optical components include displays such as liquid crystal displays, plasma displays, organic electroluminescence (EL) displays, field emission displays, and rear projection televisions; and display components such as touch panel displays that combine touch panels with displays. Examples of optical components for displays include polarizer protective films, retardation plates (such as quarter-wave plates and half-wave plates), liquid crystal optical compensation films (such as viewing angle control films), display front panels, display substrates, transparent conductive substrates for touch panels, light guide plates, and lenses (arrays). In this specification, unless otherwise specified, "lens (array)" is a general term for lenses and lens arrays. Other optical components include optical components for solar cells (transparent substrates, back films, front films, etc.); optical components used in fields such as optical communication, optical switching, and optical measurement (waveguides, lenses (arrays), optical fibers, and coating materials for optical fibers, etc.); and optical components for light-emitting elements such as light-emitting diodes (LEDs) (lenses, lens covers, etc.).

[0077] The methacrylic resin of the present disclosure is also suitable for films such as surface protection films for electronic devices such as mobile phones and personal computers, and marking films.

[0078] Examples of optical components for vehicles include rear lamp outer covers and optical components inside rear lamps; headlight inner lenses (also called projector lenses or PES lenses); front panels or molded bodies for in-vehicle meter panels and car navigation systems; door mirror housings, pillar covers (sash covers), license garnishes, front grilles, fog garnishes, emblems, light guide rods; optical components for head-up displays such as optical cover members; optical components for DMS (driver monitoring systems), OMS (occupant monitoring systems), gesture control, and LiDAR (light detection and ranging). Examples of components for transportation equipment other than those mentioned above include aircraft windshields, pilot visors, motorcycle windshields, motorboat windshields, bus sunshades, automobile side visors, rear visors, head wings, headlight covers, automobile interior components, and automobile exterior components such as bumpers.

[0079] Other uses of the methacrylic resin of the present disclosure include interior components such as furniture, wallpaper, pendant lights, and mirrors; architectural components such as doors, sashes, domes, safety window glass, partitions, staircase wainscoting, balcony wainscoting, and roofs of leisure buildings; sign components or marking films such as advertising towers, stand signs, side signs, transom signs, and rooftop signs; display components such as showcases, partitions, and store displays; lighting components such as fluorescent light covers, mood lighting covers, lampshades, lighted ceilings, lighted walls, and chandeliers; Examples of suitable applications include various home appliance parts such as TV protective masks; audiovisual nameplates, stereo covers; vending machines; medical equipment parts such as incubators and X-ray parts; equipment parts such as clock panels, machine covers, instrument covers, laboratory equipment, dial faces, and observation windows; traffic-related parts such as road signs, information boards, convex mirrors, and soundproof walls; bathroom components such as bathtubs, sanitary components; greenhouses, large aquariums, box aquariums; stationery such as rulers and desk mats; game parts, toys, musical instruments; and decorative and protective films that are provided on the surface of face protection masks used during welding.

[0080] Examples and comparative examples according to the present invention will be described. [Evaluation Items and Evaluation Methods] The evaluation items and evaluation methods are as follows. (Polymerization Conversion Rate) The polymerization conversion rate was determined by gas chromatography analysis. A gas chromatograph GC-14A manufactured by Shimadzu Corporation was connected to an INERTCAP1 column manufactured by GL Sciences Inc. (film thickness 0.4 μm, inner diameter 0.25 mmφ, length 60 m). Analysis was carried out under the following conditions, and the polymerization conversion rate was calculated from the obtained data. Injection temperature: 250°C, Detector temperature: 250°C, Temperature profile: Hold at 60°C for 5 minutes → Heat to 250°C at a heating rate of 10°C / min → Hold at 250°C for 10 minutes.

[0081] (Weight-average molecular weight (Mw), molecular weight distribution (Mw / Mn)) The weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the resin were determined by gel permeation chromatography (GPC). A GPC device "HLC-8320" manufactured by Tosoh Corporation was used as the measuring device. A series connection of "TSKguardcolumnSuperHZ-H", "TSKgelHZM-M", and "TSKgelSuperHZ4000" manufactured by Tosoh Corporation was used as the separation column. Two types of detectors were used: a differential refractive index detector (RI detector) and an absorbance detector (also called a UV detector) with a detection wavelength of 254 nm. A sample solution was prepared by dissolving 4 mg of the resin to be measured in 5 ml of tetrahydrofuran. The column oven temperature was set to 40°C. Tetrahydrofuran was used as the eluent, and the eluent flow rate was set to 0.35 ml / min. 20 μl of the sample solution was injected into the device and a chromatogram was measured. Ten standard polymethyl methacrylate (PMMA) samples with molecular weights ranging from 400 to 5,000,000 were subjected to GPC measurement, and a calibration curve showing the relationship between retention time and molecular weight was created. Based on this calibration curve, the Mw and Mw / Mn of the resin to be measured, converted to standard PMMA, were determined. In Tables 1 and 2, Mw Ｂ is the Mw determined by GPC analysis using a differential refractive index detector, and (Mw / Mn) A is the molecular weight distribution (Mw / Mn) determined by GPC analysis using an absorbance detector with a detection wavelength of 254 nm, and (Mw / Mn) Bis the molecular weight distribution (Mw / Mn) determined by GPC analysis using a differential refractive index detector.

[0082] (Monomer unit composition of methacrylic resin) １ H-NMR spectrum or １３ The C-NMR spectrum was measured, and the monomer unit composition of the methacrylic resin was determined from the ratio of the integral values ​​of the peaks derived from each monomer unit. For methyl methacrylate-α-methylstyrene copolymer (MMA-αMSt copolymer), １ The H-NMR spectrum was measured to identify the peaks derived from the protons of the methoxy groups of the methyl methacrylate (MMA) units and the peaks derived from the protons of the phenyl groups of the α-methylstyrene (αMSt) units, and the monomer unit composition was determined from the ratio of the integral values ​​of each peak.

[0083] For methyl methacrylate-α-methylstyrene-styrene copolymer (MMA-αMSt-St copolymer), measurement mode: under the conditions of the inverse gated decoupling method, １３ A C-NMR spectrum was measured to identify a peak derived from the carbon of the carbonyl group of the methyl methacrylate (MMA) unit, a peak derived from the carbon of the phenyl group of the α-methylstyrene (αMSt) unit, and a peak derived from the carbon of the phenyl group of the styrene (St) unit, and the monomer unit composition was determined from the ratio of the integral values ​​of each peak.

[0084] (Remaining amount of each monomer in the methacrylic resin) The remaining amount of each monomer in the methacrylic resin was evaluated in the same manner as in the evaluation of the "monomer unit composition of the methacrylic resin" above. １ H-NMR spectrum or １３ It was determined from the C-NMR spectrum.

[0085] (Residual Amount of Organic Disulfide Compound (D) in Methacrylic Resin) 2 g of methacrylic resin was dissolved in 10 mL of dichloromethane, and then 30 mL of hexane was added to cause reprecipitation. The supernatant obtained after this reprecipitation process was separated, and the solvent in this supernatant was removed by distillation under reduced pressure to cause concentration. The concentrate obtained was again dissolved in 1 mL of dichloromethane, and then 4 mL of hexane was added to cause reprecipitation. 25 μL of the supernatant obtained after this reprecipitation process was collected on a platinum board as a measurement sample, and after removing the dichloromethane, pyrolysis gas chromatography analysis was performed. A column, Agilent J&W Series DB-5 (inner diameter: 0.25 mm, film thickness: 0.25 μm, length: 30.0 m), manufactured by Agilent Technologies, was connected to a Gas Chromatograph GC-14A manufactured by Shimadzu Corporation. The analysis was performed under the following conditions. The remaining amount of organic disulfide compound (D) was determined based on a calibration curve obtained from pyrolysis gas chromatography analysis of standard solutions of organic disulfide compounds with different concentrations. Vaporization chamber temperature: 260°C, Column oven temperature: 100°C, Temperature profile: Heat up to 320°C at a rate of 20°C / min → Hold at 320°C for 30 minutes.

[0086] (Glass Transition Temperature (Tg)) The glass transition temperature (Tg) of the resin to be measured was measured in accordance with JIS K7121 using a differential scanning calorimeter (Shimadzu Corporation, "DSC-50"). 10 mg of the resin to be measured was placed in an aluminum pan and set in the apparatus. After nitrogen substitution for 30 minutes or more, the sample was heated from room temperature (20-25°C) to 250°C at a rate of 20°C / min in a nitrogen stream of 10 ml / min, held for 5 minutes, and cooled to room temperature (primary scan). The sample was then heated to 200°C at a rate of 10°C / min (secondary scan), and the DSC curve was measured. The midpoint glass transition temperature determined from the DSC curve obtained in the secondary scan was taken as the glass transition temperature (Tg).

[0087] (1% Thermal Weight Loss Temperature) Using a thermogravimetric analyzer (Shimadzu Corporation's "TGA-50"), approximately 5 mg of the resin to be measured was heated from room temperature (20 to 25°C) to 500°C at a heating rate of 10°C / min in a nitrogen atmosphere to obtain a TG curve. The temperature at which the weight loss rate was 1% relative to 100% of the weight before heating was determined as the 1% thermal weight loss temperature.

[0088] (Melt Flow Rate (MFR)) The melt flow rate (MFR) of the methacrylic resin was measured in accordance with JIS K7210 under conditions of 230° C. and a load of 3.8 kg.

[0089] (Deflection temperature under load (HDT)) Using an injection molding machine ("M-100C" manufactured by Meiki Seisakusho Co., Ltd.), a methacrylic resin was injection molded under conditions of a cylinder temperature of 230°C, a mold temperature of 60°C, and an injection speed of 50 mm / sec to obtain a test piece having a length of 80 mm, a width of 10 mm, and a thickness of 4 mm. The obtained test piece was conditioned in accordance with JIS K6712-2. The deflection temperature under load (HDT) of this test piece was measured in accordance with JIS K7191.

[0090] (Flexural Modulus) Test specimens were injection molded and conditioned in the same manner as in the evaluation of "deflection temperature under load (HDT)" above. The flexural modulus of the test specimens was measured in accordance with JIS-K7171 using a precision universal testing machine ("Autograph AG-IS5kN" manufactured by Shimadzu Corporation).

[0091] (Rockwell Hardness) Using an injection molding machine ("M-100C" manufactured by Meiki Seisakusho Co., Ltd.), methacrylic resin was injection molded under conditions of a cylinder temperature of 230 ° C., a mold temperature of 60 ° C., and an injection speed of 50 mm / sec to obtain two square test pieces with a side length of 50 mm and a thickness of 3 mm. Each test piece was conditioned in accordance with JIS K6712-2. These two test pieces were stacked to a total thickness of 6 mm. The Rockwell hardness of this sample was measured in accordance with JIS-K7202-2 using a Rockwell hardness tester ("DXT-FA" manufactured by Toyo Seiki Co., Ltd.) under the conditions of M scale (test load = 980.7 N, diameter of hard ball indenter = 6.35 mm).

[0092] [Additives] The additives used are as follows: <Organic disulfide compound (D)> (DDS) di-tert-dodecyl disulfide, (DBS) dibenzyl disulfide.

[0093] Example E1: An autoclave equipped with a stirrer and a collection tube was charged with 65 parts by mass of purified methyl methacrylate (MMA), 28 parts by mass of α-methylstyrene (αMSt), 7 parts by mass of styrene (St), 100 ppm of n-octyl mercaptan (n-OM) as a chain transfer agent, and 1000 ppm of di-tert-dodecyl disulfide (DDS), and mixed uniformly. To this was added 500 ppm of 2,2'-azobis(2-methylpropionitrile) (AIBN) as a polymerization initiator, and mixed uniformly to obtain a polymerization raw material. Nitrogen gas was blown into this polymerization raw material, and the dissolved oxygen concentration was adjusted to 3 ppm. This composition of the polymerization raw material is also referred to as the charge composition.

[0094] Next, a continuous flow tank reactor equipped with a brine cooling condenser was prepared, and the inside of the reactor was purged with nitrogen gas. The polymerization raw materials were continuously fed into the reactor at a constant flow rate so that the average residence time was 3.0 hours, and bulk polymerization was carried out at a polymerization temperature of 140°C. A resin solution containing the reaction product, a methacrylic resin, was continuously discharged from the reactor. The pressure inside the reactor was regulated by a pressure regulating valve connected to the brine cooling condenser. The polymerization conversion was 37%.

[0095] A twin-screw extruder was prepared, which had a die including a resin inlet for introducing the resin solution discharged from the reactor and a resin outlet for discharging the produced resin, and further had a first vent (also called a rear vent) located relatively close to the resin inlet, a second vent (also called a front vent) located relatively close to the resin outlet, and an additive supply port located between the second vent (front vent) and the resin outlet.

[0096] The resin solution discharged from the reactor was heated using a heat exchanger and supplied to the extruder through the resin supply port. The heat exchanger temperature was set to 200°C, and the extruder cylinder temperature was set to 245°C. Volatiles, primarily composed of unreacted monomers, were flash evaporated from the resin solution supplied to the extruder cylinder and discharged through the first vent (rear vent). The resin was then conveyed axially by the screw, and the volatiles evaporated during this process were discharged through the second vent (front vent). The screw rotation speed was 164 rpm. The resin was extruded in the form of strands from the extruder's resin outlet. The molten resin temperature in the die (also referred to as the die resin temperature) was 244°C. The resulting strands were cut using a pelletizer to obtain pellets of a methacrylic resin containing a methacrylic copolymer (A-1) containing methyl methacrylate (MMA) units and α-methylstyrene (αMSt) units.

[0097] The main production conditions and evaluation results are shown in Table 1. In Tables 1 and 2, conditions not shown in the tables are common conditions. In the tables, the "raw material composition" is a composition combining the charged composition and post-added additives. In the tables, the amounts of the polymerization initiator, chain transfer agent, and organic disulfide compound (D) added before polymerization in the raw material composition are the amounts added relative to 100% by mass of the total amount of raw material monomers.

[0098] [Examples E2 to E8, Comparative Examples EC2 to EC7] Methacrylic resins containing any of methacrylic copolymers (A-2) to (A-8) and (C-2) to (C-7) containing methyl methacrylate (MMA) units and α-methylstyrene (αMSt) units were obtained in the same manner as in Example E1, except that the charging composition and / or polymerization conditions were changed. The main production conditions and evaluation results are shown in Tables 1 and 2.

[0099] Comparative Example EC1: A methacrylic resin containing 98.0% by mass or more of a methacrylic copolymer (C-1) containing methyl methacrylate (MMA) units and α-methylstyrene (αMSt) units was obtained in the same manner as in Example E1, except that DDS was added later as follows. Di-tert-dodecyl disulfide (DDS) was charged into the additive preparation tank, and a pressure operation of increasing the pressure to 0.2 MPa and releasing the pressure to atmospheric pressure was repeated a total of four times to remove oxygen and moisture, and the oxygen concentration in the additive preparation tank was set to 0%. Next, the DDS charged into the additive preparation tank was heated to a temperature higher than its melting point and stirred for 2 hours to melt it. The resulting liquid DDS was filtered using a 0.2 μm metal filter ("FLHF200-10M3F" manufactured by PALL) and injected into the additive inlet of the extruder using a metering pump. The amount of DDS added relative to 100% by mass of resin was 1,000 ppm. The main production conditions and evaluation results are shown in Table 2. In the table, the amount of DDS added after polymerization in the raw material composition is the amount added relative to 100% by mass of the resin.

[0100]

[0101]

[0102] [Summary of Results] In Examples E1 to E8, an appropriate amount of organic disulfide compound (D) was added to the polymerization raw materials, and polymerization was carried out under suitable conditions to obtain methacrylic resins containing methacrylic copolymers (A) consisting of 40 to 99% by mass of methyl methacrylate (MMA) units, 1 to 40% by mass of one or more isopropenyl aromatic compound units (UI), and 0 to 30% by mass of one or more other units (UO). In Examples E1 to E4 and E6 to E8, an appropriate amount of organic disulfide compound (D) was added to the polymerization raw materials to obtain methacrylic resins containing 1 to 1,000 ppm of organic disulfide compound (D). The methacrylic resins obtained in these Examples all had a total residual amount of raw material monomers of 0 to 1.00% by mass. In all of these Examples, the (Mw / Mn) Ａ / (Mw / Mn) Ｂ The methacrylic copolymer (A) was able to be stably produced, and had a uniform composition, such as the content of isopropenyl aromatic compound units (UI), in which the value of the copolymer (A) was 1.40 or less.

[0103] All of the methacrylic resins obtained in Examples E1 to E8 had a Tg of 120°C or higher, a 1% thermal weight loss temperature of 270°C or higher, and good heat resistance and thermal decomposition resistance (thermal stability). All of the methacrylic resins obtained in these Examples had a good melt flow rate (MFR) and good moldability. All of the methacrylic resins obtained in these Examples had a deflection temperature under load (HDT) of 105°C or higher, and good heat resistance and rigidity under load. All of the methacrylic resins obtained in these Examples had good flexural modulus and surface hardness. All of the methacrylic resins obtained in these Examples were suitable for optical components; vehicle components for automobiles, etc.

[0104] In Comparative Examples EC1, EC3, and EC4, methacrylic resins containing a methacrylic copolymer (C) consisting of 40 to 99 mass% of methyl methacrylate (MMA) units, 1 to 40 mass% of isopropenyl aromatic compound units (UI), and 0 to 30 mass% of other units (UO) were obtained. In these Comparative Examples, no organic disulfide compound (D) was added to the polymerization raw materials. In all of the methacrylic resins obtained in these Comparative Examples, the total residual amount of the raw material monomers of the methacrylic copolymer (C) exceeded 1.00 mass%. In all of the methacrylic resins obtained in these Comparative Examples, the (Mw / Mn) Ａ / (Mw / Mn) Ｂ was 1.40 or less, but the heat resistance and / or thermal decomposition resistance (thermal stability) was poor, and the evaluation results of one or more of Tg, 1% weight loss temperature, deflection temperature under load (HDT), and stability during heating and retention were poor.

[0105] In Comparative Example EC2, a methacrylic resin containing a methacrylic copolymer (C) containing methyl methacrylate (MMA) units and isopropenyl aromatic compound units (UI), the content of the methyl methacrylate (MMA) units being less than 40% by mass, and the content of the isopropenyl aromatic compound units (UI) being more than 40% by mass, was obtained. In this Comparative Example, an appropriate amount of an organic disulfide compound (D) was added to the polymerization raw materials, and a methacrylic resin containing 1 to 1,000 ppm of the organic disulfide compound (D) was finally obtained. The methacrylic resin obtained in this Comparative Example had a total residual amount of the raw material monomers of the methacrylic copolymer (C) exceeding 1.00% by mass. In this Comparative Example, (Mw / Mn) Ａ / (Mw / Mn) Ｂ The modulus of elasticity was greater than 1.40, and it was not possible to stably produce a methacrylic copolymer (C) having a uniform composition, such as the content of isopropenyl aromatic compound units (UI). Furthermore, the heat resistance and / or thermal decomposition resistance (thermal stability) were poor, and the Tg, 1% weight loss temperature, and deflection temperature under load (HDT) were poor. Furthermore, the flexural modulus and surface hardness were poor.

[0106] In Comparative Examples EC5 to EC7, methacrylic resins containing a methacrylic copolymer (C) consisting of 40 to 99 mass% methyl methacrylate (MMA) units, 1 to 40 mass% isopropenyl aromatic compound units (UI), and 0 to 30 mass% other units (UO) were obtained. In these Comparative Examples, an appropriate amount of an organic disulfide compound (D) was added to the polymerization raw materials, and a methacrylic resin containing 1 to 1,000 ppm of the organic disulfide compound (D) was finally obtained. In all of the methacrylic resins obtained in these Comparative Examples, the total residual amount of the raw material monomers of the methacrylic copolymer (C) was 0 to 1.00 mass%. In these Comparative Examples, the polymerization conditions were inappropriate, and the (Mw / Mn) Ａ / (Mw / Mn) ＢThe modulus of elasticity (Tg) and the surface hardness (HDT) of the methacrylic resin obtained in Comparative Example EC7 were poor.

[0107] The present invention is not limited to the above-described embodiments and examples, and appropriate design changes are possible without departing from the spirit of the present invention.

[0108] This application claims priority based on Japanese Patent Application No. 2023-100539, filed on June 20, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A methacrylic resin containing a methacrylic copolymer (A) consisting of 40-99% by mass of methyl methacrylate units, 1-40% by mass of one or more isopropenyl aromatic compound units (UI), and 0-30% by mass of one or more other units (UO), having a glass transition temperature of 120°C or higher, and satisfying the following formula (1): (Mw / Mn) Ａ / (Mw / Mn) Ｂ ≦1.40 (1) (wherein, (Mw / Mn) A is the molecular weight distribution (Mw / Mn) determined by gel permeation chromatography analysis using an absorbance detector with a detection wavelength of 254 nm, and (Mw / Mn) B is the molecular weight distribution (Mw / Mn) determined by gel permeation chromatography analysis using a differential refractive index detector.

2. The methacrylic resin according to claim 1, wherein the total residual amount of the raw material monomers of the methacrylic copolymer (A) is 0 to 1.00 mass%.

3. The methacrylic resin according to claim 1, wherein the one or more isopropenyl aromatic compound units (UI) include α-methylstyrene units.

4. The methacrylic resin according to claim 1, wherein the methacrylic copolymer (A) contains, as the other units (UO), aromatic vinyl compound units other than isopropenyl aromatic compound units.

5. The methacrylic resin according to claim 1, further comprising 1 to 1,000 ppm of one or more organic disulfide compounds (D).

6. The methacrylic resin according to claim 5, wherein the one or more organic disulfide compounds (D) include at least one selected from the group consisting of di-tert-dodecyl disulfide (DDS) and dibenzyl disulfide (DBS).

7. The methacrylic resin according to claim 1, wherein a test piece obtained by molding the methacrylic resin and having a length of 80 mm, a width of 10 mm and a thickness of 4 mm has a flexural modulus of 3,000 MPa or more, as measured in accordance with JIS K7171.

8. The methacrylic resin according to claim 1, wherein a square test piece, obtained by molding the methacrylic resin and measuring 50 mm on a side and 3 mm in thickness, has a Rockwell hardness of 85 or more, as measured under M-scale conditions in accordance with JIS K7202-2.

9. A methacrylic resin composition comprising the methacrylic resin according to any one of claims 1 to 8.

10. A molded article comprising the methacrylic resin according to any one of claims 1 to 8.

11. A method for producing a methacrylic resin according to any one of claims 1 to 8, comprising: a step (S1) of preparing a polymerization raw material containing, as raw material monomers, 30 to 99 mass% methyl methacrylate, 1 to 59 mass% of one or more isopropenyl aromatic compounds (I), and 0 to 49 mass% of one or more other monomers (O), and further containing a polymerization initiator; a step (S2) of polymerizing the polymerization raw material under conditions where the polymerization conversion rate is 30 to 60 mass% to obtain a resin solution containing the methacrylic resin; and a step (S3) of volatilizing and removing at least a portion of the raw material monomers present in the resin solution in one or more steps to obtain the methacrylic resin, wherein 10 to 2000 ppm of one or more organic disulfide compounds (D) are added to at least one of the polymerization raw materials, the resin solution obtained after completion of step (S2), and the resin solution during the implementation of step (S3).

12. A method for producing a methacrylic resin as described in claim 11, in which one or more organic disulfide compounds (D) are added to at least the polymerization raw materials, among the polymerization raw materials, the resin solution obtained after completion of step (S2), and the resin solution during step (S3).

13. A method for producing a methacrylic resin as described in claim 11, wherein step (S3) includes a step of heating the resin solution at 190 to 250°C to volatilize raw material monomers present in the resin solution.

14. A method for producing a methacrylic resin according to claim 11, wherein step (S3) comprises the steps of feeding the resin solution into an extruder having one or more vents, volatilizing raw material monomers present in the resin solution and discharging the resin from the vents, and extruding the methacrylic resin from a die of the extruder, wherein the temperature of the molten resin in the die is 230 to 260°C.