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

Abstract

The present disclosure provides a methacrylic resin composition that has good heat resistance and thermal decomposition resistance (thermal stability), has suppressed discoloration such as yellowing, and has good moldability. A methacrylic resin composition according to the present disclosure comprises a first methacrylic copolymer (A) having 10-99% by mass of a methyl methacrylate unit, 1-40% by mass of one or more isopropenyl aromatic compound units (UI) and 0-60% by mass of one or more other units (UO) and having a glass transition temperature of 120-150° C. The methacrylic resin composition further contains 1-1000 ppm of one or more organic disulfide compounds (D). The total residual amount of the raw material monomers of the methacrylic copolymer (A) is 0-1.00% by mass.

Description

Methacrylic resin composition, its production method, and molded article

[0001] The present disclosure relates to a methacrylic resin composition, a method for producing the same, 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; components for vehicles such as automobiles (e.g., vehicle interior and exterior materials); and various components for buildings, household goods, office automation equipment, and lighting equipment. Heat resistance is required for methacrylic resins depending on the application. For example, in backlights of liquid crystal displays that include a light source and a light guide plate, the use of high-power light-emitting diodes (LEDs) (e.g., LEDs with an output of 1 W or more) as light sources has increased due to the increased optical path length and improved brightness of the light guide plate. Generally, to prevent light leakage from the light-receiving end face of the light guide plate, it is preferable that the light-emitting surface of the LED and the light-receiving end face of the light guide plate be as close as possible to each other. However, when using high-power LEDs, which generate a large amount of heat, the closer the light-emitting surface of the LED is to the light-incident end face of the light guide plate, the more exposed the light-incident end face of the light guide plate is to the heat emitted by the LED, and therefore higher heat resistance is required.

[0003] One known methacrylic resin with improved heat resistance is a methacrylic copolymer 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, in which a monomer mixture containing methyl methacrylate (MMA) and α-methylstyrene (αMSt) is bulk-polymerized by adding a polyfunctional organic peroxide having a 10-hour half-life temperature in the range of 60 to 110°C as a polymerization initiator (claim 1).

[0004] JP 4-218515 JP 3-281648 JP 7-292202 JP 6-345932 JP 5-279547 JP 2001-294722 JP 2013-104042

[0005] However, methacrylic copolymers containing MMA units and isopropenyl aromatic compound units such as αMSt units tend to have relatively low thermal decomposition temperatures. Therefore, in methacrylic resin compositions containing such copolymers, the copolymer may be thermally decomposed 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 residence time in a heated and molten state during resin production and molding is long, the thermal decomposition of the methacrylic copolymer may cause poor appearance, such as foaming.

[0006] As a method for improving the thermal decomposition resistance of the above-mentioned methacrylic copolymer, the addition of various antioxidants has been proposed. For example, Patent Documents 2 and 3 disclose methacrylic resin compositions in which a hindered phenol compound and a phosphite compound are added as antioxidants to a methacrylic copolymer containing MMA units and αMSt units (Claim 1 of Patent Document 2, Claim 1 of Patent Document 3). Patent Document 4 discloses a methacrylic resin composition in which a phenol-acrylate bifunctional compound and a hindered phenol compound are added as antioxidants to a methacrylic copolymer containing MMA units and αMSt units (Claim 1 of Patent Document 4).

[0007] The antioxidants used in Patent Documents 2 and 3 cannot effectively capture alkyl radicals generated by thermal decomposition of the main chain of a methacrylic copolymer containing MMA units and isopropenyl aromatic compound units such as αMSt units, and therefore cannot be said to have a sufficient effect of improving thermal decomposition resistance.The antioxidant used in Patent Document 4 has alkyl radical scavenging ability, but its effect of improving thermal decomposition resistance is insufficient, and increasing the amount added may cause discoloration (e.g., yellowing) of the resin.

[0008] Examples of rubber-reinforced styrene resins include high-impact polystyrene (HIPS resin), methyl methacrylate-butadiene-styrene resin (MBS resin), and acrylonitrile-butadiene-styrene resin (ABS resin). These rubber-reinforced styrene resins have transparency and excellent mechanical properties, moldability, electrical properties, colorability, and design properties, and are used in a variety of applications, such as miscellaneous goods; housings and parts for electrical equipment and office automation equipment; and interior and exterior vehicle components. Generally, rubber-reinforced styrene resins have good impact resistance but tend to have insufficient heat resistance. By blending a heat-resistant (meth)acrylic resin with a refractive index that matches the rubber-reinforced styrene resin, it is possible to improve heat resistance without impairing transparency.

[0009] For example, Patent Document 5 discloses a thermoplastic resin composition containing a graft copolymer (rubber-reinforced transparent resin) obtained by graft copolymerizing diene rubber or acrylic rubber with methyl methacrylate and styrene, and an α-methylstyrene-methyl methacrylate copolymer (claim 1). Patent Document 6 discloses a thermoplastic resin composition containing a rubber-modified thermoplastic resin and a heat-resistant (meth)acrylic copolymer containing methacrylic acid ester units and maleimide units (claim 1). Patent Document 7 discloses a rubber-modified styrene-based resin composition containing a graft copolymer consisting of a diene rubber-like polymer and a styrene-methacrylic acid ester copolymer, and a (meth)acrylic copolymer consisting of (meth)acrylic acid ester units, aromatic vinyl monomer units, and unsaturated dicarboxylic acid anhydride units (claim 1).

[0010] However, heat-resistant (meth)acrylic resins generally tend to have high melt viscosities. Therefore, in methacrylic resin compositions containing a rubber-reinforced styrene-based resin and a heat-resistant (meth)acrylic resin, relatively high temperatures are required during melt-kneading of the multiple resins and during heating and melting during molding of the resin composition. In this case, gelation may occur due to thermal degradation of the rubber-reinforced styrene-based resin. This problem is particularly likely when the rubber-reinforced styrene-based resin contains butadiene units. Gelation is undesirable because it can cause a decrease in impact resistance at low temperatures (e.g., below freezing) and poor appearance of molded articles.

[0011] The present disclosure has been made in view of the above circumstances, and aims to provide a methacrylic resin composition that has good heat resistance and thermal decomposition resistance (thermal stability), is inhibited from discoloration such as yellowing, and has good moldability. Another aim of the present disclosure is to provide a methacrylic resin composition that contains a graft copolymer containing butadiene units and a methacrylic copolymer, and that has good transparency, heat resistance, surface hardness, and impact resistance at room temperature and low temperature.

[0012] The present disclosure provides the following methacrylic resin compositions [1] to

[15] , a method for producing the same, and a molded article.

[0013] [1] A methacrylic resin composition comprising a first methacrylic copolymer (A) which is composed of 10 to 99% by mass of methyl methacrylate units, 1 to 40% by mass of one or more isopropenyl aromatic compound units (UI), and 0 to 60% by mass of one or more other units (UO), and which has a glass transition temperature of 120 to 150°C; further comprising 1 to 1,000 ppm of one or more organic disulfide compounds (D); and wherein the total residual amount of raw material monomers of the methacrylic copolymer (A) is 0 to 1.00% by mass.

[0014] [2] 10 to 95% by mass of a first methacrylic copolymer (A) comprising 10 to 99% by mass of methyl methacrylate units, 1 to 40% by mass of one or more isopropenyl aromatic compound units (UI), and 0 to 60% by mass of one or more other units (UO), and having a glass transition temperature of 120 to 150°C; 5 to 40% by mass of a graft copolymer (B) obtained by graft copolymerizing a butadiene rubber-like polymer (BR) containing 60 to 100% by mass of butadiene units with a methacrylic copolymer (M) containing 10 to 90% by mass of methyl methacrylate units, 90 to 10% by mass of aromatic vinyl compound units, and 49 to 0% by mass of vinyl cyanide compound units; A methacrylic resin composition according to [1], comprising: 0 to 85 mass% of a second methacrylic copolymer (C) containing 10 to 90 mass% of methyl methacrylate units, 70 to 10 mass% of aromatic vinyl compound units other than isopropenyl aromatic compound units, and 49 to 0 mass% of vinyl cyanide compound units; and 1 to 1,000 ppm of an organic disulfide compound (D), and satisfying the following formula (1): 0≦|n ｂ -n ｍ |≦0.01 (1) In the above formula, n ｍ is defined by the following formula (2): ｍ = (n ａ ×w ａ +n ｃ ×w ｃ ) / (w ａ +w ｃ ) (2) In the above formula, n ａ , n ｂ , n ｃ are the refractive indices at 23°C for the sodium D line of the first methacrylic copolymer (A), the graft copolymer (B), and the second methacrylic copolymer (C), respectively. ａ , w ｂ , w ｃ and w are the mass ratios of the first methacrylic copolymer (A), the graft copolymer (B), and the second methacrylic copolymer (C) to the total mass of the first methacrylic copolymer (A), the graft copolymer (B), and the second methacrylic copolymer (C) in the methacrylic resin composition. ａ +w ｂ +w ｃ=1.

[0015] [3] The methacrylic resin composition of [1] or [2], wherein the one or more isopropenyl aromatic compound units (UI) contain an α-methylstyrene unit. [4] The methacrylic resin composition of any of [1] to [3], wherein the first methacrylic copolymer (A) contains, as the other units (UO), an aromatic vinyl compound unit other than an isopropenyl aromatic compound unit. [5] The methacrylic resin composition of any of [1] to [4], wherein the first methacrylic copolymer (A) contains, as the other units (UO), one or more ring structure units (UR) selected from the group consisting of an acid anhydride unit, an imide unit having a ring structure, and a lactone ring unit.

[0016] [6] The methacrylic resin composition according to [2], wherein the butadiene rubber polymer (BR) is one or more rubber polymers selected from the group consisting of polybutadiene, copolymers containing butadiene units and aromatic vinyl compound units, and hydrogenated products thereof.

[0017] [7] The methacrylic resin composition according to [2] or [6], wherein the graft copolymer (B) is a core-shell type graft copolymer particle in which at least a part of the surface of a core particle made of a butadiene rubber polymer (BR) is covered with a shell layer made of a methacrylic copolymer (M).

[0018] [8] The methacrylic resin composition according to any one of [1] to [7], 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).

[0019] [9] The methacrylic resin composition according to any one of [1] to [8], further comprising 0.0001 to 1.0 mass% of one or more organic phosphorus compounds (P).

[10] The methacrylic resin composition according to any one of [1] to [9], further comprising 1,000 to 5,000 ppm of one or more lubricants (L).

[0020]

[11] The methacrylic resin composition according to any one of [1] to

[10] , wherein a 3 mm thick plate made of the methacrylic resin composition has a haze value of 0 to 10% as measured in accordance with JIS K 7136.

[12] The methacrylic resin composition according to any one of [1] to

[11] , wherein a 1% thermal weight loss temperature as measured by thermogravimetric analysis under an inert gas atmosphere is 270°C or higher.

[0021]

[13] A method for producing a methacrylic resin composition according to any one of [1] to

[12] , comprising: a step (S1-1) of preparing polymerization raw materials containing multiple raw material monomers including methyl methacrylate and one or more isopropenyl aromatic compounds (I), and a polymerization initiator; a step (S1-2) of polymerizing the polymerization raw materials under conditions of a polymerization conversion rate of 30 to 60 mass% to obtain a resin solution containing a first methacrylic copolymer (A) or a precursor resin thereof; and a step (S1-3) of volatilizing and removing at least a portion of the raw material monomers present in the resin solution in one or more steps, wherein 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 (S1-2), and the resin solution being carried out in step (S1-3) so that the one or more organic disulfide compounds (D) are present in an amount of 1 to 1,000 ppm in the finally obtained methacrylic resin composition.

[0022]

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

[13] , 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 (S1-2), and the resin solution during step (S1-3).

[0023]

[15] A molded article comprising the methacrylic resin composition according to any one of [1] to

[12] .

[0024] According to the present disclosure, it is possible to provide a methacrylic resin composition that has good heat resistance and thermal decomposition resistance (thermal stability), is suppressed from discoloration such as yellowing, and has good moldability. According to the present disclosure, it is also possible to provide a methacrylic resin composition that contains a graft copolymer containing butadiene units and a methacrylic copolymer, and that has good transparency, heat resistance, surface hardness, and impact resistance at room temperature and low temperature.

[0025] 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.

[0026] [Methacrylic Resin Composition] The methacrylic resin composition of the present disclosure contains one or more first methacrylic copolymers (A) comprising 10 to 99 mass% of methyl methacrylate (MMA) units, 1 to 40 mass% of one or more isopropenyl aromatic compound units (UI), and 0 to 60 mass% of one or more other units (UO). The content of the methacrylic copolymers (A) in the methacrylic resin composition of the present disclosure (the total amount when multiple copolymers are present) is not particularly limited, but is preferably 10 to 99.9999 mass%. The methacrylic resin composition of the present disclosure has a total residual amount of raw material monomers of the methacrylic copolymer (A) of 0 to 1.00 mass%. The methacrylic resin composition of the present disclosure contains 1 to 1,000 ppm of one or more organic disulfide compounds (D).

[0027] The methacrylic resin composition of the present disclosure may further contain one or more optional components, as necessary. The methacrylic resin composition of the present disclosure may contain, as an optional component, one or more graft copolymers (B) obtained by graft copolymerizing a butadiene-based rubbery polymer (BR) containing 60 to 100% by mass of butadiene units with a methacrylic copolymer (M) containing 10 to 90% by mass of methyl methacrylate (MMA) units, 90 to 10% by mass of one or more aromatic vinyl compound units, and 49 to 0% by mass of one or more vinyl cyanide compound units. The methacrylic resin composition of the present disclosure may contain, as an optional component, one or more second methacrylic copolymers (C) containing 10 to 90% by mass of methyl methacrylate (MMA) units, 70 to 10% by mass of aromatic vinyl compound units other than isopropenyl aromatic compound units, and 49 to 0% by mass of vinyl cyanide compound units. In the methacrylic resin composition of the present disclosure, the content of the first methacrylic copolymer (A) may be 10 to 95% by mass, the content of the graft copolymer (B) may be 5 to 40% by mass, and the content of the second methacrylic copolymer (C) may be 0 to 85% by mass.

[0028] (Organic Disulfide Compound (D)) The methacrylic resin composition of the present disclosure contains 1 to 1,000 ppm of one or more organic disulfide compounds (D) as an additive. The lower limit is preferably 10 ppm, more preferably 20 ppm, even more preferably 50 ppm, even more preferably 70 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 900 ppm, more preferably 800 ppm, even 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.

[0029] As explained in the section "Problems to be Solved by the Invention," methacrylic copolymers containing MMA units and isopropenyl aromatic compound units (UI), such as αMSt units, generally tend to have relatively low thermal decomposition temperatures. Therefore, in methacrylic resin compositions containing such copolymers, the copolymer may thermally decompose 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 left in a 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.

[0030] 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.

[0031] Furthermore, as explained in the section entitled "Problems to be Solved by the Invention," heat-resistant (meth)acrylic resins generally tend to have high melt viscosities. Therefore, methacrylic resin compositions containing a rubber-reinforced styrene-based resin and a heat-resistant (meth)acrylic resin require relatively high temperatures during melt-kneading of multiple resins and during heating and melting during molding of the resin composition. In this case, gelation may occur due to thermal degradation of the rubber-reinforced styrene-based resin. This problem is particularly likely when the rubber-reinforced styrene-based resin contains butadiene units. Gelation is thought to occur due to crosslinking reactions between alkyl radicals under high-temperature heating. Gelation is undesirable because it can lead to reduced impact resistance at low temperatures (e.g., below freezing) and poor appearance of molded articles.

[0032] In the methacrylic resin composition 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 composition having a low residual monomer content and excellent heat resistance and thermal decomposition resistance (thermal stability) can be stably produced. Furthermore, the presence of the 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) having 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) having good heat resistance and mechanical properties, such as rigidity and surface hardness.

[0033] The methacrylic resin composition of the present disclosure, which contains an appropriate amount of organic disulfide compound (D), has excellent heat resistance and resistance to thermal decomposition (thermal stability) because the presence of the appropriate amount of organic disulfide compound (D) effectively suppresses thermal decomposition of the methacrylic copolymer (A), even when heated and melted during molding or other processing after resin production. The methacrylic resin composition of the present disclosure, which contains an appropriate amount of organic disulfide compound (D), can suppress poor appearance such as foaming due to thermal decomposition of the methacrylic copolymer (A), and can suppress discoloration such as yellowing, odor, and the like, even if the residence time in a heated and melted state is long during resin production, molding, or other processing.

[0034] In the methacrylic resin composition of the present disclosure, which contains a methacrylic copolymer (A), a graft copolymer (B), and an appropriate amount of an organic disulfide compound (D), the presence of an appropriate amount of the organic disulfide compound (D) can effectively suppress thermal degradation and thermal decomposition of each copolymer during heat melting, such as during production of the resin composition and molding processing. The appropriate amount of the organic disulfide compound (D) can suppress thermal degradation of the graft copolymer (B) containing butadiene units, and can effectively suppress gelation of the graft copolymer (B) containing butadiene units during heat melting, such as during production of the resin composition and molding processing. As a result of effectively suppressing thermal degradation and resulting gelation of the graft copolymer (B) containing butadiene units, a methacrylic resin composition with excellent impact resistance at room temperature (20 to 25°C) and low temperatures (e.g., below freezing) can be stably produced. Furthermore, even if the residence time in the heated and molten state is long during the production, molding, or other processes of the resin composition, poor appearance due to foaming caused by thermal decomposition of each copolymer and gelation of the graft copolymer (B) containing butadiene units can be suppressed, and discoloration such as yellowing and odors can be suppressed during the production, molding, or other processes of the resin composition.

[0035] It is believed that the organic disulfide compound (D) can effectively suppress the thermal decomposition of each copolymer by effectively capturing alkyl radicals generated by the thermal decomposition of each copolymer with thiyl radicals generated by cleavage of disulfide bonds.

[0036] For the above reasons, the methacrylic resin composition of the present disclosure containing the methacrylic copolymer (A) and an appropriate amount of the organic disulfide compound (D), and a molded article containing the same, can be excellent in heat resistance and thermal decomposition resistance (thermal stability), mechanical properties such as rigidity and surface hardness, moldability, appearance, etc. Furthermore, the methacrylic resin composition of the present disclosure containing the methacrylic copolymer (A), the graft copolymer (B), and an appropriate amount of the organic disulfide compound (D), and a molded article containing the same, can be excellent in heat resistance and thermal decomposition resistance (thermal stability), mechanical properties such as surface hardness and impact resistance at room temperature and low temperature, moldability, appearance, etc.

[0037] 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 any timing, such as before, during, or after the polymerization of the first methacrylic copolymer (A), the graft copolymer (B), or the second methacrylic copolymer (C), or during the production of the methacrylic resin composition.

[0038] (First Methacrylic Copolymer (A)) The methacrylic resin composition of the present disclosure contains one or more first methacrylic copolymers (A). The first methacrylic copolymer (A) contains methyl methacrylate (MMA) units and one or more isopropenyl aromatic compound units (UI), and may further contain one or more other units (UO).

[0039] The content of MMA units in the first methacrylic copolymer (A) is 10 to 99% by mass. The lower limit is preferably 20% by mass, more preferably 30% by mass, even more preferably 40% by mass, even more preferably 50% by mass, even more preferably 55% by mass, particularly preferably 60% by mass, and most preferably 65% ​​by mass. The upper limit is preferably 95% by mass, more preferably 90% by mass, particularly preferably 85% by mass, and most preferably 80% by mass.

[0040] The content of one or more isopropenyl aromatic compound units (UI) in the first methacrylic copolymer (A) (unless otherwise specified, the total amount when there are 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.

[0041] If the content of the isopropenyl aromatic compound unit (UI) is less than the above lower limit, the heat resistance of the first methacrylic copolymer (A) may be insufficient. If the content of the isopropenyl aromatic compound unit (UI) exceeds the above upper limit, the polymerizability, thermal decomposition resistance, and moldability of the first 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 first 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.

[0042] When the content of the MMA unit and the content of the isopropenyl aromatic compound unit (UI) are within the above ranges, the first methacrylic copolymer (A) can have good transparency, heat resistance, thermal decomposition resistance, polymerizability, 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 first methacrylic copolymer (A) is relatively easy to control, and the first methacrylic copolymer (A) having a uniform composition such as the content of the isopropenyl aromatic compound unit (UI) can be stably produced, and the first methacrylic copolymer (A) having good heat resistance and mechanical properties such as rigidity and surface hardness can be stably produced.

[0043] The first 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)).

[0044] 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 aromatic vinyl compounds other than the isopropenyl aromatic compound (I), such as 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 1,1-diphenylethylene. From the viewpoints of the melt flowability and productivity of the first methacrylic copolymer (A), styrene (St) is preferred.

[0045] The first methacrylic copolymer (A) may contain, as the one or more other units (UO), one or more ring structural units (UR) selected from the group consisting of an acid anhydride unit, an imide unit having a ring structure, and a lactone ring unit, instead of or in addition to the aromatic vinyl compound unit other than the isopropenyl aromatic compound unit. The methacrylic copolymer (A) containing the ring structural unit (UR) has high heat resistance and is therefore preferred.

[0046] The first methacrylic copolymer (A) having no cyclic structural unit (UR) in the main chain can be produced by copolymerizing a monomer mixture containing methyl methacrylate (MMA) and one or more isopropenyl aromatic compounds (I), and optionally one or more other monomers (O), by a known method. Examples of methods for producing the first methacrylic copolymer (A) having a cyclic structural unit (UR) in the main chain include a method of copolymerizing multiple monomers, including methyl methacrylate (MMA), one or more isopropenyl aromatic compounds (I), raw monomers for the cyclic structural unit (UR), and optionally other monomers, by a known method; and a method of copolymerizing a methacrylic copolymer having an MMA unit and one or more isopropenyl aromatic compound units (UI) but no cyclic structural unit (UR), by a known method, and then introducing a cyclic structure into the main chain to form the cyclic structural unit (UR). Examples of polymerization methods for methacrylic copolymers include radical polymerization methods such as (continuous) bulk polymerization, suspension polymerization, solution polymerization, and emulsion polymerization; and anionic polymerization.

[0047] The content of the ring structural unit (UR) in the first methacrylic copolymer (A) (unless otherwise specified, the total amount when there are multiple types) is 0 to 60% by mass. The lower limit is preferably 5% by mass. The upper limit is preferably 55% by mass, more preferably 50% by mass, even more preferably 40% by mass, particularly preferably 30% by mass, and most preferably 20% by mass.

[0048] Examples of the acid anhydride unit include a maleic anhydride (Mah) unit, a glutaric anhydride unit, and an itaconic anhydride unit, and preferred is a maleic anhydride (Mah) unit. Examples of the imide unit containing a ring structure include an unsubstituted or N-substituted glutarimide unit and an unsubstituted or N-substituted maleimide unit.

[0049] The glutarimide (GI) unit is a unit having an unsubstituted or N-substituted 2,6-dioxopiperidinediyl structure, and examples thereof include units represented by the following general formula (I):

[0050] (I)

[0051] In formula (I), two R １are each independently a hydrogen atom or a methyl group, and two R １ Preferably, both R are methyl groups. ２ represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an organic group having 6 to 15 carbon atoms and containing an aromatic ring, and is preferably a hydrogen atom, a methyl group, an n-butyl group, a cyclohexyl group, or a benzyl group, more preferably a methyl group, an n-butyl group, or a cyclohexyl group, and particularly preferably a methyl group.

[0052] The first methacrylic copolymer (A) containing glutarimide (GI) units can have properties such as a high glass transition temperature (Tg), good impact resistance, and good dimensional and shape stability against temperature. The first methacrylic copolymer (A) containing glutarimide (GI) units can be produced by known methods described in, for example, WO 2005 / 108438, JP 2010-254742 A, JP 2008-273140 A, and JP 2008-274187 A.

[0053] A method for producing the first methacrylic copolymer (A) containing glutarimide (GI) units may include an imide cyclization reaction step in which an imidizing agent is added to a precursor resin having two adjacent methyl methacrylate (MMA) units and reacted with the precursor resin. Examples of the imidizing agent include ammonia; aliphatic hydrocarbon group-containing amines such as methylamine (also referred to as monomethylamine), ethylamine, diethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, t-butylamine, and n-hexylamine; aromatic hydrocarbon group-containing amines such as aniline, toluidine, trichloroaniline, and n-methylbenzylamine; alicyclic hydrocarbon group-containing amines such as cyclohexylamine and n-methylcyclohexylamine; and urea compounds such as urea, 1,3-dimethylurea, 1,3-diethylurea, and 1,3-dipropylurea. Among these, methylamine is preferred.

[0054] The unsubstituted or N-substituted maleimide unit is a unit having an unsubstituted or N-substituted 2,5-pyrrolidinedione structure, and examples thereof include a unit represented by the following formula (II) (also referred to as maleimide unit (II)).

[0055] (II)

[0056] In formula (II), two R １１ are each independently a hydrogen atom or a methyl group, and two R １１ Preferably, both R are methyl groups. １２ represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an organic group having 6 to 15 carbon atoms and containing an aromatic ring, and is preferably a methyl group, an n-butyl group, a cyclohexyl group, or a benzyl group, more preferably a methyl group, an n-butyl group, or a benzyl group, and particularly preferably a methyl group.

[0057] Examples of methods for producing the first methacrylic copolymer (A) containing maleimide units include a method of polymerizing a monomer mixture containing a monomer containing a maleimide unit, and a method of reacting maleic anhydride units in a polymerization reaction product of a monomer mixture containing maleic anhydride with an imidizing agent. For the latter method, see JP-B Nos. 61-026924, 7-042332, 9-100322, and 2001-329021.

[0058] Examples of monomers containing a maleimide unit include N-alkylmaleimides such as N-methylmaleimide, N-ethylmaleimide, N-butylmaleimide, and N-cyclohexylmaleimide (ChMI); and N-arylmaleimides such as N-phenylmaleimide (PhMI), N-methylphenylmaleimide, and N-chlorophenylmaleimide. N-cyclohexylmaleimide (ChMI) and N-phenylmaleimide (PhMI) are preferred.

[0059] A lactone ring unit is a unit containing a >CH—O—C(═O)— group in its ring structure. The unit containing a >CH—O—C(═O)— group in its ring structure preferably has 4 to 8, more preferably 5 to 6, and most preferably 6, ring constituent elements. Examples of units containing a >CH—O—C(═O)— group in its ring structure include lactone diyl units such as β-propiolactone diyl unit, γ-butyrolactone diyl unit, and δ-valerolactone diyl unit. In the formula, ">C" means that the carbon atom C has two bonds.

[0060] For example, the δ-valerolactonediyl unit may be a unit represented by the following formula (III) (also referred to as lactone ring unit (III)).

[0061] (III)

[0062] In formula (III), R ２１ , R ２２ , and R ２３ are each independently a hydrogen atom or an organic group having 1 to 20 carbon atoms, preferably a hydrogen atom or an organic group having 1 to 10 carbon atoms, more preferably a hydrogen atom or an organic group having 1 to 5 carbon atoms. Here, the organic group is not particularly limited as long as it has 1 to 20 carbon atoms, and examples thereof include a linear or branched alkyl group, a linear or branched aryl group, -OCOCH ３ The organic group may contain a heteroatom such as an oxygen atom. ２２ is a methyl group, and R ２１ and R ２３ is a hydrogen atom.

[0063] The lactone ring unit can be obtained by intramolecular cyclization of a hydroxy group and an ester group, for example, by intramolecular cyclization of a 2-(hydroxyalkyl)acrylate unit and a methyl (meth)acrylate unit (see JP-A Nos. 2000-230016, 2001-151814, 2002-120326, 2002-254544, and 2005-146084).

[0064] The glutaric anhydride unit is a unit having a 2,6-dioxodihydropyrandiyl structure, and examples thereof include a unit represented by formula (IV) (also referred to as glutaric anhydride unit (IV)).

[0065] (IV)

[0066] In formula (IV), two R ３１ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and are preferably a methyl group.

[0067] The glutaric anhydride unit can be obtained by intramolecular cyclization of two adjacent (meth)acrylic acid units, or intramolecular cyclization of a (meth)acrylic acid unit and a methyl (meth)acrylate unit, etc. See JP-A-2007-197703 and JP-A-2010-96919, etc.

[0068] The weight average molecular weight (Mw) of the first methacrylic copolymer (A) is not particularly limited and is preferably 40,000 to 400,000. The lower limit is more preferably 50,000, and particularly preferably 60,000. The upper limit is more preferably 300,000, and particularly preferably 200,000. When the Mw of the first methacrylic copolymer (A) is equal to or greater than the lower limit, the copolymer can have excellent mechanical properties. When the Mw is equal to or less than the upper limit, the copolymer can have excellent melt fluidity and moldability. Unless otherwise specified, in this specification, the "weight average molecular weight (Mw)" refers to the weight average molecular weight calculated in terms of standard polymethyl methacrylate (PMMA) as determined by gel permeation chromatography (GPC) analysis using a differential refractive index detector.

[0069] The molecular weight distribution (Mw / Mn) of the first methacrylic resin (A) is not particularly limited and is preferably 1.5 to 2.5. The lower limit is more preferably 1.8, and the upper limit is more preferably 2.3. When Mw / Mn is equal to or greater than the lower limit, the methacrylic resin (A) tends to have excellent melt fluidity and moldability, and when Mw / Mn is equal to or less than the upper limit, the methacrylic resin (A) tends to have excellent mechanical properties such as impact resistance and toughness.

[0070] The glass transition temperature (Tg) of the first methacrylic copolymer (A) is preferably 120°C or higher. The lower limit is preferably 123°C, more preferably 125°C, and particularly 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 first methacrylic copolymer (A), which is preferable. A molded article containing a first methacrylic copolymer (A) with a high Tg is 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 section [Examples] below.

[0071] The methacrylic resin composition of the present disclosure, which contains a methacrylic resin (A), a methacrylic copolymer (A), and an appropriate amount of an organic disulfide compound (D), can exhibit excellent molding processability. The melt flow rate (MFR) can be used as an indicator of molding processability. The MFR of the methacrylic resin composition of the present disclosure, which contains a methacrylic resin (A), a methacrylic copolymer (A), and an appropriate amount of an organic disulfide compound (D), 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, and particularly preferably 3 g / 10 min. The upper limit is more preferably 15 g / 10 min, and particularly preferably 10 g / 10 min. Unless otherwise specified, the MFR of a methacrylic resin (composition) 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.

[0072] The content of the first methacrylic copolymer (A) in the methacrylic resin composition of the present disclosure is preferably 10 to 99.9999% by mass from the viewpoints of heat resistance, surface hardness, etc. The lower limit is more preferably 15% by mass, even more preferably 20% by mass, even more preferably 30% by mass, particularly preferably 40% by mass, and most preferably 50% by mass. The upper limit can be 99.9%, 99.5%, 99%, 98%, 97%, 96%, 95%, 92%, 90%, 88%, or 85% by mass.

[0073] The methacrylic resin composition of the present disclosure contains one or more organic disulfide compounds (D). The timing of adding the organic disulfide compound (D) is not particularly limited. The methacrylic resin composition of the present disclosure is preferably an organic disulfide compound-added methacrylic copolymer (AD) containing a first methacrylic copolymer (A) and an organic disulfide compound (D), or may contain such an organic disulfide compound-added methacrylic copolymer (AD).

[0074] (Total Amount of Residual Raw Material Monomers) In the methacrylic resin composition 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. The methacrylic resin composition of the present disclosure contains 1 to 1,000 ppm of one or more organic disulfide compounds (D). In the method for producing a methacrylic resin composition of the present disclosure, one or more organic disulfide compounds (D) can be added to the polymerization raw materials and / or intermediate products so that the one or more organic disulfide compounds (D) are present in an amount of 1 to 1,000 ppm in the final methacrylic resin composition of the present disclosure. According to the methacrylic resin composition and its production method of the present disclosure, 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, the decrease in heat resistance of the methacrylic resin composition due to the presence of residual monomers can be effectively suppressed. The organic disulfide compound (D) can effectively suppress the thermal decomposition of the methacrylic copolymer (A) even when used in a small amount, so that discoloration such as yellowing of the methacrylic resin composition due to the addition of the organic disulfide compound (D) can be suppressed.

[0075] In the methacrylic resin composition of the present disclosure, the total residual amount of raw material monomers of the methacrylic copolymer (A) is 0 to 1.00 mass%, with the upper limit being preferably 0.80 mass%, more preferably 0.75 mass%, even more preferably 0.70 mass%, even more preferably 0.65 mass%, even more preferably 0.60 mass%, particularly preferably 0.55 mass%, and most preferably 0.50 mass%.

[0076] The amount of methyl methacrylate (MMA) remaining in the methacrylic resin composition 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.

[0077] The content of the isopropenyl aromatic compound (I) remaining in the methacrylic resin composition 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%.

[0078] The content of the other monomer (O) remaining in the methacrylic resin composition 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%.

[0079] Unless otherwise specified, in this specification, the "weight average molecular weight (Mw)" is the weight average molecular weight calculated as a standard polymethyl methacrylate (PMMA) determined by gel permeation chromatography (GPC) analysis using a differential refractive index detector. Similarly, the "number average molecular weight (Mn)" is the number average molecular weight calculated as a standard polymethyl methacrylate (PMMA) determined by gel permeation chromatography (GPC) analysis using a differential refractive index detector.

[0080] (Graft Copolymer (B)) The methacrylic resin composition of the present disclosure may contain one or more graft copolymers (B) as an optional component. The graft copolymer (B) is obtained by graft copolymerizing a methacrylic copolymer (M) with a butadiene rubber-like polymer (BR) that contains butadiene units and may further contain one or more other units. The methacrylic copolymer (M) contains methyl methacrylate (MMA) units and one or more aromatic vinyl compound units. The methacrylic copolymer (M) may further contain one or more vinyl cyanide compound units and may further contain one or more other units.

[0081] The butadiene rubber polymer (BR) has a butadiene unit content of 60 to 100% by mass. The lower limit is preferably 65% ​​by mass, more preferably 70% by mass. The present disclosure can effectively suppress gelation during heat melting even when a graft copolymer (B) having a high butadiene unit content is used.

[0082] The content of MMA units in the methacrylic copolymer (M) is 10 to 90% by mass. The lower limit is preferably 20% by mass, more preferably 30% by mass, particularly preferably 40% by mass, and most preferably 50% by mass. The upper limit is preferably 85% by mass, more preferably 80% by mass. The content of one or more aromatic vinyl compound units in the methacrylic copolymer (M) (total amount if multiple types are present unless otherwise specified) is 90 to 10% by mass. The lower limit is preferably 15% by mass, more preferably 20% by mass. The upper limit is preferably 80% by mass, more preferably 70% by mass, particularly preferably 60% by mass, and most preferably 50% by mass. The content of one or more vinyl cyanide compound units in the methacrylic copolymer (M) (total amount if multiple types are present unless otherwise specified) is 49 to 0% by mass. The upper limit is preferably 45% by mass, more preferably 40% by mass, particularly preferably 35% by mass, and most preferably 30% by mass. The content of one or more other monomer units in the methacrylic copolymer (M) (unless otherwise specified, the total amount in the case of a plurality of types) is not particularly limited, and is preferably 0 to 5% by mass.

[0083] When the contents of the MMA unit, aromatic vinyl compound unit, and vinyl cyanide compound unit in the methacrylic copolymer (M) are within the above ranges, the methacrylic copolymer (M) can have good heat resistance and polymerizability. It is relatively easy to control the copolymerization of the aromatic vinyl compound unit, and it is easy to obtain a methacrylic copolymer (M) having a uniform composition, such as the content of the aromatic vinyl compound unit.

[0084] Examples of units other than butadiene units that can be contained in the butadiene-based rubbery polymer (BR) include conjugated diene compound units other than butadiene units, aromatic vinyl compound units, and vinyl cyanide compound units. The conjugated diene compounds other than butadiene are not particularly limited, and include isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. Preferred examples of aromatic vinyl compounds, vinyl cyanide compounds, and other monomers are the same as those for the second methacrylic copolymer (C) described below.

[0085] The butadiene-based rubbery polymer (BR) may be a hydrogenated product in which at least a portion of one or more conjugated diene compound units containing butadiene units has been hydrogenated (also referred to as hydrogenation).The butadiene-based rubbery polymer (BR) may be one or more rubbery polymers selected from the group consisting of polybutadiene, a copolymer containing butadiene units and aromatic vinyl compound units (preferably styrene units), a copolymer containing butadiene units and vinyl cyanide compound (preferably acrylonitrile units), and hydrogenated products thereof.

[0086] The content of the butadiene-based rubbery polymer (BR) in the graft copolymer (B) is not particularly limited and is preferably 40 to 80% by mass. The upper limit is more preferably 55% by mass. The content of the methacrylic copolymer (M) in the graft copolymer (B) is not particularly limited and is preferably 60 to 20% by mass. The lower limit is more preferably 45% by mass. When the content of the butadiene-based rubbery polymer (BR) in the graft copolymer (B) is equal to or greater than the above-mentioned lower limit, the graft copolymer (B) and the methacrylic resin composition of the present disclosure containing the same can have excellent impact resistance. When the content of the methacrylic copolymer (M) in the graft copolymer (B) is equal to or greater than the above-mentioned lower limit, the graft copolymer (B) and the methacrylic resin composition of the present disclosure containing the same can have excellent heat resistance and molding processability.

[0087] The form of the graft copolymer (B) is not particularly limited, and is preferably a core-shell type graft copolymer particle in which at least a part of the surface of a core particle made of a butadiene rubber-like polymer (BR) is covered with a shell layer made of a methacrylic copolymer (M). The shell layer made of a methacrylic copolymer (M) is also called a graft layer.

[0088] The volume average particle diameter (d50) of the graft copolymer (B) is not particularly limited and is preferably 0.20 to 0.60 μm. The lower limit is more preferably 0.25 μm, particularly preferably 0.30 μm, and most preferably 0.35 μm. The upper limit is more preferably 0.50 μm, particularly preferably 0.40 μm. When the volume average particle diameter (d50) is equal to or greater than the above lower limit, the graft copolymer (B) and the methacrylic resin composition of the present disclosure can have excellent impact resistance. When the volume average particle diameter (d50) is equal to or less than the above upper limit, the methacrylic resin composition of the present disclosure can have excellent transparency and moldability.

[0089] The volume average particle size (d50) of the graft copolymer (B) can be adjusted by the volume average particle size (d50) of the core particles made of the butadiene rubber-like polymer (BR) and the polymerization conditions such as the mass ratio of the butadiene rubber-like polymer (BR) to the methacrylic copolymer (M). In this specification, unless otherwise specified, the "volume average particle size (d50)" refers to the volume-based median size measured using a light-scattering particle size distribution analyzer.

[0090] The graft copolymer (B) can be produced by a known method. The production method of the graft copolymer (B) can include the steps of: (SB-1) preparing core particles made of a butadiene rubber-like polymer (BR) and a plurality of raw material monomers for the methacrylic copolymer (M) (specifically, a plurality of monomers containing methyl methacrylate (MMA) and one or more aromatic vinyl compound units); and (SB-2) copolymerizing the plurality of raw material monomers for the methacrylic copolymer (M) in the presence of the core particles.

[0091] Examples of copolymerization methods used in step (SB-2) include bulk polymerization, solution polymerization, suspension polymerization, bulk-suspension polymerization, and emulsion polymerization, with emulsion polymerization being preferred. In step (SB-2), a polymerization initiator and, if necessary, a chain transfer agent can be used. Examples of polymerization initiators and chain transfer agents are the same as those in step (S1-1) described below. The amount of polymerization initiator used is not particularly limited, and is preferably 0.1 to 0.5 parts by mass, more preferably 0.5 to 3.5 parts by mass, per 100 parts by mass of the total amount of raw material monomers. The polymerization temperature is not particularly limited, and is preferably 50 to 98°C. The lower limit is more preferably 55°C, and the upper limit is more preferably 90°C.

[0092] In step (SB-2), a methacrylic copolymer that is not bonded to the butadiene-based rubber-like polymer (BR) may be produced as a by-product. Therefore, the graft copolymer (B) may contain a small amount (for example, about 0 to 15% by mass) of a by-product methacrylic copolymer that is not bonded to the butadiene-based rubber-like polymer (BR). The unit composition of the methacrylic copolymer (M) that constitutes the graft chain of the graft copolymer (B) is usually the same as the unit composition of the by-product methacrylic copolymer that is not bonded to the butadiene-based rubber-like polymer (BR).

[0093] When the methacrylic resin composition of the present disclosure contains graft copolymer (B), the content of graft copolymer (B) in the methacrylic resin composition of the present disclosure is preferably 5 to 40% by mass. The lower limit is more preferably 8% by mass, particularly preferably 10% by mass, and most preferably 15% by mass. The upper limit is more preferably 35% by mass, particularly preferably 30% by mass, and most preferably 25% by mass. When the content of graft copolymer (B) is equal to or greater than the lower limit, the methacrylic resin composition of the present disclosure can have excellent impact resistance, and when the content is equal to or less than the upper limit, the methacrylic resin composition can have excellent heat resistance and surface hardness.

[0094] (Second Methacrylic Copolymer (C)) The methacrylic resin composition of the present disclosure can contain one or more second methacrylic copolymers (C) as an optional component. The second methacrylic copolymer (C) contains methyl methacrylate (MMA) units and one or more aromatic vinyl compound units other than isopropenyl aromatic compound units. The second methacrylic copolymer (C) can further contain one or more vinyl cyanide compound units, and can further contain one or more other units. The second methacrylic copolymer (C) can be free of isopropenyl aromatic compound units.

[0095] The content of MMA units in the second methacrylic copolymer (C) is 10 to 90% by mass. The lower limit is preferably 20% by mass, more preferably 30% by mass, particularly preferably 40% by mass, and most preferably 50% by mass. The upper limit is preferably 85% by mass, more preferably 80% by mass, and particularly preferably 75% by mass. The content of one or more aromatic vinyl compound units in the second methacrylic copolymer (C) (total amount in the case of multiple types unless otherwise specified) is 70 to 10% by mass. The lower limit is preferably 5% by mass, more preferably 10% by mass, even more preferably 12% by mass, particularly preferably 15% by mass, and most preferably 20% by mass. The upper limit is preferably 60% by mass, more preferably 50% by mass, even more preferably 40% by mass, particularly preferably 30% by mass, and most preferably 25% by mass. The content of one or more vinyl cyanide compound units in the second methacrylic copolymer (C) (the total amount if there are multiple types unless otherwise specified) is 49 to 0 mass%. The upper limit is preferably 45 mass%, more preferably 40 mass%, particularly preferably 35 mass%, and most preferably 30 mass%. The content of one or more other monomer units in the second methacrylic copolymer (C) (the total amount if there are multiple types unless otherwise specified) is not particularly limited, and is preferably 0 to 5 mass%.

[0096] When the contents of the MMA unit, the aromatic vinyl compound unit, and the vinyl cyanide compound unit are within the above ranges, the second methacrylic copolymer (C) can have good transparency, heat resistance, polymerizability, and moldability. Furthermore, when the contents of the MMA unit and the aromatic vinyl compound unit are within the above ranges, the copolymerization of the aromatic vinyl compound unit in the second methacrylic copolymer (C) is relatively easy to control, and a second methacrylic copolymer (C) having a uniform composition, such as the content of the aromatic vinyl compound unit, can be stably produced, and a second methacrylic copolymer (C) having good heat resistance and mechanical properties, such as rigidity and surface hardness, can be stably produced.

[0097] The second methacrylic copolymer (C) is obtained by copolymerizing methyl methacrylate (MMA), one or more aromatic vinyl compounds, optionally one or more vinyl cyanide compounds, and optionally one or more other monomers. The aromatic vinyl compounds other than the isopropenyl aromatic compounds are not particularly limited, and examples thereof 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 1,1-diphenylethylene. From the viewpoints of the melt flowability and productivity of the second methacrylic copolymer (C), styrene (St) is preferred.

[0098] The vinyl cyanide compound is not particularly limited, and examples thereof include acrylonitrile (AN), methacrylonitrile, fumaronitrile, and vinylidene cyanide. From the viewpoints of availability and refractive index adjustment, acrylonitrile (AN) is preferred. Examples of other monomers include vinyl monomers having one polymerizable unsaturated bond per molecule other than methyl methacrylate (MMA) and aromatic vinyl compounds. Examples include (meth)acrylic acid; (meth)acrylic acid esters other than MMA; and (meth)acrylamide.

[0099] The weight average molecular weight (Mw) of the second methacrylic copolymer (C) is not particularly limited and is preferably 40,000 to 400,000. The lower limit is more preferably 50,000, and particularly preferably 60,000. The upper limit is more preferably 300,000, and particularly preferably 200,000. When the Mw of the second methacrylic copolymer (C) is equal to or greater than the lower limit, the copolymer can have excellent mechanical properties, and when the Mw is equal to or less than the upper limit, the copolymer can have excellent melt fluidity and molding processability.

[0100] The glass transition temperature (Tg) of the second methacrylic copolymer (C) is not particularly limited, and from the viewpoint of heat resistance, it is preferably 95°C or higher. The lower limit is more preferably 98°C, particularly preferably 100°C. From the viewpoint of the molding processability of the methacrylic resin composition of the present disclosure, the Tg of the second methacrylic copolymer (C) is preferably lower than the Tg of the first methacrylic copolymer (A). The upper limit of the Tg of the second methacrylic copolymer (C) is preferably 125°C, more preferably 120°C, even more preferably 115°C, even more preferably 110°C, particularly preferably 107°C, and most preferably 105°C.

[0101] The content of the second methacrylic copolymer (C) in the methacrylic resin composition of the present disclosure is preferably 0 to 85% by mass. The lower limit is more preferably 5% by mass, and particularly preferably 10% by mass. The upper limit is more preferably 70% by mass, and particularly preferably 60% by mass. The methacrylic resin composition of the present disclosure containing an appropriate amount of the second methacrylic copolymer (C) can have excellent moldability.

[0102] (Relationship between refractive indexes) The methacrylic resin composition of the present disclosure, which contains the first methacrylic copolymer (A) and the graft copolymer (B) and may optionally contain the second methacrylic copolymer (C), preferably satisfies the following formula (1): 0≦|n ｂ -n ｍ |≦0.01 (1) In the above formula, n ｍ is defined by the following formula (2): ｍ = (n ａ ×w ａ +n ｃ ×w ｃ ) / (w ａ +w ｃ ) (2) In the above formula, n ａ , n ｂ , n ｃ are the refractive indices at 23°C for the sodium D line of the first methacrylic copolymer (A), the graft copolymer (B), and the second methacrylic copolymer (C), respectively. ａ , w ｂ , w ｃand w are the mass ratios of the first methacrylic copolymer (A), the graft copolymer (B), and the second methacrylic copolymer (C) to the total mass of the first methacrylic copolymer (A), the graft copolymer (B), and the second methacrylic copolymer (C) in the methacrylic resin composition. ａ +w ｂ +w ｃ =1.

[0103] n ｍ is the average refractive index of the matrix resin composed of the first methacrylic copolymer (A) and the second methacrylic copolymer (C) which may be contained as an optional component. ｂ -n ｍ | is the difference between the refractive index of the graft copolymer (B) as the rubber component and the average refractive index of the matrix resin (also referred to as the refractive index difference (Δn)). When the refractive index difference (Δn) is 0.01 or less, the methacrylic resin composition of the present disclosure, which includes the first methacrylic copolymer (A) and the graft copolymer (B) and may also include the second methacrylic copolymer (C), can have reduced light scattering at the boundary between the matrix resin and the rubber component and have high transparency. A smaller refractive index difference (Δn) is preferable, and the upper limit is preferably 0.008, more preferably 0.005, even more preferably 0.003, particularly preferably 0.002, and most preferably 0.001. The ideal value of the refractive index difference (Δn) is 0.

[0104] As long as the above formula (1) is satisfied, the refractive index (n) of each copolymer is not particularly limited. ａ ) can be, for example, 1.500 to 1.570. The lower limit is more preferably 1.505, particularly preferably 1.510, and most preferably 1.515. The upper limit is preferably 1.560, more preferably 1.550, even more preferably 1.540, particularly preferably 1.530, and most preferably 1.520. The refractive index (n ｂ) can be, for example, 1.500 to 1.570. The lower limit is more preferably 1.505, particularly preferably 1.510, and most preferably 1.515. The upper limit is preferably 1.560, more preferably 1.550, even more preferably 1.540, particularly preferably 1.530, and most preferably 1.520. The refractive index (n ｃ ) can be, for example, 1.500 to 1.570. The lower limit is more preferably 1.505, particularly preferably 1.510, and most preferably 1.515. The upper limit is preferably 1.560, more preferably 1.550, even more preferably 1.540, particularly preferably 1.530, and most preferably 1.520. |n ａ -n ｂ is not particularly limited, the smaller the better, and is preferably 0 to 0.01. The upper limit is preferably 0.008, more preferably 0.005, and even more preferably 0.003. ａ -n ｃ | and |n ｂ -n ｃ The preferred range of | is |n ａ -n ｂ |Same as.

[0105] Since the refractive index of the methacrylic copolymers (A) and (C) mainly depends on the unit composition of the copolymer, the refractive index of the methacrylic copolymers (A) and (C) can be adjusted to a desired range by adjusting the raw material monomer composition. The refractive index of the methacrylic copolymers (A) and (C) can be estimated from the refractive index of the homopolymer of each monomer and the mass ratio of each monomer. For example, the refractive index (n ＸＹＺ The theoretical value of n ＸＹＺ = n Ｘ ×w Ｘ +n Ｙ ×w Ｙ +n Ｚ ×w Ｚ In the above formula, n Ｘ , n Ｙ , n Ｚare the refractive indices of the homopolymer of monomer X, the homopolymer of monomer Y, and the homopolymer of monomer Z, respectively. Ｘ , w Ｙ , w Ｚ are the mass fractions of the monomer X unit, the monomer Y unit, and the monomer Z unit in the copolymer, respectively. Ｘ +w Ｙ +w Ｚ =1.

[0106] The refractive index of the graft copolymer (B) can be adjusted to a desired range by adjusting the unit composition of the butadiene rubber polymer (BR) and / or the raw material monomer composition of the methacrylic copolymer (M) which is the graft chain. The refractive index of the graft copolymer (B) can also be estimated from the unit composition of the butadiene rubber polymer (BR) and the unit composition of the methacrylic copolymer (M) which is the graft chain, similar to the refractive indexes of the methacrylic copolymers (A) and (C).

[0107] The average refractive index (n ｍ ), and the refractive index (n ｂ ) can be measured as follows. A solvent in which a matrix resin composed of a first methacrylic copolymer (A) and a second methacrylic copolymer (C), which may be contained as an optional component, is soluble is added to the methacrylic resin composition of the present disclosure to dissolve the matrix resin. The resulting cloudy solution is separated into a solvent-soluble component and a solvent-insoluble component by a procedure such as centrifugation. The soluble component (matrix resin) and the insoluble component (graft copolymer (B)) are each purified, and the refractive index is measured. In this specification, unless otherwise specified, the "refractive index" refers to the refractive index at 23°C relative to the sodium D line, and is determined by the method described in the "Examples" section below.

[0108] (Other Polymers) The methacrylic resin composition of the present disclosure can contain one or more other polymers to the extent that the effects of the present disclosure are not impaired. Examples of other polymers include methacrylic resins other than the above-mentioned methacrylic copolymers (A) and (C); polyolefin resins such as polyethylene, polypropylene, polybutene-1, poly-4-methylpentene-1, and polynorbornene; styrene resins such as polystyrene, styrene-maleic anhydride copolymer (SMA 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, methacrylic butadiene styrene (MBS) resin, and silicon-acrylonitrile-styrene (SAS) resin; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; and polyamide resins such as nylon 6, nylon 66, and polyamide elastomer. Examples of the thermoplastic resin include olefin-based resins; polyimides, polyetherimides; polycarbonate-based resins; other thermoplastic resins such as polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polyvinyl alcohol, ethylene-vinyl alcohol copolymers, polyacetal, ethylene-vinyl acetate copolymers, phenoxy-based resins, polysulfones, polyphenylene sulfide, polyether ether ketones, polyphenylene oxides, modified polyphenylene ethers, and ethylene-based ionomers; thermosetting resins such as phenol-based resins, melamine-based resins, silicone-based resins, and epoxy-based resins; polyurethanes and chlorinated polyurethane resins; silicone-modified resins; acrylic rubbers, silicone rubbers; acrylic thermoplastic elastomers such as acrylic multilayered polymer particles and acrylic block copolymers; styrene-based thermoplastic elastomers such as SEPS, SEBS, and SIS; and olefin-based rubbers such as IR, EPR, and EPDM.

[0109] The total content of the first methacrylic copolymer (A), the graft copolymer (B), and the second methacrylic copolymer (C) in the methacrylic resin composition of the present disclosure is preferably 90 to 100% by mass. The lower limit is more preferably 95% by mass. The amount of other polymers in the methacrylic resin composition of the present disclosure (total amount if multiple types are present, unless otherwise specified) is preferably 10 to 0% by mass. The upper limit is more preferably 5% by mass.

[0110] (Organic Phosphorus Compound (P)) The methacrylic resin composition 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.

[0111] 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.

[0112] 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.).

[0113] 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.).

[0114] 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.

[0115] The content of the organophosphorus compound (P) in the methacrylic resin composition 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.

[0116] 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 composition of the present disclosure.

[0117] In the methacrylic resin composition 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 viewpoints 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.

[0118] (Lubricant (L)) The methacrylic resin composition of the present disclosure may contain one or more lubricants (L) as additives, if necessary. The methacrylic resin composition of the present disclosure containing one or more lubricants (L) can 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; aliphatic 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), aliphatic alcohols and glycerin fatty acid monoesters may be used in combination. In this case, the mass ratio of the aliphatic alcohol to the glycerin fatty acid monoester 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 composition of the present disclosure (the total amount if multiple types are used unless otherwise specified) is not particularly limited, but is preferably 1000 to 5000 ppm. The upper limit is more preferably 4500 ppm, particularly preferably 4000 ppm, and most preferably 3500 ppm.

[0119] (Filler) The methacrylic resin composition of the present disclosure may contain one or more fillers as additives, as needed, to the extent that the effects of the present disclosure are not impaired. Examples of fillers include inorganic fine particles containing metal oxides such as silicon oxide (silica) and titanium oxide, metal carbonates such as calcium carbonate and magnesium carbonate, metal sulfates such as barium sulfate, carbon black, talc, clay, or combinations thereof; organic fine particles such as polysiloxane-based crosslinked polymer fine particles; and combinations thereof. The filler can function as a light diffusing agent or a matting agent. From the viewpoint of transparency, the content of the filler in the methacrylic resin composition of the present disclosure is preferably as low as possible, preferably 0 to 3% by mass. The upper limit is more preferably 1.5% by mass, particularly preferably 1% by mass, and most preferably 0.5% by mass. The methacrylic resin composition of the present disclosure preferably does not contain any particles other than the core-shell graft copolymer particles composed of the graft copolymer (B).

[0120] (Additives Other Than the Above) The methacrylic resin composition of the present disclosure may optionally contain one or more additives other than the organic disulfide compound (D), the organic phosphorus compound (P), the lubricant (L), and the filler. Examples of such additives include non-phosphorus antioxidants, heat degradation inhibitors, UV absorbers, light stabilizers, mold release agents, polymer processing aids, antistatic agents, flame retardants, colorants (dyes, pigments, organic dyes, etc.), fluorescent materials, antistatic agents, plasticizers, surfactants, foaming agents, and defoamers. The content of the additives other than the organic disulfide compound (D), the organic phosphorus compound (P), the lubricant (L), and the filler in the methacrylic resin composition of the present disclosure (the total amount if multiple additives are present, unless otherwise specified) is preferably 0 to 7% by mass, from the viewpoint of suppressing poor appearance such as silver in the molded article. The upper limit is more preferably 5% by mass, and particularly preferably 4% by mass. The timing of adding other polymers that can be contained in the methacrylic resin composition of the present disclosure and additives other than the organic disulfide compound (D) is not particularly limited and may be arbitrarily added, similar to the timing of adding the organic disulfide compound (D).

[0121] (Physical Properties) The methacrylic resin composition of the present disclosure can have excellent transparency. The haze value of a 3 mm thick flat plate made of the methacrylic resin composition of the present disclosure, measured in accordance with JIS K7136, can be 0 to 10%. The upper limit is preferably 7%, more preferably 5%, and particularly preferably 4%. The lower limit can be, for example, 0.01%.

[0122] The methacrylic resin composition of the present disclosure can have 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 composition of the present disclosure can be, for example, 270°C or higher, 275°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, 360°C or 350°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, a TG curve can be obtained by performing thermogravimetric analysis (TGA) under conditions of heating from room temperature (20-25°C) to 500°C at a heating rate of 10°C / min under a nitrogen atmosphere, and the 1% thermal weight loss temperature can be determined from this TG curve.

[0123] The methacrylic resin composition of the present disclosure can have excellent heat resistance and rigidity even under load. The deflection temperature under load (HDT) of a test piece made of the methacrylic resin composition of the present disclosure, which is 80 mm long, 10 mm wide, and 4 mm thick, measured in accordance with JIS K7191, can be, for example, 85°C or higher. The lower limit is preferably 88°C, more preferably 90°C, even more preferably 95°C, even more preferably 100°C, particularly preferably 105°C, and most preferably 110°C. The upper limit is not particularly limited and is, for example, 160°C or 150°C.

[0124] The methacrylic resin composition of the present disclosure is one that is inhibited from discoloration such as yellowing. The yellow index (YI) value, measured in accordance with JIS K-7105 on a square test piece having sides of 50 mm and a thickness of 3 mm obtained by molding the methacrylic resin composition of the present disclosure, may be 5.0 or less or 4.0 or less. The lower limit is not particularly limited, and may be, for example, 1.0.

[0125] The methacrylic resin composition of the present disclosure, which contains a methacrylic copolymer (A), a graft copolymer (B), and an appropriate amount of an organic disulfide compound (D), can have excellent impact resistance at room temperature and low temperatures. A test piece of 80 mm in length, 10 mm in width, and 4 mm in thickness made of the methacrylic resin composition of the present disclosure, which contains a methacrylic copolymer (A), a graft copolymer (B), and an appropriate amount of an organic disulfide compound (D), is formed with a notch having a tip radius of 0.25 mm and a depth of 2 mm, and the Charpy impact strength measured at room temperature (23±2°C) in accordance with JIS K7111 is, for example, 4 kJ / m ２ The lower limit is preferably 4.5 kJ / m ２ , more preferably 5 kJ / m ２ The upper limit is not particularly limited, and is, for example, 25 kJ / m ２ , 20 kJ / m ２ , or 15 kJ / m ２ A test piece having a length of 80 mm, a width of 10 mm, and a thickness of 4 mm, made of the methacrylic resin composition of the present disclosure containing the methacrylic copolymer (A), the graft copolymer (B), and an appropriate amount of the organic disulfide compound (D), is formed with a notch having a tip radius of 0.25 mm and a depth of 2 mm, and the Charpy impact strength measured at −30° C. in accordance with JIS K7111 is, for example, 4 kJ / m ２ The upper limit is not particularly limited, and may be, for example, 15 kJ / m ２ , 10 kJ / m ２ , or 8 kJ / m ２ is.

[0126] For specific evaluation methods for the haze value, 1% thermal weight loss temperature, deflection temperature under load (HDT), yellow index (YI) value, and Charpy impact strength, please refer to the section [Examples] below.

[0127] [Method for producing methacrylic resin composition] The methacrylic resin composition of the present disclosure can be produced by a known method. The method for producing the methacrylic resin composition of the first embodiment according to the present invention can include a step (S1) of producing an organic disulfide compound-added methacrylic copolymer (AD) containing a first methacrylic copolymer (A) and an organic disulfide compound (D).

[0128] Step (S1) may include: a step (S1-1) of preparing polymerization raw materials containing multiple raw material monomers including methyl methacrylate (MMA) and one or more isopropenyl aromatic compounds (I), and a polymerization initiator; a step (S1-2) of polymerizing the polymerization raw materials under conditions of a polymerization conversion rate of 30 to 60 mass% to obtain a resin solution containing a first methacrylic copolymer (A) or a precursor resin thereof; and a step (S1-3) of volatilizing and removing at least a portion of the raw material monomers present in the resin solution in one or more steps. When step (S1-3) is a step of obtaining a precursor resin of the first methacrylic copolymer (A), step (S1) may further include a step (S1-4) of obtaining the first methacrylic copolymer (A) from the precursor resin by glutarimide cyclization or the like. In the method for producing a methacrylic resin composition of the present embodiment, one or more organic disulfide compounds (D) can be added to at least one of the polymerization raw materials, the resin solution obtained after completion of step (S-2), and the resin solution during step (S1-3).

[0129] (Step (S1-1)) 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 10 to 99% by mass. The lower limit is more preferably 15% by mass, even more preferably 20% by mass, even more preferably 25% by mass, even more preferably 30% by mass, particularly preferably 45% by mass, and most preferably 50% by mass. The upper limit is more preferably 95% by mass, particularly preferably 90% by mass, and most preferably 87% by mass. The content of one or more isopropenyl aromatic compounds (I) in the polymerization raw material is preferably 1 to 59% by mass, more preferably 5 to 40% by mass, and more preferably 10 to 30% by mass. The content of one or more other monomers (O) in the polymerization raw material is preferably 0 to 49% by mass, more preferably 0 to 30% by mass, and particularly preferably 0 to 25% by mass.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] (Step (S1-2)) Polymerization can be carried out by a known method, with bulk polymerization being preferred. For example, a continuous bulk polymerization method is preferred, in which the polymerization raw materials prepared in step (S1-1) 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 the methacrylic resin (A) or a precursor resin thereof, 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%.

[0134] (Step (S1-3)) At least a portion of the unreacted raw material monomers present in the resin solution are removed by volatilization in one stage or multiple stages. Examples of the volatilization method include adiabatic flash evaporation, equilibrium flash evaporation, and combinations thereof, with adiabatic flash evaporation being preferred. The volatilization of the unreacted raw material monomers present in the resin solution can be carried out by a known method using a heat exchanger, a vented extruder, or a combination thereof, with the combined use of a heat exchanger and a vented extruder being preferred.

[0135] The heating temperature by 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. The upper limit is more preferably 270°C, particularly preferably 260°C, and most preferably 250°C. Examples of extruders include single-screw extruders, twin-screw extruders, and multi-screw extruders. 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 (A) or its precursor resin obtained after step (S1-3), and may optionally have an additive supply port. 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 and 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, and particularly preferably 250°C.

[0136] 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) or its precursor resin is suppressed, and a methacrylic resin composition having excellent heat resistance and thermal decomposition resistance (thermal stability) can be produced. Furthermore, a methacrylic copolymer (A) or its precursor resin having a uniform composition, such as the content of isopropenyl aromatic compound units (UI), can be stably produced, and a methacrylic copolymer (A) or its precursor resin 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.

[0137] In the method for producing a methacrylic resin composition of the present disclosure, 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 (S1-2), and the resin solution being carried out in step (S1-3) so that the one or more organic disulfide compounds (D) are present in an amount of 1 to 1,000 ppm in the final methacrylic resin composition. 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 (S1-2), and the resin solution being carried out in step (S1-3). The amount of one or more organic disulfide compounds (D) added to the polymerization raw materials is preferably 10 to 2,000 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.

[0138] In the method for producing a methacrylic resin composition 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 (S1-2), and the resin solution being produced during step (S1-3). The one or more organic phosphorus compounds (P) can be supplied, for example, through an additive supply port of an extruder.

[0139] In the method for producing a methacrylic resin composition according to the present disclosure, one or more lubricants (L) can be added, as necessary, to at least one of the polymerization raw materials, the resin solution obtained after completion of step (S1-2), and the resin solution being produced during step (S1-3). The one or more lubricants (L) can be supplied, for example, from an additive supply port of the extruder.

[0140] (Step (S1-4)) When step (S1-3) is a step of obtaining a precursor resin of the first methacrylic copolymer (A), step (S1) may include step (S1-4) of obtaining the first methacrylic copolymer (A) from the precursor resin by glutarimide cyclization reaction or the like.

[0141] The content of the organic disulfide compound (D) in the organic disulfide compound-added methacrylic copolymer (AD) obtained after step (S1) (unless otherwise specified, the total amount when multiple types are used) 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 150 ppm. The upper limit is more preferably 1500 ppm, particularly preferably 1200 ppm, and most preferably 1000 ppm. The organic disulfide compound-added methacrylic copolymer (AD) contains a first methacrylic copolymer (A) containing isopropenyl aromatic compound units (UI) and an appropriate amount of the organic disulfide compound (D), and can have excellent heat resistance, thermal decomposition resistance (thermal stability), and surface hardness.

[0142] The method for producing a methacrylic resin composition of the present disclosure, which comprises a first methacrylic copolymer (A), a graft copolymer (B), and optionally a second methacrylic copolymer (C), may include, for example, a step of melt-kneading one or more first methacrylic copolymers (A), one or more graft copolymers (B), optionally one or more second methacrylic copolymers (C), and optionally one or more other polymers. In this method, one or more additives including an organic disulfide compound (D) may be added at any timing.

[0143] A method for producing a methacrylic resin composition according to a second embodiment of the present invention can include: a step (S1) of producing an organic disulfide compound-added methacrylic copolymer (AD) containing a first methacrylic copolymer (A) and an organic disulfide compound (D); and a step (S2) of melt-kneading 10 to 95% by mass of the organic disulfide compound-added methacrylic copolymer (AD), 5 to 40% by mass of the graft copolymer (B), and 0 to 85% by mass of a second methacrylic copolymer (C).

[0144] Step (S1) in the method for producing a methacrylic resin composition of the second embodiment is the same as step (S1) in the method for producing a methacrylic resin composition of the first embodiment.

[0145] Generally, methacrylic copolymers containing MMA units and isopropenyl aromatic compound units such as αMSt units tend to have a relatively low thermal decomposition temperature. Therefore, when these copolymers are heated and melted during resin production and molding, the copolymers may be thermally decomposed, increasing the amount of residual monomers in the resin and reducing its heat resistance. Furthermore, when the resin is heated and melted during resin production and molding, the thermal decomposition of the methacrylic copolymer may cause foaming and other defects in appearance.

[0146] In the production method of this embodiment, in step (S1), the presence of an appropriate amount of organic disulfide compound (D) effectively suppresses thermal decomposition of the first methacrylic copolymer (A). As a result, a first methacrylic copolymer (A) with a small amount of residual monomer and excellent heat resistance and thermal decomposition resistance (thermal stability) can be stably produced. Furthermore, in step (S1), the presence of an appropriate amount of organic disulfide compound (D) makes it relatively easy to control the copolymerization of the isopropenyl aromatic compound (I), allowing for the stable production of a first 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 first methacrylic copolymer (A) with excellent heat resistance and mechanical properties, such as rigidity and surface hardness. In step (S1), poor appearance, such as foaming due to thermal decomposition of the first methacrylic copolymer (A), is suppressed even if the residence time in a heated and molten state is long.

[0147] The organic disulfide compound-added methacrylic copolymer (AD) can effectively suppress thermal decomposition of the first methacrylic copolymer (A) and the second methacrylic copolymer (C) that may be contained as an optional component, and gelation of the graft copolymer (B) due to the presence of an appropriate amount of the organic disulfide compound (D), even during heating and melting in step (S2) and subsequent molding processing.

[0148] (Step (S2)) The melt-kneading can be carried out in one stage or multiple stages, and the procedure for blending multiple types of copolymers is optional. The melt-kneading can be carried out using a known mixing or kneading device such as an extruder (preferably a twin-screw extruder), a kneader-ruder, a mixing roll, or a Banbury mixer.

[0149] The methacrylic resin composition of the present disclosure can be processed into a form suitable for use as a molding material, such as pellets or powder, by a known method.

[0150] As described above, the present disclosure can provide a methacrylic resin composition that has good heat resistance and thermal decomposition resistance (thermal stability), is inhibited from discoloration such as yellowing, and has good moldability, as well as a method for producing the same. The present disclosure can also provide a methacrylic resin composition that contains a graft copolymer containing butadiene units and a methacrylic copolymer, and that has good transparency, heat resistance, surface hardness, and impact resistance at room temperature and low temperature, as well as a method for producing the same.

[0151] [Molded Article] The molded article of the present disclosure may contain the 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 composition of the present disclosure and a layer or member made of other resins or various materials other than resins. The molded article obtained by a known molding method may be subjected to surface treatments such as printing, painting, plating, vapor deposition, and sputtering; or shape processing such as curving, bending, and cutting (also referred to as secondary molding), as necessary. Generally, the terms "film," "sheet," and "plate" are used for thin film molded articles depending on their thickness, but there are no clear definitions or clear distinctions between them.

[0152] The molding method is not particularly limited, and examples thereof include melt molding methods such as extrusion molding, injection molding, inflation molding, blow molding, and calendar molding; compression molding (also referred to as press molding); vacuum molding and pressure molding; and solution casting (also referred to as solution casting). Among the above, melt molding is preferred. The melt molding temperature is not particularly limited, and is preferably 180 to 280°C, more preferably 200 to 260°C. The methacrylic resin composition of the present disclosure containing one or more organic disulfide compounds (D) has excellent thermal decomposition resistance (thermal stability), and therefore thermal decomposition and gelation are suppressed even when heated at relatively high temperatures, making it possible to provide a high-quality molded product with good appearance.

[0153] [Applications] The methacrylic resin composition of the present disclosure can be used for any application. The methacrylic resin composition of the present disclosure has excellent heat resistance and thermal decomposition resistance (thermal stability), and is characterized by suppressed discoloration such as yellowing. Therefore, it is 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.).

[0154] The methacrylic resin composition 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.

[0155] 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.

[0156] Other uses of the methacrylic resin composition of the present disclosure include interior parts such as furniture, wallpaper, pendant lights, and mirrors; architectural parts such as doors, sashes, domes, safety window glass, partitions, staircase wainscoting, balcony wainscoting, and roofs of leisure buildings; sign parts or marking films such as advertising towers, stand signs, side signs, transom signs, and rooftop signs; display parts such as showcases, partitions, and store displays; and lighting parts such as fluorescent light covers, mood lighting covers, lampshades, lighted ceilings, lighted walls, and chandeliers. various home appliance parts such as television 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 parts such as bathtubs, sanitary parts; greenhouses, large aquariums, box aquariums; stationery such as rulers and desk mats; game parts, toys, musical instruments; decorative and protective films provided on the surface of face protection masks used during welding, etc.

[0157] 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.

[0158] (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 Tosoh Corporation GPC device "HLC-8320" was used as the measurement device. A Tosoh Corporation TSKguardcolumn Super HZ-H, TSKgel HZM-M, and TSKgel Super HZ4000 column connected in series was used as the separation column. A differential refractive index detector (RI detector) was used as the detector. 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 the chromatogram was measured. Ten standard polymethyl methacrylate (PMMA) samples with molecular weights ranging from 400 to 5,000,000 were analyzed by GPC, and a calibration curve was created showing the relationship between retention time and molecular weight. Based on this calibration curve, the Mw and Mw / Mn of the resins to be measured, converted to standard PMMA, were determined.

[0159] (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).

[0160] (Unit composition of methacrylic copolymer) １ H-NMR spectrum or １３ The C-NMR spectrum was measured, and the unit composition of the methacrylic copolymer was determined from the ratio of the integral values ​​of the peaks derived from each unit. An example of a specific measurement method is shown below.

[0161] Regarding 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 unit composition was determined from the ratio of the integral values ​​of each peak.

[0162] 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 unit composition was determined from the ratio of the integral values ​​of each peak.

[0163] For methyl methacrylate-α-methylstyrene-maleic anhydride copolymer (MMA-αMSt-Mah 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 carbonyl group of the maleic anhydride (Mah) unit, and the unit composition was determined from the ratio of the integral values ​​of each peak.

[0164] For methyl methacrylate-α-methylstyrene-cyclohexylmaleimide copolymer (MMA-αMSt-ChMI 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 carbonyl group of the cyclohexylmaleimide unit, and the unit composition was determined from the ratio of the integral values ​​of each peak.

[0165] For methyl methacrylate-styrene-cyclohexylmaleimide-phenylmaleimide copolymer (MMA-St-ChMI-PhMI copolymer), measurement mode: inverse gated decoupling method conditions: 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 styrene (St) unit, a peak derived from the carbon of the carbonyl group of the cyclohexylmaleimide unit, and a peak derived from the carbon of the carbonyl group of the phenylmaleimide unit, and the unit composition was determined from the ratio of the integral values ​​of each peak.

[0166] Regarding methyl methacrylate-α-methylstyrene-styrene-methyl glutarimide copolymer (MMA-αMSt-St-MeGI copolymer), １ H-NMR spectra were measured to identify the peaks derived from the protons of methyl methacrylate (MMA) and the peaks derived from the protons of the glutarimide units. The integral values ​​of these two peaks were calculated, and the glutarimide cyclization rate (mol %) was calculated based on the following formula: [Glutarimide cyclization rate] (mol %) = [SG / (SM+SG)] × 100. In the formula, SM is the integral value of the peak derived from the MMA units, and SG is the integral value of the peak derived from the glutarimide units. The glutarimide cyclization rate (mol %) was converted to the glutarimide cyclization rate (mass %) using the molecular weight of each unit. The unit composition of the methyl methacrylate-α-methylstyrene-styrene-methylglutarimide copolymer (MMA-αMSt-St-MeGI copolymer) was calculated from the unit composition of the methyl methacrylate-α-methylstyrene-styrene copolymer (MMA-αMSt-St copolymer) before glutarimidination and the glutarimide cyclization rate (mass %).

[0167] (Remaining Amount of Each Monomer in Methacrylic Resin Composition) The remaining amount of each monomer in the methacrylic resin composition 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.

[0168] (Volume Average Particle Diameter (d50) of Graft Copolymer (B)) N,N-Dimethylformamide (DMF) was added to the graft copolymer (B) and stirred for 24 hours to prepare a 1% by mass solution of the graft copolymer (B), which was then subjected to ultrasonic dispersion treatment for about 1 hour. Using this as a sample solution, the particle size distribution was measured using a light scattering particle size distribution analyzer (Coulter Multisizer LS230 manufactured by Beckman Coulter, Inc.). The volume-based median diameter (d50) was determined as the volume average particle diameter of the graft copolymer (B).

[0169] (Composition of the Graft Layer of Graft Copolymer (B)) Methyl ethyl ketone was added to the graft copolymer (B), and the mixture was stirred at 23°C for 24 hours. The insoluble matter was separated by centrifugation for 60 minutes at -9°C and 20,000 rpm, and the mixture was allowed to stand for 30 minutes. The supernatant was separated, and methanol was added to precipitate the methacrylic copolymer by-product that was not bonded to the butadiene rubber polymer (BR). This precipitate was collected and dissolved in deuterated chloroform. １ The unit composition was determined by measuring the H-NMR spectrum. Since the unit composition of the methacrylic copolymer (M) constituting the graft layer of the graft copolymer (B) can be considered to be the same as the unit composition of the methacrylic copolymer by-product, the unit composition of the methacrylic copolymer by-product was taken as the unit composition of the graft layer.

[0170] (Refractive index of each copolymer (n ａ , n ｂ , n ｃ ), the average refractive index of the methacrylic copolymer (n ｍ ), |n ｂ -n ｍ |) Refractive index (n ａ ), the refractive index (n ａ ), the refractive index (n ｂ ), the refractive index (n ｃ) were measured in accordance with Method A of JIS K7142. The refractive index at 23°C for the sodium D line was measured using an Abbe refractometer ("NAR-3T" manufactured by Atago Co., Ltd.). The average refractive index (n ｍ ) and |n ｂ -n ｍ | was requested.

[0171] (Content of Organic Disulfide Compound (D)) The content of the organic disulfide compound (D) in the methacrylic resin composition was measured as follows. 2 g of the methacrylic resin composition was dissolved in 10 mL of dichloromethane, and then 30 mL of hexane was added to cause reprecipitation. The supernatant obtained after this reprecipitation treatment was separated, and the solvent in this supernatant was removed by distillation under reduced pressure to concentrate the mixture. 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 treatment was collected on a platinum board as a measurement sample, and after removing the dichloromethane, pyrolysis gas chromatography analysis was performed. A Shimadzu Gas Chromatograph GC-14A was connected to an Agilent J&W Series DB-5 column (inner diameter: 0.25 mm, film thickness: 0.25 μm, length: 30.0 m) manufactured by Agilent Technologies. The analysis was carried out under the following conditions. The content of the 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.

[0172] (Haze Value) Using an injection molding machine ("M-100C" manufactured by Meiki Seisakusho Co., Ltd.), a methacrylic resin composition was injection molded at a cylinder temperature of 250°C to obtain a test piece having a side length of 50 mm and a thickness of 3 mm. The haze value of this test piece was measured in accordance with JIS K7361 using a haze meter ("HM-150" manufactured by Murakami Color Research Institute Co., Ltd.).

[0173] (1% Thermal Weight Loss Temperature) Using a thermogravimetric analyzer ("TGA-50" manufactured by Shimadzu Corporation), approximately 5 mg of a methacrylic resin composition 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.

[0174] (Melt Flow Rate (MFR)) The melt flow rate (MFR) of the methacrylic resin composition was measured in accordance with JIS K7210 under conditions of 230°C and a load of 3.8 kg.

[0175] (Stability during Heat Retention) Injection molding was performed using an injection molding machine ("M-100C" manufactured by Meiki Seisakusho Co., Ltd.). After the methacrylic resin composition was retained in a cylinder set at 260°C for 30 minutes, 10 shots were used to mold a flat plate with a length of 200 mm, a width of 50 mm, and a thickness of 2 mm under conditions of a mold temperature of 60°C and an injection speed of 50 mm / sec. The appearance of each flat plate was visually observed and evaluated according to the following criteria. A (Excellent): No foaming was observed from the first shot. B (Good): A slight amount of foaming was observed between the first and third shots, but no foaming was observed from the fourth shot onwards. C (Fair): A large amount of foaming was observed between the first and third shots. D (Unacceptable): Sprue breakage occurred between the first and tenth shots.

[0176] (Deflection temperature under load (HDT)) Using an injection molding machine ("M-100C" manufactured by Meiki Seisakusho Co., Ltd.), a methacrylic resin composition 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.

[0177] (Yellow Index (YI) Value) Using an injection molding machine ("M-100C" manufactured by Meiki Seisakusho Co., Ltd.), a methacrylic resin composition 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 square test piece with a side length of 50 mm and a thickness of 3 mm. The yellow index (YI) value of this test piece was measured under the following conditions. The test piece was set in a spectrophotometer ("PC-2200" manufactured by Shimadzu Corporation), and light transmittance was measured at 1 nm intervals within a wavelength range of 340 to 700 nm using a C light source. From the obtained data, XYZ values ​​were determined in accordance with JIS Z-8722, and the yellow index (YI) value was calculated in accordance with JIS K-7105.

[0178] (Pencil hardness) Using an injection molding machine ("M-100C" manufactured by Meiki Seisakusho Co., Ltd.), a methacrylic resin composition was injection molded at a cylinder temperature of 250°C to obtain test pieces with a side length of 50 mm and a thickness of 3 mm. Using a moving table pencil scratch tester ("Model P" manufactured by Toyo Seiki Co., Ltd.), the presence or absence of scratches was confirmed while pressing a pencil lead against the surface of each test piece at an angle of 45° and a load of 500 g or 750 g. The hardness of the pencil lead gradually increased, and the hardness of the lead one level softer than the point at which scratches occurred was taken as the pencil hardness.

[0179] (Charpy Impact Strength) Using an injection molding machine ("M-100C" manufactured by Meiki Seisakusho Co., Ltd.), a methacrylic resin composition was injection molded at a cylinder temperature of 250°C to obtain a test specimen having a length (l) of 80 mm, a width (b) of 10 mm, and a thickness (h) of 4 mm. A notch with a tip radius (rN) of 0.25 mm and a depth of 2 mm (i.e., the remaining width (bN) of the notched test specimen = 8 mm) was formed in this test specimen using a notching machine in accordance with JIS K7111. The Charpy impact strength was measured at room temperature (23°C) and / or at a low temperature (-30°C) in accordance with JIS K7111.

[0180] [Additives] The additives used are as follows: <Organic disulfide compound (D)> (DDS) di-tert-dodecyl disulfide.

[0181] <Organic phosphorus compounds (P)> (PEP-36) Phosphite antioxidant, "ADEKA STAB PEP-36" manufactured by ADEKA Corporation, (TPP) Triphenylphosphine.

[0182] <Antioxidants other than phosphorus-based> (GS) Phenol-based antioxidant, "Sumilizer GS" manufactured by Sumitomo Chemical Co., Ltd.

[0183] <Lubricant (L)> (StMg) glycerol monostearate, (StOH) stearyl alcohol.

[0184] Example E1-1: 85 parts by mass of purified methyl methacrylate (MMA), 15 parts by mass of α-methylstyrene (αMSt), 400 ppm of n-octyl mercaptan (n-OM) as a chain transfer agent, and 300 ppm of di-tert-dodecyl disulfide (DDS) were charged into an autoclave equipped with a stirrer and a collection tube, and mixed uniformly. 500 ppm of 2,2'-azobis(2-methylpropionitrile) (AIBN) was added as a polymerization initiator, and the mixture was mixed uniformly to obtain a polymerization raw material. Nitrogen gas was blown into this polymerization raw material, adjusting the dissolved oxygen concentration to 3 ppm. This composition of the polymerization raw material is also referred to as the charge composition.

[0185] 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 3.3 hours, and bulk polymerization was carried out at a polymerization temperature of 120°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 30%.

[0186] 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.

[0187] The resin solution discharged from the reactor was heated using a heat exchanger and then fed into the extruder through the resin inlet. 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 fed into the extruder cylinder and discharged through the first vent (rear vent). The resin was then transported 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 temperature of the molten resin in the die was 244°C. The resulting strands were cut using a pelletizer to obtain pellets of a methacrylic resin composition containing a methacrylic copolymer (A-1) containing methyl methacrylate (MMA) units and α-methylstyrene (αMSt) units.

[0188] The main production conditions and evaluation results are shown in Table 1. In Tables 1 to 3, conditions not listed 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 in the raw material composition are the amounts added relative to 100% by mass of the total amount of raw material monomers.

[0189] [Examples E1-4 to E1-6, E1-8, E1-10, Comparative Examples EC1-2 to EC1-5] A methacrylic resin composition containing any of methacrylic copolymers (A-4) to (A-6), (A-8), (A-10), and (AC-2) to (AC-5) containing methyl methacrylate (MMA) units and α-methylstyrene (αMSt) units was obtained in the same manner as in Example E1-1, except that the charging composition and / or polymerization conditions were changed. The main production conditions and evaluation results are shown in Tables 1 to 3.

[0190] [Examples E1-2, E1-3, E1-7, E1-9, E1-11, E1-12, Comparative Examples EC1-1, EC1-6, EC1-7] A methacrylic resin composition containing any one of methacrylic copolymers (A-2), (A-3), (A-7), (A-9), (A-11), (A-12), (AC-1), (AC-6), and (AC-7) containing methyl methacrylate (MMA) units and α-methylstyrene (αMSt) units was obtained in the same manner as in Example E1-1, except that the charging composition and / or polymerization conditions were changed and one or more additives were post-added as follows.

[0191] One or more additives were added to the additive preparation tank, and the pressure was increased to 0.2 MPa and then released to atmospheric pressure, a total of four times to remove oxygen and moisture, resulting in an oxygen concentration of 0% in the additive preparation tank. The one or more additives added to the additive preparation tank were then heated to a temperature higher than their melting point and stirred for two hours to melt them. The resulting liquid additive was filtered using a 0.2 μm metal filter ("FLHF200-10M3F" manufactured by PALL) and injected into the extruder through the additive inlet using a metering pump. For example, in Example E1-2, the types of one or more additives added later and the amounts of each additive added relative to 100% by mass of resin were as follows: (PEP-36) 1000 ppm, (StMg) 1000 ppm, (StOH) 2000 ppm. The main production conditions and evaluation results are shown in Tables 1 to 3. In the table, the amount of additives added after polymerization in the raw material composition is the amount added relative to 100% by mass of the resin.

[0192]

[0193]

[0194]

[0195] [Summary of Results] In Examples E1-1 to E1-12, methacrylic resin compositions were obtained containing a methacrylic copolymer (A) consisting of 10 to 99% by mass of methyl methacrylate (MMA) units, 1 to 40% by mass of isopropenyl aromatic compound units (UI), and 0 to 60% by mass of other units (UO). In these examples, an appropriate amount of organic disulfide compound (D) was added to the polymerization raw materials, and methacrylic resin compositions were finally obtained containing 1 to 1,000 ppm of organic disulfide compound (D). All of the methacrylic resin compositions obtained in these examples had a total residual amount of raw material monomers of 0 to 1.00% by mass. All of the methacrylic resin compositions obtained in these examples had a Tg of 120°C or higher, a 1% thermal weight loss temperature of 270°C or higher (280°C or higher), and good heat resistance and thermal decomposition resistance (thermal stability). All of the methacrylic resin compositions obtained in these Examples had a good melt flow rate (MFR), good thermal stability even when retained in a heated state during molding, and good molding processability. All of the methacrylic resin compositions obtained in these Examples had a deflection temperature under load (HDT) of 105°C or higher (110°C or higher), and good heat resistance and rigidity under load. All of the methacrylic resin compositions obtained in these Examples had a yellow index (YI) value of 5.0 or lower (4.0 or lower), and discoloration such as yellowing was suppressed. All of the methacrylic resin compositions obtained in these Examples were suitable for optical components; vehicle components for automobiles, etc.

[0196] In Comparative Examples EC1-1 to EC1-3, EC1-6, and EC1-7, methacrylic resin compositions containing a methacrylic copolymer (AC) were obtained. In these Comparative Examples, the amount of organic disulfide compound (D) added to the polymerization raw materials was 0 ppm or insufficient, and therefore the content of organic disulfide compound (D) in the finally obtained methacrylic resin composition was 0 ppm. In all of the methacrylic resin compositions obtained in these Comparative Examples, the total amount of raw material monomers of the methacrylic copolymer (AC) remaining exceeded 1.00% by mass. All of the methacrylic resin compositions obtained in these Comparative Examples had poor heat resistance and / or thermal decomposition resistance (thermal stability), and the evaluation results for one or more of Tg, 1% heat weight loss temperature, deflection temperature under load (HDT), and stability during heating and retention were poor.

[0197] In Comparative Example EC1-4, a methacrylic resin composition was obtained containing a methacrylic copolymer (AC) having an isopropenyl aromatic compound unit (UI) content of more than 40% by mass. In this comparative example, an appropriate amount of an organic disulfide compound (D) was added to the polymerization raw material, and a methacrylic resin composition containing 1 to 1,000 ppm of the organic disulfide compound (D) was finally obtained. The methacrylic resin composition obtained in this comparative example had a total residual amount of the raw material monomers of the methacrylic copolymer (AC) of more than 1.00% by mass. The methacrylic resin composition obtained in this comparative example had poor heat resistance and / or thermal decomposition resistance (thermal stability), and was poor in Tg, 1% heat weight loss temperature, deflection temperature under load (HDT), and stability during heating and retention.

[0198] In Comparative Example EC1-5, a methacrylic resin composition containing a methacrylic copolymer (AC) was obtained. In this comparative example, an organic disulfide compound (D) was added to the polymerization raw material, and a methacrylic resin composition containing more than 1,000 ppm of the organic disulfide compound (D) was finally obtained. The methacrylic resin composition obtained in this comparative example had a total residual amount of raw material monomers of 0 to 1.00 mass% and had good heat resistance and thermal decomposition resistance (thermal stability). However, the yellow index (YI) value of the obtained methacrylic resin composition was poor, exceeding 10.0.

[0199] [Example E2-11] Production of DDS-added methacrylic copolymer (AD-11) 65 parts by mass of purified methyl methacrylate (MMA), 35 parts by mass of α-methylstyrene (αMSt), 400 ppm of n-octyl mercaptan (n-OM) as a chain transfer agent, and 900 ppm of di-tert-dodecyl disulfide (DDS) were charged into an autoclave equipped with a stirrer and a collection tube and mixed uniformly. 500 ppm of 2,2'-azobis(2-methylpropionitrile) (AIBN) was added as a polymerization initiator and mixed uniformly to obtain a polymerization raw material. Nitrogen gas was blown into this polymerization raw material to adjust the dissolved oxygen concentration to 3 ppm.

[0200] 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 4.0 hours, and bulk polymerization was carried out at a polymerization temperature of 120°C. A resin solution containing the reaction product, a methacrylic copolymer, 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 28%.

[0201] 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.

[0202] The resin solution discharged from the reactor was heated using a heat exchanger and then fed into the extruder through the resin inlet. The heat exchanger temperature was set to 200°C, and the extruder cylinder temperature was set to 255°C. Volatiles, primarily composed of unreacted monomers, were flash evaporated from the resin solution fed into the extruder cylinder and discharged through the first vent (rear vent). Furthermore, the resin was transported in the axial direction of the cylinder by the screw, and the volatiles evaporating during this process were discharged through the second vent (front vent). The resulting strands were cut using a pelletizer. In this manner, pellets of DDS-added methacrylic copolymer (AD-11) were obtained. The unit composition of the copolymer, the DDS content in the DDS-added methacrylic copolymer (AD), and the physical property evaluation results are shown in Table 4.

[0203] [Example E2-12] Production of DDS-added methacrylic copolymer (AD-12) The charged composition was changed to 69 parts by mass of methyl methacrylate (MMA), 25 parts by mass of α-methylstyrene (αSt), 6 parts by mass of styrene (St), 100 ppm of n-octyl mercaptan (n-OM), and 500 ppm of di-tert-dodecyl disulfide (DDS). Pellets of DDS-added methacrylic copolymer (AD-12) were obtained in the same manner as in Example E2-11, except that the average residence time was changed to 3.0 hours and the polymerization temperature to 140 ° C. The unit composition of the copolymer, the DDS content in the DDS-added methacrylic copolymer (AD), and the results of physical property evaluation are shown in Table 4.

[0204] [Example E2-13] Preparation of DDS-added methacrylic copolymer (AD-13) The charged composition was changed to 75 parts by mass of methyl methacrylate (MMA), 15 parts by mass of α-methylstyrene (αMSt), 10 parts by mass of maleic anhydride (Mah), 200 ppm of n-octyl mercaptan (n-OM), and 300 ppm of di-tert-dodecyl disulfide (DDS). The amount of 2,2'-azobis(2-methylpropionitrile) (AIBN) was changed to 300 ppm, and the average residence time was changed to 2.5 hours. The polymerization temperature was changed to 130 ° C., but pellets of DDS-added methacrylic copolymer (AD-13) were obtained in the same manner as in Example E2-11. The unit composition of the copolymer, the DDS content in the DDS-added methacrylic copolymer (AD), and the physical property evaluation results are shown in Table 4.

[0205] [Example E2-14] Preparation of DDS-added methacrylic copolymer (AD-14) The charged composition was changed to 60 parts by mass of methyl methacrylate (MMA), 23 parts by mass of α-methylstyrene (αMSt), 17 parts by mass of cyclohexylmaleimide (ChMI), 300 ppm of n-octyl mercaptan (n-OM), and 400 ppm of di-tert-dodecyl disulfide (DDS), and the amount of 2,2'-azobis(2-methylpropionitrile) (AIBN) was changed to 300 ppm. The average residence time was 3.0 hours, and the polymerization temperature was changed to 130 ° C., but pellets of DDS-added methacrylic copolymer (AD-14) were obtained in the same manner as in Example E2-11. The unit composition of the copolymer, the content of DDS in the DDS-added methacrylic copolymer (AD), and the physical property evaluation results are shown in Table 4.

[0206] [Example E2-15] Production of DDS-added methacrylic copolymer (AD-15) (Precursor resin production process) The charged composition was changed to 78 parts by mass of methyl methacrylate (MMA), 17 parts by mass of α-methylstyrene (αMSt), 5 parts by mass of styrene (St), n-octyl mercaptan (n-OM) 530 ppm, and di-tert-dodecyl disulfide (DDS) 500 ppm, and the amount of 2,2'-azobis (2-methylpropionitrile) (AIBN) was changed to 400 ppm. The average residence time was changed to 3.0 hours, and the polymerization temperature was changed to 140 ° C. In the same manner as in Example E2-11, pellets of DDS-added methacrylic copolymer (AD-15-Pre) (precursor resin) were obtained. This DDS-added methacrylic copolymer (AD-15-Pre) had a copolymer unit composition of 75% by mass of methyl methacrylate (MMA) units, 10% by mass of α-methylstyrene (αMSt) units, and 5% by mass of styrene (St) units, and a DDS content of 610 ppm.

[0207] (Glutarimide Cyclization Step) A twin-screw extruder ("TEX30α-77AW-3V" manufactured by Nippon Steel Corporation) was prepared. The extruder had a transport section, a melt-kneading section, a devolatilizing section, and a discharge section, and the screw rotation speed was set to 150 rpm and the temperature to 210 to 270°C. Pellets of DDS-added methacrylic copolymer (AD-15-Pre) (precursor resin) were fed to the transport section of the twin-screw extruder at a rate of 15 kg / hr. Monomethylamine was injected as an imidizing agent through the additive supply port of the twin-screw extruder in an amount such that the content of methyl glutarimide (MeGI) units was the amount listed in Table 4. The precursor resin and monomethylamine were reacted in the melt-kneading section, which included a kneading block. By-products and excess monomethylamine were volatilized from the resulting molten resin in the devolatilizing section and discharged through multiple vents. The molten resin was extruded in the form of strands from a die installed at the end of the discharge section of the twin-screw extruder, cooled in a water bath, and cut with a pelletizer to obtain pellets of DDS-added methacrylic copolymer (AD-15). The unit composition of the copolymer, the DDS content in the DDS-added methacrylic copolymer (AD), and the results of physical property evaluation are shown in Table 4.

[0208] Example E2-16 Production of DDS-Added Methacrylic Copolymer (AD-16) (Precursor Resin Production Process) The charged composition was changed to 65 parts by mass of 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), and 700 ppm of di-tert-dodecyl disulfide (DDS). Pellets of DDS-added methacrylic copolymer (AD-16-Pre) (precursor resin) were obtained in the same manner as in Example E2-11, except that the average residence time was changed to 3.0 hours and the polymerization temperature was changed to 140°C. This DDS-added methacrylic copolymer (AD-16-Pre) had a copolymer unit composition of 77% by mass of methyl methacrylate (MMA) units, 16% by mass of α-methylstyrene (αMSt) units, and 7% by mass of styrene (St) units, and a DDS content of 750 ppm.

[0209] (Glutarimide cyclization step) Pellets of DDS-added methacrylic copolymer (AD-16) were obtained in the same manner as in the glutarimide cyclization step of Example E2-15, except that DDS-added methacrylic copolymer (AD-16-Pre) was used as the precursor resin and the amount of monomethylamine added as the imidizing agent was changed. The unit composition of the copolymer, the DDS content in the DDS-added methacrylic copolymer (AD), and the results of physical property evaluation are shown in Table 4.

[0210] [Comparative Example EC2-17] Preparation of methacrylic copolymer (AC-17) Pellets of a comparative methacrylic copolymer (AC-17) containing no DDS were obtained in the same manner as in Example E2-11, except that di-tert-dodecyl disulfide (DDS) was not used. The unit composition of the copolymer, the content of DDS in the methacrylic copolymer (AC), and the results of physical property evaluation are shown in Table 4.

[0211] [Comparative Example EC2-18] Production of Methacrylic Copolymer (AC-18) Pellets of a comparative methacrylic copolymer (AC-18) (methyl methacrylate-styrene-cyclohexylmaleimide-phenylmaleimide copolymer, MMA-St-ChMI-PhMI copolymer) containing no DDS were obtained in the same manner as in Reference Example 1 of Patent Document 2 cited in the [Background Art] section, except for adjusting the mass ratio of the charged monomers. The unit composition of the copolymer, the DDS content in the methacrylic copolymer (AC), and the results of physical property evaluation are shown in Table 4.

[0212] [Production Example PE1] Production of Graft Copolymer (B-1) A latex containing 31.5 kg of polybutadiene particles (particle diameter 0.34 μm) in terms of solid content was charged into a 200 L autoclave equipped with a stirrer, 98 kg of pure water was added, and the mixture was heated to 50° C. under a nitrogen stream while stirring. Next, 2 kg of an aqueous solution prepared by dissolving 1.25 g of ferrous sulfate, 2.5 g of sodium ethylenediaminetetraacetate, and 100 g of sodium formaldehyde sulfoxylate dihydrate (Rongalit) in the pure water was added, and the mixture was stirred and mixed. Next, to this solution under stirring, a monomer mixture consisting of 15.4 kg of methyl methacrylate (MMA), 5.7 kg of styrene (St), 7.4 kg of acrylonitrile (AN), and 60 g of t-dodecyl mercaptan, and 8 kg of a dispersion prepared by dissolving 450 g of potassium oleate in pure water and dispersing 120 g of diisopropylbenzene hydroperoxide, were continuously added dropwise over 6 hours using separate dropping pumps. After completion of these additions, the temperature of the reaction solution was raised to 70°C, and 30 g of diisopropylbenzene hydroperoxide was added. The mixture was maintained with stirring for 2 hours to complete the polymerization. An antioxidant was added to the resulting latex, and the mixture was diluted with pure water at room temperature (10 to 30°C) to a solids content of 15% by mass, and then the temperature was raised to 60°C. Dilute sulfuric acid was added under vigorous stirring to carry out salting out, and the temperature was then raised to 90°C to cause coagulation, followed by dehydration, washing with water, and drying to obtain a powdery graft copolymer (B-1). The obtained graft copolymer (B-1) is a core-shell type graft copolymer particle in which at least a part of the surface of a core particle made of polybutadiene particle is covered with a shell layer (graft layer) made of a methacrylic copolymer, and has a refractive index (n ｂ The graft layer had a composition of 54% by mass of methyl methacrylate (MMA) units / 20% by mass of styrene (St) units / 26% by mass of acrylonitrile (AN) units, and the volume average particle size (d50) was 0.36 μm.

[0213] [Production Example PE2] Production of Graft Copolymer (B-2) Powdery graft copolymer (B-2) was obtained in the same manner as in Production Example PE1, except that the monomer mixture was changed to a monomer mixture consisting of 22.2 kg of methyl methacrylate (MMA), 6.3 kg of styrene (St), and 60 g of t-dodecyl mercaptan. The obtained graft copolymer (B-2) was a core-shell type graft copolymer particle in which at least a portion of the surface of a core particle consisting of a polybutadiene particle was coated with a shell layer (graft layer) consisting of a methacrylic copolymer, and had a refractive index (n ｂ The graft layer had a composition of 78% by mass of methyl methacrylate (MMA) units / 22% by mass of styrene (St) units, and the volume average particle size (d50) was 0.36 μm.

[0214] [Production Example PE3] Production of Graft Copolymer (B-3) A latex containing 36 kg of styrene-butadiene copolymer particles (styrene unit / butadiene unit (mass ratio) = 30 / 70, particle size 0.30 μm) in terms of solid content was charged into a 200 L autoclave equipped with a stirrer, pure water was added, and the temperature was raised to 50°C under a nitrogen stream while stirring. The total amount of water in the latex and the amount of pure water added was 100 kg. Next, 2 kg of an aqueous solution prepared by dissolving 1.8 g of ferrous sulfate, 3.6 g of sodium ethylenediaminetetraacetate, and 108 g of sodium formaldehyde sulfoxylate dihydrate (Rongalit) in pure water was added, and the mixture was stirred and mixed. Next, to this solution under stirring, a monomer mixture consisting of 13.2 kg of methyl methacrylate (MMA), 10.8 kg of styrene (St), and 240 g of t-dodecyl mercaptan, and 8 kg of a dispersion prepared by dissolving 450 g of potassium oleate in pure water and dispersing 48 g of diisopropylbenzene hydroperoxide, were continuously added dropwise over 6 hours using separate dropping pumps. After completion of these additions, the temperature of the reaction solution was raised to 70°C, and 24 g of diisopropylbenzene hydroperoxide was added. The mixture was maintained with stirring for 2 hours to terminate the polymerization. An antioxidant was added to the resulting latex, and the solids content was diluted to 15% by mass with pure water at room temperature (10 to 30°C), and the temperature was then raised to 70°C. Dilute sulfuric acid was added with vigorous stirring to perform salting out, and the temperature was then raised to 95°C to coagulate, followed by dehydration, washing with water, and drying to obtain a powdery graft copolymer (B-3). The obtained graft copolymer (B-3) is a core-shell type graft copolymer particle in which at least a part of the surface of a core particle made of a styrene-butadiene copolymer particle is covered with a shell layer (graft layer) made of a methacrylic copolymer, and has a refractive index (n ｂ The graft layer had a composition of 55% by mass of methyl methacrylate (MMA) units / 45% by mass of styrene (St) units, and the volume average particle size (d50) was 0.35 μm.

[0215] [Production Example PE4] Production of methacrylic copolymer (C-1) Methyl methacrylate-styrene-acrylonitrile copolymer (MMA-St-AN) was polymerized as methacrylic copolymer (C-1) in the same manner as in Reference Examples 1 to 4 of JP-A-7-324153, except that the mass ratio of the charged monomers was adjusted. The resulting copolymer had a unit composition of 54% by mass of methyl methacrylate (MMA) units, 20% by mass of styrene (St) units, and 26% by mass of acrylonitrile (AN) units, a weight average molecular weight (Mw) of 84,000, a glass transition temperature (Tg) of 101°C, and a refractive index (n ｃ ) was 1.517.

[0216] [Production Example PE5] Production of methacrylic copolymer (C-2) A methyl methacrylate-styrene copolymer (MMA-St copolymer) was polymerized as the methacrylic copolymer (C-2) in the same manner as in Experimental Example (B)-1 of Patent Document 3 cited in the [Background Art] section, except that the mass ratio of the charged monomers was adjusted. The resulting copolymer had a unit composition of 75 mass% methyl methacrylate (MMA) units / 25 mass% styrene (St) units, a weight average molecular weight (Mw) of 115,000, a glass transition temperature (Tg) of 104°C, a refractive index (n ｃ ) was 1.520.

[0217] [Examples E2-1 to E2-9, Comparative Examples EC2-1 to EC2-5] In each of Examples E2-1 to E2-9 and Comparative Examples EC2-1 to EC2-5, the DDS-added methacrylic copolymer (AD) or the comparative methacrylic copolymer (AC), the graft copolymer (B), and the methacrylic copolymer (C) were blended in the formulation shown in Table 5 or Table 6, and the blends were melt-kneaded and extruded at 245 ° C. using a twin-screw extruder with an L / D = 32.5 and a shaft diameter of 62.5 mm to obtain a methacrylic resin composition (R) or (RC). Note that L / D is the ratio of the effective length (L) of the screw to the diameter (D) of the screw. The physical property evaluation results are shown in Tables 5 and 6. In these tables, conditions not listed in the tables were common conditions.

[0218]

[0219]

[0220]

[0221] [Summary of Results] The DDS-added methacrylic copolymers (AD) obtained in Examples E2-11 to E2-16 all contained an appropriate amount of organic disulfide compound (D) and had good heat resistance, thermal decomposition resistance (thermal stability), surface hardness, and impact resistance at room temperature. In Examples E2-1 to E2-9, methacrylic resin compositions were obtained containing 10 to 95% by mass of a DDS-added methacrylic copolymer (AD) containing a first methacrylic copolymer (A) and an organic disulfide compound (D), 5 to 40% by mass of a graft copolymer (B), 0 to 85% by mass of a methacrylic copolymer (C), and 1 to 1,000 ppm of an organic disulfide compound (D). Because the methacrylic resin compositions obtained in these Examples all contained a DDS-added methacrylic copolymer (AD) having the above-described properties, they had good heat resistance, surface hardness, and impact resistance at room temperature.

[0222] It is believed that the inclusion of an appropriate amount of organic disulfide compound (D) in each of the methacrylic resin compositions obtained in these examples suppressed thermal decomposition of the first methacrylic copolymer (A) and the second methacrylic copolymer (C), which may be included as an optional component, thereby improving heat resistance and thermal decomposition resistance (thermal stability). The inclusion of an appropriate amount of organic disulfide compound (D) in each of the methacrylic resin compositions obtained in these examples suppressed gelation of the graft copolymer (B) during the production of the methacrylic resin composition and molded article. As a result, each of the obtained methacrylic resin compositions had good impact resistance at low temperatures (below freezing).

[0223] In all of the methacrylic resin compositions obtained in these examples, the refractive index difference (|n ｂ -n ｍ |, Δn) was 0.01 or less. The methacrylic resin compositions obtained in these examples had reduced light scattering at the boundary between the matrix resin and the rubber component, and had good transparency.

[0224] In Comparative Examples EC2-1 and EC2-2, methacrylic resin compositions were obtained that did not contain the first methacrylic copolymer (A) or the organic disulfide compound (D). The methacrylic resin compositions obtained in these Comparative Examples had low heat resistance and surface hardness. The methacrylic resin composition obtained in Comparative Example EC2-2 also had low impact resistance at low temperatures. In Comparative Example EC2-3, a methacrylic resin composition was obtained in which the content of the graft copolymer (B) was more than 40% by mass. The obtained methacrylic resin composition had low heat resistance and surface hardness.

[0225] The comparative methacrylic copolymer (AC-17) obtained in Comparative Example EC2-17 had low thermal decomposition resistance because the organic disulfide compound (D) was not added to the polymerization raw materials. In Comparative Example EC2-4, a methacrylic resin composition containing this comparative methacrylic copolymer (AC-17) but not containing the organic disulfide compound (D) was obtained. The obtained methacrylic resin composition had low heat resistance and low impact resistance at low temperatures.

[0226] The comparative methacrylic copolymer (AC-18) obtained in Comparative Example EC2-18 had improved heat resistance by increasing the content of maleimide units, but its impact resistance was reduced. In Comparative Example EC2-5, a methacrylic resin composition containing this comparative methacrylic copolymer (AC-18) but not containing the organic disulfide compound (D) was obtained. The resulting methacrylic resin composition had low impact resistance at room temperature and low temperatures.

[0227] 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.

[0228] This application claims priority based on Japanese Patent Application No. 2023-100520 filed on June 20, 2023, and Japanese Patent Application No. 2023-138673 filed on August 29, 2023, the disclosures of which are incorporated herein in their entireties.

Claims

1. A methacrylic resin composition comprising a first methacrylic copolymer (A) which is composed of 10-99% by mass of methyl methacrylate units, 1-40% by mass of one or more isopropenyl aromatic compound units (UI), and 0-60% by mass of one or more other units (UO) and has a glass transition temperature of 120-150°C, further comprising 1-1000 ppm of one or more organic disulfide compounds (D), and wherein the total residual amount of raw material monomers of the methacrylic copolymer (A) is 0-1.00% by mass.

2. 10-95% by mass of a first methacrylic copolymer (A) which is composed of 10-99% by mass of methyl methacrylate units, 1-40% by mass of one or more isopropenyl aromatic compound units (UI), and 0-60% by mass of one or more other units (UO) and has a glass transition temperature of 120-150°C; 5-40% by mass of a graft copolymer (B) obtained by graft copolymerizing a butadiene rubber-like polymer (BR) containing 60-100% by mass of butadiene units with a methacrylic copolymer (M) containing 10-90% by mass of methyl methacrylate units, 90-10% by mass of aromatic vinyl compound units, and 49-0% by mass of vinyl cyanide compound units; The methacrylic resin composition according to claim 1, comprising: 0 to 85 mass% of a second methacrylic copolymer (C) containing 10 to 90 mass% of methyl methacrylate units, 70 to 10 mass% of aromatic vinyl compound units other than isopropenyl aromatic compound units, and 49 to 0 mass% of vinyl cyanide compound units; and 1 to 1,000 ppm of an organic disulfide compound (D), and satisfying the following formula (1): 0≦|n ｂ -n ｍ |≦0.01 (1) In the above formula, n ｍ is defined by the following formula (2): ｍ = (n ａ ×w ａ +n ｃ ×w ｃ ) / (w ａ +w ｃ ) (2) In the above formula, n ａ , n ｂ , n ｃ are the refractive indices of the first methacrylic copolymer (A), the graft copolymer (B), and the second methacrylic copolymer (C) at 23° C. for the sodium D line. ａ , W ｂ , W ｃ are respectively the mass ratios of the first methacrylic copolymer (A), the graft copolymer (B), and the second methacrylic copolymer (C) to the total mass of the first methacrylic copolymer (A), the graft copolymer (B), and the second methacrylic copolymer (C) in the methacrylic resin composition. ａ +w ｂ +w ｃ = 1.

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

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

5. The methacrylic resin composition according to claim 1, wherein the first methacrylic copolymer (A) contains, as the other units (UO), one or more ring structure units (UR) selected from the group consisting of an acid anhydride unit, an imide unit having a ring structure, and a lactone ring unit.

6. The methacrylic resin composition according to claim 2, wherein the butadiene rubber polymer (BR) is one or more rubber polymers selected from the group consisting of polybutadiene, copolymers containing butadiene units and aromatic vinyl compound units, and hydrogenated products thereof.

7. The methacrylic resin composition according to claim 2, wherein the graft copolymer (B) is a core-shell type graft copolymer particle in which at least a portion of the surface of a core particle made of a butadiene rubber-like polymer (BR) is covered with a shell layer made of a methacrylic copolymer (M).

8. The methacrylic resin composition according to claim 1, 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).

9. The methacrylic resin composition according to claim 1, further comprising 0.0001 to 1.0 mass % of one or more organic phosphorus compounds (P).

10. The methacrylic resin composition according to claim 1, further comprising 1,000 to 5,000 ppm of one or more lubricants (L).

11. The methacrylic resin composition according to claim 1, wherein a haze value of a 3 mm thick flat plate made of the methacrylic resin composition, measured in accordance with JIS K7136, is 0 to 10%.

12. The methacrylic resin composition according to claim 1, which has a 1% thermal weight loss temperature of 270°C or higher, as measured by thermogravimetric analysis under an inert gas atmosphere.

13. A method for producing a methacrylic resin composition according to any one of claims 1 to 12, comprising: a step (S1-1) of preparing polymerization raw materials containing multiple raw material monomers including methyl methacrylate and one or more isopropenyl aromatic compounds (I) and a polymerization initiator; a step (S1-2) of polymerizing the polymerization raw materials under conditions of a polymerization conversion rate of 30 to 60 mass% to obtain a resin solution containing a first methacrylic copolymer (A) or a precursor resin thereof; and a step (S1-3) of volatilizing and removing at least a portion of the raw material monomers present in the resin solution in one or more steps, wherein 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 (S1-2), and the resin solution being carried out in step (S1-3) so that the one or more organic disulfide compounds (D) are present in an amount of 1 to 1000 ppm in the finally obtained methacrylic resin composition.

14. The method for producing a methacrylic resin composition according to claim 13, 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 (S1-2), and the resin solution during the implementation of step (S1-3).

15. A molded article comprising the methacrylic resin composition according to any one of claims 1 to 12.

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