WO2019093385A1

WO2019093385A1 - Methacrylic copolymer and molded article thereof

Info

Publication number: WO2019093385A1
Application number: PCT/JP2018/041382
Authority: WO
Inventors: 伸崇平岡; 竹友山下; 淳裕中原
Original assignee: 株式会社クラレ
Priority date: 2017-11-09
Filing date: 2018-11-07
Publication date: 2019-05-16
Also published as: JPWO2019093385A1

Abstract

The present invention provides a methacrylic copolymer comprising 90 mass% or more structural units derived from methyl methacrylate, the methacrylic copolymer containing combined sulfur atoms derived from a mercaptan-based chain-transfer agent with a molecular weight of 200 or less in an amount of 0.4 mol% or larger with respect to the amount of the structural units derived from methyl methacrylate and having a melt flow rate, as measured under the conditions of 230°C and a load of 3.8 kg, of 25-50 g/10 min.

Description

Methacrylic copolymer and its molded article

The present invention relates to a methacrylic copolymer excellent in transparency, flowability and mechanical strength, and a molded article comprising the methacrylic copolymer.

The methacrylic copolymer produced by radical polymerization is used as a molded article in various applications such as OA equipment field, automobile field, electric / electronic field, and has high transparency, so it has a front plate of a display device and a light guide plate Are widely used in optical applications such as

In recent years, with the increase in size and thickness of display devices, improvement in the formability of methacrylic copolymers used therein is required.

Although the moldability of the methacrylic copolymer can be realized by reducing the weight-average molecular weight (Mw) of the methacrylic copolymer to improve the flowability, the problem arises that the strength of the resulting molded article decreases.

Patent Document 1 discloses that when polymerizing a monomer mixture containing methyl methacrylate alone or methyl methacrylate in an amount of 50% by mass or more, 0.01 to 2% by weight of a peroxide or per monomer as a polymerization initiator There is a description of a process for producing a methacrylic copolymer characterized in that it is polymerized using an azo compound and 0.02 to 3% by weight of a polyfunctional mercaptan per monomer as a chain transfer agent. The production method is a method for producing a methacrylic copolymer excellent in thermal decomposition resistance, and sufficient examination has not been made regarding flowability and impact resistance.

Moreover, although the method of polymerizing methacrylic resin using a polyfunctional chain transfer agent is disclosed by patent document 2 as a method of making flowability and impact resistance compatible, there is a room for improvement regarding the color. was there.

JP-A-61-272206 WO 2013-141106

An object of the present invention is to provide a methacrylic copolymer which has transparency suitable for optical applications and is excellent in flowability and mechanical strength. Another object of the present invention is to provide a molded article having an excellent appearance obtained from the methacrylic copolymer.

In order to achieve the above object, the present invention is
[1] A methacrylic copolymer containing 90% by mass or more of a structural unit derived from methyl methacrylate, wherein the methacrylic copolymer is a mercaptan chain transfer having a molecular weight of 200 or less relative to a structural unit derived from methyl methacrylate Copolymer derived from a lubricant and having an amount of bound sulfur atoms of 0.4 mol% or more and a melt flow rate of 25 g / 10 minutes or more and 50 g / 10 minutes or less under conditions of 230 ° C. and 3.8 kg load ,
[2] The methacrylic copolymer according to [1], wherein the value of the molecular weight distribution (Mw / Mn) of the methacrylic copolymer is 1.85 or less.
[3] The methacrylic copolymer according to [1] or [2], wherein the mercaptan chain transfer agent is a bifunctional mercaptan,
[4] The methacrylic copolymer according to any one of [1] to [3], which is obtained by continuous bulk polymerization,
[5] A methyl methacrylate, a bifunctional mercaptan chain transfer agent having a molecular weight of 200 or less, containing a radical polymerization initiator, 0.2 per 100 parts by mass of all the polymerizable monomers to be subjected to polymerization. A raw material liquid containing ~ 0.5 parts by mass, optionally containing acrylic acid alkyl ester, and having a mass ratio of acrylic acid alkyl ester / methyl methacrylate of 0/100 to 10/90, The reaction product is continuously supplied, and bulk polymerization is carried out at a polymerization conversion rate of 40 to 70% by mass in the tank reactor to obtain a reaction product, and the reaction product is continuously withdrawn from the tank reactor, and the reaction is carried out. A process for producing a methacrylic copolymer according to any one of [1] to [4], comprising the step of removing volatile components from the product.
[6] A pellet-like molding material comprising the methacrylic copolymer according to any one of [1] to [4],
[7] An optical member obtained by injection molding the molding material according to [6], wherein the optical length is 200 mm or less and the yellow index (YI) is 5 or less.
[8] An optical member obtained by press-molding the methacrylic copolymer according to any one of [1] to [4].

According to the present invention, it is possible to provide a methacrylic copolymer which has transparency suitable for optical applications and is excellent in fluidity and mechanical strength under slow deformation. Further, since the methacrylic copolymer has high moldability, a molded article excellent in appearance can be provided.

The methacrylic copolymer of the present invention is a methacrylic copolymer comprising 90% by mass or more, preferably 90.5 to 99% by mass, more preferably 91 to 97% by mass of structural units derived from methyl methacrylate, In the methacrylic copolymer, the amount of bound sulfur atoms derived from a mercaptan-based chain transfer agent having a molecular weight of 200 or less is 0.4 mol% or more, preferably 0.45 mol% or more, based on the structural unit derived from methyl methacrylate . The upper limit of the amount of bound sulfur atoms is 1.50 mol%, preferably 1.00 mol%. The molecular weight of the mercaptan chain transfer agent is preferably 100 to 200, more preferably 120 to 200, and most preferably 130 to 200.

By using a mercaptan chain transfer agent having a molecular weight of 200 or less, the unreacted chain transfer agent can be easily volatilized in the pelletizing step, and the optical properties of the resulting resin become good. Mercaptan chain transfer agents having a molecular weight of less than 100 are highly volatile, and the odor at the time of production is a problem. The mercaptan chain transfer agent is preferably bifunctional. By using a bifunctional chain transfer agent, the balance of strength, flowability and optical properties can be highly maintained. When a monofunctional chain transfer agent is used, the strength of the resulting methacrylic copolymer tends to be insufficient when the fluidity of the resin is enhanced. A trifunctional chain transfer agent having a molecular weight of 200 or less is difficult to obtain industrially, and the use of a polyfunctional chain transfer agent having a molecular weight of 200 or more tends to deteriorate the optical properties.

In the present invention, radical polymerization is carried out using a mercaptan chain transfer agent having a molecular weight of 200 or less (hereinafter sometimes referred to as mercaptan chain transfer agent (A)) to obtain a methacrylic copolymer derived from methyl methacrylate which is obtained. The molecular weight distribution of the methacrylic copolymer obtained (==) while maintaining the optical properties by controlling the amount of the bound sulfur atom derived from the mercaptan chain transfer agent (A) to the structural unit to 0.4 mol% or more The weight average molecular weight (Mw) / number average molecular weight (Mn) can be narrowed, and flowability and strength can be enhanced.

As the mercaptan chain transfer agent (A), for example, a difunctional compound such as 1,4-butanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, 3,6-dioxa-1,8-octanedithiol and the like Mercaptan is mentioned. These mercaptan chain transfer agents (A) may be used alone or in combination of two or more.

The amount of bound sulfur atoms of the methacrylic copolymer is a value determined as follows. The methacrylic copolymer is dissolved in chloroform to obtain a solution. This solution is added to n-hexane to obtain a precipitate. The precipitate is dried at 80 ° C. for more than 12 hours under vacuum. An appropriate amount of the obtained dried product is precisely weighed, set in a sulfur combustion apparatus, decomposed in a reactor at a temperature of 400 ° C., and generated gas is passed through a furnace at a temperature of 900 ° C., and then 0.3% hydrogen peroxide solution Absorb with The resulting solution (decomposed gas aqueous solution) is appropriately diluted with pure water, and the sulfate ion is quantified by ion chromatography (ICS-1500 manufactured by DIONEX, column: AS12A). The mass W _p (mass%) of sulfur atoms per mass of the dried product is calculated. Using the mass W _MMA (% by mass) of the structural unit derived from methyl methacrylate to the methacrylic copolymer, in the following formula, the amount S _p (mol%) of the bound sulfur atom to the structural unit derived from methyl methacrylate calculate.
_{_{S p = W p × (100/32}} ) / (W MMA / 100)

The copolymer of the present invention contains 10% by mass of a structural unit derived from a radically polymerizable monomer (hereinafter sometimes referred to as a radically polymerizable monomer (B)) other than methyl methacrylate monomer The content is preferably 1.0 to 9.5% by mass, more preferably 3.0 to 9.0% by mass. As such radically polymerizable monomers, methacrylic acid alkyl esters other than methyl methacrylate such as ethyl methacrylate and butyl methacrylate; aryl methacrylate esters such as phenyl methacrylate; methacrylic acid cyclohexyl, 2-isobornyl methacrylic acid Methacrylic acid cycloalkyl esters such as 8-tricyclo [5.2.1.0 ^2,6 ] decanyl methacrylate, 2-norbornyl methacrylate, 2-adamantyl methacrylate; 2-methylene-1,3-dioxepane etc. Cyclic ketene acetals; vinyl aromatic hydrocarbons such as styrene, α-methylstyrene, p-methylstyrene, m-methylstyrene, etc .; vinylcyclohexane, vinylcyclopentane, vinylcyclohexene, vinylcycloheptane, vinylcyclohepte Vinyl cycloaliphatic hydrocarbons such as styrene and vinyl norbornene; ethylenically unsaturated carboxylic acids such as maleic anhydride, maleic acid and itaconic acid; olefins such as ethylene, propylene, 1-butene, isobutylene and 1-octene; butadiene, Isoprene, conjugated dienes such as myrcene; acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, vinyl acetate, vinyl ketone, vinyl chloride, vinylidene chloride, vinylidene fluoride; methyl acrylate, ethyl acrylate, n-propyl acrylate, acrylic acid Isopropyl, n-butyl acrylate, isobutyl acrylate, s-butyl acrylate, t-butyl acrylate, amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, acrylate Acrylic acid alkyl esters such as pentadecyl lactate and dodecyl acrylic acid; 2-hydroxyethyl acrylate; 2-ethoxyethyl acrylate; glycidyl acrylate; allyl acrylate; acrylic acid ester derivatives such as benzyl acrylate; 2-vinylfuran , 2-isopropenylfuran, 2-vinylbenzofuran, 2-isopropenylbenzofuran, 2-vinyldibenzofuran, 2-vinylthiophene, 2-isopropenylthiophene, 2-vinyldibenzothiophene, 2-vinylpyrrole, N-vinylindole, N-vinylcarbazole, 2-vinyloxazole, 2-isopropenyloxazole, 2-vinylbenzoxazole, 3-vinylisoxazole, 3-isopropenylisoxazole, 2-vinylthiazo 2-vinylimidazole, 4 (5) -vinylimidazole, N-vinylimidazole, N-vinylimidazoline, 2-vinylbenzimidazole, 5 (6) -vinylbenzimidazole, 5-isopropenylpyrazole, 2-isopropenyl 1 , 3,4-oxadiazole, vinyltetrazole, 2-vinylpyridine, 4-vinylpyridine, 2-isopropenylpyridine, 3-vinylpyridine, 3-isopropenylpyridine, 2-vinylquinoline, 2-isopropenylquinoline, 4-vinylquinoline, 4-vinylpyrimidine, 2,4-dimethyl-6-vinyl-S-triazine, 3-methylidene dihydrofuran-2 (3H) -one, 4-methyl-3-methylidene dihydrofuran-2 (3H) -one, 4-decyl-3-methylidene dihydrofura Ethylenically unsaturated heterocyclic compounds such as n-2 (3H) -one; phosphates having an ethylenically unsaturated group such as dimethylmethacryloyloxymethyl phosphate and 2-methacryloyloxy-1-methylethyl phosphate; Be Among these, from the viewpoint of transparency, the acrylic acid alkyl ester and acrylic acid ester such as the acrylic acid derivative are preferable, the alkyl ester having 1 to 6 carbon atoms of acrylic acid is more preferable, and methyl acrylate is most preferable. preferable. These radically polymerizable monomers (B) may be used alone or in combination of two or more.

The methacrylic copolymer of the present invention has a weight-average molecular weight / number-average molecular weight ratio (hereinafter, this ratio may be referred to as a molecular weight distribution) is 1.85 or less, preferably 1.60 to 1.85. And more preferably 1.70 to 1.79. If the molecular weight distribution is small, the molding processability of the methacrylic copolymer tends to decrease. When the molecular weight distribution is large, the impact resistance of a molded article obtained from the methacrylic copolymer is lowered, and it tends to be brittle.
In addition, a weight average molecular weight and a number average molecular weight are the value of standard polystyrene conversion calculated based on the chromatogram obtained by gel permeation chromatography (GPC).
The weight average molecular weight and molecular weight distribution of the methacrylic copolymer can be controlled by adjusting the type and amount of the polymerization initiator and the mercaptan chain transfer agent having a molecular weight of 200 or less.

In the case of a methacrylic copolymer having a low weight average molecular weight, the strength of the low molecular weight polymer tends to affect the strength of the entire resin, so the effect of improving the strength by narrowing the molecular weight distribution tends to be noticeable is there. The weight average molecular weight of the methacrylic copolymer obtained by the present invention is preferably 35,000 to 90,000, more preferably 40,000 to 70,000, and particularly preferably 40,000 to 65,000. If the Mw is too small, the impact resistance and toughness of the molded article obtained from the methacrylic copolymer tend to decrease. If the Mw is too large, the flowability of the methacrylic copolymer will decrease, and the moldability tends to decrease accordingly.

Each monomer contained in the polymerization reaction raw material preferably has a measured length of 200 mm and a yellow index (YI) of 2 or less, more preferably 1 or less. When the yellow index of the monomer is small, when the resulting methacrylic copolymer is molded, a molded product having little coloring is easily obtained with high production efficiency. The yellow index is a value measured according to JIS Z8722 using a colorimetric color difference meter ZE-2000 manufactured by Nippon Denshoku Kogyo Co., Ltd.

The polymerization reaction of the polymerization reaction raw material is preferably carried out by bulk polymerization or solution polymerization, more preferably by bulk polymerization. Bulk polymerization is preferably continuous bulk polymerization. The polymerization reaction is initiated by adding a polymerization initiator and a mercaptan chain transfer agent having a molecular weight of 200 or less to the polymerization reaction raw material. By adding a chain transfer agent to the polymerization reaction raw material, the weight average molecular weight and the like of the resulting methacrylic copolymer can be adjusted. The raw material for the polymerization reaction preferably has a dissolved oxygen content of 10 ppm or less, more preferably 5 ppm or less, still more preferably 4 ppm or less, and most preferably 3 ppm or less. When the amount of dissolved oxygen is in such a range, the polymerization reaction proceeds smoothly, and a molded article free of silver or coloring is easily obtained from the obtained methacrylic copolymer.

The polymerization initiator is not particularly limited as long as it generates reactive radicals. For example, 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 1,1-bis (t-hexylperoxy) cyclohexane, benzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, lauroyl peroxide, 2,2'-azobis (2-methylpropionitrile), 2, 2'-azobis (2-methylbutyronitrile), dimethyl 2,2'-azobis ( 2-methyl propionate). Among these, t-hexylperoxy 2-ethylhexanoate, 1,1-bis (t-hexylperoxy) cyclohexane, dimethyl 2,2'-azobis (2-methylpropionate) and the like are preferable.

The polymerization initiator preferably has a one-hour half-life temperature of 60 to 140 ° C., and more preferably 80 to 120 ° C. The polymerization initiator used for bulk polymerization preferably has a hydrogen extraction ability of 20% or less, more preferably 10% or less, and still more preferably 5% or less. These polymerization initiators can be used alone or in combination of two or more. Further, the addition amount, addition method, and the like of the polymerization initiator may be appropriately set according to the purpose, and are not particularly limited. For example, the amount of the polymerization initiator used for bulk polymerization is preferably 0.0001 to 0.02 parts by mass, more preferably 0.001 to 0.01 parts by mass, and further 100 parts by mass of the polymerization reaction raw material. Preferably, it is 0.005 to 0.007 parts by mass.

In addition, know the hydrogen extraction ability from the technical data of the polymerization initiator manufacturer (for example, Nippon Oil and Fats Co., Ltd. technical data "Hydrogen extraction ability and initiator efficiency of organic peroxide" (created in April 2003) etc. Can. Also, it can be measured by a radical trapping method using α-methylstyrene dimer, ie, α-methylstyrene dimer trapping method. The said measurement is generally performed as follows. First, the polymerization initiator is cleaved in the coexistence of α-methylstyrene dimer as a radical trapping agent to form radical fragments. Among the generated radical fragments, radical fragments having low hydrogen abstraction ability are captured by being attached to the double bond of α-methylstyrene dimer. On the other hand, radical fragments having high hydrogen abstraction ability abstract hydrogen from cyclohexane to generate cyclohexyl radicals, and the cyclohexyl radicals are added and captured to the double bond of α-methylstyrene dimer to form a cyclohexane capture product. Therefore, the hydrogen extraction ability is defined as the ratio (molar fraction) of radical fragments having a high hydrogen extraction ability to the theoretical amount of radical fragment generation, which is determined by quantifying cyclohexane or a cyclohexane scavenging product.

The solvent used for the solution polymerization is not particularly limited as long as it has a dissolving ability to the polymerization reaction raw material and the methacrylic copolymer obtained therefrom, but aromatic hydrocarbons such as benzene, toluene and ethylbenzene are preferable. These solvents can be used singly or in combination of two or more. The amount of the solvent used is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, based on 100 parts by mass of the polymerization reaction raw material. The greater the amount of solvent used, the lower the viscosity of the reaction solution and the better the handling, but the productivity tends to decrease.

The polymerization conversion ratio of the polymerization reaction raw material is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and still more preferably 35 to 65% by mass. When the polymerization conversion rate is too high, a large stirring power tends to be required to increase the viscosity. If the polymerization conversion rate is too low, removal of the remaining monomer tends to be insufficient, and the monomer content in the resulting methacrylic resin tends to be high. As a result, when a methacrylic resin is molded, the molded product tends to have an appearance defect such as silver. Unreacted monomers can be recovered from the polymerization reaction solution and used again for the polymerization reaction. The yellow index of the recovered monomer may be high due to the heat applied at the time of recovery and the like. The recovered monomer is preferably purified by an appropriate method to reduce the yellow index.

The apparatus for performing the bulk polymerization method or the solution polymerization method includes a tank reactor with a stirrer, a tubular reactor with a stirrer, and a tubular reactor with a static stirring ability. One or more of these apparatuses may be used, or two or more different reactors may be used in combination. Also, the device may be either batch or continuous flow. The stirrer used can be selected according to the type of reactor. Examples of the stirrer include a dynamic stirrer and a static stirrer. An apparatus most suitable for obtaining the methacrylic copolymer used in the present invention is one having at least one continuous flow tank reactor. The plurality of continuous flow tank reactors may be connected in series or in parallel.

In the tank type reactor, usually, a stirring means for stirring the liquid in the reaction tank, a supply unit for supplying polymerization reaction raw materials, polymerization auxiliary materials and the like to the reaction tank, and a reaction product for extracting reaction products from the reaction tank Has an extraction part of In the continuous flow type reaction, the amount supplied to the reaction vessel and the amount withdrawn from the reaction vessel are balanced so that the amount of liquid in the reaction vessel becomes substantially constant. The amount of liquid in the reaction vessel relative to the volume of the reaction vessel is preferably at least 1/4, more preferably 1/4 to 3/4, and still more preferably 1/3 to 2/3.

The stirring means may, for example, be a Max-blend type stirring device, a stirring device having a grid-like blade rotating along with the vertical rotation shaft disposed at the center, a propeller type stirring device, a screw type stirring device and the like. Among these, the Max Blend type stirring apparatus is preferably used from the viewpoint of uniform mixing.

The monomer containing at least methyl methacrylate, and the polymerization initiator and the chain transfer agent may be mixed and supplied to the reaction tank before they are all supplied to the reaction tank, or they may be separately supplied to the reaction tank It may be supplied. In the present invention, a method in which all are mixed before being supplied to the reaction vessel and supplied to the reaction vessel is preferable.

The mixing of the monomers, the polymerization initiator and the chain transfer agent contained in the polymerization reaction raw material is preferably carried out in an inert atmosphere such as nitrogen gas. In addition, in order to smoothly carry out continuous flow operation, the mixture obtained by mixing while continuously supplying from the storage tank to the mixer provided in the previous stage of the reaction tank through the tube is reacted It is preferred to flow continuously into the tank. The mixer can be equipped with a dynamic stirrer or a static stirrer.

The temperature during the polymerization reaction is preferably 100 to 150 ° C., more preferably 110 to 140 ° C. When the temperature at the time of the polymerization reaction is in such a range, it is easy to adjust the melt flow rate to the range described later. By setting the polymerization temperature to 100 ° C. or higher, the polymerization rate is increased, and the viscosity of the polymerization solution is lowered, so that the productivity tends to be improved. Moreover, coloring of the molded article obtained from the methacrylic copolymer obtained can be suppressed by setting superposition | polymerization temperature to 150 degrees C or less.

The polymerization reaction time is preferably 0.5 to 4 hours, more preferably 1.5 to 3.5 hours, and still more preferably 1 to 3 hours. In the case of a continuous flow reactor, the polymerization reaction time is the average residence time in the reactor. If the polymerization reaction time is too short, the necessary amount of polymerization initiator will increase. In addition, the control of the polymerization reaction becomes difficult by increasing the amount of the polymerization initiator, and not only the control of the molecular weight becomes difficult, but also the amount of chain transfer agent necessary to adjust with the melt flow rate of the obtained methacrylic copolymer decreases. The amount of bonded sulfur atoms to the structural unit derived from methyl methacrylate is decreased, and the thermal stability is deteriorated. On the other hand, when the polymerization reaction time is too long, it takes time for the reaction to reach a steady state, and the productivity tends to decrease. The polymerization is preferably carried out in an inert gas atmosphere such as nitrogen gas.

After completion of the polymerization, unreacted monomers and solvents are removed, if necessary. The removal method is not particularly limited, but heat degassing is preferred. The volatilization method may, for example, be an equilibrium flash method or an adiabatic flash method. In the adiabatic flash method, in particular, the degassing is performed at a temperature of preferably 200 to 300 ° C., more preferably 200 to 280 ° C., still more preferably 220 to 270 ° C., particularly preferably 220 to 260 ° C. If it is less than 200 ° C., it takes a long time to degas, and it tends to be insufficient. When the degassing is insufficient, appearance defects such as silver may occur in the molded product. Conversely, if the temperature exceeds 300 ° C., not only the formation of by-products causing coloring, ie, dimers and trimers of methyl methacrylate increases, but the resin tends to be colored due to oxidation, burning, etc. is there.

The heating time of the resin in the adiabatic flush method is preferably 0.3 to 5 minutes, more preferably 0.4 to 3 minutes, and particularly preferably 0.5 to 2 minutes. If the heating time is less than 0.3 minutes, the heating of the resin is insufficient and the amount of unreacted monomers is increased. Moreover, when it is made to retain for 5 minutes or more, the molded article obtained from the obtained methacrylic copolymer becomes easy to color.

The methacrylic copolymer of the present invention may further contain various additives in an amount of 0.5% by mass or less, preferably 0.2% by mass or less, as necessary. When the content of the additive is too large, appearance defects such as silver may occur in the molded article.
Additives include antioxidants, heat deterioration inhibitors, ultraviolet light absorbers, light stabilizers, lubricants, mold release agents, polymer processing aids, antistatic agents, flame retardants, dyes and pigments, light diffusing agents, organic dyes , Matting agents, impact modifiers, phosphors and the like.

The antioxidant has an effect of preventing oxidative deterioration of the resin alone in the presence of oxygen. For example, phosphorus-based antioxidants, hindered phenol-based antioxidants, thioether-based antioxidants and the like can be mentioned. These antioxidants can be used singly or in combination of two or more. Among them, phosphorus antioxidants and hindered phenol antioxidants are preferred from the viewpoint of the effect of preventing deterioration of optical properties due to coloring, and the combination of phosphorus antioxidant and hindered phenol antioxidant is more preferable. preferable.
When the phosphorus-based antioxidant and the hindered phenol-based antioxidant are used in combination, the ratio is not particularly limited, but the mass ratio of phosphorus-based antioxidant / hindered phenol-based antioxidant is preferably 1/5. It is preferably 2 to 1, more preferably 1/2 to 1/1.

Examples of phosphorus-based antioxidants include 2,2-methylenebis (4,6-di-t-butylphenyl) octyl phosphite (Asahi Denka Co., Ltd .; trade name: Adekastab HP-10), tris (2,4-di-t). -Butylphenyl) phosphite (manufactured by Ciba Specialty Chemicals; trade name: IRGAFOS 168) and the like are preferable.

As a hindered phenol-based antioxidant, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] (manufactured by Chiba Specialty Chemicals; trade name IRGANOX1010), Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (manufactured by Chiba Specialty Chemicals; trade name IRGANOX 1076) is preferable.

The thermal deterioration inhibitor is capable of preventing thermal deterioration of the resin by trapping polymer radicals generated when exposed to high heat under substantially oxygen-free conditions.
As the thermal degradation inhibitor, 2-t-butyl-6- (3′-t-butyl-5′-methyl-hydroxybenzyl) -4-methylphenyl acrylate (manufactured by Sumitomo Chemical Co., Ltd .; trade name: SMILIZER GM), 2,4-di-t-amyl-6- (3 ′, 5′-di-t-amyl-2′-hydroxy-α-methylbenzyl) phenyl acrylate (Sumitomo Chemical; trade name: SMILIZER GS) etc. preferable.

The ultraviolet light absorber is a compound having the ability to absorb ultraviolet light. UV absorbers are compounds that are said to mainly have the function of converting light energy into thermal energy.
As the ultraviolet absorber, benzophenones, benzotriazoles, triazines, benzoates, salicylates, cyanoacrylates, oxalic acid anilides, malonic esters, formamidines and the like can be mentioned. These can be used singly or in combination of two or more.
Among these, benzotriazoles or UV absorbers having a maximum value ε _max of the molar absorption coefficient at a wavelength of 380 to 450 nm of 1200 dm ³ · mol ⁻¹ cm ⁻¹ or less are preferable.

Since benzotriazoles have a high effect of suppressing deterioration of optical properties such as coloring due to ultraviolet irradiation, an ultraviolet absorber used when the methacrylic copolymer of the present invention is applied to applications requiring the above-mentioned properties. As preferred.

As benzotriazoles, 2- (2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol (manufactured by Ciba Specialty Chemicals; trade name TINUVIN 329), 2 -(2H-benzotriazol-2-yl) -4,6-bis (1-methyl-1-phenylethyl) phenol (manufactured by Chiba Specialty Chemicals; trade name TINUVIN 234) and the like are preferable.

In addition, the ultraviolet absorber having a maximum value ε _max of molar absorption coefficient at a wavelength of 380 to 450 nm of 1200 dm ³ · mol ⁻¹ cm ⁻¹ or less can suppress the yellowish taste of the obtained molded article.

In addition, maximum value (epsilon) _max of the molar absorption coefficient of a ultraviolet absorber is measured as follows. Add 10.00 mg of a UV absorber to 1 L of cyclohexane, and dissolve it so that there is no undissolved matter by visual observation. This solution is injected into a 1 cm × 1 cm × 3 cm quartz glass cell, and the absorbance at a wavelength of 380 to 450 nm is measured using a Hitachi U-3410 spectrophotometer. The molar absorption coefficient maximum value ε _max is calculated from the molecular weight (Mw) of the ultraviolet absorber and the maximum value (A _max ) of the measured absorbance according to the following equation.

ε _max = [A _max / (10 × 10 ^-3 )] × Mw

A 2-ethyl-2'-ethoxy-oxalanilide (manufactured by Clariant Japan Co., Ltd.) as a UV absorber having a maximum value ε _max of molar extinction coefficient at a wavelength of 380 to 450 nm of 1200 dm ³ · mol ^-1 cm ^-1 or less (Trade name: Sanduiboa VSU) and the like.
Among these ultraviolet absorbers, benzotriazoles are preferably used from the viewpoint of suppressing resin deterioration due to ultraviolet irradiation.

A light stabilizer is a compound that is said to have the function of capturing radicals generated mainly by oxidation by light. Suitable light stabilizers include hindered amines such as compounds having a 2,2,6,6-tetraalkylpiperidine backbone.
As the lubricant, for example, stearic acid, behenic acid, stearoamic acid, methylene bis stearoamide, hydroxystearic acid triglyceride, paraffin wax, ketone wax, octyl alcohol, hydrogenated oil and the like can be mentioned.

The release agent is a compound having a function of facilitating the release of the molded article from the mold. As a mold release agent, higher alcohols such as cetyl alcohol and stearyl alcohol; glycerin higher fatty acid esters such as monoglyceride stearate and diglyceride stearate are mentioned. In the present invention, it is preferable to use a higher alcohol and a glycerin fatty acid monoester in combination as a release agent. When the higher alcohol and the glycerin fatty acid monoester are used in combination, the ratio is not particularly limited, but the mass ratio of the higher alcohol / glycerin fatty acid monoester is preferably 2.5 / 1 to 3.5 / 1, Preferably, it is 2.8 / 1 to 3.2 / 1.

The polymer processing aid is a compound that exerts an effect on thickness accuracy and thinning when molding a methacrylic copolymer. The polymer processing aid is usually a polymer particle having a particle size of 0.05 to 0.5 μm, which can be produced by an emulsion polymerization method.
The polymer particle may be a single layer particle consisting of a polymer having a single composition ratio and a single intrinsic viscosity, or a multilayer particle consisting of two or more polymers different in composition ratio or intrinsic viscosity. May be Among these, particles of a two-layer structure having a polymer layer having a low intrinsic viscosity in the inner layer and a polymer layer having a high intrinsic viscosity of 5 dl / g or more in the outer layer are preferably mentioned.

The polymer processing aid preferably has an intrinsic viscosity of 3 to 6 dl / g. If the intrinsic viscosity is too small, the effect of improving formability tends to be low. When the intrinsic viscosity is too large, the melt flowability of the methacrylic resin tends to be lowered.
Examples of flame retardants include organic halogen flame retardants such as tetrabromobisphenol A, decabromodiphenyl oxide and brominated polycarbonate; non-halogen flame retardants such as antimony oxide, aluminum hydroxide, zinc borate and tricresyl phosphate Etc.
As the antistatic agent, for example, stearoamidopropyl dimethyl-β-hydroxyethyl ammonium nitrate and the like can be mentioned.
Examples of dyes and pigments include titanium oxide and bengala.

An impact modifier may be used in the methacrylic copolymer of the present invention. The impact modifier includes, for example, a core-shell modifier containing an acrylic rubber or a diene rubber as a core layer component; and a modifier containing a plurality of rubber particles.

As the organic dye, a compound having a function of converting ultraviolet light, which is harmful to the resin, into visible light is preferably used.
Examples of the light diffusing agent and the matting agent include glass particles, polysiloxane based crosslinked particles, crosslinked polymer particles, talc, calcium carbonate and barium sulfate.
As the fluorescent substance, fluorescent pigment, fluorescent dye, fluorescent white dye, fluorescent whitening agent, fluorescent bleach and the like can be mentioned.

These additives may be added to the polymerization reaction solution for producing the methacrylic copolymer, or may be added to the methacrylic copolymer produced by the polymerization reaction.

The methacrylic copolymer of the present invention has a melt flow rate of 25 g / 10 min or more, preferably 25 to 50 g / 10 min, more preferably 27 to 45 g / 10 min, more preferably at 230 ° C. and a load of 3.8 kg. Is 28 to 42 g / 10 min. The melt flow rate is a value measured under the conditions of 230 ° C., 3.8 kg load, and 10 minutes in accordance with JIS K 7210. When the melt flow rate is in this range, the effect of the present invention in which the strength of the methacrylic copolymer in a high flow region is excellent can be characteristically exhibited.

The yellow index (YI) of the optical path length of 200 mm of the injection molded article obtained by obtaining the methacrylic copolymer of the present invention at a cylinder temperature of 280 ° C. and a molding cycle of 1 minute is preferably 5 or less, more preferably 4 or less, more preferably Is less than 3.5. The yellow index is a value measured according to JIS Z8722 using a colorimetric color difference meter ZE-2000 manufactured by Nippon Denshoku Kogyo Co., Ltd.

The methacrylic copolymer of the present invention can be formed into a pellet-like molding material in accordance with a known method to facilitate handling. The pellet-like molding material can be obtained, for example, by injecting the methacrylic copolymer of the present invention, which has been melted in an extruder, into a die plate, and cooling and cutting the resin extruded in the form of a strand. As a method of cutting the strands into pellets, methods such as underwater cutting, hot cutting, strand cutting and the like can be adopted.

Since the methacrylic copolymer of the present invention is excellent in transparency, moldability and mechanical strength, it is useful as various molded articles. For example, molded articles excellent in mechanical strength and appearance of various shapes are formed by molding (melting and heating molding) by a conventionally known molding method such as press molding, injection molding, compression molding, extrusion molding, vacuum molding and the like. You can get it.
The molded article of the present invention is preferably an optical member. The optical member is preferably manufactured by injection molding, press molding. Examples of the optical member include a light guide, a diffuser, a prism, a lens, an optical filter, an optical disc, and an optical member having two or more functions among those described above. These optical members are suitably used as, for example, liquid crystal display devices, plasma display devices, light emitting diode display devices, field emission display devices, organic electroluminescent display devices, projection display devices, light receiving members of automatic toll systems for highways, etc. Used.

Since the methacrylic copolymer of the present invention is excellent in transparency, moldability and mechanical strength, it is useful as various molded articles. Examples of applications of molded articles obtained include billboard articles such as advertising towers, stand signs, sleeve signs, cross signs, roof signs and the like; display articles such as showcases, partition plates, store displays; fluorescent light covers, mood lighting covers, Lighting products such as lampshades, light ceilings, light walls and chandeliers; interior products such as pendants and mirrors; doors, domes, safety glass panes, partitions, stairwells, balcony waistboards, architectural parts such as leisure roofs Transportation parts such as aircraft windshields, pilot visors, motorcycles, motor boat windshields, bus shades for cars, side visors for cars, rear visors, head wings, headlight covers, meter covers, tail lamp covers etc. nameplates for audio visuals, stereo Cover, TV protective mask, vending machine Which electronic equipment parts; medical equipment parts such as incubators, X-ray parts; machine related parts such as instrument covers, instrument covers, experimental equipment, rulers, dials, observation windows etc; LCD protective plates, light guide plates, light guide films, fresnels Optical components such as lenses, lenticular lenses, front plates of various displays, diffusion plates, etc. Traffic related components such as road signs, guide plates, curved mirrors, sound barriers, etc. Surface materials for car interiors, surface materials for mobile phones, marking films Film members, such as washing machine canopy and control panel, rice cooker top panel etc. Other, greenhouse, large water tank, box water tank, clock panel, bathtub, sanitary, desk mat, game parts, etc. Toys, masks for face protection at the time of welding, etc. may be mentioned.

Hereinafter, the present invention will be more specifically described with reference to examples and comparative examples. The present invention is not limited by the following examples. In addition, the present invention includes all aspects in which the above-described matters representing technical characteristics such as characteristic values, forms, manufacturing methods, applications and the like are arbitrarily combined.

Measurement of physical property values and the like in Examples and Comparative Examples were carried out by the following methods.

(Compositional unit composition analysis of copolymer)
Device: Nuclear magnetic resonance device (Bruker ULTRA SHIELD 400 PLUS)
Solvent: Heavy chloroform Measurement nuclide: ¹ H
Measurement temperature: Room temperature Integration number: 64 times (weight average molecular weight (Mw), number average molecular weight (Mn), molecular weight distribution)
The chromatogram was measured by gel permeation chromatography (GPC) under the following conditions, and the value converted to the molecular weight of standard polystyrene was calculated. In the baseline, the slope of the high molecular weight peak of the GPC chart changes from zero to positive when the retention time is earlier, and the slope of the low molecular weight peak is negative to zero when the retention time is earlier The line connecting points that change to
GPC apparatus: Tosoh Corp. HLC-8320
Detector: Differential Refractive Index Detector Column: Two TSKgel SuperMultipore HZM-M's manufactured by Tosoh Corporation and Super HZ 4000 connected in series were used.
Eluent: Tetrahydrofuran Eluent flow rate: 0.35 ml / min Column temperature: 40 ° C.
Calibration curve: made using data of 10 standard polystyrene

(Melt flow rate (MFR))
The methacrylic copolymer was measured at 230 ° C. under a load of 3.8 kg for 10 minutes in accordance with JIS K7210.

(Amount of bound sulfur atom)
The amount of bound sulfur atoms of the methacrylic copolymer is a value determined as follows. The methacrylic copolymer is dissolved in chloroform to obtain a solution. This solution is added to n-hexane to obtain a precipitate. The precipitate is dried at 80 ° C. for more than 12 hours under vacuum. An appropriate amount of the obtained dried product is precisely weighed, set in a sulfur combustion apparatus, decomposed in a reactor at a temperature of 400 ° C., and generated gas is passed through a furnace at a temperature of 900 ° C., and then 0.3% hydrogen peroxide solution Absorb with The resulting solution (decomposed gas aqueous solution) is appropriately diluted with pure water, and the sulfate ion is quantified by ion chromatography (ICS-1500 manufactured by DIONEX, column: AS12A). The mass W _p (mass%) of sulfur atoms per mass of the dried product is calculated. Using the mass W _MMA (% by mass) of the structural unit derived from methyl methacrylate to the methacrylic copolymer, in the following formula, the bound sulfur atom (molecular weight 32) to the structural unit (molecular weight 100) derived from methyl methacrylate Calculate the quantity S _p (mol%).
_{_{S p = W p × (100/32}} ) / (W MMA / 100)

(Glass-transition temperature)
The methacrylic copolymer obtained in the examples is heated up to 250 ° C. once using a differential scanning calorimeter (DSC-50 (product number) manufactured by Shimadzu Corporation) in accordance with JIS K 7121 and then room temperature The DSC curve was measured under the conditions of cooling to room temperature and then raising the temperature from room temperature to 200 ° C. at 10 ° C./min. The midpoint glass transition temperature determined from the DSC curve measured at the second temperature rise was taken as the glass transition temperature in the present invention.

(1% thermal weight loss temperature)
The methacrylic copolymer is heated from 25 ° C. to 500 ° C. at a flow rate of 50 ml / minute in an air atmosphere at a temperature of 10 ° C./minute using a thermogravimetric apparatus (manufactured by Shimadzu Corporation, TGA-50 (product number)) The thermal weight loss was measured under the conditions of temperature rise. Based on a weight (X1) of 200 ° C. (100%), the temperature at which a 1% weight loss was observed was evaluated.

(Color of injection molded product (YI))
Made by Japan Steel Works, Ltd. Injection molding machine: J-110EL, pelletized methacrylic copolymer is injection molded at a cylinder temperature of 280 ° C, a mold temperature of 68 ° C and a molding cycle of 1 minute, A flat plate of 200 mm in width, 60 mm in width and 30 mm in thickness was manufactured, and the yellow index (YI) of 200 mm in measurement length was measured.

(Total light transmittance)
The total light transmittance at an optical path length of 3 mm of the flat plate was measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory) according to JIS K7361-1.

(Bending strength of press-formed products)
The methacrylic copolymer obtained in Examples and Comparative Examples was heat-pressed at 230 ° C. to form a flat plate of 50 mm × 20 mm × 3 mm. Using this flat plate, using an autograph (AG-IS manufactured by Shimadzu Corporation), perform a 3-point bending test at a test speed of 2 mm / min at 23 ° C. in accordance with ISO 178 with a distance between supporting points of 30 mm. The maximum point stress was taken as the bending strength.

Hereinafter, methyl methacrylate is MMA, methyl acrylate is MA, azobisisobutyronitrile is AIBN, n-octylmercaptan is n-OM, 1,4-butanedithiol is 1,4-BDT, 3,6-dioxax The 1,1,8-octanedithiol is denoted as DMDO, pentaerythritol tetrakisthiopropionate as PETP, and ethylene glycol thiobisglycolate as EGTG. Note that DMDO is manufactured by Tokyo Chemical Industry Co., Ltd., and all other reagents are manufactured by Wako Pure Chemical Industries, Ltd.

Example 1
In a polymerization reactor equipped with a stirrer, a monomer mixture consisting of 93.3 parts by mass of MMA and 6.7 parts by mass of MA, 0.007 parts by mass of AIBN as a radical polymerization initiator, DMDO 0. 2 as a polyfunctional chain transfer agent. A mixed solution consisting of 435 parts by mass was continuously fed, bulk polymerization was carried out under conditions of a polymerization temperature of 140 ° C. and an average residence time of 2 hours, and the polymerization reaction solution was continuously withdrawn. Then, the reaction liquid coming out of the polymerization reactor was heated to 230 ° C., and was fed to a twin-screw extruder controlled to 260 ° C. In the twin-screw extruder, the volatile component mainly containing unreacted monomer was separated and removed, and the polymer was extruded in the form of a strand. The strand was cut by a pelletizer to obtain a pellet-like methacrylic copolymer [1].
Injection molded articles and press molded articles were produced using the methacrylic copolymer, and used for the above evaluation. The evaluation results are shown in Table 1.

(Example 2)
A pellet-like methacrylic copolymer [2] was obtained in the same manner as in Example 1 except that the amount of DMDO in Example 1 was changed to 0.480 parts by mass.
Molded articles were produced using the methacrylic copolymer [2] and used for the above evaluation. The evaluation results are shown in Table 1.

(Example 3)
In a polymerization reactor equipped with a stirrer, a monomer mixture comprising 88.0 parts by mass of MMA and 12.0 parts by mass of MA, 0.007 parts by mass of AIBN as a radical polymerization initiator, BDT 0. 2 as a polyfunctional chain transfer agent. A mixed solution consisting of 256 parts by mass was continuously supplied, bulk polymerization was carried out under conditions of a polymerization temperature of 140 ° C. and an average residence time of 2 hours, and the polymerization reaction solution was continuously withdrawn. Then, the reaction liquid coming out of the polymerization reactor was heated to 230 ° C., and was fed to a twin-screw extruder controlled to 260 ° C. In the twin-screw extruder, the volatile component mainly containing unreacted monomer was separated and removed, and the polymer was extruded in the form of a strand. The strand was cut by a pelletizer to obtain a pellet-like methacrylic copolymer [3].
Molded articles were produced using the methacrylic copolymer [3] and used for the above evaluation. The evaluation results are shown in Table 1.

(Example 4)
A pellet-like methacrylic copolymer [4] was obtained in the same manner as in Example 3 except that the amount of BDT in Example 3 was changed to 0.285 parts by mass.
A molded article was produced using the methacrylic copolymer [4] and used for the above evaluation. The evaluation results are shown in Table 1.

(Example 5)
A pellet-shaped methacrylic copolymer [5] was obtained in the same manner as in Example 3, except that 0.340 parts by mass of DMDO was used as a polyfunctional chain transfer agent in place of BDT in Example 3.
A molded article was produced using the methacrylic copolymer [5] and used for the above evaluation. The evaluation results are shown in Table 1.

(Comparative example 1)
A pellet-shaped methacrylic copolymer [6] was obtained in the same manner as in Example 1 except that 0.480 parts by mass of n-OM was used as a monofunctional chain transfer agent instead of DMDO in Example 1.
Molded articles were produced using the methacrylic copolymer [6] and used for the above evaluation. The evaluation results are shown in Table 1.

(Comparative example 2)
A pellet-shaped methacrylic copolymer [7] was obtained in the same manner as in Example 1 except that 0.525 parts by mass of n-OM was used as a monofunctional chain transfer agent instead of DMDO in Example 1.
Molded articles were produced using the methacrylic copolymer [7], and used for the above evaluation. The evaluation results are shown in Table 1.

(Comparative example 3)
A pellet-shaped methacrylic copolymer [8] was obtained in the same manner as in Example 3 except that 0.440 parts by mass of n-OM was used as a monofunctional chain transfer agent instead of BDT in Example 3.
Molded articles were produced using the methacrylic copolymer [8], and used for the above evaluation. The evaluation results are shown in Table 1.

(Comparative example 4)
A pellet-shaped methacrylic copolymer [9] was obtained in the same manner as in Example 3 except that 0.470 parts by mass of EGTG was used as a polyfunctional chain transfer agent instead of BDT in Example 3.
A molded article was produced using the methacrylic copolymer [9], and used for the above evaluation. The evaluation results are shown in Table 1.

(Comparative example 5)
A pellet-shaped methacrylic copolymer [10] was obtained in the same manner as in Example 3 except that 0.660 parts by mass of PETP as a polyfunctional chain transfer agent was used instead of BDT in Example 3.
A molded article was produced using the methacrylic copolymer [10] and used for the above evaluation. The evaluation results are shown in Table 1.

(Comparative example 6)
In a polymerization reactor equipped with a stirrer, a monomer mixture consisting of 85.0 parts by mass of MMA and 15.0 parts by mass of MA, 0.007 parts by mass of AIBN as a radical polymerization initiator, and DMDO 0.340 as a polyfunctional chain transfer agent The mixed solution consisting of parts by mass was continuously supplied, bulk polymerization was carried out under conditions of a polymerization temperature of 140 ° C. and an average residence time of 2 hours, and the polymerization reaction solution was continuously withdrawn. Then, the reaction liquid coming out of the polymerization reactor was heated to 230 ° C., and was fed to a twin-screw extruder controlled to 260 ° C. In the twin-screw extruder, volatile components mainly containing unreacted monomers were removed, and the polymer was extruded in the form of a strand. The strand was cut by a pelletizer to obtain a pellet-like methacrylic copolymer [11].
A molded article was produced using the methacrylic copolymer [11] and used for the above evaluation. The evaluation results are shown in Table 1.

In the embodiment of the present invention, which is a methacrylic copolymer derived from a mercaptan chain transfer agent having a molecular weight of 200 or less and having a binding sulfur atom content of 0.4 mol% or more, the binding sulfur atom content is 0. It can be seen that the mechanical strength is excellent while having the same MFR value as compared with Comparative Examples 1 to 3 different from the present invention in that it is less than 4 mol%.
Moreover, compared with Comparative Examples 4 and 5 which are different from the present invention in that they are methacrylic copolymers derived from mercaptan chain transfer agents having a molecular weight of 200 or more and having a binding sulfur atom amount of 0.4 mol% or more. And the color indicated by YI is excellent.
Further, it is understood that the color indicated by YI is superior as compared with Comparative Example 6 which is different from the present invention in the content of the MMA structural unit.
As described above, the methacrylic copolymer of the present invention has transparency suitable for optical applications, and is excellent in both MFR and flexural strength. From this, by using the methacrylic copolymer of the present invention, a molded article excellent in mechanical strength and appearance can be obtained.

Claims

A methacrylic copolymer comprising 90% by mass or more of a structural unit derived from methyl methacrylate, wherein the methacrylic copolymer is derived from a mercaptan chain transfer agent having a molecular weight of 200 or less relative to a structural unit derived from methyl methacrylate. And a methacrylic copolymer having an amount of bound sulfur atoms of 0.4 mol% or more and a melt flow rate of 25 g / 10 minutes to 50 g / 10 minutes under conditions of 230 ° C. and 3.8 kg load.
The methacrylic copolymer according to claim 1, wherein the value of the molecular weight distribution (Mw / Mn) of the methacrylic copolymer is 1.85 or less.
The methacrylic copolymer according to claim 1 or 2, wherein the mercaptan chain transfer agent is a bifunctional mercaptan.
The methacrylic copolymer according to any one of claims 1 to 3, which is obtained by continuous bulk polymerization.
A methyl methacrylate, a bifunctional mercaptan chain transfer agent having a molecular weight of 200 or less, containing a radical polymerization initiator, is added in an amount of 0.2 to 0. 0 based on 100 parts by mass of all the polymerizable monomers to be subjected to polymerization. A raw material liquid containing 5 parts by mass, optionally containing acrylic acid alkyl ester, and having a weight ratio of acrylic acid alkyl ester / methyl methacrylate of 0/100 to 10/90, is continuously fed to the tank reactor. In the tank reactor, bulk polymerization is carried out at a polymerization conversion rate of 40 to 70% by mass to obtain a reaction product, and the reaction product is continuously withdrawn from the tank reactor, from the reaction product The method for producing a methacrylic copolymer according to any one of claims 1 to 4, comprising the step of removing volatile components.
A pellet-like molding material comprising the methacrylic copolymer according to any one of claims 1 to 4.
An optical member obtained by injection molding the molding material according to claim 6, wherein the yellow index (YI) with a measuring length of 200 mm is 5 or less.
An optical member obtained by press-molding the methacrylic copolymer according to any one of claims 1 to 4.