JP2021107563A - Methacrylic resin and process for producing the same - Google Patents

Abstract

To provide a methacrylic resin that has high heat resistance, excellent color tone and transparency, and excellent moldability.SOLUTION: Provided are: a methacrylic resin containing 3 to 50 mass% of a structural unit (B) having a ring structure in the main chain, the methacrylic resin characterized that, the weight average molecular weight (Mw) is 60,000 to 250,000, the ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) is 1.5 to 4.0, the glass transition temperature (Tg) is 105 to 130°C, and the amount of the THF-insoluble matter of the methacrylic resin is less than 0.5 mass%; and a process for producing the same.SELECTED DRAWING: None

Description

The present invention relates to a methacrylic resin having high heat resistance, highly controlled birefringence, excellent color tone and transparency, and excellent moldability, and a method for producing the same.

In recent years, methacrylic resins are excellent in transparency, surface hardness, etc., and also have small double refraction, which is an optical characteristic. Therefore, for example, various optical products such as liquid crystal displays, plasma displays, and organic EL displays. Flat panel displays such as, small infrared sensors, fine optical waveguides, ultra-small lenses, pickup lenses for DVD / BlueRayDisc that handle short-wavelength light, etc., attracting attention as optical resins for optical materials such as optical disks, optical films, and plastic substrates The market is expanding significantly.

In particular, it is known that a methacrylic resin having a ring structure in the main chain and a composition containing the methacrylic resin have excellent performance in both heat resistance and optical properties (for example, a patent). (Refer to Reference 1), the demand is expanding rapidly year by year. However, the methacrylic resin having a ring structure in the main chain with improved heat resistance and optical properties as described above sometimes becomes colored by absorption in the visible light region due to the ring structure or the like, or the transmittance is reduced. There is a problem such as. Therefore, in order to obtain a methacrylic resin having a ring structure in the main chain, which is less colored and has high transparency, a method for reducing the unreacted cyclic monomer remaining in the methacrylic resin is disclosed.

For example, Patent Document 2 uses a monomer component containing an N-substituted maleimide (a) and a methacrylate ester (b), supplies a part of the monomer component to initiate polymerization, and then polymerizes. In the production method in which the remainder of the monomer component is supplied on the way, the ratio of the N-substituted maleimide (a) in the unreacted monomer component present in the reaction system at the end of the supply of the monomer component is simply By controlling the amount to be less than the ratio of the N-substituted maleimide (a) in the total amount of the polymer component supplied, the amount of the residual N-substituted maleimide monomer is reduced, and the heat resistance is excellent in transparency and less coloring. A method for obtaining a sex methacrylic resin has been proposed.
Further, Patent Document 3 proposes a polymer having a lactone ring formed by an intramolecular cyclization reaction after polymerization as a ring structure having less colorability.
Further, Patent Document 4 describes residual maleimide by allowing an acidic substance to exist in the reaction system in a methacrylic ester monomer / maleimide monomer polymerization system using a sulfur-based chain transfer agent such as mercaptan. A method has been proposed in which the amount of similar monomers and the maleimides generated by heating during molding processing are reduced to suppress coloring.

International Publication No. 2011/149808 Japanese Unexamined Patent Publication No. 9-324016 JP-A-2007-297620 Japanese Unexamined Patent Publication No. 2001-233919

However, in recent years, the application has been expanded from the optical film application to the thick molded article application such as a lens and a molded plate. The provision of a resin capable of exhibiting high transparency has been eagerly desired.

In Patent Documents 2 and 4, as a method for reducing coloring, attention is paid to N-substituted maleimide having strong coloring as the monomer itself, reduction of the amount of N-substituted maleimide remaining in the methacrylic resin, molding processing, etc. Attention is paid to the amount of N-substituted maleimide based on the thermal history of the above, and a method of trying to solve the problem by reducing it has been proposed.

However, as described above, it has been found that, for example, as a methacrylic resin for expanding into molded articles having a long optical path length, it is insufficient for improving the degree of coloring and transparency.

Therefore, it is strongly desired to further improve the colorability and transparency of the methacrylic resin by paying attention not only to the remaining colorable monomer such as N-substituted maleimide but also to the polymer itself. ing.

On the other hand, the polymer having the lactone ring structure of Patent Document 3 is superior to the N-substituted maleimide system in terms of coloring and the like, but has the following problems.
For example, during the intramolecular cyclization reaction of lactone ring formation, an intermolecular cyclization reaction also occurs at the same time, and as a result, a high molecular weight gel component is produced. Since the same reaction occurs during the molding process of the resin, the formation of the gel component in the polymer is observed after the molding.
Further, in the case of a methacrylic resin having a lactone structure, since it contains a component containing a large amount of unreacted hydroxyl groups and a low molecular weight component that is easily decomposed, an unfavorable intermolecular reaction may occur or a low molecular weight such as an oligomer due to decomposition may occur. Problems such as deterioration of moldability may occur due to component generation.
Further, since these components are highly hygroscopic, they have a plurality of problems to be solved, such as a concern that problems such as whitening of a molded product may occur under high humidity conditions.

An object of the present invention is to provide a methacrylic resin having high heat resistance, excellent color tone and transparency, and excellent moldability by solving the above problems.

As a result of diligent studies to solve the above-mentioned problems of the prior art, the present inventors have confirmed that the methacrylic resin having the above-mentioned lactone structure is more excellent for improving the color tone. Furthermore, as a result of diligent studies on problems such as gelation of methacrylic resins having a lactone structure, these problems are the primary structure of the polymer, the hydroxyl groups that remain as unreacted substances during the cyclization reaction, and the moisture absorbed after the polymerization. It was presumed that it was caused by the hydroxyl group generated from the hydrolysis by. As a result of polymerization analysis, the methacrylic monomer having a hydroxy group, which is a precursor of the lactone structure, has a higher polymerization rate than the comonomer MMA and maleimide, and therefore tends to be consumed at the initial stage of polymerization by simple batch polymerization. found. From this, there is a tendency that a methacrylic monomer chain having a hydroxy group is easily formed at the initial stage of polymerization, and when there is a monomer chain having a hydroxyl group, intermolecular cyclization is likely to occur in addition to intramolecular cyclization. As a result, it was estimated that gelation may have occurred. However, it is difficult to quantitatively grasp the above factors by the current polymer analysis methods such as IR and NMR. Therefore, while diligently studying the methods for producing polymers, we diligently investigated whether or not we could find a factor different from the above-mentioned analytical method that controls the susceptibility of gelling and decomposition reactions of those polymers.

As a result, it was found that the generation of gel can be suppressed by appropriately controlling the concentration of comonomer in the reactor during polymerization and suppressing the formation of comonomer chains.

Furthermore, in the case of a methacrylic resin having a lactone structure, the polarity changes significantly before and after the intramolecular cyclization reaction, and the polymer before the cyclization reaction has a large amount of reprecipitated solvent-soluble components during the methanol reprecipitation operation, whereas the ring After the chemical reaction, it was found that the reprecipitated solvent-soluble content during the methanol reprecipitation operation was significantly reduced. Since these reprecipitated solvent-soluble components are presumed to be components containing a large amount of unreacted hydroxyl groups and easily degradable low molecular weight components, it is necessary to suppress their formation as much as possible. In addition, it is necessary to sufficiently proceed the cyclization reaction in order to reduce the hydroxyl groups. As an index of the progress of the cyclization reaction, there is a method of calculating by measurement by a specific TGA described in Patent Document 3, but the error is large and it cannot be used as a practical index. Therefore, as a result of diligent studies on a new index for the polymer polymerized by the above method, the difference in the decomposition start temperature of the methanol-soluble and methanol-insoluble components of the methacrylic resin in the TGA causes gelation and decomposition reaction. Found to be relevant. Furthermore, it was also found that the methanol-soluble components after the cyclization reaction contained a particularly large amount of coloring components. As a result, it was clarified that the above problems can be solved by controlling the amounts and thermal decomposition characteristics of the reprecipitated solvent-soluble component and the reprecipitated solvent-insoluble component after reprecipitation of methanol, respectively, and the present invention is completed. It has reached.
Further, the method found in the present invention is not limited to a resin having a lactone ring structure unit as a methacrylic resin having a ring structure in the main chain, for example, a resin having a ring structure derived from an N-substituted maleimide monomer and the like. It can also be applied to.

That is, the present invention is as follows.
[1]
A methacrylic resin containing 3 to 50% by mass of a structural unit (B) having a ring structure in the main chain.
The weight average molecular weight (Mw) is 60,000 to 250,000.
The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 1.5 to 4.0.
The glass transition temperature (Tg) is 105-130 ° C.
The amount of THF insoluble in the methacrylic resin is less than 0.5% by mass.
A methacrylic resin characterized by this.
[2]
The amount of the methanol-soluble component of the methacrylic resin is 0.5 to 10% by mass with respect to 100% by mass of the total amount of the methanol-soluble component and the methanol-insoluble component, according to [1]. Methanol resin.
[3]
The temperature at which the weight loss rate is 5% measured by thermogravimetric analysis (TGA) under nitrogen is 320 ° C. or higher, and the methanol-soluble component is measured by TGA under nitrogen to reduce the weight. The methacrylic resin according to [2], wherein the temperature at which the rate is 5% is 220 ° C. or higher.
[4]
The methacrylic resin according to any one of [1] to [3], wherein the amount of change in the THF insoluble content before and after molding at a temperature of 240 ° C. or higher is less than 1% by mass.
[5]
The methacrylic resin according to any one of [2] to [4], wherein the 20 w / v% chloroform solution having an insoluble methanol has a transmittance of 90% or more at 680 nm measured using a 10 cm optical path length cell.
[6]
The methacrylic resin according to any one of [1] to [5], wherein the methacrylic resin contains 50 to 97% by mass of the methacrylic acid ester monomer unit (A) with the methacrylic resin as 100% by mass. resin.
[7]
The methacrylic resin is a structural unit (B) having a ring structure in the main chain, with the methacrylic resin as 100% by mass, and 3 to 30% by mass, and other vinyl copolymerizable with the methacrylic ester monomer. The methacrylic resin according to any one of [1] to [6], which contains a system monomer unit (C): 0 to 20% by mass.
[8]
The content of the (B) structural unit is 45 to 100% by mass, where the total amount of the (B) structural unit and the (C) monomer unit is 100% by mass, [1] to [7]. ] The methacrylic resin according to any one of.
[9]
[1] to [1] to [1], wherein the structural unit (B) includes at least one structural unit selected from the group consisting of a lactone ring structural unit (B-1) and an N-substituted maleimide-based structural unit (B-2). 8] The methacryl-based resin according to any one of.
[10]
The monomer unit (C) contains at least one structural unit selected from the group consisting of an acrylic acid ester monomer, an aromatic vinyl-based monomer, and a vinyl cyanide-based monomer [1] to. The methacrylic resin according to any one of [9].
[11]
The ratio (Mz / Mw) of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) is 1.3 to 2.0, [1] to [10]. ] The methacrylic resin according to any one of.

[12]
Two or more kinds of monomers containing a methacrylic acid ester monomer and a monomer forming a structural unit (B) having a ring structure in the main chain are subjected to radical or semi-batch in a solvent. In the method of polymerization
A radical polymerization initiator having a half-life at the polymerization temperature of 1 minute or more and less than 60 minutes was used.
The radical polymerization initiator is added into the reactor while gradually reducing the amount of the radical polymerization initiator added per unit time to allow the polymerization of the monomer to proceed and to proceed with the polymerization.
The amount of the radical polymerization initiator added after the time when the polymerization conversion rate reaches 85% is 10 to 25% by mass, with the total amount of the radical polymerization initiator added being 100% by mass. A method for producing a methacrylic resin.
[13]
Two or more kinds of monomer components including a methacrylic acid ester monomer and a monomer forming a structural unit (B) having a ring structure in the main chain are subjected to a batch method or a semi-batch method in a solvent. In the method of radical polymerization
A radical polymerization initiator having a half-life of 60 minutes or more at the polymerization temperature was used.
Within 30 minutes from the start of addition of the radical polymerization initiator, 25% by mass or more of the total amount of the radical polymerization initiator added is added, and
A method for producing a methacrylic resin, which comprises adding 25% by mass or more of the total amount of the monomer added 30 minutes or more after the start of addition of the radical polymerization initiator.
[14]
The structural unit (B) having a ring structure in the main chain contains a lactone ring structural unit (B-1).
While gradually increasing the ratio of the cumulative input amount of the methacrylic acid ester monomer to the cumulative input amount of the monomer forming the lactone ring structure unit (B-1), the two or more kinds of monomers are used in the reactor. The method for producing a methacrylic resin according to [12] or [13], which is added therein.
[15]
The ratio of the polymerization conversion rate of the methacrylic acid ester monomer to the polymerization conversion rate of the monomer forming the structural unit (B) having a ring structure in the main chain during the polymerization reaction is 0.8 to 1. 20. The method for producing a methacrylic resin according to [14].

According to the present invention, it is possible to provide a methacrylic resin having high heat resistance, excellent color tone and transparency, and excellent moldability.

Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail, but the present invention is not limited to the following description and is within the scope of the gist thereof. It can be modified in various ways.

(Methacyl resin)
The methacrylic resin in the present embodiment is a methacrylic acid ester monomer unit (A), a lactone ring structural unit (B-1), and / or a structural unit derived from an N-substituted maleimide monomer (B-2, " It contains a structural unit (B) having at least one ring structure in the main chain selected from the group consisting of "N-substituted maleimide-based structural unit"), and can be optionally copolymerized with a methacrylic acid ester monomer. Other vinyl-based monomer units (C) are also included.
Hereinafter, each monomer structural unit will be described.

-Structural unit derived from methacrylic ester monomer (A)-
First, the structural unit (A) derived from the methacrylic ester monomer will be described.
The structural unit (A) derived from the methacrylic ester monomer is formed from, for example, a monomer selected from the methacrylic esters shown below.
Examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate and methacrylic acid. Cyclopentyl, cyclohexyl methacrylate, cyclooctyl methacrylate, tricyclodecyl methacrylate, dicyclooctyl methacrylate, tricyclododecyl methacrylate, isobornyl methacrylate, phenyl methacrylate, benzyl methacrylate, 1-phenylethyl methacrylate, methacrylic acid Examples thereof include 2-phenoxyethyl, 3-phenylpropyl methacrylate, 2,4,6-tribromophenyl methacrylate and the like.
These monomers may be used alone or in combination of two or more.
Among the above methacrylic acid esters, methyl methacrylate and benzyl methacrylate are preferable because the obtained methacrylic acid resin is excellent in transparency and weather resistance.
The structural unit (A) derived from the methacrylic ester monomer may contain only one type or two or more types.
The content of the structural unit (A) derived from the methacrylic acid ester monomer is determined from the viewpoint of sufficiently imparting heat resistance to the methacrylic resin by the structural unit (B) having a ring structure in the main chain, which will be described later. With 100% by mass of the methacrylic resin, preferably 50 to 97% by mass, more preferably 55 to 97% by mass, still more preferably 55 to 95% by mass, still more preferably 60 to 93% by mass, and particularly preferably 60. ~ 90% by mass.

Hereinafter, the structural unit (B) having a ring structure in the main chain will be described.

-Lactone ring structure unit (B-1)-
Examples of the methacrylic resin having a lactone ring structural unit in the main chain include JP-A-2001-151814, JP-A-2004-168882, JP-A-2005-146084, JP-A-2006-96960, and JP-A. It can be formed by the methods described in JP-A-2006-171464, JP-A-2007-63541, JP-A-2007-297620, JP-A-2010-180305, and the like.

上記一般式（１）〜（４）において、Ｒ^１、Ｒ^２及びＲ^３は、互いに独立して、水素原子、又は炭素数１〜２０の有機残基である。
有機残基としては、例えば、メチル基、エチル基、プロピル基等の炭素数１〜２０の飽和脂肪族炭化水素基（アルキル基等）；エテニル基、プロペニル基等の炭素数２〜２０の不飽和脂肪族炭化水素基（アルケニル基等）；フェニル基、ナフチル基等の炭素数６〜２０の芳香族炭化水素基（アリール基等）；これら飽和脂肪族炭化水素基、不飽和脂肪族炭化水素基、芳香族炭化水素基における水素原子の一つ以上が、ヒドロキシ基、カルボキシル基、エーテル基、エステル基からなる群から選ばれる少なくとも１種の基により置換された基；等が挙げられる。 The lactone ring structural unit constituting the methacrylic resin of the present embodiment may be formed after resin polymerization.
The lactone ring structure unit in the present embodiment is preferably a 6-membered ring because of its excellent ring structure stability.
As the lactone ring structural unit which is a 6-membered ring, for example, the structures represented by the following general formulas (1) to (4) are particularly preferable.

In the above general formulas (1) to (4), R ¹ , R ² and R ³ are hydrogen atoms or organic residues having 1 to 20 carbon atoms independently of each other.
Examples of the organic residue include a saturated aliphatic hydrocarbon group having 1 to 20 carbon atoms (alkyl group, etc.) such as a methyl group, an ethyl group, and a propyl group; Saturated aliphatic hydrocarbon group (alkenyl group, etc.); Aromatic hydrocarbon group having 6 to 20 carbon atoms (aryl group, etc.) such as phenyl group and naphthyl group; these saturated aliphatic hydrocarbon group and unsaturated aliphatic hydrocarbon A group in which one or more hydrogen atoms in a group or an aromatic hydrocarbon group is substituted with at least one group selected from the group consisting of a hydroxy group, a carboxyl group, an ether group and an ester group; and the like.

In the lactone ring structure, for example, an acrylic acid-based monomer having a hydroxy group and a methacrylic acid ester monomer such as methyl methacrylate are copolymerized to form a hydroxy group and an ester group or a carboxyl group in the molecular chain. After the introduction, it can be formed by causing dealcoholization (esteration) or dehydration condensation (hereinafter, also referred to as "cyclization condensation reaction") between these hydroxy groups and an ester group or a carboxyl group.

Examples of the hydroxy group-containing acrylate-based monomer used for polymerization include 2- (hydroxymethyl) acrylate, 2- (hydroxyethyl) acrylate, and alkyl 2- (hydroxymethyl) acrylate (for example, 2-). Methyl (hydroxymethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, isopropyl 2- (hydroxymethyl) acrylate, n-butyl 2- (hydroxymethyl) acrylate, t- (hydroxymethyl) acrylate Examples thereof include butyl) and alkyl 2- (hydroxyethyl) acrylate, preferably alkyl 2- (hydroxymethyl) acrylate and alkyl 2- (hydroxymethyl) acrylate, which are monomers having a hydroxyallyl moiety. , Particularly preferably methyl 2- (hydroxymethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate.
The acrylic acid-based monomer having a hydroxy group described above can be used as a monomer forming a structural unit (B) having a ring structure in the main chain in the method for producing a methacrylic resin of the present embodiment (described later). Can be used.

The content of the lactone ring structural unit (B-1) in the methacrylic resin having the lactone ring structural unit in the main chain is not particularly limited as long as it satisfies the range of the glass transition temperature preferable for the composition of the present embodiment. However, it is preferably 3 to 50% by mass, more preferably 5 to 35% by mass, based on 100% by mass of the methacrylic resin.
When the content of the lactone ring structure unit is in this range, the ring structure introduction effect such as improvement of solvent resistance and improvement of surface hardness can be exhibited while maintaining molding processability.
The content of the lactone ring structure in the methacrylic resin can be determined by using the method described in Patent Document 3 (Japanese Unexamined Patent Publication No. 2007-297620) described above.

A methacrylic resin having a lactone ring structural unit may have a structural unit derived from another monomer copolymerizable with the above-mentioned methacrylic acid ester monomer and acrylic acid-based monomer having a hydroxy group. good.
Examples of such copolymerizable monomers include styrene, vinyltoluene, α-methylstyrene, α-hydroxymethylstyrene, α-hydroxyethylstyrene, acrylonitrile, methacrylonitrile, metallic alcohol, and allyl. Monomer having a polymerizable double bond such as alcohol, ethylene, propylene, 4-methyl-1-pentene, vinyl acetate, 2-hydroxymethyl-1-butene, methylvinyl ketone, N-vinylpyrrolidone, N-vinylcarbazole, etc. The body etc. can be mentioned.
These other monomers (constituent units) may have only one kind or two or more kinds.
The content of the structural unit derived from these other copolymerizable monomers is preferably 0 to 20% by mass with respect to 100% by mass of the methacrylic resin, and 10% by mass from the viewpoint of weather resistance. It is more preferably less than%, and even more preferably less than 7% by mass.
The methacrylic resin in the present embodiment may have only one type of structural unit derived from the above-mentioned other copolymerizable monomer, or may have two or more types.

-N-Structural unit derived from substituted maleimide monomer (B-2)-
Next, a structural unit derived from the N-substituted maleimide monomer (B-2, also referred to as “N-substituted maleimide-based structural unit”) will be described.
The structural unit (B-2) derived from the N-substituted maleimide monomer is at least selected from the monomer represented by the following formula (5) and / or the monomer represented by the following formula (6). As one, it is preferably formed from both the monomers represented by the following formula (5) and the following formula (6).

式（５）中、Ｒ^１は、炭素数７〜１４のアリールアルキル基、炭素数６〜１４のアリール基のいずれかを示し、Ｒ^２及びＲ^３は、それぞれ独立に、水素原子、炭素数１〜１２のアルキル基、炭素数６〜１４のアリール基のいずれかを示す。
また、Ｒ^２がアリール基の場合には、Ｒ^２は、置換基としてハロゲンを含んでいてもよい。

In the formula (5), R ¹ represents any of an arylalkyl group having 7 to 14 carbon atoms and an aryl group having 6 to 14 carbon atoms, and R ² and R ³ are independent hydrogen atoms and carbon atoms, respectively. It indicates any of an alkyl group of 1 to 12 and an aryl group of 6 to 14 carbon atoms.
When R ² is an aryl group, R ² may contain a halogen as a substituent.

式（６）中、Ｒ^４は、水素原子、炭素数３〜１２のシクロアルキル基、炭素数１〜１２のアルキル基のいずれかを示し、Ｒ^５及びＲ^６は、それぞれ独立に、水素原子、炭素数１〜１２のアルキル基、炭素数６〜１４のアリール基のいずれかを示す。

In formula (6), R ⁴ represents a hydrogen atom, a cycloalkyl group having 3 to 12 carbon atoms, or an alkyl group having 1 to 12 carbon atoms, and R ⁵ and R ⁶ are independent hydrogen atoms. , An alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 14 carbon atoms.

A specific example will be shown below.
Examples of the monomer represented by the formula (5) include N-phenylmaleimide, N-benzylmaleimide, N- (2-chlorophenyl) maleimide, N- (4-chlorophenyl) maleimide, and N- (4-bromo). Phenyl) maleimide, N- (2-methylphenyl) maleimide, N- (2-ethylphenyl) maleimide, N- (2-methoxyphenyl) maleimide, N- (2-nitrophenyl) maleimide, N- (2, 4) , 6-trimethylphenyl) maleimide, N- (4-benzylphenyl) maleimide, N- (2,4,6-tribromophenyl) maleimide, N-naphthylmaleimide, N-anthrasenyl maleimide, 3-methyl-1 -Phenyl-1H-Phenyl-2,5-dione, 3,4-Dimethyl-1-phenyl-1H-Phenyl-2,5-dione, 1,3-Diphenyl-1H-Pyrol-2,5-dione, 1 , 3,4-Triphenyl-1H-pyrrole-2,5-dione and the like.
Of these monomers, N-phenylmaleimide and N-benzylmaleimide are preferable because the obtained methacrylic resin has excellent heat resistance and optical properties such as birefringence.
These monomers may be used alone or in combination of two or more.

Examples of the monomer represented by the formula (6) include N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, N-isopropylmaleimide, Nn-butylmaleimide, and N-isobutylmaleimide. Ns-butylmaleimide, Nt-butylmaleimide, Nn-pentylmaleimide, Nn-hexylmaleimide, Nn-heptylmaleimide, Nn-octylmaleimide, N-laurylmaleimide, N-stearyl Maleimide, N-cyclopentylmaleimide, N-cyclohexylmaleimide, 1-cyclohexyl-3-methyl-1-phenyl-1H-pyrrole-2,5-dione, 1-cyclohexyl-3,4-dimethyl-1-phenyl-1H- Examples thereof include pyrrole-2,5-dione, 1-cyclohexyl-3-phenyl-1H-pyrol-2,5-dione, 1-cyclohexyl-3,4-diphenyl-1H-pyrol-2,5-dione and the like.
Among these monomers, N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, and N-cyclohexylmaleimide are preferable from the viewpoint of excellent weather resistance of the methacrylic resin, and the low level required for optical materials in recent years. N-cyclohexylmaleimide is particularly preferable because it has excellent hygroscopicity.
These monomers may be used alone or in combination of two or more.
The monomer represented by the above formula (5) and the monomer represented by the formula (6) have a ring structure in the main chain in the method for producing a methacrylic resin (described later) of the present embodiment. It can be used as a monomer forming the structural unit (B) having.

In the methacrylic resin of the present embodiment, the use of the monomer represented by the formula (5) and the monomer represented by the formula (6) in combination provides highly controlled birefringence characteristics. It is particularly preferable because it can be expressed.
The molar ratio (B5 /) of the content (B5) of the structural unit derived from the monomer represented by the formula (5) to the content (B6) of the structural unit derived from the monomer represented by the formula (6). B6) is preferably more than 0 and 15 or less, and more preferably more than 0 and 10 or less.
When the molar ratio B5 / B6 is in this range, the methacrylic resin of the present embodiment maintains transparency, does not cause yellowing, and does not impair environmental resistance, and has good heat resistance and good photoelasticity. Express the properties.

The content of the structural unit (B-2) derived from the N-substituted maleimide monomer is not particularly limited as long as the obtained composition satisfies the range of the glass transition temperature of the present embodiment, but is a methacrylic resin. Is 100% by mass, preferably 3 to 50% by mass, and more preferably 5 to 35% by mass.
When it is within this range, the methacrylic resin can obtain a more sufficient heat resistance improving effect, and can obtain a more preferable improving effect on weather resistance, low water absorption, and optical characteristics. If the content of the structural unit derived from the N-substituted maleimide monomer is 40% by mass or less, the reactivity of the monomer component decreases during the polymerization reaction, and the amount of unreacted monomer remains large. It is effective in preventing the deterioration of the physical properties of the methacrylic resin due to the formation.

The methacrylic resin having the structural unit (B-2) derived from the N-substituted maleimide monomer in the present embodiment is a methacrylic acid ester monomer and a single amount of the N-substituted maleimide as long as the object of the present invention is not impaired. It may contain structural units derived from other monomers copolymerizable with the body.
For example, other copolymerizable monomers include aromatic vinyl; unsaturated nitriles; acrylic acid esters having cyclohexyl groups, benzyl groups, or alkyl groups with 1 to 18 carbon atoms; glycidyl compounds; unsaturated carboxylic acids. And so on. Examples of the aromatic vinyl include styrene, α-methylstyrene, divinylbenzene and the like. Examples of the unsaturated nitrile include acrylonitrile, methacrylonitrile, and etacrylonitrile. Examples of the acrylic acid ester include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate and the like. Examples of the glycidyl compound include glycidyl (meth) acrylate and allyl glycidyl ether. Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and semi-esterified products or anhydrides thereof.
The structural unit derived from the other copolymerizable monomer may have only one type, or may have two or more types.

The content of the structural unit derived from these other copolymerizable monomers is preferably 0 to 20% by mass, preferably 0.1 to 15% by mass, with the methacrylic resin as 100% by mass. Is more preferable, and 0.1 to 10% by mass is further preferable.
When the content of the structural unit derived from other monomers is in this range, the moldability and mechanical properties of the resin can be improved without impairing the original effect of introducing the ring structure into the main chain, which is preferable.

The content of the structural unit (B) having a ring structure in the main chain is 3 with 100% by mass of the methacrylic resin from the viewpoint of heat resistance, thermal stability, strength and fluidity of the methacrylic resin of the present embodiment. It is preferably ~ 50% by mass, the lower limit is more preferably 5% by mass or more, further preferably 7% by mass or more, still more preferably 8% by mass or more, and the upper limit is more preferably. It is 48% by mass or less, more preferably 46% by mass or less, and even more preferably 44% by mass or less.

From the viewpoint of color tone, the methacrylic resin in the present embodiment preferably contains a lactone ring structural unit (B-1) among the ring structures described above as the structural unit (B) having a ring structure in the main chain. .. However, if necessary, a maleimide skeleton such as an N-substituted maleimide-based structural unit (B-2) may be contained.

-Other vinyl-based monomer units copolymerizable with the methacrylic ester monomer (C)-
Other vinyl-based monomer units (C) (hereinafter, (C) monomer units) copolymerizable with the methacrylic ester monomer that can constitute the methacrylic resin of the present embodiment may be described. ) Is an aromatic vinyl-based monomer unit (C-1), an acrylic acid ester monomer unit (C-2), a vinyl cyanide-based monomer unit (C-3), and other simple units. Quantitative unit (C-4) can be mentioned.
As the other vinyl-based monomer unit (C) copolymerizable with the methacrylic acid ester monomer, only one type may be used alone, or two or more types may be combined.

As the monomer unit (C), a material can be appropriately selected according to the properties required for the methacrylic resin of the present embodiment, but thermal stability, fluidity, mechanical properties, chemical resistance and the like can be selected. When the characteristics are particularly required, it is composed of an aromatic vinyl-based monomer unit (C-1), an acrylonitrile-based monomer unit (C-2), and a vinyl cyanide-based monomer unit (C-3). At least one selected from the group is suitable.

[Aromatic vinyl monomer unit (C-1)]
The monomer forming the aromatic vinyl-based monomer unit (C-1) constituting the methacrylic resin of the present embodiment is not particularly limited, but is represented by the following general formula (7). Aromatic vinyl-based monomers are preferred.

In the general formula (7), R ¹ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and the alkyl group may be substituted with, for example, a hydroxyl group.
R ² is composed of a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 8 carbon atoms, and an aryloxy group having 6 to 8 carbon atoms. Whichever is selected, R ² may be all the same group or different groups. Also, it may form a ring structure with R ² to each other.
n represents an integer from 0 to 5.

Specific examples of the monomer represented by the above general formula (7) are not particularly limited, but are styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, and 2,4-dimethyl. Styrene, 2,5-dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene, p-ethylstyrene, m-ethylstyrene, о-ethylstyrene, p-tert-butylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, 1,1-diphenylethylene, isopropenylbenzene (α-methylstyrene), isopropenyltoluene, isopropenylethylbenzene, isopropenylpropylbenzene, isopropenylbutylbenzene, isopropenylpentylbenzene, isopropenylhexylbenzene, Examples thereof include isopropenyloctylbenzene.
Among the above, styrene and isopropenylbenzene are preferable, and styrene is more preferable from the viewpoint of imparting fluidity and reducing unreacted monomers by improving the polymerization conversion rate.

These may be appropriately selected depending on the required characteristics in the methacrylic resin of the present embodiment.
When the aromatic vinyl-based monomer unit (C-1) is used, the content is (A) monomer unit and (B) in consideration of the balance between heat resistance, reduction of residual monomer species, and fluidity. When the total amount with the structural unit is 100% by mass, it is preferably 23% by mass or less, more preferably 20% by mass or less, still more preferably 18% by mass or less, still more preferably 15% by mass or less. Even more preferably, it is 10% by mass or less.

When the aromatic vinyl-based monomer unit (C-1) is used in combination with the above-mentioned N-substituted maleimide-based structural unit (B-2), (B-2) is (C-1) with respect to the content of the structural unit. As the ratio (mass ratio) of the content of the monomer unit (that is, the (C-1) content / (B-2) content), the processing fluidity at the time of molding the film and the reduction of the residual monomer are reduced. From the viewpoint of reducing silver streaks due to the above, the value is preferably 0.3 to 5.
Here, from the viewpoint of maintaining good color tone and heat resistance, the upper limit value is preferably 5 or less, more preferably 3 or less, and further preferably 1 or less. Further, from the viewpoint of reducing residual monomers, the lower limit value is preferably 0.3 or more, and more preferably 0.4 or more.
As the above-mentioned aromatic vinyl-based monomer (C-1), only one type may be used alone, or two or more types may be used in combination.

[Acrylic ester monomer unit (C-2)]
The monomer forming the acrylic acid ester monomer unit (C-2) constituting the methacrylic resin of the present embodiment is not particularly limited, but the acrylic represented by the following general formula (8). Acid ester monomers are preferred.

前記一般式（８）中、Ｒ^１は、水素原子、又は炭素数が１〜１２のアルコキシ基を表し、Ｒ^２は、炭素数が１〜１８のアルキル基を表す。
前記アクリル酸エステル単量体単位（Ｃ−２）を形成するための単量体としては、本実施形態のフィルム用のメタクリル系樹脂において、耐候性、耐熱性、流動性、熱安定性を高める観点から、アクリル酸メチル、アクリル酸エチル、アクリル酸ｎ−プロピル、アクリル酸ｎ−ブチル、アクリル酸ｓｅｃ−ブチル、アクリル酸２−エチルヘキシル、アクリル酸シクロヘキシル、アクリル酸フェニル等が好ましく、より好ましくは、アクリル酸メチル、アクリル酸エチル、アクリル酸ｎ−ブチルであり、入手しやすさの観点から、アクリル酸メチル、アクリル酸エチルがさらに好ましい。
上記アクリル酸エステル単量体単位（Ｃ−２）は、１種のみを単独で用いてもよく、２種以上を併用してもよい。
アクリル酸エステル単量体単位（Ｃ−２）を使用する場合の含有量は、耐熱性及び熱安定性の観点から、（Ａ）単量体単位と（Ｂ）構造単位との合計量を１００質量％とした場合に、５質量％以下であることが好ましく、より好ましくは３質量％以下である。

In the general formula (8), R ¹ represents a hydrogen atom or an alkoxy group having 1 to 12 carbon atoms, and R ² represents an alkyl group having 1 to 18 carbon atoms.
As the monomer for forming the acrylic acid ester monomer unit (C-2), the methacrylic resin for the film of the present embodiment enhances weather resistance, heat resistance, fluidity, and thermal stability. From the viewpoint, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, sec-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate and the like are preferable, and more preferable. Methyl acrylate, ethyl acrylate, and n-butyl acrylate, and methyl acrylate and ethyl acrylate are more preferable from the viewpoint of availability.
As the acrylic acid ester monomer unit (C-2), only one type may be used alone, or two or more types may be used in combination.
When the acrylic acid ester monomer unit (C-2) is used, the total content of the (A) monomer unit and the (B) structural unit is 100 from the viewpoint of heat resistance and thermal stability. In terms of mass%, it is preferably 5% by mass or less, and more preferably 3% by mass or less.

[Vinyl cyanide monomer unit (C-3)]
The monomer forming the vinyl cyanide monomer unit (C-3) constituting the methacrylic resin of the present embodiment is not particularly limited, and is, for example, acrylonitrile, methacrylonitrile, and cyanide. Examples thereof include vinylidene, and among them, acrylonitrile is preferable from the viewpoint of easy availability and imparting chemical resistance.
As the vinyl cyanide-based monomer unit (C-3), only one type may be used alone, or two or more types may be used in combination.

When the vinyl cyanide-based monomer unit (C-3) is used, the content is the total amount of the (A) monomer unit and the (B) structural unit from the viewpoint of maintaining solvent resistance and heat resistance. When is 100% by mass, it is preferably 15% by mass or less, more preferably 12% by mass or less, and further preferably 10% by mass or less.

[Monomer units (C-4) other than (C-1) to (C-3)]
The monomer forming the monomer unit (C-4) other than (C-1) to (C-3) constituting the methacrylic resin of the present embodiment is not particularly limited, but for example. , Amids such as acrylamide and methacrylic amide; ethylene glycol such as ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate and tetraethylene glycol di (meth) acrylate or its oligomer. Both terminal hydroxyl groups are esterified with acrylic acid or methacrylic acid; hydroxyl groups of two alcohols such as neopentyl glycol di (meth) acrylate and di (meth) acrylate are esterified with acrylic acid or methacrylic acid; tri Polyhydric alcohol derivatives such as methylolpropane and pentaerythritol esterified with acrylic acid or methacrylic acid; polyfunctional monomers such as divinylbenzene and the like can be mentioned.

Among the monomers constituting the monomer unit (C) described above, at least one selected from the group consisting of methyl acrylate, ethyl acrylate, styrene, and acrylonitrile is preferable from the viewpoint of availability.

The content of the other vinyl-based monomer unit (C) copolymerizable with the methacrylic acid ester monomer is 100% by mass of the methacrylic resin from the viewpoint of enhancing the effect of imparting heat resistance by the structural unit (B). It is 0 to 20% by mass, preferably 0 to 18% by mass, and more preferably 0 to 15% by mass.
In particular, when a crosslinkable polyfunctional (meth) acrylate having a plurality of reactive double bonds is used as the (C) monomer unit, the content of the (C) monomer unit is the fluidity of the polymer. From the viewpoint of the above, it is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and further preferably 0.2% by mass or less.

In particular, in the present embodiment, from the viewpoint of heat resistance and optical properties of the methacrylic resin, the structural unit (B) is based on the total amount of the structural unit (B) and the monomer unit (C) being 100% by mass. The content of is 45 to 100% by mass. At this time, the content of the structural unit (C) is 0 to 55% by mass. The content of the structural unit (B) is preferably 50 to 100% by mass, more preferably 50 to 90% by mass, and further preferably 50 to 80% by mass.

Hereinafter, the characteristics of the methacrylic resin of the present embodiment will be described.

The glass transition temperature (Tg) of the methacrylic resin in the present embodiment is 105 to 130 ° C.
If the glass transition temperature of the methacrylic resin exceeds 105 ° C., it is possible to more easily obtain the necessary and sufficient heat resistance as an optical film for a lens molded product or a film molded product for a liquid crystal display in recent years. The glass transition temperature (Tg) is more preferably 110 ° C. or higher, still more preferably 115 ° C. or higher, from the viewpoint of dimensional stability under the operating environment temperature.
On the other hand, when the glass transition temperature (Tg) of the methacrylic resin is 130 ° C. or lower, melt processing at an extremely high temperature can be avoided, thermal decomposition of the resin or the like can be suppressed, and a good product can be obtained. The glass transition temperature (Tg) is preferably 125 ° C. or lower for the reasons described above.
The glass transition temperature (Tg) can be determined by measuring in accordance with JIS-K7121. Specifically, it can be measured by using the method described in Examples described later.

The amount of THF insoluble in the methacrylic resin in the present embodiment is less than 0.5% by mass, preferably 0.4% by mass or less, and more preferably 0.3% by mass or less. When the amount of THF insoluble is in this range, the formation of high molecular weight gel, that is, the intermolecular cyclization reaction is sufficiently suppressed, and the color tone, transparency and moldability are sufficiently excellent.
The amount of THF insoluble at this time can be determined by dissolving the methacrylic resin in THF, filtering and drying using a filter, and then measuring the weight of the filter before and after filtration.
That is, the THF insoluble content in the methacrylic resin can be obtained by using the following formula.
THF insoluble matter in methacrylic resin = [(filter weight after filtration-filter weight before filtration) / weight of dissolved methacrylic resin] x 100
The polymer gel produced by the intermolecular cyclization reaction during the cycloaddition reaction is insoluble in THF. In the methacrylic resin of the present embodiment, the intermolecular cyclization reaction is suppressed and the amount of polymer gel produced is reduced, so that the amount of THF insoluble is suppressed to a certain amount or less.

Further, in the methacrylic resin of the present embodiment, the amount of change in the THF insoluble content before and after the molding process at a temperature of 240 ° C. or higher is preferably less than 1% by mass, more preferably 0.7% by mass or less. It is more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less. When the amount of change in the THF insoluble matter before and after the molding process at a temperature of 240 ° C. or higher is within this range, the formation of the high molecular weight gel component during the molding process, that is, the intermolecular cyclization reaction is sufficiently suppressed. After the molding process, that is, the color tone and transparency of the product, and the molding processability are sufficiently excellent.
The amount of change in the THF insoluble matter before and after the molding process can be obtained by subtracting the amount of the THF insoluble matter before the molding process from the amount of the THF insoluble matter after the molding process. The amount of THF insoluble before molding can be determined by the method described above. The amount of THF insoluble after molding is determined by putting a methacrylic resin into, for example, a twin-screw extruder (for example, a technobel 50 mm screw diameter twin-screw kneading extruder) and pelletizing it at a predetermined temperature of 240 ° C. or higher. After that, the THF insoluble content of a predetermined amount of pellets (for example, 10 g) can be determined by the method described above.

The amount of the methanol-soluble component of the methacrylic resin of the present embodiment is preferably 10% by mass or less with respect to 100% by mass of the total amount of the methanol-soluble component and the methanol-insoluble component. It is more preferably mass% or less, still more preferably 4.5 mass% or less, still more preferably 4 mass% or less, and particularly preferably 3 mass% or less. When the amount of the methanol-soluble component is in this range, the amount of the low molecular weight component (for example, the monomer which is the unreacted polymerization component) and the unreacted cyclization component are sufficiently reduced.
The lower limit of the amount of the soluble methanol is ideally 0% by mass, but when a methacrylic resin is obtained by synthesis, unreacted monomers, low molecular weight polymers, etc. may be contained, so that the amount is actually 0. It may contain about 5.5% by mass of a methanol-soluble component.
The solubility of the methacrylic resin in the present embodiment in a solvent changes significantly before and after the cyclization reaction. Although it depends on the amount of comonomer having a hydroxyl group, it is generally soluble in methanol before the cyclization condensation reaction, so THF is a good solvent and methanol is a poor solvent, as is usually done with methyl polymethacrylate or the like. In this system, purification by reprecipitation cannot be performed. On the other hand, after the cyclization reaction has proceeded sufficiently, the polymer becomes soluble in THF, and reprecipitation purification in a system using THF as a good solvent and methanol as a poor solvent becomes possible. That is, when the polymer after the cyclization condensation reaction is reprecipitated with the reprecipitation solvent, it is highly possible that the soluble component is a low molecular weight component or a cyclization unreacted component. Therefore, it is important to control the amount of these soluble components below a certain level in order to obtain a good polymer.

In the methacrylic resin of the present embodiment, it is important to keep the thermal decomposition temperature of the methanol-insoluble component and the methanol-soluble component within a certain range. The pyrolysis temperature can be determined by thermogravimetric analysis (TGA) under nitrogen under the conditions described in Examples. The thermal decomposition temperature of the methanol-insoluble matter and the methanol-soluble matter is preferably 310 ° C. or higher, more preferably 310 ° C. or higher, when the temperature at which the weight loss rate is 5% as measured by TGA is used as an index. It is 320 ° C. or higher. The methanol-soluble content is preferably 200 ° C. or higher, more preferably 210 ° C. or higher, and even more preferably 220 ° C. or higher.

By controlling the ratio of the amount of methanol-soluble components and the thermal decomposition temperature within the above range, it is possible to suppress molding troubles such as cast roll stains during film molding and silver streaks during injection molding. be able to.

The methanol-soluble and methanol-insoluble components were reprecipitated by dissolving the methacrylic resin in THF to prepare a THF solution, and then dropping the THF solution into methanol to separate the filtrate and the filter medium. Those obtained by drying each of them after that are referred to, and specifically, they can be obtained by the method described in Examples described later.

The methacrylic resin in the present embodiment has a yellowness index (YI) of 0 to 7, preferably 0.5 to 6, measured using a 10 cm optical path length cell with respect to a 20 w / v% chloroform solution having an insoluble methanol. It is more preferably 0.8 to 5, still more preferably 1 to 4.

Further, the methacrylic resin in the present embodiment preferably has a transmittance of 90% or more, more preferably 91% or more, and more preferably 92% or more, measured at 680 nm under the same conditions as those in the above-mentioned YI measurement. It is more preferably% or more.
When the yellowness index (YI) and the transmittance are in this range, a molded product suitable for optical use can be obtained. The yellowness index (YI) and transmittance can be measured by the method described in Examples described later.

In the methacrylic resin of the present embodiment, the weight average molecular weight (Mw) in terms of polymethylmethacrylate measured by gel permeation chromatography (GPC) is 60,000 to 250,000, preferably 80,000 to 200. It is 000, more preferably 90,000 to 180,000, and even more preferably 90,000 to 150,000.
When the weight average molecular weight (Mw) is in the above range, the balance between mechanical strength and fluidity is also excellent.
Regarding the ratios between the Z average molecular weight (Mz), the weight average molecular weight (Mw), and the number average molecular weight (Mn) as parameters representing the molecular weight distribution, the methacrylic resin in the present embodiment has fluidity and machine. Considering the balance with the strength, Mw / Mn is 1.5 to 4.0, preferably 1.5 to 3.5, and more preferably 1.8 to 3.0. It is more preferably 2.0 to 3.0; the Mz / Mw is preferably 1.3 to 2.0, more preferably 1.3 to 1.8, and 1.4 to 1.8. It is more preferably 1.7.
When Mz / Mw is in this range, it is possible to obtain a methacrylic resin having an excellent color tone.
The Z average molecular weight, the weight average molecular weight, and the number average molecular weight of the methacrylic resin can be measured by the methods described in Examples described later.

(Manufacturing method of methacrylic resin)
Hereinafter, the method for producing the methacrylic resin of the present embodiment will be described. In the production method in this embodiment, polymerization of a monomer by radical polymerization is used.

In the method for producing a methacrylic resin of the present embodiment, two or more kinds of monomers containing a methacrylic acid ester monomer and a monomer forming a structural unit (B) having a ring structure in the main chain are used. In a method of radical polymerization in a solvent in a batch system or a semi-batch system, a radical polymerization initiator having a half-life at a polymerization temperature of 1 minute or more and less than 60 minutes is used, and the radical polymerization initiator is used as a unit thereof. The radical polymerization initiator is added into the reactor while gradually reducing the amount added per hour to promote the polymerization of the monomer, and is added after the time when the polymerization conversion rate reaches 85%. The amount of the radical polymerization initiator added is 10 to 25% by mass, with the total amount of the radical polymerization initiator added being 100% by mass. This polymerization method is also hereinafter referred to as "first polymerization method".

The second method for producing a methacrylic resin of the present embodiment is a single amount of two or more kinds containing a methacrylic acid ester monomer and a monomer forming a structural unit (B) having a ring structure in the main chain. In a method of radically polymerizing a body component in a solvent in a batch or semi-batch system, a radical polymerization initiator having a half-life at a polymerization temperature of 60 minutes or more is used, and the polymerization initiator is added from the start. Within 30 minutes, 25% by mass or more of the total amount of the radical polymerization initiator added, and 30 minutes after the start of addition of the polymerization initiator, 25% by mass of the total amount of the monomer added. It is characterized by adding the above. This polymerization method is also hereinafter referred to as a "second polymerization method".

The methacrylic resin produced by the first production method and / or the second production method described above has a lactone ring structural unit (B-1) and N- as structural units (B) having a ring structure in the main chain. It can contain any one or more of the structural units (B-2) derived from the substituted maleimide monomer, and is not particularly limited, but from the viewpoint of color tone, transparency and moldability, the lactone ring structural unit ( It is preferable to include B-1).

Hereinafter, a method for producing a methacrylic resin containing a lactone ring structural unit (B-1) as a structural unit (B) having a ring structure in the main chain will be described in detail.

In the production method in this embodiment, a solution polymerization method or the like is used as the polymerization form. As the polymerization method, a batch type or a semi-batch type can be used. Here, the batch type is a process in which the reaction is started and progressed after all the raw materials (monomers, etc.) are charged into the reactor, and the product is recovered after the completion. The semi-batch type is a process in which the raw materials are charged. Alternatively, it is a process in which either one of the product recovery is performed simultaneously while the reaction is in progress. As a method for producing a methacrylic resin having a lactone ring structure unit (B-1) in the main chain in the present embodiment, for example, a semi-batch type in which a part of the raw material is added after the reaction is started is preferable.

The polymerization solvent to be used is not particularly limited as long as it can increase the solubility of the copolymer obtained by polymerization and maintain the viscosity of the reaction solution appropriately for the purpose of preventing gelation and the like.
Specific polymerization solvents include, for example, aromatic hydrocarbons such as toluene, xylene, ethylbenzene and isopropylbenzene; ketones such as methyl isobutyl ketone, butyl cellosolve, methyl ethyl ketone and cyclohexanone; and polar solvents such as dimethylformamide and 2-methylpyrrolidone. Can be used.
These solvents may be used alone or in combination of two or more.
Further, alcohols such as methanol, ethanol and isopropanol may be used in combination as the polymerization solvent as long as the dissolution of the polymerization product during polymerization is not inhibited. Alcohols inhibit the cyclization condensation reaction described later, but on the other hand, they also have the effect of suppressing gelation due to the cyclization reaction during polymerization, and thus may be added as necessary.

The amount of the solvent at the time of polymerization is not particularly limited as long as the polymerization proceeds and the copolymer and the monomer used do not precipitate at the time of production and can be easily removed. When the total amount is 100 parts by mass, it is preferably 10 to 200 parts by mass. It is more preferably 25 to 200 parts by mass, further preferably 50 to 200 parts by mass, and even more preferably 50 to 150 parts by mass.

In order to sufficiently suppress the gelation of the polymerization solution and promote the cyclization reaction after the polymerization, the polymerization is carried out so that the concentration of the produced polymer in the reaction mixture obtained after the polymerization is 50% by mass or less. Is preferable.
Further, it is preferable to appropriately add a polymerization solvent to the reaction mixture to control the content to 50% by mass or less. The method of appropriately adding the polymerization solvent to the reaction mixture is not particularly limited, and for example, the polymerization solvent may be added continuously or intermittently. The polymerization solvent to be added may be a single solvent of only one kind or a mixed solvent of two or more kinds.

The polymerization temperature is not particularly limited as long as the polymerization proceeds, but is preferably 50 to 200 ° C, more preferably 70 to 180 ° C. It is even more preferably 80 to 160 ° C, even more preferably 90 to 150 ° C, and particularly preferably 100 to 150 ° C. From the viewpoint of productivity, the temperature is preferably 50 ° C. or higher, and the temperature is preferably 200 ° C. or lower in order to suppress side reactions during polymerization and obtain a polymer having a desired molecular weight and quality.

The polymerization time is not particularly limited as long as the desired conversion rate is satisfied, but is preferably 0.5 to 10 hours, more preferably 1 to 8 hours from the viewpoint of productivity and the like.

The polymerization conversion rate of the methacrylic resin having a structural unit derived from a lactone ring in the main chain in the present embodiment at the end of polymerization is preferably 99% or more.
Here, the polymerization conversion rate is a value obtained by subtracting the total mass of the monomers remaining at the end of the polymerization from the total mass of the monomers added in the polymerization system, and the monomer added in the polymerization system. Is the ratio of to the total mass of.

The amount of monomer remaining in the solution after polymerization is preferably less than 300 ppm in the case of a methacrylic acid ester or a hydroxyl group-containing methacrylic acid ester.

At the time of the polymerization reaction, a chain transfer agent may be added as needed for polymerization.
As the chain transfer agent, a chain transfer agent used in general radical polymerization can be used, and for example, n-butyl mercaptan, n-octyl mercaptan, n-decyl mercaptan, n-dodecyl mercaptan, 2-ethylhexyl thioglycolate and the like can be used. Examples thereof include mercaptan compounds; halogen compounds such as carbon tetrachloride, methylene chloride and bromoform; unsaturated hydrocarbon compounds such as α-methylstyrene dimer, α-terpinene, dipentene and turpinolene; and the like.
These may be used alone or in combination of two or more.
These chain transfer agents may be added at any stage as long as the polymerization reaction is in progress, and are not particularly limited.
The amount of the chain transfer agent added may be 0.01 to 1 part by mass, preferably 0.05 to 0.5 part by mass, when the total amount of the monomers used for the polymerization is 100 parts by mass.

In solution polymerization, it is important to reduce the dissolved oxygen concentration in the polymerization solution as much as possible. For example, the dissolved oxygen concentration is preferably 10 ppm or less.
The dissolved oxygen concentration can be measured using, for example, a dissolved oxygen meter DO meter B-505 (manufactured by Iijima Electronics Co., Ltd.).
The dissolved oxygen concentration as a way to lower reduction, a method of bubbling an inert gas into the polymerization solution, an operation depressurized through the vessel containing the prepolymerization the polymerization solution after pressurizing to about 0.2MPa with an inert gas A repeating method, a method of passing an inert gas through a container containing a polymerization solution, and the like can be appropriately selected.

At the time of the polymerization reaction, a polymerization initiator is added.
As the polymerization initiator, any initiator generally used in radical polymerization can be used, and for example, cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, and benzoylper. Organic peroxides such as oxides, t-butylperoxyisopropyl carbonate, t-amylperoxy-2-ethylhexanoate, t-amylperoxyisononanoate, 1,1-dit-butylperoxycyclohexane; 2,2'-Azobis (isobutyronitrile), 1,1'-azobis (cyclohexanecarbonitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), dimethyl-2,2'-azobis An azo compound such as isobutyrate; and the like can be mentioned.
These may be used alone or in combination of two or more.
The amount of the polymerization initiator added may be appropriately set according to the combination of monomers, reaction conditions, etc., and is not particularly limited, but when the total amount of the monomers used for polymerization is 100 parts by mass. In addition, it may be 0.01 to 1 part by mass, preferably 0.05 to 0.5 part by mass.

In the polymerization of the methacrylic resin having the lactone ring structural unit in the present embodiment, when the polymerization initiator and the monomer are added during the polymerization, the amount of the addition thereof is controlled so that the polymerization initiator and the monomer are added in the system during the polymerization. It is possible to reduce the fluctuation of the ratio between the concentration of the monomer and the concentration of the radical, suppress the formation of low molecular weight components at the final stage of polymerization, and improve the colorability and moldability.

In the first polymerization method, when the polymerization is carried out in a semi-batch method, a radical polymerization initiator having a half-life at the polymerization temperature of 1 minute or more and less than 60 minutes is used, and the radical polymerization initiator is used for a unit time thereof. The amount of the monomer added is gradually reduced and added into the reactor to promote the polymerization of the monomer.
In the second polymerization method, when the polymerization is carried out in a semi-batch method, a radical polymerization initiator having a half-life at the polymerization temperature of 60 minutes or more is used, and the polymerization is carried out in the reactor within a predetermined time after the start of the polymerization. A part of the radical polymerization initiator is added, and a part of the monomer is added after a predetermined time after the start of the polymerization to proceed the polymerization.
Each polymerization method will be described below.

In the first polymerization method, as described above, a radical polymerization initiator having a half-life at the polymerization temperature of 1 minute or more and less than 60 minutes is used, and the amount of the radical polymerization initiator added per unit time is increased. It is added into the reactor while being gradually reduced to allow the polymerization of the monomer to proceed.
Here, the radical polymerization initiator having a half-life at the polymerization temperature of 1 minute or more and less than 60 minutes is a radical polymerization initiator having a polymerization temperature of 1 minute or less and higher than the 1-hour half-life temperature. In other words.
If the initiator has a half-life of 1 minute or more at the polymerization temperature, the initiator can be added to the polymerization reactor, sufficiently mixed with the content liquid, and then decomposed to initiate polymerization. preferable. Further, by adding an initiator having a half-life significantly shorter than the polymerization time during the polymerization, the fluctuation of the ratio of the residual monomer concentration to the radical concentration in the reaction system can be kept small, and the residual monomer concentration at the final stage of the polymerization can be kept small. It is possible to keep the radical concentration low at the stage where the amount is lowered, and thereby it is possible to suppress the formation of low molecular weight components during polymerization.
The half-life of the radical polymerization initiator at the polymerization temperature is preferably 3 minutes or more and less than 60 minutes, and more preferably 5 minutes or more and less than 60 minutes.

The above-mentioned 1-minute half-life temperature and 1-hour half-life temperature are described in literature and technical data of peroxide manufacturers, and by using data on activation energy of decomposition reaction, they can be used at other times. Half-life temperature can also be calculated.

Examples of half-life temperatures for some radical initiators are shown in Table 1.

In the first polymerization method, the amount of the initiator added after the polymerization conversion rate reaches 85% is 100% by mass, and the total amount of the radical polymerization initiator added during the polymerization period is 100% by mass. It is preferably 10 to 25% by mass, more preferably 10 to 20% by mass.

Further, in the first polymerization method, one having a half-life at the polymerization temperature of 1 minute or more and less than 60 minutes is used, and the radical polymerization initiator is added into the reactor while gradually reducing the amount of the radical polymerization initiator added per unit time. In advancing the polymerization of the monomer by addition, the addition rate of the initiator when the polymerization conversion rate reaches 85% is preferably 1/10 to 1/3 of the maximum addition rate. It is more preferably 1/10 to 1/4.
It is preferable that it is at least the lower limit from the viewpoint of obtaining a sufficient conversion rate, and it is preferable that it is at least the upper limit from the viewpoint of suppressing the formation of polymer components that adversely affect the color tone and processability.

Further, in the first polymerization method, a part of the monomer is charged in the reactor before the start of the polymerization, a polymerization initiator is added, and the rest of the monomer is supplied after the start of the polymerization. Since the formation of the ultra-high molecular weight component is suppressed along with the formation of the molecular weight component, the molecular weight distribution can be narrowed and Mw / Mn and Mz / Mw can be adjusted to a desired range. In addition, by introducing an acrylic acid-based monomer having a hydroxy group into the molecule uniformly and as discontinuously as possible, the intramolecular cyclization rate is increased, gelation is suppressed, and the color tone is further deteriorated. In consideration of this, it is preferable to add a monomer after the start of polymerization.

The ratio of the amount of the initial charged monomer to the amount of the monomer added after the start of polymerization is preferably 1: 9 to 8: 2, and more preferably 2: 8 to 7.5: 2.5. It is more preferably 3: 7 to 5: 5.

In the second polymerization method, as described above, a radical polymerization initiator having a half-life at the polymerization temperature of 60 minutes or more is used, and the radical polymerization initiator is placed in the reactor within a predetermined time after the start of polymerization. A part of the monomer is added, and a part of the monomer is added after a predetermined time after the start of the polymerization to proceed the polymerization.

When a radical initiator having a half-life that cannot be said to be significantly shorter than the polymerization time is used, the radical concentration is maintained relatively high even at the final stage of polymerization.
Here, by additionally adding the monomer at the final stage of the polymerization, the fluctuation of the ratio of the residual monomer concentration to the radical concentration can be reduced during the polymerization period. In addition, by adding a large amount of radical initiator at the initial stage of polymerization, the radical concentration can be kept low at the stage where the residual monomer concentration at the final stage of polymerization is lowered, thereby producing low molecular weight components during polymerization. It can be suppressed.

In the second polymerization method, the radical initiator is added in an amount of 25% by mass or more of the total addition amount within 30 minutes from the start of addition of the polymerization initiator, preferably 33% by mass or more of the total addition amount. However, more preferably 50% by mass or more is added.
Further, as the monomer, 25% by mass or more of the total addition amount is added 30 minutes or more after the start of addition of the polymerization initiator, preferably 33% by mass or more of the total addition amount, and more preferably. 50% by mass or more is added, and more preferably 66% by mass or more is added.

Further, in the second polymerization method, preferably within 4 hours from the start of addition of the polymerization initiator, more preferably within 3 hours from the start of addition of the polymerization initiator, and even more preferably 2 hours from the start of addition of the polymerization initiator. Within, the total amount of radical initiator added is completed.

In the first polymerization method and the second polymerization method of the method for producing a methacrylic resin containing a lactone ring structure unit (B-1) as a structural unit (B) having a ring structure in the main chain, the radical initiator is 2 Seeds and above can be used in combination.
In all of the two or more radical initiators, when the half-life at the polymerization temperature is 1 minute or more and less than 60 minutes, and when the half-life at the polymerization temperature is 60 minutes or more, the first The addition amount and addition rate of the radical initiator in the polymerization method and the second polymerization method may be the total addition amount and addition rate of the two or more radical initiators.
When a combination of a half-life at the polymerization temperature of 1 minute or more and less than 60 minutes and a half-life at the polymerization temperature of 60 minutes or more is used, the second polymerization method is adopted. That is, within 30 minutes from the start of addition of the polymerization initiator, 25% by mass or more of the total amount of the radical polymerization initiator added is added, and 30 minutes or later from the start of addition of the polymerization initiator, the monomer is added. Add 25% by mass or more of the total amount added.

The method for adding the monomer at the time of polymerization is as follows: 1) First, only a part of the solvent is charged in the reactor, and when the polymerization is started, the monomer dissolved in the solvent is added into the reactor. 2) First, all the solvents are charged in the reactor, and the monomer is added to the reactor at the start of polymerization. 3) The solvent and some monomers are added to the reactor in advance. There is a method of charging the mixture, starting the polymerization, and then gradually adding the remaining monomer and the solvent into the reactor.
Regarding 3), when there are two or more types of monomers, a method in which one type of monomer is charged in the reactor in advance and the remaining monomers are added after the start of polymerization is also included.

In the production method of the present embodiment, the methacrylic resin containing the lactone ring structural unit (B-1) in the main chain is a monomer forming the lactone ring structural unit (B-1) (hereinafter, “lactone ring structural unit”). (B-1) Forming monomer ”), for example, an acrylic acid-based monomer having a hydroxy group and a methacrylic ester monomer such as methyl methacrylate are copolymerized to form a hydroxy in the molecular chain. After introducing a group and an ester group or a carboxyl group, dealcoholization (esteration) or dehydration condensation (hereinafter, also referred to as "cyclization condensation reaction") is performed between the hydroxy group and the ester group or the carboxyl group in the same molecular chain. It can be formed by an intramolecular cyclization reaction that causes (referred to as). The problems associated with this reaction are as follows. Since the lactone ring structure unit (B-1) forming monomer has higher polymerization activity than the methacrylic acid ester monomer and the N-substituted maleimide monomer, the copolymer of these monomers may be used as a copolymer. Copolymer portions (comonomer chains) in which lactone ring structural unit (B-1) forming monomers are continuous are likely to be formed. In the copolymer portion, when the hydroxyl group undergoes an intramolecular cyclization reaction, an unnatural ring structure such as a spiro ring is formed, so that the intramolecular cyclization reaction does not occur and the reaction remains unreacted or intermolecular cyclization. There is a high possibility that a high molecular weight gel will be produced by the reaction.

In order to solve the above problems, the ratio of the molar concentration (B1C) of the lactone ring structure unit (B-1) forming monomer to the molar concentration (AC) of the methacrylate ester monomer in the polymerization solution ( B1C / AC) is always below a predetermined value determined by the inverse of the ratio of the polymerization activity (reactivity) of the lactone ring structure unit (B-1) forming monomer to the polymerization activity of the methacrylate ester monomer. It is preferable to carry out the polymerization while controlling the amount of the monomer added into the reactor.
Here, since the lactone ring structure unit (B-1) forming monomer has higher polymerization activity than the methacrylate ester monomer, the chain of the lactone ring structure unit (B-1) forming monomer is suppressed. Should be such that the molar concentration of the lactone ring structural unit (B-1) forming monomer (B1C) <molar concentration of the methacrylic ester monomer (AC), and 0 <(B1C / AC) <1. It is preferable that the relationship is established.

Therefore, as a method for adding the monomer, the ratio (mol) of the concentration (B1C) of the lactone ring structure unit (B-1) forming monomer to the concentration (AC) of the methacrylate ester monomer in the polymerization solution is used. ) (B1C / AC) is preferably added into the reactor so that it is always below 0.9, more preferably below 0.7.
The addition of the monomer may be intermittent or continuous.

As a method for adding the monomer, the ratio of the cumulative input amount (B1AI) of the lactone ring structure unit (B-1) forming monomer to the cumulative input amount (AAI) of the methacrylic ester monomer (B1AI /). Monomers may be added into the reactor while increasing AAI). Here, the cumulative input amount is the cumulative amount of the target monomer charged into the reactor by an arbitrary time point, and is not limited to the amount charged into the reactor after the start of polymerization. It is calculated as the cumulative sum including the amount charged in the reactor in advance before the start of polymerization.
The addition of the monomer may be intermittent or continuous.

As a method for adding the monomer, the ratio of the total input amount (B1I) of the lactone ring structure unit (B-1) forming monomer to the total input amount (AI) of the methacrylic ester monomer (B1I /). The ratio (B1i / Ai) of the input amount (B1i) of the lactone ring structure unit (B-1) forming monomer to the input amount (Ai) of the methacrylic ester monomer with respect to AI) is set at the time of preparation or After that, the monomer may be added into the reactor while gradually increasing, for example, 1-fold, 1.5-fold, 2-fold, etc., so as to be as small as possible at the time of the first addition.
The addition of the monomer may be intermittent or continuous.

By adding the monomer by any of the above-mentioned addition methods while using the first polymerization method and the second polymerization method regarding the above-mentioned method for adding the polymerization initiator, the initial stage of the polymerization reaction is in the polymerization solution. The ratio (B1C / AC) of the molar concentration (B1C) of the lactone ring structural unit (B-1) forming monomer to the molar concentration (AC) of the methacrylic acid ester monomer is relatively low, and the lactone ring The consumption of the structural unit (B-1) forming monomer with respect to the methacrylic acid ester monomer is suppressed.
The ratio (B1PC / APC) of the polymerization conversion rate (B1PC) of the lactone ring structure unit (B-1) forming monomer to the polymerization conversion rate (APC) of the methacrylic ester monomer is equivalent, that is, close to 1. It becomes a value.
Then, the lactone ring structure unit (B-1) forming monomer and the methacrylate ester monomer are likely to form a chain alternately, and at the same time, the chain of only the lactone ring structure unit (B-1) forming monomer is formed. Is also suppressed.
As a result, it is possible to facilitate the dealcoholization (esterification) or dehydration condensation (hereinafter, also referred to as “cyclization condensation reaction”) reaction in the copolymer molecule, and at the same time, reduce the intermolecular cyclization reaction. The methacrylic resin produced in this manner suppresses the formation of a high molecular weight gel component, and can sufficiently improve the color tone, transparency and moldability.

As a method for adding the monomer, the polymerization conversion rate (APC) of the methacrylic acid ester monomer having the polymerization conversion rate (B1PC) of the lactone ring structure unit (B-1) forming monomer during the polymerization reaction. ), It is also preferable to add the monomer so that the ratio (B1PC / APC) is 0.80 to 1.20. The ratio (BC / AC) of the polymerization conversion rate (B1PC) of the lactone ring structure unit (B-1) forming monomer to the polymerization conversion rate (APC) of the methacrylate ester monomer during the polymerization reaction is in the above range. By controlling the addition of the monomer as described above, the formation of a chain of lactone ring structural unit (B-1) forming monomers is suppressed, and the formation of a high-molecular-weight gel by the intermolecular cyclization reaction is produced. It can be suppressed, and the color tone, transparency and moldability can be sufficiently improved.
The ratio of the polymerization conversion rate of the lactone ring structure unit (B-1) forming monomer to the polymerization conversion rate of the methacrylic acid ester monomer, that is, the polymerization conversion rate of the lactone ring structure unit (B-1) forming monomer. The polymerization conversion rate of the / methacrylic acid ester monomer is more preferably 0.85 to 1.15, still more preferably 0.99 to 1.10, and even more preferably 0.95 to 1.05.
The ratio (B1PC / APC) of the polymerization conversion rate (B1PC) of the lactone ring structure unit (B-1) forming monomer to the polymerization conversion rate (APC) of the methacrylic acid ester monomer is during the polymerization reaction. At any time, the polymerization solution can be sampled from the reactor and the polymerization conversion rate of each monomer can be calculated and obtained.

Sampling of the polymerization solution may be performed at any time between the start and the end of the polymerization reaction, but if the addition of the monomer is continuous or intermittent, the first half of the polymerization time is optional. It may be carried out at the time point of, for example, 30 minutes, 1 hour, or 2 hours after the start of polymerization. Here, the first half of the polymerization time means the time from the start of the polymerization reaction to the time when half of the polymerization time elapses in the polymerization time. In the production method of the present embodiment, the polymerization activity of the lactone ring structure unit (B-1) forming monomer at the initial stage of polymerization is relatively reduced to chain the lactone ring structure unit (B-1) forming monomer. This is because it is important to suppress the generation of.
Further, when the addition of the monomer is intermittent, sampling of the polymerization solution may be performed before and after the addition of the monomer. This is because the polymerization conversion rate is likely to fluctuate before and after the addition of the monomer.

In the case of producing a methacrylic resin containing the lactone ring structural unit (B-1) and the N-substituted maleimide structural unit (B-2) as the structural unit (B), N- during the first half of the polymerization time. It is preferable to add the total amount of the substituted maleimide monomer. Since the N-substituted maleimide monomer has a lower polymerization activity than the methacrylate ester monomer, when it is added in the latter half of the polymerization time, it remains as a coloring monomer or a low molecular weight component, and methanol is acceptable. This is because the amount of the dissolved substance also increases, which may adversely affect the color tone and the moldability. Here, the latter half of the polymerization time means from the time when half of the polymerization time elapses to the end of the polymerization reaction.
The total amount of the N-substituted maleimide monomer added is more preferably during the first quarter of the polymerization time, and even more preferably 1 hour before the start of the polymerization. The addition of the monomer may be intermittent or continuous.

The methacrylic resin having the lactone ring structural unit in the present embodiment can be obtained by carrying out a cyclization reaction after the completion of the above-mentioned polymerization reaction. Therefore, it is preferable to carry out the lactone cyclization reaction in a state containing the solvent without removing the polymerization solvent from the polymerization reaction solution.
The copolymer obtained by polymerization undergoes a cyclization condensation reaction between a hydroxyl group (hydroxyl group) existing in the molecular chain of the copolymer and an ester group by heat treatment, and has a lactone ring structure. To form.

During the heat treatment for forming the lactone ring structure, a vacuum device for removing alcohol that may be produced as a by-product by cyclization condensation, a reaction device equipped with a volatilization device, an extruder equipped with a volatilization device, or the like can also be used. ..

When forming the lactone ring structure, if necessary, heat treatment may be performed using a cyclization condensation catalyst in order to promote the cyclization condensation reaction.
Specific examples of the cyclization condensation catalyst include methyl phosphite, ethyl phosphite, phenyl phosphite, dimethyl phosphite, diethyl phosphite, diphenyl phosphite, trimethyl trimethyl phosphite, and sub-phosphate. Monoalkyl phosphite such as triethyl phosphate, dialkyl ester or triester; methyl phosphate, ethyl phosphate, 2-ethylhexyl phosphate, octyl phosphate, isodecyl phosphate, lauryl phosphate, stearyl phosphate, phosphoric acid Isostearyl, dimethyl phosphate, diethyl phosphate, di-2-ethylhexyl phosphate, diisodecyl phosphate, dilauryl phosphate, distearyl phosphate, diisostearyl phosphate, trimethyl phosphate, triethyl phosphate, triisodecyl phosphate, Examples thereof include phosphoric acid monoalkyl esters such as trilauryl phosphate, tristearyl phosphate and triisostearyl phosphate; dialkyl esters or trialkyl esters; organic zinc compounds such as zinc acetate, zinc propionate and octyl zinc; and the like.
These may be used alone or in combination of two or more.

The amount of the cyclization condensation catalyst used is not particularly limited, but is preferably 0.01 to 3 parts by mass, and more preferably 0.05 to 0.05 parts by mass with respect to 100 parts by mass of the methacrylic resin. It is 1 part by mass.
If the amount used is less than 0.01 parts by mass, the reaction rate of the cyclization condensation reaction may not be sufficiently improved. On the contrary, if the amount of the catalyst used exceeds 3 parts by mass, the obtained polymer may be colored or the polymer may be crosslinked, making melt molding difficult.

The timing of addition of the cyclization condensation catalyst is not particularly limited, and for example, it may be added at the initial stage of the cyclization condensation reaction, during the reaction, or at both of them. good.

When the cyclization condensation reaction is carried out in the presence of a solvent, it is also preferably used to carry out the volatilization at the same time.
The apparatus used when the cyclization condensation reaction and the devolatilization step are performed at the same time is not particularly limited, but is a devolatilization apparatus consisting of a heat exchanger and a devolatilization tank, an extruder with a vent, and devolatilization. It is preferable that the apparatus and the extruder are arranged in series, and a twin-screw extruder with a vent is more preferable.

As the twin-screw extruder with a vent to be used, an extruder with a vent having a plurality of vent ports is preferable.
When an extruder with a vent is used, the reaction treatment temperature is preferably 150 to 350 ° C, more preferably 200 to 300 ° C. If the reaction treatment temperature is less than 150 ° C., the cyclization condensation reaction may be insufficient and the residual volatile matter may increase. On the contrary, when the reaction treatment temperature exceeds 350 ° C., coloring or decomposition of the obtained polymer may occur.
When the extruder with a vent is used, the degree of vacuum is preferably 10 to 500 Torr, more preferably 10 to 300 Torr. If the degree of vacuum exceeds 500 Torr, volatile matter may easily remain. On the contrary, if the degree of vacuum is less than 10 Torr, industrial implementation may be difficult.

It is also preferable to add an alkaline earth metal and / or an amphoteric metal salt of an organic acid at the time of granulation for the purpose of inactivating the remaining cyclization condensation catalyst when the above cyclization condensation reaction is carried out.
As the alkaline earth metal and / or amphoteric metal salt of the organic acid, for example, calcium acetyl acetate, calcium stearate, zinc acetate, zinc octylate, zinc 2-ethylhexylate and the like can be used.

After undergoing the cyclization condensation reaction step, the methacrylic resin is melted and extruded into strands from an extruder equipped with a porous die, and is subjected to a cold cut method, an aerial hot cut method, an underwater strand cut method, and an underwater cut method. Process into pellets.

The lactonization for forming the above-mentioned lactone ring structural unit may be performed after the production of the resin and before the production of the resin composition (described later), and during the production of the resin composition, the resin and components other than the resin are used. It may be carried out in combination with the melt-kneading with.

Next, a method for producing a methacrylic resin when only the N-substituted maleimide structural unit (B-2) is contained as the structural unit (B) having a ring structure in the main chain will be described.

(B) The method for producing a methacrylic resin of the present embodiment containing only the N-substituted maleimide structural unit (B-2) as the structural unit is a lactone ring structural unit (B-1) except for the polymerization conditions particularly described below. The above-mentioned various polymerization conditions and the first and second polymerization methods can be similarly used for the method for producing the methacrylic resin of the present embodiment including).

The method for adding the monomer in the present embodiment is not particularly limited, but for example, a semi-batch method in which a part of the raw material is added after the reaction is started is preferable.

The polymerization time is not particularly limited as long as the required degree of polymerization can be obtained at the required conversion rate, but from the viewpoint of productivity and the like, it is preferably 2 to 15 hours, more preferably. Is 3 to 12 hours, more preferably 4 to 10 hours.
The polymerization conversion rate at the end of polymerization is preferably 93 to 99.9%, more preferably 95 to 99.5%, and even more preferably 97 to 99%.

The amount of N-substituted maleimide monomer (residual amount of N-substituted maleimide) at the end of polymerization is preferably 100 to 7000 mass ppm or less, more preferably 200 to 5000 mass ppm or less, and 300 to 300 mass ppm or less. It is more preferably 3000 mass ppm or less.
The higher the polymerization conversion rate and the smaller the residual amount of N-substituted maleimide, the less the monomer that goes to the solvent recovery system, so the load on the purification system is reduced, and the basic unit is increased, which is economical. If the polymerization conversion rate is set too high or the residual amount of N-substituted maleimide is reduced too much, the amount of low molecular weight components of colorability and the amount of methanol-soluble components increase, which may adversely affect the color tone and moldability. There is.
In the first polymerization method, the amount of the methacrylic acid ester monomer that tends to be polymerized first at the time of copolymerization is reduced at the time of initial preparation and increased at the time of additional addition, whereby N-substituted maleimide monomer at the end of polymerization is used. The residual amount of the monomer can be reduced, which is preferable from the viewpoint of improving the color tone.

Further, the residual amount of the N-substituted maleimide monomer can be reduced by adding a monomer such as styrene having high alternating copolymerizability with the N-substituted maleimide monomer during the polymerization.

The method for recovering the polymer from the polymerization solution obtained by solution polymerization is not particularly limited, but for example, a poor solvent such as a hydrocarbon solvent or an alcohol solvent that does not dissolve the polymerization product obtained by the polymerization. After adding the polymerization solution in the presence of an excess amount of the solvent, the unreacted monomer is treated with a homogenizer (emulsion dispersion), and the unreacted monomer is subjected to pretreatment such as liquid-liquid extraction and solid-liquid extraction. Examples thereof include a method of separating from the polymerization solution; or a method of separating the polymerization solvent and the unreacted monomer through a step called a devolatilization step and recovering the polymerization product.

Here, the devolatile step refers to a step of removing volatile components such as a polymerization solvent, a residual monomer, and a reaction by-product under heating and reduced pressure conditions.
Examples of the device used in the volatilization process include a volatilization device consisting of a tubular heat exchanger and a volatilization tank; a thin film evaporator such as Wybren and Exeva manufactured by Shinko Environmental Solutions Co., Ltd., and a contra and inclined blade contra manufactured by Hitachi, Ltd .; Extruders with vents that have sufficient residence time and surface area to exhibit volatilization performance; etc. can be mentioned.
A volatilization step or the like using a devolatilization device in which any two or more of these devices are combined can also be used.

The treatment temperature in the devolatilizer is preferably 150 to 350 ° C, more preferably 170 to 300 ° C, and even more preferably 200 to 280 ° C. Residual volatile matter can be suppressed by setting the temperature below the lower limit, and coloring and decomposition of the obtained acrylic resin can be suppressed by setting the temperature below the upper limit.
The degree of vacuum in the devolatilizer is preferably in the range of 10 to 500 Torr, particularly preferably in the range of 10 to 300 Torr. By setting this degree of vacuum to the upper limit or less, the residual amount of volatile matter can be suppressed. Moreover, the degree of vacuum above the lower limit is realistic in industrial practice.
The treatment time is appropriately selected depending on the amount of residual volatile matter, but the shorter the treatment time is, the more preferable it is in order to suppress the coloring and decomposition of the obtained acrylic resin.

The polymer recovered through the devolatile step is processed into pellets in a step called a granulation step.

In the granulation step, the molten resin is extruded into a strand shape from a porous die and processed into a pellet shape by a cold cut method, an aerial hot cut method, an underwater strand cut method, and an underwater cut method.

When an extruder with a vent is used as the devolatilization device, the devolatilization step and the granulation step may be combined.

The methacrylic resin of the present embodiment produced as described above can be directly molded to produce various optical products.
Alternatively, a methacrylic resin composition can be prepared using the methacrylic resin of the present embodiment.

(Methacrylic resin composition)
The methacrylic resin composition contains the methacrylic resin of the present embodiment, and may contain the following other thermoplastic resins, additives, and the like as optional components. Various optical products can be produced from the prepared methacrylic resin composition by performing molding processing or the like.

-Other thermoplastic resins-
Other thermoplastic resins may be blended with the methacrylic resin of the present embodiment for the purpose of adjusting the birefringence and improving flexibility without impairing the object of the present invention.
Other thermoplastic resins include, for example, polyacrylates such as polybutyl acrylate; polystyrene, styrene-methyl methacrylate copolymer, styrene-butyl acrylate copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene. A styrene polymer such as a block copolymer; further, for example, JP-A-59-202213, JP-A-63-27516, JP-A-51-129449, JP-A-52-56150. , Etc.; Acrylic rubber particles having a three- to four-layer structure; a rubbery polymer disclosed in Japanese Patent Application Laid-Open No. 60-17406 and Japanese Patent Application Laid-Open No. 8-245854; , A methacrylic rubber-containing graph copolymer particles obtained by multi-stage polymerization; and the like.
Among these, from the viewpoint of obtaining good optical properties and mechanical properties, the composition is compatible with the styrene-acrylonitrile copolymer and the methacrylic resin containing the structural unit (X) having a ring structure in the main chain. Rubber-containing graft copolymer particles having a graft portion on the surface layer thereof are preferable.
The average particle diameters of the above-mentioned acrylic rubber particles, methacrylic rubber-containing graph copolymer particles, and rubbery polymer are from the viewpoint of enhancing the impact strength and optical properties of the film obtained from the composition of the present embodiment. Therefore, it is preferably 0.03 to 1 μm, and more preferably 0.05 to 0.5 μm.

The content of the other thermoplastic resin is preferably 0 to 50 parts by mass, more preferably 0 to 25 parts by mass, when the methacrylic resin is 100 parts by mass.

-Additives-
The methacrylic resin according to the present embodiment may contain various additives as long as the effects of the present invention are not significantly impaired.
The additive is not particularly limited, but for example, an inorganic filler; a pigment such as iron oxide; a lubricant such as stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, ethylene bisstearoamide, etc. Molding agents: Paraffin-based process oils, naphthen-based process oils, aromatic process oils, paraffins, organic polysiloxanes, mineral oils and other softeners / plasticizers; Hindered phenol-based antioxidants, sulfur-based antioxidants, etc. Antioxidants; Hindered amine-based light stabilizers; Bentriazole-based UV absorbers; Flame retardants; Antistatic agents; Reinforcing agents for organic fibers, glass fibers, carbon fibers, metal whiskers, etc.; Colorants; Stearic acid esters, phosphonite Species, organic phosphorus compounds such as phosphate esters; other additives; or mixtures thereof.

Hereinafter, the contents of the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited to the following examples.

<1. Measurement of polymerization conversion rate>
A part of the polymerization solution in Examples and Comparative Examples was taken, and this polymerization solution sample was dissolved in chloroform to prepare a 5% by mass solution, n-decane was added as an internal standard substance, and gas chromatography (Shimadzu Seisakusho) The concentration of the monomer remaining in the sample was measured using GC-2010), and the total mass (a) of the monomer remaining in the polymerization solution was determined. Then, the total mass (a), the total mass (b) assuming that the total amount of the monomers added by the time the sample was collected remained in the polymerization solution, and the simple addition by the end of the polymerization step. From the total mass (c) of the monomer, the polymerization conversion rate (%) was calculated by the calculation formula: (ba) / c × 100.

<2. Structural unit analysis>
Unless otherwise specified in each of the production examples described below, the structural units of the methacrylic resin produced in the production examples described below were identified by ¹ H-NMR measurement and ^{13 C-NMR measurement, and the abundance thereof was calculated. The measurement conditions for 1 1} H-NMR measurement and ¹³ C-NMR measurement are as follows.
-Measuring equipment: Bruker DPX-400
-Measuring solvent: CDCl ₃ or DMSO-d ₆
・ Measurement temperature: 40 ° C
The content of the lactone ring structural unit was determined according to the method described in JP-A-2007-297620. The determined content is the total content of all lactone ring structural units including the above general formulas (1) to (4).

<3. Measurement of molecular weight and molecular weight distribution>
The Z average molecular weight (Mz), weight average molecular weight (Mw), and number average molecular weight (Mn) of the methacrylic resin produced in the production examples described later were measured with the following devices and conditions.
-Measuring device: Gel Permeation Chromatography (HLC-8320GPC) manufactured by Tosoh Corporation
·Measurement condition:
Columns: 1 TSKguardcolum SuperH-H, 2 TSKgel SuperHM-M, and 1 TSKgel SuperH2500 were connected in series and used. Column temperature: 40 ° C
The developing solvent: tetrahydrofuran, the flow rate: 0.6 mL / min, and 0.1 g / L of 2,6-di-t-butyl-4-methylphenol (BHT) was added as an internal standard.
Detector: RI (differential refractometer) detector, detection sensitivity: 3.0 mV / min Sample: 0.02 g of methacrylic resin or a solution of methacrylic resin in tetrahydrofuran in 20 mL. Injection volume: 10 μL
Standard sample for calibration curve: Weight peak of monodispersity The following 10 types of polymethyl methacrylate (manufactured by Polymer Laboratories; PMMACalibration Kit M-M-10) having a known molecular weight and different molecular weights were used.
Weight peak molecular weight (Mp)
Standard sample 1 1,916,000
Standard sample 2 625,500
Standard sample 3 298,900
Standard sample 4 138,600
Standard sample 5 60, 150
Standard sample 6 27,600
Standard sample 7 10,290
Standard sample 8 5,000
Standard sample 9 2,810
Standard sample 10 850
Under the above conditions, the RI detection intensity with respect to the elution time of the methacrylic resin was measured.
Z average molecular weight (Mz), weight average molecular weight (Mw), number average molecular weight (Mn), molecular weight distribution of methacrylic resin and methacrylic resin based on the calibration line obtained by the measurement of the standard sample for calibration line. (Mw / Mn) and the ratio (Mz / Mw) of the Z average molecular weight to the weight average molecular weight were determined.

<4. Cyclization condensation reaction rate>
The cyclization condensation reaction rate was determined according to the method for determining the dealcoholization reaction rate described in JP-A-2007-297620.

<5. Glass transition temperature>
The glass transition temperature (Tg) (° C.) of the methacrylic resin was measured according to JIS-K7121.
First, about 10 mg of each of 4 test pieces (4 points) was cut out from a sample whose state was adjusted (leaved at 23 ° C. for 1 week) under standard conditions (23 ° C., 65% RH).
Next, using a differential scanning calorimeter (Diamond DSC manufactured by Perkin Elmer Japan Co., Ltd.) under the condition of a nitrogen gas flow rate of 25 mL / min, the temperature rises from room temperature (23 ° C) to 200 ° C at 10 ° C / min. Warm (primary temperature rise) and hold at 200 ° C. for 5 minutes to completely melt the sample, then cool down from 200 ° C. to 40 ° C. at 10 ° C./min, hold at 40 ° C. for 5 minutes, and then Of the DSC curves drawn while the temperature is raised again (secondary temperature rise) under the above temperature rise conditions, the stepwise change partial curve at the time of the second temperature rise and each baseline extension line are equidistant in the vertical axis direction. The intersection with a certain straight line (intermediate point glass transition temperature) was measured as the glass transition temperature (Tg) (° C.). Four points were measured per sample, and the arithmetic mean of the four points (rounded to the nearest whole number) was used as the measured value.

<Measurement of 6.5% pyrolysis temperature>
After dissolving 5 g of the methacrylic resin obtained in Examples and Comparative Examples in 100 mL of THF, the solution was placed in a dropping funnel and added dropwise to 1 L of methanol stirred with a stirrer over about 1 hour. And reprecipitation was performed. After dropping the entire amount and allowing it to stand for 1 hour, suction filtration was performed using a membrane filter (T05A090C manufactured by Advantech Toyo Co., Ltd.) as a filter.
The filter medium was vacuum dried at 60 ° C. for 16 hours to obtain a methanol insoluble matter. Further, the filtrate remains in the eggplant-shaped flask after removing the solvent by using a rotary evaporator at a bath temperature of 40 ° C. and gradually lowering the degree of vacuum from the default setting of 390 Torr to finally 30 Torr. The soluble component was recovered and used as a methanol-soluble component.
The methanol-soluble and methanol-insoluble components of the methacrylic resin were pulverized with a pulverizer and placed in a predetermined amount (10 to 15 mg) in an aluminum pan for measurement to prepare a measurement sample. The aluminum pan containing the sample was set in a thermogravimetric analyzer TGA (manufactured by Hitachi), and the temperature was raised under the following conditions under nitrogen gas flow rate conditions.
30 ° C-100 ° C: 40 ° C / min
Hold at 100 ° C for 5 minutes 100-150 ° C: 10 ° C / min
150-400 ° C: 2 ° C / min
The temperature at which the weight loss rate of the sample was 5% was measured and used as the 5% thermal decomposition temperature.
The measurement was performed three times, and the average value was used as the measured value.

<7. Measurement of the amount of THF insoluble>
10 g of the methacrylic resin obtained in Examples and Comparative Examples was dissolved in 1 L of THF. This THF solution was suction-filtered with a 2 μm Teflon (registered trademark) membrane filter which was previously dried under vacuum at 100 ° C. for 2 hours and weighed. The filtered membrane filter was dried under vacuum at 100 ° C. for 2 hours and then weighed. The difference in filter weight before and after filtration calculated by the following formula was defined as the THF insoluble matter.
THF insoluble matter in methacrylic resin =
[(Weight of filter after filtration-Weight of filter before filtration) / Weight of dissolved methacrylic resin] x 100

<8. Measurement of the amount of methanol-soluble and methanol-insoluble>
As described in <Measurement of 6.5% Pyrolysis Temperature> above, methanol-soluble and methanol-insoluble components of the methacrylic resin obtained in Examples and Comparative Examples were obtained.
Weigh each of the mass of methanol-insoluble matter and the mass of methanol-soluble matter, and the ratio (mass) of the amount of methanol-soluble matter to the total amount (100% by mass) of the amount of methanol-soluble matter and the amount of methanol-insoluble matter. %) (Methanol-soluble fraction) was calculated.

<9. Measurement of Yellowness Index (YI) and 680 nm transmittance>
The methanol-insoluble content of the methacrylic resin obtained in Examples and Comparative Examples was used as a 20 w / v% chloroform solution (that is, a solution prepared by dissolving 10 g of a sample in chloroform to make a 50 mL solution). Then, it was filtered using a syringe filter (PTFE013045, manufactured by Membrane-Solutions LLC) to prepare a measurement sample. Using an ultraviolet visible spectrophotometer (UV-2500PC, manufactured by Shimadzu Corporation), measurement wavelength 380-780 nm, slit width 2 nm, 10 cm optical path length cell, viewing angle 10 °, auxiliary illuminant C, reference object: chloroform , The transmittance was measured.
According to JIS K 7373, YI (Yellowness Index) was calculated by the following formula using the XYZ color system.
YI = 100 (1.2769X-1.0592Z) / Y
In addition, the transmittance (%) at a wavelength of 680 nm was also recorded under the same conditions as in the above YI measurement.

<10. Evaluation of methacrylic resin film formation>
The methacrylic resin obtained in Examples and Comparative Examples described later was dried at 90 ° C. for 24 hours with dehumidified air to reduce the water content to 300 mass ppm or less, and then a film was formed by the method shown below. Was done.
A film was prepared using a 15 mmφ twin-screw extruder (manufactured by Technobel Co., Ltd.) in which a 300 mm wide T-die was installed at the tip of the extruder. At that time, the film forming conditions were as follows: extruder tip temperature set temperature 260 ° C., T-die temperature setting 255 ° C., discharge rate 1 kg / hour, cooling roll set temperature: glass transition temperature -10 ° C., and a film having a film thickness of 80 μm. Obtained. After continuous operation for 6 hours under these conditions, an evaluation film was collected in a length of 1 m.
Then, using a roll that has been thoroughly cleaned before the start of film formation, visually observe the dirt on the roll surface after 6 hours, and if it is almost the same as before film formation and only a small part is slightly dirty, "○" The molding processability was evaluated as "Δ" when the roll surface was slightly dirty on the entire surface and "x" when the roll surface was completely dirty and needed to be cleaned again.

[material]
The raw materials used in Examples and Comparative Examples described later are shown below.
[[Monomer]]
-Methyl methacrylate (MMA): manufactured by Asahi Kasei Chemicals Co., Ltd.-Methyl 2- (hydroxymethyl) acrylate (MHMA): manufactured by Combi Bloks Co., Ltd.-N-phenylmaleimide (phMI): manufactured by Nippon Catalyst Co., Ltd.-N-cyclohexylmaleimide ( chMI): Manufactured by Nippon Catalyst Co., Ltd. [[Polymerization initiator]]
-T-Amilperoxyisononanoate: "Luperox 570" manufactured by Arkema Yoshitomi Co., Ltd.

[Example 1] Production of a methacrylic resin having a lactone ring structural unit Methyl methacrylate in ^{a 1 m 3} autoclave equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen gas introduction tube in which the inside is previously replaced with nitrogen. 15 parts by mass, 2 parts by mass of methyl 2- (hydroxymethyl) acrylate, 15 parts by mass of toluene, and 0.025 parts by mass of tris (2,4-di-t-butylphenyl) phosphite as an organic phosphorus compound were charged.
Then, while introducing nitrogen gas, the temperature was raised to 100 ° C., and 0.05 parts by mass of t-amylperoxyisononanoate was added as a polymerization initiator, and at the same time, t-amylperoxyisononanoate 0.075. The dropping of the toluene solution containing a part by mass was started, and while dropping this over 1.5 hours, solution polymerization was carried out at about 105 to 110 ° C. under reflux, and the polymerization was further continued for 8 hours. Further, 10 parts by mass of methyl methacrylate, 2 parts by mass of methyl 2- (hydroxymethyl) acrylate, and 15 parts by mass of toluene were added at a constant rate from 15 minutes after the start of polymerization over 1 hour. Then, over 1 hour, 10 parts by mass of methyl methacrylate, 4 parts by mass of methyl 2- (hydroxymethyl) acrylate, and 15 parts by mass of toluene were added at a constant rate. Then, over another 30 minutes, 5 parts by mass of methyl methacrylate, 2 parts by mass of methyl 2- (hydroxymethyl) acrylate, and 5 parts by mass of toluene were added at a constant rate.
To the obtained polymer solution, 0.05 parts by mass of a mixture of stearyl phosphate / distearyl phosphate, which is an organic phosphorus compound, was added as a cyclization catalyst, and cyclization condensation was carried out at about 90 to 102 ° C. for 2 hours under reflux. The reaction was carried out.
The 1-hour half-life temperature of t-amylperoxyisononanoate used as an initiator is 114 ° C., the half-life of the polymerization temperature at 110 ° C. is 101 minutes, and the half-life at 105 ° C. is 180 minutes. The polymer solution was sampled 30 minutes, 1 hour, 2 hours, and 4 hours after the start of polymerization, and the polymerization conversion rate was analyzed from the remaining monomer concentration. After 15 minutes, methacrylic acid was analyzed. Methyl 55.1%, Methyl 2- (hydroxymethyl) acrylate 56.2%, Methyl methacrylate 74.3% after 1 hour, Methyl 2- (hydroxymethyl) acrylate 76.5%, 2 hours later Methyl methacrylate was 83.3%, methyl 2- (hydroxymethyl) acrylate was 85.4%, and after 4 hours, methyl methacrylate was 98.2% and methyl 2- (hydroxymethyl) acrylate was 99.1%. .. The time average of the polymerization temperature from 0 hour to 8 hours after the start of polymerization was 105 ° C.
Next, the obtained polymer solution is heated to 240 ° C. with a heater consisting of a multi-tube heat exchanger, and a biaxial structure equipped with a plurality of vent ports and a plurality of side feed ports downstream for volatilization. By introducing it into an extruder, the cyclization reaction proceeded while devolatile.
In the twin-screw extruder, the obtained copolymer solution was supplied so as to have a resin equivalent of 15 kg / hour, and the conditions were a barrel temperature of 250 ° C., a rotation speed of 100 rpm, and a vacuum degree of 10 to 300 Torr.
The resin composition melt-kneaded with a twin-screw extruder was extruded from a strand die, cooled with water, and pelletized to obtain a resin composition.
When the composition of the obtained resin composition was confirmed, the content of the lactone ring structural unit was 33.6% by mass. The weight average molecular weight of the obtained resin composition was 124,000, Mz / Mw was 1.62, and Mw / Mn was 2.13. Other physical characteristics are shown in Table 2.

[Example 2] Production of a methacrylic resin having a lactone ring structure unit The amount to be charged is 12 parts by mass of methyl methacrylate, 3 parts by mass of methyl 2- (hydroxymethyl) acrylate, and 15 parts by mass of toluene, and 20 minutes after the start of polymerization. After 1 hour from the above, 10 parts by mass of methyl methacrylate, 3 parts by mass of methyl 2- (hydroxymethyl) acrylate, and 15 parts by mass of toluene were added dropwise at a constant speed, and then 10 parts by mass of methyl methacrylate, 2-( Add 4 parts by mass of methyl acrylate and 15 parts by mass of toluene at a constant rate over 1 hour, then 5.5 parts by mass of methyl methacrylate, 2.5 parts by mass of methyl 2- (hydroxymethyl) acrylate, and toluene. It was produced in the same manner as in Example 1 except that 5 parts by mass was added at a constant speed over 30 hours. The polymer solution was sampled 30 minutes, 1 hour, 2 hours, and 4 hours after the start of polymerization, and the polymerization conversion rate was analyzed from the remaining monomer concentration. After 30 minutes, methyl methacrylate was used. 58.5%, methyl 2- (hydroxymethyl) acrylate 60.1%, methyl methacrylate 77.3% after 1 hour, methyl 2- (hydroxymethyl) acrylate 79.1%, methacrylic after 2 hours Methyl acrylate was 90.8%, methyl 2- (hydroxymethyl) acrylate was 91.9%, and after 4 hours, methyl methacrylate was 96.7% and methyl 2- (hydroxymethyl) acrylate was 97.6%. .. The time average of the polymerization temperature from 0 hour to 8 hours after the start of polymerization was 105 ° C.
When the composition of the obtained resin composition was confirmed, the content of the lactone ring structural unit was 42.7% by mass. The weight average molecular weight of the obtained resin composition was 112,000, Mz / Mw was 1.42, and Mw / Mn was 2.11. Other physical characteristics are shown in Table 2.

^{[Example 3] Production of methacrylic resin having a lactone ring structural unit In a 1 m 3} glass flask equipped with a stirrer, a temperature sensor, a reflux condenser, and a nitrogen gas introduction tube in which the inside is previously replaced with nitrogen, methacrylic is placed. 15 parts by mass of methyl acrylate, 2 parts by mass of methyl 2- (hydroxymethyl) acrylate, 15 parts by mass of toluene, and 0.025 parts by mass of tris (2,4-di-t-butylphenyl) phosphite as an organic phosphorus compound were charged. is.
Then, while introducing nitrogen gas, the temperature was raised to 100 ° C., and 0.05 parts by mass of t-amylperoxyisononanoate was added as a polymerization initiator, and at the same time, t-amylperoxyisononanoate 0.075. The dropping of the toluene solution containing a part by mass was started, and while dropping this over 1.5 hours, solution polymerization was carried out at about 105 to 110 ° C. under reflux, and the polymerization was further continued for 8 hours. Further, 10 parts by mass of methyl methacrylate, 2 parts by mass of methyl 2- (hydroxymethyl) acrylate, and 15 parts by mass of toluene were added at a constant rate from 15 minutes after the start of polymerization over 1 hour. Then, over 1 hour, 10 parts by mass of methyl methacrylate, 4 parts by mass of methyl 2- (hydroxymethyl) acrylate, and 15 parts by mass of toluene were added at a constant rate. Then, over another 30 minutes, 5 parts by mass of methyl methacrylate, 2 parts by mass of methyl 2- (hydroxymethyl) acrylate, and 5 parts by mass of toluene were added at a constant rate.
The polymer solution was sampled 30 minutes, 1 hour, 2 hours, and 4 hours after the start of polymerization, and the polymerization conversion rate was analyzed from the remaining monomer concentration. After 30 minutes, methyl methacrylate was used. 54.1%, 2- (hydroxymethyl) methyl acrylate 55.8%, 1 hour after 1 hour methyl methacrylate 73.2%, 2- (hydroxymethyl) methyl acrylate 75.1%, 2 hours after methacryl Methyl acrylate was 87.1%, methyl 2- (hydroxymethyl) acrylate was 89.1%, and after 4 hours, methyl methacrylate was 97.6% and methyl 2- (hydroxymethyl) acrylate was 98.9%. ..
To the obtained polymer solution, 0.05 parts by mass of a mixture of stearyl phosphate / distearyl phosphate, which is an organic phosphorus compound, was added as a cyclization catalyst, and cyclization condensation was carried out at about 90 to 102 ° C. for 2 hours under reflux. The reaction was carried out.
The time average of the polymerization temperature from 0 hour to 8 hours after the start of polymerization was 105 ° C.
The reflux condenser of the flask was replaced with a Liebig condenser equipped with a flask as a receiver.
Next, the solvent was removed from the obtained polymer solution under reduced pressure until the polymer concentration became 80% or more, and then the temperature was raised to 240 ° C. while maintaining the reduced pressure. A cyclization condensation reaction was carried out for 30 minutes under reduced pressure at 240 ° C. to obtain a resin composition.
When the composition of the obtained resin composition was confirmed, the content of the lactone ring structural unit was 33.6% by mass. The weight average molecular weight of the obtained resin composition was 133,000, Mz / Mw was 1.72, and Mw / Mn was 2.33. Other physical characteristics are shown in Table 2.

[Example 4] Production of a methacrylic resin having a lactone ring structure unit A methacrylic resin was produced by the same method as in Example 3 except that the preparation conditions and the monomer feed conditions were the same as in Example 2. The polymer solution was sampled 30 minutes, 1 hour, 2 hours, and 4 hours after the start of polymerization, and the polymerization conversion rate was analyzed from the remaining monomer concentration. After 30 minutes, methyl methacrylate was used. 55.1%, methyl 2- (hydroxymethyl) acrylate 57.3%, methyl methacrylate 76.3% after 1 hour, methyl 2- (hydroxymethyl) acrylate 78.1%, methacrylic after 2 hours Methyl acrylate was 86.3%, methyl 2- (hydroxymethyl) acrylate was 88.6%, and after 4 hours, methyl methacrylate was 96.5% and methyl 2- (hydroxymethyl) acrylate was 98.1%. ..
When the composition of the obtained resin composition was confirmed, the content of the lactone ring structural unit was 42.7% by mass. The weight average molecular weight of the obtained resin composition was 138,000, Mz / Mw was 1.81, and Mw / Mn was 2.45. Other physical characteristics are shown in Table 2.

^{[Example 5] Production of a methacrylic resin having a lactone ring structure and an N-substituted maleimide ring structure unit 1 m 3} provided with a stirrer, a temperature sensor, a cooling tube, and a nitrogen gas introduction tube whose inside is previously replaced with nitrogen. In the autoclave of, 19 parts by mass of methyl methacrylate, 3 parts by mass of methyl 2- (hydroxymethyl) acrylate, 0.5 parts by mass of N-cyclohexylmaleimide, 0.5 parts by mass of N-phenylmaleimide, 20 parts by mass of toluene, organic. 0.025 parts by mass of tris (2,4-di-t-butylphenyl) phosphite was charged as a phosphorus compound.
Then, while introducing nitrogen gas, the temperature was raised to 100 ° C., and 0.05 parts by mass of t-amylperoxyisononanoate was added as a polymerization initiator, and at the same time, t-amylperoxyisononanoate 0.075. The dropping of the toluene solution containing a part by mass was started, and while dropping this over 1.5 hours, solution polymerization was carried out at about 105 to 110 ° C. under reflux, and the polymerization was further continued for 8 hours. Further, 15 parts by mass of methyl methacrylate, 4 parts by mass of methyl 2- (hydroxymethyl) acrylate, and 25 parts by mass of toluene were added at a constant rate from 15 minutes after the start of polymerization over 1 hour. Then, over 1 hour, 5 parts by mass of methyl methacrylate, 3 parts by mass of methyl 2- (hydroxymethyl) acrylate, and 5 parts by mass of toluene were added at a constant rate.
To the obtained polymer solution, 0.05 parts by mass of a mixture of stearyl phosphate / distearyl phosphate, which is an organic phosphorus compound, was added as a cyclization catalyst, and cyclization condensation was carried out at about 90 to 102 ° C. for 2 hours under reflux. The reaction was carried out.
The 1-hour half-life temperature of t-amylperoxyisononanoate used as an initiator is 114 ° C., the half-life of the polymerization temperature at 110 ° C. is 101 minutes, and the half-life at 105 ° C. is 180 minutes. The polymer solution was sampled 4 hours and 8 hours after the start of polymerization, and the polymerization conversion rate was analyzed for the entire system from the remaining monomer concentration. As a result, 83.6% and 8 hours after 4 hours. The rest was 96.8%. The time average of the polymerization temperature from 0 hour to 8 hours after the start of polymerization was 105 ° C.
Next, the obtained polymer solution is heated to 240 ° C. with a heater consisting of a multi-tube heat exchanger, and a biaxial structure equipped with a plurality of vent ports and a plurality of side feed ports downstream for volatilization. By introducing it into an extruder, the cyclization reaction proceeded while devolatile.
In the twin-screw extruder, the obtained copolymer solution was supplied so as to have a resin equivalent of 15 kg / hour, and the conditions were a barrel temperature of 250 ° C., a rotation speed of 100 rpm, and a vacuum degree of 10 to 300 Torr.
The resin composition melt-kneaded with a twin-screw extruder was extruded from a strand die, cooled with water, and pelletized to obtain a resin composition.
When the composition of the obtained resin composition was confirmed, the content of the lactone ring structural unit was 32.6% by mass. The weight average molecular weight of the obtained resin composition was 135,000, Mz / Mw was 1.62, and Mw / Mn was 2.03. Other physical characteristics are shown in Table 2.

^{[Example 6] Production of a methacrylic resin having a lactone ring structure and an N-substituted maleimide ring structure unit 1 m 3} provided with a stirrer, a temperature sensor, a cooling tube, and a nitrogen gas introduction tube whose inside is previously replaced with nitrogen. 19.8 parts by mass of methyl methacrylate, 3 parts by mass of methyl 2- (hydroxymethyl) acrylate, 0.3 parts by mass of N-cyclohexylmaleimide, 0.3 parts by mass of N-phenylmaleimide, and 20 parts by mass of toluene in the autoclave. , 0.025 parts by mass of tris (2,4-di-t-butylphenyl) phosphite was charged as an organic phosphorus compound.
Then, while introducing nitrogen gas, the temperature was raised to 100 ° C., and 0.05 parts by mass of t-amylperoxyisononanoate was added as a polymerization initiator, and at the same time, t-amylperoxyisononanoate 0.075. The dropping of the toluene solution containing a part by mass was started, and while dropping this over 1.5 hours, solution polymerization was carried out at about 105 to 110 ° C. under reflux, and the polymerization was further continued for 5.5 hours. In addition, 15 parts by mass of methyl methacrylate, 4 parts by mass of methyl 2- (hydroxymethyl) acrylate, 0.2 parts by mass of N-cyclohexylmaleimide, and 0.2 parts by mass of N-phenylmaleimide took 1 hour from 15 minutes after the start of polymerization. 25 parts by mass of toluene was added at a constant rate. Then, over 1 hour, 5 parts by mass of methyl methacrylate, 3 parts by mass of methyl 2- (hydroxymethyl) acrylate, and 5 parts by mass of toluene were added at a constant rate.
To the obtained polymer solution, 0.05 parts by mass of a mixture of stearyl phosphate / distearyl phosphate, which is an organic phosphorus compound, was added as a cyclization catalyst, and cyclization condensation was carried out at about 90 to 102 ° C. for 2 hours under reflux. The reaction was carried out.
The polymer solution was sampled 4 hours and 8 hours after the start of polymerization, and the polymerization conversion rate was analyzed for the entire system from the remaining monomer concentration. As a result, 84.6% and 8 hours after 4 hours. The rest was 94.8%. The time average of the polymerization temperature from 0 hour to 7.5 hours after the start of polymerization was 105 ° C.
Next, the obtained polymer solution is heated to 240 ° C. with a heater consisting of a multi-tube heat exchanger, and a biaxial structure equipped with a plurality of vent ports and a plurality of side feed ports downstream for volatilization. By introducing it into an extruder, the cyclization reaction proceeded while devolatile.
In the twin-screw extruder, the obtained copolymer solution was supplied so as to have a resin equivalent of 15 kg / hour, and the conditions were a barrel temperature of 250 ° C., a rotation speed of 100 rpm, and a vacuum degree of 10 to 300 Torr.
The resin composition melt-kneaded with a twin-screw extruder was extruded from a strand die, cooled with water, and pelletized to obtain a resin composition.
When the composition of the obtained resin composition was confirmed, the content of the lactone ring structural unit was 41% by mass. The weight average molecular weight of the obtained resin composition was 138,000, Mz / Mw was 1.63, and Mw / Mn was 2.21. Other physical characteristics are shown in Table 2.

[Comparative Example 1] Production of methacrylic resin having a lactone ring structural unit Methyl methacrylate was placed in ^{a 1 m 3} autoclave equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen gas introduction tube in which the inside was previously replaced with nitrogen. 40 parts by mass, 10 parts by mass of methyl 2- (hydroxymethyl) acrylate, 50 parts by mass of toluene, and 0.025 parts by mass of tris (2,4-di-t-butylphenyl) phosphite as an organic phosphorus compound were charged.
Then, while introducing nitrogen gas, the temperature was raised to 100 ° C., and 0.05 parts by mass of t-amylperoxyisononanoate was added as a polymerization initiator, and at the same time, t-amylperoxyisononanoate 0.075. The dropping of the toluene solution containing a part by mass was started, and while dropping this over 1.5 hours, solution polymerization was carried out at about 105 to 110 ° C. under reflux, and the polymerization was further continued for 8 hours. To the obtained polymer solution, 0.05 parts by mass of a mixture of stearyl phosphate / distearyl phosphate, which is an organic phosphorus compound, was added as a cyclization catalyst, and cyclization condensation was carried out at about 90 to 102 ° C. for 2 hours under reflux. The reaction was carried out.
The polymer solution was sampled 30 minutes, 1 hour, 2 hours, and 4 hours after the start of polymerization, and the polymerization conversion rate was analyzed from the remaining monomer concentration. After 30 minutes, methyl methacrylate was used. 58.1%, methyl 2- (hydroxymethyl) acrylate 91.4%, methyl methacrylate 75.6% after 1 hour, methyl 2- (hydroxymethyl) acrylate 95.1%, methacryl after 2 hours Methyl acrylate was 82.2%, methyl 2- (hydroxymethyl) acrylate was 97.6%, and after 4 hours, methyl methacrylate was 98.2% and methyl 2- (hydroxymethyl) acrylate was 99.9%. .. The time average of the polymerization temperature from 0 hour to 8 hours after the start of polymerization was 105 ° C.
Next, the obtained polymer solution is heated to 240 ° C. with a heater consisting of a multi-tube heat exchanger, and a biaxial structure equipped with a plurality of vent ports and a plurality of side feed ports downstream for volatilization. By introducing it into an extruder, the cyclization reaction proceeded while devolatile.
In the twin-screw extruder, the obtained copolymer solution was supplied so as to have a resin equivalent of 15 kg / hour, and the conditions were a barrel temperature of 250 ° C., a rotation speed of 100 rpm, and a vacuum degree of 10 to 300 Torr.
The resin composition melt-kneaded with a twin-screw extruder was extruded from a strand die, cooled with water, and pelletized to obtain a resin composition.
When the composition of the obtained resin composition was confirmed, the content of the lactone ring structural unit was 33.6% by mass. The weight average molecular weight of the obtained resin composition was 144,000, Mz / Mw was 1.86, and Mw / Mn was 2.56. Other physical characteristics are shown in Table 3.

^{[Comparative Example 2] Production of methacrylic resin (E) having a lactone ring structure unit In a 1 m 3} autoclave equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen gas introduction tube in which the inside is previously replaced with nitrogen. 20 parts by mass of methyl methacrylate, 5 parts by mass of methyl 2- (hydroxymethyl) acrylate, 25 parts by mass of toluene, and 0.025 parts by mass of tris (2,4-di-t-butylphenyl) phosphite as an organic phosphorus compound. I prepared it.
Then, while introducing nitrogen gas, the temperature was raised to 100 ° C., and 0.05 parts by mass of t-amylperoxyisononanoate was added as a polymerization initiator, and at the same time, t-amylperoxyisononanoate 0.075. The dropping of the toluene solution containing a part by mass was started, and while dropping this over 2.5 hours, solution polymerization was carried out at about 105 to 110 ° C. under reflux, and the polymerization was further continued for 5.5 hours. Further, 20 parts by mass of methyl methacrylate, 5 parts by mass of methyl 2- (hydroxymethyl) acrylate, and 25 parts by mass of toluene were added at a constant rate from 30 minutes after the start of polymerization over 2 hours.
To the obtained polymer solution, 0.05 parts by mass of a mixture of stearyl phosphate / distearyl phosphate, which is an organic phosphorus compound, was added as a cyclization catalyst, and cyclization condensation was carried out at about 90 to 102 ° C. for 2 hours under reflux. The reaction was carried out.
The polymer solution was sampled 30 minutes, 1 hour, 2 hours, and 4 hours after the start of polymerization, and the polymerization conversion rate was analyzed from the remaining monomer concentration. After 30 minutes, methyl methacrylate was used. 56.5%, methyl 2- (hydroxymethyl) acrylate 88.9%, methyl methacrylate 71.2% after 1 hour, methyl 2- (hydroxymethyl) acrylate 92.2%, methacryl after 2 hours Methyl acrylate was 85.3%, methyl 2- (hydroxymethyl) acrylate was 97.6%, and after 4 hours, methyl methacrylate was 98.5% and methyl 2- (hydroxymethyl) acrylate was 99.8%. .. The time average of the polymerization temperature from 0 hour to 8 hours after the start of polymerization was 105 ° C.
Next, the obtained polymer solution is heated to 240 ° C. with a heater consisting of a multi-tube heat exchanger, and a biaxial structure equipped with a plurality of vent ports and a plurality of side feed ports downstream for volatilization. By introducing it into an extruder, the cyclization reaction proceeded while devolatile.
In the twin-screw extruder, the obtained copolymer solution was supplied so as to have a resin equivalent of 15 kg / hour, and the conditions were a barrel temperature of 250 ° C., a rotation speed of 100 rpm, and a vacuum degree of 10 to 300 Torr.
The resin composition melt-kneaded with a twin-screw extruder was extruded from a strand die, cooled with water, and pelletized to obtain a resin composition.
When the composition of the obtained resin composition was confirmed, the content of the lactone ring structural unit was 32.8% by mass. The weight average molecular weight of the obtained resin composition was 134,000, Mz / Mw was 1.74, and Mw / Mn was 2.36. Other physical characteristics are shown in Table 3.

[Comparative Example 3] Production of methacrylic resin having a lactone ring structural unit Methyl methacrylate was placed in ^{a 1 m 3} autoclave equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen gas introduction tube in which the inside was previously replaced with nitrogen. 19 parts by mass, 5 parts by mass of methyl 2- (hydroxymethyl) acrylate, 0.5 parts by mass of N-cyclohexylmaleimide, 0.5 parts by mass of N-phenylmaleimide, 25 parts by mass of toluene, Tris (2,) as an organic phosphorus compound. 0.025 parts by mass of 4-di-t-butylphenyl) phosphite was charged.
Then, while introducing nitrogen gas, the temperature was raised to 100 ° C., and 0.05 parts by mass of t-amylperoxyisononanoate was added as a polymerization initiator, and at the same time, t-amylperoxyisononanoate 0.075. The dropping of the toluene solution containing a part by mass was started, and while dropping this over 1.5 hours, solution polymerization was carried out at about 105 to 110 ° C. under reflux, and the polymerization was further continued for 5.5 hours. Further, 20 parts by mass of methyl methacrylate, 5 parts by mass of methyl 2- (hydroxymethyl) acrylate, and 25 parts by mass of toluene were added at a constant rate from 30 minutes after the start of polymerization over 2 hours.
To the obtained polymer solution, 0.05 parts by mass of a mixture of stearyl phosphate / distearyl phosphate, which is an organic phosphorus compound, was added as a cyclization catalyst, and cyclization condensation was carried out at about 90 to 102 ° C. for 2 hours under reflux. The reaction was carried out.
The following operations were the same operations and post-processing as in Example 3.
When the composition of the obtained resin composition was confirmed, the content of the lactone ring structural unit was 32.8% by mass. The weight average molecular weight of the obtained resin composition was 142,000, Mz / Mw was 1.72, and Mw / Mn was 2.43. Other physical characteristics are shown in Table 3.

The methacrylic resin of the present invention has high heat resistance, excellent color tone and transparency, and excellent moldability.
The methacrylic resin of the present invention is a polarizing plate protective film used as an optical material for, for example, a liquid crystal display, a plasma display, an organic EL display, a field emission display, a display such as a rear projection television; a 1/4 wave plate, 1 / Phase difference plate such as 2 wave plate; Liquid crystal optical compensation film such as viewing angle control film; Display front plate; Display substrate; Lens; Transparent substrate used for solar cells, Transparent conductive substrate such as touch panel; Optical communication system, In the fields of optical exchange systems and optical measurement systems, it can be suitably used as a waveguide, a lens, a lens array, an optical fiber, a coating material for an optical fiber; an LED lens; a lens cover and the like.

Claims (15)

A methacrylic resin containing 3 to 50% by mass of a structural unit (B) having a ring structure in the main chain.
The weight average molecular weight (Mw) is 60,000 to 250,000, the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 1.5 to 4.0, and the glass. The transition temperature (Tg) is 105-130 ° C.
The amount of THF insoluble in the methacrylic resin is less than 0.5% by mass.
A methacrylic resin characterized by this. The methacrylic resin according to claim 1, wherein the amount of the methanol-soluble component of the methacrylic resin is 5% by mass or less with respect to 100% by mass of the total amount of the methanol-soluble component and the methanol-insoluble component. .. The 5% pyrolysis temperature of the methanol-insoluble matter measured by thermogravimetric analysis (TGA) under nitrogen is 310 ° C. or higher, and the 5% pyrolysis temperature of the methanol-soluble content measured by TGA under nitrogen is 200 ° C. The methacryl-based resin according to claim 2, which is the above. The methacrylic resin according to any one of claims 1 to 3, wherein the amount of change in the THF insoluble content before and after molding at a temperature of 240 ° C. or higher is less than 1% by mass. The methacrylic resin according to any one of claims 2 to 4, wherein the methanol-insoluble 20 w / v% chloroform solution has a transmittance of 90% or more at 680 nm measured using a 10 cm optical path length cell. The methacrylic resin according to any one of claims 1 to 5, wherein the methacrylic resin contains 50 to 97% by mass of the methacrylic ester monomer unit (A) with the methacrylic resin as 100% by mass. resin. The methacrylic resin is a structural unit (B) having a ring structure in the main chain, with the methacrylic resin as 100% by mass, and 3 to 50% by mass, and other vinyl copolymerizable with the methacrylic ester monomer. The methacrylic resin according to any one of claims 1 to 6, which contains a system monomer unit (C): 0 to 20% by mass. The content of the (B) structural unit is 45 to 100% by mass, where 100% by mass is the total amount of the (B) structural unit and the (C) monomer unit. The methacrylic resin according to any one item. Claims 1 to 8 wherein the structural unit (B) includes at least one structural unit selected from the group consisting of a lactone ring structural unit (B-1) and an N-substituted maleimide-based structural unit (B-2). The methacryl-based resin according to any one of the above. Claims 1 to 1, wherein the monomer unit (C) contains at least one structural unit selected from the group consisting of an acrylic acid ester monomer, an aromatic vinyl-based monomer, and a vinyl cyanide-based monomer. The methacrylic resin according to any one of 9. Claims 1 to 10, wherein the ratio (Mz / Mw) of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) is 1.3 to 2.0. The methacrylic resin according to any one item. Two or more kinds of monomers containing a methacrylic acid ester monomer and a monomer forming a structural unit (B) having a ring structure in the main chain are subjected to radical or semi-batch in a solvent. In the method of polymerization
A radical polymerization initiator having a half-life at the polymerization temperature of 1 minute or more and less than 60 minutes was used.
The radical polymerization initiator is added into the reactor while gradually reducing the amount of the radical polymerization initiator added per unit time to allow the polymerization of the monomer to proceed and to proceed with the polymerization.
The amount of the radical polymerization initiator added after the time when the polymerization conversion rate reaches 85% is 10 to 25% by mass, with the total amount of the radical polymerization initiator added being 100% by mass. A method for producing a methacrylic resin. Two or more kinds of monomers containing a methacrylic acid ester monomer and a monomer forming a structural unit (B) having a ring structure in the main chain are subjected to radical or semi-batch in a solvent. In the method of polymerization
A radical polymerization initiator having a half-life of 60 minutes or more at the polymerization temperature was used.
Within 30 minutes from the start of addition of the radical polymerization initiator, 25% by mass or more of the total amount of the radical polymerization initiator added is added, and
A method for producing a methacrylic resin, which comprises adding 25% by mass or more of the total amount of the monomer added 30 minutes or more after the start of addition of the radical polymerization initiator. The ratio (BI / AI) of the cumulative input amount (BI) of the monomer forming the structural unit (B) having a ring structure in the main chain to the cumulative input amount (AI) of the methacrylic ester monomer is gradually increased. The method for producing a methacrylic resin according to claim 12 or 13, wherein the monomer is added into the reactor. The ratio (BC / AC) of the polymerization conversion rate (BC) of the monomer forming the lactone ring structural unit (B-1) to the polymerization conversion rate (AC) of the methacrylic ester monomer during the polymerization reaction. ) Is 0.80-1.20, the method for producing a methacrylic resin according to claim 14.