JPH1045850A - Production of thermoplastic resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the generation of coloring component and obtain a thermoplastic resin having faint color in high efficiency by polymerizing a monomer component in the presence of a part of an oxidation inhibitor and adding the remaining part of the oxidation inhibitor after the polymerization of the monomer component. SOLUTION: The objective thermoplastic resin can be produced by polymerizing a radically polymerizable monomer component in the presence of (A) a part of an oxidation inhibitor (preferably a hindered phenol-type oxidation inhibitor) and adding the remaining part of the oxidation inhibitor after the polymerization of the monomer component. Preferably, the total amount of the component A is 0.0001-1 pt.wt. based on 100 pts.wt. of the monomer component and the weight ratio of the oxidation inhibitor added during the polymerization to the agent added after the polymerization is 1/99 to 99/1. The discoloration during the polymerization can be suppressed without inhibiting the polymerization of the monomer component, the discoloration of the resin in heating after the polymerization such as in the molding of the resin is sufficiently suppressed and the resin can be used as a base for optical material, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a thermoplastic resin having transparency and heat resistance. More specifically, the present invention relates to a method for producing a thermoplastic resin suitable for optical materials and automotive materials, which requires shape stability at high temperatures due to excellent heat resistance and colorless transparency.

[0002]

2. Description of the Related Art Conventionally, N-substituted maleimides are rich in copolymerizability, and when copolymerized with other monomers such as methacrylic acid esters, heat resistance, heat stability, mechanical strength, moldability, etc. It is known to provide a thermoplastic resin having a balance of various physical properties.

[0003] Among such thermoplastic resins, a thermoplastic resin obtained by copolymerizing a methacrylic acid ester with an N-substituted maleimide is particularly excellent in heat resistance and transparency, and is suitable for use in automobile materials and optical materials. It has been increasingly used in fields requiring high heat resistance and transparency.

Further, when higher heat resistance is required for the obtained thermoplastic resin, it is necessary to introduce more N-substituted maleimide units. However, N-
When a monomer mixture containing a substituted maleimide is polymerized, it is likely to be colored during heating during polymerization, molding, or the like, and it is difficult to obtain a less colored thermoplastic resin.

Therefore, as a method for improving the coloring property of a thermoplastic resin containing a large amount of N-substituted maleimide units upon heating, a method using an antioxidant such as a phosphorus compound or a phenol compound has been proposed.

For example, Japanese Patent Application Laid-Open No. 1-256551 discloses that a methyl methacrylate-styrene resin obtained by polymerizing a monomer component consisting of methyl methacrylate, styrene and a maleimide compound is thermally stable. A method for producing a methyl methacrylate-styrene resin composition in which a thioether-based organic sulfur stabilizer and a phosphite compound are blended for the purpose of improving the phenolic content, and a bisphenol-based antioxidant is further blended if desired.

Japanese Patent Application Laid-Open No. 63-304045 discloses a method for producing a methacrylic resin composition having improved thermal decomposition resistance, which comprises obtaining a methacrylic polymer obtained by copolymerizing methyl methacrylate and a maleimide compound. For coalescence,
A method for adding an organic phosphorus compound is disclosed. Further, the above-mentioned publication discloses a method of adding an organic sulfur-based compound to a methacrylic polymer and a method of adding an organic sulfur-based compound as a chain transfer agent during polymerization in the above-mentioned method.

Further, JP-A-6-116331 discloses that a monomer mixture containing an N-substituted maleimide is
There is disclosed a method for producing a transparent heat-resistant resin material by polymerizing a composition obtained by adding a phosphorus compound for the purpose of reducing yellowing upon heating.

The use of an antioxidant such as a phosphorus compound or a phenol compound for the purpose of improving the thermal stability and the coloring properties is disclosed in the above publications.

[0010]

SUMMARY OF THE INVENTION However, Japanese Patent Laid-Open No.
The method in which the antioxidant is not added during the polymerization but added in its entirety after the completion of polymerization as in the method described in Japanese Patent No. 256551 has a problem that the effect on the coloring source generated during the polymerization may not be sufficiently exhibited. .

Further, as described in JP-A-63-304055 and JP-A-6-116331,
In the method of casting polymerization (casting polymerization) by adding the whole amount of the antioxidant to the monomer mixture, the polymerization of the monomer mixture is inhibited, and the conversion rate of each monomer to the polymer becomes low. There is. Therefore, the production efficiency of the thermoplastic resin decreases,
There is a problem that the coloring of the thermoplastic resin may be more likely to occur.

Further, in the method described in JP-A-63-304045, even when an organic sulfur-based compound is added as a chain transfer agent during polymerization, there is a problem that the effect of reducing coloration during polymerization is insufficient. Has occurred.

The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide a method for producing a thermoplastic resin capable of efficiently producing a less colored thermoplastic resin. It is in.

[0014]

According to the first aspect of the present invention, there is provided a method for producing a thermoplastic resin, which comprises polymerizing a radically polymerizable monomer component. In this case, a part of the antioxidant is allowed to coexist during the polymerization of the monomer component, and the remaining antioxidant is added after the polymerization of the monomer component is completed.

According to the above-mentioned method, by causing a part of the antioxidant to coexist during the polymerization, it is possible to suppress the generation of a coloring component during the polymerization without inhibiting the polymerization. Further, since the remaining antioxidant is added after the completion of the polymerization, coloring during the heating after the polymerization, for example, during the desolvation step or the molding can be sufficiently reduced. As a result, a less colored thermoplastic resin can be efficiently produced.

The method for producing a thermoplastic resin according to the second aspect of the present invention is intended to solve the above-mentioned problems.
In the method for producing a thermoplastic resin described above, the antioxidant is at least one selected from the group consisting of a phenolic antioxidant and a phosphorus antioxidant.

According to the above method, coloring of the obtained thermoplastic resin can be further suppressed.

According to a third aspect of the present invention, there is provided a method for producing a thermoplastic resin, wherein the antioxidant comprises:
It is a hindered phenolic antioxidant.

According to the above method, coloring of the obtained thermoplastic resin can be further suppressed.

According to a fourth aspect of the present invention, there is provided a method for producing a thermoplastic resin, comprising the steps of: Parts, the total amount of the antioxidant used is 0.0001 to 1 part by weight, and the weight ratio of the amount of the antioxidant coexisting during the polymerization to the amount of the antioxidant added after the completion of the polymerization is 1/1. It is characterized by being 99-99 / 1.

According to the above-mentioned method, inhibition of polymerization can be avoided more reliably, and coloring of the obtained thermoplastic resin can be suppressed more reliably.

According to a fifth aspect of the present invention, there is provided a method of manufacturing a thermoplastic resin according to any one of the first to fourth aspects. It is characterized in that the polymerizable monomer component contains an N-substituted maleimide.

According to the above method, a thermoplastic resin having excellent heat resistance can be obtained.

According to a sixth aspect of the present invention, there is provided a method of manufacturing a thermoplastic resin according to any one of the first to fifth aspects. It is characterized in that the polymerizable monomer component contains a methacrylic acid ester.

According to the above method, a thermoplastic resin having excellent transparency can be obtained.

Hereinafter, the present invention will be described in detail.
In the method for producing a thermoplastic resin according to the present invention, a radically polymerizable monomer component is polymerized. The radically polymerizable monomer component may be any component as long as coloring at the time of polymerization or heating after polymerization can be prevented by an antioxidant.
-A monomer component containing a substituted maleimide is particularly preferable because a thermoplastic resin having excellent heat resistance can be obtained.
Further, the monomer component desirably contains methacrylic acid ester in order to improve the transparency of the thermoplastic resin.

The monomer component containing the N-substituted maleimide may be only the N-substituted maleimide, or a mixture of the N-substituted maleimide and a copolymerizable polymerizable monomer (hereinafter, referred to simply as “monomeric”). Monomer mixture).

As the above N-substituted maleimide, N-substituted maleimide
Cyclohexylmaleimide, N-phenylmaleimide,
N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, Nt-butylmaleimide, N
-Tribromophenylmaleimide, N-laurylmaleimide, N-benzylmaleimide and the like.

Among the above exemplified N-substituted maleimides, N-phenylmaleimide and N-cyclohexylmaleimide are used to obtain the thermoplastic resin having transparency, low colorability,
It is preferable because of its high industrial value such as heat resistance. further,
Among these, N-cyclohexylmaleimide is more preferable in consideration of coloring properties. Further, when N-tribromophenylmaleimide is used as the N-substituted maleimide, it is possible to impart flame retardancy to the obtained thermoplastic resin in addition to heat resistance and transparency. In addition, only one kind of the above-mentioned N-substituted maleimide may be used, or two or more kinds thereof may be used by appropriately mixing.

Examples of the polymerizable monomer copolymerizable with the above-mentioned N-substituted maleimide (hereinafter, referred to as a copolymerizable monomer) include methacrylates represented by methyl methacrylate, acrylates, and fragrances. Group vinyl compounds. As the methacrylic acid ester, for example,
Examples include methyl methacrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate. Examples of the acrylate include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and the like. Examples of the aromatic vinyl compound include styrene, α-methylstyrene, and the like.

When a thermoplastic resin is used for an optical material or the like,
It is preferable to use a methacrylic acid ester as the copolymerizable monomer, and among them, methyl methacrylate is particularly preferable. Thereby, a thermoplastic resin having excellent transparency can be obtained. Methacrylic acid ester may be used alone or may be used in combination with other copolymerizable monomers, but as the other copolymerizable monomer used in combination with methacrylic acid ester, it has excellent reactivity. It is preferable to use styrene, α-methylstyrene and methyl acrylate.

The compounding amount of the N-substituted maleimide and the copolymerizable monomer is such that the N-substituted maleimide is 5 to 60% by weight, more preferably 15 to 50% by weight. Of methyl methacrylate is 95 to 40% by weight, more preferably 85 to 50% by weight, and the other copolymerizable monomer as the above copolymerizable monomer is preferably 0 to 20% by weight. . When the amount of each monomer is out of the above range, the heat resistance and transparency of the obtained thermoplastic resin may be reduced.

In the production method of the present invention, an antioxidant for reducing coloring of the thermoplastic resin is used, a part of the antioxidant coexists during the polymerization of the monomer component, and the remaining antioxidant is used. In this method, the agent is added after the polymerization of the monomer component is completed.

The antioxidant coexisting during the polymerization of the monomer component may be any as long as it can suppress the generation of coloring components during the polymerization without inhibiting the polymerization reaction. And at least one selected from the group consisting of phosphorus-based antioxidants. Of these, it is desirable to use at least a phenolic antioxidant.

As the above-mentioned phenolic antioxidant, a hindered phenolic antioxidant in which the approach of another molecule to its hydroxyl group is sterically hindered is particularly preferred. As the above hindered phenolic antioxidant,
For example, 2,4-bis (n-octylthio) -6- (4
-Hydroxy-3,5-di-t-butylanilino)-
1,3,5-triazine, 2,2′-thiobis- (4-
Methyl-6-t-butylphenol), triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], pentaerythrityl-tetrakis [3- (3,5- Di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2,2-thiodiethylenebis [3- (3,5 -Di-tert-butyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], tris- (3
5-di-t-butyl-4-hydroxybenzyl) -isocyanurate, 1,3,5-trimethyl-2,4,6-
Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, N, N′-hexamethylenebis (3
5-di-t-butyl-4-hydroxy-hydrocinnamamide), 3,5-di-t-butyl-4-hydroxy-benzylphosphonate-diethyl ester and the like. Alternatively, two or more kinds can be used. Among these compounds, it is particularly preferable to use pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate].

The phenolic antioxidant may be used alone, but when used in combination with a phosphorus antioxidant, the coloring of the thermoplastic resin can be further reduced. Examples of the phosphorus antioxidant include trisnonylphenyl phosphite, triphenyl phosphite, trilauryl trithiophosphite, trioctadecyl phosphite, diisodecyl pentaerythritol diphosphite, distearyl pentaerythritol diphosphite,
3,5-tris (3,5-di-t-butyl-4-hydroxybenzyl) -S-triazine-2,4,6- (1
H, 3H, 5H) trione, tris (2,4-di-t-)
Butylphenyl) phosphite, dinonylphenylpentaerythritol diphosphite, di (2,4-di-t
-Butylphenyl) pentaerythritol diphosphite, tetraphenyldipropylene glycol diphosphite, 4,4'-isobutylidenebis- (3-methyl-
6-t-butylphenyl-ditridecyl phosphite), 4,4'-isopropylidenediphenyltetradodecyl phosphite, 1,1,3-tris [(2-methyl-4-ditridecyl phosphite-5-t- Butyl)
Phenyl] butane, tetraphenyltetradecylpentaerythritol tetraphosphite, poly (dipropylene glycol) phenyl phosphite, bisphenol A pentaerythritol phosphite, hydrogenated bisphenol A phosphite resin, 9,10-dihydro-9-
Oxa-10-phosphaphenanthrene-10-oxide, 10-decyloxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene, tetrakis (2
4-di-t-butylphenyl) -4,4'-biphenylenephosphonite, o-cyclohexylphenyl phosphite, tris (2,4-di-t-butylphenyl) phosphite and the like. Species or two or more can be used.

The amount of the antioxidant coexisting during the polymerization of the monomer component is 0.00
0.01 to 0.05 part by weight is preferable, and 0.001 to 0.0 part by weight.
2 parts by weight is more preferred. If the antioxidant is present in an amount exceeding 0.05 parts by weight during the polymerization of the monomer component, the polymerization is inhibited, and the conversion is undesirably reduced. If the amount of the antioxidant coexisting during the polymerization of the monomer component is less than 0.0001, the generation of the coloring component during the polymerization may not be sufficiently suppressed.

As a method for allowing an antioxidant to coexist during the polymerization of the monomer component, a method of adding the antioxidant before the polymerization of the monomer component is started is preferable, but the method is particularly limited. Instead, for example, a method may be used in which after the polymerization of the monomer component is started, an antioxidant is sequentially added during the polymerization.

On the other hand, as the antioxidant added after the completion of the polymerization of the monomer component, any antioxidant can be used as long as it can suppress generation of a coloring component during heating in a desolvation step after the completion of the polymerization or molding. At least one selected from the group consisting of phenolic antioxidants and phosphorus antioxidants
Although seeds can be used, it is desirable to use at least a phenolic antioxidant.

As the phenolic antioxidant, the above-mentioned hindered phenolic antioxidant is particularly preferred. The phenolic antioxidant may be used alone, but when used in combination with the phosphorus antioxidant, the coloring of the thermoplastic resin can be further reduced. The antioxidant added after the completion of the polymerization of the monomer component may be the same as or different from the antioxidant coexisting during the polymerization of the monomer component.

The amount of the antioxidant added after the completion of the polymerization of the monomer component is 0.0 to 100 parts by weight of the monomer component.
1 to 1.0 part by weight is preferable, and 0.02 to 0.5 part by weight is more preferable. If the amount of the antioxidant added after the polymerization of the monomer component is less than 0.01 part by weight, there is a possibility that coloring during heating after the polymerization is not sufficiently suppressed. Further, even if the amount exceeding 1.0 part by weight is added after the completion of the polymerization of the monomer component, the coloring reduction effect commensurate with the increase in the amount is not obtained, which is not efficient.

Further, the total amount of the antioxidant used (the amount of the antioxidant coexisting with the antioxidant during the polymerization and the amount of the antioxidant added after the polymerization is completed) is based on 100 parts by weight of the monomer component. Is a total of 0.0001 to 1 part by weight, and the weight ratio of the amount of the antioxidant coexisting during the polymerization to the amount of the antioxidant added after the polymerization is 1/99 to 99/1. Is preferred. Thereby, while preventing the polymerization reaction from being inhibited by the antioxidant and improving the conversion, it is possible to sufficiently suppress both the generation of the coloring component during the polymerization and the coloring at the time of heating after the completion of the polymerization. .

The total amount of antioxidants used is 0.0001
If the amount is less than parts by weight, coloring during heating after completion of the polymerization may not be sufficiently suppressed. Further, even if the amount exceeding 1.0 part by weight is added after the completion of the polymerization of the monomer component, the coloring reduction effect commensurate with the increase in the amount is not obtained, which is not efficient.

As a method for adding an antioxidant after the polymerization of the monomer component, a method prior to treating the polymerization solution obtained after the polymerization of the monomer component, for example, in the case of solution polymerization, Is preferably a method of adding an antioxidant before the solvent removal step.

As a method for polymerizing the monomer component, a conventionally known polymerization method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, or a method of appropriately combining them can be used. In the case of bulk polymerization, the effect of the present invention is easily obtained. In addition, the polymerization is usually carried out by 4
It is performed at 0 to 150 ° C. for about 4 to 24 hours.

As the polymerization initiator used in the above polymerization, benzoyl peroxide, lauryl peroxide,
t-butylperoxy-2-ethylhexanoate, t
-Amyl peroxy-2-ethylhexanoate persulfate, hydrogen peroxide, azobisisobutyronitrile and the like can be mentioned.

In the production method of the present invention, various known additives typified by ultraviolet absorbers can be further added during or after the polymerization reaction, depending on the intended use of the obtained thermoplastic resin. .

The thermoplastic resin obtained by the production method of the present invention can be used as it is, but is extruded with another synthetic resin, for example, polymethyl methacrylate resin, methyl methacrylate-styrene resin and the like. It can also be used by blending with a machine or the like.

The thermoplastic resin according to the present invention is excellent in heat resistance and transparency, and has little coloring. For example, it can be used as a base material of optical materials such as optical disks, automobile parts, lighting covers, electric equipment parts and the like. It is particularly suitable as a material requiring not only transparency but also aesthetics.

[0050]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited thereto. In the following Examples and Comparative Examples, "parts" indicates parts by weight. In addition, the yellowness (Y
I) and the glass transition temperature were measured by the following methods.

Further, conversion rate of monomer to polymer (%)
Is measured by gas chromatography the weight fraction (%) of the residual monomer with respect to the total amount of the residual monomer and the polymer in the polymerization solution obtained by polymerization, and from 100%, the residual monomer The value obtained by subtracting the weight fraction was used.

Method for measuring yellowness (YI) A copolymer pellet was dissolved in chloroform and dissolved in 15% by weight.
It is made into a chloroform solution, and according to JIS K 7103,
It was measured by transmitted light.

Measurement method of glass transition temperature The glass transition temperature of the obtained copolymer was measured according to JIS K7.
121, differential scanning calorimeter (Rigaku Denki Co., Ltd.)
(Trade name: DSC-8230), using a-alumina as a reference under a nitrogen gas atmosphere, and measuring the temperature from normal temperature to 220 ° C. at a rate of 10 ° C./min., DSC (Differential Scanning Colorimetry) ) Calculated from the curve by the midpoint method.

Example 1 First, methyl methacrylate was placed in a 20-liter stainless steel polymerization tank equipped with a first dropping tank, a second dropping tank, a third dropping tank, and a stirrer.
5.75 parts, N-cyclohexylmaleimide 6.25
Parts, 25 parts of toluene, and 0.0025 part of pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] as a hindered phenolic antioxidant, 30
After bubbling nitrogen gas for 10 minutes while stirring at 0 rpm, heating was started under a nitrogen atmosphere.

The first dropping tank was charged with 15.75 parts of methyl methacrylate, 6 parts of styrene, and 10 parts of toluene, and was previously bubbled with nitrogen gas. Further, 6.25 parts of N-cyclohexylmaleimide and 10 parts of toluene were charged into the second dropping tank, and bubbled with nitrogen gas in advance. Also, in the third dropping tank,
0.108 parts of t-butyl peroxyisopropyl carbonate as an initiator and 10 parts of toluene were charged and bubbled with nitrogen gas in advance.

Next, when the temperature in the polymerization tank reached 110 ° C., 0.02 parts of t-butylperoxyisopropyl carbonate was added to the polymerization tank, and a first dropping tank, a second dropping tank, Dropping was started from the third dropping tank. Then, while dropping from each of the first dropping tank, the second dropping tank and the third dropping tank over 3.5 hours, the polymerization temperature 11
The polymerization reaction was carried out under reflux at 0 ° C. for 7 hours.

Further, after the completion of the polymerization reaction, pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4
-Hydroxyphenyl) propionate] 0.0475
Was added to obtain a polymerization solution. About the obtained polymerization liquid,
The conversion of the monomer to the polymer was measured by gas chromatography and was found to be 96.4%.

This polymerization solution is supplied to a 30 mm twin-screw extruder equipped with a vent controlled at a cylinder temperature of 240 ° C., devolatilized in vacuo from a vent port, and the extruded strands are pelletized to obtain a thermoplastic resin according to the present invention. Was obtained.

The obtained copolymer pellets have a yellowness (Y
I) was 3.1 and the glass transition temperature was 136 ° C. Table 1 shows the main reaction conditions and results.

Example 2 Further, pentaerythrityl-tetrakis [3- (3,5)
-Di-t-butyl-4-hydroxyphenyl) propionate], except that the amount was changed from 0.0475 parts to 0.0275 parts, to thereby obtain a polymerization solution. The conversion of the monomer into the polymer of the obtained polymerization solution was measured by gas chromatography to be 95.2%.

This polymerization solution was supplied to a vented 30 mm twin screw extruder controlled at a cylinder temperature of 240 ° C., devolatilized in vacuum from a vent port, and extruded strands were pelletized to obtain a thermoplastic resin according to the present invention. Was obtained.

The obtained copolymer pellets have a yellowness (Y
I) was 2.8 and the glass transition temperature was 136 ° C. Table 1 shows the main reaction conditions and results.

Example 3 First, methyl methacrylate was placed in a 20-liter stainless steel polymerization tank equipped with a first dropping tank, a second dropping tank, a third dropping tank, and a stirrer.
5.75 parts, N-cyclohexylmaleimide 6.25
Parts, 25 parts of toluene, 0.0025 parts of pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], and di (2,2) as a phosphorus-based antioxidant. 4-di-t-butylphenyl) pentaerythritol diphosphite 0.005
The polymerization reaction was carried out in the same manner as in Example 1.

Further, after the completion of the polymerization reaction, pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4
-Hydroxyphenyl) propionate] 0.0275
Parts and 0.055 parts of di (2,4-di-t-butylphenyl) pentaerythritol diphosphite,
A polymerization liquid was obtained. The conversion of the monomer into the polymer of the obtained polymerization liquid was measured by gas chromatography, and was 95.5%.

This polymer solution was supplied to a vented 30 mm twin-screw extruder controlled at a cylinder temperature of 240 ° C., devolatilized in vacuo from a vent port, and extruded strands were pelletized to obtain a thermoplastic resin according to the present invention. Was obtained.

The obtained copolymer pellets have a yellowness (Y
I) was 2.2 and the glass transition temperature was 135 ° C. Table 1 shows the main reaction conditions and results.

[Comparative Example 1] First, methyl methacrylate was placed in a 20-liter stainless steel polymerization tank equipped with a first dropping tank, a second dropping tank, a third dropping tank, and a stirrer.
5.75 parts, N-cyclohexylmaleimide 6.25
And 25 parts of toluene, and nitrogen gas was bubbled for 10 minutes while stirring at 300 rpm, and then the temperature was raised in a nitrogen atmosphere.

The first dropping tank was charged with 15.75 parts of methyl methacrylate, 6 parts of styrene, and 10 parts of toluene, and was previously bubbled with nitrogen gas. Further, 6.25 parts of N-cyclohexylmaleimide and 10 parts of toluene were charged into the second dropping tank, and bubbled with nitrogen gas in advance. Also, in the third dropping tank,
0.108 parts of t-butyl peroxyisopropyl carbonate as an initiator and 10 parts of toluene were charged and bubbled with nitrogen gas in advance.

Next, when the temperature in the polymerization tank reached 110 ° C., 0.02 parts of t-butyl peroxyisopropyl carbonate was added into the polymerization tank, and the first dropping tank, the second dropping tank, Dropping was started from the third dropping tank. Then, while dropping from each of the first dropping tank, the second dropping tank and the third dropping tank over 3.5 hours, the polymerization temperature 11
The polymerization reaction was carried out at 0 ° C. under reflux for 7 hours to obtain a polymerization solution.

The conversion of the monomer into the polymer of the obtained polymerization solution was measured by gas chromatography, and it was 95.4%.

The polymer solution was supplied to a vented 30 mm twin screw extruder controlled at a cylinder temperature of 240 ° C., devolatilized in vacuo from a vent port, and extruded strands were pelletized to obtain a thermoplastic resin according to the present invention. Was obtained as a copolymer pellet.

The obtained copolymer pellets have a yellowness (Y
I) was 5.0 and the glass transition temperature was 136 ° C. Table 1 shows the main reaction conditions and results.

Comparative Example 2 After completion of the polymerization reaction, pentaerythrityl-tetrakis [3- (3,5-di-t-
[Butyl-4-hydroxyphenyl) propionate], except that the addition of [butyl-4-hydroxyphenyl) propionate] was not carried out, thereby obtaining a polymerization solution. The conversion of the monomer into the polymer of the obtained polymerization solution was measured by gas chromatography, and was 95.1%.

This polymer solution was supplied to a vented 30 mm twin screw extruder controlled at a cylinder temperature of 240 ° C., devolatilized in vacuum from a vent port, and the extruded strands were pelletized to obtain a thermoplastic resin according to the present invention. Was obtained as a copolymer pellet.

The obtained copolymer pellets have a yellowness (Y
I) was 4.2 and the glass transition temperature was 136 ° C. Table 1 shows the main reaction conditions and results.

Comparative Example 3 Pentaerythrityl-tetrakis [3- (3,5-di-
[t-butyl-4-hydroxyphenyl) propionate] was changed from 0.0025 parts to 0.05 parts to carry out the same reaction and operation as in Example 1 to obtain a polymerization solution. When the conversion of the monomer to the polymer was measured for the obtained polymerization solution by gas chromatography, it was found to be 9%.
2.4%.

This polymerization solution is supplied to a vented 30 mm twin screw extruder controlled at a cylinder temperature of 240 ° C., devolatilized in vacuo from a vent port, and the extruded strands are pelletized to obtain a thermoplastic resin according to the present invention. Was obtained as a copolymer pellet.

The obtained copolymer pellets have a yellowness (Y
I) was 4.1 and the glass transition temperature was 136 ° C. Table 1 shows the main reaction conditions and results.

[0079]

[Table 1]

Examples 1 to 3 and Comparative Example 1 shown in Table 1
As is clear from the results of Nos. To 3, the thermoplastic resin obtained by the production method of the present invention has a high glass transition temperature and excellent heat resistance, as well as a high conversion rate of the monomer,
Moreover, it can be seen that the yellowness (YI) is small.

[0081]

According to the production method of the present invention, a part of the antioxidant is allowed to coexist during the polymerization of the monomer component, and the remaining antioxidant is added after the completion of the polymerization of the monomer component.

Thus, it is possible to suppress the generation of the coloring component during the polymerization of the monomer component without inhibiting the polymerization of the monomer component. For example, coloring during the desolvation step or molding can be sufficiently reduced. Therefore, there is an effect that a thermoplastic resin with little coloring can be efficiently produced.

Since the obtained thermoplastic resin is less colored, it is required to have not only transparency but also aesthetic appearance, such as a base material of an optical material such as an optical disk, a car part, a lighting cover, and an electric equipment part. It is particularly suitable as a material to be used.

The antioxidant is preferably at least one selected from the group consisting of a phenolic antioxidant and a phosphorus antioxidant, and among them, a hindered phenolic antioxidant is particularly preferable. Thereby, coloring in the obtained thermoplastic resin can be further suppressed.

Further, based on 100 parts by weight of the monomer component,
The total amount of the antioxidant used is 0.0001 to 1 part by weight, and the weight ratio of the amount of the antioxidant coexisting during the polymerization to the amount of the antioxidant added after the completion of the polymerization is 1/99 to 99.
/ 1 is preferred. Thereby, inhibition of polymerization can be avoided more reliably, and coloring in the obtained thermoplastic resin can be more reliably suppressed.

Further, it is preferable that the monomer component contains an N-substituted maleimide. Thereby, a thermoplastic resin having excellent heat resistance can be obtained. Further, the monomer component preferably contains a methacrylic acid ester. Thereby, a thermoplastic resin having excellent transparency can be obtained.

Claims (6)

[Claims] 1. A process for producing a thermoplastic resin which polymerizes a radically polymerizable monomer component, wherein a part of an antioxidant is allowed to coexist during the polymerization of the monomer component, and the remaining antioxidant is used. Is added after the completion of the polymerization of the monomer component. 2. The method according to claim 1, wherein the antioxidant is at least one selected from the group consisting of a phenolic antioxidant and a phosphorus antioxidant. . 3. The method for producing a thermoplastic resin according to claim 1, wherein the antioxidant is a hindered phenol-based antioxidant. 4. The total amount of the antioxidant to be used is 0.0001 to 1 part by weight, based on 100 parts by weight of the monomer component, the amount of the antioxidant coexisting during the polymerization and the oxidation added after the completion of the polymerization. The method for producing a thermoplastic resin according to any one of claims 1 to 3, wherein a weight ratio to the amount of the inhibitor is 1/99 to 99/1. 5. The method according to claim 1, wherein the radically polymerizable monomer component is N
The method for producing a thermoplastic resin according to any one of claims 1 to 4, wherein the method comprises a substituted maleimide. 6. A method according to claim 1, wherein said radically polymerizable monomer component contains a methacrylic acid ester.
The method for producing a thermoplastic resin according to any one of the above.