JPH1087737A - Impurity removal method in continuous solution polymerization - Google Patents

Abstract

(57) [Problem] To provide a method for producing a methacrylic resin having excellent optical properties and excellent thermal decomposition resistance. SOLUTION: In a continuous solution polymerization of a methacrylic resin, a solvent having a higher boiling point than the solvent used for the polymerization is present at the bottom of the distillation column, and impurities generated during the polymerization are intermittently or continuously withdrawn by removing the bottom liquid. Remove.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for removing impurities in a continuous polymerization method of a methacrylic resin.

[0002]

2. Description of the Related Art Methacrylic resins can be used, for example, in lighting equipment, signboards, various decorative articles, nameplates, tail lamps, etc. due to their excellent transparency, good mechanical properties, workability, and beautiful appearance of molded articles. Widely used for automobile parts and tableware. Recently, it has been widely used in optical fields such as various lenses, optical disks, and light guide plates. Therefore, advanced optical characteristics are being demanded.

[0003] As a method for producing a methacrylic resin, a suspension polymerization method is widely employed. However, the greatest disadvantage of this production method is that the suspension stabilizer used remains partially in the polymer, and the polymer properties, especially the optical properties, are degraded. As methods for improving the drawbacks of the suspension polymerization method, there are a bulk polymerization method (JP-A-49-37993 and JP-A-3-111408) and a solution polymerization method (JP-A-6-111408).
3-57613 and JP-B-7-119259) have been proposed.

According to these methods, unlike the suspension polymerization method, a methacrylic resin having excellent optical properties can be produced because no suspension stabilizer is used. However,
Bulk polymerization has a problem that it is difficult to control a stable polymerization reaction, and sometimes the diffusion of polymer molecules is restricted as the viscosity of the polymerization system increases, and the termination reaction is reduced. . Furthermore, there is another major problem when producing this bulk polymerization continuously on an industrial level. That is, in general, when methacrylic resin is continuously and industrially produced by bulk polymerization, polymerization is generally carried out using a complete mixing type polymerization reactor.
If it is set to 00%, there is a problem that the viscosity of the polymerization solution becomes too high to stir, so that the polymerization is usually carried out while keeping the polymerization conversion rate at 70% or less. Therefore, a recycled liquid composed of unreacted methyl methacrylate after polymerization is reused. However, since the recycle liquid contains impurities and the like generated during polymerization, it is purified by a distillation column or a partial condenser.

In the case of methacrylic resins that require optical properties, it is necessary to purify the recycle liquid in order to remove impurities generated during polymerization, particularly, colored impurities. As described above, a distillation column or a partial condenser is used to purify the recycle solution. However, since a partial condenser having a low impurity boiling point is difficult to remove, a method using a distillation column is usually used. When purifying in a distillation column, impurities are not distilled because they have a higher boiling point than monomers such as methyl methacrylate and remain at the bottom of the distillation column, and the main component is a methyl methacrylate monomer at the bottom of the distillation column. Remove by withdrawing with bottom liquid. However, because the residence time of the bottom liquid containing methyl methacrylate monomer as a main component is long and the temperature is high, polymerization of methyl methacrylate monomer proceeds at the bottom of the distillation column, and the heat exchange efficiency in the reboiler decreases. And clogging of the piping by the generated polymer occurs. Or, in an extreme case, there is a large problem in industrially stable production such as polymerization progressing and solidifying in the entire bottom of the distillation column.

[0006] On the other hand, solution polymerization can solve the above problems. That is, according to this method, since the viscosity of the reaction system is reduced by the solvent, the gel effect can be suppressed and the runaway reaction can be suppressed. Also, if a solvent having a boiling point higher than that of a monomer such as methyl methacrylate is used as a solvent, the bottom of the distillation column is mainly composed of the solvent, and the polymerization here hardly occurs, and impurities generated by the polymerization can be extracted together with the solvent. A methacrylic resin can be produced extremely stably. However, the polymerization liquid obtained during the production of the methacrylic resin is devolatilized to separate the polymer and the recycle liquid. However, if a solvent having a high boiling point is used, the devolatilization is burdensome and is not economically preferable. Alternatively, there is a problem that a residual solvent remains in the polymer and the quality is not preferable.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for continuously polymerizing a methacrylic resin having excellent optical properties by removing impurities and the like generated during polymerization stably on an industrial scale.

[0008]

Means for Solving the Problems As a result of intensive studies on the method for solving the above problems, the present inventors have distilled out a solvent B having a higher boiling point than a monomer used in polymerization such as methyl methacrylate monomer. It is present at the bottom of the tower, and a recycled liquid containing unreacted monomer and solvent A after polymerization or a recycled liquid and a new monomer are distilled, and the distilled monomer and solvent A are supplied to the polymerization reactor, By continuous polymerization, a runaway reaction due to a gel effect caused by bulk polymerization can be suppressed, and without causing a problem due to progress of polymerization at the bottom of the distillation column, by-products produced at the time of polymerization efficiently and efficiently,
Further, the present inventors have found that it is possible to remove impurities such as a polymerization inhibitor and impurities contained in the raw material or a polymerization inhibitor added for preserving a recycled solution, and to produce a high-quality methacrylic resin in an industrially stable manner. It was completed.
Further, the solvent B is not present at the bottom of the distillation column, and a solvent A having a boiling point equal to or lower than that of a monomer such as methyl methacrylate is used.
When continuous solution polymerization is carried out only by itself, the monomer concentration increases at the bottom of the distillation column, and a problem occurs due to the progress of polymerization at the bottom of the distillation column as in the case of bulk polymerization. If it is carried out, even when a solvent having a low boiling point is used in the solution polymerization, the methacrylic resin can be industrially stably removed to remove impurities, no load is applied to devolatilization of the polymerization solution, and the residual amount in the obtained polymer is reduced. It has also been found that foreign matter can be eliminated, and a high-quality methacrylic resin can be industrially produced stably, and the present invention has been completed.

That is, the present invention relates to (A) a recycled liquid containing (a) a monomer mainly composed of unreacted methyl methacrylate after polymerization and a solvent A, and (b) a recycled liquid containing a new methyl methacrylate as a main component. To the distillation column continuously,
Distilled monomer and solvent A are continuously supplied to the polymerization reactor, polymerization is performed, and then the polymerization solution is devolatilized to remove the polymer, and at the same time, unreacted monomer and solvent A are recycled and used. A continuous solution polymerization process or (B) (a) after the polymerization, a recycle liquid containing a monomer mainly composed of unreacted methyl methacrylate and a solvent A is continuously supplied to a distillation column, and a distilled single And the solvent A and (b) a new monomer containing methyl methacrylate as a main component are continuously supplied to the polymerization reactor to polymerize, and then the polymerization solution is devolatilized to take out the polymer. In a continuous solution polymerization process in which the monomer and solvent A of the reaction are recycled, a solvent B having a boiling point higher than the boiling point of the monomer is present at the bottom of the distillation column, and the bottom liquid is continuously fed from the bottom of the distillation column. Or if you pull out intermittently The same amount of solvent B taken out when
Is continuously or intermittently supplied to the bottom of the distillation column to produce by-products during polymerization, impurities such as polymerization inhibitors added for stabilizing the recycled liquid, or impurities such as polymerization inhibitors contained in the raw materials Is a continuous solution polymerization method using a solvent A.

The monomer having methyl methacrylate as a main component in the present invention includes a monomer which can be copolymerized with methyl methacrylate alone or methyl methacrylate. Monomers copolymerizable with methyl methacrylate include alkyl methacrylates such as ethyl methacrylate, butyl methacrylate, and cyclohexyl methacrylate; and alkyl acrylates such as methyl acrylate, ethyl acrylate, and butyl acrylate. , Aromatic vinyl compounds such as styrene, vinyltoluene and α-methylstyrene; vinyl cyanides such as acrylonitrile and methacrylonitrile; maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide; and unsaturated acids such as maleic anhydride. Examples thereof include unsaturated acids such as carboxylic anhydrides, acrylic acid, methacrylic acid, and maleic acid. Among the monomers copolymerizable with methyl methacrylate, acrylates have good thermal decomposition resistance, and methacrylic resins obtained by copolymerizing acrylates are preferred because of high fluidity during molding. . When the acrylates are copolymerized with methyl methacrylate, the amount of the acrylates used is preferably 15% by weight or less. When the content is 15% by weight or more, the effect of improving the thermal decomposition resistance and the fluidity is high, but the heat resistance, that is, the heat deformation temperature is lowered, which is not preferable. Of these acrylates, methyl acrylate and ethyl acrylate have the most remarkable improvement effect even when a small amount thereof is copolymerized with methyl methacrylate. Monomers copolymerizable with methyl methacrylate can be used alone or in combination of two or more.

The solvent A in the present invention dissolves the monomer used in the polymerization and the resulting polymer and does not adversely affect the polymerization reaction. Examples of the solvent A include benzene, toluene, xylene, ethylbenzene and diethylbenzene. Aromatic compounds, hexane, heptane, octane, aliphatic compounds such as decane, alicyclic compounds such as decalin, butyl acetate, ester compounds such as pentyl acetate, 1,1,1,1,
A halogen compound such as 2-tetrachloroethane and 1,1,2,2-tetrachloroethane can be used. The boiling point of the solvent A may be lower or higher than the boiling point of the monomer used.
In order to reduce the load during devolatilization and to reduce the residual solvent in the obtained polymer, a solvent close to the boiling point of the monomer is preferable. The boiling point of the solvent A is preferably ± 20 ° C. of the boiling point of the monomer. Further, ± 10 ° C. is more preferable. As the type of the solvent, particularly, an aromatic compound or an aliphatic compound does not adversely affect the polymerization, and the solubility of impurities generated by the polymerization is preferably high. In addition, among aromatic compounds, benzene, toluene, and hexane and heptane among the aliphatic compounds have an appropriate boiling point, have a small load for devolatilization, have a small residual solvent in the obtained polymer, and have a low boiling point. It is preferable because it has no adverse effect and can be obtained industrially at low cost.

The amount of the solvent A is 50% by weight or less, preferably 25% by weight or less, more preferably 15% by weight or less, and still more preferably 1% by weight or less, based on the weight of the whole mixture at the time of polymerization.
0% by weight or less. It is more preferable that the amount of the solvent is small because it is excellent in thermal decomposition resistance. The lower limit for the use of solvent A is 0.1% by weight. Even at 0.1% by weight, the runaway reaction due to the gel effect is suppressed as compared with the bulk polymerization. The solvent A used can be used alone or in combination of two or more.

The solvent B in the present invention dissolves impurities to be removed at the bottom of the distillation column and has a higher boiling point than methyl methacrylate monomer and a monomer copolymerizable with methyl methacrylate. Usually, xylene, ethylbenzene, aromatic compounds such as diethylbenzene, octane, aliphatic compounds such as decane, alicyclic compounds such as decalin, butyl acetate, ester compounds such as pentyl acetate,
1,1,1,2-tetrachloroethane, 1,1,2,2
Examples thereof include halogen compounds such as 2, -tetrachloroethane. The boiling point of the solvent B is higher than the boiling points of the methyl methacrylate monomer and the monomer copolymerizable with methyl methacrylate, preferably 10 ° C. or higher, more preferably 20 ° C.
It is desirable that the temperature is higher by at least 30 ° C, more preferably at least 30 ° C. Further, it is necessary that the boiling point be higher than that of the solvent A. Among them, aromatic compounds are particularly preferred because of high solubility of impurities. In addition, among the aromatic compounds, xylene and ethylbenzene are particularly preferable since they have high solubility of impurities generated by polymerization and can be obtained industrially at low cost. If the boiling point of the solvent B is high, the bottom of the distillation column becomes only the solvent B, and the trouble caused by the polymerization can be prevented. Solvent B
May be one kind or a combination of two or more kinds.

The polymerization inhibitor added to prevent the polymerization of the recycle solution or the polymerization of the raw material monomer is not particularly limited as long as it is soluble in the solvent and the monomer. , Hydroquinone, methoxyhydroquinone, t-butylcatechol and the like can be used.
The impurities contained in the raw material include those contained in the raw material methyl methacrylate monomer and those contained in the polymerization initiator, chain transfer agent, solvent and the like used in the continuous solution polymerization process.

[0015] By-products formed during the polymerization are, among the products formed in the polymerization reactor, components separated and recovered from the polymer in the devolatilization step. Examples of the by-products include catalytic decomposition products and methyl methacrylate. Examples include monomeric dimers and trimers, and oligomer components. FIG. 1 shows an example of a typical distillation column, and FIG. 2 shows an example of a continuous solution polymerization process. The present invention is not limited to this, but is carried out as follows using, for example, equipment as shown in the drawings. That is, (A) (a) a monomer mainly composed of unreacted methyl methacrylate after polymerization and a recycled liquid containing solvent A, and (b) a new monomer mainly composed of methyl methacrylate. It is continuously supplied to the distillation column, and impurities are continuously or intermittently extracted together with the solvent B from the bottom of the distillation column where the solvent B is present, and at the same time, the polymerization initiator and the molecular weight are adjusted to the distilled monomer and the solvent A. An additional agent is added, continuously supplied to the polymerization reactor, polymerized into the polymerization reactor, and then the polymerization solution is devolatilized to take out the polymer, and at the same time, the unreacted monomer and the solvent A are recycled and used. To perform continuous solution polymerization. Alternatively, (A) (a) a recycle liquid containing a monomer containing methyl methacrylate as the main component after polymerization is continuously supplied to the distillation column, and impurities are removed from the bottom of the distillation column where the solvent B is present. A monomer and solvent A which are continuously or intermittently extracted together with B and distilled simultaneously, and (b) a new monomer containing methyl methacrylate as a main component, and further a polymerization initiator and a molecular weight regulator are added. After the addition, the mixture is continuously supplied to a polymerization reactor for polymerization, and then the polymerization solution is devolatilized to take out a polymer. At the same time, unreacted monomer and solvent A are recycled and subjected to continuous solution polymerization.

The distillation is carried out, for example, by a distillation column of a packed column type, a tray type or the like. In the distillation method, for example, a recycle solution containing impurities to be removed or a mixed solution of this and a new monomer is supplied from the middle or upper stage of the distillation column, and the bottom solution of the distillation column is heated by a heater such as a reboiler. This is carried out by condensing a monomer containing methyl methacrylate as a main component and a solvent A vapor distilled from the top of the distillation column with a condenser. At this time, impurities higher than the monomer are concentrated at the bottom of the distillation column composed of the solvent B. The impurities can be continuously or intermittently taken out together with the solvent B from the bottom of the distillation column, and can be continuously removed by adding the amount of the solvent B taken out. The additional addition of the solvent B may be carried out directly or intermittently at the bottom of the distillation column, or may be carried out by continuously distilling the recycled liquid before distillation or a new monomer. Further, as described above, there are two types of distillation: a method in which a new monomer and a recycled liquid containing an unreacted monomer after polymerization are distilled together, and a method in which only the recycled liquid is distilled. Is more preferable because impurities contained in a new monomer can be removed. It is necessary for the distillation column to have a number of stages such that the monomer having methyl methacrylate as a main component and the solvent A are not mixed into the bottom liquid of the distillation column in carrying out the solution polymerization of the present invention. is there.
However, when the boiling point of the solvent A is higher than that of a monomer such as methyl methacrylate depending on the boiling point to be used, the bottom of the distillation column may be a mixture of the solvent A and the solvent B in some cases. Even in this case, polymerization of the monomer can be prevented at the bottom of the distillation column. In the distillation column of the present invention, the boiling point of the solvent B used is higher than the boiling point of the monomer containing methyl methacrylate as a main component, and the boiling point of impurities to be removed is almost higher than the boiling point of the monomer. , Impurities
It is concentrated to the distillation column bottom liquid, so that the distillation column bottom contains only the impurities to be removed and the solvent B. Therefore, while heating the bottom liquid of the distillation column using a heater such as a reboiler, a part of the bottom liquid is continuously or intermittently withdrawn to the outside of the system to prevent the impurities to be removed from the system from being discharged and accumulated. I can measure. At this time, if the amount to be withdrawn is small, the impurity concentration in the bottom liquid of the distillation column becomes high, and the heat exchange efficiency in the heater deteriorates due to the increase in liquid viscosity, and the pipes and the heater are clogged due to the precipitation of impurities. there is a possibility. On the other hand, if the amount to be extracted is too large, no operational problem occurs, but it is not economical. Therefore, when removing impurities, it is preferable to reduce the amount of the bottom liquid withdrawn to the extent that impurities do not precipitate as long as the heater has the capability.

A monomer having methyl methacrylate as a main component and a solvent A distilled as described above, a new monomer having methyl methacrylate as a main component, a polymerization initiator, a molecular weight modifier and the like may be used. Individually or mixed and supplied to a polymerization reactor for polymerization. The monomer solution comprising the monomer and the solvent A is continuously supplied to, for example, a countercurrent contact tower to replace the inert gas and improve the dissolved oxygen in the monomer solution in order to improve the optical characteristics. To 1 ppm or less. Further, in order to remove foreign substances such as metal foreign substances, it is preferable to filter the monomer solution with a filter having a size of 0.5 μm or less.

In this case, the polymerization initiator used is one which is decomposed into active groups at the polymerization temperature to generate radicals. Examples thereof include di-tert-butyl peroxide, di-cumyl peroxide, methyl ethyl ketone peroxide, di-tert.
-Butyl perphthalate, di-tert-butyl perbenzoate, tert-butyl peracetate, 2,5
-Dimethyl-2,5-di (tert-butylperoxy) hexane, 1,1-bis (t-butylperoxy)
-3,3,5-trimethylcyclohexane, di-ter
Organic peroxides such as t-amyl peroxide, benzoyl peroxide, cumene hydroperoxide and lauryl peroxide, azobisisobutanol diacetate, 1,1′-azobiscyclohexanecarbonitrile, 2-phenylazo 2,4 An azo compound such as -dimethyl-4-methoxyvaleronitrile, 2-cyano-2-propylazoformamide and 2,2'-azobisisobutyronitrile can be used. These can be used alone or in combination of two or more. The use amount of these polymerization initiators is preferably in the range of 0.0010 to 0.03% by weight based on the weight of the whole reaction mixture.

Further, as the molecular weight modifier used at this time, mercaptans are mainly used. Examples of the mercaptans include n-butyl mercaptan, isobutyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, sec-dodecyl mercaptan, te
Primary or secondary and tertiary mercaptans having an alkyl group or a substituted alkyl group such as rt-butyl mercaptan, aromatic mercaptans such as phenyl mercaptan, thiocresol, thioglycolic acid and its esters, ethylene thioglycol, etc. Can be used. These can be used alone or in combination of two or more. The amount of use of these molecular weight regulators is appropriately determined according to the molecular weight of the polymer to be produced, but is usually selected in the range of 0.01 to 0.5% by weight based on the weight of the whole reaction mixture.

As the polymerization reactor, use is made of a device such as a double helical ribbon or a pitched paddle type which is uniformly stirred by a stirring blade. In the polymerization, the monomer solution is continuously supplied to the polymerization reactor, and the polymerization is performed at a temperature of 120 to 160 ° C. so that the polymerization conversion of the monomer is substantially constant within a range of 40 to 70%. Perform the polymerization reaction. If the polymerization conversion is less than 40%,
The load of the devolatilization step due to the volatile component is large, and devolatilization may be insufficient due to, for example, the restriction of the heat transfer area of the preheater, which is not preferable. On the other hand, if it exceeds 70%, for example, the pipe pressure loss between the polymerization reactor and the pre-heater becomes large, and it becomes difficult to transport the polymerization liquid, which is not preferable. When the polymerization temperature is lower than 120 ° C., the polymerization rate is too slow to be practical, and when it exceeds 160 ° C., the polymerization rate is too high, and it becomes difficult to adjust the polymerization conversion rate or the thermal decomposition resistance decreases. Not preferred.

The polymerization solution obtained by such a polymerization reaction is devolatilized to take out a polymer, and at the same time, a monomer containing volatile unreacted methyl methacrylate as a main component and a solvent A are separated. The volatile components are distilled and reused as a recycle liquid to continuously produce a methacrylic resin. In addition,
It is usually preferable to add a polymerization inhibitor to the recycle liquid in order to prevent polymerization during storage. As the devolatilizing device, an extruder with a multi-stage vent, a devolatilizing tank, or the like is used. Preferably, the polymerization liquid is heated to a temperature of 200 to 290 ° C. by a pre-heater or the like, has a sufficient space above, and
The polymer is fed to a devolatilization tank under vacuum at a temperature of 250 ° C. and a temperature of 20 to 100 torr to take out the polymer, and at the same time, a volatile component consisting of a monomer mainly composed of unreacted methyl methacrylate and a solvent A is separated and recycled Reuse as liquid.
The volatile matter remaining in the polymer is at most 1% by weight, preferably at most 0.5% by weight, more preferably at most 0.3% by weight. This method of introducing a polymerization solution into a devolatilization tank held under reduced pressure causes instantaneous volatilization of volatile components and foaming thereby, forming an extremely large evaporation area, and using a high boiling point solvent. This is a preferred devolatilization method in which volatile components are efficiently removed in a short time, the amount of solvent or residual monomer remaining in the polymer is small, the coloring of the polymer is small, and the optical properties are excellent.

Hereinafter, the method of removing impurities in the distillation column will be supplementarily described with reference to FIG. The monomer containing impurities to be removed is continuously supplied from line 1 to distillation column 2. The inside of the distillation tower 2 is structured to be filled with a filler such as Raschig rings or the like or a shelf such as a sieve tray is installed so that distillation can be performed efficiently. The impurities and the solvent B accumulated at the bottom of the tower are heated by the reboiler 4 via the retained liquid circulation pump 3 and then returned to the inside of the tower. Generally, a multi-tube heat exchanger is used for the reboiler 4, and the supply amount and the temperature of the heating medium are controlled by installing an appropriate control mechanism so that the temperature in the distillation column and the amount of the retained liquid at the bottom of the distillation column are constant. Is done. The solvent B containing impurities is continuously or intermittently discharged from the extraction line 5 branched from the outlet of the circulation pump 3. After the distilled monomer and the solvent A are cooled and condensed in the condenser 6, they are continuously supplied to the polymerization reactor. The pressure in the distillation column is controlled to a constant pressure by a control valve installed in the vacuum line 7.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Each property of a polymer was measured as follows. (1) The intrinsic viscosity of the polymer was measured by dissolving 150 mg of the polymer in 50 ml of chloroform and using an Ostwald viscometer at a temperature of 25 ° C. (2) The total light transmittance was measured based on the ASTM D-1003 method.

[0024]

Example 1 77.1% by weight of methyl methacrylate, 1.7 parts by weight of methyl acrylate added with 0.01 part of hydroquinone were discharged from a polymerization reactor and devolatilized and recovered in a devolatilization tank.
Recycled solution of 21.3% by weight of toluene (solvent A) /97.9% by weight of methyl methacrylate and 2.1% by weight of methyl acrylate in a fresh monomer solution / 46.9% of ethylbenzene (solvent B). /52.9/0.2 and continuously fed to the distillation column. The distillation column has a stainless steel structure as shown in FIG. 1 and is filled with Raschig rings inside. The distillation column is heated with steam by a reboiler with a reboiler so that the amount of the retained liquid at the bottom of the distillation column is kept constant at 80 Torr by a control valve installed in the vacuum line 7. The bottom portion of the distillation column was substantially composed of only ethylbenzene and impurities contained in the recycle liquid, and the same amount of ethylbenzene containing impurities was supplied from the extraction line 5 continuously to the distillation column. The distilled monomer solution was 88.1% by weight of methyl methacrylate, 1.9% by weight of methyl acrylate, and 10.0% by weight of toluene. 1,1-bis (t-butylperoxy)-as a polymerization initiator was added to this monomer solution.
3,3,5-trimethylcyclohexane 100 ppm,
1700 ppm of octyl mercaptan was added, and the mixture was polymerized at a polymerization temperature of 155 ° C. and a residence time of 2.0 hours in a complete mixing type polymerization reactor, and was continuously polymerized to a polymerization conversion rate of 53%. The polymerization solution was continuously taken out of the polymerization reactor, heated to 260 ° C. with a heating plate, and cast into a devolatilization tank through an interval between the heating plates. The polymer was separated from the unreacted monomer and the solvent while maintaining the temperature in the devolatilization tank at 30 Torr and 230 ° C. The polymer was extruded from an extrusion die, and the unreacted monomer and solvent were distilled and reused as a recycle liquid, and a continuous operation was performed for one week. Methyl acrylate content in the obtained methacrylic resin pellets was 1.9% by weight, residual monomer was 2350 ppm, and residual solvent was not detected. In addition, the intrinsic viscosity was 55 ml / g, and the total light transmittance was 93%. There was no large foreign matter in the polymer and no coloring of the product. In addition, no clogging occurred due to the formation of polymer in the distillation column during one week of continuous operation.

[0025]

Example 2 The same conditions as in Example 1 were used except that the distilled monomer solution was mixed with 95.0% by weight of methyl methacrylate, 2.0% by weight of methyl acrylate, and 3.0% by weight of n-heptane (solvent B). %, And the same operation as in Example 1 was performed except that the polymerization initiator and the chain transfer agent were slightly modified so as to have the same polymerization conversion and molecular weight as in Example 1. Methyl acrylate content in the obtained methacrylic resin pellets was 2.0% by weight, residual monomer was 2300 ppm, and residual solvent was not detected. or,
The intrinsic viscosity was 54 ml / g, and the total light transmittance was 93%.
There was no large foreign matter in the polymer and no coloring of the product. In addition, no clogging occurred due to the formation of polymer in the distillation column during one week of continuous operation.

[0026]

Comparative Example 1 The same operation as in Example 1 was performed except that the solvent A and the solvent B were changed to diethylbenzene, and the polymerization initiator and the chain transfer agent were slightly modified so as to have the same polymerization conversion and molecular weight as in Example 1. Was. The resulting methacrylic resin pellets had a methyl acrylate content of 1.9% by weight and a residual monomer content of 24%.
00 ppm and residual solvent was 2250 ppm.

[0027]

COMPARATIVE EXAMPLE 2 Ethylbenzene as the solvent B was changed to n-heptane, and the pressure in the distillation column was changed from 80 Torr to 120 Ton.
Except for changing to rr, the same operation as in Example 2 was performed. Six days after the start of the operation, the polymer precipitated on the line for extracting from the liquid retained at the bottom of the distillation column. On the eighth day, the operation was stopped because the extraction line was blocked.

[0028]

Comparative Example 3 The same operation as in Example 1 was performed under the same conditions as in Example 1 except that the distillation operation was not performed. The polymethyl methacrylate recovered as a product gradually colored.

[0029]

According to the polymerization method of the present invention, impurities can be removed, and the coloration of the product can be prevented, and a long-term continuous solution polymerization can be carried out stably. Therefore, high quality products can be manufactured with high productivity by the continuous solution polymerization method.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a distillation column used in the impurity removing method of the present invention.

FIG. 2 is a diagram illustrating a schematic view of a continuous solution polymerization apparatus using a distillation column used in the impurity removing method of the present invention.

[Explanation of symbols]

 1, supply line for vinyl monomer and solvent 2, distillation column 3, circulation pump 4, reboiler 5, impurity extraction line 6, condenser 7, vacuum line 8, polymerization reaction tank 9, liquid supply pump 10, heating plate 11, Devolatilization tank 12, vacuum line

Claims (7)

[Claims] 1. A recycled liquid containing (A) (a) a monomer mainly composed of unreacted methyl methacrylate after polymerization and a solvent A, and (b) a monomer composed mainly of new methyl methacrylate. The monomer and the solvent A are continuously supplied to the polymerization reactor, the polymerization is performed, and then the polymerization liquid is devolatilized to remove the polymer and simultaneously react unreacted. In the continuous solution polymerization process using the monomer and the solvent A recycled, the solvent B having a boiling point higher than the boiling point of the monomer is present at the bottom of the distillation column, and the bottom liquid is continuously or from the bottom of the distillation column. A continuous solution polymerization method comprising intermittently extracting and simultaneously or intermittently supplying the same amount of solvent B to the bottom of the distillation column. 2. (B) (a) A recycled liquid containing unreacted methyl methacrylate as a main component and a solvent A after polymerization is continuously supplied to a distillation column, and the distilled monomer is obtained. And the solvent A and (b) a monomer mainly composed of new methyl methacrylate are continuously supplied to the polymerization reactor to polymerize, and then the polymerization solution is devolatilized to take out the polymer and simultaneously react unreacted. In a continuous solution polymerization process in which the monomer and the solvent A are recycled, a solvent B having a boiling point higher than the boiling point of the monomer is present at the bottom of the distillation column, and the bottom liquid is continuously or continuously fed from the bottom of the distillation column. A continuous solution polymerization method comprising intermittently extracting and simultaneously or intermittently supplying the same amount of solvent B to the bottom of the distillation column. 3. The continuous solution polymerization method according to claim 1, wherein the boiling point of the solvent B is at least 10 ° C. higher than the boiling point of the vinyl monomer. 4. The continuous solution polymerization method according to claim 1, wherein the solvent B is an alkylbenzene. 5. The continuous solution polymerization method according to claim 4, wherein the solvent B is selected from xylene and ethylbenzene. 6. The method according to claim 1, wherein the monomer containing methyl methacrylate as a main component comprises methyl methacrylate alone or a methyl methacrylate monomer and 15% by weight or less of an acrylate monomer. 3. The continuous solution polymerization method according to 1 or 2. 7. The continuous solution polymerization method according to claim 6, wherein the acrylate monomer is a methyl acrylate monomer or an ethyl acrylate monomer.