JP2000053708A - Production of methacrylic polymer with excellent production stability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain the subject methacrylic polymer that has excellent thermal stability and optical properties in high productivity by continuous solution polymerization under specific conditions using specific amounts of monomers, a specific amount of non-polymerizable solvent and a specific free-radical initiator. SOLUTION: (A) Methyl methacrylate monomer, (B) an acrylic alkyl ester monomer of a 1-8 alkyl carbon atoms and (C) a non-polymerizable solvent are purified by distillation so that the distillate mixture satisfies formula I and formula II [A is the parts by weight of the component A, B is the parts by weight of the component B and C is the parts by weight of the component C]. Then, the feed solution comprising the distillate mixture, (D) a free-radical initiator with a half-life of 5.55×10-5-2.30 hours and (E) a chain transfer agent is brought into contact with gaseous nitrogen counter-currently to reduce the dissolved oxygen concentration less than 1 ppm, then passed through a filter with a permeation particle size of <=2 μm to remove solid foreign substances. Finally, the purified feed solution is continuously fed into the reactor to effect continuous polymerization reaction, as the temperature in the reactor, the mean residence time, the polymer concentration and the like are controlled, then the reaction mixture is driven away and treated under reduced pressure to remove the volatile components.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a methacrylic polymer which is excellent in optical transparency and weather resistance and is suitable for a material for thermoforming such as injection molding and extrusion molding and has excellent productivity. .

[0002]

2. Description of the Related Art An acrylic resin comprising a methyl methacrylate polymer or a methacrylic copolymer containing methyl methacrylate as a main component has excellent transparency, weather resistance, and good mechanical properties, surface hardness, workability, and the like. Depending on the beauty of the appearance of the molded product, for example, optical applications such as various optical lenses, optical disks, light guide plates, lighting equipment, signboards, various decorative products, nameplates, tableware, exterior parts such as tail lamps for automobiles, exterior products, etc. Widely used for outdoor applications.

[0003] Of these methacrylic polymers, methacrylic polymers generally produced by bulk polymerization and solution polymerization have less impurities and optical properties than methacrylic polymers produced by suspension polymerization. Not only can produce a good polymer, but also can provide a continuous process with excellent productivity. For this reason, continuous bulk polymerization and continuous solution polymerization are particularly attracting attention as processes capable of producing high-quality polymers under high productivity conditions, and advanced techniques are required.

On the other hand, problems that occur when the methacrylic resin is molded by injection molding include silver marks (silver streaks) of molded products, generation of bubbles, reduction in heat-resistant deformation, and generation of gas. The work environment deteriorated. In general, these problems are often suppressed by lowering the temperature of the molten resin at the time of molding, but in that case, molding of large or thin-walled molded products becomes difficult due to a decrease in melt fluidity. In some cases, the use of the molded product is limited due to reasons such as a decrease in product quality due to residual distortion of the molded product.

[0005] These problems are caused by the fact that in the case of methacrylic polymers, the decomposition reaction of the polymer occurs during molding because the thermal decomposition temperature is close to the temperature at which the polymer exhibits the melt fluidity required for molding. It is considered to be a problem inherent to the methacrylic resin caused by the above. Although methacrylic resins have better optical properties and weather resistance than other resins, it is clear that they show yellowing due to heat history during molding and yellowing due to outdoor exposure. Development of a production method capable of producing an improved polymer is still an important issue.

Conventionally, as a method for improving the thermal stability and optical properties of a polymer in a continuous polymerization method, bulk polymerization (JP-A-54
-42035), a solution polymerization method (JP-A-63-57).
613) has been proposed. JP-A-54-42035 discloses that in a raw material cycle type process in which unreacted volatiles are reused as a raw material, a low-polymerization degree polymer is removed from recovered volatile components,
In addition, there is disclosed a technique for improving the optical characteristics of a polymer by controlling the impurity concentration within a certain range. Japanese Patent Application Laid-Open No. 63-57613 discloses that an inert gas is introduced into a feed solution containing 10 to 25% by weight of an inert polymerization solvent to reduce the dissolved oxygen concentration to 1 ppm or less.
A method has been proposed in which the mixture is supplied after being filtered through a filter of μm or less and polymerized under specific conditions.

Further, Japanese Patent Application Laid-Open No. 3-111408 discloses that when supplying a monomer mixture to a reactor in continuous bulk polymerization, the dissolved oxygen in the monomer obtained by introducing an inert gas into the monomer is reduced to 1 ppm or less. There has been disclosed a technique in which the mixture is supplied to a vessel to stably and continuously polymerize under specific conditions. However, there is no description about the thermal decomposability of the polymer.

Japanese Patent Publication No. Hei 8-19193 discloses that a polymer produced by a continuous bulk polymerization method under specific conditions and having a double bond terminal content within a specific range is excellent in thermal decomposition resistance and optical properties. Is disclosed. However, the publication does not disclose the thermal decomposition resistance of the polymer and the conditions at the time of polymerization.

On the other hand, the productivity in the continuous polymerization method is as follows:
The scale of the polymerization equipment, the average residence time in the reactor, and the reaction conversion of the monomer at the final outlet of the reactor are important, the average residence time is short, and the reaction conversion of the monomer at the final exit of the reactor is important. The higher the rate, the better the productivity. Further, when the polymer concentration at the final outlet of the reactor is compared under a constant condition, it can be said that the shorter the average residence time, the smaller the scale of the polymerization equipment and the more excellent the productivity.

Therefore, the polymer concentration s at the final outlet of the reactor s
The value s / τ of the ratio between the (weight fraction) and the average residence time τ (time) in the reactor is an index representing the productivity under the same conditions of the polymerization reactor (the total weight of the reaction solution in the reactor). It is. In general, it is known that the polymerization reaction type, composition, and polymerization conversion rate under similar conditions, the residence time in the reactor, and the thermal stability of the polymer tend to be contradictory. Methods for improving the balance of thermal stability are important technical issues with little knowledge.

For example, Examples and Comparative Examples in JP-B-8-19193 disclose examples in which the residence time in the reactor is 5,6.7 hours and the polymerization rate is 46 to 59%. No method is described for controlling thermal stability under general conditions with different polymerization rates in the vessel. The value of s / τ, which is an index of productivity, is 0.11 in the examples.
(1 / hour) is the largest. In the same publication, it is shown that in a continuous polymerization process using a complete mixed polymerization reactor, the coloring of the polymer is reduced by controlling the dissolved oxygen concentration and the content of minute foreign substances. There is no description of its relationship to productivity.

Further, a suitable range for the concentration of the solvent is 10 to 25% by weight, and as an example, 20% by weight of ethylbenzene is mentioned as the solvent. 1 solvent
If the amount is less than 0% by weight, it is described that the viscosity of the polymerization reaction system is high and it is difficult to control the stability of the polymerization system. However, there is no description about factors other than the content of the solvent. Also,
It also does not describe the relationship between the polymerization conditions and the thermal stability of the polymer.

On the other hand, Japanese Patent Application Laid-Open No. Hei 8-253507 discloses a method for producing a methacrylic resin which is less likely to generate silver streaks, foaming, coloring and odor during thermoforming and which is excellent in thermal decomposition resistance, as a radical initiator. The amount of the solvent 29 to 5 with the half-life, average residence time, radical initiator concentration, chain transfer agent concentration and monomer conversion of
A production method using a one-stage complete mixing tank, which is a percentage by weight, is disclosed.

[0014] As the reason for limiting the amount of the solvent, it is described that if the amount is less than 5% by weight, the phenomenon of abnormal acceleration of the polymerization rate due to the effect of automatically promoting the polymerization is likely to occur, and the polymerization cannot be maintained stably. However, there is no description other than the amount of solvent for stably controlling the polymerization. The maximum value of s / τ calculated from the embodiment is 0.132 (1 / hour).
It is.

As exemplified above, it is obvious that the smaller the value of s / τ is, the higher the industrial value is, but in order to keep the thermal stability at a practicable level within the conventionally disclosed range, It can be said that s / τ was limited to a certain range value or less. On the other hand, when there is no restriction on the level of thermal stability, it is considered that there is little restriction on the productivity, and a continuous bulk polymerization method having a large s / τ and excellent productivity is disclosed in
No. 126308. The same publication discloses a production method in which the inside of a complete mixing type reaction tank is filled with water, and is in an adiabatic state where heat does not flow in and out, and continuous bulk polymerization is performed under specific conditions. / Τ is 0.33
製造 1.34 (1 / hour), which describes the production conditions of higher productivity than before, and the description of polymerization stability is seen, but the thermal stability of the polymer is not described at all, and the chromaticity of the polymer is not described. However, the specific relationship with the polymerization reaction has not been clarified.

As described above, the production technology for stably producing a methacrylic polymer having excellent thermal decomposition resistance by a continuous solution polymerization method is known only in a limited condition range in which productivity is largely limited. Met. Especially s /
At present, a continuous solution polymerization technique for producing a polymer having a high productivity of τ of 0.2 (1 / hour) or more and having excellent thermal stability has not been obtained. Therefore, a continuous solution polymerization technique capable of producing a high quality polymer excellent in optical properties, weather resistance and thermal stability with higher productivity than before has not yet been established, and its establishment is strongly desired. Was.

[0017]

SUMMARY OF THE INVENTION The present invention meets the above-mentioned demands and provides a continuous solution polymerization method capable of producing a methacrylic polymer excellent in optical properties and weather resistance with high productivity. The task is to do so.

[0018]

Means for Solving the Problems The present inventors have conducted intensive studies to find a method for solving the above-mentioned problems, and have found that they have a specific amount of monomer, a specific amount of non-polymerizable solvent, and a specific range of half-life. Using a free radical generator, a continuous solution polymerization method under specific conditions, it has been found that a methacrylic polymer having excellent heat stability and optical properties can be stably produced with higher productivity than ever before, and the present invention has been completed. Reached.

That is, according to the present invention, a methyl methacrylate monomer, an alkyl acrylate monomer having an alkyl group having 1 to 8 carbon atoms and a non-polymerizable solvent are each represented by the following formula: 0.70 ≦ A / (A + B) ≦ 0.998 0.050 ≦ C / (A + B + C) ≦ 0.100 (where A is parts by weight of methyl methacrylate monomer, B is parts by weight of alkyl methacrylate monomer, and C is (A part by weight of a non-polymerizable solvent), and a half-life in a reactor of 5.
The dissolved oxygen content is reduced to 1 ppm or less, and the permeation particle size is reduced by bringing a feed solution comprising a free radical generator, which is 55 × 10 ^{−5 to} 2.30 hours, and a chain transfer agent into countercurrent contact with gaseous nitrogen. After removing solid foreign matter by passing through a filter of 2 μm or less, the reaction liquid in the reactor is continuously supplied to the reactor, and uniformly stirred and mixed while keeping the inside of the reactor at 130 to 170 ° C. And the ratio of the half-life of the free radical generator to the average residence time of the reaction solution in the reactor is from 5.0 × 10 ^{-4 to} 2.5.
0, the polymer concentration (weight fraction) in the reactor is 0.40 to 0.40.
0.70, the ratio of the concentration of the generated free radicals (mol · g ⁻¹ ) of the free radical generator in the whole supply liquid to the polymer concentration (weight fraction) of the polymerization liquid in the reactor is 0.5 × 10 ^{− 6 to} 6.0 × 10 ^-6
mol · g ⁻¹ , and the number average molecular weight of the polymer is 2.5 ×
A methacrylic polymer characterized in that the polymerization reaction is continuously controlled in the range of 10 ^{4 to} 15.0 × 10 ⁴ , and then the reaction solution is continuously discharged from the reactor and subjected to devolatilization under reduced pressure. Production method,

And a method for producing the above methacrylic polymer, wherein the non-polymerizable solvent used is at least one solvent selected from ethylbenzene, toluene, o-xylene, m-xylene and p-xylene. is there.

Hereinafter, the present invention will be described in detail. In the method for producing a methacrylic polymer of the present invention, a methyl methacrylate monomer, an alkyl acrylate monomer having an alkyl group having 1 to 8 carbon atoms, and a non-polymerizable solvent are each represented by the following formula 0.70 ≦ A / (A + B) ≦ 0.998 0.050 ≦ C / (A + B + C) ≦ 0.100 (where A is the weight part of the methyl methacrylate monomer, B is the weight part of the alkyl acrylate monomer) , C are parts by weight of the non-polymerizable solvent), and a half-life in the reactor of 5.55 in the reactor.
× a 10 ^-5 to 0.60 hours at a free radical generator, by a feed consisting of a chain transfer agent contacting gaseous nitrogen countercurrent, the dissolved oxygen content and 1ppm or less, and transmittance particle size 2μm By passing through the following filters,
After the removal of the solid foreign matter, it is carried out by continuously feeding the reactor.

The alkyl acrylate monomer having an alkyl group having 1 to 8 carbon atoms in the liquid supplied to the reactor is a component for imparting heat decomposition resistance and melt fluidity of the polymer to be produced. is there.

The composition of the feed solution is as follows: when A is a part by weight of a methyl methacrylate monomer and B is a part by weight of an alkyl acrylate monomer having an alkyl group having 1 to 8 carbon atoms. It is necessary to satisfy 70 ≦ A / (A + B) ≦ 0.998. The above A / (A + B) represents the ratio of the methyl methacrylate monomer to the total monomer components in the obtained feed solution, and is obtained when the value of A / (A + B) is less than 0.70. Since the characteristics of the polymer as a methacrylic polymer are impaired, it is not preferable. On the other hand, if the value of A / (A + B) exceeds 0.998, the effect of copolymerizing the alkyl ester monomer is small, which is not preferable.

Examples of the alkyl acrylate having an alkyl group having 1 to 8 carbon atoms include methyl acrylate, ethyl acrylate, n-propyl acrylate, sec-propyl acrylate, tert-propyl acrylate, and acryl acrylate. N-butyl acid, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, sec-propyl acrylate and the like. Of these, methyl acrylate and ethyl acrylate are particularly preferred in view of the effects of improving the thermal decomposition resistance and the melt fluidity by copolymerization.

In the present invention, the non-polymerizable solvent in the liquid supplied to the reactor is a component necessary for improving the thermal stability of the polymer and controlling the stability of the polymerization reaction. An organic compound having no copolymerizability in polymerization.
Specific examples of the non-polymerizable solvent used in the present invention include toluene, o-xylene, m-xylene, p-xylene, aromatic compounds such as ethylbenzene, octane, decane, aliphatic compounds such as cyclohexane, decalin and the like. Alicyclic compounds, butyl acetate, ester compounds such as pentyl acetate,
Examples include alcohols such as methanol and ethanol. Particularly, from the viewpoint of polymerization stability, toluene, o-xylene, m-xylene, p-xylene and ethylbenzene are preferred.

In the present invention, A in the feed to the reactor
Is a weight part of a methyl methacrylate monomer, B is a weight part of an alkyl acrylate monomer having an alkyl group having 1 to 8 carbon atoms, and C is a weight part of a non-polymerizable solvent. 050 ≦ C / (A + B + C) ≦ 0.100 Preferably, 0.055 ≦ C / (A + B + C) ≦ 0.095. If the value of C / (A + B + C) exceeds 0.100, the optical transparency, weather resistance and thermal stability of the polymer tend to decrease, which is not preferable. On the other hand, when the value of C / (A + B + C) is less than 0.050, the range of conditions under which the polymerization reaction can be stably performed becomes narrow, which is not preferable.

In the present invention, the free radical generator supplied to the reactor is a component which initiates the radical polymerization of the acrylic polymer, and has a half life of 5.55 × 10 5 in the polymerization reactor. ^{-5 to} 2.3 hours. If the half-life is less than 5.55 × 10 ⁻⁵ hours, the thermal stability of the polymer obtained under the same production rate conditions tends to decrease, which is not preferable, while the half-life is 2.3. If the time is exceeded, the stability controllability of the polymerization reaction tends to decrease, which is not preferable.

Examples of the free radical generator used in the present invention include, for example, di-tert-butyl peroxide, di-cumyl peroxide, methyl ethyl ketone peroxide, di-tert-butyl perphthalate, di-tert-butyl peroxide.
t-butyl perbenzoate, tert-butyl peracetate, 2,5-dimethyl-2,5-di (tert-butyl perbenzoate)
Butylperoxy) hexane, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, di-tert-amyl peroxide, benzoyl peroxide, cumene hydroperoxide and lauryl peroxide. Organic peroxide, azobisisobutanol diacetate, 1,1′-azobiscyclohexanecarbonitrile, 2-phenylazo 2,4-dimethyl-
Examples include azo compounds such as 4-methoxyvaleronitrile, 2-cyano-2,2-propylazoformamide and 2,2′-azobisisobutyronitrile. These can be used alone or in combination of two or more.

The free radical generator has a ratio I / s of the concentration I (mol · g ⁻¹ ) in terms of free radicals generated in the reactor to the polymer concentration s (weight fraction) of the polymerization liquid in the reactor of 0. 5 × 10 ^-6 ~
6.0 × 10 ⁻⁶ mol · g ⁻¹ , preferably 0.6 × 10
^{−6 to} 5.5 × 10 ⁻⁶ mol · g ⁻¹ is supplied to the reactor.

Here, the concentration of the generated free radical in terms of the generated free radical refers to an amount defined as follows. That is, when the free radical generator is an organic peroxide, it can be determined from the concentration of the free radical generator based on the whole in the feed solution and the amount of active oxygen of the free radical generator.
g ⁻¹ )] = [free radical generator concentration (mol · g ⁻¹ )] ×
It is calculated by [(amount of active oxygen of free radical generator / 16) / 100]. [Amount of active oxygen (%)] is [weight of RO / radical O atom generated per unit weight of free radical generator] × 1
It is defined as 00 (%).

These can be determined by calculation from the chemical structure and purity of the free radical generator used, or by analysis of the product at the time of complete decomposition of the initiator. In the case of an azo compound or the like, it can be similarly determined based on the number of moles of free radicals generated per mole of the initiator.

The value of I / s is 0.5 × 10 ⁻⁶ m.
If it is less than ol · g ⁻¹ , the polymerization rate is low and productivity is inferior, and if it exceeds 6.0 × 10 ⁻⁶ mol · g ⁻¹ , the optical transparency, weather resistance and heat The stability tends to decrease, which is not preferable.

In the method for producing a polymer according to the present invention, when the feed solution is supplied to the reactor, the feed solution is purified by distillation.
In addition, the gaseous nitrogen and the supply liquid are brought into countercurrent contact to reduce the concentration of dissolved oxygen in the supply liquid to 1 ppm or less, and the foreign matter is removed by passing the supply liquid through a filter having a transmission particle size of 2 μm or less. By the above operation, a polymer having particularly excellent optical properties and weather resistance can be produced.

The distillation purification of the methyl methacrylate monomer, acrylic acid ester monomer, and inert polymerization solvent, which are the feed liquid raw materials, is effective in removing impurities and foreign substances contained in the monomer and non-polymerizable solvent. Is the optical transparency of the polymer,
It has the effect of removing foreign substances contained in the polymer. At that time, the distillation purification is carried out, for example, by a packed column type, a tray type distillation column or the like. The distillation method supplies the raw material mixture from the middle or upper stage of the distillation column, distills while heating the distillation column bottom liquid with a heater such as a reboiler, and mainly contains methyl methacrylate flowing out from the top of the distillation column. It is carried out by condensing the vapors of the monomer and the non-polymerizable solvent in a condenser.

At this time, when the non-polymerizable solvent used has a higher boiling point than that of the monomer, the non-polymerizable solvent is added to stabilize the storage of the high boiling impurities, foreign substances, and monomer concentrated in the bottom of the distillation column. The polymerization inhibitor or the like can be removed by continuously or intermittently removing the bottom liquid of the distillation column and adding the removed solvent at the same time. As a part of the raw material, when the unreacted monomer and the non-polymerizable solvent recovered and devolatilized and recovered from the reaction solution after the polymerization reaction are recycled, the recovered unreacted monomer may be purified by distillation. As a result, methyl methacrylate dimer and oligomer can be removed.

The feed liquid purified by distillation is further subjected to countercurrent contact using a countercurrent contact tower to replace the inert gas, thereby reducing the concentration of dissolved oxygen in the feed liquid to 1 ppm or less. Although the dissolved oxygen concentration in the inert gas bubbling method in the tank is 10 to 20 ppm, the dissolved oxygen concentration which cannot be achieved by the countercurrent contact method can be reduced to 1 ppm or less.

In the present invention, when the feedstock is purified by distillation, the amount of solid foreign matter is reduced, but the dissolved oxygen concentration is reduced to 1 pp.
m or less, it is necessary to remove the remaining foreign matter by filtering through a filter having a transmission particle size of 2 μm or less. The type of the filter is not particularly limited as long as it is chemically stable to the supply liquid, does not contaminate the supply liquid, and has a structure capable of removing solid foreign matter from the supply liquid. Examples include a filter and an ultrafiltration membrane. By such a filtration treatment, the content of solid foreign matters having a particle diameter of 2 μm or more in the obtained polymer can be reduced, and the yellowness and weather resistance of the polymer can be improved.

As the polymerization reactor for the present invention, a reactor equipped with a mixing device and a temperature control device, and having a supply port and a discharge port capable of continuously supplying raw materials and discharging the reaction solution is provided. Is used. The reactor in the present invention needs to be provided with a stirrer in order to stir and mix uniformly, and examples of stirring blades that can be used include a double helical ribbon blade, a pitched paddle, a turbine, and an anchor type.

As a method of removing the reaction heat in the present invention, a condenser is provided at the upper part of the reactor, the pressure inside the reactor is controlled to boil the reaction solution, and the above is condensed and circulated by the condenser to evaporate. A method of removing the heat of reaction by latent heat,
A method of removing the reaction heat by sensible heat of the supply liquid by controlling the temperature of the supply liquid supplied to the reactor to a low temperature, and circulating the reaction liquid to an external cooling device provided outside the reaction liquid to react by heat exchange Any method such as a method of cooling a liquid may be used, and a plurality of heat removal methods may be used in combination.

The pressure in the polymerization reactor in the present invention is not particularly limited as long as it is within the upper limit of the design of the reactor and within the limit, and under the condition that the internal pressure is appropriately adjusted according to the heat removal system of the reaction solution. The reaction can take place.

In the present invention, the temperature in the polymerization reactor is 1
It needs to be 30 to 170 ° C, preferably 135 to 160 ° C. If the temperature in the reactor is lower than 130 ° C., the stability of the polymerization control decreases due to an increase in the viscosity in the reactor,
Further, the thermal stability of the obtained polymer tends to decrease, which is not preferable. On the other hand, if the temperature in the reactor exceeds 170 ° C., the thermal stability of the polymer tends to decrease, and the chromaticity tends to deteriorate.

In the present invention, the average residence time of the reaction solution in the reactor is 0.3 to 1.9 hours, preferably 0.5 to 1.
It needs to be 8 hours. Average residence time 0.5
If the time is shorter than the above, the stability controlling body of the polymerization reaction tends to decrease, and if the average residence time exceeds 1.9 hours, the productivity decreases, which is not preferable.

In the present invention, the weight fraction of the polymer in the reaction solution in the reactor is 0.40 to 0.70, preferably 0.1 to 0.70.
It is necessary to control in the range of 45 to 0.65. When the weight fraction of the polymer is less than 0.40, the production rate of the polymer is inferior, and the load at the time of devolatilization and recovery after polymerization and the recovery of unreacted components required per unit weight of the polymer are required. Energy consumption becomes excessive, which is not preferable.

In general, in a continuous polymerization method, the scale of the polymerization equipment, the average residence time in the reactor, and the reaction conversion of the monomer at the final outlet of the reactor are important.
It can be said that the shorter the average residence time and the higher the reaction conversion of the monomer at the final outlet of the reactor, the better the productivity. Further, when the polymer concentration at the final outlet of the reactor is compared under a constant condition, it can be said that the shorter the average residence time, the smaller the scale of the polymerization equipment and the more excellent the productivity.

Therefore, the value of the ratio between the polymer concentration (weight fraction) at the final outlet of the reactor and the average residence time in the reactor is determined under the condition that the scale of the polymerization reactor (total weight of the reaction solution in the reactor) is the same. It is considered to be an index indicating productivity in The ratio s / τ of the polymer concentration s (weight fraction) in the reactor and the residence time τ (time) in the reactor in the present invention is in the range of 0.21 to 2.33 (1 / hour). According to the invention, it is possible to manufacture with higher productivity as compared with the manufacturing method according to the prior art.

In the present invention, the reaction in the liquid fed to the reactor is
Half-life of the radical generator in the reactor and average residence time in the reactor
Is 5.0 × 10^-Four~ 2.50, preferably 1.0x
10 ^-3２．０2.0. The above ratio value
Is 5.0 × 10^-FourIf it is less than the heat resistance of the obtained polymer,
The qualitative tendency tends to decrease, while exceeding 2.50
And a decrease in polymerization stability, that is, a tendency of poor controllability of the conversion.
Appears, which is not preferable.

In the present invention, the ratio I / s of the concentration I (mol · g ⁻¹ ) of the generated free radical in the feed liquid to the concentration s (weight fraction) of the polymerization liquid in the reactor is 0. .5 × 10 ^-6
６6.0 × 10 ⁻⁶ mol · g ⁻¹ , preferably 0.6 ×
It is necessary to be in the range of 10 ^{−6 to} 5.5 × 10 ⁻⁶ mol · g ⁻¹ . The above-mentioned ratio is important as an index of the thermal decomposability of the polymer. In order to make the ratio less than 0.5 × 10 ⁻⁶ mol · g ⁻¹ , it is necessary to control the polymerization reaction under low productivity conditions. Is undesirable, while 6.0 × 10 ⁻⁶ mo
If the ^value exceeds l · g ⁻¹ , the thermal stability decreases, and the tendency to generate defects such as silver streaks during molding becomes greater than that of conventional methacrylic polymers, which is not preferable.

In the method for producing a methacrylic polymer according to the present invention, the chain transfer agent is a component added for controlling the molecular weight of the polymer. Having a number average molecular weight of 2.5 × 10
⁴ to 15 × 10 ⁴ , preferably 3.0 × 10 ^{4 to} 12 × 1
0 falls within the ^fourth range as to adjust the addition concentration. In the present invention, the number average polymerization degree of the polymer in the reactor is 2.5
If it is less than × 10 ⁴ , the mechanical strength of a molded product obtained by molding tends to decrease, which is not preferable.
If it exceeds × 10 ⁴ , the range of polymerization conditions under which the polymerization reaction can be stably controlled becomes narrow, which is not preferable.

In the present invention, the number average molecular weight of the polymer is
It is a numerical value measured by a gel permeation (GPC) method, and the PM of the sample is determined by a gel permeation chromatograph calibrated using standard polymethyl methacrylate (PMMA) having a narrow molecular weight distribution as a standard sample.
It is a numerical value calculated from data obtained by measuring the molecular weight distribution in terms of MA.

In the present invention, the concentration of the chain transfer agent in the supply liquid supplied to the reactor is set according to the target molecular weight so that the number average molecular weight of the polymer falls within the above-mentioned range. The chain transfer agent in the present invention, for controlling the molecular weight,
A compound that is supplied to the reactor in addition to the monomer, non-polymerizable solvent, and free radical generator.The concentration is determined according to the polymerization conditions and the target value of the molecular weight of the acrylic polymer, and then supplied to the reactor. Is done.

Examples of the chain transfer agent include methyl mercaptan, ethyl mercaptan, propyl mercaptan, isopropyl, n-butyl mercaptan, isobutyl mercaptan, t-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, sec-dodecyl mercaptan, Primary, secondary and tertiary mercaptans having an alkyl group or a substituted alkyl group such as t-butyl mercaptan, aromatic mercaptans such as phenyl mercaptan, thiocresol, thioglycolic acid and its esters, ethylene thioglycol, etc. No. These can be used alone or in combination of two or more. Of these, use of n-butyl, t-butyl and n-octyl mercaptan is particularly preferred in view of the color tone of the polymer and the ease of separation and removal from the reaction mixture.

In the present invention, the reaction solution continuously discharged from the reactor is devolatilized to take out the polymer, and at the same time, the monomer and the solvent mainly composed of unreacted methyl methacrylate, which is a volatile component, are removed. To separate. As the devolatilizing device, an extruder with a multi-stage vent, a devolatilizing tank, or the like can be used.
In particular, the reaction solution is heated to a temperature of 200 to 290 ° C, has a sufficient space above, and is heated to a temperature of 200 to 280 ° C,
A method of feeding a polymer to a devolatilization tank under vacuum at a temperature of 100 torr to remove a polymer and simultaneously separating volatile components composed of a monomer mainly composed of unreacted methyl methacrylate and a non-polymerizable solvent is preferable.

The method of introducing the polymerization liquid into the devolatilization tank held under reduced pressure involves the instantaneous volatilization of volatile components and the resulting foaming, forming an extremely large evaporation area and removing the solvent having a high boiling point. Even when used, volatile components are efficiently removed in a short time, and unreacted monomers, dimers,
This is an excellent devolatilization method in that the amount of volatile components such as oligomers and non-polymerizable solvents is small, and a polymer having excellent optical transparency is obtained. In this devolatilization step, the content of the non-polymerizable solvent contained in the polymer can be controlled within the range of 2 to 500 ppm, preferably 2 to 300 ppm.

One example of a process diagram of a continuous polymerization apparatus used in the solution polymerization process of the present invention described above is shown in FIG. 1 (first half) and FIG. 2 (second half).

In the method for producing a methacrylic polymer of the present invention, a releasing agent, an antioxidant, a light diffusing agent, a dye, a pigment, a fluorescent brightener, a lubricant,
Impact modifiers and the like can be added to the polymer at each stage of the manufacturing process.

[0056]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to examples, but the present invention is not limited by these examples. In addition, the number average molecular weight, the thermal decomposability, and the occurrence rate of silver streaks of the polymers in Examples and Comparative Examples were measured according to the methods described below.

(1) Number average molecular weight of polymer The reaction solution was withdrawn from the polymerization reactor during the polymerization reaction, and determined as follows using gel permeation chromatography (GPC). After completely dissolving 2 g of the reaction solution in 20 g of acetone, the polymer was separated by reprecipitation in 2,000 g of n-hexane, and dried under vacuum to obtain a polymer sample. 20 mg of a polymer sample was dissolved in 40 cm ³ of tetrahydrofuran: THF to obtain a sample solution. The obtained chromatogram was converted into a molecular weight distribution using a calibration line created by standard PMMA (manufactured by Polymer Laboratories), and the number average molecular weight was calculated.

[GPC measurement conditions] Apparatus: HL manufactured by Tosoh
C8120, column: Tosoh TSKgel, sup
erHM-M2 in series, solvent: tetrahydrofuran (T
HF), column temperature: 40 ° C., flow rate: 0.2 cm ³ / min

(2) Injection molding of polymer and evaluation of chromaticity of molded piece A 15 × 20 × 220 mm test piece was molded at 250 ° C. cylinder temperature using an injection molding machine IS-75S manufactured by Toshiba Machine Co., Ltd. After the molding cycle was stabilized, four shots were formed after the molding cycle was stabilized. Four test pieces were stacked in the thickness direction, and the yellowness ΔYI based on air in the length direction (no test piece)
(Optical path length 220 mm) using a color difference meter (TC-
1500MC type).

(3) Evaluation of Weather Resistance of Molded Article The molded piece molded in (2) was subjected to a sunshine weatherometer (SWOM) at a temperature of 56 ° C. under rainfall conditions.
The yellowness (ΔYI) after exposure for 00 hours was measured in the same manner as in (4).

(4) Generation rate of silver streaks The generation rate of silver streaks during molding was evaluated by the following method. Dry the resin pellets with a hot air dryer,
After drying until the moisture concentration in the pellets became 300 ppm, an injection molding test was performed under the following conditions. Using FANUC injection molding machine T-100D, cylinder temperature 280 ° C, mold temperature 55 ° C, filling pressure 750kgf / c
A spiral molded product (thickness: 2 mm) for evaluation of spiral flow length (SFD) was molded under the condition of m ² . After the SFD was stabilized, 50 shots were molded further, and the molded product was observed for the presence of silver streaks and foaming. The measurement was performed twice by the same method, and the number of occurrences of silver streaks or foaming observed in a total of 100 shots was recorded.

[0062]

Example 1 A mixture of methyl methacrylate, methyl acrylate and ethylbenzene was purified by simple distillation. The distillation conditions were as follows: the degree of pressure reduction was 80 torr, the bottom temperature was 95 ° C., and the reflux ratio was 0.11. The mixed composition after the distillation was methyl methacrylate.
6% by weight, 1.9% by weight of methyl acrylate, and 5.5% by weight of ethylbenzene.

As a free radical generator, 1,1
-Bis (t-butylperoxy) -3,3,5-trimethylcyclohexane was continuously added and mixed in an amount of 128 ppm and n-octylmercaptan in an amount of 1720 ppm to form a supply solution. (Nitrogen: supply weight ratio of supply liquid = 1/10000)
After passing through a filter having a permeation particle size of 2 μm after being deoxygenated and having a dissolved oxygen concentration of 2 ppm or less, it is continuously supplied to a 10 L complete mixing type polymerization reactor equipped with a pitched paddle blade stirrer. The polymerization was carried out under the condition of an average residence time of 1.00 hour, the polymerization liquid was continuously discharged from the reactor, and then the polymerization liquid was passed through the gap between the heating plates to exchange heat and heated to 260 ° C. It was dropped. Since the average residence time (τ) in the reactor in the reactor is 1.00 hr and the half-life (θ) of the free radical generator in the reactor is 0.0083 hr,
θ / τ was 0.0083.

The internal pressure of the devolatilization tank was reduced to 30 by vacuum devolatilization.
The torr and the temperature were maintained at 230 ° C., and the unreacted monomer and the polymerization solvent were separated and recovered. The polymer is discharged by a gear pump at the bottom of the devolatilization tank, extruded from an extrusion die, and the strand is pelletized by a strand cutter and recovered as pellets. did. Table 1 shows the composition of the liquid supplied to the polymerization reactor, the reaction conditions, and the characteristics of the polymer. The weight fraction s of the polymer in the reactor determined from the pellet production rate and the feed liquid supply rate is 0.5.
It was 7. Therefore, s / τ which is an index of the production speed
Is 0.57 hr ^-1 , which indicates that a polymer having excellent characteristics can be produced stably under high productivity conditions.

Examples 2 to 8 The same operation as in Example 1 was performed except that the conditions in Example 1 were changed as shown in Table 1. In each case, the operation was continuously performed for 10 days to produce a polymer, which was sampled. Table 1 shows the composition of the liquid supplied to the polymerization reactor, the reaction conditions, and the characteristics of the polymer. It can be seen that a polymer having excellent properties can be produced stably and under high productivity conditions as in Example 1.

COMPARATIVE EXAMPLE 1 The composition of the feed solution and the polymerization conditions were changed as shown in Table 1.
The operation was performed for one day to obtain polymer pellets. Table 1 shows the properties of the polymer. Among the polymer characteristics, the silver generation rate was high and the moldability was poor.

Comparative Example 2 The composition of the feed solution and the polymerization conditions were changed as shown in Table 1, and the same operation as in Example 1 was performed on the outside. After the polymerization was started, the operation was stopped because the polymer weight fraction in the reactor and the temperature inside the reactor became unstable.

Example 9 A mixture of the unreacted monomer and the non-polymerizable solvent recovered after the operation of Example 1 (hereinafter referred to as recycle liquid) 43.
A mixture consisting of 0% by weight, 55.8% by weight of new methyl methacrylate and 1.2% by weight of new methyl acrylate is continuously fed to the distillation column, and continuously fed at a bottom temperature of 90 ° C. and a pressure of 70 torr. Distilled. The composition of the mixture mainly composed of the distilled monomers is methyl methacrylate 9
2.6% by weight, 1.9% by weight of methyl acrylate, and 5.5% by weight of ethylbenzene.

To this mixture, 107 ppm of 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane and 193 of n-octylmercaptan were added.
The mixture was continuously added to an amount of 0 ppm to form a supply liquid, and after being deoxygenated by a nitrogen AC contact tower, passed through a filter having a permeation particle size of 2 μm and continuously supplied to the polymerization reactor. Polymerization was performed under the conditions of a temperature of 155 ° C. and an average residence time in the reactor of 1.00 hr, the polymer solution was continuously discharged from the reactor, and then the polymer solution was passed through a gap of a heating plate, heat-exchanged, and heated to 260 ° C. It was cast and dropped into a devolatilization tank.

The oxygen concentration in the feed immediately before being fed to the reactor was 0.2 ppm or less. The devolatilization tank maintained the internal pressure at 30 Torr and the temperature at 230 ° C. by vacuum devolatilization to separate the unreacted monomer and the polymerization solvent. The polymer was discharged by a gear pump below the devolatilizing tank, extruded from an extrusion die, and the strand was pelletized by a strand cutter and collected as pellets. The composition of the unreacted monomer and solvent separated and recovered by devolatilization is
It was equivalent to Example 3. The collected recycle liquid is stored in a tank and operated continuously for 10 days by a method of reusing it as a recycle liquid to produce a polymer.
Sampled.

At that time, the mixing ratio of the recycled liquid and the new monomer was adjusted according to the change in the composition of the recycled liquid, and the composition of the feed liquid was maintained at the composition shown in Table 2. No increase in viscosity due to polymer formation at the bottom of the distillation column was observed during the operation period, and the reboiler at the bottom of the rectification column was capable of continuous stable operation. The evaluation results of the polymer are shown in Table 2. As in Example 1, a polymer having excellent characteristics was obtained.

Example 10 The same operation as in Example 9 was carried out except that the composition of the feed solution and the polymerization conditions were changed as shown in Table 2, and the operation was continuously performed for 10 days to produce a polymer. did. No increase in viscosity due to polymer formation at the bottom of the distillation column was observed during the operation period, and the reboiler at the bottom of the rectification column was capable of continuous stable operation. The evaluation results of the polymer are shown in Table 2.
The s / τ value, which is an index of productivity, was 0.57. As in Example 2, it was possible to produce a polymer having excellent characteristics stably and under high productivity conditions.

Example 11 The same operation as in Example 9 was carried out except that the composition of the feed solution and the polymerization conditions were changed as shown in Table 2, and the operation was continuously performed for 10 days to produce a polymer. did. No increase in viscosity due to polymer formation at the bottom of the distillation column was observed during the operation period, and the reboiler at the bottom of the rectification column was capable of continuous stable operation. The evaluation results of the polymer are shown in Table 2.
The s / τ value, which is an index of productivity, was 0.95. As in Example 5, it was possible to produce a polymer having excellent characteristics under stable and high productivity conditions.

Comparative Example 3 A polymer pellet was obtained in the same manner as in Example 1 except that the supply liquid was not deoxygenated in the countercurrent contact tower. The oxygen concentration in the feed before being fed to the reactor was 10 ppm. The properties of the polymer are shown in Table 2. The result was inferior optical properties and weather resistance of the polymer.

[0075]

[Table 1]

[0076]

[Table 2]

[0077]

Industrial Applicability According to the present invention, it is possible to improve the productivity and stable productivity of a methacrylic polymer excellent in optical transparency, weather resistance and thermal decomposition resistance and suitable for materials for thermoforming such as injection molding and extrusion molding. This has the effect of providing an excellent manufacturing method.

[Brief description of the drawings]

FIG. 1 is a process diagram (first half) showing an example of a continuous polymerization apparatus in a solution polymerization process of the present invention.

FIG. 2 is a process diagram (second half) showing an example of a continuous polymerization apparatus in the solution polymerization process of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 New monomer supply line 2 Recovered volatiles storage tank 3 Recovered volatiles supply line 4 Metering pump 5 Rectification tower 6 Condenser 7 High boiling point discharge line 8 Chain transfer agent supply line 9 Countercurrent contact tower 10 Nitrogen supply Line 11 Buffer tank 12 Free radical generator supply line 13 Filter 14 Complete mixing type reactor 15 Dispense pump 16 Polymer heating plate 17 Devolatilization tank 18 Condenser 19 Recovered volatile liquid sending line 20 Vacuum pump 21 Polymer extrusion die 22 Strand bath 23 Strand cutter

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08F 220/14 C08F 220/14 // (C08F 220/14 220: 10) F-term (Reference) 4J011 AA04 AA05 AB02 AB05 AB08 BA01 HA03 HA10 HB02 HB05 HB10 HB12 HB22 4J015 AA01 BA03 4J100 AL03P AL03Q CA04 DA01 FA03 FA04 FA19 FA28 FA30 FA37 FA39 FA41 FA47 GB05 GD01

Claims (2)

[Claims] 1. A methyl methacrylate monomer, an alkyl acrylate monomer having an alkyl group having 1 to 8 carbon atoms and a non-polymerizable solvent are each represented by the following formula: 0.70 ≦ A / (A + B) ≦ 0.998 0.050 ≦ C / (A + B + C) ≦ 0.100 (where A is part by weight of methyl methacrylate monomer, B is part by weight of alkyl acrylate monomer, and C is non-polymerizable solvent And a half-life in a reactor of 5.50 parts by weight.
The dissolved oxygen content is reduced to 1 ppm or less, and the permeation particle size is reduced by bringing a feed solution comprising a free radical generator, which is 55 × 10 ^{−5 to} 2.30 hours, and a chain transfer agent into countercurrent contact with gaseous nitrogen. After removing solid foreign matter by passing through a filter of 2 μm or less, the reaction liquid in the reactor is continuously supplied to the reactor, and uniformly stirred and mixed while keeping the inside of the reactor at 130 to 170 ° C. And the ratio of the half-life of the free radical generator to the average residence time of the reaction solution in the reactor is from 5.0 × 10 ^{-4 to} 2.5.
0, the polymer concentration (weight fraction) in the reactor is 0.40 to 0.40.
0.70, the ratio of the concentration of the generated free radicals (mol · g ⁻¹ ) of the free radical generator in the whole supply liquid to the polymer concentration (weight fraction) of the polymerization liquid in the reactor is 0.5 × 10 ^{− 6 to} 6.0 × 10 ^-6
mol · g ⁻¹ , and the number average molecular weight of the polymer is 2.5 ×
A methacrylic polymer characterized in that the polymerization reaction is continuously controlled in the range of 10 ^{4 to} 15.0 × 10 ⁴ , and then the reaction solution is continuously discharged from the reactor and subjected to devolatilization under reduced pressure. Production method. 2. The method for producing a methacrylic polymer according to claim 1, wherein the non-polymerizable solvent is at least one solvent selected from ethylbenzene, toluene, o-xylene, m-xylene, and p-xylene.