KR101780846B1 - Method for producing methacrylic polymer - Google Patents

Abstract

Methyl methacrylate and a monomer containing another alkyl (meth) acrylate if desired, is fed to a fully mixed reactor (A) 11, and polymerization is carried out by a first radical polymerization initiator to obtain a first syrup Steps (a),
(B) a step of supplying a first syrup and a second radical polymerization initiator to the reactor (B) (12, 13) disposed downstream of the reactor (A) and performing polymerization to obtain a second syrup; and
(C) devolatilizing the second syrup,
A process for producing a methacrylic polymer satisfying the following formula is disclosed.
8.5x + 123? Y? -2.6x + 45
y is the mass ratio (ppm) of the amount of the second radical polymerization initiator supplied to the reactor (B) in terms of the amount of the first syrup supplied per unit time, x is the content of the alkyl (meth) acrylate in the monomer (% by mass)

Description

[0001] METHOD FOR PRODUCING METHACRYLIC POLYMER [0002]

The present invention relates to a method for producing a methacrylic polymer capable of realizing a high monomer conversion and productivity.

Industrial production methods of methacrylic resins include a suspension polymerization method and a bulk polymerization method. In the bulk polymerization method, it is known that it is possible to produce a resin having excellent transparency without the use of an additive such as a dispersant used in a suspension polymerization method. Patent Document 1 and Patent Document 2 disclose a method for producing an acrylic resin in which polymerization is carried out in a fully mixed type reactor in the production of an acrylic resin and then polymerization is carried out in a tubular reactor such as a plug flow type reactor .

Japanese Patent Application Laid-Open No. 2000-26507 Japanese Patent Application Laid-Open No. 2003-2912

Patent Document 1 discloses a method for producing an acrylic resin in which productivity and physical properties are balanced by using a tubular reactor following a molding (tank) reactor in the production of an acrylic resin. In this document, there is a description of an example in which the maximum polymerization rate of 72% is reached, but there is no description of a method of further increasing the polymerization rate.

Patent Document 2 discloses that polymerization is terminated by using the equilibrium polymerization rate, and the degree of arrival polymerization is determined by the final temperature of the polymer. In this document, there is a description of an example in which the ultimate value of the ultimate degree of polymerization is 68%, but it is considered that the ultimate degree of polymerization exceeding this value can not be achieved. In addition, the factors that determine the equilibrium polymerization degree are not described at all.

An object of the present invention is to provide a method for producing a methacrylic polymer capable of realizing a high monomer conversion (rate of arrival polymerization) and productivity in bulk polymerization of methacrylic monomers and the like.

According to the thinking method based on the equilibrium polymerization rate, it was thought that even when the amount of the initiator to be added to the tubular reactor was increased, the rate of polymerization of the polymer could not be improved. However, the inventors of the present invention have conducted intensive studies, and as a result, have found that the addition of the initiator in a predetermined amount in the polymerization in the tubular reactor can improve the monomer conversion rate. It has also been found that by increasing the amount of methyl acrylate used as the copolymerization component of the methacrylic polymer, the monomer conversion can be improved despite the amount of initiator used in the same amount as in the prior art. Based on these findings, the present inventors have found that by adjusting the concentration of the radical polymerization initiator and the concentration of the alkyl (meth) acrylate in the second polymerization at the downstream thereof after polymerization of the fully mixed type reactor to a predetermined range, The present invention has been accomplished.

That is, the present invention relates to a process for producing a prepolymer by reacting methyl methacrylate alone or a monomer containing an alkyl (meth) acrylate other than methyl methacrylate and methyl methacrylate to a fully mixed type reactor (A) (A), (b) and (c) to obtain a first syrup,

(B) a step of supplying a first syrup and a second radical polymerization initiator to the reactor (B) disposed downstream of the fully mixed reactor (A) and performing polymerization to obtain a second syrup; and

A step (c) of devolating the second syrup;

Are successively carried out to prepare a methacrylic polymer,

X [mass%] of the alkyl (meth) acrylate other than methyl methacrylate in the monomer, and a mass ratio of the amount of the second radical polymerization initiator supplied per unit time to the amount of the first syrup supplied per unit time in the reactor (B) y [ppm], x and y satisfy the following formulas.

8.5x + 123? Y? -2.6x + 45

According to the present invention, it is possible to provide a method for producing a methacrylic polymer capable of realizing a high monomer conversion and productivity even when bulk polymerization of a methacrylic monomer is performed.

1 is a schematic configuration diagram of an apparatus used in the embodiment.

In the present invention, the methacrylic monomer is polymerized to produce a methacrylic polymer. The "methacrylic polymer" means a homopolymer of methyl methacrylate or a copolymer of a copolymerizable component (monomer) such as alkyl (meth) acrylate other than methyl methacrylate and methyl methacrylate. Further, "(meth) acrylate" means acrylate or methacrylate.

Examples of the polymerization method include a bulk polymerization method, a suspension polymerization method and a solution polymerization method. Particularly, from the viewpoints of monomer conversion and productivity, bulk polymerization is preferable. The polymerization method may be a continuous method or a batch method.

Specific examples of the alkyl (meth) acrylate other than methyl methacrylate as the copolymerization component include methyl acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n- (Meth) acrylate, n-butyl (meth) acrylate, tert-butyl (meth) acrylate, sec- , Stearyl (meth) acrylate, tridecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate and cyclohexyl (meth) acrylate. Of these, methyl acrylate, ethyl acrylate and butyl acrylate are preferred. The alkyl (meth) acrylate as the copolymerization component may be used alone or in combination of two or more.

As the copolymerization component, monomers other than alkyl (meth) acrylate may be used in combination. Specific examples of such monomers include monobasic acid or dibasic acid vinyl monomers such as methacrylic acid, acrylic acid, crotonic acid, vinylbenzoic acid, fumaric acid, itaconic acid, maleic acid and citraconic acid; Dibasic acid anhydride vinyl monomers such as maleic anhydride; (Meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (Meth) acrylate, (meth) acrylic acid ester having a hydroxyalkyl group such as 6-hydroxyhexyl (meth) acrylate; Butyrolactone ring addition adducts to 2-hydroxyethyl (meth) acrylate, epsilon -caprolactone ring addition adducts to 2-hydroxyethyl (meth) acrylate, ethylene oxide adducts of (meth) A ring-opening adduct, a ring-opening adduct of propylene oxide to (meth) acrylic acid, a hydroxyl group at the terminal of a dimer or trimer of 2-hydroxyethyl (meth) acrylate or 2-hydroxypropyl (meth) (Meth) acrylic acid ester having a functional group; Other vinyl group-containing vinyl monomers such as 4-hydroxybutyl vinyl ether, p-hydroxystyrene and the like; Phenyl (meth) acrylate, benzyl (meth) acrylate, isobornyl (meth) acrylate, styrene; methyl styrene, p-methyl styrene, p-ethyl styrene, 2,4-dimethyl styrene, p-butyl styrene, p-tert-butyl Styrene-based monomers such as styrene; Vinyl monomer containing an epoxy group such as acrylonitrile, methacrylonitrile, vinyl acetate, glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate and allyl glycidyl ether, (Meth) acrylate, N-methoxymethyl methacrylamide, N-ethoxymethylacrylamide, N-propoxymethylacrylamide, N - < / RTI > butoxymethyl acrylamide; (Meth) acrylate having a hydroxyalkyl group such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate.

Of the monomers used for the polymerization, the amount of the alkyl (meth) acrylate other than methyl methacrylate is preferably 0.5 to 20% by mass. When a monomer other than alkyl (meth) acrylate is used as a copolymerization component, the amount thereof is preferably 20% by mass or less. The monomer used for the polymerization is preferably composed of 80 to 99.5 mass% of methyl methacrylate and 0.5 to 20 mass% of alkyl (meth) acrylate other than methyl methacrylate. When the content of the alkyl (meth) acrylate is 0.5% by mass or more, the obtained methacrylic polymer has good thermal stability, thermal decomposition of the resin is difficult to proceed during molding, and appearance defects such as generation of bubbles in the molded article are eliminated. When the content of the alkyl (meth) acrylate is 20% by mass or less, the resulting methacrylic polymer has good heat resistance, and the molded article is free from deformation by heat and can be favorably used in general applications.

[Step (a)]

The step (a) in the present invention is a step of supplying the above-mentioned monomer to the fully-mixed reactor (A) and performing the polymerization with the first radical polymerization initiator to obtain the first syrup.

The first radical polymerization initiator may be any one that decomposes at the temperature of the reaction system in step (a) to generate radicals.

Specific examples thereof include tert-butylperoxy-3,5,5-trimethylhexanate, tert-butylperoxy laurate, tert-butylperoxy isopropyl monocarbonate, tert-hexylperoxy isopropyl monocarbonate, tert -Butylperoxyacetate, 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (tert-butylperoxy) cyclohexane, tert- Hexylperoxy oxy-2-ethylhexanoate, di-tert-butylperoxide, 2,5-dimethyl-2,5-bis ( organic peroxides such as tert-butylperoxy) hexane; Azo compounds such as 2- (carbamoyl azo) -isobutyronitrile, 1,1'-azobis (1-cyclohexanecarbonitrile), 2,2'-azobisisobutyronitrile, 2,2'-azo Bis (2-methylbutyronitrile), dimethyl 2,2'-azobisisobutyrate, 2,2'-azobis (2,4,4-trimethylpentane), 2,2'-azo Azo compounds such as bis (2-methylpropane); Persulfates such as potassium persulfate; And a redox-based polymerization initiator. The first radical polymerization initiator may be used alone, or two or more thereof may be used in combination.

The radical polymerization initiator preferably has a half-life of not less than 10 seconds and not more than 30 minutes with respect to the temperature to be used. When the half-life period is appropriately long, the radical polymerization initiator is decomposed after uniformly diffusing into the polymerization system, and generation of oligomers which are likely to be thermally decomposed is suppressed. In addition, when the half-life is adequately short, when the operation is stopped in an emergency, the problem of difficulty in restarting due to the high viscosity of the reaction liquid becomes hard to occur.

The amount of the first radical polymerization initiator to be used may be appropriately determined according to various conditions such as the polymerization temperature of the reaction system in the step (a), the average residence time of the reactants, and the target conversion of the monomer. In particular, the amount of the first radical polymerization initiator to be used is preferably 5.0 x 10 < ^-5 > mol or less based on 1 mol of the monomer in view of obtaining a methacrylic polymer having a small amount of terminal double bond and excellent heat- Is preferably 5.0 x 10 < ^-6 > mol or more.

A chain transfer system can be used for the polymerization in process (a). Particularly, it is preferable to use a mercaptan compound. Specific examples of mercaptan compounds include alkyl groups such as n-butylmercaptan, isobutylmercaptan, n-octylmercaptan, n-dodecylmercaptan, sec-butylmercaptan, sec-dodecylmercaptan and tert- Secondary, or tertiary mercaptans having substituted alkyl groups; Aromatic mercaptans such as phenyl mercaptan, thiocresol and 4-tert-butyl-O-thiocresol; Cyoglycolic acid and its ester; And mercaptans having 3 to 18 carbon atoms such as ethylene thioglycol. Among them, tert-butylmercaptan, n-butylmercaptan, n-octylmercaptan and n-dodecylmercaptan are preferable. As the chain transfer agent, only one kind may be used, or two or more kinds may be used in combination.

The amount of the chain transfer agent to be used is not particularly limited so long as it has an appropriate degree of polymerization capable of molding while maintaining the strength of the product (generally, the range of industrial use as a molding material is such that the weight-average molecular weight of the polymer after removal of volatile components is 70,000 to 150,000) Is preferably from 0.01 to 1 mol%, more preferably from 0.05 to 0.5 mol%, based on 100 mol% of the monomer, from the standpoint of obtaining a methacrylic polymer excellent in heat resistance and decomposition resistance.

When the step (a) is carried out by solution polymerization, an inert solvent is used. Specific examples thereof include methanol, ethanol, toluene, xylene, acetone, methyl isobutyl ketone, ethylbenzene, methyl ethyl ketone, and butyl acetate. Among them, methanol, toluene, ethylbenzene and butyl acetate are preferable. As the inert solvent, only one type may be used, or two or more types may be used in combination.

The amount of the inert solvent used is preferably less than 5% by mass in the reaction liquid composition. However, when the amount of the inert solvent used is less than 5% by mass in the reaction liquid composition, the thermal decomposability is hardly impaired, and by using the gel effect similarly to the bulk polymerization, a small amount The use of the radical polymerization initiator of the present invention can effectively increase the monomer conversion rate.

The fully mixed type reactor (A) is an apparatus which reacts the supplied raw materials in a state of being uniformly mixed by an agitating device or the like. The fully mixed reactor (A) may be a batch-type shaped reactor and may be a continuous tubular reactor. As the molding reactor, it is possible to use a molding reaction device provided with a supply port, an outlet, and a stirring device. The stirring apparatus preferably has a mixing performance over the entire reaction region. As the tubular reactor, a plug flow type reactor is preferable and a jacketed tubular reactor having a static mixer is more preferable. If a stationary mixer is incorporated, uniformity of the reaction and flow of the reaction liquid can be stabilized by the stirring effect. As the stationary mixer, a stationary mixer manufactured by Noritake Co., Ltd. or a through-the-mixer manufactured by Sumitomo Heavy Industries, Ltd. is suitable. The complete mixed-type reactor (A) may be used alone or in combination of two or more. Further, one kind of reactor may be connected in series.

In the step (a), a raw material composition containing a monomer and a first radical polymerization initiator in a fully mixed type reactor (A) is heated under appropriate conditions to polymerize a part of the methacrylic monomer to obtain a first syrup. The polymerization temperature may be suitably set within a range in which the first syrup having the desired monomer conversion rate is obtained. When the step (a) is carried out using the molding reactor as the fully mixed type reactor (A), it can be selected from the range of 110 to 180 캜 (preferably 120 to 160 캜). When the step (a) is carried out in the tubular reactor in addition to the molding reactor, it is preferable to carry out the step (a) at an inlet temperature of 110 to 170 캜 (preferably 120 to 140 캜) and an outlet temperature of 120 to 180 캜 ° C.) and an average temperature of 115 to 175 ° C. (preferably 135 to 155 ° C.).

The monomer conversion in the first syrup obtained in the step (a) is preferably 35 to 70 mass%, more preferably 45 to 60 mass%. The upper limit of these ranges is significant in that uniformity in the bath is maintained in the molding reactor, mixing and heat transfer in the bath are sufficiently achieved, and stable operation is performed. Further, the lower limit value is significant in that productivity is improved as a sufficient monomer conversion rate.

The temperature of the first syrup obtained in the step (a) is preferably 110 to 180 ° C, more preferably 120 to 160 ° C. The lower limit of these ranges is significant in that the formation of dimers is suppressed and transparency and mechanical strength of the polymer after volatile matter removal are maintained. Further, the upper limit value is significant in that the acceleration phenomenon of the polymerization rate due to the gel effect is suppressed, and the polymer is stably operated at a high monomer conversion rate.

In the molding reactor, for example, polymerization can be carried out as follows. The dissolved oxygen concentration is set to 2 mass ppm or less, more preferably 1 mass ppm or less, by introducing an inert gas such as nitrogen into the raw material monomer or by keeping the raw material monomer under a reduced pressure for a predetermined time. When the dissolved oxygen concentration is set to such a low level, the polymerization reaction proceeds stably, and even if the polymerization process is maintained at a high temperature for a long time, little coloring component is generated, and a high quality polymer can be obtained.

Subsequently, the first syrup is withdrawn from the fully mixed reactor (A) and fed to the reactor (B) arranged next thereto. The first syrup may be cooled before being sent to the reactor (B).

[Process (b)]

The step (b) of the present invention is characterized in that the first syrup and the second radical polymerization initiator obtained in the above-mentioned step (a) are fed to the reactor (B) disposed downstream of the fully mixed type reactor (A) This is the process of obtaining the second syrup.

In this step (b), the content of the alkyl (meth) acrylate other than methyl methacrylate in the monomer is represented by x [mass%], the amount of the second radical polymerization initiator supplied to the first syrup supplied per unit time in the reactor (B) Is expressed by y [ppm], x and y satisfy the following equations.

8.5x + 123? Y? -2.6x + 45

By satisfying the relationship of y? -2.6x + 45 in the above formula, the monomer conversion rate can be increased in a short time. Further, by satisfying the relationship of 8.5x + 123 ≥ y, it becomes possible to produce a methacrylic polymer having excellent thermal stability. When the thermal stability is excellent, thermal decomposition of the resin hardly proceeds at the time of molding, and appearance defects such as generation of bubbles in the molded article are eliminated.

As the second radical polymerization initiator, for example, the same as the first radical polymerization initiator can be used. The amount of the second radical polymerization initiator to be used is the same as that of the first radical polymerization initiator as long as the above formula is satisfied.

In the step (b), it is preferable to conduct the polymerization at a higher temperature than the step (a) in order to raise the monomer conversion rate in a short time. It is also preferable that the second radical polymerization initiator is a radical polymerization initiator of higher decomposition type than the first radical polymerization initiator. Specifically, it is preferable to use, as the second radical polymerization initiator, a radical polymerization initiator having a half-life longer than the half-life of the first radical polymerization initiator at the average temperature in the step (b). As the second radical polymerization initiator, a radical polymerization initiator having a half-life longer than the half-life period of the first radical polymerization initiator at the average temperature in the step (b) may be used in combination with a radical polymerization initiator such as the first radical polymerization initiator have. The amount of the polymerization initiator required to obtain the same monomer conversion can be reduced by using two kinds of radical polymerization initiators in combination.

The second radical polymerization initiator may be added in multiple steps. In this case, the sum of the mass ratio [ppm] of the second radical polymerization initiator to the syrup supplied per unit time at each revolution is set to y [ppm].

Specific examples of the reactor (B) include the same ones as the specific examples of the fully mixed reactor (A) described above, but a tubular reactor is particularly preferable. Only one type of reactor (B) may be used, or two or more types may be used in combination. Further, one kind of reactor may be connected in series.

In the step (b), a composition containing the first syrup and the second radical polymerization initiator in the reactor (B) is heated under appropriate conditions to polymerize a part of the monomers present in the first syrup to obtain a second syrup . The polymerization temperature may be appropriately set so that the second syrup has a desired monomer conversion rate.

The monomer conversion in the second syrup obtained in the step (b) is preferably 50 to 90% by mass, and more preferably 70 to 80% by mass. The upper limit of these ranges is significant in that the viscosity of the syrup is appropriately suppressed and the pressure loss when flowing in the process is reduced. Further, the lower limit value is significant in that the remaining monomer is decreased and the burden of the subsequent devolatilization process is reduced.

The temperature of the inner wall of the reactor (B) is preferably 125 to 210 占 폚, more preferably 150 to 195 占 폚. The lower limit of these ranges is significant in that the conversion rate of the monomer is 70% or more. Further, the upper limit value is significant in that the polymer in the process maintains fluidity and performs stable operation.

[Step (c)]

The step (c) of the present invention is a step of devolatilizing the second syrup obtained in the above-mentioned step (b) to take out the methacrylic polymer. By this step (c), the amount of monomer remaining in the methacrylic polymer decreases, and the heat resistance is improved.

Step (c) can be carried out, for example, by introducing the second syrup into a devolatilizing extruder. The temperature of the second syrup in the state obtained in the step (b) may be the same or may be further heated. When the second syrup is further heated, it is preferable to set the temperature to not exceed 250 ° C. In the devolatilizing extruder, it is preferable to release the second syrup under a reduced pressure of 0.0001 to 0.1 MPa to continuously remove and remove most of the volatiles mainly composed of the methacrylic monomer.

The content of the monomer in the methacrylic polymer obtained by removing the volatiles is preferably 0.3 mass% or less, and the content of the dimer of the monomer as a by-product of the polymerization reaction is preferably 0.1 mass% or less, The content is preferably 50 mass ppm or less.

Volatiles such as unreacted methacrylic monomers are preferably recycled as a raw material for the step (a) after being condensed in a condenser and recovered from the viewpoint of economy. At this time, it is more preferable to separate and remove high boiling point components such as a dimer of the methacrylic monomer contained in volatiles by distillation, and then reuse them as a raw material in the step (a).

The methacrylic polymer thus produced can be used, for example, as a molding material. In this case, a lubricant such as higher alcohols and higher fatty acid esters, an ultraviolet absorber, a heat stabilizer, a colorant, an antistatic agent and the like may be added, if necessary.

Example

Hereinafter, the present invention will be described in more detail by way of examples, but they should not be construed as limiting the present invention. On the other hand, the measurement of the molecular weight of the polymer was carried out by the following method.

≪ Measurement of molecular weight by GPC &

As a GPC apparatus, HLC-8020 manufactured by Tosoh Corporation was used, and two GMHXLs manufactured by Tosoh Corporation were used as columns. As a solvent, tetrahydrofuran (THF) was used, and a calibration curve was prepared using TSK standard polystyrene manufactured by Tosoh Corporation. As a sample, a solution with a concentration of 0.1 g / dl was used. The weight average molecular weight Mw was determined by a GPC data processor (Data Device SC-80.10 manufactured by Tosoh Corporation).

≪ Evaluation of formability &

PS-60E (manufactured by Nissei Kogyo K.K.) was used as a molding machine, and the molding temperature was set at 300 캜 to prepare a spiral-shaped molded body, and the appearance thereof was observed.

≪ Example 1 >

The present invention was carried out as follows using the apparatus shown in Fig.

[Step (a)]

Nitrogen was introduced into a monomer mixture composed of 98% by mass of purified methyl methacrylate and 2% by mass of methyl acrylate to make the dissolved oxygen to 0.5 ppm. To this monomer mixture, 0.157 mol% (0.23 mass%) of n-octylmercaptan was used as a chain transfer agent and 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclo (80 ppm) of hexane and 2.67 × 10 ^-5 mol / mol of monomer was continuously supplied to a fully-mixed reactor, which was a first reactor (11) controlled at a polymerization temperature of 135 ° C., with stirring and mixing, Was carried out at an average residence time in the reaction zone of 2.5 hours to obtain a first syrup. On the other hand, the half life of 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane at this polymerization temperature (135 ° C) is 230 seconds.

[Process (b)]

Subsequently, the first syrup is continuously withdrawn from the first reactor 11 by the gear pump 31, and the initiator injector 21 (piping containing SMX through-the-mixer made by Sumitomo Heavy Industries, Ltd.) (Tert-butylperoxy) 3,3,5-trimethylsiloxane as a second radical initiator was added so that the mass ratio to the syrup feed per unit time was 40 ppm, and this was added to the second reactor 12 (Plug flow type reactor) equipped with a fixed mixer made by Noritake Co., Ltd., and the polymerization was carried out at an inner wall temperature of 150 ° C and an average residence time of syrup of 20 minutes. On the other hand, the half-life of 1,1-bis (tert-butylperoxy) 3,3,5-trimethylsiloxane at this temperature (150 ° C) is 54 seconds.

Subsequently, the polymerized syrup in the second reactor 12 is led to the same type of initiator feeder 22 as above, and further the di-tert-butylperoxide as the second radical initiator is added to the syrup feed mass per unit time (Plug flow type reactor) equipped with a fixed mixer made by Noritake Company, which is the same third reactor 13 as the second reactor 12, and the inner wall temperature was adjusted to 170 Deg.] C, an internal pressure of 25 kg / cm ² G and an average residence time of 20 minutes to obtain a second syrup. On the other hand, the half-life of di-tert-butylperoxide at this temperature (170 ° C) is 250 seconds.

[Step (c)]

Subsequently, the second syrup was fed continuously from the outlet of the second reactor 12 to the devolatilizer extruder 14 (vent extruder extruder) at 195 DEG C, and volatiles containing unreacted monomer as the main component at 270 DEG C The polymer was separated and removed to obtain a methacrylic polymer.

The amount of the methacrylic polymer taken out from the devolatilizing extruder 14 and the amount of the added raw material monomer were measured, and the monomer conversion to the charged raw material was 78 mass%. Further, even in the continuous operation for 360 hours, there was no problem in the control of polymerization, and no adherence to the apparatus or generation of foreign matter was observed even after observation in the reactor after the operation was completed. Further, when the obtained methacrylic polymer was evaluated for moldability as described above, the presence of bubbles was not confirmed, and the appearance of the molded article was good. The results are shown in Table 1.

≪ Example 2 >

Except that the amount of the initiator added to the second reactor 12 (first reactor (B)) was changed to 60 ppm and the amount of the initiator added to the third reactor 13 (the second reactor (B)) was changed to 60 ppm. The same operation was performed. The amount of the methacrylic polymer taken out from the devolatilizing extruder 14 and the amount of the added raw monomers were measured. The monomer conversion to the charged raw material was 80 mass%. Further, even in the continuous operation for 360 hours, there was no problem in the control of the polymerization, and no adherence to the apparatus or generation of foreign matter or the like was observed even after observation in the reactor after the operation was completed. Further, when the moldability evaluation was performed on the obtained methacrylic polymer, the presence of bubbles was not confirmed, and the appearance of the molded article was good. The results are shown in Table 1.

≪ Example 3 >

The amount of methyl methacrylate in the monomer mixture was changed to 85 mass% and the amount of methyl acrylate was changed to 15 mass%, the amount of the initiator added to the second reactor 12 (first reactor (B)) was changed to 20 ppm, 3 The procedure of Example 1 was repeated except that the amount of the initiator added to the reactor 13 (second reactor (B)) was changed to 15 ppm. The amount of the methacrylic polymer removed from the devolatilizing extruder 14 and the amount of the added raw material monomer were measured. As a result, the monomer conversion to the charged raw material was 73 mass%. Further, even in the continuous operation for 360 hours, there was no problem in the control of the polymerization, and no adherence to the apparatus or generation of foreign matter or the like was observed even after observation in the reactor after the operation was completed. Further, when the moldability evaluation was performed on the obtained methacrylic polymer, the presence of bubbles was not confirmed, and the appearance of the molded article was good. The results are shown in Table 1.

<Example 4>

Except that the amount of the initiator added to the second reactor 12 (first reactor (B)) was changed to 60 ppm and the amount of the initiator added to the third reactor 13 (the second reactor (B)) was changed to 60 ppm. The same operation was performed. The amount of the methacrylic polymer removed from the devolatilizing extruder 14 and the amount of the added raw material monomer were measured, and the monomer conversion to the charged raw material was 77 mass%. Further, even in the continuous operation for 360 hours, there was no problem in the control of the polymerization, and no adherence to the apparatus or generation of foreign matter or the like was observed even after observation in the reactor after the operation was completed. Further, when the moldability evaluation was performed on the obtained methacrylic polymer, the presence of bubbles was not confirmed, and the appearance of the molded article was good. The results are shown in Table 1.

&Lt; Example 5 >

Except that the amount of the initiator added to the second reactor 12 (first reactor (B)) was changed to 100 ppm and the amount of the initiator added to the third reactor 13 (the second reactor (B)) was changed to 100 ppm. The same operation was performed. The amount of the methacrylic polymer removed from the devolatilizing extruder 14 and the amount of the added raw material monomer were measured. The monomer conversion to the charged raw material was 83 mass%. Further, even in the continuous operation for 360 hours, there was no problem in the control of the polymerization, and no adherence to the apparatus or generation of foreign matter or the like was observed even after observation in the reactor after the operation was completed. Further, when the obtained methacrylic polymer was evaluated for moldability as described above, the presence of bubbles was not confirmed, and the appearance of the molded article was good. The results are shown in Table 1.

&Lt; Comparative Example 1 &

Except that the initiator amount added to the second reactor 12 (first reactor (B)) was changed to 20 ppm and the amount of the initiator added to the third reactor 13 (second reactor (B)) was changed to 15 ppm. The same operation was performed. The amount of the methacrylic polymer taken out from the devolatilizing extruder 14 and the amount of the charged raw material monomers were measured. As a result, the monomer conversion to the charged raw material was as low as 68 mass% and the amount of resin obtained per unit time was small. The results are shown in Table 1.

&Lt; Comparative Example 2 &

The same operation as in Example 3 was carried out except that the amount of the initiator added to the second reactor 12 (the first reactor B) and the amount of the initiator added to the third reactor 13 (the second reactor B) was changed without addition. The amount of the methacrylic polymer taken out from the devolatilizing extruder 14 and the amount of the raw material monomers added were measured. As a result, the monomer conversion to the charged raw material was as low as 50 mass%, and the amount of resin obtained per unit time was small. The results are shown in Table 1.

&Lt; Comparative Example 3 &

Example 1 was repeated except that the initiator amount added to the second reactor 12 (first reactor B) was changed to 80 ppm and the amount of the initiator added to the third reactor 13 (the second reactor B) was changed to 80 ppm. The same operation was performed. The amount of the methacrylic polymer removed from the devolatilizing extruder 14 and the amount of the added raw material monomer were measured. The monomer conversion to the charged raw material was 83 mass%. Further, even in the continuous operation for 360 hours, there was no problem in the control of the polymerization, and no adherence to the apparatus or generation of foreign matter or the like was observed even after observation in the reactor after the operation was completed. However, when the moldability evaluation was performed on the obtained methacrylic polymer, the presence of bubbles was confirmed, and the appearance of the molded article contained a white band called silver, which was a defective molding. The results are shown in Table 1.

&Lt; Comparative Example 4 &

Example 3 was repeated except that the initiator amount added to the second reactor 12 (first reactor B) was changed to 150 ppm and the amount of the initiator added to the third reactor 13 (the second reactor B) was changed to 150 ppm. The same operation was performed. The amount of the methacrylic polymer removed from the devolatilizing extruder 14 and the amount of the added raw material monomer were measured. The monomer conversion to the charged raw material was 90 mass%. Further, even in the continuous operation for 360 hours, there was no problem in the control of the polymerization, and no adherence to the apparatus or generation of foreign matter or the like was observed even after observation in the reactor after the operation was completed. However, when the obtained methacrylic polymer was subjected to the above formability evaluation, the presence of bubbles was confirmed, and a white band called silver entered into the appearance of the molded article and the molding was defective. The results are shown in Table 1.

Table 1 shows the conditions of each example and each comparative example and the characteristics of the obtained polymer.

The abbreviations in the table are as follows.

&Quot; MMA &quot;: methyl methacrylate,

&Quot; MA &quot;: methyl acrylate,

&Quot; Ga &quot;: 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane,

&Quot; I &quot;: di-tert-butylperoxide,

&Quot; F &quot;: n-Octylmercaptan

As apparent from the table, the monomer conversion rate in each example was sufficient, but it was insufficient in each comparative example.

11: First reactor
12: Second reactor
13: Third reactor
14: Devolution extruder
21: Initiator injector
22: Initiator injector
31: Gear pump

Claims (2)

A step of supplying a monomer containing an alkyl (meth) acrylate other than methyl methacrylate and methyl methacrylate to the fully-mixed type reactor (A) and carrying out polymerization with the first radical polymerization initiator to obtain a first syrup a),
(B) a step of supplying a first syrup and a second radical polymerization initiator to the reactor (B) disposed downstream of the fully mixed reactor (A) and performing polymerization to obtain a second syrup; and
A step (c) of devolating the second syrup;
Are successively carried out to prepare a methacrylic polymer,
X [mass%] of the alkyl (meth) acrylate other than methyl methacrylate in the monomer, and a mass ratio of the amount of the second radical polymerization initiator supplied per unit time to the amount of the first syrup supplied per unit time in the reactor (B) y [ppm], wherein x and y satisfy the following formulas.
8.5x + 123? Y? -2.6x + 45,
15.0? X? 2.0,
200? Y? 35 delete

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