WO2011142384A1

WO2011142384A1 - Method for producing methacrylic polymer

Info

Publication number: WO2011142384A1
Application number: PCT/JP2011/060842
Authority: WO
Inventors: 昌大林田; 壽晃好村; 大輔野中; 裕介森田; 光弘松尾
Original assignee: 三菱レイヨン株式会社
Priority date: 2010-05-13
Filing date: 2011-05-11
Publication date: 2011-11-17
Also published as: TW201202268A; CN102933610A; CN102933610B; JP5786712B2; KR101780846B1; KR20130108086A; JPWO2011142384A1; TWI518100B

Abstract

Disclosed is a method for producing a methacrylic polymer that satisfies the formula. The method comprises a step (a) for obtaining a first syrup by supplying methyl methacrylate and, if desired, another monomer containing an alkyl (meth)acrylate to a complete mixing reactor (A) (11) and carrying out polymerization using a first radical polymerization initiator, a step (b) for obtaining a second syrup by supplying the first syrup and a second radical polymerization initiator to reactors (B) (12, 13) disposed downstream of the reactor (A) and carrying out polymerization, and a volatilizing/removing step (c) for the second syrup. 8.5x + 123 ≥ y ≥ -2.6 + 45 [y is the mass ratio (ppm) of the amount of the second radical polymerization initiators supplied to the amount of the first radical syrup supplied per unit time to the reactor (B), and x is the alkyl (meth)acrylate content (% by mass) in the monomer.]

Description

Method for producing methacrylic polymer

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

There are two methods for industrial production of methacrylic resins: suspension polymerization and bulk polymerization. In the bulk polymerization method, it is known that an additive such as a dispersant used in the suspension polymerization method is not used, and a resin having excellent transparency can be produced. Patent Document 1 and Patent Document 2 describe productivity and physical properties in the production of acrylic resin by performing polymerization in a completely mixed reactor and then polymerizing in a tubular reactor such as a plug flow reactor. A method for producing a balanced acrylic resin is disclosed.

JP 2000-26507 A JP 2003-2912 A

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

Patent Document 2 describes that the polymerization is terminated using the equilibrium polymerization rate, and the ultimate polymerization rate is determined by the final temperature of the polymer. In this document, there is a description of an example in which the ultimate polymerization rate is 68%, but it is considered that an ultimate polymerization rate exceeding this value cannot be achieved. In addition, there is no mention of factors that determine the equilibrium polymerization rate.

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

According to the idea based on the equilibrium polymerization rate, it was considered that the ultimate polymerization rate of the polymer could not be improved even if the amount of initiator added to the tubular reactor was increased. However, as a result of intensive studies by the present inventors, it has been found that the monomer conversion rate can be improved by adding a predetermined amount of initiator in the polymerization in the tubular reactor. It was also found that the monomer conversion rate can be improved by increasing the amount of methyl acrylate used as a copolymerization component of the methacrylic polymer, despite the same amount of initiator used as before. Based on these findings, the present inventors adjust the concentration of the radical polymerization initiator and the concentration of the alkyl (meth) acrylate in the second polymerization downstream thereof after the polymerization in the complete mixing reactor to a predetermined range. As a result, it was found that the monomer conversion can be improved, and the present invention has been completed.

That is, the present invention supplies methyl methacrylate alone or a monomer containing alkyl methacrylate (meth) acrylate other than methyl methacrylate and methyl methacrylate to the fully mixed reactor (A), and performs polymerization with the first radical polymerization initiator, Obtaining a first syrup (a),
Step (b) of supplying the first syrup and the second radical polymerization initiator to the reactor (B) arranged downstream of the fully mixed reactor (A) to perform polymerization to obtain the second syrup. And (c) devolatilizing the second syrup
In order to produce a methacrylic polymer,
The content of alkyl (meth) acrylate other than methyl methacrylate in the monomer is x [mass%], the second radical polymerization per unit time with respect to the first syrup supply amount per unit time in the reactor (B) When the mass ratio of the initiator supply amount is y [ppm], x and y satisfy the following formula: A method for producing a methacrylic polymer.

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 rate and productivity even in bulk polymerization of a methacrylic monomer.

It is a schematic block diagram of the apparatus used in the Example.

In the present invention, a methacrylic monomer is polymerized to produce a methacrylic polymer. The “methacrylic polymer” means a homopolymer of methyl methacrylate or a copolymer of copolymerization components (monomers) such as methyl methacrylate and alkyl (meth) acrylate other than methyl methacrylate. “(Meth) acrylate” means acrylate or metallate.

Examples of the polymerization method include a bulk polymerization method, a suspension polymerization method, and a solution polymerization method. In particular, the bulk polymerization method is preferred from the viewpoint of monomer conversion and productivity. The polymerization method may be a continuous method or a batch method.

Specific examples of alkyl (meth) acrylates other than methyl methacrylate as a copolymer component include methyl acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) ) Acrylate, tert-butyl (meth) acrylate, sec-butyl (meth) acrylate, n-pentyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, tridecyl (meth) ) Acrylate, 2-ethylhexyl (meth) acrylate, and cyclohexyl (meth) acrylate. Of these, methyl acrylate, ethyl acrylate, and butyl acrylate are preferable. Only 1 type may be used for the alkyl (meth) acrylate which is a copolymerization component, and 2 or more types may be used together.

Furthermore, monomers other than alkyl (meth) acrylate can be used in combination as a copolymerization component. Specific examples of such monomers include methacrylic acid, acrylic acid, crotonic acid, vinyl benzoic acid, fumaric acid, itaconic acid, maleic acid, citraconic acid and other monobasic acid or dibasic vinyl monomers; maleic anhydride, etc. Dihydroxy anhydride vinyl monomer of 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl ( (Meth) acrylate, (meth) acrylic acid ester having a hydroxyalkyl group such as 6-hydroxyhexyl (meth) acrylate; β-butyrolactone ring-opening adduct to 2-hydroxyethyl (meth) acrylate, 2-hydroxyethyl (meta) ) Ε-Cap to acrylate Lolactone ring-opening adduct, ethylene oxide ring-opening adduct to (meth) acrylic acid, propylene oxide ring-opening adduct to (meth) acrylic acid, 2-hydroxyethyl (meth) acrylate or 2-hydroxypropyl (meth) ) (Meth) acrylic acid ester having a hydroxyl group at the terminal of acrylate dimer or trimer; other hydroxyl group-containing vinyl monomers such as 4-hydroxybutyl vinyl ether and p-hydroxystyrene; phenyl (meth) acrylate, benzyl (Meth) acrylate, isobornyl (meth) acrylate, styrene; o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, pn-butyl Styrene such as styrene and p-tert-butylstyrene Monomers: Epoxy group-containing vinyl monomers such as acrylonitrile, methacrylonitrile, vinyl acetate, glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, allyl glycidyl ether, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-ethoxymethylacrylamide, N-propoxymethylacrylamide, N-butoxymethylacrylamide; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4 -(Meth) acrylates having a hydroxyalkyl group such as hydroxybutyl (meth) acrylate;

In the monomer used for polymerization, the amount of alkyl (meth) acrylate other than methyl methacrylate is preferably 0.5 to 20% by mass. Moreover, when using monomers other than alkyl (meth) acrylate together as a copolymerization component, the amount is preferably 20% by mass or less. Further, the monomer used for the polymerization is preferably composed of 80 to 99.5% by mass of methyl methacrylate and 0.5 to 20% by mass of alkyl (meth) acrylate other than methyl methacrylate. When the content of alkyl (meth) acrylate is 0.5% by mass or more, the thermal stability of the methacrylic polymer obtained is improved, the thermal decomposition of the resin is difficult to proceed during molding, generation of bubbles in the molded product, etc. , No appearance defects. Further, when the alkyl (meth) acrylate content is 20% by mass or less, the heat resistance of the resulting methacrylic polymer is improved, and the molded product is not deformed by heat and is used well for general purposes. it can.

[Step (a)]
Step (a) in the present invention is a step of supplying the above-mentioned monomer to the complete mixing reactor (A) and performing 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-butylperoxylaurate, tert-butylperoxyisopropylmonocarbonate, tert-hexylperoxyisopropylmonocarbonate, tert- Butyl peroxyacetate, 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (tert-butylperoxy) cyclohexane, tert-butylperoxy 2-ethylhexanate , Tert-butylperoxyisobutyrate, tert-hexyl-hexylperoxy 2-ethylhexanate, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis (tert-butylperoxy) hexane Etc. 2- (carbamoylazo) -isobutyronitrile, 1,1′-azobis (1-cyclohexanecarbonitrile), 2,2′-azobisisobutyronitrile, 2,2′-azobis ( 2-methylbutyronitrile), dimethyl 2,2′-azobisisobutyrate, 2,2′-azobis (2,4,4-trimethylpentane), 2,2′-azobis (2-methylpropane), etc. Azo compounds; persulfates such as potassium persulfate; redox polymerization initiators. Only 1 type may be used for a 1st radical polymerization initiator, and it may use 2 or more types together.

The radical polymerization initiator preferably has a half-life of 10 seconds to 30 minutes with respect to the temperature used. If the half-life is moderately long, the radical polymerization initiator is uniformly diffused in the polymerization system and then decomposed to suppress the generation of oligomers that are easily thermally decomposed. Also, if the half-life is reasonably short, when the operation is stopped in an emergency, the reaction solution becomes so viscous that it is difficult to restart.

The amount of the first radical polymerization initiator used may be appropriately determined according to various conditions such as the polymerization temperature of the reaction system in step (a), the average residence time of the reactants, and the target monomer conversion rate. In particular, the first radical polymerization initiator is used in an amount of 5.0 × 10 ⁻⁵ mol or less per 1 mol of the monomer in order to obtain a methacrylic polymer having a small amount of terminal double bonds and excellent thermal decomposition resistance. In view of industrial productivity, 5.0 × 10 ⁻⁶ mol or more is preferable.

A chain transfer agent can also be used for the polymerization in step (a). In particular, it is preferable to use a mercaptan compound. Specific examples of mercaptan compounds include alkyl groups or substituted alkyl groups such as n-butyl mercaptan, isobutyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, sec-butyl mercaptan, sec-dodecyl mercaptan, and tert-butyl mercaptan. Primary, secondary or tertiary mercaptans; aromatic mercaptans such as phenyl mercaptan, thiocresol, 4-tert-butyl-O-thiocresol; thioglycolic acid and its esters; carbon number 3 such as ethylenethioglycol -18 mercaptans. Of these, tert-butyl mercaptan, n-butyl mercaptan, n-octyl mercaptan, and n-dodecyl mercaptan are preferable. A chain transfer agent may use only 1 type and may use 2 or more types together.

The amount of chain transfer agent used is an appropriate degree of polymerization that can be processed while maintaining product strength (generally the range of industrial use as a molding material is the polymer after the final removal of volatiles. In terms of weight average molecular weight of from 70,000 to 150,000), and from the viewpoint of producing a methacrylic polymer having excellent thermal decomposition resistance, 0.01 to 1 mol% is preferable to 100 mol% of the monomer. 0.05 to 0.5 mol% is more preferable.

When using step (a) 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. Of these, methanol, toluene, ethylbenzene, and butyl acetate are preferable. Only 1 type may be used for an inert solvent and it may use 2 or more types together.

The amount of the inert solvent used is preferably less than 5% by mass in the reaction solution composition. It is more preferable to carry out bulk polymerization without using an inert solvent. However, if the amount of the inert solvent used is less than 5% by mass in the reaction solution composition, the thermal decomposition resistance is hardly impaired and the same as in bulk polymerization. By utilizing the gel effect, the monomer conversion can be effectively increased by using a small amount of radical polymerization initiator.

The complete mixing reactor (A) is an apparatus for reacting the supplied raw materials in a state of being uniformly mixed by a stirring device or the like. The fully mixed reactor (A) may be a batch tank reactor or a continuous tube reactor. As the tank reactor, a tank reactor equipped with a supply port, a discharge port, and a stirring device can be used. The stirrer preferably has mixing performance over the entire reaction zone. As the tubular reactor, a plug flow reactor is preferable, and a jacketed tubular reactor having a static mixer built therein is more preferable. If the static mixer is installed, the reaction can be made uniform and the flow of the reaction liquid can be stabilized by the stirring effect. As the static mixer, a static mixer manufactured by Noritake Co., Ltd. and a through-the mixer manufactured by Sumitomo Heavy Industries, Ltd. are suitable. Only one type of complete mixing reactor (A) may be used, or two or more types may be used in combination. One type of reactor may be connected in series.

In the step (a), the raw material composition containing the monomer and the first radical polymerization initiator is heated in an appropriate condition in the fully mixed reactor (A) to polymerize a part of the methacrylic monomer, Get the first syrup. The polymerization temperature may be appropriately set within a range in which a first syrup having a desired monomer conversion rate is obtained. When the step (a) is carried out using a tank reactor as the complete mixing reactor (A), it can be selected from the range of 110 to 180 ° C. (preferably 120 to 160 ° C.), for example. When step (a) is carried out in a tubular reactor following the tank reactor, for example, an inlet temperature of 110 to 170 ° C. (preferably 120 to 140 ° C.) and an outlet temperature of 120 to 180 ° C. (preferably 140 to 140 ° C.) 160 ° 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% by mass, more preferably 45 to 60% by mass. The upper limit of these ranges is significant in that the uniformity in the tank is maintained in the tank reactor, mixing and heat transfer in the tank are sufficiently achieved, and stable operation is performed. Further, the lower limit value is significant in terms of improving productivity by setting a sufficient monomer conversion rate.

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

In the tank reactor, for example, polymerization can be performed as follows. By introducing an inert gas such as nitrogen into the raw material monomer or holding the raw material monomer for a certain period of time under reduced pressure, the dissolved oxygen concentration is set to 2 mass ppm or less, more preferably 1 mass ppm or less. When the dissolved oxygen concentration is lowered in this way, the polymerization reaction proceeds stably, and even when kept at a high temperature for a long time in the polymerization step, little colored components are produced, and a high-quality polymer is obtained.

Next, the first syrup is extracted from the fully mixed reactor (A), and then supplied to the reactor (B) arranged thereafter. The first syrup may be cooled before being sent to the reactor (B).

[Step (b)]
In the step (b) of the present invention, the reactor (B) in which the first syrup and the second radical polymerization initiator obtained in the above step (a) are arranged downstream of the complete mixing reactor (A). The second syrup is obtained by performing polymerization by supplying to the polymer.

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

8.5x + 123 ≧ y ≧ −2.6x + 45

In the above formula, by satisfying the relationship y ≧ −2.6x + 45, 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, the thermal decomposition of the resin is difficult to proceed during molding, and appearance defects such as generation of bubbles in the molded product are eliminated.

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

In step (b), it is preferable to perform polymerization at a higher temperature than in step (a) in order to increase the monomer conversion rate in a short time. Therefore, the second radical polymerization initiator is preferably a higher temperature decomposition type radical polymerization initiator than the first radical polymerization initiator. Specifically, it is preferable to use a radical polymerization initiator having a half-life longer than that of the first radical polymerization initiator at the average temperature in step (b) as the second radical polymerization initiator. Furthermore, as the second radical polymerization initiator, a radical polymerization initiator having a longer half-life than the first radical polymerization initiator at the average temperature in step (b), and the same as the first radical polymerization initiator A radical polymerization initiator can also be used in combination. By using two kinds of radical polymerization initiators in combination, the amount of polymerization initiator necessary for obtaining the same monomer conversion rate can be reduced.

The second radical polymerization initiator can be added in multiple portions. In this case, the total of the mass ratio [ppm] of the second radical polymerization initiator to syrup supplied per unit time in each time is defined as y [ppm].

Specific examples of the reactor (B) are the same as the specific examples of the complete mixing 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. One type of reactor may be connected in series.

In the step (b), the composition containing the first syrup and the second radical polymerization initiator is heated in an appropriate condition in the reactor (B), and one monomer present in the first syrup is obtained. The part is polymerized 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 rate 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 syrup is moderately suppressed and the pressure loss when flowing in the process is reduced. The lower limit is significant in that it reduces the residual monomer and reduces the burden on the subsequent devolatilization process.

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

[Step (c)]
The step (c) in the present invention is a step for removing the methacrylic polymer by devolatilizing the second syrup obtained in the above step (b). By this step (c), the amount of residual monomer in the methacrylic polymer is reduced and the heat resistance is improved.

Step (c) can be performed, for example, by putting the second syrup into a devolatilizing extruder. The second syrup may remain at the temperature obtained in step (b) or may be further heated. When the second syrup is further heated, it is preferable that the temperature does not exceed 250 ° C. In the devolatilizing extruder, it is preferable that the second syrup is discharged under a reduced pressure of 0.0001 to 0.1 MPa to continuously separate and remove most of the volatiles mainly composed of methacrylic monomers.

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

It is preferable from the viewpoint of economy that volatiles such as unreacted methacrylic monomers are condensed and recovered by a condenser and reused as a raw material in the step (a). At this time, it is more preferable to reuse as a raw material of the step (a) after separating and removing high-boiling components such as a dimer of a methacrylic monomer contained in the volatile matter by distillation.

The methacrylic polymer thus produced can be used as a molding material, for example. In that case, if necessary, lubricants such as higher alcohols and higher fatty acid esters, ultraviolet absorbers, heat stabilizers, colorants, antistatic agents and the like can be added.

Hereinafter, the present invention will be described in more detail by way of examples, but these examples do not limit the present invention. The molecular weight of the polymer was measured by the following method.

<Measurement of molecular weight by GPC>
Tosoh HLC-8020 was used as the GPC apparatus, and two Tosoh GMHXL were used as the columns. Tetrahydrofuran (THF) was used as a solvent, a calibration curve was made using TSK standard polystyrene manufactured by Tosoh Corporation, and a solution having a concentration of 0.1 g / dl dissolved by standing was used. The weight average molecular weight Mw was determined by a GPC data processing device (data device SC-80 / 10 manufactured by Tosoh Corporation).

<Evaluation of formability>
PS-60E (manufactured by Nissei Plastic Industry Co., Ltd.) was used as a molding machine, the molding temperature was set to 300 ° C., a spiral molded body was produced, and the appearance was observed.

<Example 1>
The present invention was implemented as follows using the apparatus shown in FIG.

[Step (a)]
Nitrogen was introduced into the purified monomer mixture consisting of 98% by mass of methyl methacrylate and 2% by mass of methyl acrylate, so that the dissolved oxygen was 0.5 ppm. To this monomer mixture, 0.157 mol% (0.23 mass%) of n-octyl mercaptan as a chain transfer agent and 1,1-bis (tert-butylperoxy) 3 as a first radical initiator , 3,5-trimethylcyclohexane 2.67 × 10 ⁻⁵ mol / monomer 1 mol (80 ppm) mixed raw material composition as a first reactor 11 controlled at a polymerization temperature of 135 ° C. The mixture was continuously fed while stirring and mixing, and the polymerization was carried out with an average residence time in the reaction zone of the raw material composition of 2.5 hours to obtain a first syrup. The half-life of 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane) at this polymerization temperature (135 ° C.) is 230 seconds.

[Step (b)]
Subsequently, the first syrup is continuously extracted from the first reactor 11 by the gear pump 31, and the second radical initiator is started with an initiator charging device 21 (a pipe equipped with an SMX through the mixer manufactured by Sumitomo Heavy Industries, Ltd.). 1,1-bis (tert-butylperoxy) 3,3,5-trimethylsiloxane was added so that the mass ratio to the amount of syrup supplied per unit time was 40 ppm, and this was the second reactor 12. Polymerization was carried out by supplying the reactor to a tubular reactor (plug flow reactor) equipped with a static mixer manufactured by Noritake Campan Co., Ltd., with an inner wall temperature of 150 ° C. and an average residence time of syrup of 20 minutes. The half-life of 1,1-bis (tert-butylperoxy) 3,3,5-trimethylsiloxane at this temperature (150 ° C.) is 54 seconds.

Subsequently, the syrup polymerized in the second reactor 12 is led to an initiator charging device 22 of the same type as described above, and di-t-butyl peroxide is further added as a second radical initiator in a mass ratio with respect to the supply amount of syrup per unit time. Is added to a tubular reactor (plug flow reactor) equipped with a static mixer manufactured by Noritake Campan Co., Ltd., which is the same third reactor 13 as the second reactor 12. Then, polymerization was carried out with an inner wall temperature of 170 ° C., an internal pressure of 25 kg / cm ² G, and an average residence time of 20 minutes to obtain a second syrup. The half-life of di-t-butyl peroxide at this temperature (170 ° C.) is 250 seconds.

[Step (c)]
Next, the second syrup is continuously supplied from the outlet of the second reactor 12 to the devolatilizing extruder 14 (bent extruder type extruder) at 195 ° C., and the unreacted monomer is the main component at 270 ° C. Volatiles were separated and removed to obtain a methacrylic polymer.

When the amount of the methacrylic polymer taken out from the devolatilizing extruder 14 and the integrated amount of the raw material monomer charged were measured, the monomer conversion ratio relative to the raw material charged was 78% by mass. In addition, in the continuous operation for 360 hours, there was no problem in the control of polymerization, and in the observation in the reactor after the operation was completed, the production of deposits and foreign matters on the apparatus was not recognized. Moreover, when said moldability evaluation was performed about the obtained methacrylic polymer, presence of a bubble was not recognized but the external appearance of the molded article was favorable. The results are shown in Table 1.

<Example 2>
The amount of initiator added to the second reactor 12 [first reactor (B)] was changed to 60 ppm, and the amount of initiator added to the third reactor 13 [second reactor (B)] was changed to 60 ppm. Except that, the same operation as in Example 1 was performed. When the amount of the methacrylic polymer taken out from the devolatilizing extruder 14 and the integrated amount of the raw material monomer charged were measured, the monomer conversion rate relative to the raw material charged was 80% by mass. In addition, in the continuous operation for 360 hours, there was no problem in the control of polymerization, and in the observation in the reactor after the operation was completed, the production of deposits and foreign matters on the apparatus was not recognized. Moreover, when said moldability evaluation was performed about the obtained methacrylic polymer, presence of a bubble was not recognized but the external appearance of the molded article was favorable. The results are shown in Table 1.

<Example 3>
The amount of methyl methacrylate in the monomer mixture was changed to 85% by mass, the amount of methyl acrylate was changed to 15% by mass, and the amount of initiator added to the second reactor 12 [first reactor (B)] was 20 ppm. The same operation as in Example 1 was performed except that the amount of initiator added to the reactor 13 [second reactor (B)] was changed to 15 ppm. When the amount of the methacrylic polymer taken out from the devolatilizing extruder 14 and the integrated amount of the raw material monomer charged were measured, the monomer conversion rate relative to the raw material charged was 73% by mass. In addition, in the continuous operation for 360 hours, there was no problem in the control of polymerization, and in the observation in the reactor after the operation was completed, the production of deposits and foreign matters on the apparatus was not recognized. Moreover, when said moldability evaluation was performed about the obtained methacrylic polymer, presence of a bubble was not recognized but the external appearance of the molded article was favorable. The results are shown in Table 1. The results are shown in Table 1.

<Example 4>
The amount of initiator added to the second reactor 12 [first reactor (B)] was changed to 60 ppm, and the amount of initiator added to the third reactor 13 [second reactor (B)] was changed to 60 ppm. Except that, the same operation as in Example 3 was performed. When the amount of the methacrylic polymer taken out from the devolatilizing extruder 14 and the integrated amount of the raw material monomer charged were measured, the monomer conversion rate with respect to the raw material charged was 77% by mass. In addition, in the continuous operation for 360 hours, there was no problem in the control of polymerization, and in the observation in the reactor after the operation was completed, the production of deposits and foreign matters on the apparatus was not recognized. Moreover, when said moldability evaluation was performed about the obtained methacrylic polymer, presence of a bubble was not recognized but the external appearance of the molded article was favorable. The results are shown in Table 1.

<Example 5>
The amount of initiator added to the second reactor 12 [first reactor (B)] was changed to 100 ppm, and the amount of initiator added to the third reactor 13 [second reactor (B)] was changed to 100 ppm. Except that, the same operation as in Example 3 was performed. When the amount of the methacrylic polymer taken out from the devolatilizing extruder 14 and the integrated amount of the raw material monomer charged were measured, the monomer conversion rate relative to the raw material charged was 83% by mass. In addition, in the continuous operation for 360 hours, there was no problem in the control of polymerization, and in the observation in the reactor after the operation was completed, the production of deposits and foreign matters on the apparatus was not recognized. Moreover, when said moldability evaluation was performed about the obtained methacrylic polymer, presence of a bubble was not recognized but the external appearance of the molded article was favorable. The results are shown in Table 1.

<Comparative Example 1>
The amount of initiator added to the second reactor 12 [first reactor (B)] was changed to 20 ppm, and the amount of initiator added to the third reactor 13 [second reactor (B)] was changed to 15 ppm. Except that, the same operation as in Example 1 was performed. When the amount of the methacrylic polymer taken out from the devolatilizing extruder 14 and the integrated amount of the charged raw material monomer were measured, the monomer conversion rate with respect to the charged raw material was as low as 68% by mass, and the amount of resin obtained per unit time was small. Less. The results are shown in Table 1.

<Comparative Example 2>
Example 3 except that the amount of initiator added to the second reactor 12 [first reactor (B)] and the third reactor 13 [second reactor (B)] was changed to no addition. The same operation was performed. When the amount of the methacrylic polymer taken out from the devolatilizing extruder 14 and the integrated amount of the raw material monomer charged were measured, the monomer conversion rate with respect to the raw material charged was as low as 50% by mass, and the amount of resin obtained per unit time was small. Less. The results are shown in Table 1.

<Comparative Example 3>
The amount of initiator added to the second reactor 12 [first reactor (B)] was changed to 80 ppm, and the amount of initiator added to the third reactor 13 [second reactor (B)] was changed to 80 ppm. Except that, the same operation as in Example 1 was performed. When the amount of the methacrylic polymer taken out from the devolatilizing extruder 14 and the integrated amount of the raw material monomer charged were measured, the monomer conversion rate relative to the raw material charged was 83% by mass. In addition, in the continuous operation for 360 hours, there was no problem in the control of polymerization, and in the observation in the reactor after the operation was completed, the production of deposits and foreign matters on the apparatus was not recognized. However, when the above methacrylic polymer was evaluated for the moldability as described above, the presence of bubbles was recognized, and the appearance of the molded product contained a white band called silver, resulting in poor molding. The results are shown in Table 1.

<Comparative Example 4>
The amount of initiator added to the second reactor 12 [first reactor (B)] was changed to 150 ppm, and the amount of initiator added to the third reactor 13 [second reactor (B)] was changed to 150 ppm. Except that, the same operation as in Example 3 was performed. When the amount of the methacrylic polymer taken out from the devolatilizing extruder 14 and the integrated amount of the raw material monomer charged were measured, the monomer conversion rate relative to the raw material charged was 90% by mass. In addition, in the continuous operation for 360 hours, there was no problem in the control of polymerization, and in the observation in the reactor after the operation was completed, the production of deposits and foreign matters on the apparatus was not recognized. However, when the above methacrylic polymer was evaluated for the moldability as described above, the presence of bubbles was recognized, and the appearance of the molded product contained a white band called silver, resulting in poor molding. 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.

Abbreviations in the table are as follows.
"MMA": methyl methacrylate,
"MA": methyl acrylate,
"I": 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane,
・ "Ha": di-t-butyl peroxide,
・ "F": n-octyl mercaptan

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

11 First Reactor 12 Second Reactor 13 Third Reactor 14 Devolatilizing Extruder 21 Initiator Charger 22 Initiator Charger 31 Gear Pump

Claims

A monomer containing methyl methacrylate alone or an alkyl (meth) acrylate other than methyl methacrylate and methyl methacrylate is supplied to the fully mixed reactor (A), and polymerization is performed with the first radical polymerization initiator, and the first syrup is formed. Obtaining step (a),
Step (b) of supplying a first syrup and a second radical polymerization initiator to a reactor (B) arranged downstream of the fully mixed reactor (A) to carry out polymerization to obtain a second syrup. And (c) devolatilizing the second syrup
In order to produce a methacrylic polymer,
The content of alkyl (meth) acrylate other than methyl methacrylate in the monomer is x [mass%], and the second radical polymerization per unit time with respect to the first syrup supply amount per unit time in the reactor (B). A method for producing a methacrylic polymer, wherein x and y satisfy the following formula when the mass ratio of the initiator supply amount is y [ppm].
8.5x + 123 ≧ y ≧ −2.6x + 45
The methacrylic monomer according to claim 1, wherein the monomer fed to the complete mixing reactor (A) comprises 80 to 99.5% by mass of methyl methacrylate and 0.5 to 20% by mass of alkyl (meth) acrylate other than methyl methacrylate. A method for producing a polymer.