SG177832A1

SG177832A1 - Devolatilizing extruder, and devolatilizing extrusion method of polymer composition using the same and method of producing methacrylic polymer

Info

Publication number: SG177832A1
Application number: SG2011049749A
Authority: SG
Inventors: Sumida Masakazu; Yamazaki Kazuhiro; Nishitani Akira
Original assignee: Sumitomo Chemical Co
Priority date: 2010-07-08
Filing date: 2011-07-07
Publication date: 2012-02-28
Also published as: KR20120005410A; CN102371664B; CN102371664A; JP4995948B2; JP2012016886A

Abstract

DEVOLATILIZING EXTRUDER, AND DEVOLATILIZING EXTRUSION METHOD OF POLYMER COMPOSITION USING THE SAME AND METHOD OF 5 PRODUCING METHACRYLIC POLYMERThe present invention provides a devolatilizingextruder which can suppress contamination of a polymer composition and a methacrylic polymer to be produced.10 Disclosed is a devolatilizing extruder comprising.: cylinder 10 having a polymer composition supply port 12, a gas discharge port 14, a polymer outlet 16 and a through-hole 18; a rotatable screw 20 inserted into the cylinder 10 through the through-hole 18; and a shaft seal bear15 portion 30 supporting a shaft portion 20a of the screw 20 extending from the through-hole 18 to the outside of the cylinder 10; wherein a shaft seal portion 32 of the shaftseal bearing portion 30 is formed of a mechanical seal using at least one kind selected from the group consisting20 of an adipate ester, a phthalate ester, a diisobutyrate ester and acetylated glyceride as a mechanical seal liquid.Figure 1

Description

DESCRIPTICN

DEVOLATILIZING EXTRUDER, AND DEVOLATILIZING EXTRUSION

METHCD OF POLYMER COMPOSITION USING THE SAME AND METHOD OF

PRODUCING METHACRYLIC POLYMER

Technical Field

[0001]

The present invention relates to a devolatilizing extruder to be used in a production of a methacrylic polymer, and a method for devolatilizing extrusion of a polymer composition using the same, and a method for producing a methacrylic polymer.

Background Art

[0002]

There have been known, as a method for producing a polymer such as a methacrylic polymer, methods in which a polymer composition containing a methacrylic polymer and a volatile component is cbtained by a solution polymerization method or a bulk polymerization method, and then the obtained polymer composition is supplied to a screw type devolatilizing extruder to remove a volatile component, thus cbtaining a methacrylic polymer (see, for example,

Patent Documents 1 and 2).

[0003]

A screw inserted into a devolatilizing extruder used _ 1 —

in the aforementioned method is supported by a shaft seal bearing portion of a deveolatilizing extruder, and a shaft seal portion is provided around a screw in the shaft seal bearing portion. Various types of seal structures are known as a seal structure that forms this shaft seal portion, and a mechanical seal is known as one of typical seal structures.

Pricer Art Documents

Patent Documents

[0604]

Patent Document 1: JP-A-3-49925

Patent Document 2: JP-A-2003-96105

Disclosure of the Invention

Problems tc be Solved by the Invention

[0005]

In a mechanical seal, a mechanical seal liguid is used as a lubricating liquid of a sealing face. Therefore, a conventional devolatilizing extruder using the mechanical seal had a problem that a part of the mechanical seal liquid leaks out through a shaft seal portion when an operation is continuously carried out over a leng period and thus a polymer composition and a methacrylic pelymer to be produced may be contaminated. When the polymer composition and the methacrylic polymer to be produced are contaminated, there arises a problem that transparency of a methacrylic polymer deteriorates and the methacrylic polymer is likely to be colored during molding.

[0006]

In light of the problems of the prior art, the present invention has been made and an object thereof is to provide a devolatilizing extruder that can suppress contamination of a polymer composition and a methacrylic polymer to be produced, and a method for devolatilizing extrusion of a polymer composition using the same, and a methed for producing a methacrylic polymer.

Means for Solving the Problems

[0007]

In order to achieve the aforementioned object, the present invention provides a devolatilizing extruder for producing a methacrylic polymer, including a cylinder that includes a polymer composition supply port, a gas discharge port, a polymer outlet and a through-hole; a rotatable screw inserted into the cylinder through the through-hole; and a shaft seal bearing portion that supperts a shaft portion of the screw extending from the through-hole to the cutside of the cylinder; wherein the shaft seal portion of the shaft seal bearing portion is formed of a mechanical seal using at least one kind selected from the group consisting of an adipate ester, a phthalate ester, a diisobutyrate ester and acetylated glyceride as a mechanical seal liquid.

[0008]

At least one kind selected from the group consisting of an adipate ester, a phthalate ester, a diisobutyrate ester and acetylated glyceride, used as the aforementioned mechanical seal liquid, has a property of being less likely to exert an adverse influence such as deterioration of transparency of a methacrylic polymer or coloration during molding even if mixed in a polymer composition. Therefore, in the aforementioned devolatilizing extruder, since a shaft seal portion is formed of a mechanical seal and also at least one kind selected from the group consisting of an adipate ester, a phthalate ester, a diisobutyrate ester and acetylated glyceride is used as a mechanical seal liquid, it is possible to suppress contamination of a polymer composition and a methacrylic polymer to be produced even if the mechanical seal liquid leaks out into a cylinder by a continuous operation over a long period. Accordingly, according to the aforementioned devolatilizing extruder, it is possible to efficiency produce a methacrylic polymer whose contamination has been suppressed even if an operation is continuously carried out over a long period.

[0009]

The present invention also provides a method for devolatilizing extrusion of a polymer compositien, which includes supplying a polymer composition containing a methacrylic polymer and a volatile component into the cylinder through the polymer composition supply port in the develatilizing extruder of the present invention; and then discharging the volatile component through the gas discharge port and discharging a methacrylic polymer after devolatilization through the polymer outlet, respectively.

[0010]

According to such the devolatilizing extrusion method, since the aforementioned devolatilizing extruder of the present invention is used, contamination of a polymer composition and a methacrylic polymer to be produced can be suppressed. Therefore, according to the aforementioned devolatilizing extrusion method, it is possible to efficiency produce a methacrylic polymer whose contamination has been suppressed even if an operation is continuously carried out over a long period. [00111

The present invention further provides a method for producing a methacrylic polymer, which include the steps of continuously supplying a raw material that contains a monomer component containing a methacrylic monomer as a main component, a radical polymerization initiator and a chain transfer agent into a polymerization reaction vessel;

polymerizing the monomer component in the polymerization reaction vessel to obtain a polymer composition that contains a methacrylic polymer and a volatile component containing an unreacted monomer; and supplying the polymer composition inte the cylinder through the polymer composition supply port in the devolatilizing extruder according to claim 1, and then discharging the volatile component through the gas discharge port and discharging a methacrylic polymer after devolatilization through the polymer outlet, respectively.

[0012]

According to such the methacrylic a method for producing a polymer, since the aforementioned devolatilizing extruder of the present invention is used, contamination of a polymer composition and a methacrylic polymer to be produced can be suppressed. Therefore, according to the aforementioned devolatilizing extrusion method, it is possible to efficiency produce a methacrylic polymer whose contamination has been suppressed even if an operation is continuously carried out over a long period.

Effects of the Invention

[0013]

According to the present invention, it is possible to provide a devolatilizing extruder that can suppress contamination of a polymer composition and a methacrylic polymer to be produced, and a method for devolatilizing extrusion of a polymer composition using the same, and a method for producing a methacrylic polymer.

Brief Descripticn of the Drawings

[0014]

Fig. 1 is a schematic view showing an internal structure of a devolatilizing extruder according to preferred embodiment of the present invention.

Fig. 2 is a partial sectional view of a shaft seal bearing portion of a devolatilizing extruder according to preferred embodiment of the present invention.

Fig. 3 is a schematic block diagram showing a production system of a methacrylic polymer using a devolatilizing extruder of the present invention.

Mode for Carrying Out the Invention

[0015]

Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same numerals are used for the same or identical portions in the drawings, and repetitive descriptions are omitted. Also, dimensional ratios of the drawings are not limited to the illustrated ratios.

[0016]

Fig. 1 is a schematic view showing an internal structure of a devolatilizing extruder according to preferred embodiment of the present invention. As shown in

Fig. 1, a devolatilizing extruder 100 is provided with a cylinder 10 including a polymer composition supply port 12 for supplying a polymer composition centaining a methacrylic polymer and a volatile compenent, a gas discharge port 14 for discharging a volatile component, a polymer outlet 16 for discharging a methacrylic polymer after devolatilization, and a through-hole 18; a rotatable screw 20 inserted into the cylinder 10 through the through- hole 18; and a shaft seal bearing portion 30 that supports a shaft portion 20a of the screw 20 extending from the through-hole 18 to the outside of the cylinder 10. The cylinder 10 is provided with four gas discharge ports 14, and one gas discharge port (back vent) 14a is provided at the side of the shaft seal bearing portion 30 when viewed from the polymer composition supply port 12, and three gas discharge ports (fore vents) l4b, ld4c, 14d are respectively provided at the side of the polymer outlet 16. The shaft seal bearing portion 30 includes a shaft seal portion 32.

[0017]

Fig. 2 is a partial sectional view of a shaft seal bearing portion of a devolatilizing extruder according to preferred embodiment of the present invention. As shown in

Fig. 2, a shaft seal portion 32 is formed of a mechanical seal. A driving device (not shown) for rotationally driving the screw 20 is provided on the opposite side of the shaft seal portion 32.

[0018]

There is no particular limitation on the type of the mechanical seal that form the shaft seal portion 32, and a known type mechanical seal can be used. For example, as shown in Fig. 2, the mechanical seal includes a rotating ring 32a fixed on the side of a screw 20 and a fixed ring 32b fixed on the side of a shaft seal bearing portion body (casing), and is constituted so that the rotating ring 32a and the fixed ring 32b are pressed by a given force using a spring {not shown) or the like and thus they tightly adhere to each other. In order to decrease friction of a contact surface between the rotating ring 32a and the fixed ring 32b, a mechanical seal liquid 32c¢ is filled into the mechanical seal 32. In Fig. 2, a constitution of a mechanical seal including two palr of combinations of the rotating ring 32a and the fixed ring 32b, namely, a double mechanical seal is shown. Usually, the mechanical seal liquid 32c¢c is continuously supplied through a mechanical seal liguid introduction port (not shown) using a pump Or the like, and then continuously discharged through a mechanical seal liguid discharge port (not shown}. It is preferred that the mechanical seal liquid is circulatorily supplied. The filling pressure 1s appropriately set according to the size, extrusion conditions and the like of the devolatilizing extruder, and is set to a pressure higher than that of the gas discharge port 14a of the devolatilizing extruder 100. Since the devolatilizing extruder is provided with a pressure gauge and a safety valve according to a maximum working pressure, the filling pressure is adjusted so that the safety valve does not operate.

[0019]

As the mechanical seal liguid 32¢, at least one kind selected from the group consisting of an adipate ester, a phthalate ester, a diisobutyrate ester and acetylated glyceride is used. Examples of the adipate ester include bis (2-ethylhexyl) adipate, diiscnonyl adipate, diisodecyl adipate and the like. Examples of the phthalate ester include bis (2-ethylhexyl) phthalate, diisononyl phthalate, diisodecyl phthalate and the like. Examples of the diisobutyrate ester include 2,2,4-trimethyl-1,3-pentanedicl diisobutyrate and the like. Examples of the acetylated glyceride include glycerin diacetomonolaurate, glycerin diacetomonostearate, glycerin diacetomonooleate, glycerin diacetomonolinoleate, glycerin diacetomono 12- hydroxystearate, glycerin diacetomonomyristate, glycerin diacetomonopalmitate, glycerin monoacetomcnostearate, glycerin monocacetomonomyristate, glycerin moncacetomonopalminate, glycerin monocacetomonoricinoleate, glycerin monoacetomono l1l2-hydroxystearate, glycerin monoacetomonobehenate, glycerin monoacetomonooleate, glycerin monoacetomonolaurate, glycerin monoacetodioleate, glycerin monoacetodiricincleate, glycerin monoacetodicaprylate, glycerin monoacetodilaurate, glycerin monoacetodistearate and the like. Among these, an adipate ester and a diisobutyrate ester are preferred, and an adipate ester is particularly preferred. The adipate ester, phthalate ester, diisobutyrate ester and acetylated glyceride have a merit that they do not accelerate a polymerization reaction of a monomer containing an unreacted methacrylic monomer as a main component even if mixed in a polymer composition, and are also less likely to cause an adverse influence such as coloration of the obtained methacrylic polymer.

[0020]

There is no particular limitation on the material of the rotating ring 32a and the fixed ring 32b, and these rings may be constituted from a known material. Examples of the material of the rotating ring 32a and the fixed ring 32b include carbon, silicon carbide, cemented carbide, chromium oxide coating and the like.

[0021]

In the devolatilizing extruder 100, a polymer composition is supplied through a polymer composition supply port 12. At this time, the liquid polymer composition is converted into a vapor mist by adjusting the pressure in the vicinity of the polymer composition supply port 12 and at least a part of the volatile component contained in the polymer composition is discharged through gas discharge ports 14a, 14b close to the polymer composition supply port 12. The polymer composition goes forward to the side of the polymer outlet 16 by rotation of the screw 20 and most of the volatile component contained in the polymer composition is vaporized until the polymer composition reaches the polymer outlet 16, and then is discharged through gas discharge ports 14b, lic, 14d. In additicen to the unreacted monomer, a solvent and additives used optionally and a volatile by-product produced during the polymerization process are contained in the volatile component that is discharged through the gas discharge port 14. Thus, it is possible to obtain a methacrylic polymer after devolatilization, in which most of the volatile compcenent has been removed, through the polymer outlet 16.

The methacrylic polymer can be obtained, for example, in a state of pellets.

[0022]

The aforementioned devolatilizing extruder 100 can be suitably used to produce a methacrylic polymer that is obtained by polymerizing a monomer mixture containing methyl methacrylate as a main component among methacrylic polymers. {00231

In the devolatilizing extruder 100, there is no particular limitation on the number of gas discharge ports 14 formed in the cylinder 10. While the constriction in which four gas discharge ports 14 are provided was described in Fig. 1, the number of gas discharge ports 14 may be from 1 to 3, or 5 or more. From the viewpoint of efficiently discharging the volatile component in the polymer composition, the cylinder 10 preferably includes one or more of gas discharge ports (back vents) provided between the polymer composition supply port 12 and the shaft seal bearing portion 30, and one or more of gas discharge ports (fore vents) provided between the polymer composition supply port 12 and the polymer outlet 16, and more preferably one back vent and one to three fore vent.

[0024]

There is no particular limitation on the number of screws 20 used in the devolatilizing extruder 100. The number of screws is preferably one to two, and more preferably two. A twin-screw devolatilizing extruder including two screws 20 is preferred since a methacrylic polymer can be efficiently produced. There is no particular limitation on the diameter of the screw 20, and is usually from 9l00 to 450 mm.

[06025]

The method for devolatilizing extrusion of a polymer composition and the method for producing a methacrylic polymer of the present invention will be described below.

[0026]

The method for producing a methacrylic polymer of the present invention is a method comprising: a step of continuously supplying a raw material containing a monomer component containing as a main component a methacrylic monomer, a radical polymerization initiator and a chain transfer agent into a polymerization reaction vessel; a step of polymerizing the monomer component in the polymerization reaction vessel to obtain a polymer composition containing a methacrylic polymer and a volatile component containing an unreacted monomer; and a step of supplying the polymer composition into a cylinder through a polymer composition supply port in the devolatilizing extruder of the present invention to discharge the volatile component through the gas discharge port and to discharge the methacrylic polymer after devolatilization through a polymer outlet , respectively. The respective steps will be described in detail below.

[0027]

Fig. 3 is a schematic block diagram showing a production system of a methacrylic polymer. As shown in

Fig. 3, first, an initiator composition and a monomer compositicn are blended in an initiator blending vessel 101 and a moncmer blending vessel 102, respectively. The initiator compositicn is prepared by mixing a radical polymerization initiator, a monomer component containing as a main component a methacrylic monomer and a chain transfer agent. The monomer compesition is prepared by mixing a monomer and a chain transfer agent. Then, the blended initiator composition and moncmer composition are continuously supplied to a polymerization reaction vessel 103, where a polymerization reaction is carried out.

[0028]

Herein, the monomer component containing as a main component a methacrylic monomer, the radical polymerization initiator and the chain transfer agent are selected according to a methacrylic polymer to be produced. Fach component will be described below as preferred embodiment.

In the present description, “(meth)acryl” means “acryl” and “methacryl” corresponding thereto.

[0029]

The moncmer component containing a methacrylic moncmer as a main component is a methacrylic monomer alone, or a mixture of a methacrylic monomer and the other monomer that is copolymerizable with the methacrylic monomer. When the monomer other than the methacrylic monomer is mixed, the content of the methacrylic monomer is 50% by mass or more, and preferably 75% by mass or more, based on the entire monomer amount.

[0030]

There is no particular limitation on the methacrylic monomer, and examples thereof include alkyl methacrylate (an alkyl group has 1 to 4 carbon atoms). Examples of the alkyl of the alkyl methacrylate (an alkyl group has 1 to 4 carbon atoms) include methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl and the like and, among alkyl methacrylates, methyl methacrylate is preferred. These methacrylic monomers can be used alone, or two or more kinds of them can be used in combination. When two or more kinds of them are used in combination, the monomer component centaining the methacrylic monomer as a main component is a mixture of two or more kinds of methacrylic monomers, or a mixture of two or more kinds of methacrylic moncmers and the other monomer that is copolymerizable with the methacrylic monomer. When two or more kinds of methacrylic monomers are mixed with the other monomer that is copolymerizable with the methacrylic monomer, the total content of two or more kinds of methacrylic monomers is 50% by mass or more, and preferably 75% by mass or more , based on the entire monomer amount.

[0031]

Examples of the other monomer, which can be used in combination with the methacrylic monomer, include other vinyl monomer that is copolymerizable with the methacrylic monomer. Examples of the other vinyl monomer include alkyl acrylates having an alkyl group of 1 to 18 carbon atoms, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate and stearyl acrylate; unsaturated carboxylic acids and acid anhydrides thereof, such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, maleic anhydride and itaconic anhydride; hydroxyl group-containing monomers such as 2- hydroxyethyl acrylate, 2-hydroxypropyl acrylate, monoglycerol acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate and monoglycerol methacrylate; nitrogen-containing monomers such as acrylamide, methacrylamide, acrylonitrile, methacrylenitrile, diacetoneacrylamide and dimethylaminoethyl methacrylate; epoxy group-containing monomers such as allyl glycidyl ether, glycidyl acrylate and glycidyl methacrylate; and styrenic monomers such as styrene and o-methylstyrene.

[0032]

In the present invention, examples of the polymerization initiator to be supplied to a reaction vessel include a radical polymerization initiator.

Examples of the radical polymerization initiator include azo compounds such as azcbisisobutyronitrile, azobisdimethylvaleronitrile, azobiscyclohexanenitrile, 1,1’ -azobis (l-acetoxy-1l-phenylethane), dimethyl 2,2'- azobisisobytylate and 4,4'-azobis-4-cyanovaleric acid; and organic peroxides such as benzoyl peroxide, lauroyl peroxide, acetyl percxide, capryl peroxide, 2,4- dichlorobenzoyl peroxide, isobutyl peroxide, acetylcyclohexylsulfonyl peroxide, t-butyl peroxypivalate, t-butylperoxy-2-ethyl hexanocate, 1,1-di-t- butylperoxycyclohexane, 1,l-di-t-butylperoxy-3,3,5- trimethylcyciochexane, 1,1l-di-t-hexylperoxy-3,3,5- trimethylcyclohexane, isopropyl peroxydicarbonate, isobutyl peroxydicarbonate, s-butyl peroxydicarbonate, n-butyl peroxydicarbonate, 2-ethylhexyl peroxydicarbonate, bis (4-t- butylcyclohexyl) peroxydicarbonate, t-amylperoxy-Z-ethyl hexanoate, 1,1,3,3-tetramethylbutyl percxy-ethyl hexanoate, 1,1,2-trimethylpropyl peroxy-2-ethylhexanoate, t-butyl peroxyisopropyl monocarbonate, t-amyl peroxyisopropyl monocarbonate, t-butyl peroxy-2-ethyl hexylcarbonate, t- butyl peroxvyallyl carbonate, t-butyl peroxyiscpropyl carbonate, 1,1,3,3-tetramethylbutyl peroxyisopropyl monocarbonate, 1,1,2-trimethylpropyl peroxylsopropyl monocarbonate, 1,1,3,3-tetramethylbutyl percxyisononanocate,

1,1,2-trimethylpropyl peroxyisononancate and t-butyl peroxybenzoate. These polymerization initiators may be used alone, or a mixture of two or more kinds may be used.

[0033]

There is no particular limitation on the blend amount of the radical polymerization initiator, and the blend amount is usually from 0.001 to 1 part by mass based on 100 parts by mass of the monomer component as a raw material.

When a mixture of two or more kinds of radical polymerization initiators is used, the total used amount may be within this range. The polymerization initiator supplied intc the reaction vessel is selected according to the methacrylic polymer to be produced and the kind of a raw monomer component used and is not particularly limited in the present invention. For example, the radical polymerization initiator is preferably a radical pclymerization initiator in which a half-life at a polymerization temperature is within 1 minute. When the half-life at the polymerization temperature is more than 1 minute, the reaction rate decreased, and thus the radical polymerization initiator may be unsuited for the polymerization reaction in a continuous polymerization device. A relationship between the temperature of the radical polymerization initiator and the half-life is described in various documents and technical data of manufacturers for each kind of the radical polymerization initiator. In the present invention, values described in a known products catalog of Wako Pure Chemical Industries,

Ltd., KAYAKU AKZO CO., LTD. or the like were used.

[0034]

In the present invention, a chain transfer agent can be blended in a reaction vessel so as to adjust the molecular weight of the methacrylic polymer to be produced.

The chain transfer agent may be either a monofunctional or pelyfunctional chain transfer agent. Specific examples thereof include alkylmercaptans such as propylmercaptan, butylmercaptan, hexylmercaptan, cctylmercaptan, 2- ethylhexylmercaptan and dodecylmercaptan; aromatic mercaptans such as phenylmercaptan and thioccresol; mercaptans having not more than 18 carbon atoms, such as ethylene thioglycel; polyhydric alcchcls such as ethylene glycol, neopentyl glycol, trimethylclpropane, pentaerythritol, dipentaerythritol, tripentaerythritol and sorbitol; those obtained by esterifying a hydroxyl group with thioglyecclic acid or 3-mercaptopropionic acid, 1,4- dihydronaphthalene, 1,4,5,8-tetrahydronaphthalene, £- terpinene, terpinolene, 1,4-cyclohexadiene, hydrogen sulfide and the like. These chain transfer agents may be used alone, or two or more kinds may be used in combination.

[0035]

Since the blend amount of the chain transfer agent varies depending on the kind of the chain transfer agent used and the like, there is no particular limitation on the blend amount. For example, when mercaptans are used, the blend amount is preferably from (0.01 to 3 parts by mass, and more preferably from 0.05 to 1 part by mass, based on 100 parts by mass of the monomer component as a raw material. The use amount within this range is preferred since thermostability is satisfactorily maintained without impairing mechanical properties of the methacrylic polymer.

When two or more kinds of chain transfer agents are used in combination, the total use amount may be adjusted within this range.

[00386]

A polymerization reaction vessel 103 used in the present embodiment is a vessel type reactor equipped with a stirrer. The stirrer enables a solution in a vessel to convert into a substantially completely mixed state. It is possible to use, as a stirring impeller, a Maxblend impeller manufactured by Sumitomo Heavy Industries, Ltd., a paddle impeller, a double helical ribbon impeller, an MIG impeller, a full zone impeller manufactured by Shinko

Pantech Co Ltd. and the like, however, there is no particular limitation. It is preferred to attach a buffle so as to increase the stirring effect.

[0037]

As a matter of course, it is preferred that the stirring efficiency is as high as possible. The stirring power that is more than the necessity is not preferred since only surplus heat is applied to a reaction vessel.

Therefore, the stirring power is from 0.5 to 20 kW/m’, and preferably from 1 to 15 kW/m’. It is necessary that this stirring power is increased as the viscosity of a content liguid, namely, the content of the pelymer becomes larger.

[0038]

The polymerization reaction vessel 103 is preferably in a state of being filled with a liquid, which is substantially free from a vapor phase. When the polymerization reaction vessel is in a state of being filled with a liquid, adhesion and production of the polymer on a vapor phase porticn and a vessel inner wall face as a gas-liquid interface are suppressed, and thus deterioration in quality due to mixing of them in the product can be suppressed. Moreover, since the entire volume of the polymerization reaction vessel 103 can be effectively utilized, productivity can be improved.

[0039]

In order to fill the polymerization reaction vessel 103 with a liquid, it is most simple to dispose an outlet of a solution in a vessel on the top portion of a reaction vessel. In this case, a supply port of a raw material (an initiator composition and a monomer composition) is preferably provided at the lower portion of the polymerization reaction vessel 103. It is desired to prevent a gas of a monomer from generating in the polymerization reaction vessel 103. For that purpose, it is preferred to adjust the pressure in the vessel to a vapor pressure or more at a temperature of a content liquid.

This pressure is generally from about 10 to 20 kg/cm? . 1¢C [0040]

The interior of the pclymerization reaction vessel 103 is preferably in an insulated state that is substantially free from infilow/outflow of heat from the outside. Namely, it is preferred to adjust the temperature in the reaction vessel and the temperature on the side of the reaction vessel outer wall face tc about the same temperature. Specifically, a jacket 1s disposed, for example, at the side of the reaction vessel cuter wall face and the temperature of the reaction vessel outer wall is allowed to follow the temperature in the reaction vessel using steam, other heat medium or the like, and thus nearly the same temperature can be achieved.

[0041]

The polymerization reaction vessel 103 is kept in an a) insulated state since a formation of a polymer on the reaction vessel inner wall face can be prevented and self- controllability of being capable of suppressing a runaway reaction by stabilizing the polymerization reaction is imparted. It is not preferred to adjust the temperature of the reaction vessel inner wall face to a temperature that is excessively higher than that of the content liquid since surplus heat is applied to the interior of the reaction vessel. It is preferred that a temperature difference between the interior of the reaction vessel and the reaction vessel outer wall is as small as possible.

However, the temperature may be actually adjusted to a variation within a range of about *5°C.

[0042]

In the present embodiment, heat generated in the polymerization reaction vessel 103, namely, polymerization heat and stirring heat is preferably well-balanced with guantity of heat taken by a liquid (syrup-like) pclymer composition that is discharged from the polymerization reaction vessel 103. Quantity of heat taken by the polymer composition is determined by the amount, specific heat and temperature (polymerization temperature) of the polymer composition.

[0043]

The polymerization temperature varies depending on the kind of the radical polymerization initiator used and w 24 -

is preferably from about 120 to 180°C, and more preferably from 130 te 180°C. When this temperature is too high, the obtained methacrylic polymer exhibits low syndiotacticity, and thus the amount of oligomer produced may increase and heat resistance of the resin may deteriorate.

[0044]

The average residence time in the polymerization reaction vessel 103 is preferably not less than 15 minutes nor more than 2 hours, and more preferably not less than 20 minutes nor more than 1.5 hours. When the average residence time is longer than the necessity, the amcunt of an oligomer such as dimer or trimer produced increases and thus heat resistance of the product may detericrate. The average residence time can be adjusted by changing the supply amount of the monomer per unit time.

[0045]

Tt is possible to use, as the initiator blending vessel 101 and the monomer blending vessel 102 used in the present embodiment, a blending vessel equipped with the same stirrer as that of the aforementioned olymerization reaction vessel 103. In the initiator blending vessel 101, a radical polymerization initiator is completely dissolved in a monomer to obtain an initiator soluticn. The temperature in the initiator blending vessel 101 is mainatiend at a temperature at which a polymerization reaction does not proceed, and preferably maintained at -20 to 10°C. In contrast, the temperature in the monomer blending vessel 102 is mainatiend at a temperature at which the monomer is not volatilized, and is preferably maintained at -20 to 10°C. An initiator compcsition and a monomer composition as raw materials of the methacrylic polymer are continuously supplied into the polymerization reaction vessel 103 from the initiator blending vessel 101 and the monomer blending vessel 102 by a pump or the like.

[0046]

The amount of the initiator composition supplied from the initiator blending vessel 101 to the polymerization reaction vessel 103 varies depending on the capacity or the like of the polymerization reaction vessel 103 and the amount is, for example, preferably from 0.1 te 10 kg/hr, and more preferably from 0.5 to 5 kg/hr, when the capacity of the polymerization reaction vessel 103 is 10 L. The amount of the monomer composition supplied from the monomer blending vessel 102 to the polymerization reactlon vessel 103 varies dependging on the capacity or the like of the pclymerization reaction vessel 103 and the amount is, for example, preferably from 4 to 40 kg/hr, and more preferably from 10 to 30 kg/hr, when the capacity of the polymerization reaction vessel 103 is 10 L.

[0047]

There may be used, as the monomer blended in the monomer blending vessel 102, not only a fresh monomer, but also a monomer separated and recovered in an unreacted state as shown in Fig. 3. When the monomer is blended, it is common that an inert gas is bubbled into the monomer blending vessel 102 or dissolved oxygen is removed by pressure reducing deaeration, so as te prevent an influence by dissolved oxygen. In the method of the present embodiment, it is not necessarily required to strictly remove dissolved oxygen, and a polymerization reaction can be stably carried out even though about 1.5 to 3 ppm of dissolved oxygen exist. When the blended monomer composition is supplied into the pclymerization reaction vessel 103, it is particularly preferred te filter with a filter having an appropriate size selected according to the purposes so as to remove foreign matters in the case of using the obtained methacrylic polymer in the material for an optical equipment.

[0048]

In the method for producing a methacrylic polymer of the present embodiment, as described above, an initiator composition and a monomer composition as raw materials of the methacrylic polymer are continuously supplied into the polymerization reaction vessel 103 from the initiator blending vessel 101 and the monomer blending vessel 102,

and then at least a part of a monomer is polymerized in the polymerization reaction vessel 103 to obtain a polymer composition containing the methacrylic polymer and the unreacted monomer. In the polymerization reaction vessel 103, a pelymerization method ¢f the methacrylic polymer may be either a bulk polymerization using no sclvent or a solution polymerization using a solvent, and a bulk polymerization method is particularly preferred.

[0049]

The polymerization is carried cut by a continuous solution pelymerization method in the same manner as in the aforementioned continuous bulk polymerization method, except that the solvent is used in the polymerization reaction. The solvent used in the polymerization reaction may be appropriately set according to a raw monomer component of the continuous solution polymerization reaction or the like and is not particularly limited, and examples thereof include toluene, xylene, ethylbenzene, methyl iscbutyl ketone, methyl alcohol, ethyl alcohol, octane, decane, cyclohexane, decalin, butyl acetate, pentyl acetate and the like. Among these solvents, toluene, methanol, ethylbenzene and butyl acetate are preferred.

The solvent can be added to one or both of an initiator composition and a monomer composition. There is no particular limitation on the proportion of the solvent, and the proportion is preferably from 5 to 30% by mass, and more preferably from 1 to 20% by mass, based on the entire polymer composition.

[0050]

The content of the polymer in the polymer composition is preferably from 40 to 70% by mass. When the content of the polymer is tco high, efficiency of mixing and heat transfer may decrease and thus stability may become worse.

In contrast, when the content of the polymer is toc low, it may become difficult to separate a volatile component containing an unreacted monomer as a main component.

[0051]

The polymer composition produced in the polymerization reaction vessel 103 is continuously extracted from the polymerization reaction vessel 103 and then optionally lead to a heater 104. In the heater 104, a liquid polymer composition is preheated for the purpose of increasing efficiency of subsequent devolatilization in a devolatilizing extruder 100. At this time, the preheating temperature is preferably adjusted within a range of 180 to 220°C. When the preheating temperature is higher than the aforementioned range, a volatile component may be gasified and thus it may become difficult to deliver a liquid at a given flow rate.

[0052]

Next, the polymer composition is supplied to the devolatilizing extruder 100. As the develatilizing extruder 100, the aforementioned develatilizing extruder 100 of the present invention is used. The devolatilizing extrusion is carried out by continuously supplying a polymer composition into a cylinder 10 through a polymer composition supply port 12 in the devolatilizing extruder 100 to discharge a volatile component containing an unreacted mcnomer as a main component through a gas discharge port 14 and to discharge a methacrylic polymer after develatilization through a polymer outlet 16, respectively.

[0053]

The devolatilizing extrusion is carried out by heating a polymer composition to be continuously supplied at 200 to 290°C thereby continuously separating and removing most of the volatile component containing an unreacted monomer as a main component. With respect to the pressure condition at the time of devolatilizing extrusion, the pressure of a gas discharge port (back vent) lda is adjusted within a range of about -0.05 to 0.15 MPaG {in terms of gauge pressure) and the pressures of gas discharge ports (fore vents) 14b, ldc, 14d are respectively adjusted within a range of about -0.09 to -0.02 MPaG (in terms of gauge pressure). The gasified volatile component and methacrylic pelymer enter into the devolatilizing extruder 100 through the polymer composition supply port 12. At this time, when the pressure of the back vent is decreased to -0.05 MPaG, an entrainment phenomenon arises at the back vent, and thus it is preferred to adjust the pressure wihin the aforementioned range. In order to remove the volatile component, the pressures of four vents are preferably adjusted within the aforementioned range. Usually, a pressure regulating valve is disposed between the heater 104 and the devolatilizing extruder 100, thereby adjusting the pressure at the time of devolatilizing extrusion.

[0054]

On or after the aforementioned devolatilizing extrusion, lubricants such as higher alcohols and higher fatty acid esters, an ultraviolet absorber, a heat stabilizer, a coloring agent, an antistatic agent and the like can be added to the methacrylic polymer.

[0055]

The volatile component containing an unreacted monomer as a main component discharged through the gas discharge port 14 is sent to a monomer recovery tower 105.

The volatile component containing an unreacted monomer as a main component contains impurities contained originally in a monomer, oligomers such as a dimer and a trimer, and impurities such as a radical polymerization initiator residue. When the polymerization is carried out by the continuous solution polymerization method, a solvent can be contained in addition to these impurities. When impurities are accumulated, the obtained methacrylic polymer undergoes ccleoration. Therefore, impurities are removed from the unreacted monomer by a means such as distillation or adsorption in the monomer recovery tower 105, and then the obtained monomer is recycled as a monomer for pclymerization. For example, in the monomer recovery tower 105, the monomer is recovered as a distillateory solution from a tower top of the monomer recovery tower 105 by continuous distillation, and then recycled to the monomer blending vessel 102. Impurities removed in the monomer recovery tower 105 are discarded as wastes. The volatile component containing an unreacted monomer as a main component usually refers to those in which not less than 30% by mass of the unreacted monomer is contained in the volatile component.

[0056]

According to the method for devolatilizing extrusion of a polymer composition and the method for producing a methacrylic polymer as described above, it is possible to efficiently produce a methacrylic polymer with contamination suppressed even when continuously operated for a long term.

[0057]

The aforementioned method for devolatilizing extrusion of a polymer composition and method for producing a methacrylic polymer can be suitably used in the production of a methacrylic polymer obtained by polymerizing a monomer mixture containing methyl methacrylate as a main component among some methacrylic polymers.

[0058]

The methacrylic polymer obtained by the aforementioned method can be suitably in various fields such as illuminations, signboards and vehicles since excellent transparency and weatherability can be obtained.

The methacrylic polymer can be used particularly suitably in materials for an optical disk substrate; materials for an optical equipment such as Fresnel lens, lenticular lens, a light guide plate and a diffuser panel used in a backlight system of a liquid crystal display, and a protective front panel of a liquid crystal display: vehicle members such as a tail lamp cover, a head lamp cover, a visor and a meter panel; and the like.

Description of Reference Symbols {0059] 10: Cylinder 12: Polymer composition supply port

14: Gas discharge port lé: Polymer outlet 18: Through-hole 20: Screw 20a: Shaft portion 30: Shaft seal bearing portion 32: Shaft seal portion 100: Devolatilizing extruder

Claims

1. A devolatilizing extruder for producing a methacrylic polymer, comprising: a cylinder having a polymer composition supply port, a gas discharge port, a polymer outlet and a through-hcle; a rotatable screw inserted into the cylinder through the through-~hole; and a shaft seal bearing portion supporting a shaft i0 portion of the screw extending from the through-hocle to the outside of the cylinder; wherein the shaft seal portion of the shaft seal bearing portion is formed of a mechanical seal using at least one kind selected from a group consisting of an adipate ester, a phthalate ester, a diisobutyrate ester and acetylated glyceride as a mechanical seal liquid.

2. A method for devolatilizing extrusion of a polymer composition, comprising: supplying a polymer composition containing a methacrylic pclymer and a volatile component into the cylinder through the polymer composition supply port in the devolatilizing extruder according to claim 1 to discharge the volatile component through the gas discharge pert and to discharge a methacrylic polymer after devolatilization through the polymer cutlet, respectively.

3. A method for producing a methacrylic polymer, comprising the steps of: continuously supplying a raw material that contains a monomer component containing a methacrylic mencomer as a main component, a radical polymerization initiator and a chain transfer agent into a pelymerization reaction vessel; polymerizing the monomer component in the polymerization reaction vessel to obtain a polymer composition that contains a methacrylic polymer and a volatile component containing an unreacted monomer; and supplying the polymer composition into the cylinder through the polymer composition supply port in the deveolatilizing extruder according to claim 1 to discharge the volatile component through the gas discharge port and to discharge a methacrylic polymer after deveclatilization through the polymer outlet, respectively.