JPH11129319A - Production of thermoplastic polymer and screw devolatilizing extruder used therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove a volatile component and to prevent the closure of an injection port by once supplying an inert liquid into a cylinder while adjusting the pressure thereof during a period when a raw material is introduced and extruded into the cylinder and discharging the volatile component in the raw material to the outside of the cylinder under vacuum from a vent hole. SOLUTION: A rear vent 3 and fore-vents 5a, 5b, 5c are provided to the side surface of the cylinder 10 of an extruder 1. A raw material is introduced into the cylinder from a raw material introducing port 2 and allowed to generate heat while sent forwardly by a screw to volatilize and separate a volatile component from a thermoplastic polymer. Next, an inert liquid is injected into the cylinder from injection ports 9a-9c through pressure adjusting valves 11a-11c and discharged to the outside of the cylinder along with the volatile component from vent holes. As a result, since pulsated stream are not generated in the inert liquid, the devolatilizing degree and efficiency of the volatile component become also well. Further, the closure of the injection ports by the back flow of the raw material is not generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a thermoplastic polymer for removing a volatile component from a raw material containing a thermoplastic polymer and a volatile component by using a screw type devolatilizing extruder, and an implementation of the method. And a screw type devolatilizing extruder used for

[0002]

2. Description of the Related Art As a method for producing a thermoplastic polymer such as polymethyl methacrylate or polystyrene, a bulk polymerization method in which a vinyl monomer as a raw material thereof is polymerized in the absence of a solvent, or a method in which a solvent is used. A solution polymerization method in which the polymerization is carried out by using is industrially performed. Since the thermoplastic polymer obtained by these methods is a mixture containing volatile components such as unreacted monomers and solvents, in order to obtain a thermoplastic polymer useful as a molding material, a volatile polymer is required. It is necessary to remove the components.

[0003] If volatile components remain in the thermoplastic polymer, a molded article obtained by molding the thermoplastic polymer will have reduced physical properties such as heat resistance and poor appearance. In order to solve such a problem, various proposals have been made regarding removal of volatile components. For example, a method of adding a reaction solution containing a thermoplastic polymer after completion of polymerization to a solvent in which the volatile component is dissolved but the thermoplastic polymer is not dissolved, to extract and remove the volatile component (Japanese Patent Application Laid-Open No. 58-1983). 162616), a method in which volatile components are evaporated using a flash evaporator, and then a thermoplastic polymer is extracted in a molten state (JP-A-61-276807, JP-A-62-1).
No. 29334 and JP-A-3-205411), the reaction solution containing the thermoplastic polymer after polymerization is supplied directly or after heating and drying to a screw-type devolatilizing extruder to obtain volatile components. (Japanese Unexamined Patent Publication No.
JP-A-9-126411, JP-A-59-58006, JP-A-57-135814, JP-A-50-4
0687, JP-A-50-40688, JP-A-57-49603, JP-A-63-147501
And Japanese Patent Application Laid-Open No. 3-49925).

In the above-mentioned method using a screw type devolatilizing extruder, a high heat is generated due to the kneading action of the screw, which may cause deterioration of the thermoplastic polymer. An inert liquid that does not react with the polymer is injected during devolatilization and extrusion, and this inert liquid is mixed with the thermoplastic polymer, devolatilized under reduced pressure at the vent portion, and volatile components are removed by evaporation together with the inert liquid. That is, there is also known a method of suppressing the deterioration of a thermoplastic polymer by utilizing a cooling effect by latent heat of evaporation (Japanese Patent Application Laid-Open Nos. Hei 6-1808 and Hei 7-18014).

[0005] In the above-mentioned improvement method, it is preferable to inject an inert liquid into a cylinder portion sandwiched between kneading sections at the front and rear. Otherwise, before and after the injection portion is not sealed by the thermoplastic polymer, the injected inert liquid does not sufficiently mix with the thermoplastic polymer to flow to the vent portion and does not exert a sufficient effect, This is because it causes vent up. The injection portion is provided between the vents, and is kept in a pressurized state by a sealing effect of the front and rear thermoplastic polymers.

[0006]

In the above-mentioned conventional method, since the supply source of the inert liquid is directly connected to the injection port of the cylinder, when the pressure of the inert liquid changes, a pulsating flow is generated. Occur. When a pulsating flow occurs, the supply of the inert liquid becomes unstable, and there is a problem that the efficiency of removing volatile components is reduced or uneven, and foaming occurs in the raw material inside the cylinder, thereby venting up. And there is also a problem that the thermoplastic polymer strand coming out of the extrusion port of the cylinder is cracked or cut. Further, since the inert liquid is injected against the polymer pressure in the cylinder, if there is a pulsating flow, the polymer pressure may be higher than the injection pressure, and the polymer flows back to the injection port, There was also the problem of blocking the inlet. In particular, when the supply of the inert liquid is stopped to stop the operation of the extruder, the injection port is easily blocked due to the backflow, making stable operation difficult.

Accordingly, an object of the present invention is to provide a method for producing a thermoplastic polymer which efficiently removes volatile components from the thermoplastic polymer and does not cause clogging of an injection port, and a screw type used for carrying out the method. An object of the present invention is to provide a devolatilizing extruder.

[0008]

In order to solve the above-mentioned problems, a method for producing a thermoplastic polymer according to the present invention comprises the steps of: forming a raw material containing a thermoplastic polymer and a volatile component in a spiral form around a rotation axis; A screw having a blade, and having an inner wall surface surrounding the screw in a cylindrical shape along the axial direction thereof, and
A method for obtaining a thermoplastic polymer from which the volatile components have been removed by introducing into a cylinder having a plurality of vent holes and extruding from the cylinder by rotating the screw, wherein the raw material is contained in the cylinder. Until the liquid is introduced into the cylinder and extruded, the inert liquid is once supplied into the cylinder while adjusting the pressure, and is discharged under reduced pressure from the vent hole to the outside of the cylinder together with the volatile component in the raw material. It is characterized by removing components.

In order to solve the above problems, a screw type devolatilizing extruder according to the present invention is used to volatilize and separate the volatile component from a raw material containing a thermoplastic polymer and a volatile component. A screw having a helical blade around, a cylinder having an inner wall surface surrounding the screw in a cylindrical shape along the axial direction thereof, and a drive unit for rotating and driving the screw, the cylinder comprising the screw Having an inlet for the raw material at a position corresponding to the rear portion, and having an extruding portion for extruding the thermoplastic polymer after volatile component separation outside the cylinder at a position corresponding to a position forward of the tip of the screw, further comprising the inlet And a plurality of vent holes for discharging the separated volatile components to the outside of the cylinder between the extruder and the extruder. A screw type devolatilizing extruder, which is coupled to devolatilizing means for discharging under reduced pressure to the outside of the cylinder and volatilizes and separates the volatile component from the raw material while feeding the raw material introduced into the cylinder toward the tip of the screw. And further comprising liquid supply means for pressurizing the inert liquid into the cylinder, and discharging the volatile component out of the cylinder at a position where the cylinder is located between an inlet of a raw material and an extruding section. An inlet for the inert liquid is provided in a region provided with a vent hole, and the inlet is connected to the liquid supply means via a pressure regulating valve.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A screw type devolatilizing extruder according to the present invention comprises a screw having a spiral blade around a rotating shaft and a cylinder having an inner wall surface surrounding the screw in a cylindrical shape along the axial direction. And a drive unit for driving the screw to rotate. The cylinder has an inlet for the raw material at a position corresponding to the rear part of the screw, and an extruding unit that extrudes the thermoplastic polymer after the volatile component separation into a strand shape outside the cylinder at a position corresponding to the front of the screw, and A plurality of vent holes for discharging the volatile components to the outside of the cylinder at least at a position between the introduction port and the extruding section, and these vent holes reduce the pressure of the separated volatile components to the outside of the cylinder. To the devolatilization means.

[0011] The screw and the cylinder are adapted to feed the raw material introduced into the cylinder toward the tip of the screw by the rotation of the screw. Meanwhile, the rotation of the screw applies a shearing force to the raw material to generate heat. Let it. The exothermic action volatilizes and separates the volatile components from the thermoplastic polymer. The screw type devolatilizing extruder of the present invention further includes a liquid supply unit for press-fitting the inert liquid into the cylinder. And the cylinder is
An inert liquid inlet is provided in a region where the vent hole is provided, and the inlet is connected to the liquid supply means via a pressure regulating valve.

In the present invention, a raw material containing a thermoplastic polymer and a volatile component includes an unreacted monomer, a solvent and / or
Alternatively, it is a thermoplastic polymer mixture containing a volatile component such as a volatile by-product, and is obtained by, for example, solution polymerization, bulk polymerization, or the like. As the thermoplastic polymer, those which are mixed with volatile components to form a solution, or
The polymer is not particularly limited as long as it is dispersed in a slurry state, and is not particularly limited as long as it is a polymer having thermoplasticity that can be taken out of a screw type extruder in a molten state.

Examples of industrially used monomer components constituting these polymers include methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, and methacrylic acid. Methacrylates such as t-butyl, cyclohexyl methacrylate, benzyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, acrylic Acrylates such as cyclohexyl acid and benzyl acrylate, aromatic vinyls such as styrene and α-styrene, acrylonitrile, metalylonitrile, N-phenylmaleimide, N-
Examples include olefins such as phenylmethacrylamide, methacrylic acid, acrylic acid, maleic anhydride, butadiene, and isopropylene.

These monomers can change the physical properties of the thermoplastic polymer either alone or by copolymerization. The thermoplastic polymer targeted by the present invention includes a polycondensation polymer produced by a melt polymerization method or a solution polymerization method, in addition to a vinyl polymer. This is because the production method of the present invention is also effective for removing a solvent used for dissolving low molecular weight substances and raw materials generated during the polycondensation reaction.

The unreacted monomer is an unpolymerized residual monomer present in the thermoplastic polymer after the above-mentioned monomer is polymerized or copolymerized. The solvent is not particularly limited as long as it can be generally used as a solution polymerization, and has a boiling point of 50 to
Benzene, toluene, alkylbenzene such as cumene, methyl ethyl ketone, ethyl acetate in the range of 250 ° C.,
Organic solvents such as methanol and cyclohexane are preferred.
If the boiling point is lower than 50 ° C., the handleability is deteriorated.
If the temperature is higher than 50 ° C., the efficiency of desolvation decreases, which is not preferable.

The volatile by-product is a volatile low-molecular-weight product by-produced during the reaction or a volatile component contained in the raw material. The ratio of the volatile component is preferably in the range of 10 to 80%, particularly preferably in the range of 20 to 60. Next, FIG. 1 shows an example of the screw type extruder according to the present invention. Screw extruders have one or more shafts. Any of them can be used effectively, but two axes are preferable from the viewpoint of efficiency and availability.

As shown in FIG. 1, a screw type extruder 1
Has a cylinder 10. The cylinder 10 is usually composed of a plurality of parts (barrels), and a vent port is provided on a side surface of the cylinder 10. The vent port is a rear vent 3 behind the raw material supply unit 2,
A plurality, for example, two to five forevents (three forevents 5a, b, and c in this figure) are provided in front of the thermoplastic polymer 4 side after devolatilization, respectively.
It is preferable to gradually lower the exhaust pressure as the devolatilization from the raw material progresses, since the devolatilization rate is greatly improved.
If the number of forevents is one, the efficiency of removing volatile components may be significantly reduced, and even if six or more are used, the efficiency of removal may not be changed. The pressure of the rear vent 3 is 30
0 to 760 mmHg, and the pressure at the vent 5c near the polymer outlet 4 is preferably 600 mmHg or less.
0 mmHg or less is more preferable. It is preferable to lower the pressure as the desolvation proceeds (as it approaches the outlet), since the efficiency of desolvation can be further increased. The pressure in each vent is evacuated to a predetermined pressure by using a vacuum pump. In FIG. 1, reference numeral 6 denotes a screw drive unit, and reference numeral 7 denotes a raw material storage tank. In particular, when the proportion of the volatile component is large, a heat exchanger is added between the raw material storage tank and the raw material introduction port 2 to give the raw material a part or all of the heat required for volatilization of the volatile component in advance. Heating is preferred.

In this case, the heating may be performed by a well-known method, and is performed at a pressure of about 150 to 280 ° C. continuously so that volatile components are not vaporized. In the present invention, injection holes 9 for injecting an inert liquid into the cylinder 10 are provided in a region of the cylinder 10 where the fore vent is provided. Each inlet 9 is connected to a liquid supply source 12 via a back pressure valve 11 as a pressure regulating valve. As the inert liquid, for example, a liquid that does not react with a polymer such as water or alcohol is selected, and steam can also be used.

The use amount of the inert liquid is preferably 0.5 to 10% by weight based on the thermoplastic polymer. If the addition amount of the inert liquid is less than 0.5% by weight, the effect of removing volatile components is insufficient, and if it exceeds 10% by weight, the effect does not change and venting is easily performed, which is not preferable. . The cylinder temperature of the extruder is preferably between 160 and 320
° C, more preferably 200 to 300 ° C. If the cylinder temperature is lower than 160 ° C., volatile components cannot be removed effectively. If the cylinder temperature is higher than 320 ° C., the thermoplastic polymer is undesirably colored due to thermal decomposition or a decrease in molecular weight.

The temperature of the cylinder may be changed depending on its position. The pressure regulating valve 11, which is a feature of the present invention, is preferably made of bronze or stainless steel in a portion that comes into contact with a liquid in consideration of rust prevention and corrosion resistance. In particular, a back pressure valve is preferable in structure. Is intended pressure regulating valve to set a constant pressure to the water to be sent to the inlet, in order to achieve the set pressure of 10-15 kg / cm ^2, those allowable pressure range of up to 20 kg / cm ^2, preferably Items up to 40 kg / cm ² can be selected.

It is preferable that the pressure regulating valve be installed as close to the cylinder as possible.

[0022]

The present invention will be specifically described below based on examples and comparative examples. The present invention is not limited by these examples. Hereinafter, “parts” indicates “parts by weight”. [Example 1-1] 20 parts of styrene, acrylonitrile 6
, A solution polymerization reaction using 16 parts of N-phenylmaleimide, 58 parts of toluene and 0.2 part of a polymerization initiator,
A thermoplastic polymer was obtained. The composition of the reaction solution at the end of the polymerization reaction was 41.5% by weight of the thermoplastic polymer, and the volatile components toluene and unreacted monomer were 5% each.
8.0% by weight and 0.7% by weight, and the ratio of each structural unit constituting the thermoplastic polymer is styrene structural unit 4
It was 7% by weight, acrylonitrile structural unit 14% by weight and N-phenylmaleimide structural unit 39% by weight.

As a vent type screw extruder, a twin-screw co-engaging type extruder manufactured by Nippon Steel Works shown in FIG. 1 was prepared. This extruder has a screw diameter (D) of 120 m.
m, cylinder length (L) 5460 mm, L / D = 45.
5, number of vents 4 (rear vent: 1, fore vent: 4)
Met. After the reaction solution was heated to 230 ° C. using a heater, the pressure was adjusted to 20 kg / cm ² with a pressure regulating valve, and the material was introduced into the screw extruder from the material inlet 2 of the screw extruder at a rate of 1000 kg / hr. Supplied. The pressure of each vent portion was 700 mmHg for vent 3 and 25 mm for vent 5a, vent 5b and vent 5c, respectively.
It was adjusted to 0 mmHg, 20 mmHg and 20 mmHg. Next, water was injected from the inlets 9a, 9b, and 9c of the inert liquid. Immediately before the above inlet,
Back pressure valve 11a, back pressure valve 11b and back pressure valve 1 respectively
1c was installed. These back pressure valves (manufactured by Tescom)
The allowable pressure was 40 kg / cm ² . Set amount of water supply from each inlet (ratio to thermoplastic polymer in reaction liquid)
Is 2.0% by weight at the inlet 9a, respectively,
2.0% by weight for b and 1.3% by weight at inlet 9c
Set to. At this time, the average flow rate of water injected from each inlet is 6.28 l / hr at the inlet 9a, 6.39 l / hr at the inlet 9b, and the inlet 9c.
Are 4.09 liters / hr, and ± 0.09 liters / hr, respectively.
It was supplied stably with a variation (variation) within 1 liter / hr. The obtained thermoplastic polymer is added every 3 hours.
Times, the amount of volatile components remaining in the thermoplastic polymer was 240 ppm for the first time and 255 pp for the second time.
m, the third time: 255 ppm, and it was stable. Comparative Example 1 Water was injected in the same manner as in Example 1-1 except that an extruder without a pressure control valve was used.

The average flow rate of the water injected from each inlet was the same as that of Example 1-1, however, the flow rate variation due to the pulsating flow was large, and ± 1 liter / hr at the inlet 9a. The flow rate was ± 0.2 liter / hr at the inlet 9b and ± 1 liter / hr at the inlet 9c. An abnormal water eruption occurred shortly after starting water injection. The amount of volatile components measured in the same manner as in Example 1-1 was the first time:
690 ppm, 2nd time: 440 ppm, 3rd time: 650
ppm, which was not constant.

[0025]

According to the screw type devolatilizing extruder and the method for producing a thermoplastic polymer using the same according to the present invention, the inert liquid injected into the cylinder does not generate a pulsating flow, so that the volatilization in the thermoplastic polymer is prevented. The devolatilization efficiency of the volatile component is improved and the devolatilization efficiency is also improved. Further, the inlet is not blocked due to the backflow of the raw material, and the operation is easily stabilized.

[Brief description of the drawings]

FIG. 1 is a schematic view of a screw extruder according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Screw extruder 2 Raw material introduction port 3 Rear vent 4 Polymer outlet 5a-5c Forevent 6 Screw drive part 7 Raw material storage tank 9a-9c Injection port 10 Cylinder 11a-11c Pressure control valve 12 Liquid supply source

Claims (6)

[Claims] 1. A screw having a helical blade around a rotation axis, and an inner wall surface surrounding the screw in a cylindrical shape along an axial direction of a raw material containing a thermoplastic polymer and a volatile component. And, in a method of obtaining a thermoplastic polymer from which the volatile components have been removed by introducing into a cylinder having also a plurality of vent holes and extruding from the cylinder by the rotation of the screw, the raw material Until the liquid is introduced into the cylinder and extruded, the inert liquid is once supplied into the cylinder while adjusting the pressure, and is discharged under reduced pressure from the vent hole to the outside of the cylinder together with the volatile component in the raw material. A method for producing a thermoplastic polymer, wherein the volatile component is removed. 2. The method for producing a thermoplastic polymer according to claim 1, wherein a raw material containing 20 to 80 wt% of a volatile component is supplied. 3. The method for producing a thermoplastic polymer according to claim 1, wherein the inert liquid is water vapor or water. 4. The pressure adjustment is performed via a back pressure valve.
4. The method for producing a thermoplastic polymer according to any one of items 1 to 3. 5. A screw used to volatilize and separate said volatile component from a raw material containing a thermoplastic polymer and a volatile component, said screw having a helical blade around a rotation axis, A cylinder having an inner wall surface that surrounds a cylindrical shape along with a driving unit that drives the screw to rotate, the cylinder has an inlet for the raw material at a position corresponding to the rear of the screw, At the position hitting forward from the tip, there is an extruding section for extruding the thermoplastic polymer after the volatile component separation outside the cylinder, and further, the separated volatile component between the introduction port and the extruding section to the outside of the cylinder. A plurality of vent holes for discharging the volatile components, the vent holes being connected to devolatilizing means for discharging the volatile components to the outside of the cylinder under reduced pressure; A screw-type devolatilizing extruder that volatilizes and separates the volatile components from the raw material while feeding the raw material introduced into the cylinder toward the tip of the screw, comprising: a liquid supply unit that press-fits an inert liquid into the cylinder. In addition to the above, the cylinder has the inlet for the inert liquid in a region where the cylinder is located between the inlet of the raw material and the extruding part and a vent hole for discharging the volatile component to the outside of the cylinder is provided. And a screw-type devolatilizing extruder, wherein the inlet is connected to the liquid supply means via a pressure regulating valve. 6. The screw type devolatilizing extruder according to claim 5, wherein the pressure regulating valve is a back pressure valve.