JPS63314207A - Method of recovering polymer - Google Patents

Abstract

PURPOSE:To recover polymer with high efficiency, by treating polymer in a vented extruder having a pump provided between a screw head and a discharge die of the extruder to enhance the screw rotation speed. CONSTITUTION:Unpurified polymer containing a solvent and an unreacted monomer is supplied to a vented extruder 1 from a supply port 10, kneaded with screws and at the same time pressurized at an elevated temperature. The polymer is freed of pressure at vents 5, 6, and 7, and evaporated gas is carried to a recovering apparatus through vent gas lines 11, 12, and 13. After passing the final vent 7, the polymer containing substantially no volatile component is introduced into a pump, preferably a gear pump, and discharged from a discharge die 3. The discharged polymer 4 is cooled with water, if required, and cut into pieces to obtain a product (e.g. pellet). Owing to the presence of pump 2, it is possible to prevent temperature rise at an extruder head, where it is most likely to happen, and so to raise the screw rotation speed, thus diminishing volatile material in the product and also improving the productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION a. Industrial Application Field The present invention is directed to polymerization of unpurified polymers using an extruder,
The present invention relates to a method for treating a polymer solution or dispersion, a polymer containing a volatile substance, or a composition thereof in a vent extruder, removing the volatile substance, and recovering the polymer.

b. Conventional technology Polymers are usually produced by polymerization methods such as solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization.

In solution polymerization, volatile components such as a solvent and unreacted monomers are mixed in the polymerization product before the drying step.

In addition, in bulk polymerization and suspension polymerization, media, unreacted monomers, etc. are mixed in the produced polymer. In emulsion polymerization, after polymerization is completed, a coagulant is usually added to the resulting latex to coagulate the polymer into a water slurry, and then a purified polymer is recovered through dehydration and drying steps. Before drying, water and polymer are mixed together.

For example, in solution polymerization, the solvent is removed using steam.
When the stripping method is used, the purified product after removing the solvent is a slurry consisting of water and polymer. Therefore, these solvents, monomers, and water are separated from the polymer, and
It is necessary to recover the pure polymer and make it into a product.

If these substances remain in the recovered polymer, they may deteriorate the inherent mechanical properties of the polymer such as strength, thermal properties such as heat resistance, chemical properties such as chemical resistance, and the appearance of its molded products. cause it to happen. Furthermore, these substances ooze out from the polymer during molding and cause contamination of the mold, or are released into the atmosphere, deteriorating the working environment and reducing working efficiency. Furthermore, when used in food or medical containers, it is fully expected that these substances contained in the polymer will migrate to food or medicine, and in fact, in the United States and EC countries, specific A number of regulatory measures have been taken.

Since all of these substances have volatility with respect to the polymer, various methods have been adopted for their removal.

For example, in solution polymerization and emulsion polymerization, the polymer solution after polymerization is brought into direct contact with steam and heated to evaporate and remove volatile substances. For example, "Polymer Manufacturing Process" by Koji Saeki, p. 322).

In addition, in solution polymerization and bulk polymerization, solvents and monomers are evaporated and removed by indirect heating (for example, polypropylene [Polymer Manufacturing Process] by Yasuji Saeki, Vol. 10).
2 pages).

As one of the latter indirect heating methods, a method of removing volatile substances from the polymer using a vent extruder has been proposed and is widely practiced (for example, JP-A-47-6031, JP-A-51- No. 41087, etc.).

This method is particularly useful when the residual volatile substances in the polymer (including water in the polymer, hereinafter the same) are relatively small. In addition, the product form of the polymer is usually pellets,
In order to obtain this form, it is necessary to finally process it using an extruder. Therefore, this method has the advantage that it can be carried out at a lower cost than other methods in terms of equipment costs and operating costs, since the removal of volatile substances and pelletization can be performed simultaneously using one extruder. The types of bent extruders used in this method are -shaft type and multi-shaft type with two or more screws, and in the case of two-shaft types, there are non-intermeshing type, intermeshing type, and types in which the rotation direction is the same or different. There are a wide variety of implementation formats,
In actual operation, the type of vent extruder to be used is determined by taking into consideration the properties of the polymer, the removal rate of volatile substances, etc.

-m, if you want to remove volatile substances efficiently, ■ Regarding vents, I, increase the number of venturos, Make the mouth and ventro wider, C. Lower the vent internal pressure.

■ The operating conditions for the extruder are as follows: (1) Increase the polymer temperature (jacket temperature); (2) Increase the screw rotation speed to promote friction of the polymer, thereby raising the temperature and improving the surface renewability of the polymer. increase.

■ Regarding the screw, a. Increase the residence time in the vent. B. Promote heat generation of the polymer with a seal ring, kneading disk, etc. before the vent to increase the polymer temperature. C. Measures can be taken such as creating shallow grooves to promote surface renewal.

However, basically it boils down to three points: (a) prolonging the residence time of the polymer; (b) increasing the temperature at the vent; and (promoting C1 surface renewal). Increasing the rotation speed is an extremely useful method for satisfying the conditions (b) and (C) above, and it is a great method that requires less cost because existing extruders can handle up to a certain range. There are advantages.

Problems to be Solved by the C0 Invention However, this method has the following serious drawbacks. That is, although devolatilization within the vent is promoted, on the other hand, in order to turn the polymer into pellets after passing through the vent, it is necessary to extrude the polymer through a die provided at the tip of the extruder.

Since the extrusion opening of the die is narrow, the molten polymer cannot be extruded against the passage resistance in the die unless the extrusion pressure of the molten polymer in front of the die is increased considerably. In order to raise the pressure of the molten polymer in front of the die to the required height, it must be increased by the screw of the extruder, and increasing the pressure by the screw with low feed efficiency is accompanied by a large temperature increase, which can lead to polymer deterioration. invite In addition, increasing the number of revolutions of the screw further increases the temperature, which accelerates the deterioration of the polymer. This is because a vented extruder is used to accelerate the removal of volatile substances in the polymer.
This was the biggest obstacle when adopting a method of increasing the rotational speed of the screw.

The present invention provides a method for efficiently removing volatile substances from a polymer using a vented extruder.

d. Means for Solving the Problems The present invention provides a method for recovering a polymer from a polymer solution or dispersion obtained by polymerization, a polymer containing a volatile substance, or a composition thereof, using a vent extruder. The present invention provides a method for recovering a polymer, which is characterized in that the polymer is recovered using a vent extruder having a pump between a screw tip and a discharge die.

Polymers to which the polymer recovery method of the present invention can be applied include polystyrene resins, acrylonitrile, styrene resins, styrenic thermoplastic resins such as HeBS resins, MBS resins, and MS resins, aromatic resins such as SR, SBS, and SIS. Representative examples include elastomers such as vinyl-conjugated diene block copolymers, olefinic thermoplastic resins and rubber-like polymers such as polyethylene, polypropylene, polybutene, ethylene-propylene copolymers, ethylene-butene copolymers, etc. However, in addition to the above, thermoplastic resins such as polyamide and polyester, thermoplastic elastomers, diene-based or non-diene-based rubbery polymers, etc.
Even if it is a polymer other than the above, it is not limited to the above as long as it can be melted by kneading in a normal extruder.

The volatile substances contained in the above polymer and removed vary depending on the polymerization method used to obtain the polymer, but are generally monomers, solvents, water, etc., and are usually bulk polymerization, In suspension polymerization, unreacted monomers are also
In the case of solution polymerization, unreacted monomers and solvent are also
In the case of emulsion polymerization, water and unreacted monomer correspond to each other. Specifically, unreacted monomers such as styrene, α-methylstyrene, acrylonitrile, butadiene, methyl methacrylate, isoprene, ethylene, propylene, butene, N-substituted maleimide, benzene, toluene, ethylbenzene, hexane, cyclohexane J These include solvents such as heptane and pentane, and water.

The amount of volatile substances contained in the polymer is such that it can be economically removed by the venting mechanism of the extruder, and
(based on weight, the same applies hereinafter), it is preferably 20 or less, more preferably 5 or less, particularly preferably 3 or less.゛Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of carrying out the method of the present invention using a vented extruder.

In the figure, extruder 1 is a vented extruder having a three-stage vent with vent sections 5, 6, and 7. The type of extruder may be either a single-screw extruder or a multi-screw extruder having two or more screws, but a multi-screw extruder is preferable in view of the effect of removing volatile components. In a multi-screw extruder, especially a two-wheel bent extruder, the screw flights may be engaged or disengaged depending on the mutual gap between them, and the screws may rotate in the same direction or in different directions, and may rotate internally or internally. There are a variety of types, including those with external rotation, and these are selected in consideration of the physical properties of the polymer to be recovered, the allowable amount of residual volatile substances, etc. . Note that the screw inside the extruder is not shown in the figure (the same applies to FIG. 2).

The number of stages in which the vent section is installed is determined based on the difficulty of devolatilizing volatile substances (removing volatile matter), and is not limited to three stages as shown in FIG. 1.

A polymer containing a solvent and unreacted monomer is supplied into the extruder 1 from the supply port IO. The concentration of the polymer to be recovered in the unpurified polymer fed through the supply port 10 is 20 to 95%, preferably 30 to 90%, and more preferably 40 to 90%. If the polymer concentration is too low, devolatilization using only an extruder will be extremely inefficient and economically undesirable, so a preconcentration step is usually provided to bring the polymer concentration to the above-determined concentration. After adjustment, feed to the extruder.

The unrefined polymer supplied to the extruder 1 is kneaded within the extruder, generates heat, and rises in temperature.

The shape of the screw used in the extruder 1 includes, in addition to a normal flight screw, a seal ring, a disk, a rotor, a retrograde flight, a dalmage screw, a pin screw, etc. They can be used in combination as appropriate, taking into consideration the degree of deterioration caused by cutting.

Furthermore, the higher the screw rotation speed, the higher the amount of polymer throughput. Furthermore, what is important from the perspective of devolatilization is that the higher the screw rotation speed, the more the free surface of the polymer is renewed and the degree of kneading becomes stronger, which increases the temperature of the polymer and releases the volatile substances contained in it. degassing is greatly promoted. However, increasing the screw speed places high shear stresses on the polymer.

Therefore, if an adverse effect such as molecular cleavage of the polymer is expected, the rotation speed is determined taking this into consideration.

The polymer, which has been pressurized and heated by the screw, passes through the vent section 5.
．． At point 6.7, the pressure is released and the volatile substances contained in the polymer evaporate. The pressure in each vent section is usually maintained at reduced pressure or vacuum to promote evaporation of volatile substances. The substances evaporated in each vent section are removed from the vent exhaust route 1). 12 and 13, it is led to a device for recovering these substances, and then to a vacuum or pressure reduction device (none of which is shown).

The polymer that has passed through the final vent section 7 is substantially free of volatile substances. This polymer is introduced into pump 2. The pressure on the suction side of pump 2 only needs to be equal to the suction source head of the pump, usually 200 tm) from IgA to 5 kg/
It is about rrrG. Unnecessarily increasing the suction pressure needs to be compensated for by increasing the pressure of the screw, but since increasing the pressure by the screw is inefficient, the temperature of the polymer at the extruder tip increases, which affects the physical properties of the polymer. This is not desirable as it causes deterioration.

In the method of the present invention, by attaching a pump to the tip of the extruder, the temperature of the polymer can be prevented from increasing at the tip of the extruder, where the temperature is most likely to rise, so the screw is operated at a higher rotation speed than usual. can do. Therefore, ■ The concentration of residual volatile substances contained in the final product can be lowered, improving product properties; ■ If the concentration is to be maintained at the same level as before, the amount of polymer extruded in the extruder can be reduced This has the two advantages of increasing the throughput of the extruder.

The type of the pump 2 used in the present invention is not particularly limited as long as it can transfer and pressurize a high-viscosity molten resin, but gear pumps are preferred. The discharge pressure of the pump may be any pressure that allows the molten polymer to be discharged from the die 3 in the form of a strand.
As for the structure of the pump, it is preferable to reduce the suction pressure of the pump as much as possible, so it is desirable that the suction side of the pump has a large diameter so that the polymer can be easily introduced even under vacuum.

The polymer 4 discharged from the die 3 is cooled with water or the like if necessary, and then cut using a pelletizer (not shown) or the like.
Cut it into a suitable length and make it into a product (such as a beret). The die 3 can also be used as a die for under water cutting or hot cutting, if necessary.

As described above, in the method of the present invention, there is no need to further raise the temperature of the molten polymer that has passed through the final vent (in this example, the third vent), and the polymer does not deteriorate due to temperature rise. There is no. In addition, instead of extruding using a screw with poor transport efficiency, a pump with high transport efficiency is installed between the screw tip and the die, and by extruding the molten polymer from the die, the temperature of the polymer at the time of discharge is lowered. It is possible to prevent deterioration of the polymer.

FIG. 2 shows an example of carrying out the method of the invention using a vented extruder equipped with squeezing dewatering means. In the figure, the same reference numerals as in FIG. 1 indicate the same parts as in FIG. Indicates the water drainage route.

The unpurified polymer supplied from the feedlot 10 is subjected to dehydration and separation of the water contained therein by the squeezing dehydration means 14, and is then subjected to the same treatment as the example shown in FIG. 1 above in the latter stage.
It is recovered from the die 3 as a polymer 4.

The throttle dewatering means 14 is installed at an intermediate position between the supply port 10 and the first vent 6. An opening is provided on the side or lower side of the cylinder/barrel of the extruder in the above position, and a dewatering material selected from mesh screens, cage bars, wedge wire screens, etc., taking into consideration strength, screen gap, etc. Install the means.

The screen gap is appropriately selected based on the polymer particle diameter, allowable polymer leakage rate, etc. The length of the dewatering means 14 in the screw axial direction is determined as appropriate depending on the water content, dewatering rate, etc. of the polymer. Further, the number of dehydrating means 14 to be installed is not limited to - locations, but is determined by the water content and dehydration rate of the polymer, similar to the above-mentioned length.

Water squeezed from the polymer compressed under pressure by the screw in the extruder 1 is discharged from the extruder through the screen gap of the squeezing and dewatering means 14.

The water dehydrated and separated in the squeezing dewatering means 14 is discharged through a water discharge path 15.

The example of the method of the present invention shown in FIG. 2 above is an effective means when the volatile substance contained in the polymer is mainly water. That is, the polymer produced by the emulsion polymerization method is generally in a latex state, and is coagulated with an acid or salt, dehydrated as a water slurry, and dried to recover the polymer. In addition, when recovering polymers produced by solution polymerization, there is a method in which the polymer solution after reaction is poured into hot water, desolubilized by steam stripping to form a water slurry, and then dehydrated and dried. Usually done. The use of a squeeze dehydrator in the dehydration/drying process has already been widely practiced (for example, Japanese Patent Publication No. 17227/1983, Japanese Patent Publication No. 131656/1983, Japanese Patent Application Laid-open No. 218614/1989, etc.). Furthermore, by combining the installation of a pump at the tip of the extruder,
Effective treatment can be performed in the same manner as in the above-mentioned example in which the polymer contains a solvent, and similar effects can be obtained.

In addition, in the above explanation, an example was given in which the volatile substance in the polymer treated with a vent extruder having a squeezing dehydration means is water, but the present invention is not limited to this. If the same substance contained in the polymer can be squeezed out by squeezing with a screw, any system can be applied. For example, systems where the polymer and unreacted monomers or dispersion medium are not compatible, such as slurry polymerization. can be targeted.

e. Examples Examples of the present invention will be shown below, but the present invention is not limited thereto.

Example 1 75 parts by weight of styrene, 25 parts by weight of acrylonitrile, 30 parts by weight of toluene, and 0.1 part by weight of t-dodecylmercaptan were supplied to a reactor at a temperature of 150°C, an average residence time of 4 hours, and no catalyst was used. Thermal polymerization was carried out to obtain a polymer solution with a polymerization conversion rate of 80%.

Next, the obtained polymer solution was supplied through the supply port of an extruder having the same configuration as that shown in FIG.

The extruder used here was a two-screw three-stage vented extruder with an inner diameter of 65 m, and a gear pump of VACORBX45 type manufactured by Maag was attached to the tip. Further, the pressure at each vent was controlled between 200 and 20 Torr. Furthermore, the rotation speed of the gear pump was controlled so that the suction pressure was 0.7 to 3 kg/aJA.

The polymer discharged from the die was drawn into a string and passed through water, cooled, and then cut into products using a pelletizer. Table-1
shows the operating conditions and evaluation results of the obtained polymer.

Example 2 EPDM (JSREP 22 manufactured by Japan Synthetic Rubber) 20
parts by weight, 56 parts by weight of styrene, 120 parts by weight of toluene,
0.1 part by weight of t-dodecyl mercaptan, 1 part by weight of acrylonitrile, 0.5 part by weight of benzoyl peroxide, and 0.1 part by weight of dicumyl peroxide were supplied to a reactor and reacted at 80°C for 6 hours. Thereafter, the temperature was raised to 120° C. over 1 hour, and polymerization was continued for another 2 hours to obtain a polymer solution with a polymerization conversion rate of 97%.

The subsequent treatments were performed in the same manner as in Example 1.

The results are shown in Table-1.

Example 3 A 35% by weight polymer solution of an A-B-A type styrene-butadiene block copolymer containing 1t80% by weight of styrene was prepared by copolymerizing n-butyllithium as a polymerization initiator in a cyclohexane solvent. This was further preconcentrated to remove residual monomers and solvent to obtain a polymer solution with a polymer concentration of 70% by weight.

Next, the obtained polymer solution was treated in the same manner as in Example 1. The results are shown in Table-1.

Comparative Example 1 In the same apparatus as that used in Example 1, the polymer obtained in Example 1 was produced in the same manner as in Example 1, except that the pump was removed and the die was attached directly to the tip of the extruder. The solution was processed. Table 1 shows the operating conditions and the evaluation results of the recovered polymer.

Comparative Example 2 The polymer solution obtained in Example 2 was treated in the same manner as in Comparative Example 1. Table 1 shows the operating conditions and the evaluation results of the recovered polymer.

Comparative Example 3 A polymer was obtained in the same manner as in Comparative Example 1, except that the polymer solution of Example 3 was used. Table 1 shows the operating conditions and the evaluation results of the recovered polymer.

As is clear from Examples 1 to 3 and Comparative Examples 1 to 3 above, in the examples of the present invention in which a pump was attached to the tip of the extruder, the temperature of the polymer at the tip of the extruder was low, and the physical properties of the polymer In contrast, in Comparative Examples 1 to 3 in which the pump was removed, the polymer temperature at the tip of the extruder was high, so the polymer deteriorated and the color tone and cloudiness were good.
Both the degree of haze was poor and a satisfactory product could not be obtained.

Example 4 40 parts by weight of polybutadiene latex, 1 part by weight of sodium stearate, 200 parts by weight of distilled water, 0.3 parts by weight of sodium birophosphate, 0.35 parts by weight of glucose, and 0.005 parts by weight of ferrous sulfate. , 0.6 parts by weight of cumene hydroperoxide were mixed, a mixture consisting of 43 parts by weight of styrene and 17 parts by weight of acrylonitrile was added dropwise thereto, and the polymerization conversion was carried out by emulsion polymerization at a reaction temperature of 85°C and a reaction time of 5 hours. A polymer latex with a yield of 98% was obtained.

To this was added 2 parts of Mg5On as a coagulant and coagulated at 95° C. to finally obtain a thermoplastic resin water slurry with a slurry concentration of 25%. This water slurry was dehydrated using a Gina-type centrifugal dehydrator manufactured by Ishikawajima-Harima Heavy Industries ■ to obtain a hydrous thermoplastic resin with a water content of 30%.

Next, the obtained hydrous thermoplastic resin was supplied to the extruder through the supply port of the extruder having the same configuration as that shown in FIG. The extruder used here was a two-wheel, two-stage vent extruder with an inner diameter of 65M, and a dewatering slit (slit gap 0.
2B) was used, and the pump attached to the tip was the gear pump manufactured by Mark Co., Ltd. mentioned above. The dewatering slit liberates water contained in the resin by a squeezing effect, and the separated water is discharged from the discharge path. Also,
Each vent is for drying the polymer by evaporating the water in the polymer that cannot be discharged from the dehydration slit.
The pressure in each vent was controlled at 200-20 Torr. The processing after passing through the gear pump is the same as in Example 1.
The polymer was recovered in the same manner as above. Table 2 shows the evaluation results of the obtained polymer.

Example 5 The polymer solution obtained in Example 3 was fed into hot water at 105°C to remove residual monomers and solvents from the polymer by evaporation to obtain an aqueous slurry of the polymer.

This was dehydrated to a water content of 20% using a centrifugal dehydrator, and then processed using an extruder in the same manner as in Example 4.

Table 2 shows the evaluation results of the obtained polymer.

Comparative Example 4 The polymer slurry obtained in Example 4 was treated in the same manner as in Example 4, except that the pump in the apparatus used in Example 4 was removed and a die was attached directly to the tip of the extruder. Table 2 shows the evaluation results of the obtained polymer.

Comparative Example 5 A polymer was recovered in the same manner as in Comparative Example 4, except that the Example 50 polymer slurry was used. Table 2 shows the evaluation results of the obtained polymer.

As is clear from Examples 4 to 5 and Comparative Examples 4 to 5 above, the polymer in the water slurry state has the same effect as the polymer solution.
It has been found that by attaching a pump to the tip of the extruder, it is possible to obtain a recovered polymer with good physical properties, particularly good color tone and degree of haze.

The examples described above are examples in which a polymer is recovered using a vent extruder equipped with a pump according to the present invention, while the comparative example is an example in which a polymer is recovered using a vent extruder without a pump. This is an example. In Examples and Comparative Examples, those with the same number are examples in which the same thermoplastic polymer solution or dispersion was fed to a vent extruder and the polymer was recovered.

Regarding the evaluation results of the obtained recovered polymers shown in Tables 1 and 2, when comparing Examples and Comparative Examples with the same number, it is found that the amount of residual monomer in the recovered polymers is almost the same. On the other hand, in Examples, the temperature of the polymer at the time of discharge was low, and the color tone of the polymer was high in whiteness and there was little color change to yellow.

In addition, looking at the throughput of the extruder, by installing a gear pump, the throughput (discharge volume) of the polymer can be increased.
It was found that in the examples, the productivity increased by 1.4 to 1.6 times that in the comparative examples, and it was confirmed that the productivity increased dramatically without impairing the physical properties of the polymer.

f9 Effects of the Invention As is clear from the above examples and the like, according to the method of the present invention, it is possible to process the polymer by increasing the rotational speed of the extruder slew compared to the conventional method. Because there is
Productivity improves. In addition, compared to the conventional method that uses only an extruder, it has higher performance in removing volatile matter and higher production capacity, and also does not impart thermal history to the polymer, while maintaining a high level of performance balance. The polymer can be recovered, and its industrial benefits are extremely large.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of a vent extruder included in the method for producing a thermoplastic polymer of the present invention, and FIG. 2 is a schematic diagram showing the configuration of the vent extruder of type 1. 1--Extruder, 2--Pump, 3--Die, 4--11-Recovered polymer, 5.6.7--Vent part , 10 knees --- supply port, 1). 12.13---vent exhaust route, 14---throttling dehydration means,
15・-1111・Water discharge route. Fig. 1 Ws 2 Fig. 1 Procedures Written by the principal author (spontaneous) 1. Indication of the case Patent Application No. 150007 of 1988 2. Name of the invention Method for recovering polymers 3. Person making the amendment Relationship with the case Patent applicant Name (417) Japan Synthetic Rubber Co., Ltd. 4, Agent
107 Address: 3-2-3 Akasaka, Minato-ku, Tokyo (2 idiots) 5. Subject of amendment Contents of amendment + 1) End line of page 1 of specification [Polymerization J by extruder It is about the method of collection, so please provide more details.'' (2) In the same book, page 8, lines 4 to 5, [acrylonitrile, styrene resin] is corrected to "acrylonitrile-styrene resin." (3) On page 21 of the same book, line 7, "Made by Mark Co., Ltd." is corrected to "Made by Mark Co., Ltd."

Claims (3)

[Claims] (1) When recovering a polymer from a polymer solution or dispersion obtained by polymerization, a polymer containing volatile substances, or a composition thereof, a pump is pumped between the screw tip of the vent extruder and the discharge die. 1. A method for recovering a polymer, comprising recovering the polymer using a vent extruder equipped with a vent extruder. (2) A method for recovering a polymer according to claim (1), characterized in that a squeeze dehydration means is provided in the vent extruder. (3) The method for recovering a polymer according to claim (1), wherein the pump is a gear pump.