JPH0718014A - Production of alpha-methylstyrene polymer - Google Patents

Abstract

PURPOSE:To provide a method by which volatile matter, such as unreacted monomers or solvents, contained in an '-methylstyrene polymer are efficiently removed while preventing the decrease in mol.wt of the polymer as far as possible. CONSTITUTION:Volatile matters are removed from an '-methylstyrene polymer by using a twin-screw extruder which has at least one vent hole with an area of the opening larger than D<2>mm<2> (provided the diameter of the screw is Dmm) between the hopper and the die of the extruder and by adding 1-20wt.% water to a polymer soln. in the course of transporting the soln. under heating from the hopper to the die to thereby evaporate and remove the volatile matters through the vent hole. Thus, the degradation of the polymer is prevented and the volatile matters are efficiently removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing volatile substances from an .alpha.-methylstyrene polymer solution obtained by polymerizing a monomer containing .alpha.-methylstyrene.

[0002]

2. Description of the Related Art As a method for producing a polymer such as polymethylmethacrylate or polystyrene, a bulk polymerization in which a vinyl monomer (hereinafter referred to as a monomer) as a raw material thereof is polymerized in the absence of a solvent or Solution polymerization in which polymerization is performed in the presence of a solvent is industrially used. When a polymer is produced by these polymerization methods, the resulting reaction product is a mixture of the polymer and the unreacted monomer, or a mixture of the polymer, the unreacted monomer and the solvent, and finally as a molding material. In order to obtain the polymer (1), it is essential to sufficiently remove volatile substances such as unreacted monomers and solvents.

By the way, the above-mentioned polymethylmethacrylate is not only a resin having a very excellent transparency but also has a good weather resistance, so that its application is wide-ranging. However, since the heat resistance is poor, in recent years, the demand for higher heat resistance of the resin has been increased, and a heat resistant component such as α-methylstyrene has been introduced by copolymerization. This α-methylstyrene polymer is
It has high heat resistance, high surface hardness, and excellent elasticity and strength, but it has a high viscosity when removing volatiles from a polymer solution during production. It was impossible to remove volatiles to a high degree.

In Japanese Patent Publication No. 48-29,797, a polymer solution is exposed from a polymerization apparatus to a tank-shaped tank whose pressure is reduced in advance, so that volatile matter in the polymer solution is removed by evaporation. A method of doing so is disclosed. However, according to this method, the latent heat of vaporization is removed when the volatiles are vaporized and vaporized, and the temperature of the polymer solution is remarkably lowered, whereby the devolatilization efficiency is lowered. Therefore, in order to prevent the reduction of the devolatilization efficiency, a method of keeping the temperature of the decompression tank at a high temperature by a heating medium is also conceivable, but in the case of α-methylstyrene-based polymer, when devolatilizing at a high temperature, Part of the polymer is decomposed, which causes new generation of volatile matter (monomer).
In addition, the viscous polymer after removing the volatiles is extracted from the bottom of the vacuum tank, but because of its low flow rate,
Occurrence of long-term residence in a decompression tank heated to a high temperature. If such a state occurs, the polymer is thermally decomposed and new volatiles (monomers) are generated as in the case of devolatilization at high temperature. Or a phenomenon such as a marked decrease in molecular weight occurs. For this reason, there is an adverse effect that the mechanical properties and heat resistance of the polymer finally obtained are lowered. In addition, this method is not a structure that mechanically forcibly renews the surface of the polymer solution, so that the removal of volatiles from the inside of the solution is not effective, and the volatiles from the highly viscous polymer solution are not particularly effective. Was not suitable for the removal of.

Further, in JP-A-1-99,601, a polymer solution is introduced into a heated tube, and a thin film of the polymer solution is formed on the inner wall of the tube by a rotating blade.
A method is thereby disclosed whereby the volatiles are evaporated from this polymer solution and the polymer is then expelled from the tube. However, in this method, although the devolatilization efficiency is high because the surface of the polymer solution is renewed by the rotating blade, the renewal of the surface of the thin film is hindered unless the gap between the inner wall of the tube and the blade is adjusted accurately. As a result, the devolatilization efficiency is reduced, and a large shearing force acts on the polymer solution, which causes new generation of volatile matter. Furthermore, when the polymer solution is introduced into a heated tube, it rapidly foams before forming a thin film, and the scattered foam may adhere to the rotary shaft of the inclined blade. Since the mechanical force for flowing down is not transmitted to the foam, a long thermal history acts, causing discoloration or carbonization, which causes undesired coloring of the product.

[0006]

SUMMARY OF THE INVENTION The present invention was devised under these circumstances, and its object is to use α-methyl containing a monomer or monomer and a volatile substance such as a solvent. An object of the present invention is to provide a method capable of removing volatile matter from a styrene-based polymer while suppressing the deterioration such as a decrease in the molecular weight of the polymer as much as possible, and removing the volatile matter with high efficiency. .

[0007]

That is, according to the present invention, when the volatile matter is removed from the α-methylstyrene polymer containing the volatile matter, when the screw diameter is D (mm), the area of the opening is Using a twin-screw extruder equipped with one or more exhaust vent holes exceeding D ² (mm ² ) between the extruder hopper and the die, heating the polymer solution from the extruder hopper side to the die side. In the process of transferring, 1 to 20% by weight of water is added to the polymer solution and the volatiles are removed under reduced pressure from the exhaust vent hole. . Hereinafter, the present invention will be described in detail.

In the present invention, the α-methylstyrene-based polymer containing a volatile substance is a vinyl-based monomer (monomer) mixture containing α-methylstyrene in the presence of an organic peroxide or by an organic oxidation. It is an α-methylstyrene polymer solution obtained by polymerizing in the absence of substances. Here, the α-methylstyrene polymer is an α-methylstyrene unit in an amount of 5% by weight or more, preferably 10 to 4
It is contained in the range of 0% by weight, and the monomer to be copolymerized is not particularly limited. Representative examples of monomers industrially used for polymerization include methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, and methacrylic acid. Methacrylic acid esters such as benzyl, methyl acrylate,
Ethyl acrylate, propyl acrylate, acrylic acid n
-Butyl, i-butyl acrylate, t-butyl acrylate, cyclohexyl acrylate, benzyl acrylate, and the like, styrene, acrylonitrile, methacrylonitrile, N-phenylmaleimide, N
-Phenylmethacrylamide, methacrylic acid, acrylic acid, maleic anhydride and the like can be mentioned. These monomers can be copolymerized by combining various monomers in order to change the physical properties of the obtained polymer.

A radical generator such as a peroxide or an azo initiator can be used. For example, as the organic peroxide, monofunctional benzoyl peroxide, difunctional 1,1-
Di-t-butylperoxycyclohexane or tetrafunctional 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane is industrially used, but is not limited thereto. Not a thing. Furthermore, azobisisobutyronitrile or the like is used as an azo initiator.

In the case of polymerizing a vinyl-based monomer, the conversion rate into a polymer generally increases with the passage of time. At that time, the viscosity of the polymer increases as the conversion rate increases, and a large load may be applied to the rotating blades of the polymerization tank, or the transfer in the pipe may become difficult. To prevent this, a solvent may be added to the system as needed. As the solvent added as necessary, for example, ethylbenzene,
Toluene, xylene, methyl ethyl ketone, benzene,
Isopropanol etc. can be raised. It is necessary to select a solvent depending on the kind of polymer to be produced, but generally, a solvent in which the polymer is dissolved and which does not have a bad influence such as corrosion of the apparatus must be selected.

Various chain transfer agents can also be added to control the molecular weight. As the chain transfer agent, mercaptans such as n-butyl mercaptan, s-butyl mercaptan, t-butyl mercaptan, n-octyl mercaptan, and n-dodecyl mercaptan can be industrially used. The polymerization method of the vinyl-based polymer includes bulk polymerization not containing the solvent, solution polymerization in which a solvent is added, suspension polymerization in which a monomer is polymerized in water, and a water-soluble polymerization initiator and an emulsifier in water are added. Although there are emulsion polymerization and the like in which polymerization is performed, the method for removing volatile substances from the polymer solution of the present invention can be applied to any polymerization method.

The volatile matter removing method of the present invention is also used for removing the volatile matter of the polycondensation type polymer produced by the melt polymerization method or the solution polymerization method other than the vinyl polymer. When producing a polymer by polycondensation, low molecular weight products are produced during the polycondensation reaction. Further, particularly in solution polycondensation, the raw material is dissolved in a solvent to carry out polycondensation, and thus the produced polymer also contains a solvent.
Removal of these volatiles is an essential step for using the polymer as a molding material.

By the method of removing volatiles from the polymer of the present invention
Is a twin-screw extruder. Two of the twin screw type extruder
The rotation direction of the screw of the book is
There is. The method for removing volatiles from the polymer of the present invention
Offset type twin-screw extruders can also be used. two
In the axial extruder, the pressure inside the barrel was reduced to reduce the volatile matter in the polymer solution.
One or more vent holes are provided to remove the. Biaxial push
When the screw diameter of the starter is D (mm), twin screw extruder
At least one of the vent holes in the
Area is D²(Mm²) Is needed. Preferred
The area of the opening is 2D²(Mm ²) The above is better.
The area of the opening is D²(Mm²) The devolatilization efficiency is below
Decrease, the concentration of volatiles remaining in the polymer increases and the final
The mechanical properties and heat resistance of the polymer
I will Also, the opening area is D²(Mm²) Beyond
The vent hole is located closest to the hopper in the position of the vent hole provided in the extruder.
It is desirable to install it at a close position. Press the polymer solution
During the transfer from the hopper side to the die side in the barrel of the machine
Volatiles are removed through the vent holes at
On the hopper side, which has the largest amount,
This is because it is effective to use.

Each vent hole is connected to an exhaust device such as a vacuum pump. The evacuation speed of the vacuum pump depends on the volume of the extruder used and the amount of volatiles contained in the polymer solution, but is 200 torr or less, preferably 100 torr or less, more preferably during the removal of volatiles. It is desirable that a vacuum degree of 50 Torr or less can be achieved. Vacuum degree is 200
If it exceeds torr, the devolatilization efficiency decreases, and the amount of residual volatiles in the polymer increases. It is also desirable to provide a trap for trapping volatile matter between each vent hole and the exhaust device. This is to prevent volatile matter from being released into the atmosphere and to prevent deterioration of the oil in the exhaust system. Moreover, since the trap changes the volatile matter into a liquid and captures it, a desired high vacuum can be maintained as a result.

In the method for removing volatiles from the polymer solution of the present invention, it is necessary to add water to the polymer when removing the volatiles from the polymer. Addition of water to the polymer solution promotes foaming of the polymer solution and has the effect of renewing the surface, so that volatile matter can be effectively removed. Also,
The water becomes water vapor, and the partial pressure of the volatiles decreases, so that the volatiles are more effectively evaporated. Since this effect becomes large when the amount of volatiles is small, it becomes preferable to add water downstream of the extruder. Further, when the boiling point of the volatile substance is high, it has an effect of forming an azeotropic mixture with water and lowering the boiling point of the volatile substance.

The amount of water added is 1 to 20% by weight, preferably 2 to 10% by weight, based on the resin solution. If the amount of water added is less than 1% by weight, the effect of removing volatile matter as described above does not appear. If the amount of water added exceeds 20% by weight,
Large amounts of heat are required to remove the water, or water remains in the final product. It is also possible to add water by dividing it from a plurality of addition holes. It is desirable to add water to the part sandwiched by the kneading part before and after. Except for the part sandwiched by the kneading part, the front and back are not sealed by the polymer solution, so the polymer solution causes vent up from the vent hole on the unsealed side or the resin escape path is not preferable. .

The barrel temperature of the extruder is 180 to 260 ° C,
It is preferably 200 to 240 ° C. Barrel temperature is 18
If the temperature is lower than 0 ° C., not only volatile matter cannot be effectively removed, but also the viscosity of the polymer solution becomes large and a large load is applied to the motor and the like. Also, the barrel temperature is 26
If the temperature is higher than 0 ° C., thermal decomposition of the resin may occur, the molecular weight of the polymer may decrease, or a low molecular weight product may be produced, which adversely affects the thermal and mechanical properties.

The flow rate of the polymer solution depends on the size of the twin-screw extruder used. For example, when the screw diameter is 30 mm, the flow rate is 4 to 40 kg / hr, preferably 10 to 30 kg / hr. When the screw diameter is 45 mm, it is 9 to 90 kg / hr, preferably 25 to 70 kg / hr, and the screw diameter is 60.
In the case of mm, 16 to 160 kg / hr, preferably 4
The flow rate is 0 to 120 kg / hr. When the flow rate of the polymer solution is smaller than the lower limit flow rate when each screw is used, the residence time of the polymer solution in the extruder becomes long,
Not only the heat deterioration of the polymer easily occurs, but also the cost becomes high. On the other hand, if the flow rate is higher than the upper limit of the flow rate when each screw is used, the surface of the polymer solution will not be effectively renewed.

In the polymer solution, undesired decomposition may occur during the removal of volatile matter, resulting in a decrease in the molecular weight of the polymer or formation of a low molecular weight product. Various kinds of additives can be added to prevent such a situation. As the additive, those used industrially can be used.
Examples of the additive include n-octadecyl-3-
(3 ′, 5′-Di-tert-butyl-4′-hydroxyphenyl) propionate, pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4 ′)
-Hydroxyl) propionate] and other hindered phenol compounds, tris (2,4-di-tert-butylphenyl) phosphite and other phosphite compounds, tetrakis [methylene-3- (dodecylthio) propionate] methane, etc. Thioether compounds, such as tetrabromobisphenol A and decabromodiphenyl oxide as flame retardants,
Electrostatic stopper series [made by Kao Corporation] as antistatic agent, dasper series [Miyoshi Yushi Co., Ltd.]
Manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.] and the like. Furthermore, an ultraviolet absorber such as a benzotriazole-based compound and a light stabilizer such as a hindered amine-based compound can be added as necessary. Further, various improvers, release agents, dyes and contents can be added.

[0020]

EXAMPLES The present invention will be specifically described below based on Examples and Comparative Examples. The present invention is not limited to these examples and comparative examples.

It was carried out using the twin-screw extruder shown in FIG.
The twin screw extruder has a screw diameter D = 32 mm and a major diameter ratio L / D =
45.5, same direction rotating type was used. The twin-screw extruder has four vent holes. The area of the opening of each vent hole is 3,600 mm ^{2 for} the vent hole 3 and 600 for the vent hole 4.
mm ² , vent hole 5 is 600 mm ² , vent hole 6 is 60
It is 0 mm ² . The polymer solution 2 is introduced into the extruder from the hopper 1 upstream of the extruder. Volatile substances in the polymer solution transferred to the downstream by the screw of the two-axis co-rotating type are removed from the vent holes 3, 4, 5 and 6 through the pressure reducing line 10. In addition, the water addition holes 7, 8, 9 may be added during the transfer of the polymer solution.
Water is added to the inside of the extruder. The polymer from which the volatile substances have been removed is shaped into strands through the die 11.

In each of the examples and comparative examples described below, α
-Methylstyrene 30% by weight, methyl methacrylate 70
2,2-bis (4,4-di-t-butylperoxycyclohexyl) as a polymerization initiator with respect to a mixed solution of weight%
Propane was dissolved in 1,200 ppm ethylbenzene, added, polymerized at 120 ° C. for 5 hours, and then volatile matter was roughly removed in advance and used. The amount of volatile matter in the polymer solution used was 5,600 ppm of methyl methacrylate, 19,500 ppm of α-methylstyrene, 3,1 of ethylbenzene.
It was 00 ppm. Examples 1 to 7 Using the twin-screw extruder shown in FIG. 1, the operation was carried out under the operating conditions shown in Table 1. The results are shown in Table 2.

Comparative Examples 1 to 7 A co-rotating twin-screw extruder having only two vent holes having an opening area of 160 mm ² was used. The screw diameter D = 30 mm and the major axis ratio L / D = 31.5. The experiment was conducted under the operating conditions shown in Table 3. The results are shown in Table 4.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

EFFECTS OF THE INVENTION According to the present invention, volatile substances can be removed with high efficiency while suppressing deterioration of the α-methylstyrene polymer.

[Brief description of drawings]

FIG. 1 is an explanatory view of a twin-screw extruder used for carrying out the method of the present invention.

[Explanation of symbols]

1 ... Hopper, 2 ... Supply direction, 3, 4, 5, 6 ... Vent hole, 7, 8, 9 ... Water addition hole, 10 ... Decompression line, 11 ...
Die, 12 ... screw.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ikuo Yamaoka 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa, Nippon Steel Corporation Advanced Technology Research Laboratories (72) Masao Kimura Ida, Nakahara-ku, Kawasaki-shi, Kanagawa 1618, Nippon Steel Corporation Advanced Technology Research Center

Claims (1)

[Claims] 1. When removing a volatile substance from an α-methylstyrene polymer containing a volatile substance, the screw diameter is D (m).
m), the polymer solution is prepared by using a twin-screw extruder having at least one exhaust vent hole having an opening area exceeding D ² (mm ² ) between the extruder hopper section and the die section. In the process of transferring from the extruder hopper side to the die side while heating, 1 to 20% by weight of water is added to the polymer solution,
A method for producing an α-methylstyrene-based polymer from which volatile matter has been removed, characterized in that volatile matter is removed under reduced pressure from an exhaust vent hole.