JPH0696618B2 - Method for producing vinyl chloride polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a vinyl chloride polymer, and to a method for producing the polymer in good yield without impairing the physical properties.

[Conventional technology]

In the conventional polymerization of vinyl chloride, when the polymerization rate reaches about 85%, the monomer gas in the reaction vessel space decreases and the pressure falls, and the reaction hardly progresses beyond this, so the pressure is 1 to 3 kg / cm
^The reaction was considered to be complete when the temperature dropped by about ² and proceeded to the next step. The next step is to remove unreacted vinyl chloride monomer from the polymerization vessel under reduced pressure, and then treat the slurry (polymer aqueous dispersion) with a demonomerization device or the like to collect.
The recovered vinyl chloride monomer gas is separated from water, liquefied and purified, and reused.

That is, T / m ³ Month (T: vinyl chloride polymer can be produced with high tonnage, m
³ : To increase the capacity of the polymerization vessel, Month: 1 month), it takes less time than the method in which the internal pressure of the polymerization vessel is lowered by 1 to ³ kg / cm ^{2 and then the} operation is carried out for a long time to slightly increase the yield. Round up 1
The method of shortening the cycle time was adopted.

[Problems to be solved by the invention]

An object of the present invention is to provide a method for producing a vinyl chloride polymer, which impairs the quality of the obtained polymer and increases the yield in a short time.

[Means for solving problems]

The present invention uses a partially saponified polyvinyl alcohol having a saponification degree of 70 to 78% as a suspending agent in suspension polymerization of a vinyl chloride monomer or a mixture containing a vinyl chloride monomer in an aqueous medium. Polymerization of vinyl-based monomer mixture containing monomer or vinyl chloride monomer proceeds, and the temperature of the slurry is changed within 40 minutes from the time when the internal pressure of the polymerization reactor begins to decrease. More than 5
This is a method for producing a vinyl chloride polymer in which the monomer is recovered when the temperature rises to a predetermined temperature by raising the temperature by 10 ° C.

The suspending agent used in the present invention preferably has a saponification degree of 70 to 78%. This is because if the saponification degree is higher than this, the plasticizer absorbability is deteriorated. It is considered that this is because the skin layer of the vinyl chloride polymer produced when a suspending agent having a high degree of saponification is used becomes thicker and the internal porosity becomes smaller as the polymerization proceeds. On the other hand, a suspending agent having a saponification degree of less than 70% is not used alone because the polymerization is usually unstable.

It is appropriate to raise the temperature within 40 minutes from the start of depressurization. If the temperature rise is started before the pressure drop, the reaction is still at a stage where the pressure inside the polymerization vessel rises, which is not preferable for safety. Further, since the degree of polymerization is also affected, it becomes difficult to adjust the degree of polymerization stably. On the other hand, if the temperature rise is started more than 40 minutes after the pressure drop starts, not only the time for raising the temperature to the predetermined temperature will be added but also the temperature of the slurry cannot be increased efficiently by utilizing the end-stage heat generation and the temperature rise. It is disadvantageous because it takes time.

In the present invention, the vinyl chloride monomer does not come out of the system during the temperature rise. This is because the vinyl chloride monomer in a liquid state is changed to a gas state when it is taken out of the system during this period, so that the polymerization reaction practically does not occur and the yield cannot be improved.

The temperature rise is 5 to 10 ° C above the temperature of the slurry just before the start of pressure reduction.
Higher. This is because if it is lower than 5 ° C, the polymerization rate is slow and the yield is not increased in a short time. On the other hand, the higher the temperature, the better the yield, but if the temperature exceeds 10 ° C., the vinyl chloride polymer produced is unfavorably deteriorated in thermal stability and its quality is deteriorated. Further, if it is possible to raise the temperature to a predetermined temperature, it is desirable to immediately perform a cooling operation so that the temperature does not become higher than that. If this operation is not carried out, the temperature of the slurry becomes too high and the thermal stability of the vinyl chloride polymer produced for the same reason as above may be impaired.

In the present invention, the temperature control at the time of raising the temperature is usually performed above and below the temperature of the fluid (usually water) in the polymerization vessel jacket.

When the slurry is withdrawn from the polymerization vessel, in order to reduce the amount of vinyl chloride monomer remaining in the vinyl chloride polymer, the withdrawal is usually performed after the amount becomes about 5 kg / cm ² G or less. By the way, surprisingly, if the temperature is raised within 40 minutes from the start of depressurization and the vinyl chloride monomer is not recovered outside the system during that time, the temperature is raised even though it takes time to reach the prescribed temperature. The time required for the internal pressure of the polymerization vessel to fall to a pressure of 5 kg / cm ² G or less is almost the same as that when the vinyl chloride monomer is recovered without it.

In the present invention, another dispersant may be used together during the polymerization. Examples of the dispersant that can be used in combination include a saponification degree of 70.
PVA out of the range of up to 78%, cellulose derivatives such as methylcellulose and hydroxypropylcellulose, synthetic polymer substances such as polyvinylpyrrolidone, maleic anhydride-vinyl acetate copolymer, and nonionic surfactants such as sorbitan monolaurate And the like, and any of those usually used for suspension polymerization may be used.

The method of the present invention is no different from the usual suspension polymerization method except that the specific dispersant is used and the polymerization is performed under the specific conditions.

Therefore, as the initiator, lauroyl peroxide, benzoyl peroxide, t-butyl peroxypivalate, diisopropyl peroxy dicarbonate, dicyclohexyl peroxy dicarbonate, di (3-methoxybutyl) peroxy dicarbonate, acetylcyclohexyl sulfonyl peroxide are used. Organic peroxides such as oxides or α,
One type of azo compound such as α'-azobisisobutyronitrile, α, α'-azobis-2,4-dimethylvaleronitrile, α, α'-azobis-4-methoxy-2,4-dimethylvaleronitrile Alternatively, a mixture of two or more kinds can be used.

Further, addition of known additives other than the dispersant and the initiator to the polymerization system does not depart from the scope of the present invention.

The method of the present invention is mainly applied to a method for polymerizing vinyl chloride monomer, which is also applicable to vinyl chloride monomer containing 50% or more of vinyl chloride monomer and copolymerizable vinyl monomer. It can also be applied to copolymerization. Examples of such vinyl monomers include alkyl vinyl esters such as vinyl acetate, alkyl vinyl ethers such as cetyl vinyl ether, α-monoolefin monomers such as ethylene or propylene, acrylic acid alkyl esters such as ethyl acrylate, or Examples thereof include methacrylic acid alkyl esters such as methyl methacrylic acid. Furthermore, the method of the present invention can also be applied to the graft polymerization of vinyl chloride monomer onto an olefin polymer such as an ethylene-vinyl acetate copolymer or an ethylene / propylene copolymer.

The polymerization reaction of the vinyl chloride monomer of the present invention is usually 35 to 70 ° C.
With stirring at the temperature of.

〔effect〕

According to the method of the present invention, the yield can be improved in a short time without impairing the quality of the obtained polymer.

〔Example〕

Examples will be shown below, but the present invention is not limited thereto. In the following description, “part” means part by weight unless otherwise specified.

The qualities of the vinyl chloride polymers described in the examples and comparative examples were measured by the following measuring methods.

(A) Absorbency of plasticizer Using a planetary mixer connected to a plastograph, add 400 g of vinyl chloride polymer and 200 g of dioctyl phthalate into a container kept at 80 ° C and stir the kneading torque every hour while stirring. The kneading time is recorded and displayed at the point where the kneading torque has decreased. The shorter the time when the torque decreases, the faster the plasticizer absorbability is.

(B) Thermal stability Soft formulation 100 parts vinyl chloride polymer, 50 parts dioctyl phthalate,
Mix 2 parts of epoxy stabilizer, 0.5 part of calcium stearate and 1 part of zinc stearate and roll 1 at 150 ℃.
Sheet obtained by kneading and molding for 0 minutes (film thickness 0.1 mm, width 30
mm x 45 mm) is expressed by the time until it is blackened by heating with a heat aging tester at 170 ° C. The longer the time, the better the thermal stability.

Hardener formulation 100 parts of vinyl chloride polymer, 4 parts of butyltin mercapto stabilizer and 0.5 parts of calcium stearate are mixed, and the temperature is 150 ° C.
Sheet (film thickness)
0.1mm, width 30mm x length 45mm) is the time required to heat and blacken with a heat aging tester at 190 ℃. The longer the time, the better the thermal stability.

Examples 1 to 3 and Comparative Examples 1 to 3 In a stainless steel polymerization vessel having an internal volume of 200, 100 kg of pure water, 26 g of polyvinyl alcohol having a saponification degree of 70%, 12 g of di (3-methoxybutyl) peroxydicarbonate, acetylcyclohexylsulfonylperoxide 10 g of oxide and 50 kg of vinyl chloride monomer were charged and polymerized at a polymerization temperature of 52 ° C. with stirring. After the polymerization proceeded and the pressure drop started, the temperature was raised after the time shown in Table 1 and the temperature reached the set temperature shown in Table 1 (while the vinyl chloride monomer remaining in the polymerization vessel was not recovered), the residual vinyl chloride monomer Was recovered, and when it reached 5 kg / cm ² G, the slurry was taken out from the polymerization vessel, dehydrated and dried.

Table 1 shows the time from the start of depressurization to the start of recovery of residual vinyl chloride monomer and the time until slurry withdrawal. The thermal stability and plasticizer absorbency of the dry vinyl chloride polymer are also shown in this table.

From this table, it can be seen that if the temperature rising start time is too late, it takes too much time to extract the slurry after the pressure drop starts. Further, it is understood that if the temperature rise temperature is too high, the thermal stability and plasticizer absorbency deteriorate, and if the temperature rise temperature is too low, the yield does not increase.

Comparative Examples 4 to 7 The procedures for charging additives and the like and for the polymerization method were exactly the same as in Example 1, but the procedure after the pressure drop was as shown in Table 2, and the internal pressure of the polymerization vessel was
When the amount reached 5 kg / cm ² G, the slurry was taken out from the polymerization vessel, dehydrated and dried.

Table 2 shows the thermal stability and plasticizer absorbency of the dried vinyl chloride polymer during the time until the slurry was discharged.

From this table, it can be seen that even if the temperature is raised, the yield does not increase at all when the vinyl chloride monomer is recovered during that time. Also, at this time, it can be seen that the quality is not adversely affected even if the temperature rise setting temperature is high. It will be understood that the yield does not increase without recovering the vinyl chloride monomer when the temperature is not raised.

Comparative Examples 8 to 10 The same operations as in Examples 1 to 3 were performed except that the dispersant used was polyvinyl alcohol having a saponification degree of 80% and the amount used was 40 g. The results are shown in Table 3.

Comparative Example 11 The same operation as in Comparative Example 8 was carried out except that the vinyl chloride monomer was recovered after the start of heating. The results are shown in Table 3.

From this table, it can be seen that when polyvinyl alcohol having a saponification degree of 80% is used, the plasticizer absorbability is deteriorated.

Examples 4 to 6 and Comparative Examples 12 to 13 In a stainless steel polymerization vessel having an inner volume of 200, 100 kg of pure water, 25 g of polyvinyl alcohol having a saponification degree of 70%, 11 g of di (3-methoxybutyl) peroxydicarbonate, and acetylcyclohexylsulfonylperoxide were used. 7 g of oxide and 50 kg of vinyl chloride monomer were charged and polymerization was carried out at a polymerization temperature of 57 ° C. with stirring. After the polymerization proceeded and the pressure drop started, the temperature was raised after the time shown in Table 4 and the temperature reached shown in Table 3 (while the vinyl chloride monomer in the polymerization vessel was not recovered during that period), the residual vinyl chloride monomer was recovered. When the amount reached 5 kg / cm ² G, the slurry was taken out from the polymerization vessel, dehydrated and dried.

Table 4 shows the time from the start of depressurization to the start of recovery of residual vinyl chloride monomer and the time to withdraw slurry. The thermal stability and plasticizer absorbency of the dry vinyl chloride polymer are also shown in this table.

Comparative Example 14 The same operation as in Example 4 was performed except that the vinyl chloride monomer was recovered at the time of heating. The results are shown in Table 4.

From this table, it is understood that Examples 4 to 6 are different from Examples 1 to 3 in polymerization temperature, but similar results can be obtained in these cases.

Examples 7 to 8 and Comparative Examples 15 to 16 In a stainless steel polymerization vessel having an internal volume of 200, 100 kg of pure water, 36 g of polyvinyl alcohol having a saponification degree of 70%, α, α′-azobis-2,4-dimethylvaleronitrile 21 g, 40 kg of vinyl chloride monomer and 10 kg of vinyl acetate monomer were charged and polymerized at 63 ° C. with stirring. After the polymerization proceeded and the pressure drop started, the temperature started to rise after the time shown in Table 5 and reached the temperature shown in Table 5 (while the residual vinyl chloride monomer in the polymerization vessel was not recovered).
The residual vinyl chloride monomer was recovered, and when it reached 5 kg / cm ² G, the slurry was taken out from the polymerization vessel, dehydrated and dried.

Table 5 shows the time from the start of depressurization to the start of recovery of residual vinyl chloride monomer and the time until slurry withdrawal. The thermal stability (hardness) of the dry vinyl chloride resin is shown in Table 5.
For rigid applications, no plasticizer was used, so no test for plasticizer absorption was done.

From this table, it can be seen that even in the case of a vinyl chloride / vinyl acetate copolymer, if the temperature rising temperature after the start of the pressure drop is too high, the thermal stability deteriorates, and if the temperature rising temperature is too low, the yield does not increase.

Claims (1)

[Claims] 1. A partially saponified polyvinyl alcohol having a saponification degree of 70 to 78% is used as a suspending agent for suspension polymerization of a vinyl chloride monomer or a vinyl-based monomer mixture containing a vinyl chloride monomer in an aqueous medium. The polymer aqueous dispersion (hereinafter referred to as “slurry”) is used within 40 minutes from the time when the polymerization of the vinyl chloride monomer or the vinyl-based monomer mixture containing the vinyl chloride monomer proceeds and the internal pressure of the polymerization reactor starts to decrease. 5) to 10 ° C above the temperature of the slurry just before the internal pressure of the polymerization reactor begins to drop.
A method for producing a vinyl chloride polymer, characterized in that an operation of raising the temperature is carried out, and the monomer is recovered when the temperature rises to a predetermined temperature.