JPH0717712B2 - Method for producing vinyl chloride polymer for soft molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a vinyl chloride-based polymer for soft molding, and particularly, to a vinyl chloride-based monomer in an aqueous medium without delaying the polymerization time so much. Polymerized under high productivity,
The present invention relates to a method for producing a vinyl chloride polymer having a high bulk density and excellent plasticizer absorbability, which is suitable for soft molding.

(Prior Art) A vinyl chloride-based polymer generally contains an aqueous medium in a polymerization vessel,
It is manufactured by charging a dispersant (suspension agent), a polymerization initiator and a monomer, and raising the temperature to cause a polymerization reaction. In recent years, in this polymerization, the polymerization conversion rate after starting the polymerization reaction was 70%.
It has been proposed to additionally charge an amount of vinyl chloride-based monomer that does not exceed 50% by weight with respect to the initially charged monomer at the time of reaching 80% to 80% to terminate the polymerization. According to this, the production amount per batch can be increased without significantly delaying the polymerization time, and a polymer having a high bulk density can be obtained (see JP-B-59-28209).

However, when this method is used, the desorption of the unreacted monomer stored in the polymer is poor, which makes it difficult to desorb the unreacted monomer after completion of the polymerization, and the quality of the polymer is not constant and varies. There is a defect that can be seen. Further, the polymer has poor plasticizer absorbability, and there is a problem that a large amount of ungelled particles are present during molding processing (heat gelation) with a soft compounding formulation.

(Structure of the Invention) The present inventors have solved the technical problem in improving productivity by additional charging, increased the production amount per batch without significantly delaying the polymerization time, and absorbed a plasticizer having a large bulk density. We have completed a method for easily producing a vinyl chloride polymer with excellent properties as a high-quality grade suitable for soft molding.

That is, the present invention, in the polymerization vessel, an aqueous medium, a dispersant, a polymerization initiator and a vinyl chloride-based monomer are charged to start the polymerization reaction, and while the polymerization conversion rate reaches 45 to 65%, vinyl chloride-based An additional charge of monomer is added, and a partially saponified polyvinyl alcohol having a polymerization degree of 200 to 400 and a saponification degree of 30 to 75 mol% is additionally charged at a time within ±5% of the polymerization conversion rate at the time of the additional charge. The present invention relates to a method for producing a vinyl chloride polymer for soft molding, which comprises adding 0.01 to 5% by weight to the amount of the vinyl chloride monomer to complete the polymerization reaction.

The present invention will be described in detail below.

The method of the present invention is characterized in that a specific partially saponified polyvinyl alcohol is added during the additional charging of the vinyl chloride-based monomer in an amount not exceeding 50% by weight of the initial charging amount during the polymerization reaction. However, the timing of the additional charging of the monomer needs to be between 45% and 65% of the polymerization conversion rate of the initially charged vinyl chloride-based monomer,
If additional charging is carried out when the polymerization conversion rate is less than 45%, the intended polymer (powder) having a high bulk density cannot be obtained. On the other hand, if the additional charging is carried out at a time of exceeding 65%, not only the bulk density will not rise but the polymerization time will be greatly delayed, and the purpose of improving the production efficiency cannot be achieved.

As the partially saponified polyvinyl alcohol added to the polymerization system at a time within the range of ±5% of the polymerization conversion rate during the additional charging, those having a polymerization degree of 200 to 400 and a saponification degree of 30 to 75 mol% are included. used. If the polymerization degree and saponification degree out of these ranges are used, the resulting polymer tends to produce a large amount of ungelled particles during molding, and the desorption of the monomer occluded in the polymer after the completion of the polymerization. However, there is a disadvantage that the monomer is likely to remain in the product polymer.

It is necessary to add this partially saponified polyvinyl alcohol to the polymerization system before or after the time when the vinyl chloride monomer is additionally charged, and this time will be described with reference to the accompanying drawings.
That is, the drawing shows the relationship between the polymerization time and the polymerization conversion rate for the monomers initially charged in the polymerization vessel.At the time when the additional conversion of vinyl chloride-based monomer reached the polymerization conversion rate of 50%, In the case of starting at (point P on the polymerization curve in the figure), the addition timing of the partially saponified polyvinyl alcohol is in the range of A in the figure (range of polymerization conversion rate of ±5% of point P). If the addition time of the partially saponified polyvinyl alcohol is too early, the added partially saponified polyvinyl alcohol is mostly adsorbed by the polymer particles existing in or generated in the polymerization system, and the polyvinyl chloride-based monomer is added during the additional charging period. The effect of sit up will be lost, and if it is added too early (the initial stage of polymerization), the resulting polymer particles will become too fine, and the agitator torque will become abnormally high at the end of polymerization, which will be disadvantageous. . There is no point in adding the vinyl chloride-based monomer at a later time after the additional charging.

The amount of the partially saponified polyvinyl alcohol added to the polymerization system needs to be 0.01 to 5% by weight with respect to the amount of the vinyl chloride monomer additionally charged. If the amount added is too small, the effect of reducing the amount of ungelled particles during molding of the polymer and facilitating the desorption of the occluded monomer in the polymer cannot be obtained. Even if added in a large amount exceeding 5% by weight, no further effect can be obtained, which is economically disadvantageous.

The additional charging of the vinyl chloride-based monomer is performed by a method such as pump charging or batch charging with a head tank. The additional charging amount is automatically limited depending on the initial charging conditions, polymerization vessel volume, stirring conditions, etc., but it is also possible to continuously add, for example, a portion corresponding to volume contraction accompanying the progress of the polymerization reaction for a certain period. is there. It should be noted that water may be appropriately added to control the increase in stirring torque at the final stage of polymerization during the additional charging.

There are no particular restrictions on the charging conditions at the beginning of the polymerization. For example, the amount of the vinyl chloride-based monomer with respect to the amount of the aqueous medium may be generally in the range of 0.5 to 1.0 in terms of weight ratio, and the polymerization initiator, the dispersant (suspension agent), etc. are conventionally known. Stuff used.

As the polymerization initiator, acetylcyclohexyl sulfonyl peroxide, isobutyroyl peroxide, 2,
2'-azobis(4-methoxy-2,4-dimethyl)valeronitrile, di-2-ethylhexyl peroxydicarbonate, di-sec-butyl peroxydicarbonate,
Cumyl peroxy neodecanoate, tert-butyl peroxypivalate, tert-butyl peroxy neodecanoate, 2,2'-azobis-2,4-dimethylvaleronitrile,
Lauroyl peroxide, tert-butylperoxy-
Examples include 3,5,5-trimethylhexanoate and 3,5,5-trimethylhexanoyl peroxide. In addition, these are not limited to one type, and two or more types may be used in combination,
The amount used is generally 0.01 to 1 for vinyl chloride-based monomers.
It is about 5% by weight.

Examples of the dispersant used for the initial charging in the present invention include water-soluble cellulose ethers such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose, partially saponified polyvinyl alcohol, acrylic acid polymers, water-soluble polymers such as gelatin, and sorbitan mono. Laurate, sorbitan trioleate, glycerin tristearate, oil-soluble emulsifiers such as ethylene oxide propylene oxide block copolymer, polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerin oleate, water-soluble emulsifiers such as sodium laurate, etc. are exemplified. These are used alone or in combination of two or more. The amount of the dispersant charged in the initial stage is generally in the range of 0.005 to 2.0% by weight based on the vinyl chloride monomer.

The vinyl chloride-based monomer to be polymerized by the method of the present invention includes vinyl chloride alone and a monomer mixture mainly composed of vinyl chloride (50% by weight or more of vinyl chloride), which is copolymerized with vinyl chloride. Examples of the comonomer to be used include vinyl acetate such as vinyl acetate and vinyl propionate, acrylic ester or methacrylic ester such as methyl acrylate and ethyl acrylate, olefins such as ethylene and propylene, maleic anhydride, acrylonitrile, styrene and vinylidene chloride. , And other monomers copolymerizable with vinyl chloride.

Furthermore, it is also optional to appropriately add a polymerization regulator, a chain transfer agent, a polymerization inhibitor, a gelation improving agent, an antistatic agent, a pH adjusting agent and the like which are usually used for the polymerization of vinyl chloride type monomers.

As described above, according to the present invention, the yield per batch can be increased without significantly delaying the polymerization time, and the bulk density is large and the plasticizer absorbability is excellent. It is possible to manufacture a united body.

Examples will be described below, but the scope of the present invention is not limited by these. The physical properties described in the examples were according to the following methods.

Degree of polymerization: According to JIS K 6721.

Bulk specific gravity: Based on JIS K 6721.

Residual monomer amount: A certain amount of the sample resin was dissolved in tetrahydrofuran and the monomer content in the resin was quantified by gas chromatography. Residual monomer amount is pp per dry resin
Expressed in m.

Particle size distribution: According to JIS Z 8801.

Plasticizer absorption: Glass fiber is packed in the bottom of an aluminum alloy container with an inner diameter of 25 mm and a depth of 85 mm, and 10 g of sample resin is sampled and charged. Dioctyl phthalate (DO
P) Add 15cc and let stand for 30 minutes to allow DOP to penetrate the resin sufficiently. After that, excess DOP is centrifuged under an acceleration of 1500 G, and the amount of DOP absorbed by the resin is obtained as a value per 100 parts by weight of the resin.

Fish-eye test: 100 parts by weight of sample resin, 1 part by weight of tribasic lead sulfate, 1.5 parts by weight of lead stearate, 0.2 parts by weight of titanium dioxide, 0.1 parts by weight of carbon black, and 25 g of compound at 145° C., which is mixed with 50 parts by weight of DOP. Knead for 5 minutes on a roll and separate as a 0.2 mm thick sheet.
It is shown by the number of transparent particles in cm ² .

Comparative Example 1 Partial saponification with 910 kg of deionized water heated to 50° C., degree of polymerization 2500, and degree of saponification 80 mol% was added to a stainless steel polymerization vessel equipped with a jacket having an inner volume of 2.1 m ³ (inner diameter 1.05 m) and a stirring blade. After charging 305 g of polyvinyl alcohol and 115 g of hydroxypropylmethyl cellulose and degassing the inside of the polymerization vessel to 50 mm Hg, 700 kg of vinyl chloride monomer was charged, and while stirring, the temperature was raised to 58.7°C and at the same time di-2-
365 g of ethylhexyl peroxydicarbonate was added, the polymerization reaction was carried out while controlling the internal temperature to 58.7° C., and the unreacted monomer was recovered when the internal pressure of the polymerization vessel dropped to 6 kg/cm ² G. At the same time, hot water was passed through the jacket to raise the internal temperature of the polymerization vessel to 75°C. Recovery of unreacted monomers to the polymerization vessel internal pressure of 0 kg / cm ² G is carried by its own pressure, to start the suction in the vacuum blower from reaching 0 kg / cm ² G, the polymerization vessel internal pressure -0.5 kg / The vacuum blower was stopped 15 minutes after reaching cm ² G. After the internal pressure of the polymerization vessel was returned to 0 kg/cm ² G with air, cooling water was passed through the jacket to cool the polymerization content (slurry). The taken out slurry was dehydrated and dried and used for various tests.

Examples 1 to 5 and Comparative Examples 2 to 6 The same polymerization vessel as in Comparative Example 1 was charged with deionized water heated to 50°C.
910 kg, degree of polymerization 2500, saponification degree of 80 mol% 305 g of partially saponified polyvinyl alcohol and 115 g of hydroxypropyl methylcellulose were charged, and the inside of the polymerization vessel was degassed to 50 mm Hg, then 700 kg of vinyl chloride monomer was charged and stirred. However, the temperature starts to rise to 58.7°C and at the same time 365 g of di-2-ethylhexyl peroxydicarbonate is added to proceed the polymerization, and at the specified time, the partially saponified polyvinyl alcohol shown below is added and the vinyl chloride monomer is added. After the charging, the polymerization reaction was terminated and post-treatment was performed. However, the additional charging of the vinyl chloride monomer was performed at a speed of 1 m ³ /hr. The results are as shown in Table 1.

[Partially saponified polyvinyl alcohol (partially saponified PVA)]

A: Polymerization degree of 310 to 390, saponification degree of 45 to 51 mol% B: Polymerization degree of 1500 or more, saponification degree of 86.5 to 89 mol% C: Polymerization degree of 310 to 390, saponification degree of 71 to 75 mol% D: Degree of polymerization 310 to 390, degree of saponification 69.5 to 72.5 mol% From the results of Table 1, according to the method of the present invention, the plasticizer absorbency of the obtained polymer, residual monomer, fish eye,
It is possible to obtain a material suitable for soft molding, which has a good particle size and distribution and a high bulk density. Furthermore, it is possible to increase the yield per batch without significantly delaying the polymerization time, and it is possible to produce a balanced and high quality polymer with high productivity, and its industrial value is important. is there.

[Brief description of drawings]

The drawing shows the relationship between the polymerization time and the polymerization conversion rate, and shows that the addition timing of the partially saponified polyvinyl alcohol is in the range of A when the monomer is additionally charged at point P. It was done.

Claims (1)

[Claims] 1. A polymerization vessel is charged with an aqueous medium, a dispersant, a polymerization initiator and a vinyl chloride-based monomer to initiate a polymerization reaction, and a vinyl chloride-based resin is added while the polymerization conversion rate reaches 45 to 65%. The monomer is additionally charged, and the polymerization degree is 200 to 400 and the saponification degree is 30 at a time within ±5% of the polymerization conversion rate at the time of the additional charge.
Partially saponified polyvinyl alcohol having a content of ~75 mol% is added to the amount of the vinyl chloride-based monomer additionally charged.
A method for producing a vinyl chloride polymer for soft molding, which comprises adding 01 to 5% by weight to complete a polymerization reaction.