JPH0410887B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an improved method for producing vinyl chloride polymers, and in particular, an object of the present invention is to obtain high quality vinyl chloride polymers that have a high bulk specific gravity and very little buildup. (Prior art) Conventionally, vinyl chloride polymers have been mass-produced by suspension polymerization of monomers in an aqueous medium using an oil-soluble polymerization initiator. From the viewpoint of productivity (increase in the amount of extrusion per hour) when extrusion molding products, etc., a polymer with a high bulk specific gravity is required. It is well known that when vinyl chloride is subjected to suspension polymerization in an aqueous medium, the bulk specific gravity of the resulting polymer is generally largely dependent on the type of dispersant and stirring conditions. Various proposals have been made for doing so.
However, when the bulk specific gravity becomes high, the porosity of the polymer decreases and there is a problem that the porosity of the polymer increases. On the other hand, from the viewpoint of gelation properties during molding and plasticizer absorption, a polymer with high porosity is desired, and this porosity can be improved by methods such as adding surfactants to the polymerization system. However, in this case, the bulk specific gravity becomes low. As described above, increasing the bulk specific gravity and improving the porosity are in a contradictory relationship, and it is extremely difficult to satisfy both of these requirements at the same time. Recently, in order to solve this problem,
A method using a water-insoluble crosslinked polymer containing a carboxyl group and a nonionic surfactant as a dispersant has been proposed (Publication Patent Publication No. 57-500614).
No. 57-500650) is effective to some extent in increasing the bulk specific gravity, but it is insufficiently effective in improving the porosity and obtaining polymers free of fibers, especially the problem with fibers. This is a major drawback in obtaining high-quality molded products and must be solved. (Structure of the Invention) The present inventors completed the present invention as a result of intensive research aimed at obtaining a high-quality polymer that has a particularly high bulk specific gravity and is free of fish eyes (glass bead particles). That is, the present invention provides a method for polymerizing vinyl chloride or a monomer mixture mainly composed of vinyl chloride in an aqueous medium containing an oil-soluble polymerization initiator and a nonionic surfactant. The polymerization reaction is started by adding the polymer in an amount of 1 to 30% (preferably 1 to 20%) of the total amount added into an aqueous medium, and at a point when the polymerization conversion rate reaches 1% to 20%. The present invention relates to a method for producing a vinyl chloride polymer characterized by adding the remaining amount of the crosslinked carboxyl group-containing copolymer. High-quality polymers with extremely low buildup can be stably obtained. The present invention will be explained in detail below. Glass bead particles, which cause fish eyes in vinyl chloride polymers, are generated due to non-uniform dispersion of the polymerization initiator in the vinyl chloride monomer at the initial stage of polymerization. In order to uniformly disperse the polymerization initiator into the monomers, the polymerization initiator must be thoroughly stirred after it is charged into the reactor and before the temperature is raised to start polymerization. Possible methods include a method in which the polymerization initiator is dissolved in the monomer in advance and then charged. However, in the former method of frequent stirring, if the dispersant added to the aqueous medium has a high viscosity, uniform dispersion of the polymerization initiator cannot be achieved, and if The charging method has the disadvantage that scale is generated in the dissolution tank and the charging piping. Furthermore, uniform mixing of the polymerization initiator cannot be achieved even if the polymerization initiator is dissolved and charged in a small amount of monomer and then a large amount of monomer is added to provide a washing effect. As a result of considering these matters and conducting repeated experiments, the present invention has revealed that vinyl chloride or a monomer mainly composed of vinyl chloride can be used in an aqueous medium containing a polymerization initiator and a nonionic surfactant, as described above. When polymerizing the body mixture, a crosslinked carboxyl group-containing copolymer (hereinafter simply referred to as a crosslinked copolymer) is used.
A small amount of the crosslinked copolymer is present in the aqueous medium to start the polymerization reaction, and when the polymerization conversion rate reaches 1% to 20%, the crosslinked copolymer is added again to carry out the polymerization reaction. According to this method, the monomer dispersion system at the start of the polymerization reaction is maintained stably, and a high-quality polymer having a high bulk specific gravity and no fish eyes (glass bead particles) can be obtained. If the entire amount of the crosslinked copolymer is added from the beginning or when the polymerization conversion rate is less than 1%, glass bead particles will be produced in large numbers for reasons that are not clear, and as a result, the polymer will be of low quality with a lot of stickiness. On the other hand, if the cross-linked copolymer is added at a point when the polymerization conversion rate exceeds 20%, the amount of fisheye will not increase, but the resulting polymer particles will coalesce during the polymerization, so the polymer particles will become immobile. It becomes uniform and has a low bulk specific gravity. Furthermore, if the proportion of the monomer in the feed is increased in order to improve production efficiency through polymerization, the dispersion system may become unstable depending on operating conditions, resulting in the formation of glass beads. According to the method of the present invention, both of these problems can be solved at once. The crosslinked copolymer used in the present invention is an important additive for obtaining a polymer with a high bulk specific gravity, and by making it present in an aqueous medium, it has a very strong effect on monomer droplets. It has the advantage of exhibiting excellent dispersant action (stabilizing action) and producing polymers of uniform particle shape. This crosslinked copolymer is a crosslinked copolymer of a compound (crosslinking agent) having two or more terminal polymerizable CH ₂ =C= groups in one molecule and a polymerizable unsaturated carboxylic acid compound. Examples of the crosslinking agent include divinylbenzene, divinylnaphthalene, soluble polymerized dienes such as polybutadiene, ethylene glycol diacrylate, ethylene glycol dimethacrylate, acryl acrylate, methylene bisacrylamide, divinyl ether, diallyl ether, pentaerythritol, mannitol, etc. , sorbitol, glucose, sutucarose, polyallyl, polyvinyl, etc., as well as general formula (R in the formula is a hydrogen atom or a methyl group, l, m,
n indicates a number satisfying 0<l+m+n≦500,
However, only when R represents a hydrogen atom and n=0, numbers that satisfy l+m=1 are excluded. Allyl ether, diethylene glycol bismethallyl ether, is exemplified. On the other hand, examples of polymerizable unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, chloroacrylic acid, cyanoacrylic acid, α-phenylacrylic acid, α-benzylacrylic acid, crotonic acid, maleic acid, fumaric acid, Examples include sorbic acid. Note that the crosslinking agent and the polymerizable unsaturated carboxylic acid are not limited to one type each, and two or more types may be used in combination. The copolymerization ratio of the crosslinking agent and the polymerizable unsaturated carboxylic acid is preferably 0.05 to 10 parts by weight, preferably 0.1 to 5 parts by weight, per 100 parts by weight of the polymerizable unsaturated carboxylic acid. If the amount is too small, the crosslinking effect will not be obtained, and if the amount is too large, the crosslinking will be excessive and the copolymer will no longer exhibit the effect of a dispersant. The crosslinking copolymerization reaction is carried out using an azo-based, peroxide-based, redox-based catalyst, etc. as a polymerization initiator, such as azobisisobutyronitrile, 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile). ), benzoyl peroxide, cumene hydroperoxide, tertiary butyl hydroperoxide, persulfates, combinations of persulfates and percarbonates,
This is carried out by using a combination of persulfate and sulfite and reacting in a solvent such as benzene, toluene, n-hexane, or ethyl acetate. Next, examples of nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene polystyrylphenyl ether, polyoxyethylene polyoxypropylene block copolymer, glycerin fatty acid partial ester, and sorbitan. Fatty acid partial ester, pentaerythritol fatty acid partial ester, propylene glycol monofatty acid ester, sucrose fatty acid partial ester, polyoxyethylene sorbitan fatty acid partial ester,
Polyoxyethylene sorbitol fatty acid partial ester, polyoxyethylene glycerin fatty acid partial ester, polyethylene glycol fatty acid ester, polyglycerin fatty acid partial ester, polyoxyethylated castor oil, fatty acid diethanolamide, N,N-bis-2-hydroxyalkylamine, poly Examples include oxyethylene alkylamine, triethanolamine fatty acid ester, and trialkylamine oxide, which may be used alone or as a mixture of two or more. In the present invention, a nonionic surfactant is added to the aqueous medium, and the crosslinked copolymer is divided into two stages: before the start of the polymerization reaction and after the start of the polymerization reaction, when the polymerization conversion rate reaches the above-mentioned constant value. The amount of the nonionic surfactant is 0.005 to 1 part by weight (preferably 0.01 to 0.5 part by weight) per 100 parts by weight of monomer to be added, and the total amount of crosslinked copolymer is 0.01 part by weight. ~2 parts by weight (preferably 0.02-0.5 parts by weight)
It is better to Polymerization initiators used in carrying out the method of the present invention include diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, acetylcyclohexylsulfonyl peroxide, t-butylperoxypivalate, Organic peroxides such as benzoyl peroxide and lauroyl peroxide, azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, and azobis-2,4-dimethoxy-2,4-dimethylvaleronitrile. etc. are exemplified. The method of the present invention is particularly suitably applied to suspension polymerization of vinyl chloride or a monomer mixture mainly composed of vinyl chloride, but when the purpose is to obtain a copolymer, comonomers such as vinyl acetate etc. vinyl esters, vinyl ethers, acrylic acid or methacrylic acid and their esters, maleic acid or fumaric acid or their esters,
Examples include maleic anhydride, aromatic vinyl compounds, unsaturated nitrile compounds such as acrylonitrile, vinylidene halides such as vinylidene fluoride and vinylidene chloride, and olefins such as ethylene and propylene. Note that the amount of polymerization initiator added, polymerization temperature, polymerization time, etc. may be determined according to the conditions conventionally adopted when vinyl chloride is polymerized in an aqueous medium, and these are not particularly limited. . According to the method of the present invention, in addition to the above-mentioned effects, the amount of scale adhesion on the inner wall of the polymerization vessel and the surface of the stirring device section is reduced. Further improvement can be achieved by adding a basic substance in an amount of 0.1% by weight or less based on the monomers charged. Next, specific examples will be given. Examples 1 to 2, Comparative Example 1 In a stainless steel polymerization vessel with an internal volume of 100, 60 kg of deionized water, 30 g of poly(20) polyoxyethylene sorbitan monooleate as a nonionic surfactant, and the following crosslinked copolymer were placed. an aqueous solution containing the parts by weight shown in Table 1, and di-2 as a polymerization initiator.
-20g of ethylhexyl peroxydicarbonate
After deaerating the inside of the polymerization vessel, 30 kg of vinyl chloride monomer was charged. Polymerization was initiated by raising the temperature to 57°C while stirring. When the polymerization conversion rate shown in Table 1 was reached (2% or 15%), an aqueous solution containing the following crosslinked copolymer in the parts by weight shown in Table 1 was added to the polymerization system to cause a polymerization reaction. . Crosslinked copolymer: (1) Crosslinked copolymer of 100 parts by weight of acrylic acid and 1 part by weight of diethylene glycol bisallyl ether The polymerization reaction was carried out in this manner, and the internal pressure of the polymerization vessel became 6.0 Kg/cm ² G. At this point, the polymerization was stopped, unreacted monomers were collected, and the polymer slurry was taken out and dehydrated and dried to obtain a polymer. When this polymer was measured for bulk specific gravity, plasticizer absorption, and firm eye, the results shown in Table 1 were obtained. In addition, the results of Comparative Example 1 below are also listed in the same table. Comparative Example 1 The same procedure as in Example 1 was carried out except that the crosslinked copolymer was added at a time when the polymerization conversion rate was 0%. As shown in Table 1, in Examples 1 and 2, high-quality polymers with a bulk specific gravity of 0.53 g/ml or more, a large amount of plasticizer absorption, and extremely low buildup were obtained. can get.
On the other hand, in Comparative Example 1, although the bulk specific gravity is high, the plasticizer absorbability is poor, and there is an extremely large amount of fisheye, so that the object of the present invention cannot be achieved.

[Table] Example 3 In Example 2, in order to increase productivity, the amount of deionized water was 54 kg and the amount of vinyl chloride monomer was 36 kg, and accordingly the amount of crosslinked copolymer added was 10.8 kg before polymerization.
g, during polymerization (added when polymerization conversion rate is 15%) 36.0g
Polymerization was carried out in the same manner except for the following. As a result, the bulk specific gravity was 0.58g/ml, and the amount of plasticizer absorbed
24.0% polymer was obtained. Moreover, this polymer had three fish eyes.

Claims (1)

[Scope of Claims] 1. When vinyl chloride or a monomer mixture mainly composed of vinyl chloride is polymerized in an aqueous medium containing a polymerization initiator and a nonionic surfactant, crosslinked carboxyl group-containing A polymerization reaction is started by adding 1 to 30% of the total amount of the copolymer added to an aqueous medium, and when the polymerization conversion rate reaches 1% to 20%, the crosslinked carboxyl groups are added. A method for producing a vinyl chloride polymer, which comprises adding the remaining amount of the copolymer contained therein. 2 The crosslinked carboxyl group-containing copolymer has the general formula (R in the formula is a hydrogen atom or a methyl group, l, m,
n indicates a number satisfying 0<l+m+n≦500,
However, only when R represents a hydrogen atom and n = 0, numbers satisfying l + m = 1 are excluded) obtained by copolymerizing a crosslinking agent represented by the formula 1 and a polymerizable unsaturated carboxylic acid compound. A method for producing a vinyl chloride polymer according to claim 1. 3. Claim 1, wherein the crosslinked carboxyl group-containing copolymer is obtained by crosslinking and copolymerizing 100 parts by weight of acrylic acid and 0.05 to 10 parts by weight of diethylene glycol bisallyl ether.
A method for producing a vinyl chloride polymer as described in Section 1. 4. The chloride according to claim 1, wherein the crosslinked carboxyl group-containing copolymer is obtained by crosslinking and copolymerizing 100 parts by weight of acrylic acid and 0.05 to 10 parts by weight of diethylene glycol bismethallyl ether. A method for producing a vinyl polymer.