JPS6228163B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dispersion stabilizer for suspension polymerization of vinyl chloride. When producing vinyl chloride resins industrially, a suspension polymerization method is widely used in which vinyl chloride monomers are dispersed in an aqueous medium in the presence of a suspension dispersion stabilizer and polymerized using an oil-soluble catalyst. There is. In general, the factors that control the quality of the resin include the polymerization rate, water-monomer ratio, polymerization temperature, amount of catalyst, and type and amount of dispersion stabilizer, among which it is said that the dispersion stabilizer has the greatest influence. It is being said. The performance required for a dispersion stabilizer for vinyl chloride polymerization is that it exhibits sufficient dispersion power even when used in small amounts.
In order to sharpen the particle size distribution of the vinyl chloride polymer particles obtained, and to increase the plasticizer absorption rate of the polymer particles and facilitate molding, the particles are made with a porous material with a large porosity. In order to remove vinyl chloride monomer remaining in porous particles and prevent the formation of fissures in molded products, the porosity of each polymer particle is kept within a nearly constant range. For example, it has the function of making people fall in love. Particularly recently, there has been a strong demand for satisfying the performance mentioned above. In other words, due to pollution issues, the number of residual monomers in vinyl chloride polymer particles has to be reduced.
It is considered an essential condition to reduce the residual monomer to below ppm, and for this purpose, a method is usually used to blow steam into a packed tower filled with polymer particles to drive out the remaining monomer. If so, the purification efficiency such as the rate of demonomerization will be almost constant for all particles, so only the minimum amount of steam treatment is required and process control is extremely easy. Since the particles are uniformly welded together during molding, there is a great advantage that a molded product of good quality can be obtained without any build-up eyes or the like. Conventionally, polyvinyl alcohol has been widely used as a dispersion stabilizer. Polyvinyl alcohol is usually produced by polymerizing vinyl acetate in methyl alcohol (methanol) and saponifying the resulting polyvinyl acetate, but the dispersion stabilizer satisfies the requirements to some extent. Even if it is possible, it is completely impossible to satisfy the requirements that are not necessarily sufficient.
The reality is that a dispersion stabilizer that satisfies both of these requirements has not yet been found. However, as a result of intensive research in order to solve this problem, the present inventor found that under the temperature during polymerization,
Manufactured by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate in an alcohol with a chain transfer constant of 20 × 10 ^-4 or more. Average degree of saponification 60 to 90 mol%, average degree of polymerization 100 to 1500. When using polyvinyl alcohol as a dispersion stabilizer, the resulting vinyl chloride polymer particles have a large porosity, and the porosity is almost constant among each particle, and the particle size distribution is sharp, etc. In addition, the average degree of saponification of polyvinyl alcohol and the average degree of polymerization produced in the above-mentioned methanol solvent is 60 to 90 mol%, and the average degree of polymerization is 100 to 100.
When used together with 3000 polyvinyl alcohol,
The present invention was completed by discovering that polymerization stability can be further improved. As mentioned above, a major feature of the dispersion stabilizer of the present invention is that it is produced in a specific alcohol solvent. The reason why such an effect is obtained is not clear, but when vinyl acetate is polymerized in an alcohol with a chain transfer constant of 20 × 10 ^-4 or more, even if the average degree of polymerization is within the same range, the polymerization occurs in a methanol solvent. Polyvinyl acetate with a different degree of polymerization distribution than that obtained in methanol is obtained, and even in the next saponification step, polyvinyl acetate obtained in methanol has a different degree of saponification distribution even though it is within the same degree of saponification range. It is presumed that polyvinyl alcohols with different numbers of polyvinyl alcohols can be produced, and that this difference in distribution changes the dispersion of vinyl chloride monomers and polymers in water to a desirable state. The alcohol used in the present invention has a chain transfer constant for vinyl acetate of 20×10 ^-4 or more at the polymerization temperature, and includes ethyl alcohol, isopropyl alcohol, isobutyl alcohol, sec-butyl alcohol, amyl alcohol, 2- Ethylhexyl alcohol, dodecyl alcohol, hexadecyl alcohol, octadecyl alcohol,
Examples include furfuryl alcohol, cyclopentanol, cyclohexanol, ethylene glycol, diethylene glycol, and the like. Further, the dispersion stabilizer of the present invention has an average saponification degree of 60.
90 mol% and an average degree of polymerization of 100 to 1,500, and the effects of the present invention cannot be obtained outside of any of the above ranges. In the present invention, vinyl acetate is polymerized using these alcohols as a solvent and a radical polymerization catalyst under pressure or normal pressure. After the polymerization is completed, the obtained polyvinyl acetate is replaced with the same solvent as the polymerization solvent or with a methanol solvent, and then saponified according to a conventional method. During polymerization, it is also possible to use vinyl acetate together with a monomer that can be copolymerized with vinyl acetate, such comonomers include ethylene, propylene,
Isobutylene, α-octene, α-dodecene, α
- Olefins such as octadecene, acrylic acid,
Unsaturated carboxylic acids or their salts such as methacrylic acid, crotonic acid, and marinic acid, or their alkyl esters, nitrites such as acrylonitrile and methacrylonitrile, amides such as acrylamide and methacrylamide, ethylene sulfonic acid, allylsulfonic acid, and methalyl. Olefin sulfonic acids or salts such as sulfonic acids, basic monomers such as N-vinylimidazole, 2-, 3- or 4-vinylpyridine, dimethylaminoethyl acrylate, mono(2-hydroxyethyl acrylate) acid phosphate, mono Phosphate group-containing monomers such as (2-hydroxyethyl methacrylate) acid phosphate, vinyl ether,
Examples include vinyl ketone, N-vinylpyrrolidone, vinyl halide, and vinylidene halide. When these comonomers are used, their proportion in the copolymer is preferably less than 50 mol%, particularly less than 20 mol%. For saponification, the polymer is dissolved in alcohol, hydrous alcohol, or alcohol-methyl acetate mixture and saponified with acid or alkali.
Examples of the alcohol include methanol, ethanol, propanol, etc., and methanol is preferably used. The concentration of polymer in the alcohol is usually selected from the range 10-80% by weight. Saponification catalysts include alkali catalysts such as alkali metal hydroxides and alcoholates such as potassium hydroxide, sodium hydroxide, sodium methylate, sodium ethylate, potassium methylate, and potassium ethylate, or acid catalysts such as sulfuric acid and hydrochloric acid. is used. The amount of such catalyst used is usually 5 to 100 mmol based on vinyl acetate. The temperature of the saponification reaction is not particularly limited, but is preferably 10 to 50℃, preferably 20 to 50℃.
A range of 40°C is chosen. In addition to the above-mentioned method, the saponification reaction can also be carried out by the following method. A saponification catalyst is added to an alcohol solution of polyvinyl acetate or an alcohol-methyl acetate mixed solution,
A so-called dispersion saponification method is carried out in which the polyvinyl acetate is dispersed in an alcohol solution or an alcohol-methyl acetate solution and an inert medium that has little compatibility with the produced polyvinyl alcohol, and saponification is carried out. At this time, if necessary, it is also possible to use a small amount of intervening surfactant. Examples of the inert medium include liquid paraffin, spindle oil, kerosene, etc., and the weight ratio of the inert medium to the alcoholic solution of polyvinyl acetate is suitably 0.2:1 to 5:1. The saponification temperature in the dispersion saponification method is selected from the range of 5 to 60°C, preferably 20 to 40°C. Such a dispersion saponification method is a useful method for producing partially saponified polyvinyl alcohol with a relatively low degree of saponification. In the present invention, the polyvinyl alcohol (A) obtained as described above and the polyvinyl acetate obtained in a normal methanol solvent are saponified to produce an average saponification degree of 60 to 90 mol% and an average polymerization degree of 100. -3000 polyvinyl alcohol (B), the effect is further improved, so the combination is desirable. This effect is due to the fact that the coexistence of components (A) and (B) makes the polymerization degree distribution and saponification degree distribution of polyvinyl alcohol very broad compared to conventional polyvinyl alcohol. It is thought that preferable performance as a dispersion stabilizer possessed by each polyvinyl alcohol component can be obtained by taking advantage of the multifaceted properties depending on the degree of saponification. Among these combinations, (A) has an average degree of saponification of 65 to 80 mol% and an average degree of polymerization of 100 to 500, and (B) has an average degree of saponification of 70 to 85 mol% and an average degree of polymerization of
Combined use with polyvinyl alcohol of 500-3000
It is particularly desirable in terms of surfactant ability and protective colloidal power. If the average degree of saponification of the dispersion stabilizer (B) is less than 60 mol%, the protective colloid property will decrease and the particle size distribution of the particles will become broad, and if it is more than 90 mol%, the surface activity will decrease and the porosity of the particles will decrease. There are drawbacks to doing so. On the other hand, when the average degree of polymerization is 100 or less, a product with a large polymer particle size is likely to be obtained, and when it is 3000 or more, the particle size distribution becomes broad. When (A) and (B) are used in combination, the mixing weight ratio is suitably selected from (A)/(B) = 9/1 to 0.1/9.9, preferably 7/3 to 0.5/9.5. When using such combinations, (A) and (B) do not simply mix polyvinyl alcohol produced separately; for example, during the polymerization of vinyl acetate, the chain transfer constant of methanol etc. is maintained until a certain polymerization rate is reached. A method in which polymerization is carried out in a small solvent or without a solvent, and then the alcohol solvent of the present invention is substituted halfway through the polymerization to continue the polymerization, or conversely, the alcohol solvent of the present invention is present at the beginning of the polymerization, and the solvent is substituted with methanol midway through. Polyvinyl alcohol produced by saponifying polyvinyl acetate obtained by any method such as a method in which the polymerization is continued can also be used. In industrial practice, it is advantageous to produce polyvinyl alcohol by the latter two methods. In addition, the dispersion stabilizer of the present invention can be used by mixing two or more types with different degrees of saponification and polymerization, as long as both (A) and (B) satisfy the provisions of the present application. . When polyvinyl alcohol obtained by the method of the present invention is used as a dispersion stabilizer to carry out suspension polymerization of vinyl chloride, the dispersion stabilizer is usually added to the aqueous medium, the vinyl chloride monomer is dispersed, and the oil-soluble catalyst is done in the presence of The dispersion stabilizer is added to the aqueous medium as a powder or in the form of a solution. When added in the form of a solution, it can be added as an aqueous solution, or as a solution dissolved in an organic solvent such as alcohol, ketone, ester, or a mixed solvent with water. The dispersion stabilizer is used in an amount of 0.01 to 5% by weight, preferably 0.01 to 3% by weight, based on the vinyl chloride monomer. The catalyst used may be any oil-soluble catalyst, such as benzoyl peroxide, lauroyl peroxide, diisopropyl peroxydicarbonate, α・α′-azobisisobutyronitrile, α・α′- Azobis-2,4-dimethylvaleronitrile, acetylcyclohexylsulfonyl peroxide or mixtures thereof are used. The polymerization temperature is selected from a range of about 30 to 70°C. It is also possible to appropriately use various surfactants, protective colloids, inorganic dispersants, etc. as auxiliaries during polymerization. Furthermore, not only vinyl chloride is homopolymerized, but also copolymerized with monomers copolymerizable with vinyl chloride. Examples of copolymerizable monomers include vinylidene halide, vinyl ether, vinyl acetate, vinyl benzoate, acrylic acid, methacrylic acid and its esters, maleic acid and its anhydride, styrene, and the like. Next, the present invention will be explained in more detail by giving examples. Example 1 Manufacture of polyvinyl alcohol Mix 100 parts of vinyl acetate (parts by weight, the same applies hereinafter) and 15 parts of isopropyl alcohol, and use azobisisobutyronitrile as a polymerization catalyst at a temperature of 70 to 75%.
C. and polymerized for 5 to 6 hours, and when the polymerization rate reached 75%, the polymerization was stopped, unpolymerized vinyl acetate was expelled, and isopropyl alcohol was replaced with methyl alcohol to obtain a methyl alcohol solution of polyvinyl acetate. The solution was maintained at 35° C. and a saponification reaction was carried out to obtain polyvinyl alcohol with a degree of saponification of 75 mol% and a degree of polymerization of 700. Suspension polymerization of vinyl chloride 100 parts of vinyl chloride monomer, 150 parts of water in a 100 capacity stainless steel autoclave equipped with a stirrer.
1 part, 0.1 part of the above-mentioned dispersion stabilizer, and 0.2 part of lauroyl peroxide as a polymerization catalyst, and suspension polymerization was carried out by adjusting the temperature to 60° C. while stirring at a rotational speed of 400 rpm. Table 1 shows the performance of the obtained vinyl chloride resin particles. Example 2 0.02 part of polyvinyl alcohol with a saponification degree of 69 mol% and a polymerization degree of 280 produced according to Example 1 and polyvinyl alcohol with a polymerization degree of 800 and a saponification degree of 72 mol% (by mixing vinyl acetate in a methyl alcohol solvent) Suspension polymerization was carried out in the same manner as in Example 1 except that 0.08 part of the obtained product was used in combination. Table 1 shows the performance of the vinyl chloride resin obtained. Examples 3 to 9 Experiments were conducted in accordance with Example 1, except that the dispersion stabilizers shown in Table 1 were used. The results are shown in Table 1.

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Claims (1)

[Claims] 1 Average saponification degree of 60 to 90 produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate in an alcohol having a chain transfer constant of 20 × 10 ^-4 or more at the temperature during polymerization. Mol%, average degree of polymerization 100
A dispersion stabilizer for suspension polymerization of vinyl chloride consisting of ~1500 polyvinyl alcohol.