JP2003327607A - Process for manufacturing vinyl chloride based polymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process for manufacturing a vinyl chloride based polymer that has an excellent fish eye characteristic of formed articles, even when the productivity is increased, and an excellent initial colorability of formed articles. <P>SOLUTION: The process for manufacturing the vinyl chloride based polymer is characterized in that, when a vinyl chloride based monomer is suspension- polymerized in an aqueous medium in the presence of an oil-soluble polymerization initiator, (A) a partially saponified polyvinyl alcohol which has a saponification value of 60-80% mol and the 4 wt.%. aqueous solution of which has a viscosity of 6.0-9.0 cps at 20°C, (B) hydroxypropyl methylcellulose which contains 25-30 wt.% of methoxyl group and 4-15 wt.% of hydroxypropoxyl group and the 2 wt.%. aqueous solution of which has a viscosity of 10-8.0 cps at 20°C, and (C) a polyethylene oxide, are jointly used as dispersion stabilizing agents for suspending and dispersing the vinyl chloride based polymer. <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a vinyl chloride-based polymer, and more particularly, to a method for producing a molded article having excellent fisheye characteristics. The present invention relates to a method for producing a vinyl chloride polymer having excellent initial coloring properties with good production efficiency. [0002] A vinyl chloride polymer is a polymer material having a well-balanced processability, physical properties and price, and is therefore used in a wide range of fields from hard to soft. For example, in the soft field, there are wire coverings, wrap films, sheets and the like, and in the hard field, pipes, window frames, films and the like. Of these, in the field of softness, since a relatively large amount of a plasticizer is blended, it is desired that the plasticizer absorbs quickly and that the resulting molded article has less fish eyes. In order to improve the fish eye, for example, a partially saponified polyvinyl alcohol having a saponification degree of 65 to 75 mol% and a saponification degree of 3
A method in which 5 to 45 mol% of partially saponified polyvinyl alcohol and hydroxypropylmethylcellulose having a methoxy group content of 28 to 30% and a hydroxypropoxy group content of 7 to 12% (JP-A-61-152703), A partially saponified polyvinyl alcohol having a degree of hydrolysis of 65 to 75 mol% and a hydroxypropoxy group content of 50
A method using a combination of 80% and 80% of hydropropyl methylcellulose (Japanese Patent Application Laid-Open No. 63-275606) is known, but in any of these methods, in order to improve the production efficiency, the amount of the initiator is increased or the concentration is reduced by a reflux condenser or the like. When the heat ratio was increased, the improvement of fish eyes was insufficient, and the polymerization stability was sometimes impaired. In order to improve the mechanical properties and strength of molded products in the field of softness, a high degree of polymerization of a vinyl chloride polymer is used. Longer, lower production efficiency compared to general-purpose products. Therefore, even if the polymerization time is shortened by increasing the amount of the initiator or changing the type of the initiator in order to increase the production efficiency, similar problems as described above, such as coarse particles, deterioration of fish eyes, poor heat removal and lack of polymerization stability. May occur. In addition, when a vinyl chloride polymer is produced by suspension polymerization, the dispersion stabilizer is incorporated into the polymer particles by grafting or adsorbing on the particle surface of the vinyl chloride polymer. Depending on the method of use of the dispersion stabilizer, the initial coloring property of a vinyl chloride-based polymer may be greatly impaired. If the amount of initiator is increased or the heat removal rate of the reflux condenser is increased to further increase production efficiency, the amount of dispersion stabilizer is increased to prevent problems such as coarsening, deterioration of fish eyes, and broadening of particle size distribution. It is necessary, and the above-mentioned problems appear particularly remarkably. In order to achieve such an improvement in production efficiency, there are certain restrictions on the type and amount of the dispersion stabilizer, so it is more difficult to solve the problem of deterioration in initial coloring while maintaining the balance of performance. It is. SUMMARY OF THE INVENTION The present invention relates to fisheye properties and initial coloring properties of molded articles, and all of them are vinyl chloride-based heavyweights satisfying the high demands currently required. It is an object of the present invention to provide a method for producing a united product with high production efficiency. [0006] That is, the present invention relates to a method for producing a vinyl chloride-based monomer in suspension polymerization in an aqueous medium in the presence of an oil-soluble polymerization initiator. (A) a part having a saponification degree of 60 to 80 mol% and a 4% by weight aqueous solution having a viscosity at 20 ° C. of 6.0 to 9.0 cps. Saponified polyvinyl alcohol, (B) a methoxy group content of 25 to 30% by weight, and a hydroxypropoxy group content of 4%;
It is characterized in that hydroxypropylmethylcellulose having a viscosity of 10 to 80 cps at 20 ° C. of a 2% by weight aqueous solution of １５15% by weight and (C) polyethylene oxide are used in combination. The present invention will be described in detail below. The dispersion stabilizer (A) used in the present invention has a degree of saponification of at least 60 mol% and less than 80 mol%, and a 4 wt% aqueous solution having a viscosity at 20 ° C. of 6.0 to 9.0 cps. A partially saponified polyvinyl alcohol, preferably 70 mol% or more and less than 80 mol%. If the saponification degree is less than 60 mol%, the polymerization stability is impaired, and if the saponification degree is 80 mol% or more, the fish eye deteriorates. If the viscosity is less than 6.0 cps, the polymerization may become unstable when the production efficiency is increased, and the viscosity may be 9.0 cp.
If it exceeds s, the fish eye deteriorates. The amount is from 0.02 to 0.15 parts by weight, preferably from 0.04 to 0.1 parts by weight, based on 100 parts by weight of the vinyl chloride monomer. If it is less than 0.02 parts by weight, the polymerization stability is impaired, and if it is 0.15 parts by weight or more, the color tone of the molded article is deteriorated. As the dispersion stabilizer (B) used in the present invention, hydroxypropyl methylcellulose is used. Hydroxypropyl methylcellulose has a methoxy group content of 25 to 30% by weight, a hydroxypropoxy group content of 4 to 15% by weight, and a 2% by weight aqueous solution having a viscosity at 20 ° C. of 10 to 80 cps.
Preferably 20-75 cps, more preferably 40-6
0 cps. When the methoxy group content and the hydroxypropoxy group content deviate from the range of the aqueous solution viscosity, problems such as deterioration of polymerization stability and fish eye and foaming at the time of recovery occur. The amount is 0.005 to 0.05 part by weight, preferably 0.01 to 0.03 part by weight, based on 100 parts by weight of the vinyl chloride monomer. 0.005
If the amount is less than 5 parts by weight, the fish eye improving effect and the polymerization stability are impaired. As the dispersion stabilizer (C) used in the present invention, polyethylene oxide is used. The polyethylene oxide preferably has an average molecular weight of 600,000 or more, and the amount is 0.001 to 0.02 parts by weight, preferably 0.001 to 0.02 parts by weight, per 100 parts by weight of the vinyl chloride monomer.
0.01 parts by weight. When the amount is less than 0.001 part by weight or the average molecular weight is 600,000 or less, the protective power of the initially dispersed monomer is insufficient, so that the coarse particles of the generated resin increase and the fish eye deteriorates. Or, in extreme cases, the polymerization may not be performed normally and the whole may form a coagulum. On the other hand, if the amount exceeds 0.02 parts by weight, the protective power is too strong, and the particle size distribution of the produced resin is widened and the number of fine particles is increased. As the upper limit of the average molecular weight of polyethylene oxide, those having a molecular weight of 8,000,000 or less are usually used. Therefore, as the dispersion stabilizer (C), polyethylene oxide having an average molecular weight of 600,000 or more and 8,000,000 or less is used in an amount of 0.001 to 0.00 per 100 parts by weight of the vinyl chloride monomer.
It is recommended to use 2 parts by weight. The vinyl chloride monomer used in the production method of the present invention may be a vinyl chloride monomer alone, a vinyl chloride monomer, or one end copolymerizable with the vinyl chloride monomer. Is a mixture of a polymerizable compound having a vinyl group and the vinyl chloride monomer, and the polymerizable compound is not particularly limited as long as it can be copolymerized with the vinyl chloride monomer. Alkyl vinyl esters such as vinyl acetate, alkyl vinyl ethers such as cetyl vinyl ether, α-monoolefin monomers such as ethylene or propylene, alkyl acrylates such as methyl acrylate, methacrylic acids such as methyl methacrylate Comonomers such as alkyl esters can be exemplified. The polymerization initiator used in the present invention includes:
Tertiary butyl peroxy neodecanoate, tertiary hexyl peroxy neodecanoate, tertiary hexyl peroxy pivalate, tertiary butyl peroxy pivalate, tertiary hexyl peroxy neohexanoate, α-cumyl par Oxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, 1-cyclohexyl-1-
Perester compounds such as methyl ethyl peroxy neodecanoate, perester compounds such as 1,1-dimethyl-3-hydroxybutyl peroxy neodecanoate,
Percarbonate compounds such as diisopropylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate, di-2-ethoxyethylperoxydicarbonate, dimethoxyisopropylperoxydicarbonate, benzoyl peroxide, cumene hydroperoxide, acetylcyclohexyl Peroxide compounds such as peroxide, 2,2′-azobis-
Azo compounds such as 2,4-dimethylvaleronitrile can be mentioned, and these can be used alone or in combination of two or more. Further, other additives usually used for suspension polymerization within a range not impairing the effects of the present invention, for example, a stabilizer which can prevent adhesion of scale to the inner wall of a polymerization vessel, an antioxidant, etc. A chain transfer agent for adjusting the average degree of polymerization, an antifoaming agent, a pH adjuster for adjusting the pH of the aqueous polymerization medium, or the like may be added without any problem. In the method for producing a vinyl chloride polymer according to the present invention, for example, the amount of a medium used, the amount of a polymerization initiator and the amount of a vinyl chloride monomer, and optionally other comonomers, etc. The polymerization temperature, polymerization temperature and the like may be controlled under conventionally known conditions. As for the productivity efficiency of the present invention, the average degree of polymerization of the obtained vinyl chloride polymer is from 1500 to 4000.
In the range of. In addition, the initial coloring property of the vinyl chloride polymer composition of the present invention is remarkably good in a lead compound. EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In addition, the evaluation method implemented in the Example and the comparative example was based on the following method. Average degree of polymerization Measured according to JIS K-6721. Average particle size 42, 60, 80, 1 according to JIS K-6721
Using a sieve of 00, 120, 145, 200 mesh,
The particles were sieved with a sieve shaker, and the average particle diameter was defined as the 50% by weight passage diameter. After mixing 60 parts by weight of trimellitic acid-based plasticizer, 4 parts by weight of lead-based stabilizer and a small amount of carbon black with 100 parts by weight of fisheye vinyl chloride-based polymer, the surface temperature is reduced to 150 ° C. Pour and knead into the adjusted 8-inch roll,
The number of fish eyes observed in 25 cm ^{2 of a} 0.3 mm thick roll sheet obtained by kneading for 7 minutes and 7 minutes was counted. To 100 parts by weight of the initial coloring vinyl chloride-based polymer, 50 parts by weight of dioctyl phthalate and 3 parts by weight of a lead-based stabilizer are blended, and 150 g of the blend is mixed with 8 parts at a roll surface temperature of 160 ° C.
The mixture was kneaded with an inch roll for 5 minutes to obtain a sheet molded body having a thickness of 1 mm. Subsequently, the formed bodies were laminated, and a 5 mm pressed body was obtained under the conditions of preheating at 170 ° C. for 4 minutes, forming pressure of 50 kg / cm ² and pressing time of 5 minutes. The initial colorability was determined by measuring the molded product with a yellow value (YI) color difference meter. The smaller the YI value, the better the initial coloring property. Color difference meter ($ 80 CO
LOR MEASURING SYSTEM, Nippon Denshoku Industries Co., Ltd.). After the completion of the polymerization, the slurry in the polymerization vessel was taken out, the inside of the polymerization vessel was washed with water, and the scale adhesion on the vessel wall was visually observed according to the following criteria. ○ (little scale adhesion) △ (small scale adhesion) × (large scale adhesion) Example 1 732 kg of deionized water dispersed in a 1.7 m ³ stainless steel polymerization vessel equipped with a stirrer and jacket 237 g of a partially saponified polyvinyl alcohol having a saponification degree of 72 mol% and a viscosity of 6.3 cps at 20 ° C. of a 4 wt% aqueous solution as a stabilizer (A); a methoxy group content of 29 wt% as a dispersion stabilizer (B); 157 g of a hydroxypropylmethylcellulose having a hydroxypropoxy group content of 10% by weight and a 2% by weight aqueous solution having a viscosity of 50 cps, 8.0 g of polyethylene oxide having an average molecular weight of 4.5 million as a dispersion stabilizer (C), and di-2-ene as a polymerization initiator 166 g of ethylhexyl peroxydicarbonate, 1,1,
278 g of 3,3-tetramethylbutyl peroxy neodecanoate was charged, and air in the autoclave was degassed by a vacuum pump. Then 565 kg of vinyl chloride monomer
And the average degree of polymerization of the vinyl chloride polymer is 1 under stirring.
Polymerization was started under polymerization conditions (polymerization temperature: 45 ° C.) so as to be about 800. 7.5 hours after the start of the polymerization, the pressure in the polymerization vessel was reduced by 0.5 kg / cm ² , so the polymerization reaction was stopped. When the slurry was taken out of the polymerization vessel and dehydrated and dried, a vinyl chloride polymer was obtained at a polymerization conversion of 80%. Table 1 shows the evaluation results of the obtained vinyl chloride polymers. The obtained vinyl chloride polymer had excellent initial coloring properties and fish eyes. The scale adhesion to the polymerization vessel wall was also good. Example 2 A vinyl chloride polymer was obtained in the same manner as in Example 1 except that the type and amount of the dispersion stabilizer were changed. The obtained vinyl chloride polymer had excellent initial coloring properties and fish eyes. The scale adhesion to the polymerization vessel wall was also good. Comparative Examples 1 and 2 Except that the type and amount of the dispersion stabilizer and the amount of the polymerization initiator were changed as shown in Table 1, and dispersion stabilizer D (partially saponified polyvinyl alcohol) was used in addition to dispersion stabilizer B. It carried out like Example 1. In Comparative Example 1, the polymerization reaction was stopped because the internal pressure of the polymerization reactor decreased by 0.5 kg / cm ² 9 hours after the start of polymerization. However, in Comparative Example 2, the heat removal was insufficient during the polymerization reaction, and the polymerization was stopped by the polymerization inhibitor. . Comparative Example 3 A vinyl chloride polymer was obtained in the same manner as in Example 1 except that the dispersion stabilizer A was changed as shown in Table 1. Comparative Example 4 Example 1 except that the dispersion stabilizer B was changed as shown in Table 1.
And a vinyl chloride polymer was obtained. Comparative Example 5 Example 1 except that dispersion stabilizer A was changed as shown in Table 1.
And a vinyl chloride polymer was obtained. [Table 1] The formulations and evaluation results of the dispersion stabilizers of Examples and Comparative Examples are shown in Table 1. Compared to Comparative Example 2, the conventional fisheye improving formulation resulted in abnormal polymerization when the amount of the initiator was increased. Shows excellent fisheye properties and initial coloring properties.

Claims (1)

Claims: 1. A method for suspending and dispersing a vinyl chloride monomer in suspension polymerization of an vinyl chloride monomer in an aqueous medium in the presence of an oil-soluble polymerization initiator. As the dispersion stabilizer to be used, (A) the saponification degree is 60 to 80 mol%, and the viscosity of the 4% by weight aqueous solution at 20 ° C. is 6.0 to 9%.
A partially saponified polyvinyl alcohol having 0 cps, (B) a methoxy group content of 25 to 30% by weight, a hydroxypropoxy group content of 4 to 15% by weight, and a 2% by weight aqueous solution having a viscosity at 20 ° C. of 10 to 80 cps. A method for producing a vinyl chloride-based polymer, comprising using hydroxypropylmethylcellulose and (C) polyethylene oxide in combination.