JPH04279603A - Production of vinyl polymer granules and expandable vinyl polymer granules - Google Patents

Abstract

PURPOSE:To provide the title granules free from problems of effluent treatment and quality, narrow in size distribution with reduced fine particles. CONSTITUTION:In suspension polymerization of a vinyl monomer in an aqueous medium in the presence of a poorly soluble phosphate and anionic surfactant, a peroxohydrogensulfate is added to the aqueous medium, and also, within the period when said monomer's polymer conversion rate falls between 0 and 30wt.%, the pH value of the aqueous medium is set at 10-13.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing vinyl polymer particles having a narrow particle size distribution and excellent quality, and a method for producing expandable vinyl polymer particles.

0002

[Prior Art] Conventionally, when suspension polymerizing polymerizable monomers such as styrene in an aqueous medium, polyvinyl alcohol,
A water-soluble polymer such as polyvinylpyrrolidone or methylcellulose, or a fine powder of a sparingly soluble inorganic salt in combination with an anionic surfactant has been used as a suspension stabilizer. However, when the former is used as a suspension stabilizer, the COD load of the polymerization effluent increases and wastewater treatment is required, and when the latter is used as a suspension stabilizer, the obtained polymer particles The disadvantage was that the particle size distribution of the particles was wide.

[0003] The use of polymer particles for expandable polystyrene varies depending on the particle size, and the particle size ranges from 300 μm to 700 μm.
m is suitable for instant food cups with a particle size of 70.
Those with a particle size of 0 μm to 1800 μm are used for various packaging and fish boxes, and those with a particle size of 1500 μm to 3000 μm are used for boards for building materials.

[0004] The particle size of the polymer obtained by suspension polymerization using a slightly soluble inorganic salt fine powder and an anionic surfactant as a suspension stabilizer ranges from 100 μm to 3000 μm, and the particle size distribution is wide. Polymer particles for expandable polystyrene used in the above applications have been provided for various uses by sieving. However, the properties required of polymer particles for expandable polystyrene are now becoming diverse due to differences in uses, and it is now necessary to manufacture polymer particles for each use. Therefore, a suspension polymerization method that can obtain polymer particles of a desired particle size in high yield is strongly desired. At the same time, a suspension polymerization method that generates fewer microparticles is also strongly desired. When a large number of microparticles are generated, it is difficult to completely remove the microparticles even by dehydration treatment and sieving, and if the microparticles are mixed between particles of the desired particle size, it will cause molding defects. In addition, recovering microparticles mixed into wastewater is not an easy task.

[0005] The purpose is to improve the above problems in suspension polymerization using a sparingly soluble inorganic salt and an anionic surfactant as a suspension stabilizer, and to obtain styrenic polymer particles having a narrow particle size distribution. Methods using various additives have been proposed. For example, Japanese Patent Publication No. 55-50042 discloses a method of adding peroxodisulfate. In addition, a method of adding a water-soluble inorganic salt exhibiting neutrality, such as sodium chloride or sodium sulfate, is also known. In addition, many suspension stabilizers consisting of a combination of poorly soluble inorganic salts and various surfactants have been disclosed (Japanese Patent Application Laid-open No. 12609/1989).
Publication No. 4, JP-A-59-176309, JP-A-6
0-147406, Japanese Patent Publication No. 58-10406, Japanese Patent Publication No. 59-41448, etc.).

Japanese Patent Publication No. 42-17497 discloses a method in which zinc oxide is used as a suspension stabilizer for the purpose of increasing the dispersion effect, and the aqueous phase of the suspension is maintained at at least pH 9.3 to initiate polymerization. , Japanese Patent Publication No. 45-39549 discloses a method of using sodium silicate in a suspension system to obtain transparent polymer particles with uniform particle sizes, and Japanese Patent Publication No. 62-51961 discloses a method of using sodium silicate in a suspension system to obtain transparent polymer particles with uniform particle sizes. A method is disclosed in which the hydrogen ion concentration of an aqueous phase, which is a dispersion medium, is maintained in the range of pH 7 to pH 5 in order to obtain polymer particles. In addition, special public service No. 64-70508
In order to obtain polymer particles of uniform particle size, the publication discloses that in the presence of an organic protective colloid and an inorganic suspension stabilizer, 5% is added to the aqueous phase.
A method of adding 0 ppm to 500 ppm carbonate or bicarbonate is disclosed.

[0007]

[Problem to be solved by the invention] JP-A-55-5004
Although the method shown in Publication No. 2 generates fewer microparticles and can obtain polymer particles with a narrower particle size distribution than the conventional method,
When viewed by application, there is still a problem that there are many polymer particles outside the required particle size range.

The method disclosed in Japanese Patent Publication No. 45-39549 has the problem of increasing the COD load of the polymerization effluent because it is necessary to use sodium silicate and an organic polymer compound in combination.

[0009] Japanese Patent Publication No. 42-17497 requires a large amount of zinc oxide as a suspending agent, which has the problem of deterioration of quality since it is contained in the polymer particles. Furthermore, the particle size distribution of the obtained polymer particles is also wide-ranging.

The method disclosed in Japanese Patent Publication No. 62-51961 has the problem that when a water-soluble polymer is used as a suspending agent, the COD load of the polymerization effluent increases, requiring wastewater treatment. However, when a poorly soluble inorganic salt is used, a large amount of suspending agent is required, which has the problem of being included in the polymer particles, resulting in a decrease in quality, and the disadvantage that the reproducible operating range is narrow.

[0011] The method disclosed in JP-A-64-70508 uses an organic protective colloid and a water-insoluble inorganic powder as a suspension stabilizer, so it also has the problem of increasing the COD load of the polymerization effluent. Further, there is a problem that the water content in the polymer particles is high, resulting in non-uniform cell structure.

[0012] Polymer particles for expanded polystyrene are required to have a uniform particle size and a small number of fine particles, but in terms of quality, when the polymer particles are pre-foamed and molded, there are no gaps between the expanded particles. It is required that the expanded particles are sufficiently fused and have sufficient strength as a molded product. In order to satisfy this requirement, it is preferable that the content of impurities such as water and suspending agents in the polymer particles is small. Further, during suspension polymerization, if emulsion polymerization occurs concurrently, the emulsion itself acts as an impurity, and water, suspending agent, etc. are likely to be incorporated into the polymer particles, so it is preferable to suppress the concurrent occurrence of emulsion polymerization. These impurities affect the foaming of particles and disturb the cell structure, making it impossible to satisfy the above-mentioned required properties. Therefore, conventional suspension polymerization methods cannot provide polymer particles with uniform particle size, few fine particles, and excellent quality. The present invention provides a manufacturing method that does not cause problems in wastewater treatment or quality, and can obtain vinyl polymer particles having a narrow particle size distribution with a reduced number of fine particles.

[0013]

[Means for Solving the Problem] The present inventors controlled the hydrogen ion concentration in an aqueous medium in suspension polymerization using a sparingly soluble phosphate and an anionic surfactant as a suspension stabilizer, The present inventors have also discovered that by adding a small amount of hydrogen peroxosulfate, it is possible to produce vinyl polymer particles with good reproducibility, free of quality problems, and having a small number of fine particles and a narrow particle size distribution, leading to the completion of the present invention. Ta.

That is, the present invention involves adding hydrogen peroxosulfate to the aqueous medium during suspension polymerization of the vinyl monomer in the aqueous medium in the presence of a sparingly soluble phosphate and an anionic surfactant. A method for producing vinyl polymer particles, characterized in that the hydrogen ion concentration in the aqueous medium is adjusted to pH 10 to pH 13 within a period in which the polymerization conversion rate of the vinyl monomer is 0% to 30% by weight. The present invention also relates to a method for producing expandable vinyl polymer particles in which a blowing agent is further impregnated during or after polymerization.

In the present invention, the hydrogen ion concentration in the aqueous medium is set to pH 10 to pH 13 during the period when the polymerization conversion rate of the vinyl monomer is 0% to 30% by weight, but if the hydrogen ion concentration is less than pH 10, If the pH exceeds 13, the particle size distribution of the polymer particles becomes wide. In addition, the hydrogen ion concentration was adjusted to pH 10~p.
The period of H13 is within a period in which the polymerization conversion rate of the polymerizable monomer is 0% by weight to 30% by weight, preferably within a period in which the polymerization conversion rate is 5% by weight to 15% by weight. When the polymerization conversion rate exceeds 30% by weight, the viscosity of the oil droplets increases significantly.
The effects of the present invention are difficult to obtain, and polymer particles with a narrow particle size distribution cannot be obtained. As a means of adjusting the hydrogen ion concentration in the aqueous medium to the above range, addition of basic metal (alkali metal) hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, etc., which causes less deterioration in quality due to concurrent emulsion polymerization, can be used. is most preferred, followed by sodium carbonate, potassium carbonate,
Preferably, a soluble basic metal carbonate such as lithium carbonate or sodium hydrogen carbonate is added. Addition of calcium hydroxide (alkaline earth metal salt) destabilizes the system and leads to particle agglomeration phenomena. calcium carbonate, magnesium carbonate,
Insoluble or poorly soluble carbonates such as zinc carbonate, barium carbonate, and copper carbonate have no effect on narrowing the particle size distribution. In the present invention, the hydrogen ion concentration in the aqueous phase is adjusted to pH 1.
Only additives that adjust the pH to 0 to 13 exhibit the effect of narrowing the particle size distribution.

In the present invention, the hydrogen peroxosulfate added to the aqueous medium is preferably a sodium salt, a potassium salt, or a lithium salt of hydrogen peroxosulfate. The amount added is 0.0005% by weight to 0.05% by weight based on the vinyl monomer.
% by weight is preferred, particularly preferably from 0.002% by weight
It is 0.03% by weight. If the amount added is less than 0.0005% by weight, the effect of suppressing concurrent emulsion polymerization will not be sufficient, the quality of the polymer particles will not be constant, and the effect of reducing fine particles will be small. When the amount added exceeds 0.05% by weight, the particle size distribution of the resulting polymer particles tends to become broader.

[0017] The hydrogen peroxosulfate may be used as a complex salt in combination with other salts. For example, 2K
HSO5, KHSO4, K2SO4, etc. can be used. In this case, it is of course preferable to use hydrogen peroxosulfate (KHSO5 in the example above) in the amounts mentioned.

In the present invention, vinyl monomers to be polymerized include styrene, α-methylstyrene, chlorostyrene, styrene derivatives such as vinyltoluene, acrylonitrile, vinylpyrrolidone, vinylpyridine, vinylcarbazole, polybutadiene, and carbon atoms of 1. Although alcohols of 5 to 8 and esters of acrylic acid or methacrylic acid can be used, styrene or styrene derivatives can be used.
It is preferable to use 0% by weight or more.

As the polymerization initiator, organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-butyl perbenzoate, and di-t-butyl peroxide, which are soluble in vinyl monomers, and azobisisobutyl peroxide are used. Azo compounds such as lonitrile can be used, but
Preference is given to using organic peroxides.

As the poorly soluble phosphate, tricalcium phosphate, hydroxyapatite, magnesium phosphate, barium phosphate, strontium phosphate, aluminum phosphate, iron phosphate, cobalt phosphate, calcium pyrophosphate, etc. may be used. However, tricalcium phosphate,
Hydroxyapatite is preferred. The amount added is preferably 0.1% to 0.8% by weight, particularly preferably 0.15% to 0.40% by weight, based on the polymerizable monomer.

As the anionic surfactant, sodium dodecylbenzenesulfonate, sodium styrenesulfonate, sodium dodecylsulfonate, sodium dioctylsulfosuccinate, etc. can be used. The amount added is 0.0001% by weight to 0.00% by weight based on the polymerizable monomer.
01% by weight is preferred.

[0022] The polymerization temperature in suspension polymerization is preferably 70°C to 140°C, and the weight ratio of the polymerizable monomer to the aqueous medium is preferably about 0.8/1 to 1.2/1 (former/latter).

Ethylene vinyl acetate copolymer, ethylene bis stearyl amide, methylene bis stearyl amide, etc. may be added to the polymerizable monomer as a cell forming agent.

In the present invention, when producing expandable vinyl polymer particles, during or after the polymerization, hydrocarbons such as propane, butane, pentane, hexane, cyclopentane, cyclohexane, methylene chloride, dichlorodifluoromethane, etc. , a halogenated hydrocarbon such as trifluorofluoromethane, or a mixture thereof as a blowing agent can be impregnated by a known method to form expandable vinyl polymer particles.

[0025]

[Function] In the present invention, by adjusting the hydrogen ion concentration in the aqueous medium to pH 10 to pH 13 within a period when the polymerization conversion rate of the polymerizable monomer is 0 to 30% by weight, oil droplets are Since the frequency of dispersion and coalescence can be suppressed, it is possible to prevent the particle size distribution from widening. Furthermore, hydrogen peroxosulfate has the effect of making the oil droplet size uniform, and is effective in reducing the number of microparticles. Furthermore, hydrogen peroxosulfate has the effect of suppressing emulsion polymerization, reducing the amount of water and suspending agent taken into the oil droplets together with the emulsion. A foam molded product with a uniform structure and excellent surface smoothness can be obtained.

[0026]

[Examples] The present invention will be explained below with reference to Examples. Here, the particle size distribution and average particle size of the polymer particles are indicated by the deviation coefficient Cv and median diameter, respectively. That is, based on the cumulative weight distribution curve, the particle diameters at which the cumulative weight is 15%, 50%, and 85% were set as d15, d50, and d85, respectively, and the deviation coefficient Cv was determined using the following formula to determine the breadth or narrowness of the particle size distribution. Cv=(d85-d15)/d50 The larger the Cv value, the wider the particle size distribution, and the smaller the Cv value, the narrower the particle size distribution. As the average diameter, the median diameter represented by the above-mentioned d50 was adopted.

[0027] Further, a scale indicating the surface smoothness of the molded article was determined by the following method and used as the surface smoothness. In other words, when black printing ink is applied thinly to the surface of a molded article using a roller, the ink is applied to the smooth areas, but the gaps between the foamed particles remain white. The ratio of the area of the black part to the total surface area was calculated using an image processing device and was defined as the surface smoothness ratio.

Example 1 In a 4-liter autoclave, 22 g of a 10% tertiary calcium phosphate dispersion (Superite 10, manufactured by Nihon Kagaku Kogyo Co., Ltd.), 0.048 g of sodium dodecylbenzenesulfonate (manufactured by Wako Pure Chemical Industries, Ltd.), and 1178 g of ion-exchanged water were added. and stir well to obtain a uniform mixed solution. Next, 3.0 g of benzoyl peroxide (manufactured by Shoko Kagaku Co., Ltd.), t-butyl peroxide
1200 g of styrene (manufactured by Denki Kagaku Kogyo Co., Ltd.) in which 0.1 g of benzoate (manufactured by NOF Corporation) and 0.6 g of ethylene bisstearylamide (manufactured by Nippon Kasei Co., Ltd.) were dissolved was added with stirring, and the atmosphere of the polymerization vessel was replaced with nitrogen gas. After replacing the mixture with the following, the temperature was raised to 90°C to start polymerization. When the polymerization conversion rate (measured by specific gravity method) reaches 10% by weight, 2KHSO5
・KHSO4・K2SO4 (manufactured by Aldrich, OXO
1.2 g of an aqueous solution containing 0.12 g of NE) and 3.0 g of a 10% aqueous solution of sodium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.) were added. The hydrogen ion concentration immediately after addition was pH 11.5. Furthermore, when the polymerization conversion rate reached 35% by weight, 1
6 g of 0% tertiary calcium phosphate dispersion was added, and the polymerization was continued as it was. When the polymerization conversion reached 95% by weight, 12 g of a 10% tertiary calcium phosphate dispersion was further added, and then 24 g of cyclohexane and 84 g of butane were introduced over a period of 1 hour. After that, it took 2 hours to raise the temperature to 120℃,
After maintaining the temperature at 120° C. for 5 hours, the mixture was cooled to room temperature to obtain desired expandable polystyrene polymer particles. As a result of sieving the obtained polymer particles, the average particle diameter d50 was 870 μm.
The deviation coefficient Cv value was 0.30, which was a very narrow particle size distribution. The amount of fine particles of 300 μm or less was 0.6% by weight. The content of water and suspending agent in the obtained polymer particles was small as shown in Table 1, and after pre-foaming the polymer particles to 50 ml/g, observation of the cut surface of the pre-foamed particles revealed uniform bubbles. The structure was recognized. The pre-expanded particles were aged for 24 hours and then molded. The molded product obtained had few gaps between expanded particles and a surface smoothness of 96%.

Example 2 3 g of a 10% aqueous solution of sodium hydroxide in Example 1
Suspension polymerization was carried out in the same manner as in Example 1 except that 3.6 g of a 10% aqueous solution of sodium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) was used to obtain polymer particles. The hydrogen ion concentration immediately after the addition of sodium carbonate was pH 10.5. The average particle diameter d50 of the obtained polymer particles was 900 μm, and the deviation coefficient Cv value was 0.32, indicating a very narrow particle size distribution. 30
The amount of fine particles of 0 μm or less was 0.7% by weight. The water and suspending agent contents in the polymer particles were low, and the cell structure of the pre-expanded particles was relatively uniform. When the pre-expanded particles were molded, the surface smoothness of the molded product was 93%.

Comparative Example 1 In Example 1, 2KHSO5・KHSO4・K2SO
Suspension polymerization was carried out in the same manner as in Example 1 except that 1.2 g of the aqueous solution containing 40.12 g was removed to obtain polymer particles. The hydrogen ion concentration immediately after adding sodium hydroxide is pH 11.5.
Met. The average particle diameter d50 of the obtained polymer particles was 91
At 0 μm, the deviation coefficient Cv value was 0.30, which was a very narrow particle size distribution, but the amount of fine particles of 300 μm or less increased to 1.5% by weight. Furthermore, the content of water and suspending agent in the polymer particles increased, and the cell structure of the pre-expanded particles was somewhat non-uniform. When the pre-expanded particles were molded, the surface smoothness of the molded product was 90%.

Comparative Example 2 In Example 2, 2KHSO5・KHSO4・K2SO
Polymer particles were obtained in the same manner as in Example 2, except that 1.2 g of the aqueous solution containing 0.12 g of No. 4 was used. Immediately after adding sodium carbonate, the hydrogen ion concentration was pH 10.6. The average particle diameter d50 of the obtained polymer particles was 930 μm, and the deviation coefficient Cv value was 0.32, indicating a narrow particle size distribution. 300μ
The amount of microparticles smaller than m increased to 1.7% by weight. Also, the water and suspending agent content in the polymer particles increased, the cell structure of the pre-expanded particles was non-uniform, and the cells near the particle surface became considerably smaller. When the pre-expanded particles were molded, the surface smoothness of the molded product was 85%.

Comparative Example 3 3 g of a 10% aqueous solution of sodium hydroxide in Example 1
Calcium carbonate fine powder (manufactured by Wako Pure Chemical Industries, Ltd.) 0.36
Suspension polymerization was carried out in the same manner as in Example 1, except that the amount was changed to 1.g, and polymer particles were obtained. The hydrogen ion concentration immediately after addition of calcium carbonate was pH 7.0. The average particle diameter d50 of the obtained polymer particles was 860 μm, and the deviation coefficient Cv value was 0.
．． 49, which had a wide particle size distribution. The amount of fine particles of 300 μm or less was 2.9% by weight. The water and suspending agent contents in the polymer particles were low, and the cell structure of the pre-expanded particles was uniform. When the pre-expanded particles were molded, the surface smoothness of the molded product was 93%.

Comparative Example 4 3 g of a 10% aqueous solution of sodium hydroxide in Example 1
Suspension polymerization was carried out in the same manner as in Example 1 except that 6 g of a 10% aqueous solution of sodium chloride (manufactured by Wako Pure Chemical Industries, Ltd.) was used to obtain polymer particles. The hydrogen ion concentration immediately after addition of sodium chloride was pH 6.5. The average particle diameter d50 of the obtained polymer particles was 940 μm, and the deviation coefficient Cv value was 0.42. 2.5 for microparticles of 300 μm or less
% by weight. The water and suspending agent contents in the polymer particles were low, and the cell structure of the pre-expanded particles was uniform. When the pre-expanded particles were molded, the surface smoothness of the molded product was 93.
%Met.

Example 3 In Example 1, 2KHSO5・KHSO4・K2SO
4 1.2 g of an aqueous solution containing 0.12 g of 2KHSO5.
15g of aqueous solution containing 1.5g of KHSO4/K2SO4
Polymer particles were obtained by carrying out suspension polymerization in the same manner as in Example 1, except that the following was changed. The hydrogen ion concentration immediately after the addition of sodium hydroxide was pH 10.5. The average particle diameter d50 of the obtained polymer particles was 850 μm, and the deviation coefficient Cv value was 0.
．． It was 34. The amount of fine particles of 300 μm or less was 0.5% by weight. The water and suspending agent contents in the polymer particles were low, and the cell structure of the pre-expanded particles was uniform. When pre-expanded particles were molded, the surface smoothness of the molded product was 96%.
Met.

Comparative Example 5 In Example 1, 10% aqueous solution of sodium hydroxide was added at 3.0%.
Suspension polymerization was carried out in the same manner as in Example 1 except that g was changed to 0.3 g of calcium hydroxide, but the continuous phase and dispersed phase were reversed immediately after adding calcium hydroxide, making it impossible to obtain polymer particles. could not.

Example 4 In a 4-liter autoclave, 18 g of a 10% aqueous calcium phosphate solution and 0.0 g of sodium dodecylbenzenesulfonate were placed in a 4-liter autoclave.
060g, 2KHSO5・KHSO4・K2SO40.
2.4 g of a 24 g aqueous solution and 1182 g of ion-exchanged water were added and stirred well to obtain a uniform mixed solution. Then 3.2 g of benzoyl peroxide, 0.1 g of t-butyl perbenzoate and 0.6 g of ethylene bisstearylamide.
1200 g of styrene dissolved in was added with thorough stirring, and the temperature was raised to 90° C. to initiate polymerization. Polymerization conversion rate is 7
When the weight percent was reached, 3.6 g of a 10% aqueous solution of potassium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.) was added. The hydrogen ion concentration immediately after addition was pH 11.8. Further, when the polymerization conversion rate reached 40% by weight, 9 g of a 10% aqueous solution of tertiary calcium phosphate was added, and the polymerization was continued as it was. When the polymerization conversion rate reached 95% by weight, 12g of 10% tribasic calcium phosphate aqueous solution was added, and then 24g of cyclohexane was added.
and 84 g of butane were introduced over a period of 1 hour. then 120
After raising the temperature to 120°C for 2 hours and keeping it at 120°C for 5 hours,
It was cooled to room temperature to obtain expanded polystyrene polymer particles. The average particle diameter d50 of the obtained polymer particles was 890 μm,
The deviation coefficient Cv value was 0.29, indicating a very narrow particle size distribution. The amount of fine particles of 300 μm or less was 0.6% by weight. The water and suspending agent contents in the polymer particles were low, and the cell structure of the pre-expanded particles was uniform. When the pre-expanded particles were molded, the surface smoothness of the molded product was 97%.

Example 5 In Example 4, a 10% aqueous solution of potassium hydroxide 3.6
Suspension polymerization was carried out in the same manner as in Example 1, except that g was changed to 4.0 g of a 10% aqueous solution of potassium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) to obtain polymer particles. The hydrogen ion concentration immediately after the addition of potassium carbonate was pH 10.8. The average particle diameter d50 of the obtained polymer particles was 900 μm, and the deviation coefficient Cv value was 0.32, indicating a very narrow particle size distribution. The amount of fine particles of 300 μm or less was 0.5% by weight. The water and suspending agent contents in the polymer particles were low, and the cell structure of the pre-expanded particles was relatively uniform. When the pre-expanded particles were molded, the surface smoothness of the molded product was 94%.

Example 6 3 g of a 10% aqueous solution of sodium hydroxide in Example 1
Suspension polymerization was carried out in the same manner as in Example 1 except that 3.6 g of a 10% aqueous solution of lithium hydroxide was used to obtain polymer particles. The hydrogen ion concentration immediately after addition of sodium hydroxide was pH 11.3. The average particle diameter d50 of the obtained polymer particles was 910 μm, and the deviation coefficient Cv value was 0.29, indicating a very narrow particle size distribution. The amount of fine particles of 300 μm or less was 0.6% by weight. The water and suspending agent contents in the polymer particles were low, and the cell structure of the pre-expanded particles was uniform. When the pre-expanded particles were molded, the surface smoothness of the molded product was 98%.

Table 1 summarizes the formulations and characteristics of each of the above Examples and Comparative Examples. The water content in the polymer particles was determined by the Karl Fischer method after washing the polymer particles with methanol and air drying. The content of the suspending agent calcium phosphate (TCP) in the polymer particles was calculated by dissolving the polymer particles in chloroform, extracting with a 10% aqueous hydrochloric acid solution, and determining the concentration of calcium ions in the aqueous solution using an atomic absorption photometer. .

[0040]

[Table 1]

[0041]

As is clear from the above, the present invention can provide vinyl polymer particles with a narrow particle size distribution and excellent quality. Furthermore, the method for producing expandable vinyl polymer particles of the present invention has a particularly small amount of fine particles produced and can reduce the number of defective molded products, so it is extremely useful industrially in terms of productivity and quality.

Claims (6)

[Claims] Claim 1: When suspension polymerizing a vinyl monomer in an aqueous medium in the presence of a sparingly soluble phosphate and an anionic surfactant, hydrogen peroxosulfate is added to the aqueous medium, and the vinyl monomer is The hydrogen ion concentration in the aqueous medium was adjusted to pH 10 within the period when the polymerization conversion rate of the system monomer was 0% to 30% by weight.
A method for producing vinyl polymer particles characterized by adjusting the pH to 13. Claim 2: The hydrogen ion concentration in the aqueous medium is set to pH1.
2. The method for producing vinyl polymer particles according to claim 1, wherein a basic metal hydroxide is used as the means for adjusting the pH to 0 to 13. Claim 3: The hydrogen ion concentration in the aqueous medium is set to pH1.
2. The method for producing vinyl polymer particles according to claim 1, wherein a soluble basic carbonate is used as the means for adjusting the pH to 0 to 13. 4. The method for producing vinyl polymer particles according to claim 1, 2 or 3, wherein a sodium salt, potassium salt or lithium salt of hydrogen peroxosulfate is used as the hydrogen peroxosulfate. 5. The vinyl polymer according to claim 1, wherein the amount of hydrogen peroxosulfate added is 0.0005% to 0.05% by weight based on the vinyl monomer. Method of manufacturing particles. 6. The method for producing vinyl polymer particles according to claim 1, wherein the expandable vinyl polymer particles are further impregnated with a blowing agent during or after polymerization.