JP3097170B2 - Method for producing vinyl polymer particles and expandable vinyl polymer particles - Google Patents

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]

2. Description of the Related Art Conventionally, when a polymerizable monomer such as styrene is subjected to suspension polymerization in an aqueous medium, polyvinyl alcohol,
Water-soluble polymers such as polyvinylpyrrolidone and methylcellulose or hardly soluble inorganic salt fine powders which are used in combination with anionic surfactants have been used as suspension stabilizers. However, when the former is used as a suspension stabilizer, there is a disadvantage that the COD load of the polymerization effluent is increased, so that wastewater treatment is required. There is a disadvantage that the particle size distribution becomes 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 for a cup of instant food, particle size 70
Those having a particle size of 0 μm to 1800 μm are used for various packings and fish boxes, and those having a particle size of 1500 μm to 3000 μm are used for building material boards.

[0004] The particle size of the polymer obtained by suspension polymerization using a hardly soluble inorganic salt fine powder and an anionic surfactant as a suspension stabilizer is in a wide range of 100 µm to 3000 µm, and the particle size distribution is wide. The polymer particles for expandable polystyrene used in the above applications have been provided for various applications by sieving. However, the properties required for the polymer particles for expandable polystyrene are now becoming various due to the difference in applications, and it is necessary to produce polymer particles for each application. Therefore, there is a strong demand for a suspension polymerization method capable of obtaining polymer particles having a desired particle size in high yield.
At the same time, a suspension polymerization method in which generation of fine particles is small is strongly desired. When a large number of fine particles are generated, it is difficult to completely remove the fine particles even by dehydration treatment and sieving. If the fine particles are mixed between particles having a target particle size, it causes molding failure. In addition, collecting fine particles mixed in the wastewater is not an easy task.

In suspension polymerization using a poorly soluble inorganic salt and an anionic surfactant as a suspension stabilizer, an object of the present invention is to improve the above problems and obtain styrene-based polymer particles having a narrow particle size distribution. A method using various additives has been proposed. For example, Japanese Patent Publication No. 55-50042 discloses a method of adding peroxodisulfate. In addition, a method of adding a neutral water-soluble inorganic salt such as sodium chloride or sodium sulfate is also known. Also, a large number of suspension stabilizers comprising a combination of a poorly soluble inorganic salt and various surfactants have been disclosed (JP-A-53-1260).
94, JP-A-59-176309, JP-A-60-147406, JP-B-58-10406, JP-B-59-41448 and the like.

[0006] Japanese Patent Publication No. 42-17497 discloses a method in which zinc oxide is used as a suspension stabilizer to increase the dispersing effect, and the aqueous phase of the suspension is kept at least at pH 9.3 to initiate polymerization. Japanese Patent Publication No. 45-39549 discloses a method in which sodium silicate is used in a suspension system to obtain transparent polymer particles having a uniform particle diameter. A method for maintaining the hydrogen ion concentration of an aqueous phase as a dispersion medium in the range of pH 7 to pH 5 in order to obtain polymer particles is disclosed. In addition, Japanese Patent Publication No. 64-70508
In order to obtain polymer particles having a uniform particle size, Japanese Unexamined Patent Publication (Kokai) No. 5-5
A method for adding 0 ppm to 500 ppm of carbonate or bicarbonate is disclosed.

[0007]

Problems to be Solved by the Invention
In the method disclosed in JP-A No. 2 (1994), polymer particles having a smaller particle size distribution and a narrower particle size distribution than those of the conventional method can be obtained.
When viewed by application, there is a problem that many polymer particles are out of the required particle size range.

[0008] The method disclosed in Japanese Patent Publication No. 45-39549 has a problem that the COD load of the polymerization effluent is increased because it is necessary to use sodium silicate and an organic polymer compound in combination.

In Japanese Patent Publication No. 42-17497, there is a problem that since a large amount of zinc oxide is required as a suspending agent, the zinc oxide is contained in the polymer particles, so that the quality deteriorates. Further, the particle size distribution of the obtained polymer particles also has a wide disadvantage.

The method disclosed in Japanese Patent Publication No. Sho 62-51961 has a problem that when a water-soluble polymer is used as a suspending agent, the COD load of the polymerization effluent is increased, so that wastewater treatment is required. In addition, when a poorly soluble inorganic salt is used, a large amount of a suspending agent is required, and therefore, there is a problem that this is contained in the polymer particles to deteriorate the quality and a drawback that the reproducible operation range is narrow.

The method disclosed in Japanese Patent Application Laid-Open No. Sho 64-70508 has a problem that the organic protective colloid and the water-insoluble inorganic powder are used as suspension stabilizers, so that the COD load of the polymerization effluent is also increased. Further, there is a problem that the water content in the polymer particles is large and the cell structure is not uniform.

[0012] The polymer particles for expanded polystyrene are required to have a uniform particle size and a small number of fine particles. However, from the viewpoint of quality, there is no gap between the expanded particles when the polymer particles are pre-expanded and molded. It is required that the expanded particles be sufficiently fused and have sufficient strength as a molded product. In order to satisfy this requirement, the content of impurities such as water and a suspending agent in the polymer particles is preferably small. In addition, when emulsion polymerization occurs concurrently with suspension polymerization, the emulsion itself acts as an impurity, and water, a suspending agent, and the like are easily incorporated into the polymer particles. Therefore, simultaneous occurrence of emulsion polymerization is preferably suppressed. These impurities have an effect on the expansion of the particles and disturb the cell structure, so that the above-mentioned required characteristics cannot be satisfied. Therefore, conventional suspension polymerization cannot provide polymer particles having a uniform particle size, a small number of fine particles, and excellent quality. The present invention provides a method for producing vinyl polymer particles having a narrow particle size distribution with reduced fine particles without wastewater treatment and quality problems.

[0013]

Means for Solving the Problems In the suspension polymerization using a sparingly soluble phosphate and an anionic surfactant as a suspension stabilizer, the present inventors controlled the hydrogen ion concentration in an aqueous medium, By adding a small amount of hydrogen peroxosulfate, it was found that vinyl polymer particles having no quality problems and having small particle size and a narrow particle size distribution can be produced with good reproducibility and completed the present invention. Was.

That is, in the present invention, when a vinyl monomer is subjected to suspension polymerization in an aqueous medium in the presence of a sparingly soluble phosphate and an anionic surfactant, a hydrogen peroxide salt is added to the aqueous medium. A method for producing vinyl polymer particles, wherein the hydrogen ion concentration in the aqueous medium is adjusted to pH 10 to pH 13 within a period in which the polymerization conversion of the vinyl monomer is 0% by weight to 30% by weight. The present invention also relates to a method for producing expandable vinyl polymer particles in which a foaming agent is further impregnated during or after polymerization in the production method.

In the present invention, the hydrogen ion concentration in the aqueous medium is adjusted to pH 10 to pH 13 while the polymerization conversion of the vinyl monomer is 0 to 30% by weight. If it is, the effect of narrowing the particle size distribution is insufficient, and if the pH exceeds 13, the particle size distribution of the polymer particles becomes wide. Further, the hydrogen ion concentration is adjusted to pH 10 to p.
The period during which H13 is set is within the period where the polymerization conversion of the polymerizable monomer is 0% to 30% by weight, preferably within the period where the polymerization conversion is 5% to 15% by weight. If the polymerization conversion exceeds 30% by weight, the viscosity of the oil droplets increases significantly,
The effect of the present invention is difficult to obtain, and polymer particles having a narrow particle size distribution cannot be obtained. Means for adjusting the hydrogen ion concentration in the aqueous medium to the above range include adding a basic metal (alkali metal) hydroxide such as sodium hydroxide, potassium hydroxide, lithium hydroxide or the like, which causes little deterioration in quality due to concurrent emulsion polymerization. Are most preferred, then sodium carbonate, potassium carbonate,
It is preferable to add a soluble basic metal carbonate such as lithium carbonate and sodium hydrogen carbonate. Addition of calcium hydroxide (alkaline earth metal salt) destabilizes the system and results in agglomeration of particles. Calcium carbonate, magnesium carbonate,
Insoluble or poorly soluble carbonates such as zinc carbonate, barium carbonate and copper carbonate have no effect of narrowing the particle size distribution. In the present invention, the hydrogen ion concentration in the aqueous phase is adjusted to pH 1
Only the additives that are adjusted to 0 to pH 13 exert the effect of narrowing the particle size distribution.

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

The hydrogen peroxosulfate may be used as a complex salt with other salts. For example, 2K
HSO ₅ · KHSO ₄ · K ₂ SO ₄ or the like can be used. In this case, it is naturally preferable that hydrogen peroxosulfate (KHSO _{5 in the} above example) is used in the above-mentioned amount.

In the present invention, the vinyl monomer to be polymerized includes styrene, α-methylstyrene, chlorostyrene, styrene derivatives such as vinyltoluene, acrylonitrile, vinylpyrrolidone, vinylpyridine, vinylcarbazole, polybutadiene, and a compound having 1 carbon atom. Esters of acrylic acid or methacrylic acid, etc. can be used.
It is preferable to use 0% by weight or more.

Examples of the polymerization initiator include organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-butyl perbenzoate and di-t-butyl peroxide which are soluble in a vinyl monomer, and azobisisobutyrate. Although azo compounds such as lonitrile can be used,
Preferably, an organic peroxide is used.

As the sparingly soluble phosphate, tricalcium phosphate, hydroxyapatite, magnesium phosphate, barium phosphate, strontium phosphate, aluminum phosphate, iron phosphate, cobalt phosphate, calcium pyrophosphate and the like can be used. Can be, but tricalcium phosphate,
Hydroxyapatite is preferred. The addition amount is preferably from 0.1% by weight to 0.8% by weight, particularly preferably from 0.15% by weight to 0.40% by weight, based on the polymerizable monomer.

As the anionic surfactant, sodium dodecylbenzenesulfonate, sodium styrenesulfonate, sodium dodecylsulfonate, sodium dioctylsulfosuccinate and the like can be used. The addition amount is 0.0001% by weight to 0.1% based on the polymerizable monomer.
01% by weight is preferred.

The polymerization temperature of the 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 in the former / latter.

To the polymerizable monomer, an ethylene-vinyl acetate copolymer, ethylene bisstearyl amide, methylene bis stearyl amide, etc. may be added as a bubble-forming agent.

In the present invention, when producing expandable vinyl polymer particles, hydrocarbons such as propane, butane, pentane, hexane, cyclopentane and cyclohexane, methylene chloride and dichlorodifluoromethane are used during or after the polymerization. A halogenated hydrocarbon such as trifluoromethane or a mixture thereof is impregnated with a known method as a foaming agent to obtain foamable vinyl polymer particles.

[0025]

According to the present invention, the hydrogen ion concentration in the aqueous medium is adjusted to pH 10 to pH 13 within a period in which the polymerization conversion of the polymerizable monomer is 0% by weight to 30% by weight, so that the oil droplets in this period are reduced. Since the frequency of dispersion and coalescence can be suppressed, it is possible to prevent the particle size distribution from broadening. In addition, hydrogen peroxosulfate has an effect of making the oil droplet diameter uniform, and is effective in reducing fine particles. Furthermore, hydrogen peroxosulfate has the effect of suppressing emulsion polymerization, and reduces the amount of water and suspending agent taken into the oil droplets together with the emulsion. A foam molded article having a uniform structure and excellent surface smoothness can be obtained.

[0026]

The present invention will be described below with reference to examples. Here, the particle size distribution and the average particle size of the polymer particles are represented by a deviation coefficient Cv and a median diameter, respectively. That is, based on the cumulative weight distribution curve, the particle diameters at which the cumulative weight becomes 15%, 50%, and 85% are d ₁₅ , d ₅₀ , and d ₈₅ , respectively, and the deviation coefficient Cv
Was determined by the following equation, and the width of the particle size distribution was determined. _{Cv = (d 85 -d 15)} / d 50 Cv value is greater Hodotsubu size distribution is wide, small Hodotsubu size distribution is narrow. The average diameter was adopted median diameter represented by d ₅₀ described above.

Further, a scale indicating the surface smoothness of the molded article was obtained by the following method, and was defined as the surface smoothness. That is, when the printing black ink is thinly applied to the surface of the molded article by a roller, the ink is applied to the smooth portion, but the gap between the foam particles remains white. The ratio of the area of the black portion to the total surface area was calculated by an image processing apparatus and defined as the surface smoothness.

Example 1 In a 4 l autoclave, 22 g of 10% tribasic calcium phosphate dispersion (Superitite 10 manufactured by Nippon Chemical Industry Co., Ltd.), 0.048 g of sodium dodecylbenzenesulfonate (manufactured by Wako Pure Chemical Industries, Ltd.), and 1178 g of ion-exchanged water were placed. The mixture was stirred well to form a uniform mixed solution. Then, 3.0 g of benzoyl peroxide (manufactured by Shoko Chemical Co., Ltd.) and t-butyl
Benzoate (manufactured by NOF Corporation) 0.1 g and ethylene bisstearylamide (manufactured by Nippon Kasei Co., Ltd.) dissolved in styrene (manufactured by Denki Kagaku Kogyo Co., Ltd.) 1200 g were added thereto with stirring, and the atmosphere in the polymerization vessel was nitrogen gas And the temperature was raised to 90 ° C. to initiate polymerization. When the polymerization conversion (measured by the specific gravity method) reaches 10% by weight, 2KHSO ₅
・ KHSO ₄・ K ₂ SO ₄ (Aldrich, OXON
E) 1.2 g of an aqueous solution containing 0.12 g 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 the addition was pH 11.5. Further, when the polymerization conversion reaches 35% by weight, 10
6 g of a 3% calcium phosphate dispersion was added, and the polymerization was allowed to proceed as it was. When the polymerization conversion reached 95% by weight, 12 g of a 10% tribasic calcium phosphate dispersion was further added, and then 24 g of cyclohexane and 84 g of butane were introduced for 1 hour. Thereafter, the temperature was raised to 120 ° C. for 2 hours,
After maintaining at 20 ° C. for 5 hours, the mixture was cooled to room temperature to obtain the target expandable polystyrene polymer particles. As a result of sieving the obtained polymer particles, the average particle size d ₅₀ was 870 μm,
The deviation coefficient Cv was 0.30, which was a very narrow particle size distribution. The amount of the fine particles having a size of 300 μm or less was 0.6% by weight. The contents of water and suspending agent in the obtained polymer particles are shown in Table 1.
As shown in the figure, after pre-expanding the polymer particles to 50 ml / g, the cut surface of the pre-expanded particles was observed, and a uniform cell structure was observed. After aging the pre-expanded particles for 24 hours, molding was performed. The obtained molded article had few gaps between the foamed particles and had a surface smoothness of 96%.

Example 2 In Example 1, 3 g of a 10% aqueous solution of sodium hydroxide was used.
Was changed to 3.6 g of a 10% aqueous solution of sodium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) in the same manner as in Example 1 to obtain polymer particles. The hydrogen ion concentration immediately after the addition of sodium carbonate was pH 10.5. The average particle size d ₅₀ of the obtained polymer particles is 900 μm, and the coefficient of deviation C
The v value was 0.32, which was a very narrow particle size distribution. 300
The fine particles having a size of not more than μm were 0.7% by weight. The content of water and the suspending agent in the polymer particles was 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, 2KHSO ₅ · KHSO ₄ · K ₂ SO
₄ Except for removing 1.2 g of an aqueous solution containing 0.12 g, suspension polymerization was carried out in the same manner as in Example 1 to obtain polymer particles. The hydrogen ion concentration immediately after the addition of sodium hydroxide was pH 11.5
Met. The average particle diameter d ₅₀ of the obtained polymer particles is 910.
At μm, the coefficient of variation Cv had a very narrow particle size distribution of 0.30, but the fine particles of 300 μm or less increased to 1.5% by weight. Further, the content of water and the suspending agent in the polymer particles increased, and the cell structure of the pre-expanded particles was slightly non-uniform. When the pre-expanded particles were molded, the surface smoothness of the molded product was 90%.

Comparative Example 2 In Example 2, 2KHSO ₅ · KHSO ₄ · K ₂ SO ₄
Example 2 except that 1.2 g of an aqueous solution containing 0.12 g was removed.
Polymer particles were obtained in the same manner as described above. Immediately after the addition of sodium carbonate, the hydrogen ion concentration was pH 10.6. The average particle diameter d ₅₀ of the obtained polymer particles is 930 μm, and the deviation coefficient Cv
The value was a narrow particle size distribution of 0.32. Fine particles having a size of 300 μm or less increased to 1.7% by weight. Further, the content of water and the suspending agent in the polymer particles was increased, and the cell structure of the pre-expanded particles was non-uniform and the number of cells near the particle surface was considerably reduced. When the pre-expanded particles were molded, the molded article had a surface smoothness of 85%.

Comparative Example 3 In Example 1, 3 g of a 10% aqueous solution of sodium hydroxide was used.
To calcium carbonate fine powder (Wako Pure Chemical Industries, Ltd.) 0.36
The suspension polymerization was carried out in the same manner as in Example 1 except that the amount was changed to g, to obtain polymer particles. The hydrogen ion concentration immediately after the addition of calcium carbonate was pH 7.0. The average particle diameter d ₅₀ of the obtained polymer particles is 860 μm, and the deviation coefficient Cv is 0.5.
The particle size distribution was as wide as 49. Microparticles having a size of 300 μm or less accounted for 2.9% by weight. The content of water and the suspending agent in the polymer particles was small, 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 In Example 1, 3 g of a 10% aqueous solution of sodium hydroxide was used.
Was changed to 6 g of a 10% aqueous solution of sodium chloride (manufactured by Wako Pure Chemical Industries, Ltd.), and suspension polymerization was carried out in the same manner as in Example 1 to obtain polymer particles. The hydrogen ion concentration immediately after the addition of sodium chloride was pH 6.5. The average particle diameter d ₅₀ of the obtained polymer particles was 940 μm, and the coefficient of deviation Cv was 0.42. Microparticles of 300 μm or less are 2.5
% By weight. The content of water and the suspending agent in the polymer particles was small, 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.

Embodiment 3 In Embodiment 1, 2KHSO ₅ · KHSO ₄ · K ₂ SO ₄
1.2 g of an aqueous solution containing 0.12 g is added to 2KHSO ₅ · KH
Suspension polymerization was carried out in the same manner as in Example 1 except that the aqueous solution containing 1.5 g of SO ₄ · K ₂ SO ₄ was changed to 15 g to obtain polymer particles. The hydrogen ion concentration immediately after the addition of sodium hydroxide was pH 10.5. The average particle diameter d ₅₀ of the obtained polymer particles was 850 μm, and the coefficient of deviation Cv was 0.34. Microparticles having a size of 300 μm or less accounted for 0.5% by weight. The content of water and the suspending agent in the polymer particles was small, 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 96%.

Comparative Example 5 A 10% aqueous solution of sodium hydroxide 3.0 in Example 1 was used.
The 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. However, immediately after the addition of calcium hydroxide, the continuous phase and the dispersed phase were reversed to obtain polymer particles. could not.

Example 4 18 g of a 10% aqueous solution of tribasic calcium phosphate, sodium dodecylbenzenesulfonate 0.1 g in a 4 l autoclave.
060 g, 2KHSO ₅ · KHSO ₄ · K ₂ SO ₄ 0.24
g of an aqueous solution (2.4 g) and ion-exchanged water (1182 g) were added thereto and stirred well to form a uniform mixed solution. Subsequently, 3.2 g of benzoyl peroxide, 0.1 g of t-butyl per-benzoate and 1200 g of styrene in which 0.6 g of ethylenebisstearylamide were dissolved were added with good stirring, and the temperature was raised to 90 ° C. to initiate polymerization. Polymerization conversion rate is 7
At the time of reaching the weight%, 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 the addition was pH 11.8. When the polymerization conversion reached 40% by weight, 9 g of a 10% aqueous solution of tribasic calcium phosphate was added, and the polymerization was allowed to proceed. When the polymerization conversion reached 95% by weight, 12 g of a 10% tribasic calcium phosphate aqueous solution was added, and then 24 g of cyclohexane was added.
And 84 g of butane were introduced in one hour. Then 120
Temperature for 2 hours and kept at 120 ° C for 5 hours,
After cooling to room temperature, expanded polystyrene polymer particles were obtained.
The resulting average particle size d ₅₀ of the polymer particles in 890Myuemu, deviation coefficient Cv value was very narrow particle size distribution 0.29. The amount of the fine particles having a size of 300 μm or less was 0.6% by weight. The content of water and the suspending agent in the polymer particles was small, and the cell structure of the pre-expanded particles was uniform. When the pre-expanded particles were molded, the molded article had a surface smoothness of 97%.

Example 5 A 10% aqueous solution of potassium hydroxide 3.6 in Example 4 was used.
The 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 obtained polymer particles had an average particle size d ₅₀ of 900 μm and a very narrow particle size distribution with a coefficient of variation Cv of 0.32. Microparticles having a size of 300 μm or less accounted for 0.5% by weight. The content of water and the suspending agent in the polymer particles was low, and the cell structure of the pre-expanded particles was relatively uniform. When the pre-expanded particles were molded, the molded article had a surface smoothness of 94%.

Example 6 3 g of a 10% aqueous solution of sodium hydroxide in Example 1
Was changed to 3.6 g of a 10% aqueous solution of lithium hydroxide in the same manner as in Example 1 to obtain polymer particles. The hydrogen ion concentration immediately after the addition of sodium hydroxide was pH 11.3. The resulting average particle size d ₅₀ of the polymer particles in 910Myuemu, deviation coefficient Cv value was very narrow particle size distribution 0.29. The fine particles having a size of 300 μm or less were 0.6% by weight. The content of water and the suspending agent in the polymer particles was small, and the cell structure of the pre-expanded particles was uniform. When the pre-expanded particles were molded, the molded article had a surface smoothness of 98%.

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

[0040]

[Table 1]

[0041]

As apparent from the above, the present invention can provide vinyl polymer particles having a narrow particle size distribution and excellent quality. In addition, the method for producing expandable vinyl polymer particles of the present invention is extremely industrially useful in terms of productivity and quality, since the amount of fine particles produced is particularly small and defective molded articles can be reduced.

Continuing from the front page (72) Inventor ▲ Yoshi ▼ Tohru 4-13-1, Higashicho, Hitachi City, Ibaraki Prefecture Within Hitachi Chemical Co., Ltd.Ibaraki Research Laboratories (72) Inventor Kazuhiko Kunitake 14-14 Goi Minami Coast, Ichihara City, Chiba Prefecture Hitachi In the Goi Plant of Chemical Industry Co., Ltd. (72) Shingo Hibino, 14 Goi South Coast, Ichihara City, Chiba Prefecture In the Goi Plant of Hitachi Chemical Co., Ltd. (56) References JP-A-2-147602 (JP, A) JP-A-49-53982 (JP, A) JP-A-59-202202 (JP, A) JP-A-58-89603 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08F 2 / 00-2/18

Claims (6)

(57) [Claims] When a suspension polymerization of a vinyl monomer in an aqueous medium in the presence of a sparingly soluble phosphate and an anionic surfactant, a hydrogen peroxide salt is added to the aqueous medium,
In addition, the hydrogen ion concentration in the aqueous medium is adjusted to pH 10 to 10 in a period in which the polymerization conversion of the vinyl monomer is 0 to 30% by weight.
A process for producing vinyl polymer particles, wherein the pH is adjusted to 13. 2. An aqueous medium having a hydrogen ion concentration of pH 10
The method for producing vinyl polymer particles according to claim 1, wherein a basic metal hydroxide is used as a means for adjusting the pH to pH 13. 3. An aqueous medium having a hydrogen ion concentration of pH 10
The method for producing vinyl polymer particles according to claim 1, wherein a soluble basic carbonate is used as a means for adjusting the pH to pH 13. 4. The method for producing vinyl polymer particles according to claim 1, wherein the sodium peroxosulfate, potassium salt or lithium salt is used as the hydrogen peroxide salt. 5. The vinyl polymer according to claim 1, wherein the amount of the hydrogen peroxide salt is 0.0005% by weight to 0.05% by weight relative to the vinyl monomer. Method for producing particles. 6. The method for producing vinyl polymer particles according to claim 1, wherein a foaming agent is further impregnated during or after polymerization.