JPH0826084B2 - Method for producing vinyl polymer particles and expandable vinyl polymer particles - Google Patents

Description

The present invention relates to a method for producing vinyl polymer particles having a narrow particle size distribution, and a method for producing expandable vinyl polymer particles used as a raw material for foamed molded articles. Regarding

(Prior Art) In a method for producing vinyl polymer particles by subjecting a conventional vinyl monomer, for example, a monomer mainly containing styrene to suspension polymerization, a sparingly soluble phosphate is used as a main suspending agent. , An anionic surfactant as a suspending agent and a water-soluble metal salt as a growth agent for particles, and the combination of chemical factors such as type, concentration or addition time and mechanical factors such as stirring causes the particles The diameter and particle size distribution were controlled. Specifically, (1) a method of carrying out polymerization while maintaining the hydrogen ion concentration in the aqueous phase within the range of 10 ⁻⁷ to 10 ⁻⁵ g ion (JP-A-62-169801).
(2) A method of using a calcium phosphate salt containing 5 to 20% by weight of calcium acetate or calcium propionate as a main suspending agent (JP-A-58-63702), (3) A method of using a water-soluble organic polymer compound and sodium silicate as a main suspending agent (Japanese Patent Publication No. 45395/1985), (4) Trisodium phosphate is added during the polymerization to continuously generate calcium phosphate in the system. A method of synthesizing (Japanese Patent Publication No. 59-19136) has been proposed.

However, the above-mentioned conventional methods are insufficient in terms of suppressing the generation of fine particles, and the particle size of the polymer particles obtained by these methods is in the range of 100 to 3000 μm, and the particle size distribution thereof is small. Was a wide variety.

Therefore, as a method for suppressing the generation of fine particles and producing a vinyl-based polymer having a narrow particle size distribution, the inventors have previously
A method has been proposed in which the hydrogen ion concentration in the aqueous phase is controlled within the range of 10 ⁻¹⁰ to 10 ⁻¹³ gram ion while the polymerization conversion rate is 0 to 30% by weight (JP-A-1-10455).

(Problems to be Solved by the Invention) Generally, vinyl polymer particles mainly composed of styrene obtained by a suspension polymerization method include butane,
Expandable polystyrene resin particles are obtained by impregnating lower hydrocarbons such as pentane as a foaming agent. Expandable polystyrene resin particles are used for their excellent properties,
It is used in various fields such as packaging cushioning materials and heat insulating materials.

A molded product of expandable polystyrene resin particles can be obtained by filling a mold with particles that have been pre-expanded by steam or hot air in a predetermined multiple and secondary-foaming with steam.
The obtained molded product is used as a cushioning material and a heat insulating material, and the required performance at that time is that the gap between the pre-expanded particles is sufficiently filled and the appearance is good, and the pre-expanded particles are sufficiently They are fused and the molded product itself has some strength.

However, the expandable polystyrene resin particles obtained by the conventional suspension polymerization method still have a problem that the gap between the pre-expanded particles is not sufficiently filled and the appearance of the molded product is deteriorated.

That is, according to the present invention, it is possible to obtain vinyl polymer particles having a narrow particle size distribution, and to obtain a molded product having a good appearance when the expandable polystyrene resin particles are used. An object is to provide a method for producing vinyl polymer particles.

(Means for Solving the Problems) The present invention provides a method for oxidizing a vinyl-based monomer in an aqueous medium during suspension polymerization in the presence of a sparingly soluble phosphate and an anionic surfactant. The vinyl ion is characterized in that the hydrogen ion concentration in the polymerization system is adjusted to 10 ^-9 to 10 ^-13 gram ion while the agent is added and the polymerization conversion rate of the vinyl monomer is 0 to 30% by weight. The present invention relates to a method for producing polymer particles and a method for producing expandable vinyl polymer particles in which a foaming agent is impregnated during or after the polymerization.

As the vinyl-based monomer in the present invention, styrene,
Styrene derivatives such as α-methylstyrene, vinyltoluene and parachlorostyrene, vinyl cyanide such as acrylonitrile and methacrylonitrile, acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate and butyl acrylate, and the like. There are methacrylic acid ester, vinyl pyridine, vinyl carbazole, butadiene, etc. When making vinyl polymer particles into expandable vinyl polymer particles, styrene or styrene derivative is used.
It is preferable to use 50% by weight or more.

Polymerization initiators for suspension polymerization of these vinyl monomers in an aqueous medium include organic peroxides such as benzoyl peroxide and butyl perbenzoate, and azo compounds such as azobisisobutyronitrile. A polymerization initiator generally used for radical polymerization of vinyl monomers can be used. They are,
It is preferably used in an amount of 0.05 to 10% by weight based on the monomer component.

As the main suspending agent for stably presenting the dispersed phase in the aqueous medium, sparingly soluble phosphates such as tricalcium phosphate and magnesium phosphate can be used, and these are preferably 0.05 to 1% by weight in the aqueous medium. %used.

As the anionic surfactant, an alkylbenzene sulfonate such as dodecylbenzene sulfonic acid, a higher fatty acid salt such as sodium alkylsulfonate, sodium oleate, etc. can be used. Used at 0.1% by weight.

In the present invention, during the suspension polymerization, the hydrogen ion concentration in the polymerization system is 10 ⁻⁹ to 10 ⁻¹³ g ion, preferably between 0 to 30% by weight of the vinyl monomer. 10 ^-10 ~
By having a period of 10 ⁻¹² gram ions, it is possible to suppress the generation of fine polymer particles. Even if the hydrogen ion concentration is adjusted after the polymerization conversion exceeds 30% by weight, a sufficient effect cannot be obtained. The hydrogen ion concentration is 10
^If it exceeds ^-9 gram ions, the effect of suppressing fine polymer particles becomes insufficient, and if it is less than 10 ^-13 gram ions, the growth of polymer particles is promoted and the particle size distribution becomes broad.

As a method of adjusting the hydrogen ion concentration as described above,
A method of adding a water-soluble basic salt is effective. As the water-soluble basic salt, a water-soluble carbonate and / or a hydroxide compound is preferable because of its great effect, and sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide and the like are particularly preferable, and sodium hydroxide and water are preferred. A hydroxide compound such as potassium oxide is most effective and is more preferable.

These water-soluble basic salts are generally used in an amount of 0.005 to 0.005 to an aqueous medium in order to achieve the above hydrogen ion concentration.
0.1% by weight, particularly preferably 0.01 to 0.1% by weight, is used. Further, the addition of these water-soluble basic salts needs to be carried out while the polymerization conversion rate of the vinyl-based monomer is 0 to 30% by weight, and the effect is not sufficiently exhibited by the addition thereafter.

Further, in the present invention, an oxidizing agent is added to the aqueous medium during suspension polymerization. The addition timing is preferably such that the polymerization conversion rate of the vinyl monomer is between 0 and 15% by weight. Also,
The amount is 0.001 to 0.1% by weight, especially 0.
It is preferable to add 002 to 0.01%.

Even if the above-mentioned oxidizing agent is added after the polymerization conversion exceeds 15% by weight, it is difficult to obtain a sufficient effect.

Further, it is difficult to obtain a sufficient effect even if the amount of the oxidizing agent added is less than 0.001% by weight. If added in excess of 0.1% by weight, the polymerization system will become unstable and the particle size distribution of the polymer particles will tend to be broad.

Here, hydrogen peroxide, silver oxide, silver nitrate or the like can be used as the oxidizing agent, and the three types of oxidizing agents exemplified above are particularly preferable because of their excellent effects.

By the above method, vinyl polymer particles having an average particle diameter of 400 to 1500 μm and a narrow particle size distribution are generally obtained.

Further, the expandable vinyl polymer particles can be obtained by impregnating a foaming agent such as propane, butane or pentane by a known method during or after the polymerization. According to this method, it is possible to obtain expandable vinyl polymer particles having a smooth surface and giving a molded article having an excellent appearance.

(Example) Hereinafter, the Example of this invention is described.

In addition, the notation method of the average particle diameter of the particle size distribution of the polymer particles is expressed by the deviation coefficient Cv median diameter. That is, the cumulative weight distribution is based on the curve and the cumulative weight%
With particle diameters of 15%, 50%, and 85% are d ₁₅ , d ₅₀ , and d, respectively.
_The deviation coefficient Cv is calculated as Cv = (d ₈₅ −d ₁₅ ) / d ₅₀ to determine the size distribution of the particle size distribution.

Therefore, the larger the value of Cv, the wider the particle size distribution, and the smaller the value, the narrower the distribution. The average diameter is adopted Medeian diameter represented by d ₅₀ described above.

The smoothness of the surface of the molded product was determined by the following method and expressed as the surface smoothness.

First, apply a thin layer of printing ink to the surface of the molded product with a roller. Ink is applied to the smooth part to turn black, and the gaps between the expanded particles remain white. This area was applied to an image processing device to determine the area (%) of the black portion with respect to the entire area, and this was taken as the surface smoothness.

Example 1 Tricalcium phosphate 2.4 using a 4 l autoclave
g, sodium dodecylbenzenesulfonate 0.06 g and hydrogen peroxide 0.12 g were dispersed and dissolved in 1200 g of ion-exchanged water. To this, 2.4 g of benzoyl peroxide dissolved in 1200 g of styrene was added with stirring, and the temperature was raised to 91 ° C to initiate polymerization.

Next, the polymerization conversion rate (measured by the specific gravity method) is 10% by weight.
0.48g of sodium carbonate was added to the deionized water.
It was dissolved in 9.12 g and added. At this time, the hydrogen ion concentration in the polymerization system was 10 ^-10.8 gram ion. Further, when the conversion of polymerization reached 30 to 35% by weight, 0.6 g of tricalcium phosphate was added and the polymerization was proceeded as it was.

When the polymerization conversion rate reached 95% by weight, 1.2 g of tricalcium phosphate was further added, and then 2.4 g of cyclohexane and 8.4 g of butane were introduced over 1 hour. Thereafter, the temperature was raised to 120 ° C. over 2 hours, the temperature was maintained at the same temperature for 5 hours, and then the temperature was cooled to room temperature to obtain the target expandable polystyrene resin particles.

As a result of sieving the obtained polymer particles, an average particle diameter d
₅₀ was 0.95 mm and the deviation coefficient Cv was 0.30, showing a very sharp particle size distribution.

The obtained polymer particles were pre-foamed to 50 ml / g, aged for 24 hours and then molded. The obtained molded product had few gaps between the expanded particles and had a surface smoothness of 95%.

Example 2 Except that 0.12 g of hydrogen peroxide was changed to 0.12% of silver nitrate,
Polymer particles were obtained in the same manner as in Example 1 above.

As a result of sieving the obtained polymer particles, the average particle size was 0.
The particle size distribution was 93 mm and the deviation coefficient was 0.31 with a very sharp particle size distribution.

Further, the obtained polymer particles were prefoamed and molded in the same manner as in Example 1. As a result, a molded product having a smooth surface with few gaps between the foamed particles was obtained, and the surface smoothness was 95%.

Example 3 Polymer particles were obtained in the same manner as in Example 1 except that 0.48 g of sodium carbonate was changed to 0.36 g of sodium hydroxide. The hydrogen ion concentration after adding sodium hydroxide is 10
^-11.6 grams ion.

As a result of sieving the obtained polymer particles, an average particle diameter d
₅₀ was 0.92 mm and the deviation coefficient Cv was 0.28, showing a very sharp particle size distribution.

Further, the obtained polymer particles were prefoamed and molded in the same manner as in Example 1, and as a result, a molded product having a smooth surface with few gaps between the foamed particles was obtained, and the surface smoothness was 96%.

Example 4 Polymer particles were obtained in the same manner as in Example 1 except that 0.48 g of sodium carbonate was changed to 0.36 g of sodium hydroxide and 0.12 g of hydrogen peroxide was changed to 0.12 g of silver nitrate. The hydrogen ion concentration after the addition of sodium hydroxide was 10 ^-11.6 gram ion.

As a result of sieving the obtained polymer particles, an average particle diameter d
₅₀ was 0.90 mm and the deviation coefficient Cv was 0.27, showing a very sharp particle size distribution.

Further, the obtained polymer particles were prefoamed and molded in the same manner as in Example 1, and as a result, a molded product having a smooth surface with few gaps between the foamed particles was obtained, and the surface smoothness was 97%.

Comparative Example 1 Polymer particles were obtained in the same manner as in Example 1 except that 0.12 g of hydrogen peroxide was removed.

As a result of sieving the obtained polymer particles, an average particle diameter d
₅₀ was 0.95 mm and deviation coefficient Cv was 0.30, showing a sharp particle size distribution.

However, the polymer particles obtained were pre-expanded to 50 ml / g,
As a result of molding after aging for 4 hours, there were many gaps between the expanded particles, and the molded product had poor surface smoothness. The surface smoothness of this molded product was as low as 85%.

Comparative Example 2 Polymer particles were obtained in the same manner as in Example 3 except that 0.12 g of hydrogen peroxide was removed.

As a result of sieving the obtained polymer particles, an average particle diameter d
₅₀ was 0.92 mm and deviation coefficient Cv was 0.29, showing a sharp particle size distribution.

However, as a result of pre-expanding the obtained polymer particles and molding, there were many gaps between the expanded particles and the molded product had poor surface smoothness. The surface smoothness rate was as low as 87%.

Comparative Example 3 Polymer particles were obtained in the same manner as in Example 2 except that 0.48 g of sodium carbonate was changed to 0.48 g of sodium chloride. The hydrogen ion concentration after adding sodium chloride is 10 ^-6.5.
It was Gram Ion.

As a result of sieving the obtained polymer particles, the average particle size was
The particle size distribution was wide with 0.97 mm and the deviation coefficient Cv was 0.45.

As a result of pre-expanding the obtained polymer particles and molding, a molded product with a smooth surface with few gaps between the expanded particles was obtained.
The surface smoothness was 93%, but because the particle size varies,
The appearance was inferior to that of the example.

Table 1 shows a summary of the results of the above Examples and Comparative Examples.

(Effects of the Invention) The vinyl polymer particles obtained by the production method of the present invention have few fine particles and a narrow distribution. Therefore, the yield of particles in the target particle size range is improved.

Moreover, when molded as expandable vinyl-based polymer particles, there can be obtained a molded product having a small gap between the expanded particles and excellent surface smoothness and a good appearance.

Claims (6)

[Claims] 1. When an vinyl monomer is suspension-polymerized in the presence of a sparingly soluble phosphate and an anionic surfactant in an aqueous medium, an oxidizing agent is added to the aqueous medium, and a vinyl-based monomer is added. A method for producing vinyl polymer particles, characterized in that the hydrogen ion concentration in the polymerization system is 10 ^-9 to 10 ^-13 gram ions while the polymerization conversion rate of the monomer is 0 to 30% by weight. 2. A polymerization conversion ratio of an oxidizer for a vinyl monomer is 0.
The method for producing vinyl-based polymer particles according to claim 1, wherein the amount is from about 15 to 15% by weight. 3. The method for producing vinyl polymer particles according to claim 1, wherein hydrogen peroxide, silver oxide and / or silver nitrate is used as an oxidizing agent. 4. The method for producing vinyl polymer particles according to claim 1, 2 or 3, wherein 0.001 to 0.1% by weight of an oxidizing agent is added to the aqueous medium. 5. The hydrogen ion concentration of the aqueous medium is set to 10 ^-9 to 10 ^-13.
Water-soluble basic carbonate and / or gram ion
Alternatively, the method for producing vinyl polymer particles according to claim 1, 2, 3 or 4, wherein a hydroxyl compound is used. 6. The method for producing vinyl polymer particles according to claim 1, wherein the foaming vinyl polymer particles are further impregnated with a foaming agent during or after the polymerization.