JPS5928582B2 - Method for producing expandable polymer particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing expandable styrenic polymer particles, particularly expandable styrenic polymer particles having a relatively low expansion ratio and good surface hardness of molded articles.

Obtaining expandable styrene polymer particles by a suspension impregnation method is described, for example, in Japanese Patent Publication No. 36-10628 and Japanese Patent Publication No. 36-10628.
-10837, US Pat. No. 2,893,963, and US Pat. No. 2,950,261.

All of these known methods are aimed at obtaining pre-expanded particles having a high expansion ratio of 30 times or more, and using the expandable polymer particles obtained by these methods, the expansion ratio is 20 times or less. In particular, in order to obtain pre-expanded particles with a low expansion ratio of around 5 times, the blowing agent contained in the particles must be heated to a temperature at which foaming does not occur, or stored for a long time to reduce the amount to a certain amount. It is necessary to perform foaming treatment. In addition, when this method is adopted, moldability is inhibited due to a decrease in secondary foaming power, and the surface hardness of the pre-expanded particles is also weak. It also has the disadvantage of having a weak body. A method for increasing the surface hardness of pre-expanded particles is known from Japanese Patent Publication No. 48-44656.

However, this method involves copolymerizing styrene and a small amount of divinylbenzene on the surface of expandable styrene polymer particles containing a blowing agent to slightly crosslink the entire surface, but this method does not allow for high expansion ratios. The purpose of this method is to obtain a molded product, and in this method, it is necessary to pressurize the expandable styrene polymer particles in a suspension with an inert gas to prevent them from foaming. As a result, the styrene monomer containing the crosslinking agent penetrates into the center of the particles, and as a result, it is difficult to efficiently surface-crosslink and polymerize only the outside, and the resulting surface-crosslinked expandable styrene polymer particles requires a long aging period. Also,
Japanese Patent Publication No. 33-795 is known as a method for crosslinking polymerization. This method applies not only to the surface of each particle, but also to
The interior thereof is also uniformly crosslinked throughout. Since the entire particle is uniformly crosslinked, the foaming force is suppressed, inhibiting the expansion ratio or fusion of the molded product, making it difficult to obtain a low-foaming molded product with good surface hardness and a uniform expansion ratio. It is. The present inventors have developed a material that is suitable for the core material of sandals and other materials, that is, has sufficient surface hardness,
Moreover, repeated research was conducted to find a method for obtaining pre-expanded particles having a low expansion ratio of 20 times or less, especially around 5 times.

It is not impossible to obtain pre-expanded particles with a low expansion ratio of around 5 times from conventional expandable polymer particles with an expansion ratio of 30 times or more, but since the expansion of the particles proceeds rapidly, the pre-expansion ratio must be controlled. In addition, it is difficult to do so, and it is necessary to extend the cooling time during molding, making it impossible to obtain pre-expanded particles having a uniform expansion ratio. In order to obtain expandable polymer particles having a low expansion ratio of 30 times or less, the polymer particles are suspended in an aqueous suspension,
When foaming polymer particles are produced by adding a blowing agent and suspending a solvent in this to shorten the impregnation time, particles with a high expansion ratio can be obtained, and particles with sufficient surface hardness can be obtained. Furthermore, when formed into a molded article, a satisfactory degree of fusion bonding could not be obtained.

In addition, it has been found that when a solvent is not used in this manufacturing method, a long time of 20 hours or more is required for impregnation with the blowing agent, which is not suitable for practical use. Therefore, as a result of research, the present inventors gradually dropped a styrene monomer solution containing a polymerization catalyst and a crosslinking agent onto styrene polymer particles, polymerized and crosslinked the styrene monomer on the polymer surface, and then It has been found that expandable styrene polymer particles that satisfy the object of the present invention can be obtained by impregnating the foam with a mixed blowing agent consisting of two or more blowing agents having different boiling points.

That is, the present invention involves dispersing styrene polymer particles in an aqueous suspension and maintaining the temperature at 80-100°C;
A monomer obtained by adding 5-10% by weight of styrene monomer to the polymer particles, 0.2-0.5% by weight of a crosslinking agent to the monomer, and a small amount of polymerization catalyst. The solution is gradually dropped, and while the solution is absorbed by the polymer particles, the monomer is polymerized and crosslinked on the surface of the polymer particles, and after the dropwise addition of the solution is finished, the obtained styrene polymer is obtained. 3-4% by weight of a low-boiling blowing agent having a boiling point below the softening point of the particles, and 1-2% by weight of a high-boiling blowing agent, based on the particles.
The gist of the present invention is a method for producing expandable styrene polymer particles, which comprises gradually impregnating the particles with a mixed blowing agent consisting of at least two blowing agents having different boiling points. Styrene polymer particles used in the present invention include styrene, vinyltoluene, isopropylstyrene, α-methylstyrene, nuclear methylstyrene,
Styrene polymer particles obtained by polymerizing vinyl aromatic monomers such as chlorostyrene and tert-butylstyrene, and styrene polymer particles obtained by polymerizing vinyl aromatic monomers such as chlorostyrene and tert-butylstyrene, and styrene polymer particles such as styrene monomers and 1,3-butadiene, butyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, etc. Styrene monomers obtained by copolymerization with alkyl acrylates, alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate, acrylonitrile, vinyl acetate, α-methylethylene, etc. Examples include styrene copolymer particles containing 50% by weight or more. These polymer particles have an average size of 0.2-6 mm
It has a particle size of

The polymer particles are dispersed in water, the amount of water being 0.7-5 times the weight of the polymer particles used, preferably 0.8-2 times the weight of the polymer particles used.
It is twice the weight. To enhance the dispersion effect of the polymer in water, a suspending agent is added to the water to form an aqueous suspension.

Suspending agents include tricalcium phosphate, calcium pyrophosphate, sodium pyrophosphate, calcium carbonate, calcium silicate, bentonite, calcium hydroxide, magnesium oxide, and other water-insoluble fine powders, calcium stearate, and stearic acid. Metal salts of fatty acids such as zinc, fatty acid bisamides such as ethylene bisstearamide, or water-soluble polymer compounds such as polyvinyl alcohol, methyl cellulose, and polyacrylamide are used. The amount used is 0.23% by weight based on water. The styrene monomer may be methylstyrene in addition to styrene, and styrene may contain a small amount of copolymerizable monomers such as α-methylstyrene, methyl methacrylate, ethyl acrylate, butyl acrylate. As the polymerization catalyst, catalysts normally used for styrene polymerization, ie, benzoyl peroxide, tertiary butyl peracetate, tertiary butyl perbenzoate, lauryl peroxide, etc., are used.

In the present invention, styrene polymer particles are dispersed in an aqueous suspension and heated to a temperature of 80-100°C,
At this temperature a solution of styrene monomer is slowly added.

The reason for maintaining the temperature at 80-100 DEG C. is to accelerate the polymerization rate of the styrene monomer so that the surface of the styrene polymer particles is crosslinked and polymerized, and the interior of the particles is not crosslinked and polymerized.

By crosslinking and polymerizing only the surface of the styrene polymer particles, it also has the effect of shortening the impregnation time with the blowing agent.
At temperatures below 80°C, the rate of polymerization and crosslinking is slow and the rate of impregnation to the center of the polymer increases. 0.20.5% by weight based on monomer
Added.

Further, a crosslinking agent made of polyvinylbenzene such as divinylbenzene is added in an amount of 0.2 to 0.4% by weight based on the styrene monomer. Then, a styrene monomer solution containing a polymerization catalyst and a crosslinking agent is added at a ratio of 510% by weight to the styrene polymer particles. Beyond this limit,
That is, 10% or more of styrene monomer and 0.5% of crosslinking agent.
If used above, the crosslinked resin layer becomes too thick, the heat resistance increases too much, and the foaming power and moldability are inhibited. Furthermore, during molding, the fusion properties of the particles are inhibited. When the crosslinking agent content is 0.2% or less, hardly any crosslinked resin layer is formed, and therefore a product with good surface hardness cannot be obtained. In the present invention, copolymerization and bead formation proceed simultaneously, and the styrene monomer solution is added in an aqueous suspension at a temperature of 80-100°C, and other copolymerization agents such as other solvents and blowing agents are added. Since there is no substance that inhibits the polymerization reaction, the crosslinking and polymerization reactions proceed extremely quickly, and a crosslinked resin layer is formed on the surface of the styrene polymer particles. It is necessary to gradually drop the styrene monomer solution into the suspension of styrene polymer particles. This is because if the styrene monomer solution is added all at once, the impregnation into the interior of the polymer particles will be faster than the polymerization rate, resulting in particles that are uniformly crosslinked and polymerized to the inside of the particles. The styrene monomer solution containing the polymerization catalyst and crosslinking agent is gradually dropped into an aqueous suspension at 80 to 100° C. in which styrene polymer particles are dispersed, and then a blowing agent is added thereto.

As the blowing agent, a mixed blowing agent of a high boiling point blowing agent and a low boiling point blowing agent is used. When a mixed blowing agent is used, the low-boiling point blowing agent increases the pressure in the system during impregnation to promote the impregnation of the high-boiling point blowing agent into the polymer particles, and the resulting expandable polymer particles are pre-expanded. The high boiling point foaming agent has the effect of preventing the foaming ratio from decreasing due to changes over time and also increasing the foaming power during molding. When obtaining a polymer having a low expansion ratio, it is difficult to control the foamability using only the crosslinked resin layer due to the problem of fusion properties, so control using a foaming agent is required. However, when propane is used alone as a blowing agent, the resulting expandable polymer particles have a high gas dissipation rate and cannot be stored for a long time. In addition, if butane is used alone, the secondary foaming power is too strong, and when molding in the mold, only the surface layer in contact with the mold is molded quickly while the inside is not fully molded.
Therefore, a porous molded body is obtained in which the internal particles are insufficiently fused. It has been found that when two or more blowing agents having different boiling points are used in combination, the above-mentioned drawbacks are mutually compensated for and favorable results can be obtained. Better results are obtained by using more blowing agents with lower boiling points than blowing agents with higher boiling points. That is, based on the obtained styrene polymer particles (the sum of the initial styrene polymer particles and the added styrene monomer), 3-4% by weight of the low-boiling point blowing agent and 1-2% by weight of the high-boiling point blowing agent. Use a mixture of %. If the mixed blowing agent is used in an amount greater than the above amount, the foaming power will be too strong and it will be difficult to control the foaming ability to obtain a product with a low expansion ratio.On the other hand, if the amount is less than the above amount, the foaming power will be too strong. In addition, it takes a long time for impregnation, which is not preferable. In order to obtain expandable polymer particles having a low expansion ratio of 20 times or less, especially around 5 times, the above usage amount is most preferable.

Both high boiling point blowing agents and low boiling point blowing agents have boiling points below the softening point of the polymer particles, and high boiling point and low boiling point do not mean absolute temperatures, but are relative. This means that two or more blowing agents have a temperature difference.

Examples of the blowing agent include the following substances. The area within the active arc is the boiling point. Propane (-42℃), propylene (-477℃), n-butane (-0.5℃), isobutane (-10℃), butylene-1 (-63℃), cis-butylene (37℃), trans-butylene ( 0.9℃)
, isobutylene (-6.9℃), neopentane (-9℃
), butadiene (-4.4℃), n-pentane (36℃
), isopentane (30℃), benzene-1 (29.9
℃). Two or more of these blowing agents are used in combination,
Combinations of blowing agents having a temperature difference of 10°C or more, preferably 30°C or more are preferred. For example, propane and butane
Combinations such as propane and pentane, butane and pentane are preferably used. The expandable polymer particles obtained by the method of the present invention do not require an aging period and can be used immediately, and particles having a pre-expansion ratio of 20 times or less, particularly around 5 times, are easily prepared. Moreover, pre-expanded particles having a uniform expansion ratio can be obtained, and the pre-expansion ratio can be easily adjusted since the particles do not foam rapidly. Furthermore, the cooling time during molding can be shortened, a molded article with good surface hardness can be obtained, and a foamed resin can be obtained which has properties particularly suitable as a core for sandals (for women). Examples of the present invention will be shown below along with comparative examples. Example 1 In a 5.61 ml reaction vessel, 0.87 ml of sodium dodecylbenzenesulfonate and 67 ml of magnesium pyrophosphate were added as a dispersant to 2000 ml of water to form an aqueous suspension, and to this an aqueous suspension with an average particle size of 16-20 mesh was added. (1.00-0
．． Adding 84m0 of styrene polymer particles 20007
The monomer solution obtained by dissolving 0.67% of benzoyl peroxide and 0.57% of divinylbenzene in styrene monomer 2007 was then added to 30-4.
Gradually dripping took 0 minutes, and after the dripping was completed, a mixture of butane 227 and propane J Camo V was gradually forced into it,
After press-fitting, the temperature was raised to 95°C.

Stirring was continued for 9 hours at this temperature, and at the 9th hour, a part of the styrene polymer particles being impregnated was taken out and foamed in a steam bath maintained at a temperature of 97°C, and the resulting foamed particles were cut. When I looked inside, I could see a slight core in the center. 1 more
Stirring was continued for a period of time, and at the 10th hour, the inside of the foamed particles was observed in the same manner as at the 9th hour, and it was found that there was no core at all. Thereafter, it was cooled and the particles obtained at a temperature of 30°C were taken out. Therefore, the impregnation time until the core disappeared was 10 hours. Comparative Example 1 In Example 1, impregnation was carried out under the same conditions as in Example 1, except for the addition of a monomer solution consisting of a styrene monomer, benzoyl peroxide, and divinylbenzene, and one of the styrene polymer particles during impregnation was A sample was taken out and the interior was observed in the same manner as in Example 1. As a result, the required impregnation time to become core-free was 24 hours.

Comparative Example 2 In Comparative Example 1, in order to shorten the impregnation time, toluene 307 was added as a solvent to the aqueous suspension, and the same impregnation and internal observation as in Comparative Example 1 were performed. It took 12 hours.

The properties of the expandable styrene polymer particles obtained in Example 1, Comparative Example 1, and Comparative Example 2 and the porous molded articles obtained using the same are shown in the following table. From the above results, the expansion ratio and hardness of the expandable styrene polymer particles obtained by the present invention can be easily controlled, and the reaction time until coreless K is obtained is short.

In addition, a porous molded article with excellent fusion properties, mold releasability, surface hardness, etc. can be obtained. Furthermore, the fact that the expandable particles require almost no aging period is an extremely advantageous feature for improving factory productivity. The hardness of the expandable particles of the present invention expanded 6 times is almost equal to or higher than that of the expandable particles expanded 5 times by other manufacturing methods. Comparative Example 3 In this comparative example, the order of addition of the styrene monomer solution and blowing agent in Example 1 was reversed.

That is, after the blowing agent was injected, the temperature was maintained at 80°C for 15 hours to impregnate the blowing agent, and then the temperature of the system was raised to 90°C.
A monomer solution of 10 wt % styrene monomer to 3 wt % divinylbenzene and styrene polymer particles.
After gradually dropping over a period of time, the temperature was raised to 110°C, and 1
The reaction was continued for a period of time to complete polymerization, and the mixture was cooled to obtain expandable styrene polymer particles. These particles were foamed in the same manner as in Example 1, and as a result of observing the inside of the expanded particles, they were found to have a core, and the state of the crosslinked resin layer was also much weaker than that of the particles in Example 1, making it impossible to obtain a satisfactory low-foamed resin. Ta. From this result, it can be seen that if the order of addition is reversed, even if the impregnation time is increased, core-free properties do not occur.

Comparative Example 4 At the 15th hour of the impregnation time in Comparative Example 3, 0.97% of divinylbenzene and 0.757% of benzoyl peroxide were added to the styrene monomer.
After gradually dropping the monomer solution dissolved in 007, 11
The temperature was raised to 0°C, the reaction was continued for 1 hour to complete polymerization, and the mixture was cooled to obtain expandable styrene polymer particles.

These particles were foamed in the same manner as in Example 1, and as a result of observing the inside of the expanded particles, they were found to have a core, and the crosslinked resin layer was
However, a satisfactory low-foaming resin could not be obtained. Example 2 Expandable styrene polymer particles were obtained in the same manner as in Example 1 using a mixture of 4% butane and 2% pentane based on the obtained styrene polymer particles as a blowing agent.

Claims (1)

[Claims] 1 Styrene polymer particles are dispersed in an aqueous suspension and maintained at a temperature of 80-100°C, and 5-10% by weight of styrene monomer and the monomer are dispersed in an aqueous suspension. A monomer solution obtained by adding 0.2 to 0.5% by weight of a crosslinking agent and a small amount of polymerization catalyst to the polymer particles is gradually added dropwise to the polymer particles, while absorbing the solution into the polymer particles. A low boiling point blowing agent 3-4 which advances polymerization and crosslinking of the monomer on the surface of the particles and has a boiling point below the softening point of the styrene polymer particles obtained after the dropwise addition of the solution is completed.
% by weight, and 1-2% by weight of a high-boiling point blowing agent. manufacturing method.