JPH05140363A - Production of foamed styrenic resin particle - Google Patents

Abstract

PURPOSE:To obtain the subject particles capable of shortening a cooling time on their molding processing by coating styrenic resin particles with a higher fatty acid bisamide, dispersing the coated particles in an aqueous medium and subsequently impregnating the dispersed particles with an easily evaporable foaming agent. CONSTITUTION:(A) Styrenic resin particles are coated with (B) a higher fatty acid bisamide, dispersed in an aqueous medium and subsequently impregnated with (C) an easily evaporable foaming agent to produce the objective foamable styrenic resin particles. Before the particles are impregnated with the component C, a solvent having an ability to dissolve the component A is preferably dispersed in the aqueous medium. The component B is preferably ethylene bisstearyl amide, methylene bisstearylamide or ethylene bisoleic acid amide.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing expandable styrene resin particles. More specifically, the present invention relates to a method for producing expandable styrene-based resin particles capable of shortening the cooling time during the molding process of expandable styrene-based resin particles.

[0002]

2. Description of the Related Art Molding of expandable styrene resin particles requires a long time for cooling. In particular, in the molding method of cooling under reduced pressure, which has been widely used in recent years, the proportion of cooling in the molding step is 70 to 80%. That is, shortening the cooling time shortens the molding cycle, increases the number of moldings per unit time, and improves the productivity of the foamed molded product.

As a method of shortening the cooling time, there is a method of modifying a resin, for example, a method of adding a fatty acid bisamide at the initial stage of polymerization (Japanese Patent Laid-Open No. 48-48588). A method in which a certain additive is present on or near the surface of the expandable styrene resin particles, for example, a method of coating the surface or the vicinity of the expandable styrene resin particles with triglyceride of a fatty acid (Japanese Patent Publication No. Sho 54-19022). Gazette), a method of coating paraffin wax having a melting point of 40 to 70 ° C. as an aqueous emulsion on or near the surface of expandable styrenic resin particles (JP-A-60-1951).
No. 36) is known.

[0004]

However, in the method described in JP-A-48-48588, the polymerization system becomes unstable when the amount of the fatty acid bisamide added is increased.
The amount of fatty acid bisamide used is limited, and the effect of shortening the cooling time is also limited. In addition, Japanese Patent Publication No.
According to the method disclosed in JP-A No. 022 or JP-A-60-195135, the skin of the expanded particles is attacked, and the appearance of the molded body surface and the strength of the molded body are reduced. The present invention is a method for producing expandable styrenic resin particles which can reduce the cooling time in the molding step without causing the above problems.

[0005]

The present invention is characterized in that styrenic resin particles are coated with a higher fatty acid bisamide, which is then dispersed in an aqueous medium, and a volatile foaming agent is added and impregnated. The present invention relates to a method for producing expandable styrene resin particles.

The styrenic resin particles used in the present invention are polystyrene or a copolymer containing styrene as a main component (preferably 50% by weight or more of styrene),
It is in the form of particles such as spheres and pellets, and particularly spherical particles obtained by suspension polymerization are preferred. Preferred examples of the monomer copolymerizable with styrene include acrylic or methacrylic acid esters such as acrylonitrile, butyl acrylate and cetyl methacrylate, and styrene derivatives such as α-methyl styrene and t-butyl styrene. The styrene resin particles can be produced by a known method.

As the higher fatty acid bisamide, there are methylenebisstearylamide, ethylenebisstearylamide, ethylenebisoleic acid amide, and the like. It is preferable to use one selected from the three exemplified types because the cooling time shortening effect is high. .. The amount used is preferably 0.01 to 0.2% by weight with respect to the uncoated styrene resin particles. If it is less than 0.01%, the effect of shortening the cooling time is small,
If it exceeds 0.2% by weight, the appearance of the molded article and the strength of the molded article are deteriorated.

The higher fatty acid bisamide can be coated by stirring and mixing the styrenic resin particles and the higher fatty acid bisamide, and in particular, a high rotation type mixer such as a Henschel mixer is used to stir by mechanical force accompanied by frictional heat. Preferably.

Next, in the present invention, the styrene resin particles whose surface is coated with the higher fatty acid bisamide are dispersed in an aqueous medium to impregnate the volatile foaming agent. At that time, as a dispersant, a water-soluble polymer colloid, a sparingly soluble phosphate or the like is usually made to exist in an aqueous medium. Examples of the water-soluble polymer colloid include polyvinyl alcohol, acrylonitrile, alkyl cellulose, carboxyalkyl cellulose, and other cellulose derivatives. Further, examples of the sparingly soluble phosphate include tricalcium phosphate, magnesium phosphate and the like.

The dispersant is preferably used in an amount of 0.1 to 1% by weight with respect to the styrene resin particles. When a sparingly soluble phosphate is used as the dispersant, at the same time, sodium dodecylbenzene sulfonate or the like is used. It is preferable to use the anionic surfactant in an amount of 0.005 to 0.5% by weight based on the styrene resin particles.

Further, in the present invention, before adding the volatile foaming agent, toluene, ethylbenzene, xylene, styrene, etc. are added to the aqueous medium in which the styrene resin particles coated with the higher fatty acid bisamide are dispersed. A solvent having the ability to dissolve styrene resin particles is added and stirred, or the solvent is previously added to an aqueous medium before the styrene resin particles are dispersed, and then the styrene resin particles are dispersed. It is preferable to let it be stirred. This can promote the adsorption or absorption of the higher fatty acid bisamide on the styrene resin particles. The solvent is preferably used in an amount of 0.1 to 2.0% by weight based on the styrene resin particles. If there is too little solvent, the above effect does not occur,
If it is too large, the aesthetic appearance of the surface of the molded article will deteriorate.

As the volatile foaming agent, an aliphatic hydrocarbon having a boiling point lower than the softening point of the styrene resin particles, such as propane, butane, pentane, hexane, etc., can be used. Further, an alicyclic hydrocarbon such as cyclohexane can be used as a foaming aid.

The volatile foaming agent can be impregnated in a conventional manner by adding the volatile foaming agent to an aqueous medium in which the styrene resin particles coated with the fatty acid bisamide are dispersed, preferably by press-fitting. .. Impregnation of the foaming agent is 65 to 11
It is preferably carried out at 0 ° C. The volatile foaming agent is preferably impregnated in the styrene resin particles in an amount of 3 to 10% by weight.

After the impregnation of the easily volatile foaming agent is completed, the expandable styrenic resin particles impregnated with the target higher fatty acid bisamide are separated from the aqueous medium, washed with water and dried if necessary for use in foam molding and the like. Can be offered.

[0015]

EXAMPLES Next, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto. Example 1 A Henschel mixer with an internal volume of 10 l had a particle size of 0.7-
5000 g of polystyrene beads obtained by suspension polymerization having a size of 1.2 mm and ethylenebisstearylamide 2.5
g and mixed for 2 minutes at 2000 rpm to make coated polystyrene beads.

Next, in an autoclave with an internal volume of 12 liters equipped with a rotary stirrer, 5000 g of ion-exchanged water, 20 g of tricalcium phosphate, 1 sodium dodecylbenzenesulfosulfonate.
g and the above-mentioned polystyrene beads of 5000 g were added and stirred. 35 g of toluene was added at room temperature, and the temperature was raised to 100 ° C. in 90 minutes. After heating, 80 g of cyclohexane and 700 ml of butane gas were injected under pressure, kept warm for 3 hours, and then cooled to 40 ° C.

After removing from the autoclave at 40 ° C., dehydrating and drying, 0.05% by weight of zinc stearate with respect to the beads was mixed on the surface of the beads to obtain expandable styrene resin particles.

Example 2 In Example 1, the amount of ethylenebisstearylamide was changed to 5 g to obtain expandable styrene resin particles.

Example 3 In Example 1, 5 g of ethylenebisoleic acid amide was used as the higher fatty acid bisamide instead of ethylenebisstearylamide to obtain expandable styrene resin particles.

Example 4 In Example 1, 5 g of methylenebisstearylamide was used as the higher fatty acid bisamide instead of ethylenebisstearylamide to obtain expandable styrene resin particles.

Example 5 In Example 1, the amount of ethylenebisstearylamide was changed to 15 g to obtain expandable styrene resin particles.

Comparative Example 1 Expandable styrene resin particles were obtained in the same manner as in Example 1 except that ethylenebisstearylamide was not used.

Comparative Example 2 In an autoclave with an internal volume of 12 liters equipped with a rotary stirrer, 6000 g of ion-exchanged water, 13 g of calcium phosphate,
1 g of sodium dodecylbenzene sulfonate was dispersed. Next, styrene 60 having 15 g of benzoyl peroxide, 3 g of t-butylperoxybenzoate, 35 g of toluene and 3 g of ethylenebisstearylamide dispersed therein was added to styrene 60.
00 g was added with stirring, and suspension polymerization was initiated at 90 ± 1 ° C. After 2 hours and 40 minutes, 3 g of tricalcium phosphate was added to the reaction solution, and further 3 g of tricalcium phosphate was added when the polymerization conversion rate reached 95%, then the temperature was raised to 100 ° C., and 80 g of cyclohexane and 700 ml of butane gas were added. Was pressed in. After that, the temperature was raised to 115 ° C., and after keeping the temperature for 3 hours, 4
Cooled to 0 ° C. It was taken out from the autoclave at 40 ° C., dehydrated and dried, and then zinc stearate was mixed on the bead surface in an amount of 0.05% by weight with respect to the bead to obtain expandable styrene resin particles. The average diameter of the obtained particles is
It was 0.96 mm, and the deviation coefficient (Cv) was 0.42.

Comparative Example 3 In Comparative Example 2, the amount of ethylenebisstearylamide was changed to 9 g to obtain expandable styrene resin particles. The obtained particles had an average diameter of 1.13 mm and a deviation coefficient (Cv) of 0.63.

Comparative Example 3 Expandable styrenic resin particles were obtained in the same manner as in Comparative Example 2 except that ethylenebisstearylamide was not used. The obtained particles had an average diameter of 0.94 mm and a deviation coefficient (Cv) of 0.41.

The particle size distributions and average diameters of the polymer particles in Comparative Examples 2 to 4 are represented by the deviation coefficient Cv and the median diameter, respectively. That is, based on the curve of the cumulative weight distribution, the cumulative weight% is 15%, 50%, 8
The particle diameters of 5% are d ₁₅ , d ₅₀ , and d ₈₅ , respectively, and the deviation coefficient Cv is calculated by the equation of Cv = (d ₈₅ −d ₁₅ ) / d ₅₀ ,
Judgment of 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. Also,
As the average diameter, the median diameter represented by the above d ₅₀ is adopted.

Evaluation The expandable styrene resin particles of Examples 1 to 5 and Comparative Examples 1 to 4 obtained as described above have an apparent specific gravity of 0.017 g /
After pre-foaming to ml and aging at room temperature for 24 hours,
Molding was performed in a molding machine in which a mold capable of obtaining a 80 × 80 (mm) molded body was incorporated. The molding conditions at this time were steam pressure of 0.7 kgf / cm ² , heating time of 30 seconds, and cooling was allowed to cool. In Table 1, the cooling time means that the side pressure of the molded body is 0.3 kgf / cm after the end of heating.
^It means the time required to go down to ² . The strength of the molded product was measured according to JIS-A-9511. The results are shown in Table 1.
Shown in. Further, the foamed molded articles using the expandable styrene resin particles of any of the examples had a good surface appearance.

[0028]

[Table 1]

[0029]

According to the present invention, it is possible to obtain expandable styrenic resin particles capable of shortening the cooling time in the molding step without impairing the strength and surface aesthetics of the foamed molded product.

Claims (4)

[Claims] 1. Production of expandable styrenic resin particles, characterized in that styrenic resin particles are coated with a higher fatty acid bisamide, and then dispersed in an aqueous medium, and an easily volatile foaming agent is added and impregnated. Method. 2. The method for producing expandable styrenic resin particles according to claim 1, wherein a solvent having a dissolving ability for the styrenic resin particles is dispersed in an aqueous medium before adding the volatile foaming agent. 3. The method for producing expandable styrenic resin particles according to claim 1, wherein the higher fatty acid bisamide is selected from the group consisting of ethylenebisstearylamide, methylenebisstearylamide and ethylenebisoleic acid amide. .. 4. The expandable styrenic resin particles according to claim 1, wherein the coating amount of the higher fatty acid bisamide is 0.01 to 0.2% by weight based on the uncoated styrenic resin particles. Production method.