JPS6261225B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing expandable synthetic resin particles, and more specifically, to a method for producing expandable synthetic resin particles with excellent expandability and moldability from a polymer obtained by emulsion polymerization. . Expandable styrene resin particles are well known as expandable synthetic resin particles. The expandable styrene resin particles are produced by suspension polymerizing styrene monomers in an aqueous medium in the presence of a dispersant and a polymerization initiator.
This is done by impregnating a foaming agent in the latter half of the polymerization or after completion. Although this method is efficient because polymerization and impregnation can be carried out continuously, it has the drawback that the resulting suspended particle size is broader than the desired particle size range and a large amount of undesirable particles are also produced. . Furthermore, in suspension polymerization, α-methylstyrene, etc.
-Copolymerization of alkylstyrene with styrene has the disadvantage that the reactivity of the monomer is particularly low in suspension polymerization systems. Improvements in this respect can be achieved by employing emulsion polymerization. That is, polymerization is usually carried out by emulsion polymerization, and the resulting polymer latex is coagulated, heat treated, and dried to obtain a synthetic resin powder, and the powder is made into pellets of a desired size using an extruder. The particle size of the obtained pellets can be approximately the desired particle size depending on the extruder die size and the cutting conditions of the cutter, and the width of the particle size distribution is also significantly narrower than that of those produced by ordinary suspension polymerization. The synthetic resin pellets produced by extrusion are again impregnated with a blowing agent in an aqueous medium to obtain expandable synthetic resin particles. However, the expandable synthetic resin particles produced by emulsion polymerization, pelletization, and impregnation with a blowing agent have extremely poor expandability and moldability, and cannot be put to practical use. The present inventors conducted extensive research in view of the above points, and found that when a synthetic resin powder obtained by emulsion polymerization is extruded into pellets and the pellets are impregnated with a blowing agent in an aqueous medium, a dispersing agent,
The present inventors have discovered that it is possible to produce expandable synthetic resin particles with excellent foamability and moldability by adding a large amount of water-soluble inorganic salt together with an emulsifier, leading to the completion of the present invention. The polymerization monomers used in the emulsion polymerization in the present invention are not particularly limited, and include, for example, styrene, α-methylstyrene, acrylonitrile, t-butylstyrene, methyl methacrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. , ethyl acrylate, etc.
These may be used alone or in combination. When the extruded pellets are then impregnated with a blowing agent in an aqueous medium, a dispersant is used to prevent the pellets from adhering to each other during this impregnation step. The dispersant used may be any one normally used in suspension polymerization and is not limited in the present invention. However, in consideration of environmental regulations such as COD in wastewater, inorganic dispersants are preferred. As an inorganic dispersant, there is tertiary calcium phosphate, and in this case, when a small amount of an anionic surfactant is used in combination, the effect of the dispersant becomes remarkable. The amount of anionic surfactant used in combination is 0.006 to 0.1% by weight based on water.
is sufficient. Examples of anionic surfactants include, but are not limited to, sodium alkylbenzene sulfonate, sodium α-olefin sulfonate,
Examples include sodium lysinate. In this case, there is no problem even if a small amount of nonionic surfactant is used in combination.
Further, when the pellets are impregnated with a blowing agent in an aqueous medium, a large amount of an inorganic salt is used together with a dispersant. Examples of inorganic salts include monovalent metal salts such as sodium chloride, sodium sulfate, sodium carbonate,
Potassium chloride, potassium sulfate, potassium carbonate, 2
Examples of trivalent metal salts include magnesium chloride and magnesium sulfate, and trivalent metal salts include aluminum sulfate, and the amount thereof is significantly larger than that used in ordinary dispersion systems, that is, 2.0 parts or more based on water, preferably 4.0 parts. It is more than 100%. The upper limit of the amount to be used is not particularly limited, but the effect will not change even if it is used in excess of 10 parts based on water; therefore, less than 10 parts is sufficient. The blowing agent used in the present invention is a commonly used easily volatile blowing agent. Examples include propane, butanepentane, petroleum ether, trichloromonofluoromethane, dichlorodifluoromethane, and these may be used alone or in combination. Furthermore, in order to improve the foamability of the foamable synthetic resin particles obtained during or before impregnation with a blowing agent, the pellets may be impregnated with a solvent such as toluene, ethylbenzene, methylene chloride, etc., and these do not violate this patent in any way. There's nothing wrong with that. Examples of the present invention are shown below. Example 1 (1) Production of polymer The following materials were charged into a reactor equipped with a stirrer. Water 250 parts (weight parts, same below) Sodium laurate 3 parts Sodium formaldehyde sulfoxylate
0.4 parts ethylenediaminetetraacetic acid disodium
0.01 part ferrous sulfate 0.0025 part After deoxidizing, the mixture was heated and stirred at 60°C in a nitrogen stream, and then the monomers shown in Table 1 were continuously polymerized dropwise.
After the dropwise addition was completed, stirring was further continued at 60°C, and then the polymerization was completed. After the produced polymer latex was coagulated with calcium chloride, it was washed with water, filtered, dried, and pelletized. The pellets obtained had a diameter of about 1 mm.

[Table] (2) Production of expandable synthetic resin particles The following materials were placed in an autoclave equipped with a stirrer. Water 100 parts Pellet 100 parts Tertiary calcium phosphate 0.5 parts Sodium α-olefin sulfonate 0.010 parts Inorganic salts As shown in Table 2, Toluene 1.0 parts Next, after purging with nitrogen, heating to 90°C and stirring for 2 hours, 9 parts of butane was introduced under pressure. After raising the temperature to 110°C and maintaining it for 6 hours, the mixture was cooled to 40°C, dehydrated and dried to obtain expandable synthetic resin particles.

[Table] When the obtained resins A-1 to A-6 were foamed with water vapor, all exhibited good foaming properties. Furthermore, resins A-1 to A-6 each have an apparent magnification of 40.
After pre-foaming to double the original size and leaving it for 24 hours, it was molded using a Pearl Star 90 molding machine manufactured by Toyo Kikai Kinzoku Co., Ltd. The mold used is a mold for molding a single plate of 300 x 200 x 20 mm. The molding results are shown in Table 4. Comparative Example Expandable synthetic resin particles B-1 to B- were prepared in the same manner as in Example except that the amount of inorganic salt was changed as shown in Table 3.
I got 4.

[Table] When the obtained resins B-1 to B-3 were foamed with water vapor, the foaming could not be performed sufficiently, and particles that had contracted and become hard were found here and there. Further, resins B-1 to B-4 were pre-foamed to an apparent magnification of 30 times, and after being left for 24 hours, molding was carried out in the same manner as in the examples. The molding results are shown in Table 4.

【table】

Claims (1)

[Scope of Claims] 1 Synthetic resin powder obtained by emulsion polymerization is pelletized by extrusion, and the pellets are impregnated with a blowing agent in an aqueous medium, and 100 parts by weight of the aqueous medium is added together with a dispersant and an emulsifier to the aqueous medium. A method for producing expandable synthetic resin particles with excellent expandability and moldability, characterized by adding 2.0 parts by weight or more of a water-soluble inorganic salt. 2. The method for producing expandable synthetic resin particles according to claim 1, wherein the dispersant is basic tribasic calcium phosphate. 3. The method for producing expandable synthetic resin particles according to claim 1, wherein the emulsifier used in the polymerization is an anionic surfactant. 4. The method for producing expandable synthetic resin particles according to claim 1, wherein the water-soluble inorganic salt is a monovalent metal salt, a divalent metal salt, or a trivalent metal salt. 5 Monovalent metal salts of water-soluble inorganic salts include sodium chloride, sodium sulfate, sodium carbonate, potassium chloride, potassium sulfate, and potassium carbonate; divalent metal salts include magnesium chloride and magnesium sulfate; and trivalent metal salts include aluminum sulfate. A method for producing expandable synthetic resin particles according to claim 4. 6. The method for producing expandable synthetic resin particles according to claim 1, wherein the amount of water-soluble inorganic salt is 2.0 parts or more based on water.