JPH09132607A - Method for producing foamable styrene resin particles, expandable styrene resin particles and method for producing the same - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain foamable styrene resin particles and expandable styrene resin particles having a narrow particle size distribution. [Structure] In suspension polymerization of a styrene monomer in the presence of a sparingly water-soluble phosphate and a water-soluble sulfite or water-soluble persulfate, the stirring speed of the polymerization tank is set to the tip speed of the stirring blade. A method for producing styrenic resin particles for foaming, which comprises setting 2.3 to 5.5 m / sec.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to foaming styrene resin particles and a method for producing expandable styrene resin particles. More specifically, the present invention relates to a styrene resin particle for foaming having a narrow particle size distribution and a method for producing expandable styrene resin particle. Foaming styrenic resin particles and expandable styrenic resin particles according to the production method of the present invention are for cups such as instant foods, for full mold method in casting, for various packaging, for fish boxes, for blocks such as lightweight embankment method It is preferably used as a raw material for various types of OA equipment, audio equipment, electric appliances, and other cushioning packaging materials.

[0002]

2. Description of the Related Art A method for producing styrene resin particles for foaming is as follows. A suspension stabilizer is prepared by adding a suspension stabilizer to a styrene monomer in an aqueous medium and polymerizing. Legal is known. As the suspension stabilizer used in this suspension polymerization method, a poorly water-soluble inorganic salt is used from the viewpoint of heat stability, mechanical strength, transparency, and the like. Since this poorly water-soluble inorganic salt has a poor affinity with the monomer, a small amount of a surfactant is usually used as a suspension stabilizing aid.

However, in the suspension polymerization method using a poorly water-soluble inorganic salt and a surfactant, it is difficult to arrange particles in a specific particle size range, and only resin particles having a wide particle size distribution range can be obtained. . On the other hand, in order to produce particles with a uniform particle size, a method of polymerizing a styrene-based monomer in the presence of a sparingly water-soluble phosphate without using a surfactant (hereinafter, soap-free weight It is known to be legal (Japanese Patent Publication No. 46-15112, US Pat. No. 2,652,392). As an essential additive for soap-free polymerization, JP-B-46-15112 discloses a water-soluble sulfite as disclosed in US Pat.
No. 2652392, a water-soluble persulfate is added.

The expandable styrenic resin particles generally have a particle size of
Particles of 0.25-2.0 mm are used. Particle size 0.25-0.5
mm particles are for hot water containers such as cups, for full mold method in casting, etc., particle size is 0.5 ~ 1.2 mm particles are 0.7 ~ 2.0 mm as a molded object for various packing, fish boxes, etc., lightweight embankment It is mainly used for construction methods, heat insulation materials for houses, etc., and blocks as cushioning packaging materials.

Therefore, the method for producing expandable styrenic resin particles is capable of satisfying each of the above-mentioned applications, and from the viewpoint of productivity, the required particle size is efficiently produced and unnecessary particle size is generated. A polymerization method with a narrow particle size distribution is required to reduce the amount.

Further, Japanese Patent Publication No. 46-15112, US Patent No.
According to the soap-free polymerization method according to the specification of 2652392, it was difficult to produce particles having a sufficiently uniform particle size. Therefore, in view of such problems, the inventors of the present invention have earnestly studied, and as a result, in the soap-free polymerization method, the stirring speed of the polymerization tank greatly affects the particle size distribution, and the particle diameters are aligned at a specific stirring speed. The inventors have found that particles can be obtained, and completed the present invention.

[0007]

The present invention thus provides a suspension-polymerization of a styrene monomer in the presence of a sparingly water-soluble phosphate and a water-soluble sulfite or water-soluble persulfate. The stirring speed of the tank is 2.3 to the tip speed of the stirring blade.
It is 5.5 m / sec, preferably 2.6 to 4.5 m / sec.

When the tip speed of the stirring blade is less than 2.33 m / sec, it is not preferable because particles having a uniform particle size cannot be produced. 5.5
At m / sec or higher, the effect does not change and only the required power increases, which is uneconomical. Furthermore, the present invention is a method for producing expandable styrenic resin particles in which a foaming agent is impregnated during or after the above-mentioned foaming styrene resin particles are polymerized.

The stirring blade used in the present invention is usually used for suspension polymerization, and for example, a flat paddle blade,
The shape is a pitched paddle blade, an anchor blade, or the like, and it can be used in a single stage or multiple stages, and is not particularly limited. The styrenic monomer of the present invention is a styrene monomer or a monomer mixture containing styrene as a main component, that is, styrene alone or a main component containing styrene, and a monomer containing a small amount of another monomer. It is a mixture. Other monomers include, for example, α-
Styrene-based monomers such as methylstyrene, p-methylstyrene, t-butylstyrene, chlorostyrene, methacrylate monomers such as methylmethacrylate, butylmethacrylate, isobutylmethacrylate, and acrylates such as ethyl acrylate and 2-ethylhexyl acrylate Examples thereof include vinyl cyanide-based monomers such as acrylonitrile, acrylonitrile and methacrylonitrile, and polyfunctional monomers such as divinylbenzene and polyethylene glycol dimethacrylate.

In the present invention, the poorly water-soluble phosphate is used as a dispersant. As the poorly water-soluble phosphate, there are tricalcium phosphate, hydroxyapatite, magnesium phosphate and the like, which are used in the state of powder or aqueous slurry. The amount used is 0.03% by weight or more based on the solid content based on the styrene-based monomer. If it is less than 0.03% by weight, the dispersed state cannot be maintained, and if it is 1% by weight or more, the reaction is possible but there is no further effect and it is not economical.

In the present invention, the water-soluble sulfite is
Examples thereof include sodium bisulfite, potassium bisulfite, ammonium bisulfite and the like. Further, a substance which dissolves in water and reacts in the polymerization reaction system to form a sulfite can be used. As these precursors, water-soluble pyrosulfite,
Examples thereof include pyrosulfate, dithionite, thiosulfate, sulfoxylate and sulfate.

Of these, sodium bisulfite,
Sodium pyrosulfite, sodium dithionite, formaldehyde sodium sulfoxylate are preferred,
The styrene monomer is used alone in an amount of 1.5 to 100 ppm, preferably 2 to 50 ppm. If it is less than 1.5 ppm, the effect of addition does not appear or the quality of the foamed molded product deteriorates, which is not preferable, and if it exceeds 100 ppm, there is no problem in quality but there is no effect of increasing the amount.

Further, in the present invention, the water-soluble persulfate is
Examples thereof include sodium persulfate, potassium persulfate, ammonium persulfate and the like. Of these, potassium persulfate is particularly preferable, and it is used alone in the range of 1.5 to 50 ppm, preferably 2 to 10 ppm, based on the styrene monomer. If it is less than 1.5 ppm, the effect of addition does not appear, or the particle size distribution is broadened and the quality of the foamed molded product is inferior, and if it is more than 50 ppm, the quality of the foamed molded product is inferior.

When the water-soluble sulfite and the water-soluble persulfate are used in combination, the sum of the addition amounts of both should be 1.5 ppm or more. If it is less than 1.5 ppm, the dispersion may be poor during the polymerization reaction and the reaction may not be completed, which is not preferable. Further, the water-soluble persulfate used in combination is used in the range of 0.1 to 10 ppm.

As the radical polymerization initiator used in the present invention, benzoyl peroxide, t-butyl peroxyacetate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxybenzoate,
Polymerization initiators used for general radical polymerization such as organic peroxides such as 2,2-bis-t-butylperoxybutane and azo compounds such as azobisisobutyronitrile are used.

Further, in the present invention, general additives can be used. For example ethylene bis-stearyl amide,
Nucleating agents such as polyethylene wax and flame retardants such as hexabromocyclododecane can be used.

Furthermore, the present invention is a method for producing expandable styrene resin particles by adding a foaming agent to the styrene resin particles during or after the polymerization of the styrene resin particles. Examples of the foaming agent used in the present invention include various known ones. Saturated hydrocarbons having 3 to 6 carbon atoms such as propane, butane, pentane, hexane, cyclopentane and cyclohexane, methyl chloride, dichlorodifluoro. Examples thereof include halogenated hydrocarbons such as methane, etc., which may be used alone or in combination of two or more kinds.

The amount of the foaming agent added and impregnated is preferably 3 to 15% by weight based on the styrene resin particles. The timing of addition or impregnation may be either during the polymerization or after the polymerization, but it is preferable that the polymerization conversion rate is 85% or more. The expandable styrenic resin particles produced as described above can be heated, if desired, to give pre-expanded particles, and can be used as an expanded molded article by using a mold having a predetermined shape.

Next, examples of the present invention and comparative examples will be described. In addition, here, the peak 3 sieve is JI.
S standard sieve opening 2.36 mm (7.5 mesh), opening 2.00
mm (8.6 mesh), opening 1.70 mm (10 mesh), opening 1.40 mm (12 mesh), opening 1.18 mm (14 mesh), opening 1.00 mm (16 mesh), opening 0.85 mm (18
Mesh), mesh opening 0.71mm (22 mesh), mesh opening 0.60
mm (26 mesh), opening 0.50 mm (30 mesh), opening 0.425 mm (36 mesh), opening 0.355 mm (42 mesh), opening 0.300 mm (50 mesh), opening 0.250 mm
(60 mesh), mesh size 0.212 mm (70 mesh), mesh size 0.180 mm (83 mesh), and the particle size (median diameter) at which the cumulative weight is 50% is D50 based on the cumulative weight distribution curve. , And the ratio of the particle size distribution in the range of the three sieves having a large distribution ratio from the range to which the particle size of D50 belongs.

Examples 1 to 14 and Comparative Examples 1 to 7 120 g of tricalcium phosphate (manufactured by Taihei Chemical Co., Ltd.) in a 100-liter autoclave, and sodium bisulfite and potassium persulfate in the amounts shown in Tables 1 and 2. 140g
Benzoyl peroxide (purity 75%), 30 g of t-butyl peroxybenzoate, 40 kg of ion-exchanged water and 40 kg of styrene monomer were mixed and charged, and dissolved and dispersed under stirring to form a suspension. .

Next, the styrene monomer was polymerized under the stirring conditions shown in Tables 1 and 2 at 90 ° C. for 6 hours and then at 115 ° C. for 2 hours. After completion of the reaction, the mixture was cooled, the contents were taken out from the autoclave, subjected to a centrifugation step, and then dried styrene resin particles were obtained. The median particle size (D50) and particle size distribution (Peak 3 sieve) of the obtained styrene resin particles are shown in Table 1, and the results of suspension polymerization when sodium hydrogen sulfite is used, Table 2
The results of suspension polymerization when potassium persulfate is used and the results of suspension polymerization when both are used are shown.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

The method for producing styrenic resin particles for foaming according to the present invention is carried out in an aqueous medium in which a surfactant is not added in the presence of a poorly water-soluble phosphate and a water-soluble sulfite or water-soluble persulfate. In suspension polymerization of styrene-based monomer, the styrene-based monomer having a narrow particle size distribution is characterized by polymerizing the styrene-based monomer at a stirring speed of the polymerization tank of 2.3 to 5.5 m / sec at the tip speed of the stirring blade. Since the resin particles can be produced, excellent economic effects such as productivity and inventory control can be obtained.

Further, according to the present invention, expandable particles can be easily produced by impregnating the styrene resin particles having a narrow particle size distribution with a foaming agent, and since the particle size distribution is narrow, for cups, full molds, respectively. It can be suitably used for blocks and for each application.

Claims (4)

[Claims] 1. In suspension polymerization of a styrene monomer in the presence of a sparingly water-soluble phosphate and a water-soluble sulfite or water-soluble persulfate, the stirring speed of the polymerization tank is set to the tip of a stirring blade. A method for producing styrenic resin particles for foaming, characterized in that the speed is 2.3 to 5.5 m / sec. 2. The method according to claim 1, wherein the central particle size is 0.20 to 2.0 mm. 3. Expandable styrenic resin particles obtained by impregnating the foaming styrenic resin particles obtained in claim 1 with a foaming agent. 4. The method for producing expandable styrenic resin particles according to claim 1, wherein a foaming agent is impregnated during or after the polymerization.