JP3192916B2 - Method for producing styrene resin particles and expandable styrene resin particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing styrene resin particles and expandable styrene resin particles. More specifically, the present invention relates to a method for producing styrene resin particles having a narrow particle size distribution and expandable styrene resin particles.
The styrene-based resin particles and expandable styrene-based resin particles according to the production method of the present invention are used for cups of instant foods, etc., for full molding in casting, for various packing, for fish boxes, for blocks such as lightweight embankment methods, and for various types. It is suitably used as a raw material for buffer packaging materials for OA equipment, audio equipment, electric appliances and the like.

[0002]

2. Description of the Related Art As a method for producing styrene resin particles, there is known a suspension polymerization method in which a suspension stabilizer is added to a styrene monomer in an aqueous medium and polymerized. Have been. As the suspension stabilizer used in this suspension polymerization method, a poorly water-soluble inorganic salt is used from the viewpoint of thermal stability, mechanical strength, transparency and the like. Since this poorly water-soluble inorganic salt has poor affinity for 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 can be obtained. . On the other hand, in order to produce particles having 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 (so-called soap-free weight). Is known (Japanese Patent Publication No. 46-15112, U.S. Pat. No. 26523).
92). As an essential additive for soap-free polymerization,
In Japanese Patent Publication No. 46-15112, a water-soluble sulfite is used, and in U.S. Pat. No. 2,652,392, a water-soluble persulfate is used.

In a soap-free polymerization method using a water-soluble sulfite, resin particles having a narrow particle size distribution can be easily controlled when a polymerization reaction is carried out so that the central particle size becomes 0.6 to 1.5 mm. However, when the polymerization reaction is carried out to small particles having a center particle diameter of 0.5 mm or less, the particle size distribution width is widened, and the foamed molded article is a mixture of coarse and dense bubbles, the printability is poor in a cup using this, and the particles Fusing also worsens.

On the other hand, in a soap-free polymerization method using a water-soluble persulfate, resin particles having a narrow particle size distribution width can be easily controlled when a polymerization reaction is carried out so that the central particle size becomes 0.3 to 0.5 mm. Can be However, the polymerization reaction of large particles having a center particle size exceeding 0.5 mm makes the reaction system unstable and difficult to control, and if the polymerization reaction is forcibly performed, the whole will become a rice cake in the latter stage of the polymerization. Almost impossible.

[0006] The expandable styrene resin particles generally have a particle size of
Particles of 0.25-2.0 mm have been used. Particle size 0.25-0.5
Particles of mm are used for hot water containers such as cups, for full molding in casting, etc., and particles with a particle size of 0.5 to 1.2 mm are used for various packing, for molded products such as fish boxes, 0.7 to 2.0 mm. Particles are mainly used for lightweight embankment methods, insulation materials for houses and the like, and blocks used as buffer packaging materials.

For this reason, the method for producing expandable styrene resin particles must be satisfactory for all the above uses. However, in the production of expandable styrenic resin particles using the conventional soap-free polymerization method, in order to satisfy the quality of the expanded molded article, 0.25 ~ 0.5m
For small-grain applications, the polymerization method using water-soluble persulfate is 0.5 ~
For 2.0mm large grain applications, a double-column production is required, in which a polymerization method using a water-soluble sulfite is used, and there are problems such as complicated production, inventory control and unnecessary particle treatment,
The advantage of a polymerization method with a narrow particle size distribution width could not be utilized.

Therefore, it is very important to be able to cope with this one polymerization method in terms of productivity and inventory control. In view of such problems, the inventors of the present invention have conducted intensive studies and found that by using a water-soluble sulfite and a water-soluble persulfate in combination, a desired particle size and a narrow particle size distribution width can be obtained. The present inventors have found that it is possible to obtain resin particles having excellent quality when formed into a foamed molded article, and have reached the present invention.

[0009]

Thus, according to the present invention, a styrene monomer is suspension-polymerized in an aqueous medium in the presence of a sparingly water-soluble phosphate without using a surfactant. In making the water-soluble sulfite and water-soluble persulfate ,
With respect to the styrene monomer, 0.2 to 100 ppm and
0.1 to 10 ppm, and the sum of the added amounts of both salts is 1.5 ppm or more.
Thus, a method for producing styrene-based resin particles, characterized by adding to an aqueous medium and polymerizing a styrene-based monomer while stirring the aqueous medium, is provided. Furthermore, according to the present invention, during or after the polymerization of the styrene resin particles,
Provided is a method for producing expandable styrene resin particles which obtains expandable styrene resin particles by adding a foaming agent to the styrene resin particles.

The styrene monomer used in the present invention is:
Styrene monomer or a monomer mixture containing styrene as a main component, that is, styrene alone or styrene as a main component,
This is a monomer mixture of this and a small amount of another monomer. As other monomers, for example, α-methylstyrene, p
Styrene monomers such as -methylstyrene, t-butylstyrene and chlorostyrene, methacrylate monomers such as methyl methacrylate, butyl methacrylate and isobutyl methacrylate, acrylate monomers such as ethyl acrylate and 2-ethylhexyl acrylate, acrylonitrile, Examples thereof include vinyl cyanide monomers such as methacrylonitrile, and polyfunctional monomers such as divinylbenzene and polyethylene glycol dimethacrylate.

In the present invention, a poorly water-soluble phosphate is used as a dispersant. Examples of poorly water-soluble phosphates include tricalcium phosphate, hydroxyapatite, and magnesium phosphate, and are used in the form of a powder or an aqueous slurry. The used amount is 0.03% by weight or more in terms of solid content based on the styrene monomer. When the amount is less than 0.03% by weight, the dispersion state cannot be maintained, and when the amount is more than 1% by weight, the reaction is possible, but there is no further effect and it is not economical.

The water-soluble sulfite used in the present invention includes sodium bisulfite, potassium bisulfite, ammonium bisulfite and the like. Further, substances that dissolve in water and react in a polymerization reaction system to form sulfites can also be used. These precursors include water-soluble pyrosulfites,
Examples include pyrosulfate, dithionite, thiosulfate, sulfoxylate, sulfate and the like.

[0013] Of these, sodium bisulfite,
Sodium pyrosulfite, sodium dithionite, sodium formaldehyde sulfoxylate are preferred,
0.2-100 ppm, preferably 2-5 ppm, based on styrene monomer
Used in the range of 0 ppm. If it is less than 0.2 ppm, the effect of addition will not be exhibited or the quality of the foamed molded article will be poor, so that it is not preferable. If it is more than 100 ppm, there is no quality problem but there is no effect of increasing the amount.

Further, examples of the water-soluble persulfate used in the present invention include sodium persulfate, potassium persulfate, and ammonium persulfate. Of these, potassium persulfate is particularly preferred, and is used in the range of 0.1 to 10 ppm, preferably 0.5 to 5 ppm, based on the styrene monomer. When the amount is less than 0.1 ppm, the effect of addition is not obtained, and the particle size distribution is slightly widened, so that the quality of the foamed molded article is inferior.

Further, the sum of the amounts of water-soluble sulfite and water-soluble persulfate added must be at least 1.5 ppm. If the amount is less than 1.5 ppm, the dispersion becomes insufficient during the polymerization reaction, and the reaction cannot be completed. Benzoyl peroxide, t-butyl peroxyacetate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxybenzoate, 2,2
Polymerization initiators used in general radical polymerization, such as organic peroxides such as 2-bis-t-butylperoxybutane and azo compounds such as azobisisobutyronitrile, are used.

In the present invention, general additives can be used. For example, ethylene bisstearyl amide,
A nucleating agent such as polyethylene wax and a flame retardant such as hexabromocyclododecane can be used. In the present invention, the peak 3 mesh is defined as JIS standard sieve opening 2.36.
mm (7.5 mesh), 2.00 mm (8.6 mesh), 1.70 mm (10 mesh), 1.40 mm (12 mesh), 1.18 mm (14 mesh), 1.00 mm (16 mesh)
Mesh), aperture 0.85mm (18 mesh), aperture 0.71
mm (22 mesh), aperture 0.60 mm (26 mesh), aperture 0.50 mm (30 mesh), aperture 0.425 mm (36 mesh), aperture 0.355 mm (42 mesh), aperture 0.300 mm (50
Mesh), aperture 0.250mm (60 mesh), aperture 0.21
2 mm (70 mesh), then classified by a mesh opening 0.180 mm (83 mesh) particle size of which cumulative weight is 50 percent based on the cumulative weight distribution curve (median diameter) and D ₅₀ particle size D ₅₀ of It indicates the ratio of the particle size distribution in the range of 3 meshes having a large distribution ratio from the belonging range.

Further, according to the present invention, there is provided 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. You. As the blowing agent used in the present invention, various known ones may be mentioned, but a saturated hydrocarbon having 3 to 6 carbon atoms such as propane, butane, pentane, hexane, cyclopentane, and cyclohexane;
Examples thereof include halogenated hydrocarbons such as methyl chloride and dichlorodifluoromethane, and these may be used alone or in combination of two or more.

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 and impregnation may be during or after polymerization, but is preferably at the time of polymerization conversion of 85% or more. The expandable styrene-based resin particles produced as described above can be heated to form pre-expanded particles when desired, and further formed into a foamed molded article using a mold having a predetermined shape.

In the pre-expansion, the expandable styrene-based resin particles are subjected to, for example, steam of 0.05 kg / cm ² in a pre-expansion apparatus.
It can be performed by press-fitting with a vapor pressure of about G. The injection time is generally between 30 and 180 seconds. The obtained pre-expanded particles are preferably aged at room temperature for about one day, aged, and then subjected to foam molding. Foam molding is carried out in a mold having the desired shape and capable of closing but not sealing the pre-expanded particles, for example by introducing steam with a vapor pressure of 0.5 to 1.5 kg / cm ² G into the mold. be able to. The obtained molded foam is taken out of the mold after cooling.

The water-soluble sulfite is a reducing substance, and the water-soluble persulfate is an oxidizing substance and a somewhat unstable substance.
Therefore, care must be taken in the method of addition to the reaction system. When the water-soluble sulfite is used as the base, the addition of the water-soluble persulfate has little effect on the narrowness of the particle size distribution as long as it is between the time of charging and the start of the reaction until the polymerization conversion reaches 40%. Affects the center particle size and reproducibility. That is, it was found that when the water-soluble persulfate was added at the start of the temperature rise of the polymerization reaction, the particle size control and the reproducibility were excellent. It is presumed that the water-soluble sulfite and the water-soluble persulfate are decomposed and the effective amount is changed due to the difference in the working time during the preparation. In addition, it is presumed that variations in particle size and reproducibility due to addition after the start of temperature rise may occur because reactivity varies depending on temperature.

Similar results were obtained when persulfate was used as a base. Even when added after the polymerization conversion rate became 40% or more, it was found that the polymerization had already progressed too much and the effect of the additive could not be obtained.

[0022]

【Example】

Examples 1 to 7 and Comparative Examples 1 to 10 To a 100 liter autoclave, 120 g of tricalcium phosphate (manufactured by Ohira Chemical Co., Ltd.) and the amounts of sodium bisulfite and potassium persulfate shown in Table 1 were added, followed by 140 g. Of benzoyl peroxide (75% pure), 30 g of t-butyl peroxybenzoate, 40 kg of ion-exchanged water and 40 kg of a styrene monomer were charged and dissolved and dispersed under stirring to form a suspension. .

Next, the styrene monomer was stirred at 200 rpm.
The polymerization reaction was carried out at 90 ° C. for 6 hours and further at 115 ° C. for 2 hours.
After completion of the reaction, the mixture was cooled, the content was taken out of the autoclave, subjected to a centrifugation step, and then dried to obtain styrene resin particles. Table 1 shows the central particle size (D ₅₀ ) and particle size distribution (peak 3 mesh) of the obtained styrene resin particles.

The obtained styrene resin particles were classified into small particles of 0.3 to 0.4 mm and large particles of 0.6 to 0.7 mm, impregnated with a foaming agent as described below, and used for foam molding. In the case of Comparative Example 4, the central particle size was too large to collect particles of 0.3 to 0.4 mm,
The foam molding evaluation could not be performed. The small particles were evaluated as cup-shaped foamed molded articles, and the large particles were evaluated as block-shaped foamed molded articles. (Impregnation, foaming and molding of small particles) In a 5 liter autoclave, 2000 g of water, 12 g of magnesium pyrophosphate and
0.3 g of sodium dodecylbenzenesulfonate was charged and used as an aqueous medium.
Stirred at pm.

Next, the temperature was raised to 100 ° C., 120 g of pentane was injected while maintaining the temperature, and the small particles were impregnated for 2 hours, and then cooled to obtain expandable styrene resin particles. 24 hours for the obtained expandable styrene resin particles
After allowing to stand and aged at 15 ° C., it was subjected to a preliminary foaming step. By this pre-expansion, pre-expanded particles having a bulk magnification of 10 times were obtained. Furthermore, the pre-expanded particles are left to mature at room temperature for 24 hours, and are filled into a cup-shaped cavity having an internal volume of 450 ml and a meat pressure of 2 mm,
By heating with 1.8 kg / cm ² G steam for 7 seconds and then cooling, a cup-shaped styrene resin foam molded article was obtained from the mold cavity.

Table 1 shows the results of evaluation of the printability and the leakiness of the curry soup of the obtained cup-shaped foam molded article. In the printability in Table 1, ◎ is very good, ○ is good, and △ is good.
X indicates slightly inferior, and X indicates inferior. The printability is one of the required qualities as a cup container for an instant food, and the factors include a bubble size, a bubble state, and surface growth of a molded product.

Regarding the leakiness of the curry soup, the powdered curry soup is packed in a cup-shaped foamed molded product, left in a constant temperature room at 60 ° C. for 24 hours, and the state of leakage to the surface of the foamed molded product is evaluated. Regarding the curry soup leakage in Table 1, ○ indicates that leakage is less than 0 to 5%, Δ indicates that leakage is less than 5 to 20%, and X indicates that leakage is more than 20%. (Impregnation, foaming and molding of large particles) In a 5 liter autoclave, 2000 g of water, 9 g of magnesium pyrophosphate and
An aqueous medium was charged with 0.3 g of sodium dodecylbenzenesulfonate, and 2,000 g of large particles were added to the aqueous medium, and 300 rpm
And stirred.

Then, the temperature was raised to 90 ° C., while maintaining this temperature, 180 g of butane was press-fitted, the large particles were impregnated for 3 hours, and then cooled to obtain expandable styrene resin particles. The obtained expandable styrene resin particles are kept at 15 ° C. for 4 days.
And aged, followed by a preliminary foaming step. By this pre-expansion, pre-expanded particles having a bulk magnification of 60 times were obtained.
Further, the pre-expanded particles are aged at room temperature for 24 hours, aged, and filled into a mold cavity of a known foamed polystyrene steam molding machine.
Heat with 0.6 kg / cm ² G steam for 30 seconds, water-cool for 20 seconds,
A block-shaped foamed molded article of 300 × 450 × 100 mm was obtained from the mold cavity.

Table 1 shows the degree of cell density, the degree of surface expansion and the degree of fusion of the obtained block-shaped foam molded article. In Table 1, ○ indicates that there is no density, Δ indicates that the density is slightly high, X indicates that density is high, ○ indicates good, Δ indicates slightly inferior, and × indicates inferiority. ○: fusion of 80% or more, △: fusion of 60 to less than 80%, ×: fusion
% Fusion is shown. Comparative Example 11 (Example of large particle polymerization reaction in soap-free polymerization using water-soluble persulfate) In a 100-liter autoclave, 20 g of tricalcium phosphate (manufactured by Ohira Chemical Co., Ltd.) and styrene monomer were added in an amount of 1.
5 ppm potassium persulfate, 140 g benzoyl peroxide (75% pure), 30 g t-butyl peroxybenzoate,
40 kg of ion-exchanged water and 40 kg of a styrene monomer were mixed and charged, and dissolved and dispersed under stirring to form a suspension.

Next, the temperature was raised to 90 ° C. with stirring at 200 rpm to polymerize the styrene monomer. As a result, 90 ° C during polymerization
In the third hour, the entire contents are made into a rice cake in an autoclave,
This resulted in so-called poor dispersion, and the polymerization reaction became impossible.
This result indicates that the polymerization of large particles is difficult when only the water-soluble persulfate is used. Comparative Example 12 (Example of Polymerization Reaction Using Conventional Surfactant) In a 100-liter autoclave, 60 g of tricalcium phosphate (manufactured by Ohira Chemical Co., Ltd.) and a surfactant α as a suspension stabilizing agent were added. -2.2 g of olefin sulfonate and 1
40 g of benzoyl peroxide (purity 75%), 30 g of t-butyl peroxybenzoate, 40 kg of ion-exchanged water and 40 g of
kg of styrene monomer was mixed and charged, and dissolved and dispersed under stirring to form a suspension.

Next, the styrene monomer was mixed with 90 rpm under stirring at 115 rpm.
The polymerization reaction was carried out at a temperature of 115 ° C for 2 hours. On the way 9
At 2 and 3 hours after the reaction at 0 ° C., 6 g of tricalcium phosphate (manufactured by Ohira Chemical Co., Ltd.) was additionally added. After the completion of the reaction, the same treatments as in Examples 1 to 7 were performed, and the polymerization results and the evaluation results of the foamed molded product are shown in Table 1. As can be seen from the results, there is no problem with the quality of the foamed molded product, but the particle size yield is poor.

[0032]

[Table 1]

Examples 8-14, Comparative Example 13 20 ppm / styrene monomer sodium bisulfite and 2 pp
Examples 1 to 10 except that m / styrene monomer potassium persulfate was used and the respective addition times were changed as shown in Table 2.
In the same manner as in Example 6, styrene resin particles were produced. Table 2 shows the central particle size (D ₅₀ ) and particle size distribution (peak 3 mesh) of the obtained styrene resin particles. The same reaction was repeated three times to evaluate reproducibility.

[0034]

[Table 2]

[0035]

The method for producing styrenic resin particles of the present invention is suitable for suspension polymerization of styrenic monomers in an aqueous medium to which a surfactant is not added in the presence of a poorly water-soluble phosphate. In addition, a water-soluble sulfite and a water-soluble persulfate are added to an aqueous medium, and the styrene monomer is polymerized under high-speed stirring. Resin particles are obtained.

By using a water-soluble sulfite (0.2 to 100 ppm / styrene-based monomer) and a water-soluble persulfate (0.1 to 10 ppm / styrene-based monomer) together, foam molding when each is used alone Styrene-based resin particles and expandable styrene-based resin particles that can compensate for the defects of the body and can use all particle sizes can be obtained. Thus, when producing styrene-based resin particles by the soap-free polymerization method, large particles use water-soluble sulfite, and small particles use water-soluble persulfate. Therefore, it is possible to obtain excellent effects such as productivity and inventory control.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-7407 (JP, A) JP-B-46-15112 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08F 2/18

Claims (2)

(57) [Claims] When a styrene monomer is subjected to suspension polymerization in an aqueous medium in the presence of a poorly water-soluble phosphate, a water-soluble sulfite and a water-soluble persulfate are converted into a styrene monomer. To the body
And 0.2 to 100 ppm and 0.1 to 10 ppm, respectively, and both
A method for producing styrene-based resin particles , comprising adding a salt to an aqueous medium such that the sum of the amounts of the salts becomes 1.5 ppm or more, and polymerizing the styrene-based monomer while stirring the aqueous medium. 2. The method for producing expandable styrene resin particles according to claim 1, wherein a foaming agent is added to the styrene resin particles during or after polymerization to obtain expandable styrene resin particles.