JPH04258646A - Expandable polystyrene resin bead and its production - Google Patents

Abstract

PURPOSE:To economically and stably produce the title beads which can be molded into an article contg. a very small amt. of voids among expanded beads and having a good appearance and excellent physical properties. CONSTITUTION:The title beads contg. a blowing agent which is liq. at room temp. and a specified amt. of a silicone oil. The silicone oil is impregnated into the beads in such a manner that the largest amt. of it is present near the surface of each bead. The blowing agent is present only inside each bead because the agent at the surface layer is removed by heating to at least the b.p. of the agent or under a decreased pressure after the impregnation with the oil.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expandable polystyrene resin particles and a method for producing the same.

0002

[Prior Art] In-mold molded products are generally obtained by the conventional method of filling pre-foamed expandable polystyrene resin particles into a mold and molding them into a desired shape by heating with steam. There is a problem that voids (pinholes) occur between particles on the surface and inside. The existence of these voids not only causes a deterioration in the appearance of the molded product, but also leads to deterioration in physical properties such as an increase in water absorption and an increase in thermal conductivity, so a solution to this problem has always been desired in the industry. . Conventionally, countermeasures to reduce the above-mentioned pinholes include: (1) increasing the vapor pressure during molding, extending the heating time, etc.; (2) using polystyrene resin as the base resin of the resin particles; A method of adding fatty acid esters, phthalate esters, etc. during polymerization has been proposed.

0003

[Problem to be solved by the invention] However, the above ■
In method (2), pinholes do not necessarily decrease even if the heating exceeds a certain limit, but rather new problems such as shrinkage of the molded product and lengthening of the molding cycle occur, which is undesirable. In addition, the method (2) above also has the disadvantage that the effect of reducing pinholes is insufficient and that molded products may shrink depending on the method. Furthermore, increasing the heating time, etc. as in method (2) above will lengthen the molding cycle, resulting in poor moldability, but in order to improve such moldability, it is possible to reduce the amount of blowing agent. Are known. However, when the amount of foaming agent is reduced, sufficient foaming is not achieved, and pinholes are more likely to occur, resulting in poor appearance of the molded product.

The present invention has been made to solve the problems of the above-mentioned prior art, and has very few voids between particles.
It is an object of the present invention to provide expandable polystyrene resin particles that can economically and reliably obtain molded products with good appearance and various physical properties, and a method for producing such resin particles.

[0005]

[Means for Solving the Problems] That is, the expandable polystyrene resin particles of the present invention are expandable polystyrene resin particles containing a foaming agent that is liquid at room temperature, and the largest amount is present near the surface layer of the resin particles. 0.01 to 2 parts by weight of silicone oil is present per 100 parts by weight of the resin particles so that the foaming agent near the surface of the resin particles is removed. be. In addition, in the production method of the present invention, the amount of foaming polystyrene resin particles containing a liquid blowing agent is 0.01 to 2 parts by weight per 100 parts by weight of the resin particles so that the largest amount is in the vicinity of the surface layer of the expandable polystyrene resin particles.
After the presence of part by weight of silicone oil by impregnation,
The method is characterized in that only the blowing agent present near the surface of the resin particles is removed by carrying out a blowing agent dissipation treatment under heating at a temperature equal to or higher than the boiling point of the blowing agent.

[0006] The resin particles of the present invention and the method for producing the same particularly include:
Other than the restrictions of using a foaming agent that is liquid at room temperature as a foaming agent, having the largest amount of silicone oil present near the surface layer of the resin particles, and selectively dissipating and removing the foaming agent near the surface of the resin particles. is basically a manufacturing method to which a conventionally known method for manufacturing expandable polystyrene resin particles can be applied, and is a resin particle that can be obtained by basically applying the manufacturing method. As the blowing agent, those that are liquid at 25° C. and 1 atm, such as normal pentane, isopentane, hexane, isohexane, and cyclohexane, are used. Under these conditions, if a gas blowing agent is used, the dissipation rate is high and it is difficult to control, and there are problems such as the inability to increase the desired expansion ratio during pre-foaming. In addition to polystyrene, the polystyrene resin used in the present invention includes copolymer resins mainly composed of polystyrene (e.g., ethylene-styrene copolymer, polymethyl methacrylate, propylene-styrene copolymer, etc.)
can be mentioned.

[0007] The resin particles of the present invention are impregnated with silicone oil so that most of the silicone oil is present near the surface layer. Here, the area near the surface layer where the oil is present in the largest amount differs depending on the size of the resin particles, but preferably corresponds to a depth of about 0.02 to 0.1R, where R is the particle radius. It is. However, the impregnation depth in the present invention is not limited to the above range. Silicone oil is usually added in an amount of 0.01 to 2 parts by weight, preferably 0.05 to 0.5 parts by weight, per 100 parts by weight of resin particles (impregnation).
be done. If the amount added does not reach 0.01 part by weight, the good in-mold foam molded product that is the object of the present invention cannot be obtained, and even if it exceeds 2 parts by weight, the effect remains unchanged and is not economical. Specifically, polydimethylsiloxane, methylphenylsiloxane, methylhydrogensiloxane, etc. are used as the silicone oil. If the viscosity of this silicone oil is too high, it will not penetrate the surface layer of the resin particles sufficiently due to its large molecular weight, and if the viscosity is too low, it will penetrate into the center of the particles. The viscosity is selected. Generally, it is preferable that the viscosity at 25°C is in the range of 100 to 3000 cs, but the viscosity is not limited to this numerical range.

[0008] Impregnation with silicone oil may be carried out after the particles have stabilized in shape without coalescence or dispersion during polymerization. Specifically, it can be added at any time from the time when the polymerization rate exceeds 70% until the so-called impregnation step in which a liquid blowing agent is infiltrated into the resin particles at room temperature. A certain degree of effect is expected even when the polymerization rate is less than 70%, but when the polymerization rate is too low, it is not possible to selectively impregnate the layer near the surface of the polymer particles. Further, the impregnation time of the silicone oil needs to be set appropriately because if it is too short, the oil cannot penetrate into the surface layer of the resin particles. For example, for a material with a viscosity of 100 cs, the impregnation time may be 3 hours or more at a temperature of 110°C. When impregnating with the above oil, an impregnation aid may be used, such as an aromatic hydrocarbon solvent such as toluene, benzene, xylene, or styrene monomer, or a softener or plasticizer for the base resin. Those that can be used include, for example, dibutyl stearate, dioctyl phthalate, butyl stearate, and the like.

[0009] Only the blowing agent present near the surface of the resin particles of the present invention has been removed. The blowing agent is removed by a blowing agent dissipation treatment, which is carried out on the resin particles after they have been impregnated with the silicone oil. The blowing agent dissipation treatment is carried out, for example, by allowing the resin particles to exist in an atmosphere heated to a temperature above the boiling point of the blowing agent, preferably above the boiling point of the blowing agent and below 80°C. Specifically, using a rotary dryer, fluidized bath dryer, jacketed ribbon blender, hot water tank, fluidized hot water tank, etc., resin particles are made to exist in hot air or hot water heated to the above-mentioned heating temperature. This is done by heating directly or indirectly. Further, the dissipation treatment can also be carried out by making the resin particles exist in a reduced pressure atmosphere, and in this case, the reduced pressure atmosphere may be in either a heated or non-heated state. The dissipation treatment time varies depending on heating temperature conditions, vacuum conditions, etc., but for example, it is preferably about 5 to 15 minutes in hot air (airflow) at 60 °C, and at 30 °C and 700 °C.
In a reduced pressure atmosphere of mmHg, about 10 to 30 minutes is preferable. By performing the dissipation treatment under heating at a temperature range above the boiling point of the foaming agent, the foaming agent can be efficiently removed in a short time, and furthermore, there are advantages such as being able to prevent the foaming ratio from decreasing during pre-foaming as much as possible. There is. In addition, if the heating temperature condition in the dissipation treatment is lower than the boiling point of the blowing agent, it may take a long time to dissipate the blowing agent, or the dissipation treatment may not be performed sufficiently.On the other hand, if the heating temperature exceeds 80°C, the treatment There are problems such as undesirable foaming of the resin particles inside.

In the present invention, the surfaces of the resin particles may be coated with an antiblocking agent, an antistatic agent, a coloring agent, etc., if necessary. The expandable polystyrene resin particles having the above-mentioned structure are pre-foamed and then filled into a mold by a conventional method and foam-molded to form a desired molded article. The molded product thus obtained can be used for various purposes, but it is particularly suitable for use as packaging boxes for fish, packaging materials, insulation materials, reclaimed blocks for civil engineering, and the like.

[0011]

[Examples] The present invention will be described in detail below with reference to Examples. Examples 1 to 6, Comparative Examples 1 to 3 2 liters of water in a 5 liter glass-lined autoclave
Add 130 g of trilime phosphate, 5.5 g of trilime phosphate, and 60 mg of sodium dodecylbenzenesulfonate, and add sodium hydroxide to adjust the pH to 7.5. Add 3.3 g of benzoyl peroxide and t-butyl peroxide while stirring at 350 rpm. Benzoate 1.65g, liquid paraffin 3.42g
1670 g of styrene monomer dissolved in was added. This was heated to 90°C and held for 6 hours. Next, silicone oil of the type and amount shown in Table 1 below, and polyvinyl alcohol (manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd.: GH) were added.
-17) Add 0.2g and 7.2g of calcium carbonate, seal the autoclave, and add 200ml of normal pentane.
After pressurizing 7 ml of toluene, the temperature was raised to 110°C.
Holds time. Next, the slurry was cooled to 30°C, and 100 ml of 1N hydrochloric acid was added to neutralize the resulting slurry. Water was separated and washed with water to obtain spherical expandable polystyrene resin particles. After performing blowing agent dissipation treatment on these particles using the treatment method and heating temperature conditions shown in Table 1, 0.1 ethylene bisstearamide was added as an antiblocking agent.
part by weight and 0.1 part by weight of behenic acid triglyceride were coated on the particle surface. Table 1 shows the amount of blowing agent in the particles at this time. Next, the particles were expanded to a volume ratio of about 50 times to obtain pre-expanded particles, and then the pre-expanded particles were left at room temperature for 24 hours, and then a 300 mm x 300 m
A predetermined amount of the mixture was filled into a molding machine equipped with a m x 50 mm mold, and foam molding was performed under the following molding conditions: steam pressure of 0.8 kg/cm2, heating time of 10 seconds, and water cooling time of 10 seconds. Table 1 shows the fusion rate, surface finish, and molding cycle of the obtained molded product.
Shown below.

[0012] In the resin particles of Examples 1 to 6, the foaming agent near the particle surface layer was well removed, and the molded products made of these particles had good fusion between the foamed particles and no pinholes. It was confirmed that the surface finish was beautiful and the molding cycle was short. On the other hand, in Comparative Example 1, there was almost no dissipation of the blowing agent, resulting in extremely poor fusion and surface finish of the molded product, and poor moldability, and in Comparative Example 3, there was a lot of blowing agent dissipation from inside the particles, resulting in fusion. Both moldability was poor. In Examples 1 to 6 and Comparative Examples 1 to 2, n-pentane was used as the blowing agent, but in Comparative Example 3, butane was used. Example 6 was carried out in the same manner as Example 1, except that the blowing agent dissipation treatment was carried out after coating the particle surface with an antiblocking agent. In addition, in the dissipation treatment method shown in Table 1, "hot air flow" refers to leaving resin particles in hot air at the temperature shown in the table for about 5 minutes.
"Hot water" means 500 mg of resin particles in hot water 2 at the temperature shown in the table.
000ml and held for 30 minutes while stirring."Vacuum" means to vacuum the resin particles at 700mmH at a temperature of 30℃.
The sample was placed in a vacuum dryer for 20 minutes.

Furthermore, the expandable polystyrene resin particles (particle size 0.7 to 1.0 mm) obtained in Example 6 and Comparative Example 2 were
) was pre-foamed to a bulk foaming ratio of 60 times, and
After leaving at room temperature for an hour, 925mm x 415mm x 18
It was subjected to foam molding using a block molding machine (manufactured by Daisen Kogyo: 1800-4V) equipped with a 40 mm mold to obtain a block molded body. The molding cycle at this time was 13 minutes in the case of molding using the resin particles of Example 6, but it required 20 minutes for the resin particles of Comparative Example 2. In addition, when each of the obtained block molded bodies was cut with a nichrome wire and the pinhole area at the center of the cross section was measured, the molded body obtained with the resin particles of Example 6 was 1%, and its surface finish was However, the molded product obtained using the resin particles of Comparative Example 2 was only 5%, and the surface finish also had many pinholes.

[0014]

[Table 1]

*a...Shin-Etsu Chemical: KF-96 (viscosity 10
0cs) *b...Made by Toray Dow Corning Silicone: SH-51
0 (viscosity 100cs) *c...Shin-Etsu Chemical: KF-99 (viscosity 100cs) *1
...The fusion rate was determined by bending and breaking the molded product, and expressed as the percentage of material destruction of the resin particles on the broken surface. *2...Surface finish was evaluated by visually observing pinholes on the surface of the molded product and using the following criteria. ◎: Not at all, ○: Almost none, ×: A lot. *3...In the molding cycle, the surface pressure of the molded product is 0k from the start of molding.
g/cm2 (that is, until the molded product no longer shows blisters after being demolded), left to cool, and demolding.

[0016]

Effects of the Invention As explained above, since the resin particles of the present invention have the above-described structure, it is possible to obtain an in-mold molded product with extremely few voids between the particles. Furthermore, according to the resin particles of the present invention, it is possible to prevent deterioration of the surface finish caused by the plasticizing effect of the blowing agent present near the surface layer. A decrease in foaming ratio can be prevented. Furthermore, the molded product exhibits almost no shrinkage after molding and has excellent dimensional stability, and also has little moisture adhesion or content, so no complicated drying process is required. In addition, the method of the present invention can produce the above-mentioned excellent molded products without the need to heat the expandable polystyrene resin particles more than necessary as in the conventional method, and even with a reduced amount of blowing agent. Excellent resin particles that do not adversely affect the appearance of molded products can be produced in a relatively short molding cycle. Furthermore, since a foaming agent that is liquid at room temperature is used, a relatively small amount of the foaming agent can be effectively and easily dissipated and removed from near the surface of the resin particles by the foaming agent dissipation process. Furthermore, when obtaining a block molded product using the resin particles of the present invention, plasticization of the surface of the resin particles by the foaming agent is inhibited, so that the timing of the passing of heated steam between particles and the timing of interparticle fusion during in-mold molding is slightly different.
This not only makes it possible to significantly reduce pinholes inside the molded product, but also shortens the molding cycle.

Claims (2)

[Claims] 1. Expandable polystyrene resin particles containing a blowing agent that is liquid at room temperature, the amount being the largest near the surface layer of the resin particles, from 0.01 to 0.01 parts by weight per 100 parts by weight of the resin particles. 1. Expandable polystyrene resin particles, characterized in that 2 parts by weight of silicone oil are present, and the foaming agent near the surface of the resin particles is removed. 2. From 0.01 to 100 parts by weight of the resin particles so that the largest amount is near the surface layer of the expandable polystyrene resin particles containing the blowing agent that is liquid at room temperature.
After impregnating 2 parts by weight of silicone oil, a blowing agent dissipation treatment is performed under heating at a temperature higher than the boiling point of the blowing agent or under reduced pressure to remove only the blowing agent present near the surface of the resin particles. A method for producing expandable polystyrene resin particles characterized by: