JPS595135B2 - Method for producing improved expandable polystyrene resin particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing expandable polystyrene resin particles, and more specifically, when impregnated with a blowing agent, the polystyrene resin particles do not adhere to each other and the resulting expandable polystyrene When heating system resin particles to form pre-expanded particles, filling the particles into a mold gap that can be closed but cannot be sealed (hereinafter simply referred to as the mold gap) and heating, to obtain an arbitrary molded article, The present invention relates to a method for producing expandable polystyrene-based resin particles that yield molded articles having extremely excellent moldability and excellent properties.

Extremely excellent moldability means that the molded product obtained by filling the space between the molds with pre-foamed particles and further heating them sufficiently fills the voids between the particles and the particles are fused together very well. It has a beautiful surface, a wide molding heating range, and a short cooling time during molding.

The method for obtaining a foamed polystyrene molded article is generally carried out through the steps of producing expandable polystyrene resin particles, pre-foaming, ripening the foamed particles, and molding15.

The qualities conventionally required of expandable polystyrene resin particles are that the impregnation method with a blowing agent is easy, that the expanded particles do not coalesce together and form lumps during pre-foaming, and
When aging the foamed grains, even if the foamed grains have been pre-foamed for more than 3 days, the moldability is not inferior, and when molding, the heating molding width is wide, and even if the so-called molding vapor pressure is low, the foamed grains cannot interact with each other. The particles are well fused, the voids between particles are sufficiently filled, the cooling time is short, and even if the molding steam pressure is increased to increase work efficiency, the molded product obtained has good 25 fusion bond. It is desired that there is no melting due to heat and no dimensional shrinkage. Various methods for obtaining expandable resin particles have been proposed in the past, and many of them are aimed at obtaining expandable resin particles with excellent moldability and a short cooling time30.
It has been stated.

For example, in Japanese Patent Publication No. 44-2469, thermoplastic polymer particles and an amount of polymerizable monomer that does not completely dissolve the particles but are sufficient to swell the particles are suspended in an aqueous medium, and a gas is added to the suspension in a normal state. In addition, in Japanese Patent Publication No. 45-132623, a method of polymerizing while pressurizing a blowing agent is disclosed, in which a granular thermoplastic resin mainly composed of an aliphatic olefin polymer is dissolved in i, P! A vinyl monomer that can be swelled or polymerized, a polymerization catalyst, and a crosslinking agent consisting of an organic peroxide are dispersed in an aqueous medium, and a blowing agent in the form of a gas or liquid is normally pressurized into the medium, followed by heating. A method is disclosed in which polymerization of vinyl monomers, impregnation with a blowing agent, and crosslinking reaction are carried out simultaneously under pressure.

However, in these methods, since the foaming agent is impregnated at the same time as the polymerization reaction, the foaming agent lowers the viscosity and therefore the polymerization reaction takes a long time. When using styrene monomer in polyethylene resin particles to prevent this, the amount of styrene monomer used is limited to 30% by weight or less, and since the polymerization of styrene monomer is carried out at high temperatures, polyethylene resin Many of the polystyrene resins in the particles have a low degree of polymerization. Therefore, when heated to form pre-expanded particles,
There are disadvantages in that the bubbles in the pre-expanded particles are non-uniform and the secondary foaming power is poor, making it impossible to obtain products with excellent moldability. In addition, when using a normally gaseous blowing agent (n-propane, n-butane, dichlorodifluoromethane, etc.),
The reaction system becomes under high pressure, requiring a high-pressure autoclave, which is not practical. Furthermore, the product is a fine powder in which only monomers are polymerized, and this powdered polymer also contains a blowing agent, so it is necessary to collect it to produce large polymer particles, for example. The disadvantage was that it could not be used as a raw material. In addition, special public service No. 49-19106
- No. 19108, a styrenic monomer and a catalyst for suspension polymerization are added to a suspension of small particles of a styrenic polymer, polymerized to form styrenic polymer particles, and a blowing agent is added to this. A method for obtaining expandable styrenic polymer particles by impregnation is disclosed. These inventions attempt to grow small particles, which cannot be used as they are, out of styrenic polymer particles obtained by suspension polymerization into large particles for use. Therefore, the particles obtained are polymers of styrene monomers and do not contain ethylene polymers. Also, JP-A-48-101457 and JP-A-48-101457
In No. 5473, 30 to 100% by weight of a styrene monomer based on the resin and a catalyst for polymerizing the monomer are added to polyethylene resin particles, and then the monomer is polymerized. A method has been proposed in which polyethylene resin particles containing polystyrene resin produced by polymerization are impregnated with a foaming agent to produce expandable polyethylene resin particles. This method is a method for producing foamed polyethylene resin particles whose main component is polyethylene and whose properties are improved.Styrenic monomers are added within a range that does not impede the properties specific to polyethylene resin. It was intended to increase the foaming properties of the liquid, and was not intended to shorten the cooling cycle, and the effect could not be achieved. Generally, polyethylene resin particles have extremely low affinity for styrene monomers, and even if styrene monomers are added to polyethylene resin particles, the styrene monomers do not penetrate into the polyethylene resin particles, and the styrene monomers do not penetrate into the polyethylene resin particles. It was thought that only styrene polymer particles could be obtained. Therefore, as described in Japanese Patent Publication No. 4726097, a method is known in which polyethylene is ground into polystyrene polymer, mixed in a blender, extruded in an extruder, and then cut into pellets. . However, in this method, since it is only physically mixed, it is impossible to mix the rice uniformly, and layer separation occurs, resulting in non-uniform impregnation of the blowing agent, foaming ratio, etc. However, it had the disadvantage of lacking stability. As a result of extensive research in order to produce expandable thermoplastic resin particles with even better properties, the present inventors discovered that styrene monomer and polymer When the catalyst is gradually added, the styrenic monomer penetrates into the ethylene polymer particles and undergoes graft copolymerization and block copolymerization with the ethylene polymer to form a complex copolymer. Even if the monomer is used in a larger amount than the ethylene polymer, a styrene homopolymer is not produced, and the resulting polymer particles are different from those obtained by simply mixing a styrene polymer and an ethylene polymer. In addition, polymer particles mainly composed of styrene with properties not found in any of the above can be obtained, and by impregnating them with a blowing agent, excellent functions and effects never before seen can be achieved, as described below. Discovered that expandable polystyrene resin particles could be obtained,
The invention has been completed.

That is, in the present invention, polyethylene resin particles are dispersed in an aqueous medium to form a suspension, and the particles 10 are dispersed in the suspension.
125 to 500 parts by weight of a styrene monomer and a catalyst for polymerizing the monomer are gradually added to 0 parts by weight to polymerize the monomer, and then the resin is added to the resulting resin particles. The gist of this invention is a method for producing expandable polystyrene resin particles, which is characterized by impregnating the particles with a blowing agent that does not dissolve the particles or only slightly swells the particles. In addition to ethylene homopolymer particles, the polyethylene resin particles used in the present invention include copolymers mainly composed of ethylene, such as copolymers of ethylene and vinyl acetate, copolymers of ethylene and vinyl chloride, and copolymers of ethylene and vinyl acetate. Copolymer particles of and methyl methacrylate are also used.

These polyethylene resin particles are spherical, pellet-like, etc. particles, and the particle size is preferably 8 to 30 mesh. The styrenic monomer used in the present invention includes styrene or a mixture of styrene containing 50 parts by weight or more with monomers that can be copolymerized, such as d-methylstyrene, methyl methacrylate, and divinylbenzene. Used. However, the blending amount of the styrene monomer is 12 parts by weight per 100 parts by weight of the polystyrene resin particles.
The amount is 5 to 500 parts by weight, preferably 125 to 400 parts by weight. Resin particles polymerized using less than this amount of polyethylene resin particles with the addition of a styrene monomer cannot exhibit the various remarkable effects characteristic of the present invention. Furthermore, if more polyethylene resin particles are used than the above amount, the retention of the blowing agent will be poor and it will be difficult to foam at a high multiple when pre-foaming is performed, which is not preferred.
In the present invention, as the catalyst for polymerizing the styrene monomer absorbed into the polyethylene resin particles, catalysts generally used as catalysts for polymerizing styrene monomers can be used as they are.

For example, organic peroxides such as benzoyl peroxide, t-butyl perbenzoate, lauroyl peroxide, t-butyl peroxy-12-ethylhexanate, azo compounds such as azobis-isobutylnitrile, azobis-dimethylvaleronitrile, etc. be. These catalysts may be used alone or in combination of two or more. These catalysts are used by being dissolved in the styrene monomer absorbed into the polyethylene resin particles or in a solvent that does not interfere with the polymerization reaction. In the present invention, for example, dicumyl peroxide, t-butylcumyl peroxide, 1,1-bis(t-butylperoxy)3,5,5-trimethylcyclohexane, 2,5-dimethyl-2 - Organic peroxides such as 5-di(t-butylperoxy)-hexane can also be used.

By crosslinking, it is possible to further widen the width of the heated molding, and more specifically, during molding, the heating vapor pressure is increased, and even when heated for a long time, it is possible to obtain the effect that melt dimensional shrinkage does not easily occur in the molded product. In the present invention, a blowing agent is used to obtain expandable polystyrene resin particles.

This is a blowing agent that does not dissolve or only slightly swells the resin particles, such as propane, n-
Examples include aliphatic hydrocarbons such as butane, i-butane, n-pentane, and i-pentane, and halogenated hydrocarbons such as methyl chloride, ethyl chloride, trichloromonofluoromethane, dichlorodifluoromethane, and dichlorotetrafluoroethane. be able to. These blowing agents can be used alone or in combination of two or more. When the polystyrene resin particles in the method of the present invention are impregnated with a blowing agent, the blowing agent penetrates quickly, and even when butane or propane is used as a blowing agent, the amount of solvent used is lower than that used in the production of conventional expanded polystyrene resin particles. A small amount is sufficient, and naturally there is no need to leave it in the form of styrene monomer.

To impregnate the blowing agent, polystyrene resin particles are dispersed in an aqueous medium, conventionally using polyvinyl alcohol, tricalcium phosphate or other sparingly soluble phosphates, calcium carbonate, zinc stearate, methylene bisstearate, etc. It has been necessary to use a suspending agent such as Roamide to prevent particles from adhering to each other during impregnation, or to prevent foamed particles from coalescing during pre-foaming. However, the polystyrene resin particles obtained in the present invention require only water and a small amount of emulsifier as an aqueous medium, and even if a solvent is used as necessary, no coalescence of the particles occurs. This is due to the effect of polyethylene contained within the polystyrene resin particles. This has made it dramatically easier to dispose of the waste liquid after impregnation with the blowing agent. Further, in the pre-foaming process, the foamable resin particles of the present invention use only a very small amount of solvent or no solvent, so that the foamed particles do not coalesce with each other. When these pre-foamed particles are filled into a mold cavity and heated and molded, a molded article with good fusion bonding can be obtained since no substances are used that inhibit fusion bonding during impregnation with a blowing agent. Furthermore, during molding, the fusion bond is good, and the heating width, so-called molding width, is wide, which allows you to obtain a beautiful molded product without melting the surface of the molded product or shrinking the size, and after the completion of heat molding, A major feature is that when the mold cavity is cooled by water or air cooling, the molded body is removed from the mold cavity in a short cooling time until it can be taken out without further expansion. Usually, the expandable polystyrene resin particles are matured, that is, the expandable polystyrene resin particles impregnated with a blowing agent are aged for 3 to 5 days after being taken out from the reaction pressure vessel before being subjected to pre-foaming.
It is maintained at a temperature of around 20°C for days.

If pre-foaming is carried out immediately after impregnation with the blowing agent or after about two days without this aging, the bubbles formed in the foamed particles will be non-uniform and wrinkles will form on the surface of the foamed particles. Otherwise, a beautiful molded product cannot be obtained. In addition, when pre-foaming is performed, the foaming speed is too fast and it is difficult to control the foaming ratio, resulting in non-uniform foaming. Aging of the expandable polystyrene resin particles according to the present invention can be carried out in a short period of time, and depending on the combination of compositions, even if the particles are pre-foamed immediately after being dried after being taken out, the cells in the expanded particles have an excellent uniform surface condition. can get. When this is molded after being left at room temperature for 24 hours, a molded product with good fusion bonding, a beautiful molded surface, and no uneven foaming can be obtained. In this way, by shortening the aging time of the expandable polystyrene resin particles,
It does not require many days of storage, and the expandable polystyrene resin particles can be shipped to the molding manufacturer immediately after production, so it does not require a lot of space such as a refrigerated warehouse, making it extremely economical. Furthermore, regarding pre-foamed foamed particles, the time required for normal polystyrene foamed particles after pre-foaming before molding is 10 to 55 hours.
If the time is shorter than this, dimensional shrinkage or other deformation will occur when molded, and if a long time elapses, the secondary foaming power of the expanded beads will be poor and the surface of the molded product will not be beautiful.
There were drawbacks such as a large amount of moisture being contained inside the molded body during molding and poor fusion bonding. The polystyrene foam particles obtained according to the present invention have good secondary foaming power even after 20 days have passed after pre-foaming.
Even under the same conditions as when molding expanded beads after 4 hours, the molding surface is beautiful and no large amount of water is contained inside.

Moreover, good fusion bonding can always be obtained. The molded product obtained by pre-foaming the expandable polystyrene resin particles according to the present invention and post-foaming in the mold cavity has the rigidity of polystyrene and the flexibility unique to polyethylene, so it is easily damaged. For this reason, for example, packaging that conventionally required the use of large amounts of expanded polystyrene moldings can be replaced with packaging that uses a small amount of material as a molded product that protects only the corners of the product. It has become possible to safely package

In addition, it can be used not only for packaging materials, but also for all fields of conventionally used expanded polystyrene resin molded products.
It is extremely useful for obtaining so-called strong molded products. Hereinafter, a more specific explanation will be given with reference to Examples.

Example 1 20% pure water in an autoclave with an internal volume of 5.61%
007, and magnesium pyrophosphate 9 as a suspending agent.
y1 Add 0.47 ml of sodium dodecylbenzenesulfonate to form an aqueous medium, and then add polyethylene resin particles (
Product name: Mirason ACE-30N (manufactured by Mitsui Polychemical Co., Ltd.)
4007 was suspended at a stirring speed of 320 r. p. m. Stir with.

Separately, benzoyl peroxide 10' is used as a polymerization catalyst.
! 7 and t-butyl perbenzoate 17 at 160
Dissolve it in the styrene monomer of No. 07 to make a monomer solution,
This solution was gradually dropped into the aqueous medium and absorbed into the polyethylene resin particles while maintaining the temperature at 85° C. for 8 hours to perform polymerization, and then the solution was cooled, taken out, washed with water, and dried. Next, the internal volume is 4.0f! autoclave with water 1
Add 5007 and 0.37 of sodium dodecylbenzenesulfonate as an emulsifier, add 127 of toluene, and make 400.
r. p. m. Stir with.

15,007 ml of the polystyrene resin particles obtained above were added to this, and 3,007 ml of butane was further press-fitted as a blowing agent. The temperature was further raised to 80°C, stirring was continued for 5 hours, and then the mixture was cooled and taken out. The expandable polystyrene resin particles thus obtained contained 9% butane and were free of coalescent particles. After the particles were kept at a temperature of 15° C. for 3 days, they were pre-foamed to obtain expanded beads with a bulk multiplier of 50 times without any blocking between the expanded beads. Furthermore, after keeping this foamed pellet at room temperature for 24 hours, 30C771×30
cTn x 10 (V7!, steam pressure 0.8'K9)
/Cd for 60 seconds and then cooled with water for 3 minutes. The molded product taken out from the mold cavity had a beautiful surface and good welding with no dimensional change. Comparative Example 1 Using the sample shown in Table 1 below, 1,500 y of water, sodium dodecylbenzenesulfonate as an emulsifier, toluene as a solvent, and a dispersant were added to an autoclave with an internal volume of 4.01 ml, and the mixture was heated to 400>R. p. m. Stirred.

After 1500 y of polystyrene resin particles were put into this, 300 y of butane was press-fitted as a blowing agent. temperature for 6 hours 8
After being maintained at 0°C, it was cooled and taken out. The obtained expandable polystyrene resin particles were washed with water, dried, and then stored at a temperature of 15° C. for 3 days to perform preliminary foaming to a bulk multiple of 50 times.
The pre-foamed expanded particles were left at room temperature for 24 hours, then filled into a mold cavity and heated and molded for 60 seconds at a heating steam pressure of 0.8k9/Cd. The properties of the obtained particles and molded body were as shown in Table 1 below. Example 2 600y of polystyrene resin particles (trade name Sumikasen G7Ol manufactured by Sumitomo Chemical Co., Ltd.) and 9y of benzoyl peroxide
y) Polymerization and blowing agent impregnation were carried out under the same conditions as in Example 1, except that the amount of t-butyl benzoate was changed to 0.9y, the amount of styrene monomer was changed to 1400t, and the polymerization time was changed to 7 hours.

The thus obtained expandable polystyrene resin particles contained 8.5% butane, and were immediately pre-foamed to a bulk ratio of 50 times after washing with water and drying. These foam particles had a uniform expansion ratio and a beautiful surface condition with no coalescent particles, and when the particles were cut and the air bubbles inside were observed, they were uniform. After the foamed beads were left at room temperature for 24 hours, they were placed in a mold cavity and heated and molded for 60 seconds at a heating steam pressure of 0.8 kg/Cd.
This molded product had a beautiful surface, no dimensional shrinkage, and good welding. Comparative Example 2 In exactly the same manner as Experiments 3 and 4 of Comparative Example 1, expandable polystyrene resin particles obtained by impregnating with a blowing agent, taking out, washing with water, and drying were immediately pre-foamed to a bulk ratio of 50 times. It was difficult to control the expansion ratio, and wrinkles appeared on the surface of the foamed particles.

When the particles were cut, the bubbles were coarse and non-uniform. Example 3 The polyethylene resin particles used in Example 1 were 8007, benzoyl peroxide 87, and t-butyl benzoate 0.
．． Polymerization was carried out in the same manner as in Example 1 except that 1200 tons of styrene monomer No. 87 was used and the polymerization time was changed to 7 hours, and then the polymerization was cooled to 50°C.

Next, 400 tons of butane was injected under pressure and impregnated with a blowing agent at a temperature of 80° C. for 5 hours. It was cooled to 25°C, taken out, washed with water, and dried.

The thus obtained expandable polystyrene resin particles were used in the same manner as in Example 1 to produce pre-expanded particles having a bulk factor of 50 times.
Leave these particles at room temperature for 12 hours, 1 day, 3 days, 10 days, 20 days.
After leaving it for several days, 30 (V7lX3O(1)
1.0kg/CrA by filling into a mold cavity of 771 x 10cm
When the foamed particles were heated and molded for 60 seconds at a heated steam pressure of 1, the same molded products were obtained even when the foamed particles were left for 12 hours, for 3 days, and even for 20 days.

Comparative Example 3 Commercially available expandable polystyrene resin particles were pre-foamed to a bulk multiple of 50 times.

These pre-expanded particles were left at room temperature for 12 hours, 1 day, 2 days, 3 days, and 5 days.
X3Ocm×10? Fill the mold cavity with 1.0kg/Cd
The foamed particles were heated and molded for 60 seconds at a heating steam pressure of
If the molded product was left for a day, the elongation of the surface of the molded product deteriorated, and if the molded product was used for more than 3 days, the fusion was poor and a large amount of water was contained in the molded product. Example 4 Pre-expanded particles obtained in exactly the same manner as in Example 3 were left at room temperature for 24 hours, and then 30cm x 30c7rL x 10
The molded product obtained by filling a cm mold cavity and heat-sealing has good welding and no melting on the surface.

The range in which dimensional shrinkage of the molded product does not occur is within the range shown by the solid line in FIG. When the molding vapor pressure was 051<9/CrA, the heating time was 60 seconds, and the molded product was 45 seconds at 1.0 kg/C77f, the shortest cooling time without dimensional expansion in the molded product taken out was 180 seconds and 195 seconds, respectively. Comparative Example 4 Commercially available expandable polystyrene resin particles were pre-foamed to a volume multiple of 50 and left at room temperature for 24 hours, after which the molding area was observed in the same manner as in Example 4.

The results are shown by the broken line in FIG. Molding steam pressure 0.5k9
/Cd, heating time 60 seconds, and 1 kg/Cd, 45 seconds, the shortest cooling time without dimensional expansion of the molded body was 220 seconds and 225 seconds, respectively.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the range in which dimensional shrinkage does not occur in a molded product when the expandable polystyrene resin particles are pre-foamed and then heated and fused in a mold cavity to form a molded product. When the thus obtained expandable polystyrene resin particles are used, the broken line indicates the range when commercially available expandable polystyrene resin particles are used. In the drawings, horizontal lines indicate heat forming time (seconds), and vertical lines indicate heat forming steam pressure (Kg/Cri.).

Claims (1)

[Claims] 1 Disperse polyethylene resin particles in an aqueous medium to form a suspension, and polymerize 125 to 500 parts by weight of a styrene monomer and the monomer to 100 parts by weight of the particles in the suspension. The method is characterized in that the monomer is polymerized by gradually adding a catalyst to cause the monomer to polymerize, and then the resulting resin particles are impregnated with a blowing agent that does not dissolve the resin particles or only slightly swells the resin particles. A method for producing expandable polystyrene resin particles.