JPH07165973A - Method for producing expanded synthetic resin particles - Google Patents

Abstract

(57) [Abstract] [Purpose] In a method of impregnating resin particles dispersed in a dispersion medium in a closed container with a foaming agent, and then discharging the resin particles from the container under a low pressure to foam the resin particles, Solves the disadvantage of the conventional method in which the expansion ratio of expanded particles obtained between foaming devices varies even if foaming is performed under the same conditions, and efficiently produces expanded particles with a small difference in expansion ratio between the devices used for manufacturing. Provide a method that can be done. [Structure] Resin particles dispersed in a dispersion medium in a closed container are stirred under heating to impregnate the resin particles with a foaming agent, and then the resin particles and the dispersion medium are discharged under low pressure to foam the resin particles. In the method, the gas phase containing the foaming agent is forcibly circulated in the dispersion medium at least immediately before the resin particles and the dispersion medium are discharged out of the container.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing expanded synthetic resin particles.

[Prior art]

[0002] Synthetic resin particles are dispersed in a dispersion medium in a closed container, a foaming agent is introduced into the closed container, and the resin particles are impregnated with the foaming agent by heating and stirring. A method of simultaneously discharging a dispersion medium and a dispersion medium under a low pressure to foam resin particles is widely used as a method for producing synthetic resin expanded particles.

The expansion ratio of the expanded particles obtained by the above-mentioned method depends on the type and mixing ratio of the dispersion medium, resin particles, foaming agent or other various additives mixed in the container, and the foaming agent added. It is known that the gas phase volume is affected by conditions such as volume occupancy in the container.

[0004]

However, even when foaming is performed under exactly the same conditions that have been known to affect the foaming ratio, the average of the foamed particles obtained for each foaming device used. There is a problem that the expansion ratio is different, and the expansion ratio of the obtained expanded particles tends to decrease, especially in an apparatus having a larger closed container inner volume.

In the above-mentioned method, the foaming agent in the gas phase in the container is dispersed or dissolved in the dispersion medium by stirring the contents of the container with heating, and then the resin particles are impregnated to form the resin particles. Although the foaming is possible, according to the study by the present inventors, even if the foaming is performed under the same conditions, the foaming ratio of each foaming device varies, and the foaming ratio decreases as the volume of the device increases. Has been found to be due to unequal amounts of blowing agent impregnated in the resin particles.

[0006] Furthermore, when the stirring ability of the apparatus is increased or the stirring time is lengthened, the expansion ratio of the expanded particles obtained is also increased, and it is also understood that the difference in the stirring ability when stirring the contents of the apparatus has a great influence. It was

As one of the methods of making the stirring ability of each apparatus equal, there is a method of replacing all the foaming apparatuses currently used in the expanded particle manufacturing plant with exactly the same apparatus. However, it is extremely difficult to easily adopt this method because of the problem of depreciation of the currently used equipment and the capital investment cost for replacing the equipment with a new one.

It is also conceivable to replace only the stirring blades of the currently used apparatus so that the stirring ability becomes equal between the apparatuses. However, in most of the devices currently used in the expanded particle manufacturing plant, the shape and the internal volume of the closed container are not the same, and only the replacement of stirring blades is required while using the closed container with the different shape and internal volume. Therefore, it is extremely difficult to make the stirring ability of each device the same, and this method cannot be an effective solution.

Further, it is not preferable to increase the stirring time in order to increase the impregnation rate of the foaming agent into the resin particles from the viewpoint of production efficiency. Further, it is also unrealistic to use a stirring blade having an extremely large stirring ability so that the foaming agent can be efficiently impregnated into the resin particles in a short time. Further, in order to efficiently and quickly impregnate the resin particles with an amount of the foaming agent capable of obtaining a desired expansion ratio, more foaming agent than the necessary amount to be impregnated into the resin particles is used. A method of supplying it into the container is also conceivable, but this method has a problem that the foaming agent is wasted a lot.

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have found that even if the amount of foaming agent used is the minimum necessary, the amount of foaming agent between the foaming apparatuses can be improved by adding a slight improvement to the currently used apparatus. The inventors have found a method capable of efficiently and easily obtaining expanded beads having a uniform expansion ratio, and completed the present invention.

[0011]

That is, the method for producing expanded synthetic resin particles of the present invention is to disperse synthetic resin particles in a dispersion medium in a closed container and introduce a foaming agent into the closed container to heat the mixture. The synthetic resin particles dispersed in the dispersion medium are impregnated with the foaming agent in the gas phase in the closed container, and then the synthetic resin particles and the dispersion medium are simultaneously discharged outside the container to foam the resin particles. In the method, the gas phase containing the foaming agent is forcibly circulated in the dispersion medium at least immediately before the resin particles and the dispersion medium are discharged to the outside of the container.

In the method of the present invention, a preferred mode for forcibly circulating the gas phase in the closed container is to use a pump.

As the base resin of the synthetic resin particles used in the present invention, polyethylene resin such as low density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, propylene-ethylene random copolymer, propylene- Propylene resin such as ethylene block copolymer, propylene-butene random copolymer, propylene-ethylene-butene random copolymer, polystyrene, polyparamethylstyrene, styrene-maleic anhydride copolymer, styrene-acrylonitrile copolymer Examples thereof include styrene resins such as polymer, styrene-butadiene copolymer, styrene-acrylonitrile-butadiene copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer.

As the dispersion medium for dispersing the synthetic resin particles in the closed container, any dispersion medium which does not dissolve the synthetic resin particles may be used. As such a dispersion medium, for example,
Water, ethylene glycol, glycerin, methanol, ethanol and the like can be mentioned, but water is usually used.

The mixing ratio of the resin particles to the dispersion medium is preferably 150 to 500 parts by weight per 100 parts by weight of the resin particles in order to enhance the stirring efficiency of the resin particles. The occupancy rate of the liquid phase volume (the sum of the volume of the dispersion medium and the volume of the resin particles and other additives) with respect to the internal volume of the closed container is 60 to 9
5% is preferable.

In the method of the present invention, if necessary, in addition to the resin particles, a fusion preventing agent for preventing fusion of the resin particles can be added to the dispersion medium. The anti-fusion agent is
Organic or inorganic materials can be used as long as they do not dissolve in the dispersion medium and do not melt by heating, but inorganic materials are generally preferred. Examples of the inorganic anti-fusing agent include aluminum oxide, titanium oxide, aluminum hydroxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, tricalcium phosphate, magnesium pyrophosphate, talc, kaolin, clay and the like. To be

The anti-fusing agent has a particle size of 0.001 to 100 μm,
Particularly, those having a thickness of 0.001 to 30 μm are preferable. The amount of the anti-fusing agent added is usually preferably 0.01 to 10 parts by weight per 100 parts by weight of the resin particles.

The above-mentioned inorganic anti-fusing agent is preferably used in combination with an emulsifier. As the emulsifier, anionic surfactants such as sodium dodecylbenzene sulfonate, sodium α-olefin sulfonate, sodium alkyl sulfonate and sodium oleate are suitable. The emulsifier is usually 0.00 per 100 parts by weight of the resin particles.
It is preferable to add 1 to 5 parts by weight.

In the present invention, as the foaming agent, a volatile foaming agent and an inorganic gas type foaming agent may be used alone or in combination, or a mixture of the volatile foaming agent and the inorganic gas type foaming agent may be used. it can.

As the volatile foaming agent, for example, propane,
Aliphatic hydrocarbons such as butane, pentane, hexane, heptane, cycloaliphatic hydrocarbons such as cyclobutane, cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride, methylene Examples thereof include halogenated hydrocarbons such as chloride. As the inorganic gas type foaming agent, nitrogen, carbon dioxide, argon, air or the like can be used.

The amount of the foaming agent added varies depending on the type of resin particles and the foaming agent, the target expansion ratio, etc., but is generally 5
The amount of the foaming agent required to obtain about 60 times as many foamed particles varies depending on the type of the foaming agent used, but the resin particles
It is about 2 to 50 parts by weight per 00 parts by weight.

In the method of the present invention, the resin particles are dispersed in the dispersion medium in a closed container, the foaming agent is supplied into the container, and the contents of the container are agitated under heating to form the foaming agent in the resin particles. After impregnating, the resin particles and the dispersion medium are foamed by releasing the resin particles under a low pressure from the container, usually under atmospheric pressure, but in the method of the present invention, at least the resin in this step is used. The gas phase containing the foaming agent is forcibly circulated in the dispersion medium until just before the particles and the dispersion medium are discharged from the container.

A pump is preferably used to forcibly circulate the gas phase containing the blowing agent through the dispersion medium, for example, the gas phase in the container and the dispersion medium phase (preferably the bottom of the container) are piped. It is possible to employ a method in which the gas phase is circulated in the dispersion medium by a pump through this pipe. The gas phase circulation can be selected at any time. The circulation may be started from the beginning of stirring, or the circulation may be started after the temperature of the contents of the container reaches the softening point of the resin particles. If you circulate for several tens of seconds to several minutes just before the start of foaming, generally good results are obtained. The circulation amount of the gas phase varies depending on the volume of the closed container used and the like, but it is preferable that the volume of the gas phase in the closed container is circulated at a rate within 2 minutes.

The heating temperature when stirring the contents of the container in a closed container while heating is the temperature at which the resin particles can foam when depressurized. For example, non-crosslinked polyolefin resin particles can be used. If used, the melting point of the resin -1
An arbitrary temperature of about 5 ° C. to the melting point + 15 ° C. is selected.

According to the method of the present invention, a uniform amount of the foaming agent can be efficiently impregnated into the resin particles by stirring for a short time without using an unnecessarily large amount of the foaming agent. For example, using a closed container having an internal volume of 400 liters, the base resin of the resin particles is propylene-ethylene random copolymer,
When the foaming agent is carbon dioxide, when foaming is carried out under the condition that the stirring and holding time is about 15 minutes, it is attempted to obtain foamed particles having an expansion ratio of 32 times. In the conventional method, the foaming agent is added per 100 parts by weight of the resin particles. Although 9 to 10 parts by weight was required, in the method of the present invention, the amount of the foaming agent used is about 8 parts by weight per 100 parts by weight of the resin particles.

[0026]

EXAMPLES The present invention will be described in more detail with reference to examples.

Examples 1 to 4, Comparative Examples 1 to 4 Per 100 parts by weight of the resin particles shown in Table 1, 0.3 parts by weight of a foaming agent and a dispersant (kaolin) shown in Table 1, a surfactant (dodecylbenzenesulfone) Acid soda) 0.002 parts by weight together with 300 parts by weight of water were charged into a closed container shown in Table 1 (liquid phase occupancy rate 80% by volume), and resin particles, a foaming agent, a dispersant, etc. were stirred in the closed container. Was dispersed in water, the temperature was raised to the foaming temperature shown in the same table with stirring, and then the mixture was maintained at the same temperature for 15 minutes with stirring. In each example, the gas phase in the closed container was forcibly circulated in the dispersion medium by the pump of 80 liters / minute during the 10 minutes before the start of the temperature maintenance, but in the comparative example, the gas phase was circulated. Did not do. Next, while introducing high-pressure carbon dioxide into the container, one end of the container was opened at the same temperature, and water and resin particles in the container were released under atmospheric pressure to foam the resin particles. After drying the obtained expanded particles, the average expansion ratio was measured for each expanded particle obtained in each container. The results are shown in Table 1.

[0028]

[Table 1]

[0029]

As described above, according to the conventional method, even when foaming is performed under the same foaming condition, due to the difference in the foaming device,
Although there were variations in the expansion ratio of the obtained expanded beads, in the method of the present invention, expanded particles having a small difference in expansion ratio can be easily obtained by performing expansion under the same expansion conditions even if the expansion device is different. Further, without using an unnecessarily large amount of foaming agent, it is possible to obtain foamed particles having an expansion ratio equivalent to that of the conventional method in a shorter time than the conventional method, reducing the raw material cost of the foaming agent and expanding the foamed particles. It is possible to shorten the time of one cycle in manufacturing. Further, the method of the present invention can be easily carried out by simply modifying the conventional device, so that there is an advantage that the conventional device can be used as it is.

Claims (2)

[Claims] 1. A synthetic resin particle is dispersed in a dispersion medium in a closed container, and a foaming agent is introduced into the closed container and stirred under heating to disperse the foaming agent in the gas phase in the closed container. In a method of impregnating synthetic resin particles dispersed in a medium, and then simultaneously discharging the synthetic resin particles and the dispersion medium outside the container to foam the resin particles, at least the resin particles and the dispersion medium are discharged outside the container. A method for producing expanded beads of synthetic resin, characterized in that a gas phase containing a blowing agent is forcibly circulated in a dispersion medium until immediately before. 2. The method for producing expanded synthetic resin particles according to claim 1, wherein the gas phase in the closed container is forcibly circulated in the dispersion medium by a pump.