JPH0488035A - Production of pre-expanded particle - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing pre-expanded synthetic resin particles, and in particular, to a method for producing pre-expanded synthetic resin particles, in particular a pre-expanded method that allows control of the expansion ratio without variation in the expansion ratio between foamed particles. The present invention relates to a method for producing particles.

[Conventional technology]

Conventionally, when manufacturing foamed resin molded products, the molded product is usually produced by pre-foaming the raw resin particles at a certain magnification in advance, and then charging the pre-expanded particles into a mold and foaming them to the final magnification. It is common to manufacture

For this pre-foaming, for example, foamable polymer particles are continuously fed into the lower part of a cylindrical container equipped with a rotary stirring device while a constant flow of steam is fed into the bottom of the cylindrical container, and the foamed beads are foamed and lightened. There is a method of overflowing from the top and taking it out to obtain continuously pre-foamed particles. In addition, instead of the continuous method, there is also a patch-type pre-foaming method in which a certain amount of foamable polymer particles are placed in a cylindrical container equipped with a rotating stirring device, heated steam is blown into the container to cause foaming, and then the product is removed from one end of the container. Are known. Furthermore, a method of heating and foaming expandable particles with an infrared heater is also known. Furthermore, after enclosing the foamable resin particles in a device that can pressurize heated gas into a closed container, heated gas is pressurized into the container from the valve side at the bottom, and the temperature inside the container is raised to the foaming temperature while stirring. After that, there is a method in which the pressure-resistant container is opened (for example, the upper valve is opened) to reduce the internal pressure of the container to atmospheric pressure to promote foaming and obtain expanded particles. (Japanese Patent Publication No. 56-1344) [Problems to be Solved by the Invention] However, although the method of foaming by introducing water vapor can be applied to polystyrene polymer particles, it cannot be applied to foamable ethylene polymer particles. Even when applied, particles with a high softening temperature will not foam, and even if foamed, the particles tend to fuse together and form large clumps during the pre-foaming process, and once foamed particles are overheated, they may wither. It is very difficult to control pre-foaming, as it can lead to foaming. Furthermore, when a method using infrared heating is applied to a foamable ethylene polymer, the particles tend to fuse together during the pre-foaming process, making it impossible to obtain a good granular foam on an industrial scale.

Furthermore, the above-mentioned release foaming method is suitable for foaming polystyrene resin particles because the foaming agent in the resin dissipates slowly, the resin has excellent thermal stability, and has a stable foaming temperature over a wide temperature range. However, if these methods are applied directly to polyolefin resin particles, there are the following drawbacks.

○There are variations in magnification among foam particles.

○ Difficult to control foaming ratio.

○ Due to explosive foaming, the cell membrane is likely to break and become open cells.

The present invention solves the above-mentioned problems in foaming olefin resin particles, and provides a method for producing pre-expanded particles that have uniform closed cells, a beautiful surface, and extremely little variation between particles. The purpose is

[Means to solve the problem]

In order to achieve the above object, the present inventors have conducted intensive research and found that by removing only the gaseous blowing agent from the container at a constant rate from the high temperature and high pressure conditions of the conventional method, the expansion ratio and the air bubbles can be improved. The present invention was completed based on the discovery that it is possible to control the

That is, in the production of pre-expanded particles of the present invention, (dispersion medium + resin) is not released from high temperature and high pressure, but after completion of gas impregnation into the particles, degassing is performed at the appropriate temperature for foaming, and the pressure is reduced to foam (the same (gas impregnation and foaming are performed in the container).

[For production]

The structure and operation of the present invention will be explained.

The polyolefin resins targeted by the present invention, particularly polypropylene, polyethylene, etc., have a property that gas as a blowing agent easily penetrates into them, but on the other hand, the gas easily escapes. In consideration of this point, in the conventional discharge foaming method, the internal pressure changes at the beginning and end of discharge from the pressure container, and therefore the expansion ratio also changes, making it impossible to obtain uniform foamed particles.

However, in the present invention, in the step of charging the resin and foaming agent in a pressure-resistant container and heating to a softening temperature for impregnation, the impregnation temperature is 10'C to +50' above the melting point in the case of a crystalline resin such as a polyolefin resin. In the case of non-grade resins such as C, polystyrene resins, the softening temperature is +10 to +70''C1 impregnation pressure is 5 kg/crd to 100 kg/ct.

(10 kg/cnf to 50 kg/cnr), then in the step of removing the blowing agent and foaming under reduced pressure, the decompression rate is set to 10 kg/cnf/sec to 1 kg/cnr/min, preferably 5 kg/cnr/min. Foaming is performed under conditions of seconds to 5 kg/crl/min. The variation in magnification among expanded particles is uniform over all resin particles because the pressure is reduced within the same container. In addition, the expansion ratio can be controlled by the degassing speed, and since the decompression speed is slow, it is difficult for bubbles to burst or open cells to form.

〔Example〕

Although the present invention will be described in detail, the present invention is not limited thereto.

Examples 1 to 9 100 parts by weight of propylene-ethylene random copolymer,
400 parts by weight of water, 5 parts of magnesium pyrophosphate produced by metathesis
Part by weight, sodium dodecylbenzenesulfonate 0.05
Stir parts by weight of crepe (5,.

200 parts by weight of Freon 1 while stirring.
2 (dichlorodifluoromethane), and after sealing, the temperature was raised to the temperature shown in Table 1. After raising the temperature, maintain this temperature for 3 hours, then reduce the pressure from the initial pressure shown in Table 1 to to, Okg/cnf at the pressure reduction rate shown in Table 1 while stirring, and then cool to 30°C. After removing the residual pressure, the pre-expanded grains were taken out. The bulk ratio of the pre-expanded grains was as shown in Table 1, and the grains had uniform and fine bubbles.

Comparative Examples 1 to 3 For the same formulations as in the examples, impregnation temperature, pressure reduction rate,
The test was carried out by changing the final pressure. The results are shown in Table 1.

(Margins below this page) Comparative Example 1 had an extremely low decompression rate (0.8 kg/cI
Tr/min), the bubbles were very small and did not result in foaming. In addition, Comparative Example 2 was released foaming (final pressure Okg/c
o? ), and there was a large variation in bubble damage. In Comparative Example 3, the impregnation temperature was lower than the melting point of the raw material polymer (135
°C) Since it was lower than -10 °C, almost no foaming occurred.

Reference Example The pre-expanded grains obtained by the methods of Examples 2 and 4.7 and Comparative Examples 1 and 2.3 were dried and left at room temperature, and then heated to 2.5 k
Steam heating of g/cr& was performed for 20 seconds and the foaming bulk ratio was measured. The results are shown in Table 2.

(Margins below this page) Table 2 [Effects of the Invention] Since the present invention is configured as explained above, the obtained pre-expanded particles are obtained by performing a slow cooling section after foaming, compared to the discharge foaming. It produces remarkable effects such as increased crystallinity, improved retention of foaming gas, and increased physical strength.
It is extremely useful in industry.

Claims (1)

[Scope of Claims] 1. A first step of charging resin particles to be foamed and a foaming agent into a pressure-resistant container and impregnating them with the foaming agent by heating the resin to a temperature higher than the temperature at which the resin softens or melts; and a pressure-resistant container. A method for producing pre-expanded particles, comprising a second step of removing a gaseous blowing agent from the container at a predetermined rate, reducing the pressure inside the container, and foaming the resin particles. 2. The removal rate (decompression rate) of gaseous foaming agent is 10 kg/
2. The method for producing pre-expanded particles according to claim 1, wherein the rate is cm^2/sec to 1 kg/cm^2/min.