JPH0464541B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing pre-expanded particles. In-mold foam molded products obtained by filling pre-expanded particles into a mold and heating and foaming them have recently been used in a wide range of applications such as insulation, cushioning, packaging, construction materials, flotation materials, etc. . The present inventors have conducted research for many years on the pre-expanded particles used in the molding of the above-mentioned in-mold foamed product, and as a result, we have developed a novel method that can easily and reliably produce excellent pre-expanded particles with uniform bubbles. They succeeded in developing a manufacturing method and completed the present invention. That is, in the present invention, resin particles containing a substantially undecomposed decomposable blowing agent are dispersed in a dispersion medium in a closed container, heated and held at a temperature equal to or higher than the decomposition temperature of the decomposable blowing agent for a predetermined period of time, and an inorganic gas is The gist of the present invention is a method for producing pre-expanded particles, which is characterized by pressurizing the inside of the container while opening one end of the container and releasing the resin particles from the inside of the container into a lower pressure atmosphere to cause foaming. The base material of the resin particles used in the present invention includes styrene homopolymer, styrene-based resin such as styrene-maleic anhydride copolymer, styrene-acrylonitrile copolymer, styrene-acrylonitrile-butadiene copolymer, and ethylene monopolymer. Examples include polyolefins such as polymers, propylene homopolymers, ethylene-propylene block copolymers, and ethylene-propylene random copolymers, among which polyolefins are preferred, with low-density polyethylene and ethylene-propylene random copolymers being particularly preferred. These may be either crosslinked or non-crosslinked, but non-crosslinked ones are preferred. Examples of decomposable blowing agents used in the present invention include azodicarbonamide, dinitrosopentamethylenetetramine, diazoaminobenzene, azobisisobutyronitrile, P,P'-oxybisbenzenesulfonyl hydrazide, and sodium bicarbonate. These decomposable blowing agents can be used alone or in combination of two or more.
It is preferable to select and use a resin particle whose decomposition temperature is 5° C. or higher, preferably 10 to 100° C. higher than the melting point of the base material of the resin particles. The decomposition medium in the present invention may be any solvent that does not dissolve the resin, and examples include one or a mixture of two or more of water, ethylene glycol, glycerin, methanol, ethanol, etc.
Usually water is used. In addition, when dispersing resin particles in a dispersion medium, fine particles of aluminum oxide, titanium oxide, basic magnesium carbonate,
A dispersant such as basic zinc carbonate or calcium carbonate can be added, and the amount of the dispersant is usually 0.1 to 10 parts by weight per 100 parts by weight of the resin particles. The heating temperature of the resin particles is not particularly limited as long as it is higher than the decomposition temperature of the decomposable blowing agent, but usually T+10°C to T+, where the decomposition temperature of the decomposable blowing agent is T (°C).
The temperature is preferably 100°C, and the heating holding time is usually about 5 to 120 minutes. The resin particles containing the substantially undecomposed decomposable blowing agent can be obtained by, for example, melting and kneading the resin and the decomposable blowing agent in an extruder at a temperature below the decomposition temperature of the decomposable blowing agent, and then extruding the resin particles from the extruder as appropriate. It can be obtained by cutting into pieces of size, or by impregnating a liquid decomposable foaming agent into resin particles in the presence of a dispersion medium in a closed container. In the present invention, the resin particles are heated and held in a closed container at a temperature higher than the decomposition temperature of the decomposable blowing agent for a predetermined period of time, and one end of the container is opened while the inside of the container is pressurized with an inorganic gas to lower the pressure from the inside of the container. The inorganic gas at this time includes oxygen, nitrogen, helium, neon, carbon dioxide, air, etc., and these can be used in combination. In addition, pressurization pressure using inorganic gas is usually
The pressure is 10Kg/cm ² (G) or more, preferably 25 to 40Kg/cm ² (G), and after maintaining the pressure for a predetermined period of time (usually 5 minutes or more), the pressure is maintained (that is, while replenishing the inorganic gas) in the container. One end is opened to allow the particles to foam. As described above, the resin particles are foamed by discharging the resin particles from the inside of the container into a lower pressure atmosphere (usually under atmospheric pressure), and pre-expanded particles having an expansion ratio of 2 to 40 times are usually obtained. As explained above, according to the present invention, it is possible to easily and reliably produce pre-expanded particles, and since resin particles containing a substantially undecomposed decomposable blowing agent are used, the blowing agent is uniformly dispersed in the resin particles. As a result, the pre-expanded particles produced according to the present invention have excellent physical properties such as uniform cells and fine cell texture, and are suitable for molding in-mold foamed products. Further, according to the manufacturing method of the present invention, since resin particles containing a substantially undecomposed decomposable blowing agent are used, the resin particles are heated and maintained at a temperature higher than the decomposition temperature of the blowing agent, and the shape of the resin particles is changed. This has the effect of obtaining foamed particles that are formed into a spherical shape close to a true sphere and have good moldability. Furthermore, since the present invention uses a decomposable blowing agent, when the blowing agent decomposes, nitrogen gas, carbon dioxide gas, water vapor, etc. are generated, but these gases are not combustible gases such as those found in volatile blowing agents. It is possible to provide a method for producing pre-expanded particles that is safe and does not pollute the environment, without problems such as air pollution caused by fluorocarbon gas or other dangers. Hereinafter, the present invention will be explained in more detail with reference to Examples. Examples 1 to 3 To 100 parts by weight of the resin shown in Table 1, the decomposable foaming agent shown in the same table was added, melted and kneaded in an extruder, extruded from the extruder, cut, and rapidly cooled to substantially Resin particles containing an undecomposed decomposable blowing agent were obtained. 100 parts by weight of these resin particles were supplied into an autoclave together with 300 parts by weight of water and 1 part by weight of finely divided aluminum oxide, heated at the temperature shown in Table 1 for the time shown in the same table, and then pressurized with air and held there. Adjust the foaming temperature, increase the pressure inside the container with air, hold it for the time shown in the same table, then open one end of the container while maintaining the pressure shown in the same table to release the resin particles under atmospheric pressure and foam. Pre-expanded particles were obtained. The properties of the obtained pre-expanded particles are also shown in Table 1.

[Table] *1 Pre-expanded particles were cut and the state of bubbles on the cut surface was observed using a microscope.

Claims (1)

[Claims] 1. Resin particles containing a substantially undecomposed decomposable blowing agent are dispersed in a dispersion medium in a closed container, heated and held at a temperature higher than the decomposition temperature of the decomposable blowing agent for a predetermined period of time, and the inside of the container is heated with an inorganic gas. 1. A method for producing pre-expanded particles, which comprises: opening one end of the container while pressurizing the resin particles, and releasing the resin particles from inside the container into a low-pressure atmosphere to cause foaming.