Kanegafuchi Kagaku Kogyo Kabushiki Kaisha

Hirofumi Maeda

Kyoichi Nakamura

Kenichi Senda

Naruhiko Akamatsu

Masao Ando

Hisatoshi Fukui

Toshihiro Hatamoto

Tadayuki Ichimura

Kazuyoshi Watanabe

Shunichi Nishioka

A pre-expanded particle of a non-crosslinked linear low density polyethylene having an average cell diameter as large as 120 to 1,200 .mu.m which can be molded, without further imparting an expandability prior to molding or without aging under pressure, by heating in a closed mold permeable to a fluid heating medium such as steam to form a well bonded unitary cellular molded article having a good appearance, a high expansion ratio and improved heat resistance and mechanical property with a slight volumetric shrinkage.

Pre-expanded particles of non-crosslinked linear low density polyethylene

The present invention provides a process for production of expansion-molded articles in a mold of a linear low density polyethylene resin which comprises compressing pre-expanded linear low density polyethylene resin beads having two melting points when measured by differential scanning calorimetry and, when the melting point at a low temperature side and the melting point at a high temperature side are designated T.sub.ML and T.sub.MH respectively, between said two melting points and the peak fusion area at said T.sub.ML is designated A.sub.L and the peak fusion area at said T.sub.MH is designated A.sub.H satisfying:

Process for production of expansion-molded articles in a mold of linear

The present invention provides that, in a process for production of foamed articles of a polyproplene resin which comprises compressing pre-expanded beads of propylene resins under a gaseous pressure, filling a mold capable of closing but incapable of sealing with the compressed beads, then venting from the mold and heating and fusing with steam thereby to produce the molded article in the shape of the mold, the improvement wherein the pre-expanded beads of the polypropylene resins having two melting points when measured by differential scanning calorimetry and having a quantity of the peak fusion heat QH based on a melting point at a high temperature peak of the two melting points being 0.3 to 3.5 cal/g are introduced compressively into the mold so that a compressive rate is 10 to 60%. According to the present invention, the foamed articles of polypropylene having a minimized dimensional shrinkage rate (good dimensional accuracy) and excellent fusion rate and surface appearance can be produced in high productivity.

Process for production of foamed articles in mold of polypropylene resins

A process for preparing pre-expanded particles of a thermoplastic resin, which comprises heating an aqueous dispersion of thermoplastic resin particles containing a volatile blowing agent to a high temperature under pressure in a pressure vessel, and releasing the dispersion into an atmosphere maintained at a lower pressure than the pressure in the pressure vessel and at a temperature of not lower than 40.degree. C. According to the process of the present invention, there can be obtained pre-expanded thermoplastic resin particles with a large average diameter of cells. By molding the pre-expanded particles obtained by the present invention, molded articles which are small in dimensional shrinkage and excellent in surface appearance can be obtained without imparting expandability to the particles or aging the particles under pressure prior to molding.

Process for preparing pre-expanded particles of thermoplastic resin

A process and apparatus for preparing pre-expanded particles of a thermoplastic resin which comprises; heating under an elevated pressure an aqueous dispersion comprising thermoplastic resin particles containing a volatile foaming agent and an aqueous medium in a pressure vessel; releasing the dispersion from the pressure vessel into a space within a sealed low-pressure vessel wherein the pressure is lower than that in the pressure vessel, whereby expanding the thermoplastic resin particles to give pre-expanded particles; and simultaneously recovering the foaming agent volatilized from the thermoplastic resin particles by discharging the foaming agent out of the space in the low-pressure vessel with controlling the pressure in the low-pressure vessel to substantially a given pressure. According to the process, the release of the volatile foaming agent into the air is prevented.

Apparatus for preparing pre-expanded thermoplastic resins

A process and apparatus for preparing pre-expanded particles of a thermoplastic resin which comprises; heating under an elevated pressure an aqueous dispersion comprising thermoplastic resin particles containing a volatile foaming agent and an aqueous medium in a pressure vessel; releasing the dispersion from the pressure vessel into a space within a sealed low-pressure vessel wherein the pressure is lower than that in the pressure vessel and the space is sealed with an aqueous medium which exists in the lower portion of the vessel and communicates with the outside of the vessel, whereby expanding the thermoplastic resin particles to give pre-expanded particles; and sinking the resulting pre-expanded particles under the aqueous medium by means of a rotary impeller provided in the pressure vessel so that the pre-expanded particles are taken out of the low-pressure vessel through the aqueous medium towards the outside of the vessel, while recovering the foaming agent volatilized from the thermoplastic resin particles by discharging the foaming agent out of the space in the low-pressure vessel with controlling the pressure in the low-pressure vessel to substantially a given pressure. According to the process, the release of the volatile foaming agent in the air is prevented, the productivity is increased and extraneous matters on the pre-expanded particles are removed.

Apparatus for thermoplastic resins pre-expanding process

The present invention provides a method of recovering volatile foaming agent contained in prefoamed beads of polyolefin resin characterized in that the volatile foaming agent contained in the prefoamed beads is recovered by bringing into contact with heated air prefoamed beads obtained by heating polyolefin resin beads containing the volatile foaming agent. According to the invented method it is possible to avoid not only aggravation of the working environments and atmospheric pollution but also risk of explosion etc. and, furthermore, material cost can be saved through reutilization of the recovered volatile foaming agent.

Method of recovering volatile foaming agent from prefoamed beads of

A method for aging an expansion-molded body of polyolefin prepared by heating pre-expanded polyolefin particles within a mold involves cooling the molded body within the mold so that the molded body is not substantially smaller than the volume of the mold cavity and is temporarily expandable after being removed from the mold to not more than 110% relative to the volume in the mold cavity, removing the molded body from the mold, placing the molded body in an atmosphere substantially under atmospheric pressure and having a temperature of 25.degree. to 55.degree. C. lower than the melting point of the polyolefin while the volume of the molded body is 70 to 110% relative to the volume of the mold cavity and holding the molded body in this atmosphere until the temperature of the molded body is at least equal to the temperature of the atmosphere.

Method of aging expansion-molded body of polyolefin

A process for preparing pre-expanded particles of a thermoplastic resin which comprises; heating under an elevated pressure an aqueous dispersion comprising thermoplastic resin particles containing a volatile foaming agent and an aqueous medium in a pressure vessel; releasing the dispersion from the pressure vessel into a space within a sealed low-pressure vessel wherein the pressure is lower than that in the pressure vessel, whereby expanding the thermoplastic resin particles to give pre-expanded particles; and simultaneously recovering the foaming agent volatilized from the thermoplastic resin particles by discharging the foaming agent out of the space in the low-pressure vessel with controlling the pressure in the low-pressure vessel to substantially a given pressure. According to the process, the release of the volatile foaming agent into the air is prevented.

Pre-expanding process and apparatus for the same

A process for preparing pre-expanded particles of a thermoplastic resin which comprises; heating under an elevated pressure an aqueous dispersion comprising thermoplastic resin particles containing a volatile foaming agent and an aqueous medium in a pressure vessel; releasing the dispersion from the pressure vessel into a space within a sealed low-pressure vessel wherein the pressure is lower than that in the pressure vessel and the space is sealed with an aqueous medium which exists in the lower portion of the vessel and communicates with the outside of the vessel, whereby expanding the thermoplastic resin particles to give pre-expanded particles; and sinking the resulting pre-expanded particles under the aqueous medium by means of a rotary impeller provided in the pressure vessel so that the pre-expanded particles are taken out of the low-pressure vessel through the aqueous medium towards the outside of the vessel, while recovering the foaming agent volatilized from the thermoplastic resin particles by discharging the foaming agent out of the space in the low-pressure vessel with controlling the pressure in the low-pressure vessel to substantially a given pressure. According to the process, the release of the volatile foaming agent in the air is prevented, the productivity is increased and extraneous matters on the pre-expanded particles are removed.

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Takatsuki, Japan

Hirofumi Maeda