Abstract: An object of the present invention is to provide an inmold foaming method of a polyolefin based resin foamed article, wherein a pre-foamed particle having a large bulk density, which could be molded only by an impregnation method based on conventional technology having defect of expensive plant-and-equipment investment expense, may be molded using a compression filling molding method advantageous in productivity and plant-and-equipment investment expense, and thereby a charging ratio and surface appearance of the foamed article to be obtained may also be improved.

Abstract: Pre-expanded particles of polyolefin resin having less fluctuation in expansion ratio, uniform particle size and low expansion ratio are provided without using any volatile foaming agent. The low expansion ratio means 2 to 10 times, preferably 3 to 8 times. Resin particles to be released are uniformly contacted with saturated vapor at the time of pre-expanding polyolefin resin particles by dispersing the resin particles into an aqueous dispersion medium in a closed vessel, heating the resin particles to temperature of at least the softening point of the polyolefin resin and releasing the particles from the closed vessel into an atmosphere of lower pressure than the inner pressure of the closed vessel.

Abstract: A water-containing polyolefin resin composition containing a polyolefin resin and a hydrophilic polymer and having a water content of 1 to 50% by weight which is suitable for use in preparation of polyolefin resin pre-expanded particles, and pre-expanded particles of a polyolefin resin prepared by pre-expanding the water-containing polyolefin resin composition the particles having a an apparent expansion ratio of 5 to 60, a closed cell ratio of 80 to 100% and an average cell diameter of 50 to 500 &mgr;m.

Abstract: To provide a process for preparing polyolefin resin pre-expanded particles which enables to prepare pre-expanded particles having lower fluctuation in expansion ratios. Polyolefin resin pre-expanded particles are prepared by a process comprising steps of dispersing polyolefin resin particles into an aqueous dispersion medium in an autoclave; heating the resin particles to temperature of at least the softening point of the polyolefin resin and pressuring the same; releasing said resin particles from the autoclave through a release port into an atmosphere of lower pressure than the inner pressure of the autoclave; thereby pre-expanding the resin particles, wherein at the releasing step, the resulting pre-expanded particles are contacted with gas of at least 60° C. and collided with a collision board or a container wall disposed at a distance of 5 mm<D, D representing the distance from the release port to the collision board or the container wall.

Abstract: A process for preparing pre-expanded particles of a thermoplastic resin without washing the prepared pre-expanded particles to remove a dispersing agent remaining thereon and without discharging waste water, which comprises charging particles of a thermoplastic resin and an aqueous dispersion medium containing a dispersing agent into a closed pressure vessel, heating the resulting aqueous dispersion to a temperature of not less than the softening point of the thermoplastic resin, thereby impregnating the particles with water to have a water content of 1 to 50% by weight, releasing the dispersion into a lower pressure atmosphere, thereby expanding the particles, recovering the dispersion medium containing the dispersing agent, and recycling it as a dispersion medium to the pressure vessel.

Abstract: To provide a process for preparing polyolefin resin pre-expanded particles which enables to prepare pre-expanded particles having lower fluctuation in expansion ratios. Polyolefin resin pre-expanded particles are prepared by a process comprising steps of dispersing polyolefin resin particles into an aqueous dispersion medium in an autoclave; heating the resin particles to temperature of at least the softening point of the polyolefin resin and pressuring the same; releasing said resin particles from the autoclave through a release port into an atmosphere of lower pressure than the inner pressure of the autoclave; thereby pre-expanding the resin particles, wherein at the releasing step, the resulting pre-expanded particles are contacted with gas of at least 60° C. and collided with a collision board or a container wall disposed at a distance of 5 mm<D, D representing the distance from the release port to the collision board or the container wall.

Abstract: Pre-expanded particles of polyolefin resin having less fluctuation in expansion ratio, uniform particle size and low expansion ratio are provided without using any volatile foaming agent. The low expansion ratio means 2 to 10 times, preferably 3 to 8 times. Resin particles to be released are uniformly contacted with saturated vapor at the time of pre-expanding polyolefin resin particles by dispersing the resin particles into an aqueous dispersion medium in a closed vessel, heating the resin particles to temperature of at least the softening point of the polyolefin resin and releasing the particles from the closed vessel into an atmosphere of lower pressure than the inner pressure of the closed vessel.

Abstract: There is provided pre-expanded particles of a propylene resin having a high expansion ratio and excellent molding adhesion without using a volatile blowing agent or increasing an expansion pressure. The pre-expanded particles of a propylene resin are prepared by the process comprising dispersing resin particles comprising a propylene resin composition, which contains 100 parts by weight of (A) a random copolymer of ethylene and propylene having an ethylene content of 1.5 to 4.5% by weight and 0.

Abstract: There is provided pre-expanded particles of a propylene resin having a high expansion ratio and excellent molding adhesion without using a volatile blowing agent or increasing an expansion pressure. The pre-expanded particles of a propylene resin are prepared by the process comprising dispersing resin particles comprising a propylene resin composition, which contains 100 parts by weight of (A) a random copolymer of ethylene and propylene having an ethylene content of 1.5 to 4.5% by weight and 0.

Abstract: Post-treatment method of polyolefin resin pre-expanded particles comprising: introducing the polyolefin resin pre-expanded particles foamed by using an inflammable blowing agent into an extraction vessel filled with steam previously; feeding an additional steam into the extraction vessel; extracting the inflammable blowing agent gas from the polyolefin resin pre-expanded particles; discharging the resulting steam which contains the extracted inflammable blowing agent gas from the extraction vessel continuously or intermittently; and liquefying the steam to separate and recover the inflammable blowing agent gas. According to the post-treatment method of polyolefin resin pre-expanded particles, the inflammable blowing agent can be extracted from the pre-expanded particles in a short period of time and the extracted inflammable blowing agent can be re-used.

Abstract: A process for post-treating pre-expanded polyolefin resin particles which comprises charging in a vessel pre-expanded polyolefin resin particles which are pre-expanded by using an inflammable blowing agent, supplying an inert gas into the vessel, and then discharging the inert gas with the inflammable blowing agent gas extracted from the pre-expanded polyolefin resin particles, from the vessel. According to the process of the invention, the inflammable blowing agent can be extracted efficiently, safely and in a short time from the pre-expanded polyolefin resin particles which are pre-expanded by using the inflammable blowing agent. Consequently, the spontaneous cambustion of the particles can be completely avoided even if sparks are generated on the surface of the pre-expanded particles, therefore, it becomes easy to handle the pre-expanded polyolefin resin particles because the particles can be dried and transported by a pneumatic conveyer.

Abstract: 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.

Abstract: 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.