Abstract: A thermoplastic resin having a Vicat softening point of 115.degree. C. or higher and containing a blowing agent is extruded and foamed into a foamed tubular body. The foamed tubular body is subjected to biaxial orientation and then pressed in antipodal directions, whereby the foamed tubular body is flattened and fusion-bonded at the resultant mutually-opposing inner walls thereof to obtain a foamed base material suitable for use in the fabrication of a car ceiling member. The foamed base material has not only excellent mechanical strength but also superb thermal strength. The foamed base material is not required to laminate films, sheets or the like thereon and is hence provided at a low cost.

Abstract: Pre-foamed particles are produced by dispersing resin particles, which contain nucleocells, in a dispersing medium in a closed vessel, heating the contents to a temperature of the softening point of the particles or higher and holding the contents at the temperature for a predetermined period of time while pressurizing the contents with an inorganic gas, and then opening the vessel at one end thereof so as to release the particles and medium into an atmosphere of a pressure lower than the internal pressure of the vessel, thereby causing the resin particles to foam. The above production process provides good pre-foamed particles with ease and without failure. It is also possible to avoid deleterious effects due to the swelling action of foaming agents.

Abstract: An apparatus is provided for the heat treatment of polyolefin resin particles. The apparatus is equipped with an autoclave in which the particles are heated and agitated in the presence of an aqueous medium and dispersing agent. The autoclave has a tilted bottom wall portion, over which an impeller, preferably, a turbine-type impeller is provided.

Abstract: A process is disclosed for the production of expanded particles of polymeric material wherein unexpanded particles of the material are contacted with a nitrogen-containing inorganic gas under a first pressure condition to impregnate the particles with the gas. The gas impregnated particles are heated to a temperature higher than the softening point of the material, and dispersed into a liquid medium. The resulting dispersion is subjected to a lower pressure to expand the particles. The expanded particles may be used as prefoamed particles for the molding of foamed articles.

Abstract: A sheet of a cross-linkable and foamable polyolefin resin is thermally treated on an endless conveyor belt formed of a plain weave wire net. A plurality of parallel, spaced apart rolls are disposed in a direction perpendicular to the direction in which the conveyor belt runs for supporting engagement and rolling contact with the conveyor belt to maintain the flatness of the conveyor belt.