Abstract: A process for the production of expanded resin particles is disclosed, wherein an aqueous dispersion containing expandable particles of a polyolefin resin is discharged at a temperature higher than the softening point of the resin from a high pressure condition to a low pressure condition to expand the expandable particles and wherein the expandable particles contain fine particles of an inorganic material coated with an agent selected from isopropyltriisostearic titanate, tetraoctadecyl titanate, acetoalkoxyaluminum diisopropylates, stearic acid, methyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, phenyltriethoxysilane and vinyltriethoxysilane.

Abstract: Pre-foamed particles of an uncrosslinked, linear low-density polyethylene have a crystalline structure characterized in that two endothermic peaks appear on a DSC curve obtained by differential scanning calorimetry of the pre-foamed particles (said DSC curve having been obtained by heating 1-5 mg of the pre-foamed particles to 220.degree. C. at a rate of 10.degree. C./min by a differential scanning calorimeter) and the energy at the endothermic peak on the higher-temperature side is 5 J/g or more. A process for the production of the pre-foamed particles of the uncrosslinked, linear low-density polyethylene is also disclosed.

Abstract: Pre-formed particles of an uncrosslinked, linear low-density polyethylene have a crystalline structure characterized in that two endothermic peaks appear on a DSC curve obtained by differential scanning calorimetry of the pre-foamed particles (said DSC curve having been obtained by heating 1-5 mg of the pre-foamed particles to 220.degree. C. at a rate of 10.degree. C./min by a differential scanning calorimeter) and the energy at the endothermic peak on the higher-temperature side is 5 J/g or more. A process for the production of the pre-foamed particles of the uncrosslinked, linear low-density polyethylene is also disclosed.

Abstract: Expanded particles obtained by a method including the steps of: providing unexpanded particles formed of a polyethylene resin; impregnating the unexpanded particles with a liquid containing a polymerizable monomer including an acrylic monomer, and optionally a styrenic monomer; subjecting the impregnated polymerizable monomer to polymerization conditions so that at least a portion of the polymerizable monomer is grafted on the polyethylene resin to obtain modified polyethylene particles; and subjecting the modified polyethylene particles to an expansion treatment. Further expansion of the expanded particles within a mold gives a foamed article suitable for use as a consumable pattern in full mold casting.

Abstract: A consumable pattern of an expanded polyolefin resin and a bulk density of 0.025-0.012 g/cm.sup.3 is embedded in a mold body, a gating system leading to the pattern is formed in the mold body, and molten metal is poured into the gating system to volatilize and replace the pattern. The polyolefin resin is selected from noncrosslinked polypropylene resins, crosslinked polypropylene resins, crosslinked high-density polyethylene and mixtures thereof.

Abstract: An energy absorber suitable for use as a bumper core or the like is formed of an expansion-molded article of prefoamed particles. The prefoamed particles use, as the base resin thereof, a resin obtained by impregnating high-density polyethylene with an aromatic vinyl monomer and polymerizing the monomer. The absorber has a density (.rho.) of 0.015-0.15 g/cm.sup.3 and satisfies the following relation:E.sub.20 /.rho..gtoreq.45 kg.multidot.cm/gwherein E.sub.20 (kg.multidot.cm/cm.sup.3) means the quantity of energy absorbed upon 70% compression at 20.degree. C. and .rho. has the same meaning as defined above.