Abstract: Prefoamed particles consisting essentially of an ethylene/propylene random copolymer, wherein said prefoamed particles are obtained by foaming particles of an ethylene/propylene random copolymer containing 1 to 4% by weight of random-copolymerized ethylene at a temperature in the range of from Tm - 15.degree. C. to Tm - 5.degree. C. (in which Tm is a temperature at which to terminate melting of the copolymer) and within the range of 141.degree. to 151.degree. C., and wherein said prefoamed particles have a crystal structure characterized in that in a DSC curve obtained by heating 1 to 3 mg of the copolymer prefoamed particles to 220.degree. C. at a heating rate of 10.degree. C./min. with a differential scanning calorimeter, there appear a peak (characteristic peak) characteristic of the copolymer and another peak (high temperature peak) at a higher temperature than a temperature at which the characteristic peak appears.

Abstract: An expansion-molded article of a polypropylene resin is produced by filling pre-foamed particles of the polypropylene resin, which have a crystalline structure featuring an inherent peak inherent to the polypropylene resin and a high-temperature peak on the temperature side higher than the temperature corresponding to the inherent peak on a DSC curve obtained by differential scanning calorimetry of the pre-foamed particles and a bulk density of 0.04 g/cm.sup.3 or higher and require melting energy of 8-12 J/g at the high-temperature peak, in a mold without applying any pretreatment to the pre-foamed particles to build up an internal pressure therein, and then heating the pre-foamed particles, whereby the pre-foamed particles are caused to expand into the expansion-molded article conforming with the mold. The pre-foamed particles may alternatively have a bulk density lower than 0.04 g/cm.sup.3 and require melting energy of at least 8 J/g.

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: 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: Prefoamed polypropylene-base particles have a crystalline structure featuring a high-temperature peak appeared on the higher temperature side than the peak inherent to polypropylene-base resins on a DSC curve obtained by differential scanning calorimetry upon heating 1-3 mg of the prefoamed polypropylene-base particles at a constant heating rate of 10.degree. C./min. to 220.degree. C. by means of a differential scanning calorimeter and the internal pressure decreasing velocity coefficient k of the particles is either equal to or smaller than 0.70 (k.ltoreq.0.70) at 25.degree. C. and 1 atm. The prefoamed polypropylene-base particles can be formed into an expansion-molded polypropylene-base article by imparting foamability to the particles, filling the resultant particles in a mold and then heating the particles so as to cause their expansion.

Abstract: Propylene-base random copolymer particles suitable for use in the production of pre-foamed particles are obtained by heating starting copolymer particles of ethylene-propylene random copolymer to the crystallization temperature thereof and then quenching them in a medium at a temperature of (the crystallization temperature-30.degree. C.) or lower. Pre-foamed particles produced using the copolymer particles contain large cells are columnar in shape with an average diameter D of 1.7 mm or less and an L/D.gtoreq.1. They can thus provide foamed moldings which are substantially free of shrinkage and have good flexibility.

Abstract: A process for the production of expanded particles, which comprises providing an aqueous dispersion containing expandable particles which are formed of a polypropylene resin and which contain a blowing agent and an expansion aid and maintained at a temperature higher than the softening point of the resin and under a pressurized condition, and subjecting the dispersion to a lower pressure so that the expandable particles are expanded. The expansion aid is organic or inorganic solids having a particle size of 0.1 to 150 .mu.m and a melting point higher than the temperature at which the expansion of the expandable particles is performed and serves to improve the expansion ratio.

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.

Abstract: Prefoamed crosslinked propylene-type resin particles prepared by using as a base resin a propylene random copolymer whose amount of heat of crystallization determined by a DSC method is 19 to 10 cal/g. The prefoamed particles have a gel fraction of 1 to 65%. Also provided is a molded article of a crosslinked propylene-type resin which is a fused aggregate of the aforesaid prefoamed particles in which the number of cells, N per mm.sup.2, and the density, d (g/cm.sup.3), have the relation represented by the expression 2<N.sup.1/2 /d.sup.1/3 <45.

Abstract: Disclosed herein are propylene-base random copolymer particles suitable for use in the production of pre-foamed particles. The copolymer particles are obtained by heating starting copolymer particles to the crystallization temperature thereof and then quenching them in a medium of (the crystallization temperature-30.degree. C.) or lower. Processes for obtaining the copolymer particles are also disclosed. Pre-foamed particles produced using the copolymer particles contain large cells. They can thus provide foamed moldings which are substantially free of shrinkage and have good flexibility.

Abstract: Preliminarily foamed particles of a non-crosslinked polypropylene resin based on an alpha-olefin/propylene random copolymer having an amount of the heat of crystallization in the range of 5 to 15 cal/g, said preliminarily foamed particles having such a crystal structure that when a DSC curve is drawn by means of a differential scanning calorimeter, by heating 1 to 3 mg of the preliminarily foamed particles to 220.degree. C. at a rate of 10.degree. C./min., a high temperature peak is observed at a higher temperature than the temperature of the peak inherent to the base resin.

Abstract: In pre-foamed particles of a propylene-base resin obtained by foaming raw particles of the propylene-base resin, the relation, G.sub.1 -G.sub.2 .gtoreq.10%, exists between the content G.sub.1 (%) of matter, which is contained in the pre-foamed particles and is insoluble in boiling n-heptane, and the content G.sub.2 (%) of matter contained in the raw particles and insoluble in boiling n-heptane. The pre-foamed particles have excellent moldability and can hence provide with ease low-density (highly-expanded) molded articles, which enjoy superb dimensional accuracy, good surface conditions, low percent water absorption, excellent impact and chemical resistance.

Abstract: Preliminarily foamed particles of a non-crosslinked polypropylene-type resin based on a mixture of 10 to 95% by weight of an alpha-olefin/propylene random copolymer having an amount of the heat of crystallization of not more than 10 cal/g in differential scanning calorimetry and 90 to 5% by weight of an ethylene/propylene random copolymer as a base resin, said preliminarily foamed particles having such a crystal structure that when a DSC curve is drawn by heating 1 to 3 mg of the preliminarily foamed particles to 220.degree. C. at a rate of 10.degree. C./min. by means of a differential scanning calorimeter, a high temperature peak is observed at a higher temperature than the temperature of the peak inherent to the base resin. These preliminarily foamed articles can be molded under lower vapor pressures than in the prior art.

Abstract: A process for producing particles having an increased particle diameter from a powder of a polyolefin resin, which comprises heating the polyolefin resin powder at a temperature higher than the melting point of the resin in a dispersion medium in the presence of a dispersing agent and a surface-active agent.

Abstract: A process for producing pre-foamed particles of a polypropylene resin which comprises expanding original pre-foamed particles of a polypropylene resin, said original pre-foamed particles having the following relation2<E.sup.1/3 .times.n.sup.1/2 <45wherein E is the expansion ratio of the original pre-foamed particles, and n is the number of cells per mm.sup.2 of the cross section of the original pre-foamed particles,by (1) imparting expanding ability to the original pre-foamed particles and then heating them with a heated gas to the heat distortion temperature of the base resin of the pre-foamed particles or a higher temperature or (2) heating the original pre-foamed particles with steam to the heat distortion temperature of the base resin of the particles or a higher temperature with or without imparting expanding ability thereto, whereby pre-foamed particles having an expansion ratio higher than the original expansion ratio E are obtained.

Abstract: Prefoamed polymer particles having excellent moldability are produced by a process comprising a step (impregnating step) of impregnating carbon dioxide or carbon dioxide and a volatile blowing agent in polymer particles, a step (dispersing step) of dispersing the polymer particles into a dispersion medium in a sealed vessel, a step (heating step) of heating the polymer particles to a temperature higher than the softening point of said polymer particles, and a step (releasing step) of opening one end of said vessel and simultaneously releasing the polymer particles and dispersion medium from inside the vessel to an atmosphere held at a pressure lower than that of the vessel. In this process, the impregnating step, dispersing step and heating step need not be altogether effected separately. These steps can be performed simultaneously in one and the same vessel.

Abstract: A method for pressurizing pre-foamed particles of a polyolefin resin by maintaining the pre-foamed particles in an atmosphere of a pressurized gas to impart a predetermined internal pressure thereto, which comprises first maintaining the particles under a pressure which does not cause shrinkage to the particles, and then increasing the applied pressure gradually under conditions which do not cause shrinkage to the particles.

Abstract: A process for producing a foamed and molded article of a polypropylene resin, which comprises pressurizing preliminarily-foamed particles of an ethylene/propylene copolymer having a melt index value of from 0.1 to 25, a latent heat of crystallization of not more than 28 cal/g and an ethylene content of from 1 to 30% by weight as a base resin with an inorganic gas or a gaseous mixture of the inorganic gas and a volatile blowing agent thereby to impart an elevated pressure to the inside of said particles, thereafter filling said particles in a mold capable of enclosing the particles but allowing escape of gases therefrom, and then heating said particles to expand them to the configuration of the mold.

Abstract: In a process for producing pre-foamed particles of a polyolefin resin which comprises impregnating a volatile blowing agent into particles of a polyolefin resin while dispersing the resin particles and the blowing agent in a dispersing medium under heat in a closed vessel, opening one end of the vessel and releasing the resin particles and the dispersing medium simultaneously into an atmosphere kept at a lower pressure than the inside pressure of the vessel; the improvement wherein the pressure of the inside of the vessel after opening its one end is maintained at a substantially constant pressure which is at least 0.7 times the vapor pressure of the blowing agent before opening the end of the vessel.