Improvements in a method of decreasing the density of a foam of thermoplastic resins by a second expansion.

摘要

Process for decreasing the density of a thermoplastic olefin polymer resin foam by secondary expansion comprises impregnating a closed cell prim. foamed material with a gas so that a gas pressure higher than atmospheric is produced in the cells, and heating the foam to above the m.pt. of the resin to cause further expansion. - Retention of the superatmospheric internal foam pressure during storage prior to sec. expansion is made possible using process stages (a) impregnating the prim. foam with a gas by subjecting the foam to an impregnating gas at higher than atmospheric pressure at a temp. below the m.pt. of the resin; (b) cooling the impregnated foam to below 0 deg.C whilst maintaining the external impregnating pressure at above atmospheric pressure; (c) releasing the external impregnating pressure whilst maintaining the temp. of the foam at below 0 deg.C and (d) retaining the superatmospheric internal foam pressure during storage at an external pressure lower than the impregnating pressure by maintaining the foam at below 0 deg.C. - Process allows storage and transport of foamed polyolefin particles prior to sec. foaming. EPAB- EP-109458 B A process for decreasing the density of a thermoplastic resin foam material by secondary expansion, wherein a primarily foamed material of substantially closed-cell structure is impregnated with a gas by subjecting said material to a gas at an impregnating pressure greater than atmospheric and a temperature below the melting point of the resin so that the pressure within the cells of the foamed material is increased to an amount greater than atmospheric, and then said material is heated to a temperature above the melting point of the resin, thereby further expanding the primarily foamed material and producing a lower density foam product, characterised by the steps of (a) prior to heating for secondary expansion cooling the gas impregnated foam material to a temperature below 0 deg.C while maintaining the external impregnating pressure at a pressure above atmospheric pressure; (b) releasing the external impregnating pressure while maintaining the gas impregnated foam material at a temperature below 0 deg.C; and (c) retaining a superatmospheric internal foam pressure during storage at an external pressure less than the impregnating pressure by maintaining the gas impregnated foam material at a temperature below 0 deg.C. (6pp)