GB724267A - Process of producing a closed-cell cellular thermoplastic resin article - Google Patents

Abstract

A closed-cell cellular thermoplastic resin article having wrinkled cell walls is prepared by causing the gas pressure in the closed cells of a previously formed gas expanded cellular thermoplastic resin body to be reduced to below atmospheric pressure and allowing atmospheric pressure to act partially to collapse the closed cells and cause the cell walls to be wrinkled. Specified resins are polyvinyl chloride, copolymers of vinyl chloride, particularly with vinylidene chloride, polyvinyl butyrate, acetate, alcohol, formal or butyral, polyvinylidene chloride, polystyrene, polydichlorostyrene, polyalphamethylstyrene, polymethyl or ethylacrylate and polymethyl methacrylate. Plasticizers such as dimethyl, dibutyl and dioctyl phthalates and tricresyl phosphate may be present, while the original cellular article may be made by using as solvent acetone, methyl ethyl ketone and ethyl acetate, and as blowing agent azoisobutyric dinitrile, alpha, alpha-azobisisobutyronitrile, diazoaminobenzene, 1,3-bis-(p-xenyl)-triazene, sodium bicarbonate and oleic acid, ammonium carbonate and mixtures of ammonium chloride and sodium nitrite. A quick or a slow diffusing gas may be used, or a mixture of one of each, e.g. hydrogen and carbon dioxide. The gas pressure may be reduced in the cells by causing at least a portion of the gas to escape therefrom, e.g. by applying a vacuum, preferably with heating. The outer crust is preferably removed from the cellular body which is then sliced into thin sheets having a thickness of 10-40 mm. before it is treated to reduce the gas pressure in the closed cells. The original closed-cell article may be subjected at a raised temperature and at least atmospheric pressure to an atmosphere consisting at least partly of a vapour which is a liquid at room temperature, so as to cause the vapour at least partially to replace the gas in the closed cells, and then cooled so causing the vapour to condense, the pressure inside the cells to be reduced and the cells to collapse partially so wrinkling the cell walls.