GB588210A - Improvements relating to the manufacture of electrical insulators from thermoplastic cellulose derivatives - Google Patents

Abstract

Electrical insulating components in the form of sleeves, tubes, beads and other thin-walled hollow articles having the properties of high heat-softening point, high dielectric strength and low-loss factor are obtained by forming into the desired shape under heat and pressure a thermoplastic composition comprising an ester or ether of cellulose having the said properties and a substantially water-insoluble plasticiser, cooling, removing the plasticiser by extraction with a volatile liquid which is a solvent for the plasticiser, but a non-solvent for the cellulose derivative and substantially freeing the article from the volatile liquid by evaporation. Suitable esters and ethers of cellulose are the acetate, propionate, butyrate, acetate-butyrate, acetate-propionate and ethyl-cellulose. Suitable plasticisers are dimethyl phthalate, diethyl phthalate, methyl-phthalyl ethyl glycolate, ethyl-phthalyl ethyl glycolate, triacetin, tri-(monochlorethyl) phosphate and p-toluene sulphonamide or mixtures of any of these with a plasticiser of low solvent power such as tricresyl phosphate. For cellulose acetate plasticised with dimethyl phthalate, a suitable extracting liquid is methanol, ethanol or diethyl ether, but other volatile liquids such as benzene and toluene may be employed. The insulating articles may be formed by extrusion, compression moulding, injection moulding or blowing. In an example, an insulating sleeve is made by extruding a mixture of cellulose acetate and dimethyl phthalate at 155 DEG to 160 DEG C. The tube is cut into short lengths, extracted with boiling diethyl ether to remove the plasticiser and dried at 50 DEG C. to remove the ether.