GB400597A - Improvements in the production of foils of cellulose esters and ethers - Google Patents

Abstract

<PICT:0400597/IV/1> <PICT:0400597/IV/2> <PICT:0400597/IV/3> Foils of cellulose acetate or other cellulose ester or ether are tensioned longitudinally and transversely and stretched in either or both directions preferably while in a plastic or soft condition due to the presence of solvent remaining in them after their production or produced by the application of solvent or softening agent. Stretching may be carried out continuously with the production of the foils and transverse stretching may be effected simultaneously with longitudinal stretching. Solvents, latent-solvents, and other swelling agents which may be used are acetic acid, formic acid, lactic acid, diacetone alcohol, acetone; ethers of glycols and other polyhydric alcohols and ethers and ether-esters of such alcohols particularly the methyl and ethyl ethers of ethylene glycol, glycol mono-acetate, methyl glycol mono-acetate, dioxane, diethylene dioxidedicarbinol-diacetate, ethylene methylene dioxide, mono-ethyl or methyl ether of propylene glycol or diethylene glycol, the acetins; dichlorethylene, ethyl lactate, diethyl tartrate, methylene chloride, ethylene chloride, chloroform, and tetrachlorethane. The solvent may be diluted with water, glycol, glycerol, benzene, toluene, xylene, benzine, petrol, kerosene, carbon tetrachloride, trichlorethylene, perchlorethylene, tetra- and deca-hydronaphthalene. The softening agents may be removed by evaporation, or washing with water or salt solutions. The stretched foils may be treated with glycerine and passed through polishing rollers; they may be coated with other cellulose derivatives, waxes, or resins, or printed, or embossed. As shown in Figs. 1 and 3, a film of cellulose acetate, obtained by extruding a solution from a hopper on to a rotating drum and softened by application of a solvent, is passed through a stretching device consisting of a series of rubber-covered nip rollers 14 which nip the edges of the foil 10 and are driven by gears 15 from shafts 16, these being geared together by shaft 17 driven by a chain 18. The first pair of rollers 14 stretches or tensions the foil longitudinally only, but the inclined setting of the subsequent pairs causes the foil to be stretched transversely as well as longitudinally. The stretching apparatus may be enclosed in order to maintain the plastic state of the foil. As shown in Figs. 4 and 5, the lateral stretching device consists of pairs of endless rubber-faced metal bands 20 at each side of the foil and inclined in order to effect lateral stretching. Longitudinal stretching may be effected simultaneously with the lateral stretching by adjusting the speed of the bands so that the longitudinal component is greater than the rate at which the foil is supplied. The foil 10 is nipped by the bands 20 between the rollers 21, 23 and the contact is assisted by the pressure rollers 22. The Provisional Specification describes a stretching device comprising pairs of rollers which engage the foil, film, or sheet at several points between its edges, the rollers nearer the middle being less inclined to the transverse direction than those nearer the edges. The foil may thus be stretched positively over the whole width of the material.