GB597077A - Improvements in or relating to flame resistant regenerated cellulose sheets or filmsand to flame resisting treatment of regenerated cellulose sheets or films - Google Patents

Abstract

A flame-resistant cellulose sheet or film comprises the incorporation in the regenerated cellulose sheet of at least 20 per cent of a salt of sulphamic acid, at least 10 per cent of a hydroxylated softening agent and at least 0.5 per cent of a formaldehyde yielding material. The salt of sulphamic acid to be used should be soluble in water at 25 DEG C. to the extent of at least 10 per cent; the selected salt may be ammonium, an alkali or alkaline earth salt, or a salt of such amines as methylamine, dimethylamine, ethylamine, ethylene diamine. Of these the ammonium salt is preferred. Glycerol is preferred as the softening agent, but other hydroxylated compounds such as ethylene glycol, diethylene glycol, the polyethylene glycols, hexamethylene glycol and 1,2,5-pentanetriol may be used. As regards the formaldehyde yielding compound, formalin, paraformaldehyde, hexamethylenetetramine and partially condensed resinous products of formaldehyde with urea, melamine, urethanes, guanidines or phenols may be used. The best results are obtained when the components are within the limits of 20-25 per cent, 15-25 per cent and 1-3 per cent respectively. The temperature of the bath may be from 25-75 DEG C. The invention applies to sheets impregnated while in the gel state, but it may be applied to sheets which have been previously dried out provided that they are wetted prior to impregnation. Films and sheets so treated possess improved durability and retain their transparency under variable conditions of humidity and temperature. In an example, a gel regenerated cellulose film is produced by extruding viscose through a long narrow slit into a coagulating bath, regenerated, desulphurized, bleached and washed and then impregnated by passage through a bath of an aqueous solution containing 12.5 per cent ammonium sulphamate, 12.5 per cent glycerol and 5.4 per cent commercial formalin in water at 25 DEG C. (parts by weight). After thorough impregnation, excess liquid is removed by squeeze rollers and the film dried in the usual way. The dried film is flame-resistant and is more durable than flame-resistant film made in accordance with the prior art. Specification 515,735 is referred to.