Manufacture of transparent sheet material


344,471. Transparent sheet material. WARREN CO., S. D., 101, Milk Street, Boston, and DRIESEN, W. M., 33, Thomas Street, Clifton, Passaic, New Jersey, both in U.S.A. Oct. 29, 1929, No. 32850. [Class 20 (iii).] In the manufacture of transparent sheet material, a web of paper suitably prepared is impregnated by immersion, or by spraying or brushing, in a solution comprising a cellulosic film material, a volatile solvent, and also a stable solvent. A suitable solution is composed of nitro cellulose (ester soluble) denatured alcohol, ethyl acetate, amyl acetate, butyl acetate, ethyl lactate, diamyl phthalate, and the proportions are given. Cellulose acetate may be substituted for the nitrate. In this solution diamyl phthalate, a liquid which boils at about 300‹ C., acts as a stable solvent, it remains in mutual dispersion with the solution of nitro cellulose effects a more perfect encasing of the cellulose fibres on drying out of the solvent and thus produces a more perfect transparency than would be obtained without its use. The ethyl lactate acts to retard or regulate the rate of volatilization of the high volatiles and thus helps towards the same end. In another example, anhydrous lanolin is used as a stable solvent, and the paper to be used is preferably first treated with a dilute solution of anhydrous lanolin in a volatile solvent such as ethyl acetate. Other suitable stable solvents are dibutyl phthalate, diethyl phthalate, tricresyl phosphate, triphenyl phosphate, butyl stearate, isoamyl phthalate. Suitable paper for impregnating is obtained from partially hydrated vegetable fibre, preferably of a mitscherlich process sulphite fibre stock worked a long time in the beater, the paper being moistened with water and calendered by heavy steam-heated rolls before use.




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