Improvements in and relating to converting the surfaces of sheets, layers and the like made of cellulose esters into regenerated cellulose

摘要

The surface of cellulose ester layers, sheets, &c. is saponified by a process comprising coating of the surface with a hydrophilic colloid layer, spreading the saponifying agent on this layer and after reaction has occurred, removal of the colloid layer. The process may be applied in stages in order to obtain saponification to any desired depth. The colloid layer may be a solution of gelatin which jellies at room temperature. Addition of sugar or sugar-like compounds, for instance, sorbitol may be made to the colloid to render it stable to alkali. In an example, a solution of 15 kgs. cellulose acetate in 100 litres acetone is coated in three successive layers on a band-coating machine. After drying it is covered with a solution of 15 kgs. gelatin in 30 litres of water at 55 DEG C.; at 20 DEG C. this solution jellies. The gelatin layer is treated ten times in succession with 20 per cent aqueous potassium hydroxide solution and removed. The treated band possesses a high gloss and is stable to the usual solvents, there being a coating of regenerated cellulose 100 m thick upon it. The product is useful for coating casting supports for the production of films.