Improvements in or relating to a metal support coated with casting layers for the manufacture of films and sheets

1,129,895. Coated metal. GEVAERT-AGFA N.V. 8 Sept., 1966 [24 Nov., 1965], No. 49881/65. Headings B2E and B2K [Also in Divisions B5 and C3] A casting surface for preparing films and foils by casting a film-forming solution thereon is prepared by coating a metal support with a solution of cellulose acetate, evaporating the solvent, hydrolyzing the cellulose acetate layer formed, and applying thereto a solution in a mixture of water and of a water-miscible organic solvent of (A) polyvinyl alcohol having at most 20% of residual vinyl ester units, (B) a water-soluble amino-resin and (C) 10%-20% acid, whereby a coating on the hydrolysed cellulose acetate surface of 0.01 Á to 5Á thickness is obtained, and heating the coating for 4 to 8 hours at 100 to 120‹C to cure the amino resin. The amino resins used are urea, melamineformaldyhyde resins, dimethylol urea, trimethylol or dimethylol melamine. The aminoresin is said to react during curing with free hydroxyl groups of the hydrolysed cellulose acetate surface. Preferred acids are maleic. citric, oxalic acid. The polyvinyl alcohol, amino resin, acid solution may be applied by roll coating, dip-coating, or knife-coating. The metal support may be the metal drum or endless belt of a film casting machine. In the Examples casting layers are applied to the endless belt of a film casting machine, and films of cellulose triacetate are cast from solution.