GB1337135A - Cellulose acetate film - Google Patents

Abstract

1337135 Cellulose acetate film EASTMAN KODAK CO 4 Jan 1971 [2 Jan 1970(3) 3 April 1970(2)] 309/71 Heading B5B Methods of making cellulose triacetate film containing not more than 1 weight per cent hydroxyl groups, at least 41 weight per cent acetyl groups expressed as acetic acid and intrinsic viscosity of at least one determined as hereinafter defined, at least 10% crystalline, the crystallinity being uniformly dispersed through the thickness of the film, having not more than 3% haze measured through the thickness of the film, containing not more than 5% by weight of plasticiser, having a thickness of 0À0005 to 0À030 inch (preferably 0À003 to 0À010 inch), having a shrinkage of not more than 0À5% when subjected to a specifically defined "Hot Plate" test and free of visible distortion are disclosed. In the first method essentially amorphous cellulose triacetate film of the same composition is heated to 230‹ to 270‹ C. for from 15 to 65 secs. and then rapidly cooled to below 210‹ C. while held under a lengthwise tension of at most 0À035 pounds per inch during the heating period. In the other method the essentially amorphous film is gradually heated through the temperature range 180‹ to 220‹ C. over a period of at least five minutes (and preferably no longer than 30 mins. to avoid excessive discolouration of the film) and while free of perimeter restraint. The intrinsic viscosity is measured at 25‹ C. Œ0À1‹ C. in a 90 : 10, by volume, mixture of methylene chloride and methanol.