GB1502315A - Treatment of polymeric film - Google Patents

Abstract

1502315 Controlling film curl EASTMAN KODAK CO 2 April 1975 [2 April 1974] 13454/75 Heading B5B [Also in Division G2] A film 2-50 mils thick formed from a thermoplastic polymer having a Tg above 60‹ C. is heattempered before core-setting for 0À1-1500 hrs. at 30‹ C. to 5 Celsius degrees below the midpoint or the endothermic peak of the glass transition temperature range of the polymer until the controlled curl of the heat tempered film is at least 15% less than the absolute curl of a corresponding non-heat-treated film, the curls being expressed in ANSI curl units and the difference between the absolute and controlled curl being determined from either curled or flat test samples of film by subtracting the curl of a non-core-set film sample from the curl of the core set film sample, the sample core-setting being carried out for 24 hrs. at 49‹ C. and 50% relative humidity. The film may be provided with an undercoating on one of its surfaces, e.g. a photographic emulsion layer and heat setting may be carried out before or after coating. The heat setting may be carried out after reverse winding of the film on a core while it is flat or while it is rolled up. Preferred films are made from polyesters, e.g. poly(ethylene terephthalate), poly(1,4 - cyclo - hexylene dimethylene terephthalate) or poly(ethylene - 2,6 - naphthalene dicarboxylate) or from polycarbonates, e.g. poly((2,2 - bis(4 - hydroxy phenyl) propane carbonate)) or cellulose esters.