Improvements in or relating to the production of films, foils, thin sheets and the like

摘要

In a method of reducing the tendency to curl of films or foils, produced by depositing a film-forming solution on a support, evaporating volatile solvent from the deposited solution and stripping the film or like product from the support, the film, or foil is subjected to the action of heat applied only to or in greater quantity to the air side of the film, i.e. that side of the film which is not in contact with the support during the film formation. The heat treatment is preferably effected by passing the film over heated surfaces, e.g. of polished metal drums. The air side of the film may be subjected to a higher temperature than the other side or may be heated for a greater length of time. The films preferably have a basis of cellulose derivatives containing a suitable plasticizer in the proportion of 10--75 per cent of the cellulose derivative. Suitable compositions for the formation of films are (1) cellulose acetate 100 parts by weight, triphenyl phosphate 15, diethyl phthalate 15, acetone 300, methyl alcohol 50; (2) cellulose acetate 90, cellulose nitrate 10, dibutyl tartrate 15, ethylene dichloride 300, methyl alcohol 50, ethylene glycol mono-methyl ether 15; (3) cellulose nitrate 100, diethyl phthalate 15, butyl alcohol 15, ethyl alcohol 190, ether 130; or (4) cellulose nitrate 100, camphor 10--50, acetone 190, alcohol 130. In suitable apparatus for carrying out the invention, a film 1 is cast on the wheel 2 stripped by the roller 3, and led under a drum 4, over a drum 5 and under a drum 6. The air side of the film contacts with drums 4, 6 and the other with drum 5. A pipe 8 leads a heating fluid such as steam to drums 4, 6. Drum 5 may be heated or not. Drums 4, 6 may be of larger diameter than drum 5, the temperatures then being equal. The drums may be heated electrically. The apparatus may be installed in the driers of the film-forming machine, or may be used for flattening fully seasoned films. The results of tests are quoted to show that the films remain flat substantially permanently after treatment.