| 摘要 |
310,540. Celluloid Corporation, (Assignees of Stevens, J. H., and Walsh. J. F.). April 27, 1928, [Convention date]. Cellulose esters; cellulose ethers; apparatus for making films.-Films or sheets are prepared from solutions or dopes of cellulose derivatives, such as cellulose nitrates, acetates, or propionates or methyl or ethyl celluloses, bv extruding them or causing them to flow at elevated temperature into an atmosphere which has an augmented pressure. The use of these higher temperatures enables smaller amounts of solvent, to be employed and results in more rapid setting and drying and consequently in an increased rate of production of the sheets or films. Any suitable volatile solvents such as acetone, ethyl acetate, ethyl or methyl alcohol, or higher boiling point solvents or mixtures thereof may be used. When volatile solvents are employed alone or with higher boiling point solvents, the solutions can, for example, be used at about 130‹ F. whilst when higher boiling point solvents are used alone, the solutions can be used, for example, at about 180‹ F. but the temperature naturally depends upon the boiling points of the particular solvents employed and the pressure conditions existing. The temperatures may be maintained somewhat below the boiling points of the solvents. The solution is kept at the chosen temperature at least up to the point where it is caused to flow or be extruded on to the forming surface or even during the remaining steps of the process. The augmented pressure results in a uniform product and prevents the formation of bubbles in the film or sheet. This pressure should be exerted not only during extrusion but also whilst the sheet or film is on the forming surface, for example a wheel, belt, or table. Thus, the atmosphere of the room can be maintained at a pressure nearly equal to that exerted on the solution in the feeding apparatus but not so high that it interferes with extrusion. This increased pressure also results in a reduction in the amount of solvent required to give a flowable solution. Any suitable apparatus may be employed but it is preferable to force a thin stream of solution from a hopper so that it makes a direct fall on to the forming surface, the distance of travel between the point where the film solution leaves the hopper and the forming surface being short, prefer. ably so that the wheel or belt exerts a drag or pull, which assists the extrusion of the solution. The process is suitable, for example, for the production of films or sheets for cinematographic and other photographic purposes. In an example, a solution of cellulose acetate with mono-methylxylene-sulphonamide dibutyl tartrnte, or diethyl phthalate as plastifier in acetone and dioxane is heated to 130‹ F. and extruded on to a film wheel in an atmosphere having pressure of 30 1b. per square inch above atmospheric pressure. In another example, cellulose acetate with ethyl lactate and a plastifier is dissolved in dioxane. The solution is heated to 180‹ F. and extruded as in the previous example. |
