PROCESS FOR PRODUCING POLYAMIDE FILMS HAVING IMPROVED ANTI-BLOCKING CHARACTERISTICS

摘要

1295989 Polyamide films UNITIKA KK 20 May 1970 [20 May 1969] 24478/70 Heading B5B A process for the production of polyamide films having improved anti-blocking properties involves the extrusion of a molten synthetic linear polyamide, preferably of poly-#-caproamide, polyhexamethylene adipamide, polyhexamethylene sebacamide, poly - 11 - aminoundecanamide, polylaurinamide or copolymers of at least two of the monomers thereof, on to a cooling roller and simultaneously providing a layer of inert gas of predetermined thickness over the entire width of the film between the extruded film and the roller. The layer of gas may be provided by feeding the gas between the film and the roller at a pressure whereby no inflation of the film occurs or the layer of gas may be trapped by contact of the outer edges of the extruded film on the roller. The thickness of the layer may be adjusted by control of the angle between the tangent from the roller to the point of extrusion and the direction of extrusion of the molten film and by varying the distance between the roller and the point of extrusion. The surface of the roller may be embossed to facilitate the retention of air under the film. The effective thickness of the layer of gas is preferably in the range 50-150 microns and may be calculated using the formula where T, T 0 and T 1 are the temperatures of the cooling roller, the film at commencement of cooling on the roller, and the film at time t respectively; L# and c are the thickness of the extruded film, its density and specific heat respectively; k and x are the heat conductivity of the gas and the effective thickness of the layer of gas respectively and t is the time measured from the commencement of cooling by the cooling roller. In examples, polyamide films of varying thicknesses are produced by the process of the invention using gas layers of different thicknesses and differ - enttemperatures of extrusion and of the cooling roller. The films are then subjected to simultaneous drawing in the transverse and longitudinal directions in a hot air atmosphere at draw speeds of between 17,000 and 25,000%/ minute and temperatures of 120‹ or 130‹ C.