Apparatus and process for casting film

摘要

In a process for casting cellulose film in which a film forming solution is extruded into a liquid coagulant, a thin layer of the coagulant is conveyed over a downwardly inclined tray at a speed controlled by the inclination of the tray and the extruded film is continuously drawn over and in contact with the layer of a coagulant at a speed independent of the speed of the layer. Apparatus for carrying out such a process may comprise a vessel 23 for coagulant liquid 13, a smaller vessel 14 mounted above the vessel with means for supplying coagulant thereto, e.g. inlet pipes 15, 16 connected to reservoirs 17, 18 means disposed above the smaller vessel for extruding a film forming solution below the surface of liquid in the smaller vessel, a slot 21 in the bottom of the smaller vessel to permit passage of the film therethrough, a downwardly declined tray 22 depending from and integral with the slot for conveying liquid and directing the liquid and the film into the vessel and means independent of the flow of liquid down the tray or through the vessel to draw the film from the vessel e.g. guide rolls 24, 25, 26 and drive rolls 27, 28. Preferably the extension means is so disposed with respect to smaller vessel 14 that free access of coagulant to both sides if the film is permitted. Baffles 19 and 20 may be provided in smaller vessel 14 to minimise turbulence of coagulant in the region of extrusion. The distance between the extrusion means and slot 21 is preferably less than 3 inches. The angle of tray 22 which may be varied is preferably such that the rate at which coagulant descends from smaller vessel 14 into vessel 23 is less than the rate of descension of the film. As shown in Fig. 2, the film having descended tray 22 may be drawn away on an endless belt 29 in combination with guide rolls 31, 32 and drive roll 30. Preferably the upper rim of belt 29 is slightly above the surface of coagulant contained in vessel 23, but may alternatively be positioned up to 3 inches below the surface. Belt 29 may be driven to convey coagulant on its upper run at a speed less than the drawing speed of the film. Baffles 34, 35 and 39 may serve to minimise turbulence in vessel 23. In an example viscose comprising 9% cellulose and 5,2% sodium hydroxide is cast using the modified apparatus of Fig. 2 in which vessels 14 and 23 contain coagulant containing 12% H2So4 and 18% Na2So4. The angle of tray 22 is arranged to convey coagulant at approximately the same speed of draw off of film i,e, 150 yards per minute. The film may pass on to purification stages e.g. bleaching and softening treatments. Specifications 211,446 and 852,614 are referred to.