GB897909A - Process for continuously casting an organic self-supporting film from a solution, means for carrying out this or a similar process, applications of this process and products thereby obtained - Google Patents

Abstract

A continuous film is produced by continuously depositing a solution of an organic polymeric film-forming material in a volatile solvent on to a casting surface moving in a vertical plane so that the solution spreads under the <PICT:0897909/IV (a)/1> <PICT:0897909/IV (a)/2> <PICT:0897909/IV (a)/3> <PICT:0897909/IV (a)/4> <PICT:0897909/IV (a)/5> action of gravity across the surface to form a layer, causing the solvent to evaporate from the layer until the material has set in the form of a film, and continuously stripping the film from the surface. The casting surface may be a side of a disc slowly rotating about a horizontal axis or an endless band moving slowly past the solution-depositing station. As shown in Figs. 1 and 2, a film-forming solution is deposited on the lower portion of slowly rotating polished glass disc 10 from a reservoir 21 through a pipe 22 and a nozzle 23 which has an outlet whole size is adjustable. The disc 10 is mounted on a boss 12 keyed to a shaft 13 rotably mounted in bearings 14, 15 and on which is keyed a worm-wheel 20 meshing with a worm 19 driven through a chain and sprocket transmission 18. The solution deposited on the lower portion of the disc flows downwardly along the line 24 (Fig. 2) and forms an annular coating 25 extending inwardly from the edge of the disc. The coating is maintained in the liquid state during its travel on the first quarter of the disc by means of the screen 26 which reduces the rate of evaporation of the solvent from the coating. Excess solution dripping from the edge of the disc is guided by a channel 27 to a receiver 28. When the coated portion 25 of the disc 10 leaves the screen 26 and travels through the second and third quarter of the path of travel of the coating a sufficiently large proportion of the solvent in the coating evaporates to cause the coating to become a solid solution which is stripped from the disc at the line 31, which is about 270 degrees angle of disc rotation from the solution-depositing station 23. The disc 10 is enclosed in a casing 34 provided with an air supply inlet 35 and an outlet 36 for air charged with solvent vapour. The edges of the film 25 are trimmed off by spring loaded cutters 37, 38 which determine the width of the film strip 32 continuously stripped off from the disc 10. The excess material trimmed off is taken up by a wind up roll 39. The film 25 is continuously cemented to a supporting web of film 33 (Fig. 1) which may be of cellulose acetate or other transparent material (see Group VIII). As shown in Figs. 4 to 6, a film-forming solution from a supply tank (Fig. 6) flows by gravity through a flexible pipe 140 and a nozzle 142 on to a travelling flexible endless band 101 of constant width which functions as a casting support. The band 101 is caused to travel over four fixed guide bars 102, all in the same plane, the angle between adjacent bars being 45 degrees, so that the band 101 travels alternately in a horizontal and a vertical direction. The band 101 is driven by means of rubber rollers 106, 107 disposed behind the band and co-operating with short rotatable idler pressure rolls disposed in front of the band. During the upper horizontal travel F4 and F1 of the band 101 (Fig. 5) the film is subjected to radiant heat and during the downward vertical travel F1 is thereby rendered sufficiently dry to be capable of removal from the band. The edges of the film are trimmed off by knives 166 (Figs. 4 and 5) urged against the film by weights 126 (Fig. 4). The trimmed off edges of the film 1691 and 1692 are collected on the wind up roll 170 and the trimmed film 168 is caused to travel to the roller 176, where it is laminated with a support film. The film 168 is rendered capable of polarizing light by uniting it at the roller 176 with a support film 172 (Fig. 4) while stretching it longitudinally by causing the support film to travel at a much higher speed than that of the film 168 (see Group VIII).