GB845756A - Improvements in or relating to the production of self-supporting films - Google Patents

Abstract

An apparatus for making self-supporting films comprises a rectangular hopper having a front wall 40 (Fig. 3) and a rear wall, both of which slope internally towards the centre of the hopper bottom as indicated at 42 and 44. The longi <PICT:0845756/IV(a)/1> tudinally extending opening 47 in the bottom of the hopper is narrowed by means of elongated edge members 58 and 50 to form a slot and rotatably mounted above and parallel with the slot with its underside adjacent to the edges of the slot is a roll 68 driven anti-clockwise through an infinitely variable speed reduction gear by an electric motor. The sloping surface 60 of the edge member 58 in coextensive with the sloping wall 42 and terminates in a sharp edge 62 which forms one edge of the slot and is spaced from the roll 68 by a gap 63 through which the viscous film-forming solution in the hopper is discharged. The opposed edge member 50 has an upwardly directed ridge of inverted V cross-section whose edge 54 is spaced a very short distance, e.g. 0,002 inch, from the roll 68 and functions as a stripping blade for removing all but a very thin film of the solution from the roll 68. The member 50 also has a downwardly directed ridge of V-shaped cross-section whose edge 52 serves as a doctor blade to level out the film of solution on the peripheral surface of the casting drum 16 which is slowly rotated in a clock-wise direction. The film F of solution stripped from the roll 68 by the blade 54 flows down the surface 53 of the member 50 on to the peripheral surface of the casting drum 16, leaving a thin inner layer of solution adhering to the peripheral surface of the roll 68 upon which it is carried back into the hopper and facilitates the pick-up of further solution from the body of solution in the hopper during the next revolution of the roll. The hopper is supported by shoes attached to the side walls of the hopper and adapted to ride on the peripheral surface of the drum 16. The front of hopper is also supported by means of a pair of adjustable pins 72 which screw into ears 43 projecting from the front wall of the hopper and are provided with knurled knobs 70 and engage soft metal slide buttons 12 mounted on metal leaf springs 11. The hopper may be heated by means of electrical heating elements housed in two bores in the lower portions of the hopper walls, one of which bores is shown at 45. In addition to providing films of uniform thickness, the rotating roll 68 causes air bubbles to be removed from the viscous film-forming solution before it passes through the gap 63. Specification 642,902 is referred to.