Patent GB-686265-A (GB)
Title: Films
IPC: B29C48/08
Filed: 1950-07-20
Abstract: A film-forming material on its way to an extrusion aperture is caused to flow as a shallow tortuous stream in contact with a heat-exchange member; the width of the stream at least over the whole distance between the heat-exchange member and the extrusion aperture is substantially <PICT:0686265/IV (a)/1> <PICT:0686265/IV (a)/2> <PICT:0686265/IV (a)/3> <PICT:0686265/IV (a)/4> equal to the width of the aperture, and the temperature of the heat-exchange member is controlled so as to eliminate any substantial temperature variation over the cross-section of the stream.  In passing the film-forming material in contact with the heat-exchange member, the stream is preferably reduced in depth, preferably to not more than 1/4 -inch at one or more points in its path.  Preferably the stream passes horizontally over a horizontal surface of the heat-exchange member. The stream of film-forming material may pass through a scraper-hopper which is open to the atmosphere or it may be forced through a pressure-hopper.  The extrusion aperture may be fixed or adjustable. The film-forming material may be a solution of a cellulose ester or ether, or polyvinyl compound, or polyethylene, in a volatile solvent or solvent mixture and with or without a plasticizer, dye, or other ingredient.  As shown in Figs. 1 and 5, the pressure hopper 11 comprises side walls 12, 13 and blades 14, 15, forming an adjustable aperture 16.  A header 18, through which film-forming material flows, extends along the top of the hopper.  A portion of the fluid passes through the header without diversion and is returned to conduit 19 at a point up-stream of the hopper, but the other portion of the film-forming fluid is diverted through opening 22 into slots 23 in plate 24, and then through slots 25 in plate 26.  The fluid then spreads over the upper surface of plate 27 within space 28 and then flows through slots 31 into space 32.  As the fluid flows through spaces 28 and 32, it is thoroughly blended and is brought to a uniform temperature by means of a heating medium flowing in the enclosed channels 35 in plate 27.  From space 32, the film-forming fluid passes through slots 38 in plate 34.  The slots 38 are yieldably closed by member 39 and springs 41.  This arrangement permits sufficient pressure to be built up in conduit 18 to obtain adequate circulation of the fluid without applying excessive pressure on the walls 12, 13.  As shown in Figs. 6 and 8, a plate 57 in hopper 51 has enclosed channels 58 through which flows a heating medium. Plates 62 are fixed to the ends of plate 57. Between plates 62 are baffles 63-66 and baffles 67, 68. Film-forming fluid enters through conduit 69 and is discharged through apertures 71 into the trough formed by baffles 64, 65. The fluid flows in a thin stream over the top of baffles 64, 65 into the troughs formed by baffles 64, 67 and 65, 68.  From these, the fluid flows in a thin stream under baffles 67, 68, in close contact with plate 57 into the troughs formed by baffles 63, 67 and 66, 68.  It then flows over baffles 63, 66, to the extrusion aperture 56.  A constant level of fluid between baffles 64, 65 is maintained by means of a float 72, lever 74, and sleeve 77. When the level of the fluid is too high, the float causes the sleeve to cover the apertures 71 and reduce the flow of fluid into the apparatus.  Specification 686,258 is referred to.