Patent GB-800527-A (GB)
Title: Extrusion head and extrusion process employing said head
IPC: B29C48/08
Filed: 1956-03-13
Abstract: <PICT:0800527/IV (a)/1> <PICT:0800527/IV (a)/2> <PICT:0800527/IV (a)/3> An extrusion head for forming a composite film comprises a body provided with an extrusion orifice formed by a wedge-shaped tongue and a lip member on each side of the tongue, the lip edge of each of the members terminating close to the end of the tongue and the inner surface of each of the members, and the opposite slanting surface of the tongue, forming two walls of an extrusion passage for the extrusion of a viscous liquid, two channels in the body each communicating with a respective passage and adapted to receive viscous liquid material, and means for supplying liquid material under pressure to the respective channels, at least one of the lip members being provided with adjusting means for deflecting the lip edge towards and away from the adjacent slanting surface of the tongue.  The apparatus may be used for forming a composite film and coating this film on to the surface of a moving web.  The web may travel at a speed exceeding the extrusion speed, so that the thickness of the composite film is thereby reduced.  The film produced by one of the extrusion passages may be too thin to be self-supporting and the film produced by the other extrusion passage may be sufficiently thick to be self-supporting during its reduction in thickness.  This type of composite film may comprise a silver halide emulsion layer and an extremely thin protective layer coated on a film base or sheet of paper.  As shown in Figs. 1 and 2, the extrusion head consists of an elongated body 1 having two spaced-apart longitudinally extending channels 2, 3, the bottom portions of which communicate with narrow longitudinally extending lateral passages 4, 5 respectively.  These passages have smooth straight inner walls which converge so that they meet at or close to orifice lips forming a protruding longitudinally extending wedge-shaped tongue 6.  The outer walls of the passages are shorter than the inner walls and terminate at the bottom surfaces 7, 8 respectively of the body 1.  On each side of tongue 6 are lip members 9 which preferably are identical in construction but reversed in position.  These lip members are substantially U-shaped in cross-section and the upper arm 10 of each has a flat upper surface which fits against the respective flat surface of the bottom of the body.  The construction and adjustment of the lip members is as described in Specification 792,744.  The central wall or base of each lip member has its outer surface 17 machined so that it will coact with the adjacent slanting wall of the tongue 6 of body 1 and with the outer wall of the respective passage.  This outer surface preferably slants for most of its length in the same direction as the outer surface of the tongue, but near its edge slants to a greater degree, whereby the liquid passage between the surfaces converges so that, at the bottom edge, the adjacent surfaces are only a small distance apart. These surfaces, for a short distance near their outer edges, are preferably parallel, as shown in Fig. 4.  The lip edge 91 of each lip member 9 terminates close to the end of the tongue 6. The distances between the lip edges 91 and the tongue 6, i.e. the widths of the extrusion slits, are adjusted by flexing the lip members 9 by means of the tapered screws 23, as described in Specification 792,744.  Body member 1 and lip members 9 are provided with longitudinally extending passages 24, 25 respectively for the circulation of a heat-exchange fluid.  The end plate 26, fastened to one end of the body member by screws 29, is provided with a central hub 27 having a stub shaft 18 journalled in a bearing (not shown) in a frame for supporting the extrusion head.  The heat exchange fluid is conducted away from the extrusion head by pipes and fittings 32-35 communicating with passages 24.  Similar fittings and pipes (not shown) can be connected to passages 25.  The endplate 36 attached to the other end of the body member by screws 29 has welded to it a conical sleeve 39 fitted with a tapered ring 40, the outer cylindrical bearing surface of which 41 is journalled in a bearing (not shown).  A hub plate 44 welded to the outer end of the sleeve 39 is provided with two passages 47 which communicate through two pipes 46 with two passages 45 which are extensions of channels 2, 3. Liquid film-forming materials can thus be supplied to these channels. The hub plate 44 is provided with a number of passages 48 for conducting a heatexchange fluid into the annular space between sleeve 39 and pipes 46.  In operation the extrusion head is placed in a coating position above a support roller 52 (Fig. 2), and a continuous sheet of film or paper 50 from a source (not shown) passes around guide roller 51, then over support roller 52 and on to other guide rollers in a drying or treating zone.  The tongue 6 may come to a sharp edge at the orifice but preferably has a highly polished blunt tip about 0.5 to 10 thousandths of an inch across and at an angle of 90 degrees from the central axis of the plane of the extrusion orifice, as shown in Fig. 4. Specifications 755,151 and 758,401, [both in Group VIII], and U.S.A. Specification 2,686,931 also are referred to.