Patent GB-1122021-A (GB)
Title: Coating method and apparatus
Inventor: WATERS WALTER GEORGE
IPC: B29C48/15
Filed: 1964-06-05
Abstract: A method of coating a tubular body with a layer of liquid comprises feeding the liquid so that it falls continuously and freely downwards in a curtain extending continuously round a substantially vertical axis, the liquid having a surface tension such that the curtain contracts inwards as the liquid falls, and continuously feeding the tubular body downwards and centrally within the curtain of liquid so that the tubular body meets the contracting curtain whereby it is coated over its entire periphery as it passes its point of contact with the curtain.  The speed and direction of the tubular body and liquid at the point of contact may be the same.  The liquid may be allowed to fall before contacting the tube for a period long enough to allow a horizontal section of the falling liquid acquire a uniform thickness by creating a gas pressure inside the curtain to cause the liquid to follow a more outwardly curving path.  The liquid may be aqueous gelatin solution, a silver halide emulsion.  Films e.g. cellulose acetate may be formed by feeding the coated tube through a solvent evaporating chamber, and the cast film slit and stripped off. The cast film may be further coated to form a photographic film whilst still on the casting tube.  The tubular body may be coated with at least two superimposed layers of one or more liquids by feeding the liquid in at least two curtains which may be concentric and may then touch by an outer curtain contracting inwardly onto the inner curtain to form one combined curtain.  The tubes coated may be solid or hollow, and coated, hollow flexible tubes may be slit longitudinally and formed into a flat coated sheet exhibiting no edge effects.  The tube may be of paper or a photographic film base, and the liquid a photographic silver halide emulsion. Cables may be coated with polyvinyl chloride or other insulating materials. Apparatus for coating tubes comprises a housing having at least one annular slot which may be elliptical or circular in the base thereof for feeding a liquid vertically downwards from the housing in a closed curtain extending along the slot and a conduit for supplying the coating liquid uniformly to the slot, the housing having an aperture within the slot and conduit through which a tubular body can be fed vertically downwards within the curtain of liquid.  The slot need not be continuous. In Fig. 1, annular housing 1 has a narrow annular slot 2 at the base thereof and diametrically opposed conduits 3 through which liquid coating composition is fed to the top of the slot 2. Conduit 3 leads into chambers 4 acting as reservoirs for the liquid.  The annular housing 1 has flanges 7, 8 extending inwardly from the bottom and top of the housing respectively to form an aperture 9 of diameter large enough to permit hollow cylindrical tube 10 to pass downwardly through it.  Housing 1 also comprises a conduit 11 for gas under pressure to pass into the space between flanges 8, 7, and flange 7 comprises conduits 12 to allow the gas to escape to the space between the tubular body and the curtain of coating liquid. In Fig. 2 (not shown) apparatus having two concentric annular slots is illustrated.ALSO:Tube coating apparatus comprises a housing having at least one annular slot which may be elliptical or circular in the base thereof for feeding a liquid vertically downwards from the housing in a closed curtain extending along the slot and a conduit for supplying the coating liquid uniformly to the slot, the housing having an aperture within the slot and conduit through which a tubular body can be fed vertically downwards within the curtain of liquid.  The slot need not be continuous.  In Figure 1, annular housing 1 has a narrow annular slot 2 at the base thereof and diametrically opposed conduits 3 through which liquid coating composition is fed to the top of the slot 2.  Conduit 3 lead into chambers 4 acting as reservoirs for the liquid.  The annular housing 1 has flanges 7, 8 extending inwardly from the bottom and top of the housing respectively to form an aperture 9 of diameter large enough to permit hollow cylindrical tube 10 to pass downwardly through it. Housing 1 also comprises a conduit 11 for gas under pressure to pass into the space between flanges 8, 7, and flange 7 comprises conduits 12 to allow the gas to escape to the space between the tubular body and the curtain of coating liquid.  In Figure 2 (not shown) apparatus having two concentric annular slots is illustrated.