GB855164A - Improvements in or relating to web coating - Google Patents

Abstract

855,164. Coating webs. DU PONT DE NEMOURS & CO., E. I. July 31, 1958 [Aug. 21, 1957], No. 24759/58. Class 140. Coating apparatus for applying a smooth coating of a desired predetermined web thickness on to a moving flexible web comprises means for applying a layer of liquid coating material to a moving web, a device for metering the said layer to a reduced thickness along a metering line transverse to the direction of travel of the web and air knife means for subsequently doctoring the said layer by removing excess coating material with a stream of air, along an impingement line transverse to the direction of travel of the web the metering device being so constructed and located as to prevent both the excess coating removed by the air stream and the air from passing it, the air knife means being adapted to direct a stream of air on to the said layer at an angle of 35 degrees to 90 degrees from the plane of the outrunning web at the impingement line and the metering device having an upper surface positioned at an angle as measured counter clockwise from the upper surface to the plane of the web at its metering line at least is large as the angle at which the stream of air is reflected from the said layer. As shown the apparatus comprises an air knife 1, a metering device 2, a coating roll 3 and a coating pan 4 arranged to apply a thin layer of viscous liquid coating material 5 by the skim coating method to the flexible web 6 continuously advancing in the direction indicated by the arrows. The air knife is adjustable so that a planar stream of air can be caused to impinge at any desired angle on the coated web. The metering lip 12 of the metering device 2 is located immediately preceding the point at which the outrunning web leaves contact with the coating roll and is positioned so as to permit more coating material to pass it than is required in the final product. The metering device also has an upper surface 13 and a lower surface 14 'for guiding excess coating material back into the coating pan. Excess coating material removed by lip 12 flows down lower surface 14 into the coating pan, while further excess coating material removed by the air stream issuing from the air knife returns to the coating pan in a stream flowing downwardly along the upper surface 13 of the metering device. As alternatives to the skim coating method as shown, the coating may be applied to the web by dip coating, nip roll coating, reverse roll coating or extrusion coating. Specified web materials are paper and photographic film base such as consisting of cellulose acetate. Specified coating materials are aqueous silver halide dispersions in natural and synthetic water-permeable colloids such as gelatin, albumin, agar-agar, waterpermeable polyamides, polyvinyl alcohol, partially hydrolysed polyvinyl esters and hydrophilic polyvinyl acetals; gelatino silver bromochloride or iodobromide emulsions. The process may also be used to apply gelatine layers, antiabrasion layers, anti-static layers and pigmented layers. U.S.A. Specification 2,901,376 is referred to.