Importance

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Abstract

Method and apparatus for coating both sides of a moving web and for independently controlling the coatings' width, thickness and uniformity of thickness along the length of the web. A moving web is supported on a backing surface. Two stationary and pliant smoothing films are positioned one adjacent each surface of the web, including the web surface which is supported by the backing surface. A coating liquid is metered to each side of the web at the confluence of the web and the two smoothing films, the respective metering rates being selected to produce a desired respective coating width. A pliant pressure generating means, in the form of a membrane holds a length of one smoothing film against the moving web with a static force whose magnitude is selected in accordance with a desired coating thickness. The relative position of the backing surface and the pressure generating means determines the length of coincidence of the moving web, coating liquid, stationary smoothing films and pressure generating means. This length is selected, by virtue of selecting a relative position, to thereby apply a high hydrodynamic force to the coating liquid for at least a critical time interval, such that slight variation of this time interval no longer produces appreciable variation in coating thickness along the length of the web, and uniformity of coating thickness is thus achieved. In a second embodiment, a second pliant pressure generating means functions as the backing surface.

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First Claim