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Abstract

Method and apparatus for coating a moving web and for independently controlling the coating's width, thickness and uniformity of thickness along the length of the web. A back-up roller supports the moving web on a portion of the roller's periphery. A stationary and pliant smoothing film is positioned adjacent the exposed surface of the web which is supported by the back-up roller. A coating liquid is metered to the confluence of the web and the smoothing film, the metering rate being selected to produce a desired coating width. A pliant pressure generating means, in the form of a membrane or a force web, holds a length of the 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 back-up roller and the pressure generating means determines the length of coincidence of the moving web, the coating liquid, and stationary smoothing film. This length is selected, by virtue of selecting a relative position, to apply high hydrodynamic pressure to the coating liquid for at least a critical time interval, such that slight variation of this time interval does not produce appreciable variation in coating thickness along the length of the web, and lineal uniformity of coating thickness is thus achieved.

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First Claim