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Variation of gravure coating thickness during early stages of doctor blade wear



With all operating parameters fixed, the mean coated thickness in gravure coating should ideally be a constant fraction of the volume factor of the engraving, and, hence, invariant over coated distance. Experimental data presented, however, reveal an unexpected variation of gravure coating thickness over the first few thousand meters of coated web. The observed variation is attributed to wear of the blade tip. The lubrication approximation is invoked to model a series of steady-state flows between blade tips of various profiles and a smooth surface at a fixed gap away from them. The blade tip profiles are chosen to simulate those of a continously wearing blade tip. The resulting four-parameter model is used to “fit” experimental data of gravure coating thickness variation. Then, the model is used to predict the effects of various operating parameters, including coating liquid properties, blade thickness, blade setup, and web speed, on this phenomenon.

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