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ELASTOHYDRODYNAMICS OF BLADE coating

AICHE JOURNAL 1990年第4期36卷 587-597页

作者： PRANCKH, FR SCRIVEN, LE Coating Process Fundamentals Program Department of Chemical Engineering & Materials Science University of Minnesota Minneapolis MN 55455

Blade coating is the most common method of coating paper, and it is applied in coating magnetic suspensions and adhesives. Typically, the blade's upstream edge is clamped into a rigid holder so that the blade and substrate form a converging wedge. The translating substrate drags liquid into the wedge, where liquid forces develop and deflect the elastic blade, but it is loaded externally to counteract the deflection. Liquid dragged past the blade and thus the coating thickness depend on the elastohydrodynamic interaction among blade, liquid, and loading. Shell theory and lubrication flow theory describe the interaction by means of differential equations that are shown to be equivalent to Saita and Scriven's (1985) earlier formulation but that lead to a computationally more efficient analysis. Predictions computed agree with those of the earlier formulation and with experiments. Moreover, the new predictions illustrate effects of normal force loading and broaden the theory of blade coating.

关键词： coating Techniques

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Cryogenic scanning electron microscopy of early stages of film formation in drying latex coatings

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ACS Symposium Series 2001年 790卷 174-192页

作者： Sutanto, Erwin Ma, Yue Davis, H.T. Scriven, L.E. Coating Process Fundamentals Program Ctr. Interfacial Eng. Dept. Chem. E. University of Minnesota 421 Washington Avenue S.E. Minneapolis MN 55455 United States

Cryogenic scanning electron microscopy (Cryo-SEM) was used to examine the distribution of polystyrene (PS) and of poly (butyl methacrylate) (PBMA) latex particles during drying of waterborne suspension coatings. The suspensions were coated on silicon wafer substrates and after different times of drying were rapidly frozen in liquid ethane. Top surfaces and fracture surfaces affording cross-sectional views were examined on the cold stage. The cryo-SEM micrographs demonstrate the presence of abrupt consolidation fronts advancing from the edges of the coatings in the earliest stage of drying of, e.g. suspensions of 10 wt% PS and of 15 wt% PBMA latex. Micrographs successively farther from an edge show that layers of ordered close-packed particles build sequentially downward from the top surface as drying progresses. But depending on the conditions, layered ordering gives way deeper in the coating to inter mixed regions of disordering and ordering. With care about sublimation of frozen water from the surfaces viewed, the cryo-SEM technique is useful for elucidating the compaction process in early stages of drying.

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MULTIPLE STATES OF A VISCOUS FREE SURFACE FLOW: TRANSITION FROM PRE-METERED TO A METERING INFLOW

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International Journal for Numerical Methods in Fluids 1998年第9期24卷

作者： M. S. Carvalho L. E. Scriven Coating Process Fundamentals Program Center for Interfacial Engineering and Department of Chemical Engineering and Material Science University of Minnesota Minneapolis MN 55455 U.S.A.

In a forward-roll coating gap or nip, steady laminar flow of liquid between counter-rotating cylinders or rolls is used to split the flow into a coated layer on one roll and a rejected layer on the other. Both layers have free surfaces in contact with air. Liquid may be carried into the gap as a layer on one or both rolls. If the arriving layer is not too thick, all of the liquid flows through the gap, a situation called pre-metered . If the arriving layer is too thick, part of the liquid is rejected and runs back down the lower roll. The flow rate through the gap is said to be metered and is not known a priori . The transition from a pre-metered regime to the metered situation was examined by solving the Navier–Stokes system for steady, two-dimensional flow in a domain bounded by free surfaces, two rigid roll surfaces and chosen inflow and outflow surfaces. The free boundary condition , as described by Papanastasiou et al. ( Int. j. numer methods fluids , 14 , 587 (1992)), was explored and proved to accommodate both the pre-metered and metered regimes. A run-back flow state across the synthetic inlet plane was obtained, provided a condition on the thickness of the arriving layer was replaced by a kinematic condition at a certain stage. The coupled equation system was solved by Galerkin's method with finite element basis functions. The resulting non-linear algebraic system was solved by Newton's method with initialization by pseduo-arc-length continuation and automatic parameter step adjustment. Results show the existence of multiple solutions which can lead to hysteresis. Flow regime maps were constructed to portray the operating parameter range in which a coating bead can exist and the ranges in which a coating gap operates in either the pre-metered or the metering regime. © 1997 by John Wiley & Sons, Ltd. Int. j. numer. methods fluids 24: 813–831, 1997.

关键词： pre-metered metered free boundary condition free surface flow viscous

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