Surface-tension-driven flows of coatings: Bondline readout formation |
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Authors: | Richard H J Blunk and James O Wilkes |
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Affiliation: | (1) General Motors Corporation, USA;(2) The University of Michigan, USA |
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Abstract: | Bondline readout (BLRO) is a coating defect frequently observed on adhesively bonded, polymeric automotive body panels. This
paper addresses ridging BLRO in clearcoats, not optical and mechanical BLRO, which are characterized by metalflake orientation
(dark/light effects) in basecoats and by distortion in substrates, respectively. Ridging BLRO is due to film thickness differences
and results from Marangoni-type, surface-tension-driven flows. In this study, the effects of several parameters on BLRO are
investigated experimentally. These parameters include initial film thickness, heating rate, viscosity, solvent-to-resin surface-tension
ratio, and solvent volatility. The experiments clearly demonstrate three modes of BLRO flow—formation, flow-out, and reformation—that
result from competing surface-tension-gradient forces (temperature- versus concentration-induced). Experimental results are
used to validate a proposed BLRO mechanism and, in subsequent work, a BLRO-predicting numerical code.
R & D Center, MD 480-102-000, 30500 Mound Rd, Warren, MI 48090-9055, email: rick.blunk@gm.com.
Department of Chemical Engineering, Dow Building, Ann Arbor, MI 48109-2136, email: wilkes@umich.edu. |
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