Investigating the Impact of High-Shear and In-situ Drying Rheology on Overall Appearance in High-Solids Automotive OEM Systems

摘要

One of the primary goals in developing superior automotive basecoat formulations is to achieve a distinct rheological profile providing for good atomization and sprayability. While spray application processes typically involve shear rates in excess of 50000 s-1, most commercial rheometers are designed to measure viscosities at much lower shear rates. Difficulties associated with high shear rate measurements include secondary flow generation, shear heating, and the instrumental limit in the resolution of torque and angular velocity. In this paper we describe a novel method to study the high shear rheological profiles of automotive basecoats and their impact on the spray atomization and final appearance of the coating. One of the other objectives was also to gain an understanding of the structure-property-performance relationships of cellulosic additives in high-solids (HS) solventborne coatings in order to better tailor these materials to address ongoing needs in compliant systems. In addition to the advantages they bring to high-solids systems, these additives themselves contain up to sixty percent cellulose, one of the most abundant natural renewable resources This paper explores the use of a developmental additive (DPA 2386) in helping improve brightness and appearance in HS Original Equipment Manufacturer (OEM) basecoats. Fundamental studies correlating the high-shear rheology of automotive coatings with final film properties were also undertaken. Optical profilometry was used to investigate the impact of the additive on the drying mechanism and structure development in coatings, during the initial drying period. Laser Scanning Confocal Microscopy (LSCM) helped reveal the spatial distribution of the metal flakes and the morphology of the dried coating.