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Kathy Allen + Stacey Marsh

Covestro + Eastman

Improved Scratch Resistance for OEM Clearcoat

Abstract

Over many years of research efforts within the automotive coating industry, chemical resistance and scratch resistance remain at the top of the list of desired improvements. Increased environmental pressure to reduce VOC and increase coating solids has forced formulators to adopt the use of low molecular weight polymers which, in general, adversely impact these properties.

To address these unmet needs, Eastman Chemical Company and Covestro LLC have been working together, combining the strengths of both companies to develop a higher performance resin-crosslinker solution for the automotive market. This work examines the performance of 2K polyurethane automotive OEM clearcoats formulated with Eastman polyester resins containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD) and a silane-modified polyisocyanate crosslinker from Covestro.

Five 2K clearcoat resins were evaluated: three TMCD polyester resins, one control acrylic resin and one control polyester resin. Each of these clearcoat resins were crosslinked with either the silane-modified polyisocyanate or a conventional HDI trimer and evaluated for car wash gloss retention, gloss retention after steel wool, crockmeter scratch and chemical resistance by gradient oven.

Use of the silane-modified polyisocyanate as crosslinker in 2K automotive OEM clearcoat formulations is demonstrated to be very effective in improving carwash gloss retention, while TMCD polyester resins provide superior chemical resistance compared to acrylics and conventional polyesters. Together, TMCD polyester resins and the silane-modified polyisocyanate crosslinker enable low-VOC, high performance automotive OEM 2K clearcoats with a superior balance of carwash gloss retention and chemical resistance.

Biography

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