Paint & Coatings Industry - March 2008 - (Page 76)

The Effects of TPO on Adhesion and Proposed Introduction Thermoplastic pol polyolefins (T lyolefins (TPO) are widely used in TPO) ndustry because they are durable, cause the automotive in industry bec sily d cost effective, eas easily molded into complex shapes and can be recycled. However, the major challenge in using TPO is the poor adhesion of paints (or topcoats). This is due to lack of functionality on the TPO that leads to poor wettability, inertness and low surface energy.1 Several methods have been developed to improve adhesion to TPO. In general, they can be classified as oxidation methods and primer methods. In the oxidation method, the TPO surface is oxidized by treatment with flame, corona discharge,2,3 plasma,4 UV radiation5 or chemical oxidation.6,7 As a result, a more polar surface (by formation of an oxide layer or introduction of polar functionality) enables the adhesion of topcoat to TPO. There are several disadvantages of this method. First, coating must be done soon after treatment because of the reversibly short lifetime of the radical species. Second, chain scission on the surface of the TPO can occur due to over-treating. And third, non-uniform coverage can lead to cohesive failure of the TPO’s surface.8 In the primer method, an adhesion promoter is applied to the TPO surface to increase the polarity, which in turn promotes adhesion of topcoat to TPO. The most common adhesion promoters used in the North American automotive industry are based on chlorinated polyolefin (CPO). Although it requires an additional coating layer (adhesion promoter) to increase adhesion between TPO and topcoat, this primer method is the predominant North American method because it offers flexibility on diverse applications and types of TPOs and topcoats. Previous efforts have been devoted to understanding the mechanism of CPO-TPO adhesion at their interface. The results indicated that CPO-TPO adhesion depends on many factors. Some key factors are type of test performed, baking temperature, strength of modulus, impact modifier, thickness of the interface and the residual solvent in the TPO. Studies by Williams and his coworkers showed that non-chlo- A 76 dhesion of chlorinated polyolefin (CPO) and topcoat on various types of thermoplastic polyolefins (TPO) at three different baking temperatures, 180 ºF (82 ºC), 200 ºF (93 ºC), and 220 ºF (104 ºC), was investigated using a gasoline soak test. The results showed that co-monomer in the TPO and the base used in the topcoat were critical factors in adhesion. Also, a chemical mechanism for adhesion at the interface of topcoat-CPO and CPO-TPO was proposed. Results of preliminary study on chlorinated model compounds are also reported By Timothy S. December, William Merritt, Greg Menovcik, Binh T. Nguyen | BASF Coatings, Coating Research Center, Southfield, MI; and David Choi, Todd Glogovsky | Basell, North American Advanced Polyolefins, Business and Technical Center, Lansing, MI MARCH 2008 | W W W . P C I M A G . C O M http://WWW.PCIMAG.COM

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Viewpoint Industry News Calendar of Events Company News Mergers and Acquisitions Names in the News Marketplace Quarterly Stock Watch Reaching Strict VOC Requirements With Outstanding Durability for Industrial Maintenance and Marine Coatings A Unique Fungicide for Wood-Filled Plastic deSigns of the Times: Slacking Off! From Rocks to Nanos Shear-Free Dispersion Process Fluorinated Oxetane Oligomers as Versatile Intermediates for Polymer Modification The Effects of TPO Composition on Adhesion and Proposed Chemical Mechanism Supplier Showcase Color Management Materials Watch Products Classifieds Advertiser Index

Paint & Coatings Industry - March 2008

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