Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 151 of 331

sition paint film and, due to their ability to interact with moisture, limit the cor- rosion performance of these firms. Other undesirable effects can include film staining and discoloration due to the presence of iron in the anodic films. Cathodic Electrocoats Cathodic deposition, where positively charged paint particles are attracted to a negatively charged part, involves much less iron incorporation into the deposi- tion film and consequently offers substantially improved corrosion resistance. Additionally, the polymer species are amine functional and acid solubilized, with the alkaline nature of the polymer leading to better inherent corrosion re- sistance that can be obtained with acid-functional species. Whenever high coating performance is required, cathodic electrocoat systems are generally specified. Market penetration of these coatings into the appliance and automotive industries over the last 30 years bears evidence to the attrac- tiveness of these coatings. Typical End Uses Electrocoats can be segmented into anodic or cathodic, and epoxy or acrylic. Table I illustrates common end uses for the four categories of electrocoats. CURRENT TECHNOLOGY CAPABILITIES Electrocoat research and development has fostered many exciting advance- ments over the past 40 years. Some of the significant advancements enjoyed to- day by end users include closed-loop systems with close to 100% material ef- ficiency and little wastewater discharge; near-zero VOC electrocoats; HAP-free anodic and cathodic products; lead-free cathodic electrocoat with corrosion pro- tection equal to prior lead-containing products; cathodic acrylic coatings with Fig. 4. Principles of anodic and cathodic electrocoat deposition. 150

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