Metal Finishing Guide Book


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sition paint film and, due to their ability to interact with moisture, limit the corrosion 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 deposition 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 resistance 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 attractiveness 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 advancements over the past 40 years. Some of the significant advancements enjoyed today by end users include closed-loop systems with close to 100% material efficiency and little wastewater discharge; near-zero VOC electrocoats; HAP-free anodic and cathodic products; lead-free cathodic electrocoat with corrosion protection equal to prior lead-containing products; cathodic acrylic coatings with Fig. 4. Principles of anodic and cathodic electrocoat deposition. 260

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