Cathodic electrocoating system

Both anodic and cathodic electrocoating systems are in use. The anodic systems contain carboxylated polymers where the acid groups are neutralized with amines or KOH. The cathodic systems contain amino-functional resins where the amine groups are neutralized with an acid. 

Two types of system are available anodic and cathodic. The cathodic electrocoating system is the most common with the part to be coated given a negative charge, attracting positively... 

Since particle charge in these latexes is not pH dependent, the mechanism outlined above for the conventional electrocoating systems cannot apply. It was clear from the start that the difference in the behavior of sulfonium and quaternary ammonium stabilized latexes is related to the greater reactivity of the sulfonium ion. Though stable in dilute aqueous solutions, sulfonium ions might be expected to undergo rapid decomposition under the conditions obtained at the cathode surface while current is flowing. However, the specific reactions involved were not known. 

Electrocoating vehicles were initially prepared from natural oils and maleic anhydride (21). Those adducts can then be solubilized by ammonia or other bases. Electrocoating resin systems were initially anodic because of ease of preparation and availability of acidic monomers. About 10 years after the introduction of anodic electrocoating, cathodic electrocoating was developed by Bosso and first successfully applied to air conditioner compressors (22. 23). 

A practical and effective crossHnking mechanism in cathodic electrocoating is done with polyfunctional blocked isocyanates. The mechanism involves the reaction of an isocyanate group (NCO) with the hydroxy group of the epoxy backbone and liberation of the blocking group. Other crossHnking mechanisms that have been studied are use of addition polymers, Mannich bases, Michael adducts [110] sulfonium stabilized polymers, transesterification reaction of hydroxy, alkoxy, amido and ester systems with hydroxy functional cathodic backbone (Fig. 7-5) [111-114]. 

Cathodic electrocoating is employed extensively in the automotive industry, where basically three filtration systems are commonly used ... 

Many automobiles and appliances are coated with a waterborne primer applied by electrodeposition in a process called electrocoating. The metal car or appliance is one electrode. Either anodic or cathodic electrodeposition can be used. This is better than a spray system with solvent in... 

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