Multicoat applications

Powder coatings are available in FEP, PFA, MFA, ECTFE, ETFE, and PVDF. Typically, a multicoat application is required to achieve a required thickness. The powder size ranges from 1-3.54 milli-inches (25 to 90 microns). 

For barrier coatings to be effective it is necessary to have (i) good adhesion of the barrier film on the metal surface (this is generally accomplished by multicoat procedure to a certain extent) (ii) proper choice of the polymers to control the permeability of oxygen and (iii) optimum film thickness achieved by multicoats or thin-film system, depending upon the envisaged application. 

The first and most extensive use of polyvinyl formal is an insulator for electrical wire. A 1943 General Electric patent describes the typical 105 C formulation. Folyvinyl formal resins have since been formulated into many different wire enamel applications. These include solderable enamels, high cut-through enamels. Freon-resistant enamels for hermetically sealed motors, and multicoat magnetic wires for 155-180 C performance.Work to improve wire enamels is contained in Refs. 31-35. 

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