Fluoropolymer coating compositions having improved adhesion

Claim 1

An article bearing a primer coat and topcoated with a fused fluoropolymer enamel, wherein the primer coat is produced from a primer coating composition comprising a. about 10-90%, by weight of (a) and (b) solids, of a particulate polymer of monoethylenically unsaturated hydrocarbon monomers completely substituted with fluorine atoms or a combination of fluorine atoms and chlorine atoms, having a number average molecular weight of at least 20,000; b. about 10-90%, by weight of the total of (a) and (b) solids, of a binder which comprises 1. about 5-95%, by weight of the total of (1) and (2) solids, of an alkali metal silicate having an alkali metal oxide mol content within the range of from a trace amount to about 20% of the total number of mols of alkali metal oxide and silicon dioxide, and 2. about 5-95%, by weight of the total of (1) and (2) solids, of a salt of a polyamide acid represented by the structure ##STR3## where G is hydrogen or a carboxyl group; → denotes isomerism; R is a tetravalent organic radical containing at least two carbon atoms, no more than two carbonyl groups of each polyamide acid unit being attached to any one carbon atom of said tetravalent radical; R 1 is a divalent radical containing at least two carbon atoms, the amide groups of adjacent polyamide acid units each being attached to separate atoms of said divalent radical; and n is a number large enough to give the polyamide acid an inherent viscosity of at least 0.1, measured as a 0.5% solution in N,N-dimethyl acetamide at 30° C., neutralized with a stoichiometric amount of a tertiary amine; c. about 10-90%, by weight of the polyamide acid amine salt, of N-methyl pyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, cresylic acid, sulfolane or formamide; and d. a liquid carrier.