Coating and primer formulation on the basis of a copolymer of tetrafluoroethylene and a perfluoro-(alkylvinyl) ether, and use thereof

A method for improving the coating of a substrate with a fluoropolymer which comprises applying a primer composition and subsequently without an intermediate heat treatment for sintering applying a topcoat of a tetrafluoroethylene homopolymer or copolymer wherein the improvement comprises applying a primer composition consisting essentially of

• (a) from 100 to 20 weight %, relative to the total polymer solids of the components (a) and (b), of a copolymer of copolymerized tetrafluoroethylene units;
• from 0.5 to 11 weight % of copolymerized units of a perfluoro(alkylvinyl) ether of the formula CF.sub.2 .dbd.CF--OR, in which R is a perfluoroalkyl radical having from 1 to 10 carbon atoms;
• and from 0 to 12 weight % of copolymerized units of hexafluoropropylene or vinylidene fluoride, each relative to the total weight of the copolymer;
• (b) from 0 to 80 weight %, relative to the total polymer solids of components (a) and (b), of dispersed polytetrafluoroethylene particles having a mean grain size of from 0.05 to 30 .mu.m;
• (c) from 10 to 70 weight % of the weight sum of (a) plus (b) plus (c) of lithium hydroxide and suspended, fine-particle SiO.sub.2 produced by thermal treatment;
• the molar ratio LiOH:
• SiO.sub.2 being from 1:0.5 to 1:30;
• and
• (d) water as liquid carrier.