Article coated with fluoropolymer finish with improved durability

Claim 2

An article comprising a substrate having on it multiple coatings, including a basecoat directly on the substrate, which basecoat is overlaid by at least one other coat, and wherein the basecoat is derived from a composition consisting essentially of, by weight: (a) 15-65% of a particulate polymer of monoethylenically unsaturated hydrocarbon monomers completely substituted with fluorine atoms or a combination of fluorine and chlorine atoms, the polymer having a number average molecular weight of at least 20,000; (b) 30-50% of at least one of a particulate copolymer containing (i) 99.5-92% of tetrafluoroethylene, (ii) 0.5-8% of at least one perfluorinated vinyl ether having the formula: in which R f represents one or more perfluoroalkyl radicals having from 1 to 10 atoms or a particulate perfluorinated ether having the formula: in which n is zero to 4, and, optionally, (iii) hexafluoropropylene; and (c) 0-25% of a polymer having a glass-transition temperature greater than or equal to 130°C which is also thermally stable at temperatures up to 200°C; and wherein the other topcoats are derived from a composition consisting essentially of (a), (b) and (c), with the concentration of (b) being at least 10% by weight, and also less than or equal to 0.75 times the proportion of (b) in the basecoat composition, and the concentration of (c) being 0-15%.

Claim 3

The article of claim 1 wherein the basecoat is overlaid with two coats of a composition consisting essentially of (a), (b) and (c) of claim 1, where the composition of the midcoat comprises, by weight, 55-90% (a), 10-30% (b), and 0-15% (c), and the composition of the topcoat comprises 80-100% (a), 0-10% (b), and 0-10% (c).

Claim 4

The article of claim 1 or 2 wherein (c) of the coating composition is a polyamide acid salt consisting essentially of the nonvolatile content of: (a) 10-70% by weight, based on the solution, of a salt of a polyamide acid with a tertiary amine, wherein the polyamide acid is of the general formula wherein G is a hydrogen atom or a carbonyl group; wherein the → denotes isomerism so that in any recurring unit within the polymeric structure the groups to which the arrows point may exist as shown or in an interchanged position; wherein R is an organic tetravalent radical containing at least two carbon atoms and no more than two carbonyl groups of each polyamide acid unit are attached to any one carbon atom; wherein R 1 is a divalent radical containing at least two carbon atoms, the amide groups of adjacent polyamide acid units are attached to separate carbon atoms of said divalent radical; and wherein n is an integer sufficient to provide a polyamide acid having an inherent viscosity of at least 0.1, preferably 0.3-5.0, as measured as a 0.5% solution in N, N'-dimethylacetamide at 30°C, and wherein said tertiary amine is present in at least a stoichiometrically equivalent amount to the free carbonylic acid groups in said polyamide acid; (b) 5 to 25% by weight, based on the solution, of a viscosity reducing agent which is miscible with water and has a solubility parameter range of 10-21.6 wherein said solubility parameter has a dispersion component in the range of 7.0-10.0, a polar component in the range of 2.0-11.0, and a hydrogen bonding component in the range of 7.0-14.0; (c) 5 to 35% by weight, based on the solution, of a coalescing agent, wherein said coalescing agent is at least one member selected from the group consisting of N-methylpyrrolidone, dimethyl formamide, dimethyl acetamide, dimethyl sulforide, eresylic acid, sulfolane, formamide; and wherein water comprises 30-80% by weight of the solution.

Claim 5

4', The article of claim 1 or 2 wherein (b) of the coating composition is one or more copolymers of perfluoroalkyl perfluorovinyl ethers with tetrafluoroethylene, said ether having the formula in which n is 1 to 4.

Claim 6

The article of claim 1 or 2 wherein (b) of the coating composition is a terpolymer consisting of, in copolymerized form, (a) tetrafluoroethylene, (b) between about l.and 12 weight percent hexafluoropropylene, and (c) between about 0.5 and about 6 weight percent of either perfluoro(ethyl vinyl ether) or perfluoro-(n-propyl vinyl ether).

Claim 7

The article of claim 1 or 2 wherein (a) of the coating composition is polytetrafluoroethylene.

Claim 8

The article of claim 1 or 2 wherein (b) of the coating composition is a copolymer consisting of, in copolymerized form, polytetrafluoroethylene and 3% perfluoro (propyl vinyl ether).

Claim 9

The article of claim 2 wherein the basecoat is derived from a composition comprising 30-50% (a), 40-50% (b) and 10-20% (c); the midcoat is derived from a composition comprising 70-80% (a), 15-20% (b) and 5-10 % (c);,and the topcoat is derived from a composition comprising 85-93% (a), 4-8% (b) and 3-7% (c).

Claim 10

The article of claim 2 wherein the basecoat is derived from a composition comprising 30-50% (a), 40-50% (b) and 10-201 (c); the midcoat is derived from a composition comprising 70-80% (a), 15-20% (b) and 0-10% (c); and the topcoat is derived from a composition comprising 85-93% (a), 4-8% (b) and 0-7% (c).

Claim 11

The article of claim 2 wherein the ratio of (a) to (b) is 60/40 in the basecoat, 85/15 in the midcoat, and 95/5 in the topcoat.