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: CF.sub.2 ═CF--O--R.sub.f in which R f represents one or more perfluoroalkyl radicals having from 1 to 10 atoms or a particulate perfluroinated ether having the formula: ##STR2## 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 coats 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 selected from the group of polymers consisting of polybenzimidazoles, polyimide, polyamide-imide, polythiazoles, polyhydroxy benzoic acids, polyphenylenes, polybenzoxazoles, polyquinoxalines, polyoxadiazoles, and polytriazoles.

Claim 5

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 ##STR3## 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 6

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 ##STR4## in which n is 1 to 4.

Claim 7

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 1 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 8

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

Claim 9

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 10

The article of claim 2 which is an article of cookware.

Claim 11

The article of claim 1 or 2 wherein (c) of the coating composition is the nonvolatile content of a solution consisting essentially of: (a) 25-45% by weight, based on the solution, of a salt of a polyamide acid with tertiary amine, wherein the polyamide acid is formed from trimellitic anhydride and bis(4-aminophenyl) methane and wherein the tertiary amine is a 4:1 to 1:4 by weight mixture of triethylamine and diethyl 2-hydroxyethylamine; (b) 10-20% by weight, based on the solution, of furfuryl alcohol; and (c) 10-25% by weight, based on the solution, of N-methylpyrrolidone.

Claim 12

The article of claim 1 or 2 wherein (c) of the coating composition is the nonvolatile content of a solution consisting essentially of: (a) 25-45% by weight, based on the solution, of a salt of a polyamide acid with tertiary amine, wherein the polyamide acid is formed from trimetallitic anhydride and bis(4-aminophenyl) methane and wherein the tertiary amine is a 4:1 to 1:4 by weight mixture of triethylamine and diethyl 2-hydroxyethylamine; (b) 10-20% by weight, based on the solution, of furfuryl alcohol; and (c) 10-25% by weight, based on the solution, of N-methylpyrrolidone; and wherein water comprises 30-55% by weight of the solution.

Claim 13

The article of claim 1 wherein the basecoat is derived from a composition comprising 30-50% (a), 40-50% (b), and 10-20% (c) and a single topcoat is derived from a composition of (a), (b) and (c) comprising 0-10% (c) and wherein (b) is at least 15% and also less than or equal to 0.50 times the proportion of (b) in the basecoat.

Claim 14

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 15

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 0-10% (c); and the topcoat is derived from a composition comprising 85-93% (a), 4-8% (b) and 0-7% (c).

Claim 16

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.

Claim 17

The article of claim 1 or 2 wherein (a) of the coating composition is polytetrafluoroethylene, (b) is as described in claim 8, and (c) is as described in claim 10.

Claim 18

The article of claim 16 wherein a basecoat is derived from a composition consisting essentially of, by weight, 58.68% (a), 37.88% (b) and 3.44% (c); a midcoat of 85.39% (a), 14.60% (b) and 0% (c); and a topcoat of 95.26% (a), 4.74% (b) and 0% (c).