Protective coating for machine-readable markings

Claim 1

In a method of protecting a machine-readable marking on the surface of an article by applying to said surface a coating, the improvement of applying a coating of an amorphous fluoropolymer selected from: A) copolymers of perfluoro(1,3-dioxole) with tertrafluoroethylene; B) copolymers of perfluoro(2,2-dimethyl-1,3-dioxole) with at least one comonomer selected from the class consisting of (a) tetrafluoroethylene, (b) chlorotrifluoroethylene. (c) vinylidene fluoride, (d) hexafluoropropylene, (e) trifluoroethylene, (f) perfluoro(alkyl vinyl ethers) of the formula CF 2 ═CFOR f , where R f is a normal perfluoroalkyl radical having 1-3 carbon atoms, (g) fluorovinyl ethers of the formula CF2═CFOQZ, where Q is a perfluorinated alkylene radical containing 0-5 ether oxygen atoms, wherein the sum of the C and O atoms in Q is from 2 to 10; and Z is a group selected from the class consisting of --COOR, --SO 2 F, --CN, --COF, and --OCH 3 , where R is a C 1 -C 4 alkyl, (h) vinyl fluoride, and (i) (perfluoroalkyl)ethylene, R f CH═CH 2 ; where R f is a C 1 -C 8 normal perfluoroalkyl radical; and C) cyclic aliphatic homopolymers in which the repeating unit contains an aliphatic ring of 5-9 members, at least two of the ring members being carbon atoms independently substituted either by fluorine atoms or by perfluoromethyl groups, and at most two of the ring members being oxygen atoms, the remaining portions of the repeating units, when present, being perfluoromethylene groups,