Verfahren zur Herstellung eines Kunststoffmaterials

A normally solid "surface-activated" polyfluorocarbon comprising a thermoplastic material having a molecular weight in excess of 1000 prepared by the polymerization of a compound of carbon and fluorine with or without hydrogen and/or chlorine and/or oxygen and in which there is present from 2-10 carbon atoms is coated with a polyimide having at least 20 recurring units of the structure wherein R is a tetravalent radical containing at least 2 carbon atoms, with no more than 2 carbonyl groups being attached to any one carbon atom of said tetravalent radical, and R1 is a divalent radical containing at least two carbon atoms with no more than one free valence bond of the divalent radical being situated on any one carbon atom. The polyfluorocarbon substrate may be for example polytetrafluoroethylene, polyhexafluoropropylene, polychlorotrifluoroethylene, polyvinylfluoride, polyvinylidenefluoride, copolymers of tetrafluoroethylene and hexafluoropropylene or perfluoromethyl perfluorovinyl ether or perfluoropropyl perfluorovinyl ether. By "surface-activated" is meant that the substrate is treated chemically or physically or both to provide a strong bond between it and the coating. The treatment may be by means of etching with sodium, or by treatment with an electric discharge such as a corona discharge. When a surface of polytetrafluoroethylene is to be coated it may receive a primer coating of a copolymer of tetrafluoroethylene and hexafluoropropylene. The polyimide coating is produced by applying a polyamide acid to the substrate and converting this to polyimide either thermally or chemically. Thermo conversion involves heating to above 50 DEG C., and the chemical method may involve the use of acetic anhydride and pyridine. The process is particularly suitable for coating wire, and many examples are given of coating copper and silver-plated copper wire. Specifications 898,651 and 903,271 are referred to.