METHOD FOR MULTILAYER CATHODIC WET-IN-WET LACQUERING OF METAL CONDUCTIVE SUBSTRATE

摘要

PCT No. PCT/EP85/00694 Sec. 371 Date Sep. 25, 1986 Sec. 102(e) Date Sep. 25, 1986 PCT Filed Dec. 11, 1985 PCT Pub. No. WO86/03791 PCT Pub. Date Jul. 3, 1986.The invention relates to a process for coating an electrically conductive substrate, the said substrate being immersed in an aqueous bath based on a cationic synthetic resin binder which is at least in part neutralized with acids and contains amino and/or hydroxyl groups. The said bath contains a mixture of crosslinking agents as well as pigments, fillers, corrosion inhibitors, paint auxiliary substances, and, if appropriate, catalysts, as well as organic solvents in an amount of up to 15% by weight based on the total weight of the coating, the said substrate being cathodically connected. By the action of direct current, a film is deposited on the substrate, after which the said substrate is removed from the bath and the film is cured by stoving, the mixture of crosslinking agents comprising at least two crosslinking agents of different reactivities based on activated esters and/or polyisocyanates blocked by different blocking agents. The expression "different reactivities" means that the crosslinking reaction commences by heating to temperatures which are separated by at least 10 DEG C. and that crosslinking agent which is first to react is present in an amount of 15 to 60 mol %, based on the mixture of the crosslinking agents. This first coat is rinsed and one or more further cathodic coats are deposited before stoving. After each coat has been rinsed, all the coats are cured together.