Solution the aqueous coating acid; process for a coating free from chromate.Resistant to etching on an aluminum surface; the aluminum surface; process for coating surfaces of aluminum and continuous aqueous concenttrado

摘要

A chromate-free acidic aqueous conversion-coating solution which is effective in forming a clear, colourless, corrosion-resistant conversion-coating on an aluminium surface, to which moreover subsequently-applied overlying siccative coatings will adhere tightly, contains a Group IVa metal selected from the group consisting of zirconium, titanium, hafnium and mixtures thereof, as well as fluoride and one or more additives, namely a polyhydroxy compound having no more than 7 carbon atoms, the solution being in that event free of phosphate and boron, or a surfactant or a mixture of said surfactant and said poly-hydroxy compound. The coating-solution is employed in processes for forming conversion-coatings on aluminium surfaces, especially those of aluminium cans, which may thereafter be given a decorative and/or sanitary lacquer or other siccative coating. The coated aluminium is shown to have superior properties. Concentrates are disclosed for making up and also for replenishing the coating solution.