Aqueous composition imparting improved corrosion resistance to metal surfaces contains a hydrolyzable silane and a metal chelate and optionally also an organic film-former and film-forming aid

摘要

Pre-coating of a metal surface prior to further coating or other treatment uses an aqueous composition wholly or mainly free of chromium (VI) compounds and is such that (a) the composition contains (i) an at least partially hydrolyzable silane and (ii) a metal chelate; and (b) the cleaned, etched or pretreated metal is contacted with the composition and the formed film is dried (and optionally hardened) to a thickness of 0.01-10 mu . Independent claims are also included for (1) the process in which the aqueous composition also contains (iii) an organic film-former comprising a water-soluble or -dispersible (co)polymer of acid number 3-250 and (iv) a long-chain alcohol film-forming aid.; and (2) compositions containing (i) and (ii) at 0.1-10 : 1 ratio and optionally also (iii) and (iv) .