Method for hydrophilic treatment of aluminum using an amphoteric polymer

A method for forming a hydrophilic coating on an aluminum surface comprising contacting said surface with an aqueous solution comprising at least one polymer or copolymer selected from the group consisting of

• (1) an amphoteric copolymer having the empirical formula (I).sub.l -(II).sub.m -(III).sub.n -(IV).sub.o in which
• (I) is ##STR8## wherein R.sub.1 represents H or CH.sub.3 and R.sub.2 and R.sub.3 represent H, alkyl radical of C.sub.1 -C.sub.4, benzyl radical or alkanol group of C.sub.2 -C.sub.3
• (II) is an unsaturated cationic monomer;
• (III) is an unsaturated anionic monomer;
• (IV) is a nonionic monomer capable of copolymerization;
• and wherein l, m, n and o represent mole % and l+m+n+o=100 l.gtoreq.40;
• m=1-59;
• n=1-59 and o=0-30
• and (2) an amphoteric polymer obtained by the reaction of a homopolymer or copolymer of monomer (I) by
• (i) Conversion of amide radical to carboxyl radical by hydrolysis,
• (ii) Conversion of amide radical to ##STR9## by Mannich reaction with ##STR10## and formaldehyde wherein R.sub.4, R.sub.5 are alkyl radical of C.sub.1 -C.sub.4, alkanol group of C.sub.2 -C.sub.3 or benzyl,
• (iii) Introduction of --CONH--R.sub.6 --NH.sub.2 by the Hofmann reaction between side-chain ester radical and alkylenediamine (H.sub.2 N--R.sub.6 --NH.sub.2), wherein R.sub.6 is alkylene radical of C.sub.2 -C.sub.6,
• (iv) Conversion to quaternary amino compound, by alkylating the amino radical of the reaction product of (ii) or (iii),
• and thereafter drying the solution on the surface.