Water-based metal surface treatment agent

1. A water-based metal surface treatment agent comprising components (1) to (3):

(1) a copolymer, containing in a side chain a diketene or ketoester capable of switching between keto and enol tautomeric forms, and containing at least one hydrophilic side chain containing a cationic group, an anionic group or a nonionic group;

(2) an epoxy resin modified with a phosphoric acid type compound; and

(3) a water-soluble curing agent.

2. The water-based metal surface treatment agent according to claim 1 , at least one monomer of the copolymer of (1) being a dicarbonyl compound represented by undermentioned structural formula (I);

wherein an enol tautomeric form of the dicarbonyl compound is also included, and in formula (I), R1 is a hydrogen atom or a methyl group, R2 is a C2-10 alkenyl group having a double bond at the end thereof or a C1-10 alkyl group, l is 1 to 3, and x and y are each independently 0 or 1.

3. The water-based metal surface treatment agent according to claim 1 , being a water-based metal surface treatment agent for aluminum or magnesium.

4. The water-based metal surface treatment agent according to claim 1 , being a water-based metal surface treatment agent for pre-coated aluminum.

5. A metallic material, having been treated with the water-based metal surface treatment agent according to claim 1 .

6. An aluminum material, having been treated with the water-based metal surface treatment agent according to claim 1 .

7. A magnesium material, having been treated with the water-based metal surface treatment agent according to claim 1 .

8. A pre-coated aluminum material, having been treated with the water-based metal surface treatment agent according to claim 1 .