Nippon Paint Surf Chemicals Co., Ltd.

Ayako Obora

Yuko Wada

Akira Utsunomiya

Shota Sasaki

The present invention provides an aqueous surface treatment agent which is used for surface treatment of a metal and contains a trivalent chromium compound (A), a water-soluble or water-dispersible acrylic resin (B), a polyfunctional epoxy compound (C) and a phosphoric acid compound (D), wherein: the water-soluble or water-dispersible acrylic resin (B) has a weight average molecular weight of 30,000 to 1,000,000 and a solid acid value of 500 mgKOH/g to 780 mgKOH/g; the ratio of the mass of trivalent chromium contained in the trivalent chromium compound (A) to the total mass of solids is 3% to 15%; the ratio of the mass of solid content of the polyfunctional epoxy compound (C) to the total mass of solids is 1% to 15%; and the ratio of the mass of solid content of the phosphoric acid compound (D) to the total mass of solids is 5% to 25%.

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Tokyo, Japan

Ayako Obora