Effects of azo-metal complex dyes on properties such as lightness value were investigated to examine a black thin organic coating (1-2 μm) on galvanized steel sheet for electrical appliances. This product consists of chromate coating and black thin organic coating on an electrogalvanized steel sheet or a Zn-Ni alloy plated steel sheet.
(1) Solvent azo-metal complex dye, solvent azo dye, carbon black pigment, and aniline black pigment were surveyed. The L-values of the thin coatings containing solvent azo-metal complex dye with 30-40 wt% content were less than 15, whereas the L-value of coatings containing carbon black pigment were more than 23. The dye was considered to be solved uniformly, although carbon black pigment aggregated in the thin coatings. (2)The weathering resistance of the coating containing azo-metal complex dyes was superior to that of coatings containing azo dyes. (3)The black thin coating containing azo-metal complex dyes can provide both good corrosion resistance and spot weldability. (4) Results demonstrate that the black thin organic coating (1-2 μm), consisting of azo-metal complex dye and organic resin, can provide a good black appearance, weathering resistance, corrosion resistance, and spot weldability.