PURPOSE: To prevent an electrodeposition coating bath liquor from hue change due to miscellaneous ion contamination by replenishing an electrodeposition coating bath liquor with a relevant coating specified with hue difference from the bath liquor in its preparation.
CONSTITUTION: An electrodeposition coating bath liquor is replenished with a relevant coating with the color difference from the bath liquor in its preparation being: ΔL: 0-5, Δa: -1 to 2, Δb: -10 to 1. This coating is composed of, for example, (A) 41.5 pts.wt. of titanium dioxide, (B) 0.03 pts.wt. of carbon, (C) 0.05 pts.wt. of red oxide, (D) 0.5 pts.wt. of yellow iron oxide, (E) 103.73 pts.wt. of a cationic acrylic resin, (F) 35 pts.wt. of Butyl Cellosolve and (G) 819.91 pts.wt. of demineralized water. At a time point when the electrodeposition coating bath liquor with an NV of 15% containing diacetic acid (MEQ 25) as neutralizing agent gives the following hue change, ΔL: 1.3, Δa: -0.89, Δb: 4.16 after an elapse of four months since its preparation, this bath liquor is replenished with a relevant coating having ΔL: 0.3, Δa: 0.7, Δb: -4.2, comprising 41.5 pts.wt. of the component A, 0.03 pts.wt. of the component B, 0.07 pts.wt. of the component C, 103.73 pts.wt. of the component E, 35 pts.wt. of the component F and 187 pts.wt. of the component G.
HASHIMOTO SHINICHI
TANABE TOSHIYUKI
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