A new liquid surface conditioner has been developed to improve phosphate coating quality and enable a low-temperature phosphating system designed to reduce CO₂ emissions during the pretreatment processes of automobile production. Phosphate film is formed by a phosphating treatment that provides corrosion resistance for the steel plates that make up auto bodies. In the vehicle body, pocket-shaped structures such as side sills and wheel arches are likely to collect muddy water and form rust. Regarding anticorrosion quality assurance, particular attention must be paid to these pocket structures, in which phosphating solution flows slowly, and a lower solution-volume-to-surface-area ratio contributes less to the phosphating reaction. For this reason, with the conventional liquid surface conditioner, a low-temperature phosphating system cannot coat substrate surfaces sufficiently, which would result in lower corrosion resistance. The new liquid surface conditioner developed in this research improves the phosphate coating quality of substrate surfaces using smaller seed particles, each of which has greater electrostatic charge to improve the stability of the dispersed particles. A combination of the new surface conditioner and a low-temperature phosphating agent has resulted in a low-temperature phosphating system that forms sufficient phosphate coatings even in pocket sections and ensures excellent anticorrosion performance. This system can lower the temperature of phosphating treatment without compromising anticorrosion performance and, in the process, makes it possible to meet CO₂ reduction targets.
