Development of a Highly Anti-Corrosive Organic-Inorganic Hybrid Paint 2016-01-0540

A highly anti-corrosive organic-inorganic hybrid paint for automotive steel parts has been developed. The inorganic component included in the paint is silicon dioxide (SiO₂), which has the capability to passivate zinc. By application of the paint on a trivalent chromatetreated zinc-plated steel sheet or a trivalent chromate-treated zinc-nickel-plated steel sheet, high anti-corrosion protection can be provided to steel materials. Particularly in the case of application over a zinc-nickel-plated steel sheet, 0 mm corrosion depth after a cyclic corrosion test (CCT) of 450 cycles was demonstrated. An investigation of the mechanism of this corrosion resistance leads to the following observations: 1) Even in an area where the paint coating is missing, SiO₂ is precipitated to cover the steel material and passivate the zinc. 2) The passive material is Simonkolleite (Zn₅(OH)₈Cl₂·H₂O) and it fills the area from where the paint has been lost. 3) The deposition layer is closely packed by the effect of trivalent chromate and the passivation of the deposition is maintained by nickel. With this closely packed deposited layer, the painted material demonstrates a high corrosion resistance.