Optimizing heavy-duty anticorrosive performances of coating films formed by acrylate-vinylidene chloride copolymer latexes through twice-painting technique

Twice-painting technique was adopted to prepare heavy-duty anticorrosive coating films formed by aqueous latexes of copolymers of vinylidene chloride (VDC) with an acrylate, namely methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA) or 2-ethylhexyl acrylate (EHA). Harsh salt-spray corrosion tests demonstrated that the optimized twice-painting technique was that the acidic latex solution was adjusted to pH 5–6 for the first painting, while it was utilized directly for the second painting. The test of 600 h of harsh salt-spray corrosion showed that MA-VDC85 coating could protect the steel excellently, whereas the other acrylate-VDC coatings with 75%–90% VDC content could not protect the steel so effectively. Further corrosion test showed that (1) MA-VDC85 coating protected steel from loss of metallic luster for at least 1000 h of salt-spray corrosion; (2) adhesion of MA-VDC85 coating to steel was excellent for at least 800 h of salt-spray corrosion, but became very poor after 1000 h. Differential scanning calorimetry, thermogravimetric analysis, X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy were used to evaluate the corroded MA-VDC85 film.