A series of aqueous latexes with solid contents of 56%-59% were synthesized by binary emulsion copolymerization of vinylidene chloride (VDC) with an acrylate, namely methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA), hexyl acrylate (HA), or 2-ethylhexyl acrylate (EHA). Differential scanning calorimetry (DSC) and Fourier-transform infrared (FTIR) spectroscopy showed that the acrylate units with short ester side-chains, such as MA and EA, made the copolymers hard and the crystallization tendency of their PVDC segments was reduced. Hydrophobic acrylates with relatively long ester groups, such as HA and EHA, gave flexible copolymers, and favored the crystallization of their PVDC segments. BA endowed the copolymers with medium flexibility and crystallization tendency. As coating materials, the copolymers bearing MA and EA adhered poorly to the tinplate before or after 100 hr of salt-spray corrosion, whereas those bearing BA, HA, or EHA showed good adhesion to tinplate when they had little or no crystallinity. After 100 hr of salt-spray corrosion, only BA-VDC80, containing 80% VDC, retained both excellent adhesion to metal and excellent barrier performance. Further study demonstrated that BA-VDC80 could protect tinplate from rusting for at least 250 hr under harsh salt-spray corrosion. Scanning electron microscopy, FTIR-attenuated total reflectance spectroscopy and DSC were used to evaluate the corroded BA-VDC80 film.

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), were employed to form a double-layer coating film for the heavy-duty anticorrosion of metal. Measurements of the water-vapor transmission rate and oxygen-gas transmission rate and electrochemical impedance spectroscopy (EIS) demonstrated that the barrier properties of MA–VDC and EA–VDC films were better than those of BA–VDC and EHA–VDC films. Among the MA–VDC and EA–VDC coatings, EA–VDC85 showed better comprehensive properties and, thus, was selected as the top layer of the designed double-layer coating film. Adhesion tests demonstrated that the BA–VDC and EA–VDC coatings had better adhesion to tinplates than the MA–VDC and EA–VDC coatings and, thus, were suitable for use as the bottom layer of the designed double-layer coating film. The characterizations of the double-layer coating films by adhesion tests and EIS showed that BA–VDC75 was the optimal bottom layer. Under harsh salt-spray corrosion conditions, the optimal double-layer coating film (ca. 50-μm thickness) with EA–VDC85 as the top layer and BA–VDC75 as the bottom layer could protect tinplate well for at least 800 h, and the adhesion of the coating film to the tinplate was still excellent even after 1000 h of corrosion. Scanning electron microscopy, differential scanning calorimetry, and Fourier-transform infrared spectroscopy were used to evaluate the corroded double-layer coating films.

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