Synthesis of a Water-Reducible Polyester Resin Curable with Melamine and Investigation of Anti-Corrosion and Adhesion Properties

Solvent and water-based polyester resins are used in many different applications; one of them is the automotive paints' primary layers. In this research, a water-reducible polyester resin curable with melamine was synthesized (PS۱). This resin was cured for ۳۰ minutes with a temperature of ۱۲۰ ˚C. The final product is a water-reducible resin, which was synthesized, neutralized and diluted with water, and consequently, a milky white water-based dispersion was obtained. The indicating peaks of the Fourier Transform Infrared (FTIR) test alongside the results of the Differential Scanning Calorimetry (DSC) test were proof to confirm the control over the polyester resin synthesis. To evaluate the anti-corrosion and adhesion properties, the synthesized resin in a full-coating system was compared with a commercial resin. The pull-off test was used to check the adhesion strengths. PS۱ (polyester resin) coating system revealed an adhesion strength value of ۲.۰۵ MPa compared to ۲.۵۱ MPa for RW۱۰۰. Digital images taken from the samples' surface in the salt spray test showed that after one month in a corrosive environment, synthesized resin has better anti-corrosion resistance than commercial sample. Electrochemical Impedance Spectroscopy (EIS) test indicated that after ۱۵ weeks of immersion in the ۳.۵% sodium chloride electrolyte solution, the synthesized resin system indicated an impedance resistance at low frequency of ۴.۰۵ ×۱۰۹ ohm.cm۲, which is more than the Daotan VTW ۱۲۲۵ (۲.۷۵ ×۱۰۶ ohm.cm۲).