Study On Improvement In Adhesion And Corrosion Resistance Of Organic Coatings

In order to improve the adhesion and corrosion resistance, silane coupling agents were applied in metal pretreatments and in-situ phosphatizing reagent (ISPR) was dispersed to paint in this paper. The preparation and testing the properties of the films were studied. The results were obtained as follows:KH550was selected as surface treating agent, and the parameters of hydrolysis were decided. It was found out that when the solvent was water and ethanol, pH value was between8and10, content of KH550was15%, hydrolysis time was48h at room temperature. The silane films were prepared by steel substrates dipping in silane solution through2min and curing at200℃for20min, which were prepared to be coated with polyamide-imide (PAI) resin. The multilayer coatings system obtained by curing260℃for20min was called silane-organic coatings (SOCs), and the thickness was controlled in about0.4mm.The formulation of ISPR was optimized by orthogonal test as follows:H3PO42wt%, citric acid0.3wt%, and tartaric acid0.3wt%. The optimum curing temperature of in-situ phosphating coatings (ISPCs) was280℃for15min by electrochemical test.The adhesion and corrosion resistance of coatings was studied. The results showed that the tensile stress of silane-organic coatings was6.25MPa and ISPCs was and7.29MPa, which were greater than the stress of traditional phosphating treatment. After336h immersion in3.5%NaCl solution, the SOCs and ISPCs showed great protective ability, while traditional phosphating coatings had lost efficacy. The Film-forming mechanisms of ISPCs were analyzed. The absorption peaks of P-O stretching vibration were observed at1209/1153/1090cm-1, the absorption peaks of O-P-O deformation vibration were located at678cm-1. A spectral band at930～970cm-1was attributed to the formation of a covalent P-O-C linkage between the metal-phosphate layer and the polymer resin. The result showed that the film reacted with metal substrate and organic polymer.