Direct Adhesion of Nylon Resin to Stainless Steel Plates Coated with Triazine Thiol Polymer by Electropolymerization during Injection-Molding

Abstract

6-Nylon resin (PA6) directly adhered to stainless steel (SUS) plates coated with triazine trithiol polymer (TTP) during injection-molding. TTP coating on the SUS plates was formed by electropolymerization of 1,3,5-triazine-2,4-dithiol-6-sodium thiolate in aqueous solution. Adherends between PA6 and the SUS plates had high shearing strengths of 6MPa or more. The adhesion mechanism was investigated by X-ray photoelectron spectroscopic (XPS) analyses of TTP coating on the SUS plates and model reactions of TTP prepared from s-triazine trithiol by chemical oxidation (CO-TTP) with amines and nylon oligomer. The result of XPS analyses showed that TTP formed iron or chromium mercaptide at the interfaces of SUS and TTP coating. The reactions of CO-TTP with amines gave amino triazine thiol derivatives. In NMR spectra of nylon oligomer kneaded with CO-TTP at 220°C, the proton signal of methylene adjacent to terminal amino group disappeared. The mechanism of adhesion was explained to be a formation of chemical bonds at the interface of PA6 and TTP coating, which chemically bonded to SUS by the nucleophilic substitution of terminal amino groups in PA6.