Development of Adhesion Technology for Polypropylene and Metal Utilizing Zinc Diacrylate

Polypropylene (PP) exhibits excellent rigidity, heat resistance, and low density. To enable lightweight automotive designs through the multi-material integration of PP with metal, we have developed an innovative adhesive polyolefin capable of bonding these two promising materials.The adhesive polyolefin is composed of a thermoplastic elastomer, zinc diacrylate (ZDA) as a reactive adhesion component, and a specific peroxide. Press-heated molding with this adhesive polyolefin achieved bonding between PP composites and aluminum, achieving a high tensile shear strength exceeding 10 MPa. In contrast, polyolefin without ZDA displayed no adhesion to aluminum.After the peel test with the adhesive polyolefin/aluminum bonding sample, observation of the aluminum surface using SEM-EDX revealed the presence of residues containing a high concentration of zinc elements. To elucidate the adhesion mechanism involving ZDA and peroxide, FT-IR, STEM-EDX, and XPS measurements were conducted. The results suggested that the adhesive polyolefin containing ZDA adheres to aluminum through the following mechanisms :1. During heat treatment in compression molding, ZDA segregates to the aluminum interface.2. Segregated ZDA at the interface undergoes polymerization and crosslinking with polyolefin, initiated by radicals generated from the peroxide.