Showa Denko in Japan developed an innovative technology to directly bond aluminum alloys and polycarbonate resin (a commodity amorphous engineering plastic) without using an adhesive. One possible application for this technology is the housings for smart phones, which require a high level of durability.
It is common to join aluminum alloys and polycarbonate resin through mechanical joining (bolts, screws, etc.) or adhesive bonding. In recent years, research and attention has been focused on developing new technologies that could directly bond metals to resin materials at the time of injection molding. The aim is to to simplify process, increase productivity, and enable the processing of the bonded material into complicated shapes.
However, such technologies have traditionally depended on mechanical bonding, such as the anchor effect resulting from the injection of resin into a roughened metal surface. Since this does not provide suitable bond strength, it has been believed that joining polycarbonate resin (and other amorphous engineering plastics) to metals would not be viable using metallic materials by conventional methods.
The new joining technology developed by Showa Denko addresses this challenge by implementing a special surface and primer treatment for the aluminum alloys, which provides covalent bonding (considered to be the strongest form of chemical bonding) in addition to the anchor effect provided by mechanical bonding. Covalent bonding is considered to be about 100 times as powerful as intermolecular force.
The company’s experiments show that the new technology can be used under ordinary polycarbonate molding conditions, providing sufficient bond strength of more than 25MPa (based on tension shear tests). No special conditions or equipment is required to securing the required bond strength.
Showa Denko plans to continue development work to optimize its aluminum surface treatment and primer coating technology in order to further increase the bond strength and durability. In the future, the company will aim to use the technology in the area of super engineering plastics with higher heat resistance for automotive parts applications.
This focus is inline with Showa Denko’s overall business plan, which involves promoting cooperation among various business segments. The automobile and electronic device industries have an increasing need for diversified and sophisticated materials that are lightweight and have improved characteristics regarding heat dissipation, heat accumulation, and insulation. In view of such market needs, the company is working to develop compound materials by combining its own diversified technologies. The development of the metal/resin direct bonding technology is one example of such efforts.