Japan’s Showa Denko (SDK) has developed a technology to directly bond aluminum alloys to polycarbonate resin — a non-crystalline commodity engineering plastic — without the need for use of an adhesive.

It is common to bond aluminum alloys and polycarbonate resin through mechanical joining (using bolts, and the like) or adhesive bonding (using an adhesive). In recent years, much attention has been focused on new technologies that directly bond resin materials — during injection molding — to metallic materials via insert molding.

These technologies are expected to simplify processes, increase productivity, and enable processing into complicated shapes. In many cases, however, they depend on mechanical bonding, such as realizing an anchor effect through injection of resin over a roughened metal surface. Thus, it was believed that polycarbonate resin (and other non-crystalline engineering plastics) would not be suitable for joining/bonding with metallic materials using these conventional methods.

A leading aluminum supplier in its own right, SDK has enabled such direct joining/bonding based on its expertise in aluminum alloys and polymer chemistry. Specifically, SDK has developed a bonding technology based on special surface treatment and primer treatment for aluminum alloys, realizing chemical (covalent) bonding in addition to the anchor effect.

Tests show that the new technology can be used under ordinary polycarbonate injection molding conditions, providing sufficient bond strength of more than 25 MPa (tension shear test: ISO 19095). Further, there is no need for special conditions or equipment in securing sufficient bond strength.

This technology enables the direct bonding of commodity polycarbonate resin and light-weight aluminum and is applicable to smartphone housings. SDK will continue development work to optimize its aluminum-surface-treatment technology and primer-coating conditions, thereby increasing bond strength and durability. In the future, SDK will aim to use the technology in the area of advanced engineering plastics with higher heat resistance for automotive parts applications.