Two-shot injection molding

The technique - a two-step injection-molding process, performed during a single press cycle - first injects the hard material into the mold cavity, followed instantly by the second injection, often of a TPE (thermoplastic - elastomer).

Over molding processes are used to create integrated seals, acoustic- damping elements, and non-slip, impact and vibration-absorbing surfaces. These over molded parts are used in a broad range of applications such as in automobiles, material handling and audio systems. Other potential end uses include packaging, electrical connectors, paper transport rollers in office equipment, plumbing, heating and air conditioning seals and gaskets, and soft grips on power tools.

And there is more good reason for combining soft and hard plastics. For instance, directly molding soft elements onto hard plastic substrates consolidates two or more components thus eliminating additional assembly costs. Injection molding also expands design flexibility making difficult-to-assemble parts, such as complex gaskets for hard-to-reach places, in a single step.

Two-shot molding is also beneficial in packaging applications where a secondary color is desired to give products a unique appearance.