Optimal Overmolding Grades & Substrate Considerations for Plastics

By Richard Rabe

Related links: Overmolding | Overmolding Design Considerations

Design engineers choose TPEs for improved ergonomics, enhanced grip performance, improved aesthetics, and critical impact protection. Applications that benefit from TPE overmolds range from consumer goods to medical instruments to industrial tools and can include knobs, handles, gaskets, seals and grips.

Benefits of Overmolding

With improvements in TPE materials technology, overmolded part designs have become less dependent on mechanical interlocks to hold a TPE in place.  Chemical bonds between TPE and rigid materials offer improved part integrity and longevity while eliminating the need for adhesives or surface pre-treatments.  System performance can be further optimized by including both chemical and mechanical bonds in the part design.  The net benefit is greatly expanded design freedom.

Chemical bonds in Overmolding:

Optimal Bonding Materials

Molders using multi-shot molding in combination with TPEs need to have a thorough understanding of bonding and how selection of both TPE and rigid substrates affect bond strength. RTP Company offers an expansive line of TPEs for bonding to specific engineering resins and assistance in selecting the ideal grades. The table below shows several examples:

ABS PA 6  PC  PC/ABS PBT/PC PET/PC PC/PMMA  PP  PS RTPU RTP 2700 S RTP 2740 S                   RTP 2800 B                   RTP 2899 X 106530                   RTP 6002       RTP 6003       RTP 6035                 * Checkmarks indicate combination exhibiting very good peel strength (15 pli or greater). * For simplicity, this chart does not incorporate TPE hardness. Typical hardnesses range from 45-75 Shore A, but my be customized to each application.

By offering multiple material options in combination with a variety of substrates, RTP Company’s TPE offering can meet a wide variety of applications where bonding to a rigid substrate is required. RTP Company can also offer modified rigid substrates to expand the material options to designers and engineers and make possible demanding applications that otherwise may not have been possible.