Whether you’re designing a product with soft-touch overmolded plastic or a seasoned expert in injection molding techniques, everyone can benefit from reviewing the fundamentals.
Here we package it all up for you: the essential considerations we use in our Application Development Lab to formulate and test overmolded thermoplastic elastomer (TPE) materials for optimal adhesion:
1. Molding Process Options
Will you be using insert molding or multi-shot molding?
Insert molding requires less capital investment; you can use a conventional single-shot machine and the tooling costs are lower compared to multi-shot molding. However, in most cases better adhesion is achieved with multi-shot versus insert molding.
With multi-shot molding, the substrate is still quite hot when the TPE is shot over it, which helps with the TPE-substrate interactions and leads to optimal adhesion. With insert molding, parts are often preheated (excluding certain crystalline materials) before the second shot to improve adhesion.
A rule of thumb: Use insert molding for annual production volumes less than 250,000 units.
Need troubleshooting help? Ask a question of our overmolding experts.
2. Material Selection: TPE and Substrate
What substrate material do you plan to use?
The substrate material is the primary factor in choosing the right TPE chemistry.
Styrenic TPEs and thermoplastic vulcanizes (TPV) will generally adhere to polyolefins like PP and PE. However, these standard TPEs exhibit poor adhesion to engineering plastics like polycarbonate and ABS, for example. These TPEs need to be chemically modified to adhere to a specific substrate. A TPE that is modified to bond to nylon won’t necessarily bond to PC. Teknor Apex’s TPE portfolio includes materials that adhere to the following engineering thermoplastics:
- PC, ABS, PC/ABS blends
- polyamides (standard or GF-filled Nylon 6, 66 and 12)
- polystyrenes (GPPS, HIPS, or blends)
- polyacrylates (PMMA)
- copolyesters (TritanTM)
- polyacetals (polyoxometalate, POM)
- ASA (acrylonitrile styrene acrylate copolymers)
- PBT (polybutylene terephthalate)
- PPO (polyphenylene oxide)
Tip: Need help identifying the right hard-soft match? Download our product selector guide.
Are you looking for some basic tips to get started or ways to improve your design?
Consider these helpful tips:
- Ensure the thickness of the TPE overmolding is sufficient enough not to cause delamination.
- Use mechanical interlocks to reinforce the overmolding.
- A textured mold finish for the substrate provides additional surface area and spaces for the TPE to flow into, providing a mechanical interlock on a micro level.
Need help optimizing your process? Ask our engineers!
Looking to deepen your overmolding know-how? Download our overmolding guide:
