1. Different substrates require different over-mol...
1. Different substrates require different over-molding materials. For instance, substrates made of PP cannot be over-molded with ABS; substrates made of ABS cannot be over-molded with PA. TPE over-molding materials available in the market can be classified by the substrates they can be used upon: PP, ABS, PETG, PC, PA etc.
2. TPE Adhesive Packaging Thickness:
In most over-molding applications, 1.5-3.0mm is an ideal range of thickness for a good bonding. If the TPE over-molding layer is too thin, injection molding will be difficult, bonding and touch-feel will be poor. If the TPE layer is too thick, not only will cost be higher, but other problems such as jet mark, bubbles may arise.
The thickness of the TPE plastic should be as even as possible in order to achieve an optimum molding cycle. Transitions between different wall thicknesses should be gradual so as to reduce flow ability related problems such as spray marks and bubbles.
3. Radius (minimum radius of 0.5mm) should be increased in part design to avoid local stress caused by sharp corners. Deep chambers without ventilation or vaulted portions should be avoided. Where necessary, add enough vent grooves (0.015-0.025mm) at the end of the TPE plastic. Poor ventilation may result in trapped gas, burnt rubber, poor bonding or other undesirable issues.
4. The addition of undercut onto the substrate, adding snap-fit positions in product design can mechanically improve the bonding of the TPE.
5. Mold Surface Treatments:
Mold should be polished to obtain a smooth or sharp surface.
In order to produce the typical matte effect of thermosetting rubber, the surface of tooling must be rough. In general, the rough surface generated through electrical discharge machining (EDM) inside the mold cavity will produce a good appearance and make de molding easier. Steam jets, abrasive sand blasting or shot peening and chemical etching may be used on the tooling to produce different shininess and surface effects.
To facilitate de molding, a layer of de molding agent may be used on the mold cavity or core; for example, after the discharge process(EDM) or after the sandblasting processing, put a coating of PTFE (polytetrafluoroethylene) impregnated nickel.
6. Avoid using mold release agents on the substrate. The surface of substrate must be clean and free of dust.
7. The processing temperature of TPE rubber should be based on the measured melting temperature rather than the temperature displayed on the injection molding machine.
8. If necessary, TPE can be coated on metal parts on which appropriate adhesive could be used to improve adhesion.
