specialty elastomers
Two-shot injection molding Santoprene™ TPVs
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Two-shot injection molding involves injecting one material into a mold to form the initial part or section of a part. Once formed, a second material is injected into the mold to form the remainder of the part.
Two-shot molding requires that the two materials be compatible (chemically similar), or no bonding occurs. Standard grades of Santoprene™ TPV bond to polypropylene, some polyethylenes and some TPOs. Nylon-bondable (PA series) grades bond to nylon-6 with a variety of fillers, and to some blends of nylon 6/6 (2-shot molding only). Specialty grades also exist that bond to ABS, polycarbonate, polystyrene, EPDM and metals.
Two-shot injection mold processing tips for Santoprene TPV
- Completely purge all PVC or acetal resin from the machine before or after running Santoprene TPVs.
- If possible, always mold the first shot of the harder material so that the shutoff is easier to obtain.
- Design shutoff on substrate so that clamp pressure is distributed across the interface of the second shot.
- Do not try to shut off on vertical walls
- Shrink of the second shot material will be constrained by the substrate material if a chemical bond is achieved.
- Make sure that the substrate is supported or is thick enough to cope with the injection pressure.
- Ejection of the finished part should primarily be done on the hard substrate (first shot).
- It is far more effective to increase shear rate than to raise melt temperature for filling a mold.
- Injection rate should be 10 to 50 g/sec.
- Injection times range from 0.5 to 2.5 seconds in order to optimize shear.
