Insert molding Santoprene™ TPVs

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Insert molding (sometimes called overmolding) consists of placing a solid insert into the mold and injecting Santoprene TPV around it. If the insert and the TPV are compatible materials, a melt bond occurs at the interface between the two materials. The strength of this bond is affected by several factors, including bonding grade characteristics, interface temperature, cleanliness of the insert and the melt temperature of the TPV.

Bonding can be improved by preheating the insert and ensuring that the surface of the insert is free from dirt, grease and hand oils. Noncompatible insert materials such as metal can also be used, but an adhesive must be applied to the insert so that it bonds with the TPV.

Another way of combining incompatible materials is to design the part with mechanical locks, so the molten TPV material flows into the locking area and creates a bond.

For low-volume applications requiring insert molding, the inserts can be hand-loaded. For higher volumes, robotic pick and place equipment may be a cost-effective choice. Applications need to be evaluated on a case-by-case basis to learn which method is most cost-effective.

Download our injection-molding tips and find out how Santoprene TPV grades can be easily and efficiently processed using conventional thermoplastics injection-molding equipment.

Insert molding processing tips for Santoprene TPV

  1. Completely purge all PVC or acetal resin from the machine before or after running Santoprene TPVs.
  2. Make sure the substrate is clean and free of and foreign materials.
  3. Design shutoff on substrate so that clamp pressure is distributed across the interface of the overmold.
  4. Do not try to shut off on vertical walls
  5. Shrink of the overmolded material will be constrained by the substrate material if a chemical bond is achieved.
  6. Make sure that the substrate is supported or is thick enough to cope with the injection pressure.
  7. Cooling time depends on wall thickness, grade and tool design. Please consult the Santopene TPV “Injection Molding Guide.”
  8. It is far more effective to increase shear rate than to raise melt temperature for filling a mold.
  9. Injection rate should be 10 to 50 g/sec.
  10. Injection times range from 0.5 to 2.5 seconds in order to optimize shear.