Blow molding Santoprene™ TPVs
The extrusion blow-molding process is a very common thermoplastic molding process used with Santoprene TPV . A molten tube – or parison – is extruded, then enclosed in a mold cavity and injected with a compressed gas (commonly air). The compressed gas forces the parison to expand outward, forming a hollow article in the shape of the mold. After sufficient cooling, the mold is opened and the article ejected.
Extrusion blow molding of Santoprene TPVs offers the potential for parts cost savings and design flexibility compared with traditional thermoset rubber parts.
Santoprene TPVs are well suited for most blow-molding technologies, such as single layer, multilayer, exchange blow, sequential 3D, suction blow, flashless extrusion blow, injection blow and press blow.
Blow molding tips for Santoprene TPV
- Pre-dry ALL Santoprene TPVs (except 8xxx grades) at 71°C - 82°C (160°F -180°F); 3 hours for virgin material and 4 hours for reground material.
- Use polypropylene- or polyethylene-based carriers for color concentrates.
- Gravimetric blending of regrind and virgin is preferred.
- Strive for consistent regrind ratios. Blend a minimum of 20% virgin if feeding issues persist.
- Extruder/screw recommendations:
- Minimum L/D of 24:1
- Screw compression ratio of 2.5 to 3.0 : 1
- Standard or barrier screws are appropriate.
- Use of a mixing tip or section promotes extrudate uniformity.
- Durometers 80 Shore A and higher are more easily blow molded. Santoprene TPV durometers below 55 Shore A are difficult to blow mold.
- Die recommendations
- Converging tooling is preferred over diverging, if possible
- Head designs require some back-pressure to promote reknit.
- For Santoprene TPV grades 80 Shore A and below, parison swell at die exit will be ≤ 5%.
- For Santoprene TPV grades above 80 Shore A, parison swell at die exit will be 5% – 10%.
- For top blow configurations, minimize air leakage at the head (blow pin) to prevent processing issues. Santoprene TPVs tend to cool quickly at the die exit.
- Slower mold closing speed and greater mold cushion will minimize parting line thinning/cutting. Severe issues may require modifying parting line geometry.
- Completely purge all PVC or acetal resin from the machine before or after running our materials.