Santoprene 291-XXB150 TPV Injection
™
Quick Processing Reference
This document provides a brief overview highlighting some typical tool specifications and processing parameter references. For more complete information, please refer to the Product Data Sheet.
All values included in this document are for reference purposes only and should not be construed as material specifications.
Tool Specifications
Gating
Gate thickness should be 75 to 85% of the wall thickness being gated into.
The average mold shrinkage will be controlled to a major extent by the adhesion to and presence of the substrate material. Prototyping is required to accurately determine the part shrinkage. Unrestrained shrinkage from an ISO plaque is approximately 1.5 to 2.5% in the direction of flow and 1.0% perpendicular to flow.
3° of draft per side plus 1° of draft for each 0.025 mm (0.001”) of texture depth.
Shrinkage Draft
Processing Parameters
Screw design Barrel capacity Clamp pressure Screw RPM Screw cushion Flow
Special equipment is not required - use a standard general purpose thermoplastic screw, compression ratio 2.5:1 to 3.5:1, and L/D ratio 20:1. 1.3 shots to 5 shots.
224.1 to 6.9 kN/cm (3 to 5 tons/in) of projected area. 50 to 250 RPM.
3 to 6 mm (0.12 to 0.24\").
The viscosity of this polymer is affected by melt temperature and injection speed. Smaller than normal runners should be employed to increase the shear history to further reduce the viscosity.
The overall processing melt temperature range is 175 to 275°C (350 to 525°F). The recommend-ed range is 190 to 230°C (375 to 445°F) for the best balance of adhesion and cycle time. Slightly higher bond strengths are obtained at higher temperatures, but cycle times are also significantly increased and part/runner ejection problems could arise. Bond strength may decrease below 190°C (375°F) depending upon thickness. Mold temperatures are 30 to 50°C (90 to 125°F).
Use a medium injection rate. Fill times are typically between 0.5 and 2.0 seconds.
Constituents of this grade are subject to hydrolysis and must be thoroughly dried. The maximum moisture level for acceptable processing is 0.03% or less. Use a desiccant dryer for 3 hours at 85°C (185°F) with -30°C (-20°F) dew point air. NOTE: When properly dried material (~0.01% moisture) is left exposed to room conditions, the moisture content can exceed 0.03% moisture within two hours. Re-drying is required before processing continues. There is no data demonstrating the effect of moisture on the level of adhesion. Inadequate drying manifests itself as bubbles in the parts, sticky parts, excessive sink/voids or a foamy composition in the part. Packing pressure should be 75% of filling pressure.
The addition of any carrier resin can affect material properties, including hardness, and may affect bond strength. Some pigments also affect these properties. Pre-coloring or standard color con-centrates (master batches) that use PP, TPU or SEBS as the carrier resin can be used. Carrier-less color concentrates may also be used. Color concentrate addition of up to 3% has been used without affecting bonding, however, total PP addition from a carrier resin should be under 2.5%.
Adhesion values can vary according to type of ABS, PS and PC or blends thereof, tool design and processing conditions. To achieve optimal bonding to substrates, the Santoprene TPV and substrate thickness must be at least 1.5 mm (0.060\"). Good bond has been observed down to 0.8 mm (0.030”) of Santoprene TPV thickness with proper attention to tooling and process details.
Purge using PP, LDPE or a recognized purging compound.
It is recommended that the portion of bondable Santoprene TPV regrind not exceed 20% of the
virgin/recycle stream. However, we have not finished validating recyclability as of this document date. This material is incompatible with acetal (POM) and PVC in the same melt stream.
Temperature settings
Injection fill time
Drying
Packing pressure
Coloring
Bonding
Shutting Down Regrind Warning
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Santoprene™ 291-XXB150 TPV Injection
Processing of TPVs - Start Up (from Injection Molding Guide)
Most of our TPVs process with medium-fast to fast injection rates. Fill times are typically between 0.5 and 2.0 seconds. The melt temperatures for most materials are approximately 205°C (400°F); injection pressures are moderate. Starting conditions can be found in the Product Data Sheet for each grade. These contain detailed information on processing setup and unique features. Parts made with Santoprene TPVs ordinarily release freely from the mold when following general industry guidelines for part and mold design and processing recommendations. The use of mold release sprays or powders is not recommended, except under special circumstances.
Injection Molding Pre-Start Up
1. Purge barrel using a general purpose PP or other suitable
purging compound.
2. Set heat zones to obtain melt temperature near the middle of
the recommended range for the TPV being used.
3. Set mold temperature to approximately 20 to 30°C (70 to
80°F).
4. Set screw speed to 100 to 200 rpm.
5. Check the clamp setting.
6. Check the ejector stroke and return.
7. Check to ensure that low-pressure mold protection is set
at the proper distance.
8. Ensure that the machine water supply is on and available
to the heat exchanger, feed throat, mold and other machine areas.
Process Start Up (optimizing fill and packing)
The following procedure works well for any velocity-controlled injection molding machine. The following conditions, although generally applicable, are not necessarily optimum for a specific application.
1. Set pack and hold timers to zero. 2. Set pack and hold pressures to zero.
3. Set injection pressure to the maximum setting. 4. Set transfer position to 6 to 7 mm (0.25 to 0.30\").
5. Set injection time long enough to reach transfer position.
6. Set injection speed to achieve a fill time of 0.5 to 1.5 seconds. 7. Set shot size to achieve a short shot. 8. Increase shot size until part is 95% filled.
9. Note the injection pressure required to maintain 95% fill of the
part.
10. Set injection pressure to 21 to 28 bar (300 to 400 psi) above
the injection pressure determined in the previous step; this ensures a velocity-controlled filling. The molded part should still be 95% filled at this setting.
11. Set the pack-hold pressure to 50% of the injection
pressure setting.
12. Set the pack-hold time to 2 to 3 seconds to ensure that
the remaining 5% of the part is filled and that there is enough additional material to compensate for shrinkage. 13. Fine-tune the pack-hold time by running a series of test
molding cycles. Weigh each part after each test cycle. Continue to increase the pack-hold time as required until the part weight does not increase. This ensures that gate freeze-off has occurred and that parts have a
repeatable, correct weight. Watch out for over-packing, usually indicated by a series of rings around a gate or evidenced by a “punched-in” gate.
Contact your ExxonMobil Chemical representativefor more information.
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