TROUBLESHOOTING

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Silver streaking occurs when moisture is introduced into the system or when there is degradation of the melt flow. If colorant is added, we recommend using only polyolefin carriers for colorants and additives, such as polypropylene or polyethylene. Never use polyvinyl chloride-based additives because they can react at processing temperatures typical with TPVs and cause a safety hazard. To rule out an incompatible color or additive carrier as a cause, run natural virgin material under the same conditions. More information on color compatibility can be found in the “Incompatible Color or Additive Carriers" section of our Injection Molding Guide.

Material Has Trapped Moisture
Most of our TPVs are hygroscopic. Effective moisture control ensures high quality parts that have an appealing surface appearance. With any TPV, moisture impacts processing, physical properties, product performance, appearance or a combination of these properties, along with silver streaking. We recommend drying our TPVs before processing them using a desiccant drying system. Hot air systems are not recommended, and can actually increase the moisture level of TPVs in high humidity environments. Typically, our materials are dried at 82°C (180°F) for at least 3 hours (at least 4 hours for blends with regrind). More recommendations on drying can be found in our Injection Molding Guide. Improper venting can also trap moisture in the part. Humidity in the material that is unable to vent off or in air trapped in the mold will cause silver streaking.

Melt Temperature Is Too High
Over-shearing or over-heating of our TPV materials will cause degradation. We recommend a high screw RPM (100 to 200) to ensure high shear during plasticizing. However, when screw RPM is too high, there may be an over-shearing of the TPV material which will cause scorching. Reducing barrel set point temperatures will also alleviate decomposition of our materials.

Mold Condensation
Over-cooling a mold will produce condensation on the mold cavity walls. When melt flow moves across the cavity wall, it picks up the moisture and causes silver streaking. Increasing mold temperatures will help dry mold cavities and should reduce streaking.

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