Silver Streaks on TPE Product Surfaces? Here’s How Manufacturers Address the Issue!

During injection molding or extrusion of TPE, long, thin, silvery-white streaks often appear on the product surface—a phenomenon manufacturers refer to as “silver streaks,” “silver lines,” or “silver threads.” This defect not only affects the product’s appearance but may also indicate material degradation or internal stress concentration, which can compromise the product’s mechanical properties and service life. So, how do manufacturers address this issue?

First, the causes of silver streaks involve multiple factors, including raw materials, equipment, processes, and molds. TPE manufacturers will systematically investigate each of these to identify the root cause.

• Moisture in Raw Materials: The First Factor to Check

Some TPE grades are hygroscopic. If the raw material is not sufficiently dried, moisture rapidly vaporizes at high temperatures during processing, forming bubbles that are stretched into silvery-white streaks at the melt front. The solution is to dry hygroscopic materials at appropriate temperatures and for sufficient durations using a dehumidifying dryer, and to avoid prolonged exposure of the raw material to humid environments.

• Thermal Degradation: Decomposition Caused by Excessive Temperature or Prolonged Exposure

TPE materials are sensitive to heat. When barrel temperatures are too high, screw speeds are too fast, or melt residence time is too long, polymer chains break down, releasing low-molecular-weight volatiles that form silver streaks on the surface of the finished product. It is necessary to strictly control processing temperatures so they do not exceed the material’s recommended upper limit, shorten the molding cycle, and regularly clean barrel buildup. Alternatively, SEBS-based materials with superior thermal stability can be selected to replace SBS-based materials.

• High Shear Rates: Localized Overheating Generates Gas

TPE melt has high viscosity. Small gates, thin-walled structures, or high injection speeds can cause severe shear, causing local temperatures to far exceed set values and triggering decomposition and gas generation. This type of silver streaks often appears near the gate. Reduce injection speed and pressure, increase gate size, and appropriately raise mold temperature to improve flow.

• Poor Mold Venting: Trapped Air Compressed into Silver Streaks

When air or volatiles within the cavity cannot be vented in a timely manner, they are compressed and heated under high pressure, forming silver streaks. This is commonly observed in deep cavities, blind holes, or weld line areas. Venting channels can be added at the final filling point of the melt, venting passages should be cleaned regularly, and, if necessary, vented steel inserts can be used to enhance venting capacity.

• Formulation and Recycled Material: A Commonly Overlooked Source of Volatiles

Low-molecular-weight plasticizing oils, lubricants, or recycled material reused multiple times are prone to volatilization at high temperatures, increasing the risk of silver streaks. Control the proportion of recycled material, select additives with high flash points and low volatility, and consult with suppliers to choose grades with low outgassing.

Therefore, silver streaks essentially result from volatile gases forming within the melt and then solidifying under stretching.

About Us:

During troubleshooting, Zhongsuwang follows a step-by-step approach: first drying, then adjusting temperature, followed by adjusting speed, and finally checking for venting. By scientifically controlling processing conditions and material state, we achieve high-gloss, string-free molding of TPE products, meeting the dual requirements of appearance and performance for high-end applications.