Defects in injection moulding: Silver streaking and how to avoid that

What it is:

When a machine is changing from Polycarbonate (PC) to Polymethyl Methacrylate (PMMA), the material change can lead to silver-looking polymer lines processed alongside the transparent PMMA. This problem will generate scrap parts that last throughout the process. In the manufacturing of car lighting, where parts are large and a long cycle time is common, silver streaking is a significant root cause of scrap materials.

Causes:

During the PC to PMMA material change process, only a small amount of the PC is processed with the PMMA polymer. However, their incompatibility generates a small, flat incursion within the PC polymer, and silver streaking modifies the appearance and transparency of the PMMA. This defect follows the direction of the polymer flow, and parts with silver streaking must be scrapped. The contaminated PC material cannot be reground or reused to produce transparent PMMA parts.

Solutions:

The use of a uniquely dedicated purging compound for this material and temperature transition (for example Ultra Purge™ C6090) will help you save considerable time and energy between the last quality part produced in PC and the first quality part produced in PMMA.

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