Case Study: Eliminating Paint Fisheyes on Automotive Interior Injection Moulded Parts

Case Study: Eliminating Paint Fisheyes on Automotive Interior Injection Moulded Parts

The Problem

A moulder supplying painted interior trim to an automotive tier supplier was seeing intermittent paint fisheyes and adhesion failures. The defect appeared random - the same cavity would produce good parts for hours, then suddenly a batch would fail.

Because the painting was outsourced, the blame initially went to the paint shop. But the defect persisted after the paint was changed.

Finding the Real Cause

The investigation turned to the moulding shop, and the culprit turned out to be silicone contamination from the release agent.

Silicone has extremely low surface energy. Even a few parts per million transferred to a plastic surface will cause paint to crawl away from that spot, creating the characteristic fisheye crater. What made it intermittent was the source:

• Operators used a general-purpose silicone release spray on the difficult cavities.

• Silicone migrates - it spreads across the mould, onto adjacent cavities, onto conveyors, gloves and fixtures, and into the air as aerosol overspray.

• A single spray on one cavity could contaminate parts from several machines downstream.

What We Changed

• Banned all silicone-containing products from the moulding shop - including general-purpose sprays, some rust preventives and even certain hand creams used by operators.

• Switched to a silicone-free release agent for all cavities.

• Deep-cleaned all moulds with a residue-free mould cleaner to strip existing silicone film.

• Segregated the tooling and set up a silicone-free work zone with dedicated cloths and gloves.

The Result

The Takeaway

If you paint, print, bond, plate or ultrasonic-weld your plastic parts, silicone is the enemy. It only takes trace amounts, and it travels. The fix is not a better paint - it is removing silicone from the moulding environment entirely.

How We Can Help

LONGWEI supplies a verified silicone-free release programme together with the residue-free cleaner needed to decontaminate existing tooling. Tell us your resin, surface finish and post-processing requirement, and we will specify the release agent plus the cleaning procedure to strip any existing silicone film.

Contact LONGWEI for a free sample and technical consultation. Tell us your process, material and mould temperature, and our engineers will recommend a matched grade.