Tetrahedral Metallic Pigments Cut Flow Lines in Plastics

Plastic surfaces New pigment process reduces flow lines in metallic plastic parts

2026-07-06 Source: Fraunhofer-Institut IAP 3 min Reading Time

Fraunhofer IAP and TU Berlin have developed a new method for producing metallic effect pigments that reduces visible flow lines in injection-moulded plastic parts. The tetrahedral pigments enable more uniform metallic surfaces without an additional coating step, while supporting resource-efficient, industrial-scale production.

Left: Injection molded test part filled with conventional platelet-shaped metal effect pigment particles. Right: Filled with novel tetrahedral pigment particles.(Source: Jadwiga Galties/ Fraunhofer IAP) — Left: Injection molded test part filled with conventional platelet-shaped metal effect pigment particles. Right: Filled with novel tetrahedral pigment particles.
(Source: Jadwiga Galties/ Fraunhofer IAP)

Metallic effects on plastic surfaces have become standard in many industries, from automotive interiors and exteriors to toys and household appliances. However, injection-molded parts with metallic effects suffer from a well-known drawback: visible flow lines that appear as streaks and compromise the premium look. A new method for producing metallic effect pigments, developed at the Technische Universität Berlin and further optimized at the Fraunhofer Institute for Applied Polymer Research IAP, enables high-quality metallic effects on plastic surfaces with significantly reduced flow-line visibility — without an additional coating step.

For decades, industry and researchers have been working to optimize metallic effect pigments, because conventionally used pigment particles with platelet or flake geometry tend to form visible flow lines during injection molding. To overcome this challenge, scientist Nils Demski at TU Berlin developed tetrahedral particles. This geometry promotes a more homogeneous and nearly isotropic particle orientation in the plastic melt. As a result, both flow-line formation and brightness flop — changes in brightness depending on the viewing angle — can be influenced. However, producing solid aluminum tetrahedral particles is complex and associated with a high reject rate.

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