New pigments for reduced flow-line visibility

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 address this challenge, the PYCO Polymer Composites Research Division at Fraunhofer IAP is continuing to develop 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.
 

Efficient production via soft UV imprint lithography

Together with the team from the Sustainable Lightweight Construction Technologies Group at the Research Division PYCO, researcher Nils Demski has therefore adopted a new approach: the production of tetrahedral metallic pigment particles using soft UV imprint lithography. Their goal is to minimize pigment waste while enabling a high degree of automation through roll-to-roll compatible processes. Instead of aluminum, the pigment particles consist of a metallized, UV-cured thermoset polymer that meets the thermal and mechanical requirements to maintain its shape and optical properties during injection molding. The new process reduces material consumption, significantly lowers reject rates compared with conventional production methods, and thus helps cut overall manufacturing costs. The associated patent is available for licensing to companies seeking to achieve high-quality metallic plastic surfaces without additional coating steps.

“With the new process, based on which we are currently setting up a pilot plant for automated pigment production, we can manufacture metallic effect pigments with high dimensional accuracy and consistent quality. In addition, the size and, within defined limits, the geometry of the pigment particles can be adjusted during the process,” explains Demski.

Looking ahead, the researchers aim to develop pigments with a highly controllable but narrow particle size distribution while maintaining the tetrahedral shape. This will enable even more reproducible optical effects. 

Uniform effects with reduced environmental impact

During injection molding, the novel pigment particles show a more homogeneous orientation in the polymer matrix across the entire component, including weld line areas. This leads to surfaces with significantly reduced flow-line visibility and a uniform metallic appearance. In contrast, conventional flake-shaped pigments tend to orient along the flow direction, which differs in weld lines compared to adjacent areas, which makes flow lines more pronounced. At the same time, the new pigments can be produced more resource-efficiently than conventional aluminum flakes obtained via metal atomization followed by grinding and sieving. This saves energy and materials.

The new manufacturing method for metallic effect pigments combines a premium appearance with robust, environmentally friendly processes suitable for industrial-scale production. It is suitable for any application where surface quality, cost-effectiveness, and sustainability are equally important.