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Liquid colors allow super-fast color changes in compounding of recycled resin

Liquid colors for plastic coloring need not be molten before processing and can therefore be injected further downstream in the process, bringing great advantages with respect to color change time and material consumption according to colorants supplier Rowasol. KraussMaffei Extrusion GmbH will showcase this capability with an inline colorant system from OPM Mechatronic GmbH, together with liquid colors from Rowasol at K 2019.


Liquid colors are used in compounding of recycled material for an auto application.

As part of KraussMaffei's "Circular Economy" project, PP buckets are initially produced on a GX 1100 injection molding machine and shredded externally. Afterwards the milled material will be talc-reinforced, colored and re-granulated on a ZE 28 Blue-Power twin-screw extruder.

The color is added by an eccentric-screw dosing system that injects three liquid colors directly and simultaneously into the plastic melt. The colorant is homogeneously mixed with the plastic directly by the compounding extruder's specially configured twin screw. The master and the two slave modules are controlled, and the formulation managed by KraussMaffei's central extruder control system.

The liquid colors are supplied in re-usable Rowasol Color Cube containers for clean handling. This innovative principle makes it possible to adjust the color whilst the process is running and change to production of a completely different color in a matter of seconds. The three colors on exhibition, red, yellow and blue, cover a wide spectrum of colors according to the RGB principle.

To complete the process, direct inline color measurement of the polymer melt with an UV-VIS spectrophotometer from ColVisTec AG follows shortly after the color addition near the extrusion die. This enables real-time monitoring of the color change and continuous quality assurance.

After compounding, the re-granulate is processed on a PX 320 injection molding machine from KraussMaffei into an A-pillar support for automotive applications. This entire process illustrates in a tangible way how the "Circular Economy" can be perfected using modern methods.

Publication date: 14/10/2019

Plastics Today

This project has been co-funded with the support of the LIFE financial instrument of the European Union [LIFE17 ENV/ES/000438] Life programme

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Last update: 2020-07-14