SKZ and Promix: Optimum quality for 2-component parts with liquid colors
In the production of multi-component parts, optimum surface quality is a must. In joint trials for quality optimization, SKZ and Promix used an Arburg Allrounder 570A injection molding machine to produce frisbee rings as 2-component samples. The Frisbee consists of a stiff inner ring made of PC, which is overmolded with a soft TPE. The soft component was colored using liquid color.
before: clearly visible color streaks and flow lines
Without the use of a Promix mixer, there were clearly visible color streaks, especially in the weld line area. The confluence lines between the sprue points were also clearly visible.
The back pressure had to be increased to well over 100 bar to achieve better homogenization of the color in the part. However, the raw material manufacturer's specification regarding the back pressure was only 10 bar.
Promix, in cooperation with SKZ, carried out an optimization of the frisbee production. After the installation of a Promix Mixing Nozzle, which was completed in less than 10 minutes, a parameter optimization was carried out with regard to the back pressure. A stable process at 17 bar could now be achieved. The flow lines and color streaks were successfully eliminated thanks to the mixer. A reduction to the recommended 10 bar was not feasible, as constant material conveying / metering was no longer possible at a back pressure below 17 bar.
After installation of the Promix mixing nozzle, the frisbee could be produced completely without flow lines and color streaks under stable process conditions.
The tests demonstrated that when using liquid colors in connection with TPE materials, optimized mixing nozzles can significantly improve homogenization without placing too much stress on the material during processing.