Extrusion International 1-2023

42 Extrusion International 1/2023 INDUSTRY NEWS target value of 62 for L* is set for the trial. The control system must main - tain this brightness value regard- less of the starting material used and, for this purpose, vary the ad- dition of masterbatch accordingly. For the execution, extruder 1 is fed with the light PP compound at the beginning, directly afterwards with the dark PP compound (after ap- prox. 700 s) and then switched back to the light PP compound (after ap- prox. 1200 s). Large fluctuations in L* can be observed both within the individual batches and during the batch changes (Figure 4 left). These small as well as large fluctuations in lightness are automatically compen- sated for by the color control system over the entire process duration by variable colorant addition to a con- stant L* = 62 (Fig. 4 right). To com - plete the proof of automatic con- trol, a constant result was achieved on one color axis in a further experi- ment, also with fluctuating starting material. This was shown by the example of the b* value, where the input mate- rial varied from +1 to +6 (yellow) for b* and a control was set to a con- stant b* value of -3 (blue) (Figure 5). Conclusion Color control in plastics process- ing is still mainly empirical. The implemented concept of inline measurement of the color at two points in the process in real time al- lows reliable control of the color to a defined value of one of the axes of the color space. The concept can also be transferred to three-dimen- sional color control, although here several metering and measurement control loops are necessary to map the three-dimensional color control. The necessary developments are be- ing pursued on the basis of the re- sults shown. In addition, the experi - mental data also indicate that it may be possible to reduce the complex- ity of the setup to just one measur- ing point. Interested companies are invited to become acquainted with the possibilities of the new system, also within the framework of cost- neutral trials at the SKZ. This project was funded by the German Federal Ministry of Eco- nomics and Climate Policy (BMWK) based on a resolution of the German Bundestag. SKZ - the South German Plastics Center and ColVisTec AG would like to thank the German Bundestag and the BMWK for the financial support. ColVisTec AG Max-Planck-Str. 3, 12489 Berlin, Germany www.Colvistec.de SKZ – Das Kunststoffzentrum Würzburg, Germany www.skz.de Figure 4: Used material light and dark PP flake blends (extruder 1), color control to a predefined color value, here L* = 62 (extruder 2). At a time of 700 s, a batch change was performed between two similar batches (compare measurements on extruder 1 with probe 1 on the left), which had no effect on the desired brightness of the material (compare measurements on extruder 2 with probe 2 on the right) Figure 5: Varying b* value between +1 and +6 (yellow) detected in extruder 1 with probe 1 and a constant target b* value of -3 (blue) detected in extruder 2 with probe 2