INLINE SYSTEMS | COLOUR MEASUREMENT
the process was repeated using undiluted master- batch that had been re-compounded in a twin- screw extruder a significantly better pigment distribution was achieved, see Figure 1. ColVisTec says that there are several conclusions
that can be drawn from this result. “Every master- batch pellet is different and how different they are is a measure of the consistency and therefore the quality of the masterbatch,” says Fuat Eker, Director of Sales, Marketing and Customisation. “Every compounding and masterbatching operation can be equipped to do these measurements, and tools installed to check the quality of the masterbatch. In addition, masterbatches produced in the labora- tory can be checked in the extruder, while colour strength can be determined using residence time measurement.”
Inline systems can also provide a much more
effective method of ensuring process consistency than traditional sampling. Eker says where samples are used to establish process stability it is important that they are taken at a frequency that will provide a true representation — processes vary throughout a run and that has a direct impact on quality. More samples will mean a more accurate assessment of quality can be made. However, he says a more appropriate solution is
to use continuous inline measurement to detect the spectra and eliminate the need for sampling altogether. The operator is then able to monitor the development of the process in real-time and actively intervene if necessary.
www.compoundingworld.com July 2022 | COMPOUNDING WORLD 47
Recycling gains Recycling, where control of added quantities and dosage is crucial, is a further area where inline measurement can deliver significant benefits. “One of the challenges in polymer recycling is to produce a uniformly coloured polymer with the required colour quality,” says Eker. “The starting material is a mixture of different colours in un- known quantities. The addition of the pigment masterbatch plays a major role. The question is how much pigment needs to be added to achieve a consistent colour quality?” Continuous inline measurement enables enough data to be gathered and processed so the pigment dosing system can be controlled accord- ing to the measured colour in the melt. ColVisTec and SKZ (South German Plastics Center in Wurz- burg) are collaborating in a joint project to study this. The project involves a setup consisting of a cascade of two single screw extruders producing a white masterbatch in a recycled PP. Each extruder is fitted with a probe to measure L*, a*, b* and ∆E values. The first probe showed the L* value for the recycled PP varied between 35 and 45. The automated pigment dosing resulted in a final compound with a highly consistent L* value of around 62. US-based Equitech International offers UV-Vis
spectroscopy for inline and real-time monitoring of processes where colour and/or chemical composi- tion is critical to product quality and operational productivity (Equitech and ColVisTec had a long-standing licence arrangement until late last year — both now market their technologies inde- pendently on a global basis). “UV-Vis spectrophotometry methods have been used to measure the colour of manufactured products for a long time in laboratory settings under controlled environmental conditions,” says
Left: A ColVisTec probe (circled) installed on a KraussMaffei twin screw compounding extrusion die
Below: Equitech’s IPS system uses ruggedised fibre-optic probes for direct measure- ment in the melt stream of an extruder
IMAGE: KRAUSSMAFFEI/COLVISTEC
IMAGE: EQUITECH INTERNATIONAL
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