COLOURS | MATERIALS


New colorants, equipment and measuring technologies address variability and sortability. PCR carriers for colour masterbatches have also been launched. Jennifer Markarian investigates


Colour fidelity: targeting accuracy in PCR plastics


Colour is crucial to add shelf-appeal, create or maintain brand identity, or signal a function. Increasingly for many applications, colours must not hinder recyclability. Colour masterbatches offer a wide selection to meet these needs. Consistently obtaining the desired colour in materials with recycled content can be a challenge, however, due to the potential for colour variability in the resin, particularly in post-consumer recycled (PCR) materials. New technologies for sorting mixed PCR can provide single-colour streams, which greatly aids consistency to the incoming material (see Plastics Recycling World September-October 2024 issue). In addition, new technologies for measure- ment and control offer tools for more precisely matching colour and for correcting the variability often found in PCR. ColVisTec’s in-line spectroscopic technology is used for real-time process monitoring. The InSpec- tro instruments can measure ultraviolet/visible (UV/


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Vis) or near infrared (NIR) wavelengths or use Raman spectroscopy. A new tool called RecyColor has been developed by ColVisTec with SKZ (South German Polymer Institute) in Würzburg, Germany. The tool automates colour control and maintains a predetermined colour value by measuring fluctua- tions in the input material and controlling the pigment dosing in real-time. For example, as shown in the Figure on p16, the recycled PP flake has variable colour as measured by the probe (L*, left chart), but the output is consistent in colour. The ColVisTec InSpectro X2 is an inline spec-


trometer with two probes working in parallel – one in each of two extruders, typically mounted in the die plate, although other measuring positions are possible. The first probe, in the first extruder of the cascade setup, measures the fluctuations of colour in the melted recycled flake. In the second extrud- er, the corrective colorant is added, and the second probe measures the output.


� November/December 2024 | PLASTICS RECYCLING WORLD 15


IMAGE: SHUTTERSTOCK


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