MATERIALS | COLOURS


Input: variable PP flakes


Output: steady PP strand


ColVisTec says the RecyColor algorithm can correct to a defined target colour value figure, as shown here for recycled PP flakes


“The [data from the first probe] is used to adjust the pigment quantity [using a masterbatch] according to the detected fluctuations and the set target colour value in order to achieve a stable result and process control,” said Fuat Eker, Director of Sales, Marketing and Customisation at ColVisTec. “The RecyColor algorithm can correct to a defined target colour value.” Eker explains that the system does not need to be calibrated for each colour, but only requires determination of the saturation limit and residence time. As a result, it can be used in a wide colouring range to process a wide range of colours to a preset target colour value. Eker says that the system is located at the SKZ facility and is available for interested customers to test there. Krauss Maffei’s ColorAdjust system for in-line, closed-loop automated colour correction has been demonstrated in the company’s lab and was on display at NPE 2024 in May. It is currently being tested by recyclers, said Paul Martin, Extrusion Expert at Krauss Maffei. The system uses an in-line spectrophotometer to measure colour in the pellets after the pelletiser. The colour is compared to the target L*a*b*, and if there is a difference greater than one delta E, the control system corrects the colour using up to four primary colours in liquid masterbatch form. There is a delay of about 60 s from the feeder to the pelletiser, but the in-line measurement and automated correction is still considered to be in real time, as it is much faster than taking a sample to a lab to measure colour and then making manual adjustments. The spectropho- tometer can accurately measure pellet colour if there is a bed of pellets with no gaps – approxi- mately 1 cm thick or two layers of pellets, said Lars Darnedde, Process Development Engineer at Krauss Maffei. This type of spectrophotometer is widely used for in-line film and sheet measure- ments, so it is suitable for industrial extrusion conditions and has been used successfully with


16 PLASTICS RECYCLING WORLD | November/December 2024


both strand and underwater pelletiser systems. Measuring the pellets rather than the melt also avoids the need to account for the colour difference in the melt caused by the melt’s high temperature, Darnedde said. Krauss Maffei has successfully coloured PCR PP collected from household waste in Germany, which has a high variation in colour as well as contamina- tion. Using the ColorAdjust system, the researchers were able to achieve a delta E less than one, which is a level that is imperceptible to the human eye. For many applications of PCR PP, customers find this acceptable, says Darnedde. For some applica- tions, such as in visible automotive parts, the requirement is a delta E below 0.1, which is currently very difficult to achieve with PCR other than black. Krauss Maffei has tested their colour control system with rPP and rPE, and plans to test other recycled plastics as well.


Combined system The latest equipment from Ampacet LIAD is the LIAD Smart SpectroMetric 6, a closed-loop, AI-driven automated system that measures and corrects colour in real-time to maximise PCR usage and maintain colour specifications. The Spectro- Metric 6 system eliminates colour variations by integrating the continuous loss-in-weight gravimet- ric blending system and Spectro in-line spectrom- eter, says the company. In this system, an in-line fiberoptic spectral sensor calculates the differential in colour variance between the incoming material and the target L*a*b* specification. It can measure colour in pellets or flake regardless of orientation, texture or shape of the product. The SpectroMetric 6 patented correction algorithms make incremental adjustments to the colour. The colour correction software determines the pigment formulation to correct the colour using Ampacet’s FluxQF highly loaded, quick flow pel-


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IMAGE: COLVISTEC


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