COLOUR | MEASUREMENT
when the compounder runs engineering resins and sophisticated recipes,” he says. “As Industry 4.0 continues to be adopted, plastic compounders will be forced to adopt new manu- facturing technologies based on automation, machine learning and artificial intelligence.” Gomez says that compounders must be able to
guarantee their coloured products are always in-spec, pellet-to-pellet, for each production run but that it is becoming increasingly apparent that traditional quality control laboratory checking of colour quality, for example, at the start and end of a production run, falls short of meeting this guarantee. The alternative, he says, is to measure colour continuously in real- time, enabling pellet-to-pellet colour quality assur- ance and closed-loop colour control. He says compounders and masterbatchers must consider the importance of real-time data and its correlation to laboratory values. Colour measure- ment is transitioning into this new reality. Every production machine should adopt a colour measurement device that provides production personnel real-time information on the accuracy, deviation, compliance with, and drift of the compounding process and the desired colour. This new responsibility is called colour correlation - the understanding of the behaviour of a particular colour under a set of criteria (geometry, thermody- namics, physical conditions and composition) and its translation into a new set. For example, suppose the laboratory knows that
a particular sample of ABS has a green colour with coordinates values of L=62.57, a=-36.19, and b=21.07, respectively, measured with d/8, D65, and T=25˚C. In that case, it must understand that the same ABS produced from the extruder at T=170˚C and measured with 28/0 and D65 will have L*=39.40, a*=-42.32, and b*=28.80. In addition to formulating new colour recipes, the laboratory has two other primary responsibilities. These are translating a set of colour coordinates back and forth from laboratory to production spectrophotom- eters and auditing the in-line colour measurement to ensure that these devices measure accurately. Equitech highlights several influences driving new developments in colour measurement. “Products where colour is a critical attribute — branding, aesthetics and recognition — need their colours to be on-target and consistent,” says Joe Golba, Vice-President Innovation & Implementa- tion. “Lack of accuracy and consistency of colour will result in product dissatisfaction and returns, lost revenues and loss of reputation. Colour accuracy and consistency must be guaranteed absolutely. “The highest levels of compounding manufac-
www.compoundingworld.com
turing productivity will also need to be able to firstly produce coloured products with fast and efficient start-ups and product-changeovers. Secondly, it is necessary to catch and adjust-out colour deviating material and process-related drivers, such as drifting feeders, issues related to feeder refilling, and in-line changes in filler and pigment quality,” he says. Golba says that for measuring colour in-line in
real-time, there are systems that measure pellet colour and feed the data to the quality control laboratory, process engineer and extruder operator. However, while the time lag (measurement-to-rec- ognition addressable action) is much shorter than the standard QC laboratory sampling/measurement system, it is often viewed as too long to guarantee pellet-to-pellet colour quality and optimal manufac- turing productivity. The solution is in-line, real-time colour measurement in the polymer melt. However, the measurement of colour in the melt
(at processing temperatures and pressures) does not yield the same colour values as those meas- ured on pellets under standard laboratory condi- tions. So, a correlation between the two measure- ment regimes needs to be developed. Finally, the goal is to enable closed-loop quality control of colour in a melt compounding operation. Closed- loop control has already been realised for relatively simple systems, such as white to grey. However, work is still in progress for more complex colour systems using multiple additives and pigments.
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.xrite.com �
www.konicaminolta.com �
www.colorix.com �
www.datacolor.com �
www.matchmycolor.com �
www.envalior.com �
www.equitechintl.com
July 2023 | COMPOUNDING WORLD 33
Above: Inline technology can help
compounders meet colour specification guarantees, says Equitech
IMAGE: SHUTTERSTOCK
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