COLOUR MEASUREMENT | INLINE SYSTEMS
Colour can
be measured continuously in real-time using the Equitech IPS (Inline Process Spectrophoto- meter) system
Quality Assurance (QA). In combination with the Tier 1 alarm system, the instrument is used to monitor some colour or compositional feature inline and in real-time to assure the quality of the product produced continuously over the entire production run.
Dr Joseph Golba, Vice-President – Innovation and Implementation at Equitech. “However, modern production technologies, time and materials constraints, and economic pressures are forcing the transfer of these methods to the production lines, demanding that colour be measured as any other process variable, that is inline and in real-time but with the same or more precise results than obtained in the laboratory.” Compounders and masterbatchers can measure colour intermittently during a production, says Golba, using hand-held or benchtop spectrophoto- meters to measure plaques produced production samples. However, the delay in receiving laboratory results can mean that hundreds of kilos of off-speci- fication material can be produced before the operator is aware of any quality issue, which increases production costs, forces segregation of bad product, or creates a waste disposal problem for the plant.
Direct measurement Equitech’s IPS (Inline Process Spectrophotometer) and ruggedised fibre-optic probes allow meas- urement to be made directly in the melt stream of the extruder. Golba says the company offer two application tiers. The Alarm is the simplest, easiest to implement, and least expensive option, using the instrument to detect and activate an alarm when some colour or compositional feature, for example stabilising additive, drifts out of specification. In the Alarm version, it is up to the operator to identify the source of the deviation and act appro- priately. It may be a simple, short-term perturbation that is easily identified and can be ‘adjusted out’ while production proceeds. Alternatively, it may be a more serious issue that requires analysis and a longer time to fix. The second tier is Real-Time
48 COMPOUNDING WORLD | July 2022
Closing the loop However, closing the control loop for colour is complicated and challenging when using multiple pigments to obtain a colour. Golba highlights an example of four feeders being used to mix blue, yellow, red and black to produce a purple colour. In this case, too much or too little of any one pigment will increase/decrease L* a* or b*. Which pigments are varying can be readily determined in a laboratory, but he says this is a challenging problem to determine inline and in real-time because of the interaction of the pigments with each other, as well as the base resin and because of the influences of the equipment, such as temperature fluctuation and worn out elements in the compounding extruder. Other factors present challenges to implement- ing true closed-loop control. “The extrusion equipment market is highly fragmented and there are many different vendors of extruders and feeders for dosing additives, including the pig- ments used to colour plastics,” says Golba. “Extrud- ers may be single, twin or multi-screw and come in a wide range of output capacities. Feeders may be gravimetric or volumetric and allow for multiple colourants to be dosed into the extruder for a specific recipe. Likewise, there are multiple vendors of plant-control software packages to which data and results will need to be communicated.” Last year, Equitech took an 81% stake in US- based optoelectronics hardware manufacturer and software developer CompSol. Golba says this will enable it to improve its control systems and interfaces and enhance its probe redesigns. The company currently offers two probes for use in the plastics industry. Most applicable to compounders and masterbatch producers is the Reflection Polymer Melt Probe (RPMP). This is a contact probe that can measure colour directly in the molten polymer at process conditions up to 5,000 psi and
500℃. It also offers a Large Area Surface Probe (LASP) to provide non-contact measurement of colour in sheet, film and other solid surfaces.
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.colorlite.de �
www.colvistec.de �
www.equitechintl.com
www.compoundingworld.com
IMAGE: EQUITECH INTERNATIONAL
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