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materials testing | Colour measurement


HunterLab is using its D25 NC as the basis for a new non-contact colour meas- urement technology


times better wavelength resolution (1 nm vs. 10). He expects first sales to be finalized later this year. “Interest among compounders is rising, tests at customers have been quite positive,” he says. The ERX130 works right on the line, with the spectrophotometer mounted over the sieve after the pelletizing unit. It has a coaxial geometry, with a Xenon ring flash unit around the sensor ensuring consistent shadow-free lighting that is independent of ambient conditions. It is capable of taking up to 20 measurements every minute. Variations in distance between sensor and subject of several millimetres apparently have no effect on the reading. Internal calibration is automatic. Data is sent to the operator’s control room for QC purposes, so that any deviations from set values can be immediately flagged and acted upon. Binder says the ERX130 can be used in a closed-loop control system linked to material feeders, as long as they have a PLC control.


X-Rite’s ERX130 can be used for in-line colour measurement system on compounding lines


Purpose built for in-line control The ROC-ColorControl system from ROC Rapid Optical Control in Cologne, Germany, is touted as a high precision in-line colour measurement and control system that analyses pellets sampled from the production line. The company claims a typical repeat accuracy for homogeneous uniform pellets of ∆E* < 0.1. The ROC-ColorDosage system for online colour shading and correction is an optional extra. An automatic sampling unit collects pellets directly


from the line immediately after the classifier over predefined durations. Each sample contains at least 10 sub-samples, providing a representative


average of product covering a period anywhere from 1 to 20 minutes. One system can operate with sampling units on as many as six lines, so each sampling unit has its own transport carrier to prevent cross-contamination. One ROC-ColorControl can


carry out 25 colour measurements per hour. “With today’s standard laboratory processes an operator needs at least 30 minutes for one measurement,” says company CEO Jens Dietrich. “A compounding plant with four production lines and capacity of about 700 orders/year/line and four colour measurements per order needs approxi- mately 6,000 work hours per year to do the


colour measurements only”. Dietrich adds: “Colour matching including correction


calculations, weighing of correction components, mixing and re-adjusting of production line requires about 10,000 – 12,000 hours per year. This labour together with colour measurement costs between €350,000 and €500,000 in labour per year. ROC-Color- Control technology needs only 7.5 – 10 % of today’s usual costs.” According to Dietrich, a standard laboratory process


with colour measurement on injection moulded plaques requires about 15,000 kg of material per year, whereas ROC process technology needs less than 500 kg. ROC’s system measures colour on pellets at a fixed


temperature. “We believe thermochromic effects cannot be foreseen, so we always measure at 38°C,” he says. “This is why we take the pellets away from the line to measure them. This just needs to be in an air conditioned area so we have control over the tempera- ture. Samples are stored for several minutes in order for them to reach a stable temperature. To avoid any contamination from dust etc. the system is covered. The light source is also automatically controlled so that it is always at the same intensity.” Dietrich says that the distance between the sensor and the sample can have an important effect on the measurement, as can the area of the pellet that the measurement is taken from. For this reason, the ColorControl system measures a large number of pellets per sample and produces the L-a-b values out of several thousand spectra in every single measurement.


22 COMPOUNDING WORLD | July 2015 www.compoundingworld.com


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