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materials testing | Colour measurement In-line measurement in action


The in-line colour spectrophotometer system from ColVisTec and Equitech allows processors to constantly measure the molten polymer prior to the die. This measurement can accurately predict final colour numbers (in L* a* b*) and other colour spaces (see screen shot). L-value describes the black and white content, a is for red and green and b is for blue and yellow. dE describes the vector of those three coordinates and provides and indication of deviation from a sample. Alarm capabilities provide the operator with the data resources needed to segregate off-spec material. With the use of colour measurement


as feedback to a control system, closed- loop control can be achieved to effectively dose brighteners and pigments. The colour feedback will also give insight to optimal screw configuration, screw speed and residence time. One European user is Rowasol, which specialises in high-end colour and additive dispersions, tailor-made liquid colours and additive concentrates.


Rowasol says it is “a perfect comple- ment” to Rowasol liquid colours and enables the highest possible productivity. The company says the system can also be used in combination with its Rowasol Rainbow System for in-line monitoring of the purging step during a colour change.


without having to wait for results to come back from the lab,” says Johnsen. “This becomes almost trivial for us to do. By the time the material has been flushed out, we have the curve, which in many cases provides quantita- tive information on concentrations.” But as far as colour measurement for colour


measurement’s sake is concerned, does it make sense to monitor the colour of a compound when it is in the melt state, given that many pigments change colour with temperature (thermochromism)? “Most of our customers are looking for a stable run of their process correlated to the final product, where this question is not really relevant,” Johnsen says. Nevertheless, with the imminent launch of a new probe that simultane- ously measures melt temperature and colour, and factoring in the thermochromism characteristic of the pigments, the final colour at ambient temperature can be calculated, he claims. The probe has been tested in extruder applications at the SKZ plastics institute in Würzburg, Germany. Unlike most other temperature probes, the ColVisTec model measures the actual melt temperature, rather


30 COMPOUNDING WORLD | July 2015


Any corrections of the colour recipe can be carried out online and the result is shown immediately on the monitor of the spectrophotometer. ❙ www.colvistec.dewww.equitechintl.comwww.rowasol.de


than the extruder barrel temperature. “Many thermom- eters currently in use measure the temperature of the barrel, giving readings that may be 20 degrees or more away from the actual temperature of the melt,” Johnsen says.


A ColVisTec system installed for monitoring two lines


costs around €90,000, but Johnsen reckons that it should pay for itself inside six months through higher quality output, improved capacity utilization and reduced downtime. “We never say that you can do away with the


laboratory all together, but this is a far more compre- hensive tool to complement it,” says Johnsen.


Click on the links for more information: ❙ www.datacolor.comwww.konicaminolta.comwww.xrite.comwww.hunterlab.comwww.roc-gmbh.infowww.colvistec.dewww.equitechintl.com


www.compoundingworld.com


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