Measurement | colour & masterbatch
Measuring and communicating colour
Accurate measurement, defi nition and communication of colour is vital in ensuring consistent production of plastics parts throughout the supply chain, from the compound and colour producer all the way to the brand owner. The plastics industry today has largely moved from relying on physical colour chips and expert colour matchers to instrumented colour measurement and digital communi- cation. This makes colour communication easier, faster, and clearer – as long as the measuring instruments are accurate and all parties are reporting values using the same colour scales and conditions. However, simply giving a “colour number” does not
communicate enough information, says Elaine Becker, sales and applications specialist at US-based colour control software specialist CyberChrome. “You need to know for what illuminant and observer, whether these numbers come from a colorimeter or a spectrophotom- eter, are they gloss included or gloss excluded, what instrument were they measured on, and fi nally, is this instrument measuring colour correctly.”
Colour scales Different industries may use different units to measure colour. The plastics industry has traditionally used the
www.injectionworld.com
Jennifer Markarian takes a look at the latest technologies for
measuring, matching, defi ning and sharing plastics colour information
Hunter L, a, b scale, but has now generally moved to the CIE L*,a*,b* scale. “Any colour can be expressed in either Hunter L, a, b or CIE L*, a*, b* values; both are derived from the same CIE X, Y, Z tristimulus values,” says Gordon Leggett, senior applications specialist at colour measurement instrumentation fi rm HunterLab. “CIE L*, a*, b* is considered currently to be the best scale for expression of colour and colour difference. Software of all the major colorimetric companies allows for reporting in both scales. The more diffi cult issue is agreement in reporting colour values between buyer and seller, which must be negotiated and clearly communicated.” It takes time for the industry to collect data and
make changes to measurement standards. While not an injection moulding application, the Vinyl Siding Institute
April 2015 | INJECTION WORLD 27
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