Colour monitoring | materials testing
Measuring and communicating colour more effectively
Accurately measuring colour is vital to consistently producing colour compounds and masterbatches and to communicating colour throughout the supply chain, from the compounder all the way to the brand owner. The plastics industry has largely moved from relying on physical colour chips and expert colour matchers to instrumented colour measurement and digital commu- nication. This technology 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. Just giving a “colour number” doesn’t communicate enough information, notes Elaine Becker, sales and applications at CyberChrome. “You need to know for what illuminant and observer, whether these numbers come from a colorimeter or a spectrophotometer, 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. Although the plastics industry had used the Hunter L, a, b scale, it has generally moved to the CIE L*,a*,b* scale. “Any colour can be expressed in either
www.compoundingworld.com
Jennifer Markarian looks at the latest technologies for measuring, sharing and matching plastics colours
Hunter L, a, b or CIE L*, a*, b* values; both are derived from the same CIE X, Y, Z tristimulus values,” explains Gordon Leggett, senior applications specialist at 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. The Vinyl Siding Institute (VSI) recently published a new standard using CIE L*, a*, b* values – ASTM D7856 is the Standard specifi cation for color and appearance retention of solid and variegated color plastic siding products using CIELab color space. This updates the
July 2014 | COMPOUNDING WORLD 37
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