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  • 03 Feb 2011

Enhanced inline spectral color measurement on film

Press controls manufacturer QuadTech has unveiled the first web-fed, inline inspection system that measures color on both paper and unsupported packaging film.  The new version of the company's Inspection System with SpectralCam enables continuous, inline monitoring of virtually all web-fed package materials, including transparent and translucent substrates.  The new system uses advanced algorithms to inspect the entire substrate one hundred percent of the time, providing real-time quality data, highlighting deviances as soon as they occur, and pinpointing any problems within the roll.
The SpectralCam camera uses true 31 bin spectrophotometer technology to measure spectral response and calculates accurate L*a*b*, ΔE and ΔDensity values at maximum press and rewinder speeds.  The system measures up to 72 color targets within the work, configured as 12 units with six targets, each of which is determined by the operator.  L*a*b* values, comprising references for luminescence, and red-green and yellow-blue hues, provide an exact, objective means of describing color and color variation.  Capable of detecting a small fraction of a ΔE variation, SpectralCam is many times more sensitive to subtle color differences than the human eye.
John Cusack, product manager at QuadTech, explained why accurate inline color measurement of film posed a great challenge: ‘Film material, being unsupported, is less stable than paper, as it is more susceptible to fluttering and wrinkling during production. The fluctuating distance between sensor and web makes it almost impossible to attain constant results.  In addition, idlers, though stable, are prone to contamination, which negatively affect measurement accuracy.  We have solved the problem by developing an innovative supporting device, positioned between the idlers. Its vacuum system stabilizes the web on to a low friction surface, enabling the web to maintain a stable distance from the camera at the point of measurement. This also enables the camera to record spectral responses, required by ISO standards for calculating accurate L*a*b* values.’
The new system allows film printers to take advantage of the waste saving potential of inline measurement.  Offline measurement is a risky and costly means of quality control, because checks are only possible at the beginning and end of each roll, if production stoppages are to be avoided.
Rather than having to install separate inspection and color measurement systems, package printers now have an all-in-one inline solution for maintaining the highest standards of print quality throughout the production run, whatever material format they use.

The measurements taken can be stored on QuadTech's Data Central and Waste Management Systems.  Data Central is a central repository for all production data, current and historical, allowing greater traceability in the production process. The Waste Management System presents an overview of the roll, highlighting reject and acceptable zones and stops the slitter-rewinder in exact places where splicing or removal is required.