Paper360 - July/August 2014 - (Page 32)

techlink | COLOR MEASUREMENT Measuring Color online Achieving the best color measurement and control raises the question as to whether scanning or single-point measurement is best MARK CRABLE Color, shade and appearance (meaning the properties of brightness, whiteness, opacity and gloss), are extremely important properties for paper and board products because they carry a message to the end user: they help identify the item, whether it be a letter, a billing statement, a book, a magazine, a sale circular, a food package label, a printed logo or even the contents of a box. If the color of the paper on which the message is printed is incorrect or inconsistent, it can reflect badly on the product itself. When dealing with near-white papers, we generally use the term "shade" to describe their color and the term "brightness" or "whiteness" to relate other preferred reflectance attributes. For grades with lower reflectance of light, we can use the term "color" (hue) to describe their reflectance (e.g., red, orange, yellow, green, blue, indigo, violet). For the sake of simplicity, "color" will be used in this article as a generic term for either the shade of near-white papers or the hue of more "colored" products. cuRReNt oNlINe coloR INStRuMeNtS Providers of modern online color measurement systems for paper include ABB, Honeywell, HunterLab, Metso and X-Rite, and nearly all paper machines that make colored paper are equipped with color measurement and closed-loop control. Those not equipped are at a severe disadvantage to competitors as relates to manufacturing costs, the processing of off-color broke and color variation. Online color instruments can process and display new data at typical rates of once every 15 seconds. The refresh rate of most of these instruments is limited only by the recharge time of the flash capacitor for the light source (most often Xenon). This means that the operator has nearly continuous feedback on the color of the paper as a grade/color change is made. Closed-loop color control with 15-second measurement updates can follow most changes in virgin furnish and adjustments in broke usage while maintaining the finished product well within color specifications. The majority of modern fine white paper machines are equipped with online color measurement as well, regardless of whether they produce uncoated freesheet (UFS), coated freesheet (CFS), uncoated mechanical, coated mechanical or specialty grades of paper. Even makers of containerboard grades of paper often utilize online color measurement today as it is great for diagnostics as well as for maintaining color consistency. two StepS FoRwaRd, oNe Step bacK Much effort has gone into making spectrophotometers excellent instruments for use in the paper mill laboratory as well as online. In the 1980s, that measurement was added to the cadre of online measurements on the Illustration of single point versus scanning color measurement. 32 Paper360º JULY/AUGUST 2014 paper machine in a number of paper mills. The early instruments from Macbeth did a great job and propagated. These instruments measured in a single-point position on the sheet; they did not scan the web. AccuRay went the same route when it began supplying color measurement and control systems to the paper industry. They provided the Macbeth ColorEye II sensor and at first required customers to build a frame to place that instrument on-sheet. Later, AccuRay/ABB bowed to customer pressure and began to build frames to support the color sensor, providing a turnkey system for color measurement. ABB eventually eliminated the independent color frame and incorporated the color sensor into the scanner. When Measurex first offered color measurement, it incorporated the sensor into the measurement package on the scanner from the beginning; this was prior to ABB eliminating its separate color measurement frame. The Measurex approach eliminated the need for a second frame to support a color sensor, saving the space that would have been required.

Table of Contents for the Digital Edition of Paper360 - July/August 2014

Over the Wire
Pulp and Paper Innovations
Strategic Importance of Water
Making Workers Heroes
Industry Emissions Improve
TAPPI Journal Summaries
Measuring Color Online
Consolidation Watch
Knowledge Builder
Association News
What’s New on
Advertisers Index

Paper360 - July/August 2014