TORONTO, ON, Aug. 13, 2010 (RISI) -Nordic Paper in Säffle, Sweden transferred its line of colored greaseproof papers to PM 3 in 2007. The smaller 3.25m width machine was chosen for colored grades since changing grades and colors is easier than on PM 2 which is 4.2 meters wide. The grammages range from 36 to 140 g/m².
As a vital part of the project, a new Metso PaperIQ Plus QCS was commissioned, replacing an older system. To achieve very consistent color for the mill's customers the system incorporated an online color sensor and automated color controls. At the same time, a new dye metering system was supplied by Ciba. Eight different dyes can be used, with usually three metered at one time. The color sensor and control ensures the product color meets CIE L*a*b* specifications. The control objective is to be with a delta-E target, a mathematical combination off all three specs.
Establishing color consistency is a real challenge on PM3 for several reasons. First, there are six work shifts with different levels of operating experience and, of course, running colored grades on PM3 was new to them. Moreover, colored grades are not run all the time, usually in a one month cycle. So replicating the shade is a very difficult manually, as explained by Anders Tålsgård, PM3 Production Manager: "We have about 12 color runs per year and in one color run we have normally 3 color changes. The brown color is usually 90% of the total color run and other color runs are much shorter. Sometimes 3 color changes can be made during one work shift and it can take a long time to achieve the right shade. Some colors are more difficult to regulate and maybe you just run that color once a year. So that's why it's difficult to keep each run consistent."
Anders Tålsgård says, "We have no claims for color shifts."
With the online color measurement and control that color consistency has been achieved. The color is measured every scan instead of every reel turn-up, as is the case with off-line measurements. Dye flows can therefore be controlled continuously and color kept on track during transition periods and when colored broke is being recycled to the furnish system.
Tålsgård tells how the automation has helped: "Before we would measure with our own eyes and change valves by hand but now the online measurements take care of all regulation of valves. This means shorter grade change times and less waste." This has helped to keep a good reputation for consistency with their customers. "We have no claims for color shifts," he concludes.