Monitoring Cross-Thickness Distributions of Fines and CMF by Dyeing and Optical Measurement, 18PaperCon

A methodology has been verified where the ZD-distribution of a component of the furnish (fines or CMF) can be monitored. The component to be monitored was dyed using a direct azo-dye before addition to the furnish. The produced sheets were sectioned in cross-thickness direction by sequential heat-seal lamination and splitting, using plastic pouches. The amount of dyed material in a split was monitored using the a* and L* parameters of the CIE Lab color space and the opacity, all measured simultaneously with a spectrophotometer. The value on the green-red axis, a*, the lightness, L, and the opacity were combined into a new parameter, -a*L/opac. Two mechanisms for fines retention was observed by laboratory studies, mechanical retention by filtering process in the formed fiber web and chemical retention by agglomeration to the fibers. The methodology has recently been applied for monitoring cross-thickness distributions of either CMF or fines in paper produced in pilot scale trials. For example, it was demonstrated, that the machine settings affected the mechanisms for retention of fines in the fiber web during sheet forming and dewatering, with different distributions of fines in the cross-thickness direction as result. 

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