Role of Scale of Formation In Monitoring Papermachine CD Variability of Formation, 1998 Process & Product Quality Conference Proceedings

End-use properties such as strength and print quality of paper are affected by the nature and the extent of the local nonuniformity of formation, but these relationships remain poorly defined because of the difficulty in describing that nonuniformity. Commercial test instruments provide an observer-independant quantitative index of formation, but these over-simplified measures do not reflect the complexity of the structure of local nonuniformity of grammage in paper which controls many paper properties. We recently reported a new technique for determining paper formation in which the intensity of local nonuniformity of formation is determined as a function of the scale of formation over the range from a few tenths of a millimeter to about 35mm. This technique has already been used for one type of paper and one printing process to show that formation, as determined by this new method, exerts much greater control on print quality than had previously been realized. Likewise, exceptionally high correlations between tear strength and this scale of formation based description of formation nonuniformity have been reported recently for another grade of paper.

The present study extends the application of this method of describing paper formation to the problem of CD variability of formation for linerboard. Patterns were found as to the range of scale of formation for which there is CD variability. Both CD local and CD average determination of local nonuniformity of formation as a function of scale of formation were monitored over periods of months, including at times of changes in papermachine adjustment intended to reduce CD variability. With respect to scale of formation, the quality of formation often improved over one range while getting worse over another range of scale of formation. Current formation test instruments do not have the capability to determine this reality. The new capability provides a powerful tool for addressing control of paper quality, including the aspect of providing the degree of definition of formation nonuniformity necessary for CD control of papermachine operation. Availability of this more realistic determination of formation will enable minimizing CD variability in the strength properties and print quality of paper which depend on its local nonuniformity.