CHARACTERIZATION OF TISSUE PAPER MACHINES WITH RESPECT TO THEIR DENSITY-RELATED QUALITY;

Unit Operations: Forming, Pressing, Creping.

SUMMARY.

This paper deals with the principles of characterizing the quality performance of a tissue production paper machine for three density-related properties, bulk, water absorptive capacity, and softness. It describes how density of the creped, finished product, corrected for furnish and product physical specification, can be used as the indicator of paper machine performance. The quality index thus obtained, especially when in connection with a reference handsheet, can be used to compare paper machines. The same approach can provide a description of the major unit operations in paper making, forming, overall and pattern pressing, and creping yielding a characteristic "fingerprint" for a paper machine. A graphical method is described which allows the easy visualization of the performance of the various unit operations. An approach is developed which allows the characterization of pressing and creping through a dimensionless number obtained from the ratio of the percent strength and density change during the operation. The methodology allows the treatment of pattern pressing and a comparison with the overall case.

It should be pointed out that suitable techniques are available to sample the sheet before and after each unit operations. Also, while the preferred method of density determination is the oil saturation method, the widely available water absorptive capacity test (in g. of water/g. of paper) may also be used at little loss of accuracy, especially if we compensate for the amount of water absorbed by the fibers. This amounts to subtracting about 2 g/g from the results.