Evaluating Pulps for Newsprint and Mechanical Printing Papers in Terms of Their End-Use Requirement, 1991 International Mechanical Pulping Conference Proceedings

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A method is described to evaluate furnishes for newsprint and mechanical printing papers in terms of their end-use requirement using the Dynamic Sheet Former (DSF). The controlling variables of forming are set to give the target basis weight and fibre orientation. A backing wire behind the forming wire produces more uniform sheets with less rejects than a blotter backing. The wet pressing is controlled to give the desired uncalendered specific volume. The calendering is carried out over a range of loads to give a range of specific volumes for the calendered sheets around the target.

Published equations for calculating the Jet/Wire ratio, together with jet dispersion angle measurements, can be used to obtain the desired fibre orientation with minimum effort. In addition they reveal regions where the Jet/Wire ratio decreases with increasing stock pressure to the jet, knowledge of which is essential to obtain the target orientation without extensive trial and error.

The experimental method was applied to prepare sheets using the Dynamic Sheet Former which simulated commercial sheets; four newsprint and three mechanical printing papers were evaluated. Compared to the commercial sheets from the same furnishes, the DSF sheets have similar strength properties except in the Z-direction (Scott Bond). Surface properties of the top side of the DSF sheets such as gloss and smoothness, were similar to those of the commercial sheets. Formation and Print Mottle were slightly better for the DSF sheets. The method provides an intermediate step between laboratory handsheet and pilot plant paper evaluation of furnishes for mechanical printing grades.