EFFECT OF HIGH CALENDERING TEMPERATURE AND CALENDERING SPEED ON THE GLOSS AND ROUGHNESS OF UNPRINTED AND PRINTED LWC PAPER

摘要

Mill-made LWC paper was calendered at KCL's Pilot Plant with the new 10-nip Multical calender equipped with polymer roll stack. The running speed varied from 900 m/min up to 1500 m/min and thermo roll temperatures from 100℃ up to 150℃. The nip pressure was the same in each nip. Nip pressure was adjusted for each speed-temperature combination to obtain a certain gloss level. The calendered paper was printed on a heatset web offset (HSWO) printing machine at constant print density and on a sheet-fed offset (SFO) printing machine under constant conditions. Calendering temperature had a very strong influence on the surface properties of the printed paper on HSWO printing. At a given calendered paper gloss level, print gloss increased and the roughness of the image area decreased with increasing calendering temperature and decreasing nip pressure. This means that at a given paper gloss level, paper roughening decreased during HSWO printing when the paper was calendered at high temperature and low nip pressure. The moisture content of the calendered paper correlated well with the gloss of the printed paper's non-image area and very well with the print gloss of 1-colour and 3-colour image areas. The greater roughening of the paper calendered at low temperature and high nip pressure compared to that of the paper calendered at high temperature and low nip pressure seen during HSWO printing is due mainly to the high paper moisture content before printing.