The calender is the last step in the production of coated paperboards. The calendering improves the smoothness of the paper by increasing the average gloss. At the same time, the distribution of surface porosity and gloss of the coated paper is also improved. However, the high distribution of these surface properties is often not used as an indication of the improvement of the paper surface properties. Source: Paper Research
The purpose of the completed intermediate trial study was to explore the surface properties of the paper and the appearance of spotting on the paper surface caused by coating and post-calendering in offset printing paper. A single experiment was conducted with a coating roll and a coating squeegee, and the wet-on-wet secondary coating was performed on a metered size press (MSP) coater. The coating of low-quantitative ink-containing wood pulp paper is only one-sided coating. Coated paper was calendered with a supercalender. In calendering experiments, the temperature of the steel roll and the number of nips used were studied. The calendered paper surface was analyzed, and a sheet-fed offset printing test was conducted to measure the printed piebald spots.
In order to identify the quality of the coated paper, the uncalendered paper was subjected to a burning test to determine the distribution of the coating on the surface of the original paper. Measurements show that the wet-to-wet coating is consistent with the distribution of the coating's equivalent curve and weight distribution curve. On the other hand, a single blade test shows that it has more "fill pit" effect. In this case, the material distribution of the coating is not uniform.
When calendering is performed, the coated surface is compressed and the porosity of the coating is reduced. Because the peak of the coating is compressed more than the valley, resulting in uneven distribution of the coating's porosity, the wet-on-wet coating non-calendering test shows that the coating porosity exhibits a more prominent non-uniformity.
When calendering is performed at a low temperature, the gloss and smoothness of the coated paper do not depend on the coating process. As the calendering humidity increases, the surface quality of the coated paper is significantly affected by the distribution of the coating amount. However, the increase in the number of nips in calendering, the difference in this coating process does not exist.