Effect of Precalendering of Surface and Printing Properties of Coated Sheets, 1998 Coating Conference Proceedings

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This study focusses on understanding the effect of different types of precalendering on coated woodfree paper surface and printing properties as well as binder migration and coating mass distribution. Base paper was precalendered using a machine calender, supercalender or soft nip calender (SNC). After precalendering, both uncalendered and precalendered papers were blade coated using a cylindrical laboratory coater. Part of the coated sheets were post calendered using SNC and the other part was not calendered. Coated papers were tested for coating mass distribution and surface latex content. The post calendered papers were printed in a Gravure-Press and tested for delta gloss and print density.

Precalendering enhanced the gloss and reduced the roughness of the coated paper at all coat weights. In the case of post calendered papers, any differential effect achieved through the various precalendering operations was recovered during post calendering. The type of calender used for precalendering had no influence on the final roughness and gloss values obtained. The final porosity values of precalendered and uncalendered sheets was more dependent on the coat weight at the high coat weights (10-16 g/m ). This was observed for the papers that had been subjected to the post-calendering, as well as for those 2 that were not. At low coat weights the type of calender used for precalendering influences the final porosity values.

Precalendering also increased the delta gloss and print density values of the final product. This was observed for the papers that had been subjected to the post-calendering, as well as for those that were not. The type of calendering has an influence on the final delta gloss development. In the case of print density, the type of calendering did not have any specific influence on the final print density values.

The distribution of the latex content on the surface of the sheet was affected by different types of calender and different calendering conditions in the same way. The latex distribution is found to be more uniform at higher surface latex content. The data also indicate that the surface latex distribution was not dependent on the type of precalendering and calendering intensity. Precalendering had a negative effect on coating mass distribution of coated sheets, as the uncalendered sheets had a more uniform coating mass distribution than the precalendered sheets.