Paper calendering

The calendering process improves the usability and printability of papers. During this operation, the paper web is compressed between at least two rollers (which may be heated), under high pressure (a few tens of MPa), for a short time (generally less than 1 ms). This mechanical treatment can be carried out in-line, as a unitary operation in the papermaking process, or off-line, as a separate operation alongside the paper machine. Calendering improves the paper's surface finish (smoothness and gloss), and modifies the structure (porosity) and mechanical properties of the substrate to be calendered.

In response to the ever-increasing demands on paper quality and the increasing speed of paper production, the equipment used for calendering has undergone considerable development over the last twenty years. This article reviews existing types of calender and their applications, as well as the characteristics of different calender rolls.