Calendering

Calendering is the leveling and smoothing of the surface of coated papers with coating color during paper manufacture .

This process is now understood as an embossing process in which a smooth surface smooths the initially rough paper web under pressure. In ancient times, paper was worked with a polished hammer or pressed between polished metal plates in a press. Today the calendering takes place in a calender using a rolling process. The pressure in the nip can be reduced by heating the rollers and / or moistening the paper surface. The smoothing done in this way is gentler on the paper. It retains more volume and rigidity, which is advantageous for further use.

In a modern calender, hard, heated rolls made of chilled cast iron or steel alternate with soft rolls that are provided with "soft" polymer covers. This widens the nip and the pressure on the paper web is evened out. At the same time, the time spent in the gap is extended.

The previously assumed influence of friction in the so-called calendering trough due to micro-slip does not exist. Under the microscope, the marks of scratches in the roller surface were found on the calendered paper, which should not have happened with a relative movement.

literature

• Jürgen Blechschmidt (Ed.): Pocket book of paper technology. With 85 tables . Hanser, Munich 2010, ISBN 978-3-446-41967-4 .
• Heinrich L. Baumgarten: About the calendering of printing papers . Dissertation, TH Darmstadt 1978.