November 24, 2020

Paper making – the nitty gritty: Calendering

Every now and then we dive deeper into the details of paper making by highlighting a certain part of the process. This time we are focusing on calendering, which is one of the crucial steps in achieving Multicopy’s excellent print results.

Calendering is the process by which the paper’s surface is altered to achieve a smooth finish – improving its printability properties. If not calendered, many printing papers simply wouldn’t measure up to the required printing quality. Our uncoated grades, like the office papers in the Multicopy family, manufactured at Nymölla Mill, are treated through a soft nip calendering process.

The soft calendering machine uses heat, pressure and friction to produce the required result as the paper web is pressed through two “rolling” nips. These soft rolls have an elastic cover that form a nip, replicating the surface of the tempered roll with a hard surface – that is where the smoothness is created. 

– WHY, WHAT AND HOW?

• Decreases surface roughness by flattening the paper’s surface particles.
• Adds gloss and smoothness through the “nip-action” where heat and pressure cooperate to optimise the result.
• The heat softens the cellulose fibers and adds extra power to the development of both gloss and smoothness.
• The calendering process also affects other properties of the paper – formation as well as brightness and opacity to some degree.
• Possibility to achieve a higher surface quality on a given bulk value.
• The paper becomes more uniform in thickness, which further facilitates winding and cutting of the paper web

 

The machine used for calendering Multicopy at Nymölla Mill is a Valmet Optisoft calander. Link to Valmet