TEMPERATURE-GRADIENT CALENDERING - FROM THE LABORATORY TO COMMERCIAL REALITY

In temperature-gradient calendering the paper web is treated in a sing le nip formed by two rolls heated to elevated temperatures. Because of the short contact time between the paper and the rolls, only the surf ace fibres are affected by the heat. The advantage of this effect is t hat a smooth surface can be developed for printing while minimizing da mage to the underlying fibres. Temperature-gradient calendering gives bulkier paper than conventional calendering under similar conditions, as well as lower linting propensity, higher strength, and very high gl oss. Although the benefits of temperature-gradient calendering have be en demonstrated for many years in laboratory experiments, only in the last 10 years or so have roll designs evolved to permit commercial ope ration at these elevated temperatures. Our pilot calender studies have demonstrated the potential of various heat transfer rolls and heating techniques, and we suggest configurations for commercial installation s.