Calendering of coated paper and board in an extended soft nip

Abstract Several coated paper products were calendered at different line loads with an extended soft nip, a conventional soft (polymer/steel) nip and a hard (steel/steel) nip. The central roll of the calender was heated to different temperatures; 140, 180 and 210 ^oC with the extended soft nip, 140 ^oC with the conventional soft nip and 140 and 180 "C with the hard nip. Calendering with the extended soft nip resulted in general in a paper product with a more uniform structure than that obtained when the other two types of nips were used. This was reflected in lower gloss variations of the coated surface and in a lower variance in the reflectance of paper samples subjected to a bum-out treatment. The latter may be interpreted in terms of a more uniform pore structure in the coating layer. Offset prints on a coated woodfree paper chiendered with the extended soft nip were less mottled than prints on the same paper calendered with the conventional soft nip. There was apparently a correlation between the variance in the bum-out reflectance of the paper samples and the mottle in the offset print. The effect of the extended soft nip on gloss, print gloss, surface roughness and bending stiffness is also reported.