INFLUENCE OF CALENDERING PARAMETERS ON COATING LAYERS OF AGRIRESIDUE BASE PAPER FORMED BY DIFFERENT COATING PROCESSES

摘要

The quality of coated paper is dependent on coating color composition, consisting of binders and pigments, coating process followed by quality of base paper and its source and other external process and design conditions such as type of coating equipments etc. One of the most important parameter next to coating color composition is coating process (such as blade coating, roll coating, air knife coating etc.). This is of particular importance for non wood based pulps which are relatively shorter in size and impart unevenness on the surface, thus causing the problem of fiber rising and fluff generation. It thus becomes very necessary to examine the response of coating process to non wood agro residue based pulp for growing Indian paper industry. Further, effect of calendering variables on the quality of coated paper made from agro residue needs to be examined. Unfortunately, extremely limited literature is available in this regard. In the present work, blade coating and film transfer coating processes were compared on paper made from the blend of agriculture residue pulps and that of softwood through exhaustive experimental trials made on pilot coater. Results indicated that blade coating process reduces the fiber and flock scale unevenness more efficiently than film transfer coating process resulting in improved paper gloss and print gloss mainly after the first pass only. Sheet opacity decreases more gradually in film transfer coating and occurs throughout the calendering nip. Calendering temperature plays more important role for blade coated paper and readily improved the sheet and print gloss. Reduction in PPS roughness of GCC coated paper is more during subsequent calendering trials as compare to china clay and blend of two. The effectiveness of calendering as described by "calenderability" showed increase in gloss and print gloss with increasing number of nips. The value of calenderability also founds to be in good correlation with calendering temperature and with formulations of different coating pigments.