Manufacturing Coated Mechanical Paper with the New Long Dwell Time Wet-On-Wet Coating Technology, 1997 Coating Conference Proceedings

This study presents a novel coating concept to produce coated mechanical paper grades. A new modification of Wet-on-Wet coating technology, based on long dwell time blade+blade concept, has been tested within this study in high speed coat-ing. The experimental part of the study is based on pilot trial, where machine runnability and paper quality were investigated. This study includes coating, supercalendering and heat set web off-set printing trial, where the final paper quality was confirmed. A long dwell time nozzle application unit was modified and used as a Wet-on- Wet coating unit in wood containing coated paper manufacturing. Precoatings were carried out with a noz-zle application beam and specific short dwell applicator was used as a topcoating head. The target of the trial was to find out the quality potential of Wet-on-Wet blade coating technology and on the other hand to confirm the experiences obtained from previous literature arti-cles. In this study standard paper properties and printability (according to printing trial) of Wet-on-Wet double coated pa-pers (both LWC and MWC grades) were compared to the sin-gle and double coated references. In addition, the means for coat weight control and the mixing tendency of precoat and topcoat during process were investigated. Differences of coating structure between Wet-on-Wet coating and conventional single and double coating were investigated by scanning electron microscope (SEM) analyses from micro-tome cuts of the coated paper and the paper surface. Some good quality options of Wet-on-Wet technology like an im-proved coating coverage, very good brightness/opacity ratio, low fibre roughening tendency and improved surface strength were noticed during the trial. The results obtained show that the optical properties and printability of Wet-on-Wet double blade coated papers were significantly better than conventional single coated reference and it was also proven within this study that the coating struc-ture of Wet-on-Wet coated papers was almost equal than of conventional double coated ones...