Patent DE-19824804-A1 (DE)
Title: Coating system for one or both sides of a moving paper web
Inventor: HESS HARALD
IPC: D21H23/72
Filed: 1998-06-03
Abstract: To apply a coating to the surface of a moving paper web (1), in a paper making and/or coating machine, the web (1) enters the coating station after the initial surface polishing zone. The start of the coating action on the paper is not later than 10 seconds after the section of the paper has left the initial polishing zone. Preferred Features: The start of coating is not later than 5 seconds (preferably not later than 0.1 seconds) after the section of paper has left the initial polishing zone. The temperature difference between the temperature of the incoming paper web and the temperature of the heated polishing surface is at least 20  deg C (preferably at least 120  deg C). The paper temperature on entering the coating zone is  <= 80  deg C ( preferably 0 - 30  deg C) . After the initial polishing stage, the hot paper web is abruptly cooled to give it a thermal shock. As an alternative or an addition to the initial surface polishing, the paper web is passed between the two polishing surfaces where at least one is heated, followed by a passage through at least two polishing surfaces at a lower temperature than the temperature of the incoming paper. The paper web is heated by steam or infra red radiation, by a heated cylinder or at least a heated guide surface. A number of coatings are applied to the paper surface, with smoothing between the layers. The coating is applied to one or both surfaces of the paper web (1), by an applicator (17) or a series of applicators. The paper web (1) contains raw paper with or without wood. For the initial polishing, the paper web (1) is passed through one or more polishing roller gaps (16), and the smoothing is through a number of roller gaps in direct succession without a coating application between them.  The polishing surfaces can be moved in relation to the paper web (1), at a faster or slower speed than the web movement, using roller (12,14) surfaces to give an initial polish to the paper (1) surfaces.  At least the surface of the paper web (1) to be coated or the coated surface of the paper, to be coated at a directly following applicator (17), is in contact with a heated polishing surface. The paper web (1) is cooled between smoothing and coating, and the surface to be coated is steamed before polishing. The paper web (1) is passed through one or more hard nips (16), where the heated (12) and unheated (14) rollers have hard surfaces. Or the web (1) is passed through one or more soft nips (16), where the heated roller (12) has a hard surface and the unheated roller (14) has a soft surface. The surface temperature of the heated roller (12) is set at  \- 50  deg C  ( \-90  deg C) when the web (1) is free of wood and  \- 100  deg C ( \- 140  deg C( for a paper web (1) with a wood content. The initial polishing and surface coating are effected on-line at the paper making machine, or the initially polished web is diverted to an off-line applicator station in a single pass. They can be followed by further on-line or off-line polishing and coating stages. The paper surface can be coated by a covering layer, with further layers  either on-line, or through an on-line covering layer application and further off-line coating applications. The paper web (1) surface is given its final polish at the latest in 40 seconds after the final coating application. An Independent claim is included for a paper making and/or coating machine for the paper web (1), where the length (L) of the web path between the exit from the polishing station (13) and the entry into the coating zone of the applicator (17) is less than the max. length L0, where L0 = v \* t with t = 10 seconds, and v the forward movement speed of the paper web (1). The surfaces of the polishing rollers (12,14) are of the same or different materials and the same or different hardness. At least one of the rollers (12,14) has a heated surface. A cooling unit (15) for the paper web (1) is between the roller surfaces at the polishing station (13) and the coating applicator (17). A steamer (11) for the paper web (1) is in front of the polishing station (13), in the direction of web travel. At least the heated roller surface has a system to correct the lateral profile.