In the course of developing and optimising cost-efficient high speed on-line coating processes the interest in so-called,low-impact" and, especially, non-impact" coating methods has increased strongly in recent years. When coating with non-impact procedures any contact is avoided between mechanical elements of the applicator head and the paper. This has considerable advantages concerning runnability (e. g. a voiding possible web breaks) or surface quality (e.g. a voiding defects like streaks). Non-impact coating methods allow a, real" contour coating without forced penetration, which depends on the surface topography or the wettability/penetration behaviour of the substrate. This effect cannot always be considered as an advantage, in particular when taking into account the positioning of the non-impact applicator in a mufti-stage coating concept. In this article current commercially available non-impact coating methods shall be analytically compared for surface treatment of paper - curtain coating and spray coating. In doing so, characteristic attributes of typical coating formulations for non-impact application methods, the functionality of individual components (pigments, binder, co-binder, special additives for influencing surface tension, coating hold-out...) as well as rheological requirements and characteristics (gas content/ foaming) will be discussed and compared. In this connection the question whether interactions between paper and coating colour have a less critical relevance shall be answered. Physical and rheological mechanisms and possible effects on the final paper quality are held in focus. Deduced advantages, possibilities and limitations of non-impact coating techniques compared to the classical paper coating methods with rotating rods, blades etc. will be discussed.
