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A novel method was developed for studying the ink-paper interface and the structural variations of a deposited layer of ink. Combining high-resolution x-ray tomography with laser ablation, the depth profile of ink (toner), i.e., its varying thickness, could be determined in a paper substrate. X-ray tomography was used to produce the 3D structure of paper with about 1 μm spatial resolution. Laser ablation combined with optical imaging was used to produce the 3D structure of the printed layer of ink on top of that paper with about 70 nm depth resolution. Ablation depth was calibrated with an optical profilometer. It can be concluded that a toner layer on a light-weight-coated paper substrate was strongly perturbed by protruding fibers of the base paper. Such fibers together with the surface topography of the base paper seem to be the major factors that control the leveling of toner and its penetration into a thinly coated paper substrate. [ABSTRACT FROM AUTHOR]

The most important issue when coating paper is the modelling of the moisture movement in the coating process, since the water movement pattern is strongly connected to binder movement and the final structure of fibres and coating colour, which in turn affects the final printing properties of the paper. Therefore, we are now studying a novel laboratory method to determine the dynamic water movement in a hygroscopic porous media, i.e. the liquid movement in the paper coating process. The experimentally determined physical properties yield information relevant to the mass and energy balances of a real paper coating process. We have also studied the widely used Lucas-Washburn capillary suction theory in combination with the build-up of a filter-cake in the coating colour. The study shows, that the water loss from the coating colour into a hygroscopic material can be well explained by applying vapour diffusion into the base paper as the governing mass transfer mechanism. [ABSTRACT FROM AUTHOR]

This paper investigates the moisture movement in the paper coating process experimentally and theoretically. The experimental data is obtained by coating a base paper with a laboratory coater and by scraping off some of the coating color after a certain amount of time. The moisture content of the material, which has been scraped off, is measured and the amount of liquid absorbed from the coating color by the base paper is determined. The laboratory results are similar to measurements made on a pilot-coating machine. The mathematical solution is based on the diffusion of water vapor in air and taken the vapor partial pressure in a hygroscopic material, i.e. paper. The measurements and a theory based on vapor diffusion show that the moisture content of the base paper is an important parameter when trying to determine the loss of water from the coating color to the base paper. This kind of dependency cannot be explained by theories based on water movement in the liquid phase by capillary suction, as is discussed in Berg et al., 2000, Part I: Theoretical Aspects. [ABSTRACT FROM AUTHOR]