Coating-paper interactions

The effect of roughness, absorbency, fiber mass distribution and compressibility of the basepaper on uncalendered coated paper properties was investigated using model handsheets and watermarked paper. Rougher basepapers resulted in a coated paper with high roughness and low gloss, but better coating uniformity. Poor fiber mass distribution had little effect on coated roughness and gloss. Low local fiber mass was compensated with more coating deposition. Bad coat weight uniformity resulted from poor fiber mass distribution, but it improved with the decrease of coat weight.; Experiments were designed to separate the effect of two important factors that determine sheet absorbency: hydrophobicity and porosity. The effect of hydrophobic sizing on coating pick-up depended greatly on the sheet porosity and roughness. On the dense sheets, sizing resulted in a lower coating pick-up; on the rough sheets of varied density, sizing had little effect. The coating uniformity and "hold-out" on the dense sheets were better than on the porous sheets. Shallow penetration of coating into the basepaper was observed on the porous sheets. Again, sizing had little effect.; A model was proposed to predict the deformed paper profile under the blade. The model of basepaper consists of layers of nodes which are interconnected with springs. The final shape of the paper surface profile determines the coating pickup and the uniformity of the coating layer. The predictions of the model on the influence of basepaper compressibility, basepaper roughness, wavelength of roughness, and blade pressure on the uniformity of the coating layer were studied.; A watermark paper was coated to verify the model predictions. Visual inspection and the gray-level variance from the burn-out tests agreed with the model predictions that high blade pressure improved in coating uniformity, and roughness of larger wavelength compressed easier than that of a small wavelength. The model prediction of the amount of basepaper roughness reduction agreed well with the experimental measurement of the coating thickness variations.