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The surface properties of the raw stock influence the formation of the coated layer in two ways. Surface roughness has a significant impact on the coating thickness uniformity; while surface absorptivity determines the composition of the actual coating layer. When the coating first contacts the paper surface, capillary forces within the sheet structure cause a movement of water-soluble components into the smaller pores of the sheet, leaving behind at the surface (by filtration action) a formulation richer in pigment particles. The type and amount of binder in the coating formulation has a pronounced effect on coating structure because it influences the rate of fluid penetration into the raw stock, the degree of filling between pigment particles, and the rate of drying. |
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