THE EFFECT OF PIGMENT COATING ON VARIOUS GRADES OF BASE PAPER

Abstract

The advancing technologies of printing and packaging have placed greater demands on the surface of the paper sheet. To meet the more stringent requirements, many paper surfaces are coated with suitable formulations to provide improved gloss, slickness, colour, printing properties. The coating can be applied either on- machine or off-machine, usually, light coating treatments are carried out on-machine, while heavier coating are applied as off-machine operations. Technically any paper surface application can be considered a coating. For example, The size press is really a simple form of on-machine coater, however in modern usage, a paper coating usually refers to a layer made up primarily of fine mineral pigment. The mineral pigment used is similar to a filler, but is usually somewhat finer, it is mixed with adhesives and other components to hold it onto the paper surface and provide suitable finish and rub-resistance. A coating will tend to fill in the void areas on the surface of the paper sheet. After drying and calendaring, the coating provides a smooth, even surface for printing. However, a satisfactory coated sheet can be produced only if the base sheet is well-formed and free from defects.