Production of paper and paper products such as cardboard packaging materials is a complex process. In addition, numerous types of papers (weight, wood content, brightness, etc.) are required for a multitude of applications. Paper coating formulations are comprised mainly of pigments, which account for about 80% of the materials used. The binder only comprises 10% of a paper coating. The remainder consists of brighteners, opacifiers, rheology modifiers, lubricants, dispersants, starches, and insolubilizers (crosslinking agents). Pigments used in paper coatings are typically inorganic mineral pigments such as ground and precipitated calcium carbonate, clays like kaolin, titanium dioxide, talc, alumina trihydrite, and barium and calcium sulfates. If a white coating is needed over a bright white sheet, then pigments that provide gloss will be preferred.
Paper flatness depends on the degree of finish, surface flatness expressing paper. This is one of the most important aspects for analogue or digital printing process - submission of substantially influencing the surface ink / toner. Test methods, even if they use different instruments constructed, based on the same principle: measurement under specific conditions (pressure, area, time, etc...) of the volume of air that can pass between the surface of paper samples tested and flow guiding device facets applied over the air. The values obtained vary depending on finish paper - gloss, satin or matte.
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