
Preparation of Paper Coating
Paper and board grades are sometimes coated to improve the printability, visual properties, or functionality of the sheet. Coating formulas typically contain three categories of ingredients: pigments, binders and additives.
Pigments used in paper and board coatings govern the final optical and printing properties of the sheet. They do this by providing brightness, whiteness, smoothness, and opacity. Binders adhere the pigment particles to each other and to the sheet, and additives either assist in the coating process or enhance sheet properties.
Traditionally, coatings were based on clays such as china clay (kaolin) and bentonite, but calcium carbonate is more common in modern paper coatings. Other materials are also used to achieve certain properties. These include:
- Talc – for smoothness.
- Silica – for applications that require good water absorption – eg ink jet paper.
- Titanium Dioxide – for whiteness and opacity.
- Resins – control of ink absorption rate.