Rating Performance of TIO2 Pigments in Coated Paper Applications, 2005 TAPPI Coating Conference

ABSTRACT ONLY

TiO2 pigments are produced by two different processes. The older sulfate process produces anatase or rutile crystal forms. The newer chloride process produces rutile. Chloride lines have lower manufacturing costs while producing pigments of higher quality. Therefore, a major continuing trend is the shut down of sulfate lines and construction and expansion of chloride lines. The last anatase-producing sulfate plant in the United States was shut down in 2004. Since anatase pigments are now imported, paper producers are trying to assess the key criteria of reliability of supply and pigment quality. This presentation focuses on the assessment of pigment quality.

Coating pigments such as clay or calcium carbonate that are used as a major portion of the coating formulation have large impacts on both optical properties (e.g., Brightness, Opacity, Gloss), mechanical properties and printing properties (e.g., ink absorption, print mottle, pick strength). Simultaneous optimization of all properties is a challenge that forces the coated paper producer to make “trade-offs”. The high light scattering capability of TiO2 gives it the unique ability to improve Opacity, Brightness and Appearance at very low concentrations with little or no effect on other properties. In the development of new coatings, this allows the formulator to adjust the major components to achieve most of the desired attributes and then add low concentrations of TiO2 to increase the optical properties to the required level. In process control, on-line systems can be used to adjust TiO2 concentration to hit Opacity targets without impacting other product qualities.

The above description of the role of TiO2 in coated papers accounts for the fact that the #1 quality attribute is its light scattering efficiency, S(TiO2). To accurately assess the quality of TiO2 it is critical to be able to evaluate and understand the six fundamental factors that control light scattering in a coating or coated paper.