The present invention relates to the preparation of a composition of titanium dioxide in an aqueous slurry suitable for production of coated boards, e.g., paperboards having high gloss characteristics and surface smoothness.
Titanium dioxide slurries suitable for use in paper and paperboard manufacture are relatively well known. For example, Hall et al. disclose in U.S. Pat. No. 3,702,773, a stabilized titanium dioxide slurry of 60 to 82% by weight of TiO.sub.2 for use in paper manufacturing. DeColibus discloses in U.S. Pat. No. 4,177,081 titanium dioxide slurries imparting high gloss to water-based acrylic paint systems, and Glaeser discloses in U.S. Pat. No. 4,214,913 a process for producing rutile TiO.sub.2 slurries which may be used in board coating.
In order to produce coatings with sufficient gloss and smoothness, certain finishing steps are required to be performed on the slurries. Consequently, such steps as filtration, washing, drying, micronization and reslurrying are often performed. Other advantages such as improved tinctorial strength are achieved by a reduction in particle size. As a result, various techniques are known for reduction of the particle size of such slurries, e.g., mechanical grinding (Whatley et al., U.S. Pat. No. 3,342,424), steam milling micronization (Baloga, U.S. Pat. No. 4,427,451), high shear milling (Gladu, U.S. Pat. No. 4,288,254, Hall et al., above, Slepetys, U.S. Pat. No. 3,549,091, Jester et al., U.S. Pat. No. 3,380,665, micronizing process) and ball milling (Jacobs et al., U.S. Pat. No. 3,313,492).
It is desirable, however, to have a production process that yields the improved coating smoothness of conventional finishing steps.