The present invention concerns post-treated titanium dioxide (TiO.sub.2) having pigmentary morphological and granulometric characteristics, as well as a process for producing said product.
One object of this invention is to provide a TiO.sub.2 particle with pigmentary morphological and granulometric characteristics and endowed with a new property: i.e.; to have a chemically reactive coating.
Still another object of this invention is that of conferring to such a coating a strong adherence to the TiO.sub.2 particles.
Yet another object of this invention is that of imparting to such a coating the property of being uniform and compact.
A further object of the invention is that of conferring to the TiO.sub.2 particles thus coated, a specific surface controllable at will.
Another object still, is that of providing a process for obtaining the above said chemically reactive coating.
Still another object of the invention is that of preparing a pigment superfically coated with organic molecules which impart to it an affinity for the organic substances of the vehicles, for example, paint vehicles, starting from the TiO.sub.2 with a chemically reactive coating.
All these objects and others still are achieved by the new product object of this invention, which consists of TiO.sub.2 particles with pigmentary morphological and granulometric characteristics and is characterized in that said product has a chemically reactive coating consisting of a mixture of oxides and oxychlorides selected from the group consisting of Al.sub.2 O.sub.3 and AlOCl; SiO.sub.2 and SiOCl.sub.2 ; and ZrO.sub.2 and ZrOCl.sub.2.
The chemical reactivity of these new products is due to the presence of the oxychlorides.
As a result of these reactive groups, one may, for example, fix onto the particles substances containing amine, carboxylic, or hydroxylic groups, thereby obtaining pigments with an affinity for organic vehicles, for example, vehicles for paints based on alkyd, polyester, melaminic, acrylic and phenolic resins.
In general, the atomic ratio between Cl and Al, Si or Zr, present in these new products, is between 0.10 and 0.90.
Still another object of this invention is a process for preparing TiO.sub.2 particles with pigmentary morphological and granulometric characteristics having the above mentioned chemically reactive coating, this process being characterized in that the surface of the particles is activated in a moving bed by thermal treatment with an anhydrous gas at temperatures comprised between 400.degree. and 600.degree. C., and that the particles are then reacted in a moving bed with an inorganic chloride chosen out of a group consisting of: AlCl.sub.3, SiCl.sub.4 and ZrCl.sub.4, in the presence of a carrier gas, at temperatures between 350.degree. an 600.degree. C.