*2.3.3. Solubility parameters and dispersion*

From the economical point of view, the best dispersion state of TiO<sup>2</sup> should be obtained in the shortest time and with minimum expenditure of energy.

Inorganic and organic surface treatments of TiO<sup>2</sup> could be optimized in order to maximize pigment affinity with both binder and solvents. This results in pigments with better dispersion and stabilization in a wide range of printing ink formulations, i.e., improved opacity, gloss and color [35].

The end-user of printing inks has the skill to select a range product (TiO<sup>2</sup> grade); the best suited grade for a particular purpose.

Optical properties of the pigment are defined by the particle size distribution, while the applicative properties are determined by the surface treatment. By implementation of more intensive milling, we prepared a slurry of more dispersed TiO<sup>2</sup> particles. The prepared TiO<sup>2</sup> slurry has been used for further surface treatment. Our goal was to keep the particles separated from each other through the whole process.

The influence of milling and coating process on optical properties are presented in **Table 3**. In order to improve the applicable properties, it is important to coat TiO<sup>2</sup> particles under

**Figure 19.** Alumina surface-treated TiO<sup>2</sup> intended for printing inks applications.


**Table 3.** Influence of milling and coating process on optical properties.

controlled conditions (*T*, pH, precursor dosing rate). Under such conditions, the alumina surface-treated particles are separated from each other; coating is uniform and dense, covering the entire surface of the particle (**Figure 19**). Such particles exhibit excellent optical properties, as demonstrated in **Table 3**. In the case where the process of surface treatment started from suspension with more dispersed or deagglomerated particles (intense milling), higher gloss was obtained for the system with incorporated TiO<sup>2</sup> .
