**2.2. Weather resistant grades**

Due to the light absorption in the near UV, electrons are hoisted from the energy level of the valence band of TiO<sup>2</sup> into that of the conductive band, thus leaving a positively charged hole in the valence band. The separated electron-hole pair is called an 'exciton'. The generation of excitons is the cause for the light induced semiconductor properties of TiO<sup>2</sup> . The photoactivity of TiO<sup>2</sup> is generally not preferred, since the excitons can have an oxidizing influence on its surroundings and, for example, destroy a polymer matrix in which it is embedded. Therefore, the TiO<sup>2</sup> pigment industry takes some efforts to diminish the photoactivity of TiO<sup>2</sup> . On the other hand, this property is utilized purposefully in TiO<sup>2</sup> photocatalysts [2].

From experience, anatase pigments are generally much less photo- and weather-resistant than rutile pigments [2]. Since a durable pigment is in demand, a heavy dense silica treatment is used. In addition, alumina has been chosen as the final layer over the silica treatment. Examples of surface treatment for weather resistant grades are presented in **Figures 17** and **18**. **Figure 17** presents the dense silica-alumina coating while **Figure 18** presents the dense silicazirconia-alumina coating, covering the entire surface of TiO<sup>2</sup> particles.

Due to the fact that anatase is more photocatalytically active in the crystalline form than rutile, we selected material with the highest level of rutile crystalline structure as a base material. The level of rutile crystalline structure was determined before surface treatment using XRD (see **Table 1**).

Weather resistant grades can be produced by various surface treatments. We decided on two different versions, depending on the final applications. The structure of the coatings is presented in **Table 2**.

**2.3. TiO2**

TiO<sup>2</sup>

TiO<sup>2</sup>

TiO<sup>2</sup>

TiO<sup>2</sup>

*2.3.1. Gloss effect*

 **for applications in printing inks**

**Sample** *R* **[%]**

─Al─Si 99.7

─Al─Si─Zr 99.8

.

─Al─Si 3.6 3.1 —

─Al─Si─Zr 3.4 2.1 0.39

 **[%] Al2O3**

of dispersion in the binder system [34].

to be useful for high gloss coatings [2].

A conventional, high quality TiO<sup>2</sup>

**Figure 18.** Special Al-Si-Zr surface treatment.

**Table 1.** Level of rutile crystalline structure in TiO<sup>2</sup>

**Sample SiO2**

**Table 2.** Metal oxides determination.

particles and lower the gloss [34].

Gloss is a visual impression gained when light is reflected at a surface in a preferential direction. The gloss of a coating system is determined by a number of factors. Pigments can influence the gloss of a coating through their concentration, particle size distribution and degree

approximately 0.3 μm. The particle size distribution should not exceed the 1 μm limit in order

Only those pigment particles lying directly below the surface of the coating are involved in this process. The higher the concentration of pigment, the greater the number of gloss-reducing

pigment has a mean particle diameter (weight average) of

 **[%] ZrO2**

TiO2 Applications as a Function of Controlled Surface Treatment

http://dx.doi.org/10.5772/intechopen.72945

435

 **[%]**

**Figure 17.** Dense silica-alumina coating.

**Figure 18.** Special Al-Si-Zr surface treatment.


**Table 1.** Level of rutile crystalline structure in TiO<sup>2</sup> .


**Table 2.** Metal oxides determination.

#### **2.3. TiO2 for applications in printing inks**

#### *2.3.1. Gloss effect*

**Figure 17.** Dense silica-alumina coating.

ples were evident.

**2.2. Weather resistant grades**

valence band of TiO<sup>2</sup>

of TiO<sup>2</sup>

TiO<sup>2</sup>

in **Table 2**.

wavelength, i.e., they have a yellow undertone.

434 Titanium Dioxide - Material for a Sustainable Environment

hand, this property is utilized purposefully in TiO<sup>2</sup>

zirconia-alumina coating, covering the entire surface of TiO<sup>2</sup>

uncontrolled conditions (black curve). Consequently, differences in undertone for both sam-

Smaller particles (≤0.2 μm) scatter the light of the short wavelength more strongly; therefore, they have a slightly blue undertone, while the larger particles scatter the light of a longer

Due to the light absorption in the near UV, electrons are hoisted from the energy level of the

in the valence band. The separated electron-hole pair is called an 'exciton'. The generation of

From experience, anatase pigments are generally much less photo- and weather-resistant than rutile pigments [2]. Since a durable pigment is in demand, a heavy dense silica treatment is used. In addition, alumina has been chosen as the final layer over the silica treatment. Examples of surface treatment for weather resistant grades are presented in **Figures 17** and **18**. **Figure 17** presents the dense silica-alumina coating while **Figure 18** presents the dense silica-

Due to the fact that anatase is more photocatalytically active in the crystalline form than rutile, we selected material with the highest level of rutile crystalline structure as a base material. The level of rutile crystalline structure was determined before surface treatment using XRD (see **Table 1**). Weather resistant grades can be produced by various surface treatments. We decided on two different versions, depending on the final applications. The structure of the coatings is presented

 is generally not preferred, since the excitons can have an oxidizing influence on its surroundings and, for example, destroy a polymer matrix in which it is embedded. Therefore, the

excitons is the cause for the light induced semiconductor properties of TiO<sup>2</sup>

pigment industry takes some efforts to diminish the photoactivity of TiO<sup>2</sup>

into that of the conductive band, thus leaving a positively charged hole

photocatalysts [2].

particles.

. The photoactivity

. On the other

Gloss is a visual impression gained when light is reflected at a surface in a preferential direction. The gloss of a coating system is determined by a number of factors. Pigments can influence the gloss of a coating through their concentration, particle size distribution and degree of dispersion in the binder system [34].

A conventional, high quality TiO<sup>2</sup> pigment has a mean particle diameter (weight average) of approximately 0.3 μm. The particle size distribution should not exceed the 1 μm limit in order to be useful for high gloss coatings [2].

Only those pigment particles lying directly below the surface of the coating are involved in this process. The higher the concentration of pigment, the greater the number of gloss-reducing particles and lower the gloss [34].
