*2.3.4. Optical density*

*2.3.2. Rheology*

apart from TiO<sup>2</sup>

It is vital to incorporate TiO<sup>2</sup>

*2.3.3. Solubility parameters and dispersion*

436 Titanium Dioxide - Material for a Sustainable Environment

suited grade for a particular purpose.

each other through the whole process.

**Figure 19.** Alumina surface-treated TiO<sup>2</sup>

Inorganic and organic surface treatments of TiO<sup>2</sup>

An ink with required rheological properties can be successfully applied to the image on a plate, transferred correctly to the stock and finally, retain its form as a print. Each printing technique has specific requirements. For opacity, it is important to select pigment and pigment volume concentrations that play a role on opacity, gloss and whiteness, but also on the rheology of the ink. Different pigment grades have different medium absorption. As a consequence, the rheology of the ink at the time of application will be affected. Many ingredients,

dispersion is achieved. In the case of a poor dispersion stability even viscosity could be affected.

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].

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 inten-

has been used for further surface treatment. Our goal was to keep the particles separated from

The influence of milling and coating process on optical properties are presented in **Table 3**.

intended for printing inks applications.

formulation of inks calls for much practical experience and skill.

From the economical point of view, the best dispersion state of TiO<sup>2</sup>

The end-user of printing inks has the skill to select a range product (TiO<sup>2</sup>

In order to improve the applicable properties, it is important to coat TiO<sup>2</sup>

shortest time and with minimum expenditure of energy.

sive milling, we prepared a slurry of more dispersed TiO<sup>2</sup>

pigments, will affect the final rheology of the ink. It is important to note that

pigment into the printing ink medium in a way that maximum

should be obtained in the

grade); the best

particles under

slurry

could be optimized in order to maximize pigment

particles. The prepared TiO<sup>2</sup>

A layer of alumina oxide layer can increase the amount of ─OH groups on the particle surface, which can improve the dispersibility of the particles and provide more active sites for further organic modification; this was evidenced from the results obtained by OD method. TiO<sup>2</sup> particles surface-treated under controlled conditions exhibit significantly higher light scattering efficiency due to complete aluminum layer coating the entire TiO<sup>2</sup> surface. Lower LSE was determined for TiO<sup>2</sup> particles with incomplete coatings, produced under uncontrolled conditions (**Figure 20**).

Printing ink with incorporated TiO<sup>2</sup> particles with incomplete coatings was highly viscous. For printing inks production approximately 10% more solvent was needed. Since the viscosity

**Figure 20.** Light scattering efficiency (LSE) for pigmentary TiO<sup>2</sup> with complete and incomplete coatings.

of the dispersion and the type of optical properties (especially the undertone and gloss) are strongly dependent on the degree of particulate dispersion, we can conclude that in controlled surface treatment, we obtained more dispersed particles.

The lightfastness is indicated by the grades on the Blue Wool Scale: BWS 1 = poor, BWS 2 = low, BWS 3 = average, BWS 4 = rather good, BWS 5 = good, BWS 6 = very good, BWS 7 = extremely

other substances normally tend to reduce the IEP to lower pH values (IEP of SiO<sup>2</sup> = 2, IEP of ZrO<sup>2</sup> = 4). Phosphates, used for surface treatment form acidic groups on the surface of par-

In **Figure 22**, the zeta potential as a function of pH for untreated and surface-treated TiO<sup>2</sup>

alumina layers contributed to shift IEP to higher pH values (pH 8.6), which proves a successful surface treatment, since the IEP value of surface-treated samples lies close to the IEP value characteristic for alumina. The results are in agreement with literature. Multi-layered surface treatments, alumina in combination with silica and phosphate, shifted IEP to lower pH. IEP values for all samples are presented in **Table 4**. The uniformity and the properties of hydroxide coatings influenced the surface properties of the pigment particles because the coated particles show similar surface characteristic, such as surface charge and surface active sites or groups,

 with aluminum phosphate coating successfully underwent testing by the end-user with grades 4/5 on the Gray Scale (grades 1–5) and with grade > 6 on the Blue Wool Scale; we met

particles is about pH 4. Modifying the pigment surface with inorganic layers

shifted to pH 2.5, close to IEP characteristic for SiO<sup>2</sup>

, phosphates changes the IEPs [2]. Whereas, for example,

TiO2 Applications as a Function of Controlled Surface Treatment

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

particles is about 4 and according to literature [2], IEP

is 8.65, which is close to the values determined for Al<sup>2</sup>

pig-

439

O3 .

. Complete

species (IEP is about 6.8) shifts the IEP to higher pH values,

good, BWS 8 = excellent.

IEP of pure TiO<sup>2</sup>

of, for example, Al<sup>2</sup>

the requirements of the user.

*2.4.2. Electrochemical properties determination*

O3 , SiO<sup>2</sup>

(IEP = 9) and Al(OH)<sup>3</sup>

ments are presented. IEP of pure TiO<sup>2</sup>

of aluminum surface-treated TiO<sup>2</sup>

**Figure 22.** Zeta potential as a function of pH.

IEP of Si surface-treated TiO<sup>2</sup>

as the coating material.

, ZrO<sup>2</sup>

ticles, which are acidic and becomes a potential determinant [2, 14].

TiO<sup>2</sup>

Al<sup>2</sup> O3

#### **2.4. TiO2 applications in paper laminates**

As already mentioned before, TiO<sup>2</sup> is a semi-conducting material and show some intrinsic photocatalytic activity. During weathering, interaction of UV light with TiO<sup>2</sup> occurs resulting in the formation of free electrons and electron-holes in the crystal lattice. These radicals react easily with neighboring organic molecules and, result in degradation of the medium [36–38].

The interaction of UV light with TiO<sup>2</sup> particles results in the formation of Ti3+ centers that are violet-colored species. For that reason, discoloration (greying) of the exposed area might be observed. This is usually described in terms of the lightfastness [37].

Generally, commercial TiO<sup>2</sup> grades are surface-treated with hydrated compounds of aluminum, silicon and zirconium [39–42]. Silica contributes to durability, while zirconia improves gloss and durability. Alumina is usually used as a final layer to increase dispersion stability. Sometimes, special surface treatment, for example, with aluminum phosphate is required to provide high lightfastness in applications such as decorative papers [43]. Scanning transmission electron microscopy (STEM) image of TiO<sup>2</sup> , surface treated with aluminum phosphate is presented in **Figure 21**.
