Titanium Dioxide in Coatings, Tint Strength

Tint strength is the ability of a paint or pigment to modify the color of another paint or pigment of a different color. The tint strength of the pigments in question and their degree of dispersion influence this. In the case of paints containing TiO₂, the more the color of the tinter or colored paint is changed (i.e. the less the white is changed) the higher is the tint strength of the white paint. The control and consistency of tint strength is a major consideration during the manufacture of TiO₂ pigments.

Tint strength is influenced by the particle size and particle size distribution of the pigment. The narrower the particle size distribution, and the closer the mean particle size to the optimum, the stronger the pigment will be, (Figure 1).

About Tinting Systems

Tinting systems are becoming increasingly common in paint sales worldwide, making it no longer necessary for the paint stockist to hold large volumes of different colored paints. Using a tinting system, the stockist needs only hold a few tint bases and tinters, or colorants, and still have the ability to supply a wide range of colors. Careful control of the color and tint strength of the bases and colorants is essential for the working of such a system. Consistency of undertone and tint strength of the various pigments, including the white for the bases, is absolutely essential.

The TiO₂ pigments used in tinting systems are characterized by high tinting strength, neutral undertone, ease and stability of dispersion and, most importantly, consistency of quality. Millennium Inorganic Chemicals manufacture pigments to a very narrow particle size distribution. This leads to high tinting strength and minimizes tonal differences. The surface treatments applied to Tiona^® pigments minimize flocculation in a wide variety of resins and give stable tint bases with good flood and float control. All Tiona products are manufactured to very close specification limits to ensure the high consistency required by successful tinting systems.

Once a tinting system is set up, two properties become critical, undertone and tint strength. Changing pigments in such a system is difficult if these two properties vary between the standard and new pigment. However, as long as the undertone is satisfactory, a stronger pigment can lead to significant savings. A stronger pigment will give the same tint strength at a lower pigment content in the tint base. It is then appropriate to reduce the amount of pigment in the base to balance the tint strength to its original level. The pigment removed will result in a significant cost saving, as the volume of base manufactured is large.

Tiona pigments have high tint strength and when properly dispersed and stabilized often allow the removal of pigment in tint bases originally developed on other grades of TiO₂. Savings of 5% are not uncommon. Optimized dispersion can also yield further savings by maximizing the tint strength of the base.