A New Technology in Decorative Paints to Boost the Opacity

A new technology in decorative paints to boost the opacity

In general terms, opacity can be described as the ability of a substance or mixture to hide a substrate. A typical example would be a coating film covering a given surface such as a wall.

This simple phenomenon is actually the result of a rather complex interplay of various components and parameters. In industry, opacity is often referred to using other terms such as contrast ratio or hiding power. Whatever term is used, the common functionality they describe is the ability of an applied optical layer to hide what is underneath. Simply put, the opacity of a coating is high if the difference between refractive index of the coating constituents is large.

In practice, this can be easily achieved by adding white pigment such as titanium dioxide to a coating formulation. The required amount of white pigment for high opacity (sometimes referred to as coverage or hiding efficiency) depends on the binder content, or more precisely on the so-called pigment volume concentration (PVC). However, the industry combines economic considerations with technical knowhow, the way of formulating coating materials might change significantly. In fact, the addition of mineral fillers such as calcium carbonate products can reduce formulation cost sharply, but typically have a negative impact on optical performance such as opacity. ChameleoBoost™, the technology developed by Omya, allows for the optimal adjustment of coating opacity while keeping formulation cost to a minimum through the use of qualified functional mineral fillers and it offers a wide product portfolio for water- and solvent-based as well as powder coatings.

The technology will either enhance coating performance (e.g. opacity) at equal formulation cost or reduce formulation cost (e.g. partial substitution of titanium dioxide) while maintaining performance level of the coating film. Any combination of the two is of course possible as well.

Key factors influencing opacity of a coating film are:

• Amount and type of titanium dioxide
• Volume and type of mineral filler varying in composition, particle size and shape
• Pigment volume concentration
• Spreading rate
• Film porosity

Each of these factors have a direct impact on light absorption and scattering. PVC level and film porosity are particularly important when it comes to film opacity. On one hand, coatings formulated at low

PVC typically exhibit high durability providing good weather and wet scrub resistance, but high pigment levels are required to achieve acceptable opacity performance. On the other hand, formulations with high PVC are usually less durable, but require less pigment to reach good coverage due to increased film porosity. In fact, entrapped air in the pores of the coating film has a different optical density (or refractive index) compared to mineral fillers, pigments and binder, and thus increases the difference between refractive indices. Furthermore, ultrafine mineral particles support the even distribution and stabilization of single pigment particles and provide an additional boost of opacity. The latter phenomenon is called pigment spacing which leads to more efficient light scattering by increasing particle interface surface area compared to a situation where pigment particles are agglomerated. ChameleoBoost™ by Omya allows for the optimal adjustment of coating opacity while keeping formulation cost to a minimum through the use of qualified functional mineral offered by Omya. In many cases, ChameleoBoost™ is used in combination with high quality GCC fillers such as Omyacarb® 2, 5,10 and 15 to balance additional coating properties such as wet scrub resistance, solids, rheology and workability through optimized particle packing.

Resuming, with the use of this technology coatings and paints manufacturers can have a high brightness of the formulation, spacing and stabilizing the pigment dispersion. It is possible the enhancing of the TiO₂ performance with a partial substitution of the Titanium Dioxide and manufacturers can also reduce the carbon footprint of the coating.