“Wet opacity is the only reason titanium dioxide is needed above CPVC”
At least for systems above critical pigment volume concentration titanium “wet opacity is the only reason titanium dioxide is needed”, says Detlef Gysau from Omya, a large producer of filler materials. “Insufficient binder in the coating film leaves pores after the drying process, which are filled with air. As the difference of refractive index is higher between air and mineral fillers, the opacity above the CPVC is increased”, explains Gysau.
Detlef Gysau is Head of Innovation & Technical Marketing, Construction at Omya. He is also author of the book Fillers for Paints.
Limitations for fillers
However, there are downsides to this strategy, limiting the applications where you can use it. “If we introduce air voids into the film we introduce some hiding because of the larger differential across the pigmentary air or polymer air interface. This improves hiding but often at the expense of other film properties”, says Satntiago Arias from coatings manufacturer Hempel. He adds: “Different types of fillers can partially replace titanium dioxide as a function of the type of coating you need. For this you need to consider what the main characteristic of your coating.”
Santiago Arias is Director of Protective R&D at Hempel
Generally speaking, fine particles with particles sizes close to titanium dioxide do support the opacity performance. ”When these ultrafine mineral fillers are dispersed in the presence of titanium dioxide, they help to avoid optical inefficient agglomerates of titanium dioxide. By this up to 20% of the titanium dioxide can often be substituted without los of optical properties,” explains Detlef Gysau.
Trends for fillers in coatings
Aside from reducing dependency on titanium dioxide, Gysau expects that the demand for mineral fillers with more functionalities will increase. He explains: “There are many reasons for this. The trend towards sustainability – costs and its volatility, availability and regulatory considerations, whereas regulatory covers environmental, safety, health and sustainability.”
Santiago Arias from Hempel agrees and states that “new fillers should be compatible with the global environmental trends aimed at reducing VOCs which demand coatings with higher solids content, no solvents or are water-borne.”
This article is based on the expert voices interview series in the European Coatings Journal issue 1/2019. The complete interview is available for subscribers at European Coatings 360°.
Reducing the dependency on titanium dioxide or at least using it very efficiently is a key topic in the coatings industry. Learn more about it at the European Coatings Seminar Enhancing Titanium Dioxide Efficiency in May 2019.
If you want to learn more about fillers the 3rd revised issue of the text book Fillers for Paints is a must have for everybody in the coatings industry.