“Wet opacity is the only reason titanium dioxide is needed above CPVC”
Modern day fillers can do much more than just add volume to a coating. We spoke with experts from Hempel and Omya about the latest innovations and the potential of fillers to reduce dependency on titanium dioxide.
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.
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.”
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.”
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As the biggest manufacturer of chemical pigments and solvent dyes of South China, Xinghua Pigments Group has over twenty years of professional experience in the pigments and solvent dyes industries and has been covered almost all the organic pigments, organic solvent dyes, masterbatch, Titanium Dioxide and other relative products.
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