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Titanium-dioxide is an expensive raw material, especially at the moment. A recent technical paper shows how TiO2 can be partially replaced in flexo inks and which extenders can be used instead to reduce costs and the carbon footprint.

The paper discusses seven different extenders that were evaluated as possible particial replacements. Among these extenders were ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), kaolin and talc that have a much smaller carbon footprint compared to Titanium-dioxide and are much cheaper. The paper discusses how the extenders affect Opacity, particle distribution and gloss. The extenders were evaluated against a PVC reference system that performed best at 34 VC% of TiO2.

Double digit TiO2 replacement is possible

The paper describes that 10-15% TiO2 replacement is possible by using some of these minerals, while minimising loss of gloss in flexo inks. For instance, TiO2 was directly replaced with ultrafine GCC slurry as a 1:1 dry weight in the recipe, with no other components being changed. At 10% TiO2 replacement (corresponding to 30.2%VC and 5%VC ultrafine GCC in the dry ink film) high opacity and gloss were maintained.

Opacity with 5% and 10%VC ultrafine GCC levels (partial replacement of 34%VC TiO2) ©European Coatings

At a 20% replacement level, the optical performance was reduced, due to the final ink containing an insufficient level of TiO2. In the end, fine dry PCC gave the best results for matt inks, whereas for a high gloss ink, an ultrafine GCC, fine PCC slurry or fine kaolin performed better.

The paper describes how, for instance, PCC particles separates the TiO2 particles in the dried film, allowing better light scattering and thus giving the film a superior opacity compared to some other extenders.

The complete article can be found in the European Coatings Journal 6/2016 (p. 44 ff, Optimising the cost of print) which is available in the online library. The complete paper also discusses the effect the extenders have on gloss.

Also relevant:

Titanium-dioxide proposed to be classified as suspected of causing cancer when inhaled
Titanium-dioxide: difficult times for coating manufacturers!
Substituting titanium dioxide by calcium carbonate in paint mixtures