Obtaining hiding power by appropriate preparation of the formulation with the use of volume solids is crucial today to meet market expectations in terms of coverage and compliance with the Eco-label criteria, which define the maximum amount of titanium dioxide pigment used in the coating. But why is attention not so much attached to this parameter in Europe, and in fact most on the NAFTA markets?
The Federal Specification TT-P-19D for acrylic paints for masonry and wood (last revision from 1985) requires a minimum content of 40% by volume of non-volatile components. Although this standard is very old, the requirement for a non-volatile content of 40% or higher is standard for high-quality paints in the USA. There is a growing awareness of this issue in Europe and other regions of the world and implementation these assumptions in formulations to set recipes for interior and facade paints at a minimum level of 40% volume solids, however, it is still a small percentage of all latex paints in the global market.
Below is a promotional video of one of the paint manufacturers from the USA – Dunn Edwards, who boasts that their paints meet the content of non-volatile parts by volume at the level of 40% minimum. It is unusual to draw the final consumer’s attention to a parameter such as volume soilids. In Europe, customers are not completely educated in this area, and you could get an idea from the USA and use it to build greater awareness of customers buying paint.
In paints with quite high PVC, i.e. at the level of 70% and above, it is very difficult to obtain volume solids at the level of 40% without over-filling the formulation with fillers, making its density above 1.5 g/cm3 (12.5 lbs/gal). In typical European formulations, the basic filler is calcium carbonate (GCC), which makes it impossible to obtain a volume fill without increasing the density of the paint. The solution is, among others the use of lightweight fillers that allow for a higher non-volatile content by volume without increasing the density, e.g. glass and polymer microspheres or other light fillers.
We show how the non-volatile content test is performed in a nutshell in the video from our laboratory. The question is often asked if this value cannot be calculated? Yes, of course, even ASTM D5201 Standard Practice for Calculating Formulation Physical Constants of Paints and Coatings includes a procedure for calculating volume solids in a formulation, however the calculations are always based on the data entered into the formulation calculator and do not take into account all the variables that affect the result.
As you can see in the video, the test is performed on discs immersed in the test paint. A considerable limitation is that the paint has poor rheological properties and does not allow for easy obtaining a coating in this way. Unfortunately, many paints in Europe, the viscosity of which is significantly increased by cellulose ethers, require the use of other methods for determining volume solids, e.g. from the ISO 3233 series, however, they do not provide very good precision of determination.
Paint manufacturers always indicate that the result comes from the ASTM D2697 test, according to which the content of volume solids is determined in the Spektrochem paint laboratory. The volume solids test performed in accordance with ASTM D2697 allows for the practical determination of the actual content of non-volatile components without the errors resulting from entering theoretical data into the formulation.
In addition to obtaining hiding power, a greater proportion of non-volatile components allows a thicker coating to be obtained after drying, when applied with the same spreading rate. This is of great importance when it is necessary to obtain the appropriate dry film thickness, thanks to which it is possible to achieve the recommended thickness level during the first or second painting, and not the third or fourth painting, which is also of great economic importance due to the painter’s labor costs.
An example of the effect of increasing the volume solids on the hiding power is presented in the photo below from the application test of two paints with an efficiency of ~ 11 m2/L (~ 448 sq.ft./gal). Both paints contain the same amount of titanium dioxide pigment by weight in their formulations.
In the formulations of very cheap paints with a very high filling degree, where PVC reaches even 90% and often higher, there is not much movement to increase the volume components, however, it must be remembered that such paints always have Q > 1 (PVC/CPVC > 1) and their hiding power is additionally achieved by the presence of air in the dry coating.
Of course, the examples in this article are samples. Each time, the results and correlation to the formulation should be verified for individual types of products, which must meet a number of properties other than just volume solids. The Spektrochem laboratory provides assistance and consultations in the implementation of formulation modifications in terms of changing volume solids and adapting the formulation to the quality of the NAFTA market.