Water-based coatings: “A lot of new binder technologies”

Andre van Linden, Director Scientific Academic Partnerships at Akzo Nobel R&D, looks at challenges in water-borne systems and outlines his thoughts on factors influencing new developments.

Andre van Linden
We spoke to Andre van Linden about trends and challenges in water-borne coatings.

What key trends do you expect in water-borne systems?

Andre van Linden: Water-borne systems are still improving in quality all the time. The gap to solvent-borne systems in terms of performance is closing and there is now availability in many more markets and market segments. We therefore expect continued market growth for water-borne systems. However, they are also still under development and we see a lot of new binder technologies, often with different types of crosslinking, coming to the markets.

We have also noticed a lot of new ways of formulating water-borne systems, where dedicated additives are very important for the final coating properties. In these formulations, hybrid and even “tribrid” binders can sometimes help to overcome the difficulties associated with water-borne coatings. For all coatings and paints, circularity and decarbonisation plays an important role, so the use of bio-based and “circular” materials as replacements for traditional raw materials is rapidly increasing.

We will also see further VOC reductions, without any compromises on dry-film properties. Whereas, in the past, coatings were only for providing protection and aesthetics, we now see coatings serving other functional needs. These can range from the very basic, such as scuff resistance and biocidal protection, to the more complex, such as self-cleaning and fire resistance.

How can usage in difficult application conditions be improved?

Van Linden: An important difference, which is particularly noticeable for do-it-yourself users, is that water-borne paint dries differently and that the time available for going over the paint again with your brush or roller is much shorter. This effect means that often brush marks (or roller marks) remain in the paint. This “open time” can, however, be extended with new technologies using different binders and thickeners and that helps a lot with the final coating smoothness. The advantage of water-borne products is that they have a shorter drying time and so can be re-painted more quickly and this advantage is barely affected by these new technologies.

To get the best results from water-borne coatings, using the right brush or roller is critical. Water-borne coatings contain a lot of water and therefore the layer thickness and filling of the surface are not always up to requirements. The new binder systems increase the solids content of the formulation and, in combination with rheology control, can bring improvements in the direction of the desired performance. Another important difference is that water evaporates more slowly as the temperature decreases and especially when the humidity of the air increases. We cannot change the laws of physics and the physical properties of water (especially the evaporation rate) cannot be changed with additives. However, in most cases, water-borne paints still have the advantage of drying faster than solvent-bornes.

What regulatory challenges and other external factors could contribute to faster development of waterborne systems?

Van Linden: We have so much history of dealing with solvent-borne systems that it is certain we still have unexplored areas in water-borne technologies. More (academic) research and development by companies will help to develop water-borne systems faster and push the boundaries further by delivering totally new technology options. However, in the current economic climate, research efforts are potentially directed more towards value engineering. Carbon taxation or regulated lower VOC limits would focus attention and could lead to a faster breakthrough in new technologies. For water-borne products, adequate biocidal protection mechanisms are essential, but the current (BPR) policies make it difficult to introduce anything new; this remains a challenge. If a good water-soluble crosslinking polymer that does not exert a large influence on the rheology could be found, that might really help the development of water-borne formulations and improve the flow and filling of paints.

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