Water-borne coatings: “Still challenges in some high-gloss trim paints”
Which approaches are useful for lowering solvent content without compromising performance?
Anne-Sophie Hesry: For decorative solvent-borne paints, and with current technology, it is now possible to replace most types by water-borne alternatives, although there are still challenges in some high-gloss trim paints. Optimising the polymer design to achieve maximum adhesion and ambient crosslinking enables water-borne gloss paints to be formulated with a very good balance of properties. Low-viscosity reactive resins and non-volatile liquid polymer systems of low viscosity can serve as reactive diluents and, we believe, also have the potential to lower solvent levels to help move closer to 100% solids formulations. Careful choice of other formulation components, in respect of low oil absorbency or coated pigments, can contribute to reduced solvent demand while maintaining acceptable rheology. Suppliers of raw materials to coating formulators can also play their part in minimising the VOC content of finished formulations by ensuring that binder or resin systems are as low as possible in volatile components.
For which applications will coatings with (high) solvent content still be the preferred systems?
Hesry: There are still requirements for protective paint applications where the performance requirements cannot, at present, be met by water-borne or high-solids systems. For example, metal protection in C4, C5 and offshore applications is not possible with water-borne paints. There are some applications in which the use of water-borne paints is restricted due to their poor drying properties under cold, humid conditions and in which it is likely that solvent-borne or reactive chemistries will continue to dominate.
Solvent systems still retain many benefits in terms of performance, ease of application and cost. These factors are likely to drive continued use of solvent-bornes, particularly in metal maintenance and repair for construction, in marine areas, and many exterior wood applications. VOC legislation globally is also still far from consistent, and so the drive to move from solvent-borne systems continues to vary by region.
For which applications (currently dominated by solvent-borne coatings) do you expect a shift from solvent-borne to eco-friendlier solutions?
Hesry: It is likely that there will be a drive towards water-borne metal primers and direct-to-metal coatings for highly corrosive environments over the coming years. Protection of metal protection against cellulosic fires is also an area likely to move more towards water-borne intumescent paints, for C2 and C3 environments, and for longer protection time applications. It is expected that “less demanding” wood protection applications are increasingly likely to move away from high VOC coatings.
Enhancing the durability of acrylic and alkyd waterborne decorative coatings is only one of the various topics presented at the European Coatings Future Dialogue. The event on 21-22 November in Berlin gives an overview on future technologies while allowing industry and science to meet and network.