More than two decades ago, a major shift from solvent-based coatings to aqueous and radiation-curing coating systems for wood coatings was predicted. The availability and the use of resins, dispersants and wax additives to enable differentiated performance in water-based systems have grown significantly, but the complete abandonment of organic solvent has not yet happened.
Formulators today need solutions that can help navigate numerous challenges and opportunities, such as increasing regulation, the need for more sustainable options, and rising raw materials costs, to name a few. With the appropriate additives, water-based coatings enhance sustainability benefits while delivering unique solutions that make wood more durable and more beautiful—delivering decorative and performance qualities that are on par with solvent-based systems.
Wax additives, or surface modifiers, are one component that get a lot of attention when formulating water-based wood coatings. Particularly wax emulsions, aqueous wax dispersions or wax powders are responsible for important properties of the finished coating film, such as optic and haptic properties. Haptic properties refer to surface feel. As an example, waxes can be used to create a soft, almost velvety/silky feel that can imitate the natural character of wood. Such surfaces also convey a character of warmth.
Like their solvent-based counterparts, water-based systems can be counted on to meet mechanical, chemical resistance and other requirements in application technology. Depending on the end uses, these requirements can vary. As an example, applications such as wooden toys for children have to be saliva resistant. Coatings for kitchen furniture have to be resistant to a larger group of chemical attacks from food and liquids, as well as from cleaning substances.
While water-based systems deliver desired decorative, performance and sustainability features, they can be more difficult to apply by DIY end users and craft businesses (home improvement contractors, exhibit builders, etc.) because they behave differently than solvent-based systems. Knowledge and experience in applying water-based coatings is helpful to ensure the correct processing of these systems and associated conditions and requirements. The application equipment used might also need to be replaced, switching to stainless steel to avoid rusting from water-based systems.
Two scenarios demonstrate the importance of having experience using these systems. In spray applications, foam can form if spray guns are not adjusted properly. Foam in water-based systems will not disappear as easily as foam in solvent-based systems and could lead to major issues and a poor surface appearance. Another scenario is with drying times. Water-based systems can take longer to dry and require higher energy consumption for drying, which increases the chances for dust or dirt to cause surface contamination and can increase costs.
Additional challenges can arise through the need to add biocides and a defoamer. In water-based systems, biocides are needed to ensure stability against microbial contamination. The right biocide (or biocide mix) needs to be chosen within the context of end uses and requirements on labeling and legislation (e.g. food contact or label with “Blauer Engel”).
Preventing foam formation during processing and application requires choosing the right defoamer. This can be challenging because a defoamer changes the surface tension of the liquids in the coating. The type and level of defoamer in the coating is key to avoid foam forming on one hand. On the other hand, too much defoamer can create other defects like “fisheyes” or de-wetting issues.
Coating of wooden substrates can be challenging in and of itself. During the drying process, wood fibers straighten up, creating a rough surface. Typically, a sanding step after the first layer is necessary to cut the fibers and then a smooth surface can be achieved with a second coating.
A Look Ahead
Market observations predict 4 to 5% growth in the use of water-based coatings in the next five years. The proportion of water-based wood lacquer systems could increase at a faster rate among DIY end users and craft businesses if legislation banning organic solvents increases.
As sustainability benefits become ever more important, Lubrizol continues to enhance its resins, dispersants, and wax additives portfolio and offers products precisely tailored to respective water-based wood coatings applications. These developments will continue to enable the switch from solvent-based to low-solvent or solvent-free coatings.
Lubrizol collaborates with customers to understand their unique formulation challenges and helps to enhance the capabilities of their specific water-based wood coatings. Contact a Lubrizol expert to learn more about our advanced solutions for water-based wood coatings.