High Performance Water Repellent Acrylic Latices for Exterior Wood Coatings

H. Hendrickx, N. Havaux, D. Vanaken, C. Nootens, F. Decocq, G. Badini and F. Simal, Hexion Specialty Chemicals Research S.A., Belgium

Recently a significant number of new constructions and house remodelling have witnessed the use of wood, as an aesthetical natural building material, for the creation of outdoor living space such as wooden patios, decks or porches.

Because the wood substrate is composed mainly of hygroscopic organic cellulosic elements, it is susceptible to degradation from adverse weather conditions. In addition to moisture and light degradation causing surface deterioration of wood, the attack of moulds and fungi will also create serious damage. In fact, without some type of coating to protect the surface, most wood deteriorates from exposure to the elements. The functional needs of the coating system for wood in exterior will then be to enhance the durability of the coated wooden component and keep its natural beauty. In this respect, acrylic-based waterborne systems have been the focus of most of the recent developments for exterior wood coating applications. This is due to the legislation push on the reduction of emission of volatile compounds, driving the switch from solvent borne to water borne coatings and also to their inherent protective character towards UV and moisture.

Recently, binders based on multiphase acrylic particles referred to as core/shell dispersions were introduced. This technique allows the development of a combination of a hard and a soft polymer phase that can overcome the conflicting requirements of a wood coating being resistant to blocking yet being very flexible. However, despite these advances, moisture protection remains a critical parameter still to be optimized in the field wood coating systems. Various attempts to improve hydrophobic properties of the coating film such as the use of additives such as wax and siloxane compounds did not prove to be very successful. Yet, the use of highly hydrophobic monomer is another approach to further improve the protection of wood against liquid water.

This paper will focus on the recent work performed in our R&D Centre on acrylic binders modified by highly hydrophobic vinyl ester monomers which led to the development of self cross-linkable core/shell latices having an extremely good balance between blocking resistance and outdoor durability. These emulsion polymers are particularly suitable for the formulation of high-performance exterior wood stains. A comparison of their performances with pure acrylic latices will be discussed in this presentation.