Inherent Matte Polyurethane Dispersions as Matting Agents

By Dr. Terri Carson, Dr. Mario Schoondermark, Markus Dimmers, David Folkman

Low-gloss coatings have been attracting increasing interest in recent years.1 Not only for wood substrates is this trend seen, but even matte coatings for plastic and vinyl composite tile (VCT) can be found in various markets to enhance the appearance or reduce glare. In the case of wood coatings, many consumers have grown to appreciate the more natural look of untreated wood instead of a glossy finish.

A low-glare coating is less disturbing to the eye, which is a true benefit in larger spaces. Additionally, such a coating gives the appearance that the wood is untreated in terms of color, grain, and touch resulting in a more authentic look. Due to this trend, oiled or wax-treated surfaces gained a lot of market share due to their warm appearance and low gloss. However, these finishes still need much more intense care and maintenance than most consumers realize, since oils or waxes do not form a protective film.

A true matte varnish based on polymeric binders could offer the beauty of an oil/wax finish but provide superior protection and less necessity for intensive care resulting in the desired appearance. There are several options for the coatings formula-tor to create a matte coating. Various matting agents are available including silicas, waxes, and fillers and the best choice can be made depending on the application. Among this group, conventional silicas (precipitated and pyrogenic) are known to be very effective in reducing the gloss of water-based coatings. The use of silica-based matting has advantages, such as being very efficient at low levels of addition, having high wet film clarity, and being economical.

However, there are a number of disadvantages as well, such as sensitivity to scratches, imparting water sensitivity at high concentration, and causing “stress cracking” on flexible substrates. In addition, the silica-based matting agents are very light and difficult to add during manufacturing, can show hard settling in the coating after time and offer limited matting. The objective of this work is focused on the development of an inherent matte and hard polyurethane dispersion.

Ideally, such a polymer used in a low-gloss coating already has a matte polymer film without the use of any additional matting agents to avoid the above-mentioned drawbacks. Additional technical requirements have been defined: