Nano-Scale Additives

What is the status of nano-scale additives employed in coatings technology?

A significant level of research and development is currently being pursued in order to gain a full understanding of how coatings technology is impacted by the integration of nano-materials into formulated coating systems. The principle observation for the consideration of nanothechnology in coatings is the change in properties of materials such as clays, silica, TiO2, alumina, etc., as their size is reduced to the nano scale. The changes in properties of these materials are manifested in their increase in surface area and increase in chemical reactivity.

Much of the development for application of these materials has included both the fundamental investigation of the synthesis, characterization and mechanisms of materials behavior as well as the development of problem-directed performance improvements and practical applications. Examples of these applications include the reaction these materials with various organic polymers such as acrylics, epoxies, and polyesters leading to applicable coating systems on a variety of substrates.

Some of the performance properties that the new technology has demonstrated include improved dry film scratch and abrasion resistance, UV absorption, anti-corrosion and anti-bacterial/pollution properties. Other performance characteristics being sought include improved applied coating gas barrier properties, flame retardant properties, tannin stain blocking and easy-to-clean dry film properties.

Defoam and Antifoam Differences

What is the difference between defoam and antifoam coating additives?

Foam can be described as a stable dispersion of a gas in a liquid medium that results when a surfactant layer forms around air bubbles and entrains them within it. Air can be incorporated into a coating by mixing during the polymer/pigment grinding and let-down steps, by pumping during package filling or by shear (brushing or rolling) or spraying during application.

Generally, defoam additives are intended to control foam that is already present at the surface of a liquid. Antifoam additives are intended to minimize or prevent foam formation. Because these additives have similar chemical and performance properties, they are frequently referred to interchangeably. Substances such as mineral oil, formulated polysiloxane glycol copolymers, silicone compounds and emulsions, oxalkylated compounds and glycol/ester blends have found broad application with the cross-section of applicable coating binders.

The appropriate selection of these additives require adherence to specific formulation requirements and in many instances is based on observed additive performance in specific applications. Foam-control agents function by a variety of mechanisms to prevent or rupture foam. They are generally considered efficient if they are able to enter, bridge, dewet and rupture the layers of the foam wall. The most effective defoamer formulations usually contain a combination of organo-modified polydimethylsiloxane, silica, silicone-polyethers, emulsifying agents and carrier fluids (usually water).