Driving Performance via Permanent Coalescent Choice in Low-VOC Architectural Paints

By Kyle Flack, Nicholas Foley, Tyrone Vaughn, Lisa Kicklighter, John Mangano

Proper film formation is a critical factor in high performance coatings as it ensures optimally low porosity, improves corrosion resistance, and impacts many film surface features. Through the decades, waterborne coatings have relied on volatile coalescing aids (solvents) to enable hydro-phobic latex particles to coalesce. Coalescing aids can be eliminated if the given latex has a glass transition temperature (Tg) below or near intended application temperature, but often the final paint properties suffer due to the increased softness of the final film.

Therefore, harder latexes have been developed, which require assistance from a coalescing aid to soften the system enough to form a continuous film during water evaporation (Figure 1). Coalescents aid in steps 3 to 4 of the drying process. Historically, volatile solvents such as dipropylene glycol n-butyl ether (DPnB) or 2,2,4-trimethyl-^1,3-pentanediol monoisobutyrate (Eastman Texanol™ Ester solvent, referred to as Texanol in the text), can be tuned based on compatibility with the given formulation and latex system to provide optimum film coalescence while remaining volatile during or after film formation to maximize filmic properties.

The challenge for the industry has been regulation on volatile organic compound (VOC) levels allowed, especially in interior architectural coatings, with a drive towards elimination of all VOCs from a coating. To balance the requirement of limiting VOC content, concessions in the amount of volatile coalescent are often used. To account for the reduction in volatile coalescent loading, permanent or nonvolatile coalescents have become of utmost importance.

These materials interact in a similar way to their volatile counterparts while remaining solvated in the final dry film. This permanence can have some drawbacks, namely, in secondary paint properties, such as poorer block resistance and increased leaching. Many options have become relevant in the marketspace for low- to zero-VOC coatings. Therefore, the goal of this work was to find optimum levels of coalescent required in a given system to understand the impact that an ultra-low VOC coalescent structure can have on efficiency and performance properties, and to investigate the interactions behind why one coalescent is preferred over another.