Conventionally, paint compositions containing latex polymer particles also include a coalescent in addition to pigments and fillers. The coalescent functions as a solvent as well as a plasticizer for the polymer particles to soften the latex polymer particles and assist in the formation of a continuous coating or film after applying to a surface and allowing to dry.
Useful coalescents are generally stable in the presence of water, compatible with other ingredients typically used in paint formulations, particularly the latex polymers, such that the stability of the latex-based composition is not compromised. Typical coalescent agents contain volatile organic compounds (VOC) and are sufficiently volatile to escape when the applied coating composition is allowed to dry, but sufficiently nonvolatile to evaporate more slowly than other ingredients (e.g., drying retarders, antifreezes) that delay film formation.
For environmental and regulatory reasons, it has become imperative to develop latex polymers that can be used in paint and coating compositions without the use of volatile organic compounds (VOCs). Coalescent agents of the type described in U.S. Pat. Nos. 6,762,230 and 7,812,079, for example, are low-VOC compounds that meet stringent environmental requirements, while facilitating film formation.
To make paint formulations of a desired color and finish, base paint compositions are combined at a point-of-sale with low-VOC colorant compositions of the type described in U.S. Pat. No. 7,659,340, for example. However, typical low VOC paints with low VOC colorants tend to form soft, tacky coatings that show poor performance characteristics, such as poor block resistance and poor scrub resistance, for example. This situation is further complicated in deeply colored paint formulations that require high loading of the low VOC or zero-VOC colorants, which generally have residual non-volatile soft components, making hard film formation even more difficult.
Conventionally, the methods used to assess certain performance characteristics paint formulations have relied on visual and observational tests. Such tests are only semi-quantitative and do not provide insight into structure property relationships. Moreover, some of the conventional methods are known to have low repeatability, and ratings taken by different operators and/or at different times may vary considerably. Therefore, it is often difficult to predict performance characteristics of a paint formulation relying on conventional methods of testing.
From the foregoing, it will be appreciated that there is a need for latex compositions for use in paint formulations, including deeply colored formulations that form hard films in the presence of low VOC or zero-VOC components soft components, even in the absence of coalescent agents, and demonstrate excellent performance characteristics, including block, scrub and tack resistance. There is also a need for quantitative methods or tests that can be used to predict paint performance.