Due to the higher polymer content of the paint film, there are greater performance demands for semi-gloss paints than for flat paints. These demands include gloss retention, block resistance and adhesion over previously painted glossy substrates. For exterior paints that are subjected to solar warming, block resistance performance is especially critical.

As the regulations drive allowable VOC levels in paint formulations lower, these performance properties can become more difficult to achieve. In order to achieve low-VOC coatings, the paint formulator either uses latex with a low glass transition temperature (Tg), or one with high amounts of non-volatile film formers. Unfortunately, both solutions can lead to poor block resistance, poor early water resistance and poor dirt resistance.

This problem can be overcome by using Acronal Optive® 130 from BASF, which is a multiphase latex with soft and hard phases on each latex particle. The soft phase aids in continuous film formation, whereas the hard phase helps to create outstanding block and dirt resistance.

Since the soft phase does not require a coalescent for film formation, Acronal Optive 130 can be formulated at 0 g/L of VOC, with the proper selection of other raw materials. This latex also enables the paint formulator to add up to 50 g/L of glycol in order to maximize open time and wet edge, while still meeting the South Coast Air Quality Management District (SCAQMD) VOC regulations.

With over six years of exposure, Acronal Optive 130 has proven to be the leading choice for low- to zero-VOC all-acrylic paints. Results listed in Figure 1 are based on a compilation of three years of southern exposure at a 45° angle in Florida, North Carolina and Pennsylvania.

These results show that Acronal Optive 130 offers similar block resistance, gloss and color retention, while also offering better grain crack resistance. The dirt resistance is slightly worse than the 150 g/L VOC control. However, as can be seen in Figure 2, at 18 months, Acronal Optive 130 has equal dirt resistance and gloss retention compared to the control, and superior dirt resistance compared to other low-VOC latex polymers.

Table 1 lists the latex formulations tested, the VOC level for each paint and the percent gloss retained after 18 months. Acronal Optive 130 delivered equivalent gloss retention compared to the higher-VOC control.

For more information, contact Kent Clow at kent.clow@basf.com.