Humectants are used to prevent tip drying and improve redispersibility in liquid colorants.
As an example of how they work, picture a custom color dispensing station at a paint or hardware store, where an employee adds colored tints into the base paint to achieve the desired final color. Without a humectant, the colorant can dry in the dispenser, which would eventually block the tip or allow bits of dried colorant to fall into the paint and cause streaks on application.
In this example, low molecular weight glycols have traditionally been used as humectants in water-based colorants. But these humectants are considered VOCs and are no longer used in zero and low VOC architectural paints. Now that the colorant added at the point of purchase is considered in calculation of VOC, a non-volatile humectant that can meet stringent VOC requirements (D6886 and ISO 11890-2) is needed for use in both the paint and colorant.
Meeting Stringent VOC Standards
VOC standards may have been low before, but in any amount now, emerging regulations make it much harder to use humectants with any trace amount of VOCs. The first move to meet these standards was by moving to propylene glycol, but even that still has VOCs. The next move was to polyethylene glycols. But with more exacting ASTM-type VOC tests, even those had residual VOCs.
Volatile Organic Content (VOC) is measured by how much evaporates at a given temperature over a certain time. The measurement temperature has increased from 100C°, to 110C° and is now 150C° or higher, depending on the test method. The evaporation rate is based on chemistry and vapor pressure. If a material has a vapor pressure, it will eventually evaporate. By ASTM standards, anything that eventually comes out of a paint, no matter how long it takes, is considered VOC. It has been a moving target to meet the ASTM standards as the test methods are refined.
As mentioned previously, one of the primary functions of humectants is to control drying properties—to improve open time. Open time is the time available where the paint can be worked into a previously painted area. It is a key performance property for coatings, particularly for brush applications. Humectants slow the open times for better paint drying and minimal brush lines.
Humectants also improve freeze/thaw stability. They keep the water in the formulation, which slightly depresses the freezing point. That feature can be important with shipping and storage. In addition, certain humectants can improve colorant properties, such as compatibility.
Moving Away from Volatile Glycols
By developing lower VOC humectants for water-based and universal tinting colorants in the 1990s, Lubrizol was one of the first to enable replacement of volatile glycols. Lubrizol continued to improve the range as regulations and requirements tightened, and now offers Humectant GRB2, Humectant GRB3, Humectant GRB4, and Humectant GRB5.Compared to traditional glycol technology Lubrizol humectants are more often considered high-performance additives and not as non-volatile solvents.
Lubrizol humectants also have the potential to improve colorant and paint properties, like better dispersion, color, stability and compatibility—compatibility of color into a variety of different paint systems.
Lubrizol has decades of experience developing additives for colorant systems. Based on this experience and our technical knowledge of resins and binders and additives, we’re able to design multi-functional additives to solve a range of challenges to improve paint and colorant formulations. Connect with us to explore opportunities to integrate advanced humectant technology into your next coating.