Thickener types and characteristics
Cellulosic thickeners have high thickening efficiency, especially for the thickening of the water phase; they have less restrictions on coating formulations and are widely used; they can be used in a wide range of pH. However, there are disadvantages such as poor leveling, more splashing during roller coating, poor stability, and susceptible to microbial degradation. Because it has low viscosity under high shear and high viscosity under static and low shear, the viscosity increases rapidly after coating, which can prevent sagging, but on the other hand, it causes poor leveling. Studies have shown that as the relative molecular weight of the thickener increases, the spattering of latex paint also increases. Cellulosic thickeners are prone to splashing due to their large relative molecular mass. And because cellulose is more hydrophilic, it will reduce the water resistance of the paint film.
cellulosic thickener
Polyacrylic acid thickeners have strong thickening and leveling properties, and good biological stability, but are sensitive to pH and have poor water resistance.
polyacrylic thickener
The associative structure of associative polyurethane thickener is destroyed under the action of shear force, and the viscosity decreases. When the shear force disappears, the viscosity can be restored, which can prevent the phenomenon of sag in the construction process. And its viscosity recovery has a certain hysteresis, which is conducive to the leveling of the coating film. The relative molecular mass (thousands to tens of thousands) of polyurethane thickeners is much lower than the relative molecular mass (hundreds of thousands to millions) of the first two types of thickeners, and will not promote splashing. Polyurethane thickener molecules have both hydrophilic and hydrophobic groups, and the hydrophobic groups have a strong affinity with the matrix of the coating film, which can enhance the water resistance of the coating film.
Post time: Mar-24-2023