Лако-красочные материалы — производство

Due to environmental concerns, waterborne coatings are becoming increasingly popular. The binders used for aqueous coatings, such as latex, are stabilized polymer particles in water; therefore, their rheological properties are independent of MW and more complex than simple resin solutions. Thus it is much more necessary to use a proper rheology modifier in aqueous coatings to provide a good balance of properties like storage viscosity, application viscosity, anti-settling properties, spatter resistance and flow and leveling. Also, latex is shear sensitive and therefore cannot be used at the grinding stage, meaning grinding must be done in the presence of a suitable thickener to provide enough consistency for efficient grinding. Thickeners for waterbased coatings can be categorized into two classes based on the mechanism of thickening: waterphase thickeners and associative thickeners.

Waterphase thickeners thicken the aqueous phase of the system due to dissolved polymer. Cellulose derivatives are most commonly used, but starch derivatives and acrylic thickeners are other groups in this class. The advantage of these thickeners is that they operate independently of the system, and hence rheological behavior of the paint is comparatively predictable.

Associative thickeners increase the viscosity of the paint by inter­acting with other paint ingredients through bridging of particles (surface to surface) or interaction of adsorbed layers. The interac­tions are assumed to be through hydrophobic forces. The operative mechanism is illustrated in Figure 5.9. Important groups in this class are associative acrylic thickeners, associative cellulose ethers and hydrophobically modified ethoxylated urethanes (HEUR).