Role and Function of Rheological Additives in Modern Emulsion and Industrial Coatings
With the increasing demand for low-VOC or VOC-free waterborne coating systems, there has been a call for a new class of thickeners -- known as modern rheological additives. These additives allow specific modification of the viscosity of the coating system at various shear rates.2-5 As a result, such key coating properties as vertical flow, leveling, gloss, film thickness, covering power, spattering tendency, brush and roll resistance, sedimentation tendency and pigment stabilization are significantly affected. In most cases, only small quantities of between 0.1 and 4%, calculated on the formulation, are enough to obtain ideal flow properties for a particular application. In addition, such additives also have an influence on the properties of the coating after its application, for example on adhesion and elasticity and on the resistance to soiling, abrasion, water, and corrosion.
Consequently, the right choice of rheological additives for a specific task is becoming increasingly important,3,6-7 especially as optimum flow properties play a major role in the success of waterborne coating systems. The large number of different, commercially available products does not make this choice very easy. The aim of this article is to first give a brief summary of the different rheological additives on the market, and to then make recommendations on the choice of suitable systems with the aid of a few selected examples.