Emulsion paints and water-based coatings

Less than 50 years ago, virtually all paint and other surface coating formulations were based on hydrocarbon solvents as the liquid phase. Following advances made in emulsion or latex polymer chemistry, resin systems became available which had the necessary properties of mechanical strength, durability and cost effectiveness such that today, emulsion paint dominates the decorative coatings area. This trend was assisted by the introduction of legislation which discouraged and, in some cases, prohibited the use of formulations which resulted in VOC (volatile organic carbon) emission to atmosphere. 

In such systems the thickener has to meet a number of critical requirements, some of which oppose each other  

In the context of the synthetic polymers considered in this chapter, the requirements defined above restrict the choice of products for this type of application to the water-based alkali-activated polymers discussed in Section 3.2.2 and the hydrophobicaUy modified alkali-activated polymers are now a common choice of synthetic thickener in emulsion paints. 

For other water-based formulation such as tile adhesives, cements and grouts, a little more scope exists for selecting polymers in other physical forms. In these end uses, the composition should be easy to apply or spread on such as the rear surface of a tile, whilst having sufficient viscosity to resist the force of gravity on the tile placed on a vertical surface, until drying is complete. This requirement is well met by the extreme shear thinning profile of cross-linked polymers. Consequently, precipitation polymers or alkali-activated polymers are often selected. Inverse emulsions and LDPs less well suited as the small amount of hydrocarbon oil that would be present in a formulation based on this polymer type can be undesirable in the end use. 

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