1 октября, 2015 
Malyar Emulsion polymers differ from solution types in that the polymer takes the form of a fine particle suspension (typically from 0.03 to 0.3 pm) dispersed in water. There are two major classes of waterborne polymer colloids(9) available, namely;
• aqueous polymer dispersions prepared by emulsion polymerisation
• dispersions of preformed polymers into water by solubilisation with a base or acid.
The former class includes acrylic copolymers, vinyl acrylics and styrene butadiene, whilst the latter also embraces aqueous polyurethanes, polycarbonates and polyesters. Normally an acid or base functional resin is prepared in solution of a water soluble/miscible solvent, such as butyl glycol or butanol. Upon neutralisation, the resin is dispersed into the water phase and this is sometimes refered to as ‘inversion’.
For emulsions, film formation takes place through water loss forcing the spherical particles into a closely packed network of circular platelets. The resultant ‘discs’ merge or coalesce together to give a continuous film(8).
It should be noted that the basic chemistry and structure of solvent and water based resins are similar. Functional groups for subsequent crosslinking or promoting adhesion are introduced into the acrylic resin in a similar way. Only when there may be problems with stability, either during emulsion polymerisation or after inversion or on storage of either type of water based system, is there a need to consider a different approach to incorporating functional groups into the acrylic resin. The approaches for copolymerisation are similar for water and solvent based systems. Similar glass transition temperatures can be obtained from the same monomer composition, whether solvent or water based acrylic resin. However, an additional factor is the temperature of film formation (see Section IV (2)). This becomes particularly important with emulsions. Thus the majority of the discussions and treatments for solvent based systems equally apply for water based systems, with the additional need of stability in a non-solvent.
There are truly water soluble, as distinct from water dispersible, systems available. They tend, however, to offer very poor water resistance and so find limited, if any, use in surface coating applications. Similar to solvent based systems, as the molecular weight increases, viscosity increases. For any resistance properties, a reasonably high molecular weight is required, thus they are of very low solids content at application viscosity.
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