V WATERBORNE SYSTEMS

Waterborne resins for surface coatings are not only prepared by an emulsion copolymerisation technique. They can be prepared using a solution technique with a water soluble organic solvent, or in water. This is the least common. 

The solution technique uses water soluble solvents, such as alcohols, (e.g. butanol, propanol) glycol ethers (e.g. butyl glycol), and acetates of glycol ethers (e.g. Dowanol range), following the same principles and techniques used for conventional solvent based systems. The two major differences are the inclusion of a functional comonomer, to induce water dispersibility, and neutralisation and dispersion after polymerising the resin in solution. 

The most common functionality is acid with methacrylic or acrylic acid normally being used to give the acrylic resin an acid value of about 50-80 mg KOH/g. The resin manufacturer may offer this acid functional resin in solution to formulators of coatings for them to neutralise and disperse in water. Alternatively, the resin manufacturer may partially or fully neutralise the acrylic resin, with an amine or ammonia before dispersing it in water. 

Before considering some formulations in detail, it should be remembered that all of the comments which applied to solvent based polymerisation also apply to solution polymerisation in water soluble solvents, with the added problem of Umited choice of suitable solvents. These solution polymerisations may or may not be run under reflux conditions, depending upon the solvent present. 

The alternative route of preparing water reducible resins using emulsion polymerisation of an acid functional acrylic resin has already been considered under emulsion example 7 - preparation of a water soluble acrylic copolymer. 

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