Which emulsion resins can be used for anti-corrosive paints ?
The suitability of emulsion or dispersion binders for anti-corrosive paints and metal finishes very much depends on the constitution and monomer composition of the polymers and also, of course, on the type of additives and auxiliaries contained in the formulation, e.g. emulsifiers, wetting agents, dispersing agents and hardeners.
The hydrophlic character of many binders makes their films water absorbent and water permeable, as well as allowing other potentially corrosive agents to be absorbed or to pass through. This interferes with the adhesion of films to metal surfaces, especially under damp and humid conditions. Emulsions of alkyd resins and epoxy resins esters, as well as dispersions of PVC terpolymers, styrene-acrylate copolymers and styrene-butadiene copolymers have proved suitable for use in air drying anti-corrosive paints.
Blends of copolymers dispersions with alkyd emulsions could also be suitable if the drawbacks of one component can be compensated by the advantages of the other. Synergistic effects are, however, inlikely in this case.
Water-based, two pack epoxy systems have recently been introduced as binders for anti-corrosive paints. Here alkyd resins and epoxy esters have been modified with special fatty acids and are suitable for forced drying up to 80o C. They are supplied in neutralised from and dissolved in co-solvent.
Epoxy dispersions specially suitable are those based on higher molecular weight epoxy resins where the emusifer has been condensed on to the molecule and takes part in the curing reaction.
Many of the hardeners normally used are unsuitable but modified polyamines can be used as speciality hardeners.