Amine-cured epoxy has a long history of success as a chemically resistant coating in a wide variety of applications, including industrial and marine markets. These formulations tend to be epoxy with filler and other additives on the A side, and amine curative on the B side, that when mixed together give a sprayable coating with a very workable pot life and good adhesion to a wide variety of substrates. The ultimate chemical resistance of the cured epoxy coating will depend on several factors, including the chemical structure of both the epoxy and the amine curative, the crosslink density, the stoichiometry of the epoxy to amine curative, the types of fillers and additives used, and the cure temperature and time. Figure 1 shows a representation of the crosslink density of a traditional epoxy compared to a polymer-modified epoxy that is extremely chemical resistant, such as ChemLine
®
784/32 from Advanced Polymer Coatings. By utilizing polymer technology with very high functionality, the coating can achieve up to 784 crosslinks compared to four crosslinks for a traditional bifunctional epoxy.
With a low crosslink density, the coating is susceptible to penetration from aggressive chemicals, which can eventually reach the substrate, causing corrosion and ultimately failure of the substrate. However, with a very high crosslink density, the coating forms a virtually impermeable barrier between the chemical and the substrate. In addition, chemicals do not penetrate the coating, which can occur in traditional epoxies, leading to blistering, cracking and general coating degradation. Figure 2 shows the penetration of chemicals in a thermoset of low crosslink density versus a thermoset of high crosslink density. In the low-crosslink-density coating, the chemicals are shown to penetrate through the coating to the substrate, causing substrate corrosion. In addition, because the solvent has penetrated the coating, both the epoxy and amine curing agent bonds are shown broken by chemical attack. In contrast, for the coating with high crosslink density, the chemicals are unable to penetrate the coating. This not only protects the substrate from corrosion, but also protects the coating itself from damage.