Advances Made in Epoxy Coating Technology

Single-pack epoxy coatings can be used with flooring projects.

Until the 1950s, the vast majority of coatings used for substrate protection were single-component or “one-pack” coatings that were supplied in one can in a ready-to-use condition. Some of these products, particularly the solution-vinyl products, provided excellent water and corrosion resistance and protected against many chemicals as well. These products had very high solvent content and were low in solids, which required up to four or more coats to achieve target dry film thickness (DFT).

When epoxy technology was introduced in the 1950s, epoxy coatings could be formulated at significantly higher solids content, and target DFT could be met with fewer coats. Since these epoxy products cure by a chemical reaction, the reactive constituents of the finished coating must be packaged separately (epoxy resins on the one side, and typically amine or amide-functional materials on the other side) and then combined in the proper ratio immediately before application. When U.S. regulations limited the volatile organic compounds (VOCs) in coatings in the mid-1970s, the new restrictions on solvent content could not be met by traditional single-pack coatings, and epoxy coatings replaced the older technologies as the “go-to” products for protective and marine applications.

Recently, a single-pack epoxy coating with epoxy-amine reactive functionality was developed that delivers reasonable shelf life and a high level of corrosion resistance that is comparable to two-component epoxy polyamide coatings. The technology is a high-solids, storage-stable coating comprised of an epoxy resin, a hydrocarbon compound, a functionalized silicone resin, and a ketimine curing agent that contains a polyamine compound and a ketone. Ketimine curing agents essentially are blocked amines that hydrolyze back to the original amine and ketone in the presence of water. These blocked amines are especially useful for extending the pot life of high-solids, two-pack epoxy coatings, and in theory, allow the formulator to produce one-pack amine-cured epoxy coatings provided the mixture is kept free of all traces of moisture.

Past efforts to produce one-pack epoxy coatings based on current ketimine technology had been unsuccessful because of the difficulty of producing formulated coatings that are completely free of water, and slight traces of water adsorbed on pigments or picked up from ambient air contact during processing were enough to cause instability and a short shelf life, particularly with a higher solids content (>60% by volume). The new single-pack epoxy coating technology, however, has resolved the problems of inadequate stability and limited shelf life.

In CORROSION 2016 paper no. 7345, “New Advances in Epoxy Protective Coatings” by J. McCarthy, a comparison of the performance of the new single-pack epoxy-amine coating to that of two different commercially available two-component epoxy polyamide coatings is presented. The coatings were subjected to various standard corrosion tests as well as tests of the coatings’ physical properties, and the results are reported. The author’s conclusion is the single-pack epoxy technology delivers reasonable shelf life with a high level of corrosion resistance and physical properties that are comparable to the two-component epoxy polyamide coatings.

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