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Epoxy systems have a long and successful track record in marine and protective coatings, mainly driven by their excellent barrier propera a corrosion, and chemical resistance.
There is a continuous trend in this industry to move the technology from the so-called conventional paint to high-solids coatings and, more recently, to ultra-high-solids coatings.1 This change not only brings some technical challenges that need to be addressed by the formula tors, but it also brings benefits such as lower VOCs, improved cure under adverse conditions, and the possibility to increase dry film thickness without having issues of solvent entrapment.
This article will review the basics of highsolids epoxy coatings compared to conventional epoxy technologies, and describe the fundamental technical differences.
Background
Epoxy coatings for ambient temperature cure are available as two-component systems. The epoxy resin base is typically referred to as "Fart A" and the curing agent as "Fart B." The resin and the curing agent form the coating's binder and determine most of its properties and performance,2 Pigments, fillers, additives, and suitable solvents that may be also part of the formulation can be added to either side, allowing the formulators to adjust the pigment volume concentration (PVC), gloss,and mixing ratio between Parts A and B. Solvents are used to reduce viscosity and facilitate manufacturing, handling, and application. The solvent level may change according to the application method and equipment used to apply the coating. In conventional solvent-borne epoxy coatings, a high molecular weight epoxy resin and a high molecular weight curing agent (most typically polyamide or aliphatic amine adduct types) are used to formulate a system with volume solids of ca. 50% and volatile organic compounds (VOC) level of ca. 400-450 g/1 (Table 1).
When formulating at higher solids (>7U vol.%; VOC <250 g/1}3, the most significant change in the composition above is the replacement of high molecular weight polymers, epoxy resin and curing agent, by low molecular weight alternatives, which naturally have lower viscosity. The paint viscosity can be brought further down by including some monoor difunctional epoxy-terminated diluents in the formulation.2 As a consequence, less solvent is required to adjust to application viscosity, resulting in coatings with higher solids by volume. Another important change is the use of pigments and fillers with lower oil...