Resin coatings, reformulating solvent

Technique for Reformulating Solvent Mixtures in Epoxy Resin Coatings... 

A ir pollution restrictions are now controlling the solvent mixtures used - in epoxy resin-based coatings requiring reformulation. In conforming to these restrictions, the study of alternate solvent mixtures has been systematized and simplified by epoxy resin solubility maps and ternary diagrams. This paper presents the practical application of this reformulating technique with emphasis on special effects like improvements in drying rate and lower viscosity. 

Reformulation can clearly offer a low capital investment route to avoid HAPs regulations. R D costs are often low and solvent/solvent reformulation does not normally require any of the process changes associated with low solvent systems. However, solvent choice is linked to other components of a formulation (e.g. resin in coatings). Therefore it may not always be possible to replace solvents without affecting product quality. Reformulation would typically result in a small overall increase in solvent costs. 

A separate list of resin and polymer solubility parameters are available from another Barton publication [5] and are discussed in Chapter 5. Archer [6] discussed the use of the Hansen solubility parameter theory to reformulate a solvent-based coating. The following example demonstrates the usefulness of the Hansen method. Neither xylene nor methanol are good solvents for a D.E.N. epoxy novolac 438 resin. However, calculations suggested that a 50 50 (by volume) solvent blend should be able to dissolve the epoxy resin. Using the Hansen parameters for xylene and methanol from Table 4.1 the solubility parameters for the 50 50 blend were calculated as follows ... 

Although not discussed in this chapter, changes in solvent composition will shift to be more ecologically friendly. Conversion to fully compliant hazardous air pollutant solvents (HAPS) will require complete reformulation of most coating resins. Free solvent replacement to HAPS compliant can occur immediately and substitution in all manufactured resins should be fully implemented within the next few years. Greater use of waterborne materials (primers, basecoats, and clears) is expected within the next five to ten years as long as application properties, performance, and durability can be attained. 

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