Epoxy finishes stoving

These intermediates are too small to be used alone, but need to be enlarged and modified to obtain compatibility with other resins. In the case of the phenol formaldehyde resins this is achieved by either using para-substituted phenols where the substituent contains at least four carbon atoms or by reacting the intermediate with the natural resin, rosin, and then esterifying with glycerol or pentaerythritol. These resins have a limited use in stoved epoxy finishes where colour is not an important factor. 

Assuming maximum corrosion resistance is required, then an anticorrosive primer will be needed, with best protection coming from a crosslinked epoxy stoving primer. Most other properties are dominated by the finish, which will be based on a high molecular weight-polymer, either linear or (more usually) crosslinked. The precise selection of the polymer depends on the balance of properties required, but will be constrained by the type and rate of curing necessary. 

Hot-Curing Epoxy Resin Esters. Solid epoxy resins with a molecular mass of ca. 2000 can be esterified with semidrying and/or nondrying fatty acids. These resins are used in combination with amino resins for stoving primers, can coatings, and industrial finishes. The importance of epoxy resin esters has, however, decreased in recent years. 

Uses Crosslinking agent for epoxy, afl d/polyester, or acrylic resins, for use in solv.-borne coatings, industrial stoving sterns, waterborne stoving finishes, resinous/polymeric food-contact coatings Regulatory FDA 21 CFR 175.300... 

Short-medium oil epoxy-esters can be used in stoving finishes, with or without nitrogen resins, in place of the corresponding alkyds. They make excellent primers and surfacers, especially for use under motorcar finishes. 

Epoxy-phenolic finishes are among the most chemically resistant known. 20-30 per cent phenolic resin is used with epoxy resin of molecular weight 1400 and the stoving schedule is 20 min at 180-205° C. Phenolic resins alone give excellent chemical resistance, but cross-linking with epoxy resin improves adhesion and impact resistance. The poor colour of the coatings is due to the phenolic resin. The... 

These may contain epoxy resins, epoxy-esters, epoxy-alkyds or other possible epoxidized resins. Both stoving and air-drying variants are possible. UV curing finishes are dealt with later in Chapter 16. 

These can be considered as reacting by both routes, since the unreacted acid in the alkyd may take part. Epoxy resin of molecular weight 900 n = 2) is used, since alkyd-epoxy resin compatibility is poor at higher molecular weights. Stoving is at temperatures of 150°C and above. Improvements over alkyd-melamine finishes occur in adhesion, flexibility, chemical and water resistance and mar and abrasion resistance. Uses are similar, particularly where finishing industrial and domestic equipment is concerned, since the excellent adhesion of the epoxy resin can allow the user to omit a primer. 

---