Лако-красочные материалы — производство

5.5.1

Chemistry of Epoxy Resin Adhesives

Epoxy resin adhesives are low-molecular-weight substances with a so-called ‘epoxy function’ — that is, a three-membered oxirane-ring composed of one oxygen atom linked to two carbon atoms (Figure 5.10).

H H I I

H-C-C-R

/

О Figure 5.10 The epoxy group.

Among a variety of epoxy compounds available commercially, the most important group for epoxy resins is derived from bis-phenol-A. Owing to the presence of a benzene ring, these resins are particularly stable yet at the same time they have a high polarity due to their electron configuration. Epoxy resins are produced from bis-phenol-A by reaction with epichlorohydrin to generate the diglycidyl ether of bis-phenol-A, a liquid resin used widely in adhesive manufacture (Figure 5.11).

Notably, care should be taken to avoid diglycidyl ethers coming into contact with the skin as they frequently induce allergic reactions (itching, inflammation, rash). Such sensitizing effects may be avoided by producing solid epoxy resins. In this case, the reaction of bis-phenol and epichlorohydrin can be controlled in such a way that some of the bis-phenol molecules react with each other to generate oligomers that carry epoxy groups at their ends. Owing to the bis-phenol-A unit, the resins have a high rigidity and very good adhesive properties. Another group of widely used epoxy resins are the cycloaliphatic diepoxides in which, due to a shorter distance between the reactive groups, intense crosslinking can take place at curing, providing for a high dimensional stability of the bond-line at elevated temperature.

5.5.2