Epoxy Resin

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Epoxy resins contain secondary hydroxyl groups and epoxy groups, which can react with isocyanates. Epoxy resins can be used as modifying resins for polyurethane coatings, adhesives, elastomers, etc., improving the high-temperature resistance, adhesion, hydrolysis resistance, and chemical resistance of polyurethanes.

Epoxy resins include bisphenol A epoxy resin, phenolic epoxy resin, bisphenol F epoxy resin, and aliphatic epoxy resin, with bisphenol A epoxy resin being the most commonly used. Common epoxy resins are prepared by the reaction of polyols or diphenols with epichlorohydrin.

The structural formula of bisphenol A epoxy resin is as follows:

As a hydroxyl component, the hydroxyl groups in epoxy resins can react with isocyanate groups in three ways:

(1) Simply using epoxy resin as part of the polyol component in polyurethane resins. In this method, only the hydroxyl groups participate in the reaction, and the epoxy groups do not react.

(2) Opening the epoxy ring with an acid (such as carboxylic acid or phosphoric acid) to generate hydroxyl groups, which then react with the isocyanate groups in polyurethane resins (especially adhesives).

(3) Reacting alcohol amines or amines with epoxy groups to form polyols:

The presence of tertiary nitrogen atoms in the adduct can accelerate the reaction between NCO and OH groups.

Epoxy resin is a colorless to light yellow transparent viscous liquid or solid. Besides liquid, solid granules, or block solid epoxy resins, solutions are also available.

The epoxy equivalent (E_n) refers to the number of grams of epoxy resin containing 1 mol of epoxy groups (g/mol). The epoxy value (E_v) refers to the amount of substance of epoxy groups contained in 100g of epoxy resin (mol/100g). The conversion relationship between epoxy value and epoxy equivalent is: E_n = 100/E_v, E_v = 2 × 100/M, where M is the molecular weight of the epoxy resin.

In China, E-51 or 618 are commonly used to represent the model of epoxy resin.