Heat Cure Carboxylic Acid Curatives

Carboxylic acids are used as heat-curing coreactants in epoxy adhesives with reasonable room temperature latency. The cured adhesives typically demonstrate high heat resistance and relatively low moisture sensitivity. Epoxy cures with carboxylic acid curatives are generally somewhat sluggish, requiring high cure temperatures and/or base activators to achieve cures in reasonable time periods. 

Acceleration of epoxy cures by carboxylic acids is frequently accomplished by addition of a base catalyst. Cure of epoxy resins by polymeric fatty acids (molecular weight 500-900) has been accelerated by the formation of fatty acid/melamine soaps (53). DGEBA-resin-based adhesives have also been cured with piperazine/polycarboxylic acid (e.g., succinic acid) salts (54). These adhesives showed rapid heat cures (23 min at 120°C) and good room temperature latency (shelf life of 60-65 days). The rate of cure in these adhesives was faster than comparable adhesives having dicy 

HOC—fatty acid—COHsN -N NHsOC—fatty acid—COH 

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Reactive diluents are low viscosity mono- or difunctionai epoxies based on aiiphatic aicohols, diols, alkylated phenols or carboxylic acid that are used to reduce the viscosity of standard epoxy resins and react with curatives during the curing process (Figure 2.42). They tend to reduce chemicai resistance, heat resistance and hardness of the coatings. The difunctionai diluents have fewer negative effects than monofunctional diluents. Higher vapor pressure (volatility) of some of the reactive diluents increases their toxicity, heaith risks and problems with skin irritancy. 

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