Storage stable epoxy resin adhesives based on encapsulated curatives

摘要

An advanced one-part structural adhesive that (1) is stabel under long-term (1-3 years), non-refrigerated storage conditions, (2) provides high strength service performance and (3) cna be cured using conventional schedules, i.e., one hour at 121 - 177 deg C (250 - 350 deg F) would be highly desirable as a repair adhesive. The approach for this researchprogram involved encapsulating a key epoxy resin curative in a protective shell. After screening and carefully selecting a curative, a microencapsulation process was developed and optimized. Using this approach, the curative is protected and remains inert in a one-part epoxy resin structural adhesive until it is thermally released during the cure cydle. The encapsulated curative and the total adhesive system have bene characterized. Both paste and film adhesives have bene formulated and evaluated for stability, reactivity and adhesive performance. Extensive comparisons have been made between formulations containing encapsulated curative and non-encapsulated curative. The results obtained with the adhesives containing microencapsulated curative compare favorably. Stabilities for the systems containing the encapsulated curatives are greatly increased for storage temperatures ranging from ambient to 49 deg (120 deg F). At the same time, cure rates are only slightly reduced. Adhesive performance approaches that for the formulatioons containing the non-encapsulated curative. This paper describes the performance of the paste and film adhesives.