Epoxy resin based adhesives are used in many applications

In the automotive industry, epoxy adhesives are used in many bonding applications, including metal-to-metal bonding of frames and other structures in automobiles. Some of these adhesives must be strong enough to withstand damage in the event of a vehicle crash. This type of adhesive is sometimes referred to as a “crash-resistant adhesive” or “CDA”.

Epoxy adhesives are often formulated with various rubbers and/or “tougheners” in order to obtain a good balance of properties required to meet stringent automotive performance requirements. These tougheners have closed functional groups that can become unsealed and react with epoxy resins under conditions of curing reaction. This type of toughening agent is described in US Patent 5,202,390, US Patent 5,278,257, WO 2005/118734, US Published Patent Application 2005/0070634, US Published Patent Application 2005/0209401, US Published Patent Application In 2006/0276601 and EP-A-0 308 664.

Commonly used toughening agents are terminated with phenol groups, polyurethane vinegar, and/or veins. These tougheners have been used with some success in [0005]CDA applications. However, in some cases, it is necessary to further improve the strength of these adhesives and to develop adhesives that break more often by cohesive rather than cohesive failure when curing. Another type of toughening agent is acrylate-terminated polyurethane and/or business. These have been described in WO03/078163 for single-component epoxy adhesives, and in US 5,232,996, US 6,660,805, and US Published Patent Application 2004/0229990 for two-component adhesives. Acrylic end tougheners generally perform worse than the phenolic end types used in CDA applications. Their use tends to result in poorer lap shear and impact stripping strength in cured adhesives. Adhesives containing acrylate-end tougheners also tend to break in an adhesive mode rather than a more suitable cohesive mode.