Nitrile-modified epoxy structural adhesive

Epoxy structural adhesives which employ carboxylic polybutadiene/acrylonitrile solid and liquid (CTBN) elastomers as modifiers have increased in number and proliferated in use since their introduction in the mid- 60 s. Such adhesive systems are now used in aircraft, electronics, automotive and industrial bonding operations. In the mid- 70 s, amine-reactive versions of the liquid polymers (ATBN) were issued, thereby offering another way to introduce rubber modification into a cured epoxy network. References are cited which provide detailed discussions of nitrile rubber, carboxylic nitrile rubber and both carboxyl- and amine-terminated nitrile liquid polymers (1-4). ... 

Typically tape or film epoxy adhesives are modified with synthetic thermoplastic polymers to improve flexibility in the uncured film and toughness in the cured adhesive. Epoxy resins can also be blended with phenolic resins for higher heat resistance. The most common hybrid systems include epoxy-phenolics, epoxy-nylon, epoxy-nitrile, and epoxy-vinyl hybrids. These hybrid film adhesives are summarized in Table 13.2, and structural properties are shown in Table 13.3. 

As previously mentioned in this chapter, carboxyl-reactive nitrile liquids appear to be the preferred modifiers for latent epoxy structural film adhesives. One of the major components used in formulating these adhesives is a solid epoxy resin of similar molecular weight (1000). This limited coatings study suggests that similar elastomer-modified epoxy resins are equally impressive in solution epoxy coatings. In addition. Table XI/Recipe 3 features a high impact coating modified with both liquid and solid carboxylated nitrile elastomers. 

In this Institute, there are approximately 200 research personnel and one fourth of them are working on adhesives in two laboratories, one pilot-plant, one testing group and one adhesive-film manufacturing and testing facility. Their research and development broadly covered structural adhesives, strain gauge adhesives, wood adhesives, second-generation acrylics, anaerobic adhesives and composite binders. Their products varied from J-01 to J-53. There were at least thirty different kinds of adhesive and sealant, for example, nitrile-phenolics, modified epoxies, acrylics and epoxy-phenolics. 

There are a number of types, based on their chemical structure, but the most important and most widely used is nylon 6,6. The best adhesives for bonding nylon to nylon are solvents. Various commercial adhesives, especially those based on phenol-formaldehyde (phenolics) and epoxy resins, are sometimes used for bonding nylon to nylon, although they are usually considered inferior to the solvent type because they result in a brittle joint. Adhesives recommended include nylon-phenoUc, nitrile-phenolic, nitriles, neoprene, modified epoxy, cyanoacrylate, modified phenolic, resorcinol-formaldehyde, and polyurethane. Bonds in the range of 1.7-6.9 MPa, depending on the thickness of the adherends, have been obtained. ... 

Epoxies and nitrile phenolics account for the major part of the market for structural adhesives and although they will remain important, their percentage share of the market is expected to fall. Urethanes and modified acrylics appear to have the greatest potential for growth and they are expected to pick up a more important market share in the future. 

The epoxy-nitrile adhesives were introduced commercially in the late 1960s. They consisted primarily of DGEBA epoxy resin modified with carboxyl-terminated butadiene nitrile (CTBN) rubber. These first nitrile copolymers were available from B.F. Goodrich under the trade name of Hycar. The most convenient form of epoxy nitrile adhesive, especially when one is bonding large parts (aircraft structures), is a supported film. However, solvent solutions of epoxy-nitrile adhesives have also been commercially available. 

---