Adhesives first generation epoxy

High levels of chloride ions, above 600 ppm, and sodium ion levels above 100 ppm were reported for the early first generation epoxy adhesives. The epoxy resin itself is a source of both chloride and sodium ions if not properly purified. Most epoxy resins are synthesized from epichlorohydrin and bisphenol-A in the presence of sodium hydroxide and produce sodium chloride as a byproduct (see Chapter 3). 

Epoxies became popular for the first generation of electrically conductive adhesives introduced in the mid-to-late 1960s. The early adhesive formulations contained organic solvents, which often became trapped in the bondhne during cure and resulted in voids, especially under large chips and substrates. These early adhesives also contained large amounts of ionic impurities, notably chloride ions, which, in the case of nonconductive adhesives, resulted in reduced electrical resistivity, ion migration, and corrosion, especially in humid environments. Early epoxies were also... 

Epoxies became popular for the first generation of electrically conductive adhesives introduced in the mid-to-late 1960s. The early adhesive... 

The results for the 120 C-curing epoxy film adhesives are shown in Fig. 9. Marked differences are noted here. The AF-44 nylon-toughened epoxy has very poor durability at any load and adhesion failure predominates. AF-126-2, the first-generation nitr ile-r ubber-f lexibilized epojiy has somewhat better durability and the failure mode is at least partially cohesive. AF-163 and AF-163-2, the second-generation-toughened epoxies, show a substantial... 

Radiation curable adhesives can be based on raw materials that are not greatly different from those used in acrylic adhesives (first, second, and third generations), epoxy adhesives, urethane adhesives, and anaerobic adhesives. The formulation approach, however, is somewhat different. Very important is that no solvents are used to thin the resins a monomer reactive diluent is used instead. The monomer must be matched with the resin to give the desired set of properties with respect to adhesion, substrate, flexibility or stiffness, cure behavior, and durability of the cured product. Most of the radiation curable adhesives have an acrylate (or methacrylate) basis many of the acrylics are modified. 

The next generation of adhesives (1970s) saw further improvements in purification of epoxy adhesives in which the chloride, potassium, sodium, and other ions were reduced to levels below 20 ppm. Outgassing was also reduced by changes in the hardeners used to cure the epoxies and by optimizing the cure schedules. The first specification for the qualification of adhesives was issued during this period by NASA s Marshall Space Flight Center in 1978. 

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