Epoxy adhesives hardening

Butadiene-acrylonitrile Amine Epoxy adhesive hardeners... 

The two-part epoxy adhesive, readily available in hardware stores or other consumer outlets, comes in two tubes. One tube contains the epoxy resin, the other contains an amine hardener. Common diamine room temperature epoxy curing agents are materials such as the polyamides, available under the trade name Versamid. These polyamides are the reaction products of dimer acids and aUphatic diamines such as diethylenetriamine [111-40-0] ... 

The commercial possibiUties for epoxy resins were first recognized by DeTrey Emres in Switzerland and DeVoe and Raynolds in the United States (1,2). In 1936, DeTrey Emres produced a low melting bisphenol A-based epoxy resin that gave a thermoset composition with phthaUc anhydride. Apphcation of the hardened composition was foreseen in dental products, but initial attempts to market the resin were unsuccessful. The patents were hcensed to CIBA AG of Basel, Switzerland (now CIBA-GEIGY), and in 1946 the first epoxy adhesive was shown at the Swiss Industries Eair and samples of casting resin were offered to the electrical industry. 

The DP is dependent on the ratio of reactants. Generally an excess of the epichlorohydrin is used to produce cyclic ether end groups. Epoxies are formed from the reaction of diamines with low molecular weight epoxy resins that retain their cyclic ether end groups. Figure 4.9 shows the formation of this process. These materials are often sold as two-part, or two-pot, epoxy adhesives. Most use-at-home epoxy packages contain a part A of epoxy resin and a part B of hardener (typically a diamine). These two are mixed as directed and applied. They dry fast, so they can be handled in 5 10 min. Full strength occurs after 5 7 days. 

Many epoxy adhesives are capable of being B-staged. A B-staged resin is one in which a limited reaction between the resin and hardener has taken place so that the product is in a semicured but solid state. In the B-staged state, the polymeric adhesive is still fusible and soluble. On additional heat curing, the adhesive will progress from the B stage to a completely cured state. This will usually be accompanied by moderate flow. 

Safety considerations are of special importance in the use of these tubes, since their breaking pressure varies and may depend on microscopic faults in construction. We subjected our tubes to numerous pressure tests. In two cases the tube assemblies broke in both cases the epoxy adhesive (Araldite AV 138M and a HV 998 hardener, from Ciba-Geigy) detached at about 50 MPa. These tubes have been in use for more than one year in several laboratories, with a maximum working pressure of 10 MPa. No accident has occurred to date. Nevertheless, the tubes are always used with a protection device (Fig. 4.33) developed in our laboratory that ensures that the user is never exposed directly to the tube while it is pressurized. 

Application of sheets by thermoforming and vacuum bagging. It is important to make close contact between the sheets and the metal surface when epoxy adhesive is used. All trapped air must be removed. The vacuum bag is maintained until the epoxy is hardened. Details of... 

In many adhesives formulations, the resin portion is the same or similar and what determines its properties is the hardener or catalyst that is used to cure the resin. Thus, depending on the hardener, epoxy adhesives may be referred to as amine-cured, anhydride-cured, polyamide-cured, or novolac-cured. Polyurethanes may be polyol-cured or hydroxypolyester-cured. 

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. 

Epoxy adhesives are widely used in electronics assembly and packaging. They are formed by polymerizing epoxy resins having one or more terminal glycidyl ether (epoxy) groups with a variety of curing agents, hardeners, or catalysts. 

Nielson, PO., Properties of Epoxy Resins, Hardeners and Modifiers, Adhesives Age, Vol. 42, 1982. 

Uses Epoxy curative/hardener for coatings, adhesives, castings and composites... 

Grinder-Polishers with extra wheels and Minimet (Buehler), the latter with slide holder for thin sections 2 Glass plates (300x300 mm) Vacuum impregnator Epoxy and hardener and polyethylene cups (several varieties of each) Cyanoacrylate adhesive (Super Glue )... 

Single-part epoxy adhesives are available as liquid, paste or film and require heat to cure. The resin and hardener (or catalysed) are... 

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