Two-Part Room Temperature Curing Epoxy Adhesives

B. Two-Part Room Temperature Curing Epoxy Adhesives... 

Temperature-resistant two-part, elevated-temperature curing epoxy adhesives can be formulated with aromatic amines, such as metaphenylenediamine (MPDA), methylene dianiline (MDA), or a eutectic blend of the two. These adhesives will provide relatively high temperature strength, but they are generally brittle. When mixed with epoxy resin at concentrations of about 15 pph for MPDA and 26 pph for MDA, they provide complete cure in about 30 min at 175°C. The aromatic amines also provide a working life of several hours at room temperature. Starting formulations for aromatic amine cured epoxy adhesives are shown in Table 12.4. 

All of the commercial epoxy adhesives presented in App. B bond well to aluminum and to a wide variety of other materials. Sell22 has ranked a number of aluminum adhesives in order of decreasing durability as follows nitrile-phenolics, high-temperature epoxies, elevated-temperature curing epoxies, elevated-temperature curing rubber-modified epoxies, vinyl epoxies, two-part room temperature curing epoxy paste with amine cure, and two-part urethanes. 

In most cases the resins, curing agents, etc., used in adhesive foams are similar to those used in film adhesives. Expandable adhesive foams will obviously differ in that they will contain a blowing agent, while syntactic foams will contain hollow microballoons to reduce density. One-part heat cure pastes will contain liquid resins instead of solid resins. Two-part room temperature cure epoxy paste adhesives are generally cured with active amine curing agents, while one-part epoxy pastes, adhesive... 

The outdoor durability of epoxy bonded joints is very dependent on the type of epoxy adhesive, specific formulation, nature of the surface preparation, and specific environmental conditions encountered in service. The data shown in Fig. 15.19, for a two-part room temperature cured polyamide epoxy adhesive with a variety of fillers, illustrates the differences in performance that can occur due to formulation changes. Excellent outdoor durability is provided on aluminum adherends when chromic-sulfuric acid etch or other chemical pretreatments are used. 

Data from Reference 23. The aluminum adherend was 6061-T6 alloy the adhesive was two-part, room-temperature-curing polyamide epoxy. The conversion coating was Alodine 1200. 

When using two-part urethane structural adhesives, priming of the substrates is often required in order to obtain optimum bond durability, particularly when bonding metals. Primers are generally developed for use with a particular combination of adhesive and adherends. There are various types of primers for polyurethane adhesives, including one-part heat cure epoxies, two-part heat and room temperature cure epoxies, and one-part urethanes. 

Room temperature curing, two-part epoxy adhesives are usually considered to have a lower level of outdoor performance than the heat cured adhesives. Their performance, however, can be improved by heat treatment following the room temperature cure. 

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 aliphatic diamines such as diethylenetriamine [111 -40-0], C4H13N3. Other room temperature curing agents are triethylenetetraamine [112-24-3], and the polypropylene glycol diamines, known as the Jeffamines. The... 

Of all the thermosetting plastics, epoxies are more widely used than any other plastic, in a variety of applications. There are resin/hardener systems (two-part) that cure at room temperature, as well as one-part systems that require extreme heat cures to develop optimum properties (e.g., 121°C and 177°C). Proper selection of various hardeners, resins, modifiers, and fillers allows the development of desired properties for a particular application. Because of the wide versatility and basic adhesive qualities, epoxies make excellent structural adhesives that can be engineered to widely different specifications. Essentially no shrinkage occurs during polymerization because epoxies are completely reactive producing no volatiles during cure. Epoxy adhesives can be formulated to meet a wide variety of bonding... 

Primary amine curatives are most commonly used for room temperature curing of epoxy adhesives. However, aromatic primary amines can be used as latent catalysts for one-part heat curing products (Table VI). Mixtures of bis(aminopropyl)tetraoxaspiroundecane and m-phenylenediamine or bis(aminophenyl)ether, amine, sulfoxide, or thioether have been used to cure DGEBA-type resins at two temperatures (40-100°C and 120-160°C) to give cured specimens with good fracture toughness. Aromatic primary diamines can offer improved adhesion of epoxy adhesives to metals and... 

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