Epoxy adhesives Ether

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. 

Sharman. M., Honeybone, C.A., Jickells, S.M., and Castle, L., 1995, Detection of residues of the epoxy adhesive component bisphenol A diglycidyl ether (BADGE) in microwave susceptors and its migration into food.. Food Add. Contam. 12,6,779-787. 

Diluents are higher-MW components than solvents that are also added to the epoxy adhesive formulation to lower the viscosity and modify processing conditions. The primary function of a diluent in an epoxy resin formulation is to reduce its viscosity to make it easier to compound with fillers, to improve filler loading capacity, or to improve application properties. Solvents, certain curing agents, and flexibilized epoxy resins can also lower the viscosity of epoxy adhesive formulations, but this is not their primary function. The effect of various diluents on the initial viscosity of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin is illustrated in Fig. 6.3. 

Reactive diluents can be used to reduce the modulus and increase the elongation of the cured waterborne epoxy formulations just as they are often used for 100 percent solids and solvent-borne epoxy adhesives. The reactive diluents become codispersed in the formulation with mechanical and chemical stability similar to that of the base epoxy emulsion. Polyglycidyl ether of caster oil, phenyl glycidyl ether, and diglycidyl ether of neophenyl glycol are examples of mono- and difunctional reactive diluents that have been used to improve flexibility and increase the tack-free time of waterborne epoxy adhesives. 

The number of epoxide groups per molecule and the rigidity of the molecular structure are factors that affect the hot strength of the epoxy adhesive. Thus, epoxy novolac and gly-cidyl ethers of tetraphenolethane have become important resins for incorporating into high-temperature epoxy adhesives because of their multifunctionality. 

For adhesive bonding of PES to itself or to other materials, epoxy adhesives are generally used. Cyanoacrylates provide good bond strength if environmental resistance is not a factor. Parts made from PES can be cleaned using ethanol, methanol, isopropanol, or low-boiling petroleum ether. Solvents that should not be used are acetone, MEK, perchloroeth-ylene, tetrahydrofuran, toluene, and methylene chloride. 

Structural epoxy adhesives based on DGEBA (diglycidyl ether of bisphenol A) were cured with poly(amido-amine) and HB products at room temperature for seven days. 

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. 

Some of the first commercial conductive epoxy adhesives were simply based on silver powder dispersed in a liquid epoxy resin [e.g., diglycidyl ether of bisphenol A (DGEBA)] with an aliphatic amine [e.g., triethylene tetramine (TETA)] as a curing agent. Although capable of room-temperature cure, commercialization of this type of system was hampered by severe mix ratio disparity (typically, 50 1 by weight), problematic mixing due to viscosity differences, short pot life, and safety concerns. See Table 3 for typical properties of this type of formulation. 

The base resin in epoxy adhesive products can be readily identified by IR and NMR spectrometry. The most commonly employed resin in these products (both one-part and two-part) is that based on the diglycidyl ether of bisphenol A (bisphenol A epoxy resin). Other resins of importance include the cycloaliphatic epoxies and phenolic epoxy novolaks. 

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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