Epoxy adhesives anhydride curing agents

The polyaddition reaction is the most commonly used type of reaction for the cure of epoxy resins. The curing agents used in this type of reaction have an active hydrogen compound, and they include amines, amides, and mercaptans. With this reaction mechanism, the most important curing agents for adhesives are primary and secondary amines containing at least three active hydrogen atoms and various di- or polyfunctional carboxylic acids and their anhydrides. 

Whereas most room temperature curing epoxy adhesives are cured with aliphatic amines, polyamides, or amidoamines, most elevated-temperature curing epoxy adhesives are cured with aromatic amines, modified aliphatic amines, alcoholic and phenolic hydroxyls, acid anhydrides, Lewis acids, and a host of other curatives. Latent curing agents, such as dicyan-diamide and imidazoles, are typically used in one-component epoxy adhesives systems. 

Phthalic anhydride (PA) and its derivatives are among the most common anhydride curing agents. Table 12.6 describes an anhydride cured epoxy adhesive that is accelerated with... 

Aliphatic and cycloahphatic epoxy resins have less tendency to yellow and can even be used as a basis for epoxy gelcoats. Such gelcoats are not widely available due to difficulties in application and adhesion to the substrate, as well as high costs. Use of non-aromatic anhydride curing agents such as hexahydrophthalic anhydride will produce further improvements in colour stability and these systems are suitable for high temperature curing applications. 

Fluoro-anhydride Curing Agent for Heavily Fluorinated Epoxy Resins," in Adhesion Science and Technology, L. H. Lee, Editor, 429 Plenum, New York (1975). 

Copper surfaces may be stuck with urea formaldehyde resins or, if these are too brittle to suit the application, they may be used as a priming coat above which some other adhesive is applied. Epoxy resins vary in their behaviour towards copper owing to differences in the curing agent employed. Anhydride curing agents are known to be... 

After the primary amines, acid anhydrides are the next most important class of epoxy curing agents, although these are not used as often in adhesive systems as they are in casting compounds, encapsulants, molding compounds, etc. The most common types of anhydrides are hexahydrophthalic anhydride (HHPA), phthalic anhydride (PA), nadic methyl anhydride (NMA), and pyromellitic dianhydride (PMDA), although there are several others. Chemical structures of several anhydrides are illustrated in Fig. 5.6. 

Benzyldimethylamine (BDMA) is another tertiary amine that can be used as either a sole catalyst or an accelerator with other curing agents. It is used with DGEBA epoxy resins at 6 to 10 pph. The pot life is generally 1 to 4 h, and the cure will be complete in about 6 days at room temperature. When used by itself, BDMA can provide epoxy adhesive formulations with high-temperature resistance (Chap. 15). However, BDMA is mostly used as an accelerator for anhydride and dicyandiamide cured epoxy resins. 

EMI cured epoxy adhesive formulations are claimed to have outstanding adhesion to metals, and for this reason it is added as a co-curing agent in many compositions. It is an excellent anhydride accelerator providing higher thermal resistance than typical tertiary amine accelerators. 

Other latent curing agents that are used in solid adhesives are dihydrazides and BF3-MEA complexes. These compositions are also stable at room temperature but cure when heated. Solid anhydrides can be used in one-component powder blends (e.g., 10 pph of trimellitic anhydride accelerated with 0.5 pph of 2-methylimidazole). Solid systems with aromatic diamines are prepared by comelting the solid epoxy with the amine. Typically 30 pph of curing agent is used.1... 

The hardener portion (Part B) may also be mixed with fillers, diluents, solvents, and other additives. Fillers may be mixed in the resin portion alone or partly in the resin and partly in the hardener portion. Adhesion promoters such as Dow Corning A-180 silane may also be added to enhance the adhesion of the filler particles to the resin or hardener. Examples include several electrically conductive epoxy formulations that were used to evaluate their electrical stability on non-noble metal surfaces. The base epoxy resin was the diglycidylether of bisphenol-F (DGEBF, equivalent wt. = 170 g). Methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, and 4-methylphthalic anhydride were evaluated as curing agents with 4-methylimidazole as a catalyst. The manufacturing procedure was ... 

Uses Antioxidant stabilizer catalyst intermediate R.T. epoxy curing agent activator for epoxy resins cured with wide variety of hardener types incl. polyamide, amidoamines, polymercaptans, and anhydrides for coatings, adhesives, castings, potting, encapsulation Manuf./Distrib. ChemService http //www.chemservice.com, Sigma Trade Name Synonyms Ancamine 1110 [Air Prods./Perf. Chems. http //WWW. airproducts. com]... 

All epoxy compounds contain two or more of these groups. Epoxy resins may vary from low-viscosity liquids to high melting point solids. More than two dozen types are known. Tens of curing agents, including commonly available compounds such as amines, primary and secondary amines, and anhydrides are used. Only a few of these are used widely in adhesive formulations. ... 

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