Epoxide adhesives epoxy novolacs

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. 

Generally these compositions contain an epoxy-novolac, a hardener, a catalyst, silica fillers, and an internal lubricant/mold release compound. Brom-inated epoxies and antimony trioxide are included to provide the required flame retardant characteristics. Other, unspecified additives are used to promote adhesion or to reduce corrosion rates. Because of their superior thermal capabilities and electrical properties, epoxidized novolacs are preferred over epoxy homopolymers. Near stoichiometric amounts of hardeners such as novolacs (Equation 1), anhydrides, and primary amines can be used to cure the resins in the presence of a catalyst. The linkages which are formed include ethers, esters, or secondary amines, respectively. 

The neat novolac resins are also the precursors in the manufacture of a range of (see Epoxide adhesives), such as epoxy phenol novolacs and epoxy cresol novolacs spoxy resins. 

The epoxy novolac, cyclo-aliphatic epoxy and epoxide-functional acrylic resins mentioned in Chapter 14 may be used to form coatings with good adhesion to metal and are particularly suitable for the exterior surfaces of... 

Novolac resins are broadly used in electronics because their functionality higher than two increases the crossimkmg density and yields cured resins exhibiting enhanced chemical and physical properties. Mixtures of epoxy resins and phenol novolacs 61 are excellent structural adhesives in the aerospace industry. However, the phenolic hydroxyl groups are not very reachve at moderate temperatures and most systems include catalysts or accelerators. Classical adhesive compositions are prepared by mixing a solid epoxy resin, t5rpicahy an epoxidized phenol novolac resin (60 parts), a phenol novolac resin (40 parts), a solvent such as 2-butoxyethanol or butylcehosolve acetate, an imidazole catalyst, and silver flakes. 

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