Metals Associated with Epoxy Adhesives

A number of curing agents and catalysts used in epoxies are complex metal salts that are added to cure at room temperature or with heat. Curing agents or catalysts such as cationic dinonato (acetylacetone, etc.) complexes of Si, B, Ge, and P behave as hydrolytic activated Bronsted acid precursors, e.g.  

Metal curing salts function with aliphatic or aromatic epoxy resins in the presence of trace water. 

Heat curing epoxy resins use a range of primary amines but are considered inferior to room temperature curing epoxies. Metal salts such as M[II] 4,4 ,4 ,4 -phthalocyami- 

The catalysts dibutyl tin dilaurate and dioctyl tin dilaurate typically used to prepare resins for epoxy adhesives must be removed on completion of reaction in the case of epoxy adhesives to be used in computer mainframes. The vapour generated through heat releases tin vapour salts which can damage sensitive electronic components. 

Inorganic fillers such as clays, CaCC 3, talc, silica, titanates, A1 and asbestos are commonly used in epoxy adhesives, as they are cheap and readily available. Conducting epoxies can be formulated with powdered copper metal or a mixture of a blend of Sn-Pb-Bi. 

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A list of metal catalysts associated with polyurethane adhesives will be discussed under polyurethane analysis. Some epoxy adhesives may contain metal salts that can act both as filler and catalyst. Some of these catalysts contain toxic metals that must be controlled and monitored for health and environmental requirements. 

The precedence for nitrile-epoxy alloys in other epoxy applications suggests that similar compositions in coatings should enhance film properties associated with flexibility, impact resistance and adhesion to metals. The testing scheme employed emphasizes these property features. 

Newer adhesives of the acrylic, anaerobic or radiation-curable types must, if they are structural, have a relatively high degree of toughness and durability if they are to compete with or challenge epoxy adhesive systems. Likewise, newer radiation-curable, pressure-sensitive adhesive systems must exhibit the properties of permanence largely associated with cross-linked adhesive masses deposited from an acrylic solution polymer base. Epoxy resin structural adhesives largely define the existing area on the one hand the cross-linked acrylics deposited on plastic or metallic films the other. 

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