Epoxy adhesives curing agents

The viscosity increase in a epoxy resin-curing agent system could result in poor wetting of the substrate surface, resulting in suboptimal adhesion. Several reaction mechanisms can also occur to an epoxy adhesive once it is mixed and applied to a substrate but before the substrates are mated. These mechanisms can result in a weak boundary layer, which will prevent optimal wetting and reduce the strength of the adhesive. 

It should also be emphasized that the epoxy resins are only building blocks in the development of epoxy-based adhesives. The formulation will ultimately involve one or more epoxy resins curing agents modifiers, such as plasticizers, flexibilizers, accelerators, stabilizers, and flow control agents and fillers. In general, flexibility can be controlled by the parameters shown in Table 3.8. 

Epoxy adhesive formulations demand a great variety of solvents and diluents with a wide range of evaporation rates, solvent strengths, and dispersion powers. These variations are required due to (1) the many types of epoxy resins, curing agents, and possible organic additives that can be used within a formulation and (2) the many different possible methods that can be used to apply the epoxy to the substrate (brush, spray, trowel, etc.). 

TRADE NAMES AND MANUFACTURERS EPOXY ADHESIVES, EPOXY RESINS, CURING AGENTS AND CATALYSTS, ADDITIVES AND MODIFIERS... 

Chapters 4 through 10 describe the basic raw materials that are commonly employed in formulating epoxy adhesives. These include the epoxy resins, curing agents and catalysts, solvents and diluents, resinous modifiers, flexibilizers and tougheners, fillers, and adhesion promoters. 

Uses Epoxy resin curing agent (composite aircraft bodies/components) hardener for adhesives, PWB laminates, prepregs, composites, powd. coatings exc. high temp, and chem. resist. antibacterial in treatment of dermatitis herpetiformis leprosy treatment drug veterinary medicine... 

Hazardous Decomp. Prods. Heated to decomp., emits very toxic fumes of NOx and SOx Uses Epoxy resin curing agent for prepregs/composites, castings, chem. resist, coatings, polyimide resins, elec, adhesives, high temp. elec, varnishes Manuf./Distrib. Aldrich http //www.sigma-aldrich.com, BASF http //www.basf.com, Schweizerhall http //www.susinc.com Trade Name Synonyms Ancamine 33S t[Air Prods./Perf. Chems. 

Wet adhesion is the biggest problem in order to achieve a good adhesion. For this matter, the water film on the surface of the uncmed adhesive has to be absorbed and, therefore, the formulation must be set hydrophilic. After curing of the adhesive, it should not be attacked by water or change its properties on exposme to water hence, it should be hydrophobic. The combination of hydrophobic behavior with hydrophilic epoxy amine curing agent has been proven in practice. Fillers, which react with water, can improve the wet grip considerably. Here, improvements can still be achieved (Brunner 1996). 

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 aUphatic diamines such as diethylenetriamine [111-40-0] ... 

Because the heat distortion temperature of cured epoxy resins (qv) increases with the functionality of the curing agents, pyromellitic dianhydride is used to cross-link epoxy resins for elevated temperature service. The dianhydride may be added as a dispersion of micropulverized powder in liquid epoxy resin or as a glycol adduct (158). Such epoxies may be used as an insulating layer in printed circuit boards to improve heat resistance (159). Other uses include inhibition of corrosion (160,161), hot melt traffic paints (162), azo pigments (163), adhesives (164), and photoresist compounds (165). 

The outstanding performance characteristics of the resins are conveyed by the bisphenol A moiety (toughness, rigidity, and elevated temperature performance), the ether linkages (chemical resistance), and the hydroxyl and epoxy groups (adhesive properties and formulation latitude, or reactivity with a wide variety of chemical curing agents) (see also Phenolic resins). 

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