Epoxy amine curing agents

Uncoated iron Cellulose acetate butyrate Epon 828/V125 Epoxy amine curing agent Shell/General... 

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). 

By contrast with tertiary amines used in catalytic quantities, primary and secondary amines or acid anhydrides may be used to bring about the cure of epoxy resins by reaction in stoichiometric proportions. A typical amine curing agent used at this level is diaminodiphenylmethane (DDM), which reacts with an individual epoxy-group in the way shown in Reaction 4.17. 

Epoxy resins. The reaction of Bisphenol A and epichlorohydrin gives a low molecular weight linear polymer. This polymer further reacts with an amine-curing agent, R-NH2, to give a general-purpose thermoset. See Figure 24-2.) Now that s not as complicated as it sounds. First of all, you d think... 

To attain the requirements of an epoxy matrix utilized in filament-wound C-fiber-epoxy composites we have considered the characteristics required of the amine curing agent molecule. To ensure long gel times at 23 °C requires that the primary amine-epoxide (P.A.-E) reaction rate is considerably greater than the rate of the secondary amine-epoxide (S. A.-E) reaction, and that the S.A. reaction does not occur at low temperatures. Furthermore, to attain low 23 °Cr s and low post-cure temperatures... 

A great variety of aromatic diamines and aliphatic di- and poly-amines are used as epoxy resin curing agents, and tert-amines can act as catalysts for anionic epoxide homopolymerisation. 

Figure 3. Effect of EME 58 (58 wt% mercaptoester units co-polymer) coupling agent concentration on the peel strength of flexible epoxy (amine-cured)/AD = acetone-degreased steel test panels following (a) I day and (b) 3 day exposure to 57°C condensing humidity. See Appendix 4 for epoxy resin and cure description.

Amines are one of the most important curing agents for epoxy resins. They provide fast cures with a relatively high crosslink density. Unmodified amine cured epoxy resins are generally too brittle for adhesive applications, and so there are many derivatives that have been developed. More information on amine curing agents can be found in Chap. 5. 

Table 11.12 shows two rapid-setting, room temperature cure epoxy adhesives based on epoxy acrylate resins with aliphatic amine curing agents. These adhesives have gel times of less than 5 min for a 100-g mass. The bond strength development is rapid with handling strength occurring in about 1 h at room temperature. 

Table 12.9 shows a formulation for an accelerated general-purpose one-component, dicyandiamide cured epoxy adhesive compared to one with a modified aliphatic amine curing agent. Notice that the dicyandiamide cured system provides a higher glass transition tem-... 

DADPS also provides excellent high-temperature properties and chemical resistance. Of the amine curing agents, DADPS provides the best retention of strength after prolonged exposure to elevated temperatures. It melts at 135°C and can be cured with epoxy resins at 20 to 30 pph with cure temperatures ranging from 115 to 150°C. Because of the low reactivity of this system, an accelerator, such as BF3-MEA, is usually employed at about 1 pph. 

It has been shown that tensile shear and peel strength for several latex polymers (ethylene vinyl acetate, polyvinyl alcohol, ethylene vinyl chloride, polyvinyl chloride, and acrylic) can be significantly increased by the addition of 10 percent by weight of an epoxy emulsion cured with a tertiary amine curing agent.17 The epoxy modification improves the bond strength in all cases. The degree of improvement is dependent on the selection of the latex type and the chemistry of the latex polymer. 

For maximum heat resistance, pyromellitic dianhydride is often used. The composition and properties of metal-to-metal adhesives based on a combination of epoxy novolac and a bisphenol A epoxy resin have been described in Sec. 12.5.1. Depending on the cure temperature and the choice of amine curing agent, strength as high as 3000 psi at room temperature and over 1000 psi in the range of-55 to + 150°C is possible. 

Amine curing agents for epoxies are poor in oxidizing acids. Anhydride curing agents are poor in caustics. 

Some materials involved in the epoxy adhesive formulations are more dangerous than others, and some affect certain parts of the body whereas others do not. Amine curing agents, for example, are generally the most irritating to the skin and eyes. They may also be considered to be strong caustics, and they produce serious local injury on short exposure. If they are worked in a hot condition, their fumes pose additional hazards. 

Multifunctional POSS, containing four epoxide groups on the periphery, copolymerized with aliphatic diepoxides and an amine-curing agent increased and broadened the Tg, increased the tensile modulus, but lowered the flexural modulus over that of the neat epoxy resin [2] (Fig. 3). 

Calculation of mixing ratios of epoxy resins and amine curing agents... 

Scheme 1.47. The structure of CTBN elastomer and reaction of the terminal carboxyl groups with epoxy in the presence of amine curing agent.

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