Epoxy Curing Agents and Catalysts

Some curing agents can also be used to form adducts with epoxy resins, and these adducts, in turn, offer unique curing properties with other epoxy resins. Adducts are commonly used in adhesive formulations to reduce the vapor pressure of the system, to modify the reactivity of the system, to improve mix ratios so that they are closer to equal parts of the resin component and of the curing agent component, and to provide a certain degree of flexibility into the end product. 

The advantages, disadvantages, and applications for the major types of epoxy curing agents are summarized in Table 5.1. The required mix ratios, curing temperatures, and the resulting heat distortion temperatures of the cured product are provided in Table 5.2. 

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Polysulfides and mercaptan Moisture resistance Quick set time Flexible Odor Poor elevated-temperature performance Poor tensile strength Adhesives and sealants Civil engineering Casting and encapsulation Coatings 

Aliphatic amines Convenience Room temperature cure, fast elevated-temperature cure Low viscosity Low formulation cost Moderate chemical resistance Critical mix ratios Strong skin irritant High vapor pressure Short working life, exothermic Poor bond strength above 80°C Rigid, poor peel and impact properties Adhesives and sealants Casting and encapsulation Coatings 

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Curing agents and catalysts Curing agents and catalysts react with epoxy groups to form a three-dimensional network structure by crosslinking. 

Of course, in the case of both curing agents and catalysts, suitable adjustments will have to be made for the presence of nonreactive fillers and modifiers. Such ingredients can be liquids such as a solvent, a hydrocarbon resin, or a plasticizer. Since they do not contribute any epoxide functionality, they should not be considered when one is determining stoichiometry. However, if the additives have epoxy functionality, such as in the case of reactive diluents, the stoichiometric calculations will have to take these materials into consideration, by calculating ratios similarly as with an epoxy resin. 

Future chapters describe the other raw materials that contribute to the epoxy adhesive formulation (curing agents and catalysts, Chap. 5 solvents and diluents, Chap. 6 hybrid resins, Chap. 7 flexibilizers and tougheners, Chap. 8 fillers, Chap. 9 and adhesion promoters, Chap. 10). Complete adhesive formulations are then discussed in subsequent chapters. 

A wide range of epoxy resins as well as a wide range of curing agents and catalysts are available for formulating solid epoxy adhesives. Resins with different viscosities, amounts of reactive groups, and structures are available. Additives that change the uncured resin viscosity, reduce brittleness, or impart some other property are also available. 

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. 

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. ... 

The binder system of a plastic encapsulant consists of an epoxy resin, a hardener or curing agent, and an accelerating catalyst system. The conversion of epoxies from the Hquid (thermoplastic) state to tough, hard, thermoset soHds is accompHshed by the addition of chemically active compounds known as curing agents. Flame retardants (qv), usually in the form of halogens, are added to the epoxy resin backbone because epoxy resins are inherently flammable. 

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. 

In all these stages the adhesive properties will be determined primarily by the molecular structures of the epoxy resin and curing agent or catalyst employed. Additives and modifiers, of course, will also affect these properties, and they are discussed in later chapters. 

The type of epoxy group and its location within the molecule influence reactivity. Some epoxy resin structures prefer to react with acid curing agents, and others with basic curing agents. Certain epoxy structures are extremely reactive with specific catalysts, and others are virtually inactive. Several types of epoxy resins are reactive with almost all classes of curing agents. 

Use Cross-linking agent and catalyst in urethane foams, epoxy resin curing, metal complexes, intermediate. 

USE Cross-linking agent and catalyst itt the manuf of ure-than foams in epoxy resin curing as complex in g agent, hu mectant, emulsifier, plasticizer. 

AI3-26794 Araldite accelerator 062 BDMA Benz-enemethanamine, N,N-dimethyl- Benzyl-N,N-dimethyl-amine Benzylamine, N,N-dimethyl- Benzyldimethyl-amine N-Benzyldimethylamine N-Benzyl-N,N-dimethyl-amine CCRIS 6693 Dabco B-16 Dimethyl-benzylamine N,N-Dimethylbenzylamine N,N-Dimethyl-N-benzylamine N,N-Dimethylbenzenemethanamine EINECS 203-149-1 NSC 5342 Pentamin BDMA N-(Phenylmethyl)dimethylamine Sumine 2016 UN2619. Amine-based catalyst for flexible slabstock PU foam. Used as a polyurethane catalyst and an epoxy curing agent. Liquid mp = -75° bp = 181° d° = 0.915 7.m = 252, 268, 265 nm (cyclohexane) slightly soluble in H2O, freely soluble in EtOH, Et20 LD50 (rat orl) = 265 mg/kg. Air Products Chemicals Inc. Pentagon Chems. Ltd. -... 

Metacurc . [Air Prods.] Qrganotinm ester comp. catalyst to prod, of polyarmhane coatings, adhesives, and sealants epoxy curing agent... 

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