Epoxy adhesives representative formulation

Although epoxy adhesives represent a relatively small proportion of the total adhesives market, there are perhaps more varieties of formulations available from more sources than for any other adhesive class. For many years, they have dominated the high-performance adhesives market, but the desire for increased service temperatures has led to the development of new adhesives based on imide polymers (Polyimides and Bismaleimides). 

Single-component epoxy adhesive formulations are the largest type of epoxy adhesives sold, with about 55 percent of the consumption, while two-component formulations account for another 44 percent of the volume. Radiation cure formulations represent the remainder of the market. Epoxy adhesives can also take many forms including solids, solvent-free liquids, solvent-borne systems, and waterborne systems. 

However, with the proper combination of surface treatment and adhesive, these differences in durability to aggressive environments can be minimized, as shown in Table 16.3. The initial shear strength and permanence depend on the type of alloy and the pretreatment used. Note that the data presented here show only the relative differences in joint strength for one specific epoxy adhesive and are not representative of other adhesive formulations. There was no attempt to maximize any of these values through choice of the adhesive. 

Since epoxy adhesive formulation represents a surprisingly broad area of technology, a road map to the use of this book may be valuable. Chapters 1 through 3 discuss the synthesis of raw materials, epoxy chemistry in general, and the physical and chemical properties that are important for an epoxy adhesive. These properties are important during the three primary phases or conditions of an adhesive (1) uncured, (2) during cure, and (3) fully cured. 

Fillers generally represent one of the major components by weight in an adhesive formulation. However, their concentration is quite often limited by viscosity constraints, cost, and negative effects on certain properties. The degree of improvement provided by a filler in an epoxy formulation will heavily depend on the type of filler and its properties (particle size, shape, size distribution, and concentration), surface chemistry, dispersion characteristics, dryness, and compatibility with the other components in the formulation. Table 9.3 summarizes the properties of selected fillers. 

The papers presented in the following chapters represent advances in pressure sensitive adhesives (ultraviolet light activated acrylate monomer - low Tg polyether formulations) photoinitiated cationic polymerization (light activated aryliodonium and arylsulfonium salts of lewis acids in epoxy resin formulations) polymer and formulation design criteria for radiation curable adhesives radiation curable composites (dynamic thermal analysis characterization of electron beam cured... 

The phenolic family of adhesives are very diverse in their formulations and uses. Some are filled or modified with other polymers (vinyl, nitrile or epoxy). The composition depends largely on the intended use, e.g. for temperature and chemical resistance, or for water-proof wood bonding (phenol-resorcinol-formaldehyde). The majority are heat-curing although some wood-bonding adhesives can be cured at room temperature (RT). The comparison table includes Typical Use to differentiate between the types of adhesives. Phenolic adhesives are generally poorly represented by mechanical property data. 

After the adhesive is cured and the die is packaged, any further release of volatiles by the adhesive is generally undesirable, particularly if the volatiles can combine with water vapor to cause corrosion. Table 3 shows two epoxy formulations which are representative of the best one-component silver-filled epoxies used for electronic assembly up to about 1980. Epoxy A in Table 3 is cured with a latent amine known as dicyandiamide (dicy) ... 

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