Epoxy resins for adhesives

The solvent industry has made significant strides in developing newer grades and blends of solvents for a variety of applications. Safety solvents are being developed that are low in volatility (vapor pressure), low in toxicity, and biodegradable. However, these newer solvents are finding commercial acceptance mainly as cleaning solvents rather than as a dilution medium for epoxy resins. For adhesives, rather than replace the solvent, the trend has been to develop waterborne emulsions. 

DJE.R. n>ow] Epoxy resins for adhesive, civil engineering, casting, potting, encapsulation, filament winding, powd. coatings, and wet lay-up tq>plics. 

Also used with epoxy resins for adhesives is dicyanodiamide, H2N-C(=NH)NH-CN. It is insoluble in common resins at room temperature but is soluble at elevated temperatures and thus forms the basis of a one-pack system. 

Spencer-Kellogg, Product Bulletin, TD-7922 (Revised 12/13/1979), "Kelpoxy G293-100, Elastomer-Modified Epoxy Resin for Adhesives."... 

Epoxy Structural Adhesives 119 Table II. Some Commercially Available Epoxy Resins for Adhesives ... 

A second type of uv curing chemistry is used, employing cationic curing as opposed to free-radical polymerization. This technology uses vinyl ethers and epoxy resins for the oligomers, reactive resins, and monomers. The initiators form Lewis acids upon absorption of the uv energy and the acid causes cationic polymerization. Although this chemistry has improved adhesion and flexibility and offers lower viscosity compared to the typical acrylate system, the cationic chemistry is very sensitive to humidity conditions and amine contamination. Both chemistries are used commercially. 

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). 

Few non.chemists know exactly what an epoxide is. but practically everyone has used an "epoxy glue for household repairs or an epoxy resin for a protective coating. Epoxy resins and adhesives generally consist of two components that are mixed just prior to use. One component is a liquid "prepolymer/ and the second is a "curing agent" that reacts with the prepolymer and causes it to solidify. 

Epoxy resins for printed circuits, castings, rocket motor casings, coatings, and adhesives are almost all made from bisphenol A. Polycarbonates based on bisphenol A are used in glazing applications such as aircraft windows, school windows, and other areas where a combination of toughness and high clarity are required. 

Epoxy resins 1936 Adhesives, especially for glass repair Resistant to acid, alkali and organic solvents. Tendency to yellowing with ageing... 

Title Novel Sulfur-containing Phenolic Resin, Process for Preparing the Same, Phenol Derivatives Having Thioether Structure or Disulfide Structure, Process for Preparing the Same and Epoxy Resin Composition Adhesive... 

Table 3.6 shows typical percentage volumetric shrinkage for various reactive adhesive systems during cure. One of the reasons for the great acceptance of epoxy resins as adhesive materials is their low degree of shrinkage on cure relative to other reactive adhesives. 

The highest-MW DGEBA epoxy resins are termed phenoxy resins. They are highly linear molecules that are used primarily as thermoplastic coating resins. However, they can be blended with lower-MW epoxy resins for the improvement of specific properties such as flexibility, impact and fatigue resistance, and thermal cycling. Phenoxy resins are sometimes used alone as a thermoplastic hot melt adhesive generally in film form. 

The chemical structures of important amines for curing epoxy resins in adhesive systems are identified in Fig. 5.1. Diethylenetriamine (DETA), triethylenetetramine (TETA), ra-aminoethylpiperazine (AEP), diethylaminopropylamine (DEAPA), ra-phenylenediamine (MPDA), and diaminodiphenyl sulfone (DDS) are the most commonly used members of this class. They are all primary amines. They give room or elevated temperature cure at near stoichiometric ratios. Ethylenediamine is too reactive to be used in most practical adhesive formulations. Polyoxypropyleneamines (amine-terminated polypropylene glycols) impart superior flexibility and adhesion. 

DICY is used at about 5 to 7 pph of liquid epoxy resins and 3 to 4 pph for solid epoxy resins in adhesive formulations. It is generally ball-milled into the epoxy resin. DICY forms very stable mixtures with epoxy resins at room temperature because the catalyst is not soluble at low temperatures. However, on being exposed to temperatures greater than 140°C, the DICY becomes soluble in the epoxy resin, and cure progresses rapidly. 

Solid epoxy adhesives generally rely on high-molecular-weight epoxy resin for the solid appearance of the uncured adhesive. This epoxy resin is generally formulated with either ... 

D 5686 Standard Specification for Fiberglass (Glass Fiber Reinforced Thermosetting Resin) Pipe and Pipe Fittings, Adhesive Bonded Joint Type Epoxy Resin, for Condensate Return Lines... 

The most important inference is that Chemisorption is a direct response to carboxyl group concentration indicated by the XPS photopeak component at 288.7 eV. It seems likely that weak add functionality is of minor import to applications for surface treatments, while interfacial phenomena such as practical adhesion may be sensitive to small concentrations of very high site energies. Interphase modification in epoxy resins, for example, can occur by direct reaction of epoxide groups with surface carboxyls (17), or by accelerated cure chemistry near the surface (39). Carboxyl groups on carbon surfaces may interact with basic moieties in polymers such as polycarbonate or poly(ethylene)oxide (40=42), or promote interfacial crystallinity that improves impact strength and other aspects of composite performance (43, M)-... 

Along with dental adhesives, the development of applied epoxy resins for protective or decorative purposes was one of the principal reasons for the original development of epoxy resins in the U.S.A. Some 50 years... 

Gamma irradiation curing of epoxy resins for structural adhesives — Radiation cure polymerization of commercial diglycidyl ether of bisphenol F epoxy resin has been achieved using Co-60 irradiation source, compounding the monomer with and onium salt catalyst [9],... 

Epoxy resins are the most versatile product used in aerospace composite hardware. They are employed both alone and in combination with a variety of other resins to form a broad range of products. The only limitation to the number of available products rests in the ability of the formulator to meet the ever-increasing demands for improved structural properties. Greater detail on the use of epoxy resins for bonding can be found in the section on adhesives. 

Tra-Bond. [Tra-Con] Epoxy resins for laminating, bonding, metal repair, adhesives, electronic insulating, fiber optic applies. 

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