Epoxy resin film adhesive

Epoxy-nylon film adhesive can be manufactured by solution casting processes. However, a more efficient and environmentally acceptable method is to calender dry blends of powdered nylon with a bquid epoxy resin with accelerators and other modifying resins directly... 

As previously mentioned in this chapter, carboxyl-reactive nitrile liquids appear to be the preferred modifiers for latent epoxy structural film adhesives. One of the major components used in formulating these adhesives is a solid epoxy resin of similar molecular weight (1000). This limited coatings study suggests that similar elastomer-modified epoxy resins are equally impressive in solution epoxy coatings. In addition. Table XI/Recipe 3 features a high impact coating modified with both liquid and solid carboxylated nitrile elastomers. 

Newer adhesives of the acrylic, anaerobic or radiation-curable types must, if they are structural, have a relatively high degree of toughness and durability if they are to compete with or challenge epoxy adhesive systems. Likewise, newer radiation-curable, pressure-sensitive adhesive systems must exhibit the properties of permanence largely associated with cross-linked adhesive masses deposited from an acrylic solution polymer base. Epoxy resin structural adhesives largely define the existing area on the one hand the cross-linked acrylics deposited on plastic or metallic films the other. 

Yoshida, T. Hozumi, T. Aral, M. Baba, T. Novolac epoxy resin-based adhesive film for electronic packaging. Jpn. Kokai Tokkyo Koho JP 2004273809, 2004 Chem. Abstr. 2004,141, 296985. 

Bonding sheets Acrylic resin films Epoxy resin films Polyimide films coated with acrylic adhesives on both sides New polyimide films coated with hot-melt poyimide resin on both sides... 

Whittle, B. R., Whittle, J. D., Ellis, B., Hand, R. J., et al. (2001). The effect of a silane coupling agent on the hydrolytic durability of thin epoxy resin films. Journal of Adhesion, 77(1), 1-24. 

Polyhydroxymethyl compounds phenol-formaldehyde resins, also in combination with poly(vinyl formal) resins, nitrile rubber or epoxy resins (as adhesive film), urea-fprmaldehyde resins, melamine - formaldehyde resins, resorcinol - formaldehyde resins. Uses wood (plywood manufacture), metals. 

In addition to liquid and pastelike epoxy resin adhesives, solid powdered products are also available commercially. In addition, epoxy resins are used in the form of adhesive films for certain applications. The most important are nylon epoxy resin films consisting of mixtures of relatively high molecular mass polyepoxides and polyamides, and epoxy resin-phenolic resin combinations. 

The metal film is then electroplated with copper, and the metal part brazed to the copper plating. Adhesives, usually epoxy resins, are used to join parts at low temperatures. Finally, ceramic parts can be clamped together, provided the clamps avoid stress concentrations, and are provided with soft (e.g. rubber) packing to avoid contact stresses. 

Thermosets A number of thermosets have been used as adhesives. Phenolic resins were used as adhesives by Leo Baekeland in the early 1900s. Phenolic resins are still used to bind together thin sheets of wood to make plywood. Urea resins have been used since 1930 as binders for wood chips in the manufacture of particle board. Unsaturated polyester resins are used for body repair and PUs are used to bond polyester cord to rubber in tires, and vinyl film to particle board, and to function as industrial sealants. Epoxy resins are used in the construction of automobiles and aircraft and as a component of plastic cement. 

Latexes are usually copolymer systems of two or more monomers, and their total solids content, including polymers, emulsifiers, stabilizers etc. is 40-50% by mass. Most commercially available polymer latexes are based on elastomeric and thermoplastic polymers which form continuous polymer films when dried [88]. The major types of latexes include styrene-butadiene rubber (SBR), ethylene vinyl acetate (EVA), polyacrylic ester (PAE) and epoxy resin (EP) which are available both as emulsions and redispersible powders. They are widely used for bridge deck overlays and patching, as adhesives, and integral waterproofers. A brief description of the main types in current use is as follows [87]. 

Solid, higher-MW epoxy resins are often used for adhesive formulations that are applied as solids (e.g., film and powder) or a solvent solution. The higher-MW DGEBA resins are also used where improved toughness, flexibility, and adhesion are required. These resins have a greater number of hydroxyl groups along the chain and, thus, can provide better adhesion and additional reaction mechanisms. 

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. 

Solid epoxy resins are usually formulated as solvent solutions and blends with lower-MW resins for the production of liquid adhesive systems. However, solid epoxy resins are also often employed in the manufacture of adhesive systems having solid form. There are several forms of solid epoxy adhesives that find application. The most common are supported or unsupported film, powder, and solder stick. Formulations for these adhesives are detailed in Chap. 13. 

Epoxy adhesives can be manufactured into a film form. This is most conveniently done with solid epoxy resins in solution. Epoxy film adhesives can be thermoplastic (e.g., linear ultrahigh molecular weight phenoxy resin) hot melts, but more commonly they are formulated, thermosetting materials. 

The base epoxy resin can be either liquid or solid. As molecular weight increases, the epoxy equivalent weight and the number of hydroxyl groups available for reaction increase. Waterborne epoxy adhesives provide excellent adhesion to metals and other high-energy substrates. Modified waterborne epoxy adhesives can also provide good adhesion to substrates such as vinyl and flexible plastic film. Characteristics of these epoxy dispersions are summarized in Table 4.6. 

The lower reactivity of the aromatic amines in adhesive formulations is an advantage in that epoxy resin mixtures can be B-staged at room temperature (react to a glassy but fusible and thermoplastic intermediate structure) and will not fully cure for months. In this way, dry films and solid powders can be formulated as elevated-temperature curing, one-component adhesives with long shelf life. 

DADS melts at 135°C and is employed stoichiometrically with DGEBA at 33.5 pph. Fortunately, it is relatively unreactive so it can be mixed with epoxy resin at elevated temperatures. It can also be used in epoxy solutions to provide an adhesive formulation for manufacturing supported or unsupported film with long shelf life. Because of the low reactivity of the system, DADS is generally employed at a concentration that is about 10 percent greater than stoichiometry, or an accelerator, such as BF3-MEA, is employed at about 0.5 to 2 pph. When DADS is mixed with liquid DGEBA resin, it provides a pot life of 3 h at 100°C and requires a rather extended high-temperature cure to achieve optimal physical properties. 

These blends can take a number of different forms. The added resin may be reacted with the epoxy resin, or it may be included as an unreacted modifier. The modifier may be blended into a continuous phase with the epoxy resin (epoxy alloys) or precipitated out as a discrete phase within the epoxy resin matrix (as is generally done in the case of toughening modifiers). Epoxy hybrid adhesives are often used as film (supported and unsupported) or tape because of the ease with which formulated systems can be dissolved into solvent and applied to a carrier or deposited as a freestanding film. Some systems, notably epoxyurethanes and epoxy-poly sulfides, can be employed as a liquid or paste formulation because of the low-viscosity characteristics of the components. 

Epoxy-nitrile Nitrile-epoxy adhesives are composed of solid epoxy resin modified with carboxyl-terminated butadiene nitrile (CTBN) copolymer. The CBTN is introduced into die epoxy resin at elevated temperatures. The modification provides toughness and high peel strength without sacrificing heat and chemical resistance. The film adhesives are widely used in the aerospace industry in the construction of jetliners. 

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