Epoxy Film Adhesives

A carrier or reinforcement is usually a thin fabric, cloth, or paper used to support the semicured adhesive composition to provide a tape or film. In tapes, the carrier is the backing on which the adhesive is applied. The backing may be used for functional or decorative purposes. In epoxy films or structural tape, the carrier is usually porous and the adhesive saturates the carrier. Glass, polyester, and nylon fabric are common carriers for supported B-staged epoxy adhesive films. In these cases, the carrier provides for a method of applying the adhesive and also may act as reinforcement and a internal shim to control the thickness of the adhesive. 

Fillers are available in many forms including particles, fibers, and mats or fabrics. Table 9.4 lists common forms of fillers and reinforcements that are used with epoxy adhesives. Note that epoxy adhesive film carriers such as fabrics or mats can be considered as a type of filler. 

Nylon-epoxy adhesive film Parts by weight... 

Figure 92 Hand lay down of a structural thermosetting epoxy adhesive film.

Fig. 2 shows one large application of adhesives in electronic goods that is now a very large market for high-performance adhesives and potting compounds. Fig. 3 shows an enlargement of the epoxy adhesive film on a bonded aluminum honeycomb. 

Figure 3 Close view of bonded aluminum honeycomb in a sandwich panel, showing (in white) the epoxy adhesive film after peeling of the aluminum sheet facing.

Variation of eiastic iimit shear stress with initiai eiastic strain rate and environmental temperature, and comparison with Ludwik s equation for an epoxy adhesive film with polyester knit fabric carrier cioth. The adhesive was tested in the bonded iap shear mode... 

A typical comonomer could be a polydimethylsilane to increase the toughness of the polymerized film, or an amine funetional silane for ehemieal eoupling with an epoxy adhesive. 

The corrosion resistance and polymer-bonding compatibilities of the lonizable organophosphonates and the neutral organo-silanes are directly related to their inherent chemical properties. Specifically, NTMP inhibits the hydration of AI2O2 and maintains or Improves bond durability with a nitrile-modified epoxy adhesive which is cured at an elevated temperature. The mercaptopropyl silane, in addition to these properties, is compatible with a room temperature-cured epoxy-polyamide primer and also exhibits resistance to localized environmental corrosion. These results, in conjunction with the adsorbed Inhibitor films and the metal substrate surfaces, are subsequently discussed. 

The ionic phosphonates like NTMP are effective hydration inhibitors because they can form an insoluble complex with the oxide surface. They are useful as epoxy adhesive couplers in cases where the adhesive and its curing cycle are compatible with the adsorbed phosphonate molecule. (14) Wedge test results indicate that in two epoxy-aluminum systems studied, certain organosilanes tend to both increase the epoxy-metal bond durability and maintain hydration resistance. The results of anodic polarization experiments further suggest that these silane films are effective against localized pitting. 

Abstract—The structure of films formed by a multicomponent silane primer applied to an aluminum adherend and the interactions of this primer with an amine-cured epoxy adhesive were studied using X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, and attenuated total reflectance infrared spectroscopy. The failure in joints prepared from primed adherends occurred extremely close to the adherend surface in a region that contained much interpenetrated primer and epoxy. IR spectra showed evidence of oxidation in the primer. Fracture occurred in a region of interpenetrated primer and adhesive with higher than normal crosslink density. The primer films have a stratified structure that is retained even after curing of the adhesive. 

Initial bondability of anodized surfaces was tested in the lap shear configuration using numerous commercial epoxy adhesives. With one exception, all surfaces proved to be bondable and gave acceptable lap shear values. That exception was an anodized film formed... 

A thin p-type body 2 of Hgo.79Cdo.21Te is bonded to a silicon integrated circuit 3 by an intermediate film of epoxy adhesive. The upper and lower surfaces of the body 2 are passivated by a surface layer of cadmium telluride or ZnS. Gaps 40 are etched in the body 2 to separate the islands 28 from the remainder of the body. Then, a thin p-type body 1 of Hgo.7Cdo.3Te is bonded to the upper surface of the body 2 by an intermediate film or epoxy adhesive. 

Epoxy adhesives are commercially available as liquids, pastes, films, and solids. Epoxy adhesives are generally supplied as 100 percent solids (no solvents or other volatiles), but some are available as sprayable solvent systems or water emulsions. Epoxy adhesives are also available in a wide range of chemical compositions, which allows for variations in how... 

In hot mixing or elevated-temperature curing of an epoxy system, vapor pressure could also be of concern relative to the quality of the adhesive bond. If the components in an epoxy system become too hot, boiling can occur, resulting in gas bubbles. If gas bubbles become trapped in the cured adhesive film, they can lead to reduction of cohesive strength and stress risers. For many adhesive applications, particularly those in the electrical and electronic industries (due to possible ionization of air voids), complete removal of any gas bubbles from the epoxy is essential. 

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. 

As a result of the latency and excellent properties produced by DICY cured epoxies, DICY is used in many B-staged supported film adhesives. DICY is also probably the leading catalyst used in one-component, elevated-temperature curing epoxy adhesives. 

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. 

EC-2320 (c) AF-lll, AF-126, and AF-125-2 film epoxy adhesives 1.3—5.1 pm Air drying up to 120°C Improves shear and peel strengths as well as environmental resistance... 

Heat curing epoxy systems may consist of one or two components. The nomenclature is similar to that employed with the room temperature curing adhesives (e.g., resin component, curing agent component, 2Ksystem, etc.). Many heat curing epoxy adhesives systems are liquids or pastes. However, heat curing systems also can be processed into solid adhesive forms (e.g., powders and films). This chapter describes the paste and liquid formulations solid adhesive forms are considered separately in Chap. 13. 

Although tapes, films, or coatings applied from solvent solution make up the majority of the solid epoxy adhesives, formulations in the form of a powder or shaped solids can also be employed in certain applications. These are manufactured using the second or third technique described above. 

A significant advantage of tape and film adhesives is the greater toughness that is available compared to other adhesive types. This is primarily due to the ease with which resinous modifiers can be added to the formulation via solvent solution. Thus, hybrid epoxy adhesives such as epoxy-nylon, epoxy-phenolic, etc., are often found in tape or film form. 

There are several common forms of solid epoxy adhesives. These include film, tape, powder, and preformed shapes. Certain formulations are better suited for specific forms. For example, casting of tape or film adhesive from solvent solutions lends itself to working with multicomponent hybrid systems, where each resin can be solubilized and blended together in a universal solvent. B-staged systems are generally more brittle and better suited for powders or preformed adhesives. 

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