Epoxy films

Epoxy film specimens of two different weight/weight ratios of TGDDM/DDS were evaluated (73/27 and 80/20). The films were cast between teflon sheets using a spacer. The cure cycle was 1 hr at... 

Stafford CM, Kim JH, Kawaguchi D, Royston G, Chiang MYM (2006) Probing the interfacial adhesion strength in compositional libraries of epoxy films. Mater Res Soc Symp Proc 894 129-137... 

Cross-linking of the epoxy films results in a coating that is more resistant to humidity and mechanical impact (Eslinger, 1995). 

Room-temperature-cured epoxy films on glass (hours in 70°C water to adhesion loss)... 

Effect of the crosslinkable adhesion enhancer (MeO)jSiCH CH2Si(OMe)3 on the adhesion of epoxy films to glass... 

Figure 6. (A) RAIR spectrum of neat epoxy film (B) RA1R spectrum of primed mirror that was heated in resin, extracted with MEK (C) difference spectrum between (A) and (B).

Figure 5. Time dependence at room temperature of the second harmonic coefficient, d33 of epoxy films containing Disperse Orange 1 (4) after simultaneously poling and curing at 150°C.

Figure 14.22 Arrhenius plot for amide growth in the oxidation of amine crosslinked epoxy films.

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. 

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. 

Similarly prepared solid epoxy films can be ground into powder. The powder can be pressed into preformed pellets and applied directly to the adhesive joint as annular rings or... 

Particulate fillers, on the other hand, are believed to extend the pathway along which the water must diffuse, resulting in a reduction in the rate of water absorption. Silica flour (1 to 75 pm) has been reported as improving the boiling water resistance of epoxy films. Figure 9.8 shows the water absorption rate at 40°C of water in DGEBA epoxy filled with various types of materials. 

Representative data are shown in Fig. 10.5 for aluminum joints bonded with an epoxy film adhesive and a standard chromate-containing primer. Up until recently, standard corrosion-resistant primers contained high levels of solvent, contributing to high levels of volatile organic compounds (VOCs) and chromium compounds, which are considered to be carcinogens. As a result, development programs have been conducted on waterborne adhesive primers that contain low VOC levels and little or no chrome. Data are presented on several of these primers in Tables 10.8 and 10.9. 

Tape and film adhesives are most often used to bond large areas, such as for applications in the aerospace industry. For example, the joining of aluminum honeycomb structure to flat metal skins is often accomplished with thermosetting epoxy film adhesives. These films (Fig. 13.1) can easily be applied without the need to mix, meter, or apply a liquid coating. 

FIGURE 13.1 Epoxy film adhesive with release sheets. 

In situ heating of epoxy film adhesives may be accomplished by laminating high-resistance filaments into the film and subsequently applying an electric current. This provides the advantage of a one-component adhesive without the requirements of external heat sources. Once the element is heated, the surrounding material melts, flows, and finally crosslinks. After the adhesive cures, the resistance element that is exterior to the joint is cut off. 

Extended exposure of the uncured material to temperatures or conditions outside those recommended by the manufacturer will cause change in physical properties of the uncured material and will likely reduce its resulting cohesive and adhesive strength. The reactions that occur due to ambient storage conditions are described in Chap. 3. Figure 17.5 shows the effect of aging conditions on the tensile shear strength of an epoxy film adhesive. 

FIGURE 17.5 Effect of aging conditions on epoxy film adhesive before cure (A) fresh adhesive, (B) after aging 90 days at 24°C, (C) after 90 days at 32°C, (D) after 1-h exposure to condensing humidity.5... 

Characteristics of typical film adhesives vary widely depending on the type of adhesive used. Epoxy film adhesives are made in both unsupported and supported types. The carrier for supported films is generally fibrous fabric or mat. 

Hysol EA 9602.3 Loctite-Henkel 1 h at 121°C Modified epoxy film, tacky, available supported and unsupported exceeds MMM-A-132 and MIL-A-25463... 

Hysol EA 9628H Loctite-Henkel 1 hat 121 °C Modified epoxy film, high peel strength good environmental resistance and temperature strength to 121°C... 

FM 73 Cytec Engineered Materials 60-90 min at 121°C Toughened epoxy film preferred system on the PABST program for primary bonding of aluminum... 

Pike, R. A., Lamm, F. P., Pinto, J. P. Factors affecting the processing of epoxy film adhesives 1. Room temperature aging, J, Adhesion, 12, 143 (1981)... 

Epoxy film samples were prepared with the DGEBA-TETA and N-5208 resins. Detailed Information on the DGEBA-TETA and N-5208 resin cure and sample preparation has been previously provided (2,4). Films of the N-5208 resin were made with a curing agent concentration of 25 PHR-DDS (4) 14 PHR TETA was used for curing the DGEBA epoxy (2). Dynamic mechanical properties for films were measured on strip samples cut to nominal 0.02 cm x 0.3 cm x 6.0 cm dimensions. 

Permeation experiments have been performed by Wemick and Osterhuber [54,55] on a 120 pm single crystal of zeolite NaX (Si/Al=1.29, pore diameter 7.4 A), embedded in an epoxy film. From butane permeation it was derived that as temperature increases, diffiisivity increases only slightly. Because the heat of adsorption (12 kcal/mol) is much larger than the activation energy for diffusion (2 kcal/mol), the concentration of butane on the zeolite pore walls dominates permeation in the region of 50-100°C, in contrast to the diffusion effect, resulting in a drop in the permeation. 

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