Thermoplastic Epoxy Films

Ultrahigh-molecular-weight epoxy resins can be used directly as a thermoplastic adhesive. The hydroxyl groups and good wetting characteristics provide for good adhesion to many surfaces. These adhesives are prepared in film form by solvent casting or extrusion. 

The phenoxy resin has a chemical structure similar to that of epoxy resin however, the phenoxy is a high-molecular-weight thermoplastic polymer, which needs no further conversion and has an infinite shelf life. Since the phenoxies are strongly polar polyethers, they 

TABLE 13.5 Starting Formulations for Epoxy Powder and Stick Adhesives7 

General-purpose powder adhesive Parts by weight 

Application can be by fluidized bed or electrostatic spray. Cure conditions are 3 min at 204°C or 12 min at 149°C. Shear strength on steel is 3300 psi at room temperature.  

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Thermoplastic epoxy films, electrically and thermally conductive Staystik 581, 682, 882 Cookson Electronics 98 - -... 

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. 

Essentially, physical methods are employed on natural fiber during processing in order to separate natural fiber bundles into individual filaments and also to modify the surface structure of the fibers so as to improve the use of natural fibers in composites. Physical methods can be divided into two categories viz (1) steam explosion and thermomechanical processes and (2) plasma, dielectric barrier techniques, radiation modification, ultrasonic treatment, and corona discharge. In an effort to impart and improve reactivity, these physical treatments have been used to modify thermoplastic polymeric films like polyethylene and polypropylene and thermosets, such as epoxy. 

Vinyl organosol coatings, which incorporate a high molecular weight thermoplastic PVC organosol dispersion resin, are extremely flexible. Soluble thermosetting resins, including epoxy, phenoHc, and polyesters, are added to enhance the film s product resistance and adhesion. 

Cross-file patent searches, 18 243-244 CrossFire Beilstein, 6 19 Cross-flow filtration, 11 383 15 827, 829 in porous pipes, 11 387-388 with rotating elements, 11 383-387 Cross flow model, 21 706 Cross-flow packed scrubber, 26 687-688 Crossflow plates, 6 762-763 Cross-flow screens, 22 282 Cross-flow velocity, 15 725 Crosshead mandrel, in VDC film extrusion, 25 732-733 Cross-lapping, 17 501 Cross-linkable epoxy thermoplastic system (CET), 10 436... 

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]. 

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 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. 

Typically tape or film epoxy adhesives are modified with synthetic thermoplastic polymers to improve flexibility in the uncured film and toughness in the cured adhesive. Epoxy resins can also be blended with phenolic resins for higher heat resistance. The most common hybrid systems include epoxy-phenolics, epoxy-nylon, epoxy-nitrile, and epoxy-vinyl hybrids. These hybrid film adhesives are summarized in Table 13.2, and structural properties are shown in Table 13.3. 

Flexibilized epoxy adhesives have moderate strength on flame and corona treated polyolefin substrates. Elevated cure temperature results in better adhesion because of more efficient wetting of the substrate surface. Table 16.13 shows a starting formulation for an epoxy adhesive that develops high peel strength to many difficult-to-bond substrates such as polyethylene, thermoplastic rubber, and polyester film. 

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