Tapes and Films

Tape and film are the most common forms of solid epoxy adhesives. Tape and film are terms that are used rather loosely for adhesives in a thin sheet form. The term tape generally refers to an adhesive that is supported on a web of paper or nonwoven fabric, or on an open-weave scrim of glass, cotton, or nylon. Films, on the other hand, are free of supporting material and consist only of the adhesive. Both tape and film products may be accompanied with a release liner depending on the tack or blocking characteristics of the adhesive. 

Supporting fibers in epoxy adhesive tapes are useful in that they provide for a positive stop under bonding pressure. This can be used to control bond line thickness and to help distribute stresses evenly during service. The supporting fibers that are used in these adhesives are primarily for the purposes of carrying the adhesive and convenient application to the substrate. Their reinforcing function within the epoxy matrix is generally considered to be of secondary importance. 

The final thickness of epoxy tape or film adhesives is on the order of 5 to 15 mils. These adhesives may be soft and tacky, or stiff and dry, depending on their formulation. The soft and tacky products are valuable in products requiring application to contoured or vertical surfaces. If the product is especially tacky, a release liner (e.g., polyethylene film, coated paper) is generally used to keep the film from blocking. The stiff and dry products are generally used for flat surfaces where speed and ease of application are required. 

Once the tape or film is in place between the substrates, the joint is heated under pressure so that the adhesive becomes slightly fluid, flows into the microroughness on the substrate, and wets the substrate. With additional time at the curing temperature, the adhesive completely crosslinks to a thermosetting condition. 

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. 

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Polymer News, edited by Gerry Kirshenbaum has as a longstanding series featuring academic polymer centers. Those associated with the particular institution are asked to present their programs, aspirations, intents, etc. These are typically well done. Polymer News also features a column on Polymer Education which offers a wide variety of information including booklets, tapes and films related to polymer science, special education (academic and inservice) experiments, polymer science education outside of the USA, recent activity in education committees, featured polymer chemists in academics, reports on education related conferences, etc. 

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. 

Guidelines for formulating solid epoxy adhesives are similar to those employed for liquid or paste adhesives. Table 13.4 shows starting formulations for several epoxy adhesive tapes and films. 

TABLE 13.2 Common Epoxy Hybrid Resins Used in the Formulation of Tape and Film Adhesives... 

TABLE 13.4 Starting Formulations for Epoxy Tape and Film Adhesives3... 

Starting formulations for epoxy tape and film adhesives... 

TECHNOLOGY ASSESSMENT ASSOCIATES P.O. Box 1362, Amherst NH 03031-9939, (603) 673-0312. A number of studies on Adhesives in Electronics, Bonding and Joining Composites, Markets for Adhesive Tapes and Films, Conductive Adhesives, Aerospace Sealants, and Growth Markets for Adhesives. 

In 1936, (later, Sir) Michael Perrin wrote It is felt that, of a large number of possible uses, attention should first be concentrated on those connected with the electrical industry, where the outstanding insulating properties of Alketh combined with its flexibility in the form of tape and films, and its chemical inertness, would appear to be most promising . ... 

Polyolefins In addition to stabilization of polyolefins against thermal oxidation to reduce the sensitivity to light, stabilization against exposure to light is required for articles to be used outdoors as well as those intended for indoor use [93]. Light stabilizers include UV absorbers of the benzotriazole and the benzophenone types (except for thin sections), HALS, and nickel-containing stabilizers. The latter are used for thin sections such as tapes and films and for surface protection. The type of stabilizer is dictated by the type of polyolefin, its thickness, application, and desired lifetime of the article [20]. 

The handling and reliability advantages of tape and film adhesive include ready to use, no need for mixing, no degassing, and no possibility for error in adding catalyst. Tapes permit a variety of lay-up techniques, which facilitate the production of virtually defect-free structures. The use of a mesh support helps to control the bond-line thickness with tape adhesives. 

Tape and film adhesives are generally composed of three components ... 

Table 5.4 Range of Bond Strengths of Tape and Film Adhesives at Room Temperature " ...

Tape and film adhesives are poor gap fillers but offer a uniformly thick bond line, no need for metering, and easy dispensing. Adhesive films are available as a pure sheet of adhesive or with cloth or paper reinforcement. Another form of adhesive is powder or granules that must be heated or solvent-activated to be made liquid and applicable. 

There are many publications on training programs, including the two references immediately above, and many training aids are available in the form of seminars, printed material, tapes and films, training kits, and computer software. 

Tape and film adhesives are terms used loosely and interchangeably for adhesives in sheet form. More correctly, tapes are supported on a web of paper or nonwoven fabric or on an open-weave scrim of cotton or nylon. Snpporting fibers are useful in that they provide a positive stop under bonding pressure. This can be nsed to control bond line thickness and often to help distribute stresses. Films on the other hand, are free of reinforcing fibers and consist only of the adhesive in thin, sheet form. 

In the last 40 years, many suppliers tried to find methods of clean and easy application of adhesives, glues and sealants. The main idea was to use adhesives in dry form, to avoid the stickiness and dirty application of the old glues. A need for adapted application equipment came from this. The main invention was the pressure sensitive tapes and labels, and then the hot melts supplied as dry solid granulates. There was also the preformed tape sealants, the structural adhesives supplied as film adhesives used in aircraft bonding figure 92, the heat sealable tapes and films, the hot melt sticks and lately the glue sticks for office use. 

Examples of replicating plastics (along with their solvent) are cellulose acetate (acetone), gelatin (water or dilute sodium hydroxide), acrylic resin (acetone) and poly(vinyl alcohol) (water). Solutions of 2% formvar in chloroform or dioxane and 1-4% collodion in amyl acetate are appropriate for rough surfaces where tapes and films are not easily removed. Washing and extractions are similar to those described above for one stage replicas. A major problem can be the incomplete dissolution of the plastic replica which interferes with TEM imaging. 

Rastogi S, Yao Y, Ronca S, Bos J, van der Eem J (2011) Unprecedented high-modulus high-strength tapes and films of ultrahigh molecular weight polyethylene via solvtait-liee route. Macromolecules 44 5558-5568... 

Karger-Kocsis, PP/PP Crossply Tape and film stacking 50 19 20... 

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