Film adhesives unsupported

Adhesive, film-unsupported—An adhesive material in film form without a carrier support. 

The adhesive film, unsupported, is cured between shimmed Teflon sheets in the normal cure cycle to yield films. 015 to. 025 inches thick. Dogbone tensile specimens are cut from the film, measured, and conditioned at the desired temperature-humidity for a minimum of 72 hours. This duration was found to be adequate for the films to attain equilibrium water content, and samples showed no change upon further exposure. 

Unsupported general-purpose epoxy adhesive film Parts by weight... 

There are three main polymers presently used for structural adhesive bonding and they are phenolics, epoxies and urethanes. We can also include in our classification, the initial physical state of the uncured adhesive since it governs the type of application and curing conditions. Structural adhesives are manufactured in the form of films or pastes. The films are one-part adhesives, i.e., they contain a latent catalyst which requires heat for activation. Structural adhesive films are made in a number of different thicknesses and can either be supported (containing a scrim) or unsupported. In general, film adhesives require the application of pressure during cure in order to obtain ultimate properties. Paste adhesives are either one- or two-part materials. That is, pastes can either contain a latent heat activatable catalyst, or they can be a system which is separated into two parts, one of which contains the cur a t i ve/ca talys t. Two-part pastes cure at room temperature. In this section the chemistry of one-... 

An example of a 100% solid, non-flammable, heat-activated hot-melt adhesive recommended for structural bonding of aluminum, steel, copper, brass, titanium, fabric, and some plastics is 3M Company s Scotch -Weld Thermoplastic Adhesive Film 4060. Strength data are shown in Table 5.5. " Bonding using this clear, amber, unsupported film adhesive takes place rapidly. The speed of bonding is hmited only by the heat-up time required to reach the optimum bonding temperature of 149°C at a pressure sufficient to maintain contact between the surfaces to be bonded. The adhesive... 

The gap between the parts, and therefore the thickness, of the adhesive film has an important bearing on the characteristics of the joint. In terms of simple strength, a thick bond line will generally be a weakening feature since the mechanical strength of the unsupported resin film is likely to be less than that of the substrates. 

Most textile adhesive formulations are available in a waterborne liquid or solid (film or powder) form. When supplied as a film, the adhesive is unsupported, reinforced with fabric or nonwoven, or coated on both sides of a carrier material. These film adhesives are made flowable by heating to a melt and then gain strength on cooling back to a sohd form. Film adhesives offer convenience, since no coating operation is required by the user, energy (drying costs) is minimized, and waste is eliminated ... 

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. 

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. 

TABLE 13.6 Unsupported Film Adhesive Cast from Solvent Solution9... 

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. 

Unsupported film adhesive cast from solvent solution... 

Funke and coworkers (35) have compared the moisture absorption characteristics of free and supported paint films, and have found that films that lose adhesion upon exposure to humid environments tend to absorb more water as supported films than as unsupported ones. These results are interpreted in terms of accumulation of moisture within an interfacial region. It should be noted that the moisture absorption results are subject to pronounced scatter, and relatively little weight can be attached to isolated measurements. The scatter in the results appears to be a property of variations in film properties, rather than an artifact of the experimental method ( ). 

The thermosetting resin, chosen for its high strength, is plasticized by the second resin, making the alloy tougher, more flexible, and more resistant to impact. The adhesive alloys take advantage of the most important properties of each component. They are commonly available as solvent-based solutions and as supported and unsupported films. ... 

One-part epoxy adhesives include solvent-free liquid resins, solutions in solvent, liquid resin pastes, fusible powders, sticks, pellets and paste, supported and unsupported films, and preformed shapes to fit a particular joint. Two-part epoxy adhesives are usually comprised of the resin and the curing agent, which are mixed just prior to use. The components may be liquids, putties, or liquid and hardener powder. They may also contain plasticizers, reactive diluents, fillers, and resinous modifiers. The processing conditions are determined by the curing agent employed. In general, two-part systems are mixed, applied within the recommended pot life (a few minutes to several hours), and cured at room temperature for up to 24 hours, or at elevated temperatures to reduce the cure time. Typical cure conditions range from 3 hours at 60°C to 20 minutes at 100 C. ... 

In some film adhesives, a cover or knitted fabric is used to support the polymer film. It will also carry a part of the load and will provide improved bond strength by more efficient distribution of the applied forces. Film adhesives are produced in two forms unsupported, or alternatively, supported on a flexible carrier such as glass, cloth, nylon, or paper. The carrier will usually have little effect on adhesive properties. " The adhesive polymer is usually elastomeric, blended with curing agents, fillers, and other ingredients and is usually extruded, calendered, or cast into 0.1-0.4 mm thick unsupported films. This type is called film adhesive. When the mixture... 

These alloy adhesives are thermosetting phenolic resins blended with neoprene (polychloroprene) rubber. They are available in solvent solutions in toluene, ketones, or solvent mixtures, or as unsupported or supported films. The supporting medium may be glass or nylon cloth. Neoprene-phenolic adhesive may be used to bond a variety of substrates such as aluminum. 

Film adhesives may be used only on flat surfaces or simple curves. Application requires a relatively high degree of cure to ensure non-wrinkfing and removal of separator sheets. Characteristics of available film adhesives vary widely, depending on the type of adhesives used. Film adhesives are supplied in both unsupported and supported types. The carrier for supported films is generally fibrous fabric or mat. Film adhesives are supplied in heat-activated, pressure-sensitive, or solvent-activated forms. 

Epoxy, modified epoxy, and urethane adhesive are commonly used in weldbonding aluminum. Epoxy and polyimide adhesives are used for titanium. Polyimides are particularly suitable for titanium because of their very high temperature resistance (matching the resistance of titanium). Epoxy and modified-epoxy adhesives are available in one-or two-part liquid, paste, capillary, or unsupported-film form. ... 

Of the common modified phenolic adhesives, the nitrile-phenolic blend has the best resistance to elevated temperatures. Nitrile-phenolics have high shear strengths up to 121-177 C, and their strength retention on aging at these temperatures is very good. These materials are available in solvent solutions and unsupported and supported films. 

Adhesive alloys or hybrids are made by combining thermosetting, thermoplastic, and elastomeric adhesives. They utilize the most useful properties of each material. However, the adhesive alloy is usually never better than its weakest constituent. For example, higher peel strengths are generally provided to thermosetting resins by the addition of thermoplastic or elastomeric materials, althongh nsnally at the sacrifice of temperature resistance. Adhesive alloys are commonly available in solvent solutions and as supported or unsupported film. 

Room-temperature shear strength as high as 5,000 psi is available in commercial products. Maximum operating temperature, however, is only 93°C becanse of the thermoplastic constiteent softens at elevated temperatures. Chemical resistance and impact strength are ontstanding. Vinyl phenoUc adhesives are supphed in solvent solntions and as snpported and unsupported film. The adhesive cures rapidly at elevated temperatures under pressure. 

Phenolic resins are supplied as liquids and powders and quite often they are compounded into adhesives by the addition of extenders, solvents, and catalysts just prior to use. Compounded phenolic adhesives are also supplied, as supported or unsupported films, one-part catalyzed pastes, or two-part room temperature curing pastes. 

A series of modified epoxy film adhesives curing at 175 C, available both supported on a woven nylon carrier, or unsupported, at areal weights of between 180 and 400g/ml... 

Epoxy-nylon adhesives are available as unsupported B-staged film or in solvent solutions. A moderate pressure of 25 Ib/in and temperature of 350°F are generally required for 1 hr to cure the adhesive. Because of their excellent filleting properties and high peel strength, epoxy-nylon adhesives are used to bond aluminum skins to honeycomb core in aircraft structures. 

Nitrile- phenolic Solvent solutions, unsupported and supported film Heat and pressure Excellent shear strength good peel strength superior to vinyl and neoprene—phenolics good adhesion Metals, plastics, glass, rubber Med... 

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