Unsupported films

Solution Casting. The production of unsupported film and sheet by solution casting has generally passed from favor and is used only for special polymers not amenable to melt processes. The use of solvents was generally very hazardous because of their flammabiUty or toxic nature. The cost of recovery and disposal of solvents became prohibitive for many lower price film appHcations. The nature of the drying operations leads to problems with solvent migration and retention that are not problems with melt-processed polymers. 

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. 

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

Form available Supported and unsupported films Supported films Two-part liquid and pastes One- and two-part liquids and pastes... 

FM 1000 Cytec Engineered Materials 1 h at 177°C High peel and elongation tensile shear strength of 2900-6000 psi unsupported film... 

Unsupported film adhesive cast from solvent solution... 

A second effect of the wet zone in the support is that the drying rate of a supported lyogel film is considerably smaller than that of a unsupported film of comparable thickness. Because the depth of the wetted zone varies, depending on slip cast conditions, the drying rates exhibit some uncertainty even when all external drying conditions are controlled. 

Figure 5. Excitation spectra of 400 °C cured unsupported films. 580 nm emission intensity and 616 nm emission intensity as a function of excitation wavelength for PI-2555 and PI-2545, respectively.

The objective in Part A is to identify the chromophores responsible for the fluorescence spectra of the films in the cure study. In Part B we will review the literature with respect to the aggregation and degree of ordering of polyimide with cure in order to interpret the change in fluorescence of the films with respect to changes in the morphology of polyimide with cure. In Part C we will relate the difference in spectra between supported and unsupported films to the effect of stress on morphology. 

In comparing the unsupported film excitation spectra of PI-2555 to that of PI-2545 one notices a hint of structure in the long-wavelength band of PI-2555, which can similarly be attributed to the BTDA moiety. It is important to note that the BTDA model compound spectrum has some structure to it in the region of this excitation... 

The exact nature of the stressed conformation is not known but it may in some way relate to the two dimensional ordering of the supported films as compared to the isotropic morphology of the unsupported films. 

Cellulosic plastics film and sheet, unsupported Film, plastics unsupported Photographic, micrographic, and X-ray plastics, sheet, and film unsupported... 

VPVC (polyvinyl chloride—highly plasticized, e.g., coated fabric, unsupported film)... 

Film - A product, e.g., plastic, that is extremely thin compared to its width and length. There are supported and unsupported films such as coatings and packagings, respectively. 

Latent catalysts used in conjunction with either liquid or solid resins are cast in thin films on plastic or release paper for unsupported films or onto absorbent papers or cloths for supported films and then cured to B stage. These films can subsequently be cut to shape and placed between mating surfaces for subsequent heat curing (Section VI.F). 

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... 

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... 

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. ... 

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. 

Figure 1 shows absorption spectra (corrected for surface reflections) of a single unsupported film of Polaroid type HNP B material oriented parallel and perpendicular to the plane of polarization in a spectrophotometer Commercial HNP B polars usually consist of two such films sandwiched between isotropic cellulose acetate films. Absorbances in the perpendicular (Ag) orientation were not measurable between 550 and 670 nm because of instrumental difficulties (primarily depolarization at optical surfaces in the spectrophotometer). However, in measurements with the HeNe instrumentation described previously the dichroism was seen to exceed 5 at 6328A Obviously several layers of this material would be required in each polar if a dichroism of 5 were required throughout the visible region ... 

Extrusion casting A term sometimes employed in the industry for the process of extruding unsupported film, especially a composite of two or more integral resin layers formed by coextrusion. Such extrusion-cast composite films possess desired properties on each of the respective... 

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. 

Supported and unsupported film lamination Manufacture of sandwich panels (road signs, etc.)... 

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. 

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