Peel value

Other important properties that can be measured in the laboratory include sealabiHty, printabiHty, or coating adhesion. Many of these tests have been developed by the film manufacturer in cooperation with customers and are specifically designed to measure product performance in the end use. Some tests, like sealabiHty, can be standardi2ed to time, pressure, and temperature of sealing with instmment-measured peel values, but other tests are subjective, such as evaluations of printing loss to puUoff by adhesive tape. 

Neoprene—phenohc contact adhesives, known for thein high green strength and peel values, contain a resole-type resin prepared from 4-/-butylphenol. The alkyl group increases compatibiHty and reduces cross-linking. This resin reacts or complexes with the metal oxide, eg, MgO, contained in the formulation, and increases the cohesive strength of the adhesive. In fact, the reactivity with MgO is frequently measured to determine the effectiveness of heat-reactive phenoHcs in the formulation. 

Peel values are recorded in pounds per inch of width of the bonded specimen. They tend to fluctuate more than any other adhesive test result because of the extremely small area at which the stress is localized during loading. Even during the test, the peel strength values tend to fluctuate depending on the type of adhesive, adherend, and condition of the test. In preparing the samples, care must be taken to produce void-free laminated bond lines. 

High peel strength with cohesive failure is possible by increasing the 0K/NC0 ratio. At a higher ratio, slight creep is observed at room temperature in the static shear test., 0H/NC0 ratios above 2.0 for Hycar 2103 and 1.8 for Hycar 2106 result in adhesives having incomplete cures with low peel values and poor static shear strength. 

Peel strength values were obtained by peeling 32 mm (0.125 inch) copper strips from the substrate. An end of each strip was clipped to an Ametek digital force measuring gauge which was connected to a computer processor. Force values required to lift the metal strips from the substrate were converted by the computer into grams per millimeter peel values. Multiple peel values for each strip were obtained and then averaged. 

Blend Monomer Dose (kGy) Peak peel value (g/25 mm)... 

An alternative method that has provided interesting data is to run a 90° peel test but begin this test at 0.1 in. (2.5 mm)/min, then stop the tensile tester under stress but allow the recorder to continue. It will be necessary to reduce the speed of the recorder, as the test may take minutes. Stress relaxation will be shown by the rate of drop of the peel value obtained when the tester was stopped. A useful value of stress relaxation time is that time taken when the applied stress has been reduced to 40% of its original value. 

Although the gel content indicated the presence of substantial cross-linking, the pressure-sensitive adhesive properties could be improved further by incorporating a small amount (1 percent) of pentaerythritol triacrylate (PETA). This system developed a peel value of 5.6 pli with adhesive failure and 22 hours of shear with only 6 seconds of cure time in air (Table 7). 

As stated before, when cured, each adhesive will display some combination of peel (with adhesive or cohesive failure) and shear resistance as represented by a point on the shear and peel plots. The relative position of the plots to one another determines what kind of an adhesive has been formed and how amenable to improvement it is. Thus, a relatively hard PSA will display a combination of high shear resistance and lower peel strength, probably with adhesive failure (hypothetically Fig. 6-A). Continued cure or additional cross-linking with this type of system is unlikely to generate desirable properties. At the opposite extreme, a soft system (e.g.. Fig. 6-D) may show moderate-high peels (cohesive failure), but shear values will be low. High shear may develop with additional cure, but the peel value will have already begun to decline. 

Further modifications to the system to increase "hardness" can result in additional shifting of the shear plot to the left. Systems can then be found in which the shear rises abruptly to a maximum value at a point close to where the maximum peel is reached. While this type of system (Fig. 6-C) yields high values, exposure times must be controlled very carefully as small variations will have a large effect upon performance. A more preferable system is shown in Fig. 6-B. Here, the shear is maximized early and peel then increases to its maximum value with more exposure. In this way, only the peel value is varying and exposure time is less critical. 

CELLOSOLVEWacrylate, and benzophenone (40/60/5/2). When irradiated for 6.5 seconds in air, a peel value of 5.5 pli is observed with cohesive failure while at 7.0 seconds it has changed to adhesive failure (4.0 pli). The maximum peel value for these formulations occurs just before the adhesive failure mode begins (point C->A, Figure 6-C). ... 

Typical cure conditions for the different types of phenolic adhesives are shown in Table X. Also included are representative shear and peel values, as well as an indication of the temperature performance. 

The curves in Figure 5 are a bit of a digression and are included only to show that the vulcanization time dependency of peel strength values is not necessarily diagnostic of adhesion mechanism. Both EPDM s were bonded with the fast adhesive system referred to previously. But the dicyclopentadiene terpolymer recipe was so very slow to vulcanize itself that it imposed a profile of sluggishness in the curve for peel value development. 

Figures 16 and 17 show the relationship between the amount of adhesive applied to strips of nylon and polyester fabric and the peel strength levels that were achieved after vulcanization to a standard SBR stock. These results tell us little of mechanism but they do show the critical dependency of peel values over a relatively narrow range of adhesive add-on.

The 1" X 5" bonded samples were peeled at 180° on a Scott Tester or similar machine at 2 Vininute. The peel value was recorded and the type of failure was noted [e.g., 80% R, 15 RC, 5 CF is failure within the stock (80%), some failure between the rubber and the cement (15%), and a slight amount of failure (5%) between the cement and fabric]. 

Peel values are recorded in pounds per inch of width of the bonded specimen. They tend to fluctuate more than other adhesive test results because of the extremely small area at which the stress is localized during loading. 

Values are expressed as ounces per inch (most specimens are one inch wide). Acceptable tapes, depending on end use, may have peel values as low as 25 oz./in. while tapes designed for use in high shear applications give values as high as 100-150 oz./in. 

FM 96 is one of the early adhesives that is representative of this type. It has moderate strength at temperatures up to 300 F. Oxidative stability is excellent which led to its use in areas of the engine nacelle and other hot spots where continuous exposure to temperatures up to 300°F are involved. Some improvement in toughness over unmodified epoxies is achieved through modification with a high molecular weight vinyl resin. As a result moderate metal peel and sandwich peel values can be achieved. This type of adhesive can be shipped and stored... 

Nylon-epoxy adhesives are the toughest class of structural adhesive available. Lap shears in excess of 7000 psi are obtainable. Sandwich and metal peel values are also extremely high about 140 in. Ib/in. and 80 Ib/in., respectively. Because of the high concentration of nylon this adhesive is quite susceptible to plasticization by absorbed moisture. For this reason, perfor-... 

The more interesting result is, however, related to the improvement of a peeling value for the recycled material. This means that two phases at the exit of the die adhere much better in presence of photooxidized polyethylene because of interaction between the carbonyl groups of the R2 sample and the NH2 groups of the nylon. 

To obtain significantly higher quick-stick and peel values in the temperature range of 20°C to ioo°C, acResin DS3532 can be mixed with hydrocarbon tackifier resins, which do not absorb in the UV-C wavelength band, e.g. with Regalite R-gioo. 

Removable labels Cross-linking acResin DS3532 with a UV C-dose of 2omJ/cm2 to 25 mJ/cm produces much more cohesive, less tacky adhesives. Labels coated with such a product show excellent peel values and can be removed after use from a wide variety of different surfaces without leaving any visible residues. 

The general purpose UV 2K system develops its maximum tack and peel value near 22 hours at room temperature without any heat assistance. The raw material used in... 

The peel test measures the work done on the entire tape. If the backing is stiff and elastic, such as polyethylene terephthalate (PET), no work will be done on the backing and the peel force is unaffected. However, if the backing can also yield, such as aluminum, then the peel value will be increased in proportion to the work done. If the tape is curled or otherwise distorted after the test then some work has been consumed in the backing. Even if the backing does not deform, its thickness can have an effect on the peel force since it changes the precise angle at the peel front which influences the way the adhesive deforms and thus the work done on it. Peel increases with adhesive thickness, but not proportionately, provided that the... 

PSAs are usually characterized by their three common properties of tack, peel resistance, and shear resistance, which can be determined by standard laboratory test procedures. Each of these properties is affected by temperature change. Indeed, as already noted, most adhesives exhibit different properties when subjected to temperature, and in the case of PSAs the bond is almost always thermoplastic, softening at elevated temperature and becoming more brittle at lower temperatures. As the temperature increases, the adhesive mass softens and wets the substrate more rapidly and completely, and the tack and peel properties increase. At some point, however, the adhesive has softened to the point that its cohesive strength is less than the substrate adhesion, and the adhesive mass splits, failing cohesively, that is, the locus of failure has changed from adhesion to cohesive within the adhesive. As the temperature continues to increase, the adhesive mass continues to soften, and the tack and peel values continue to go down. 

The ped strength (adhesion) is a measure of the separating force necessary to peel a label or tape off from the surface to which it was applied. The term describes the strength of adhesion or grab to a surface. Acrylate compositions require a few hours before achieving full adhesion. Rubber adhesives and hot-melt contact adhesives exhibit high peel values after only a relatively short contact time. 

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