Pressure peel test

Adhesive strength refers to the bond produced by contact of an adhesive to a surface. It used to be measured by peeling tests. This ultimate strength depends on temperature, applied pressure and time of contact. 

Samples for adhesion measurements were prepared in a separate chamber with a base pressure of 1 x 10 ° Torr under identical conditions. Typically, -1000 A silver coverages were used for adhesion measurements. Adhesion strength of the deposited Ag films was determined using a polyester adhesive tape and standard peel test procedures on an Instron tester. 

Aluminum panels, which had a thickness of 0.61 and 1.63 mm, were etched with chromic acid. ASTM procedure D3167—76 (reapproved 1981) was followed for 135° peel tests. The adhesive film was placed between the aluminum panels and press-laminated at a temperature of 177 °C for 1 h at a pressure of approximately 5 psi (34.5 x 103 Pa). The temperature was then increased to 220 °C, and the joints were kept under pressure for another hour. The heaters in the hydraulic press were then switched off and the platens air-cooled and then water-cooled until the platen temperature was down to 100 °C. The bonded panels were cut into 12.7-mm-wide joints and tested at a rate of 20 mm/min and at a peel angle of 135°. 

The strength of the seal on flexible packs (achieved by cold and heat seals) can be quantified by tensile tests as seal or peel tests or the air pressure required to create rupture of the pack. This can be carried out by a hypodermic needle arrangement followed by pressurising the pack at a specific rate until the pack bursts. Depending on the nature of the seal, the point of rupture may arise either in the body of the pack or the seals. An alternative method is to place the pack in a jig followed by a steady mechanical increase in compression. 

ABSTRACT Dif sion of acetone at the interface of a bonded pressure sensitive adhesive tape was measured using single frequency capachance measurements (SFCM) and a novel interdigitated electrode sensor design. The relative concentration of acetone at the bondline as a function of distance from the edge of the specimen and exposure time was correlated to adhesion loss measured by the 90° peel test. 

The test methods presently used to evaluate the adhesion of pressure-sensitive adhesives to release liners are modified adhesion tests, such as the 180° or 90° peel test, with the liner adhered to a test panel, or a T-peel test, where the sample is freely suspended while the tape is peeled at a controlled rate from the release liner. The values obtained by the latter method are alfected considerably by the stiffness of the liner, which alters the angle of peel. 

One method occasionally used evaluate the relationship of silicone release liners or other materials of very low surface energy to a pressure sensitive, is to bring a coated pressure sensitive into contact with the liner under pressure, to carry out an adhesion test. This is of little value, as the adhesive is unable to wet out and so come into intimate contact with the release liner. The adhesive must first be coated onto the liner, dried, or cooled in the case of a hot melt, and then a carrier laminated to it, as is standard practice for transfer coating. As low values of adhesion can be expected, the force required to bend the backing may dominate, and so a thin flexible backing should be used, to maintain a constant peel angle, 25 pm polyester being satisfactory. Then a standard 180° peel test can be carried out with the release liner secured to a test panel. 

Another important consideration is the mode of failure experienced during the 180 peel test. Pressure-sensitive adhesives with internal strength relatively low in comparison to their adhesion to a test substrate will fail cohesively while the same type of adhesive with improved internal strength will often fail adhesively. This adhesive failure can be important for temporary applications but is of less importance for high strength, permanent uses. Some systems change from the cohesive to the adhesive failure mode as the amount of cure is increased, a point which will be illustrated later. 

Peel Test (PSTC-1) - Cold rolled steel "Q-Panels" (Q-PanelCo.) were used. A one-inch wide strip of coated Mylar is bonded to the panel under pressure of a 4 1/2-lb. roller. 

A T-peel test is shown in Fig. 27.2. The specimen is usually 1 in. (2.54 cm) wide and is described in Standard Test Method ASTM D1876 [6]. This specimen is symmetrical (both adherends are the same thickness). Other peel test specimens are not symmetrical, such as the floating roller peel test [7] or the climbing drum peel test [8]. The test measures the fracture resistance of an adhesive under conditions in which the adherends may plastically deform. In the tables presented later, the peel strength is given in Newtons per centimeter of width (N/cm) and in tmits of pounds per inch width (piw). The latter is shown in parenthesis. In some cases, the peel strength is derived from climbing drum peel measurements in which the results are presented in torque, in. Ib/in. For pressure sensitive adhe-... 

Standard tests used to characterize the adhesion properties of tapes are for the assessment of shear strength (see Shear tests) (the ability of a tape joint to resist a load applied in the shear mode), peel strength (see Peel tests) (the resistance of a tape joint to peeling under specified conditions) and Tack (the ability of a pressure-sensitive adhesive to form a bond immediately on contact with another material). There are many standard test specifications laid down by different authorities to assess these properties and many differences in detail between them (e.g. see Appendix). No attempt will be made to describe them comprehensively, but the principles of the tests will be discussed separately. 

The optimal adhesive layer thickness depends on a number of factors. Some bonds, notably Tensile test specimens, are stronger when the adhesive layer thickness is redn-ced. For fracture specimens, including double cantilever beam specimens bonded with structural adhesives (see Fracture mechanics test specimens), optimal bond thicknesses have been identified, although the optimal thickness depends on the loading rate and test temperature. " Enhanced ductility plays a role in this process, and a sufficient quantity of adhesive is desired to dissipate energy (see Peel tests). This latter mechanism is also important in the peel energy of Pressure-sensitive adhesives and other systems. 

A DVS-bisBCB resin formulation witii 5 and 10 wt % elastomer was sag-plied on wafers widi SiOa, SiaN4, aluminum, and copper coatings. AP3000 was used as an adhesion promoter. The wafers were placed in a pressure vessel at 125°C and 2 atm for 96 h. The sanqrles were evaluated by the peel test, and... 

Typically, pressure-sensitive tapes are applied in region B. The effective pulling rate of the standard peel test at 180° is 2.5x10 m/s, which is in the middle of region B (indicated by an arrow in Fig. 12). At very low temperature, region C may be reached. For application under freezer conditions, special tapes with lower Tg are available. 

Peel tests involving low contact pressure and short apphcation time (e.g., the loop test). 

Most adhesive tapes are composed of a flexible backing (paper, plastic, cloth, metal foil, etc.) to which a pressure-sensitive adhesive has been applied to one side (both sides for double-sided tapes). Pressure-sensitive adhesives typically consist of a rubbery material with a modifying tactifier that may be applied to the tape by a solvent system, hot melt, or by other means. One would expect such materials to be sensitive to the mode of stress (tensile versus shear) in the region where debonding occurs. Furthermore, since tacky rubbers of the type used in pressure-sensitive adhesive are viscoelastic, one would anticipate material properties to be time- and rate-dependent. Are these expectations consistent with the observations from your simple peel test ... 

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