Adhesion is the strength of the bond between a tape and the application surface. To measure adhesion, tape is applied to a stainless steel panel. The tape is then removed. The force required to remove (or peel) the tape determines its adhesion level. The force is measured in ounces per one inch of tape.
Peel adhesion can be tested by two methods. The 90-degree peel method or pulling the tape perpendicularly to itself is the best measurement of peel adhesion of diverse substrates. This is typically used for fastening tapes. The 180-degree peel method (PSTC 3 and PSTC 1) or pulling the tape back onto itself is often used to measure the adhesion of masking and packaging tapes.
Peel adhesion is not a perfect correlation to the strength of the adhesive bond. Why? Because the test measures the initial bond, and many tapes have adhesives that build bond strength over time. Also, the test utilizes stainless steel as the surface for which the tape is applied. Typically, tape is not applied to stainless steel in real-life applications. However, the test is a good indicator of relative adhesion strength from one tape to another.
Cohesion is the internal strength of an adhesive. Cohesive failure can be observed when removing an applied tape and finding adhesive residue on both the tape backing and the applied surface. This would indicate that the adhesive has poor internal strength, or poor cohesion.
Tack, often referred to as Quick Stick, is the ability of a tape to create an immediate bond, during the initial contact of the adhesive with the substrate, without applying external pressure.
Shear is a measure of the internal or cohesive strength of the adhesive, not a measure of the bond between the adhesive and substrate. Shear is the ability of an adhesive to resist creep or slippage.
This property is measured by adhering a one-inch piece of tape to a stainless steel panel, then hanging a weight on one end of the tape. Shear is expressed in units of time prior to the tape slipping from the steel panel.
Good shear properties are especially important for applications like splicing where the tape is used for holding two substrates together, with force being applied in opposite directions.
Tensile strength is the force (or load) required to break a tape. This property is measured by taking a one-inch-wide piece of tape, grabbing it at both ends, and then pulling in opposite directions until the tape breaks. Tensile strength is measured in pounds per one inch of tape.
Elongation is the percent in which a tape can be stretched just before breaking. Some tapes have a creped, or somewhat wrinkled, backing that allows the tape to have more stretch and conformability.
This property is measured using the same method for measuring tensile strength.
The thickness of a tape is the distance between the two opposite surfaces of the whole tape. Thickness is expressed in mils, or thousandths of an inch.