What is Peel Adhesion?
A pressure-sensitive adhesive (PSA) tape is used in various fields because it can be applied instantaneously with rather weak pressure and is easy to remove. Specifically, across multiple forefront industries, such as the fabrication of liquid crystal panels, semiconductors, optical instruments, and solar batteries, as well as medical treatment, the automobile industry, architecture, and IT, the unique capability of PSA is applied to production processes and device components.
PSA tape is valued based on three basic elements: the so-called tack test, adhesion, and shear-holding power. In general, the peel test quantitatively measures adhesion forces at 90º and 180º angles, as specified in JIS Z0237:2009.
At 180º, the peel test result is influenced by the thickness and degree of elasticity of the PSA tape. At a 90º angle, the result is less influenced by these tape characteristics and is more reliable and consistent for evaluating adhesion and cohesion. However, the test result is unsatisfactory at present due to the deviation from a 90º angle arising from the sagging and elongation of the tape.
Conventional Multi-angle Peel Test Method
Peel testers for multi-angle measurements are already available. To maintain a constant peel angle, linear movement of the substrate and a tilted detector element are used, satisfying the geometrical condition shown in Figure 1. The auxiliary line does not exist, but helps clarify the measurement principle.
Figure 1: Schematics of the T-peel test
The sample stage and the load cell will be set at an angle α to the auxiliary line, using the following quotation:
𝛼 = 90º−𝜃/2
While moving the stage in the direction of the auxiliary line at a certain speed, the peel front moves from point A to point B, whereas the peel angle θ remains unchanged. Since the stage moves parallel from the peel front A at stage position I to the peel front B at stage position II, the angles at both points are identical. For example, the desired 90º peel angle is achieved by setting the stage and load cell angles to 45º.
On the other hand, when the peel distance is AB, the stage travel distance is AA’. Therefore, instead of an equal peel rate VP and test speed VS, the relationship becomes:
𝑉𝑃 = 𝑉𝑆 / 2cos 𝛼
Consequently, to evaluate the dependence on peel angle, it is necessary to adjust the peel rate for each angle using the formula mentioned above.
Also, measurements of low peel angles would require pulling the load cell upward, so this design allows measurement of peel angles in the range of 90º to 180º.
Flat Plate Cross Stage Peel Test Method
Kyowa Interface Science Co., Ltd. invented the Flat Plate Cross Stage Method. The synchronized actuator mechanism is designed to evaluate flat plate sliding at specified crossed angles relative to the pulling direction on a high-accuracy stage.
Figure 2: Principle of the Kyowa's Flat Plate Cross Stage peel test method
The peel angle C is set with the sample stage on top of the rotary table, which sits on an actuator. When the mactuator travels in direction A, the sample stage on the rotary table moves synchronously in direction B via an internal rack-and-pinion gear assembly. This mechanism maintains the peel angle C by moving the rotary table in direction A and the slide stage in direction B by equal distances.
Figure 3: Schematic of the movement of the rotary stage and sample stage (flat plate cross-stage)
The Kyowa horizontal versatile peel analyzer VPA series is the only device that enables peel tests at any peel angle from 0 to 180º while ensuring that the peel rate equals the test speed (pull rate).
Related Products
VPA series
- Peel Tester