Using a corona treatment pen to measure the surface tension of a film presents an accuracy issue. First, the accuracy of the corona treatment pen's dyne index. For example, sometimes the same film may shrink when tested with a corona treatment pen, but not when tested with a corona treatment pen. Another example is that some pens may even wet the untreated surface of the film well. Second, the timeliness of the corona treatment pen is important. "Under open conditions, ethylene glycol ether is more volatile than formamide. This means that if the same dyne pen is used repeatedly over a long period of time, the dyne value of the pen will gradually increase due to the greater volatility of ethylene glycol ether than formamide.
Furthermore, because formamide is hygroscopic, the incorporation of moisture and the generation of formic acid can also cause the actual dyne value of the pen to increase." Furthermore, repeated use of the film's surface additives can contaminate the corona treatment pen, leading to inaccurate test results. Using a corona treatment pen to test the surface tension of a film is convenient for workers, but the accuracy of the reading must be carefully considered. Comparing the reading with a surface tension solution can be used to determine the accuracy of the surface tension index. If testing the corona surface of a film, a corona treatment pen is recommended to distinguish the degree of corona treatment. For films with poor corona treatment, the actual wettability of the glue to the material can be determined by peel strength testing of the composite sample.