When painting, coating, or adhesion is applied to a plastic film, the plastic film surface must be wet (applied evenly) with ink, coating agents, or adhesives. A scale that shows this wet state is called wetting tension.
The presence of water droplets on the film surface does not mean that it is wet. To wet the surface with a liquid having a high surface tension like water, the film surface must be highly polarized for hydrophilicity. On the other hand, in case of solvents with weak surface tension such as organic solvents, the film surface gets wet even in a state where water is repelled.
Therefore, it is important to know the wetting tension of the plastic film when painting, coating, or adhesion is applied to a plastic film. The test method for wetting tension is specified in JIS K6768 "Plastics -- Film and sheeting -- Determination of wetting tension". In this test method, a series of wetting tension test mixtures having surface tensions increasing in a stepwise manner is prepared. The wetting tension is determined in observation of them dripped on the film surface. However, it is very hard to prepare a series of 36 wetting tension test mixtures. In FUJIFILM Wako, 36 wetting tension test mixtures for the wetting tension test, which were prepared in advance, are available for use.