Measurement of the treatment effect
A measure for the treatment effect is the surface tension (or surface energy) of the surface. The standard method for measuring the surface tension is the contact angle. The angle between the surface and a drop of a fluid with known surface tension has to be determined. From this the surface tension of the surface can be calculated. Measuring with different fluids gives the polar and disperse part of the surface tension as well.The main disadvantage of the contact angle method used in a production line is that it takes time to get a result. As arule, a piece of the foil has to be cut out and brought to the contact angle device. For preliminary tests of the
treatment effect it is suitable to use the test inks. These are fluids with known surface tensions. Dependent on the behaviour of a drop on the surface the surface tension can be estimated very quickly close to production. If the fluid
which may be applied to the surface with a brush or a felt pen forms drops on the surface, surface tension of the ink is higher than that of the surface. On ther other hand, if the ink spreads on the surface, surface tension is higher than
the surface tension of the ink.For paperboards this method does not work. Best information on adhesion can be gained by performing an adhesion
test. In any case this should be done for finally assessing the treatment result for all applications. High surface tension is necessary for a good contact between the surface and the coating material. But surface tension cannot
guarantee a good chemical (or any other kind of) link between coating and surface. Both coating and surface material have to be matched with each other. If this has been done surface tension ensures good adhesion properties in most cases