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A low dyne substrate can lead to adhesion and printability issues when an ink is applied to the surface. The most common, accepted method for measuring surface tension is to apply indicator solutions, known as dyne solutions, to the surface of a substrate.
Dyne Solution
Dyne solution is a mixture of Ethyl Cellosolve® and Formamide. The percent concentration of the two chemicals determines the surface tension, or energy, of the solution. The unit of measure is dyne/cm, but most refer to it as the dyne level. The solutions usually contain a dye to allow better visibility when applied to the substrate.
Solution / Cotton Swab Method
The tip of the applicator swab is immersed in a single dyne-level solution container. The solution is spread lightly over test material; the operator looks to see that the solid line does not breakup for two seconds. If the wetting solution stays intact for two seconds the surface tension is at least as high as the dyne level of that solution. The procedure is repeated with another solution using a new swab until a solution is found that beads up on the surface of the material.
The surface tension level of the substrate would be identified as the highest dyne solution that wetted out the substrate surface. A clean cotton swab should be used for each application of solution to avoid contamination of the solutions which could distort the results. When the print area is large, measurements should be taken at several points across the entire print area.
The image to the right shows four dyne solutions applied on a substrate surface. The two middle solutions do not wet out the surface and bead up. The two outer solutions wet out the surface with the lowest dyne solution of 30 (far right) showing the highest degree of wetting out. This test should be continued with solutions between 34 dynes and 40 dynes to more accurately determine this substrate’s surface tension.
The Dyne-Pen Method
Using a dyne-pen provides a quick and easy alternative to determine the substrate’s surface energy. Dyne-pens are pulled across a substrate’s surface. As the pen is drawn across the substrate, the operator looks to see that the solid line does not breakup for two seconds.
Although not as accurate as the cotton swab method because of possible contamination of the tip by multiple uses, using a dyne-pen provides a quick check.
Notes
Dyne solutions and dyne-pens have an expiration period and must be dated upon first use and sealed immediately after each use. Dyne level testing can be subjective. It is not uncommon for individual interpretations to vary beyond the typical accuracy range of +/- 2 dyne.