Question: We purchased several ACCU DYNE TESTTM Marker Pens from you recently, all at 30 dynes/cm. One test marker seems to be getting a significantly higher amount of “failure” results. Can you provide any insight on this?
Answer: The first thing to check is whether all the test markers have the same lot number, meaning they were all produced from the same master batch. It is extremely unlikely that any significant variation in actual surface tension from lot to lot would occur, but it is not impossible. If the suspect marker is the only one with a non-uniform lot number, we would want to know immediately.
Generally speaking, if one test marker reacts differently from others at the same dyne level, it is due to one of three causes: Either evaporation of test fluid from the pen’s barrel, contamination of the tip (typically by airborne silicone or residual oil from a previous processing stage), or absorption of water from extreme humidity or accidental immersion.
Evaporation will generally increase the surface tension of the test fluid, as 2-ethoxyethanol evaporates faster than formamide. However, the 30 dyne/cm formulation is 100% 2-ethoxyethanol, so any evaporation that does occur should not affect the surface tension of the test fluid.
Contaminants are usually of lower surface tension than the test fluids, but this may not be true at this low a dyne level — the suspect unit may have picked up a contaminant of higher surface tension, raising its dyne level and decreasing its wettability. This would cause false failures. Any absorption of water would also increase the surface tension of the test liquid, with the same result.
Another possibility is that the suspect unit is allowing a smaller amount of liquid to flow through its tip, which could result in a thinner film of liquid being applied. Thicker fluid films will wet somewhat more readily, due to gravitational spreading from the mass of the liquid. Taking care to saturate and then flush the tip in accord with the test procedure so that all test markers apply a similar volume of fluid on the final pass will help minimize this effect.
If you need a more concrete answer, the best thing to do is send us the suspect test marker and one that reads as expected, along with some of your material samples, and we will evaluate the issue in our test lab.