What Dyne Levels Should I Be Testing At?

Question: My ink requires a minimum of 40 dynes/cm, and my film supplier says they run their poly at 56 dynes/cm. Should I use a 40 as a threshold test, or does the marker dyne level need to match the material? What range should I be using?

Answer: If the poly were actually at 56 dynes/cm when you tested it, a test with a 40 dyne/cm test marker would probably wet out so well and have such an attraction to the treated surface that it would permanently mark the film. That would tell you that the surface was way higher than 40 dynes/cm – if it was actually only 40 dynes/cm, the test fluid would start to bead up within two seconds or so. But there’s a lot more to the story than that.

Polymers lose treatment – especially when induced by corona treatment – over time and with downstream processing, so if a film tests at 56 dynes/cm at the end of your supplier’s extrusion line, you might find it to have a surface energy of as low as 44 dynes/cm a few weeks later, when you are ready to print it. (Please don’t take these treat loss numbers as gospel – they are for explanatory purposes only!) After a few months of storage in a hot and humid environment, it may well have dropped to below 40 dynes/cm. Slip agents are especially problematic when it comes to treatment loss over time, especially at elevated temperatures.

ACCU DYNE TESTTM Marker Pens measure surface energy by testing over a range of dyne levels, starting with a low enough level that you expect it will wet out for at least several seconds. In your case, I would recommend starting at 34 dynes/cm, and having the ability to test up to 56 dynes/cm, which is at the high end of what you are likely to ever see.

While your ink supplier probably is correct about 40 dynes/cm being the minimum acceptable treat level, it will still be instructive to test filmstock as it goes to press. Keeping records of dyne levels (and any comments testers may report) along with other process data may prove to be a valuable tool in troubleshooting at some point. Also, you may find that with higher substrate dyne levels you are able to increase press speed somewhat, and/or improve print quality. Quantifying these relationships can streamline your operation and ultimately reduce costs by enabling you to develop better specifications for your purchased rollstock.

Published by

Russ Smith

Russ Smith formed Diversified Enterprises - the first business to focus specifically on applications of the dyne test - in 1986, and has served as President of the company ever since. He has over 30 years of experience in the fields of surface treatment and analysis, and deals with technical inquiries from customers worldwide on a daily basis. Russ is a member of ASTM, the Society of Plastics Engineers, the American Chemical Society, the American Society for Quality, the American Association for the Advancement of Science, and TAPPI.

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