Testing Smoothness and Coefficient of Friction (CoF) of Wax Coated Corrugated

Mark asks:

I’m looking for several answers regarding wax coated corrugated sheets. I’ll start with two quick questions.

1. Is there a permanence / half-life / shelf-life value between acceptable and unacceptable smoothness / CoF values for wax-coated (Nomar) sheets?
2. Is there a “quick and dirty” smoothness / CoF test that we can run to determine if our wax-coated board meets customer requirements?

We are a small sheet plant and provide auto parts suppliers with cartons, partitions, and layer pads.

In answer to your first question, I am not aware of any smoothness standard or requirement. The coating smoothness depends on the chemistry of the coating, the thickness of the coating, and the smoothness of the liner surface. Varying the combination of these three elements will certainly have an effect on the smoothness coated sheet.

Now, question number 2. Slide angle would be the quickest and most cost effective method to give you a smoothness measurement. It is a “cold” COF test that measures how far sheets can be tipped before they will slide. There are machines available for making this measurement.

You could also construct your own horizontal device using a weighted sled and a fish weight scale to approximate the amount of force required to move the sled and then to keep it moving. Remember, those are two separate measurements as it takes more force to initially move the device that it does to keep it moving.

There are TAPPI Test Methods for these options. You can acquire them by contacting TAPPI by email at standards@tappi.org, calling 1.770.209.7276, or visiting tappi.org and searching for “Test methods.”

You may also want to read this post on Ask Ralph Testing Coefficient of Friction of Non-Skid Coatings.

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