Adhesive Tape Testing to Cardboard

By John Johnston
PSTC Technical Advisor

Corrugated box manufacturers make a wide variety of surfaces and qualities to their boxes, depending on manufacturer, and can even recycle a percentage of old card into their pulp. The recycling process chops the cellulose fibers into shorter lengths giving a card of poorer internal strength, and so the more the recycled material there is in a card the poorer it is for a tape to adhere adequately to it, as those short fibers break away. So it is common practice for packaging tape manufacturers to work with boxes from major box manufacturers and test their tape against specific boxes of those manufacturers. Cardboard boxes with recycled material in it are usually marked, quoting the amount of recycled material.

To overcome this wide variation, adhesive tape is always tested against a standard quality card, as offered by the National Institute of Standards and Testing known as NIST SMR 1810A.

When paper is being manufactured, the high process speed results in the cellulose fibers being oriented in the machine direction, and those fibers are also at a slope in the paper. So quite a different behavior can be seen when the tape is stripped from a card in one machine direction, then repeated in the other machine direction, one direction 'catching' the ends of the fibers and pulling them away, resulting in cardboard delamination. However in the other direction it is possible to see little or no delamination with the same tape. We can see this phenomenon with the hair on our forearms, which also lies in a given direction. Pulling a surgical adhesive tape from the arm towards us can be quite painful, yet stripping it away from us is painless. The machine direction of standard NIST card is marked on the card, with instructions to test at right angles to it.

From my own experience in designing and manufacturing polypropylene packaging tapes for many years, I had always felt that if an adhesive tape, when stripped from the cardboard surface at standard testing speed and in both directions to the machine direction of the paper would delaminate the card, then the adhesion of the tape is as high as it need be, and I now need pay attention to shear resistance from the card. I'd also test in all four directions.

The machine direction of an unknown card is determined initially with another suitable tape which will delaminate the card in one direction but not the other, and certain grades of masking tape have been found to work well. This is found by trial and error. Once the grain of the card has been identified, it pays to keep a stock of the same quality appropriately marked card.

If you are going to do 180 degree peels from card, in addition to recording the adhesion value found, look at the adhesive surface after peeling and estimate the percent delamination of the card, recording that too, which is also a measure of the tape's performance. Remember that what you might wind up doing is not the adhesion of the tape to card but the delamination strength of the cardboard. Don't forget to run a PSTC #14, the 90 degree static peel test from card, which is a measure of the tendency of the tape to lift and curl away after prolonged dwell, and always use recognized competitive products as controls.

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