Imaginary Tape Faults

As was previously mentioned, many tapes are coated with a release coat to give easier unwind. The degree of unwind is often designed dependent upon the use of the tape. Someone familiar with a specified tape expects a specific release. Should the release be low, this is then related to poor adhesive properties of the tape. The adhesion of the tape may be well within the standard and well able to function for the purpose for which the tape is intended.

Just as the adhesion of a tape to its backing depends on the coating on the backing, the adhesion of a tape to various surfaces depends on the nature of the surface. Its chemical constitution determines whether a giving tape will bond to it well or not at all. A silicone release paper is an example of an unbondable surface using conventional pressure sensitive tapes. Similarly, silicone polishes and finishes are just as difficult to adhere to. There are a myriad of such non-adherable or poorly adherable surfaces around us. For such need, there are special tapes or a special tape must be specifically designed. The surface characteristics will also affect the bond a very rough surface presenting poor contact to the adhesive.

Quite often, a tape fails because a weak boundary layer exists between the tape and the surface. This could be moisture or dirt and dust, oil and grease or any other material which can be easily shear or separate. Hence, the insistence for a clean, dry surfaces. This failure may even be the surface itself. An example would be a painted wall where the adhesion of the paint to the wall was low. But , needless to say, the tape usually gets the blame. Similarly, there are those surfaces which are so treated that they act as prime coat for our adhesive. This could be a rubber-coated product or anodized aluminum or a surface-treated plastic. In this case, it often becomes impossible to remove the tape, the bond to the surface being higher than the bond of the adhesive to the tape primer.

Always remember, the tape is designed for applications at approximately room temperature, unless specifically indicated. if the tape fails to adhere at less than 0 degrees Celsius, this does not mean that the tape has poor adhesion. At these temperatures, a pressure sensitive tape will “freeze” resulting in no tack or adhesion. When the tape returns to a normal temperature, its original properties recover.

Adhesion test equipment is elaborate and costly. However, one of the most historic and simplest of the test methods is the thumb test. This test is exactly as it implies. It is highly portable, fairly sensitive, no-cost piece of test equipment and to a trained operator, it can yield useful information on tack and adhesion by watching the length of threads of adhesive when the thumb is removed. I can even yield information on cohesion. However, it has many faults. Everyone´s thumb is different in size, surface characteristics and soon. In addition , the condition of the thumb is important. Is it dirty, dry, damp, coated with perspiration or dead skin? To sum up, adhesion to human skin does not necessarily show the effectiveness of a tape for industrial use. So view the thumb test with caution, tempered with common sense. Try the tape on a hard, dry, smooth, clean surfaces (such as a filling cabinet or a desk). be careful of varnished or polished surfaces because they may act as a release coat.

The simplest test for cohesion is a mass-to-mass test. Again we must be careful how we interpret the test. It may be that the cohesion of the mass is so high that it may cause failure at the primer, thus giving the impression that the primer is faulty whereas, in fact the tape may be excellent. Also certain adhesives (such as the acrylic vinyl ethers) are self repellent and such a test may be extremely misleading.


Note: This material is an excerpt from Shuford Literature.

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