The leading adhesive manufacturers are National Starch, Monsanto, Ashland and 3M. The first three manufacturers sell their adhesive in batches to film coating companies, such as FlexCon, Avery/Fasson, Coating Sciences, WH Brady, Labelon, Lamart, Kroy and Tekra.

There are four popular types of pressure sensitive adhesives: solvent, hot melt, rubber and water-based. Due to stringent emission rules, an increasing number of adhesives use water-based coatings. Fortunately, recent gains in technology have meant that the new water-based coatings are catching up with the performance characteristics of the prior favorite, solvent-based adhesives.

In comparing different adhesives, we recommend that you look at the following:

• Quick Stick. We call this "thumb appeal". Does the adhesive appear "gooey?" Will it stick quickly and easily, even if the application surface is not clean and dry. In the real world of less than ideal surface preparation, this is a very important characteristic.
• Low Temperature Application. The user cares little about the theoretical life of the label, if he or she goes out in one of the winter months and the only way he or she can get the label to stick is to use a heat gun. The downside, though, to most low temperature adhesives has been that the performance at high temperatures is sacrificed.
• Mobility. The adhesive must flow well, which is especially important for a rough application surface. By maximizing the surface contact between the label film and the underlying application surface, the adhesive's performance is enhanced.
• Maximum Temperature. A hot pipe can reach 200ºF. Certain adhesives will soften, then ooze or lose shear strength at high temperatures. A good test here is the heated shear test (see below). In this test, a 1 pound weight is clipped on to a label that, in turn, is stuck onto a metal plate. The entire assembly is heated to 200ºF. The test measures how long it takes before the adhesive slides off of the test rack.
• Adhesion to Low Surface Energy Plastics. Sticking to metal is much easier than sticking to a low surface energy plastic (such as polyethylene). Many "quick stick" adhesives are made specifically for these low surface energy plastics. Unfortunately, these adhesives sacrifice peel and shear strength at higher temperatures.
• Peel Strength. This is the classic way to analyze an adhesive. A machine measures the force it takes to peel back a label, once it has been stuck onto a flat surface. Ten years ago, an adhesive having a 3 pound pull was unusual and costly. The new adhesives have made great strides in increasing pull strength.
• Shear Strength. This the second of the main adhesive tests. Here, a weight is attached to the bottom edge of a label. The label is stuck onto an application rack. The shear strength of the label is the time it takes before the label slides off the rack.
• Temperature Cycling. A metal surface outside can reach a temperature that is 40ºF. greater than the ambient temperature. By night, though, the metal surface cools. This constant cycling can lead to premature cracking of the adhesive. The right adhesive does not transfer this stress to the base film.
• Water Resistance. Certain of the early water-based adhesives would curl and fall off if they were immersed in water. Rain would cause the same failure.
• Chemical Resistance. Other adhesives may swell and soften after being exposed to a solvent.

Adhesive thickness does matter. From this chart, you can see that a 2 mils adhesive offers much greater peel strength than adhesive that is only 0.5.