SILICONE RELEASE COATINGS
Silicones are unique materials which enable the easy release of self-adhesive (sticky) materials. Unlike most organic polymers, silicone polymers are based on a ‘back-bone’ made up of silicon-oxygen units surrounded by organic side groups (these are most often methyl groups).
Some of the basic properties of silicones are their chemical inertness, low polarity and low surface energy, and it is the combination of these three basic properties, combined with a high degree of flexibility which makes silicone based coatings uniquely suited to be release coatings for sticky materials!
Silicones can come in many different forms from fluids to gels to elastomers, but to work as release coatings for in liner applications, it is important that the silicone doesn’t migrate and stays part of the release liner.
The silicone coatings used here start off as liquids which are coated and then converted (‘cured’ as we like to call it), into a final layer of silicone elastomer. This ‘curing’ into a silicone elastomer can be done using heat or UV-radiation, but either way the final coating is still a ‘cured’ silicone elastomer.
The final silicone coating is typically just one micron thick, and can even be less for some applications (e.g. bakery release paper where it might be just 300nm). No matter how thin, though, this layer of silicone has to completely stop any material from sticking to the liner. At the same time the silicone needs to anchor well to the liner substrate.
When the silicone release coating is doing a good job it is easy to remove a sticky material from the release liner, but even though it might be a very low force, the force required to remove a sticky material from the release liner can still be measured. This is referred to as a Release force, and in many cases the level of this force can be ‘tuned’ to the requirements of the end application by modifying the silicone coating. If the release force is too low, then it might be too easy to remove the sticky material from the liner (so that it comes away from the liner when we don’t want it to), and if it is too high, then there might be problems with damaging the sticky material as it is removed from the liner. For a release liner to work really well in an application, the release performance needs to be finely tuned to match the needs of the application where it is being used.
Photo Courtesy of The Dow Chemical Company