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Adhesive Discussion
Adhesive Discussion
Discussion of Adhesive Characteristics in Cleanroom Matting PDF Print E-mail

 The most common topic when discussing cleanroom mat’s adhesive characteristics is usually that of tack level. It is often brought up when discussing the performance of cleanroom matting. In doing so it is vital to include the other often overlooked adhesive characteristics of pressure sensitive adhesives- adhesive thickness and adhesive softness. These three characteristics together - thickness, softness and tack determine the adhesive’s ability to remove and hold dirt particles in a cleanroom entry application.

 
Tack Level PDF Print E-mail

 The tack level of a pressure sensitive adhesive is usually measured by means of a PSTC-1 test and shown in ounces or grams. This shows the force necessary to remove a one inch (25mm) wide strip from a polished stainless steel plate at a constant speed. It is used as a means of comparison between the individual layers. The purpose of tack is to remove particles from the shoe or wheel surfaces. To do so tack level has to only have a higher coefficient than the surface attraction of the dirt to the shoe or wheel surface. Since the dirt is held to the surface of the shoe or wheel only by this surface attraction and is not adhesive coated the tack level necessary to remove these particles is very low (2-3 ozs.). A very high tack level does not increase the ability to remove particles and can create operational and safety concerns.

 

 
Adhesive Softness PDF Print E-mail

 The softness of the adhesive is critical for the ongoing performance of each layer of a cleanroom mat. For the particle of dirt to be removed from the shoe or wheel surface it must be able to embed in to the adhesive. This characteristic works as the dominate partner with tack level to remove each particle. If the adhesive is too hard this will not take place. This could result in the particles remaining on the shoe or wheel surface or even if they are removed, on the surface of the adhesive. If the particles remain on the surface of the adhesive layer it can inhibit the mat from performing when the next shoe or wheel comes in contact with that exact area. The particles can even be potentially “picked up” when the next shoe or wheel that crosses over them. When the adhesive is soft enough the particles will embed providing the adhesive has enough thickness to accept the particle. Conversely the adhesive can not be too soft or adhesive transfer to the shoe or wheel can occur. Sometimes a mat layer that feels extremely “sticky” is representative of an adhesive that is very soft. This high tack with very soft adhesive can be a risk to transfer contamination to the controlled environment.

 
Adhesive Thickness PDF Print E-mail

The adhesive coating thickness on each layer is vital in the performance of the mat to function over time. When the particle is captured by the adhesive, it must have someplace to go. The softness of the adhesive allows the particles to embed in the adhesive layer so that it has someplace to go and the mat can continue to perform. Typical adhesive layers in cleanroom matting are 2-4 mils thick (50-100 microns). If the adhesive layer is too thin the particles will remain on the surface and shorten the time that the mat can continue to function. A washable mat (polymeric) is the ultimate example of a mat with no adhesive thickness. Since there is no coating to absorb the particles they remain on the surface until they are washed off. A shoe or wheel that comes in contact with a previously used spot does not actually contact the mat but only with the particles. This results in a very rapid performance decline for this type of matting.

 
Conclusion PDF Print E-mail

 The three characteristics of pressure sensitive adhesive- tack, softness and thickness all play a part in the ability of the adhesive to perform in a cleanroom mat application. The very common sense conclusion that “the higher the tack the better it should work” does not apply. The adhesive softness and thickness actually play a much larger role in the performance of the matting.

 


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