What Are the Uses of Pressure-Sensitive Adhesives?
Why should you use an adhesive seal that is pressure sensitive? In most cases, the use of
pressure-sensitive adhesives can eliminate mechanical fastening systems (staples, nails or retaining clips)
and the inherent problems associated with them, i.e., cost, weight and breakage. PSAs frequently improve
productivity during the final assembly process by providing a faster, more efficient way of attaching seals
and gaskets to the end product.
Pressure-Sensitive Adhesive FAQs
To begin the PSA selection process, it is important to have the answers for several basic questions:
To what type of substrate will the PSA be attached?
- PSA be expected to perform, and with what chemicals will it come into contact?
- Will it come into contact with moisture or sunlight?
- Will the adhesive be functional after installation?
- Will the adhesive be in shear?
- What type of radius will the adhesive need to go around?
A second consideration when specifying an adhesive seal is whether a rubber-based adhesive or acrylic-based
adhesive is most appropriate for the application. Both types have several advantages.
Rubber-Based Adhesives
Rubber-based adhesives are very thermoplastic. Exposed to heat will soften the adhesive and directly affect
its performance. These types of adhesives have good initial tack to most substrates. This is unlike
acrylics, which can take 48 to 72 hours to achieve their ultimate strength.
Advantages
The key advantages to rubber-based adhesives are that they will adhere to a wide range of materials, they are
generally very economical, and they have a high initial “grab” or tack.
Disadvantages
Some of the disadvantages of rubber-based adhesives include poor resistance to elevated temperatures, fair to
poor resistance to chemicals, and generally poor resistance to ultraviolet light and oxidation.
Acrylic Based Adhesives
Acrylic-based adhesives do not require as many additives as rubber-based adhesives. In fact, the addition of
other ingredients tends to detract from their strength. Acrylic adhesives are polar in nature and tend to
stick well to polar substrates such as metals, glass, polyesters, polycarbonates and neoprenes. If adhesion
cannot be obtained to the satisfaction of the end user, a primer or treatment of the substrate’s surface may
be useful.
Conversely, acrylics do not bond well to non-polar surfaces such as polyethylene,
polypropylene (olefins), EPDMs and silicone. In some instances, a primer may be used with acrylics to
achieve a greater bond. Acrylics are thermoplastic by nature; they soften when exposed to heat and harden
when cooled. They are formulated so that they are inherently soft at ambient temperatures. Being soft
at room temperature permits them to flow under light pressure and make good intimate contact with the
substrate. This ability to flow is very important when bonding to an irregular or rough
surface.
Acrylic-based adhesives can maintain cohesive and adhesive strength up to 350ºF (176.6ºC)
and down to -50ºF (-45.5ºC) if a good, high-quality acrylic is employed in the application. Generally,
acrylic and rubber based adhesives will resist non-polar solvents or chemicals (toluene, mineral spirits,
gasoline, oil), depending on the severity of contact (concentration, duration and temperature). Acrylics age
very well in the presence of ozone, ultraviolet light and corona due to the saturation in the polymer
backbone.
Advantages
Acrylic-based adhesives are cross-linkable and deliver good resistance to varying temperature ranges,
chemicals, ultraviolet light and oxidation. They are very color stable and can be easily removed and
reinstalled in the application if positioned incorrectly.
Disadvantages
Generally, acrylic-based PSAs have poor adhesion to polyolefins. They also tend to be more expensive than
their rubber-based adhesives, and the initial bond or tack strength is low.