Pressure sensitive adhesive
4852467
218665188
2008-06-11T17:15:48Z
Salvar
3362617
/* Structural and pressure sensitive adhesives */
'''Pressure sensitive adhesive''' ('''PSA''', '''self adhesive''', '''self stick adhesive''') is [[adhesive]] that forms a bond when [[pressure]] is applied to marry the adhesive with the adherend. No solvent, water, or heat is needed to activate the adhesive.
It is used in [[pressure sensitive tape]]s, [[label]]s, note pads, automobile trim, and a wide variety of other products.
As the name "pressure sensitive" indicates, the degree of bond is influenced by the amount of pressure which is used to apply the adhesive to the surface.
Surface factors such as smoothness, [[surface energy]], removal of contaminants, etc. are also important to proper bonding.
PSAs are usually designed to form a bond and hold properly at room temperatures. PSAs typically reduce or lose their tack at cold temperatures and reduce their shear holding ability at high temperatures: Specialty adhesives are made to function at high or low temperatures. It is important to choose an adhesive formulation which is designed for its intended use conditions.
==Structural and pressure sensitive adhesives==
Adhesives may be broadly divided in two classes: structural and pressure sensitive. To form a permanent bond, structural adhesives harden via processes such as [[evaporation]] of [[solvent]] or water (white glue), reaction with radiation (dental adhesives), [[chemical reaction]] (two part [[epoxy]]), or cooling (hot melt). In contrast, pressure sensitive adhesives (PSAs) form a bond simply by the application of light pressure to marry the adhesive with the adherend. Pressure sensitive adhesives are designed with a balance between flow and resistance to flow. The bond forms because the adhesive is soft enough to flow, or [[wetting|wet]], the adherend. The bond has strength because the adhesive is hard enough to resist flow when [[stress (physics)|stress]] is applied to the bond. Once the adhesive and the adherend are in proximity, there are also molecular interactions such as [[van der Waals' forces ]] involved in the bond, which contribute significantly to the ultimate bond strength. PSAs exhibit [[viscous]] and [[Elasticity (physics)|elastic]] properties, both of which are used for proper bonding.
==Applications==
Pressure sensitive adhesives are designed for either permanent or removable applications. Examples of permanent applications include safety labels for power equipment, foil tape for [[HVAC]] duct work, automotive interior trim assembly, and sound/vibration damping films. Some high performance permanent PSAs exhibit high adhesion values and can support kilograms of weight per square centimeter of contact area, even at elevated temperature. Permanent PSAs may be initially removable (for example to recover mislabeled goods) and build adhesion to a permanent bond after several hours or days.
Removable adhesives are designed to form a temporary bond, and ideally can be removed after months or years without leaving residue on the adherend. Removable adhesives are used in applications such as surface protection films, [[masking tape]]s, bookmark and [[Post-it note|note papers]], price marking labels, promotional graphics materials, and for skin contact (wound care dressings, [[Electrocardiogram|EKG]] electrodes, athletic tape, analgesic and [[Transdermal patch|transdermal drug patches]], etc.). Some removable adhesives are designed to repeatedly stick and unstick. They have low adhesion and generally can not support much weight.
==Manufacture==
Pressure sensitive adhesives are manufactured with either a liquid carrier or in 100% solid form. Articles such as tapes and labels are made from liquid PSAs by coating the adhesive on a support and evaporating the organic solvent or water carrier, usually in a hot air dryer. The dry adhesive may be further heated to initate a crosslinking reaction and increase molecular weight. 100% solid PSAs may be low viscosity polymers that are coated and then reacted with radiation to increase molecular weight and form the adhesive (radiation cured PSA); or they may be high viscosity materials that are heated to reduce viscosity enough to allow coating, and then cooled to their final form (hot melt PSA).
==Industry associations==
Industry associations dealing with pressure sensitive adhesives include
*[http://www.astm.org ASTM]
*[http://www.pstc.org PSTC (Pressure Sensitive Tape Council)]
*[http://www.afera.com Afera]
*[http://www.tlmi.com TLMI]
*JAPMA
*[http://www.ascouncil.org ASC (Adhesives and Sealant Council)]
==See also==
* [[Pressure sensitive tape]]
* [[Post-it note]]
* [[Rheology]]
* [[Self-adhesive stamp]]
* [[Viscoelasticity]]
==Further Reading==
* "Pressure-Sensitive Adhesives and Applications", Istvan Benedek, 2004, ISBN: 0824750594
* "Pressure Sensitive Adhesive Tapes", J. Johnston, PSTC, 2003, ISBN:0972800107
* "Pressure Sensitive Formulation", I. Benedek, VSP, 2000, ISBN:9067643300
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[[Category:Adhesives]]'''