Pressure-sensitive adhesive

Pressure-sensitive adhesive (PSA, self-adhesive, self-stick adhesive) is adhesive which 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 tapes, labels, glue dots, 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 low temperatures and reduce their shear holding ability at high temperatures; special 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.

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 (for example, white glue), reaction with UV radiation (as in dental adhesives), chemical reaction (such as two part epoxy), or cooling (as in 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 wet, the adherend. The bond has strength because the adhesive is hard enough to resist flow when 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 viscoelastic (viscous and elastic) properties, both of which are used for proper bonding.

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