The special feature of pressure sensitive adhesives is that they do not solidify to form a solid material, but remain viscous. As a result, they remain permanently tacky and have the ability to wet surfaces on contact. Bonds are made by bringing the adhesive film in contact with the substrate and applying pressure. If inadequate pressure is applied or the processing temperature is too low, bonding faults such as bubbles or detachment can occur. Since these adhesives are not true solids, the strength of pressure sensitive adhesives decreases when the temperature is increased. Pressure sensitive adhesives also exhibit a tendency to undergo creep when subjected to loads. They are typically formulated from natural rubber, certain synthetic rubbers, and polyacrylates.
Pressure sensitive adhesives can be supplied dissolved in organic solvents, as an aqueous dispersion, as a hot melt, or coated on release liner as tape. Liquid applied (solvent or water based, hot melt) pressure sensitive adhesives can be applied in bead or ribbon, sprayed, or roll coated. After coating (and drying of solvent or water based systems), parts can be bonded or the adhesive covered with release liner for bonding later. The adhesive can be coated in a pattern to provide bonded and unbonded areas, e.g. assembly of membrane switches, filter frames. Pressure sensitive adhesives are often used to temporarily hold components like gaskets in position during assembly.
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