Pressure Sensitive Hot Melts (PSA) are unique because they do not solidify to form a solid material, they remain permanently tacky and have the ability to wet-out substrates on contact. Bonds are formed by bringing the PSA adhesive in contact with the substrate and applying pressure. When inadequate pressure is applied or the application temperature is too low, bonding problems such as adhesive creep, bubbles or detachment can occur. PSA’s are not true solids, so the strength of pressure sensitive adhesive decreases when the temperature is increased. Pressure sensitive adhesives also exhibit a tendency to undergo creep when subjected to loads. They are most commonly formulated from natural rubber, synthetic rubbers, and polyacrylates.
Pressure sensitive adhesives can be supplied in many forms such as a water-based or solvent based liquid, a hot melt, or coated on release liner as tape. Liquid applied pressure sensitive adhesives can be applied as a bead or ribbon, sprayed, or roll coated. After PSA is applied, substrates can be bonded or the adhesive covered with release liner for bonding later. The adhesive can be applied in a pattern to provide bonded and unbonded areas.