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Pressure Sensitive
Pressure sensitive adhesives
Pressure sensitive adhesives (PSA) form a link by the use of light force to bond the adhesive with the substrate. They are designed with a balance between flow and resistance to flow. The bond forms as the glue is soft enough to flow the substrate. The joint has strength because the glue is firm enough to resist flow when stress is applied it. Once the adhesive and the adherend are in close proximity, molecular interactions, such as Van der Waals forces, become involved in the joint, contributing considerably to its ultimate strength.
PSAs are planned for either everlasting or removable applications. Examples of permanent applications include safety labels for power equipment, foil tape for duct work, automotive interior trim assembly, and sound/vibration damping films. A number of high performance enduring PSAs exhibit high adhesion values and can hold up kilograms of mass per square centimeter of contact area, even at elevated temperature. Permanent PSAs may be at first detachable (for example to recuperate mislabeled goods) and build adhesion to a permanent bond after some hours or days.
Removable adhesives are designed to form a temporary joint, and ideally can be detached after months or years with no remains on the substrate. Removable adhesives are used in applications such as surface protection films, masking tapes, bookmark and note papers, price marking labels, promotional graphics materials, and for skin contact (wound care dressings, EKG electrodes, athletic tape, analgesic and transdermal drug patches, etc.). Some removable adhesives are formulated to repetitively stick and unstick. They have low bonding and generally can not support enough weight.
Pressure sensitive adhesives are produced with either a liquid carrier or in 100% solid form. Articles are made from liquid PSAs by coating the adhesive and drying off the solvent or water carrier. They may be further heated to initiate a cross-linking outcome and step up 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 glue; or they may be high viscosity materials that are heated to reduce viscosity enough to permit coating, and then cooled to their ultimate form. Major raw material for PSA´s are acrylate based polymers.