A special feature of PSA (Pressure Sensitive Adhesive) adhesives is that they do not become solid after application or bonding, but remain permanently tacky. It is for this reason that PSA adhesives are also called "pressure sensitive adhesives" or "permanent sticky adhesives". The adhesive bond is formed by mechanically squeezing the materials to be bonded, hence another name "Pressure Sensitive Adhesive".
How Are The Pressure Sensitive Adhesives Produced?
Three common bases are used in the production of pressure sensitive adhesives: rubber, acrylic, silicone. If you are interested in this topic and want to learn more, you can refer to the company Elkem and especially to its blog. The latter is regularly updated and brings you useful information on pressure sensitive adhesives. Generally, PSA adhesives with residual tackiness are designed to bond and maintain an adhesive bond at room temperature. Most adhesives reduce or lose their adhesive strength at low temperatures and their shear stability at high temperatures is reduced. For specific applications, special grades of permanent adhesives have been developed that are resistant to extreme conditions.
There are three main adhesive properties of Pressure Sensitive Adhesive:
1. Initial Tackiness
Refers to the initial adhesion of the adhesive to the substrate. Measured by removing the strip of adhesive immediately upon contact with the surface.
2. Tensile Strength
Defined as the force required to separate surfaces. Adhesion continues to increase after the adhesive has been applied, tests are usually done after 24 hours.
3. Shear Strength
This is the internal or cohesive strength of the adhesive mass. It is defined as the time it takes for a strip of adhesive to fall from a surface under load.
Solvent Based Adhesives
Solvent adhesives of this type are usually acrylic or rubber dissolved in a solvent. When the solvent is applied to the surface, heat and air flow cause the solvent to evaporate, leaving a sticky residue. Solvent-based permanent tack adhesives can usually achieve high performance, but require special working conditions and occupational safety.
Emulsion Adhesives
Waterborne acrylic-based permanent tack adhesives do not require the special safety requirements of solvent-based adhesives and have a wide range of applications. These products, like solvent based tack adhesives, require heat and air flow to evaporate the water. Acrylic pressure sensitive adhesives resist well against: high temperatures, UV radiation, chemicals and exposure to solvents. Also acrylic adhesives tend to have a good resistance to aging, but have a high cost.
Fusion Adhesives
Residual sticky hot melt adhesives are a mixture of polymer, resin, and hydrocarbon diluent. These pressure-sensitive adhesives are heated to a certain temperature and are allowed to flow where they are applied to the material and cool quickly. One advantage of the thermal adhesive technology is the absence of solvents and water, thus avoiding drying.
UV-Curable Adhesives
Environmentally friendly adhesives that contain no solvents or other volatile substances, they cure quickly when exposed to UV rays. Fast curing minimizes shrinkage, ensuring dimensional accuracy that is often required in the electronics industry. UV-curable adhesives are durable, durable, and used for materials that are exposed to: chemicals, high temperatures, sunlight, adverse weather conditions.
