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An adhesive is a substance that holds or binds two different surfaces together. There are different types of industrial adhesive, and they are usually classified according on the basis of their adhesive properties, composition, or cure mechanism. Cure mechanism refers to the process of hardening of the adhesive by means of chemicals, heat, or ultraviolet light. The ways in which resin is used as an industrial adhesive depends on its physical and chemical properties.
Resins are polymers of synthetic origin. A polymer is a large molecule formed by the combination of smaller molecules. Resins can be classified into thermoplastic and thermosetting. Thermoplastic resins can be re-molded at high temperatures, and when cooled, they become rigid. On the other hand, thermosetting resins cannot be re-molded after the curing process.
Thermoplastic adhesives such as polyvinyl acetate (PVA), cyanoacrylate or superglue, silicone resins, and polyamides are used as industrial adhesives. These resins are oil resistant, but exhibit poor resistance to heat, water, and creep under high loading. This type of industrial adhesive can bind most materials, such as wood, ceramic, metal, and laminates. They are widely used in applications such as screw lock assemblies.
Some of the most common thermosetting types of industrial adhesive are epoxy resins, polyurethranes, and phenolic resins. Similar to other thermosetting resins, epoxy resins can be hardened using catalysts, hardeners, heat, or ultraviolet light, depending on the specific industrial requirement. A high-performance structural adhesive has very high chemical and heat resistance, particularly those cured at extremely high temperatures.
Epoxy adhesives are widely used in the aircraft and automobile industries. Polyurethrane resins cure fast and can even bond concrete surfaces. Phenolic resins are mainly used in the manufacture of plywood.
On the basis of the curing mechanism, adhesives can be classified into physically hardening, chemically hardening, and pressure sensitive resins. Hot-melt adhesives, plastisols, water-based adhesives, and organic solvent adhesives are different types of physically hardening industrial adhesive. In particular, this category includes adhesives that can be melted, such as thermoplastics.
Hot-melt adhesives are mainly used in the furniture, packaging, and electronics industries. These solid adhesives usually soften on heating; they evenly wet the substrates in contact with them, and solidify on cooling. Plastisol is an industrial adhesive that is widely used in the vehicle industry. Water-based adhesives are easy-to-clean adhesives that contain polymers dissolved or dispersed in water. Wet bonding adhesives and contact adhesives are two classes of water-based polymer adhesive.
Chemically hardening industrial adhesive requires a chemical reaction for bonding of two surfaces. These adhesives are classified into single-component and two-component adhesives. Single-component resins are further classified into heat cure, moisture cure, and radiation cure adhesives, and anaerobic adhesives and cyanoacrylates. These adhesives are primarily used in the automotive industry, optics, microelectronics, and medical industry. Urethane adhesive, epoxies, and silicon adhesive are different types of two-component adhesives.
Pressure sensitive resins facilitate bonding between surfaces by the application of sufficient pressure. These resins are mainly used in filter frames and membrane switch assemblies. In some cases, pressure sensitive resins are designed to be easily removable.