Pressure-sensitive adhesives (PSAs) are recognized as adhesives that are permanently tacky at room temperature and adhere to substrates with minimal pressure. In other words, they have an infinite open time to allow for bonding to a substrate.

Hot-melt PSAs are a type of PSA that are produced and processed in a molten state at high temperatures and then solidify upon cooling. Styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS) block copolymers are used as the base polymers for hot-melt PSAs. SIS copolymer is the most common material used in hot-melt adhesives, as it becomes tacky more easily than other types. This copolymer consists of a polyisoprene block between two polystyrene blocks. Due to the unsaturated bonds in the polyisoprene block's polymer structure, the resulting copolymer has low resistance to environmental conditions. At room temperature, the polystyrene block behaves as a glassy material, while the polyisoprene block behaves as a rubbery material. Important influencing factors include the molecular weight of the isoprene and the molecular weight of the terminal styrene. Therefore, a range of SIS copolymers from soft to hard can be prepared.

The formulation of pressure-sensitive adhesives is based on combining polymers with resins and/or oils, antioxidants, and plasticizers. The base polymer provides suitable strength and elasticity. Resins provide the elastomeric phase and allow the adhesive to conform to the substrate during the bonding stage. They also adjust the glass transition temperature of the elastomer phase, which stiffens the adhesive layer and increases resistance to delamination from the substrate. Antioxidants are used to prevent or reduce the oxidation and degradation of hot-melt adhesive polymers during processing and to improve adhesive stability and shelf life. Plasticizers add more flexibility to the adhesive and help it to be softer.

PSA systems are highly adaptable and generally form a good bond with surfaces while being able to be removed from the substrate without leaving residue. The most important point in selecting the appropriate resin (Tackifier) is its compatibility with the base polymer in the adhesive formulation, as it will significantly affect the final properties of the PSAs.

The parameters of tack, peel resistance, and shear resistance describe the nature of pressure-sensitive adhesives. The Tack parameter measures the adhesive's ability for rapid adhesion, the Peel parameter measures its ability to resist removal by peeling, and the Shear parameter measures its ability to hold in place when shear forces are applied.

Beneficial features of hot-melt pressure-sensitive adhesives include good strength, cost-effectiveness, high processing speed, non-toxicity, water resistance, resistance to most acids and bases, and the ability to bond to most substrates, including plastics. These adhesives are durable over time and resistant to physical and chemical factors that can damage them.

Hot-melt adhesives are solvent-free, and their advantages include the elimination of solvents and the absence of volatile organic compounds (VOCs), non-flammability, increased safety during work, and recyclability. Due to their lack of pollutants, they are considered environmentally friendly.

Hot-melt pressure-sensitive adhesives are a suitable choice for hard and non-porous substrates, and are used by a wide range of industries, including automotive parts and equipment, other household goods industries, packaging, labels, printing and bookbinding, cellulose, and woodworking. Unlike other adhesives, hot melts do not damage the substrate and are used for a wide range of automatic and semi-automatic machinery.

Based on the needs of various industries, the Iran Industrial Resins Co. is recognized as the first producer of hot-melt (or thermal) adhesives based on ethylene vinyl acetate (EVA) in the country. This company also produces hot-melt adhesives based on polyolefins (APAO, POE) and rubbers (SIS, SBS, etc.).

A wide range of products from the Iran Industrial Resins Co. are provided in molded form and meet the ever-changing needs of various industries in the country, as follows: