Views:25 Author:Site Editor Publish Time: 2019-11-19 Origin:Site
This article first reviews the key materials properties that are required generally for hot melt adhesives. The formulating principles and potential product possibilities available with EVA hot melt adhesives are then reviewed, and starting formulations are offered for specific applications. Key Material Properties Required for Hot Melt Adhesives Hot melt adhesives facilitate fast production speeds because the adhesives set simply by cooling from a molten liquid to a cohesive solid. Hot melts do not require processing time for evaporation of solvents or water carrier or for a chemical reaction to occur. This also generally results in lower energy and maintenance costs. Hot melt formulations contain polymers to provide strength and hot tack, and tackifiers and oils or plasticizers to reduce melt viscosity, adjust glass transition temperature, and improve wetting. Some formulations also contain waxes to speed setting and further reduce viscosity. These additives are generally high concentrations (comparable to the base polymer) in hot melt adhesive formulations. Fillers are also used to increase melt viscosity to reduce excessive penetration into porous substrates and to modify cohesive properties. Antioxidants are generally added to prevent thermal oxidation during processing and service. Additives often consist of blends of two or more materials to optimize certain properties. A typical EVA hot melt formulation for packaging is indicated in Table 2.