Base resin for hot-melt adhesives

The base resin for hot-melt adhesives is EVA resin, produced through the copolymerization of ethylene and vinyl acetate under high temperature and high pressure.

 

This resin is the primary component of hot-melt adhesives; the proportion and quality of the base resin determine the adhesive's fundamental properties, such as bonding capability, melting temperature, and bond strength. Typically, a vinyl acetate (VA) content of 18–33% and a melt index (MI) of 6–800 are selected. Lower VA content results in higher crystallinity and hardness, whereas higher VA content leads to lower crystallinity and increased elasticity. The choice of melt index is also critical: a lower melt index results in poor fluidity, high strength, and high melting temperature, as well as reduced wetting and penetration of the substrate. Conversely, an excessively high melt index results in a lower melting temperature and better fluidity but reduced bond strength. Regarding additives, the selection should be based on an appropriate ratio of ethylene to vinyl acetate.