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Hot Melts

Hot melt adhesives are one-part solvent-free thermoplastic adhesives that are solid at room temperature and a low to medium viscosity (750-10,000 cP) adhesive at dispense temperatures (typically greater than 175°C). After dispense, hot melt adhesives rapidly cool to form a strong bond. In the cured or cooled state, hot melt adhesives can vary in physical properties from soft, rubbery and very tacky to hard and rigid. Hot melts have excellent long term durability and resistance to moisture, chemicals, oils, and temperature extremes.

The performance of the hot melt varies widely based on their chemistry:

Ethylene vinyl acetate (EVA) hot melts are the “original” hot melt. They have good adhesive to many substrates, the lowest cost and a wide range of open times, but typically have the poorest temperature resistance.

Polyamide hot melts are a higher cost, higher performing adhesive with excellent high temperature resistance (up to 300°F). Specialty formulations are available that carry a UL-94 V-0 flammability rating.

Polyolefin hot melts are specially formulated for adhesion to polyolefins such as polypropylene and polyethylene plastics. Compared to other chemistries, they have longer open times and they have excellent resistance against polar solvents.

Reactive polyurethanes (PUR) are supplied as an urethane prepolymer, behaving much like a standard hot melt until it cools. Once the PUR cools, it reacts with moisture over time (a few days) to crosslink into a tough thermoset polyurethane. They offers lower dispense temperatures, higher adhesion to metals and improved thermal resistance.

Advantages
• One-part, solvent-free
• Fast fixturing
• High adhesion to plastics
• Wide variety of formulations available
• Low volumetric cost

Considerations
• Hot dispense point
• Poor adhesion on metals
• Cools quickly
• Equipment is required
• Thermoplastic parts may deform
• Charring in reservoir
• Moisture sensitivity

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