PUR reactive hot melts form a permanent bond by reacting with moisture. That same property means adhesive left in tanks, hoses and nozzles can cure. The right cleaning procedure extends machine life and prevents unplanned stoppages.
Golden rule: keep moisture out
PUR only cures when it contacts moisture. In closed melt systems (drum, cartridge or pail melters) the adhesive can wait for days without trouble. Open-tank systems form a thin skin quickly.
Short stops (breaks, shift change)
- Lower the tank to standby temperature (usually 80–100 °C).
- Close the nozzle or fit its protective cap.
- After a long wait, purge some adhesive before the first parts.
Weekends and long stops
- Run down the PUR level towards the end of production.
- Push out the remaining adhesive with a PUR flushing agent containing an additive that stops the reaction.
- Make sure the whole system is filled with flushing agent.
- On restart, fully purge the flushing agent with fresh PUR.
Switching between EVA and PUR
Never mix adhesive types. Flush the system first, then fill with the new adhesive. Residues can reduce the new adhesive's performance.
Nozzle and applicator head cleaning
Slot nozzles and applicator heads should be removed and cleaned with the manufacturer's recommended cleaner. Wire brushes or sharp tools can scratch precision surfaces.
Safety note
PUR adhesives contain isocyanate. Ensure good ventilation and wear gloves and safety glasses during application and cleaning. Low-monomer (MR) grades that need no hazard labelling greatly reduce this risk.
Contact our technical team for machine-specific cleaning instructions and product recommendations.
