By TEJASH MAJMUDAR

Polyurethane reactive (PUR) adhesives have revolutionised flat lamination processes in woodworking and manufacturing. This moisture-curing type of adhesive offers exceptional bond strength, water resistance and heat resistance, making it ideal for demanding applications.

PUR adhesives excel in flat lamination applications due to several unique properties, among them their superior moisture and heat resistance, compared to traditional adhesives.

They offer excellent bond strength on difficult-to-bond materials; they need low application temperatures (110-150°C) and amounts (40-100 gram per square metre).

They also offer clear glue lines; long shelf life when properly stored; and give out no formaldehyde emissions.

PUR adhesives effectively bond with wood and wood-based products, high-pressure decorative laminates, PVC and other plastics, metal foils, paper-based materials and mineral-based substrates.

Application guidelines

Among the pre-application requirements are material conditioning (65-75°F and 45-65% relative humidity for 48 hours); clean, dry and dust-free surfaces; and material moisture content of 6-12% for wood products.

During application, ensure proper adhesive temperature (110-150°C), maintain consistent pressure (30-100 PSI), and allow adequate cure time (24-48 hours) for full strength.

Some critical parameters to keep in mind during application is their pot life (20-30 minutes once exposed to moisture), open time (3-5 minutes), press time (20-60 seconds depending on materials) and cure time (initial 2-4 hours, full cure 24-48 hours).

For safety during application, the user must wear appropriate personal protective equipment, including heat-resistant gloves, safety glasses, long-sleeved clothing and respiratory protection when sanding or machining.

The workplace must have adequate ventilation, clean work area, emergency eyewash station, and ready-at-hand first aid supplies.

Common troubleshooting

For poor bond strength, check material moisture content, verify surface cleanliness, ensure proper application temperature, confirm adequate pressure and validate cure conditions.

To avoid crystallization of adhesive, store at recommended temperature (65-75°F), use heating chamber to reconstitute solution, and maintain proper application temperature.

In case of inconsistent coverage, clean the application equipment, check for proper adhesive temperature, verify proper amount of glue, and ensure uniform pressure.

Equipment maintenance is the most important in application. This can be done by purging the system with cleaner, clean application heads, check temperature controls and inspect hoses and connections daily.

Deep clean all components, check seals and gaskets, calibrate temperature sensors and verify pressure settings periodically.

Quality control measures include production testing for bond strength verification, uniform coverage checks, temperature monitoring and pressure consistency validation.

The products must undergo cross-cut testing, water and heat resistance verification, and aging performance evaluation.

PUR adhesive technology provides superior performance for flat lamination applications when properly applied and maintained. Success depends on careful attention to material preparation, application parameters, and on proper maintenance procedures.

Regular quality control and proper safety measures ensure consistent, high-quality results.

– To be continued. The writer has more than three decades of experience in the woodworking industry, with proficiency in machinery, hardware, tooling and adhesives. He can be contacted on tejash@totaltoolsin.com.

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