Isocyanate for polyurethane adhesive is extremely sensitive to moisture. When opening a barrel for the first time, care should be taken to ensure the cap or extraction tube are replaced on the bung hole cover. The vent hold in the drum should have a desiccant cartridge permanently fixed to ensure only dry air is exchanged with the adhesive as it is dispensed from the drum.
Allow the PU adhesive and hardener to reach the manufacturers recommended temperatures in the MMD before dispensing onto the metering rolls. Cold adhesive can increase the desired coat weight.
Do not use the adhesive past the expired date. Generally 1 year from manufacture. Isocyanate will lost reactive groups over time and effect final curing and bond strength. Use only new static mixers at the beginning of each day or if the machine sits idle for longer than 45 min. Gear pumps are capable of precise metering on a continuous basis but require attention to ensure they are operating properly and maintain a precise mix ratio throughout the run. Measuring the mix ratio of PU adhesive system manually by separating the adhesive and coreactant from the mix head and weighing the components individually to ensure the ratio is correct is important to do on a daily basis.
The manufacturer will have detailed instructions on how to perform this test. Mix ratios should be set in the machine by volume. Two component PU adhesive system will have its own volume ration and density on the tech data sheet, these should be confirmed with the adhesive manufacturer and input into the MMD separately to ensure correct mix ratio dispensing. Temperatures of the pots and hoses are also important to ensure a smooth delivery of the adhesive and to maintain a consistent mix ratio, coat weight and adhesive appearance.
