Moisture Sensitivity of Isocyanates
309551C
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Moisture Sensitivity of Isocyanates
Isocyanates (ISO) are catalysts used in two component
foam and polyurea coatings. ISO will react with moisture
(such as humidity) to form small, hard, abrasive crystals,
which become suspended in the fluid. Eventually a film
will form on the surface and the ISO will begin to gel,
increasing in viscosity. If used, this partially cured ISO
will reduce performance and the life of all wetted parts.
To prevent exposing ISO to moisture:
•
Always use a sealed container with a desiccant
dryer in the vent, or a “nitrogen blanket.”
Never
store
ISO in an open container.
•
Keep the wet-cup of the pump filled with Graco ISO
pump oil, Part No. 217374. The lubricant creates a
barrier between the ISO and the atmosphere.
•
Use moisture resistant hoses. The component A
(ISO) hose must be constructed of polyethylene
(PE),
polyolefin, or moisture-proof rubber
compounds.
•
Never use reclaimed solvents, which may contain
moisture. Always keep solvent containers closed
when not in use.
•
Always park component A pump when you shut-
down, see page 13.
Spray Adjustments
Flow rate, atomization, and amount of overspray are
affected by four variables.
•
Fluid pressure setting.
Too little pressure results in
an uneven pattern, coarse droplet size, low flow, and
poor mixing. Too much pressure results in excessive
overspray, high flow rates, difficult control, and
excessive wear.
•
Fluid temperature.
Similar effects to fluid pressure
setting. The A and B temperatures can be offset to
help balance the fluid pressure.
•
Mix chamber size.
Choice of mix chamber is based
on desired flow rate and fluid viscosity.
•
Cleanoff air adjustment.
Too little cleanoff air
results in droplets building up on the front of the
nozzle, and no pattern containment to control over-
spray. Too much cleanoff air results in air-assisted
atomization and excessive overspray.
The amount of film formation and rate of crystalli-
zation varies depending on the blend of ISO.
PTFE
PTFE
