Technical data

resistance superior to conventional polyurethane topcoats.
Although some degradation in fade resistance will occur if
APC is applied over PR-1422GV elestomeric polysulfide
primer, color retention still exceeds MIL-PRF-85285 require-
ments.
6.12.7.4 Mixing.
• The catalyst portion of polyurethane topcoat
contains a resin that may contain up to one
percent Hexamethylene Diisocyanate (HDI).
This material is a sensitizing agent and in low
atmospheric concentrations is a strong respi-
ratory and skin irritant. After the catalyst
portion containing HDI is mixed with the
polyester resin base component, the HDI re-
acts chemically with the resin base and the
potential for generation of HDI is significantly
reduced. Personnel mixing the isocyanate
catalyst component with the polyester resin
base component must avoid the vapors and
skin contact of these materials. Mixing shall
be done in exhaust ventilated booth or well
ventilated area.
• Personnel shall wear plastic or rubber gloves,
plastic apron, and a face shield. Requirement
for respiratory protection during mixture and
application procedures shall be determined by
Bioenvironmental Engineering.
• Even after the polyurethane components have
been mixed as noted below, painting with the
polyurethane paint, Specification MIL-PRF-
85285 still may result in a significant health
hazard to the painter. Respiratory protection
shall be specified by the local medical service
based upon the process evaluation by Bioen-
vironmental Engineering. Also, it is important
that all the precautions required for spray
painting as outlined in AFOSH STD 91-17 be
rigidly enforced. Personnel with histories of
allergies or asthma shall be cleared through
the base medical services before using any
material containing diisocyanates.
Since the polyurethane is sensitive to moisture,
ketones, and alcohols, use only clean, dry equip-
ment for mixing and keep the mixed material in
closed containers. Use adequate oil and water
separators between the air supply and pressure
pot to exclude water. Water reacts with the
catalyst and liberates carbon dioxide, causing
bubbles and craters in freshly applied polyure-
thane paint. In addition, blow down air lines at
least every hour to remove water. Reaction of
catalyst with water is evident by an accelerated
rate of increase in viscosity.
Thoroughly agitate the resin component (preferably with a
mechanical shaker) and stir the catalyst with a wooden paddle
in an exhaust ventilated booth or a well ventilated area and
pour into separate metering containers. Mix three parts resin
(Component A) with one part catalyst (Component B) by
volume, unless otherwise specified by the manufacturer, and
agitate thoroughly. Induction time (dwell time) or a waiting
period is not required before applying the coating. Use only
catalyst and resin from the same manufacturer and the same
lot, and do not mix more material than will be used in a
4-hour period. It is preferable, however, that the amount of
material mixed at one time be limited to that usable in two
hours. This polyurethane coating requires continuous agita-
tion during spraying application to prevent settlement of
pigment and ensure uniformity of color.
6.12.7.5 APC Mixing. Follow mixing instructions in
Paragraph 6.12.7.4.
NOTE
Do not use catalyst (component B) from standard
MIL-PRF-85285 coatings or catalyst from other
APC colors.
TO 1-1-8
6-12