MIL-PRF-26915D
b. Air drying, high-solids polyurethane for use on exterior metal surfaces.
4.7 Material components tests.
4.7.1 Lead content calculation. Lead content shall be determined by weight of total solids by
ASTM D 3335 (see 3.3.1).
4.7.2 Hexavalent chromium test. Place ½ gram of the primer in a 15 ml centrifuge tube. Add 5
ml of 25% aqueous KOH. Agitate the tube by shaking for one minute, then centrifuge. The
supernatant liquid should be colorless. A yellow color indicates the presence of chromate and
constitutes failure of the product (see 3.3.2).
4.7.3 Volatile organic compounds (VOC) calculation. Calculate the grams of VOC per liter of
coating, less water and less exempt compounds (exempted chlorinated solvents are not permitted
by this specification) by the following equation (see 3.3.3):
W
s - Ww - Wes
, where:
ws
=
weight of volatile compounds in grams
vs - vw - ves
ww
=
weight of water in grams
wes
=
weight of exempt compounds in grams
vs
=
volume of material in liters
vw
=
volume of water in liters
ves
=
volume of exempt compounds in liters
VOC (in g/l) =
4.7.4 Liquid vehicle test. Test the primer for the presence of rosin IAW with ASTM D 1542. A
positive indication of rosin shall constitute failure of the material (see 3.3.4).
4.8 Performance characteristics tests.
4.8.1 Color verification. Visual inspection of panels in 4.6.3.1 and 4.6.3.2 shall verify color
contrast. The color of the primer when wet and when dry shall contrast against bare white metal
(see 3.4.2).
4.8.2 Topcoating properties inspection. Panels from 4.6.3.1 and 4.6.3.2 with primer applied shall
be observed for suitability for topcoating during the preparation of panels for other tests. Panels
topcoated with enamel and polyurethane shall be observed for any tendency towards intercoat
adhesion failure during evaluation of adhesion, warm water immersion, humidity resistance , and
salt spray resistance. Any appreciable primer to topcoat separation shall be considered evidence
of unsatisfactory topcoating properties (see 3.4.3).
4.8.3 Pot life test. A sample of the mixed primer, reduced to spraying viscosity IAW with the
manufacturer's instructions, shall stand for four hours. The primer shall be covered during the
four hours. Occasional stirring is permitted to maintain emulsion and suspension. The pot life is
acceptable if the viscosity does not exceed 25 seconds in a number 2 Zahn cup after the elapsed
time (see 3.4.4).
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