Technical data

mixed with a base material prior to application, starting a
chemical reaction that continues after application to develop
a film with good performance characteristics. The Air Force
uses Specification MIL-PRF-23377 and MIL-PRF-85582
primers.
6.9.7 Polyurethane. Polyurethane resins are also cata-
lyzed coatings. The Air Force MIL-PRF-85285 polyurethane
coating, is characterized by its very high gloss retention in
gloss finishes and its flatness in camouflage finishes, its
superior toughness and outdoor durability, and good chemical
resistance.
6.10 ADHESION.
Good adhesion of organic coatings requires a surface that is
mechanically and chemically clean. A smooth or highly
polished surface will have very poor coating adhesion and
should be roughened to provide “tooth” for physical bonding.
Adhesion to smooth materials such as glass is difficult and
surface etching is essential. With plastics etching may be
augmented by solvent activation to obtain some degree of
fusion with the surface. Metal surfaces require an appropriate
surface preparation such as conversion coating for adequate
primer adhesion.
6.11 PRIMERS.
Primers are used to provide an adherent coating to which
subsequent coatings will firmly adhere and to provide corro-
sion protection for metals. The pigment portion of primers for
ferrous base metals usually consists of iron oxide, strontium
chromate, zinc chromate, zinc oxide, zinc dust, or a mixture
of these. Zinc or strontium chromate is the principal pigment
in primers used on aluminum, magnesium, and their alloys.
Primers are satisfactory for corrosion protection of metals,
but are generally not suitable as topcoats. Color, weathering
properties or physical durability may be unsatisfactory; and
for these reasons, primers require protection by topcoating.
6.12 COATINGS AND COATING SYSTEMS.
Some examples of specification coatings are as follows:
NOTE
Because of the large number of Military and
Federal Specifications approved for Air Force
use, no attempt has been made to discuss all of
them in this technical manual. In addition, many
items of Air Force equipment and components
are coated with proprietary materials making
logistic support of such equipment difficult. Ev-
ery effort should be made by responsible person-
nel to select standard Air Force approved speci-
fication material for overcoating or replacing
these proprietary materials.
6.12.1 USAF Standard Polyurethane Aircraft Coating
System. (See Chapter 8, aircraft -23 or other weapon
system specific TO’s, and paint drawings for schemes, colors,
and markings.) Optional standard polyurethane coating sys-
tems consist of epoxy primer MIL-PRF-23377, water reduc-
ible epoxy primer MIL-PRF-85582, polyurethane primer
TT-P-2760, or polysulfide primer PR-1432GV, topcoated
with high solids polyurethane coating MIL-PRF-85285, Type
I. Additionally, a light dust coat may be utilized for the
reapplication of MIL-PRF-85285, Type I over an existing
coating. Most coatings formulated for these specifications are
two-component materials intended for spray application.
NOTE
• Before applying a material, spray it on an
aluminum panel to determine its suitability.
Observe the panel for blushing, sagging, or
other defects detectable during or shortly after
application. Correct the cause of any defect
found before continuing. This test panel is in
addition to the one coated simultaneously with
the aircraft and used as a check of the com-
pleted job.
• Epoxyies and polyurethanes cure (chemically
react) rather than dry by evaporation. Use only
clean equipment for mixing and applying the
system to prevent contamination of the mate-
rials. Clean the equipment immediately after
use with a suitable solvent before the coatings
set up.
• Cure accelerators are not authorized for use in
painting aircraft exterior surfaces as they make
coatings brittle.
• Inadequate mixing or mixing in the wrong
proportions causes poor adhesion, slow or
incomplete curing, and poor performance of
the coating.
6.12.2 Primer Coating, Epoxy, For Aircraft Applica-
tion, Specification MIL-PRF-23377.
6.12.2.1 Characteristics. This is a two-component, low
VOC, solvent-borne, lead free corrosion inhibiting epoxy
primer particularly formulated for its adhesion properties. It
is compliant with the NESHAP VOC requirements of 340 g/l
(2.8 lbs/gal). It is very resistant to chemicals, lubricants, and
corrosive atmospheres; but it has only fair weathering char-
acteristics. Because it is an epoxy, this primer is difficult to
remove with standard paint removers. This primer is available
in two different types each with two different classes.
Type I Standard pigments (yellow).
Type II Low infrared reflective pigments (dark
green).
TO 1-1-8
6-6