Technical data

CHAPTER 6
USAF STANDARD COATING SYSTEMS FOR AIRCRAFT AND EQUIPMENT
6.1 CLASSIFICATION OF ORGANIC COATINGS.
Customarily, finishing materials are classed as paints, enam-
els, lacquers, and special coatings such as epoxies and
polyurethanes. The word “paint” is loosely used to mean all
finishing materials. Modern coatings now include quite dif-
ferent components in combinations that do not fall into the
old categories. Coating materials used by the Air Force are
generally identified by the basic classifications above. Gen-
eral information on materials in these categories used by the
Air Force is presented here.
NOTE
• National Stock Numbers (NSNs) for specific
coatings and related materials are to be ob-
tained from FSC (normally FSC 8000). Also,
see the current GSA Catalog and the DO43
System to convert specification and part num-
bers to NSNs.
• To determine the proper paint system for
specific equipment, refer to -23 TO’s, and
aircraft paint drawings, for aircraft; TO 35-1-3
for support equipment; or specific repair TO’s.
6.2 CONSTITUENTS OF ORGANIC COATINGS.
Modern paints may be a mixture of many things, but the
primary constituents are pigment, vehicle (the film former)
and solvents. Secondary components (although they may still
be of prime importance) may be extenders, driers, anti-
oxidants, surfactants, light-filtering agents, and/or other ad-
ditives. When special properties are required such as lumi-
nescence, fluorescence, fire retardant, etc., materials to
provide these are also added.
6.3 PIGMENTS.
Pigments are finely divided, substantially insoluble, and
usually opaque materials incorporated into paints to provide
color, hiding power, and specific qualities such as light and
heat reflectance (or heat absorption), corrosion-inhibition,
and certain flow characteristics. Pigments may be inorganic
or organic types and of either natural or synthetic origin.
Examples are the metallic compounds such as zinc oxide and
titanium dioxide in white and light tinted paints, zinc chro-
mate in primers to give yellow coloration and act as a
corrosion inhibitor, chromium oxide for green, iron oxide for
red, etc. Synthetic agents or dyes are also widely used. A
limited number of pigments are used as corrosion inhibitors
in protective primers. The particular pigment used depends
upon the metal that is to be protected, steel, aluminum,
magnesium, etc., and the environment to which it is to be
subjected.
NOTE
The theoretical function of a protective paint is to
physically exclude environment from the metal
surface; but, practically, it rarely succeeds en-
tirely. All organic films are moisture permeable to
some degree. Also, tiny physical defects in a film
are usually present to some degree or develop in
time. General practice is to supplement the physi-
cal protective properties of coatings with materi-
als that provide electrochemical protection either
by using surface conversion coating treatments
(refer to Chapter 3) or wash primers, or by
inclusion of corrosion-inhibiting pigments in the
primer coatings.
6.4 VEHICLE.
The vehicle is the liquid portion of the coating. It is the most
significant part of the coating as it furnishes desired qualities
of adhesion, toughness, flexibility and resistance to various
environments. The vehicle consists of non-volatile and vola-
tile portions. The non-volatile includes resins, drying oils and
plasticizers that become the binding agent in the cured film.
Upon evaporation of the volatile portion, the non-volatiles
form the actual film on the surface together with the pigment,
if one is present. Vehicles appear in a multitude of combina-
tions, containing many materials. A varnish vehicle in enam-
els generally contains an oil-modified alkyd resin, thinners
and driers. A lacquer vehicle consists mainly of resins,
solvents and plasticizers.
6.5 PREPARATION OF COATING MATERIALS FOR
USE, GENERAL.
Containers of paint may develop internal pressure
during storage and should be opened with
caution.
Coating materials shall be prepared for application under
clean conditions with clean equipment. Paint shops shall be
equipped with mechanical paint agitators of suitable capacity.
The proper sequence for preparing packaged materials prior
to each use is as follows:
TO 1-1-8
6-1