MIL-HDBK-1110
Section 2:
COATING COMPOSITIONS AND CURING MECHANISMS
2.1
Coating Composition. The primary ingredients used to
formulate coatings can be placed into one of three basic
categories - solvent, resin, and pigment. Each of these
categories has a special function in the formulation of coatings.
The resin (also called binder) and the solvent comprise the
liquid portion, sometimes called the vehicle. Since the solvent
evaporates as a coating cures, it is sometimes called the
volatile vehicle, and the resin the nonvolatile vehicle. The
resin and pigment which comprise the solid film after evaporation
of the solvent are sometimes called the total solids or film
solids.
Historically, the first paints utilized fish or
vegetable (e.g., linseed) oils as binders and natural earth
pigments. The first solvents were from trees (e.g., turpentine).
Now most resins and solvents are derived from petroleum, and many
pigments are derived from organic synthesis or modification of
natural minerals.
2.1.1
Solvent. Organic solvents are used to dissolve the
resin material and reduce the viscosity of the product to permit
easier application. They also control leveling, drying,
durability, and adhesion. Because the different organic polymers
in different formulations vary greatly in their solubilities,
some resins require much stronger solvents and/or greater amounts
than others to dissolve them. In most water-based coatings, the
water is a dispersing rather than a dissolving agent.
A blend of solvents is generally used in paint to
achieve all the properties desired from them. The blend must
completely dissolve the total binder system and be balanced to
ensure compatibility and stability during all stages of curing.
Improper blends may result in cloudy films, pigment float to the
wet film surface, or reduced film durability.
Paint solvents evaporate into the air and contribute to
the production of photochemical smog. Thus, there is a great
pressure to reformulate coatings to reduce the solvent content of
paints.
2.1.2
Resin. Resins, also called binders, are the film-
forming portions of coatings. They are usually high molecular
weight solid polymers (large molecules with repeating units) in
the cured film. In some cases, lower molecular weight units in
two liquid components react with each other upon mixing to
polymerize into the higher molecular weight solid.
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