MIL-HDBK-1110
c) Another example of a chemically curing coating is
an inorganic zinc coating. Different formulations may cure by
different types of reaction. Usually the cure reaction involves
the hydrolysis (reaction with water vapor from the atmosphere) of
the silicate binder. Some cure by reaction with water from the
air, and thus cure slowly in dry environments. A one-package
water-based inorganic zinc coating cures by chemical reaction
after evaporation of the water.
d) Zinc-rich organic coatings, on the other hand, cure
by the mechanism of curing of their organic binders. Thus, zinc-
rich epoxies cure by chemical reaction and zinc-rich vinyls, by
solvent evaporation.
2.3
Properties of Different Generic Types of Coatings. The
properties of coatings commonly used on military facilities will
be discussed individually below and then their properties will be
summarized in a series of tables. Special mention will be made
of the ease of formulating each generic type with a low VOC
(solvent) content, since new restrictions on VOC content may
limit or eliminate their use.
2.3.1
Alkyds and Other Oil-Containing Coatings. The
unmodified drying oil coatings initially developed were very
easily applied, did not require a high level of surface
preparation, and had good flexibility; they could readily expand
and contract with the substrate. They did, however, have several
drawbacks: they were slow to dry, had residual tack, and
provided a limited period of protection. They cannot be used in
sea water immersion service or on alkaline substrates (e.g.,
concrete), because they are easily hydrolyzed (deteriorated by
reaction with water) by alkalinity. They are used most on wood
and steel surfaces.
a) Alkyd coatings, prepared by chemically modifying
drying oil formulations, cured much faster than the unmodified
ones and did not have residual tack. They retained the good
application properties, but lost some flexibility. Silicone
alkyds were developed by incorporating silicone into the resin to
provide greater gloss retention. Epoxy esters were another
modification of drying oils that improved some performance
properties, particularly their chemical resistance, but worsened
others, such as gloss retention. Still, none of these were
suitable for a severe environment such as sea water.
Oleoresinous phenolic drying oil formulations could be
successfully used in water immersion.
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