MIL-HDBK-1110
c) Formulating oil-based coatings with low-solvent
content presents difficulties and requires major formulation
changes from those used for high-solvent coatings. Thus,
attempts are also being made to develop waterborne alkyd
products.
2.2.2
Solvent of Water Evaporation. Coatings that cure by
simple evaporation of organic solvent are sometimes called
lacquers. They are made by dissolving solid resins in an
appropriate solvent. After application of a lacquer, the solvent
evaporates to deposit the resin in a thin film. No chemical
change occurs in the resin.
a)
Examples of coatings that cure by this mechanism
are:
(1)
Shellacs
(2)
Vinyls (polyvinyl chlorides)
(3)
Chlorinated rubber
(4)
Acrylics
(5)
Bituminous coatings (coal tars and asphaltics)
b) Coatings of this type have poor solvent resistance,
since they are deposited from a solvent, but are easy to topcoat
and repair because the topcoat solvent bites into the undercoat
to bond tightly. Because lacquers are high in solvent content,
that is, volatile organic compounds (VOC), their use has been
greatly curtailed.
c) Latex and many other waterborne coatings also cure
by simple water evaporation. Emulsified particles of solid resin
coalesce to form a film as the water is lost. These coatings
usually contain some organic solvent to control curing and
improve application properties. Latex films are quite flexible
and tend to be more permeable than oil and alkyd films. Examples
of latex coatings are:
(1)
Acrylics
(2)
Vinyls (polyvinyl acetates)
d) At this time, it is important to point out that
there are other types of waterborne coatings that cure by
mechanisms other than simple water evaporation. The three basic
types of waterborne coatings are:
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