Technical data

of color or flow will indicate incomplete mixing. Comparison
of materials from the bottom and top of a container may be
made by this method.
6.7 SOLVENTS, DILUENTS AND THINNERS.
At ordinary room temperatures, the consistency or viscosity
of mixtures of oils, pigments, and resins that make up coating
materials is too high to allow spreading them effectively over
surfaces in the desired thickness. Also, most resins are solids
and need to be dissolved in a liquid before they can be
dispersed. A solvent has the essential function of reducing the
viscosity of the vehicle portion of the material to the point
where it can be managed. Solvents do not react chemically
with coating constituents or dissolve pigments; and ulti-
mately, they are lost from the coating by evaporation having
served their purpose. Most solvents are organic materials and
are classified by their chemical structure as alcohols, esters,
ketones, etc. In practice, they must be considered from the
standpoint of their powers of solvency as expressed in
reference to some material. A liquid may dissolve one
substance well, another poorly, and still others not at all.
There is no universal solvent in coating technology. A liquid
that does not actually dissolve a given substance may,
however, be used as a diluent or a thinner for that substance.
Solvents and diluents are frequently used together in coating
formulations, and the purpose of a liquid determines whether
it is “solvent” or “diluent”. For example, mineral spirits is a
solvent for linseed oil, but not for cellulose nitrate. But
solutions of cellulose nitrate in butyl acetate will tolerate
substantial amounts of mineral spirits and here the mineral
spirits is used as a diluent for the solution. Diluents and
thinners are normally less expensive than solvents. Generally,
the solvent portion of a coating is itself a blend of solvents,
each one chosen for its power to dissolve a particular
constituent of the coating, and each present in proper propor-
tion to regulate evaporation to a rate that prevents premature
segregation of any single dissolved constituent.
NOTE
• Although in practice the terms solvent, dilu-
ent, and thinner are often used interchangeably
to describe a liquid, it should be understood
that, the words have different meanings; and
the mechanism of solvents and diluents or
thinners are different. For example, a solvent
will thin incidentally while performing its
prime purpose of dissolving something;
whereas a diluent or thinner is used to reduce
viscosity and/or regulate evaporation and is
not required to, and may be unable to, dissolve
any constituents of the coating concerned. Of
course, thinner must be compatible with the
coating. Compatibility is beyond determina-
tion in the field; hence, only authorized thin-
ners specifically called out for use with a given
coating shall be used to thin it.
• To distinguish between “diluent” and “thin-
ner”, the material added by the manufacturer
to adjust viscosity is called a “diluent”, while
the same material added by the painter for the
same purpose is called “thinner”.
6.7.1 Volatility. Volatility is the rate at which a solvent
evaporates, governs the length of time a paint film remains
fluid. Thus, it affects performance characteristics of the paint
film when deposited, such as smoothness of flow-out, time an
edge remains wet to enable blending of overlapped strokes of
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