Handbook of Solvents - George Wypych - ChemTech - Ventech!

1030 Mohamed Serageldin, Dave Reeves
Thinner &
cleaning
solvents
Typical coating
Lacquer
retarder (thinner)
& cleaner
(slow) b
Lacquer
Compound,
wt%
Solubility parameter,
(cal/cm 3 ) 1/2
Relative rate,
nBUOAc =1.0
Vapor press., mmHg
@20 o C
B.P., o C @ 760
mmHg
Surface tension,
dynes/cm 20 o C
EGBE, 51% 10.2 0.072 0.6 >169 26.9 0.899 3.0
AHC, 30% 7.7 0.16 2.0 >160 23.4 0.775 0.88
1,2,4-Trimethylbenzene, 16% 8.9 19 2.1 168 30.2 0.871 0.94
Xylene (mixed), 1% 9.9 0.77 6.0 >135 27.6 0.856 0.63
*MEK=methyl ethyl ketone, **MIBK=methyl isobutyl ketone, ***EGBE=ethylene glycol monobutyl ether,
****AHC=aromatic hydrocarbon solvent; a Physical properties mainly from Industrial Solvents Handbook, 110
-114. b Material Safety Data Sheet (Mobile Paint Co. Alabama)
The lower specific gravity of ketones (see Table 14.26.2) than other materials such as
glycol ethers helps reduce total mass of VOCs (or HAPs) per volume of nonvolatiles (solids)
in a container of coating. Glycol ethers are good solvents for epoxies and acrylics. They
also have good coupling abilities in blends of poorly miscible solvents 17 and have low evaporative
rates. The properties of a solvent product are dependent on the chemical structure
and distillation range of the solvent mix in the product. The latter will affect the evaporative
rate from a coating or cleaner, affecting the solubility of the resin in the coating and viscosity
of the coating and solvent cleaner. Therefore, the viscosity of the solvent product must
be close to that of the resin in a coating. 18 The surface tension of a solvent provides a measure
of the penetrability of a cleaning solvent. A low surface tension also means the solvent
spreads more readily, which is an important property for a cleaning product. However, several
properties in Table 14.26.2 come into play in determining the effectiveness of a cleaning
solvent.
Most coating operations, due to the size and accessibility of ships, occur in open air in
drydocks, graving docks, railway, or other locations throughout a facility. Because of the
size of ships, the predominant application method is airless spray guns. The thickness of the
coating will determine if the application equipment needs to be cleaned during application
of the coating or after the job is completed. The lines from the supply tanks to the spray gun
may in some instances exceed 46 m (150 ft) in length. The ensemble of equipment and items
that have to do with the application of the coating or “unit operation system (UOS)” is
shown schematically in Figure 14.26.1. The representation depicts a layout for outdoor application
of coatings. It includes the container used to hold the coating, attached feed pump,
line transferring the coating to the spray gun, the spray gun itself, and any other item soiled
with a coating that will need to be cleaned with organic solvent before it can be reused.
The need and frequency for cleaning will depend on the individual facility or company
cleanliness standard (i.e., requirements) and the number of coating formulation or color
changes. Cleaning of spray guns, internal transfer lines, and associated tanks account for a
large part of organic solvent usage. At most shipyards, a small percentage of the coatings
are applied indoors, in spray-booths. The walls and floors of these booths are cleaned by
wiping with a solvent laden cloth. The coating application equipment UOS for most facilities
will look very similar to that shown in Figure 14.26.1, except that the coating transfer
Av. sp. gr, @ 25 o C
Viscosity, cP @ 25 o C