Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.26 Use of solvents in the shipbuilding 1033
mixing that occurs within the applicator. The thinner is often the same material as the
cleaner (as indicated in Table 14.26.2). The solvent material is often a blend of miscible materials.
Together they will dissolve a dry resin that needs to be removed or give the coating
certain needed properties such as reduced/increased viscosity or shorter drying times.
Standard spraying equipment will apply coatings up to some maximum viscosity.
Above that maximum value, thinning solvents are required. Thinning solvent is sometimes
added to enhance brushability or sprayability of a coating. The appropriate viscosity is provided
by the coating manufacturer or supplier; it will depend on the solvent content of the
coating and temperature at the point of application. 26 Since most coatings are applied outdoors,
extreme weather conditions may require adding thinning solvents to the coating. Organic
thinning solvents are added to coatings to alter their flowing properties. However, the
flow properties of a coating may be altered by using special heaters or a combination of solvent
and heat. The effect of a heater on the viscosity of a coating depends on the physical
properties of the coating and on the flow rate in the in-line heater. Under cold weather conditions,
in-line heaters may provide good viscosity control, but may not be able to solve all
application problems that are encountered in the field. Under extremely low temperatures,
the substrate surface can act as a heat sink, which may inhibit the setting or curing of the
coating. In-line heaters which are used for low volume coatings are not suitable for large
volume coatings. As a result, thinning solvents are still needed to transfer the fluid from
storage to pumps and hoses.
Under hot and humid weather conditions, certain coatings (e.g., lacquers) can rapidly
lose organic solvent prior to and during application. Often under these situations a facility
will add solvent blends to make up for the reduction in viscosity and to overcome condensation
on the surface (blushing). 27 Evaporative losses can be minimized by adopting good
work practices and by using formulations that contain organic solvents with low vapor pressures.
14.26.7 SOLVENT EMISSIONS
Several states with their own rules regulating marine coatings have separate rules addressing
solvent cleaning operations. While marine coating rules typically address VOC contents
and types of application equipment, the cleaning solvent rules are more generic and address
cleaning solvents used at any and all metal-related manufacturing operations.
Many types of solvents are used in marine coatings and in their associated cleaning
materials as shown in Table 14.26.1. Almost all solvents used at shipyards are VOC and approximately
one in three solvents contain HAPs. Of the HAPs reported, several are included
on the list of 17 high priority chemicals targeted by U.S. EPA for the 33/50 program. 28
These included xylene (commercial), toluene, and the ketones. Commercial grade xylene
represents the major portion of the volatile HAPs reported.
Many of the commonly known solvents are actually petroleum distillation fractions
and are composed of a number of compounds (e.g., mineral spirits and naphthas). There are
two general types of solvents derived from petroleum, aliphatics or aromatics. Aromatics
are stronger solvents than aliphatics since they dissolve a wider variety of resins. Most major
solvent suppliers (chemical manufacturers) produce several types and variations of these
solvents and the associated HAP contents can vary significantly from manufacturer to manufacturer
and from batch to batch. These types of solvents are used extensively and are present
in the majority of marine coatings. Table 14.26.4 provides a summary of common
petroleum distillate solvents and solvent blends and their associated HAP content. For any