Heatset Web Offset Lithographic Printing
The heatset web offset process is used primarily for long jobs at high
speed (up to 40,000 impressions per hour) for the production of magazines,
other periodicals, and catalogs.
In heatset web lithography, the paper substrate is delivered to the
facility in rolls. The paper is fed directly into the press and is termed
a "Web" since it is a continuous feed of paper as opposed to
individual sheets. After printing, the paper is folded and/or cut
"in-line" with the printing units.
Heatset web lithographic inks are paste inks that dry through
evaporation of the ink oils contained in the ink This is usually
accomplished with a recirculating hot air system (normally fueled by
natural gas) although direct flame impingement and infrared drying systems
are in limited use (Buonicore). Ink oil evaporated and emitted through
dryer stacks is a potentially significant source of VOC emissions. Because
of this many heatset web lithographic presses require an emission control
device (such as a catalytic or thermal oxidizer) to reduce VOC
concentrations in the dryer exhaust air stream. VOC emissions also occur
from isopropyl alcohol used in fountain solution and cleanup solvents used
to clean ink fountains (trays that hold ink), rollers, blankets, and other
press components. Major chemicals used are quite similar to those used in
sheetfed offset (GATF 1992b).
Heatset Web Lithography Process
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