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Print Process Descriptions: Printing Industry Overview: Lithography
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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 Flow Diagram

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