subject: Offset Printing Explained in Detail [print this page] Offset Printing Explained in Detail Offset Printing Explained in Detail
Offset Printing, or lithography, is the most commonly used form of printing in the world, and is simplified by the premise that oil and water don't mix. In lithography, an emulsion on a printing plate attracts ink (oil), and the rest of the plate attracts water (fountain solution) to ensure they don't mix. This image on the plate is then transferred to a printing blanket, which then transfers to the printing substrate (paper). This is why it is called "offset" printing.
There are two primary types of lithographic machines for direct mail forms and generic inserts sheetfed and web. Sheetfed printing is generally characterized by a shorter run, higher-quality project. Sheetfed presses can generally print on thicker printing substrates, and use cut-size paper from the mill or a paper converter. Sheetfed printing shops (commercial printers) do not normally print on paper that calipers less than 4 or 5 pt. Sheetfed production rates are typically slower, linearly, than web speeds but tend to make ready jobs quicker. Sheetfed plants use paper that has been cut to size from a paper converter, adding expense to the cost of paper.
Web offset printing uses 700-2,000 lb rolls of paper to print on that are miles long. Most presses have splicing equipment that allows the press to run continually. Paper caliper (thickness) is generally limited at 10 pt but presses have the flexibility to go down to newsprint and lightweight coated stocks. Web printers tend to become most efficient on jobs that require 5000 lbs of paper or more. With web press speeds of over 1000 feet per minute and the ability to print on 2 sides in 1 pass, web offset printing offers tremendous savings to the print buyer on large volume projects. The primary savings, however, is paper. On some jobs, paper can be 60-70% of the cost of the job; since web stock tends to cost 33% less than cut sheets, web offset is the choice for high volume direct mail printing campaigns and product inserts.
Printing inks for suitable for direct mail and generic inserts are formulated to cure by UV lamps or long ovens. UV cured ink does not produce volatile organic compound emissions and are cured after each unit to produce a sharp, crisp printing dot. Heatset presses, on the other hand, generally prevalent in the publication industry, wet-trap ink, meaning the colors are laid on top of each other and dried at once. Heatset inks are generally used in combination with heavy ink coverage and coated papers. A good printer has a portfolio of both heatset and uv cured presses to accomodate a variety of print jobs.
Along with newspapers and magazines, web offset printing is the perfect application for long run direct mail component parts and packaging literature, as well as financial and pharmaceutical printing.
