Offset Printing

Offset Printing is a printing technique whereby ink is spread on a metal plate with etched images, then transferred to an intermediary surface such as a rubber blanket, and finally applied to paper by pressing the paper against the intermediary surface. Offset printing is one of the most popular printing techniques. If it is used in combination with the lithographic process that is based on the repulsion of oil and water, the offset technique employs a flat (planographic) image carrier on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a film of water, keeping the nonprinting areas ink-free.

Generally, print shops use offset printing to produce large volumes of high-quality documents. Although the equipment and set-up costs are relatively high, the actual printing process is relatively economical. Desktop publishing generally involves producing documents on the computer, printing out drafts on a laser printer, and then offset printing the final version. To produce the plates used in offset printing, a print shop requires either film or high-resolution paper output, which the printer can then photograph. You can obtain either by taking a PostScript file to a service bureau. The three primary differences in offset printing and desktop printing (such as inkjet and laser) are the colors of ink and the way the ink is placed on the paper as well as the type of machinery used to accomplish the task.

The first step to the offset printing is that before the job can be printed, the document must be converted to film and "plates." Images from the negatives are transferred to printing plates in much the same way as photographs are developed. Secondly, the paper is fed through the press as one continuous stream pulled from rolls of paper. Each roll can weigh as much as 2,000 pounds (1 ton). Then the paper is cut to size after printing. Finally, the bindery is done where the printed product is completed. The huge rolls of now-printed paper are cut and put together so that the pages fall in the correct order. Staples or glue, in this step of the process, also binds pages together.

The advantages of offset printing include: 1. They give consistent high image quality; they are sharper and cleaner than letterpress printing because of the rubber blanket conforms to the texture of the printing surface Usability on a wide range of printing surfaces in addition to smooth paper (e.g., wood, cloth, metal, leather, rough paper) 2. It is quick and easy production of printing plates, the life of the plate is longer than on direct litho presses — because there is no direct contact between the plate and the printing surface. 3. Offset printing is one of the most dominant form of commercial printing due to its quality in respect of volume and paper costs, with this market being split between sheet-fed offset for low to medium volume (any job too large to be economic for laser printers or digital presses, but too small for web offset) and web offset for medium volume up to the 1-2 million copies market.