The printing process has three stagesprepress, press, and binding or postpress. In small print shops, job printers are usually responsible for all three stages. They check proofs for errors and print clarity and correct mistakes, print the job, and attach each copy’s pages together. In most printing firms, however, each of the stages is the responsibility of a specialized group of workers. Prepress technicians and workers are responsible for the first stage, preparing the material for printing presses. They perform a variety of tasks involved with transforming text and pictures into finished pages and making printing plates of the pages.
Advances in computer software and printing technology continue to change prepress work. Most customers today are able to provide printers with pages of material that look like the desired finished product they want printed and bound in volume. Using a process called “desktop publishing,” customers are increasingly using their own computers to do much of the typesetting and page layout work formerly done by designers on artboards. Much of this work is now done by desktop publishers or graphic designers with knowledge of publishing software. (Sections on
desktop publishers and graphic designers appear elsewhere in the Handbook.) It is increasingly common for prepress technicians or other printing workers to receive files from the customer on a computer disk or submitted electronically via e-mail or “file transfer protocol”, known as “ftp”, that contains typeset material already laid out in pages.
Prepress work is now done with the use of digital imaging technology by prepress technicians known as “preflight technicians” or production coordinators. Using this technology, these technicians take the electronic files received from customers, check it for completeness, and format it into pages using electronic page layout systems. Even though the pages may already be laid out, they still may have to be formatted to fit the dimensions of the paper stock to be used. When color printing is required, the technicians use digital color page-makeup systems to electronically produce an image of the printed pages, then use off-press color proofing systems to print a copy, or “proof,” of the pages as they will appear when printed. The technician then has the proofs delivered or mailed to the customer for a final check. Once the customer gives the “OK to print,” technicians use laser “imagesetters” to expose digital images of the pages directly onto thin aluminum printing plates.
Platemakers for a long time used a photographic process to make printing plates. The flat, a layout sheet onto which a negative has been attached, was placed on top of a thin metal plate coated with a light-sensitive resin. Exposure to ultraviolet light activated the chemical in parts of the plate not protected by the film’s dark areas. The plate was then developed in a solution that removes the unexposed nonimage area, exposing bare metal. The chemical on areas of the plate exposed to the light hardened and became water repellent. The hardened parts of the plate form the text and images to be printed. Now, the printing industry has largely moved to technology known as “direct-to-plate”, by which the prepress technicians send the data directly to a plating system, by-passing the need for stripping film onto a flat.
During the printing process, the plate is first covered with a thin coat of water. The water adheres only to the bare metal nonimage areas, and is repelled by the hardened areas that were exposed to light. Next, the plate comes in contact with a rubber roller covered with oil-based ink. Because oil and water do not mix, the ink is repelled by the water-coated area and sticks to the hardened areas. The ink covering the hardened text is transferred to paper.