How Does This Relate to Web Offset and Sheetfed Offset?
First of all, what is the difference between sheetfed and web-fed offset lithography?
Printers load stacks of press sheets (let’s say 25” x 38” sheets, even though there are any number of press sheet sizes) into their presses for sheetfed work. Unless their press is a “perfecting press” (which prints both sides of the press sheet at once), the stack of press sheets (having been printed on one side) first must be dried. Then the stack of press sheets must be flipped over and loaded back into the press so the other side of the sheet can be printed.
After printing, the press sheets can be folded, trimmed, and bound on separate, post-press (or finishing) equipment.
If you have a long press run (let’s say 60,000 copies of a textbook instead of my client’s 1,500 copies of a literary print book of poems or short stories), you may instead opt for a web offset press (and in the process save a lot of money).
Webs are rolls (as opposed to sheets) of paper. They are usually cheaper for a given volume of paper than cut press sheets. However, preparing a web press for a print job is a huge endeavor. (Also, the presses themselves are very large, so most printers don’t have them on their pressroom floors.) Therefore, the only way to make web offset printing an economical choice is to produce a long-run, multiple-press-signature print book, magazine, or catalog. For these situations a web press is ideal.
Web presses are either heatset or non heatset (also referred to as coldset). Coldset web printing involves drying the ink by having the liquid part of the ink (its vehicle) absorbed into the paper. One-color jobs printed on uncoated paper with no halftones or area screens of ink are ideal for this kind of web press. (Interestingly enough, that’s just the kind of book printing my client needs.)
An alternative web-press configuration is the heatset web, which has a drying unit (after the inking units) to flash off the solvent from the ink after printing. This allows printers to use coated paper and print the books, magazines, or catalogs in 4-color process ink. The heat of the oven allows the ink to dry and sit up on the surface of the paper rather than seep deeply into the paper fibers (as is the case with coldset web printing).