Web offset printing differs from commercial sheet fed printing primarily in three ways: 1- It prints on continuous feeding roll paper and 2- It prints at extremely high speeds, much faster than a sheet fed press. 3- Web printing presses in most cases fold the signatures as they come off the end of the press, although some web presses are capable of sheeting to flat sheets. Due to the speed efficiency of the web printing press it therefore is more suited to printing higher runs of multiple page documents than a sheet fed press, such as magazines, books, newspapers or catalogs. It like sheet fed printing is a form of offset printing in that both first transfer the inks to a “blanket”, which then transfers the inks to the paper. In the case of both, digital printing is synonymous with “direct to plate” filmless printing.
Web printing is generally further broken down into two categories: Those that can print on coated stocks and have heaters to dry the ink, and know as “heat set” webs and those that cannot and only can print on uncoated stock and thus known as “cold set” webs. While it is a rare sheet fed press that can “perfect”, meaning printing on both sides of the signature at the same time, almost all web printing presses are “perfectors” and they print on both sides of the sheet at the same time. Some web printing presses also make use of double rolls, printing two 16 page signatures at the same time, thus running 32 pages at once.
Web printing presses run at speeds of anywhere from 300-3,000 feet per minute. These presses also come in various combinations from “full” web printing presses, to “half” webs which are less costly to operate and perfect for small page counts of from 2-8. There are also “quarter” webs, such as the Didde, and label printing web presses, which is how most commercial labels are printed. These web printing presses may only have a roll width of a few inches or more.
Some of the considerations you will need to keep in mind when printing on a web printing press are as follows:
1-Acceptable file formats – Web printing companies are much more prone to only accept PDF files and how the PDF is constructed varies from press to press. They will accept the well known professional native applications, like InDesign or Illustrator, but will charge extra to convert to a PDF.
2-Bleeds – Many web printing presses require a larger bleed area, usually a quarter inch, than a sheet fed press.
3-Jiggle – This is a very important word for you to know, in that you should plan for this in your design. Jiggle is the movement of the roll of paper through the web printing press. It is worse on older and cold set presses than the newest heatset ones. Therefore you want to K.I.S.S. keep it simple stupid, as with computers. It is best not to have repetitive border art or crossover art (same image covering two opposite pages) as you may be unhappy with the results, seeing one page having a higher frame than another, or crossover art that does not come together quite perfectly.
4-Page counts – Web Printing is less forgiving on page counts. This is where, if you can, you will want to swim downstream with your magazine or catalog pages. Since the set ups are far more costly than on a sheet fed press, printing an odd lot 4 pages will also be more costly. Some web printers can have better pricing for up to a 16 page signature than for a 4 page one. This is why you see blank pages at the back of all books.
5-Papers – Paper on a web printing press differ from sheet fed in two respects: 1- as the coated ones move more rapidly through the machinery, they pick up some extra gloss, which is why web printers can brag about a glossier look to their finished product. 2- sheet-fed printers can only run stocks as thin as 60# in weight and will whine about even that, web printers can run roll stocks such as 28# news, 32# gloss, 14# NCR which are common light weight stocks.
The important thing about creating files for web printing is that you must create them in a way that keeps you “swimming downstream”, as these web presses are very anal, very efficient and very unforgiving if you do not. Therefore you want to produce files that “work with the press” and can take advantage of web printing press efficiency. Don’t try and reinvent the wheel or you will reinvent your costs well upward.
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