Here at Searles Graphics we've traditionally run sheetfed offset presses. Within the last decade we've invested heavily in digital printing as well. One thing we've never offered is web printing. Most consumers don't have any idea what type of printing press the finished piece they're looking at ran on. Luckily, you won't be one of those after reading this ;-).
I've written about digital printing and I've written about offset printing so please check those articles out to get an idea for the differences between the two, and know that both offset and digital printing provide options for sheet fed and web presses, with the primary advantages and disadvantages of both being similar.
If you follow Searles Graphics on social media or have been on our website before, you've no doubt seen pictures and video of our sheet-fed presses in action. The primary difference between web presses and sheet-fed presses is that web presses feed off of a large roll of paper, while sheet-fed presses feed individual sheets of paper.
Ok, you're asking, "So what? Why is their a difference and what does that mean to me?" Easy, I'm getting there ...
All paper is manufactured in rolls. As such, there is a cost involved in sheeting paper; that is, the process of taking a large roll of paper, slicing it into individual sheets of a certain size, and stacking and/or packaging those sheets. This makes purchasing sheets of paper more expensive than purchasing rolls.
It's also slower and more difficult to feed sheets into a press than it is to continuously feed a roll.
All that being said, in order to produce a finished product, that giant roll of paper needs to be cut, folded, and bound just the same. The difference is in where this occurs in the process.
On a web press, printing, folding, and sheeting all happens in line. After all, those rolls of paper are extremely heavy, so moving them from place to place is both cost prohibitive and difficult, so it's important to only have to do that once, rather than in between each step in the process. This video is of a monster Manroland heatset web press:
As a result, once a web press is running, the printing, folding, and sheeting/sheet handling process is significantly faster, reducing overhead and production times.
On the other hand, all that functionality comes at a cost. Web presses are larger, heavier, more expensive, costlier to maintain, and require far more in terms of infrastructure and power requirements. Some large web presses are so loud while running that they need to be run inside specially-designed sound-dampening enclosures.
Having all of that functionality inline also means that if one thing goes wrong anywhere in the process, the entire process can come to a screeching halt, so downtime is far more impactful on operating costs. With sheet-fed, downtime on a folder or cutter doesn't stop your press from running, and it's far less expensive to have a backup in place and ready to go.
Make-ready costs and waste are also much higher with web printing than with sheet-fed because of the size and complexity of the press. Here's a video of a sheet-fed Heidelberg press:
Similar to the differences between digital and offset printing, all of these trade-offs in cost and speed have break-even points where the speed of production more than makes up for the added costs. Essentially, longer runs tend to be more economical on web presses vs sheet fed (think newspapers and jobs requiring hundreds-of-thousands of impressions as a general idea, but be sure to talk to a printer about your specific needs).
Finally, there's the difference in the finished product. All that speed comes with trade-offs in quality. No matter how you put it on a sheet, ink needs to be applied wet and allowed to dry. With sheet-fed presses, ink is either allowed to dry naturally over time as it absorbs into the sheet, or the sheet itself is coated with a laminate and then dried through a heating unit on it's way to being delivered to the end of the press.
With web presses, because the folding process occurs inline and at such a high speed, it's critical to expedite the drying process.
Traditional or "cold" web presses only work with uncoated paper. Without a coating on the sheet, the ink is able to absorb into the sheet to dry. This is the newsprint you're used to when you read the newspaper. It's not an ideal process as is evident from the remnants you undoubtedly end up with on your hands after handling newsprint.
The other option is heatset web printing, which is the process used for the major publications you see every day on the magazine rack. Heatset web printing can be used on both coated and uncoated stocks.
On a heatset web press, after the roll passes through the impression units, it is run through an oven that dries the ink on top of the paper before it's absorbed into the sheet. This lack of absorbtion (mostly on coated stocks) yields a glossy shine, and it's also why the ink is more likely to rub off onto your fingers if you hold onto the page too long (anybody that's ever read a magazine on the beach or by the pool in the summer can attest to that!).
As a side note, it's also common for the covers of some magazines or catalogs to be printed on sheet-fed presses as a high-quality wrapper around lower-quality interior pages that are printed on a web press.
One final drawback of heatset web printing is a phenomenon known as fluting. Fluting doesn't happen on every job, but when it does, it's problematic. Drying ink at such high temperatures also affects the paper, which contains moisture. The heat draws moisture out of the sheet, which actually causes the paper to shrink. Depending on the amount of ink coverage on the piece, some parts of the sheet will lose more moisture than others, causing a sort of ripple, or wave effect on the page.
All of this brings us to some basic realizations. If quality is of the utmost importance and/or you're not doing very large quantities, sheetfed printing is usually your best option. If quantity and speed are the primary factors, web printing is generally the way to go.
One final caveat to all of this ... technology is constantly getting better across the board. So just as the quality of web printing has gotten significantly better over the years, so too has the speed of sheetfed printing, blurring the lines a lot more than ever before. The job that used to only be feasible on a web press might be able to run on a sheetfed press now, and the high-quality job you couldn't afford to do on a sheetfed press and didn't want to do on a web press could be a possibility on a modern heatset web press.