Any press needs the right techniques for the press to run properly.
Flexography, or flexo printing, is an up-to-date version of letterpress, the oldest printing method. Flexo allows more flexibility than traditional letterpress, with printing on cardboard, metal or even plastic film as well as paper. The substrate, or the product you're printing on, is pulled through the rotary presses from a roll, called a web. Narrow web flexo presses have different uses from their bigger cousins, the wide web presses. That means the techniques printers use to run narrow web flexo presses are different, too.
Basics
Narrow web flexo presses will print on plastic, paper, film or metal foil, called the substrate, which is usually 6 inches to 20 inches wide. Any wider substrate and you'll need to print on a wide web flexo press, metal monsters whose webs can run 100 inches wide or more. Narrow webs also run a lot slower than wide webs, with typical speeds of a few hundred feet a minute. Wide webs can travel 1,000 feet a minute or faster.
Pros and Cons
Since wide web presses can physically print more substrate, and faster, than narrow web ones, it's more economical for big press runs of big products. Advocates for narrow web turn that fact around: for short runs of smaller products, narrow web is cheaper. Narrow web is favored for printing labels, if the print run is in the low thousands. Printers have another reason to push their customers toward narrow web: The rollers and plates used are smaller, so it takes fewer workers to set up a print run.
Inks
Drying time is a crucial consideration in any printing process -- you don't want the ink to smear when the product comes off the press. It's an even bigger headache for flexo, since you're often printing on plastic or metal or other substrates that, unlike paper, don't absorb ink. Special fast-drying inks must be used. Finally, flexo inks dry faster during fast-moving press runs on wide web than they dry in slower narrow web printing. Different ink solvents, and different ink formulations, must be tailored to the narrow web. Narrow web presses also have different kinds of ink fountains (the reservoirs that hold the ink for printing) and different arrangements for doctor blades (which scrape off excess ink before ink is applied to the printing plate). That means printers also have another headache to worry about with their narrow-web presses: evaporation. Evaporation can affect the pH factor of the ink-solvent solution, which changes how the ink will look on the print job.
Quality
Ink is delivered to the printing plate with an anilox roll. That's a roller with tiny cells in it that pick up the ink from the fountain. The smaller the cells, the finer the anilox roll, and the better the ink delivery to the print job. Slower-spinning narrow webs can accommodate finer anilox rolls, for finer quality. Flexo plates, made from rubber or polymer, are flexible, unlike hard-metal letterpress plates. Plate flexibility affects image quality. Hardness or softness affects how well image lines and dot patterns will print. That flexibility is easier to manage in slower-moving press runs -- such as on narrow web flexo presses.
