Digital printing is an umbrella that covers sheetfed and roll-fed printers, monochrome and colour printers, toner and inkjet printers, and printers at different levels of performance within each category. Toner-based printer suppliers call toner ‘ink’. If toner was ink then ink could be toner; thus, we will use ‘toner’, whether dry or liquid, to describe these printers. Importantly, toner particles are imaged using electrical forces.
We all know what a ‘press’ is. It uses a removable image carrier (plate) to print high volumes of static material. ‘Printers’ are variable devices in that every page can be different. However, the word ‘printer’ brings to mind desktop machines, and there is a trend to call high-production printers ‘presses’. Thus the term ‘digital colour press’ is becoming common to indicate a very high level of production.
One of the most popular levels of digital printing is 70 pages per minute. Almost every supplier of toner-based sheetfed presses has a device at or above this level.
Digital colour printing entered the market in 1993 when both Indigo (now HP Indigo) and Xeikon (now owned by Punch Graphix) introduced systems, the former sheetfed and the latter roll-fed. Since 1993, many manufacturers entered the commercial printing and in-plant markets with printers from 10ppm to over 100ppm. More than 300,000 digital colour production printing systems have been shipped worldwide.
Worldwide, monochrome print volumes are decreasing as colour print volumes are increasing. Some users have eschewed B&W printers in favour of production-level colour printers. Certainly monochrome printers are less expensive than their colour counterparts. Printers who still have sufficient monochrome volumes are using such presses but high-speed colour printers allow colour to be inserted into what were monochrome jobs.
Features differ on all printers as suppliers offer price/performance options. Finding the right blend of features to serve existing and develop new markets is a challenge. Some features can be upgraded but some cannot, unless planned for in advance.
In terms of speed, 65ppm, 68ppm, and 70ppm are included in our definition, as well as printers at 80ppm, 90ppm, 110ppm, 120ppm, with 130ppm as the highest sheetfed colour printing speed.
Another key spec is resolution. In 1993, 600dpi and 800dpi were common resolutions. As laser imaging systems evolved, 1,200dpi and 2,400dpi have become standard with some printers at 4,800dpi. Output at 1,200dpi and 2,400dpi is excellent for high-quality work. An important measurement of quality is also bit depth. One to four bits per pixel are now commonplace. Most suppliers have proprietary technology that improves photographic and colour reproduction, and thus the numbers should take second place to evaluation of samples.
New chemical toners like the matte toner of the iGen4 and new toners from others result in quality levels very close to offset. New digital colour presses are setting the standard for quality; although, offset still has advantages in sheet size, spot colours, and customer acceptance.
Copiers began with A4 and quickly added A3 sheet sizes, and metamorphosed into printers. Today they have advanced to A3+ (13x19 inches or 329x483mm). Kodak Nexpress, MGI and Xerox iGen printers have moved beyond 13x19 inches. Nexpress and iGen have sheet sizes at 26 inches in length. The MGI Meteor DP 8700XL can print a sheet 1,020mm or 40.2 inches.
Using larger sheets with multiple A4 pages can push speeds up to 130ppm. Even with larger sheets that are available, paper suppliers tell us that A3 is still the most common sheet size but larger sheets are needed for certain book covers or multiple-up smaller pages or panorama printing.
Stocks now range from 60 to 400gsm with some at 80 to 300gsm and some at 55-350gsm but check with suppliers because the range may be different with some printers. There are also roll adaptors that allow rolls of paper to be sheeted as they enter the printer. The advantage of sheets is that different papers can be collated into sets. Look for paper weights to be increased so that printers can handle some packaging materials. Some printers can also print on plastics, both PVC coated and uncoated, polycarbonate, self-adhesive vinyl, teslin, polypropylene, and polyethylene, plus other specialty materials.
Sheet size and image area are different. No supplier has a printer that can print the same area as the sheet size. A non-printing margin of some amount is always required.
Most printing is duplex printed (or perfected) and every supplier has a different approach. Some use a duplex tray that holds the sheets with the first side printed and then feeds them from the tray to print the second side. Some use a flipper tray that prints one size and flips it over to print the second side. One uses a giant ‘mobius’ strip that turns the sheet. All methods work equally well, but keep in mind that duplexing on sheetfed printers reduces the print speed by about half. Thus, as speeds grow from 70ppm to 80 and 90 and 100ppm-plus, the duplexing speeds increase as well.
Duty cycle is a supplier-determined monthly maximum. Users can contract for levels of productivity, which then determines click charges if such are used. If monthly volume exceeds the contracted volume, there may be penalty payments. The 70ppm machines are usually over
1 million copies per month with some systems in the range of 3 million to 4 million-plus impressions per month.
Higher speed printers have larger and more paper trays so as to minimise production interruptions. These trays can be defined in terms of stock and different papers can be collated into jobs. Electronic collation is one of the fundamental advantages of digital printing. It allows the production of finished books and publications and multi-page documents.
As electro-mechanical devices, digital printers should be installed in humidity-and temperature-controlled environments. The Nexpress is vibration and environmentally robust for installation close to conventional presses.
Many digital printers look like railroad trains as additional paper units and finishing systems are added. Users have a wonderful array of saddle-wire, perfect binding, and specialty finishing systems for direct mail. Laminators and coaters can be connected. The books on-demand market exists because you can go from file to finished book in a few minutes.
All colour printers have four toner stations (cyan, magenta, yellow and black). The Fuji Xerox Color 800 and 1000 range comes with two additional toner stations (one for clear ink to amplify print and highlight imagery for visual impact, or digital watermarks for artistic effects or security). The Nexpress has one additional station with many options. These stations can have toner for denser black, light black toner, toner for matte printing effects, red, green or blue dry toner for more accurate reproduction of Pantone colours or other custom colours in brand elements or matching wide gamut colours and different coatings. The Nexpress “dimensional clear” toner can print textures (raised/3D effect) and a red fluorescing clear ink that is virtually invisible to the eye but fluoresces red when illuminated with UV light. Nexpress coatings can be matte or gloss (using an additional gloss unit).
An HP Indigo can have up to three additional toner stations. HP Indigos use liquid toners and can have specific Pantone and specialty spot colours. The liquid toner provides an appearance very close to offset. The Fuji Xerox Color 1000 uses an EA-Eco toner. Canon uses a wax toner.
Many of the high-production printers also have quality feedback system so that print is evaluated at the back end to modify colour control at the front end for more consistent colour printing. Larger production systems can afford to integrate such closed-loop colour control.
The DFE (Digital Front End) converts files into printable data. The most common front end is the EFI Fiery, followed by Creo followed by front ends developed by the printer manufacturer.
Each has a slightly different workflow with some integrating hybrid printing of offset shells and personalised information. The major differentiator may be in sophisticated workflows with web-to-print and variable data printing, as well as advanced colour control. The new Adobe Print Engine, which is available in DFEs from several suppliers, consumes PDF, not Post Script, files and supports a new standard called PDF/VT, which may help to increase the amount of personalised promotions and versioned documents.
Digital printers perform reliably and there is a robust refurbished and previously-owned business. Some systems come with spare parts kits so that certain parts can be replaced by the user. Unlike early copiers and printers, digital printers can be used for a decade or more. Advances continue in all of these areas.
Between the main suppliers (see box), there are about 20 basic models, each with many options. Some are sold directly by the manufacturer and some via agents. In addition, there is partnering in sales and distribution. Canon-Océ has partnered with Manroland; Kodak and Konica Minolta have partnered; and Heidelberg and Ricoh have partnered internationally, though in Australia, it is Heidelberg and Konica Minolta.
The sheetfed offset press is popular because paper stocks can be changed easily from job to job. The same is true of lower performance digital printers from 10ppm to about 70ppm. Some users have found that two 50ppm printers provide both production of 100ppm as well as backup. But the lower speed printers do not have the advanced functionality that the higher-level printers provide. There are interesting trade-offs.
• Fuji Xerox
• HP Indigo
• Konica Minolta