Thanks to Laser!Digital Printing has become an Independent Process

(NPES International E-commerce Website, August 26, 2008) On the 22nd October 1938 the patent agent Chester Carlson of Queens, New York invented the basic method for an electrophotographic copying process. The small firm of Haloid, a manufacturer of photographic papers in Rochester, New York state, took up the process and, under the direction of the inventor, implemented it; producing a usable copying device that for the first time was able to copy documents on to normal paper by means of a dry process that did not involve photochemicals. In order to avoid using the difficult word 'electrophotographic', Carlson coined the term 'xerography' from the Greek words for 'dry' and 'to write'. After the tremendous initial success of the copying machines, the term was incorporated in 1958 into the company name as 'Haloid Xerox' and then in 1961 the company was renamed 'Xerox'. In the year of Drupa 2008, Xerox can celebrate the 70th birthday of digital printing.

Digital printing: the new way of printing
As popularly understood today, digital printing derives from the electrophotographic process that was invented back in 1938 in the USA and that was developed for the manufacture of office copying machines. With the invention of the personal computer and its worldwide conquest of the office since the mid 80s, printers were required that could print out the documents held on PCs on normal paper. This was a task for which the output section of office copying machines could be used, and so the pure digital printer was born.
The term 'digital printing' is not really the exclusive preserve of the electrophotographic process, since inkjet printers, magnetography and electron beam printing are all just as digital in their operation. However, the trade world has resigned itself to the fact that whilst there may be various different digital printing processes, in ordinary parlance the term is exclusively used for the electrophotographic process. The distinctions we make in this Technology Guide will therefore be between monochrome and color digital printers and sheet and reel-fed ones.

HOW does digital printing work?
A digital printer contains a light sensitive drum that is electrostatically charged. A laser beam or laser diodes strike the points that will print, discharging them. Subsequently, magnetic dry toner is applied to the drum and adheres to the exposed image areas, before being transferred to the paper. In order to fix the dry toner to the paper, the paper is heated by hot rollers and the toner fuses to the paper.
After each individual impression, the cylinder needs to be cleaned, re-charged and rewritten, with the result that the printing information can be changed for every individual impression. Digital printing is therefore able to print an entire document in sequence, so that it is delivered ready gathered and can even be bound in line.
Over the last 20 years this basic principle has been further developed in the form of color printers. Besides black, these can also print additional special or the four process colors. In order to achieve this, the four colored toners are transferred on to a blanket, one after the other, and printed on to the paper in a single process. A single manufacturer, HP Indigo, uses liquid rather than dry toner, and this enables it to represent halftone dots, as in offset printing, and allows it to come closest to the look of offset printing. In the most recent development, Xerox has developed new colored dry toners that no longer require heated rollers but are flash fused to the paper without the paper as a whole being heated.
The monochrome sheet-fed printer
Two events mark the beginning of digital printing: the invention of the personal computer and the expiry of the Xerox patents to the standard copier in 1982. Xerox's fierce defence of its rights to its copiers and the electrophotographic process had meant that there were no alternatives to Xerox copiers of a comparable standard. In 1982, however, a whole host of companies started to produce office copiers.
At the same time, American companies like Apple and IBM began to develop the personal computer. The incredibly rapid worldwide spread of the PC at the hands of IBM was based on two things. Firstly, IBM was the worldwide market leader for office automation and especially for typewriters, whose ideal successor the PC was. Secondly, due to its late entry into the PC market, IBM published its designs for the PC and this made its PC, including the Operating system from Microsoft, into today's industry standard. In consequence, the demand for digital printers in offices mushroomed.
There were copy centers that offered digital printing to the office market as a service and ever larger and better printing systems started to compete with the offset printer. In 1990 Xerox launched the Docutech 6000 family, a system printer that could print up to 180 A4 pages per minute and stitch or bind them inline. Consequently, these systems increasingly began to be used by jobbing printers, who were able to produce short black and white runs with them more cheaply and faster than they could with offset printing. Till today Xerox has sold more than 25,000 Docutech systems. In 1998 Kodak launched a comparable system printer, the 'Digimaster', which is today the prime competitor to the Docutech family.
The production printers referred to here handle oversize A3 sheets in order to be able to produce bleed pages. Transfer of the A3 sheets through the press needs to be reliable and this requirement has so far prevented a top speed of 180 A4 pages or 90 A3 sheets per minute being exceeded.
In order to be able to achieve higher page outputs whilst still printing paper in the form of sheets, Oce designed sheet-fed printers with two printing units that printed both sides of the sheet in a single pass without turning. The fastest model is currently the Varioprint 6250, which is capable of printing 250 A4 pages or 132 A3 pages per minute and which is rated for a monthly output of up to eight million A4 pages.
Xerox has taken up the challenge with the Nuvera family of printers and its Nuvera 288 offers a printing system that is even faster, being capable of printing 288 A4 or 144 A3 pages per minute. It has a recommended monthly output of three million A4 pages but can print up to six million.
The image processing and printing resolution is so high that offset quality halftone images can be printed, and to the lay person digital printing cannot be distinguished from offset printing. Therefore, many jobbing printers and other graphics firms use digital printing for black and white work. As a rule, offset printing is only used for longer run, larger format and higher pagination black and white jobs.

The monochrome reel-fed printer
In the 70s computer centers emerged with mainframe computers that needed to print out enormous numbers of pages. In the 80s reel-fed output systems were developed for these that could print the data out on webs of paper up to 45 cm wide. For the simultaneous printing of the reverse side, also referred to as duplex printing, a second printing unit had to be installed in tandem and the web turned in between. Today, most such printing systems have two printing units in one system. The new IBM Infoprint 4100, for example, prints up to 1,354 A4 pages in duplex operation. At Drupa 2008, Xerox is showing its new model, which is capable of printing 650 or 1300 A4 pages per minute on paper webs.
The form and continuous stationery printers of the 80s developed into digital printers in the 90s and so moved into transactional printing, in which they are no longer primarily printing forms but statements for financial service providers. Credit card and telecommunication companies are examples of the type of customer that needs to print millions of statements every month, and for these reel-fed printers are used. In most cases, reels of paper that have been offset pre-printed in color are used and the statement data are then printed in black and white. The same procedure happens in the direct mail sector, with color pre-prints being personalized in black and white.
Two monochrome reel-fed printers should be mentioned here that do not use the electrophotographic principle. The first manufacturer is Nipson, which uses mag- netography and a tuner that is flash fused to the paper in a contact-free process for its Varypress systems. The Varypress 500 can print 1,010 A4 pages per minute and a tandem installation is capable of up to 2,020 A4 pages.
The second manufacturer is Delphax, which uses electron beam imaging and dry toner in its printers, which can produce up to 2,054 A4 pages per minute. This level of productivity is achieved through duplex printing of two pages positioned alongside each other on 45 cm wide webs of paper.

Sheet-fed digital color laser printers
Digital color printers have originated from two different markets. On the one hand from the world of office communications and on the other from the manufacturers of graphics systems.
At the end of the 80s the digital printing systems that had been developed from photocopiers began to offer color, with Canon as the pacesetter, although until 2004 it concentrated on the office market. In 2002 Xerox established the Docucolor 2000 family. This encouraged other suppliers from the office segment to invest in the demanding printing industry market, with the result that at Drupa 2008 Canon, Konica Minolta and Ricoh will all be showing and receiving great attention for their new color print production systems.
    In the period between 1990 and 1995 two manufacturers developed color presses for the demanding printing industry: the Israeli company Indigo, today HP Indigo, and the Agfa-founded Xeikon. Drupa 2000 saw the appearance of the Nexpress, jointly developed by Kodak and Heidelberger, whilst Xerox launched the iGen 3, which had been designed for the printing industry. The printing systems of these four manufacturers are on a par with offset printing in terms of the quality of color printing, even though the look of color toner printing is somewhat different, and their production is considerably more stable than that of normal sheet-fed printers. Working to full capacity, the Xeikon 6000, for example, produces up to six million A4 pages per month, whilst Xerox specifies up to three million for the Gen 3.

Reel-fed digital transpromo printers
The move from sheet to reel-fed is made for several reasons. Firstly, webs can move through the printer much faster than sheets; secondly, the paper can be thinner, and, taken together, these open up production possibilities for color laser printing that otherwise are restricted to inkjet printing. With fast, four color transactional printing, reels pre-printed in color can be dispensed with, which increases flexibility. In addition, it also becomes possible to personalize and individualize the pages in all four colors. As such, transactional printing can be combined with the printing of direct mail promotional material, hence the term 'transpromo'.
Up until now, this market has been the exclusive property of Versamark inkiet printing systems, which are capable of delivering up to and beyond 2,052 fully personalized A4 pages in colour per minute. At this Drupa, there are other inkjet system suppliers in the form of Agfa with the Dotrix Transcolor, Dainippon Screen with the Truepress Jet 520, as well as Oce with the Jetstream 1100//2200, which can print up to 2,052 A4 pages per minute.
Electrophotographic color toner printers are not yet capable of this level of performance but they are already halfway there, delivering up to 1,000 pages per minute. For example, the Xerox 490//980 reel-fed printer produces up to 980 A4 pages, Oce offers the Variostream 10000 delivering up to 800 pages and IBM/Ricoh has the Infoprint 5000, which prints 862 A4 pages per minute.
Over all these various models, whose ever higher printing performance offers an increasingly attractive alternative to offset printing, there hovers the claim of Kodak that its StreamJet injket technology, which is currently under development, will soon be more attractive than offset for the jobbing printing of runs below 10000. The Stream Concept Press promised for the Kodak stand could be an interesting digital press at Drupa 2008.