Greenprint Guide to digital printing
The most exciting recent developments in printing have come from digital technology. Digital imaging, using computers to create and reproduce an image, has transformed all of the printing techniques described above. Litho and flexo printing both now use computer-to-plate technology to make printing plates direct from PDF files, eliminating lengthy processes which required a series of colour-separated films to be exposed, developed and shone onto the plate before developing the plate. Gravure cylinders can be automatically engraved without manual intervention by computer-controlled engraving lines. Screen stencils can be imaged directly via computer, using either an an inkjet head to apply a heated wax or ink which fills in the non-image areas or a laser beam to remove the emulsion to reveal the image area. Even rotary letterpress formes can now be made using a computer-to-plate system to create a photopolymer plate which replaces the traditional forme.
But digital technology has brought about a whole raft of new printing techniques which come under the heading of digital printing. This can be inkjet or laser-based, which can be summarised as follows:
An inkjet head sprays a fine jet of ink onto a substrate as it passes the head, forming characters and pictures in multiple colours by using multiple inkjet heads. Most printers used with home computers use inkjet technology, but industrial inkjet printers are very sophisticated and can print to a very high resolution and in very wide formats, up to 5 metres wide! Most home-use inkjet printers use water-based inks but industrial printers tend to be solvent-based to allow faster drying at higher speeds. Some models use special UV sensitive inks which cure immediately on exposure to UV light, enabling them to print on a wide range of materials. The third main type of ink used is called dye sublimation and is used for printing onto polyester or acrylic-based fabrics, as the dye in the ink "sublimates" (changes from gas to solid) and bonds to the fibres of the fabric when heated. The ink can either be applied directly to the fabric or via a carrier sheet.
Industrial digital inkjet printing is used for all sorts of short-to-medium print runs of products such as Point Of Sale displays for shops, book printing, mailers, greetings cards, calendars, T-shirts, CDs - almost anything, provided the quantity is not too great.
Laser printers use toner-based inks which are attracted to an electrostatically-charged print image area on a roller drum and are then transferred to the material. Heat is used to fuse the inks to the surface, allowing the material to be handled immediately. Mono (black ink) laser presses are widely used in the printing trade, but colour lasers are prohibitively expensive to buy and to run, so inkjet dominates the colour digital print market.
The most common applications for laser printing are for personalised bills and statements for utilities companies, banks and stores and for overprinting address information onto letters and carriers for large volume mailings.
Why the future is set to be digital...
There are two major advantages of digital presses over conventional ones.
The first is that they have no initial set-up costs, other than formatting the data to drive the printer. All of the traditional printing methods require an original from which copies are made - a plate, a cylinder, a forme, a screen - and the cost of preparing the original and making the press ready means that small runs incur a very high initial charge, making the unit cost prohibitively high. A four-colour litho job needs 4 plates to be made and set up on the press, which can cost hundreds of pounds, depending on the size of the plate. If you only need a few copies, the set up cost will be very high per copy. Digital printing can print just a single copy, or up to several hundred copies very economically. Currently, digital presses can only run at a fraction of the speed of litho presses, so once the print quantity reaches the break-even point where the set-up cost plus the running cost of conventional presses is the same as the running cost on a digital press, then the conventional press will print each subsequent copy at a fraction of the cost of the digital press. However, technological advances are allowing digital press manufacturers to run faster and it has been predicted that digital will be able to match some litho presses in terms of quality and output speeds within the next 10 years.
The second advantage is that every copy printed on a digital press can be different from the copy printed before it, allowing personalisation to be driven by databases which can make the printed item appeal to each person receiving their personalised copy. This allows companies to target their printed marketing towards each client, increasing the chances of the client taking up their offer. If your database tells you a potential client's favourite colour and type of car they drive, you can create a personalised printed mailer with their initials on the number plate of their ideal car in their favourite colour! New technologies such as directsmile(http://www.directsmile.de/) enable printer fonts to be created from almost any image, so a potential client's name can be printed using letters which look like they have been created by hand, such as pebbles on a beach or a tattoo on someone's arm. This type of highly-targeted print personalisation is significantly more expensive per copy, but marketing companies tend to print much smaller quantities using accurate databases instead of mass-mailing to many thousands of people who will not have any interest in their product. This is a better for the environment as it uses less resources and as the technology improves and personalisation costs decrease, this area of digital printing, known as variable-data printing, is set to grow exponentially.