Direct Imaging Technologies Similar but not the Same?
A glance at different digital printing process
As production times become shorter and job sizes shrink, digital production processes are becoming more and more important. This issue has been on everyone’s lips in the printing industry for some years now, and the progression from Computer-to-Film to Computer-to-Plate and now to Computer-to-Print is a logical response to the demands of the market.
But many print purchasers have been confused by the wealth of systems available, and are often put off by the fact that quality can be lower and the range of printing stocks limited.
There are numerous digital printing systems, and they differ in their external appearance as well as in the printing technologies and materials they employ. We continue to hear a lot about the advantages and disadvantages of various systems such as computer to print. There are basically 5 processes to choose from: Inkjet printers, electrophotographic printing using dry toner, electrophotographic printing use liquid toners, thermosublimation printers and digital offset printing.
INKJET PRINTERS
Inkjet printers are well known for home use and in proofing. There are basically two different processes here. In the continuous Inkjet process, a constant stream of tiny ink droplets is generated and, depending on the image to be printed the charged droplets are then deflected in a downstream electrical field while the uncharged droplets are deposited onto the paper. Usually only a small fraction of the droplet stream is deposited onto the printing stock, and the rest is fed back into the system.
In the drop-on-demand process, used by bubble-jet and piezo printers, the ink is squeezed out of the printing nozzle to form dots in the right places. This is achieved by mechanical deformation of the nozzle chamber triggered by an electric signal and by the piezoelectronic properties of the material, which makes up the chamber wall. This principle is used in both large industrial printers and small inkjet addressing units, such as are employed in newspaper mailing rooms or for customized check card printing.
ELECTROPHOTOGRAPHIC PRINTING USING DRY TONERS
Laser printer and large digital copiers use the electrophotographic principle with dry toners. The printing pattern is transferred using a laser beam or light emitted by an LED array. Fine toner particles are applied to the paper by the image drum and fixed using heat and pressure.
The Heidelberg Digimaster 9110 is such a machine. It is the ideal solution for even the most demanding users for publishing books and manuals.
You get sharper lines, more impact halftones and clearer, crisper, more readable text. The Nexpress 2100 from Heidelberg with the NexStation front end combines the strengths of the printing press with the flexibility of electrophotographic printing. This permits numerous new and specialized applications, particularly for short color runs, personalized variable printing in-target-group-specific communication.
ELECTROPHOTOGRAPHIC PRINCIPLE USING LIQUID TONERS
Some digital presses also use the electrophotographic principle, but with liquid instead of dry toners. The photographicly imaged printing foil accepts the electrically charged ink in the areas to be printed and deposits them onto a blanket which in turn applies it to the paper. The use of liquid toners is not yet particularly widespread.
THERMOSUBLIMATION PRINTERS
In addition to the processes explained above, thermosublimation printers and thermotransfer printers are also classed as digital printers. In these printers, an ink wax is either sub- limed or melted to color the surface or the inside of the printing stock.
Anyone who appreciates the quality of conventional offset printing will surely find Direct Imaging technology a must.
DIRECT IMAGING
The desire to print short color runs in a minimum of time and to high offset quality standards was the reason Heidelberg developed its Direct Imaging Technology. Computer-to-Press with the QMDI and Speedmaster 74 DI set the standards in digital offset printing. In these Computer-to-Press systems from Heidelberg, the printing plates are imaged directly in the press (Direct Imaging). The Speedmaster 74 DI, uses conventional offset printing inks (process colors), the QMDI uses waterless ink. In contrast to other processes, the range of printing stocks, which can be used, is almost unlimited. This process is also perfect for gloss and dull, offset paper, covers and packaging. Direct Imaging also offers numerous possibilities for inline production and coating.