Digital Printing

Types of Digital Printers

Types of digital printers include

1. Laser Printers (Electrophotographic) - Includes monochrome copier/printers such as Xerox DocuTech, along with color copier/printers from multiple sources and some digital presses.

2. Inkjet Printers - Includes desktop printers, addressing printers in-line with finishing operations, wide format printers and high quality proofing printers.

3. Thermal Transfer Printers - Includes thermal wax and hot stick printers.

4. Dye Sublimation Printers - Includes some color proofing devices “photo quality” continuous tone printers.

5. Electrographic Printers (Electrostatic) - Basis for original Versatec printers and newer wide format devices.

6. Magnetographic Printers - Includes units sold by Nipson printing systems.

7. Ionographic Printers - Includes Delphax printers from Dennison Manufacturing.

8. Digital Stencil Duplicators - Includes devices, evolved from old stencil machines, from Riso, A.B. Dick and Ricoh.

9. Imagesetters and Platesetters - Includes devices that image film and plates (Computer to plate systems).

10. Direct Imaging Conventional Presses - Includes digital offset presses from Heidelberg, Omni-Adast and MAN-Roland.

These devices can be used as a design aids or proofing devices in addition to production devices.

PostScript laser printers are good proofing devices for monochrome (single color) jobs. Currently, no desktop printer is a reliable proofing device for color work. Spot colors cannot be reproduced reliably with a desktop printer. Nonimpact printers for higher production volumes and high quality color are being developed. Unlike conventional printing devices, digital printers are falling in price along with improving in performance.

Digital color printing currently supports:

1. Just in time production - Printed items often have unpredictable demand. With shorter runs a purchaser can buy smaller lots more frequently.

2. Individual or variable output - It is just as easy to print every copy different as the same. Can tailor a communication to different readers.

3. In-house production - Simple document production through in-house reprographics. High quality color work now contracted will be done in-house as devices get cheaper and better.

4. Distributed information - Reference items such as encyclopedias, manuals and catalogs are now distributed more efficiently in electronic forms. High quality digital printers at business locations allow distribute and print model rather than traditional print and distribute model.

5. Visualization and prototyping - Can produce single copies or short runs to test and approve visual concepts. Can view printed on local printer or soft proof on CRT.

6. Compilation and offprints -If journal or magazine articles are stored in a digital database then individual articles (or even bound custom collections) can be printed and distributed (or distributed and printed) easily.

Electrophotographic Printers

Often called electrostatic, but we prefer the terminology of original Xerox patent.
Includes desktop and office monochrome laser printers, color laser printers, color copiers with digital interfaces and digital color presses from Xeikon and Indigo.
Xeikon uses fixed LED’s instead of lasers.
Indigo uses liquid toners.
Usually include PostScript interpreters either built in or add-on.
Uses essentially the original Xerographic process of office copiers where a charged photoconducting drum is selectively discharged by the laser or LED.

The drum is toned by charged pigment particles and the image is transferred (offset) to the substrate.

Can print on almost any kinds of papers as well as other substrates.
Higher resolution than solid toners is possible with liquid toners which can suspend finer particles (1-2 microns).
Color laser printers use the same processes as monochrome printers and copiers.
Toners have purer colors than printing inks so that gamuts are wider.
Xeikon DCP-32 & 50 Digital Color Presses use solid toner, LED's and 10 independent perfecting toning stations.
Essentially same print engine is sold as Agfa Chromapress, IBM Infocolor and Xerox Docucolor series.
Can produce 64 shades of gray (dot sizes) for each color (18-bit color) at 600 dpi.
Very high quality output, supports stochastic screening and high frequency halftones. 13" - 20" web at 35 duplex pages per minute.

Indigo E-Print series

Sheet fed press using offset electrophotography.
Uses liquid toners consisting of a dispersion of very small (1-2 microns) pigmented polymer particles dispersed in a hydrocarbon medium.
Pigment particles are transferred to a blanket and then offset to substrate.
Single printing unit with multiple passes. Up to 6 colors (Indichrome).
800dpi variable sized dots. Halftones up to 150 lpi using the variable dots.
Indigo recently introduced a web fed digital press, the Omnius.
Indigo digital presses print on a wide range of substrates. They support variable data text and images.

Ink Jet

Use tiny nozzles to precisely spray onto paper. Continuous ink-jet printing - A thin stream of liquid is ejected from a container through a tiny orifice and is broken up into a steady stream of uniform droplets when subjected to a high frequency vibration.

When electrically charged, the drops can be placed by an electrostatic deflector. (See figure ).

Undeflected drops are recirculated.
Used in Iris printers from Scitex, which are often used for digital proofing.

Drop on Demand ink-jet printing

Ink droplets are expelled from tiny orifices and directed immediately to the substrate.
Most commonly uses heat to vaporize a small amount of water-based ink in a chamber to form a gas bubble (bubble-jet).

Used in most desktop ink-jet printers (Canon, HP, etc.)
HP DeskJet's employ multiple dot sizes to enhance resolution.
Piezo ink jet uses pressure pulses instead of heat to expel ink drops.
Epson ink jet printers use piezo with resolutions up to 720 x 1440. Available in multiple formats from letter size to 60 " wide web.
Wide format ink jet printers available from HP, Epson, Xerox, ColorSpan, Encad and others.
Wide format ink jets used for posters, banners POP displays.

Thermal Transfer Printers

Often called thermal wax printers.
Employs ribbon of wax coated material (hot melt ink) on a roll.
The ribbon is transported past the print head which is heated by semiconductor resistors to melt the ink and transfer it to the paper.
Can be thought of as digital version or iron-on.
Generally are binary printers but some variable dot-size versions exist.

Requires special smooth paper.
Hot stick printers from Tektronix combine thermal transfer and ink jet technology.

Dye Sublimation

Also called dye diffusion printers.
Similar to thermal transfer printers except that they use transparent dyes instead of hot melt inks.
This allows production of a nearly continuous tone or “photographic” quality output.
When dye sub ribbon is contacted by printhead the dye sublimes (vaporizes) and then diffuses into a special coated substrate.
The 3M Rainbow proofer in our laboratory is a dye sublimation device. (The Fargo printer does both thermal wax and dye sublimation.)

Electrographic

Also called electrostatic printers or electrostatic plotters.
An Electrical charge is applied directly to paper.
The process uses liquid toners consisting of pigments suspended in a hydrocarbon medium
Requires special media with dielectric surface on print side and conducting surface on back side. Thus, can only print on one side.
Available in wide formats up to 54” webs and 400 dpi resolution.

We have a 44" unit from Xerox Colorgrafx.

Magnetographic

Oldest nonimpact printing process.
Limited by the unavailability of color toners.
Involves creation of latent image on a magnetic metal surface via the application of a magnetic field. This is similar to the magnetic recording process used in magnetic tape and disk systems.
The magnetic surface is toned by a magnetic toner consisting of pigmented fine iron particles.

The toner is transferred to the substrate in a manner similar to electrophotographic printing. Units are sold by Nipson printing systems.

Ionographic

Can be thought of as a major simplification of electrophotographic process.
The image carrier, called a dielectric cylinder, is charged with an ion beam which is controlled by a series of electrodes.
Employs Aluminum oxide as the cylinder. Has not been applied to color as yet.
Are able to sustain high throughputs.

Process was developed by Dennison Manufacturing and is known as Delphax.
The EBI process by Digital Print is an improved ion-deposition digital printing system.
Speeds up to 225 fpm at resolutions up to 300 dpi can be obtained.

Imagesetters and Platesetters

Essentially the same technology as laser printers except that they print at a higher resolution on photosensitive paper or film instead of a photoconducting cylinder.
Some imagesetters can directly expose plates (platesetter or “computer to plate”, see next section).
Can produce very high resolutions with correspondingly high frequency halftones or high quality stochastic screens.

Systems can be Capstan or drum. Many use IR lasers, such as our AGFA ProSet 9800.