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Printer Technology

Printer Technologies: An Intro

Inkjet, Laser, Solid Ink, Thermal and Dye Sublimation A gentle introduction to modern, non-impact, printer technologies. This article offers a concise summary of common printer technologies including: Inkjet, Laser, Solid Ink, Thermal and Dye Sublimation. This article does not cover impact printing techniques such as those used in modern dot-matrix printers. For information on impact printing; please see the references at the end of this article.

The Printer: From Virtual to Actual
The invention of the printer was an important factor in success of the personal computer. Consumers were no-doubt eased into widespread acceptance of the mysterious black-box that was the personal computer by allowing information to be transferred from the virtual/digital world inside the computer to the “real” world outside; via the printer.

– In 1953 Remington-Rand invented the first high-output printer for the Univac computer.
– In 1938 Electrophotography was invented by Xerox. This dry printing process served as the predecessor for modern laser printing.
– In 1971Xerox completed development of the first laser printer: EARS.
– In 1976, the inkjet printer was invented. However it was not released as a home consumer item until 1988 with Hewlett-Parkard’s release
of the DeskJet inkjet printer. MSRP: $1000.
– In 1977 The Xerox 9700 Electronic Printing System, the first xerographic laser printer product was released. The 9700 was the product of
pioneering research conducted at the Xerox Palo Alto Research Center. Inkjet Printing Modern inkjet printers generally use one of two technologies:
-Continuous (CIJ)
-Drop-on-Demand (DOD).

Continuous inkjet printing is powered by an ink pump that directs ink from a reservoir to a tiny nozzle mounted on a gunbody.
The liquid is broken into droplets by a crystal that vibrates within the gunbody. The droplets are then electrostatically charged and some are directed to their target on the print medium while the rest are allowed to fall into a collection receptacle for later re-use.

– The first continuous inkjet devices were used in hospitals for making hard copies of medical strip chart recordings.

Benefits of Continuous Inkjet Technology:
The primary benefit of continuous Inkjet technology is that it allows for high speed printing because the ink is ejected at such high velocity. Additionally because the continuous Inkjet nozzle is always in use; it does not clog; thereby reducing maintenance and down-time. By using alcohol or ketone solvents; the ink can be made to dry very quickly.

Thermal Drop-on-Demand Inkjet printing is the technology used in most consumer inkjet printers. In Thermal Drop-on-Demand inkjet systems a print cartridge is used that contains tiny chambers. Chambers eject a drop of ink by a thermally induced pressure increase within the chamber. In a thermal Drop-on-Demand system, a heating element vaporizes the ink in the chamber causing a bubble to form. The resulting increase in chamber pressure propels a droplet out of the chamber. This is where Canon’s Bubble Jet mark came from.
The ink cartridges are usually filled with a water-based pigment ink that has a volatile component which is necessary to form the vapor bubble that causes the ink to eject from the chamber.

– The thermal inkjet principle was discovered by Canon engineer Ichiro Endo in August 1977.

Piezoelectric Drop-on-Demand inkjet printers are generally found in commercial or industrial applications with the exception of Epson, which produces piezoelectric Drop-on-Demand inkjet printers for consumers. The inclusion of a piezoelectric material ( PZT, lead zirconium titanate) in the ink-filled chamber instead of a heating element is what makes this technology differ from thermal drop-on-demand inkjet. Chamber pressure is increased by applying voltage to the piezoelectric material, causing it to change shape and thereby force a droplet of ink from the nozzle. Piezoelectric Drop-on-Demand systems use a different ink from than the thermal variety as no volatile component is required.

Common applications of piezoelectric Drop-on-Demand inkjet printing includes printing expiration dates on production line products such as milk cartons.

Laser Printing

Laser printing uses a laser beam to project the print image onto a charged rotating drum coated with a photoconductor. Dry ink (called toner) is then collected by the charged areas of the drum which presses the image onto paper and fuses it to the paper thermally.

This process generally involves the following steps to produce the final printed page.

Raster image processing
The image to be printed is translated into a series of horizontal dots called raster lines. This process is accomplished by a Raster Image Processor (RIP) inside the printer.

Charging
A negative charge is passed to the drum unit via a primary charge roller which projects a charge onto a photoconductor unit which is capable of holding a surface electrostatic charge.

Exposing
The Rasterized image is written to the photosensitive drum using a complex reflector and lens array. The raster data is used to create on/off signals for the laser which creates the dots on the rotating drum through this pulsed action. The laser creates a positive charge on the drum in the shape of the rasterized image.

Developing
The surface with the drum, now charged with the image is exposed to printer toner particles that have been negatively charged and are therefore attracted to the photoreceptor areas that have been touched by the laser. The areas not touched by the laser retain their original negative charge; repelling the similarly charged toner ensuring a clean image.

Transferring
The drum is now rolled over the paper, transferring the image.

Fusing
The toner which is composed of a plastic powder is fused to the paper as it passes through a fuser assembly which uses high temperatures and pressure to bond the toner and the paper.

Cleaning
A soft plastic blade now wipes any excess toner from the drum which is then swept by a discharge lamp to remove any remaining charge. Solid Ink Printing Solid ink printing technology (also called phase change ink or hot melt ink) utilizes oil based solid ink sticks to produce printed media. Solid ink printing is generally thought to produce higher quality prints and more vibrant colors than either laser or inkjet printers and so it is commonly used within the graphic arts industry.

Solid Ink Printing generally involves the following 3 steps:

1. The drum surface is wiped by a cleaning unit to remove any residual ink from a previous print. A very thin layer of silicone is applied to the print drum surface.

2. The printhead is heated and then sprays droplets of melted ink onto the rotating print drum (mechanically similar to the laser printer drum and is made of anodized aluminum ). The print drum is kept at a slightly cooler temperature which allows the ink to become semi-solid.

3. The print media is heated and fed into a press formed by a pressure roller and the print drum. The heat and pressure causes the image to transfer from the drum onto the paper.

The ink is not liquid and therefore there is no drying time before the print is ready for use.

Solid ink technology was originally developed in 1986 by Tektronix, which was acquired by Xerox in 2000.
In 1991 Xerox released the Phaser III Solid Ink Printer. Pricetag: $10,000.

A common selling point of Solid Ink printers is the fact that the ink sticks are non-toxic. As a publicity stunt, the president of Tektronix ate part of a stick of solid ink, testifying to their safety.

In May of 2009 Xerox released the ColorQube 9200 series: a multifunction printer capable of Tabloid Extra printing. Thermal Printing
Thermal printing technology (also called direct thermal printing) uses a selective heating process that is applied to special (thermochromic) paper by a thermal print head. The thermal paper has a special coating that turns black in the areas that are heated thus producing an image.

Thermochromic paper is fed between the thermal print head and a rubber sheet feeder. The printer sends a signal to the thermal print head which which heats up in the form of the print pattern. The heat activates the thermo-sensitive compound in the paper; ( Composed of a dye and a suitable medium. For example a combination of a fluoran leuco dye and an octadecylphosphonic acid.) producing a color change in the shape of the print pattern.

Common applications are point of sale systems like receipt printers, medical applications like fetal ultrasound scan images and older fax machine printers. Dye-Sublimation Printing Dye-sublimation printer technology (also called dye-sub print) uses heat to transfer the dye onto mediums such as plastic or photographic print paper. For example ID cards are often printed using dye-sub printers. The dye transitions from a solid to a gas state without becoming a liquid (sublimation).

Dye-sublimation lays one color at a time. Dye is held on a ribbon with each color being on a separate panel. The color configuration of dye-sub printers (CMYO [cyan, magenta, yellow, and clear overcoating]) is different from the more common CMYK color configuration used in other printers (key black is eliminated and replaced instead with a clear protective overcoating.).

A roller moves the medium and the colored panels together underneath a thermal print head which uses heat to sublimate the dye using very precise and rapid temperature changes to control the amount of dye diffused into the medium. This process is repeated 3 more times: 1 per color panel and the final result is ejected from the printer.

One major difference from other print technologies is that Dye-sublimation printers are generally produced to print on a single size medium. Colored ribbons, thermal print head and the print media must all be the same size.

References & Citations Wikipedia. “CMYK color Model.” Web. 7 July 2010. http://en.wikipedia.org/wiki/CMYK_color_modelC. Wayne Jaeger, Ph.D., Xerox Corporation. “Color Solid Ink Printing.” Imaging.org. Web. http://www.imaging.org/ist/resources/tutorials/solid_ink.cfmWikipedia. “Solid Ink” Web. 5 July 2010. http://en.wikipedia.org/wiki/Solid_inkMathieu. “What Are Direct Thermal and Thermal Transfer RFID Printers? (Episode 006).” Web. July 31st, 2007. in Podcast by Harold Boeck. http://www.rfidradio.com/?p=13Ink Guides. “Printer Manufacturers – A list of all existing printer manufacturers on today’s market.” Web. Ink Guides. http://www.inkguides.com/list-of-all-printer-manufacturers.aspMy Office Portal. “All you need to know about printer technologies.” Web. June 15th 2010. MyOfficePortal.org. http://www.myofficeportal.org/printer-technologies.htm

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