The physics of XEROGRAPHY:

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The physics of XEROGRAPHY
Howard Mizes Xerox Corporation Wilson Center for
Research Technology Webster, New York
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Outline/Acknowledgements

• Outline
• History of Xerography
• Physics of Xerography
• Xerographic research
• Acknowledgements
• Shu Chang
• Dan Hays
• Nancy Goodman
• Lotfi Belkhir

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History of Xerography

• Chester Carlson

The first xerographic image10-22-1938, Astoria,
NY.

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History of Xerography
1906 Haloid Corp. founded
1938 1st xerographic image
1949 1st copier - Model A
1900
1910
1920
1930
1940
1950
1959 Xerox 914, 1st plain paper automatic
copier - 7 1/2 copies/min
1988 Xerox 5090 - 135 copies/min
1973 Xerox 6500 - 1st color copier
1997 Docutech digital printer (180 copies/min)
1950
1960
1970
1980
1990
2000
1997 Docucolor 70 - 70 color prints/min
1977 Xerox 9700 - 1st laser printer
1964 LDX (long distance xerography) - 1st fax
Today Xerox has 91,400 employees (50,200 in US)
and 18.2 billion in revenues
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What is Xerography?
Xero-graphy Dry-Writing (Greek)

• Creation of a visible image using surface
  charge pattern on a photoconductor.
• Visible images consist of fine charged
  particles called toners.

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Xerographic Prints are composed of toners
5-10 microns
COLOR
prints are halftones
Digital
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Inside a xerographic printer
Photoreceptor
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Photoreceptor

• A semiconductor whose conductivity is a strong
  function of light exposure.

• Requirements
• Insulator in the dark.
• Conductor when exposed to light
• Builds up enough voltage.
• Uniform properties

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Charging Subsystem (Corotron)
Free ions are attractedto wire Free electrons
are repelled. Counter-charges build up on
grounded surfaces.
Rapidly moving electronsand ions collide with
airmolecules, ionizing them and creating a
corona.
Electrons continue tofollow Electric Field
linesto Photoreceptor until uniform charge
builds up
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Imaging/Exposure subsystem
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Development Subsystem
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Transfer to paper

• Electric field moves particles from photoreceptor
  to paper or transparency
• Detachment field must overcome toner adhesion to
  photoreceptor

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Fusing Subsystem

• Permanently affix the image to the final
  substrate
• paper of various roughness
• transparency (plastic)
• Apply heat and/or pressure

Hot Roll Fuser
Pressure Roll
Paper
Heat Roll
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Cleaning and Erase Subsystems

• Removes unwanted residual toner and charge from
  photoreceptor before next imaging cycle
• Physical agitation removes toner (blade or brush)
• Light neutralizes charge by making entire
  photoreceptor conductive

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Adhesion must be controlled
Toner must flow smoothly down dispenser
Toner must develop onto roll uniformly
Toner must transfer from roll to paper
paper
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Atomic force microscopy adhesion technique
Bring toner near surface
Push toner against surface
Retract toner until probe releases
200 mm
20 mm
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Additives control adhesion
Changing type type of additive modifies adhesion
Atomic Force Microscopy results
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Electrical Field Detachment of Fine Particles
E. Eklund, W. Wayman, L. Brillson, D. Hays, 1994
IST Proc., 10th Int. Cong. on Non-Impact
Printing, 142-146
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Electrical Field Detachment of Fine Particles
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Cloud Visualization Technique
Photoreceptor
Light Source
Digital Image Capture
Cloud Generator
Donor Roll
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Developing edge

• Shutter opened for long exposure to give average
  local toner density.

Background
Image
Voltage attracts toner
Voltage repels toner
Receiver
Donor
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Toner velocities in nip

• Time lapse photography exposes toner motion.

Development voltage 50 volts
150 volts
250 volts
350 volts

• Average toner velocity determined from averaging
  all path lengths divided by shutter speed.

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Cloud and line width measured simultaneously
1.0
Light attenuation
0.5
Toner pile height
0.0
Receiver
Donor
Distance Along Receiver
Distance across nip
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Future of Xerography

• Color Wide gamut, offset quality
• High Image Quality High resolution, continuous
  tone
• High Speed Full color at 200 pages per min, and
  higher
• Higher reliability No paper jams
• Lower cost Xerography vs. inkjet

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Conclusions

• Research in Xerographic printing means working
  with a lot of exciting physics.