National Science Foundation CRCD project lecture (April 14, 2003)

1. Particle Transport, Deposition, and
Removal in Xerography
NSF CRCD Project Lecture
April 14, 2003
Fa-Gung Fan
Wilson Center for Research & Technology
Xerox Corporation
Webster, NY
http://chester.xerox.com/innovation/wcrt.html
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

2. Outline of the Lecture
General Overview of Xerography
Transport, Adhesion/Cohesion and Removal of Fine
Particles (Toner) in Xerography
Measuring Toner Charge --- Cage Blowoff, Charge Spectrograph
Electrostatic Adhesion, Detachment of Toner Particles
Measuring Toner Adhesion --- Atomic Force Microscopy (AFM),
Centrifuge Detachment, Electric Field Detachment
Measuring Cohesion --- Fluidized Bed
Modeling of Electrostatics in Subsystems
(in MAE Seminar 4:00-5:00pm today)
Q&A
Acknowledgements:
S. Chang, C. Duke, D. Hays
N. Goodman, H. Mizes
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

3. Xerographic Process
5
2 Fusing
Exposure
1 6
Cleaning
Charging
4
Transfer
Photoreceptor
SN
SN
Substrate
N
S N
Development
Paper
3
C. Duke, J. Noolandi, T. Thieret, “The surface
science of xerography,” Surface Science, 500, p.
1005, (2002)
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

4. Xerox Phaser 7700 Color Desktop Laser
Printer
22 prints/min, full-color
Xerography is a versatile technology that scales from desktop, to
office, to production machines; black-and-white, hightlight color,
and full color.
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

5. DocuColor 40 Pro Color Office
Multifunction Machine
40 prints/min, full-color
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

6. DocuTech 6180 Production Publisher
180 prints/min
Black-and-White
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

7. DocuColor iGen3 Digital Production Color
Press
100 prints/min, full-color
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

8. iGen3
Xerographic Unit
Finisher/Binder
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

9. Photoreceptor
A semiconductor whose
conductivity is a strong 0
0 5
Voltage on Surface (V)
function of light exposure.
_ _ _ _ _ _ _ _ _ _ _
_+_+
-1000
++ + + + + + ++ ++ + + +
Exposure (ergs/cm2)
Electron/hole pairs
• Requirements
– Insulator in the dark.
– Conductor when exposed to light
– Builds up enough voltage.
– Uniform properties
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

10. Charging Subsystem
HV Power HV Power HV Power
Supply (-) Supply (-) Supply (-)
Free ions are attracted Rapidly moving electrons Electrons continue to
to wire; Free electrons are and ions collide with air follow Electric Field lines
repelled. Counter-charges molecules, ionizing them to Photoreceptor until
build up on grounded surfaces. and creating a corona. uniform charge builds up
Positive Ions
Electrons
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

11. Imaging/Exposure
Traditional Analog Copier Laser Printer
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

12. Development
Photoreceptor Photoreceptor
Toner
Apply E
Field E
Development roll Development roll
Development
Photoreceptor
Roll
Charge particles
triboelectrically
Electric field moves
Mixing
Charging particles from developer
roll to photoreceptor
Triboelectrification of
toner particles and carrier
beads
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

13. Toner
• Charging
• Adhesion/cohesion
• Powder flow
• Rheology
5-10 microns
• Color - hue and density
• Pigment dispersion
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

14. Toned Carrier Bead
q ≅ 2 x 104 e
m ≅ 2 x 10-10 gm
q/m ≅ 16 µC/gm
20 µm
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

15. Transfer
Paper
Apply E Paper
Paper Field &
Separate E
Photoreceptor Photoreceptor
Photoreceptor
Electric field moves particles from
photoreceptor to paper or transparency
Detachment field must overcome toner
adhesion to photoreceptor
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

16. Fusing Subsystem
Permanently affix the image to the final substrate
paper of various roughnesses and surface treatment
transparency (plastic)
Apply heat and/or pressure
Hot Roll Fuser: Pressure Roll
Unfused toner Fused toner Paper
Elastomer Heat Roll
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

17. Cleaning and Erase
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
Photoreceptor
_
_
_
_
_
Charge
Residual toner
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

18. Transport, Adhesion/Cohesion and Removal
of Fine Particles (Toner) in Xerography
Toner must flow smoothly
down dispenser
Toner must develop
onto roll uniformly
Toner must transfer from
roll to paper
paper
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

19. Toner Charge Measurements
Blowoff Tribo
Air
50
40
Q/M (µC/gm)
30
Blow toner
µ
from toned 20
beads in cage
10
Measure
charge & mass 0
difference 0 1 2 3 4
Calculate Toner Concentration (%)
average Q/M
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

20. Toner Charge Measurements
Charge Spectrograph
1.5
99%
95%
q/D (fC/µm)
1 90%
Air Flow
µ 80%
E Field 50%
0.5 Lycopodium
0
Inject toner
0 5 10 15 20 25 30 35
Displacement
∝ q/D -0.5 Diameter (µm)
µ
Measure
position &
size of
particles
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

21. Toner Adhesion Forces
Fa Particle adhesion
depends on:
++ + ++
+ Size, shape, &
roughness
+ Materials
+
+
+ + Flow agents
++ ++
Charge
Surface charge
Fad distribution on
particle
Detachment when Fa > Fad
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

22. Electrostatic Image Force Model
Q
Fa σ=
E R 4 π R2
Fi
Image Force Applied Force
Q2
Fi = − α Fa = β QE − γ π ε o R 2 E 2
16 π ε o R2
αQ
Ed ≅ ≈ 1 V / µm
β 16 π ε o R 2
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

23. Charge Patch Adhesion Model
Q = σ At
Fa
Ac
Ac
Fad f =
At
2
σ
F ad = − A c − W A c
2 εo
 σ W
= −Qf 
 2ε + 
 o σ 

Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

24. Additives Control Adhesion
Changing type of additive modifies adhesion
Atomic Force Microscopy results
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

25. Atomic Force Microscopy (AFM)
Bring toner Push toner Retract toner until
near surface against surface probe releases
200 µm
20 µm
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

26. AFM
Measure Single Particle Adhesion
Laser
Photodetector
Particle
Cantilever
Piezoelectric:
moves up
and down
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

27. Centrifuge Detachment
Measure Many Particle Adhesion
Putt, putt, putt,... Vroom, vroom,... Whoosh,...
Observe Donor Plate after Each Spin
H. Mizes, “Adhesion of Small Particle”, Electro. Soc. Amer.
Univ. of Rochester, 6/23/95
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

28. Electric Field Detachment
Measure Many Particle Adhesion
transparent
conductive
electrodes
Donor Receiver
V
E. Eklund, W. Wayman, L. Brillson, D. Hays, 1994 IS&T Proc.,
10th Int. Cong. on Non-Impact Printing, 142-146
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

29. Electrical Field Detachment of
Charged Toner
Detachment Cell
Adhesion of Triboelectrically Charged Toner
1
Transferred Fraction
0.8
0.6
0.4
0.2
0
0 2 4 6 8 10 12 14 16 18
Detachment Field (V/µm)
µ
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

30. Toner Transferred
When FE > FAD
FE
-
-
Donor Surface
- -
FAD
E. Eklund, W. Wayman, L. Brillson, D. Hays, 1994 IS&T Proc.,
10th Int. Cong. on Non-Impact Printing, 142-146
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

31. Fluidized Bed
Measure Powder Cohesion
Stresses on the toner bed
τ σ
α α
h
σ
∆P
Tension Compression
σ = ρ (1−ε) gh cos α − ∆ P
(1−
Shear
τ = ρ (1−ε) gh sin α
(1−
P.K. Watson, “Yield Locus of Cohesive Granular Materials”, Workshop on
Dynamics of Granular Materials: Understanding & Control, Univ. of Chicago,
5/11/95
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

32. 70
Te nsi on
60 C ompression Less Additives
τ , She ar Stre s s (N/m2 )
50
More Additives
40
30
20
10
0
-30 -20 -10 0 10 20 30 40 50 60 70
σ , Compre s s ive Stre s s (N/m2 )
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003

33. Q&A
Fa-Gung Fan, Xerox Corporation MAE Dept., Clarkson University, 4/14/2003