particle transport, deposition, and removal in xerography (fa-gung fan)

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

NSF CRCD Project Lecture

April 14, 2003

Fa-Gung Fan

Wilson Center for Research & Technology

Xerox Corporation

Webster, NYhttp://chester.xerox.com/innovation/wcrt.html

Particle Transport, Deposition, and Removal in Xerography

Outline of the Lecture

� General Overview of Xerography

� Transport, Adhesion/Cohesion and Removal of Fine Particles (Toner) in XerographyMeasuring Toner Charge --- Cage Blowoff, Charge SpectrographElectrostatic Adhesion, Detachment of Toner ParticlesMeasuring Toner Adhesion --- Atomic Force Microscopy (AFM), Centrifuge Detachment, Electric Field DetachmentMeasuring Cohesion --- Fluidized Bed

�� Modeling of Electrostatics in SubsystemsModeling of Electrostatics in Subsystems(in MAE Seminar 4:00(in MAE Seminar 4:00--5:00pm today)5:00pm today)

�� Q&AQ&A

Acknowledgements:

S. Chang, C. Duke, D. Hays

N. Goodman, H. Mizes

Xerographic Process

ChargingCleaning

Exposure

Fusing

Transfer

PhotoreceptorSubstrate

S NS N

Development

C. Duke, J. Noolandi, T. Thieret, “The surface

science of xerography,” Surface Science, 500, p.

1005, (2002)

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.

DocuColor 40 Pro Color Office Multifunction Machine

DocuTech 6180 Production Publisher

180 prints/min

Black-and-White

DocuColor iGen3 Digital Production Color Press

Xerographic Unit

Finisher/Binder

�A semiconductor whose

conductivity is a strong

function of light exposure.

Exposure (ergs/cm2)

Electron/hole pairs

_ _ _ _

+ + + + ++ +

_ _ _ __ _ _ _

+ + + + ++ ++ + + + ++ + + + ++ +

_ _ __ _ _

_ _ _ _

+ + ++ ++ +

_ _ _ __ _ _ _

+ + ++ ++ +

• Requirements

– Insulator in the dark.

– Conductor when exposed to light

– Builds up enough voltage.

– Uniform properties

Photoreceptor

Charging Subsystem

Electrons

Positive Ions

Electrons

Positive Ions

Free ions are attracted

to wire; Free electrons are

repelled. Counter-charges

build up on grounded surfaces.

Rapidly moving electrons

and ions collide with air

molecules, ionizing them

and creating a corona.

Electrons continue to

follow Electric Field lines

to Photoreceptor until

uniform charge builds up

HV Power

Supply (-)

HV Power

Supply (-)

HV Power

Supply (-)

HV Power

Supply (-)

HV Power

Supply (-)

HV Power

Supply (-)

Imaging/Exposure

Traditional Analog Copier Laser Printer

Development

� Charge particles

triboelectrically

� Electric field moves

particles from developer

roll to photoreceptor

Apply E

Development roll

Photoreceptor Photoreceptor

Development roll

r Development

Mixing

Charging

r Development

Mixing

Charging

Triboelectrification of

toner particles and carrier

5-10 microns5-10 microns

• Charging

• Adhesion/cohesion

• Powder flow

• Rheology

• Color - hue and density

• Pigment dispersion

q ≅≅≅≅ 2 x 104 em ≅≅≅≅ 2 x 10-10 gm

q/m ≅≅≅≅ 16 µµµµC/gm

20 µm

Toned Carrier Bead

Transfer

Apply E

Field &

Separate

Photoreceptor

� Electric field moves particles from

photoreceptor to paper or transparency

� Detachment field must overcome toner

adhesion to photoreceptor

Photoreceptor

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

Heat Roll

Pressure Roll

Heat Roll

Elastomer

Unfused toner Fused toner

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

Residual toner

Charge

Transport, Adhesion/Cohesion and Removal of Fine Particles (Toner) in Xerography

Toner must transfer from

roll to paper

Toner must flow smoothly

down dispenser

Toner must develop

onto roll uniformly

Toner Charge Measurements

Blowoff Tribo

� Blow toner from toned beads in cage

� Measure charge & mass difference

� Calculate average Q/M

0 1 2 3 4

Toner Concentration (%)

(µµ µµ

Toner Charge Measurements

Charge Spectrograph

0 5 10 15 20 25 30 35

Air Flow

E Field

Diameter (µµµµm)

/ µµ µµm

� Inject toner

� Displacement ∝∝∝∝ q/D

� Measure position & size of particles

Lycopodium50%

90%95%

Particle adhesion depends on:

� Size, shape, & roughness

� Materials

� Flow agents

� Charge

� Surface charge distribution on particle

Toner Adhesion Forces

++++ +

Detachment when Fa > Fad

σσσσππππ

oR==== −−−− αααα

ππππεεεε

Fa QE o R E==== −−−−ββββ γγγγ ππππ εεεε 2 2

o R≅≅≅≅ ≈≈≈≈

αααα

ββββ ππππ εεεεµµµµ

16 21 V / m

Image Force Applied Force

Electrostatic Image Force Model

Q At==== σσσσ

At====

Charge Patch Adhesion Model

ad AWAF −−−−−−−−====εεεε

σσσσ

++++−−−−====

σσσσεεεε

σσσσ WQf

Additives Control Adhesion

Changing type of additive modifies adhesionChanging type of additive modifies adhesion

Atomic Force Microscopy results

Atomic Force Microscopy (AFM)

Bring toner

near surface

Push toner

against surface

Retract toner until

probe releases

200 µm

20 µm

Measure Single Particle Adhesion

Cantilever

Photodetector

Particle

Piezoelectric:

moves up

and down

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

Electric Field Detachment

VVDonor ReceiverV

transparent

conductive

electrodes

Measure Many Particle Adhesion

E. Eklund, W. Wayman, L. Brillson, D. Hays, 1994 IS&T Proc.,

10th Int. Cong. on Non-Impact Printing, 142-146

Electrical Field Detachment of Charged Toner

Detachment Cell

0 2 4 6 8 10 12 14 16 18

Detachment Field (V/µµµµm)

Adhesion of Triboelectrically Charged Toner

Toner Transferred

When FE >>>> FAD

Donor Surface-

Toner Transferred

When FE >>>> FAD

Donor Surface

E. Eklund, W. Wayman, L. Brillson, D. Hays, 1994 IS&T Proc.,

10th Int. Cong. on Non-Impact Printing, 142-146

Fluidized Bed

Measure Powder Cohesion

P.K. Watson, “Yield Locus of Cohesive Granular Materials”, Workshop on

Dynamics of Granular Materials: Understanding & Control, Univ. of Chicago,

5/11/95

αααα

∆ ∆ ∆ ∆ P

ααααττττ σσσσ

σσσσ

Stresses on the toner bed

σ = ρ (1σ = ρ (1σ = ρ (1σ = ρ (1−−−−ε)ε)ε)ε) gh cos α α α α −−−− ∆ ∆ ∆ ∆ P

τ = ρ (1τ = ρ (1τ = ρ (1τ = ρ (1−−−−ε)ε)ε)ε) gh sin αααα

Tension \ Compression

αααα

∆ ∆ ∆ ∆ P

ααααττττ σσσσ

σσσσ

Stresses on the toner bed

σ = ρ (1σ = ρ (1σ = ρ (1σ = ρ (1−−−−ε)ε)ε)ε) gh cos α α α α −−−− ∆ ∆ ∆ ∆ P

τ = ρ (1τ = ρ (1τ = ρ (1τ = ρ (1−−−−ε)ε)ε)ε) gh sin αααα

Tension \ Compression

ττ ττ,, ,,

Tension

Compression

-30 -20 -10 0 10 20 30 40 50 60 70

σσσσ ,,,, Compress ive Stress (N/m2)

Less Additives

More Additives

ττ ττ,, ,,

Tension

Compression

-30 -20 -10 0 10 20 30 40 50 60 70

σσσσ ,,,, Compress ive Stress (N/m2)

Less Additives

More Additives

Q&AQ&A

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