1

On Counter-Charges in

Development Rollers for

Electrophotography

Inan Chen and Ming-Kai Tse

Quality Engineering Associates (QEA), Inc.

Burlington, MA, USA

www.qea.com

NIP22NIP-22 Denver, September. 2006

2

Counter-Charges in Development Rollersfor Electrophotography

Latent images developed by moving Charged Toners

- Extensively studied.

Counter-charges : Little attention

- Reside in carrier beads (2-component development),

or development rollers (Single-Component Dev.)

Objectives:

• Quantitative analyses of roles of counter-charges

in Toner-charging and Toner-deposition in SCD

• Requirements for ideal roller coating materials,

and characterization method for SCD rollers

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3

Single-Component Development (SCD)

2. Toner Charging at

Metering Blade (MB):

Charges supplied to toner,

Counter-charges to Roll coating

3. Toner deposition:

Charged toners move to PR,

Counter charges impede toner motion,

must be removed (neutralized)

to improve deposition efficiency

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1. Development Rolls:

Conductive elastomer core

Semi-insulator Coating

MB

Dev.Roll

PR

VB

VB

4

Single-component Development

Induction at charging, and

Neutralization at deposition of Counter Charges

Charge injection and transport

in Semi-insulator Coating layer

Charge-Transport Model

Non-Ohmic nature

Applied and reported :

Roller charging of PR (NIP21)

Electrostatic toner transfer (NIP16, 20, ICIS’06)

Liquid development (J. App. Phy. 80, 6796)

Counter-charges in SCD (This talk)

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MB

Dev.Roll

PR

VB

VB

MB

Dev.Roll

PR

VBVB

VB

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Charge Transport Model

Semi-insulators characterized by 3 parameters

1. Densities of mobile charges, qp(y, t), qn(y, t),

Initial (intrinsic) value: qi = qp(y, 0) = –qn(y, 0)

2. Charge mobility: (E) - field dependent

3. Charge injection strength s

Injection currents from boundary at y

Ji = sE(y), E(y) = field at y ( = 0 or L)

Continuity eq. q(y, t)/t = – (qE)/y

Poisson’s eq. E(y, t)/y = (qp + qn)/

Results for SCD charging and deposition

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+ + + + + +sp, sn

– – – – – –

y

L

0

6

Bias voltage VB

Toner charge density:

QT(t) = [VB – QR(t)DR – UR(t)]/(DT/2 + DR) (D = L/ = 1/C)

• QR(t) = Interface charge density

• UR(t) = 0LR dy0

y’(qP + qN)dy’/R

• Transport equations, calculate QR(t), UR(t) QT(t)

NIP22 Toner Charging in SCD (1)

Toner Coating

Thickness: LT LR

Permittivity: T R

} Counter-charges

–VB

Metering Blade

– – Toner – – QT

Roll-Coating

QR + + + + + + + +

yR

yT

0

0

LR

s

7

Toner Charging in SCD (2)

Growth of toner charge QT(t)

with time

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Dependence on Injection Strength s very significant at t 100to

High speed printing -- short charging time: high s important

0

1

2

3

4

5

1 10 100 1000Time

-To

ner

Ch

arg

e D

ensi

ty

Vb = 0.2qi = 0.1up= un= 1 Lr = 1Lt = 0.3 r = 1 t = 1

SCDC060107/1

s = 1

0.3

0.1 0.03

0.01

Units: to = LR

2/oVB 10 msec so = oqo = o/to 3x10–11 S/cm qo= oVB/LR

2 3x10–6 C/cm3

–VB

Metering Blade

– – Toner – – QT

Roll-Coating

QR + + + + + + + +

yR

yT

0

0

LR

s

–VB

Metering Blade

– – Toner – – QT

Roll-Coating

QR + + + + + + + +

yR

yT

0

0

LR

s

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Toner Charging in SCD (3)

Dependence on mobility p, n

in RC

For QT< 0

• Smaller pos mobility p

has significant effect (A, B, C)

• Insensitive to neg n (A, D)

• Build-up of counter-charge

mostly from injection of

pos charge from VB,

not from depletion of

neg charge in coating layer

Units

Mobility: o 10–5 cm2/ Vs

Time: to = LR2/oVB 10–2 sec

Chg density: qo= oVB/LR2

3x10–6 C/cm3

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0

1

2

3

4

5

1 10 100 1000Time

-To

ner

Ch

arg

e D

ensi

ty

Vb = 0.2qi = 0.1s = 0.1

SCDC060107/1

A

B

D

C

up un A: 1.0 1.0B: 0.1 1.0C: 0.01 1.0D: 1.0 0.0 –VB

Metering Blade

– – Toner – – QT

Roll-Coating

QR + + + + + + + +

yR

yT

0

0

LR

s

–VB

Metering Blade

– – Toner – – QT

Roll-Coating

QR + + + + + + + +

yR

yT

0

0

LR

s

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Toner Deposition in SCD (1)

Fields and Voltages in layers

• Photoreceptor: EP, VP

• Toner-layer: ET(y), VT

• Roller coating: ER(y), VR

Bias voltage: -VB = VP + VT + VR

Gauss’ theorem relates charges QP, QR, QT to E’s

Field in toner layer:

ET(y, t) = ET0 + (QT/)(y/LT(detail in Proc.

paper)

= func.[VB, QP, QT, QR(t), UR(t), L’s, ’s]

Injection & transport of Counter-charges in RC

contribute to QR(t), UR(t)

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–LPPR

Roll Coating (RC)

–VB

– – Toner – –

QP

LT

0

y

+ + + + QR

–LPPR

Roll Coating (RC)

–VB

– – Toner – –

QP

LT

0

y

+ + + + QR

QT

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Toner Deposition in SCD (2)

Negative toner deposition: ET(y, t) > 0

Demarcation line at y = YD

ET > 0 for y < YD

ET < 0 for y > YD

ET(YD) = ET0 + (QT/T)(YD/LT) = 0

Deposition efficiency:

YD/LT = – TET0/QT

= func.[VB, QP, QT, QR(t), UR(t), L’s, ’s] (in proc. paper)

QR(t), UR(t) from Transport Eqs.

Time evolution of Deposition efficiency YD/LT

–LP

PR

Roll Coating (RC)

–VB

– – Toner – QT QP

LT

0

y

+ + + +QR

YD

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Toner Deposition in SCD (3)

Deposition efficiency YD/LT vs. time

Dependence on strength s

of injection into RC from VB

Significant effects

due to small s,

in time 10 < t <100

Time unit:

to = LR2/oVB 10 msec

0.5

0.6

0.7

0.8

0.9

1.0

0.1 1 10 100 1000Time

Yd

/Lt

Vd =1qt = 5qi = 0.1Lt =0.2up=un=1

0.01

SCD060227/1

s = 1

0.3

0.1

0.03

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–LPPR

Roll Coating (RC)

–VB

– – Toner – QT

QP

LT

0

y

+ + + + QR

YD

–LPPR

Roll Coating (RC)

–VB

– – Toner – QT

QP

LT

0

y

+ + + + QR

YD

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0.5

0.6

0.7

0.8

0.9

1.0

0.1 1 10 100 1000Time

Yd

/Lt

Vd =1qt = -5qi = 0.1s = 0.1Lt =0.2

up un A: 1 1B: 1 0.1 C: 1 0.01D: 0 1

A

B

C

D

SCD060227/2

Toner Deposition in SCD (4)

Charge mobility (P, N) dependence of YD/LT (QT< 0)

Neg. n reduced (A B C)

Significant decrease Pos. p reduced (A D)

No effects Neutralize Counter-charge

requires negative charge

injection and transport

opposite to polarity

required at chargingFor efficient charging & deposition, it requires

good injection (s) and transport () for bothpos and neg charges in SCD roller-coating

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Summary and Conclusions (1)

In SCD, Counter Charges in semi-insulator coating

Induced at toner Charging, and

Neutralized at toner Deposition steps Analyses: Charge-Transport model Good bi-polar charge injection and transport

e.g., for negative toners,

Pos. charge inject. & transport for Charging

Neg. charge inject. & transport for Deposition

Process time > 100 to (to = LR2/VB)

High speed printing requires high mobility (+ and –) Dev. Roller performance can’t be evaluated properly

with closed-circuit resistance measurements

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Summary and Conclusions (2)

Alternative evaluation method:

Electrostatic Charge Decay (ECD) technique

(NIP-11, 15, 16, 17; ICIS’02; JHC-00, 02, 05)

Open-circuit voltage decay

- simulating actual process in Electrophotography

Field applied by Corona charging

- Scan and map large area,

efficient, non-destructive

Applied to transfer belts, paper,

charge rolls, dev- rolls, PR

Consistently predict device performance

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Voltageprobe

-------

Corona

sample

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ECD Data for Intermediate Transfer Belt

© 2005 Quality Engineering Associates (QEA), Inc. All Rights Reserved

(a) Voltage

0

100

200

300

0 50 100 150 200 250

Position (mm)

Vo

ltag

e (V

)Voltage *

Rolls and Belts Testing Fixture

Exhibit Booth #210

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Thank you for your attention

Please visit

Exhibition Booth #210

Inan Chen and Ming-Kai Tse

Quality Engineering Associates (QEA), Inc.

Burlington, MA, USA

www.qea.com

NIP22

NIP-22 Denver, September. 2006