Small particle adhesion: measurement and control

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Small Particle Adhesion Measurement and Control
Howard Mizes Elliott Eklund Mary Ott Dan Hays
Xerox Corporation
August 26, 1996
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Inside the Docucolor 40
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Adhesion control is key for high image quality
Toner must flow smoothly down dispenser
Toner must develop onto roll uniformly
Toner must transfer from roll to paper
paper
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Toners are highly variable particles

• Characteristics
• Typically 10 ?m in diameter
• Polymers
• Variations effect adhesion
• Irregularly shaped
• Size variations
• Charge variations
• Neighboring particle influence.

Can the variations be measured? What measures can
be taken to control the variations?
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Tools used to probe adhesion
Atomic Force Microscopy
Electric Field Detachment
Centrifugal Detachment
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Atomic Force Microscopy
Probes adhesion and attraction of single
particles to surfaces with high precision.
20 ?m
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Centrifugal Detachment
Probes adhesion of heterogenous particles to a
surface and any spatial effects.
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Electric Field Detachment
Uses evanescent waves to monitor the toner
removed from a plate by an applied electric field.
Receiver
Donor
V
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Comparison of techniques
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Physical factors that control adhesion



E

• Neighboring particles?
• Particle charge
• Surface morphology

FA F0 ?q2 - ?qE ?E2
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How morphology can effect adhesion
Adhesion can be modified by roughening a particle
or adding small particles to it.
Mechanism is area in contact (Derjaguin
approximation)
Higher adhesion
Lower adhesion
Quantified with
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Adhesion distributions for rough particles
1) Determine 3D particle topography with atomic
force microscopy.
2) Perform simulated random contacts - determine
curvatures.
Smooth particle
Rough particle
3) Extract adhesion distribution
toner
1.0
0.8
0.6
Relative number of occurences
0.4
0.2
carrier
0.0
0.00
0.10
0.20
0.30
0.40
Adhesion relative to perfect sphere
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Additives lower adhesion
Coating toner with a high coverage of nm size
particles significantly decreases
particle-surface adhesion
Centrifugal Detachment results
Covered with additives
No additives
1.0
0.8
0.6
Fraction removed
0.4
0.2
0.0
0
100
200
300
400
500
Removal Force (nN)
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Additives control adhesion
Changing type type of additive modifies adhesion
Atomic Force Microscopy results
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AFM measures electric field increasing adhesion
Parameters from the adhesion expression for
charged particles can be experimentally
determined.
FA F0 ?q2 - ?qE ?E2
y intercept
curvature of quadratic fit
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Particle charge can dominate toner adhesion
Centrifuge detachment of particles charged to 3
different levels. Force to remove given fraction
of 10 ?m particles extracted from force spectrum.
1000
100
Applied force (nN)
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50 removal
20 removal
10 removal
1
No charge
Low charge
High charge
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Adhesion of charged particles larger than theory
Toner is too adhesive
Charge patches explain why
Electric field detachment
uniform charge
theory for uniformly charged particle
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nonuniform charge
typical experimental value
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Toner contact area ( of sensor area)
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4
1
3
Calculated adhesion (V/?m)
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1
0
0
0
2
4
6
8
10
12
14
16
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uniform charge
nonuniform charge
Detachment Field (V/?m)
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Nonuniform charged affects toner layer adhesion
Neighboring particles can be quantified from
centrifugal detachment image.
Fringe fields increase adhesion
Neighboring particles have no effect
0.4
Increase less for charge patches
0.2
Fraction surrounding area
0
0
5
10
15
20
Centrifugal spin speed (kRPM)
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Summary

• Three characterization tools to measure different
  aspects of particle adhesion.
• Adhesion can be controlled with particle
  morphology and measured with these tools.
• Charge uniformity can dominate microscopic
  adhesion behavior.