Small Particle Adhesion: Measurement and Control

1. Small Particle Adhesion: Measurement and Control Howard Mizes Elliott Eklund Mary Ott Dan Hays Xerox Corporation August 26, 1996

2. Inside the Docucolor 40

3. 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

4. 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?

5. Tools used to probe adhesion Atomic Force Microscopy Electric Field Detachment Centrifugal Detachment

6. laser diode split photodiode transparent electrode cantilever particle piezoelectric: moves up and down Atomic Force Microscopy Probes adhesion and attraction of single particles to surfaces with high precision. 20 m

7. Centrifugal Detachment Probes adhesion of heterogenous particles to a surface and any spatial effects.

8. V Electric Field Detachment Uses evanescent waves to monitor the toner removed from a plate by an applied electric field. Receiver Donor V

9. Comparison of techniques

10. Physical factors that control adhesion + + + E + + + + + • Neighboring particles? • Particle charge • Surface morphology FA = F0 + q2 - qE + E2

11.   R R t s F  W   A R  R   t s 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

12. 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

13. 1.0 0.8 0.6 Fraction removed 0.4 0.2 0.0 0 100 200 300 400 500 Removal Force (nN) 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)

14. Additives control adhesion Changing type type of additive modifies adhesion Atomic Force Microscopy results

15. Adhesion of 37 m glass particle 200 150 100 Adhesion (nN) 50 0 0.00 0.01 0.02 0.03 Electric field (V/m) 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

16. 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) 10 50% removal 20% removal 10% removal 1 No charge Low charge High charge

17. 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 3 nonuniform charge typical experimental value 2 Toner contact area (% of sensor area) 5 4 1 3 Calculated adhesion (V/m) 2 1 0 0 0 2 4 6 8 10 12 14 16 18 uniform charge nonuniform charge Detachment Field (V/m)

18. 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)

19. 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.