A spherical aluminum oxide abrasive is the best choice for polishing resins like polycarbonate and acrylic. Here's why. Learn more: http://nanophase.com/markets/optical-surface-polishing/ "Nano Alumina Slurries for Improved Polishing on Thermoset and Thermoplastic Resins" was presented by Abigail Hooper at Optifab 2015 in Rochester, NY.

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Nano Alumina Slurries for Improved
Polishing on Thermoset and
Thermoplastic Resins
Abigail Hooper, Christopher Boffa, and
Harry Sarkas

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Outline
• Overview of plastic and aluminum oxide
• Experiments to analyze removal rate when varying size,
shape, and phase of alumina
• Impact of pad type on removal rate and surface finish
• Conclusions
• Questions
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Overview: Plastic Lenses
• Plastic lenses have gained popularity due to their favorable
characteristics over glass
– Lightweight optics
– Cheaper, high volume production at a lower cost
– Impact resistant
– Easily tinted
– Greater design freedoms
– High consistency
• Polishing plastic can be a challenge due to its high susceptibility to
scratching
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Overview: Aluminum Oxide alternative to Ceria
• Cerium oxide is a common polishing
abrasive
– Provides chemical and mechanical
benefits in glass polishing
– Chemical mechanism is not
accessible in polymer systems
– Expensive rare earth
• Aluminum oxide is a superior
alternative
– Highly customizable
– Superior economics
– Harder than cerium oxide allowing
for higher mechanical MRR
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Temperature transformation of hydroxides or oxohydroxides to corundum
via the formation of transitional alumina phases
•Sakar, A. M. “Preparation and characterization of alumina powders and suspensions.” Izmir Institute of
Technology. 2000. http://library.iyte.edu.tr/tezler/master/malzemebilimivemuh/T000043.pdf

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Plastics Polishing
• Objective: Examine the impact of alumina particle size,
shape, and crystal phase on removal rate and surface
finish when polishing plastic substrates
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http://syntecoptics.com/wp-content/uploads/2015/06/mold_min.jpg

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Experiment Setup
• PR Hoffman PR-1 66T Double-Sided Polisher
• Suba X non-embossed polyurethane pad and GNP-510CN High Loft felt pad
• Run Conditions Fixed
– 51 RPM
– 225 mL/min Flow Rate
– 2.0 PSI Downforce
• 5 kilograms of alumina slurry at 20 wt% solids
• Acrylic, Polycarbonate, and Zeonex® K26R Substrates
– 5 discs per run, 1-disc per 66T carrier
– Discs are 2 inches in diameter and 0.5 inches thick
• Removal Rate Gravimetrically determined (Å/min)
• Surface Roughness and scratching evaluated via Zygo NewView 8000 (RMS, nm)
– 20X Mirau objective, 2X zoom
– Zernike piston, tilt, power and sphere removal
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Polishing Slurries
• Experimental Aluminum Oxide polishing slurries produced by Nanophase
– Size
• 20, 40, and 150 nm
– Shape
• 20 and 40 nm = spherical
• 150 nm = tabular
– Phase
• 20 and 40 nm = delta/gamma
• 150 nm = alpha
– Additive
• With and without Aluminum Nitrate
– Used to facilitate hydrolysis of the polymer layer on the surface that is in direct contact with the slurry
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Results: Acrylic Substrates
• Significant advantage to using
150 nm alumina
• Use of accelerant is positive in
all cases, but more significant
on smaller particle sizes
• 20 nm alumina is significantly
faster than 40 nm alumina
• Heavy, deep scratching
observed with 40 nm, fewer
more shallow scratches with
150 nm
Acrylic
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Results Discussion: Acrylic Substrate
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• Question: Why would a 20 nm particle display higher rate than a 40 nm particle on
acrylic?
– Same shape and phase
• Hypothesis: Higher quantity of particles per unit space
– Acrylic is soft, more particles = more mechanical action to abrade surface
• Conclusion: More experiments needed; test 65 nm spherical particle for trend
Particle Size
Number of particles
per 1 mm3 Space
20 nm 238,732,415
40 nm 29,841,552
150 nm 565,884
Calculation assumes particles are aligned and touching diameter-to-diameter

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Results: Polycarbonate Substrate
Polycarbonate
• MRR increases as particle size
increases when using the
accelerant
• No MRR change among any
particle size when not using
accelerant
• Heavy, deep scratching observed
with 40 nm, fewer more shallow
with 150 nm
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Results Discussion: Polycarbonate Substrate
Polished with 40 nm Alumina Polished with 150 nm Alumina
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Results
Zeonex K26R
• No MRR advantage between 40
and 150 nm alumina when using
accelerant
• Accelerant does not appear
advantageous with any particle
size
• Removal rate can be
substantially increased when
using 150 nm without accelerant
• Results are very different from
acrylic and polycarbonate
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Results Discussion: Surface Finish
• Question: Why does the 150 nm
alumina have better surface
finish than the 40 nm alumina?
– Different shape, size, and phase
• Hypothesis: Spherical particle
rolls while tabular particle lies
flat against substrate when a
force is applied
• Conclusion: More experiments
needed; examine smaller tabular
particles
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Confirmation Testing
• Optimal Slurry for each substrate type selected
– Acrylic
• 150 nm Alumina with accelerant
– Polycarbonate
• 150 nm Alumina with accelerant
– Zeonex K26R
• 150 nm Alumina without accelerant
• Explored removal rate and surface finish on a high loft, felt like pad
designed for plastics and compared against a standard
polyurethane
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Confirmation Testing Results
Pad Type Measurement Acrylic Polycarbonate Zeonex® K26R
SubaX
Surface Roughness
RMS, nm
6.1 3.3 4.9
Removal Rate
Angstroms/min
66,707 5,112 22,409
GNP-510CN
Surface Roughness
RMS, nm
9.3 6.3 7.2
Removal Rate
Angstroms/min
79,404 9,334 24,876
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Conclusions
• Shape, size, and phase of the aluminum oxide particles can impact
the material removal rate and surface finish
• Particle size alone does not dictate the removal rate characteristics
observed
• Accelerants, when combined with the correct particle size and
morphology, can yield stepwise changes in removal rate
• Pad type can be utilized to tune in further rate improvements or
lower surface roughness values
• Additional experiments are needed to further understand how
particle morphology plays into creating a novel polishing slurry for
plastic substrates
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Thank you for joining us!
To request more information, visit
us at Booth 304 or go to
www.nanophase.com/slurry