nano alumina for improved plastic polishing (optifab 2015)

We Make NanoTechnology Work!® |

Nano Alumina Slurries for Improved Polishing on Thermoset and Thermoplastic Resins

Abigail Hooper, Christopher Boffa, and Harry Sarkas

We Make NanoTechnology Work!® | 2

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


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


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

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


Plastics Polishing

• Objective: Examine the impact of alumina particle size, shape, and crystal phase on removal rate and surface finish when polishing plastic substrates

http://syntecoptics.com/wp-content/uploads/2015/06/mold_min.jpg


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


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


Results Discussion: Acrylic Substrate

• 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 SizeNumber of particles

per 1 mm3 Space20 nm 238,732,41540 nm 29,841,552

150 nm 565,884Calculation assumes particles are aligned and touching diameter-to-diameter


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


Results Discussion: Polycarbonate Substrate

Polished with 40 nm Alumina Polished with 150 nm Alumina


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


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


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


Confirmation Testing Results

Pad Type Measurement Acrylic Polycarbonate Zeonex® K26R

Suba X

Surface RoughnessRMS, nm 6.1 3.3 4.9

Removal RateAngstroms/min 66,707 5,112 22,409

GNP-510CN

Surface RoughnessRMS, nm 9.3 6.3 7.2

Removal RateAngstroms/min 79,404 9,334 24,876


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


Thank you for joining us!To request more information, visit

us at Booth 304 or go towww.nanophase.com/slurry

nano alumina for improved plastic polishing (optifab 2015)

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