Anionic abrasive particles treated with positively charged polyelectrolytes for cmp
A polyelectrolyte, electropositive technology for use in the field of polishing compositions
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Embodiment 1
[0033] This embodiment illustrates a method for manufacturing the polyelectrolyte-coated abrasive particles exhibiting colloidal stability according to the present invention.
[0034] The poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine) solution (50% by weight, MW~75,000) was dissolved in deionized water, and the pH was adjusted with concentrated sulfuric acid until the silica was added. The pH is 4.5. The mixture was then blended at a speed of 20,000 rpm. During the blending, a suspension of colloidal silica particles (50% by weight, 120 nm, Zeta (ζ) potential at pH 4.5 from -15 to -20 mV) was slowly added to the mixture over a period of 6 minutes. in. This mixture was blended for an additional minute to produce a final composition containing 12% by weight silica and 2.5% by weight polyelectrolyte. The average particle diameter of the obtained polyelectrolyte-coated silica particles was 132 nm. The zeta (ζ) potential measured at pH 4.5 is +28 mV.
[0035] The polyelectro...
Embodiment 2
[0038] This example shows that the abrasive particles coated with polyelectrolyte will not agglomerate over time.
[0039] 0.625% by weight of polyethylenimine was dissolved in deionized water at pH 7, and the resulting solution was used to treat the fumed silica dispersion (5% by weight, the zeta potential of pH 7 was -20 mV, 156 nm ). High shear is applied to the mixture for about 20 minutes to produce a colloidal stable composition with a zeta (ζ) potential of +15 millivolts at pH 7. The average particle size of the obtained abrasive composition was 158 nm. After 27 days, the average particle size was 167 nm.
[0040] This example proves that the abrasive particles coated with the positively charged polyelectrolyte are highly stable.
Embodiment 3
[0042] This example demonstrates that abrasive particles with a positive zeta (ζ) potential can convert charges when contacted with a charge reversing agent, and are covered with a positively charged polyelectrolyte to produce a stable dispersion of abrasive particles coated with polyelectrolyte.
[0043] A fumed alumina dispersion (3% by weight, zeta potential = +30 to +40 mV at pH 6) was mixed with tartaric acid (1.25% by weight). The zeta (ζ) potential of the obtained abrasive particle dispersion at pH 7 was -15 millivolts, so it was proved that an abrasive having a positive zeta (ζ) potential can switch charges by contacting the abrasive with a charge reversing agent.
[0044] Similarly, the same type of baking alumina dispersion (3% by weight, pH 6 Zeta (ζ) potential = +) was treated with an aqueous solution containing tartaric acid (100 ppm) and polyethylenimine (0.125% by weight). 30 to +40 millivolts) and apply high shear for 20 minutes. The stability of the obtained polye...
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