Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Reexamination Certificate
1999-07-14
2001-04-24
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
C051S307000, C106S003000, C510S167000, C510S180000, C510S181000, C510S397000, C451S036000
Reexamination Certificate
active
06221119
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention pertains to methods for polishing glass or glass ceramic substrates used to manufacture of magnetic disks. This invention also pertains to slurry compositions for polishing such glass or glass ceramic substrates
A typical prior art process for manufacturing a magnetic disk comprises the following steps:
1. A substrate is polished and textured.
2. An underlayer (e.g. Cr, an alloy of Cr, NiP, NiAl or other materials), a magnetic alloy layer (e.g. a Co alloy), and a protective overcoat (e.g. carbon or hydrogenated carbon) are sputtered, in that order, onto the substrate.
3. A lubricant layer is applied to the protective overcoat. Typical substrates used for magnetic disks comprise NiP-plated aluminum, chemically strengthened glass, or glass-ceramic.
It is necessary to polish a glass or glass ceramic substrate before depositing the various layers thereon. The most effective polishing slurries for polishing glass contain CeO
2
, ZrO
2
, or Fe
2
O
3
. Of these, CeO
2
is the most commonly used.
It would be desirable to increase the polishing rate exhibited by slurries. However, in doing so, there are several slurry characteristics one would want to improve.
1. Slurry particles have a tendency to “settle”. It would be desirable to slow the rate of settling.
2. It would also be desirable to prevent the slurry from foaming during use.
3. It would also be desirable to ensure that the slurry is “redispersible.” By redispersible, I mean that if the slurry particles settle, they can be redispersed within the slurry.
SUMMARY
A slurry in accordance with my invention comprises oxide polishing particles and a polyacrylate. In one embodiment, the polishing particles are CeO
2
particles, and the polyacrylate is sodium polyacrylate. However, in lieu of sodium, other monovalent ions can be used. For example, potassium polyacrylate or ammonium polyacrylate can be used. The CeO
2
particles and the polyacrylate are typically in an aqueous solution. This solution can contain other additives as well.
In one embodiment, the slurry of the present invention is used to polish a glass or a glass ceramic substrate. The slurry can be used in conjunction with any of a number of types of polishing apparatus, e.g. ring polishers, planetary polishing apparatus, or other polishing machines. The polishing apparatus typically comprises one or more polishing pads that push against a surface of the substrate being polished. The slurry is introduced into the space between the polishing pad and the substrate so that the slurry can be used to polish the substrate.
I have discovered that adding the polyacrylate to a CeO
2
slurry enhances the polishing rate of the slurry without adversely impacting the slurry settling rate, without negatively impacting redispersibility, and without causing excessive foaming.
In addition to, or in lieu of using CeO
2
particles, other oxide particles can be used in conjunction with my invention, e.g. oxides such as ZrO
2
, ThO
2
, SnO
2
, Cr
2
O
3
, Al
2
O
3
or Fe
2
O
3
can be used.
After polishing, the substrate is used to manufacture a magnetic disk. This is typically accomplished by sputtering an underlayer, a magnetic layer, and a protective overcoat on the substrate. (Additional layers can also be deposited on the substrate, depending upon the design of the magnetic disk. In addition, deposition techniques other than sputtering such as plating or evaporation can also be used.)
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Komag, Inc.
Marcheschi Michael
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