Appeal 2006-2350
Application 10/444,104
INTRODUCTION
The claims are directed to a method of polishing a glass or glass-
ceramic substrate using a particular aqueous slurry composition that retards
hard settling. Slurry compositions normally used to polish glass or glass-
ceramic substrates contain abrasive particles dispersed in deionized water
and/or other liquids (Specification ¶ 0004). Cerium oxide is a commonly
used abrasive in such slurry compositions (id.). Unfortunately, cerium oxide
abrasives tend to hard settle, i.e., the abrasive particles fall out of the
dispersion and cannot be redispersed (Specification ¶ 0005). Hard settling
results in a sludge that clogs pipes and processing equipment, a condition
that is highly problematic in an industrial operation (id.). Appellants’
Specification describes a number of additives useful for retarding hard
settling among which is a combination of sodium alginate with a divalent
metal salt, such as a calcium salt (Specification ¶¶ 0007 and 0022). Claim
19 is illustrative of the subject matter on appeal:
19. A method of polishing a glass or glass-ceramic substrate
comprising introducing an aqueous slurry composition between a polishing
pad and the substrate when the polishing pad and substrate are pressed into
contact with each other and moving relative to each other, wherein the
aqueous slurry composition comprises from about 1% to about 20% by
weight of a solids portion comprising:
abrasive particles, the abrasive particles comprising high purity
cerium oxide and/or cerium-containing mixed rare earth oxides,
provided that the amount by weight of cerium oxide present as
a percent of the total rare earth oxide is greater than or equal to
50%;
a polyacrylate in an amount within the range of from about 0.5% to
about 10% by weight of the solids portion;
sodium alginate in an amount within the range of from about 0.1% to
about 10% by weight of the solids portion; and
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