Patent ID: 8834589
Filing Date: 2014-09-16
Classification: C09G,C09K,G11B

Abstract:
1. A polishing composition for a magnetic disk substrate comprising: water; silica particles; and at least one or more selected from the group consisting of an acid, a salt of the acid, and an oxidizing agent, wherein the silica particles have a value (SF1) of 113, wherein the value is obtained by dividing an area of a circle whose diameter is the maximum diameter of the silica particle by the projected area of the silica particle and multiplying the result by 100, when observed with a transmission electron microscope to measure the maximum diameter and the projected area of each particle, wherein the silica particles have a value (SF2) of 102, wherein the value is obtained by dividing an area of a circle whose circumference is a perimeter of the silica particle by the projected area of the silica particle and multiplying the result by 100, when observed with a transmission electron microscope to measure the perimeter and the projected area of each particle, and wherein in a graph of particle size versus cumulative volume frequency obtained by plotting a cumulative volume frequency (%) of the silica particles from a smaller particle size side against a particle size (nm) of the silica particles measured by transmission electron microscope observation, the cumulative volume frequency (V) and the particle size (R) satisfy the following formula (5): where R is in a range of 40 to 45 nm, and the cumulative volume frequency of the silica particles with a particle size of 15 nm is 20% or less.