Polishing Composition for Magnetic Disk Substrates
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Solution Overview
Problem
Conventional polishing compositions for magnetic disk substrates with electroless nickel-phosphorus plated films face challenges in achieving a high polishing rate while maintaining surface smoothness and minimizing roll-off, particularly when using alumina particles, which can be embedded in the substrate and reduce polishing efficiency when replaced by silica particles alone.
Innovation Solution
A polishing composition combining colloidal silica and wet-process silica particles, along with a specific water-soluble polymer compound containing monomers with carboxylic acid, amide, and sulfonic acid groups, is used to enhance the polishing rate and surface smoothness without alumina particles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If alumina particles are used in the polishing composition, then the polishing rate is improved, but alumina particles are embedded in the substrate causing harmful effects
Solution Approach 1:
The patent extracts and removes alumina particles from the polishing composition entirely, replacing them with silica particles of specific characteristics. This eliminates the source of the harmful embedding effect while maintaining polishing functionality through the silica-based system.
Solution Approach 2:
The patent changes the fundamental parameter of particle material from alumina to silica, and further specifies the particle size parameter (0.01 μm to 1 μm) and shape parameters (angular or irregular). These parameter changes enable achieving high polishing rates without the harmful embedding effects of alumina particles.
2Object-affected harmful factors
If only silica particles are used to avoid embedding, then particle embedding is reduced, but the polishing rate becomes insufficient
Solution Approach 1:
The patent applies local quality by specifying particular properties for silica particles at different locations in the polishing composition - angular or irregular shaped particles for cutting action, and controlled size distribution (0.01 μm to 1 μm) for effective material removal. This localized optimization of particle characteristics enables high polishing rates without embedding.
Solution Approach 2:
The patent creates a composite polishing system combining silica particles with specific additives (polishing aids and dispersants). This composite approach enhances the polishing rate of silica-based composition to match or exceed alumina-based compositions while maintaining the advantage of reduced particle embedding.
3Object-affected harmful factors
If the polishing composition contains both alumina particles and silica particles, then embedded particles can be removed to some extent, but the properties of particles are mutually canceled deteriorating polishing rate and surface smoothness
Solution Approach 1:
The patent completely removes alumina particles from the polishing composition, eliminating the mutual cancellation effect between alumina and silica properties. The harmful embedded particles are prevented from forming in the first place rather than attempting to remove them later, preserving surface smoothness while avoiding the polishing rate degradation caused by mixed particle systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composition achieves a high polishing rate and favorable surface smoothness, reducing roll-off and embedding issues, while maintaining a balance between polishing efficiency and substrate quality.
Implementation Method 1
a polishing composition for a magnetic disk substrate, including colloidal silica, pulverized wet-process silica particles
Data Source
AI summary
Embodiments relate to a polishing composition is an aqueous composition containing at least colloidal silica, wet-process silica particles, and a water-soluble polymer compound. The water-soluble polymer compound is a copolymer containing a monomer having a carboxylic acid group, a monomer having an amide group, and a monomer having a sulfonic acid group as essential monomers.