JP7458732B2 - Polishing composition and magnetic disk substrate manufacturing method - Google Patents

Description

The present invention relates to a polishing composition and a method for manufacturing a magnetic disk substrate using the polishing composition.

Conventionally, a manufacturing process for a substrate that requires a highly accurate surface includes a step of polishing an object to be polished, which is a raw material of the substrate, using a polishing liquid. For example, in the production of magnetic disk substrates plated with nickel phosphorus (hereinafter also referred to as Ni-P substrates), polishing (primary polishing) that emphasizes polishing efficiency and finishing to achieve the surface precision of the final product are generally performed. Final polishing (finish polishing) is performed for this purpose. Patent Document 1 is mentioned as a technical document regarding a polishing composition used for polishing a magnetic disk substrate.

Japanese Patent Application Publication No. 2012-142064

Due to recent demands for higher recording densities in magnetic disk drives, polishing compositions used for polishing magnetic disk substrates have a magnetic There is a need for performance that reduces defects (eg, scratches) that occur on the surface of disk substrates.

The present invention has been made in view of the above circumstances, and aims to provide a polishing composition that is used for polishing Ni-P substrates and has excellent scratch reduction performance while maintaining a practical polishing rate. Another related aim is to provide a method for efficiently producing Ni-P substrates with high-quality surfaces using such a polishing composition.

According to the present invention, a polishing composition used for polishing a magnetic disk substrate (Ni--P substrate) plated with nickel phosphorus is provided. This polishing composition contains silica particles, an acid, an oxidizing agent, a defect reducing agent, and water. Here, the polishing composition includes an allylamine polymer as the defect reducing agent. Further, the content of the allylamine polymer in the polishing composition is preferably 10 ppm or less. According to this configuration, it is possible to realize a polishing composition that is used for polishing a Ni--P substrate and has excellent scratch reduction performance while maintaining a practical polishing rate.

A polishing composition according to a preferred embodiment includes, as the allylamine polymer, a polymer having structural units derived from monoallylamines. According to the structure containing the allylamine polymer as a defect reducing agent, it is easy to realize a polishing composition that can exhibit excellent scratch reduction performance while maintaining a practical polishing rate.

In another preferred embodiment, the polishing composition contains a polymer having a constitutional unit derived from a diallylamine as the allylamine polymer. By including the allylamine polymer as a defect reducing agent, it is easy to realize a polishing composition that can exhibit excellent scratch reducing performance while maintaining a practical polishing rate.

The polishing composition according to a preferred embodiment has a pH of 4.0 or less. Under such a pH environment, the defect reducing agent can exhibit even more excellent scratch reducing performance.

In one preferred embodiment, the silica particles are colloidal silica. When the technique disclosed herein is applied to a polishing composition containing such silica particles, scratch reduction performance is likely to be improved.

As the silica particles, those having an average primary particle diameter of 1 nm or more and 50 nm or less can be preferably used. A polishing composition containing silica particles having an average primary particle size within the above range can also be preferably used in a polishing process that requires high surface quality after polishing. It is particularly meaningful to apply the technique disclosed herein to a polishing composition that can be used in such a polishing process.

Also, according to this specification, a method of manufacturing a magnetic disk substrate is provided. The manufacturing method includes the step of polishing a magnetic disk substrate plated with nickel phosphorus using any of the polishing compositions disclosed herein. According to this manufacturing method, a magnetic disk substrate (Ni--P substrate) having a high-quality surface with few scratches can be efficiently manufactured.

Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than those specifically mentioned in this specification that are necessary for implementing the present invention can be understood as matters designed by those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the field.

<Polishing composition>
The polishing composition disclosed herein is a polishing composition used for polishing (preferably final polishing) a magnetic disk substrate (hereinafter also referred to as a Ni-P substrate) plated with nickel phosphorus, and includes: It contains silica particles as abrasive grains, an acid, an oxidizing agent, a defect reducing agent, and water.

(abrasive grain)
The polishing composition disclosed herein contains abrasive grains. The abrasive grains have the function of mechanically polishing the surface of the Ni--P substrate. The average primary particle diameter of the abrasive grains is not particularly limited. In one preferred embodiment, the average primary particle diameter of the abrasive grains measured by the BET method is 1 nm or more. Higher polishing rates can be achieved by increasing the average primary particle size. From the viewpoint of polishing efficiency, etc., the average primary particle diameter is preferably 3 nm or more, more preferably 5 nm or more, still more preferably 10 nm or more, particularly preferably 15 nm or more. Further, from the viewpoint of obtaining a surface with higher surface precision, the average primary particle diameter is preferably 50 nm or less, more preferably 45 nm or less, still more preferably 40 nm or less, particularly preferably 35 nm or less. In some embodiments, the average primary particle diameter may be, for example, 30 nm or less, and typically 25 nm or less (for example, 20 nm or less).

In the technology disclosed herein, the average primary particle size of the abrasive grains refers to the average particle size determined based on the BET method. For example, when the abrasive grains are silica abrasive grains (i.e., abrasive grains made of silica particles), the average primary particle size of the silica abrasive grains can be calculated from the specific surface area S ( ^m2 /g) measured by the BET method using the formula D1 (nm) = (6000/2.2)/S. In this formula, 2.2 is the specific gravity of silica. The specific surface area can be measured using, for example, a surface area measuring device manufactured by Micromeritics, under the product name "Flow Sorb II 2300".

Although not particularly limited, the average aspect ratio of all particles in the cumulative particle size distribution based on the number of abrasive grains is, in principle, 1 or more, and the lower limit thereof is not particularly limited, but is typically 1.03 or more, for example. may be 1.08 or more. Further, from the viewpoint of efficiently increasing the surface precision, in some embodiments, it is appropriate that the average aspect ratio of the entire particle is usually 1.30 or less. By reducing the average aspect ratio of the entire particles, the abrasive grains can easily roll and move, resulting in stable processing and a more favorable reduction in scratches. The average aspect ratio of the entire particle is preferably 1.28 or less, more preferably 1.25 or less (for example, 1.2 or less). Here, the average aspect ratio of the abrasive grains refers to the average value of the length/breadth ratio of individual particles constituting the abrasive grains, that is, the number average aspect ratio. Hereinafter, unless otherwise specified, the average aspect ratio in this specification means the number average aspect ratio.

In addition, the average aspect ratio of D _0-5 particles of cumulative 0 to 5% in the cumulative particle size distribution from the small diameter side of the abrasive grains is, in principle, 1 or more, and the lower limit thereof is not particularly limited, but for example, 1.05. Above, it may be typically 1.08 or more. Here, D _0-5 particles have a particle size in which the cumulative number from the small diameter side falls within the range of 0 to 5% in the cumulative particle size distribution based on the number of abrasive grains (cumulative number distribution from the small diameter side). Refers to particles. The above-mentioned cumulative number distribution typically extends from cumulative 0% and the small diameter end (bottom left) of the particle size to the top right in a graph where the horizontal axis is the particle diameter and the vertical axis is the cumulative number (%). , is represented by a curve that reaches 100% cumulatively and the end of the large diameter side of the particle size (top right). The D _0-5 particles are small-diameter particles that account for 5% in terms of number from the small-diameter side. From the viewpoint of better reducing scratches, in some embodiments, it is appropriate that the average aspect ratio of the D _0-5 particles is usually 1.25 or less. Even if silica is generally spherical, the small diameter side may contain irregularly shaped particles whose shape is distorted from the spherical shape. Even if there is, the abrasive grains will be difficult to roll locally and scratches will easily occur on the surface after polishing. By reducing the average aspect ratio of the D _0-5 particles, the small-diameter particles that can serve as wedges take on a more spherical shape. Small-diameter particles with high sphericity are less likely to form the above-mentioned wedge during polishing, making it less likely that the abrasive grains will locally become difficult to roll, so that scratches can be more preferably reduced. The average aspect ratio of the D _0-5 particles is preferably 1.24 or less, more preferably 1.23 or less, even more preferably 1.22 or less.

The number average aspect ratio of abrasive grains is measured, for example, by the following method. That is, using a transmission electron microscope (TEM, STEM HD-2700 manufactured by Hitachi High-Technologies), the abrasive grains to be measured (which may be one type of abrasive grain, or two or more types of abrasive grains) 1,000 or more particles that can be observed with a TEM, which are included in a mixture of grains (may be a mixture of particles), are photographed at a magnification (for example, 200,000 times to 400,000 times) that allows about 100 particles to be observed in one field of view, Obtain a TEM image. Then, for the smallest rectangle circumscribing each particle image, the length of the long side (value of the major axis) is divided by the length of the short side (value of the short axis), and the value is calculated as the major axis/breadth axis ratio of each particle ( Aspect ratio). Further, the area of each particle is calculated from the image of each particle, and the diameter of an ideal circle (perfect circle) having the same area as the calculated area is calculated as the particle diameter of each particle. In other words, the cumulative particle size distribution of the abrasive grains to be measured is obtained by plotting the particle diameter calculated above for each particle constituting the abrasive grains on the horizontal axis and the cumulative number (%) on the vertical axis. . Then, from the aspect ratio of the predetermined number of particles, the average aspect ratio of all particles can be determined by arithmetic averaging the number average aspect ratio of particles in a predetermined cumulative range in the cumulative particle size distribution from the small diameter side. . Each of the above aspect ratios can be determined using image analysis software MacView manufactured by Mountech.

The polishing composition disclosed herein contains silica particles as abrasive grains. The silica particles contained in the polishing composition disclosed herein may be various types of silica particles containing silica as a main component. Here, the silica particles containing silica as a main component refer to particles in which 90% by weight or more, usually 95% by weight or more, typically 98% by weight or more of the particles are silica. Examples of silica particles that can be used include, but are not limited to, colloidal silica (eg, sodium silicate silica, alkoxide silica, etc.), fumed silica, precipitated silica, and the like. Examples of surface modification include introduction of functional groups and chemical modification such as metal modification. The abrasive grains in the technology disclosed herein may contain one type of such silica particles alone or in combination of two or more types.

Colloidal silica is a preferred example of silica particles that can be used as a component of silica abrasive grains in the technology disclosed herein. Among these, it is preferable to use colloidal silica synthesized through particle growth in an aqueous phase, such as sodium silicate method silica and alkoxide method silica. With silica abrasive grains containing this type of colloidal silica, a high polishing rate and good surface precision can be suitably achieved. When the silica abrasive grains disclosed herein contain colloidal silica, the silica abrasive grains may contain one type of colloidal silica, or may contain two or more types of colloidal silica having different manufacturing conditions and/or physical properties. . Furthermore, the silica abrasive grains may be composed of one or more types of colloidal silica, or may be composed of a combination of colloidal silica and other silica particles, that is, silica particles other than colloidal silica. Good too. In one preferred embodiment, the abrasive grains contained in the polishing composition contain colloidal silica alone. By using colloidal silica alone, better surface precision (for example, a surface with a reduced number of scratches) can be achieved while maintaining a high polishing rate.

The particle shape of colloidal silica is not particularly limited, and may be, for example, spherical or non-spherical. When the polishing composition disclosed herein is used in the final polishing process of a Ni--P substrate, a shape close to a spherical shape is preferable.

In the polishing composition disclosed herein, the content of silica particles in the solid content contained in the polishing composition is not particularly limited. The content of the silica particles is preferably 40% by weight or more of the total solid content, more preferably 50% by weight or more, and even more preferably 60% by weight or more, from the viewpoint of facilitating the effects of the present invention. , even more preferably 80% by weight or more, particularly preferably 90% by weight or more, for example 99% by weight or more. In this specification, the solid content contained in the polishing composition refers to the residual content, that is, the nonvolatile content, after water is evaporated from the polishing composition at a temperature that does not remove bound water, for example, 60 ° C. .

The polishing composition disclosed herein can be preferably implemented in an embodiment that does not substantially contain alumina particles. Examples of alumina particles include α-alumina particles. Such a polishing composition prevents quality degradation caused by the use of alumina particles. Examples of quality degradation include the occurrence of scratches and dents, residual alumina, and defects due to the penetration of abrasive grains. In this specification, "substantially free of a specific abrasive grain, for example, alumina particles," means that the proportion of the abrasive grains in the total solid content contained in the polishing composition is 1% by weight or less, more preferably 0.5% by weight or less, and typically 0.1% by weight or less. A polishing composition with a proportion of 0% by weight of alumina particles, that is, a polishing composition that does not contain alumina particles, is particularly preferred. The polishing composition disclosed herein can also be preferably implemented in an embodiment that does not substantially contain α-alumina particles.

The polishing composition disclosed herein can be preferably implemented in an embodiment that is substantially free of particles other than silica particles, i.e., non-silica particles. Here, "substantially free of non-silica particles" means that the proportion of non-silica particles in the total amount of solids contained in the polishing composition is 1% by weight or less, more preferably 0.5% by weight or less, and even more preferably 0.1% by weight or less. In such an embodiment, the application effect of the technology disclosed herein can be suitably exhibited.

The polishing composition disclosed herein contains substantially only silica particles as abrasive grains. Here, "containing substantially only silica particles" means that the proportion of silica particles in the total solid content of the polishing composition is 99% by weight or more, more preferably 99.5% by weight or more, and even more preferably 99.9% by weight or more. In such an embodiment, the application effect of the technology disclosed herein can be suitably exhibited.

The content of abrasive grains in the polishing composition is not particularly limited, but is typically 0.1% by weight or more, preferably 0.5% by weight or more, and more preferably 1% by weight or more. The content is preferably 3% by weight or more, and more preferably 3% by weight or more. The above content is the total content when multiple types of abrasive grains are included. Higher polishing rates tend to be achieved by increasing the abrasive content. From the viewpoint of the surface smoothness of the substrate after polishing and the dispersion stability of the abrasive grains, the above content is usually suitably 25% by weight or less, preferably 20% by weight or less, more preferably 15% by weight or less, More preferably it is 10% by weight or less, for example 8% by weight or less.

(Defect reducing agent)
The polishing composition disclosed herein includes a defect reducing agent. The defect reducing agent has the function of suppressing the occurrence of defects (typically scratches) during polishing of the Ni--P substrate.

The polishing composition disclosed herein contains an allylamine polymer as the defect reducing agent. Here, in this specification, "allyl amine polymer" refers to a polymer having a structural unit derived from an amine compound having an allyl group (hereinafter also referred to as allyl amines). According to the polishing composition containing the allylamine polymer, scratches on the surface to be polished after polishing are easily reduced. The reason why the allylamine polymer acts as a defect reducing agent may be, for example, as follows, but is not limited thereto. That is, the allylamine polymer tends to be positively charged under acidic conditions and is easily adsorbed onto the surface of silica particles. The allylamine polymer adsorbed on the surface of the silica particles acts to relieve the pressure acting between the silica particles and the object to be polished (Ni--P substrate), and scratches generated during polishing can be reduced.

The allylamine polymer disclosed herein is preferably water-soluble. A water-soluble allylamine polymer can be used in a water-containing polishing composition to exhibit better scratch reduction performance. The allylamine polymer may be a cationic compound or an amphoteric compound in the polishing composition disclosed herein.

The allylamine polymer may be a homopolymer or a copolymer. The allylamines mentioned above may be primary amines, secondary amines, tertiary amines, or quaternary ammonium cations. Moreover, the number of allyl groups that the allylamines have is not particularly limited. For example, the number of allyl groups that the allylamines have may be 1, 2, or 3.

In a preferred embodiment of the technology disclosed herein, the allylamine polymer is a polymer having a structural unit derived from an amine compound having one allyl group (hereinafter also referred to as "monoallylamines").

In a preferred embodiment of the technology disclosed herein, the structural unit derived from the monoallyl amines is a structural unit represented by the following general formula (1) or (2).

In the above general formula (1), R ¹ and R ² each represent a hydrogen atom or a hydrocarbon group which may be partially substituted with a substituent. From the viewpoint of improving scratch reduction performance, in the above general formula (1), R ¹ and R ² each preferably represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom, a methyl group or an ethyl group, and even more preferably a hydrogen atom or a methyl group. In a preferred embodiment, R ¹ and R ² each represent a hydrogen atom. In another preferred embodiment, one of R ¹ and R ² is a hydrogen atom, and the other is a methyl group. In another preferred embodiment, R ¹ and R ² each represent a methyl group.

The structural unit represented by the above general formula (1) may be in the form of a salt. Examples of the above salts include hydrochloride, hydrobromide, acetate, sulfate, nitrate, sulfite, phosphate, amidosulfate, methanesulfonate, and the like.

In the above general formula (2), R ³ , R ⁴ and R ⁵ all represent a hydrogen atom or a hydrocarbon group which may be partially substituted with a substituent, and X represents a monovalent anion. Each is shown below. From the viewpoint of improving scratch reduction performance, R ³ , R ⁴ and R ⁵ in the above general formula (2) are each preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom. , a methyl group or an ethyl group, more preferably a hydrogen atom or a methyl group. In one preferred embodiment, R ³ , R ⁴ and R ⁵ are all hydrogen atoms. In another preferred embodiment, at least one of R ³ , R ⁴ and R ⁵ is a hydrogen atom, and at least one is a methyl group. In another preferred embodiment, R ³ , R ⁴ and R ⁵ are all methyl groups.

In another preferred embodiment of the technology disclosed herein, the allylamine polymer is a polymer having a structural unit derived from an amine compound having two allyl groups (hereinafter also referred to as "diallylamines"). .

In a preferred embodiment of the technology disclosed herein, the structural unit derived from the diallylamine is a structural unit represented by the following general formula (3), (4), (5), or (6).

In the above general formulas (3) and (4), R ⁶ represents a hydrogen atom or a hydrocarbon group which may be partially substituted with a substituent. From the viewpoint of improving scratch reduction performance, in the above general formulas (3) and (4), R ⁶ is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom, a methyl group, or It is an ethyl group, more preferably a hydrogen atom or a methyl group.

The structural units represented by the above general formulas (3) and (4) may be in the form of a salt. Examples of the above salts include hydrochloride, hydrobromide, acetate, sulfate, nitrate, sulfite, phosphate, amidosulfate, methanesulfonate, and the like.

In the above general formulas (5) and (6), R ⁷ and R ⁸ each represent a hydrogen atom or a hydrocarbon group which may be partially substituted with a substituent, and X is a monovalent anion. are shown respectively. From the viewpoint of improving scratch reduction performance, R ⁷ and R ⁸ in the above general formula (5) or (6) are each preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably hydrogen Atom, methyl group or ethyl group, more preferably a hydrogen atom or methyl group. In one preferred embodiment, R ⁷ and R ⁸ are both hydrogen atoms. In another preferred embodiment, at least one of R ⁷ and R ⁸ is a hydrogen atom, and the other is a methyl group. In another preferred embodiment, R ⁷ and R ⁸ are both methyl groups.

The allylamine polymer disclosed herein preferably has one type of structural unit selected from the structural units represented by the above general formulas (1), (3) and (4) alone or in combination of two or more structural units. In particular, from the viewpoint of improving scratch reduction performance, it is more preferable that the allylamine polymer has one type of structural unit selected from the structural units represented by the above general formulas (1) and (3) alone or in combination of two or more structural units.

The total proportion of the structural units represented by the general formulas (1), (3) and (4) in all the structural units of the allylamine polymer is not particularly limited. From the viewpoint of improving scratch reduction performance, the above ratio is preferably 20 mol% or more, more preferably 30 mol% or more, and still more preferably 40 mol% or more (for example, more than 50 mol%). The upper limit of the total proportion of the structural units represented by the general formulas (1), (3) and (4) in all the structural units of the allylamine polymer is not particularly limited. In principle, the above ratio is 100 mol% or less, may be 95 mol% or less, or may be 90 mol% or less.

In a preferred embodiment of the technology disclosed herein, the allylamine polymer is a homopolymer (hereinafter referred to as monoallylamine monopolymer) having only one type of structural unit selected from the structural units represented by the general formula (1) above. (Also called polymer.) A preferred example of the monoallylamine homopolymer includes a monoallylamine homopolymer containing a structural unit in which R ¹ and R ² of the above general formula (1) are both hydrogen atoms. In another preferred embodiment, the allylamine polymer is a homopolymer (hereinafter referred to as diallylamine homopolymer) having solely one type of structural unit selected from the structural units represented by the general formulas (3) and (4) above. ). A preferred example of the diallylamine homopolymer is a diallylamine homopolymer containing a structural unit in the above general formula (3) in which R ⁶ is a hydrogen atom.

In another preferred embodiment, the allylamine polymer is a copolymer having two or more types of structural units selected from the structural units represented by the general formula (1). Specific examples of such copolymers include monoallylamine/dimethylallylamine copolymers.

The allylamine polymer may have structural units other than those of the general formulas (1) to (6). Other structural units are not particularly limited. Examples of other structural units include structural units derived from sulfur dioxide, structural units derived from ethylenically unsaturated carboxylic acid compounds, structural units derived from ethylenically unsaturated sulfonic acid compounds, structural units derived from acrylamide compounds, and triallylamines. Examples include structural units derived from Alternatively, examples of other structural units include structural units in which a part of the amine structure in the structural units represented by the above general formulas (1) to (6) is ureated or carbonylated.

Examples of the ethylenically unsaturated carboxylic acid compound include acrylic acid, 3-butenoic acid, methacrylic acid, and maleic acid.

Examples of the ethylenically unsaturated sulfonic acid compounds include styrene sulfonic acid, α-methylstyrene sulfonic acid, vinyltoluenesulfonic acid, vinylnaphthalenesulfonic acid, vinylbenzyl sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, Examples include acryloyloxyethylsulfonic acid and methacroyloxypropylsulfonic acid.

Examples of the acrylamide compounds include acrylamide, N-methylacrylamide, N-(hydroxymethyl)acrylamide, N,N-dimethylacrylamide, N-ethylacrylamide, N,N-diethylacrylamide, N-(isopropyl)acrylamide, etc. Can be mentioned.

In a preferred embodiment of the technology disclosed herein, the allylamine polymer is a copolymer having one type of structural unit selected from the structural units represented by the general formula (1) and the other structural units described above. It is. The total proportion of the structural units represented by the above general formula (1) in all the structural units of such a copolymer is not particularly limited. From the viewpoint of improving scratch reduction performance, the above ratio is preferably 20 mol% or more, more preferably 30 mol% or more, and still more preferably 40 mol% or more (for example, more than 50 mol%). In principle, the above ratio is 100 mol% or less, may be 95 mol% or less, or may be 90 mol% or less.

In another preferred embodiment, it is a copolymer having one type of structural unit selected from the structural units represented by the above general formula (3) and the other structural units described above. The total proportion of the structural units represented by the above general formula (3) in all the structural units of such a copolymer is not particularly limited. From the viewpoint of improving scratch reduction performance, the above ratio is preferably 20 mol% or more, more preferably 30 mol% or more, and still more preferably 40 mol% or more (for example, more than 50 mol%). In principle, the above ratio is 100 mol% or less, may be 95 mol% or less, or may be 90 mol% or less.

Non-limiting examples of allylamine polymers having the above-mentioned other structural units include monoallylamine/maleic acid copolymer, monoallylamine/diallylamine copolymer, monoallylamine/dimethylallylamine copolymer, monoallylamine-partial methoxy Examples include carbonylated allylamine polymer, monoallylamine-partially methylcarbonylated allylamine polymer, monoallylamine-partially ureated allylamine polymer, diallylamine salt/sulfur dioxide copolymer, diallylamine salt/acrylamide copolymer, and the like. Among these, from the viewpoint of improving scratch reduction performance, monoallylamine-dimethylallylamine copolymer, monoallylamine/maleic acid copolymer, monoallylamine-partially methoxycarbonylated allylamine polymer, and diallylamine salt/sulfur dioxide copolymer are preferred. .

The weight average molecular weight (Mw) of the allylamine polymer is not particularly limited. From the viewpoint of improving scratch reduction performance, the Mw of the allylamine polymer is preferably 500 or more, more preferably 800 or more. In a more preferred embodiment, the Mw is, for example, 950 or more, and may also be 1,500 or more, or 1,900 or more. From the viewpoint of maintaining a practical polishing rate, the Mw of the allylamine polymer can be approximately 50,000 or less, preferably 20,000 or less. The above Mw may be, for example, 16,000 or less, 10,000 or less, or 6,000 or less.

In this specification, as the Mw of the allylamine polymer, a value based on gel permeation chromatography (GPC) (aqueous, polyethylene glycol equivalent) can be adopted. As an example of GPC measurement, Mw can be determined using a Hitachi L-6000 high performance liquid chromatograph under the following measurement conditions.
[GPC measurement conditions]
Sample concentration: Adjusted to 0.5g/100mL with eluent Column: Used by connecting Shodex Asahi Pack GS-220HQ and GS-620HQ in series Detector: Shodex RI-101 differential refractive index detector Eluent: 0 .4 mol/L sodium chloride aqueous solution Flow rate: 1.0 mL/min Measurement temperature: 30°C
Sample injection volume: 20μL

The above allylamine polymers can be used alone or in combination of two or more.

In the technology disclosed herein, the content of the allylamine polymer in the polishing composition (when two or more types of allylamine polymers are used, the total content) is equal to or less than a predetermined upper limit. If the amount of allylamine polymer added to the polishing composition is excessive, the silica particles tend to aggregate, which may cause the surface quality of the polished surface to be polished after polishing to be impaired. According to the technology disclosed herein, even if the content of the allylamine polymer in the polishing composition is reduced, excellent scratch reduction performance can be exhibited. The content of the allylamine polymer in the polishing composition may be, for example, 28 ppm or less, advantageously 25 ppm or less, 20 ppm or less, or 15 ppm or less. In a preferred embodiment of the technology disclosed herein, the content of the allylamine polymer in the polishing composition may be 10 ppm or less (i.e., 0.001 wt.% or less). According to a polishing composition containing the allylamine polymer at such a concentration, it is easy to exhibit excellent scratch reduction performance while maintaining practical polishing maintenance when used for polishing Ni-P substrates. The content of the allylamine polymer in the polishing composition is preferably 8 ppm or less, and even more preferably 7 ppm or less (e.g., 6 ppm or less). From the viewpoint of optimally exerting the function as a defect reducing agent, the content of the allylamine polymer in the polishing composition is preferably 0.05 ppm or more, more preferably 0.1 ppm or more, and even more preferably 0.5 ppm or more.

(water)
The polishing composition disclosed herein contains water. As water, ion-exchanged water, pure water, ultrapure water, distilled water, etc. can be preferably used. The ion-exchanged water may be deionized water.

(acid)
The polishing composition disclosed herein contains an acid. The acid functions to chemically polish the Ni-P substrate. As the acid, either an inorganic acid or an organic acid can be used. The acid can be used alone or in combination of two or more kinds.

Specific examples of inorganic acids include phosphoric acid (orthophosphoric acid), nitric acid, sulfuric acid, hydrochloric acid, boric acid, sulfamic acid, phosphinic acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, hexametaphosphoric acid, carbonic acid, and fluorinated acid. Hydrogen acid, sulfite, thiosulfuric acid, chloric acid, perchloric acid, chlorous acid, hydroiodic acid, periodic acid, iodic acid, hydrobromic acid, perbromic acid, bromic acid, chromic acid, nitrous acid, etc. Can be mentioned.

Examples of organic acids include organic carboxylic acids, organic phosphonic acids, organic sulfones, amino acids, and the like. The number of carbon atoms contained in these organic acids is typically about 1 to 18, preferably about 1 to 10, for example.
Specific examples of organic acids include malonic acid, citric acid, isocitric acid, 1,2,4-butanetricarboxylic acid, maleic acid, malic acid, glycolic acid, succinic acid, itaconic acid, iminodiacetic acid, gluconic acid, and lactic acid. , mandelic acid, tartaric acid, formic acid, acetic acid, propionic acid, butyric acid, adipic acid, oxalic acid, valeric acid, enanthic acid, caproic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid , stearic acid, cyclohexanecarboxylic acid, phenylacetic acid, benzoic acid, crotonic acid, oleic acid, linoleic acid, linolenic acid, ricinolenic acid, methacrylic acid, glutaric acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, tartronic acid, Glyceric acid, hydroxybutyric acid, hydroxyacetic acid, hydroxybenzoic acid, salicylic acid, methylene succinic acid, gallic acid, ascorbic acid, nitroacetic acid, oxaloacetic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, pyridine carboxylic acids such as nicotinic acid and picolinic acid Organic carboxylic acids such as methyl acid phosphate, ethyl acid phosphate, ethyl glycol acid phosphate, isopropyl acid phosphate, phytic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetra(methylene phosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane-hydroxy-1, 1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid organic phosphonic acids such as α-methylphosphonosuccinic acid and aminopoly(methylenephosphonic acid); ethanesulfonic acid, aminoethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, 2-naphthalenesulfonic acid, sulfosuccinic acid, Organic sulfonic acids such as 10-camphorsulfonic acid and taurine; glycine, alanine, glutamic acid, aspartic acid, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, phenylalanine, tryptophan, tyrosine, proline, cystine, glutamine, asparagine, Examples include amino acids such as lysine and arginine.

Preferred acids from the viewpoint of polishing efficiency include phosphoric acid, phosphonic acid, malonic acid, citric acid, maleic acid, hydrochloric acid, nitric acid, sulfuric acid, sulfamic acid, phytic acid, and 1-hydroxyethylidene-1,1-diphosphonic acid. be done. Among these, preferred acids include phosphoric acid, phosphonic acid, malonic acid, citric acid, and maleic acid.

The polishing composition disclosed herein may further include a salt of any of the acids mentioned above. Thereby, a good defect reduction effect tends to be stably exhibited. Examples of salts include metal salts, ammonium salts, alkanolamine salts, etc. of the above-mentioned inorganic acids and organic acids. Examples of metal salts include alkali metal salts such as lithium salts, sodium salts, and potassium salts. Examples of ammonium salts include quaternary ammonium salts such as tetramethylammonium salt and tetraethylammonium salt. Examples of alkanolamine salts include monoethanolamine salts, diethanolamine salts, and triethanolamine salts.

Specific examples of salts that can be contained in the polishing composition disclosed herein include tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, and phosphoric acid. Alkali metal phosphates and alkali metal hydrogen phosphates such as sodium dihydrogen; alkali metal salts of the organic acids listed above; other alkali metal salts of glutamic acid diacetic acid, alkali metal salts of diethylenetriaminepentaacetic acid, hydroxyethylethylenediamine Examples include alkali metal salts of triacetic acid and alkali metal salts of triethylenetetraminehexaacetic acid. The alkali metal in these alkali metal salts can be, for example, lithium, sodium, potassium, and the like.

In some embodiments, inorganic acid salts such as alkali metal salts and ammonium salts of inorganic acids can be preferably employed as the above-mentioned salts. For example, in addition to the alkali metal phosphates and alkali metal hydrogen phosphates mentioned above, potassium chloride, sodium chloride, ammonium chloride, potassium nitrate, sodium nitrate, ammonium nitrate, etc. can be preferably used. Among these, preferred examples include alkali metal phosphates and alkali metal hydrogen phosphates. Particularly preferred are alkali metal hydrogen phosphates.

The acid content in the polishing composition is not particularly limited. The acid content is usually suitably 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 0.8% by weight or more, for example 1.2% by weight or more. If the acid content is too low, the polishing rate tends to be insufficient, which may not be practical. The acid content is usually suitably 15% by weight or less, preferably 10% by weight or less, more preferably 5% by weight or less, for example 3% by weight or less. If the acid content is too large, the surface precision of the object to be polished tends to deteriorate, which may not be practical.

(Oxidant)
The polishing composition disclosed herein contains an oxidizing agent. Examples of oxidizing agents include peroxides, nitric acid or its salts, periodic acid or its salts, peroxo acids or its salts, permanganic acid or its salts, chromic acid or its salts, oxyacids or its salts, metal salts. , sulfuric acids, etc., but are not limited to these. One type of oxidizing agent can be used alone or two or more types can be used in combination. Specific examples of oxidizing agents include hydrogen peroxide, sodium peroxide, barium peroxide, nitric acid, iron nitrate, aluminum nitrate, ammonium nitrate, peroxomonosulfate, ammonium peroxomonosulfate, peroxomonosulfate metal salts, peroxodisulfate, peroxodisulfate, etc. Ammonium sulfate, metal peroxodisulfate, peroxolinic acid, peroxosulfuric acid, sodium peroxoborate, performic acid, peracetic acid, perbenzoic acid, perphthalic acid, hypobromous acid, hypoiodic acid, chloric acid, bromic acid, Iodic acid, periodic acid, perchloric acid, hypochlorous acid, sodium hypochlorite, calcium hypochlorite, potassium permanganate, metal salts of chromate, metal salts of dichromate, iron chloride, iron sulfate, Examples include iron citrate and iron ammonium sulfate. Preferred oxidizing agents include hydrogen peroxide, iron nitrate, periodic acid, peroxomonosulfuric acid, peroxodisulfuric acid, and nitric acid. It preferably contains at least hydrogen peroxide, and more preferably consists of hydrogen peroxide.

The content of the oxidizing agent in the polishing composition is preferably 0.01% by weight or more, more preferably 0.05% by weight or more, and even more preferably 0.1% by weight or more based on the amount of active ingredients. , 0.2% by weight or more, or 0.3% by weight or more. If the content of the oxidizing agent is too small, the polishing efficiency will decrease, which may be practically undesirable. Further, the content of the oxidizing agent in the polishing composition is preferably 5% by weight or less, more preferably 1% by weight or less based on the amount of active ingredients. If the content of the oxidizing agent is too large, the surface precision of the object to be polished tends to deteriorate, which may not be practical.

(basic compound)
The polishing composition can contain a basic compound as necessary for the purpose of pH adjustment and the like. Here, the basic compound refers to a compound having the function of increasing the pH of the polishing composition by being added to the polishing composition. Examples of basic compounds include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, quaternary ammonium compounds such as quaternary ammonium hydroxide, ammonia, and amines. One type of basic compound can be used alone or two or more types can be used in combination.

(Other ingredients)
The polishing composition disclosed herein may contain polishing agents such as water-soluble polymers other than allylamine polymer, surfactants, chelating agents, preservatives, antifungal agents, etc., to the extent that the effects of the present invention are not significantly impaired. If necessary, the polishing composition may further contain known additives that can be used in polishing compositions for magnetic disk substrates (for example, polishing compositions for magnetic disk substrates such as Ni--P substrates). For example, examples of preservatives and fungicides include isothiazoline preservatives such as 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one, and paraoxybenzoic acid. Examples include, but are not limited to, esters and phenoxyethanol.

(pH)
The pH of the polishing composition disclosed herein is not particularly limited, but is preferably 4.0 or less. From the viewpoint of polishing efficiency, etc., the pH of the polishing composition is preferably 3.7 or less, more preferably 3.5 or less, may be 3.2 or less, may be 3.0 or less, and may be 2.5 or less. It may be 2.2 or less. The pH of the polishing composition is usually higher than 1.0, preferably 1.2 or higher, more preferably 1.5 from the viewpoint of suppressing roughening of the substrate surface after polishing. or more (for example, more than 1.5), and may be 1.7 or more. The technique disclosed herein can be preferably implemented in an embodiment in which the pH of the polishing composition is, for example, 1.5 or more and 3.7 or less. The above-mentioned pH can be particularly preferably applied to a polishing composition for final polishing of a Ni--P substrate.

In addition, in the technology disclosed herein, the pH of the polishing composition can be determined by calibrating the polishing composition at three points using a pH meter and then inserting a glass electrode into the composition to be measured. . Standard solutions include, for example, oxalate pH standard solution: pH 1.68 (25°C), phthalate pH standard solution: pH 4.01 (25°C), neutral phosphate pH standard solution: pH 6.86 (25°C). ℃), carbonate pH standard solution: pH 10.01 (25℃).

<Concentrated liquid>
The polishing composition disclosed herein may be in a concentrated form (that is, in the form of a concentrated polishing liquid) before being supplied to the object to be polished (for example, a magnetic disk substrate). The polishing composition (concentrate) in such a concentrated form is advantageous from the viewpoint of convenience and cost reduction during manufacturing, distribution, storage, and the like. The concentration ratio can be, for example, about 1.5 to 20 times in terms of volume. From the viewpoint of storage stability of the concentrated solution, a concentration ratio of about 2 to 10 times is usually appropriate. Such a concentrated liquid can be diluted at a desired timing to prepare a polishing composition (polishing liquid), and the polishing liquid can be used in a manner of supplying the polishing liquid to an object to be polished. The dilution can typically be performed by adding water to the concentrate and mixing.

<Multi-component polishing composition>
The polishing composition disclosed herein may be a single-component type or a multi-component type including a two-component type. For example, part A containing some of the constituent components (typically, components other than water) of the polishing composition and part B containing the remaining components are mixed to polish the object to be polished. It may be configured to be used for. A multi-component polishing composition according to a preferred embodiment includes a part A containing abrasive grains (typically, a dispersion liquid further containing a dispersion medium for the abrasive grains), and at least a part of components other than the abrasive grains ( For example, part B containing acids, defect reducing agents, etc.). Usually, these are stored separately before use and can be mixed at the time of use to prepare a one-part polishing composition. At the time of mixing, for example, an oxidizing agent such as hydrogen peroxide, water for dilution, etc. may be further mixed.

<Polishing process>
The polishing composition disclosed herein can be suitably used for polishing an object to be polished (here, a Ni--P substrate), for example, in a mode including the following operations. Hereinafter, a preferred embodiment of a method for polishing an object to be polished using the polishing composition disclosed herein will be described.
That is, a polishing liquid (working slurry) containing one of the polishing compositions disclosed herein is prepared. Preparing the polishing liquid may include preparing the polishing liquid by subjecting the polishing composition to operations such as concentration adjustment (for example, dilution) and pH adjustment. Alternatively, the polishing composition may be used as it is as a polishing liquid.

The polishing liquid is then supplied to the object to be polished, and the object is polished in a conventional manner. For example, the object to be polished is set in a general polishing device, and the polishing liquid is supplied to the surface of the object to be polished (the surface to be polished) through the polishing pad of the polishing device. Typically, the polishing liquid is continuously supplied while the polishing pad is pressed against the surface of the object to be polished, and the two are moved relative to each other (e.g., rotated).

Thereafter, an alkaline cleaning step is carried out to clean the object to be polished with an alkaline cleaning solution. The alkaline cleaning step typically involves contacting at least the surface of the object to be polished with an alkaline cleaning solution. For example, the surface of the object to be polished can be brought into contact with the alkaline cleaning solution by immersing the object to be polished in the alkaline cleaning solution. An ultrasonic treatment may be carried out to apply ultrasonic waves to the object to be polished immersed in the alkaline cleaning solution. In addition to or instead of applying ultrasonic waves, scrubbing may be carried out using a polyvinyl alcohol sponge, a nonwoven fabric, a nylon brush, or the like.
The pH of the alkaline cleaning solution used in the alkaline cleaning step may be, for example, 7.5 or more, and from the viewpoint of improving cleaning properties, it is preferably 8.0 or more, more preferably 8.5 or more, for example 8.8 or more. In addition, from the viewpoint of preventing roughening of the substrate surface due to cleaning, the pH of the alkaline cleaning solution is usually 11 or less, preferably 10 or less, and more preferably 9.5 or less. As the alkaline cleaning solution, an aqueous solution containing one or more of the above-mentioned basic compounds can be used. Among them, an aqueous solution of an alkali metal hydroxide is preferred, and for example, an aqueous potassium hydroxide solution can be preferably used. The alkaline cleaning step may be performed using a commercially available alkaline cleaning solution.

Note that after the polishing using the polishing liquid is completed, the object to be polished may be cleaned with a non-alkaline rinsing liquid before proceeding to the alkaline cleaning step. As the rinsing liquid, water such as pure water or ion-exchanged water, or an acidic aqueous solution (for example, an aqueous solution having a composition obtained by removing abrasive grains from a polishing liquid) can be used.

<Application>
The polishing composition disclosed herein can be used to polish a magnetic disk substrate (Ni-P substrate) plated with nickel phosphorus, and can effectively reduce the number of defects on the surface of the Ni-P substrate. The Ni-P substrate is typically a magnetic disk substrate having a nickel phosphorus plating layer on the surface of the base material.The material of the base material may be, for example, aluminum alloy, glass, glassy carbon, etc. The polishing composition disclosed herein can be preferably used, for example, for polishing a Ni--P substrate having a nickel-phosphorous plating layer on a base material made of an aluminum alloy.
According to this specification, a method for manufacturing a Ni--P substrate comprising a polishing step using the polishing composition disclosed herein and an alkali cleaning step performed after the polishing step, and a Ni--P substrate manufactured by the method. -P substrate may be provided.

Since the polishing composition disclosed herein can highly reduce defects on the surface of a Ni--P substrate, it can be particularly preferably used in a final polishing step (finish polishing step) of a Ni--P substrate. According to this specification, a method for producing a Ni--P substrate comprising a final polishing step using the polishing composition disclosed herein and an alkali cleaning step performed after the final polishing step, and a method for producing an Ni--P substrate are provided. A Ni--P substrate can be provided. Note that final polishing refers to the last polishing step in the process of manufacturing a target product (that is, a step in which no further polishing is performed after that step).

The polishing composition disclosed herein may be used in a polishing step upstream of the final polishing. Here, the polishing step upstream of the final polishing refers to a preliminary polishing step between the rough polishing step and the final polishing step. The preliminary polishing step typically includes at least a primary polishing step, and may further include secondary, tertiary, etc. polishing steps. The above-mentioned polishing composition can be used in any of the polishing steps, and the same or different polishing compositions can be used in these polishing steps. The polishing composition disclosed herein may be used, for example, in a polishing step performed immediately before the final polishing.

The polishing composition disclosed herein can be preferably used, for example, for polishing Ni-P substrates whose surface roughness has been adjusted to 20 Å or less by an upstream process. Here, the surface roughness refers to the surface roughness (arithmetic mean roughness (Ra)) measured using a laser scanning surface roughness meter "TMS-3000WRC" manufactured by Schmitt Measurement Systems. It is particularly preferable to use the composition for polishing Ni-P substrates whose surface roughness has been adjusted to 10 Å or less. This allows Ni-P substrates with high-quality surfaces to be manufactured with good productivity.

Hereinafter, some examples relating to the present invention will be described, but the present invention is not intended to be limited to what is shown in these examples.

In the following examples, the following compounds were used as the allylamine polymer.
Monoallylamine polymer: A homopolymer of monoallylamine (primary amine).
Monoallylamine-dimethylallylamine copolymer: A copolymer of monoallylamine (primary amine) and dimethylallylamine (tertiary amine).
Monoallylamine/partially methoxycarbonylated allylamine polymer: A copolymer of monoallylamine (primary amine) polymer partially methoxycarbonylated.
Monoallylamine-maleic acid copolymer: A copolymer of monoallylamine (primary amine) and maleic acid.
Diallylamine polymer: A homopolymer of diallylamine (a secondary amine).
Diallylamine acetate-sulfur dioxide copolymer: A copolymer of diallylamine acetate (secondary amine) and sulfur dioxide.

<Preparation of polishing composition>
(Example 1)
Contains abrasive grain (5% by weight), acid (1.5% by weight), defect reducer (0.6ppm), hydrogen peroxide (0.4% by weight) and deionized water, pH 2.0 with potassium hydroxide. A polishing composition was prepared. Colloidal silica having an average primary particle diameter of 18 nm was used as the abrasive grain. As the acid, phosphoric acid (orthophosphoric acid) was used. As the defect reducing agent, a monoallylamine polymer having an Mw of 1600 was used.

(Examples 2 to 11)
A polishing composition of this example was prepared in the same manner as in Example 1, except that the type of defect reducing agent, its Mw, and content were as shown in Table 1.

(Comparative example 1)
A polishing composition of this example was prepared in the same manner as in Example 1 except that no defect reducing agent was used.

(Comparative Examples 2 to 4)
A polishing composition of this example was prepared in the same manner as in Example 1, except that the type of defect reducing agent, its Mw, and content were as shown in Table 1.

<Polishing of Ni-P substrate>
The polishing composition according to each example was used as it was as a polishing liquid to polish an object to be polished under the following conditions. The object to be polished was an aluminum substrate for hard disks with an electroless nickel phosphorus plating layer on the surface. The material used was pre-polished so that the roughness (Ra) value was 6 Å. The polishing object had a diameter of 3.5 inches (doughnut-shaped with an outer diameter of about 95 mm and an inner diameter of about 25 mm), and a thickness of 1.27 mm.

(polishing conditions)
Polishing equipment: Double-sided polishing machine manufactured by Speed Fam, model "9B-5P"
Polishing pad: Suede non-buff type Number of substrates to be polished: 10 ((2 sheets/carrier) x 5 carriers x 1 batch))
Polishing liquid supply rate: 130mL/min Polishing load: 120g/ ^cm2
Lower surface plate rotation speed: 20 rpm
Polishing time: 5 minutes

<Cleaning>
The Ni-P substrate after polishing was immersed in pure water and subjected to ultrasonic treatment at a frequency of 170 kHz, and then an alkaline cleaning solution (cleaning solution "CSC-102B" available from Speedfam Co., Ltd.) was used at a volume of 200 times larger. The specimen was immersed in a diluted solution (diluted) and scrubbed with a polyvinyl alcohol sponge while applying ultrasonic waves at a frequency of 170 kHz. Next, the substrate was immersed in pure water and subjected to ultrasonic treatment at a frequency of 950 kHz, and then taken up into an isopropyl alcohol atmosphere and dried.

<Polishing speed>
A total of 6 substrates (3 substrates/1 batch) were randomly selected from among the substrates obtained by polishing and cleaning with the polishing composition according to each example, and the weight loss of each substrate due to polishing was The polishing rate was calculated by measuring and the polishing rate of each example was determined by averaging the values. Specifically, the polishing rate was determined based on the following formula.
Polishing speed [μm/min] = Weight loss of substrate due to polishing [g] / (Single side area of substrate [cm ² ] x Density of nickel phosphorus plating [g/cm ³ ] x Polishing time [min]) x 10 ⁴
Here, the calculation was performed assuming that the area of one side of the substrate was 66 cm ² and the density of the nickel phosphorus plating was 7.9 g/cm ³ . The obtained values were converted into relative values with the value of Comparative Example 1 as 100, and are shown in the "Polishing Rate" column of Table 1.

<Scratch Evaluation>
Five substrates were randomly selected from the substrates obtained by polishing and cleaning with the polishing compositions according to each example, and scratches on both sides of each substrate were detected under the following conditions. The total number of scratches on the five substrates (total of 10 sides) was divided by 10 to calculate the number of scratches (number/side) per side of the substrate. The number of scratches thus obtained was converted into a relative value with the number of scratches in Comparative Example 1 taken as 100, and shown in the "Scratch" column of Table 1.

(Scratch detection conditions)
Measuring device: Candela OSA7100 manufactured by KLA-Tencor Co., Ltd.
Spindle speed: 10000rpm
Measurement range: 17000-47000μm
Step size: 4μm
Encoder multiplier:×16
Detection channel: P-Sc channel

In addition, when scratch evaluation was performed on the polishing compositions of Comparative Examples 3 and 4, a number of scratches exceeding the upper limit of detection under the above scratch detection conditions occurred on the surface of the substrate after polishing, so it was difficult to detect the number of scratches. could not.

As shown in Table 1, the polishing compositions of Examples 1 to 11 containing an allylamine polymer as a defect reducing agent had a higher level of practical use than the polishing composition of Comparative Example 1 which did not contain a defect reducing agent. Scratches on the surface to be polished after polishing were clearly reduced while maintaining the same polishing speed. Furthermore, the polishing compositions of Examples 1 to 11, in which the allylamine polymer content was within an appropriate range, had improved polishing speeds compared to Comparative Examples 2 to 4, in which the allylamine polymer content was too high. , and showed excellent scratch reduction performance. It has been confirmed that scratches after polishing can be suitably reduced when using either a polymer having constitutional units derived from monoallylamines or a polymer having constitutional units derived from diallylamines as the allylamine polymer. It was done.

Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The techniques described in the claims include various modifications and changes to the specific examples illustrated above.

Claims (7)

A polishing composition used for polishing a magnetic disk substrate plated with nickel phosphorus, the composition comprising:
Contains silica particles, an acid, an oxidizing agent, a defect reducing agent, and water,
The defect reducing agent includes an allylamine polymer,
The content of the allylamine polymer is 10 ppm or less,
A polishing composition, wherein the proportion of alumina particles in the total solid content contained in the polishing composition is 1% by weight or less . The polishing composition according to claim 1, wherein the allylamine polymer is a polymer having structural units derived from monoallylamines. The polishing composition according to claim 1 or 2, wherein the allylamine polymer is a polymer having structural units derived from diallylamines. The polishing composition according to any one of claims 1 to 3, having a pH of 4.0 or less. The polishing composition according to any one of claims 1 to 4, wherein the silica particles are colloidal silica. The polishing composition according to any one of claims 1 to 5, wherein the silica particles have an average primary particle diameter of 1 nm or more and 50 nm or less. A method for producing a magnetic disk substrate, comprising a step of polishing a nickel-phosphorus-plated magnetic disk substrate with the polishing composition according to claim 1 .