JPWO1998021289A1 - Abrasive composition for magnetic recording medium substrate and method for manufacturing magnetic recording medium substrate using the same - Google Patents

Abstract

(57) [Abstract] This abrasive composition for magnetic recording medium substrates contains at least an abrasive, a polishing aid, and water, and is characterized in that the polishing aid is an aliphatic organic sulfate, an oxyalkylene alkyl ether sulfate compound, or an amphoteric surfactant, and the pH is 1 to 13.

Description

[Detailed Description of the Invention] Abrasive Composition for Magnetic Recording Media Substrates and Method for Manufacturing Magnetic Recording Media Substrates Using the Same Technical Field The present invention relates to an abrasive composition for magnetic recording media substrates that can improve removal rate and reduce surface roughness. The present invention also relates to a method for manufacturing magnetic recording media substrates using the abrasive composition, particularly a method for manufacturing magnetic recording media substrates using Ni-P plated aluminum alloy substrates or carbon substrates.

BACKGROUND ART Abrasive compositions containing abrasive grains and aliphatic organic sulfates, oxyalkylene alkyl ether sulfate compounds, or amphoteric surfactants are known, such as those described in Japanese Patent Application Laid-Open Nos. 51-16308 (corresponding to U.S. Pat. No. 3,985,668), 51-76685 (corresponding to U.S. Pat. No. 4,051,056), 62-43482, 2-73898, 4-291723, 5-230440, and 8-41443.

Among these publications, the abrasive compositions described in JP-A-51-16308 and JP-A-51-76685 are household hard surface cleaners known as cleansers.

Japanese Patent Application Laid-Open No. 2-73898 also discloses a cleanser, the purpose of which is to prevent the settling of abrasive grains after long-term storage (to improve suspension stability) and to improve fluidity. Furthermore, the abrasive grains used are not sufficiently hard.

Therefore, even if such an abrasive composition is used, it is not possible to improve the removal rate of magnetic recording medium substrates or to achieve low surface roughness.

The abrasive composition described in JP 62-43482 A is intended to prevent the abrasive grains from settling over time and to improve their wettability and spreadability on the workpiece being polished. However, use of this abrasive composition does not improve the polishing rate or achieve low surface roughness for magnetic recording medium substrates.

The abrasive composition described in JP 4-291723 A is an abrasive for silicon wafers, and its purpose is to prevent clouding on the silicon wafer surface. There is no mention of improving the removal rate or achieving low surface roughness for magnetic recording medium substrates.

The abrasive composition described in JP-A-5-230440 uses diamond as the abrasive, and its purpose is to prevent chips remaining between the workpiece and the platen from coming into contact with the workpiece and scratching its surface. There is no mention of improving the polishing rate of magnetic recording medium substrates or achieving low surface roughness.

The abrasive composition described in JP-A-8-41443 is a composition for buffing, and its purpose is to improve the gloss of the surfaces of stainless steel, non-ferrous metals, etc. in order to improve the appearance of electrical appliances, interior decorations, etc. However, there is no mention of improving the polishing rate or achieving low surface roughness for magnetic recording media substrates.

Other prior art related to abrasive compositions includes abrasive compositions comprising abrasive grains, such as diamond, alumina, or SiC, generally ranging in size from submicron to several tens of microns, dispersed in water, and used for polishing the surfaces of brittle materials such as glass substrates, carbon substrates, and ceramic materials, and ductile materials such as Ni-P plated aluminum (see, for example, Japanese Patent Application Laid-Open Nos. 54-89389, 1-205973, 1-97560, and 1997-143455).

However, conventional abrasive compositions lack sufficient dispersion of abrasive grains and sufficient dispersion, removal, and prevention of redeposition of polishing dust (waste generated during polishing). This results in defects such as pits and scratches on the surface of the workpiece being polished, and also limits the polishing rate and the ability to reduce costs.

DISCLOSURE OF THE INVENTION Accordingly, an object of the present invention is to provide an abrasive composition for magnetic recording medium substrates that can improve the polishing rate and reduce the surface roughness of the substrate without causing defects such as pits or scratches on the surface of the substrate.

Another object of the present invention is to provide an abrasive composition for magnetic recording medium substrates that is particularly suitable for polishing substrates made of brittle materials such as glass, carbon, and ceramics.

Another object of the present invention is to provide an abrasive composition for magnetic recording medium substrates that is suitable for polishing substrates made of ductile materials such as metals such as Al, Si, W, and Cu, and in particular for polishing Ni-P plated aluminum alloy substrates.

Another object of the present invention is to provide an abrasive composition suitable for polishing substrates for magnetic recording media, particularly substrates for hard disk drives.

Another object of the present invention is to provide a method for manufacturing a substrate for a magnetic recording medium that prevents the occurrence of pits and scratches.

As a result of extensive research, the inventors have discovered that the above-mentioned objectives can be achieved by an abrasive composition for magnetic recording medium substrates that uses a specific grinding aid and has a pH within a specific range, and by a method for manufacturing a magnetic recording medium substrate using the same.

The present invention was made based on the above findings and achieves the above object by providing an abrasive composition for magnetic recording medium substrates, which comprises at least an abrasive, a polishing aid, and water, wherein the polishing aid comprises one or more aliphatic organic sulfates, and the pH is 1 to 13.

The above-mentioned object is also achieved by providing an abrasive composition for magnetic recording medium substrates, which comprises at least an abrasive, a polishing aid, and water, wherein the polishing aid comprises one or more oxyalkylene alkyl ether sulfate compounds represented by the following general formula (2), and the pH of the abrasive composition is 1 to 13:

R-O-(AO) _n - _SO3M (2) In the formula, R represents a linear or branched alkyl group, aryl group, or alkylaryl group having 5 to 21 carbon atoms, AO represents an oxyalkylene group having 2 or 3 carbon atoms, n represents a natural number of 1 to 30, and M represents an alkali metal, alkaline earth metal, or organic cation.

The present invention also achieves the above-mentioned object by providing an abrasive composition for magnetic recording medium substrates, which comprises at least an abrasive, a grinding aid, and water, wherein the grinding aid comprises one or more amphoteric surfactants, and the pH is 1 to 13.

The present invention also provides a method for manufacturing a magnetic recording medium substrate, which includes a polishing step using an abrasive composition containing at least an abrasive, a polishing aid, and water, wherein the abrasive composition is the abrasive composition for magnetic recording medium substrates of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic front view of the main components of a double-sided processing machine preferably used in the manufacturing method of magnetic recording medium substrates of the present invention, and FIG. 2 is a view taken along line X-X in FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION The abrasive composition for magnetic recording medium substrates of the present invention (hereinafter simply referred to as the "abrasive composition") is described in detail below.

First, we will explain the abrasive composition using an aliphatic organic sulfate as a grinding aid.

The aliphatic organic sulfate is a water-soluble anionic surfactant. The aliphatic organic sulfate may be used alone or in combination. The use of the aliphatic organic sulfate, combined with the pH of the abrasive composition being adjusted to 1 to 13, improves the removal rate and reduces surface roughness.

In the present invention, the term "aliphatic organic sulfate" includes both aliphatic organic sulfates and aromatic organic sulfates.

The aliphatic organic sulfate is preferably blended in the abrasive composition of the present invention in an amount of 0.01 to 20 wt %. If the amount of the aliphatic organic sulfate is less than 0.01 wt %, the effects of improving the removal rate and reducing the surface roughness may not be fully achieved. If the amount exceeds 20 wt %, the abrasive composition may thicken, reducing workability and increasing the wastewater load of the abrasive composition. Therefore, it is preferable to keep the amount within this range. The amount of the aliphatic organic sulfate is more preferably 0.05 to 10 wt %, and even more preferably 0.1 to 5 wt %.

The aliphatic organic sulfate particularly preferably used in the present invention is represented by the following general formula (1):

R-O- _SO3M (1) In the formula, R represents a linear or branched alkyl group having 5 to 21 carbon atoms, an aryl group or an alkylaryl group, and M represents an alkali metal, an alkaline earth metal or an organic cation.

In the above general formula (1), if the number of carbon atoms in R is less than 5, the ability to disperse and remove abrasive powder generated during polishing and to prevent redeposition may be insufficient. If the number of carbon atoms in R exceeds 21, the solubility and dispersion stability of the aliphatic organic sulfate salt itself in the abrasive composition may decrease, or the solubility and dispersion stability may decrease during use of the abrasive composition. The number of carbon atoms in R is preferably 8 to 14, and more preferably 10 to 14.

Specific examples of alkyl groups represented by R include pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, octadecyl, nonadecyl, eicosyl, t-butyl, isooctyl, and isododecyl. Examples of aryl groups include phenyl, biphenyl, naphthyl, and anthryl. Examples of arylalkyl groups include tolyl, xylyl, and octylphenyl.

It is particularly preferred that R is an alkyl group from the viewpoints of oxidation stability and stability against decomposition due to mechanical wear.

Examples of M in the general formula (1) include alkali metals such as sodium and potassium, alkaline earth metals such as calcium and magnesium, quaternary ammonium ions, and organic amines such as triethanolamine.

Specific examples of the aliphatic organic sulfate represented by general formula (1) include, but are not limited to, heptyl sulfate, octyl sulfate, lauryl sulfate, higher alcohol (coconut oil) sulfate, myristyl sulfate, palmityl sulfate, and stearyl sulfate. Of these, octyl sulfate, lauryl sulfate, myristyl sulfate, and stearyl sulfate are particularly preferred.

Additionally, commercially available products such as Emeral 40, Emeral TD, Emeral TD-L, Emeral AD-25, Emeral AD-25 R, Emeral 0, Emeral 10 Powder, Emeral 10 Needle, Emeral 2F Paste, Emeral 2F Needle, Emeral 40 Powder, Emeral 40 Paste, Emeral 71, and Latemul PS (all trade names, manufactured by Kao Corporation) can also be used as the aliphatic organic sulfate represented by general formula (1).

The aliphatic organic sulfates represented by the above general formula (1) can be blended into the abrasive composition of the present invention either individually or in combination.

Next, an abrasive composition using an oxyalkylene alkyl ether sulfate compound represented by the above general formula (2) as a grinding aid will be described.

The oxyalkylene alkyl ether sulfate compound is a water-soluble compound commonly known as an anionic surfactant. The oxyalkylene alkyl ether sulfate compounds can be used singly or in combination. The use of the oxyalkylene alkyl ether sulfate compound, combined with the pH of the abrasive composition being adjusted to 1 to 13, improves the removal rate and reduces surface roughness.

In the present invention, the term "oxyalkylene alkyl ether sulfate compound" includes all of oxyalkylene alkyl ether sulfate compounds, oxyalkylene aryl ether sulfate compounds, and oxyalkylene alkyl aryl ether sulfate compounds.

For the same reasons as in the case of using the aliphatic organic sulfate as a grinding aid, the oxyalkylene alkyl ether sulfate compound is blended in the abrasive composition of the present invention in an amount of preferably 0.01 to 20 wt %, more preferably 0.02 to 10 wt %, and even more preferably 0.05 to 5 wt %.

In the oxyalkylene alkyl ether sulfate compound represented by the general formula (2), R is a linear or branched alkyl group, aryl group, or alkylaryl group having 5 to 21 carbon atoms. If R has fewer than 5 carbon atoms, the ability to disperse and remove abrasive powder generated during polishing and to prevent redeposition is insufficient. If R has more than 21 carbon atoms, the solubility and dispersion stability of the compound itself in the abrasive composition is reduced, or the solubility and dispersion stability during use of the abrasive composition is reduced.

Specific examples of R in the general formula (2) above include the same as those listed as specific examples of R in the general formula (1) above.

As in the case of general formula (1), the number of carbon atoms in R in general formula (2) is preferably 8 to 14, and more preferably 10 to 14. Furthermore, from the viewpoints of oxidation stability and stability against decomposition due to mechanical wear, it is particularly preferable that R be an alkyl group.

In the above general formula (2), AO is an oxyalkylene group having 2 or 3 carbon atoms. If the number of carbon atoms is other than these, the dispersibility of the abrasive powder will be insufficient, and neither the polishing rate nor the surface roughness will be at a satisfactory level.

In the general formula (2), n is a natural number between 1 and 30. When n is within this range, an appropriate amount of fine bubbles can be generated during polishing, and these bubbles facilitate the removal of polishing powder from the system (flotation-like removal). Preferably, n is between 2 and 4.

Examples of M in the general formula (2) include the same as those listed as specific examples of R in the general formula (1).

Specific examples of the oxyalkylene alkyl ether sulfate compound represented by general formula (2) include, but are not limited to, oxyethylene lauryl ether sulfate (two or three oxyethylene groups per molecule), oxyethylene nonyl ether sulfate (three oxyethylene groups per molecule), oxyethylene octylphenyl ether sulfate (three oxyethylene groups per molecule), and oxyethylene nonylphenyl ether sulfate (three oxyethylene groups per molecule). Of these, oxyethylene lauryl ether sulfate (three oxyethylene groups per molecule), oxyethylene octylphenyl ether sulfate (three oxyethylene groups per molecule), and oxyethylene nonylphenyl ether sulfate (three oxyethylene groups per molecule) are particularly preferred.

In addition, as the oxyalkylene alkyl ether sulfate compound represented by the above general formula (2), commercially available products such as EMERAL 20C, EMERAL 20CM, EMERAL 20T, EMERAL NC-35, EMERAL E-27C, EMERAL E-70C, LEVENOL WZ, LEVENOL WX, and LATEMULL WX (all trade names, manufactured by Kao Corporation) can also be used.

The oxyalkylene alkyl ether sulfate compounds represented by the above general formula (2) can be blended into the abrasive composition of the present invention either singly or in combination.

In the present invention, by adjusting the number of oxyalkylene groups added to the oxyalkylene alkyl ether sulfate compound according to the type of abrasive and the surface condition of the workpiece, the foaming properties of the abrasive composition, the dispersibility of the abrasive, and the re-adhesion of the abrasive to the workpiece can be controlled, facilitating the design of grinding aids.

Next, abrasive compositions using the above amphoteric surfactants as grinding aids will be described.

The amphoteric surfactant may be a water-soluble one known as a general amphoteric surfactant. One or more amphoteric surfactants may be used. The use of such an amphoteric surfactant, combined with the pH of the abrasive composition being adjusted to 1 to 13, improves the polishing rate and reduces scratches on the surface of the workpiece, resulting in a high-quality surface.

For the same reasons as in the case of using the aliphatic organic sulfate as a grinding aid, the amphoteric surfactant is blended in the abrasive composition of the present invention in an amount of preferably 0.01 to 20 wt %, more preferably 0.05 to 10 wt %, and even more preferably 0.1 to 5 wt %.

The amphoteric surfactant particularly preferably used in the present invention is represented by the following general formula (3):

In the formula, R1, ^R2 , and ^R3 each represent a linear or branched alkyl group, alkyl derivative group, alkenyl group, hydrogen, or ^R5 -Ar- group ( ^R5 represents an alkyl group, alkenyl group, alkyl derivative group, or hydrogen, and Ar represents an aromatic group), and may be the same or different; ^R4 represents a direct bond or an alkylene group; ^Y- represents an anionic group. ^R2 and ^R3 may also form a ring.

In the above general formula (3), ^R1 , ^R2 , and ^R3 represent a linear or branched alkyl group, alkyl derivative group, alkenyl group, hydrogen, or ^R5 -Ar- group. Among these, the alkyl group, alkyl derivative group, and alkenyl group preferably have 1 to 24 carbon atoms, more preferably 8 to 16 carbon atoms, from the viewpoint of the ability to disperse and remove abrasive powder generated by polishing, the ability to prevent redeposition, and the solubility and dispersion stability of the amphoteric surfactant itself in the abrasive composition. Specific examples of the alkyl group include methyl group, ethyl group, butyl group, heptyl group, octyl group, decyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, octadecyl group, nonadecyl group, eicosyl group, t-butyl group, isooctyl group, isododecyl group, etc. Furthermore, examples of the alkyl derivative group include the above alkyl groups having functional groups such as hydroxyl group, amino group, mercapto group, amide group, and phospho group. Examples of the alkenyl group include a propenyl group, a butenyl group, a butadienyl group, a pentenyl group, and an octenyl group.

In the ^R5 -Ar- group, examples of the alkyl group, alkenyl group, and alkyl derivative group represented by ^R5 are the same as the examples of the alkyl group, alkenyl group, and alkyl derivative group represented by ^R1 , ^R2 , and ^R3 . Examples of the aromatic group represented by Ar include a phenylene group, a tolylene group, a biphenylene group, a naphthylene group, and an anthrylene group.

In particular, it is desirable that one of ^R1 , ^R2 and ^R3 is a long-chain alkyl group having 5 to 24 carbon atoms, preferably 8 to 16 carbon atoms, and the other two are short-chain alkyl groups having 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms.

When ^R2 and ^R3 form a ring, the ring may be formed only from the atoms contained in ^R2 and ^R3 , or may be formed by including other atoms in addition to the atoms contained in ^R2 and ^R3 . Examples of rings formed in this way include an imidazoline ring.

Examples of the alkylene group represented by ^R4 in the above general formula (3) are alkylene groups having 1 to 24 carbon atoms, preferably 1 to 8, and more preferably 1 to 3, and specific examples include a methylene group, a propylene group, a butylene group, an amylene group, a hexylene group, an octylene group, a dodecylene group, a tetradecylene group, an acetylene group, an eicosylene group, etc. These alkylene groups may have a functional group such as a hydroxyl group.

Examples of Y ⁻ in the above general formula (3) include inorganic anion groups derived from inorganic acids such as phosphoric acid, sulfuric acid, nitric acid, and sulfonic acid; organic anion groups derived from organic acids such as acetic acid, citric acid, and formic acid; and halogen ion groups such as chloride ion groups and bromide ion groups.

Specific examples of amphoteric surfactants represented by general formula (3) include, but are not limited to, carboxybetaines such as lauryldimethylaminoacetic acid betaine, aminocarboxylates such as lauryldimethylamine oxide and octadecylamine acetate, and imidazolinium betaines such as 2-lauryl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine. Of these, lauryldimethylaminoacetic acid betaine, octadecylamine acetate, and lauryldimethylamine oxide are particularly preferred.

Commercially available amphoteric surfactants represented by general formula (3), such as Amphitol 24B, Amphitol 86B, Amphitol 20BS, Amphitol 20N, Amphitol 20Y, Amphitol 20Z, and MX-968 (all trade names, manufactured by Kao Corporation), can also be used.

The amphoteric surfactant represented by the above general formula (3) can be blended in the abrasive composition of the present invention either alone or in combination of two or more.

Next, the abrasive used in the abrasive composition containing the above-mentioned grinding aids will be described. Abrasive grains commonly used for polishing can be used as the abrasive. Specific examples of the abrasive include alumina-based particles, SiC particles, diamond particles, _ZrO2 particles, MgO particles, cerium oxide particles, zirconium oxide particles, colloidal silica particles, fumed silica particles, etc., or composite particles containing two or more of these particles. Among these abrasives, using one or more of alumina-based particles, SiC particles, cerium oxide particles, zirconium oxide particles, colloidal silica particles, or fumed silica particles is preferred because it further increases the polishing rate. In particular, alumina-based particles, cerium oxide particles, zirconium oxide particles, colloidal silica particles, or fumed silica particles, among which alumina-based particles are particularly suitable for polishing magnetic recording medium substrates. Furthermore, using intermediate alumina particles as the alumina-based particles is preferred because it can significantly reduce the surface roughness of the polished object. In this specification, intermediate alumina particles is a general term for alumina particles other than α-alumina particles, and specific examples thereof include γ-alumina particles, δ-alumina particles, θ-alumina particles, η-alumina particles, and amorphous alumina particles.

It is also preferable to use alumina-based particles in which secondary particles are redispersed into primary particles when the abrasive composition of the present invention is mechanically stirred or used for polishing.

The abrasive is used in the abrasive composition of the present invention in a so-called slurry state using water as a medium. The amount of the abrasive in the abrasive composition of the present invention can be selected depending on the viscosity of the abrasive composition of the present invention and the required quality of the object to be polished, but the amount generally ranges preferably from 0.01 to 30 wt. %, more preferably from 0.02 to 10 wt. When the amount of the abrasive is within the above range, low surface roughness can be achieved with good production efficiency.

Furthermore, in relation to the amount of the grinding aid, it is preferable to blend the abrasive so that the concentration ratio of the abrasive to the grinding aid [abrasive concentration (wt%)/grinding aid concentration (wt%)] is 0.01 to 100. A concentration ratio of less than 0.01 can result in problems such as poor abrasive slippage (i.e., a decrease in the grinding removal efficiency (the ratio of actual removal to the set removal amount)). A concentration ratio exceeding 100 can result in the insufficient effect of blending the grinding aid, so it is preferable to keep the ratio within the above range. The concentration ratio is more preferably 0.01 to 50, even more preferably 0.01 to 25, even more preferably 0.02 to 10, and most preferably 0.02 to 5.

The average particle size of the primary particles of the abrasive is preferably 0.002 to 3 μm. If the average particle size of the primary particles is less than 0.002 μm, the material removal efficiency (removal rate) during polishing may be significantly reduced. If the average particle size of the primary particles exceeds 3 μm, it may be difficult to reduce the surface roughness of the workpiece, especially when polishing workpieces made of hard, brittle materials such as glass, carbon, and ceramics. Therefore, it is preferable to keep the particle size within the above range. The average particle size of the primary particles of the abrasive is more preferably 0.002 to 1 μm, even more preferably 0.01 to 1.0 μm, even more preferably 0.01 to 0.5 μm, particularly preferably 0.02 to 0.5 μm, and most preferably 0.02 to 0.2 μm.

In particular, when alumina-based particles are used as the abrasive, the average particle size of the primary particles is preferably 0.01 to 0.5 μm, and more preferably 0.02 to 0.3 μm. In particular, the average particle size of secondary particles formed by agglomeration of primary particles having such an average particle size is preferably 0.1 to 1.5 μm, and even more preferably 0.3 to 1.2 μm.

The average particle size of the primary particles of the above abrasive was determined by adding a predetermined dispersant (e.g., sodium polystyrene sulfonate) to 0.1 g of the abrasive, dispersing the abrasive by applying ultrasonic waves, and then drying the abrasive. The resulting abrasive was observed under an SEM and analyzed by image analysis. Alternatively, if the average particle size is 2 μm or greater, it may be measured using a Coulter Counter (Model MULTISIZER-II, manufactured by Coulter, Inc.).

The abrasive preferably has a Knoop hardness (JIS Z-2251) of 700 to 9000. A Knoop hardness of less than 700 may result in an insufficient polishing rate, resulting in reduced productivity. A Knoop hardness of more than 9000 may increase the thickness of the processing damage layer (i.e., the layer of microcracks and chipping) on the surface of the workpiece, resulting in reduced surface quality. Therefore, it is preferable to keep the Knoop hardness within the above range. The Knoop hardness is more preferably 1000 to 5000, and even more preferably 1500 to 3000.

The specific gravity of the abrasive is preferably 2 to 6, more preferably 2 to 4, from the viewpoints of dispersibility, ease of supply to a polishing apparatus, and ease of recovery and reuse.

Particularly preferred abrasives are α- _{Al2O3 particles} or γ- _{Al2O3 particles} with a purity of 98% by weight or more, preferably 99% by weight or more, and particularly preferably 99.9% by weight or more, and a Knoop hardness of 1500 to 3000. Such abrasives can be produced by a crystal growth method (such as the Verneuil method) using high-purity aluminum salts, and are significantly different in shape and purity from alumina produced by commonly used pulverization methods. The use of such abrasives is preferred because, although the reason is not necessarily clear, a significant synergistic effect with the addition of the grinding aid is achieved.

The purity of the abrasive can be determined as follows: 1 to 3 g of the abrasive is dissolved in an acid or alkaline aqueous solution, and the aluminum ions are quantified by inductively coupled plasma (ICP) emission spectroscopy.

The water blended into the abrasive composition of the present invention is used as a medium, and its blending amount is preferably 60 to 99.8% by weight, more preferably 70 to 99.8% by weight, and even more preferably 90 to 99.4% by weight. When the blending amount of water is within the above range, the workpiece can be polished with high production efficiency.

In addition to the essential components described above, the abrasive composition of the present invention may contain other components as additives, as needed. Examples of such additives include metal salts of monomeric acid compounds (hereinafter, these metal salts of monomeric acid compounds are referred to as "monomeric aids"). The combined use of the above-described polishing aid and the monomeric aid further improves the removal rate due to the synergistic effect of the two.

The metal salt of a monomeric acid compound (monomeric auxiliary) refers to a metal salt of a non-polymerizable (i.e., monomeric) acid compound.

The acid compound is not particularly limited as long as it has some oxidizing activity. Specific examples of the acid compound include nitric acid, sulfuric acid, sulfurous acid, persulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, carbonic acid, lactic acid, oxalic acid, and benzoic acid, as well as organic acids having these as functional groups.

Examples of metals in the metal salts of the acid compounds include aluminum, magnesium, nickel, sodium, potassium, and iron, with aluminum, magnesium, and sodium being preferred. Ammonium salts may also be used in place of the metal salts. Ammonium salts may also be used in place of the metal salts.

The above monomeric additives can be used alone or in combination of two or more.

In particular, when the abrasive composition of the present invention is used for polishing a carbon substrate, it is preferable to use, as the monomer-type auxiliary, one or more selected from the group consisting of metal salts of nitrate, metal salts of sulfate, metal salts of oxalate, metal salts of lactate, and metal salts of benzoate. In particular, the use of aluminum nitrate, aluminum oxalate, nickel sulfate, sodium lactate, aluminum lactate, or nickel benzoate is preferred because it further enhances the polishing rate.

The monomeric auxiliary is preferably blended in the abrasive composition of the present invention in an amount of 0.001 to 10 wt %, more preferably 0.01 to 5 wt %, and even more preferably 0.04 to 0.4 wt %. When the amount of the monomeric auxiliary is within the above range, the polishing rate is sufficiently improved. However, if the amount exceeds 10 wt %, the polishing rate saturates and waviness or the like may occur on the surface of the workpiece to be polished, resulting in a deterioration in surface quality and an increase in costs.

In addition to the monomer-type auxiliary agent, the abrasive composition of the present invention may also contain additives such as various surfactants, alkaline substances, various thickeners, various dispersants, various rust inhibitors, chelating agents, and organic solvents. These additives are preferably incorporated into the abrasive composition of the present invention in an amount of 0.01 to 5 wt. % each.

From the viewpoints of substrate cleanability, corrosion prevention for processing machinery, and human safety, the abrasive composition of the present invention has a pH of 1 to 13, preferably 2 to 11, and more preferably 2 to 9. Furthermore, a pH within this range allows the grinding aid to exist stably and facilitates adsorption of the grinding aid to the abrasive and polishing powder. Furthermore, when polishing carbon substrates such as glassy carbon substrates, it is preferable for the abrasive composition of the present invention to have a pH on the acidic side, i.e., 1 to 6, particularly 2 to 6, and especially 3 to 5, because this improves the polishing rate and surface quality, resulting in a good balance between productivity and quality.

In order to adjust the pH of the abrasive composition of the present invention to fall within the above range, for example, the above-mentioned grinding aid and, if necessary, the above-mentioned monomeric aid may be blended in a predetermined amount.

The reason why the polishing rate is improved and the surface roughness is reduced when the abrasive composition of the present invention containing the above-mentioned grinding aids and having a pH of 1 to 13 is used is not entirely clear, but is presumed to be as follows.

That is, the abrasive adsorbs to the surface of the workpiece, reducing surface energy and facilitating the removal of abrasive particles from the workpiece. The abrasive acts on the workpiece in this state, which is believed to dramatically increase the polishing rate compared to conventional methods. Furthermore, when using a polishing pad during polishing, clogging of the pad's surface with abrasive particles during polishing can slow the polishing rate and cause scratches. However, the abrasive particles are removed and dispersed in the rinse water by the action of the abrasive aid, eliminating these problems. Furthermore, because the abrasive acts on the workpiece while the surface is still soft, the surface roughness is believed to be lower than conventional methods.

The materials of the workpieces to be polished using the abrasive composition of the present invention include, for example, metals such as aluminum, silicon, tungsten, and copper, carbon such as glass, glassy carbon, and amorphous _carbon , ceramic materials such as _Al2O3.TiC and silicon dioxide, and resins such as polyimide resins. Among these, when a workpiece made of brittle materials such as glass, carbon, and ceramics is polished using the abrasive composition of the present invention, particularly a carbon workpiece, it is preferable that the polishing can be performed at high speed while suppressing the occurrence of surface defects such as pits and scratches and reducing the surface roughness compared to conventional abrasive compositions. Furthermore, when a workpiece made of ductile materials such as aluminum and silicon, particularly a Ni-P plated aluminum alloy substrate, is polished using the abrasive composition of the present invention, it is preferable that the polishing can be performed at high speed while suppressing the occurrence of surface defects such as pits and scratches and reducing the surface roughness compared to conventional abrasive compositions.

There are no particular limitations on the shape of the object to be polished, and the abrasive composition of the present invention can be used to polish objects with flat surfaces, such as disks, plates, slabs, and prisms, as well as objects with curved surfaces, such as lenses. Among these, the abrasive composition of the present invention is particularly effective for polishing disk-shaped objects.

In particular, as will be apparent from the examples described below, the abrasive composition of the present invention is remarkably effective in polishing carbon substrates such as glassy carbon substrates and Ni-P plated aluminum alloy substrates.

The abrasive composition of the present invention is highly effective for polishing substrates of magnetic recording media such as hard disks, optical disks, and magneto-optical disks, and is particularly effective for polishing hard disk substrates.

According to the present invention, there is provided a method for manufacturing a substrate for a magnetic recording medium, which includes a polishing step using an abrasive composition containing at least an abrasive, a polishing aid, and water, and which is characterized by using the above-described abrasive composition.

In this specification, the term "substrate" is not limited to shapes having flat surfaces such as disks, plates, slabs, and prisms, but also includes shapes having curved surfaces such as lenses.

A preferred embodiment of the method for manufacturing such a substrate will be described with reference to Figures 1 and 2, taking as an example a polishing (finish polishing) step, which is one of the polishing steps in the manufacturing process of a substrate for a magnetic recording medium. Here, Figure 1 is a schematic front view of a double-sided processing machine used in the polishing step of a glassy carbon substrate or a Ni-P plated aluminum alloy substrate, and Figure 2 is a view taken along line X-X in Figure 1.

The double-sided processing machine 1 shown in FIG. 1 is configured to include a lower surface plate 2, an upper surface plate 3 disposed above the lower surface plate 2, and a surface plate support portion 4 that contacts and supports the upper surface plate 3.

As shown in Figure 1, the upper surface plate 3 is rotatably attached via a bracket 12 to the tip of the output rod 11a of an air cylinder 11. The upper surface plate 3 is raised and lowered by the air cylinder 11, and when lowered, it engages with a groove in a rotor 13 that rotates in the direction of arrow D on the base 5 side in Figure 2, causing it to rotate in the same direction. A polishing pad is disposed on the underside of the upper surface plate 3. The upper surface plate 3 is tightly secured to the surface plate support 4 with bolts (not shown) and is rotatable together with the surface plate support 4.

As shown in Figure 2, the lower surface plate 2 is rotatably mounted on the base 5 in the direction of arrow A, and a polishing pad 6 of the same type as the polishing pad mounted on the upper surface plate 3 is mounted on its upper surface. The lower surface plate 2 also has four planetary gear-like carriers 9 that rotate and revolve around a central sun gear 7 that rotates in the direction of arrow B and an internal gear 8 that rotates on the outer periphery in the direction of arrow C. Each carrier 9 has eight holes into which a magnetic recording medium substrate 10, the workpiece to be polished, is placed.

The magnetic recording medium substrate used in this embodiment is disk-shaped and made of glassy carbon, which is a carbon material, or an aluminum alloy with a Ni-P plated surface.

A predetermined amount of the abrasive composition of the present invention is supplied between the upper platen 3 and the lower platen 2 by a slurry supply pipe (not shown).

Then, by lowering the upper surface plate 3 using the air cylinder 11, the magnetic recording medium substrate 10, which moves integrally with the carrier 9, is sandwiched between the lower surface plate 2 and the upper surface plate 3 and polished.

The magnetic recording medium substrates subjected to the polishing process are obtained by first processing a specified material into a disk shape, then subjecting it to a lapping (rough polishing) process to achieve a specified surface roughness, and then subjecting it to a chamfering process.

The polishing process conditions in this embodiment are generally as follows:

That is, the processing pressure is preferably 10 to 2000 gf/cm ² , and more preferably 50 to 500 gf/cm ² .

The processing time is preferably 2 to 120 minutes, more preferably 2 to 30 minutes.

When polishing brittle materials, particularly carbon substrates, the Shore hardness (according to JIS A (JIS K-6301)) of the polishing pads mounted on the upper and lower plates of the double-sided polishing machine is preferably 88 to 98, and more preferably 88 to 95. It is preferable to use a polishing pad made of a resin such as polyurethane foam or a resin composite such as a composite of polyester nonwoven fabric and polyurethane, as this further improves the polishing rate and reduces the surface roughness.

The rotation speed of the lower platen of the double-sided processing machine depends on the size of the processing machine. For example, in the case of a SPEED FAM 9B type double-sided processing machine, the rotation speed is preferably 5 to 100 rpm, and more preferably 10 to 60 rpm.

The supply flow rate of the abrasive composition depends on the size of the processing machine. For example, in the case of a SPEEDF AM 9B double-sided processing machine, the flow rate is preferably 5 to 300 cc/min, and more preferably 10 to 150 cc/min.

The average particle size of the primary particles of the abrasive in the abrasive composition is 0.002 to 3 μm, particularly 0.002 to 1 μm, and the concentration thereof is 0.01 to 30 wt %, particularly 0.02 to 10 wt %.

By polishing a lapped glassy carbon substrate or a Ni-P plated aluminum alloy substrate under the above conditions, the surface roughness (center line average roughness Ra) is generally about 4 to 35 Å, preferably about 4 to 25 Å, and particularly preferably about 4 to 20 Å.

The polishing process using the above-described abrasive composition is particularly effective in a polishing process, but it can also be applied to other polishing processes, such as a lapping process.

In the lapping process, a double-sided processing machine as shown in Figures 1 and 2 can be used, as in the polishing process. The operation differs from the polishing process in that, instead of using polishing pads on the upper and lower platens, platens with polishing surfaces made of cast iron or the like are used, and the abrasive composition is supplied through holes in the upper platen. Furthermore, the particle size of the abrasive grains contained in the abrasive composition is larger than that used in the polishing process, with the average primary particle size preferably being 3 to 100 μm. The abrasive concentration is also higher than that used in the polishing process, preferably 1 to 30 wt %, and more preferably 2 to 20 wt %.

Although the method for manufacturing a magnetic recording medium substrate of the present invention has been described above based on its preferred embodiment, the present invention is not limited to the above embodiment and various modifications are possible.

For example, in the polishing process, other processing machines may be used instead of the double-sided processing machine described above.

Furthermore, as will be apparent from the examples described later, the workpiece material may also _be glass, ceramic materials such as _Al2O3 and TiC, metal materials such as silicon and aluminum, or carbon materials other than glassy carbon.

Furthermore, the substrate manufacturing method of the present invention is not limited to the manufacture of substrates for magnetic recording media, but can be similarly applied to the manufacture of precision component substrates that require a polishing process, such as the manufacture of semiconductor wafers, semiconductor elements, optical lenses, optical mirrors, half mirrors, and optical prisms. Polishing of semiconductor elements includes, for example, polishing performed in interlayer insulating film planarization processes, buried metal wiring formation processes, buried device isolation film formation processes, buried capacitor formation processes, etc.

The effectiveness of the present invention will be illustrated by the following examples, but the scope of the present invention is not limited to these examples.

[Examples I-1 to I-16 and Comparative Examples I-1 to I-9] The abrasives, grinding aids, and polishing accelerators shown in Table I-1 were mixed and stirred with the remaining water at the concentrations shown in Table I-1 to obtain abrasive compositions. The types of grinding aids and polishing accelerators used are shown in Tables I-3 and I-4, respectively. The purities of α-Al ₂ O ₃ and γ-Al ₂ O ₃ shown in Table I-1 were each 99.98 wt %. However, the purity of α-Al ₂ O ₃ used in Example I-3 and Comparative Example I-3 was 99.80 wt %.

A glassy carbon (GC) substrate, a glass substrate, an Al ₂ O ₃ ·TiC substrate and a silicon wafer, each having a diameter of 1.8 inches and having a centerline average roughness Ra of 0.1 μm by lapping, were polished using the abrasive composition on a double-side processing machine.

In this case, the double-sided processing machine was used under the following conditions.

<Double-Sided Processing Machine Settings> Double-Sided Processing Machine Used: SPEED FAM 9B Double-Sided Processing Machine Processing Pressure: 150 gf/cm² Polishing pad Shore hardness: 90 [According to JIS A (JIS K-6301)] Lower platen rotation speed: 40 rpm Abrasive composition supply flow rate: 50 cc/min Each substrate in the examples and comparative examples was polished for 30 minutes, and the amount of removal was measured. The relative removal rate was calculated based on the comparative example. The results are shown in Table I-2. In addition, the centerline average roughness (Ra) of each substrate surface after polishing was measured, and the degree of scratching was evaluated according to the following criteria. The results are shown in Table I-2.

[Center line average roughness Ra]

Measurements were taken using a Tally Step manufactured by Rank Taylor Hobson.

〔scratch〕

Using an optical microscope (differential interference contrast microscope) at 50x magnification, the surface of each substrate was measured at six locations, spaced 60 degrees apart. Scratch depth was measured using a Zygo (Zygo Corporation). The evaluation criteria were as follows:

S: 0 scratches exceeding 500 Å in depth per visual field. A: Less than 0.5 scratches exceeding 500 Å in depth per visual field on average. B: 0.5 to less than 1 scratch exceeding 500 Å in depth per visual field on average. C: 1 or more scratches exceeding 500 Å in depth per visual field on average. *1... Average primary particle diameter (μm) *2... Weight% As is clear from the results shown in Table I-2, when a substrate is polished using the abrasive composition of the present invention (Examples I-1 to I-16) which contains an aliphatic organic sulfate as a polishing aid and has a pH adjusted to the range of 1 to 13, the polishing rate is improved, the surface roughness is reduced, and the occurrence of scratches is suppressed compared to when a substrate is polished using an abrasive composition (Comparative Examples I-1 to I-9) which does not contain an aliphatic organic sulfate.

[Examples II-1 to II-14 and Comparative Examples II-1 to II-8] Abrasive compositions were obtained in the same manner as in Example I-1, except that the abrasives, grinding aids, and polishing accelerators shown in Table II-1 were mixed and stirred with the balance water at the concentrations shown in Table II-1. The types of polishing accelerators used are as shown in Table II-3. The types of polishing accelerators used are as shown in Table I-4. The purities of the α _{- Al2O3} and γ _{- Al2O3} shown in Table II-1 were each 99.98% by weight. However, the purity of _the α- _Al2O3 used in Example II-3 and Comparative Example II-3 was 99.80% by weight.

Various substrates prepared in the same manner as in Example I-1 were polished using the above abrasive composition on a double-sided polishing machine under the same conditions as in Example I-1. As in Example I-1, the relative removal rate was determined, the centerline average roughness (Ra) of the polished surface of each substrate was measured, and the degree of scratching was evaluated. The results are shown in Table II-2.

*1... Average primary particle size (μm) *2... Weight% As is clear from the results shown in Table II-2, when a substrate is polished using the abrasive compositions of the present invention (Examples II-1 to II-14) which contain an oxyalkylene alkyl ether sulfate compound represented by the above general formula (2) as a polishing aid and have a pH adjusted to the range of 1 to 13, the polishing rate is improved, the surface roughness is reduced, and the occurrence of scratches is suppressed compared to when a substrate is polished using abrasive compositions (Comparative Examples II-1 to II-8) which do not contain the oxyalkylene alkyl ether sulfate compound.

[Examples III-1 to III-13 and Comparative Examples III-1 to III-7] Abrasive compositions were obtained in the same manner as in Example I-1, except that the abrasives, grinding aids, and polishing accelerators shown in Table III-1 were mixed and stirred with the balance water at the concentrations shown in Table III-1. The types of polishing aids used are as shown in Table III-3. The types of polishing accelerators used are as shown in Table _I -4. The purities of α _{- Al2O3} and γ- _Al2O3 shown in Table III-1 were each 99.98% by weight.

Various substrates prepared in the same manner as in Example I-1 were polished using the above abrasive composition on a double-sided polishing machine under the same conditions as in Example I-1. The relative removal rate was determined in the same manner as in Example I-1 (except that polishing was carried out for 120 minutes), and the degree of scratch generation was evaluated. The results are shown in Table III-2.

*1... Average primary particle size (μm) *2... Weight% As is clear from the results shown in Table III-2, when a substrate is polished using the abrasive compositions of the present invention (Examples III-1 to III-13) containing an amphoteric surfactant as a polishing aid and having a pH adjusted to the range of 1 to 13, the polishing rate is improved and a high-quality surface with reduced scratching is obtained compared to when a substrate is polished using abrasive compositions not containing an amphoteric surfactant (Comparative Examples III-1 to III-7).

[Examples IV-1 to IV-20 and Comparative Examples IV-1 to IV-3] Abrasive compositions were obtained in the same manner as in Example I-1, except that the abrasives and grinding aids shown in Table IV-1 were mixed and stirred with the remainder water at the concentrations shown in Table IV-1. The types of grinding aids used are as shown in Table IV-3. The pH was adjusted with sulfuric acid in Examples IV-4 to IV-6 and IV-18, and with sodium hydroxide in Example IV-20.

A 2.5-inch diameter Ni-P plated aluminum alloy substrate, which had been lapped to a centerline average roughness Ra of 0.1 μm, was polished using the abrasive composition with a double-sided polishing machine. The double-sided polishing machine was used under the following conditions:

<Double-Sided Milling Machine Settings> Double-Sided Milling Machine Used: Kyoritsu Seiki 6B Type Milling Pressure: 100 gf/cm² Polishing pad: Politex DG Lower platen rotation speed: 40 rpm Abrasive composition supply flow rate: 30 cc/min Each substrate in the examples and comparative examples was polished for 7 minutes, and the relative removal rate was determined as in Example I-1. The surface roughness of each substrate after polishing was also measured as in Example I-1, and the relative value was determined using the comparative example as the standard. The degree of scratch occurrence was also evaluated as in Example I-1. The results are shown in Table IV-2.

*1: Average particle diameter of primary particles (μm) *2: Weight% As is clear from the results shown in Table IV-2, even when a Ni-P plated aluminum alloy substrate, which is a ductile material, is used, the abrasive compositions of the present invention (Examples IV-1 to IV-20) which contain a fatty acid organic sulfate, an oxyalkylene alkyl ether sulfate compound, and an amphoteric surfactant as polishing aids and which have a pH adjusted to a range of 1 to 13, have improved polishing speed, reduced surface roughness, and suppressed the occurrence of scratches, compared to abrasive compositions which do not contain these polishing aids (Comparative Examples IV-1 to IV-3).

INDUSTRIAL APPLICABILITY The present invention provides an abrasive composition for magnetic recording medium substrates and a method for manufacturing magnetic recording medium substrates that can improve polishing rates and reduce surface roughness without causing defects such as pits or scratches on the surface of the workpiece. This shortens the manufacturing process for magnetic recording medium substrates, significantly improving productivity and reducing costs.

The abrasive composition for magnetic recording medium substrates of the present invention is particularly excellent for polishing objects made of brittle materials such as glass, carbon, and ceramics, and objects made of ductile materials such as Ni-P plated aluminum, and is particularly suitable for polishing.

───────────────────────────────────────────────────── Continued from the front page (72) Inventor: Toshiya Hagiwara Kao Corporation Research Laboratory, 1334 Minato, Wakayama City, Wakayama Prefecture (Note) This publication is based on the publication published internationally by the International Bureau of Patents (WIPO). The effect of the international publication of the Japanese patent application (Japanese utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act) and is unrelated to this publication.

Claims (1)

[Claims] 1. An abrasive composition for magnetic recording medium substrates comprising at least an abrasive, a polishing aid, and water, wherein the polishing aid comprises one or more aliphatic organic sulfates, and the pH is 1 to 13. 2. An abrasive composition for magnetic recording medium substrates according to claim 1, wherein the aliphatic organic sulfate is represented by the following general formula (1): R-O- _SO3M (1) wherein R represents a linear or branched alkyl group, aryl group, or alkylaryl group having 5 to 21 carbon atoms, and M represents an alkali metal, alkaline earth metal, or organic cation. 3. An abrasive composition for magnetic recording medium substrates according to claim 1, wherein the concentration ratio of the abrasive to the polishing aid [abrasive concentration (wt%)/polishing aid concentration (wt%)] is 0.01 to 100. 4. 4. The abrasive composition for magnetic recording medium substrates according to claim 1, wherein the average particle size of the primary particles of the abrasive is 0.002 to 3 μm. 5. The abrasive composition for magnetic recording medium substrates according to claim 1, wherein the abrasive comprises one or more of alumina particles, SiC particles, cerium oxide particles, zirconium oxide particles, colloidal silica particles, and fumed silica _particles . 6. The abrasive composition for magnetic recording medium substrates according to claim 1, wherein the abrasive comprises α- _{Al2O3 particles} or γ- _Al2O3 particles having a purity of 98% by weight or more and a Knoop hardness of 1500 to 3000. 7. The abrasive composition for magnetic recording medium substrates according to claim 1, which is used for polishing carbon substrates. 8. The abrasive composition for magnetic recording medium substrates according to claim 1, which is used for polishing Ni-P plated aluminum alloy substrates. 9. 10. An abrasive composition for magnetic recording medium substrates comprising at least an abrasive, a polishing aid, and water, wherein the polishing aid comprises one or more oxyalkylene alkyl ether sulfate compounds represented by the following general formula (2), and wherein the pH is 1 to 13: R-O-(AO) _n - _SO3M (2) wherein R represents a linear or branched alkyl group, aryl group, or alkylaryl group having 5 to 21 carbon atoms, AO represents an oxyalkylene group having 2 or 3 carbon atoms, n represents a natural number of 1 to 30, and M represents an alkali metal, alkaline earth metal, or organic cation. 11. An abrasive composition for magnetic recording medium substrates according to claim 9, wherein the concentration ratio of the abrasive to the polishing aid [abrasive concentration (wt%)/polishing aid concentration (wt%)] is 0.01 to 100. 11. An abrasive composition for magnetic recording medium substrates comprising at least an abrasive, a polishing aid, and water, wherein the polishing aid comprises one or more amphoteric surfactants, and the abrasive composition has a pH of 1 to 13. 12. The abrasive composition for magnetic recording medium substrates according to claim 11, wherein the amphoteric surfactant is represented by the following general formula (3): wherein ^R1 , ^R2 , and ^R3 each represent a linear or branched alkyl group, alkyl derivative group, alkenyl group, hydrogen, or ^R5 -Ar- group ( ^R5 represents an alkyl group, alkenyl group, alkyl derivative group, or hydrogen, and Ar represents an aromatic group), and may be the same or different; ^R4 represents a direct bond or an alkylene group; and ^Y- represents an anionic group. ^R2 and ^R3 may also form a ring. 13. An abrasive composition for magnetic recording medium substrates according to claim 11, wherein the concentration ratio of the abrasive to the polishing aid [abrasive concentration (wt%)/polishing aid concentration (wt%)] is 0.01 to 100. 14. A method for producing a magnetic recording medium substrate, comprising a polishing step using an abrasive composition containing at least an abrasive, a polishing aid, and water, wherein the abrasive composition for magnetic recording medium substrates according to claim 1, 9, or 11 is used as the abrasive composition. 15. 15. A method for manufacturing a magnetic recording medium substrate according to claim 14, wherein said substrate is a carbon substrate. 16. A method for manufacturing a magnetic recording medium substrate according to claim 14, wherein said substrate is an Ni-P plated aluminum alloy substrate. 17. A method for manufacturing a magnetic recording medium substrate according to claim 14, wherein said substrate is a substrate for a hard disk.