JP6131749B2 - Method for polishing glass substrate for magnetic recording medium, method for manufacturing glass substrate for magnetic recording medium - Google Patents

Method for polishing glass substrate for magnetic recording medium, method for manufacturing glass substrate for magnetic recording medium Download PDF

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JP6131749B2
JP6131749B2 JP2013151951A JP2013151951A JP6131749B2 JP 6131749 B2 JP6131749 B2 JP 6131749B2 JP 2013151951 A JP2013151951 A JP 2013151951A JP 2013151951 A JP2013151951 A JP 2013151951A JP 6131749 B2 JP6131749 B2 JP 6131749B2
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polishing
glass substrate
fixed abrasive
abrasive tool
polished
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JP2015022784A (en
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哲志 中山
哲志 中山
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AGC Inc
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Asahi Glass Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B37/00—Lapping machines or devices; Accessories
    • B24B37/04—Lapping machines or devices; Accessories designed for working plane surfaces
    • B24B37/07—Lapping machines or devices; Accessories designed for working plane surfaces characterised by the movement of the work or lapping tool
    • B24B37/08—Lapping machines or devices; Accessories designed for working plane surfaces characterised by the movement of the work or lapping tool for double side lapping
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B7/00—Machines or devices designed for grinding plane surfaces on work, including polishing plane glass surfaces; Accessories therefor
    • B24B7/20—Machines or devices designed for grinding plane surfaces on work, including polishing plane glass surfaces; Accessories therefor characterised by a special design with respect to properties of the material of non-metallic articles to be ground
    • B24B7/22—Machines or devices designed for grinding plane surfaces on work, including polishing plane glass surfaces; Accessories therefor characterised by a special design with respect to properties of the material of non-metallic articles to be ground for grinding inorganic material, e.g. stone, ceramics, porcelain
    • B24B7/228—Machines or devices designed for grinding plane surfaces on work, including polishing plane glass surfaces; Accessories therefor characterised by a special design with respect to properties of the material of non-metallic articles to be ground for grinding inorganic material, e.g. stone, ceramics, porcelain for grinding thin, brittle parts, e.g. semiconductors, wafers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Manufacturing Of Magnetic Record Carriers (AREA)
  • Finish Polishing, Edge Sharpening, And Grinding By Specific Grinding Devices (AREA)

Description

本発明は、磁気記録媒体用ガラス基板の研磨方法、磁気記録媒体用ガラス基板の製造方法に関する。   The present invention relates to a method for polishing a glass substrate for a magnetic recording medium and a method for manufacturing a glass substrate for a magnetic recording medium.

磁気ディスク記録装置等に用いられる磁気記録媒体用基板としては、従来、アルミニウム合金基板が使用されてきた。しかしながら、近年、高記録密度化の要求に伴い、アルミニウム合金基板に比べて硬く、平坦性や平滑性に優れるガラス基板が主流となってきている。   Conventionally, aluminum alloy substrates have been used as substrates for magnetic recording media used in magnetic disk recording devices and the like. However, in recent years, with the demand for higher recording density, glass substrates that are harder than aluminum alloy substrates and excellent in flatness and smoothness have become mainstream.

磁気記録媒体用ガラス基板（以下、「ガラス基板」とも記載する）は、中心部に同心円状の開口部を有する円盤形状を有しており、ガラス素基板から係る形状に加工する工程や、主平面を研磨する工程、端面を研磨する工程等を行うことで製造される。   A glass substrate for a magnetic recording medium (hereinafter also referred to as “glass substrate”) has a disk shape having a concentric opening at the center, and a process of processing the glass substrate into such a shape, It is manufactured by performing a step of polishing a flat surface, a step of polishing an end surface, and the like.

ガラス基板の主平面を研磨する工程は、ガラス基板の主平面を所望の平坦度とし、ガラス基板を所望の板厚とし、ガラス基板の主平面を所望のうねりや粗さとする工程である。ガラス基板の主平面を研磨する工程での研磨方法としては、遊離砥粒を用いた研磨や、固定砥粒工具を用いた研磨等が知られている。特に固定砥粒工具を用いた研磨は、遊離砥粒による研磨と比較して研磨速度（研磨レート）が高く、ガラス基板の表面に傷、クラック等のダメージが発生しにくい。   The step of polishing the main plane of the glass substrate is a step in which the main plane of the glass substrate is set to a desired flatness, the glass substrate is set to a desired plate thickness, and the main plane of the glass substrate is set to a desired swell and roughness. As a polishing method in the step of polishing the main plane of the glass substrate, polishing using loose abrasive grains, polishing using a fixed abrasive tool, and the like are known. In particular, polishing using a fixed abrasive tool has a higher polishing rate (polishing rate) than polishing using free abrasive grains, and damage such as scratches and cracks is unlikely to occur on the surface of the glass substrate.

このため、ガラス素基板やガラス素基板から円盤形状に加工されたガラス基板の主平面を、研磨速度が高く、ガラス基板の表面にダメージを発生させにくい固定砥工具により研磨することが求められていた。   For this reason, it is required to polish a glass substrate or a main surface of a glass substrate processed into a disk shape from a glass substrate with a fixed abrasive tool that has a high polishing rate and hardly causes damage to the surface of the glass substrate. It was.

しかし、研磨対象となるガラス基板の主平面が鏡面の場合、固定砥粒工具の砥粒がガラス基板の表面に切り込むことができずに滑るため研磨速度が極端に低下するという問題があった。   However, when the main plane of the glass substrate to be polished is a mirror surface, there is a problem that the polishing rate is extremely lowered because the abrasive grains of the fixed abrasive tool cannot slide into the surface of the glass substrate and slide.

このため、例えば特許文献１には、固定砥粒を用いた研磨工程（表面研削工程）前に、板状ガラスの表面を、遊離砥粒を用いた加工や、フロスト加工により粗面化する粗面化工程を具備する磁気ディスク用ガラス基板の製造方法が提案されている。   For this reason, for example, in Patent Document 1, before the polishing step (surface grinding step) using fixed abrasive grains, the surface of the sheet glass is roughened by processing using free abrasive grains or frost processing. A method of manufacturing a glass substrate for a magnetic disk having a surfaceizing process has been proposed.

特開２０１２−１６４４１７号公報JP 2012-164417 A

しかしながら、特許文献１に記載された方法では、固定砥粒工具による研磨（研削）の前に遊離砥粒を用いた加工や、フロスト加工により、板状ガラスの表面を粗面化する粗面化工程を行う必要があった。このため、工程数が増加して生産性の低下や、コストが上昇する等の問題があった。さらに、粗面化したガラス基板を固定砥粒工具により研磨すると、固定砥粒工具の寿命が短くなるおそれもある。   However, in the method described in Patent Document 1, the surface of the sheet glass is roughened by processing using free abrasive grains or frost processing before polishing (grinding) with a fixed abrasive tool. It was necessary to carry out a process. For this reason, there are problems such as an increase in the number of processes and a decrease in productivity and an increase in cost. Furthermore, if the roughened glass substrate is polished with a fixed abrasive tool, the life of the fixed abrasive tool may be shortened.

そこで、本発明は上記従来技術が有する問題に鑑み、研磨されるガラス基板の主平面が鏡面であっても、ガラス基板の表面を、固定砥粒工具を用いて高い研磨速度により研磨できる磁気記録媒体用ガラス基板の研磨方法を提供することを目的とする。   Therefore, in view of the problems of the above-described prior art, the present invention provides a magnetic recording capable of polishing the surface of a glass substrate at a high polishing rate using a fixed abrasive tool even if the main plane of the glass substrate to be polished is a mirror surface. It aims at providing the grinding | polishing method of the glass substrate for media.

上記課題を解決するため本発明は、固定砥粒工具を用いて鏡面であるガラス基板の主平面を研磨する磁気記録媒体用ガラス基板の研磨方法であって、
前記固定砥粒工具の研磨面に表出している砥粒の平均面積は１０μｍ２以上３００μｍ２以下であり、
前記固定砥粒工具の研磨面の砥粒表出率は１．１％以上２．２％以下である磁気記録媒体用ガラス基板の研磨方法を提供する。 In order to solve the above problems, the present invention is a method for polishing a glass substrate for a magnetic recording medium, which polishes the main surface of a glass substrate that is a mirror surface using a fixed abrasive tool,
The average area of the abrasive grains exposed on the polishing surface of the fixed abrasive tool is 10 μm 2 or more and 300 μm 2 or less,
Provided is a method for polishing a glass substrate for a magnetic recording medium, wherein an abrasive grain appearance ratio of a polishing surface of the fixed abrasive tool is 1.1% or more and 2.2 % or less.

本発明の磁気記録媒体用ガラス基板の研磨方法によれば、研磨されるガラス基板の主平面が鏡面であっても、ガラス基板の表面を、固定砥粒工具を用いて高い研磨速度により研磨できる。   According to the method for polishing a glass substrate for a magnetic recording medium of the present invention, even if the main plane of the glass substrate to be polished is a mirror surface, the surface of the glass substrate can be polished at a high polishing rate using a fixed abrasive tool. .

両面研磨装置の構成例の説明図Illustration of configuration example of double-side polishing machine

以下、本発明を実施するための形態について図面を参照して説明するが、本発明は、下記の実施形態に制限されることはなく、本発明の範囲を逸脱することなく、下記の実施形態に種々の変形および置換を加えることができる。   DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and the following embodiments are not departed from the scope of the present invention. Various modifications and substitutions can be made.

まず、本実施形態の磁気記録媒体用ガラス基板の研磨方法の構成例について説明を行う。   First, a configuration example of a polishing method for a glass substrate for a magnetic recording medium according to this embodiment will be described.

本実施形態の磁気記録媒体用ガラス基板の研磨方法は、固定砥粒工具を用いて鏡面であるガラス基板の主平面を研磨する磁気記録媒体用ガラス基板の研磨方法である。そして、固定砥粒工具の研磨面に表出している砥粒の平均面積を１０μｍ２以上３００μｍ２以下、固定砥粒工具の研磨面の砥粒表出率を１．１％以上３．０％以下とすることを特徴とする。 The method for polishing a glass substrate for a magnetic recording medium according to this embodiment is a method for polishing a glass substrate for a magnetic recording medium in which a main plane of the glass substrate that is a mirror surface is polished using a fixed abrasive tool. And the average area of the abrasive grains exposed on the polishing surface of the fixed abrasive tool is 10 μm 2 or more and 300 μm 2 or less, and the abrasive grain expression rate of the polishing surface of the fixed abrasive tool is 1.1% or more and 3.0%. It is characterized as follows.

本実施形態の磁気記録媒体用ガラス基板の研磨方法は、例えば、図１に示すような両面研磨装置を用いて実施することができる。   The method for polishing a glass substrate for a magnetic recording medium of the present embodiment can be performed using, for example, a double-side polishing apparatus as shown in FIG.

図１（Ａ）は、主平面研磨を行う際に用いるキャリアの構成例を、図１（Ｂ）は、両面研磨装置の概略図を示している。   FIG. 1A shows a structural example of a carrier used when performing main surface polishing, and FIG. 1B shows a schematic diagram of a double-side polishing apparatus.

ガラス基板の主平面を研磨する際、図１（Ａ）に示すような、ガラス基板を保持可能なガラス基板保持穴１１を有するキャリア（主平面研磨用治具）１０に複数のガラス基板を設置する。なお、図中では円形のガラス基板保持穴１１を設けたキャリア１０を例に示しているが、係る形態に限定されず研磨するガラス基板の形状にあわせたガラス基板保持穴１１を形成することができる。例えば、後述のように形状付与前のガラス基板を研磨する場合には四角形状のガラス基板保持穴１１を有するキャリア１０を用いることができる。   When polishing the main surface of the glass substrate, a plurality of glass substrates are installed in a carrier (main surface polishing jig) 10 having a glass substrate holding hole 11 capable of holding the glass substrate as shown in FIG. To do. In the drawing, the carrier 10 provided with the circular glass substrate holding hole 11 is shown as an example. However, the present invention is not limited to such a form, and the glass substrate holding hole 11 can be formed according to the shape of the glass substrate to be polished. it can. For example, in the case where a glass substrate before giving a shape is polished as will be described later, a carrier 10 having a square glass substrate holding hole 11 can be used.

ガラス基板を設置したキャリア１０を、図１（Ｂ）に示すような両面研磨装置１２にセットし、サンギア１３、インターナルギア１４を所定の回転比率で回転駆動する。これにより、キャリア１０を自転させながらサンギア１３の周りを公転するように移動させる。このとき、キャリア１０に保持されたガラス基板の両主平面は、ガラス基板と対向する面にそれぞれ固定砥粒工具１６、１８が装着された上定盤１５と、下定盤１７との間に狭持、押圧されるため、ガラス基板の両主平面が同時に研磨されることになる。なお、研磨を行う際には、研磨面とガラス基板との間に研磨液（クーラント）を供給することができる。研磨の際に用いる研磨液の種類は特に限定されるものではなく、例えばメタノール、エタノールなどのアルコール、モノエタノールアミン、ジエタノールアミン、トリエタノールアミン、アミン力ルボキシレート、チオアミン塩、イソプ口パノールアミン、卜リエチレンジアミン四酢酸などのアミン化合物、ポリアルキレングリコール、アルキレングリコールモノアルキルエーテル、エチレングリコール、プ口ピレングリコール、プ口ピレングリコールメチルエーテル、ヘキシレングリコールなどの界面活性剤、パイン油、鉱油などの潤滑材、カルボン酸やスルホン酸を有するアニオン系化合物のうち１つ以上を含む水溶液を用いることができる。   The carrier 10 provided with the glass substrate is set in a double-side polishing apparatus 12 as shown in FIG. 1B, and the sun gear 13 and the internal gear 14 are rotationally driven at a predetermined rotation ratio. Accordingly, the carrier 10 is moved so as to revolve around the sun gear 13 while rotating. At this time, both main planes of the glass substrate held by the carrier 10 are narrow between the upper surface plate 15 and the lower surface plate 17 each having the fixed abrasive tools 16 and 18 mounted on the surfaces facing the glass substrate. Since it is held and pressed, both main planes of the glass substrate are polished simultaneously. When polishing, a polishing liquid (coolant) can be supplied between the polishing surface and the glass substrate. The type of polishing liquid used for polishing is not particularly limited. For example, alcohols such as methanol and ethanol, monoethanolamine, diethanolamine, triethanolamine, amine strength ruboxylate, thioamine salt, isoporanolamine, and polyethylenediamine Amine compounds such as tetraacetic acid, polyalkylene glycol, alkylene glycol monoalkyl ether, ethylene glycol, propylene glycol, propylene glycol methyl ether, surfactants such as hexylene glycol, lubricants such as pine oil and mineral oil, An aqueous solution containing one or more anionic compounds having a carboxylic acid or a sulfonic acid can be used.

本実施形態の磁気記録媒体用ガラス基板の研磨方法において用いるガラス基板は磁気記録媒体用のガラス基板であれば良く、特に限定されるものではない。例えばガラスの種類はアモルファスガラスや、結晶化ガラスでもよく、ガラス基板の表層に強化層を有する強化ガラスでもよい。また、研磨工程に供するガラス基板は中央に円形の開口部を備えた円盤形状のガラス基板であっても良く、該円盤形状に加工する前の、すなわち、形状付与工程を行う前の四角形状のガラス基板であってもよい。ガラス基板は例えば、フロート法、フュージョン法、ダウンドロー法、または、プレス成形法等で成形されたガラス基板を用いることができる。本実施形態の磁気記録媒体用ガラス基板の研磨方法は、主平面が鏡面であるガラス基板を、ガラス基板の表面に生じるダメージを抑制しながら高い研磨速度で研磨する場合に特に効果を有する。   The glass substrate used in the method for polishing a glass substrate for a magnetic recording medium of the present embodiment is not particularly limited as long as it is a glass substrate for a magnetic recording medium. For example, the glass may be amorphous glass or crystallized glass, or tempered glass having a tempered layer on the surface layer of the glass substrate. Further, the glass substrate used for the polishing step may be a disk-shaped glass substrate having a circular opening at the center, and is formed into a square shape before processing into the disk shape, that is, before performing the shape imparting step. It may be a glass substrate. As the glass substrate, for example, a glass substrate formed by a float method, a fusion method, a downdraw method, a press molding method, or the like can be used. The method for polishing a glass substrate for a magnetic recording medium according to the present embodiment is particularly effective when a glass substrate having a mirror surface as a main plane is polished at a high polishing rate while suppressing damage generated on the surface of the glass substrate.

鏡面であるガラス基板の主平面の表面粗さＲａは０．００９μｍ以下であることが好ましい。ここでいう表面粗さＲａとはＪＩＳ Ｂ ０６０１−２００１に準ずる方法により測定できる。ガラス基板の主平面は２面ある主平面が両面とも鏡面であることが好ましく、特に両面とも平面粗さＲａが０．００９μｍ以下であることがより好ましい。   The surface roughness Ra of the main surface of the glass substrate which is a mirror surface is preferably 0.009 μm or less. The surface roughness Ra here can be measured by a method according to JIS B 0601-2001. As for the main plane of the glass substrate, it is preferable that the two main planes are both mirror surfaces, and it is more preferable that the plane roughness Ra is 0.009 μm or less on both sides.

ここで、本実施形態の磁気記録媒体用ガラス基板の研磨方法において用いる固定砥粒工具について説明する。固定砥粒工具は、上述のように定盤の被研磨物と対向する面に装着される。   Here, the fixed abrasive tool used in the polishing method of the glass substrate for magnetic recording media of the present embodiment will be described. The fixed abrasive tool is mounted on the surface of the surface plate facing the object to be polished as described above.

固定砥粒工具は、砥粒（研磨砥粒）を樹脂や金属等のボンド材により固定したものであればよく、特に限定されるものではない。   The fixed abrasive tool is not particularly limited as long as the abrasive grains (polishing abrasive grains) are fixed by a bond material such as resin or metal.

例えば、砥粒としては、ダイヤモンド、アルミナ（酸化アルミニウム、ＷＡ）、炭化ケイ素（ＧＣ）、窒化ホウ素（ＣＢＮ）等を好ましく用いることができ、特に研磨速度（研磨レート）が高くなるためダイヤモンドを用いることがより好ましい。   For example, diamond, alumina (aluminum oxide, WA), silicon carbide (GC), boron nitride (CBN), or the like can be preferably used as the abrasive grains, and diamond is used because the polishing rate (polishing rate) is particularly high. It is more preferable.

また、ボンド材としては、金属、ビトリファイド、樹脂等を好ましく用いることができる。ここで、ボンド材に用いる樹脂としては、例えばフェノール樹脂や、エポキシ樹脂、アクリル樹脂等を好ましく用いることができる。なお、ボンド材は１種類に限定されるものではなく、複数のボンド材を用いることができる。例えば、砥粒をビドリファイで固めた後に樹脂に埋め込んだ固定砥粒工具を用いることができる。また、ボンド材中にはフィラー等の無機物を添加することもできる。   Further, as the bonding material, metal, vitrified, resin, or the like can be preferably used. Here, as a resin used for the bond material, for example, a phenol resin, an epoxy resin, an acrylic resin, or the like can be preferably used. Note that the bond material is not limited to one type, and a plurality of bond materials can be used. For example, it is possible to use a fixed abrasive tool in which abrasive grains are hardened by vidify and then embedded in a resin. In addition, an inorganic substance such as a filler can be added to the bond material.

また、固定砥粒工具の研磨面、すなわち、ガラス基板と対向する面の構造は特に限定されるものではなく、例えば、平坦な面とすることもできるが、研磨液の供給を均一にするための溝（凹部）が形成されていることが好ましい。溝の形状は特に限定されるものではなく、任意に選択することができるが、例えば溝の幅は、０．３ｍｍ以上２０ｍｍ以下とすることが好ましく、０．５ｍｍ以上１０ｍｍ以下とすることがより好ましい。また、溝の深さは０．１ｍｍ以上１５ｍｍ以下とすることが好ましく、０．２ｍｍ以上１０ｍｍ以下とすることがより好ましい。これは溝の幅、深さを上記範囲とすることにより、研磨速度を低下させることなく、研磨液を均一に供給することができるためである。   Further, the structure of the polishing surface of the fixed abrasive tool, that is, the surface facing the glass substrate is not particularly limited. For example, it can be a flat surface, but the supply of the polishing liquid is uniform. It is preferable that a groove (concave portion) is formed. The shape of the groove is not particularly limited and can be arbitrarily selected. For example, the width of the groove is preferably 0.3 mm or more and 20 mm or less, more preferably 0.5 mm or more and 10 mm or less. preferable. Further, the depth of the groove is preferably 0.1 mm or more and 15 mm or less, and more preferably 0.2 mm or more and 10 mm or less. This is because the polishing liquid can be supplied uniformly without reducing the polishing rate by setting the width and depth of the grooves in the above ranges.

また、溝により画された凸部の表面、すなわち、被研磨物と接する面の形状は任意の形状とすることができ、特に限定されないが、例えば、正方形、長方形等の矩形や、三角形、六角形、八角形などの多角形や、円形または楕円形等の円形状とすることができる。なお、研磨装置の定盤に装着された固定砥粒工具内で、凸部の形状は同一である必要はなく、例えば、正方形と長方形の形状が混在していてもよい。凸部が矩形である場合の短辺の長さ、凸部が多角形である場合の、該多角形の中心と各頂点を結ぶ線分のうち最も短い線分の長さ、または、凸部が円形である場合の短径の長さをＬとした場合、Ｌは例えば１ｍｍ以上３０ｍｍ以下とすることが好ましく、２ｍｍ以上２０ｍｍ以下とすることがより好ましい。Ｌが上記範囲にあることにより、ガラス基板をより高い研磨速度で研磨しつつ、ガラス基板と固定砥粒工具との間に研磨液を均一に供給できるため好ましい。   In addition, the surface of the convex portion defined by the groove, that is, the shape of the surface in contact with the object to be polished can be any shape, and is not particularly limited, but for example, a rectangle such as a square or a rectangle, a triangle, It can be a polygon such as a square or an octagon, or a circle such as a circle or an ellipse. In addition, the shape of a convex part does not need to be the same in the fixed abrasive tool with which the surface plate of the grinding | polishing apparatus was mounted | worn, for example, the shape of a square and a rectangle may be mixed. The length of the short side when the convex part is a rectangle, the length of the shortest line segment among the line segments connecting the center and each vertex of the polygon when the convex part is a polygon, or the convex part When the length of the minor axis when L is circular is L, L is, for example, preferably 1 mm or more and 30 mm or less, and more preferably 2 mm or more and 20 mm or less. It is preferable that L is in the above range since the polishing liquid can be supplied uniformly between the glass substrate and the fixed abrasive tool while polishing the glass substrate at a higher polishing rate.

なお、固定砥粒工具の研磨面全体に対する、凸部のガラス基板と接する表面の面積の合計の比率についても特に限定されるものではないが、例えば、２０％以上９５％であることが好ましく、４０％以上９０％以下であることがより好ましい。これは凸部の比率が上記範囲にあることにより、研磨液をより均一に供給し、被研磨物である磁気記録媒体用ガラス基板を特に高い研磨速度で研磨することができるためである。   The total ratio of the area of the surface in contact with the convex glass substrate to the entire polishing surface of the fixed abrasive tool is not particularly limited, but is preferably 20% or more and 95%, for example. More preferably, it is 40% or more and 90% or less. This is because when the ratio of the convex portions is in the above range, the polishing liquid can be supplied more uniformly and the glass substrate for magnetic recording medium, which is the object to be polished, can be polished at a particularly high polishing rate.

そして、上述のように、固定砥粒工具の研磨面に表出している砥粒の平均面積（以下、「表出している砥粒の平均面積」とも記載する）、すなわち、固定砥粒工具の研磨面に表出している砥粒１個当たりの平均面積は、１０μｍ２以上３００μｍ２以下であることが好ましい。 And as mentioned above, the average area of the abrasive grains exposed on the polishing surface of the fixed abrasive tool (hereinafter also referred to as “average area of the abrasive grains exposed”), that is, the fixed abrasive tool The average area per abrasive grain exposed on the polished surface is preferably 10 μm 2 or more and 300 μm 2 or less.

表出している砥粒の平均面積が１０μｍ２未満の場合、固定砥粒工具の砥粒が鏡面のガラス基板の表面を滑るため研磨できない場合があり、また、砥粒の角が早く磨耗し丸くなるため、研磨速度が早く低下するおそれがある。表出している砥粒の平均面積が３００μｍ２よりも大きい場合、研磨したガラス基板表面の傷やクラック等を含む層である加工変質層が深くなる場合がある。このため、加工変質層を除去するためにその後の研磨工程において研磨量を多くする必要があり、生産性が低下してしまう。また、場合によっては磁気記録媒体用ガラス基板の表面に潜傷が残るおそれもある。さらに、表出している砥粒の平均面積が大きいと、砥粒が適切なタイミングで研磨面から脱離しないため、自生作用が不十分となり、高い研磨速度を維持できなくなるおそれもある。特に固定砥粒工具の研磨面に表出している砥粒の平均面積は、２０μｍ２以上１８０μｍ２以下であることがより好ましい。 If the average area of the exposed abrasive grains is less than 10 μm 2 , the abrasive grains of the fixed abrasive tool may not be polished because they slide on the surface of the mirror glass substrate, and the corners of the abrasive grains wear out quickly and become round. Therefore, there is a possibility that the polishing rate is quickly reduced. When the average area of the exposed abrasive grains is larger than 300 μm 2 , the work-affected layer that is a layer containing scratches, cracks and the like on the polished glass substrate surface may become deep. For this reason, in order to remove the work-affected layer, it is necessary to increase the amount of polishing in the subsequent polishing step, and productivity is lowered. In some cases, latent scratches may remain on the surface of the magnetic recording medium glass substrate. Furthermore, if the average area of the exposed abrasive grains is large, the abrasive grains do not detach from the polishing surface at an appropriate timing, so that the self-generated action becomes insufficient and there is a possibility that a high polishing rate cannot be maintained. In particular the average area of the abrasive grains are exposed on the polished surface of the fixed abrasive tool, more preferably 20 [mu] m 2 or more 180 [mu] m 2 or less.

さらに、固定砥粒工具の研磨面の砥粒表出率（以下、「砥粒表出率」とも記載する）、が１．１％以上３．０％以下であることが好ましい。これは、砥粒表出率が１．１％よりも小さいと固定砥粒工具の研磨面の磨耗が早くなり、固定砥粒工具の寿命が短くなり、固定砥粒工具（砥石）の交換頻度が上がり生産性が低くなるおそれがある。さらには、研磨速度が低くなるおそれもあり、好ましくない。砥粒表出率が３．０％より大きい場合、固定砥粒工具の研磨面の自生作用が不十分となり、研磨面が目詰まりし、研磨速度が低下するため、研磨速度を維持できないおそれがある。砥粒表出率は、１．２％以上であることがより好ましく、また、２．２％以下であることがより好ましい。   Furthermore, it is preferable that the abrasive grain expression rate (hereinafter also referred to as “abrasive grain expression rate”) of the polishing surface of the fixed abrasive tool is 1.1% or more and 3.0% or less. This is because if the abrasive grain expression rate is less than 1.1%, the abrasive surface of the fixed abrasive tool wears quickly, the life of the fixed abrasive tool is shortened, and the fixed abrasive tool (grindstone) replacement frequency is reduced. May increase productivity. Furthermore, there is a possibility that the polishing rate is lowered, which is not preferable. When the abrasive grain expression rate is larger than 3.0%, the self-generated action of the polishing surface of the fixed abrasive tool becomes insufficient, the polishing surface becomes clogged, and the polishing rate decreases, so that the polishing rate may not be maintained. is there. The abrasive grain expression rate is more preferably 1.2% or more, and more preferably 2.2% or less.

ここで、固定砥粒工具の研磨面に表出している砥粒の平均面積、および、固定砥粒工具の研磨面の砥粒表出率、の算出方法について説明する。   Here, the calculation method of the average area of the abrasive grains exposed on the polishing surface of the fixed abrasive tool and the abrasive grain appearance rate of the polishing surface of the fixed abrasive tool will be described.

固定砥粒工具の研磨面に表出している砥粒の平均面積、固定砥粒工具の研磨面の砥粒表出率は、例えばＳＥＭ／ＥＤＸやレーザー顕微鏡を用いて測定・算出することができる。   The average area of the abrasive grains exposed on the polishing surface of the fixed abrasive tool, and the abrasive grain appearance rate of the polishing surface of the fixed abrasive tool can be measured and calculated using, for example, SEM / EDX or a laser microscope. .

例えば、ＳＥＭ／ＥＤＸを用いる場合、以下の式１、式２により算出することができる。   For example, when using SEM / EDX, it is computable by the following formulas 1 and 2.

（表出している砥粒の平均面積）＝｛（観察視野の面積）×（砥粒を構成する元素のカウントが所定値以上（例えば、砥粒を構成する元素のカウントが３０以上）の測定点の数）／（観察視野内の全測定点の数）｝／（観察された砥粒の個数）・・・式１
（砥粒表出率）＝１００×（砥粒を構成する元素のカウントが所定値以上（例えば、砥粒を構成する元素のカウントが３０以上）の測定点の数）／（観察視野内の全測定点の数）・・・式２
上記式の各パラメータの測定、算出手順について説明する。 (Average area of exposed abrasive grains) = {(area of observation field) × (count of elements constituting abrasive grains is a predetermined value or more (for example, count of elements constituting abrasive grains is 30 or more)) Number of points) / (Number of all measurement points in the observation field)} / (Number of observed abrasive grains) Equation 1
(Abrasive grain appearance ratio) = 100 × (the number of measurement points where the count of elements constituting the abrasive grains is equal to or greater than a predetermined value (for example, the count of elements constituting the abrasive grains is 30 or more)) / (within the observation field of view) Number of all measurement points) ... Equation 2
A procedure for measuring and calculating each parameter of the above formula will be described.

まず、固定砥粒工具の研磨面の任意に選択した複数箇所においてＳＥＭ観察を行う。この際、観察視野（観察領域）のサイズや倍率、観察箇所の数については特に限定されるものではないが、例えば、倍率を１５００倍とし、１回の測定で９０μｍ×１２０μｍの観察視野について観察を行うことができる。この際の観察視野のサイズが、上記式における「観察視野の面積」に当たる。また観察は固定砥粒工具の研磨面の任意の複数の箇所、例えば１０〜２０箇所で行うことが好ましい。   First, SEM observation is performed at a plurality of arbitrarily selected locations on the polishing surface of the fixed abrasive tool. At this time, the size and magnification of the observation field (observation region) and the number of observation points are not particularly limited. For example, the magnification is 1500 times, and observation is performed on a 90 μm × 120 μm observation field in one measurement. It can be performed. The size of the observation field at this time corresponds to the “area of the observation field” in the above formula. Moreover, it is preferable to observe at arbitrary several places, for example, 10-20 places of the grinding | polishing surface of a fixed abrasive tool.

そして、ＳＥＭ観察したそれぞれの観察視野についてＥＤＸ（Ｅｎｅｒｇｙ Ｄｉｓｐｅｒｓｉｖｅ Ｘ−ｒａｙ ｓｐｅｃｔｒｏｍｅｔｒｙ：エネルギー分散型Ｘ線分析）により元素マッピングを行う。元素マッピングの結果から砥粒を構成する元素のカウントが所定値以上（例えば、３０以上）の測定点（ポイント）の数、観察野内の全測定点（ポイント）の数、観察された砥粒の個数を計測する。   Then, element mapping is performed on each observation field observed by the SEM by EDX (Energy Dispersive X-ray spectroscopy). From the result of element mapping, the number of measurement points (points) where the count of elements constituting the abrasive grains is a predetermined value or more (for example, 30 or more), the number of all measurement points (points) in the observation field, the number of observed abrasive grains Count the number.

具体的には、ＥＤＸによる元素マッピングの結果から、砥粒を構成する元素のカウントが所定値以上（例えば、３０以上）の測定点（ポイント）を砥粒と判断する。そして、観察視野内の砥粒を構成する元素のカウントが所定値以上（例えば、３０以上）となった測定点（ポイント）の数を数え、該測定点（ポイント）の数を上記式における「砥粒を構成する元素のカウントが所定値以上（例えば、砥粒を構成する元素のカウントが３０以上）の測定点の数」とする。なお、砥粒を構成する元素とは、例えば砥粒がダイヤモンドの場合、Ｃ元素（炭素元素）が砥粒を構成する元素となり、Ｃ元素のカウントが所定値以上（例えば、３０以上）の測定点（ポイント）を砥粒と判断する。   Specifically, from the result of element mapping by EDX, a measurement point (point) at which the count of elements constituting the abrasive grains is a predetermined value or more (for example, 30 or more) is determined as an abrasive grain. Then, the number of measurement points (points) at which the count of the elements constituting the abrasive grains in the observation field is equal to or greater than a predetermined value (for example, 30 or more) is counted. The number of measurement points at which the count of the elements constituting the abrasive grains is equal to or greater than a predetermined value (for example, the count of the elements constituting the abrasive grains is 30 or more). The element constituting the abrasive grains is, for example, when the abrasive grains are diamond, the C element (carbon element) is an element constituting the abrasive grains, and the C element count is a predetermined value or more (for example, 30 or more). A point is determined as an abrasive.

そして、ＥＤＸによる元素マッピングを行った際の、観察視野内の全測定点（ポイント）を、上記式における「観察視野内の全測定点の数」とする。   Then, all the measurement points (points) in the observation visual field when element mapping by EDX is performed are defined as “the number of all measurement points in the observation visual field” in the above formula.

また、ＥＤＸによる元素マッピングを行った際、砥粒を構成する元素のカウント数が所定値以上（例えば、３０以上）の測定点（ポイント）は複数が固まった領域を形成して検出される。これは、ＥＤＸによるマッピングの最小単位、すなわち測定点（ポイント）のサイズよりも砥粒のサイズが大きいためである。従って、砥粒を構成する元素のカウント数が所定値以上（例えば、３０以上）の測定点（ポイント）が集合した１つの領域を１個の砥粒と判断することができる。このため、観察視野内の砥粒を構成する元素のカウント数が所定値以上（例えば、３０以上）の測定点（ポイント）が集合した領域の数を上記式における「観察された砥粒の個数」とする。   In addition, when element mapping is performed by EDX, a plurality of measurement points (points) where the count number of elements constituting the abrasive grains is a predetermined value or more (for example, 30 or more) are detected by forming a solid region. This is because the size of the abrasive grains is larger than the minimum unit of mapping by EDX, that is, the size of the measurement point (point). Therefore, it is possible to determine that one region is a collection of measurement points (points) where the count number of elements constituting the abrasive grains is a predetermined value or more (for example, 30 or more). For this reason, the number of regions in which the measurement points (points) where the count number of the elements constituting the abrasive grains in the observation field is equal to or greater than a predetermined value (for example, 30 or more) is expressed as “the number of observed abrasive grains” in the above formula. "

以上に説明した方法により各観察視野における、表出している砥粒の平均面積、砥粒表出率を算出することができる。そして、上述のように、複数の観察箇所で観察を行った場合には、全ての観察箇所（観察視野）の平均値を、該固定砥粒工具における、表出している砥粒の平均面積、砥粒表出率とすることが好ましい。   By the method described above, the average area of the exposed abrasive grains and the abrasive grain expression rate in each observation visual field can be calculated. And as mentioned above, when performing observation at a plurality of observation points, the average value of all the observation points (observation field of view) is the average area of the exposed abrasive grains in the fixed abrasive tool, It is preferable to use the abrasive grain exposure rate.

なお、ここではＳＥＭ／ＥＤＸを用いて各パラメータを算出する方法について説明したが、例えばレーザー顕微鏡を用いて観察した結果から、表出している砥粒の平均面積、砥粒表出率を算出してもよい。レーザー顕微鏡を用いて算出する場合には、撮影した画像から観察視野内の各砥粒の面積を測定し、平均値を算出することにより、表出している砥粒の平均面積とすることができる。また、観察視野内の砥粒の表出面積を、観察視野の面積で割ることにより、砥粒表出率を算出することができる。レーザー顕微鏡を用いた場合においても観察視野のサイズは特に限定されるものではないが、例えば９０μｍ×１２０μｍとすることが好ましい。また、観察は複数の箇所、例えば任意の１０〜２０箇所について観察を行うことが好ましい。そして、複数の観察箇所で観察を行った場合には、全ての観察箇所の平均値を、該固定砥粒工具における、表出している砥粒の平均面積、砥粒表出率とすることが好ましい。   In addition, although the method of calculating each parameter using SEM / EDX was described here, for example, the average area of the exposed abrasive grains and the abrasive grain expression rate were calculated from the results of observation using a laser microscope. May be. When calculating using a laser microscope, by measuring the area of each abrasive grain in the observation field from the captured image and calculating the average value, the average area of the exposed abrasive grains can be obtained. . Moreover, the abrasive grain expression rate can be calculated by dividing the exposed area of the abrasive grains in the observation visual field by the area of the observation visual field. Even when a laser microscope is used, the size of the observation visual field is not particularly limited, but is preferably 90 μm × 120 μm, for example. Moreover, it is preferable to observe about several places, for example, arbitrary 10-20 places. And when observing at a plurality of observation points, the average value of all the observation points can be set as the average area of the exposed abrasive grains in the fixed abrasive tool and the abrasive grain exposure rate. preferable.

また、上記表出している砥粒の平均面積、砥粒表出率は、ガラス基板を研磨する直前や研磨中において満たしていることが好ましい。すなわち、例えば研磨を行う前にドレッシング（目立て）を行うことにより、表出している砥粒の平均面積、砥粒表出率が所定の値となるように調整することができる。なお、図１（Ｂ）に示した両面研磨装置１２を用いた場合、上定盤側、下定盤側にそれぞれ固定砥粒工具を装着する。この場合、表出している砥粒の平均面積、砥粒表出率は、それぞれ、上定盤側の固定砥粒工具と下定盤側の固定砥粒工具との平均値が、上述の所定の範囲にあればよい。   Moreover, it is preferable that the average area of the exposed abrasive grains and the abrasive grain expression rate are satisfied immediately before or during polishing of the glass substrate. That is, for example, by performing dressing (sharpening) before polishing, the average area of the exposed abrasive grains and the abrasive grain appearance rate can be adjusted to be predetermined values. When the double-side polishing apparatus 12 shown in FIG. 1B is used, fixed abrasive tools are mounted on the upper surface plate side and the lower surface plate side, respectively. In this case, the average area of the exposed abrasive grains and the abrasive grain expression rate are the average values of the fixed abrasive tool on the upper surface plate side and the fixed abrasive tool on the lower surface plate side, respectively. If it is in range.

上述のように固定砥粒工具の研磨面において、表出している砥粒の平均面積、砥粒表出率が所定の範囲にあることにより、被研磨物であるガラス基板の表面が鏡面であっても固定砥粒工具を用いて高い研磨速度で研磨することができる。   As described above, on the polishing surface of the fixed abrasive tool, the surface area of the glass substrate that is the object to be polished is a mirror surface because the average area of the exposed abrasive grains and the abrasive grain expression rate are within a predetermined range. However, it can be polished at a high polishing rate using a fixed abrasive tool.

本実施形態の磁気記録媒体用ガラス基板の研磨方法で用いる固定砥粒工具はさらに、磁気記録媒体用ガラス基板の主平面を５０μｍ研磨したときの固定砥粒工具の研磨面の磨耗量が０．１１μｍ以上であることが好ましい。特に、磁気記録媒体用ガラス基板の主平面を５０μｍ研磨したとき固定砥粒工具の研磨面の磨耗量は０．１２μｍ以上であることがより好ましい。   In the fixed abrasive tool used in the method for polishing a glass substrate for magnetic recording medium of the present embodiment, the wear amount of the polishing surface of the fixed abrasive tool when the main plane of the glass substrate for magnetic recording medium is polished by 50 μm is 0. It is preferable that it is 11 micrometers or more. In particular, when the main plane of the glass substrate for magnetic recording medium is polished by 50 μm, the abrasion amount of the polishing surface of the fixed abrasive tool is more preferably 0.12 μm or more.

固定砥粒工具によりガラス基板の表面を研磨すると、ガラス基板の加工を重ねるにつれて、研磨速度が低下する場合がある。これは、ガラス基板を研磨することにより、固定砥粒工具の研削面が目詰まりを起こすためと考えられる。従来は研磨液中の成分を管理する等の方法により研磨速度の低下を抑制しようとしていたが、研磨液の成分を管理する方法では、研磨速度の低下を十分には抑えることは難しかった。   When the surface of the glass substrate is polished with a fixed abrasive tool, the polishing rate may decrease as the processing of the glass substrate is repeated. This is thought to be because the ground surface of the fixed abrasive tool is clogged by polishing the glass substrate. Conventionally, attempts have been made to suppress a decrease in polishing rate by a method such as managing components in the polishing liquid. However, it has been difficult to sufficiently suppress a decrease in polishing rate by a method that manages the components of the polishing solution.

本発明の発明者らが検討を行ったところ、ガラス基板を５０μｍ研磨したときの固定砥粒工具の研磨面の磨耗量を０．１１μｍ以上とすることにより、自生作用が十分となるため、研磨面の目詰まりを防止し、研磨速度の低下を抑制できることを見出した。研磨面の目詰まりを抑制するためには、ガラス基板を５０μｍ研磨したときの磨耗量は０．１２μｍ以上であることがより好ましい。   When the inventors of the present invention have studied, the amount of wear on the polishing surface of the fixed abrasive tool when the glass substrate is polished by 50 μm is set to 0.11 μm or more, so that the self-generated action is sufficient. It has been found that clogging of the surface can be prevented and a decrease in polishing rate can be suppressed. In order to suppress clogging of the polished surface, the wear amount when the glass substrate is polished by 50 μm is more preferably 0.12 μm or more.

ガラス基板を５０μｍ研磨したときの固定砥粒工具の研磨面の磨耗量の上限値は特に限定されるものではないが、例えば０．４μｍ以下であることが好ましい。これは、固定砥粒工具の研磨面の磨耗量が０．４μｍよりも大きい場合、固定砥粒工具の寿命が短くなり、固定砥粒工具の交換頻度が高くなるため、生産性が低下し、コスト上昇の原因となり好ましくないためである。また、砥粒が研磨面から脱落し易くなるため、これによりガラス基板の表面に傷を生じるおそれがあり好ましくないためである。特にガラス基板を５０μｍ研磨したときの固定砥粒工具の研磨面の磨耗量は０．３５μｍ以下であることがより好ましい。   The upper limit of the amount of abrasion on the polished surface of the fixed abrasive tool when the glass substrate is polished by 50 μm is not particularly limited, but is preferably 0.4 μm or less, for example. This is because when the amount of wear on the polishing surface of the fixed abrasive tool is larger than 0.4 μm, the life of the fixed abrasive tool is shortened, and the replacement frequency of the fixed abrasive tool is increased, resulting in a decrease in productivity. This is because it causes an increase in cost and is not preferable. Further, the abrasive grains easily fall off from the polished surface, which may cause scratches on the surface of the glass substrate, which is not preferable. In particular, the abrasion amount of the polishing surface of the fixed abrasive tool when a glass substrate is polished by 50 μm is more preferably 0.35 μm or less.

ガラス基板の主平面を５０μｍ研磨したときの固定砥粒工具の研磨面の磨耗量の計測方法は特に限定されるものではない。例えば、ガラス基板の主平面を５０μｍ研磨したとき、研磨の前後で固定砥粒工具の厚さを測定し、研磨前後の固定砥粒工具の厚さの差を固定砥粒工具の研磨面の磨耗量とする。測定は例えばマイクロメーター等を用いて測定することができる。測定に当たっては、固定砥粒工具と定盤あわせた厚さを測定し、研磨前後の厚さを比較することが操作の簡便性から好ましいが、測定の際、固定砥粒工具を定盤から外して固定砥粒工具の厚さのみを測定、比較することもでき、固定砥粒工具の研磨面に形成された溝の深さを測定、比較することもできる。   The measuring method of the abrasion amount of the polishing surface of the fixed abrasive tool when the main plane of the glass substrate is polished by 50 μm is not particularly limited. For example, when the main plane of a glass substrate is polished by 50 μm, the thickness of the fixed abrasive tool is measured before and after polishing, and the difference in the thickness of the fixed abrasive tool before and after polishing is determined by the wear of the polishing surface of the fixed abrasive tool. Amount. The measurement can be performed using, for example, a micrometer. For measurement, it is preferable from the viewpoint of simplicity of operation to measure the thickness of the fixed abrasive tool and the surface plate, and compare the thickness before and after polishing. However, when measuring, remove the fixed abrasive tool from the surface plate. Thus, only the thickness of the fixed abrasive tool can be measured and compared, and the depth of the groove formed on the polishing surface of the fixed abrasive tool can also be measured and compared.

なお、両面研磨装置によりガラス基板を研磨する場合、ガラス基板の上下面について同時に研磨することから、ガラス基板の主平面を５０μｍ研磨したときとは、ガラス基板の上面の研磨量とガラス基板の下面の研磨量とをあわせた、両主平面の研磨量の平均値が５０μｍであることを意味する。すなわち、この場合、両主平面の研磨量の合計は１００μｍである。そして、両面研磨装置の場合、上定盤側の固定砥粒工具と、下定盤側の固定砥粒工具の磨耗量の平均値が固定砥粒工具の磨耗量となる。すなわち、ガラス基板の上面の研磨量とガラス基板の下面の研磨量とをあわせた、両主平面の研磨量の平均値が５０μｍの時に、上定盤側の固定砥粒工具および下定盤側の固定砥粒工具のそれぞれについて磨耗量を測定し、両者の磨耗量の平均値を両面研磨装置の固定砥粒工具の研磨面の磨耗量とすることができる。   In addition, when polishing a glass substrate with a double-side polishing apparatus, since the upper and lower surfaces of the glass substrate are simultaneously polished, the amount of polishing of the upper surface of the glass substrate and the lower surface of the glass substrate are when the main plane of the glass substrate is polished by 50 μm. It means that the average value of the polishing amount of both main planes, combined with the polishing amount of 50 μm, is 50 μm. That is, in this case, the total polishing amount of both main planes is 100 μm. In the case of the double-side polishing apparatus, the average value of the wear amount of the fixed abrasive tool on the upper surface plate side and the fixed abrasive tool on the lower surface plate side is the wear amount of the fixed abrasive tool. That is, when the average value of the polishing amount of both main planes, which combines the polishing amount of the upper surface of the glass substrate and the polishing amount of the lower surface of the glass substrate, is 50 μm, the fixed abrasive tool on the upper surface plate side and the lower surface plate side The amount of wear can be measured for each of the fixed abrasive tools, and the average value of both wear amounts can be used as the amount of wear on the polishing surface of the fixed abrasive tool of the double-side polishing apparatus.

なお、固定砥粒工具の研磨面の磨耗量を測定するとき、ガラス基板を５０μｍ以上研磨し、その際の固定砥粒工具の磨耗量から、ガラス基板の主平面を５０μｍ研磨する際の固定砥粒工具の磨耗量を算出することが好ましい。例えば、まず、ガラス基板の主平面を４０００μm研磨したときの固定砥粒工具の磨耗量を求めて、その磨耗量を８０で割ることにより、ガラス基板の主平面を５０μｍ研磨したときの固定砥粒工具の研磨面の磨耗量とすることができる。   When measuring the wear amount of the polishing surface of the fixed abrasive tool, the glass substrate is polished by 50 μm or more, and the fixed abrasive when polishing the main plane of the glass substrate by 50 μm from the wear amount of the fixed abrasive tool at that time. It is preferable to calculate the wear amount of the grain tool. For example, first, the amount of wear of the fixed abrasive tool when the main plane of the glass substrate is polished by 4000 μm is obtained, and the amount of wear is divided by 80, whereby the fixed abrasive when the main plane of the glass substrate is polished by 50 μm. It can be the amount of wear on the polished surface of the tool.

以上に説明してきた本実施形態の磁気記録媒体用ガラス基板の研磨方法により得られるガラス基板の特性は特に限定されるものではないが、固定砥粒工具を用いて研磨した主平面の表面粗さＲａが０．７μｍ以下であることが好ましく、０．６μｍ以下であることがより好ましい。表面粗さＲａが０．７μｍを超える場合、研磨を行った際にガラス基板の主平面に傷やクラック等（加工変質層）が深く形成されているおそれがある。これは、表面粗さＲａの値が小さいほど、主平面に形成される傷等の加工変質層が深くなることを抑制して研磨できていることを示すためである。   The characteristics of the glass substrate obtained by the method for polishing a glass substrate for a magnetic recording medium of the present embodiment described above are not particularly limited, but the surface roughness of the main plane polished with a fixed abrasive tool Ra is preferably 0.7 μm or less, and more preferably 0.6 μm or less. When the surface roughness Ra exceeds 0.7 μm, there is a possibility that scratches, cracks, etc. (processed deteriorated layer) are deeply formed in the main plane of the glass substrate when polishing is performed. This is because the smaller the value of the surface roughness Ra is, the more the work-affected layer such as scratches formed on the main plane is suppressed from becoming deeper and the polishing can be performed.

以上に説明した本実施形態の磁気記録媒体用ガラス基板の研磨方法によれば、研磨されるガラス基板の主平面が鏡面であっても、固定砥粒工具を用いて高い研磨速度により研磨できる。すなわち、磁気記録媒体用ガラス基板の表面が鏡面であっても、粗面化処理等を行わずに固定砥粒工具を用いて高い研磨速度により研磨できる。そして、成形されたガラス素基板の主平面が鏡面であっても、主平面を固定砥粒工具で研磨できるため、ガラス基板の表面に傷やクラック等が生じにくくなる。また、ガラス基板の表面に傷やクラック等が生じたとしてもその深さを浅くできる。このため、その後さらに主平面を研磨する場合でもその研磨量を少なくできるため、生産性を上げ、コストを低減することができる。また、固定砥粒工具を用いているため、砥粒を後工程に持ち込むことが抑制でき、その後の加工工程において粗大粒子混入による欠点発生を低減できる。さらには遊離砥粒を用いた場合と比較すると、スラリーの交換や、廃棄を行う必要がないため生産性を上げコストを低減することが可能になる。   According to the method for polishing a glass substrate for a magnetic recording medium of the present embodiment described above, even if the main plane of the glass substrate to be polished is a mirror surface, it can be polished at a high polishing rate using a fixed abrasive tool. That is, even if the surface of the glass substrate for magnetic recording media is a mirror surface, it can be polished at a high polishing rate using a fixed abrasive tool without performing a roughening treatment or the like. And even if the main plane of the formed glass substrate is a mirror surface, the main plane can be polished with a fixed abrasive tool, so that the surface of the glass substrate is less likely to be scratched or cracked. Further, even if scratches or cracks occur on the surface of the glass substrate, the depth can be reduced. Therefore, even when the main plane is further polished thereafter, the amount of polishing can be reduced, so that productivity can be increased and costs can be reduced. Moreover, since the fixed abrasive tool is used, it can suppress that an abrasive grain is brought into a post process, and can reduce the fault generation by coarse particle mixing in a subsequent processing process. Furthermore, as compared with the case where loose abrasive grains are used, since it is not necessary to replace or discard the slurry, it is possible to increase productivity and reduce costs.

次に、上記磁気記録媒体用ガラス基板の研磨方法を用いた研磨工程を有する磁気記録媒体用ガラス基板の製造方法について説明する。   Next, the manufacturing method of the glass substrate for magnetic recording media which has the grinding | polishing process using the grinding | polishing method of the said glass substrate for magnetic recording media is demonstrated.

磁気記録媒体用ガラス基板は例えば以下の工程１〜５を含む製造方法により、製造できる。
（工程１）ガラス素基板から、中央部に円孔を有する円盤形状のガラス基板に加工する形状付与工程。
（工程２）ガラス基板の内周と外周の端面部分の面取りを行う面取り工程。
（工程３）ガラス基板の主平面を研磨する主平面研磨工程。
（工程４）ガラス基板の端面（内周端面及び外周端面）を研磨する端面研磨工程。
（工程５）ガラス基板を洗浄して乾燥する洗浄工程。 The glass substrate for magnetic recording media can be manufactured, for example, by a manufacturing method including the following steps 1 to 5.
(Step 1) A shape imparting step in which a glass substrate is processed into a disk-shaped glass substrate having a circular hole in the center.
(Step 2) A chamfering step for chamfering the inner surface and the outer edge of the glass substrate.
(Step 3) A main surface polishing step for polishing the main surface of the glass substrate.
(Step 4) An end surface polishing step for polishing the end surfaces (the inner peripheral end surface and the outer peripheral end surface) of the glass substrate.
(Step 5) A cleaning step of cleaning and drying the glass substrate.

上記工程は記載した順番に行う必要はなく、例えば、形状付与工程の前に主平面研磨工程を行ってもよい。また、各工程は１回ずつに限定されるものではなく、要求されるガラス基板の仕様等に応じて任意の回数実施することができる。例えば、形状付与工程後に主平面研磨工程を行い、その後に面取り工程と端面研磨工程を行った後、再度主平面研磨工程を実施することもできる。   The above steps need not be performed in the order described, and for example, the main surface polishing step may be performed before the shape imparting step. Further, each step is not limited to one time, and can be performed any number of times according to the required glass substrate specifications. For example, after performing the main surface polishing step after the shape imparting step, and then performing the chamfering step and the end surface polishing step, the main surface polishing step can be performed again.

ここで、（工程１）の形状付与工程は、フロート法、フュージョン法、プレス成形法、ダウンドロー法またはリドロー法で成形されたガラス素基板を、中央部に円孔を有する円盤形状のガラス基板に加工するものである。なお、用いるガラス素基板は、アモルファスガラスでもよく、結晶化ガラスでもよく、ガラス基板の表層に強化層を有する強化ガラスでもよい。   Here, the shape imparting step of (Step 1) includes a glass substrate having a circular shape in the center, and a glass substrate formed by a float method, a fusion method, a press forming method, a down draw method or a redraw method. To be processed. The glass substrate used may be amorphous glass, crystallized glass, or tempered glass having a tempered layer on the surface of the glass substrate.

（工程２）の面取り工程においては、ガラス基板の内周、外周の端面部分の面取りを行うものである。   In the chamfering step of (Step 2), chamfering is performed on end surfaces of the inner periphery and outer periphery of the glass substrate.

次に、上述の本実施形態の磁気記録媒体用ガラス基板の研磨方法は、（工程３）の主平面研磨工程に含まれる。この場合、図１に示した固定砥粒工具を備えた両面研磨装置を用い、ガラス基板の主平面に研磨液を供給しながらガラス基板の上下主平面を同時に研磨する。主平面研磨工程は、上述した磁気記録媒体用ガラス基板の研磨方法を用いる１次研磨を行うのみでもよいが、その後さらに２次研磨、さらに３次〜５次研磨を行うこともできる。２次〜５次研磨の方法は特に限定されるものではなく、上述の磁気記録媒体用ガラス基板の研磨方法と同様にして固定砥粒工具を用いて研磨を行ってもよく、遊離砥粒を用いた研磨方法を用いることもできる。   Next, the method for polishing a glass substrate for a magnetic recording medium of the present embodiment described above is included in the main plane polishing step of (Step 3). In this case, the upper and lower main planes of the glass substrate are simultaneously polished while supplying the polishing liquid to the main plane of the glass substrate using the double-side polishing apparatus provided with the fixed abrasive tool shown in FIG. In the main surface polishing step, only primary polishing using the above-described method for polishing a glass substrate for a magnetic recording medium may be performed. However, further secondary polishing and further tertiary to fifth polishing may be performed. The method of secondary to fifth polishing is not particularly limited, and polishing may be performed using a fixed abrasive tool in the same manner as the method for polishing a glass substrate for a magnetic recording medium described above. The used polishing method can also be used.

固定砥粒工具を用いて２次〜５次研磨をおこなう場合、２次〜５次研磨で用いる固定砥粒工具に含まれる砥粒のサイズは、１次研磨で用いる固定砥粒工具に含まれる砥粒のサイズより小さいものとする。   When performing secondary to quintic polishing using a fixed abrasive tool, the size of the abrasive grains contained in the fixed abrasive tool used in secondary to quintic polishing is included in the fixed abrasive tool used in primary polishing. It shall be smaller than the size of the abrasive grains.

遊離砥粒を用いた２次〜５次研磨の場合も例えば図１（Ｂ）に示した両面研磨装置１２を用いてガラス基板の上下主平面の研磨を行うことができる。遊離砥粒を用いた研磨の場合には、固定砥粒工具１６、１８に代えて研磨パッドを装着し、研磨液として、例えば酸化セリウム砥粒を含有する研磨液や、シリカ砥粒を含有する研磨液を用いて研磨を行うことができる。   In the case of secondary to fifth polishing using loose abrasive grains, for example, the upper and lower main planes of the glass substrate can be polished using the double-side polishing apparatus 12 shown in FIG. In the case of polishing using loose abrasive grains, a polishing pad is mounted instead of the fixed abrasive tools 16 and 18, and the polishing liquid contains, for example, a polishing liquid containing cerium oxide abrasive grains or silica abrasive grains. Polishing can be performed using a polishing liquid.

なお、１次研磨を行うガラス基板の主平面は鏡面であり、主平面の表面粗さＲａは０．００９μｍ以下であることが好ましい。ここでいう表面粗さＲａとはＪＩＳ Ｂ ０６０１−２００１に準ずる方法により評価できる。ガラス基板の主平面は両面とも鏡面であることが好ましく、特に両面とも平面粗さＲａが０．００９μｍ以下であることがより好ましい。   In addition, it is preferable that the main plane of the glass substrate which performs primary grinding | polishing is a mirror surface, and the surface roughness Ra of a main plane is 0.009 micrometer or less. The surface roughness Ra mentioned here can be evaluated by a method according to JIS B 0601-2001. The main surface of the glass substrate is preferably a mirror surface on both surfaces, and more preferably the surface roughness Ra is 0.009 μm or less on both surfaces.

２次〜５次研磨を行う場合、２次〜５次研磨は１次研磨に引き続き連続して行うこともできるが、１次研磨後、２次研磨前または３次研磨前に（工程２）の面取り工程や（工程４）の端面研磨工程等を行うこともできる。   When performing the secondary to fifth polishing, the secondary to fifth polishing can be performed continuously after the primary polishing, but after the primary polishing, before the secondary polishing or before the tertiary polishing (step 2). It is also possible to perform the chamfering step or the end face polishing step (step 4).

（工程４）の端面研磨工程は、ガラス基板の端面（側面部と面取り部）を端面研磨するものである。   The end surface polishing step of (Step 4) is an end surface polishing of the end surface (side surface portion and chamfered portion) of the glass substrate.

（工程５）の洗浄工程は、研磨後のガラス基板を洗浄し、乾燥する工程である。具体的な洗浄方法は特に限定されるものではない。例えば、洗剤を用いたスクラブ洗浄、洗剤溶液に浸漬した状態での超音波洗浄、純水に浸漬した状態での超音波洗浄等により洗浄を行うことができる。また、乾燥方法についても特に限定されるものではなく、例えば、イソプロピルアルコール蒸気にて乾燥する。   The cleaning step of (Step 5) is a step of cleaning and drying the polished glass substrate. A specific cleaning method is not particularly limited. For example, cleaning can be performed by scrub cleaning using a detergent, ultrasonic cleaning in a state immersed in a detergent solution, ultrasonic cleaning in a state immersed in pure water, or the like. Also, the drying method is not particularly limited, and for example, drying is performed with isopropyl alcohol vapor.

さらに、上記各工程間にガラス基板の洗浄（工程間洗浄）やガラス基板表面のエッチング（工程間エッチング）を実施してもよい。また、ガラス基板に高い機械的強度が求められる場合、ガラス基板の表層に強化層を形成する強化工程（例えば、化学強化工程）を工程３、４で挙げた研磨工程前、または研磨工程後、あるいは研磨工程間で実施してもよい。   Further, glass substrate cleaning (inter-process cleaning) and glass substrate surface etching (inter-process etching) may be performed between the above steps. Further, when high mechanical strength is required for the glass substrate, the reinforcing step (for example, chemical strengthening step) for forming a reinforcing layer on the surface layer of the glass substrate is performed before or after the polishing step mentioned in steps 3 and 4, Or you may implement between grinding | polishing processes.

そして、上記各工程を含む製造方法により得られたガラス基板はその上に磁性層などの薄膜を形成する工程をさらに行うことによって、磁気記録媒体とする。   The glass substrate obtained by the manufacturing method including the above steps is further subjected to a step of forming a thin film such as a magnetic layer on the glass substrate, thereby obtaining a magnetic recording medium.

以上に説明した本実施形態の磁気記録媒体用ガラス基板の製造方法によれば、主平面研磨工程において、上述した磁気記録媒体用ガラス基板の研磨方法を好ましく用いることができる。このため、研磨されるガラス基板の主平面が鏡面であっても、ガラス基板の主平面を、固定砥粒工具を用いて高い研磨速度により研磨できる。そして、固定砥粒工具により研磨を実施できるため、ガラス基板の表面に傷やクラック等が生じにくい、すなわち、加工変質層が生じにくく、加工変質層が生じたとしてもその厚さを薄くすることができる。このため、その後さらにガラス基板の表面を研磨する場合において、その研磨量を少なくでき、生産性を上げ、コストを低減できる。また、固定砥粒工具を用いているため、粗大な砥粒を後工程に持ち込むことを抑制でき、その後の加工工程において粗大粒子混入による欠点発生を低減できる。さらには遊離砥粒を用いた場合と比較すると、スラリーの交換や、廃棄を行う必要がないため生産性を上げコストを低減することが可能になる。   According to the method for manufacturing a glass substrate for a magnetic recording medium of the present embodiment described above, the above-described method for polishing a glass substrate for a magnetic recording medium can be preferably used in the main plane polishing step. For this reason, even if the main plane of the glass substrate to be polished is a mirror surface, the main plane of the glass substrate can be polished at a high polishing rate using a fixed abrasive tool. And since polishing can be carried out with a fixed abrasive tool, scratches and cracks are unlikely to occur on the surface of the glass substrate, that is, a work-affected layer is hard to occur, and even if a work-affected layer is generated, the thickness should be reduced. Can do. Therefore, when the surface of the glass substrate is further polished thereafter, the amount of polishing can be reduced, productivity can be increased, and cost can be reduced. Moreover, since the fixed abrasive tool is used, it is possible to suppress the introduction of coarse abrasive grains to the subsequent process, and to reduce the occurrence of defects due to the inclusion of coarse particles in the subsequent processing process. Furthermore, as compared with the case where loose abrasive grains are used, since it is not necessary to replace or discard the slurry, it is possible to increase productivity and reduce costs.

以下に具体的な実施例を挙げて説明するが、本発明はこれらの実施例に限定されるものではない。   Specific examples will be described below, but the present invention is not limited to these examples.

まず、以下の実験例における、固定砥粒工具の研磨面の特性や、研磨速度、ガラス基板表面の評価方法、について説明する。
（１）固定砥粒工具の研磨面に表出している砥粒の平均面積、固定砥粒工具の研磨面の砥粒表出率
固定砥粒工具の研磨面に表出している砥粒の平均面積、固定砥粒工具の研磨面の砥粒表出率はそれぞれ以下の式１、式２により算出した。なお、測定は後述する９Ｂ型両面研磨装置の上定盤、下定盤に固定砥粒工具を装着後、固定砥粒工具の研磨面をドレス治具を用いてドレス処理した後に行っている。 First, the characteristics of the polishing surface of the fixed abrasive tool, the polishing rate, and the evaluation method of the glass substrate surface in the following experimental examples will be described.
(1) Average area of abrasive grains exposed on the polished surface of the fixed abrasive tool, Abrasive expression rate of polished surface of the fixed abrasive tool Average of abrasive grains exposed on the polished face of the fixed abrasive tool The area and the abrasive expression rate of the polishing surface of the fixed abrasive tool were calculated by the following formulas 1 and 2, respectively. The measurement is performed after a fixed abrasive tool is mounted on an upper surface plate and a lower surface plate of a 9B type double-side polishing apparatus, which will be described later, and the polishing surface of the fixed abrasive tool is dressed using a dressing jig.

（表出している砥粒の平均面積）＝｛（観察視野の面積）×（砥粒を構成する元素のカウントが３０以上の測定点の数）／（観察視野内の全測定点の数）｝／（観察された砥粒の個数）・・・式１
（砥粒表出率）＝１００×（砥粒を構成する元素のカウントが３０以上の測定点の数）／（観察視野内の全測定点の数）・・・式２
上記式の各パラメータは、ＳＥＭ／ＥＤＸ（ＳＥＭ：株式会社日立ハイテクノロジーズ、型番：ＳＵ−８０３０／ＥＤＸ検出器：株式会社堀場製作所、型番Ｘ−ＭＡＸ８０）を用いて以下の手順により算出した。 (Average area of exposed abrasive grains) = {(Area of observation field) × (Number of measurement points where the number of elements constituting the abrasive grains is 30 or more) / (Number of all measurement points in the observation field) } / (Number of observed abrasive grains) Equation 1
(Abrasive grain appearance ratio) = 100 × (number of measurement points where the count of elements constituting the abrasive grains is 30 or more) / (number of all measurement points in the observation field).
Each parameter of the above formula was calculated according to the following procedure using SEM / EDX (SEM: Hitachi High-Technologies Corporation, model number: SU-8030 / EDX detector: Horiba, Ltd., model number X-MAX80).

固定砥粒工具の研磨面について、ＳＥＭ／ＥＤＸを用い、倍率を１５００倍とし、９０μｍ×１２０μｍの観察視野にて、固定砥粒工具の研磨面の任意の２０箇所を観察し、それぞれの観察視野についてＥＤＸによる元素マッピングを行った。なお、観察は上定盤の固定砥粒工具の研磨面で１０箇所、下定盤の固定砥粒工具の研磨面で１０箇所行った。ＥＤＸによる元素マッピングは、加速電圧は１５ｋｅＶ、エミッション電流１０μＡ、作動距離１５ｍｍ、測定時間２０ｍｉｎで実施した。   For the polishing surface of the fixed abrasive tool, SEM / EDX is used, the magnification is 1500 times, and the observation field of 90 μm × 120 μm is observed at any 20 locations on the polishing surface of the fixed abrasive tool. Element mapping by EDX was performed. The observation was carried out at 10 places on the polishing surface of the fixed abrasive tool on the upper surface plate and 10 places on the polishing surface of the fixed abrasive tool on the lower surface plate. Element mapping by EDX was performed with an acceleration voltage of 15 keV, an emission current of 10 μA, a working distance of 15 mm, and a measurement time of 20 min.

まず、上記式１中の「観察視野の面積」は、９０μｍ×１２０μｍ＝１０８００μｍ２となる。そして、この観察視野を１９２×２５６の画素で元素マッピング測定を行った。 First, the “area of the observation field” in the above formula 1 is 90 μm × 120 μm = 10800 μm 2 . Then, element mapping measurement was performed on this observation field of view with 192 × 256 pixels.

上記式１、式２中の「砥粒を構成する元素のカウントが所定値以上の測定点の数」は、ＥＤＸによる元素マッピングの結果から、観察視野内において砥粒を構成する元素のカウントが３０以上の測定点（ポイント）の数を数えた。以下の実施例、比較例では、砥粒としてダイヤモンドを用いていることから、Ｃ元素のカウントが３０以上の測定点（ポイント）の数を数えたものである。   In “Equation 1 and Equation 2”, “the number of measurement points where the count of the elements constituting the abrasive grains is equal to or greater than a predetermined value” indicates that the count of the elements constituting the abrasive grains in the observation field is based on the result of element mapping by EDX. The number of 30 or more measurement points (points) was counted. In the following examples and comparative examples, since diamond is used as the abrasive grains, the number of measurement points (points) where the count of the C element is 30 or more is counted.

上記式１、式２中の「観察視野内の全測定点（ポイント）の数」は、ＥＤＸによる元素マッピングを行った際の、観察視野（９０μｍ×１２０μｍ）内の全測定点（ポイント）の数を数えたものである。観察視野内を１９２×２５６の画素で元素マッピング測定を行っていることから、観察視野内の全測定点（ポイント）は、４９１５２点になる。   The “number of all measurement points (points) in the observation field” in the above formulas 1 and 2 is the number of all measurement points (points) in the observation field (90 μm × 120 μm) when element mapping is performed by EDX. It is a count. Since element mapping measurement is performed with 192 × 256 pixels in the observation visual field, all measurement points (points) in the observation visual field are 49152 points.

上記式１中の「観察された砥粒の個数」は、ＥＤＸによる元素マッピングを行った際、砥粒を構成する元素のカウント数が３０以上のポイントが複数固まって形成された領域の数を数えることにより算出した。   The “number of observed abrasive grains” in the above formula 1 is the number of regions formed by consolidating a plurality of points whose count number of elements constituting the abrasive grains is 30 or more when performing element mapping by EDX. Calculated by counting.

そして、各観察視野について、表出している砥粒の平均面積、砥粒表出率について算出した後、２０箇所の観察視野の平均値をさらに算出した。すなわち、上定盤側の固定砥粒工具と、下定盤側の固定砥粒工具との平均値を、表出している砥粒の平均面積、砥粒表出率とした。
（２）固定砥粒工具の研磨面の磨耗量
ガラス基板を５０μｍ研磨する際の固定砥粒工具の研磨面の磨耗量は、ガラス基板を合計で４０００μｍ研磨する前後の固定砥粒工具の厚さを測定し、以下の式３を計算することにより算出した。なお、以下の実験例では両面研磨装置を用いていることから、ガラス基板を合計で４０００μｍ研磨するとは、ガラス基板の上面の研磨量と、ガラス基板の下面の研磨量と、を合わせた両主平面の研磨量の平均値が４０００μｍであることを意味している。すなわち、両主平面の研磨量の合計は８０００μｍとなっている。
（固定砥粒工具の研磨面の磨耗量）＝｛（研磨前の固定砥粒工具の厚さ）−（ガラス基板を４０００μｍ研磨後の固定砥粒工具の厚さ）｝×５０／４０００・・・式３
ここで両面研磨装置において固定砥粒工具は、上定盤に装着した固定砥粒工具（上定盤側の固定砥粒工具）と、下定盤に装着した固定砥粒工具（下定盤側の固定砥粒工具）と、の２つがある。本実験例においては上定盤側の固定砥粒工具、及び、下定盤側の固定砥粒工具の磨耗量の平均を、固定砥粒工具の研磨面の磨耗量とした。そして、研磨前の固定砥粒工具の厚さ、ガラス基板を４０００μｍ研磨後の固定砥粒工具の厚さとは、それぞれ、研磨前、ガラス基板を４０００μｍ研磨後の、上定盤側の固定砥粒工具及び下定盤側の固定砥粒工具の厚さの平均を意味する。 And about each observation visual field, after calculating about the average area of the abrasive grain which is exposed, and an abrasive grain expression rate, the average value of 20 observation visual fields was further calculated. That is, the average value of the fixed abrasive tool on the upper surface plate side and the fixed abrasive tool on the lower surface plate side was defined as the average area of the exposed abrasive grains and the abrasive grain expression rate.
(2) Abrasion amount of the polishing surface of the fixed abrasive tool The abrasion amount of the polishing surface of the fixed abrasive tool when polishing the glass substrate by 50 μm is the thickness of the fixed abrasive tool before and after polishing the glass substrate by 4000 μm in total. Was calculated by calculating the following formula 3. In addition, since the double-side polishing apparatus is used in the following experimental examples, the total polishing of the glass substrate of 4000 μm means that both the polishing amount of the upper surface of the glass substrate and the polishing amount of the lower surface of the glass substrate are combined. It means that the average value of the polishing amount on the plane is 4000 μm. That is, the total polishing amount of both main planes is 8000 μm.
(Abrasion amount of polishing surface of fixed abrasive tool) = {(Thickness of fixed abrasive tool before polishing) − (Thickness of fixed abrasive tool after polishing glass substrate by 4000 μm)} × 50/4000・ Formula 3
Here, in the double-side polishing apparatus, the fixed abrasive tool is a fixed abrasive tool mounted on the upper surface plate (fixed abrasive tool on the upper surface plate side) and a fixed abrasive tool mounted on the lower surface plate (fixed on the lower surface plate side). Abrasive tools). In this experimental example, the average of the wear amount of the fixed abrasive tool on the upper surface plate side and the fixed abrasive tool on the lower surface plate side was defined as the wear amount of the polishing surface of the fixed abrasive tool. The thickness of the fixed abrasive tool before polishing and the thickness of the fixed abrasive tool after polishing the glass substrate of 4000 μm are the fixed abrasive on the upper platen before polishing and 4000 μm of the glass substrate, respectively. It means the average thickness of the fixed abrasive tool on the tool and lower surface plate side.

なお、固定砥粒工具の厚さはマイクロメーターを用い、各定盤と各定盤に装着された固定砥粒工具の任意の端部で測定した。
（３）研磨速度
後述する固定砥粒工具の研磨面をドレス処理した後１バッチ目と、１５バッチ目のガラス基板研磨において、ガラス基板の研磨を始めてから研磨を終えるまでの時間を測定し、研磨量を研磨時間（加工時間）で除すことにより研磨速度を算出した。すなわち、以下の式により算出した。
（研磨速度）＝｛（研磨前のガラス基板の厚さ）−（研磨後のガラス基板の厚さ）｝／（加工時間）
（４）ガラス基板の表面粗さＲａ
研磨後のガラス基板の主平面の表面粗さ（算術平均粗さ）Ｒａは、ＪＩＳ Ｂ ０６０１−２００１に準ずる方法により評価を行った。測定には接触式表面粗さ計（株式会社ミツトヨ製 商品名：サーフテストＳＶ６２４）を用いた。測定長さ４．８ｍｍ、測定速度０．５ｍｍ／ｓｅｃ、基準長さ０．８ｍｍ、カットオフ波長λｃ＝０．８ｍｍ、λｓ＝０．００２５ｍｍとして測定を行った。なお測定は、ガラス基板の上下面についてそれぞれ一点ずつ測定し、その平均値を該ガラス基板の表面粗さＲａとした。 The thickness of the fixed abrasive tool was measured using a micrometer at each surface plate and at any end of the fixed abrasive tool mounted on each surface plate.
(3) Polishing speed In the first batch and 15th batch of glass substrate polishing after dressing the polishing surface of the fixed abrasive tool described later, the time from the start of polishing of the glass substrate to the end of polishing is measured, The polishing rate was calculated by dividing the polishing amount by the polishing time (processing time). That is, it was calculated by the following formula.
(Polishing speed) = {(Thickness of glass substrate before polishing) − (Thickness of glass substrate after polishing)} / (Processing time)
(4) Surface roughness Ra of the glass substrate
The surface roughness (arithmetic average roughness) Ra of the main plane of the polished glass substrate was evaluated by a method according to JIS B 0601-2001. For the measurement, a contact-type surface roughness meter (trade name: Surf Test SV624, manufactured by Mitutoyo Corporation) was used. Measurement was performed with a measurement length of 4.8 mm, a measurement speed of 0.5 mm / sec, a reference length of 0.8 mm, a cutoff wavelength λc = 0.8 mm, and λs = 0.005 mm. In addition, the measurement was performed for each of the upper and lower surfaces of the glass substrate, and the average value was defined as the surface roughness Ra of the glass substrate.

次に各実験例について説明する。
（例１）
以下の手順により、磁気記録媒体用ガラス基板の主平面を研磨した。 Next, each experimental example will be described.
(Example 1)
The main plane of the glass substrate for magnetic recording media was polished by the following procedure.

まず、研磨に供するガラス基板を以下の手順により製造した（形状付与工程）。   First, a glass substrate used for polishing was manufactured by the following procedure (shape imparting step).

フロート法で成形されたＳｉＯ２を主成分とするシリケートガラス基板から、直径が２０ｍｍの円孔を有する、直径６５ｍｍの磁気記録媒体用ガラス基板が得られるように円盤形状ガラス基板に加工した。 A silicate glass substrate mainly composed of SiO 2 formed by a float process was processed into a disk-shaped glass substrate so that a glass substrate for a magnetic recording medium having a diameter of 65 mm and a circular hole having a diameter of 20 mm was obtained.

そして、ガラス基板の内周、外周の端面部分の面取りを行った（面取り工程）。   And the chamfering of the end surface part of the inner periphery of a glass substrate and an outer periphery was performed (chamfering process).

次いで、以下の手順により磁気記録媒体用ガラス基板の主平面を研磨した（主平面研磨工程）。   Next, the main plane of the glass substrate for magnetic recording medium was polished by the following procedure (main plane polishing step).

主平面の研磨は図１に示す９Ｂ型両面研磨装置１２により行った。両面研磨装置１２は、ガラス基板と対向する面に固定砥粒工具１６、１８が装着された上定盤１５と、下定盤１７と、を備えている。固定砥粒工具１６、１８としては、砥粒としてダイヤモンド砥粒を含有する固定砥粒工具を用いた。   The main surface was polished by a 9B double-side polishing apparatus 12 shown in FIG. The double-side polishing apparatus 12 includes an upper surface plate 15 on which fixed abrasive tools 16 and 18 are mounted on a surface facing the glass substrate, and a lower surface plate 17. As the fixed abrasive tools 16 and 18, fixed abrasive tools containing diamond abrasive grains as abrasive grains were used.

固定砥粒工具１６、１８はガラス基板の研磨を行う前に予めドレス処理を行っており、ドレス処理はドレス治具として円盤形状のホワイトアルミナを用いて行った。ドレス処理は、ドレス処理用のキャリアに上記ドレス治具をセットし、ガラス基板の両面研磨を行う場合と同様に両面研磨装置１２を運転して行う。   The fixed abrasive tools 16 and 18 were previously subjected to dressing before polishing the glass substrate, and the dressing was performed using a disk-shaped white alumina as a dressing jig. The dressing process is performed by setting the dressing jig on the dressing carrier and operating the double-side polishing apparatus 12 in the same manner as when double-side polishing the glass substrate.

ドレス処理後、ガラス基板の研磨を行う前における、固定砥粒工具の研磨面に表出している砥粒の平均面積、固定砥粒工具の研磨面の砥粒表出率を表１に示す。なお、研磨面に表出している砥粒の平均面積、研磨面の砥粒表出率は、上定盤側の固定砥粒工具と、下定盤側の固定砥粒工具と、についてそれぞれ測定を行った。そして、上定盤側の固定砥粒工具と、下定盤側の固定砥粒工具との平均値を算出し、表１に示している。   Table 1 shows the average area of the abrasive grains exposed to the polishing surface of the fixed abrasive tool and the abrasive grain appearance rate of the polishing surface of the fixed abrasive tool before the polishing of the glass substrate after the dressing process. In addition, the average area of the abrasive grains exposed on the polishing surface and the abrasive grain appearance rate of the polishing surface were measured respectively for the fixed abrasive tool on the upper surface plate side and the fixed abrasive tool on the lower surface plate side. went. The average value of the fixed abrasive tool on the upper surface plate side and the fixed abrasive tool on the lower surface plate side is calculated and shown in Table 1.

次に、円盤形状ガラス基板をキャリア１０にセットし、１バッチ当たり２５枚のガラス基板を両面研磨装置にセットして研磨を行った。なお、主平面研磨工程に供した研磨前のガラス基板の主平面の上面、下面とも表面粗さＲａは０．００１μｍであった。   Next, the disk-shaped glass substrate was set on the carrier 10, and 25 glass substrates per batch were set in a double-side polishing apparatus and polished. In addition, surface roughness Ra was 0.001 micrometer on the upper surface and lower surface of the main plane of the glass substrate before grinding | polishing used for the main plane grinding | polishing process.

主平面研磨工程においては、上定盤１５、下定盤１７により加工圧力が１０ｋＰａとなるようにガラス基板を押圧して研磨した。研磨の際、サンギア１３、インターナルギア１４を、ガラス基板と上定盤１５との相対速度が７５０ｍｍ／ｓｅｃとなるように駆動して、ガラス基板の上面、下面それぞれについて２００μｍ研磨を行った。研磨の間、固定砥粒工具の研磨面とガラス基板との間には研磨液を１．０Ｌ／ｍｉｎの流量で供給した。   In the main surface polishing step, the glass substrate was pressed and polished by the upper surface plate 15 and the lower surface plate 17 so that the processing pressure became 10 kPa. During polishing, the sun gear 13 and the internal gear 14 were driven so that the relative speed between the glass substrate and the upper surface plate 15 was 750 mm / sec, and 200 μm polishing was performed on each of the upper surface and the lower surface of the glass substrate. During polishing, a polishing liquid was supplied at a flow rate of 1.0 L / min between the polishing surface of the fixed abrasive tool and the glass substrate.

主平面研磨工程は固定砥粒工具を交換することなく、ガラス基板を交換して合計２０バッチ行った。この際、初期（１バッチ目）の研磨速度、連続加工時（１５バッチ目）の研磨速度、研磨面の磨耗量、１バッチ目のガラス基板の研磨後の表面粗さＲａの測定を上述の方法により行った。結果を表１に示す。
（例２）
主平面研磨工程において、ドレス処理後の研磨面が表１に示す特性を有する固定砥粒工具を用いた点以外は例１と同様にして磁気記録媒体用ガラス基板の研磨を行った。 The main surface polishing process was performed for 20 batches in total by replacing the glass substrate without replacing the fixed abrasive tool. At this time, the initial (first batch) polishing rate, the continuous processing (15th batch) polishing rate, the abrasion amount of the polished surface, and the measurement of the surface roughness Ra after polishing of the first batch of glass substrate are described above. By the method. The results are shown in Table 1.
(Example 2)
The glass substrate for a magnetic recording medium was polished in the same manner as in Example 1 except that a fixed abrasive tool having the characteristics shown in Table 1 as the polished surface after dressing was used in the main planar polishing step.

また、初期（１バッチ目）の研磨速度、連続加工時（１５バッチ目）の研磨速度、研磨面の磨耗量、１バッチ目のガラス基板の研磨後の表面粗さＲａの測定結果を表１に示す。
（例３）
主平面研磨工程において、固定砥粒工具１６、１８として、砥粒としてダイヤモンドを、ボンド材として銅、ニッケルを含有する合金を用いたメタルボンド砥石を用い、ドレス処理後の研磨面が表１に示す特性を有する固定砥粒工具を用いた点以外は例１と同様にして磁気記録媒体用ガラス基板の研磨を行った。 In addition, Table 1 shows the initial (first batch) polishing rate, the polishing rate during continuous processing (15th batch), the abrasion amount of the polished surface, and the surface roughness Ra after polishing of the glass substrate of the first batch. Shown in
(Example 3)
In the main surface polishing step, as the fixed abrasive tools 16 and 18, a diamond bonded as an abrasive and a metal bond grindstone using an alloy containing copper and nickel as a bonding material, the polished surface after dressing is shown in Table 1. The glass substrate for magnetic recording media was polished in the same manner as in Example 1 except that a fixed abrasive tool having the characteristics shown was used.

また、初期（１バッチ目）の研磨速度、連続加工時（１５バッチ目）の研磨速度、研磨面の磨耗量、１バッチ目のガラス基板の研磨後の表面粗さＲａの測定結果を表１に示す。
（例４）
主平面研磨工程において、ドレス処理後の研磨面が表１に示す特性を有する固定砥粒工具を用いた点以外は例１と同様にして磁気記録媒体用ガラス基板の研磨を行った。 In addition, Table 1 shows the initial (first batch) polishing rate, the polishing rate during continuous processing (15th batch), the abrasion amount of the polished surface, and the surface roughness Ra after polishing of the glass substrate of the first batch. Shown in
(Example 4)
The glass substrate for a magnetic recording medium was polished in the same manner as in Example 1 except that a fixed abrasive tool having the characteristics shown in Table 1 as the polished surface after dressing was used in the main planar polishing step.

また、初期（１バッチ目）の研磨速度、連続加工時（１５バッチ目）の研磨速度、研磨面の磨耗量、１バッチ目のガラス基板の研磨後の表面粗さＲａの測定結果を表１に示す。
（例５）
主平面研磨工程において、ドレス処理後の研磨面が表１に示す特性を有する固定砥粒工具を用いた点以外は例１と同様にして磁気記録媒体用ガラス基板の研磨を行った。 In addition, Table 1 shows the initial (first batch) polishing rate, the polishing rate during continuous processing (15th batch), the abrasion amount of the polished surface, and the surface roughness Ra after polishing of the glass substrate of the first batch. Shown in
(Example 5)
The glass substrate for a magnetic recording medium was polished in the same manner as in Example 1 except that a fixed abrasive tool having the characteristics shown in Table 1 as the polished surface after dressing was used in the main planar polishing step.

また、初期（１バッチ目）の研磨速度、連続加工時（１５バッチ目）の研磨速度、研磨面の磨耗量、１バッチ目のガラス基板の研磨後の表面粗さＲａの測定結果を表１に示す。
（例６）
主平面研磨工程において、ドレス処理後の研磨面が表１に示す特性を有する固定砥粒工具を用いた点以外は例１と同様にして磁気記録媒体用ガラス基板の研磨を行った。 In addition, Table 1 shows the initial (first batch) polishing rate, the polishing rate during continuous processing (15th batch), the abrasion amount of the polished surface, and the surface roughness Ra after polishing of the glass substrate of the first batch. Shown in
(Example 6)
The glass substrate for a magnetic recording medium was polished in the same manner as in Example 1 except that a fixed abrasive tool having the characteristics shown in Table 1 as the polished surface after dressing was used in the main planar polishing step.

本実験例においては、固定砥粒工具がガラス基板表面で滑り、ガラス基板の研磨を実施することができなかった。   In this experimental example, the fixed abrasive tool slipped on the surface of the glass substrate, and the glass substrate could not be polished.

Figure 0006131749
表１の結果によると、実施例である例１〜例３、参考例である例４、例５については、研磨されるガラス基板の主平面が鏡面であっても、固定砥粒工具を用いて高い研磨速度により研磨できることが確認できた。これに対して、比較例である例６は固定砥粒工具がガラス基板表面で滑り、研磨を行うことができなかった。これは、例６の固定砥粒工具の研磨面に表出している砥粒の平均面積、及び、研磨面の砥粒表出率が小さいため、ガラス基板に対して砥粒が切り込むことができなかったためだと考えられる。
Figure 0006131749
 According to the results of Table 1, with respect to Examples 1 to 3 as examples and Examples 4 and 5 as reference examples, a fixed abrasive tool is used even if the main plane of the glass substrate to be polished is a mirror surface. It was confirmed that polishing was possible at a high polishing rate. On the other hand, in Comparative Example 6, the fixed abrasive tool slipped on the surface of the glass substrate and could not be polished. This is because the average area of the abrasive grains exposed on the polishing surface of the fixed abrasive tool of Example 6 and the abrasive grain appearance rate of the polishing surface are small, so that the abrasive grains can be cut into the glass substrate. This is thought to be because there was not.

研磨後のガラス基板の表面粗さＲａは、ガラス基板の主平面を研磨する際にガラス基板の表面に生じた傷やクラック等の状態を反映しており、表面粗さＲａは小さい方が好ましい。表面粗さＲａが大きい場合であっても、その後さらに研磨工程を行い、傷等を除去することができるため、製品としては問題がないが、工程数が増加したり、加工時間が長くなるおそれがあるため好ましくない。そのため、ガラス基板の主平面に生じる傷やクラック等を少なくする、すなわち、加工変質層の厚さを浅くすることが好ましい。本実験例のうち固定砥粒工具を用いた研磨を行うことができた実施例である例１〜例３、参考例である例４、例５では、固定砥粒工具の研磨面に表出している砥粒の平均面積小さい、例えば３００μｍ２以下であるため、いずれも研磨後のガラス基板の表面粗さＲａが小さくなっていることが確認できた。特に、例１〜例４については、固定砥粒工具の研磨面に表出している砥粒の平均面積が特に小さいため、研磨後のガラス基板の表面粗さＲａがより小さくなることを確認できた。


The surface roughness Ra of the glass substrate after polishing reflects the state of scratches, cracks, etc. generated on the surface of the glass substrate when the main plane of the glass substrate is polished, and it is preferable that the surface roughness Ra is small. . Even if the surface roughness Ra is large, there is no problem as a product because a polishing process can be further performed thereafter to remove scratches, etc., but there is no problem as a product, but the number of processes may increase or the processing time may be increased. This is not preferable. Therefore, it is preferable to reduce scratches, cracks, and the like generated on the main plane of the glass substrate, that is, to reduce the thickness of the work-affected layer. In Examples 1 to 3 which are examples in which the polishing using a fixed abrasive tool can be performed among the experimental examples, and in Examples 4 and 5 which are reference examples, the surface is exposed on the polishing surface of the fixed abrasive tool. Since the average area of the abrasive grains is small, for example, 300 μm 2 or less, it was confirmed that the surface roughness Ra of the glass substrate after polishing was small. In particular, in Examples 1 to 4, since the average area of the abrasive grains exposed on the polishing surface of the fixed abrasive tool is particularly small, it can be confirmed that the surface roughness Ra of the polished glass substrate becomes smaller. It was.


また、研磨面の磨耗量が例１〜３と比較して小さい例４、例５においては、１５バッチ目の研磨速度が、初期（１バッチ目）の研磨速度と比較して大きく低下していることが確認できた。このことから連続加工時においても安定した研磨速度を維持するためには研磨面の磨耗量が高いことが好ましいことが確認できた。   Further, in Examples 4 and 5 in which the abrasion amount of the polishing surface is small compared to Examples 1 to 3, the polishing rate of the 15th batch is greatly reduced compared to the initial (1st batch) polishing rate. It was confirmed that From this, it was confirmed that a high amount of abrasion on the polished surface is preferable in order to maintain a stable polishing rate even during continuous processing.

なお、主平面の研磨を行えなかった例６を除いて、さらに以下の工程を実施することにより磁気記録媒体用ガラス基板を製造した。   A glass substrate for a magnetic recording medium was manufactured by carrying out the following steps except for Example 6 where the main plane could not be polished.

具体的には、まず、ガラス基板の内周および外周の端面を研磨ブラシと酸化セリウム砥粒を含有する研磨液を用いて研磨する端面研磨工程に供した。
次に、主平面研磨の２次、３次研磨工程を行った。２次研磨工程、３次研磨工程は、遊離砥粒を用いて研磨を行った。遊離砥粒を用いた研磨は図１（Ｂ）に示した両面研磨装置１２において、固定砥粒工具１６、１８に代えて研磨パッドを装着し、研磨液を供給しながら行った。２次研磨工程においては、研磨液として酸化セリウム砥粒を含有する研磨液を、３次研磨工程においては、研磨液としてシリカ砥粒を含有する研磨液を用いてそれぞれ研磨を行った。 Specifically, first, the glass substrate was subjected to an end face polishing step in which the inner and outer end faces of the glass substrate were polished using a polishing liquid containing a polishing brush and cerium oxide abrasive grains.
Next, secondary and tertiary polishing steps of main surface polishing were performed. In the secondary polishing step and the tertiary polishing step, polishing was performed using loose abrasive grains. Polishing using loose abrasive grains was performed in the double-side polishing apparatus 12 shown in FIG. 1 (B) with a polishing pad attached instead of the fixed abrasive tools 16 and 18 and supplying a polishing liquid. In the secondary polishing process, polishing was performed using a polishing liquid containing cerium oxide abrasive grains as a polishing liquid, and in the tertiary polishing process, polishing was performed using a polishing liquid containing silica abrasive grains as a polishing liquid.

そして、端面研磨工程の後、洗剤を用いたスクラブ洗浄、洗剤溶液に浸漬した状態での超音波洗浄、純水に浸漬した状態での超音波洗浄、を順次行う洗浄工程を行った後、イソプロピルアルコール蒸気にて乾燥して磁気記録媒体用ガラス基板を製造した。   Then, after the end surface polishing step, a scrub cleaning using a detergent, an ultrasonic cleaning in a state immersed in a detergent solution, and an ultrasonic cleaning in a state immersed in pure water are sequentially performed, and then isopropyl The glass substrate for magnetic recording media was manufactured by drying with alcohol vapor.

以上の磁気記録媒体用ガラス基板の製造方法においては、主平面の研磨工程において研磨されるガラス基板の主平面が鏡面であっても、固定砥粒工具により高い研磨速度で研磨できるため生産性を従来よりも高めることができた。また、固定砥粒工具による研磨は、ガラス基板の表面に傷やクラック等が生じにくく、その後の加工工程で傷等を除去する加工の負荷を低減でき、生産性を上げ、コストを低減することができた。さらに、固定砥粒工具を用いているため、粒径が大きい砥粒を後工程に持ち込むことを抑制して、粗大粒子混入による欠点発生を低減でき、また、遊離砥粒を用いた場合と比較して、スラリーの交換や、廃棄を行う必要がないため生産性を上げコストを低減することができた。   In the manufacturing method of the glass substrate for magnetic recording media described above, even if the main plane of the glass substrate to be polished in the main plane polishing step is a mirror surface, it can be polished at a high polishing rate with a fixed abrasive tool, thereby increasing productivity. It was possible to raise it more than before. Also, polishing with a fixed abrasive tool is less likely to cause scratches or cracks on the surface of the glass substrate, can reduce the processing load of removing scratches, etc. in subsequent processing steps, increase productivity, and reduce costs. I was able to. In addition, since a fixed abrasive tool is used, it is possible to reduce the occurrence of defects due to the incorporation of coarse particles by suppressing the introduction of abrasive grains with a large particle size to the subsequent process, and compared with the case where loose abrasive particles are used. Thus, since it is not necessary to replace or discard the slurry, productivity can be increased and costs can be reduced.

１０ キャリア
１３ サンギア
１４ インターナルギア
１５ 上定盤
１６、１８ 固定砥粒工具
１７ 下定盤 10 Carrier 13 Sun gear 14 Internal gear 15 Upper surface plate 16, 18 Fixed abrasive tool 17 Lower surface plate

Claims (3)

固定砥粒工具を用いて鏡面であるガラス基板の主平面を研磨する磁気記録媒体用ガラス基板の研磨方法であって、
前記固定砥粒工具の研磨面に表出している砥粒の平均面積は１０μｍ２以上３００μｍ２以下であり、
前記固定砥粒工具の研磨面の砥粒表出率は１．１％以上２．２％以下である磁気記録媒体用ガラス基板の研磨方法。 A method of polishing a glass substrate for a magnetic recording medium in which a main surface of a glass substrate that is a mirror surface is polished using a fixed abrasive tool,
The average area of the abrasive grains exposed on the polishing surface of the fixed abrasive tool is 10 μm 2 or more and 300 μm 2 or less,
A polishing method for a glass substrate for a magnetic recording medium, wherein an abrasive grain appearance ratio of a polishing surface of the fixed abrasive tool is 1.1% or more and 2.2 % or less. 磁気記録媒体用ガラス基板の主平面を５０μｍ研磨したときの前記固定砥粒工具の研磨面の磨耗量は０．１１μｍ以上である請求項１に記載の磁気記録媒体用ガラス基板の研磨方法。   The method for polishing a glass substrate for a magnetic recording medium according to claim 1, wherein the abrasion amount of the polishing surface of the fixed abrasive tool when the main plane of the glass substrate for a magnetic recording medium is polished by 50 µm is 0.11 µm or more. 請求項１または２に記載の磁気記録媒体用ガラス基板の研磨方法を用いた研磨工程を有する磁気記録媒体用ガラス基板の製造方法。   A method for producing a glass substrate for a magnetic recording medium, comprising a polishing step using the method for polishing a glass substrate for a magnetic recording medium according to claim 1.
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