KR20010114145A - Method for the production of glass substrates for magnetic recording mediums - Google Patents

Abstract

The method of manufacturing a glass substrate for a magnetic recording medium includes disk processing, grinding processing, polishing processing and cleaning steps, and the method includes thin nonferrous metal-bonded grinding containing abrasive grains. Wheel, resin-bonded grinding wheel or vitrified-bonded grinding wheel bonded to the surface of the upper and lower surface tables of the apparatus, for polishing the glass substrate for magnetic recording media. It is characterized by performing a grinding process using a double-sided grinding device and a cooling liquid for. The method of manufacturing a glass substrate for a magnetic recording medium enables a simple and efficient production of a glass substrate for a magnetic recording medium, which does not require any multi-stage cleaning process and an acid-cleaning process under ultrasonic application, and thus does not require any contamination. This can eliminate the possibility.

Description

Method for the production of glass substrates for magnetic recording mediums

The present invention relates to a method of manufacturing a glass substrate for a magnetic recording medium, and more particularly to a process of disc processing, grinding, polishing and cleaning, wherein the glass substrate is formed by ions such as Fe ions and / or abrasive grains during grinding. A method of manufacturing a glass substrate for a magnetic recording medium capable of easily and efficiently forming a glass substrate for a magnetic recording medium in which contamination is also suppressed and contamination is well suppressed.

As the storage capacity of the magnetic disk recording apparatus becomes larger and larger, it has been desirable to reduce the flying head height of the magnetic disk recording apparatus in order to improve the recording density of the magnetic recording disk. In order to reduce the floating height of the head, development of a substrate for a magnetic recording medium having excellent surface smoothness, having a small amount of deposit on the surface, and having a substantially small surface defect has been required.

As a substrate for a general magnetic recording medium having excellent surface smoothness, substrates prepared by plating an aluminum alloy plate with Ni-P and polishing the plated main surface of the plate by a multi-step process have been mainly used.

However, magnetic disk recording apparatuses have recently been employed in portable personal computers, such as notebook standard personal computers, and in order to improve the response speed of the magnetic disk recording apparatus, the magnetic recording medium must rotate at a high speed of almost 10,000 rpm or more. For this reason, development of a substrate for a magnetic disk recording medium having a high strength capable of withstanding such harsh conditions has been required. Glass substrates have been adopted as such substrates capable of satisfying the above-mentioned requirements.

This mainly adopted glass substrate for magnetic recording media melts and molds the glass in order to give a chemically strengthened glass substrate or glass substrate having improved strength by, for example, a chemical strengthening process, and the glass substrate is heated at a high temperature of 600 to 800 ° C. It includes a crystallized glass substrate prepared by maintaining for a long time in the partially prepared (separate out) the crystal phase in the substrate.

For example, a chemically strengthened glass substrate melts a glass material and molds the molten material into a glass substrate for a chemically strengthened glass substrate, and then the glass substrate is subjected to grinding and polishing treatment, for example, of sodium nitrate or potassium nitrate. A chemically strengthened glass substrate obtained by immersing a substrate in a molten salt and having a compressive stress layer formed on the surface of the substrate to improve the breaking strength of the substrate. The crystallized glass substrate is a glass substrate containing 40 to 80% of the crystalline glass phase and 20 to 60% of the amorphous glass phase, the strength of which is improved by the action of the crystal phase.

Generally, in the manufacturing method of the glass substrate for a magnetic recording medium including the disk processing, the grinding processing, the polishing processing, and the cleaning process, the above-described glass substrate is exposed to various contaminants during these processing processes. In particular, in the step (grinding processing) for reducing the thickness of the glass material (blank), the step is carried out while circulating the polishing liquid using a polishing liquid containing abrasive grains such as carborundum, alumina or zirconia. Therefore, some abrasive grains remain on the surface of the glass substrate. Moreover, a serious problem arises in that the glass surface is contaminated with Fe, for example, because the surface table used in the grinding process is made of cast iron and the polishing liquid is circulated during the grinding process.

If abrasive grains remain on the glass substrate, scratch marks are formed on the glass substrate in a subsequent polishing process, so that the scratch marks are formed into surface defects on the glass substrate if the generated scratch marks are not removed during the polishing process. Will remain.

Also, if Fe-containing contaminants remain on the magnetic disk with the final product magnetic recording medium thereon, the magnetic disk may be exposed to contaminated parts under accelerated test conditions for disk inspection for reliability in high temperature and high humidity environments. You will have serious problems with the formation of blisters.

In order to remove such contaminants, the polishing process should be performed in multiple stages. After the grinding process, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid, or formic acid, oxalic acid, etc., may be applied with ultrasonic waves as a measure to prevent contamination by Fe. It should be sufficiently cleaned by immersing the glass substrate in an organic acid such as citric acid, tartaric acid or hydroxyacetic acid. This leads to the use of devices of large specifications. In addition, effective acid cleaning requires very harsh conditions such as high temperature and high acid concentration. For this reason, such acid cleaning processes require the use of expensive equipment with high acid resistance and due care should be taken to ensure safety and hygiene.

Accordingly, it is an object of the present invention to provide a method capable of easily and efficiently producing a glass substrate for a magnetic recording medium that does not require application of ultrasonic waves and use of a multistage cleaning process under any acid cleaning step and can eliminate any possibility of contamination. It is.

In order to achieve the above object, the inventors of the present invention are most concerned with suppressing contamination of the glass substrate by ions such as Fe ions and / or abrasive grains during grinding, rather than improving the method of removing contaminants. It was found to be effective, so that the upper and lower surfaces of thin plate-like nonferrous grindstones containing abrasive grains instead of the commonly used cast iron surface tables and grinding liquids containing abrasive grains were used. The present invention has been accomplished by discovering that the above-described object can be achieved by using a double-side grinding apparatus and a cooling liquid adhered to the surface of the table.

According to an aspect of the present invention, in the method for producing a glass substrate for a magnetic recording medium including disk processing, grinding processing, polishing processing and cleaning process, the method comprises a thin plate-shaped non-ferrous metal-bonding containing abrasive grains. Double-sided grinding device in which a nonferrous metal-bonded grinding wheel, a resin-bonded grinding wheel or a glass-bonded grinding wheel is bonded to the surface of the upper and lower surface tables, and It is characterized by performing a grinding process using a cooling liquid.

Hereinafter, a method of manufacturing a glass substrate for a magnetic recording medium according to the present invention will be described in more detail.

The production process of the present invention utilizes thin plate-like nonferrous metal-bonded grinding wheels, resin-bonded grinding wheels or glass-bonded grinding wheels containing abrasive grains. In this respect, abrasive grains are not limited to any particular one, but it is preferable to use abrasive grains including, for example, diamond grains, cubic boron nitride grains, boron carbide grains, silicon carbide grains, zirconia grains or alumina grains. Particular preference is given to abrasive grains containing diamond.

Non-ferrous metal-bonded grinding wheels that can be used in the production process according to the invention are, for example, nickel-based materials-bonded, tungsten-based materials-bonded, cobalt-based materials-bonded, bronze-based materials- It can be a material-bound wheel of combined and mixtures thereof. In addition, the resin-bonded grinding wheels that can be used in the present invention can be, for example, phenolic resin-bonded and polyimide resin-bonded grinding wheels. Also, the glass-bonded grinding wheels can be, for example, glassy material-bonded and ceramic material-bonded grinding wheels.

In the production process according to the invention, the grain size of the abrasive grains is preferably about 5 to 30 μm, and the abrasive grain content in the grinding wheel is preferably in the range of 0.5 to 3 volume%. Moreover, the grinding wheel has a thin plate shape, for example, it is practical to have a disc shape with a thickness in the range of 2 to 7 mm and a diameter in the range of 5 to 30 mm.

In the production method of the present invention, for example, metal-bonded diamond grain-containing grinding wheels disclosed in, for example, Japanese Patent Laid-Open Nos. 60-21942, 61-33890, 61-33891 and 1-33309 are particularly preferred. Was used.

In the manufacturing method of the present invention, the thin grinding wheel as described above is used by adhering them to the surfaces of the upper and lower surface tables of the double-side grinding apparatus for grinding the glass substrate for the magnetic recording medium. In this regard, the thin grinding wheel is arranged and adhered to a surface table as disclosed in, for example, design registration No. 770,021 and Japanese Patent Application Laid-Open No. 6-22790, and grinding is performed while dressing is performed. do.

In the production method of the present invention, the glass component peeled off from the glass substrate during the grinding process accumulates in the circulated coolant and likewise a small amount of the grinding wheel component accumulates in the coolant to contaminate the glass substrate. Therefore, it is preferable to continuously remove these components accumulated in the circulating cooling liquid during the circulation or to remove the components present in the circulating cooling liquid intermittently every predetermined time.

Therefore, in the production method according to the present invention, it is preferable to remove the solid components present in the cooling liquid used for the grinding process and then recycle the cooling liquid.

As means for removing solid components present in the coolant used in the grinding process, for example, filtration separation through a filtration medium such as diatomaceous earth, paper or cloth; Centrifugation; And sedimentation separation. Compared to centrifugation, the efficiency of sedimentation separation is quite low. Filtration separation through paper or cloth as a filtration member has a low fine particle separation ability compared to filtration separation through diatomaceous earth. On the other hand, if large amounts of solid components have to be removed, filtration separation through diatomaceous earth has a significantly lower filtration rate. Therefore, in view of the foregoing, it is preferable to first remove most of the particles having a large particle size through centrifugation and then to remove the fine particles by filtration through diatomaceous earth of high efficiency. If a solid component present in the coolant used in the grinding process is removed using a separation system comprising a continuously arranged centrifuge and a diatomaceous earth filtration device, the amount of solid component present in the treated coolant is 0.2 g / L. It can be reduced to the following levels.

The above-described ground glass substrate is immersed in, for example, 2 minutes in an ultrasonic cleaning bath and dried while considering a method for keeping the substrate clean. If the glass substrate has been subjected to the above-described polishing processing, contamination of the glass substrate can be sufficiently suppressed by only a single ultrasonic cleaning step. In other words, it is possible to easily produce a glass substrate in which contamination is sufficiently suppressed without causing any problem in a subsequent process (polishing process).

A glass substrate for a magnetic recording medium can be produced by treating and cleaning the glass material by the above-described grinding process and then polishing and cleaning the glass material according to a general manufacturing method of the glass substrate.

Hereinafter, the present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these specific embodiments.

Example 1.

Lithium silicate crystallized glass plate (TS-10SX manufactured by K. K. Oharasa; 70-80% quartz-cristobalite and the remaining amorphous glass phase) was prepared according to a general manufacturing procedure for the production of a glass substrate for a magnetic recording medium. Inner and outer diameter processing provided a number of donut-shaped substrates having an outer diameter of 65 mm, an inner diameter of 20 mm and a thickness of 1.2 mm.

A number of circular disc-shaped metal-bonded diamond grain-containing grinding wheels with abrasive grain # 1000 diamond grain, metal bond component Ni-15Cu-15Sn-0.5P, thickness 5mm and diameter 15mm were prepared. 3,000 grinding wheels containing metal-bonded diamond grains prepared were attached to each surface of the upper and lower surface tables of the double-side grinding device (16B-5L-III manufactured by Speed Palm). Grinding the above-mentioned donut-shaped substrate having a thickness of 1.2 mm by using the Noritake Cool CG-250MD (manufactured by Noritake Co., Ltd.) as the above-described double-sided grinding device and the coolant and rotating the upper and lower surface tables in opposite directions while supplying cooling water. Processed. Grinding was carried out under the following conditions: grinding pressure of 150 g / cm ² ; Upper and lower surface table revolutions of 30 rpm; Grinding time of 15 minutes and coolant flow rate of 10 L / min. This primary grinding process provided donut shaped substrates each having a thickness of 0.85 mm. Incidentally, the coolant was filtered using a centrifuge CF-150 (manufactured by Toto Separator Co., Ltd.) and a diatomaceous earth filter device RRF-20TA (manufactured by Mitaka Industries Co., Ltd.) outside the grinding device, and then the filtered coolant was recycled.

A number of circular disc-shaped metal-bonded diamond grain-containing grinding wheels with abrasive grains of # 1500 diamond grains, Ni-15Cu-15Sn-0.5P with metal bond components, 5 mm thick and 15 mm diameter were produced. 3,000 grinding wheels containing metal-bonded diamond grains prepared were attached to each surface of the upper and lower surface tables of the double-side grinding device (16B-5L-III manufactured by Speed Palm Co.). Grinding the above-mentioned donut-shaped substrate having a thickness of 0.85 mm by rotating the upper and lower surface tables in the opposite direction while using Noritake Cool CG-250MD (manufactured by Noritake Co., Ltd.) as the above-described double-sided grinding device and the coolant, and supplying cooling water. It was. Grinding was carried out under the following conditions: grinding pressure of 100 g / cm ² ; Rotational speed of the upper and lower surface tables of 30 rpm; 12 min grinding time and 10 L / min coolant flow rate. This secondary grinding process provided donut shaped substrates each having a thickness of 0.67 mm. Incidentally, the coolant was filtered using a centrifuge CF-150 (manufactured by Toto Separator Co., Ltd.) and a diatomaceous earth filter device RRF-20TA (manufactured by Mitaka Industries Co., Ltd.) outside the grinding device, and then the filtered coolant was recycled.

A donut-shaped glass substrate having a thickness of 0.67 mm obtained after the secondary grinding step was washed by immersing for 2 minutes in an ultrasonic cleaning tank having a flow rate of 2 L / min while applying ultrasonic waves of 28 KHz. Thereafter, these substrates were dried under conditions capable of suppressing any contamination of the substrates.

Thereafter, 100 donut-shaped substrates (100 sheets) obtained after the above-described secondary grinding process were fixed to a 16B double-side polishing apparatus (manufactured by Hamai Corporation), and Mirek 801 (CeO ₂ -containing abrasive material; average grain size D ₅₀ = 1.5) as an abrasive material. These glass substrates were polished so that the reduced thickness of the glass substrates reached 15 µm per surface using MHC15A (foaming urethane; manufactured by Rodel Nitta) as a polishing cloth and manufactured by Mitsui Kogyo Co., Ltd. (primary polishing) ).

The glass substrate (100 sheets) obtained after the primary polishing process described above was similarly fixed to a 16B double-side polishing apparatus manufactured by Hama Corporation, and 100 parts by weight of CEP (manufactured by Mitsui Kogyo Co., Ltd .; cerium oxide and 1 part by weight of silicon oxide) as an abrasive. Solid solution comprising; polishing liquid containing 0.5% by weight of average particle size D ₅₀ = 0.2 μm) and polishing cloth using MHC 14E (foamed urethane) manufactured by Rodel Nitta, polishing pressure 60g / cm ² , rotation speed 30rpm and polishing Both surfaces of the substrate were polished under the condition of 20 minutes (secondary polishing). As a result of the secondary polishing, donut-shaped glass substrates having a thickness of 0.638 mm were produced.

The polished glass substrates were scrubbed in three steps (for 3 minutes per step) using a speed palm glass cleaner and a Kanebo sponge disk. Thereafter, the glass substrates were dip-cleaned using SPC 397 (weak alkaline cleaner) from Kyoto Pat & Oil Co., Ltd. as these cleaners, and then sequentially washed in five baths under ultrasonic conditions using ultrapure water. It was. The substrates were then immersed in isopropyl alcohol and then dried in isopropyl alcohol vapor.

In relation to the scratch marks formed on and remaining on the surface of the glass substrate in the grinding process, the shallow scratch marks disappear through the polishing process, but the deep scratch marks form the pit even after the polishing process. Remained. In addition, these recesses tend to be connected in a dotted line shape. The surface of 20 glass substrates arbitrarily selected from the 100 glass substrates obtained after the above-mentioned primary polishing processing process was observed using the differential interference microscope which has the magnification of 125 times. However, no defect was observed in this example.

Regarding the fine deposits remaining on the surface of the dried glass substrate, the number of deposits having a diameter of 1 to 2 µm was calculated using a laser type surface defect inspector RZ-3000 (manufactured by Hitachi Electronics Engineering). Measurement was performed using 20 glass substrates arbitrarily selected from 100 glass substrates obtained after the above-mentioned primary polishing process. A total of 68 deposits with diameters ranging from 1 to 2 μm were observed (average 3.4 per glass substrate). Moreover, these 68 deposits were analyzed by SEM-EDS, and the results indicated that no Fe ions were detected.

The glass substrate prepared according to the above-described method was free of any contamination by ions such as Fe ions, and contamination by abrasive grains was also extremely low. Therefore, the glass substrate was found to be very useful as the glass substrate for the magnetic recording medium.

Comparative Example 1.

Lithium silicate crystallized glass plate (TS-10SX manufactured by K. K. Oharasa; 70-80% quartz-cristobalite and the remaining amorphous glass phase) was prepared according to a general manufacturing procedure for the production of a glass substrate for a magnetic recording medium. Inner and outer diameter processing provided a number of donut-shaped substrates having an outer diameter of 65 mm, an inner diameter of 20 mm and a thickness of 1.2 mm.

In this comparative example, a 16B-5L-III double-sided grinding apparatus (manufactured by Speed Palm Co., Ltd.) having an upper and lower surface table made of cast iron as a polishing machine and a liquid containing 150 g / L of # 400 SiC abrasive grain as polishing liquid were used. The above-mentioned donut-shaped substrates having a thickness of 1.2 mm were ground by rotating the upper and lower surface tables in opposite directions while supplying the above-described polishing liquid. Grinding was carried out under the following conditions: grinding pressure of 200 g / cm ² ; Rotational speed of the upper and lower surface tables of 30 rpm; 25 min grinding time and 5 L / min abrasive liquid flow (primary grinding). This primary grinding process provided donut shaped substrates each having a thickness of 0.85 mm. .

Thereafter, a liquid containing a double-side grinding device 16B-5L-III (manufactured by Speed Palm Co., Ltd.) having a cast iron upper and lower surface table as a grinding machine and 100 g / L of # 1500 Al ₂ O ₃ abrasive grain was used as the polishing liquid. The upper and lower surface tables were rotated in opposite directions while feeding the polishing liquid, thereby grinding the above-described donut-shaped substrate having a thickness of 0.85 mm. Grinding was carried out under the following conditions: grinding pressure of 100 g / cm ² ; Rotational speed of the upper and lower surface tables of 30 rpm; 30 min grinding time and 5 L / min coolant flow rate (secondary grinding process). This secondary grinding process provided donut shaped substrates each having a thickness of 0.67 mm.

A donut-shaped glass substrate having a thickness of 0.67 mm obtained after the secondary grinding step was washed by immersing for 2 minutes in an ultrasonic cleaning tank having a flow rate of 2 L / min while applying ultrasonic waves of 28 KHz. Thereafter, these substrates were dried under conditions capable of suppressing any contamination of the substrates.

Thereafter, the 0.67 mm thick donut-shaped substrates obtained after the above-described secondary grinding process were subjected to primary polishing, secondary polishing, cleaning and drying treatment according to the same procedure used in Example 1. The surface of 20 glass substrates arbitrarily selected from the 100 glass substrates obtained after the above-mentioned primary polishing processing process was observed using the differential interference microscope which has the magnification of 125 times. As a result, occurrence of defects starting from scratch marks formed and remaining on the surface of the glass substrate during the grinding process in eight glass substrates among the selected 20 glass substrates was observed.

Regarding the fine deposits remaining on the surface of the dried glass substrate, the number of deposits having a diameter in the range of 1 to 2 μm was calculated by the same procedure used in Example 1. Measurement was performed using 20 glass substrates arbitrarily selected from 100 glass substrates obtained after the above-mentioned primary polishing process. A total of 104 deposits with diameters ranging from 1 to 2 μm were observed (on average 5.2 per 1 glass substrate). Moreover, these 104 deposits were analyzed by SEM-EDS, as a result of which Fe ions were found in 32 of the 104 deposits.

Glass substrates prepared according to the method described above were contaminated with abrasive grains and ions such as Fe ions. Therefore, the manufactured glass substrate for magnetic recording media is not necessarily useful as a glass substrate for magnetic recording media.

As described in detail above, the method of manufacturing a glass substrate for a magnetic recording medium according to the present invention enables easy and efficient manufacture of the glass substrate for a magnetic recording medium, which method can be used for any multi-stage cleaning process and acid-supply under ultrasonic application. No cleaning process is required, thus eliminating the possibility of any contamination.

Claims (5)

In the method of manufacturing a glass substrate for a magnetic recording medium, which comprises disk processing, grinding processing, polishing processing and cleaning steps, Laminated, nonferrous metal-bonded grinding wheels, resin-bonded grinding wheels or glass-bonded grinding wheels containing abrasive grains A method of manufacturing a glass substrate for a magnetic recording medium, characterized in that said grinding process is carried out using a double-side grinding apparatus and a coolant for polishing a glass substrate for a magnetic recording medium adhered to surfaces of upper and lower surface tables. The method of manufacturing a glass substrate for a magnetic recording medium according to claim 1, wherein the abrasive grain is diamond, cubic boron nitride, boron carbide, silicon carbide, zirconia or alumina grain. The method of manufacturing a glass substrate for a magnetic recording medium according to claim 2, wherein the abrasive grain is diamond grain. The method for manufacturing a glass substrate for a magnetic recording medium according to any one of claims 1 to 3, wherein the solid bodies existing in the cooling liquid used in the grinding process are removed and then recycled to the apparatus. The method for producing a glass substrate for a magnetic recording medium according to claim 4, wherein the solids present in the cooling liquid are removed by filtration through diatomaceous earth as a filtration medium.