JP2002346912A - Glass substrate for information recording medium and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a glass substrate for an information recording medium capable of reducing generation of orange peel and scratch and the glass substrate for the information recording medium polished by the manufacturing method. SOLUTION: In this manufacturing method for the glass substrate for the information recording medium, lapping, first polisher working and second polisher working are performed in a polishing process after substrate working is performed for the glass substrate for the information recording medium. In the first polisher working and second polisher working, cerium oxide is used as polishing agent. In the polishing agent, specific surface area of abrasive grain is 6 to 14 m<2> /g and a maximum particle size of a secondary particle size is 3.0 to 7.0 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a glass substrate for an information recording medium and a method for manufacturing the same.

[0002]

2. Description of the Related Art An information recording medium includes a magnetic disk and the like, and a glass substrate is used as a substrate for the magnetic disk. This glass substrate is suitable not only for reducing the size and thickness of the magnetic disk, but also has excellent flatness of the substrate recording surface and excellent substrate strength for high-density recording. As the glass substrate, generally, a chemically strengthened glass substrate or a crystallized glass substrate whose substrate strength is improved by chemical strengthening or crystallization is used.

[0003] Magnetic heads for reading information recorded on a magnetic disk have also changed from thin film heads to magnetoresistive heads (MR heads) and large magnetoresistive heads (GMR heads) as recording density has increased. Have been doing.

[0004] Such a glass substrate for a magnetic disk is
It is manufactured by the manufacturing method described below (for example, JP-A-11-221742).

Disk Processing Step First, a glass base material using aluminosilicate glass as a base material is cut into a disk shape by a cutter wheel.

[0006] Then the outer peripheral edge chamfering process, by using a cylindrical grindstone with opening a round hole in the center of the glass substrate is subjected to a predetermined chamfering the outer peripheral end face and the inner peripheral end face. At this time, the surface roughness (Rma
x) is 14 μm.

Inner Peripheral End Surface Polishing Step The inner peripheral end surface of the glass substrate is polished by a rotating nylon brush using a cerium oxide abrasive abrasive with the glass substrates superposed.

Recording surface lapping process The recording surface of the glass substrate housed in the hole of the resin carrier revolving around by a double-sided lapping machine is formed on a pair of cast iron platens using an alumina abrasive having a grain size of # 1000. Lapping to a surface roughness (Rmax) of about 2 μm.

Recording surface polishing step The recording surface of the glass substrate wrapped in the recording surface lapping step is polished with a cerium oxide suspension (hard cloth) to remove scratches and distortion remaining in the recording surface lapping step. ), And further polished with another polisher (soft cloth).

Cleaning Step The glass substrate polished in the recording surface polishing step is cleaned using an acidic aqueous solution and an alkaline aqueous solution.

[0011]

However, in the process of polishing the recording surface, orange peel (white clouding phenomenon) and scratches may occur. These orange peels and scratches give irregularities to the surface of the recording film when the magnetic recording film is coated, and cause reading and writing errors by the head, so it is necessary to remove them.
It cannot be removed in the cleaning step following the recording surface second polishing step. Therefore, there is a problem that the glass substrate for an information recording medium having orange peel or scratches has to be discarded, which is uneconomical.

An object of the present invention is to provide a method of manufacturing a glass substrate for an information recording medium which can prevent the occurrence of orange peel, scratches, etc. while maintaining a polishing force, and a glass substrate for an information recording medium polished by the manufacturing method. Is to do.

[0013]

According to a first aspect of the present invention, there is provided a manufacturing method of a glass substrate for an information recording medium, wherein the glass substrate for an information recording medium is precisely polished using an abrasive. In the manufacturing method, the abrasive is cerium oxide having a specific surface area of abrasive grains of 6 to 14 m ² / g.

[0014] According to the manufacturing method according to claim 1, wherein, the abrasive, orange peel and the specific surface area of the abrasive grains are cerium oxide 6m ² / g~14m ² / g, while maintaining the chemical polishing force Can be prevented.

According to a second aspect of the present invention, in the manufacturing method of the first aspect, the abrasive has a maximum secondary particle diameter of 3.0 to 7.0 μm.

According to the second aspect of the present invention, the abrasive has a maximum secondary particle diameter of 3.0 to 7.0 μm, so that it can prevent scratches while maintaining a mechanical polishing force. Can be prevented.

In order to achieve the above object, a glass substrate for an information recording medium according to claim 3 is polished by the method for manufacturing a glass substrate for an information recording medium according to claim 1 or 2.

According to the glass substrate for an information recording medium according to the third aspect, it is possible to obtain a glass substrate for an information recording medium free of orange peel, scratches, and the like.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive studies to achieve the above object, the present inventor has produced a glass substrate for an information recording medium in which the glass substrate for an information recording medium is precisely polished using an abrasive. In the method, when the abrasive is cerium oxide having a specific surface area of abrasive grains of 6 to 14 m ² / g,
It has been found that the generation of orange peel can be prevented while maintaining the chemical polishing power.

The present inventor has reported that the abrasive can prevent scratches while maintaining the mechanical polishing force when the maximum secondary particle size is 3.0 to 7.0 μm. I found it.

The present invention has been made based on the results of the above research.

Hereinafter, a method for manufacturing a glass substrate for an information recording medium according to an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a process chart for manufacturing an information recording medium including polishing of a glass substrate for an information recording medium according to an embodiment of the present invention.

As shown in FIG. 1, a glass substrate for an information recording medium is manufactured through a substrate processing step 1 → polishing step 2 → texture processing step 3 → chemical strengthening processing step 4 → finish cleaning step 5 and then forming a film. In step 6, an information recording medium is manufactured by laminating a multilayer film on the substrate.

Hereinafter, each of the above steps will be sequentially described.

(1) Substrate Processing Step In the substrate processing step 1, a sheet-like glass material is ground using a grindstone such as a diamond grindstone to produce a glass substrate having a predetermined donut shape.

The substrate material of the glass substrate is not particularly limited, and the surface processing is easy, and the elastic modulus and the rigidity are high.
High-strength glass or crystallized glass can be used, but inorganic glass that can be easily eluted with acid and can form a good texture, for example, an alkali metal oxide such as LiO ₂ or an alkaline earth such as MgO. It is preferable to use an alumina silicate-based glass containing a metal oxide and Al ₂ O ₃ or the like.

(2) Polishing Step The polishing step 2 includes a lapping process, a first polisher process,
The second polishing process and the finish polishing process are performed in four stages.

That is, first, using a lapping apparatus, lapping is performed with abrasive grains such as alumina having a predetermined grain size, and then cerium oxide (CeO ₂ ) polishing in which free abrasive grains are dispersed in a polishing solution. The first polisher processing is performed using the agent and the hard polisher, and the second polisher processing is performed instead of the hard polisher by the soft polisher.

Here, the polishing apparatus will be described with reference to FIG.

FIG. 2 is a partially cutaway perspective view of a main part of the polishing apparatus used in the polishing step in FIG. In addition,
The structure of the lapping device is the same as the structure of the polishing device 20, and the only difference between the polishing device 20 and the presence or absence of a polisher described later is the description of the lapping device.

The polishing apparatus 20 comprises a horizontal upper platen 2 made of cast iron.
1 and a horizontal lower platen 22 also made of cast iron. The polishing surface of the upper stool 21 has a width of 2.5
The polishing surface of the lower platen 22 is cut in a grid shape with a pitch of 30 mm and has a width of 2.5 mm.
The upper platen 21 has a rotation support shaft 23, and around the rotation support shaft 23, 16 supply ports 24 of slurry-like CeO ₂ abrasive abrasive are provided at equal angular intervals.

The upper platen 21 is 16-18 rpm clockwise as viewed from above (hereinafter, clockwise and counterclockwise all refer to the rotational direction as viewed from above), and the lower platen 22.
Rotates counterclockwise at 50-55 rpm.

A sun gear 25 is arranged at the center of the lower platen 22, and an internal gear 26 is arranged at the outer periphery. A carrier 2 having a planetary gear meshing with both the sun gear 25 and the internal gear 26 is provided on the lower platen 22.
7 are arranged. In the polishing apparatus 20, the sun gear 2
5 rotates counterclockwise at, for example, 15 to 22 rpm, and the internal gear 26 rotates counterclockwise at, for example, 21 to 29 rpm.
2, while revolving clockwise, revolves counterclockwise at, for example, 50 rpm. The carrier 27 is an epoxy resin containing glass fiber, and its thickness is, for example, 0.2 to 0.6 mm from the finished thickness (for example, 1 mm) of the glass substrate.
It is a small value. The material of the carrier 27 may be an epoxy containing aramid fiber.

FIG. 3 is an enlarged perspective view of the carrier 27 in FIG. The carrier 27 has, for example, seven holes 28 for accommodating glass substrates at equal angular intervals in the circumferential direction. The diameter of the hole 28 is as shown in FIG.
For example, the outer diameter of the glass substrate 30 is set to be larger by 2.25 mm. By setting the diameter of the hole 28 in this manner, damage to the outer peripheral end surface of the glass substrate 30 can be reduced. The difference between the diameter of the hole 28 and the outer diameter of the glass substrate 30 may be 1 to 2 mm. In addition, hall 28
May be attached to the wall of the carrier 27 which defines the above.

After the lapping process is performed on the glass substrate by the same lapping device as the polishing device 20, the glass substrate is polished by the polishing device 20. Polishing device 20
Is the glass substrate 3 accommodated in the carrier 27 that rotates.
The recording surface of No. 0 is polished using CeO ₂ abrasive. The CeO ₂ abrasive has a specific surface area of 6 to 14 m ² / g, and the maximum secondary particle diameter (D _max ) of the CeO ₂ abrasive in the suspension is 3.0. ~ 7.0 µm. The reason for using such an abrasive for polishing the glass substrate for an information recording medium at this time is as follows.

As shown in Tables 1 and 2 below and FIG. 5, when the specific surface area of the CeO ₂ abrasive grains is smaller than 6 m ² / g, the chemical polishing power is too small to be practical. on the other hand,
When the specific surface area of the CeO ₂ abrasive grains is larger than 14 m ² / g, orange peel is generated.

[0038]

[Table 1]

[0039]

[Table 2]

When D _max is smaller than 3.0 μm, the polishing rate is too low to be practical because the mechanical polishing power is small. On the other hand, when _Dmax is larger than 7.0 μm, scratches occur. D _max is 3.0
In the case of up to 7.0 μm, no scratch occurs, and
The polishing rate is as high as 0.45 to 0.7 μm / min. For the reasons described above, in this embodiment, the specific surface area of CeO ₂ abrasive grains and the maximum particle diameter (D _max ) of the secondary particle diameter in the respective ranges described above were used.

The free abrasive used in the abrasive is obtained by pulverizing a sintered body which has been subjected to a firing treatment. When natural CeO ₂ is used as a raw material for free abrasive, for example, CeO ₂ contains: Usually, 6 to 8 wt% of a fluorine component is contained in the form of metal fluoride.

The polishing agent can be easily obtained by irradiating the separated supernatant liquid with ultrasonic waves or stirring vigorously, or by finely pulverizing and dispersing free abrasive grains by impinging a high-pressure jet stream on the inner wall. Desired adjustments can be made.

Then, polishing is performed using the polishing agent and a suede type polishing pad.

In this case, if the suspension is used within a predetermined time T1 (for example, 40 hours) after the wet classification, it is possible to avoid aggregation of free abrasive grains and generation of bacteria in the abrasive. Therefore, the abrasive is preferably used within the predetermined time T1.

It is preferable that the abrasive grains have a polyhedral shape.

That is, in the fine compressed layer necessary for forming minute irregularities on the glass substrate, the corners of the free abrasive grains are pressed against the surface of the glass substrate, and therefore local stress is applied to the glass substrate. It is considered to be formed. Therefore, when the shape of the abrasive grains is spherical, it is difficult to form a compressed layer suitable for a desired etching process because the local stress is not applied. For this reason, the shape of the abrasive grains is preferably a polyhedral shape.

The polishing pad used for polishing is not particularly limited, and a nonwoven fabric or a foam can be used. It is preferable to use a layer (NAP layer) in which an opening is formed by finishing the surface of the continuous foam layer and a suede pad formed from the base layer, since the glass substrate is unlikely to be damaged. It is preferable to improve the homogeneity by finishing the pad surface before polishing, since an extremely fine compressive stress layer can be formed more uniformly.

(3) Texture processing step Texture processing step 3 includes a cleaning step and a drying step.

First, in the cleaning step, the polished glass substrate is cleaned using an acidic aqueous solution and an alkaline aqueous solution.

That is, in the acidic aqueous solution, some components in the glass are eluted and SiO ₂ which is a skeleton component of the glass is eluted.
It will be rich. Since this SiO ₂ is soluble in an alkaline aqueous solution, if the glass substrate 1 is washed with an acidic aqueous solution and then washed with an alkaline aqueous solution, the surface of the glass substrate 1 is easily etched.

The concentrations of the acidic aqueous solution and the alkaline aqueous solution are not particularly limited, and the washing time and the washing temperature are not particularly limited.

The cleaning method is performed, for example, by immersing the glass substrate in an acidic aqueous solution or an alkaline aqueous solution. In this case, the cleaning may be performed while irradiating the glass substrate with ultrasonic waves.
In addition to the immersion method, a shower method, an injection method, or the like may be used.

Next, the process proceeds to a drying step, and the washed glass substrate is dried.

The drying method is not particularly limited, either.
Glass substrate 1 in isopropyl alcohol (IPA) vapor
Immersion, or a spin drying method in which a glass substrate is rotated at high speed to remove washing water.

(4) Chemical strengthening treatment step In the chemical strengthening treatment step 4, the glass substrate is placed on a molten salt adjusted to a predetermined temperature, for example, a molten salt composed of a mixed solution of potassium nitrate (KNO ₃ ) and sodium nitrate (NaNO ₃ ). After immersion for a predetermined time, a chemical strengthening process is performed in which Li ⁺¹ and Na ⁺¹ in the chemical components of the glass substrate are ion-exchanged into K ⁺¹ having a large ionic radius. By performing such a chemical strengthening treatment, the surface compressive stress is increased, and thereby, even if the magnetic disk is rotated at a high speed, it can be prevented from being damaged.

Next, the glass substrate is gradually cooled to room temperature, and the molten salt attached to the glass substrate is washed away in pure water.

(5) Finish Cleaning Step In the finish cleaning step 5, the glass substrate is immersed in an alkaline aqueous solution and, if necessary, washed with alkali while irradiating ultrasonic waves to remove iron powder or the like adhered to the glass substrate. Impurities, that is, residual foreign matters are removed by etching.

(6) Film Forming Step In the film forming step 6, a seed layer, an underlayer, a magnetic layer, and a protective layer are sequentially laminated on a glass substrate by using a well-known sputtering method. A lubricating layer is formed on the surface of the substrate, whereby an information recording medium is manufactured.

[0059]

Next, embodiments of the present invention will be described specifically.

The present inventors have found that SiO 2: 67 mol%, A
l ₂ O ₃ : 10 mol%, Li ₂ O: 7 mol%, Na ₂ O: 9 mol
An aluminosilicate glass having a chemical composition of l%, MgO: 3 mol%, and CaO: 4 mol% is subjected to grinding using a diamond grindstone to have an outer diameter of 65 mm and an inner diameter of 2 mm.
A doughnut-shaped glass substrate having a thickness of 0 mm and a thickness of 1.0 mm was produced.

Then, using a lapping apparatus, lapping was performed using alumina abrasive grains having an abrasive grain size of # 1000 so that the surface roughness Ra was about 2 μm.

Next, lapping is performed in this manner.
After immersing the cleaned glass substrate in a pure water bath and cleaning it,
Uses hard polisher as pad and specific surface area
Is 6-14m^Two/ G and further in the suspension
Maximum secondary particle diameter (D_{m ax}) Is 3.0 to 7.0 μm
m CeO_TwoUsing an abrasive with abrasive particles dispersed in water
The first polisher processing and the second polisher processing were performed.

[0063]

As described above in detail, according to the manufacturing method of the first aspect, the abrasive has a specific surface area of the abrasive grains of 6%.
Since it is リ ウ ム 14 m ² / g of cerium oxide, it is possible to prevent the occurrence of orange peel while maintaining the chemical polishing force.

According to the manufacturing method of the second aspect, the abrasive has a maximum secondary particle size of 3.0 to 7.0 μm, so that the abrasive can prevent scratches while maintaining a mechanical polishing force. Can be prevented.

According to the glass substrate for an information recording medium according to the third aspect, a glass substrate for an information recording medium free of orange peel, scratches, etc. can be obtained.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of an information recording medium including polishing of a glass substrate for an information recording medium according to an embodiment of the present invention.

FIG. 2 is a partially cutaway perspective view of a main part of a polishing apparatus used in a polishing step in FIG.

FIG. 3 is an enlarged perspective view of a carrier 27 in FIG.

FIG. 4 is a partial explanatory view of a carrier 27 of FIG. 2;

FIG. 5 is a graph showing a relationship between a maximum particle diameter of cerium oxide and a polishing rate.

[Explanation of symbols]

 2 Polishing process 20 Polishing device 21 Upper surface plate 22 Lower surface plate 24 Supply port 25 Sun gear 26 Internal gear 27 Carrier 28 Hole 30 Glass substrate

Claims (3)

[Claims] 1. A method for manufacturing a glass substrate for an information recording medium, wherein the glass substrate for an information recording medium is precisely polished using an abrasive, wherein the abrasive has a specific surface area of abrasive grains of 6 to 14 m ² / g. A method for producing a glass substrate for an information recording medium, wherein the glass substrate is cerium oxide. 2. The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein the abrasive has a maximum secondary particle diameter of 3.0 to 7.0 μm. 3. A glass substrate for an information recording medium, polished by the method for producing a glass substrate for an information recording medium according to claim 1.