JPH10198942A - Glass substrate for recording medium and recording medium using this substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the strength and the durability to breakage with the lapse of time, etc., of a glass substrate by strictly controlling three of compressive stress, tensile stress and depth of the compressive stress layer generated when the glass substrate is chemically strengthening to an adequate range and polishing the end surface of the glass substrate, thereby removing the cracks, which are the causes for the breakage with the lapse of time. SOLUTION: The glass compsn. of the glass substrate 1 is formed by incorporating, by molar%, 57 to 74% SiO2 , 0 to 2.8% ZnO2 , 3 to 15% Al2 O3 , 7 to 16% LiO2 and 4 to 14% Na2 O into the compsn. This sheet glass is cut out to a disk shape of a diameter of 96mm and is ground to 1.5mm thickness. The end faces are subjected to polishing then to washing and the substrate is immersed for 0.5 to 5 hours in a chemical strengthening treatment liquid kept at 200 to 500 deg.C. Consequently, the depth of the compressive stress generated in the glass substrate 1 attains 30 to 100μm, the value of the compressive stress <=2 to 15kg/mm<2> and the value of the internal tensile stress <=1.5kg/mm<2> . As a result, the factors that affect the strength of the glass substrate 1 are most adequately controlled and the strength and the durability to the breakage with the lapse of time are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a glass substrate for a recording medium such as a computer and a recording medium using the substrate.

[0002]

2. Description of the Related Art Aluminum substrates have been widely used as substrates for magnetic recording media such as magnetic disks. However, as magnetic disks have become smaller and thinner and recording density has increased, the strength and flatness of aluminum substrates have been reduced. Is gradually being replaced by a glass substrate with excellent properties.

[0003] This is because glass substrates have characteristics such as having sufficient hardness to cope with recent small-diameter and thinner hard disks, have excellent physical and chemical durability, and have a comparative surface. Can be easily formed with high plane accuracy.
Therefore, it is more suitable for realizing high-density recording to have a property that the spacing can be reduced and the magnetic head can easily achieve a low flying running.

In order to further improve the strength of the glass substrate, the surface of the glass substrate is often subjected to a chemical strengthening treatment.

More specifically, when a glass substrate is used as a substrate for a magnetic disk, the surface of the glass substrate is formed on the surface of the glass substrate in order to improve the shock resistance and vibration resistance and to prevent the substrate from being damaged by shock or vibration. In many cases, chemical strengthening treatment is performed by a (low temperature) ion exchange method.

The chemical strengthening treatment is performed, for example, by using L in glass.
i, Na ions, etc. are converted to N
This is a process of increasing the strength by generating a strong compressive stress in the glass surface layer by replacing the ions with a, K ions or the like by ion exchange.

[0007] If the compressive stress layer generated on the surface layer of the glass substrate is excessively thickened by the chemical strengthening process accompanying the thinning of the glass substrate, it is known that a large tensile stress is generated inside the glass substrate and the strength is reduced. (Japanese Patent Laid-Open No. 7-
No. 230621). The publication states that the thickness of the compressive stress layer is preferably in the range of 5 to 25 μm.

The applicant of the present invention has made the depth of a crack usually present in the surface layer of a glass substrate substantially equal to the depth of a compressive stress layer of the surface layer of the glass substrate due to chemical strengthening.
The maximum value of the tensile stress generated inside the glass substrate is 4 kg / m
An application has been filed for a technique for improving the strength and durability by controlling the strength to m ² or less (Japanese Patent Application Laid-Open No. 2-31325).

[0009]

The thinning of the glass substrate relatively lowers the strength of the glass substrate as compared with the case where the glass substrate is thick. Therefore, control of the factors that affect the strength of the glass substrate is more important than before and needs to be strict.

However, when the conventional glass substrate is thinned, there is a problem that control of a factor which affects the strength of the glass substrate is insufficient.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and strictly controls the factors affecting the strength of a glass substrate within an optimum range to improve the strength and the durability against breakage with time. A first object is to provide a glass substrate for a recording medium.

It is a second object of the present invention to provide a recording medium having excellent strength and durability against damage with time.

[0013]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies, and as a result, the compressive stress, tensile stress, and depth of the compressive stress layer generated when the glass substrate is chemically strengthened. We found that improper balance between the three could cause damage over time (breaks caused by prolonged use), and found that it was necessary to balance the three strictly by moderate chemical strengthening. Was. Then, it has been found that by strictly controlling the three in an optimum range, the strength of the glass substrate and the durability against breakage with time are significantly improved.

Further, by removing the cracks present on the end face of the glass substrate by polishing, it is possible to prevent a decrease in strength caused by the cracks on the end face and a decrease in durability against breakage with time, and to further reduce the strength and durability against breakage with time. The inventors have found that the improvement of the performance can be achieved, and have completed the present invention.

That is, the glass substrate for a recording medium of the present invention is a chemically strengthened glass substrate, and the depth of the compressive stress layer generated in the surface layer of the glass substrate by the chemical strengthening is 30 to 1
The thickness is set to 00 μm, the value of the compressive stress is set to ² to 15 kg / mm ² or less, and the value of the tensile stress generated inside the glass substrate by chemical strengthening is set to 1.5 kg / mm ² or less.

Further, the glass substrate for a recording medium of the present invention comprises:
In the above-described glass substrate for a recording medium of the present invention, the glass composition of the glass substrate is expressed in terms of mol%, and SiO ₂ is 57 to 7%.
4%, ZnO ₂ from 0 to 2.8%, Al ₂ O ₃ from ₃ to 15
%, 7 to 16% of LiO _2, and 4 to 14% of Na ₂ O.
A configuration in which the substrate is immersed in a chemical strengthening treatment solution at 0 to 500 ° C. for 0.5 to 5 hours, a configuration in which the end surface of the glass substrate is polished to remove cracks that cause damage with time, and a polishing in the end surface of the glass substrate The amount is 0.5 to 15 μm, the end surface of the glass substrate is polished with a brush, a polishing powder (polisher) or an abrasive, or the end surface of the glass substrate has a surface roughness of Rmax: 0. 01-1 μm, R
a: It is configured to be 0.001 to 0.8 μm.

Further, the recording medium of the present invention has a configuration in which at least a recording layer is formed on the glass substrate for a recording medium of the present invention.

[0018]

According to the present invention, the strength of the glass substrate and the breakage with time are controlled by strictly controlling the three factors of compressive stress, tensile stress, and the depth of the compressive stress layer generated when the glass substrate is chemically strengthened within an optimum range. , Etc., is significantly improved.

In addition, by polishing the end face of the glass substrate to remove cracks that cause temporal damage, etc., the strength and durability against temporal damage can be further improved.

Hereinafter, the present invention will be described in detail.

In the present invention, the compression stress, the tensile stress, and the depth of the compression stress layer generated when the glass substrate is chemically strengthened are strictly controlled within an optimum range.

The depth of the compressive stress layer generated on the surface of the glass substrate by chemical strengthening needs to be 30 to 100 μm.

When the depth of the compressive stress layer is less than 30 μm, the effect of chemical strengthening (shock resistance and vibration resistance) is too small to obtain required strength. On the other hand, if the depth of the compressive stress layer exceeds 100 μm, the tensile stress becomes too large and the strength is reduced.

From the above viewpoint, the depth of the compressive stress layer is 3
0 to 200 μm, preferably 50 to 100 μm
m is more preferable.

The value of the compressive stress generated in the surface layer of the glass substrate by the chemical strengthening needs to be ^{2 to} 15 kg / mm ² or less.

If the value of the compressive stress is less than 2 kg / mm ² , the strength becomes insufficient. The value of the compressive stress is 15 kg /
If it exceeds mm ² , the strength becomes excessive and it is easily broken.

From the above viewpoint, the value of the compressive stress is from 1 to 2
0 kg / mm ² , preferably ² to 15 kg / mm ²
mm ² is more preferable.

The value of the tensile stress generated inside the glass substrate by the chemical strengthening must be 1.5 kg / mm ² or less.

When the value of the tensile stress exceeds 1.5 kg / mm ² , it is easy to break.

From the above viewpoint, the value of the tensile stress is 0.1
-10 kg / mm ² , preferably 0.5-
More preferably, it is 1.5 kg / mm ² .

In the glass substrate for a recording medium of the present invention, the compression stress, the tensile stress, and the depth of the compression stress layer, which are generated when the glass substrate is chemically strengthened, are consequently within the above-mentioned optimum ranges. The process up to that point is not particularly limited.

In order to strictly control the three of the compressive stress, the tensile stress and the depth of the compressive stress layer within the optimum range, for example, the glass composition, the chemical strengthening conditions (chemical strengthening solution, temperature, time, etc.)
May be appropriately selected and controlled to perform chemical strengthening.

The chemical strengthening method is not particularly limited as long as it is a conventionally known chemical strengthening method. The chemical strengthening of the glass substrate is performed, for example, by immersing the glass substrate in a heated chemical strengthening solution and exchanging ions in the surface layer of the glass substrate with ions in the chemical strengthening solution.

Here, as the ion exchange method, a low-temperature type ion exchange method, a high-temperature type ion exchange method, a surface crystallization method, a dealkalization method for a glass surface, and the like are known. It is preferable to use a low-temperature ion exchange method in which ion exchange is performed in a region not exceeding a transition temperature.

In the low-temperature ion exchange method, alkali ions in glass are replaced with alkali ions having a larger ionic radius in a temperature range not higher than the glass transition temperature Tg,
This is a method in which a strong compressive stress is generated in the glass surface layer by increasing the volume of the ion exchange section, thereby strengthening the glass surface.

As the chemical strengthening solution, potassium nitrate (K
Molten salts such as NO ₃ ), sodium nitrate (NaNO ₃ ) and potassium carbonate (K ₂ CO ₃ ), and molten salts of a mixture of these salts (KNO ₃ + NaNO ₃ , KNO ₃ + K ₂ CO ₃ ); Alternatively, Cu, Ag, Rb, C
Examples thereof include a molten salt of a mixture of salts of ions such as s. Note that the chemical strengthening solution may be a solution of the above salt instead of the molten salt.

The heating temperature of the chemical strengthening solution is from 280 to 660 ° C., particularly from 300 to 400 ° C. from the viewpoint of ion exchange and the like.
It is preferred that

The immersion time is preferably several hours to several tens of hours.

Before the glass substrate is immersed in the molten salt, the glass substrate must be 100 to 300 mm for the purpose of preheating.
It is preferred to preheat to ° C. Further, the glass substrate after the chemical strengthening is made into a product through a cooling step, a washing step, and the like.

The glass substrate is not particularly limited as long as it can be chemically strengthened. Further, the size, thickness, and the like of the glass substrate are not particularly limited.

The thickness of the glass substrate is 0.3 to 20.
mm, more preferably about 0.5 to 1.0 mm. If the thickness of the glass substrate is less than 0.3 mm, the required strength cannot be obtained. When the thickness of the glass substrate exceeds 20 mm, there is no need to apply the present invention.

Examples of the material of the glass substrate include aluminosilicate glass, soda lime glass, sodaaluminosilicate glass, aluminoborosilicate glass,
Examples thereof include borosilicate glass, quartz glass, chain silicate glass, and glass ceramics such as crystallized glass. In addition, aluminosilicate glass is
It is particularly preferable because it has excellent impact resistance and vibration resistance.

As the aluminosilicate glass, Si
O ₂ : 62 to 75% by weight, Al ₂ O ₃ : 5 to 15% by weight,
Li ₂ O: 4 to 10% by weight, Na ₂ O: 4 to 12% by weight,
ZrO _2: 5.5 to 15 with containing by weight% as the main component, the weight ratio of Na ₂ O / ZrO ₂ is 0.5 to 2.
0, Al ₂ O ₃ / weight ratio of ZrO ₂ of glass for chemical strengthening is 0.4 to 2.5 is preferred.

In order to eliminate projections on the glass substrate surface caused by undissolved ZrO ₂ , 57% to 74% of SiO ₂ , 0% to 2.8% of ZnO ₂ ,
The Al ₂ O ₃ 3~15%, the LiO ₂ 7~16%, Na ₂ O
It is preferable to use glass for chemical strengthening containing 4 to 14%.

Such an aluminosilicate glass is
By chemical strengthening, compressive stress, tensile stress, and the excellent balance of the three of the depth of the compressive stress layer, while also excellent in bending strength and heat resistance, without Na precipitation even under high temperature environment It maintains flatness and has excellent Knoop hardness.

In the present invention, in the above-mentioned glass substrate for a recording medium of the present invention, it is preferable that the end face of the glass substrate is polished to remove cracks which cause damage with time and the like.

Here, the end surface of the glass substrate refers to a portion other than the main surface (the surface on which the recording layer is formed) of the glass substrate, and includes an outer peripheral end surface (including a side wall portion and a chamfered portion) and an inner peripheral end surface ( (Including side wall and chamfer).

The method for polishing the end face of the glass substrate is not particularly limited, and a known polishing method can be used.

As a polishing method, for example, brush polishing,
Polishing pad (polishing powder) for soft polisher, hard polisher, etc.
Polishing, mechanical polishing such as polishing with an abrasive (abrasive particles or the like), and the like. In addition, these mechanical polishing, in order to obtain a mirror surface of the required surface roughness, different types of mechanical polishing,
Alternatively, mechanical polishing or the like having different types of polishers, different particle diameters, or the like can be performed in appropriate combination.

Here, as the soft polisher, for example,
Suedes and velours are used as materials. Examples of the hard polisher include hard velours, urethane foam, and pitch impregnated suede. Cerium oxide (CeO ₂ ), alumina (γ-
Al ₂ O ₃ ), bran (Fe ₂ O ₃ ), chromium oxide (Cr
₂ O ₃ ), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ) and the like.

The polishing of the end face of the glass substrate may be performed after any of the steps of grinding and polishing the glass substrate, or may be performed after each of the steps. The steps of grinding and polishing a glass substrate are generally roughly divided into (1) roughing (rough grinding), (2) sanding (fine grinding, lapping),
(3) First polishing (polishing) and (4) second polishing (final polishing, polishing).

In the polishing step of the end face of the glass substrate, for example,
In addition to the step after the roughing (rough grinding) step, the step may be performed after the sanding (fine grinding, lapping) step or after the first polishing (polishing) or the second polishing (final polishing, polishing) step. If the mirror surface processing of the glass substrate end surface is performed before the lapping process, the glass substrate end surface may be slightly roughened due to sand of the lap during the lapping process.

Polishing amount (polishing depth) of end face of glass substrate
It is more preferable to adjust the value appropriately from the viewpoint of removing cracks that affect temporal damage and the like.

The surface roughness of the end face of the glass substrate is preferably Rmax: 0.01 to 2 μm, Ra: 0.001 to 0.001 from the viewpoint of preventing generation of foreign matter due to the end face.
Less than 1 μm, more preferably Rmax: 0.01 to
1 μm, Ra: 0.001 to 0.8 μm, more preferably, Rmax: 0.01 to 1 μm, Ra: 0.0
01 to 0.5 μm.

By setting the surface roughness of the end surface portion of the glass substrate to a mirror surface within the above range, when the glass substrate is taken in and out of the storage container, particles generated when the glass substrate is inclined and come into contact with the container are effectively prevented. Can be suppressed.

Further, by setting the surface roughness of the end surface of the glass substrate to a mirror surface within the above range, particles causing thermal asperity (Thermal Asperity) are not generated, and the reproduction function by the thermal asperity is not generated. The drop can be prevented. In particular, the effect is remarkable for a magnetic recording medium that performs reproduction with a magnetoresistive head.

The above-described glass substrate for a recording medium of the present invention can be used as a glass substrate for a magnetic recording medium, a glass substrate for a magneto-optical disk, and a disk substrate for an electro-optical disk such as an optical disk.

Next, the recording medium of the present invention will be described.

The recording medium of the present invention is obtained by forming at least a recording layer on the glass substrate for a recording medium of the present invention.

Since the recording medium of the present invention uses a glass substrate for a recording medium having excellent strength and durability against damage over time, it has excellent strength and durability against damage over time and high reliability.

Here, a magnetic recording medium which is an example of the recording medium will be described. A magnetic recording medium is usually manufactured by sequentially laminating an underlayer, a magnetic layer, a protective layer, and a lubricating layer on a glass substrate for a magnetic disk.

The magnetic recording medium usually has a predetermined flatness and surface roughness, and is provided with an underlayer, a magnetic layer, a protective layer, and a lubricating layer on a glass substrate for a magnetic disk on which the surface is chemically strengthened. It is manufactured by sequentially laminating.

The underlayer in the magnetic recording medium of the present invention comprises:
It is selected according to the magnetic layer.

As the underlayer, for example, Cr, Mo, T
a, an underlayer made of at least one material selected from nonmagnetic metals such as Ti, W, V, B, and Al. In the case of a magnetic layer containing Co as a main component, it is preferable to use Cr alone or a Cr alloy from the viewpoint of improving magnetic properties. The underlayer is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked. For example, Cr / Cr, Cr / CrMo, Cr / CrV, Cr
V / CrV, Al / Cr / CrMo, Al / Cr / C
r, a multilayer base layer of Al / Cr / CrV, Al / CrV / CrV and the like.

The material of the magnetic layer in the magnetic recording medium of the present invention is not particularly limited.

As the magnetic layer, for example, CoPt, CoCr, CoNi, CoNiCr, C
oCrTa, CoPtCr, CoNiPt, CoNi
CrPt, CoNiCrTa, CoCrTaPt, Co
A magnetic thin film such as CrPtSiO may be used. The magnetic layer is made of a non-magnetic film (for example, Cr, CrMo, Cr).
V, etc. to reduce noise (for example, CoPtCr / CrMo / CoPtCr, CoC
rTaPt / CrMo / CoCrTaPt).

As a magnetic layer corresponding to a magnetoresistive head (MR head) or a large magnetoresistive head (GMR head), a Co-based alloy is prepared by adding Y, Si, a rare earth element, Hf, G
An impurity element selected from e, Sn, and Zn, or an element containing an oxide of these impurity elements is also included.

As the magnetic layer, in addition to the above, magnetic particles such as Fe, Co, FeCo, and CoNiPt are dispersed in a nonmagnetic film made of ferrite, iron-rare earth, SiO ₂ , BN, or the like. It may be a granular structure or the like. Further, the magnetic layer may have any of an inner surface type and a perpendicular type recording format.

The protective layer in the magnetic recording medium of the present invention is not particularly limited.

Examples of the protective layer include a Cr film, a Cr alloy film, a carbon film, a zirconia film, and a silica film. These protective films can be continuously formed with an underlayer, a magnetic layer, and the like by an in-line type sputtering apparatus. Also,
These protective films may have a single-layer structure or a multilayer structure composed of the same or different films.

In the present invention, another protective layer may be formed on the protective layer or in place of the protective layer. For example, instead of the above-mentioned protective layer, colloidal silica fine particles are dispersed and applied to a Cr film after diluting tetraalkoxylan with an alcohol-based solvent, and then fired to form a silicon oxide (SiO ₂ ) film. It may be formed.

The lubricating layer in the magnetic recording medium of the present invention is not particularly limited.

The lubricating layer is prepared, for example, by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon, and applying it to the medium surface by dipping, spin coating, or spraying. It is formed by performing heat treatment.

[0074]

EXAMPLES The present invention will be described below more specifically based on examples.

Embodiment 1

Manufacturing of Glass Substrate (1) Roughing Step First, a glass substrate made of aluminosilicate glass cut out into a disk shape having a diameter of 96 mmφ and a thickness of 3 mm with a grinding wheel from a sheet glass formed by a downdraw method was prepared.
Grinding with a relatively rough diamond wheel
It was molded to a diameter of 1.5 mm and a thickness of 1.5 mm. In this case, instead of the downdraw method, the molten glass may be directly pressed using an upper mold, a lower mold, and a body mold to obtain a disk-shaped glass body.

As the aluminosilicate glass, in terms of mol%, SiO ₂ is 57 to 74%, ZnO ₂ is 0 to 2.8%, Al ₂ O ₃ is ₃ to 15%, and LiO ₂ is 7 to 74%.
Glass for chemical strengthening containing 16% and 4 to 14% of Na ₂ O as main components (for example, Si
O ₂ : 67.0%, ZnO ₂ : 1.0%, Al ₂ O ₃ : 9.
Glass for chemical strengthening containing 0%, LiO ₂ : 12.0%, and Na ₂ O: 10.0% as main components) was used.

Next, both surfaces of the glass substrate were ground one by one with a diamond grindstone having a finer grain size than the grindstone. The load at this time was about 100 kg. As a result, the surface roughness of both surfaces of the glass substrate can be reduced to Rmax (JIS
B 0601) (about 10 μm).

Next, a hole is made in the center of the glass substrate using a cylindrical grindstone, and the outer peripheral end surface is also ground to a diameter of 95 mm. Then, the outer peripheral end surface and the inner peripheral surface are subjected to predetermined chamfering. did. At this time, the surface roughness of the end face of the glass substrate was about 4 μm in Rmax.

(2) End Surface Polishing Step Next, the end surface of the glass substrate is polished by brush polishing while rotating the glass substrate, and the surface roughness of the end surface is about 1 μm in Rmax and about 0.3 μm in Ra. Polished.

The surface of the glass substrate that had been subjected to the above edge polishing was washed with water.

(3) Sanding (Wrapping) Step Next, the glass substrate was sanded. This sanding step aims at improving dimensional accuracy and shape accuracy.
The sanding process was performed using a lapping device, and was performed twice while changing the grain size of the abrasive grains to # 400 and # 1000.

More specifically, first, a load L was set to about 100 kg using alumina abrasive grains having a grain size of # 400.
By rotating the internal rotation gear and the external rotation gear, both sides of the glass substrate housed in the carrier are surface-accurate 0-1 μm,
Lapping was performed to a surface roughness (Rmax) of about 6 μm.

Next, the particle size of the alumina abrasive grains was changed to # 1000.
Perform lapping instead of surface roughness (Rmax) 2μ
m.

The glass substrate that had been subjected to the above sanding process was washed by immersing it sequentially in a washing tank of a neutral detergent and water.

(4) First Polishing Step Next, a first polishing step was performed. This first polishing step is intended to remove scratches and distortion remaining in the above sanding step, and was performed using a polishing apparatus.

More specifically, the first polishing step was performed under the following polishing conditions using a hard polisher (cerium pad MHC15: manufactured by Speed Fam) as a polisher (polishing powder).

Polishing liquid: cerium oxide + water Load: 300 g / cm ² (L = 238 kg) Polishing time: 15 minutes Removal amount: 30 μm Lower platen rotation speed: 40 rpm Upper platen rotation speed: 35 rpm Gear rotation speed in the inner part: 14 rpm Outer gear rotation speed: 29 rpm

The glass substrate after the first polishing step is
Immerse in each washing tank of neutral detergent, pure water, pure water, IPA (isopropyl alcohol), IPA (steam drying) sequentially,
Washed.

(5) Second Polishing Step Next, using the polishing apparatus used in the first polishing step, the polisher was changed from a hard polisher to a soft polisher (Polyac: manufactured by Speed Fam), and the second polishing step was performed. Carried out. The polishing conditions were the same as in the first polishing step, except that the load was 100 g / cm ² , the polishing time was 5 minutes, and the removal amount was 5 μm.

The glass substrate after the second polishing step is
Washing was performed by sequentially immersing in a washing tank of a neutral detergent, a neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying). In addition, ultrasonic waves were applied to each cleaning tank.

(6) Chemical strengthening process Next, the glass substrate after the grinding and polishing processes was subjected to chemical strengthening. For the chemical strengthening, a chemical strengthening solution in which potassium nitrate (60%) and sodium nitrate (40%) are mixed is prepared, and the chemical strengthening solution is heated to 400 ° C., and the cleaned glass substrate preheated to 300 ° C. is washed. The immersion was performed for 3 hours. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, the immersion was performed in a state where a plurality of glass substrates were housed in a holder so as to be held at end faces.

As described above, by performing the immersion treatment in the chemical strengthening solution, the lithium ions and the sodium ions on the surface layer of the glass substrate become the sodium ions in the chemical strengthening solution,
The glass substrate is strengthened by being respectively substituted by potassium ions.

The glass substrate that has been chemically strengthened is
It was immersed in a water bath at a temperature of 10 ° C. and rapidly cooled and maintained for about 10 minutes.

The glass substrate that has been quenched is heated to about 40 ° C.
The substrate was immersed in heated sulfuric acid and washed while applying ultrasonic waves.

The surface roughness Ra of the main surface of the glass substrate obtained through the above steps was 0.5 to 1 nm.

Further, the compressive stress, the tensile stress, and the depth of the compressive stress layer of the glass substrates (8 sheets) obtained through the same steps as above were measured, and the values shown in Table 1 were obtained. .

FIG. 1 shows a stress distribution diagram (strain profile) created based on the above measurement results (average values).

[0099]

[Table 1]

Manufacture of Magnetic Disk A texture layer, a Cr underlayer, a CrMo underlayer, and a CoPtCrTa magnetic layer were formed on both surfaces of a glass substrate for a magnetic disk obtained through the above-described processes by using an in-line type sputtering apparatus. A layer and a C protective layer were sequentially formed to obtain a magnetic disk.

The obtained magnetic disk was subjected to a breaking test by high-speed rotation, a breaking test by dropping, and a durability test against breakage with time, and no breakage or breakage was observed.

A glide test was performed on the obtained magnetic disk. As a result, a hit (the head touches a protrusion on the surface of the magnetic disk) and a crash (the head hit the protrusion on the surface of the magnetic disk) were recognized. Did not.

Comparative Example 1 A glass substrate for magnetic disk (eight pieces) in which the measured values of the compressive stress, the tensile stress, and the depth of the compressive stress layer are the values shown in Table 1.
Was manufactured, and a magnetic disk was manufactured using this substrate.
FIG. 1 shows a stress distribution diagram (strain profile) created based on the measured values (average values).

The obtained magnetic disk was subjected to a breaking test by high-speed rotation, a breaking test by dropping, and a durability test against breakage with time.

Example 2 The glass composition was as follows: SiO ₂ : 62 to 75% by weight, Al
₂ O ₃ : 5 to 15% by weight, Li ₂ O: 4 to 10% by weight, N
a ₂ O: 4 to 12 wt%, ZrO _2: 5.5 to 15 wt%
And aluminosilicate glass having a weight ratio of Na ₂ O / ZrO ₂ of 0.5 to 2.0 and a weight ratio of Al ₂ O ₃ / ZrO ₂ of 0.4 to 2.5. A glass substrate for a magnetic disk and a magnetic disk were obtained in the same manner as in Example 1 except for the above.

The same test as in Example 1 was performed on the obtained magnetic disk, and no destruction or damage was found.

Examples 3 and 4 Glasses for magnetic disks were prepared in the same manner as in Example 1 except that soda lime glass (Example 3) and soda aluminosilicate glass (Example 4) were used instead of aluminosilicate glass. A substrate and a magnetic disk were obtained.

The same test as in Example 1 was performed on the obtained magnetic disk, and no destruction or damage was found.

Example 5 On both surfaces of the glass substrate for a magnetic disk obtained in Example 1, Al (film thickness: 50 Å) / Cr (100
0 Å / CrMo (100 Å), CoPtCr (120 Å) / CrMo (50 Å) / Co
A magnetic layer made of PtCr (120 Å),
A Cr (50 Å) protective layer was formed by an in-line type sputtering apparatus.

The above substrate is immersed in an organic silicon compound solution (a mixed solution of water, IPA and tetraethoxysilane) in which fine silica particles (particle size: 100 Å) are dispersed,
A protective layer having a texture function made of SiO ₂ is formed by firing, and a dip treatment is performed on the protective layer with a lubricant made of perfluoropolyether to form a lubricating layer. Got a disc.

The obtained magnetic disk was subjected to a breaking test by high-speed rotation, a breaking test by dropping, and a durability test against breakage with time, and no breakage or breakage was observed.

Example 6 The underlayer was made of Al / Cr / Cr, and the magnetic layer was made of CoNiCr.
A magnetic disk for a thin film head was obtained in the same manner as in Example 5 except that Ta was used.

It was confirmed that the above magnetic disk was the same as in Example 5.

Although the present invention has been described with reference to the preferred embodiments, the present invention is not necessarily limited to the above embodiments.

For example, the type of the glass substrate and the type of the recording layer such as the magnetic layer are not limited to those of the embodiment.

[0116]

As described above, according to the present invention, the compression stress, the tensile stress, and the depth of the compression stress layer generated when the glass substrate is chemically strengthened are strictly controlled within the optimum range. The strength and durability against breakage with time of the glass substrate are significantly improved.

Further, by polishing the end face of the glass substrate to remove cracks that cause damage with time, the strength and durability against damage with time can be further improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a stress distribution of a chemically strengthened glass substrate.

[Explanation of symbols]

 1 Glass substrate 2 Surface

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G11B 11/10 511 G11B 11/10 511A 541 541E

Claims (8)

[Claims] 1. A chemically strengthened glass substrate, wherein a depth of a compressive stress layer generated on a surface layer of the glass substrate by chemical strengthening is 30 to 100 μm, a value of compressive stress is ² to 15 kg / mm ² or less, and ,
A glass substrate for a recording medium, wherein a value of a tensile stress generated inside the glass substrate by chemical strengthening is set to 1.5 kg / mm ² or less. 2. The glass composition of a glass substrate is as follows: SiO ₂ , 57-74%; ZnO ₂ , 0-2.8%;
The Al ₂ O ₃ 3~15%, the LiO ₂ 7~16%, Na ₂ O
2. The glass substrate for a recording medium according to claim 1, wherein the composition comprises 4 to 14%. 3. The chemical strengthening of a glass substrate is performed at a temperature of 200 to
The glass substrate for a recording medium according to claim 1, wherein the glass substrate is immersed in a chemical strengthening treatment solution at 500 ° C. for 0.5 to 5 hours. 4. The glass substrate for a recording medium according to claim 1, wherein an end face of the glass substrate is polished to remove cracks that cause damage with time. 5. The polishing amount of the end face of the glass substrate is 0.5 to
The glass substrate for a recording medium according to claim 4, wherein the thickness is 15 µm. 6. The glass substrate for a recording medium according to claim 5, wherein the end surface of the glass substrate is polished with a brush, a polishing powder (polisher), or an abrasive. 7. An end face of a glass substrate having a surface roughness of Rma
x: 0.01-1 μm, Ra: 0.001-0.8 μm
The glass substrate for a recording medium according to claim 4, wherein: 8. A recording medium comprising at least a recording layer formed on the glass substrate for a recording medium according to claim 1.