JP2724136B2 - Glass substrate for recording medium, recording medium, and method for producing them - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium such as a magnetic recording medium, a magneto-optical recording medium and an optical recording medium, a substrate for a recording medium used as a substrate of these recording media, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as this type of recording medium, there is one described in Japanese Patent Application Laid-Open No. Sho 62-143243. That is, an optical recording medium in which an As—Te—Se-based recording layer is provided on a chemically strengthened disk-shaped glass substrate is known. In general, as a chemically strengthened glass substrate, a substrate made of soda lime glass containing SiO ₂ as a main component and containing sodium ions as ions to be exchanged is used as a starting material, and this starting material is added to a KNO ₃ molten salt. It is known that the glass substrate is immersed to replace Na ions and K ions to form a compressive stress bending on the surface of the glass substrate, thereby strengthening the glass substrate. Therefore, a recording medium in which a recording layer is provided on a chemically strengthened glass substrate using soda lime glass as a starting material is known.

[0003]

However, in the conventional recording medium, since the glass substrate is chemically strengthened, a recording layer is formed on an unreinforced glass substrate against breakage due to surface flaws (cracks). Although it has a higher strength than the provided recording medium, it still has a problem that if the crack penetrates as deep as 20 μm in the thickness direction of the substrate, it will break at a high rotation speed. For example, if the depth of the compressive stress layer is 20
A recording medium in which a magnetic layer is provided on a glass substrate reinforced with soda lime glass having a diameter of less than μm and a diameter of 130 mm and a thickness of 1.9 mm is broken by a high-speed rotation of 30,000 rpm. Further, recording medium substrates are required to have extremely high reliability over a long period of time, but conventional chemically strengthened glass substrates have not yet satisfied this requirement.

SUMMARY OF THE INVENTION The present invention has been made under the above-mentioned background, and there is no danger that troubles due to cracks or the like will occur even when used for a long period of time that satisfies the required service life. It is an object of the present invention to provide a glass substrate for a recording medium having sufficient reliability and a recording medium using the glass substrate.

[0005]

In order to solve the above-mentioned problems, a glass substrate for a recording medium according to the present invention comprises: (Structure 1) a compressive stress layer and a tensile stress layer which are sequentially arranged from the surface side to the inside in the thickness direction. A recording medium glass substrate having a stress layer formed thereon, wherein a curve representing the distribution of the tensile stress of the tensile stress layer draws a peak-shaped curve protruding in the direction of increasing tensile stress in the vicinity of the compressive stress layer. Wherein the maximum tensile stress value at the peak is set to be equal to or less than a reference design value capable of suppressing fracture due to cracks. A value of 4 kg / mm ² or less, and as an aspect of Configuration 1 or 2, (Configuration 3) the glass substrate contains at least SiO ₂ and Na ₂ in its composition.
A configuration characterized by being composed of a glass material containing O and LiO ₂ , and according to any one of Configurations 1 to 3, (Configuration 4) wherein the thickness of the compressive stress layer is set to 50 μm or more. And the configuration 3 or 4
In an embodiment, the glass material has a SiO ₂ content of 10% by weight or more and a LiO ₂ content of 5% by weight or more.

A recording medium according to the present invention is (structure 6) a recording medium in which at least a recording layer is formed on a substrate surface, wherein the substrate is a glass substrate for a recording medium according to any one of constitutions 1 to 5. According to a sixth aspect of the present invention, there is provided (Structure 7) wherein the recording layer is a magnetic layer.

Further, the method for manufacturing a glass substrate for a recording medium according to the present invention is characterized in that (Constitution 8) the method for manufacturing a glass substrate for a recording medium according to any one of the constitutions 1 to 5, wherein The compression stress layer and the tensile stress layer are formed by a chemical strengthening method by ion exchange.

Further, according to the present invention, there is provided a method for manufacturing a recording medium according to the above (6) or (7), wherein the compressive stress layer and the tensile stress of the glass substrate for the recording medium are provided. The layer is formed by a chemical strengthening method by ion exchange.

According to the above-described structure, it is possible to prevent a general crack entering from the surface of the glass substrate from being broken by rotation or the like by the action of the compressive stress layer, and to exceed the thickness of the compressive stress layer. Even when cracks occur, sufficient strength can be maintained by setting the maximum value of the tensile stress of the tensile stress layer further inside the substrate than the compressive stress layer to 4 kg / mm ² or less. It is more effective if the glass substrate is made of a glass material containing at least SiO ₂ , Na ₂ O and LiO ₂ in its composition. Further, if the thickness of the compressive stress layer is set to 50 μm or more, a material which can sufficiently cope with ordinary cracks can be obtained. further,
The composition of the glass material constituting the glass substrate is SiO 2
More preferably, the content of ₂ is 10% by weight or more, and the content of LiO ₂ is 5% by weight or more.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetic recording medium, a glass substrate for a magnetic recording medium, and a method for manufacturing the same according to an embodiment of the present invention will be described in detail with reference to FIGS.

As shown in FIG. 1, the magnetic recording medium 1 of this embodiment is processed into a disk having an outer diameter of 130 mm, an inner diameter (diameter of a hole formed at the center) of 40 mm, and a thickness of 1.9 mm.
The main surface thereof (the surface on the side on which the magnetic layer 13 described later is provided) is polished with cerium oxide (surface roughness Ra = 1).
A glass substrate 11 chemically strengthened by a method described later, having a tensile stress of 3.7 Kg / mm ² , and a compressive stress layer reaching 115 μm in the thickness direction (depth) from the substrate surface; An underlayer 12 (thickness: 2,000 angstroms) made of chromium (Cr) and cobalt (Co) sequentially laminated on the glass substrate 11
, A magnetic layer 13 (thickness: 700 angstroms), a protective layer 14 of carbon (C) (thickness: 300 angstroms), and a fluorocarbon-based lubricant (for example, Mo
Fomblin AM200 manufactured by NTEFLOUS
1) and a multilayer film 16 composed of a lubricating layer 15 (thickness: 30 angstroms). In addition,
The underlayer 12 made of Cr, the magnetic layer 13 made of CoNiCr, and the protective layer 14 made of C are all formed by a DC magnetron sputtering method, and a target made of Cr, a target made of CoNiCr, and a target made of C are used, respectively. . In addition, the lubricating layer 15 is formed by stacking the glass substrate 11 on the protective layer 14, placing the glass substrate 11 on a spin coater, dropping the above-described lubricant onto the protective layer 14, and applying the lubricant by spin coating.

Next, a method of strengthening the reinforced glass substrate 11 will be described. In addition, the strengthened glass substrate 11
The starting glass substrate is composed of about 64 wt% of SiO ₂ ,
It contains about 10 wt% of Na ₂ O and about 6 wt% of LiO ₂ , and does not contain K ₂ O.

(Step 1) First, a glass substrate made of a starting material, which is formed into a disk shape and whose main surface is polished by the method described above, is placed in a preheating furnace.

(Step 2) Next, the temperature of the atmosphere in the preheating furnace is raised from room temperature to about 300 ° C. in about one hour, and the glass substrate made of the starting material is preheated.

(Step 3) The starting glass substrate is chemically strengthened by immersion in a mixed molten salt of 60% KNO ₃ and 40% NaNO _{3 at} about 400 ° C. for about 4 hours. In this strengthening, first, Li ions in the glass substrate as a starting material are partially ion-exchanged with Na ions in the mixed molten salt. Next, Na ions (including Na ions previously exchanged for Li ions) in the glass substrate as a starting material are partially ion-exchanged with K ions in the mixed molten salt.

(Step 4) The ion-exchanged (strengthened) glass substrate 11 is taken out of the mixed molten salt and cooled slowly.

Thereafter, the reinforced glass substrate 11 is sequentially washed and dried with pure water, isopropyl alcohol and Freon (trademark of DuPont). Then, the above-described step of laminating the multilayer film 16 including the underlayer 12 and the like is performed.

The glass substrate 11 reinforced through the above-described steps 1 to 4 has a stress distribution as shown by a curve A in FIG. 2, a tensile stress of 3.7 Kg / mm ^{2 at the} maximum, and a compressive stress of The layer has a depth of 115 μm from the surface of the glass substrate 11.
Is formed up to. Further, the tensile stress is generated further inside the glass substrate 11 than the compressive stress layer. Therefore, even if the depth of the crack is 115 μm from the substrate surface, it has sufficient durability. Also, even if the cracks are 1 μm or 2 μm larger than 115 μm, they have sufficient durability.

FIG. 3 shows the relationship between the tensile stress and the breaking time shown in FIG. 3. As an example, a crack having a depth of 1 μm grows under a tensile stress of 4 Kgm / mm ^{2 and} the time required for the glass substrate to break. It is 10 years.
That is, FIG. 3 shows that the crack depth is 116 μm, for example.
, A value C exceeding the depth of 115 μm of the compressive stress layer
It can be considered to indicate the time until breaking when a tensile stress is applied to a glass substrate having = 1 μm. Therefore, even if the depth of the crack is 116 μm and the tensile stress is 4 kg / mm ² , it can withstand enough for about 10 years, so that it has sufficient durability even if the crack is slightly deeper than the compressive stress layer. .

Glass substrate 11 having the above characteristics
The magnetic recording medium 1 of the present example, on which the magnetic layer 13 was provided, was rotated by fitting and inserting a hole of the medium 1 into the shaft of a motor, and a rotational breakdown test was performed. As a result, the magnetic recording medium 1 was broken even at 35,000 rpm. Does not occur. In the case of a conventional magnetic recording medium in which a multilayer film 16 similar to the present example is laminated on a conventional glass substrate (a soda-lime glass chemically strengthened) having the same shape and size, 26,000 to 28, Breaks down at 000 rpm. Also, as a result of a drop test of the magnetic recording medium 1 of the present example and the above-mentioned conventional magnetic recording medium, the magnetic recording medium 1 of the present example did not break even when repeatedly dropped 10,000 times or more. The magnetic recording medium is destroyed by repeated dropping 300 to 500 times.
In addition, this drop test method is performed at a center of a glass substrate from above a concrete floor covered with a plastic tile (for example, a P-tile having a thickness of 2.0 mm manufactured by Tajima Kako Co., Ltd.).
m from the height of m, and the side of the glass substrate collides with the floor. That is, the free fall impact test is performed so that the glass substrate surface and the floor surface are at right angles. Until the confirmation, the player repeatedly falls once every 15 seconds and falls.

The present invention is not limited to the above embodiment, but may be as follows. First, the value of the tensile stress of the reinforced glass substrate and the depth of the compressive stress layer were 3.7 kg / mm, respectively.
Not limited to ² and 115 μm, if it is 4 kg / mm ² or less and at least 50 μm, a generally occurring depth of 50 μm
It has an effect of preventing breakage of cracks up to and slightly larger than this. Further, the composition of the glass substrate as a starting material of the reinforced glass substrate is not limited to the composition of the above-mentioned embodiment, and after the ion exchange treatment and the chemical strengthening, the tensile stress is 4 kg / mm ² or less and a compression responsive layer is generated. It is sufficient that the composition has a depth of at least 50 μm. Note that S
It contains iO ₂ , Na ₂ O and LiO ₂ , wherein Na ₂ O is at least 10 wt% and LiO ₂ is at least 5 wt%
Containing glass is desirable as a starting material. Also,
The conditions for the ion exchange are not limited to those in the above embodiment, but may be other conditions such as a temperature of the molten salt of 360 ° C. and a time of 16 hours. That is, it is sufficient that the tensile stress is 4 kg / mm ² or less and the depth of the compressive stress layer is at least 50 μm as described above. Further, not only the magnetic recording medium of the above embodiment but also the magnetic layer is made of CoNi, CoNiPt and CoNiC.
Other magnetic recording media such as those made of rPt or the like may be used.
Also, an optical recording medium whose recording layer is made of Te, Se, GeTe, or the like, GdFe, TbFe, TbFeCo, NdDyF
e, it can be applied to a magneto-optical recording medium having a recording layer made of NdDyFeCo or the like. Further, although the glass substrate has a disk shape, it is needless to say that the glass substrate can be applied to other shapes.

[0022]

According to the present invention, there is provided a glass substrate for a recording medium in which a compressive stress layer and a tensile stress layer are sequentially formed from the surface side toward the inside in the thickness direction. In the case where the curve to be drawn draws a convex peak-shaped curve in the direction of increasing tensile stress in the vicinity of the compressive stress layer, the maximum tensile stress value at the peak is equal to or less than a reference design value capable of suppressing fracture caused by cracks. With this configuration, there is no danger of troubles caused by cracks and the like even when used for a long period of time that satisfies the required service life, and sufficient reliability as a recording medium substrate is achieved. And a recording medium using the glass substrate.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a magnetic recording medium according to an embodiment of the present invention.

FIG. 2 is a diagram showing a stress distribution on a glass substrate of the magnetic recording medium according to the embodiment of the present invention.

FIG. 3 is a diagram showing a group of relational curves between the tensile stress in a glass substrate and the fracture time using the size of a crack in the glass substrate as a parameter.

[Explanation of symbols]

1 ... magnetic recording medium (recording medium), 11 ... reinforced glass substrate, 13 ... magnetic layer (recording layer).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location G11B 7/24 531 8721-5D G11B 7/24 531Z 7/26 8940-5D 7/26 11/10 511 11/10 511A 541 541D

Claims (9)

(57) [Claims] 1. A recording medium glass substrate in which a compressive stress layer and a tensile stress layer are sequentially formed from the surface side to the inside in the thickness direction, wherein a curve representing the distribution of the tensile stress of the tensile stress layer is provided. In the case where a convex peak-shaped curve is drawn in the direction of increasing tensile stress in the vicinity of the compressive stress layer, the maximum tensile stress value at the peak is set to a reference design value or less that can suppress fracture caused by cracks. A glass substrate for a recording medium, comprising: 2. The glass substrate for a recording medium according to claim 1, wherein the maximum tensile stress value is 4 kg / mm ² or less. 3. The glass substrate for a recording medium according to claim 1, wherein said glass substrate is made of a glass material containing at least SiO ₂ , Na ₂ O and LiO ₂ in its composition. 4. The glass substrate for a recording medium according to claim 1, wherein the thickness of the compressive stress layer is 50 μm or more. 5. The glass material according to claim 1, wherein the content of Na ₂ O is 1
5. The glass substrate for a recording medium according to claim 3, wherein the glass substrate is 0% by weight or more and the content of LiO ₂ is 5% by weight or more. 6. A recording medium having at least a recording layer formed on the surface of a substrate, wherein the substrate is formed of the glass substrate for a recording medium according to claim 1. . 7. The recording medium according to claim 6, wherein said recording layer is a magnetic layer. 8. The method for manufacturing a glass substrate for a recording medium according to claim 1, wherein the compressive stress layer and the tensile stress layer are formed by a chemical strengthening method using ion exchange. A method for producing a glass substrate for a recording medium, comprising: 9. The method for manufacturing a recording medium according to claim 6, wherein the compressive stress layer and the tensile stress layer of the recording medium glass substrate are formed by a chemical strengthening method by ion exchange. A method for manufacturing a recording medium, comprising: