JP4643863B2 - SUBSTRATE FOR INFORMATION RECORDING MEDIUM, INFORMATION MAGNETIC RECORDING MEDIUM, AND METHOD FOR PRODUCING THEM - Google Patents

Description

【００５２】
【表２】

【００５３】
【表３】

【００５４】
【表４】

【００５５】
【発明の効果】
以上説明したとおり、低温成形を可能とするアルカリイオンを含んだ情報記録媒体用ガラス基板を作製する際、次の関係式（Ｉ）〜（III）を満足する組成を有するガラスから基板を作ることにより、アルカリ溶出が少ない情報記録媒体用基板を提供することが可能となる。
【００５６】
関係式（Ｉ） ０．８≦（Ｒ_２Ｏ添加量−Ａｌ_２Ｏ_３添加量）／Ｂ_２Ｏ_３添加量≦１．２
関係式（II） ９．０モル％≦Ｂ_２Ｏ_３添加量≦１４．０モル％
関係式（III） ３．０モル％≦Ａｌ_２Ｏ_３添加量≦７．０モル％
（なお、Ｒ_２Ｏ添加量は上記関係式（Ｉ）〜（III）から必然的に導かれ、１０．２モル％≦Ｒ_２Ｏ添加量≦２３．８モル％となる。）
さらに、このような組成を持つガラス基板を用いて情報記録用媒体を作製することにより、８０℃、８５％ＲＨのような過酷な耐候性試験においても、１０００時間は初期と変わらない磁気特性を示す情報磁気記録媒体を提供することが可能となる。
【００５７】
以上のように、本発明によれば低温加工性および高耐候性といった相反する特性を満足する安価な情報記録媒体用基板および該情報記録媒体用基板を用いた情報磁気記録媒体と、それらの製造方法を提供することが可能となる。
【図面の簡単な説明】
【図１】本発明に基づく情報記録媒体用基板の一例を説明するための平面模式図である。
【図２】本発明に基づく情報記録媒体の一例を説明するための断面積層模式図である。
【符号の説明】
１ 情報記録媒体用基板
２ 孔
３ アルカリ金属含有ガラス基板
４ 磁性層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an information recording medium substrate comprising an alkali metal-containing glass substrate and an information magnetic recording medium using the information recording medium substrate.
[0002]
[Prior art]
With the recent increase in recording density of magnetic disks, there is a demand not only for improving the performance of the magnetic layer for recording digital signals, but also for improving the performance of various components such as the magnetic head that controls recording and the substrate of the magnetic disk. ing. In consideration of such a demand, as a substrate, a glass substrate has been attracting attention in place of the conventionally used aluminum substrate.
[0003]
The reason why a glass substrate has begun to attract attention as a substrate of a magnetic disk is that (i) it is easy to make a thin plate required for miniaturization and high density of a magnetic disk by using a glass material, (ii ) Securing the flatness of the substrate surface that makes it possible to reduce the flying height of the magnetic head is easy with glass materials. (Iii) In addition, the glass substrate has higher potential than an aluminum substrate. It can be mentioned. In addition, the glass material can be easily formed into a disk shape by applying a pressure above its softening temperature, so that a disk-shaped substrate can be produced at low cost using glass. Having it is one of the reasons.
[0004]
In consideration of cost reduction when manufacturing such a glass substrate, it is necessary not to shorten the life of the pressurizing device and the mold used for forming the substrate. For this purpose, the molding temperature is as low as possible. It is desirable to be.
[0005]
Generally, in order to lower the molding temperature of the glass substrate, an alkali metal such as Li, Na, or K is added to the glass raw material. However, on the other hand, the addition of an alkali metal to the glass substrate has the demerits of corroding the magnetic layer of the information magnetic recording medium, deteriorating the surface lubricating layer, or generating surface precipitates and destroying the head. It is also known to be big. Thus, from the viewpoint of using a glass material as a substrate material for an information magnetic recording medium, it is desired to suppress the elution of alkali metal ions as much as possible.
[0006]
On the other hand, several methods have heretofore been proposed as methods for preventing elution of alkali metal ions from glass to which alkali metals such as Li, Na, and K are added. The main methods include the following methods.
[0007]
(1) A tetravalent oxide such as ZrO ₂ or SnO ₂ is added.
[0008]
(2) A rare earth oxide such as La ₂ O ₃ or Gd ₂ O ₃ is added.
[0009]
[Problems to be solved by the invention]
However, in both methods (1) and (2) described above, the glass softening temperature (Ts) increases by several tens of degrees Celsius when the amount of oxide added is increased in order to suppress alkali metal elution. As is well known, since Ts is almost proportional to the molding temperature, if Ts rises by several tens of degrees Celsius, the molding temperature inevitably rises by several tens of degrees Celsius. The purpose of lowering the molding temperature cannot be fulfilled. In other words, the addition of the oxide raises the glass molding temperature, and as a result, there is a negative effect that the life of the substrate molding die is shortened and the molding tact time is lengthened. In order to lower the molding temperature, it is necessary to add an alkali metal, and only a vicious cycle occurs in the production of the glass substrate. As described above, the conventional glass substrate manufacturing technique cannot improve the trade-off relationship between low temperature molding and low alkali elution.
[0010]
Therefore, the object of the present invention is to suppress the amount of alkali elution at the time of molding, to be excellent in durability after production, to be provided more simply and inexpensively, and for the performance required for the substrate of the magnetic recording medium. It is an object of the present invention to provide an excellent alkali metal-containing glass substrate (information recording medium substrate), an information magnetic recording medium using the information recording medium substrate, and a method for producing them.
[0011]
[Means for Solving the Problems]
As a result of repeated studies on alkali elution from a conventional alkali metal-containing glass substrate (hereinafter also simply referred to as a glass substrate), the present inventors have obtained the following knowledge.
[0012]
That is, B ₂ O, which is a basic component of the glass material composition, without using an additive that significantly increases the glass softening temperature as in the conventional methods (1) and (2) described above. ₃ , Al ₂ O ₃ , R ₂ O (where R is an alkali metal such as Li, Na, K, etc.) Alcohol elution without increasing Ts if the addition ratio is controlled within a specific range with high accuracy The inventors have found that the amount can be significantly reduced as compared with the conventional glass substrate, and have completed the present invention.
[0013]
The substrate for an information recording medium according to the present invention has at least B ₂ O ₃ , Al ₂ O ₃ , and R ₂ O (R is an alkali metal) in the composition, and these components are represented by the following relational expression in terms of molar ratio. (I), (II), (III);
Relational formula (I) 0.8 ≦ (R ₂ O addition amount−Al ₂ O ₃ addition amount) / B ₂ O ₃ addition amount ≦ 1.2
Relational formula (II) 9.0 mol% ≦ B ₂ O ₃ addition amount ≦ 14.0 mol%
Relational formula (III) 3.0 mol% ≦ Al ₂ O ₃ addition amount ≦ 7.0 mol%
An alkali metal-containing glass material that satisfies the above requirements is formed.
[0014]
The R ₂ O addition amount is inevitably derived from the relational expressions (I), (II), and (III), and the value is 10.2 mol% ≦ R ₂ O addition amount ≦ 23.8. Mol% (relational formula (IV)).
[0015]
By controlling the glass material of the substrate to the component composition, the information recording medium substrate of the present application can significantly reduce the amount of alkali elution compared to the conventional substrate without increasing Ts.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
A first aspect of the present invention relates to an information recording medium substrate. The substrate for an information recording medium based on the present invention has at least B ₂ O ₃ , Al ₂ O ₃ , and R ₂ O (R is an alkali metal) in the composition, and these components are represented by the following relational expression in terms of molar ratio. (I), (II), (III);
Relational formula (I) 0.8 ≦ (R ₂ O addition amount−Al ₂ O ₃ addition amount) / B ₂ O ₃ addition amount ≦ 1.2
Relational formula (II) 9.0 mol% ≦ B ₂ O ₃ addition amount ≦ 14.0 mol%
Relational formula (III) 3.0 mol% ≦ Al ₂ O ₃ addition amount ≦ 7.0 mol%
An alkali metal-containing glass material that satisfies the requirements is formed.
[0017]
A second aspect of the present invention relates to a method for manufacturing an information recording medium substrate. The method for producing an information recording medium substrate according to the present invention has at least B ₂ O ₃ , Al ₂ O ₃ , and R ₂ O (R is an alkali metal) in the composition, and these components are converted into molar ratios, The following relational expressions (I), (II), (III);
Relational formula (I) 0.8 ≦ (R ₂ O addition amount−Al ₂ O ₃ addition amount) / B ₂ O ₃ addition amount ≦ 1.2
Relational formula (II) 9.0 mol% ≦ B ₂ O ₃ addition amount ≦ 14.0 mol%
Relational formula (III) 3.0 mol% ≦ Al ₂ O ₃ addition amount ≦ 7.0 mol%
An alkali metal-containing glass material satisfying the above requirements is prepared, and the glass material is formed on an information recording medium substrate.
[0018]
FIG. 1 is a schematic view for explaining an example of an information recording medium substrate according to the present invention. As can be seen from FIG. 1, the information recording medium substrate 1 is composed of a disc-shaped alkali metal-containing glass substrate 3 having a circular hole 2 formed in the center thereof.
[0019]
As an example, the alkali metal-containing substrate 3 is manufactured by the following procedure. First, glass powder containing an additive having a desired composition is melted to produce a disk-shaped glass having a weight of about 6 g, a thickness of about 8 mm, and a diameter of about 23 mm. Subsequently, disk-shaped glass is shape | molded by Ts vicinity, and it is set as the disk-shaped glass substrate of thickness 0.635mm and diameter 65mm. Next, a hole having an inner diameter of 20 mm is formed in the center of the disk-shaped glass substrate, and general chemical strengthening is performed in order to increase the mechanical strength of the substrate. This chemical strengthening involves immersing the glass substrate in a solution in which NaNO ₃ and KNO ₃ are mixed at a rate of 0.4 to 0.6 and maintained at 350 to 400 ° C. for 1 to 5 hours. It is carried out by doing. Finally, the glass substrate is cleaned in pure water, and scrub cleaning, pure water drop cleaning, and isopropanol alcohol (IPA) cleaning are performed.
[0020]
A third aspect of the present invention relates to an information magnetic recording medium including the information recording medium substrate 1 shown in the first aspect of the present invention. That is, the information magnetic recording medium according to the present invention has an information recording medium substrate 1 made of an alkali metal-containing glass substrate 3 and a magnetic layer 4 laminated on the substrate 1 as shown in FIG. The information recording medium substrate 1 has at least B ₂ O ₃ , Al ₂ O ₃ , and R ₂ O (R is an alkali metal) in the composition, and these components are converted into molar ratios as follows: Relational expressions (I), (II), (III);
Relational formula (I) 0.8 ≦ (R ₂ O addition amount−Al ₂ O ₃ addition amount) / B ₂ O ₃ addition amount ≦ 1.2
Relational formula (II) 9.0 mol% ≦ B ₂ O ₃ addition amount ≦ 14.0 mol%
Relational formula (III) 3.0 mol% ≦ Al ₂ O ₃ addition amount ≦ 7.0 mol%
An alkali metal-containing glass material that satisfies the requirements is formed.
[0021]
A fourth aspect of the present invention relates to a method for manufacturing the information recording medium of the third aspect. The method for producing an information recording medium based on the present invention has at least B ₂ O ₃ , Al ₂ O ₃ , R ₂ O (R is an alkali metal) in the composition, and these components are represented by the following relationship in terms of molar ratio. Formula (I), (II), (III);
Relational formula (I) 0.8 ≦ (R ₂ O addition amount−Al ₂ O ₃ addition amount) / B ₂ O ₃ addition amount ≦ 1.2
Relational formula (II) 9.0 mol% ≦ B ₂ O ₃ addition amount ≦ 14.0 mol%
Relational formula (III) 3.0 mol% ≦ Al ₂ O ₃ addition amount ≦ 7.0 mol%
An alkali metal-containing glass material satisfying the above requirements is prepared, the glass material is molded into a substrate for an information recording medium, and a magnetic recording layer is laminated on the molded substrate.
[0022]
The information recording medium of the present invention is characterized in that the amount of alkali elution from the substrate is small when the alkali metal-containing glass substrate is composed of a glass composition satisfying the above relational expression. The information magnetic recording medium configured as described above may further include an underlayer, a protective layer, a lubricating layer, and the like as necessary.
[0023]
In order to achieve a high-performance information magnetic recording medium, it is preferable to provide an underlayer on the substrate to control the orientation of the magnetic layer.
[0024]
As described above, according to the present invention, when the alkali metal-containing glass substrate is composed of a composition satisfying the above-described relational expression, the elution of alkali from the information recording medium substrate is suppressed, and is caused by the eluted alkali. It is possible to prevent corrosion, deterioration, destruction, etc. of the information magnetic recording medium. As a result, an information magnetic recording medium having excellent durability and high reliability can be provided. The structure and shape of the information magnetic recording medium are not particularly limited, and it will be easily understood by those skilled in the art that various changes can be made.
[0025]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, it should be understood that these examples do not limit the present invention and can be variously modified without departing from the gist of the present invention.
[0026]
(Manufacture of alkali metal-containing glass substrates)
The alkali metal-containing glass substrate used in the following examples was produced as follows.
[0027]
The powders of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, and K ₂ O having the composition shown in Table 1 were weighed and mixed, then placed in a crucible and melted at 1400 to 1500 ° C. This molten glass is poured from a crucible into a diamond-like carbon mold to produce a disk-shaped glass (hereinafter referred to as “marble”) having a weight of about 6 g, a thickness of about 8 mm, and a diameter of about 23 mm. did. Next, the marble is introduced into a molding die before it is sufficiently cooled, and is pressed at 0.2 to 0.6 t / cm ² for 3 minutes while maintaining the die at a temperature near Ts. By this operation, a disk-shaped glass plate having a diameter of 65 mm and a thickness of 0.635 mm was obtained. Next, a hole having a diameter of 20 mm was provided in the center of the glass plate, and chemical strengthening was performed to ensure the bending strength of the disc.
[0028]
The specific treatment conditions for the chemical strengthening are as follows. A nitrate mixed at a weight ratio of NaO ₃ : KNO ₃ = 2: 3 is melted at 370 ° C., and a glass plate is formed by punching the melt. Soaked for 2 hours.
[0029]
Finally, the glass substrate that had been chemically strengthened was washed and dried.
[0030]
Note that the sigma R ₂ O shown in Table _{1, Li 2 O, Na 2} O, shows the mole% of the sum of _{K 2} O, Rf is a value represented by the following formula.
[0031]
Rf = (ΣR ₂ O—Al ₂ O ₃ addition amount) / B ₂ O ₃ addition amount (unit: mol%)
[0032]
(Evaluation of alkali elution amount)
In the following examples, in order to evaluate the alkali elution prevention effect, the amount of alkali elution from the glass substrate was analyzed according to the following procedure.
[0033]
(A) 10 mL of pure water is put into a 0.5 L capacity Teflon (registered trademark) container with a lid, and one substrate to be evaluated is put.
[0034]
(B) The container is placed in a constant temperature bath at 80 ° C. and left for 24 hours.
[0035]
(C) A Teflon (registered trademark) container was taken out of the thermostatic bath, pure water was collected, and alkali elements eluted in the pure water were examined by ICP analysis.
[0036]
(D) The total alkali elution amount per unit area was calculated from the obtained ICP analysis value.
[0037]
Example 1
In this example, an alkali metal-containing glass substrate having the composition shown in Table 1 and Table 1 (continued) was prepared by the above-described method, and the obtained substrate was evaluated for Ts and alkali elution amount. The results are shown in Table 1 and Table 1 (continued). ○ and ● in the judgment column in the table show the judgment results, ○ shows that Ts is 650 ° C. or less and the amount of alkali elution is 5.0 mg / m ² or less, and ● shows Ts of 650 It shows that the amount of alkali elution is larger than 5.0 ° C. or more than 5.0 mg / m ² . Here, Li ₂ O addition amount: Na ₂ O addition amount: K ₂ O addition amount = 10: 6: 1 is fixed.
[0038]
As reference samples, glass compositions that have been studied conventionally are shown in Table 1 as reference # 1 and reference # 2. Referring # 1 is Ts is 590 ° C. and lower, a large substrate with an alkali elution amount is 11.7 mg / _{m 2,} see # 2, on the other hand, although the alkali elution amount is small and the 5.0 mg / _{m 2,} Since Ts is as high as 670 ° C., it is a glass substrate having a defect that the molding die life is short. Generally, as in References # 1 and # 2, there is a trade-off relationship between the alkali elution amount and Ts.
[0039]
In contrast, in the present invention, when _Al 2 _{O 3} is 3.0 to 7.0 _mol%, B 2 _{O 3} is 9.0 to 14.0 mol%, and Rf is 0.8-1 .2 in the range, Ts is 650 ° C. or lower, and the alkali elution amount is less than 5.0 mg / m ² , that is, “good” in Table 1.
[0040]
_{Incidentally,} if the amount of B 2 _{O 3} is more than 15 mol%, the amount of alkali elution _increases, the B 2 _{O 3} added amount is large, _B 2 _{O 3} is liable to evaporate from the glass in the molten For this reason, it is presumed that this is because the marble surface partially causes a composition shift.
[0041]
(Example 2)
In the first embodiment described above, by Rf is 0.8 to 1.2, and _B 2 _{O 3} added amount is at 9.0 to 14.0 mol%, has been described that the present invention is satisfied. In the second embodiment, an effective range of Al ₂ O ₃ will also be described.
[0042]
The method for preparing the sample was the same as in Example 1, and experiments were performed using combinations shown in Table 2. The criteria for determination are the same. Here, Rf is fixed to 1 which is the central value of the present invention. As apparent from Table 2, when the addition amount of Al ₂ O ₃ exceeds 3.0 to 7.0 mol%, which is the range shown in Table 1, at 2 mol% or 8 mol%, Rf = Even with 1, the determination is ●.
[0043]
Therefore, when the results of Example 1 and Example 2 are combined, the addition range of Al ₂ O ₃ is limited to 3.0 to 7.0 mol%.
[0044]
Although not shown here, when an alkali ion metal having a large ionic radius, such as K ₂ O, Rb ₂ O, or Cs ₂ O, is added, Many additions are undesirable, with a limit of approximately 1.5 mole percent.
[0045]
From the above-described Examples 1 and 2, it was revealed that the information recording medium substrate according to the present invention is excellent in suppressing alkali elution. Then, next, the information magnetic recording medium using the substrate for information recording media based on this invention was examined.
[0046]
(Example 3)
The present embodiment relates to an information magnetic recording medium configured using an information recording medium substrate according to the present invention. Using the various substrates produced in Example 1, information magnetic recording media were produced as follows.
[0047]
No. 1 produced in Example 1. An information magnetic recording medium was manufactured by sequentially laminating a Cr underlayer, a CoPtCr magnetic layer, and a C protective film on both surfaces of the 38 information recording medium substrate. In order to investigate the weather resistance of the obtained information magnetic recording medium, it was left in an atmosphere of 80 ° C. and 85% RH for 1000 hours, and then the surface condition of the substrate and the flying height test of the magnetic recording medium were performed. The results are shown in Table 3. 82.
[0048]
Further, as a reference sample, a reference # 1 substrate shown in Table 1 was similarly prepared, and the weather resistance was examined in exactly the same procedure. The results are shown in Table 3. 83.
[0049]
As can be seen from Table 3, in the glass substrate of reference # 1, precipitates having a dendrite structure with a size of several tens of μm made of a mixed carbonate of lithium and sodium were observed on the surface. For this reason, it was not possible to read / write the recording.
[0050]
On the other hand, No. produced based on this invention. In the 38 glass substrate, no precipitation of alkali carbonate was observed, and no change in the flying height was observed. Also, the magnetic properties were almost unchanged from the initial stage.
[0051]
[Table 1]

[0052]
[Table 2]

[0053]
[Table 3]

[0054]
[Table 4]

[0055]
【The invention's effect】
As described above, when producing a glass substrate for an information recording medium containing alkali ions that enables low temperature forming, the substrate is made from glass having a composition satisfying the following relational expressions (I) to (III). Thus, it is possible to provide an information recording medium substrate with little alkali elution.
[0056]
Relational formula (I) 0.8 ≦ (R ₂ O addition amount−Al ₂ O ₃ addition amount) / B ₂ O ₃ addition amount ≦ 1.2
Relational formula (II) 9.0 mol% ≦ B ₂ O ₃ addition amount ≦ 14.0 mol%
Relational formula (III) 3.0 mol% ≦ Al ₂ O ₃ addition amount ≦ 7.0 mol%
(The R ₂ O addition amount is inevitably derived from the above relational expressions (I) to (III), and 10.2 mol% ≦ R ₂ O addition amount ≦ 23.8 mol%).
Furthermore, by producing an information recording medium using a glass substrate having such a composition, even in severe weather resistance tests such as 80 ° C. and 85% RH, the magnetic characteristics remain unchanged from the initial 1000 hours. It is possible to provide the information magnetic recording medium shown.
[0057]
As described above, according to the present invention, an inexpensive information recording medium substrate satisfying conflicting characteristics such as low-temperature workability and high weather resistance, an information magnetic recording medium using the information recording medium substrate, and production thereof It becomes possible to provide a method.
[Brief description of the drawings]
FIG. 1 is a schematic plan view for explaining an example of an information recording medium substrate according to the present invention.
FIG. 2 is a schematic cross-sectional view for explaining an example of an information recording medium based on the present invention.
[Explanation of symbols]
1 Information recording medium substrate 2 Hole 3 Alkali metal-containing glass substrate 4 Magnetic layer

Claims (4)

An information recording medium substrate,
The composition is composed of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, and K ₂ O , and these components are represented by the following relational expressions (I) and (II) in terms of molar ratio. , (III);
Relational formula (I) 0.8 ≦ ( total addition amount of Li ₂ O, Na ₂ O and K ₂ O− Al ₂ O ₃ addition amount) / B ₂ O ₃ addition amount ≦ 1.2
Relational formula (II) 9.0 mol% ≦ B ₂ O ₃ addition amount ≦ 14.0 mol%
Relational formula (III) 3.0 mol% ≦ Al ₂ O ₃ addition amount ≦ 7.0 mol%, and
Substrate for information recording medium, wherein the relation K 2 _O amount <Na 2 _O amount <Li 2 _O amount <alkali metal-containing glass material satisfying the br /> is made is molded. A method for manufacturing an information recording medium substrate, comprising:
The composition is composed of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, and K ₂ O. These components are converted into molar ratios by the following relational expressions (I) and (II): , (III);
Relational formula (I) 0.8 ≦ ( total addition amount of Li ₂ O, Na ₂ O and K ₂ O− Al ₂ O ₃ addition amount) / B ₂ O ₃ addition amount ≦ 1.2
Relational formula (II) 9.0 mol% ≦ B ₂ O ₃ addition amount ≦ 14.0 mol%
Relational formula (III) 3.0 mol% ≦ Al ₂ O ₃ addition amount ≦ 7.0 mol%, and
That relationship K 2 _O amount <Na 2 _O amount <Li 2 _O amount <br /> an alkali metal-containing glass material to satisfy prepared, shaping the glass material to a substrate for information recording medium A method for manufacturing a substrate for an information recording medium. An information recording medium comprising an information recording medium substrate and a magnetic layer laminated on the substrate,
The information recording medium substrate is composed of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, and K ₂ O , and these components have the following relationship in terms of molar ratio: Formula (I), (II), (III);
Relational formula (I) 0.8 ≦ ( total addition amount of Li ₂ O, Na ₂ O and K ₂ O− Al ₂ O ₃ addition amount) / B ₂ O ₃ addition amount ≦ 1.2
Relational formula (II) 9.0 mol% ≦ B ₂ O ₃ addition amount ≦ 14.0 mol%
Relational formula (III) 3.0 mol% ≦ Al ₂ O ₃ addition amount ≦ 7.0 mol%, and
Magnetic information recording medium, wherein the relation K 2 _O amount <Na 2 _O amount <Li 2 _O amount <alkali metal-containing glass material satisfying the br /> is made is molded. The composition is composed of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, and K ₂ O. These components are converted into molar ratios by the following relational expressions (I) and (II): , (III);
Relational formula (I) 0.8 ≦ ( total addition amount of Li ₂ O, Na ₂ O and K ₂ O− Al ₂ O ₃ addition amount) / B ₂ O ₃ addition amount ≦ 1.2
Relational formula (II) 9.0 mol% ≦ B ₂ O ₃ addition amount ≦ 14.0 mol%
Relational formula (III) 3.0 mol% ≦ Al ₂ O ₃ addition amount ≦ 7.0 mol%, and
The relationship K 2 _O amount <Na 2 _O amount <Li 2 _O amount <br /> an alkali metal-containing glass material to satisfy the preparing and molding the glass material to a substrate for information recording medium, molding A method of manufacturing an information recording medium, comprising: laminating a magnetic recording layer on a substrate that has been manufactured.

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