JPWO2015033800A1 - Glass substrate - Google Patents

Abstract

The glass substrate of the present invention satisfies the content range of specific constituent components and satisfies the condition of SiO 2 + Al 2 O 3 + B 2 O 3: 67 to 76% in terms of mol%, and 0.6 ≦ Li 2 O / (Li 2 O + Na 2 O + K 2 O) ≦ 0.96, And 0.78 ≦ MgO / (MgO + CaO + SrO + BaO + ZnO) ≦ 0.98.

Description

  The present invention relates to a glass substrate.

In recent years, the recording density of hard disk drive media is required to be about 600 Gbit / inch ² . In order to achieve such a high recording density, glass substrates used as substrates for hard disk drive media need to suppress fluttering more due to the problem of head positioning accuracy. Therefore, high Young's modulus (high elasticity) )Is required.

  In addition, from the viewpoint of improving the recording density, it is necessary to cope with the heat assist method, and the formation of a recording layer (magnetic layer) adapted to the heat assist method requires a high-temperature film forming process. High heat resistance is also required for the glass substrate to be formed. For this reason, for example, Japanese Patent Laying-Open No. 2005-314159 (Patent Document 1) proposes a glass substrate having heat resistance.

JP 2005-314159 A

  The proposed glass substrate has a certain degree of heat resistance, but does not exhibit a high Young's modulus. For this reason, fluttering cannot be sufficiently suppressed. On the other hand, from the viewpoint of heat generation of the hard disk drive, a glass substrate having a low specific gravity that does not put a load on the motor is suitable. there were.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a glass substrate having excellent heat resistance, high Young's modulus, and low density. .

The glass substrate of the present invention is
In mol% display
SiO ₂ : 58 to 67%
Al ₂ O ₃ : 6.5 to 13%
B ₂ O ₃ : 0 to 3%
Li ₂ O: 2.3 to 6.5%
Na ₂ O: 0.2 to 2.5%
K ₂ O: 0 to 2%
MgO: 14-23%
CaO: 0.6 to 4.6%
SrO: 0 to 3%
BaO: 0 to 3%
ZnO: 0 to 3%
ZrO ₂ : 0 to 3%
CeO ₂ : 0 to 2%
SnO ₂ : 0 to 2%
TiO _2: 0~4%
Nb ₂ O ₅ : 0 to 3%
Satisfies the content range and in mol% display,
SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ : 67 to 76%
And 0.6 ≦ Li ₂ O / (Li ₂ O + Na ₂ O + K ₂ O) ≦ 0.96 and 0.78 ≦ MgO / (MgO + CaO + SrO + BaO + ZnO) ≦ 0.98
It is characterized by comprising a glass composition satisfying the ratio (indicating "molar ratio").

Here, the glass substrate preferably has a Young's modulus of 90 GPa or more and 101 GPa or less, a density of 2.49 g / cm ³ or more and 2.61 g / cm ³ or less, and a glass transition temperature of 635 ° C. or more and 725 ° C. It is preferable that the temperature be equal to or lower than 0 ° C., and it is preferable that there is a relationship of t / d ≦ 0.011 between the thickness t (unit: mm) and the outer diameter d (unit: mm).

  The glass substrate is preferably a glass substrate for a magnetic recording medium, and its surface is preferably chemically strengthened.

  Since the glass substrate of the present invention has the above-described configuration, it has excellent heat resistance, high Young's modulus, and low density.

Hereinafter, embodiments according to the present invention will be described in more detail.
<Glass substrate>
The glass substrate of the present embodiment can be usefully used as a substrate for an information recording medium in various information recording devices, particularly as a glass substrate for a magnetic recording medium in a magnetic recording device such as a hard disk drive device, in mol% display. ,
SiO ₂ : 58 to 67%
Al ₂ O ₃ : 6.5 to 13%
B ₂ O ₃ : 0 to 3%
Li ₂ O: 2.3 to 6.5%
Na ₂ O: 0.2 to 2.5%
K ₂ O: 0 to 2%
MgO: 14-23%
CaO: 0.6 to 4.6%
SrO: 0 to 3%
BaO: 0 to 3%
ZnO: 0 to 3%
ZrO ₂ : 0 to 3%
CeO ₂ : 0 to 2%
SnO ₂ : 0 to 2%
TiO _2: 0~4%
Nb ₂ O ₅ : 0 to 3%
Satisfies the content range and in mol% display,
SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ : 67 to 76%
And 0.6 ≦ Li ₂ O / (Li ₂ O + Na ₂ O + K ₂ O) ≦ 0.96 and 0.78 ≦ MgO / (MgO + CaO + SrO + BaO + ZnO) ≦ 0.98
It is characterized by comprising a glass composition that satisfies the ratio.

Here, in the present embodiment, “%” display indicates “mol%” (“mol%”) unless otherwise specified regarding the glass composition. An addition notation of a chemical formula such as “SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ ” indicates the total amount of components represented by such chemical formula. Therefore, “SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ ” indicates the total amount of SiO ₂ , Al ₂ O ₃ and B ₂ O _3, and in the above case, the total amount is 67% of the total glass composition. It shows -76 mol%.

The notation “Li ₂ O / (Li ₂ O + Na ₂ O + K ₂ O)” indicates the ratio (ratio) of Li ₂ O in the total amount of Li ₂ O, Na ₂ O and K ₂ O, and In this case, the ratio is 0.6 or more and 0.96 or less. Similarly, the notation “MgO / (MgO + CaO + SrO + BaO + ZnO)” indicates the ratio (ratio) of MgO in the total amount of MgO, CaO, SrO, BaO and ZnO, and in the above case, the ratio is 0.78 or more and 0.98. Indicates that:

  Since the glass substrate of the present embodiment has the above glass composition, it becomes possible to ensure sufficient elasticity (high Young's modulus), thereby improving fluttering characteristics and high Young's modulus. And exhibiting an excellent effect of being able to achieve a low specific gravity (low density) while maintaining heat resistance. Such an excellent effect is achieved by the synergistic effects of the components constituting the glass composition described below.

  The glass substrate of the present embodiment preferably has a disk shape (a hole for attaching to the information recording device may be formed in the central portion). It is suitable as a glass substrate for an information recording medium (for magnetic recording medium) assembled in a recording apparatus. In the case of a disk-like shape, the size is not particularly limited. For example, a small-diameter disk having an outer diameter of 3.5 inches, 2.5 inches, 1.8 inches, or less can be used. The thickness can be as thin as 1 mm, 0.8 mm, 0.7 mm, 0.635 mm, 0.5 mm or less.

  In particular, the glass substrate of the present embodiment preferably has a relationship of t / d ≦ 0.011 between the thickness t (unit: mm) and the outer diameter d (unit: mm). Thereby, the substrate weight per unit storage capacity in the hard disk drive can be reduced, which is preferable from the viewpoint of power consumption. From the viewpoint of fluttering characteristics, the lower limit of t / d is preferably 0.006 or more.

  In the present embodiment, the thickness of the glass substrate is the length in the direction perpendicular to the recording surface (the surface having the largest area), and is the average value in the in-plane direction of the recording surface.

<Glass composition>
Each component which comprises the glass composition of the glass substrate of this Embodiment is demonstrated below.

First, SiO ₂ constituting the glass composition of the present embodiment is an important component for forming a glass network structure. If the content of SiO ₂ is less than 58%, glass formation becomes difficult and chemical durability may be deteriorated. On the other hand, if it exceeds 67%, the meltability deteriorates. Therefore, the content of SiO ₂ needs to be in the content range of 58 to 67%. A more preferable content range of SiO ₂ is 59 to 65%. In the present embodiment, when the mol% display is indicated by a range such as “58 to 67%”, the range includes upper and lower limit numerical values. In the above case, “58% or more and 67% or less” ".

Al ₂ O ₃ is an important component for forming a network structure together with SiO ₂ and has a function of improving not only heat resistance but also ion exchange performance. If the Al ₂ O ₃ content is less than 6.5%, chemical durability and ion exchange performance may be deteriorated. On the other hand, if it exceeds 13%, the ion exchange performance is lowered and the meltability is further deteriorated. For this reason, the content of Al ₂ O ₃ needs to be in the range of 6.5 to 13%. Among these, Preferably it is 6.6 to 9.6% of range.

B ₂ O ₃ is a component that forms a network structure with SiO ₂ , and has a function of lowering the melting temperature, so is contained as necessary. If it exceeds 3%, the glass transition temperature (Tg), which serves as an index of heat resistance, is lowered. For this reason, the content of B ₂ O ₃ needs to be 0 to 3%. A more preferable content range is 0 to 2%. In the above, the 0% in content of 0 to 3% B ₂ O _3, which means that may include aspects that do not contain B ₂ O _3. In addition, the notation of “0%” in the glass composition of the present embodiment is in agreement with this, and means that an aspect not including the component may be included.

Li ₂ O is a component necessary for improving chemical durability and further improving meltability. If the content of Li ₂ O is less than 2.3%, the effect of suppressing Li elution and improving the meltability cannot be sufficiently obtained. On the other hand, if it exceeds 6.5%, the glass transition temperature (Tg) decreases, and Li elution deteriorates. Therefore, the content of Li ₂ O needs to be in the content range of 2.3 to 6.5%. Among them, the content is preferably 4.5 to 6%.

Na ₂ O has a role of improving meltability. When the content of Na ₂ O is less than 0.2%, the effect of suppressing Na elution and improving the meltability cannot be obtained sufficiently. Conversely, when the content of Na ₂ O exceeds 2.5%, the chemical durability is lowered. Therefore, the content of Na ₂ O needs to be in the content range of 0.2 to 2.5%. Among these, Preferably it is a content range of 0.5 to 2.5%.

K ₂ O has an effect of improving the meltability, and may be contained as necessary. If the content of K ₂ O exceeds 2%, the glass transition temperature (Tg) is lowered and the chemical durability is also deteriorated. Therefore, the content of K ₂ O is set to a content range of 0 to 2%. A more preferable content range is 0 to 1%.

  MgO has the effect of improving heat resistance and improving meltability. Moreover, it has the effect of increasing elasticity (Young's modulus) while keeping the density low. If the content of MgO is less than 14%, the effect of improving the heat resistance and the effect of improving the meltability cannot be obtained, the elasticity is low, and the fluttering characteristics are lowered. On the other hand, if the content exceeds 23%, the glass structure becomes unstable, devitrification resistance deteriorates, and molding becomes difficult. Therefore, the content of MgO is set to a content range of 14 to 23%. This MgO-containing range is one of the characteristic points of the present embodiment. A more preferable content range of MgO is 16 to 21%.

  CaO has the effect of improving the meltability and the effect of maintaining the glass transition temperature (Tg). If the CaO content is less than 0.6%, the effect of improving the meltability and the effect of maintaining the glass transition temperature (Tg) cannot be sufficiently obtained. Conversely, if the content exceeds 4.6%, the glass structure is It becomes unstable and chemical durability deteriorates. Therefore, the content of CaO is set to a content range of 0.6 to 4.6%. A more preferable content range is 0.6 to 2.6%.

  SrO has the effect of improving the meltability and also has the effect of maintaining the glass transition temperature (Tg), so it is contained as necessary. When the content of SrO exceeds 3%, the devitrification resistance is deteriorated and molding becomes difficult. Therefore, the SrO content is set to a content range of 0 to 3%. A more preferable content range is 0 to 2%.

  BaO has the effect of improving the meltability and also has the effect of maintaining the glass transition temperature (Tg), so is contained as necessary. When the content of BaO exceeds 3%, devitrification resistance deteriorates and molding becomes difficult. Therefore, the content of BaO is set to a content range of 0 to 3%. A more preferable content range is 0 to 2%.

  ZnO has an effect of improving the chemical durability and improving the meltability, and is therefore contained as necessary. When the content of ZnO exceeds 3%, the glass structure becomes unstable, and the devitrification resistance deteriorates. Therefore, the content of ZnO is set to a content range of 0 to 3%. A more preferable content range is 0 to 2%.

ZrO ₂ has an effect of improving the heat resistance of the glass, and may be contained as necessary. However, if the content exceeds 3%, the devitrification resistance deteriorates, and vitrification becomes difficult. Therefore, the content is set to a content range of 0 to 3%. Among these, Preferably it is 0 to 2% of content range.

CeO ₂ and SnO ₂ play a role as a clarifying agent, and may be contained as necessary. When each content exceeds 2%, devitrification resistance will deteriorate and vitrification will become difficult. Therefore, the content is in the range of 0 to 2%. A more preferable content range is 0 to 1%, respectively.

TiO ₂ has an effect of softening the high temperature viscosity and improving the chemical durability, so it is contained as necessary. If the content of TiO ₂ exceeds 4%, the glass structure becomes unstable, devitrification resistance deteriorates, and molding becomes difficult. Therefore, the content of TiO ₂ is set to a content range of 0 to 4%. A more preferable content range is 0 to 3%.

Nb ₂ O ₅ has the effect of improving the meltability and the chemical durability, so it may be contained if necessary. If the content of Nb ₂ O ₅ exceeds 3%, the liquidus temperature rises and devitrification resistance deteriorates. Also, the specific gravity increases. Therefore, the content of Nb ₂ O ₅ is in the range of 0 to 3%. A more preferable content range is 0 to 1%.

The glass composition of this Embodiment can also contain another component other than each above-mentioned component. For example, a component that plays a role as a fining agent such as Sb ₂ O ₃ can be contained without any particular limitation, and can be contained in a content range of 0 to 2%.

On the other hand, in the glass composition of the present embodiment, it is important that the total amount of SiO ₂ , Al ₂ O ₃ and B ₂ O ₃ (SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ ) is 67 to 76%. is there. That is, it is necessary that the total amount of SiO ₂ , Al ₂ O ₃ and B ₂ O ₃ in the total glass composition is 67 to 76 mol%. These are all important components for forming a glass network structure as described above, and if the content is less than 67%, glass formation becomes difficult. Conversely, if it exceeds 76%, the viscosity is too high and the meltability is deteriorated. Among these, it is preferably in the range of 68 to 75%.

Furthermore, in the glass composition of the present embodiment, the ratio of Li ₂ O to the total amount of Li ₂ O, Na ₂ O, and K ₂ O is 0.6 to 0.96, that is, 0.6 ≦ It is required that Li ₂ O / (Li ₂ O + Na ₂ O + K ₂ O) ≦ 0.96. This is because when the ratio is less than 0.6, the density (specific gravity) increases, and when it exceeds 0.96, the Li elution amount increases. More preferably, 0.8 ≦ Li ₂ O / (Li ₂ O + Na ₂ O + K ₂ O) ≦ 0.96.

  In the glass composition of the present embodiment, the ratio of MgO to the total amount of MgO, CaO, SrO, BaO, and ZnO is 0.78 to 0.98, that is, 0.78 ≦ MgO / (MgO + CaO + SrO + BaO + ZnO). ) ≦ 0.98. When the ratio is less than 0.78, the density (specific gravity) increases, and when it exceeds 0.98, the glass structure becomes unstable, devitrification resistance deteriorates, and molding becomes difficult. More preferably, 0.86 ≦ MgO / (MgO + CaO + SrO + BaO + ZnO) ≦ 0.98.

<Characteristics>
The glass substrate of the present embodiment preferably has the following characteristics.

<Young's modulus and density>
The glass substrate of the present embodiment has a glass composition as described above, so that the Young's modulus is 90 GPa or more and 101 GPa or less, and the density is 2.49 g / cm ³ or more and 2.61 g / cm ³ or less. Can do. When the Young's modulus is less than 90 GPa, fluttering characteristics may be deteriorated. Moreover, when Young's modulus exceeds 101 GPa, a problem may arise in workability. Moreover, when the density is less than 2.49 g / cm ³ , the rigidity may be easily reduced. If the density exceeds 2.61 g / cm ³ , the load on the motor increases and the heat generation of the hard disk drive may become excessive.

More preferred Young's modulus is less than 95 GPa 98GPa, more preferably the density is less than 2.52 g / cm ³ or more 2.57 g / cm ^3.

<Glass transition temperature>
The glass substrate of this embodiment preferably has a glass transition temperature (Tg) of 635 ° C. or higher and 725 ° C. or lower. When Tg is less than 635 ° C., the medium may be deformed by heating in the film forming process in the medium (information recording medium) manufacturing process for the heat assist type application. Moreover, when Tg exceeds 725 degreeC, a favorable blanks shape is not obtained in the shaping | molding process of a glass blank, and it has a bad influence on the final glass substrate shape and by extension, the dynamic characteristic of media. A more preferable glass transition temperature (Tg) is 650 ° C. or higher and 710 ° C. or lower.

<Chemical strengthening treatment>
As for the glass substrate of this Embodiment, it is preferable that the surface is chemically strengthened. Such a chemical strengthening process can be normally performed by immersing a glass substrate in the solution containing an alkali in the manufacturing process of a glass substrate. More specifically, the chemical strengthening treatment is an ion exchange treatment in which alkali metal ions such as lithium ions and sodium ions contained in the glass substrate are replaced with alkali metal ions such as potassium ions having a larger ion radius.

  When the surface of the glass substrate is thus chemically strengthened, compressive stress is generated around the ion-exchanged region due to distortion caused by the difference in ion radius, and the hardness of the glass substrate surface increases in that region. preferable.

<Manufacturing method>
The manufacturing method of the glass substrate of this Embodiment does not have limitation in particular, A conventionally well-known manufacturing method can be used. For example, the corresponding oxides, carbonates, nitrates, hydroxides, etc. are used as raw materials for the respective components constituting the glass substrate, weighed to a desired ratio, and mixed well with powder to obtain a raw material for preparation. .

  Then, this blended raw material is put into, for example, a platinum crucible in an electric furnace heated to 1300 to 1550 ° C., melted and refined, stirred and homogenized, cast into a preheated mold, and gradually cooled to glass. It is considered as a block. Next, after being held at a temperature near the glass transition temperature for 1 to 3 hours, it is gradually cooled to remove strain.

  Subsequently, the obtained glass block is sliced into a disk shape, and is cut out using a core drill with the inner and outer circumferences being concentric. Alternatively, the molten glass is press-molded and formed into a disk shape. The disk-shaped glass substrate thus obtained is further subjected to rough polishing and polishing on both surfaces, and then washed with at least one of water, acid, and alkali to form a final glass substrate. .

  The glass substrate of the present embodiment is chemically strengthened by immersing it in a mixed solution of potassium nitrate (50 wt%) and sodium nitrate (50 wt%) after rough polishing and polishing both surfaces in the above manufacturing process. Processing may be performed. Thereafter, a part of the chemical strengthening layer may be removed as necessary.

  The glass substrate of the present embodiment manufactured in this way is then formed with a magnetic layer (magnetic film) as a recording layer, and is used as an information recording medium (magnetic recording medium). This information recording medium can be used by being incorporated in an information recording device such as a hard disk drive device.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Examples 1-30 and Comparative Examples 1-8>
A predetermined amount of raw material powder was weighed into a platinum crucible and mixed so as to have the glass compositions (components and ratios) shown in Tables 1 to 4, and then melted at 1500 ° C. in an electric furnace. After the raw materials were sufficiently dissolved, a platinum stirring blade was inserted into the glass melt and stirred for 1 hour. Thereafter, the stirring blade was taken out and allowed to stand for 3 hours, and then the melt was poured into a jig to obtain a glass block. Thereafter, the glass block was held for 2 hours near the glass transition temperature of each glass, and then slowly cooled to remove strain.

  The obtained glass block was sliced into a 2.5-inch disk shape having a thickness of about 1 mm, and the inner and outer circumferences were concentrically cut out using a cutter. Then, both surfaces were subjected to rough polishing and polishing, and then washed, thereby producing glass substrates in which the thicknesses of Examples and Comparative Examples having the glass compositions shown in Tables 1 to 4 were 0.635 mm. The following physical property evaluation was performed on the glass substrate thus prepared. The results are shown in Tables 1-4.

In Tables 1 to 4, “FM” represents “SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ ”, and “Li ₂ O / R ₂ O” represents “Li ₂ O / (Li ₂ O + Na _2). “O + K ₂ O)”, and “MgO / RO” means “MgO / (MgO + CaO + SrO + BaO + ZnO)”.

<Glass transition temperature (Tg)>
Using a differential heat measuring device (trade name: “EXSTAR6000”, manufactured by Seiko Instruments Inc.), a glass sample (prepared above) adjusted to a powder form at a temperature rising rate of 10 ° C./min. The glass transition temperature was measured by heating and measuring each glass substrate. The results are shown in the “Tg” section of Tables 5-8.

<Young's modulus and density>
According to the dynamic elastic modulus test method of the elastic test method of JIS R 1602 fine ceramics, it is produced as described above using a free resonance elastic modulus measuring device (trade name: “JE-RT”, manufactured by Nippon Techno-Plus). The Young's modulus was measured for each of the glass substrates, and the density was measured by the Archimedes method. The results are shown in Tables 5-8.

<Surface roughness>
The surface roughness of each glass substrate was measured using an atomic force microscope (AFM) (trade name: “Nanoscope V”, manufactured by Veeco). The case where the measurement range was 10 nm and the surface roughness in all directions was 1.2 nm or less was evaluated as “A”, and the case where the surface roughness exceeded 1.2 nm was evaluated as “B”. The results are shown in Tables 5-8.

<Fluttering>
The fluttering amount of each glass substrate was measured using a laser Doppler displacement meter (trade name: “OFV-151”, manufactured by Polytech Japan). The measurement is performed in an open space under atmospheric pressure. A single glass substrate is concentrically clamped from the upper and lower surfaces at a position 2 mm from the inner diameter end, rotated at a rotational speed of 5400 rpm, and the amplitude in the direction perpendicular to the recording surface. Was measured. The measurement frequency band is 10 kHz, and by taking the frequency spectrum of the obtained amplitude, the case where the maximum value at 500 Hz or more is less than 1.1 nm is “S”, and the case where the maximum value is 1.1 nm or more and less than 1.2 nm is “A”. “B” when 1.2 nm or more and less than 1.6 nm, “C” when 1.6 nm or more and less than 1.8 nm, and “D” when 1.8 nm or more. The results are shown in the “Fluttering” section of Tables 5-8. As is clear from Tables 5 to 8, it can be confirmed that the amount of fluttering is small (that is, the fluttering characteristics are good) when the Young's modulus is high.

<HDD test>
A magnetic film is formed on the surface of the glass substrate by forming an Fe—Pt alloy film on the glass substrate of each example and each comparative example by sputtering, and then performing heat treatment (600 ° C., 1 hour). A magnetic recording medium was prepared. Then, this magnetic recording medium is incorporated into a hard disk drive (HDD) that is a magnetic recording drive, and a read / write analyzer (trade name: “RWA1632”, manufactured by GUZIK) and a spin stand (trade name: “S1701MP”, manufactured by GUZIK) ) Was used to confirm the SNR (signal-to-noise ratio), and those with an SNR of 20 dB or more were designated as “A”, those with 16 dB or more but less than 20 dB as “B”, and those with less than 16 dB as “C”. The results are shown in the “SNR” section of Tables 5-8. It shows that the heat resistance of the glass substrate deteriorates in the order of “A”, “B”, and “C”. This is because the heat treatment at the time of manufacturing the magnetic recording medium and the SNR have a correlation.

  As is clear from Tables 5 to 8, the glass substrates of the examples have excellent heat resistance, high Young's modulus, and low density as compared with the glass substrates of the comparative examples. I was able to confirm.

  The glass substrate of Comparative Example 1 had a low Young's modulus, and the recording characteristics were not good due to the influence of fluttering. Since the glass substrates of Comparative Example 2 and Comparative Example 7 were difficult to vitrify the material, the substrates could not be evaluated. Since the glass substrate of Comparative Example 5 could not be press molded, the substrate could not be evaluated. Since the glass substrates of Comparative Example 3 and Comparative Example 4 have a high density, an increase in power consumption accompanying the rotation of the disk was observed. The glass substrate of Comparative Example 6 was inferior in chemical durability of the substrate. The glass substrate of Comparative Example 8 had a low Young's modulus, and the recording characteristics were not good due to the influence of fluttering.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Claims (6)

In mol% display
SiO ₂ : 58 to 67%
Al ₂ O ₃ : 6.5 to 13%
B ₂ O ₃ : 0 to 3%
Li ₂ O: 2.3 to 6.5%
Na ₂ O: 0.2 to 2.5%
K ₂ O: 0 to 2%
MgO: 14-23%
CaO: 0.6 to 4.6%
SrO: 0 to 3%
BaO: 0 to 3%
ZnO: 0 to 3%
ZrO ₂ : 0 to 3%
CeO ₂ : 0 to 2%
SnO ₂ : 0 to 2%
TiO _2: 0~4%
Nb ₂ O ₅ : 0 to 3%
Satisfying the content range and in terms of mol%,
SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ : 67 to 76%
And 0.6 ≦ Li ₂ O / (Li ₂ O + Na ₂ O + K ₂ O) ≦ 0.96 and 0.78 ≦ MgO / (MgO + CaO + SrO + BaO + ZnO) ≦ 0.98
A glass substrate made of a glass composition that satisfies the above ratio. The glass substrate according to claim 1, wherein the glass substrate has a Young's modulus of 90 GPa to 101 GPa and a density of 2.49 g / cm ^{3 to} 2.61 g / cm ³ .   The glass substrate according to claim 1, wherein the glass substrate has a glass transition temperature of 635 ° C. or more and 725 ° C. or less.   The glass substrate according to claim 1, wherein the glass substrate has a relationship of t / d ≦ 0.011 between a thickness t (unit: mm) and an outer diameter d (unit: mm). .   The glass substrate according to claim 1, wherein the glass substrate is a glass substrate for a magnetic recording medium.   The glass substrate according to claim 1, wherein the surface of the glass substrate is chemically strengthened.