KR20050016376A - Glass substrate for information recording media and information recording medium - Google Patents

Abstract

When the glass substrate is held in water having a temperature of 80 ° C. for 24 hours, the ratio (Rab / Raf) of the centerline average height Raf of the measured surface to the centerline average height Rab measured before the holding is 0.8 to A glass substrate for an information recording medium having a Young's modulus of 90 GPa or more is disclosed. Also disclosed is an information recording medium having an information recording layer on the glass substrate.

Description

Glass substrates and information recording media for information recording media {GLASS SUBSTRATE FOR INFORMATION RECORDING MEDIA AND INFORMATION RECORDING MEDIUM}

The present invention relates to a glass substrate for an information recording medium and an information recording medium. More specifically, the present invention relates to a glass substrate having a high Young's modulus and high rigidity, in particular, a glass substrate suitable for a substrate for information recording media requiring surface smoothness and requiring high modulus of elasticity and high expansion coefficient. It also relates to an information recording medium comprising the above-mentioned glass substrate.

Major components of a magnetic storage device such as a computer include a magnetic recording medium and a magnetic head for magnetically reproducing the recorded data. As the former magnetic recording medium, a flexible disk and a hard disk drive are known. Among these, aluminum alloys have been mainly used as hard disks of hard disk drives. In recent years, the flying height of the magnetic head has been significantly reduced due to the miniaturization of the hard disk and the increase in magnetic recording density. Accordingly, the magnetic disk substrate is required to have a remarkably high accuracy along with the surface smoothness. However, aluminum alloys have a low hardness, and even when high accuracy abrasives and machine tools are used for polishing and lapping aluminum alloys, the polished and wrapped surfaces are plastically deformed, resulting in flat surfaces with a certain level of high accuracy. Difficult to form In addition, it is required to reduce the thickness of the magnetic disk substrate along with the reduction in the size and thickness of the hard disk drive. However, since aluminum alloys have low strength and low rigidity, it is difficult to reduce the thickness of the disk while maintaining the prescribed strength required by the specification of the hard disk drive. For this reason, glass substrates for magnetic disks requiring high strength, high rigidity, high impact resistance and high surface smoothness have been introduced. Among them, chemically strengthened glass substrates having a surface strengthened by the ion exchange method and crystallized glass substrates obtained by crystallization treatment are commercially available.

However, in recent years, hard disks have become smaller, thinner, and have higher densities of recording, so that the rise of magnetic disks is rapidly decreasing and the rotational speed of the disks is rapidly increasing. Therefore, the disk substrate material is required to satisfy stringent strength, Young's modulus and surface smoothness. In particular, with the increase in the information recording density of hard disks for personal computers and servers, substrate materials have recently been required to satisfy strict surface smoothness and strict surface flatness. In addition, with the increase in data processing speed, it is evident that there is a limit to conventional aluminum substrates, since the number of revolutions of the disk is required to be 10,000 rpm or more and the substrate material is required to satisfy more stringent rigidity. As long as hard disk capacity and disk rotation speed are unavoidable in the future, the substrate material for magnetic recording media will undoubtedly have high Young's modulus, high hardness, excellent surface flatness and surface smoothness, and good impact resistance. Required.

On the other hand, commercially available chemically strengthened glass has a Young's modulus on the order of 80 GPa, and it is clear that such glass can no longer handle the stringent demands that the hard disk must meet in the future. Commercially available crystallized glass has a high Young's modulus of about 90 GPa. However, since abnormal grains of crystal grains exist inside the material, the irregularities formed from the crystal grains remain on the surface of the polished material, and the crystallized glass has a defect of poor surface smoothness compared with chemically strengthened glass. Will have

In addition, substrates made of amorphous glass are required to have high water resistance in order to obtain excellent surface smoothness. When the substrate does not have sufficient water resistance, the smoothness of the substrate surface during substrate cleaning is reduced, and such substrate can no longer satisfy the high surface smoothness required for the substrate for the information recording medium in the future.

One of the inventors of the present invention has proposed a substrate for an information recording medium, which is made of glass having a high Young's modulus (more than 100 Pa) to cope with the increase of the rotation speed and to have a liquidus temperature of 1350 ° C or less (WO98 / 55993). Since the substrate for the information recording medium has a remarkably high Young's modulus, small injuries at high speed rotation (distance between the magnetic head and the magnetic disk during recording and reproduction) can be ensured.

By providing a substrate having excellent surface smoothness by imparting water resistance to the glass substrate having a high Young's modulus, a substrate for an information recording medium capable of completely satisfying the required characteristics can be obtained.

Under these circumstances, an object of the present invention is to provide a glass substrate suitable for an information recording medium having excellent surface smoothness, high Young's modulus and high rigidity, a glass substrate having a high expansion coefficient, and an information recording medium to which the substrate is applied.

In order to achieve the above object, the present inventors have diligently studied, and found that the above object can be achieved by a glass substrate, which is obtained after the glass substrate is held in water under certain conditions and before the surface of the glass substrate is held. The ratio of centerline average roughness is required to be within a certain range. The present invention has been completed based on the above findings.

That is, the present invention

(1) the glass substrate has a surface with a centerline average roughness ratio (Rab / Raf) of 0.8 to 1 (where Raf is the centerline average measured after the glass substrate is held in water having a temperature of 80 ° C. for 24 hours) Roughness, Rab is the centerline average roughness measured before the holding), and a glass substrate for an information recording medium having a Young's modulus of 90 GPa or more,

(2) A glass substrate for an information recording medium, comprising the substrate described in (1) above, substantially having a glass composition composed of SiO ₂ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, MgO, CaO, TiO _2, and ZrO ₂ . ,

(3) The substrate as described in (2), wherein the glass composition is mol ₂ , more than 50% and less than 70% SiO ₂ , more than 1% and less than 6% Al ₂ O ₃ , more than 12% and less than 25% Li ₂ O , At least 1% less than 3% Na ₂ O, more than 0% less than 15% MgO, more than 1% to 30% CaO, more than 0.1% less than 5% TiO ₂ and more than 3% less than 10% ZrO ₂ Glass substrates for information recording media

(4) The substrate according to any one of (1) to (3), wherein the glass substrate for chemically strengthened information recording medium,

(5) A glass substrate for an information recording medium, comprising: the substrate according to any one of (1) to (4), wherein the average linear expansion coefficient measured at 100 to 300 ° C. is 80 × 10 ⁷ / ° C. or more, and

(6) An information recording medium comprising the information recording layer formed on the glass substrate according to any one of (1) to (5) above is provided.

The glass substrate for the information recording medium provided by the present invention will be described first.

The glass substrate of the present invention has excellent water resistance, and the water resistance can be expressed by the centerline average roughness Rab / Raf, where Raf is the centerline average measured after the glass substrate is held in water having a temperature of 80 ° C. for 24 hours. Roughness, and Rab is the centerline average roughness measured before the retention. In the present invention, the Rab / Raf value is 0.8 to 1. Glass substrates with Rab / Raf values close to 1 have better water resistance, and such glass substrates have less degradation of surface roughness. It is preferable that Rab / Raf value is 0.84-1. As described above, the center line average roughness before the glass substrate is held in water is preferably 0.1 to 0.5 mm. The Rab and Raf can be measured by atomic force microscope (AFM).

The glass substrate of the present invention has the above characteristics, and has a high rigidity or a Young's modulus of 90 GPa or more, more preferably 95 GPa or more. For example, the glass composition may be determined so that the glass substrate has a Young's modulus of 90 to 120 GPa, more preferably 95 to 120 GPa.

Therefore, a glass substrate having a remarkably high surface smoothness can be provided which can be applied to an information recording medium having excellent safety at high speed.

The substrate preferably has an average linear expansion coefficient of 80 × 10 ⁷ / ° C. measured at 100 to 300 ° C. Since the information recording medium is coupled to the disk drive, it is preferable to match the average linear expansion coefficient of the glass substrate in the above range to the average linear expansion coefficient of the support material on the disc drive side.

In addition, the glass substrate of the present invention preferably satisfies the water resistance, the Young's modulus and the expansion coefficient, and has a specific gravity of 3.1 or less, more preferably 2.9 or less. The composition of the glass may be selected so that the specific gravity of the glass is 2.3 to 2.9.

The glass substrate preferably has a glass composition consisting essentially of SiO ₂ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, MgO, CaO, TiO ₂ and ZrO ₂ . First of all, the glass composition is less than, in mol%, more than 50% to 70% or less SiO _2, 1%, 6% or more is less than Al ₂ O _3, 12% excess of 25% or less Li ₂ O, 1% more than 3% Na ₂ O, MgO of more than 0% and less than 15%, CaO of 1% to 30%, TiO _{2 of} greater than 0.1% and less than 5%, and ZrO ₂ of greater than 3% and less than 10% are preferred (hereinafter, glass components Is the content by mole%).

The reason why the glass composition is preferred will be described below. The values in parentheses below indicate the preferred content by weight percent (% by weight).

SiO ₂ is a main component in forming the glass net structure, and the lower limit of the SiO ₂ content is determined in consideration of the durability, crystallization resistance and high temperature formation of the glass. The upper limit of the SiO ₂ content is determined in consideration of the Young's modulus and the expansion coefficient of the glass. The content of SiO ₂ is preferably greater than 50% and less than 70% (more than 30% and less than 66% by weight). More preferably, the content of SiO ₂ is greater than 50% and less than 65% (more than 30% and less than 66% by weight), even more preferably greater than 55% and less than 63%.

Al ₂ O ₃ is a component required to reinforce the glass mesh structure and improve the durability of the glass. Al ₂ O ₃ is also a component that prevents the glass surface from roughening when the glass substrate is immersed in water. The lower limit of the Al ₂ O ₃ content is determined in consideration of the durability of the glass and prevention of surface roughness during cleaning. The upper limit of the Al ₂ O ₃ content is determined in consideration of the moldability which may be lowered by the rise of the liquidus temperature. The content of Al ₂ O ₃ is preferably 1% or more but less than 6% (less than 12% by weight), more preferably 1% or more and less than 6% (less than 12% by weight), and more preferably less than 11% by weight. Even more preferred is less than 10% by weight.

Li ₂ O is an essential component for lowering the melting temperature of the glass in order to improve meltability, and is also a component which is ion exchanged in chemical strengthening, so the lower limit of the Li ₂ O content is determined in consideration of these points. The upper limit of the Li ₂ O content needs to be determined in consideration of the devitrification resistance of the glass. The content of Li ₂ O is preferably greater than 12% and less than 25% (more than 3% by weight), more preferably greater than 12% and less than 25% (more than 3% by weight), even more preferably greater than 13% (4% by weight). Greater than%).

Na ₂ O is an essential component, such as Li ₂ O, to lower the melting temperature of the glass in order to improve meltability, and is also a component that is ion exchanged in chemical strengthening. When Na ₂ O content is too large, the Young's modulus and chemical durability deteriorates. Therefore, it is preferable to adjust the Na ₂ O content to 1% or more but less than 3% (less than 4% by weight).

CaO is an essential ingredient for improving the Young's modulus, meltability and devitrification resistance of glass. When the CaO content is too high, the liquidus temperature rises, and the glass may degrade the meltability and devitrification resistance. Therefore, it is preferable to adjust the CaO content to 1 to 30% (5% by weight or more).

MgO is a component used to improve the Young's modulus of glass. When the MgO content is too much, the liquidus temperature of the glass rises, and the glass may also have low devitrification resistance. Therefore, the MgO content is preferably 0% or more and less than 15% (less than 12% by weight), more preferably less than 10% (11% by weight or less).

From the viewpoint of improving the Young's modulus, meltability and devitrification resistance, the total content of CaO and MgO is preferably 2 to 30%.

ZrO ₂ and TiO ₂ are essential ingredients for improving the Young's modulus and durability of the glass, and the lower limit of the content of each component is determined in consideration of the above characteristics. When the content of TiO ₂ and ZrO ₂ is too high, the liquidus temperature rises and the high temperature meltability of the glass decreases, so the upper limit of the content of each component is determined in consideration of these properties. The ZrO ₂ content is preferably more than 3% and 10% or less (greater than 6% by weight), more preferably 3.5% or more (greater than 7% by weight).

The TiO ₂ content is preferably less than the ZrO ₂ content to achieve the object of the present invention. In particular, the TiO ₂ content is preferably greater than 0.1% and less than 5% (less than 10% by weight).

In addition, when the above-mentioned improvement in Young's modulus, a drop in liquidus temperature and improvement in high temperature meltability are considered, it is preferable to adjust the total content of ZrO ₂ and TiO ₂ to 20% or less.

In addition, Sb ₂ O ₃ and As ₂ O ₃ may be added as a clarifier. When the above clarifier is added, it is preferable to add only Sb ₂ O ₃ in consideration of harmful effects on the environment. It is preferable that the content of the clarifier based on glass composition is less than 1%, and in order to obtain a defoaming effect, it is preferable to set it as 0 or more and less than 1%.

B ₂ O ₃ has the effect of lowering the liquidus temperature of the glass when a small amount is imposed. However, when the B ₂ O ₃ content increases, the Young's modulus may decrease rapidly, so care must be taken when B ₂ O ₃ is imposed. The glass substrate of the present invention can have excellent devitrification resistance and high Young's modulus without containing B ₂ O ₃ . Therefore, it is preferable not to add B ₂ O ₃ , which may sharply reduce the Young's modulus when added.

In consideration of the ion exchange efficiency, the K ₂ O content is preferably 0.1% or less, and more preferably no K ₂ O is added.

SrO and BaO each act to improve the devitrification and expansion coefficient of the glass and to lower the liquidus temperature of the glass. However, these components increase the specific gravity of the glass and decrease the Young's modulus of the glass. Therefore, it is preferable not to add these oxides.

Y ₂ O ₃ and La ₂ O ₃ have a great effect in improving the Young's modulus and water resistance of the glass. However, when they are added, the glass increases in weight and deteriorates in stability. The glass substrate of the present invention can have high Young's modulus and excellent water resistance without containing rare earth oxides such as Y ₂ O ₃ and La ₂ O ₃ . Therefore, it is preferable not to focus on the stability of the glass added to Y ₂ O ₃ and La ₂ O _3. It is also preferable not to add any other rare earth oxides.

With respect to other components, it is desirable not to add PbO in consideration of the environmental impact. ZnO, P ₂ O ₅ , SnO ₂ , CeO ₂ and F are unnecessary components.

The preferred composition of the glass substrate of the present invention can be realized based on the combination of the above preferred contents of the above components.

The glass substrate of the present invention is basically made of glass (glass made of amorphous phase) containing no crystalline phase.

The glass substrate of the present invention is suitable for chemical strengthening. Chemical strengthening is performed by immersing the glass substrate in a molten salt containing Na ions and / or K ions. The temperature of the molten salt can be set at a temperature higher than the distortion point of the glass and below the glass transition temperature T _g . When the temperature of the molten salt is too low, it is difficult to form a compressive stress layer on the surface of the substrate, and the effect of chemical strengthening is not fully exhibited. When the temperature of the molten salt is too high, the glass substrate may be deformed.

In chemical strengthening, Li ions and Na ions in the glass are ion exchanged with Na ions and / or K ions in the molten salt to form a compressive stress layer, thus increasing the breakdown strength of the glass by several orders of magnitude.

In view of the chemical strengthening process and / or the process of making the information recording medium, it is preferable to adjust the glass transition temperature (T _g ) of the glass substrate material to 500 ° C or higher. When the glass transition temperature is too low, salts used for chemical strengthening, such as sodium nitrate and potassium nitrate, cannot be melted under the transition temperature, or the glass substrate may be removed by heating performed to form an information recording layer on the glass substrate. The problem of deformation is caused. Glass composition may be determined in consideration of the above points so that the glass substrate material has a glass transition temperature (T _g ) of 500 to 600 ° C.

The Young's modulus, the expansion coefficient, the glass transition temperature, the specific gravity, etc. of the glass substrate before the chemical strengthening hardly change even after the chemical strengthening. Rab / Raf does not change or increase after chemical strengthening (the upper limit of Rab / Raf is 1).

The chemical strengthening process is as described above. The process of making the substrate and the information recording medium will be described below.

A hot melt method, ie, a predetermined amount of glass material is melted in air or in an inert gas atmosphere, and the formed glass is homogenized by bubbling and stirring to make a homogeneous molten glass free of bubbles. Then, the molten glass is molded into plate glass by any one of a known pressing method, a known down-drawing method, and a known floating method, and the plate glass is gradually cooled. Then, the plate glass is processed into a circle, a center hole is made, the inner and outer surfaces are processed, polished and wrapped, and a substrate for an information recording medium having a desired size and shape is made. Polishing and lapping is performed by lapping with abrasive or diamond pellets and polishing with an abrasive such as cerium (Ce) oxide, so that the surface on which the information recording layer is to be formed is finished to be flat and smooth. Polishing and lapping can form a surface with a surface accuracy of 0.1-0.6 nm. The chemical strengthening process may be performed before or after the lapping process. According to the glass substrate of the present invention, the surface roughness caused by the cleaning after polishing and lapping is reduced, and not only a high level of smoothness can be maintained but also the reattachment of the eluting material during cleaning can be reduced.

The manufacturing method of the information recording medium of the present invention will be described below.

The information recording medium of the present invention includes an information recording layer formed on the glass substrate for the information recording medium. For example, when a magnetic recording medium (magnetic disk) is formed, an underlayer, a magnetic layer (information recording layer), a protective layer and a lubricating layer are sequentially formed on a glass substrate. Although not particularly limited, the magnetic layer is formed of Co-Cr, Co-Cr-Pt, Co-Ni-Cr, Co-Ni-Pt, Co-Ni-Cr-Pt, or Co-Cr-Ta Magnetic layers are preferred. The base layer includes a Ni layer, a Ni-P layer, and a Cr layer. The protective layer comprises a carbon film, and a lubricant containing perfluoropolyether or the like may be used to form the lubricating layer. The layer may be a known layer.

The glass substrate for an information recording medium provided in the present invention is not only suitable as a substrate for a magnetic recording medium, but also as a substrate for various information recording media such as an optical magnetic recording medium and an optical disc. Thus, by selecting the information recording layer in accordance with various recording methods, various information recording media such as an optical magnetic recording medium and an optical disc can be provided.

The present invention will be described in detail with reference to the following examples, but the present invention will not be limited by this embodiment.

Examples 1-11 and Comparative Example 1

As starting materials to obtain the composition shown in Table 1 or 2, SiO ₂ , Al ₂ O ₃ , Al (OH) ₃ , MgO, Mg (OH) ₂ , MgCO ₃ , CaCO ₃ , Li ₂ CO ₃ , Na ₂ CO ₃ , TiO ₂ , ZrO _2, etc. were weighed and mixed thoroughly to form a formulated batch. The combination was placed in a platinum crucible and melted in air at a temperature of 1,400-1,600 ° C. for about 3-8 hours. The molten glass resulting therefrom flowed into a carbon mold having a size of 40 x 40 x 20 mm, cooled to the glass transition temperature, and immediately placed in an annealing furnace. There the glass was retained for 1 hour and cooled to room temperature in the furnace. In the glass thus obtained, no crystals that could be observed through the microscope were precipitated.

In order to evaluate the physical properties by processing the glass thus obtained, samples of 40 × 20 × 15 mm, 5φ × 20 mm, and 30 × 30 × 2 mm were made, and the physical properties of the samples were measured in the following manner. Table 1 shows glass compositions (mol%) and physical properties in Examples 1 to 6, and Table 2 shows glass compositions (weights) in Examples 1 to 6 based on the glass compositions (mol%) described in Table 1 %). Table 3 shows glass compositions (mol%) and physical properties in Examples 7 to 11 and Comparative Example 1, and Table 4 shows Examples 7 to 11 and comparisons calculated based on the glass compositions (mol%) described in Table 3. The glass composition (weight%) in Example 1 is shown.

(1) glass transition temperature (T _g )

Using a thermomechanical analyzer (TMA8140) manufactured by Rigakusha, a sample of 5 mm diameter x 20 mm was measured at a temperature increase rate of + 4 ° C / min. SiO ₂ was used as the standard sample.

(2) mean linear expansion coefficient

An average linear expansion coefficient means the average linear expansion coefficient in 100-300 degreeC, and the linear expansion coefficient was measured at the time of glass transition temperature measurement.

(3) specific gravity

The sample of 40x20x15 mm was measured by the Archimedean method.

(4) Young's modulus

The sample of 40x20x15 mm was measured by the ultrasonic method.

(5) Alkali elution amount

First, an average roughness Rab of a 30 × 30 × 2 mm sample ultrasonically cleaned in an ethanol solution was measured by an atomic force microscope (AFM). The sample was then placed in an acid washed polypropylene container and weighed to obtain dry mass. About 20 ml of 80 ° C. very pure water was added to the vessel, and the vessel covered with the oven at 80 ° C. was maintained for 24 hours. The door of the oven was then half open and the electrical switch was turned off to allow the sample to cool for 30 minutes and the vessel was taken out of the oven. After the treatment, the vessel was weighed, then the glass was taken out to obtain a sample solution. The solution amount was defined as the weight value after the treatment minus the dry mass. The amount eluted was determined by ICP-AES (ICP emission spectrometer "VISTA AX" made by Barian).

(6) Rab / Raf

In (5), the glass (sample) taken out of the container after drying was dried, and the average roughness (Raf) of the sample was measured by atomic force microscope (AFM), and the ratio of Rab to Raf (Rab / Raf) Was calculated. A value closer to 1 means higher water resistance.

TABLE 1

TABLE 2

TABLE 3

Note: Comparative Example 1 shows data for tempered glass disclosed in JP-A-239036 / 1989.

TABLE 4

As clearly shown in Tables 1 and 3, in Examples 1 to 11, the glass substrate had a high Young's modulus of 90 kPa or more, and the average linear expansion coefficient of 80 × 10 ⁻⁷ / ° C. or higher or an appropriate value measured at 100 to 300 ° C. Showed. Also, the alkali elution amount was as small as 0.3 μmol / cm 2 or less, and the ratio of surface roughness (Rab / Raf) was 0.8 or more.

In contrast, in Comparative Example 1, the glass had a low Young's modulus of 79 GPa and also had a small roughness (Rab / Raf) of 0.21, so that the glass in Comparative Example 1 was used for high-density recording and high-speed rotating hard disks. It is obvious that not.

Therefore, according to the glass of the present invention, a glass substrate for magnetic recording medium having high rigidity and excellent surface smoothness can be provided, and the glass substrate of the present invention is suitable for manufacturing a magnetic recording medium of high density and high speed rotation.

In Examples 1 to 11, a substrate blank was formed from glass having excellent properties as a substrate material for a magnetic recording medium. The substrate blank was slowly cooled and processed to form a disc having a defined size, which was polished and wrapped on both surfaces of the disc to create a flat, smooth glass substrate. The resulting glass substrate was chemically strengthened by being contained in a molten salt containing a mixture of sodium nitrate and potassium nitrate (the molten salt was set at a temperature higher than the strain point and below the glass transition temperature). It was confirmed that the glass substrates with the chemical strengthening and the glass substrates without the chemical strengthening corresponding to the glass of the example obtained the same results as those shown in Table 1. These glass substrates were cleaned, and as a result, no surface roughness was found, and no adhesion material was found.

A base layer, a magnetic layer, a protective layer, a lubricating layer and the like were formed on the above-described various glass substrates to obtain a magnetic recording medium.

The above description can be applied to a substrate for a magnetic recording medium and a magnetic recording medium having such a substrate, and the glass substrate of the present invention can also be applied to a substrate for other information recording media such as an optical magnetic medium and an optical recording medium.

The glass substrate for an information recording medium provided by the present invention has excellent water resistance, has a significantly high durability against a decrease in surface smoothness, has a high Young's modulus, and is suitable as a glass substrate for an information recording medium having a significantly low deformation at high speed rotation. Do.

The glass substrate of the present invention is particularly suitable as a glass substrate containing an alkali metal oxide for chemical strengthening.

In addition, the glass substrate of the present invention has high rigidity and high surface smoothness, and therefore, most of such characteristics make it possible to obtain an information recording medium suitable for high-speed rotation and high density recording.

Claims (6)

A glass substrate for an information recording medium, wherein the glass substrate has a surface having a centerline average roughness ratio (Rab / Raf) of 0.8 to 1 (where Raf is held in water at which the glass substrate has a temperature of 80 ° C. for 24 hours). And the center line average roughness measured after the measurement, and Rab is the center line average roughness measured before the holding), and also has a Young's modulus of 90 GPa or more. The information recording medium according to claim 1, wherein the glass substrate has a glass composition substantially composed of SiO ₂ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, MgO, CaO, TiO _2, and ZrO ₂ . Glass substrate. The glass composition of claim 2, wherein the glass composition is mole%, more than 50% and less than 70% SiO ₂ , more than 1% and less than 6% Al ₂ O ₃ , more than 12% and less than 25% Li ₂ O, 1% At least 3% Na ₂ O, at least 0% and less than 15% MgO, 1% to 30% CaO, more than 0.1% and less than 5% TiO ₂ and more than 3% and less than 10% ZrO ₂ Glass substrates for information recording media. The glass substrate according to any one of claims 1 to 3, wherein the glass substrate is chemically strengthened. The glass substrate for an information recording medium according to any one of claims 1 to 4, wherein the average linear expansion coefficient measured at 100 to 300 ° C is 80 × 10 ⁷ / ° C or more. An information recording medium comprising an information recording layer formed on the glass substrate according to any one of claims 1 to 5.