Glass substrate and method for producing glass substrate

Abstract

The purpose of the present invention is to provide a glass substrate for data recording that achieves both processability and long-term storability. The present disclosure relates to a glass substrate which is for data recording and to the inside of which information can be written with a laser, said glass substrate comprising a first main surface and a second main surface opposite from the first main surface, wherein: an outer peripheral end surface that constitutes the outer periphery of the glass substrate is formed between the first main surface and the second main surface; the thickness of the glass substrate is 0.3-5.0 mm; the glass substrate has a glass composition that contains, in molar percentages based on oxides, 55-88 mol% of SiO2, 0-25 mol% of Al2O3, 0-30 mol% of B2O3, 0-25 mol% of an alkali metal oxide, and 0-25 mol% of an alkaline earth metal oxide; and in a region from the first main surface of the glass substrate to a depth of 0.1 μm, the concentration of sodium ions as measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) is not more than 9,000 ppm.

Description

Glass substrate and method for manufacturing the same

[0001] The present invention relates to a glass substrate and a method for manufacturing a glass substrate.

[0002] 2. Description of the Related Art Recording media such as hard disk drives are used to store electronic data. In recent years, various recording media have been developed in addition to hard disk drives. For example, Patent Document 1 discloses a recording method in which a laser beam is focused inside an optical recording medium to form a plurality of recording dots with a refractive index different from that of the surrounding area.

[0003] Furthermore, Patent Documents 2 and 3 disclose glass substrates in a disk shape. For example, Patent Document 2 discloses an optical data storage system having a specific configuration, in which a substrate onto which data is written in the system is shown in the form of a rotating disk. Furthermore, Patent Document 3 discloses a method for reading stored data on a computing device, in which a data storage medium onto which data is written in the method is shown in the form of a rotating disk.

[0004] International Publication No. WO 2014 / 041676 International Publication No. WO 2019 / 156740 International Publication No. WO 2019 / 079076

[0005] An object of the present embodiment is to provide a glass substrate for data recording that is resistant to deterioration even when stored for a long period of time and that is resistant to difficulty in recording and reading data, that is, that can suppress deterioration of long-term storage properties.

[0006] One embodiment of the present disclosure is a glass substrate for data recording, into which information can be written using a laser, the glass substrate having a first main surface and a second main surface opposite to the first main surface, and an outer peripheral end face constituting the outer periphery of the glass substrate being formed between the first main surface and the second main surface, the glass substrate having a thickness of 0.3 to 5.0 mm, and the glass substrate having a SiO content of 55 to 88 mol % expressed in mol % on an oxide basis. ２ , 0 to 25 mol% Al ２ O ３ , 0 to 30 mol% B ２ O３ , 0 to 25 mol % of an alkali metal oxide, and 0 to 25 mol % of an alkaline earth metal oxide, and the concentration of sodium ions in a region of the glass substrate to a depth of 0.1 μm from the first main surface is 9000 ppm or less as measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0007] One embodiment of the present disclosure is a glass substrate for data recording, into which information can be written using a laser, the glass substrate having a first main surface and a second main surface opposite to the first main surface, and an outer peripheral end face constituting the outer periphery of the glass substrate being formed between the first main surface and the second main surface, the glass substrate having a thickness of 0.3 to 5.0 mm, and the glass substrate having a SiO content of 55 to 88 mol % expressed in mol % on an oxide basis. ２ , 0 to 25 mol% Al ２ O ３ , 0 to 30 mol% B ２ O ３ , 0.01 to 25 mol % of alkali metal oxide (R ２ and 0 to 25 mol % of an alkaline earth metal oxide, wherein the glass substrate is left in an environment of 85°C and 85% RH, and the haze value (%) measured after 240 hours is 20% or less.

[0008] One embodiment of the present disclosure is a method for manufacturing a glass substrate for data recording, into which information can be written by a laser, the manufacturing method including a surface treatment step of performing a sodium concentration reduction treatment on a surface of the glass substrate, the glass substrate having a first main surface and a second main surface opposite to the first main surface, and an outer peripheral end face constituting an outer periphery of the glass substrate being formed between the first main surface and the second main surface, the glass substrate having a thickness of 0.3 to 5.0 mm, and the glass substrate having a SiO 2 content of 55 to 88 mol %. ２ , 0 to 25 mol% Al ２ O ３ , 0 to 30 mol% B ２ O ３%, 0 to 25 mol % of an alkali metal oxide, and 0 to 25 mol % of an alkaline earth metal oxide.

[0009] According to this embodiment, it is possible to provide a glass substrate for data recording that can suppress deterioration of long-term storage properties.

[0010] FIG. 1 is a perspective view of a glass substrate according to an embodiment of the present invention.

[0011] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary. However, the present invention is not limited to this embodiment, and various modifications are possible without departing from the spirit of the present invention. In the drawings, the same elements are given the same reference numerals, and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0012] [First Embodiment] A glass substrate according to a first embodiment is a glass substrate for data recording, into which information can be written using a laser, the glass substrate having a first main surface and a second main surface opposite to the first main surface, an outer peripheral end face constituting the outer periphery of the glass substrate being formed between the first main surface and the second main surface, the thickness of the glass substrate being 0.3 to 5.0 mm, and the glass substrate having a SiO content of 55 to 88 mol % expressed in mol % on an oxide basis. ２ , 0 to 25 mol% Al ２ O ３ , 0 to 30 mol% B ２ O ３ , 0 to 25 mol % of an alkali metal oxide, and 0 to 25 mol % of an alkaline earth metal oxide, and the concentration of sodium ions measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) in a region of the glass substrate to a depth of 0.1 μm from the first main surface is 9000 ppm or less.

[0013] <Sodium ion concentration> In a region from the first main surface of the glass substrate to a depth of 0.1 μm, the sodium ion concentration measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) is 9000 ppm or less. When information is written to a glass substrate and stored for a long period of time, it is desirable to prevent the surface of the glass substrate from being altered during long-term storage in order to prevent the information from becoming unable to be read normally.

[0014] During long-term storage of a glass substrate on which information is written, moisture may adhere to the surface of the glass substrate. If the glass substrate has a large amount of sodium on its surface, the sodium is likely to dissolve in the moisture. When sodium dissolves, the Si—O network structure, which is the main skeleton of the glass, is broken, and color unevenness and cloudiness tend to occur on the surface of the glass substrate, which tends to make it difficult to read the written information.

[0015] Since the glass substrate of this embodiment has the sodium ion concentration of 9000 ppm or less, even if moisture adheres to the first main surface during long-term storage of the glass substrate, color unevenness or cloudiness due to fading is unlikely to occur on the first main surface, and written information tends to be easy to read. In other words, the glass substrate tends to have excellent long-term weather resistance and storage properties.

[0016] In a region from the first main surface to a depth of 0.1 μm, the sodium ion concentration measured by TOF-SIMS is 9000 ppm or less, preferably 100 to 8500 ppm, more preferably 200 to 8000 ppm, and even more preferably 300 to 7500 ppm. When the sodium ion concentration is within the above range, the long-term storage stability tends to be better.

[0017] In a region from the second main surface to a depth of 0.1 μm of the glass substrate, the sodium ion concentration measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) is preferably 9000 ppm or less. This makes it easy to read information from the second main surface even after long-term storage. In a region from the second main surface to a depth of 0.1 μm, the sodium ion concentration measured by TOF-SIMS is preferably 9000 ppm or less, more preferably 100 to 8500 ppm, even more preferably 200 to 8000 ppm, and still more preferably 300 to 7500 ppm.

[0018] Furthermore, in this embodiment, when measuring the sodium ion concentration by TOF-SIMS, a region from the first main surface to a depth of 0.1 μm is selected as the region near the surface of the glass substrate. Here, this region is a reference value for a region where sodium is present that dissolves in moisture adhering to the first main surface of the glass substrate when the glass substrate is stored for a long period of time. In this regard, depending on the conditions for long-term storage of the glass substrate, it is expected that sodium present in a region deeper than 0.1 μm in depth will dissolve in moisture adhering to the first main surface of the glass substrate. However, even if sodium dissolves from a region deeper than this, it can be said that the long-term storage properties of the glass substrate are improved when the sodium ion concentration measured based on the region from the first main surface to a depth of 0.1 μm satisfies a predetermined range.

[0019] The sodium ion concentration measured by TOF-SIMS in the region from the first main surface to a depth of 0.1 μm can be reduced by carrying out a surface treatment process that reduces the sodium concentration on the surface of the glass substrate, or can be adjusted by changing the sodium content.

[0020] In SIMS, the surface of the glass substrate 1 is gradually scraped away by irradiation with primary ions, and so continuous acquisition of data makes it possible to analyze the glass substrate in the depth direction. The vertical axis of the obtained data represents the sodium ion concentration, and the horizontal axis represents the primary ion irradiation time. Here, by determining the sputtering rate of the primary ions, the horizontal axis can be converted into the depth from the surface. The sputtering rate can be determined by measuring the depth of holes formed after SIMS. The number of sodium ions (atoms / cm) obtained by TOF-SIMS measurement is ３ The concentration was calculated from the sodium ion concentration (ppm) using the following formula: sodium ion concentration (ppm) = number of sodium ions (atoms / cm ３ ) / (6.02 x 10 ２３ ) × atomic weight of sodium (g) × 10 ６ / density of glass substrate (g / cm ３ )

[0021] [Second Embodiment] A glass substrate according to a second embodiment is a glass substrate for data recording, into which information can be written by a laser, the glass substrate having a first main surface and a second main surface opposite to the first main surface, an outer peripheral end face constituting the outer periphery of the glass substrate being formed between the first main surface and the second main surface, the thickness of the glass substrate being 0.3 to 5.0 mm, and the glass substrate having a SiO content of 55 to 88 mol % in terms of mol % on an oxide basis. ２ , 0 to 25 mol% Al ２ O ３ , 0 to 30 mol% B ２ O ３ , 0.01 to 25 mol % of alkali metal oxide (R ２ The glass substrate has a glass composition containing 0 to 25 mol % of an alkaline earth metal oxide, and the haze value (%) of the glass substrate measured after 240 hours of standing in an environment of 85°C and 85% RH is 20% or less.

[0022] The haze value is preferably 0 to 20%, more preferably 0 to 18%, and even more preferably 0 to 16%. When the haze value is within the above range, the long-term storage stability of the glass substrate tends to be further improved.

[0023] The haze value can be measured, for example, using a haze meter (NDH8000 manufactured by Nippon Denshoku Industries Co., Ltd.).

[0024] The method for reducing the haze value to 20% or less is not particularly limited, but examples thereof include a method of reducing the sodium content in the raw materials of the glass substrate to thereby reduce the sodium content contained in the glass substrate, and a method of reducing the sodium content in a region near the surface of the glass substrate by performing a surface treatment of the glass substrate, which will be described later.

[0025] When information is written on a glass substrate and the glass substrate is stored for a long period of time, it is important to prevent the glass substrate from being altered during the long-term storage in order to prevent the information from becoming unable to be read normally.

[0026] During long-term storage of a glass substrate on which information is written, moisture may adhere to the surface of the glass substrate. If the glass substrate has a large amount of sodium on its surface, the sodium is likely to dissolve in the moisture. When sodium dissolves, the Si—O network structure, which is the main skeleton of the glass, is broken, and color unevenness and cloudiness tend to occur on the surface of the glass substrate, which tends to make it difficult to read the written information.

[0027] In the glass composition of the glass substrate, R ２ Na content relative to O content ２ Molar ratio of O content (Na ２ O / R ２O) is preferably 0.6 or less, more preferably 0.3 to 0.6, and even more preferably 0.4 to 0.5. When the molar ratio is within the above range, even if the content of alkali metal oxide is relatively high, the diffusion rate of alkali ions is reduced due to the mixed alkali effect by mixing multiple alkali components at a predetermined ratio rather than a single alkali component. As a result, sodium is less likely to dissolve in moisture adhering to the glass substrate surface, and the long-term storage stability of the glass substrate tends to be further improved.

[0028] Also, R ２ The content of O is preferably 0.01 to 10.00 mol %, more preferably 0.02 to 7.50 mol %, and even more preferably 0.03 to 5.00 mol %. ２ When the O content is within the above range, the long-term storage stability of the glass substrate tends to be further improved.

[0029] Preferred aspects of the glass substrate 1 of the first embodiment and the glass substrate 1 of the second embodiment will be described below.

[0030] <Composition> The glass substrate is made of 55 to 88 mol% SiO ２ , 0 to 25 mol% Al ２ O ３ , 0 to 30 mol% B ２ O ３ , 0 to 25 mol % of alkali metal oxide, and 0 to 25 mol % of alkaline earth metal oxide. This tends to achieve both strength and workability. The glass composition of the glass substrate may consist of these components. Also, SiO ２ When the content is within the above range, the glass substrate can be prevented from becoming too hard, and the processability of the glass substrate tends to be improved.

[0031] SiO ２ is a glass network forming component. SiO ２From the viewpoint of enhancing the stability of the glass and improving the melting property during production, the content of SiO is preferably 55.0 to 85.0 mol %, more preferably 57.5 to 84.0 mol %, and even more preferably 60.0 to 83.0 mol %. ２ When the content is within the above range, the glass substrate has an appropriate softness, which makes it easy to process, and the processability tends to be improved.

[0032] Al ２ O ３ From the viewpoint of improving the heat resistance of the glass and enhancing the stability of the glass, the content of is preferably 0.5 to 25.0 mol %, more preferably 1.0 to 22.5 mol %, and even more preferably 2.0 to 20.0 mol %.

[0033] B ２ O ３ is a glass network forming component. ２ O ３ The content is preferably 0.0 to 12.5 mol %, more preferably 0.5 to 10.0 mol %, and even more preferably 1.0 to 7.5 mol %.

[0034] The alkali metal oxides include Li ２ O, Na ２ O.K. ２ O. The glass substrate 1 may or may not contain an alkali metal oxide, and when it contains an alkali metal oxide, the content thereof is preferably 0.01 to 30 mol %, more preferably 0.1 to 30.0 mol %, still more preferably 0.5 to 27.5 mol %, and particularly preferably 1.0 to 25.0 mol %.

[0035] Li as alkali metal oxide ２ It may or may not contain O, Li ２ When O is contained, the content thereof is preferably 0.1 to 25.0 mol %, more preferably 0.5 to 22.5 mol %, and even more preferably 1.0 to 20.0 mol %, from the viewpoint of improving heat resistance.

[0036] Na as alkali metal oxide ２It may or may not contain O, Na ２ When O is contained, the content thereof is preferably 0.01 to 15.0 mol %, more preferably 0.01 to 14.0 mol %, and even more preferably 0.01 to 13.0 mol %. ２ The content of O is preferably 5.0 mol% or less. ２ When the O content is within the above range, the processability of the glass substrate 1 tends to be improved.

[0037] K as alkali metal oxide ２ It may or may not contain O, K ２ When O is contained, the content thereof is preferably 0.1 to 3.0 mol %, more preferably 0.2 to 2.0 mol %, and even more preferably 0.3 to 1.0 mol %.

[0038] Examples of alkaline earth metal oxides include MgO, CaO, SrO, and BaO. The content of the alkaline earth metal oxide is preferably 0.5 to 20 mol%, more preferably 1.0 to 19.0 mol%, and even more preferably 3.0 to 18.0 mol%. When the content of the alkaline earth metal oxide is within the above range, the Young's modulus can be adjusted, and the processability of the glass substrate 1 tends to be improved.

[0039] The glass substrate 1 may or may not contain MgO as an alkaline earth metal oxide. When MgO is contained, the content thereof is preferably 0.5 to 20.0 mol %, more preferably 1.0 to 19.0 mol %, and even more preferably 2.5 to 18.0 mol %, from the viewpoint of adjusting the Young's modulus and improving the processability of the glass substrate 1.

[0040] The alkaline earth metal oxide may or may not contain CaO. When CaO is contained, the content thereof is preferably 0.1 to 10.0 mol %, more preferably 0.5 to 8.0 mol %, and even more preferably 1.0 to 6.0 mol %, from the viewpoint of improving productivity.

[0041] The alkaline earth metal oxide may or may not contain SrO. When SrO is contained, the content thereof is preferably 0.1 to 5.0 mol %, more preferably 0.5 to 4.0 mol %, and even more preferably 1.0 to 3.0 mol %, from the viewpoint of decreasing the photoelastic coefficient of the glass substrate.

[0042] BaO may or may not be contained as the alkaline earth metal oxide. When BaO is contained, the content thereof is preferably 0.5 to 5.0 mol %, more preferably 1.0 to 4.5 mol %, and even more preferably 2.0 to 4.0 mol %, from the viewpoint of decreasing the photoelastic coefficient of the glass substrate.

[0043] The glass composition of the glass substrate 1 may or may not contain other components in addition to the above-mentioned components. Examples of other components include TiO ２ , ZrO ２ , Fe ２ O ３ , SnO ２ , P ２ O ５ The content of the other components is not particularly limited, but is, for example, 0.1 to 5.0 mol %, 0.5 to 4.0 mol %, or 1.0 to 3.0 mol %.

[0044] The glass substrate preferably contains one or more materials selected from the group consisting of soda-lime glass, aluminosilicate glass, alkali-free glass, and borosilicate glass. This tends to improve the writability of the glass substrate. Soda-lime glass is glass containing the elements Si, Na, and Ca. Aluminosilicate glass is glass containing the elements Si and Al. Alkali-free glass is glass that is substantially free of alkali metal elements. While not particularly limited, "substantially free of alkali metal elements" refers to, for example, an alkali metal element content expressed in mole percent on an oxide basis of 0 to 2.0 mol%, 0 to 1.5 mol%, 0 to 1.0 mol%, 0 to 0.5 mol%, or 0 to 0.1 mol%. "Substantially free of alkali metal elements" encompasses cases where no alkali metal elements are present. Borosilicate glass is glass that contains the element B.

[0045] In the present disclosure, the glass composition is expressed as a glass composition based on oxides. Here, "glass composition based on oxides" means a glass composition obtained by converting the glass raw materials into oxides that are present in the glass after being completely decomposed during melting.

[0046] The glass composition in the present disclosure can be determined by a method such as ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Quantitative analysis is performed for each element using ICP-AES. The analytical values ​​are then converted into oxide notation. The analytical values ​​obtained by ICP-AES may contain a measurement error of, for example, about ±5% of the analytical value. Therefore, the oxide notation values ​​converted from the analytical values ​​may also contain an error of about ±5%.

[0047] In the present disclosure, a content of 0 mol% of a constituent component means that the constituent component is substantially absent, and indicates that the content of the constituent component is at or below the impurity level, for example, less than 0.01 mol%.

[0048] 1 is a perspective view showing an example of a glass substrate according to this embodiment. Glass substrate 1 has a first main surface 10 and a second main surface 12 opposite to first main surface 10. An outer peripheral edge surface 14 that forms the outer periphery of glass substrate 1 is formed between first main surface 10 and second main surface 12.

[0049] In this embodiment, a laser may be incident from the first main surface 10 to write information inside the glass substrate 1. Furthermore, the altered portion formed by the laser incidence may be read from the first main surface 10 side, and the written information may be read.

[0050] In this embodiment, information may be written inside the glass substrate by irradiating a laser from first main surface 10. Furthermore, the altered portion formed by the laser irradiation may be read from the first main surface 10 side, and the written information may be read.

[0051] While FIG. 1 illustrates the glass substrate 1 as having a circular ring shape, the shape of the glass substrate 1 is not limited thereto and may be a prism such as a square prism or a truncated cone such as a pentagonal pyramid. Also, while FIG. 1 illustrates the spindle hole 16 as a hole having a circular disk or columnar shape, the shape is not limited thereto and may be a prism such as a square prism or a truncated cone such as a pentagonal pyramid. If the glass substrate 1 has a shape obtained by hollowing out a smaller circular disk or columnar shape from a larger circular disk or columnar shape, the shape of the hollowed-out smaller circular disk or columnar shape coincides with the shape of the spindle hole 16. In this case, the center of the larger circle may coincide with the center of the smaller circle.

[0052] <Thickness> The thickness of the glass substrate 1 of this embodiment is 0.3 to 5.0 mm, preferably 0.5 to 5.0 mm, more preferably 0.5 to 4.0 mm, even more preferably 0.8 to 4.0 mm, and still more preferably 0.8 to 3.5 mm. When the thickness of the glass substrate 1 is within the above range, the long-term storage stability of the glass substrate 1 tends to be improved.

[0053] <Absorption coefficient> Absorption coefficient A at a wavelength of 355 nm on a glass substrate３５５ is preferably 0.8 to 6.0 cm －１ and more preferably 0.70 to 6.50 cm －１ and more preferably 0.70 to 4.00 cm －１ and even more preferably 0.75 to 3.00 cm －１ and particularly preferably 0.80 to 3.00 cm －１ and more particularly preferably 0.95 to 2.00 cm －１ The absorption coefficient A ３５５ When the absorption coefficient A is equal to or greater than the lower limit of the above range, it tends to be easier to write information on the glass substrate with light having a wavelength of 355 nm. ３５５ When the value is equal to or less than the upper limit of the above range, the affected portion tends to be formed at an appropriate position in the plate thickness direction.

[0054] In the glass substrate, the absorption coefficient A at a wavelength of 1064 nm １０６４ is preferably 0.6 to 2.0 cm －１ and more preferably 0.62 to 1.80 cm －１ and more preferably 0.64 to 1.60 cm －１ and even more preferably 0.66 to 1.40 cm －１ and particularly preferably 0.68 to 1.00 cm －１ and particularly preferably 0.68 to 0.80 cm －１ The absorption coefficient A １０６４ When the absorption coefficient A is equal to or greater than the lower limit of the above range, it tends to be easier to write information on the glass substrate with light having a wavelength of 1064 nm. １０６４ When the value is equal to or less than the upper limit of the above range, the affected portion tends to be formed at an appropriate position in the plate thickness direction.

[0055] In addition, when the absorption coefficient at a certain wavelength is equal to or less than a certain value, it tends to be easier to adjust the shape and degree of the alteration of the altered portion. In this regard, it can be said that when the upper limit of the absorption coefficient is as described above, it becomes easier to adjust the shape and degree of the alteration of the altered portion. The absorption coefficient A for light with a wavelength of 355 nm ３５５ and the absorption coefficient A for light with a wavelength of 1064 nm １０６４By setting the wavelength of the recording medium within a predetermined range, the writability tends to improve with lasers having a wide range of wavelengths, for example, with a laser having a wavelength of 532 nm.

[0056] The absorption coefficient can be calculated from the transmittance measured using a spectrophotometer. The absorption coefficients at 355 nm and 1064 nm were evaluated using a Hitachi High-Technologies U2900 spectrophotometer.

[0057] In this embodiment, unless otherwise specified, the absorption coefficient is a value measured at room temperature (25° C.).

[0058] The absorption coefficient of the glass substrate can be adjusted by changing the glass composition of the glass substrate. ２ By reducing the content from 100%, the absorption coefficient A ３５５ and A １０６４ In addition, oxides of alkali metals such as sodium, oxides of alkaline earth metals such as calcium, and aluminum oxide tend to improve SiO ２ By replacing part of the composition of silica glass consisting only of ３５５ and A １０６４ On the other hand, if the amount of oxides of iron, chromium, cobalt, etc. is increased, the absorption coefficient tends to become even higher.

[0059] <Photoelastic Coefficient> The photoelastic coefficient of the glass substrate is preferably 3.4×10 －１２ / Pa or less, and more preferably 0.1 × 10 －１２ ~3.4 x 10 －１２ / Pa, and more preferably 0.5×10 －１２ ~3.3 x 10 －１２ / Pa, and more preferably 0.6×10 －１２ ~3.0 x 10 －１２ When the photoelastic coefficient of the glass substrate is within the above range, the readability of the glass substrate tends to be improved.

[0060] The photoelastic coefficient of the glass substrate was measured using a birefringence measurement device (WPA200 manufactured by Photonic Lattice, Inc.). The birefringence measurement device was positioned so that the optical path of the device was at the center of a glass substrate with a thickness of d (cm), and birefringence at a wavelength of 543 nm occurring at the center of the glass was measured while applying stress σ (Pa) to the glass substrate. If the optical path difference due to birefringence is δ (nm), the relationship δ = β × σ × d holds, and the photoelastic coefficient (β) can be calculated from the optical path difference value obtained by measurement. A compressive load or tensile load within the range of 0.1 to 5 MPa that does not cause damage to the glass substrate was applied as stress to the glass substrate, and the absolute values ​​of the optical path difference and birefringence were measured.

[0061] In this embodiment, unless otherwise specified, the photoelastic coefficient is a value measured at room temperature (25° C.).

[0062] The photoelastic coefficient of the glass substrate can be adjusted by changing the glass composition of the glass substrate. ２ By decreasing the content from 100%, the photoelastic coefficient tends to decrease. In addition, oxides of alkali metals such as sodium, oxides of alkaline earth metals such as calcium, and aluminum oxide can reduce the photoelastic coefficient. ２ By replacing a part of the composition of silica glass consisting only of quartz glass with fluorine, the photoelastic coefficient tends to be reduced. Note that external stresses such as fluttering caused by the rotation of the glass substrate during reading can cause birefringence, which may affect reading. The tendency for birefringence to occur in a glass substrate is proportional to the photoelastic coefficient, but is also affected by the stress to which the glass substrate is subjected and the thickness of the substrate. It is therefore preferable to set the composition so that birefringence due to external stress does not occur during reading.

[0063] <Young's Modulus> The Young's modulus of the glass substrate at room temperature is preferably 70 GPa or more, more preferably 70 to 120 GPa, even more preferably 71 to 110 GPa, and still more preferably 72 to 100 GPa.

[0064] When the Young's modulus is within the above range, the rigidity of the glass substrate 1 is improved, and the glass substrate is less likely to be displaced by external stress during reading, improving data reading.

[0065] The Young's modulus of the glass substrate can be adjusted by changing the glass composition of the glass substrate. ２ While keeping the content of Al below a certain level ２ O ３ Alternatively, by increasing the content of alkaline earth metal oxides, the Young's modulus tends to increase.

[0066] The Young's modulus of the glass substrate can be measured, for example, in accordance with the method described in JIS R1602:1995.

[0067] <Thermal expansion coefficient> The average value of the thermal expansion coefficient of the glass substrate at 100 to 300°C is preferably 45×10 －６ / °C or less, and more preferably 1.0 × 10 －６ ~40 x 10 －６ / °C, and more preferably 2.0 × 10 －６ ~30 x 10 －６ / °C, and even more preferably 3.0 x 10 －６ ~20 x 10 －６ / °C or less, and particularly preferably 3.5 × 10 －６ ~12 x 10 －６ / °C or less.

[0068] When the average value of the thermal expansion coefficient of the glass substrate is within the above range, deformation of the substrate when the inside of the recording device is subjected to high temperature conditions is suppressed, and therefore the ease of use and reading accuracy of the glass substrate at high temperatures tend to improve.

[0069] The thermal expansion coefficient of the glass substrate can be adjusted by changing the glass composition of the glass substrate. ２ O, Na ２ O and K ２ Decreasing the O content tends to decrease the thermal expansion coefficient.

[0070] <Refractive Index> The refractive index (R) of the glass substrate is preferably 1.30 to 1.70, more preferably 1.35 to 1.60. When the refractive index of the glass substrate is within the above range, the writability and readability of the glass substrate tend to be further improved. The refractive index of the glass substrate can be adjusted by changing the glass composition of the glass substrate. For example, SiO ２ The refractive index of the glass substrate can be measured, for example, according to the method described in JIS B 7071-1:2015.

[0071] <Density> The density (D) of the glass substrate is preferably 1.5 to 5.0 g / cm ３ and more preferably 1.7 to 4.0 g / cm ３ and more preferably 2.0 to 3.0 g / cm ３ and even more preferably 2.2 to 2.9 g / cm ３ and particularly preferably 2.3 to 2.8 g / cm ３ When the density of the glass substrate is within the above range, the processability of the glass substrate tends to be improved. The density of the glass substrate can be adjusted by changing the glass composition of the glass substrate. For example, SiO ２ The density tends to increase by decreasing the content.

[0072] The ratio of refractive index to density (R / D) of the glass substrate is preferably 0.30 to 0.65, more preferably 0.40 to 0.65, and even more preferably 0.50 to 0.65. When the ratio (R / D) of the glass substrate 1 is within the above range, the glass substrate tends to be able to achieve both processability, writability, and readability. The ratio (R / D) of the glass substrate can be adjusted by changing the glass composition of the glass substrate. For example, SiO ２ The ratio (R / D) tends to decrease by decreasing the content.

[0073] <Softening Point> The softening point of the glass substrate is preferably 1500°C or less, more preferably 300 to 1250°C, and even more preferably 500 to 1000°C. When the softening point of the glass substrate is within the above range, it tends to be possible to achieve both ease of use of the glass substrate at high temperatures and ease of processing of the glass substrate. The softening point of the glass substrate can be adjusted by changing the glass composition of the glass substrate. For example, SiO ２ The softening point tends to decrease by decreasing the content.

[0074] The softening point of the glass substrate can be measured, for example, in accordance with the method described in JIS R3103-1:2001.

[0075] <Internal Defects> The number of internal defects in the glass substrate is preferably 10 / cm ３ More preferably, 9 particles / cm or less. ３ More preferably, 8 particles / cm or less. ３ The internal defects are optically non-uniform parts such as parts that locally reduce light transmittance or parts where the refractive index changes locally. For example, tiny bubbles, foreign matter, and striae present inside the glass substrate are optically non-uniform parts. Alternatively, foreign matter and bubbles with a diameter of 10 μm or more are also examples of internal defects. When the number of internal defects in the glass substrate is within the above range, the writability and readability of the glass substrate tend to be improved.

[0076] The number of internal defects in a glass substrate can be adjusted by the manufacturing method of the glass substrate. For example, in manufacturing a glass substrate, the number of internal defects can be reduced by slowing down the cooling rate after melting the raw material.

[0077] <Retardation Value> The maximum retardation value when a stress of 0.1 MPa is applied to the glass substrate in the tensile or compressive direction is preferably 40 nm or less, more preferably 0 to 30 nm, and even more preferably 0 to 20 nm. When the maximum retardation value is within the above range, the writability and readability of the glass substrate tend to be improved. "Retardation" refers to the phase difference between light in the direction of the molecular main chain and light in the direction perpendicular thereto. Generally, glass substrates can be formed into any shape by heating and melting, but it is known that retardation occurs due to stress generated during the heating and cooling processes. In this specification, "retardation" refers to in-plane retardation unless otherwise specified.

[0078] The maximum retardation value can be adjusted by reducing residual stress inside the glass substrate by adjusting the glass composition of the glass substrate, controlling the thickness of the substrate and the pressure during molding, and adjusting the cooling conditions.

[0079] <Arithmetic mean roughness> The arithmetic mean roughness of the first main surface of the glass substrate is preferably 0.2 to 70 nm, more preferably 0.2 to 50 nm, and even more preferably 0.2 to 30 nm. When the arithmetic mean roughness is within the above range, light scattering on the first main surface of the glass substrate can be suppressed, and the writability and readability of the glass substrate tend to be improved. The arithmetic mean roughness of the first main surface of the glass substrate can be reduced by polishing the main surface. The arithmetic mean roughness can be measured in accordance with the method described in JIS B0601:2013.

[0080] The arithmetic mean roughness of the second main surface of the glass substrate is preferably 0.2 to 70 nm, more preferably 0.2 to 50 nm, and even more preferably 0.2 to 30 nm. When the arithmetic mean roughness is within the above range, writing and reading of information from the second main surface side of the glass substrate is facilitated, which is preferable.

[0081] <Flatness> The flatness of the first main surface of the glass substrate is preferably 30 μm or less, 0.1 to 25 μm, or 0.2 to 20 μm. When the flatness is within the above range, when light is irradiated from the first main surface side of the glass substrate to form an altered portion therein, the altered portion can be formed more accurately, and the writability and readability of the glass substrate tend to be improved. The flatness of the first main surface of the glass substrate can be reduced by polishing the main surface or by manufacturing the glass substrate on a flatter surface.

[0082] The flatness of the second main surface of the glass substrate is preferably 30 μm or less, 0.1 to 25 μm, or 0.2 to 20 μm. When the flatness is within the above range, writing and reading of information can be easily performed from the second main surface side of the glass substrate, which is preferable.

[0083] <Parallelism> The parallelism of the main surfaces of the glass substrate is preferably 30 μm or less, 1 to 25 μm, or 2 to 15 μm. When the parallelism is within the above range, when light is irradiated from the main surface side of the glass substrate to form an altered portion therein, the altered portion can be formed more accurately, and the writability and readability of the glass substrate tend to be improved. The parallelism of the main surfaces of the glass substrate can be reduced by using a double-side polisher during production of the glass substrate.

[0084] <Arithmetic mean roughness of outer peripheral edge surface> The arithmetic mean roughness of the outer peripheral edge surface of the glass substrate is preferably 2000 nm or less, more preferably 0.1 to 1500 nm, and even more preferably 0.2 to 1000 nm. When the arithmetic mean roughness is within the above range, the writability and readability of the glass substrate 1 tend to be improved. The arithmetic mean roughness of the outer peripheral edge surface of the glass substrate can be reduced by polishing the outer peripheral edge surface.

[0085] <Applications> The glass substrate of the first embodiment and the glass substrate of the second embodiment are used for data recording, in which information can be written by a laser. As described above, in the first embodiment, the glass substrate has a sodium ion concentration of 9000 ppm or less in the region from the first surface to 0.1 μm, and therefore has excellent long-term storage properties. Therefore, the glass substrate of the first embodiment is suitably used in applications where data is recorded over a long period of time. In addition, in the second embodiment, the glass substrate has a molar ratio (Na ２ O / R ２ Since the glass substrate of the second embodiment has a glass surface roughness (SSR) of 0.6 or less, it has excellent long-term storage properties. Therefore, the glass substrate of the second embodiment is suitable for use in applications where data is recorded over a long period of time. Furthermore, the glass substrates of both embodiments are suitable for use in recording devices. The recording device is a recording device that includes the glass substrate of this embodiment.

[0086] <Manufacturing Method> The manufacturing method of a glass substrate may include a glass substrate preparation step of preparing a glass substrate. In the glass substrate preparation step, a commercially available glass substrate may be purchased, or raw materials containing the elements to be contained in the glass substrate may be melted and mixed, and then slowly cooled and formed into a desired shape. The raw materials containing the elements are not limited to oxides, and may also be carbonates, nitrates, hydroxides, or simple substances.

[0087] The method for manufacturing a glass substrate includes a surface treatment step of reducing the sodium concentration on the surface of the glass substrate prepared as described above, wherein the glass substrate has a first main surface and a second main surface opposite to the first main surface, an outer peripheral edge surface constituting the outer periphery of the glass substrate is formed between the first main surface and the second main surface, the glass substrate has a thickness of 0.3 to 5.0 mm, and the glass substrate is made of a SiO 2 film containing 55 to 88 mol % of SiO 2 . ２ , 0 to 25 mol% Al ２ O ３ , 0 to 30 mol% B ２ O ３ The glass composition includes 0 to 25 mol % of alkali metal oxides and 0 to 25 mol % of alkaline earth metal oxides. Examples of the sodium concentration reduction treatment include sulfur treatment, hot concentrated sulfuric acid treatment, and ion exchange treatment.

[0088] In the sulfur treatment, the surface of the glass substrate is reacted with a sulfur compound at high temperature to selectively extract and remove sodium from the surface of the glass substrate. The reaction temperature is preferably 100 to 300°C. The reaction time is preferably 10 minutes to 10 hours, more preferably 1 to 5 hours. The sulfur compound is not particularly limited, but examples include ammonium hydrogen sulfate and ammonium sulfate.

[0089] In the hot concentrated sulfuric acid treatment, the surface of the glass substrate is reacted with hot concentrated sulfuric acid at a high temperature to selectively extract and remove sodium from the surface of the glass substrate. The reaction temperature is preferably 100 to 300° C. The reaction time is preferably 10 minutes to 10 hours, more preferably 1 to 5 hours.

[0090] In the ion exchange treatment, the surface of the glass substrate is reacted with an alkali metal compound other than sodium at a high temperature, and sodium on the surface of the glass substrate is replaced with the alkali metal contained in the alkali metal compound. The reaction temperature is preferably 200 to 500°C. The reaction time is preferably 10 minutes to 10 hours, more preferably 1 to 5 hours. The alkali metal compound is not particularly limited, but is a potassium compound such as potassium nitrate. The alkali metal compound is preferably in the form of a molten salt. The ion concentration ratio (Na ２ O / R ２ O) is preferably in the range of 0.4 to 0.6.

[0091] Only the first main surface of the glass substrate may be subjected to the surface treatment step, or both the first and second main surfaces may be subjected to the surface treatment.

[0092] [Additional Notes] The embodiments of the present disclosure include the following aspects: [1] A glass substrate for data recording, into which information can be written using a laser, the glass substrate having a first main surface and a second main surface opposite to the first main surface, an outer peripheral end face constituting the outer periphery of the glass substrate being formed between the first main surface and the second main surface, the glass substrate having a thickness of 0.3 to 5.0 mm, and the glass substrate having a SiO content of 55 to 88 mol % expressed in mol % on an oxide basis. ２ , 0 to 25 mol% Al ２ O ３ , 0 to 30 mol% B ２ O ３ %, 0 to 25 mol % of an alkali metal oxide, and 0 to 25 mol % of an alkaline earth metal oxide, and the concentration of sodium ions measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) in a region of the glass substrate to a depth of 0.1 μm from the first main surface is 9000 ppm or less. [2] A glass substrate for data recording into which information can be written using a laser, wherein the glass substrate has a first main surface and a second main surface opposite to the first main surface, and an outer peripheral end face constituting the outer periphery of the glass substrate is formed between the first main surface and the second main surface, the thickness of the glass substrate is 0.3 to 5.0 mm, and the glass substrate has a glass composition containing, in mole % on an oxide basis, 55 to 88 mol % of SiO ２ , 0 to 25 mol% Al ２ O ３ , 0 to 30 mol% B ２ O ３ , 0.01 to 25 mol % of alkali metal oxide (R ２ [3] A glass substrate having a glass composition containing, in mole percent on an oxide basis, 0.01 to 10 mol % of an alkali metal oxide (R O), and 0 to 25 mol % of an alkaline earth metal oxide, wherein the glass substrate is left in an environment of 85°C and 85% RH, and the haze value (%) measured after 240 hours is 20% or less. ２[4] The glass substrate according to [1] or [2], having a glass composition containing, in mole percent on an oxide basis, 5.0 mol % or less of Na. ２ The glass substrate according to any one of [1] to [3], having a glass composition containing O. [5] The glass substrate has an absorption coefficient A at a wavelength of 355 nm ３５５ 0.8 to 6.0 cm －１ [6] The glass substrate according to any one of [1] to [4], wherein the absorption coefficient A of the glass substrate at a wavelength of 1064 nm is １０６４ 0.6 to 2.0 cm －１ [7] The glass substrate according to any one of [1] to [5], wherein the photoelastic coefficient of the glass substrate is 3.4 × 10 －１２ [8] The glass substrate according to any one of [1] to [7], wherein the Young's modulus of the glass substrate is 70 GPa or more. [9] The glass substrate according to any one of [1] to [7], wherein the thermal expansion coefficient of the glass substrate is 45×10 －６

[10] The glass substrate according to any one of [1] to [8], wherein the refractive index (R) of the glass substrate is set to a value equal to or less than the density (D (g / cm ３

[11] The glass substrate according to any one of [1] to [9], wherein the value (R / D) obtained by dividing the internal defects of the glass substrate by the number of internal defects is 10 / cm. ３

[10] The glass substrate according to any one of [1] to

[10] , wherein the maximum retardation value of the glass substrate is 20 nm or less.

[12] The glass substrate according to any one of [1] to

[11] , wherein the maximum retardation value of the glass substrate is 20 nm or less.

[13] The glass substrate according to any one of [1] to

[12] , wherein the arithmetic mean roughness of the first main surface is 0.2 to 100 nm.

[14] The glass substrate according to any one of [1] to

[13] , wherein the flatness of the first main surface is 30 μm or less.

[15] The glass substrate according to any one of [1] to

[14] , wherein the parallelism of the first main surface is 30 μm or less.

[16] The glass substrate according to any one of [1] to

[15] , wherein the arithmetic mean roughness of the outer peripheral edge surface of the glass substrate is 2.0 μm or less.

[17] A method for manufacturing a glass substrate for data recording, into which information can be written by a laser, the manufacturing method comprising a surface treatment step of performing sodium concentration reduction treatment on a surface of the glass substrate, the glass substrate having a first main surface and a second main surface opposite to the first main surface, an outer peripheral end face constituting the outer periphery of the glass substrate being formed between the first main surface and the second main surface, the glass substrate having a thickness of 0.3 to 5.0 mm, and the glass substrate comprising 55 to 88 mol % SiO ２ , 0 to 25 mol% Al ２ O ３ , 0 to 30 mol% B ２ O ３ % of an alkali metal oxide and 0 to 25 mol % of an alkaline earth metal oxide.

[18] The manufacturing method according to

[17] , wherein the sodium concentration reduction treatment is a sulfur treatment or a hot concentrated sulfuric acid treatment.

[19] The manufacturing method according to

[17] , wherein the sodium concentration reduction treatment is an ion exchange treatment.

[0093] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited to the following examples. Unless otherwise specified, the experiments in the examples were carried out at room temperature (25°C).

[0094] The physical properties and shape of the glass substrates of each example were measured. Specifically, the measurements were as follows.

[0095] [Absorption Coefficient] The absorption coefficient of light at each wavelength was measured for the glass substrate of each example. Specifically, the absorption coefficient at 355 nm and 1064 nm was measured using a spectrophotometer U2900 manufactured by Hitachi High-Technologies Corporation.

[0096] [Photoelastic Coefficient] The photoelastic coefficient of each glass substrate was measured using a birefringence measuring device (WPA200 manufactured by Photonic Lattice, Inc.).

[0097] [Young's Modulus] The Young's modulus E of the glass substrate was measured in accordance with JIS R1602: 1995. A test piece for measurement was cut out from the glass substrate as a rectangular parallelepiped having a length of 50 mm, a width of 10 mm, and a thickness equal to the thickness of the glass substrate, and the measurement was carried out at room temperature.

[0098] [Thermal Expansion Coefficient] Regarding the thermal expansion coefficient of the glass substrate, a sample having dimensions of 50 mm in length and 10 mm in width was cut out from the glass substrate, and the change in length in a predetermined temperature range was determined using a thermal dilatometer based on laser interferometry, and this was taken as the average linear expansion coefficient value at 100 to 300°C.

[0099] [Density] The density was measured by the Archimedes method.

[0100] [Refractive Index] The refractive index (nd) was measured by the refractive index measurement method of JIS B 7071-1:2015.

[0101] [Softening Point] The softening point of the glass substrate was measured by the softening point measuring method specified in JIS R 3103-1:2001.

[0102] [Substrate Thickness] The thickness of the glass substrate of each example was measured with a micrometer.

[0103] [Number of Internal Defects] For each glass substrate, inspection light with a wavelength of 200 nm or less was irradiated onto the glass substrate, and the transmitted inspection light that passed through the substrate was received by a plate-shaped fluorescent member and converted into fluorescence. Internal defects in the substrate were detected from the intensity distribution of the fluorescence. Foreign matter and bubbles with a diameter of 10 μm or more were considered internal defects and the number of such defects was counted.

[0104] [Maximum Retardation Value] The maximum retardation value when a stress of 0.1 MPa was applied to the glass substrate of each example in the tensile or compressive direction was measured using a birefringence measuring device PA100 manufactured by Photonic Lattice Co., Ltd. The retardation value is obtained by measuring within the range of a circle centered on the centroid of the shape represented by the periphery of the glass substrate of each example, and drawing a circle tangent to the periphery. The maximum of these retardation values ​​was taken as the maximum retardation value.

[0105] [Arithmetic Mean Roughness of Main Surface] Using an AFM manufactured by Hitachi High-Technologies Corporation, the arithmetic mean roughness was measured in a region within a radius of 15 to 30 mm on one surface of the glass substrate.

[0106] [Arithmetic Mean Roughness of Outer Circumferential Edge Surface] The arithmetic mean roughness of the outer circumferential edge surface of the glass substrate was measured using a VK-X3000 laser microscope manufactured by Keyence Corporation.

[0107] [Flatness] The flatness was measured as the maximum height difference (PV value) on the surface of the glass substrate by using an Optiflat manufactured by KLA Corporation using interference fringes of a semiconductor laser.

[0108] [Parallelism] The parallelism of the glass substrate of each example was measured using a parallelism measuring device (Verifire™ laser interferometer, manufactured by ZYGO Corporation).

[0109] [Evaluation of Long-Term Storage Properties] For long-term storage, glass substrates are generally stored under mild conditions, such as room temperature and low humidity. In this example, the glass substrates were stored for a relatively short period under high temperature and high humidity conditions, and the color unevenness and cloudiness of the glass substrates were evaluated. If the degree of color unevenness and cloudiness of the glass substrate is small when the glass substrate is stored for a relatively short period under high temperature and high humidity conditions, it can be said that the degree of color unevenness and cloudiness of the glass substrate will also be small when the glass substrate is stored for a long period under general conditions for long-term storage of glass substrates (room temperature and low humidity). In other words, it can be said that the long-term storage properties of the glass substrate are high.

[0110] In this example, specifically, the long-term storage stability was evaluated as follows. That is, the glass substrates of various examples and comparative examples were subjected to an accelerated test in a high-temperature, high-humidity environment of 85°C and 85% RH (relative humidity) for 240 hours, and then the haze value (%) was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name NDH8000). It can be said that the smaller the haze value, the smaller the degree of color unevenness and cloudiness of the glass substrate.

[0111] [Examples 1 to 5, Comparative Examples 1 and 2] Glass substrates having the circular ring shape shown in Fig. 1 were produced using glasses having the compositions shown in Table 1. The diameter of the glass substrate was 97 mm, and the inner diameter was 25 mm. The thickness of the glass substrate was as shown in Table 2.

[0112] The glass substrates of Example 1 and Comparative Examples 1 and 2 were obtained by laser cutting from glass plates formed by the float process. The glass substrates of Examples 2, 3, and 5 were obtained by laser cutting from glass substrates formed by the down-draw process. The glass substrate of Example 4 was obtained as follows. First, a blank was formed by press molding, and then cut using a laser to obtain a glass substrate. The cut glass substrate was then annealed for 30 minutes at a temperature 150°C lower than the glass transition temperature (Tg) to reduce internal strain. Thus, the glass substrate of Example 4 was obtained. The glass substrates of each example obtained by various manufacturing methods were cut into a disk shape using a laser, and then polished so that the arithmetic mean roughness of the outer peripheral edge was 2.0 μm or less. Furthermore, they were polished using a cerium oxide polishing slurry or a silica oxide polishing slurry so that the arithmetic mean roughness of the first and second main surfaces was within the range of 0.2 to 100 nm.

[0113] Next, in order to prevent the written information from becoming difficult to read due to color unevenness or cloudiness caused by the occurrence of tarnish, the glass substrates of Examples 1 to 4 and Comparative Example 2 were subjected to a sodium concentration reduction treatment as shown in Table 1. Detailed conditions are shown below. Sulfur treatment: The surface of the glass substrate was treated by reacting it with ammonium sulfate at 100°C for 1 hour. Hot concentrated sulfuric acid treatment: The surface of the glass substrate was treated by reacting it with hot concentrated sulfuric acid at 130°C for 30 minutes. Ion exchange treatment: The surface of the glass substrate was brought into contact with a molten salt such as potassium nitrate for 3 hours to replace some of the sodium ions with potassium ions. The ion exchange treatment reduced the ratio of ion concentrations (Na ２ O / K ２ O) was set to be in the range of 0.4 to 0.6.

[0114]

[0115]

[0116] For each example, various physical properties were measured by the above-mentioned methods, and the results are shown in Table 2. The values ​​obtained as a result of the measurements regarding physical properties and shape are expressed in the units shown in the table.

[0117] In comparison with Comparative Examples 1 and 2, Examples 1 to 5 had smaller haze values.

[0118] 1... glass substrate, 10... first main surface, 12... second main surface, 14... outer peripheral edge, 16... spindle hole

Claims

1. A glass substrate for data recording in which information can be written by a laser, the glass substrate having a first main surface and a second main surface opposite to the first main surface, an outer peripheral end face constituting the outer periphery of the glass substrate being formed between the first main surface and the second main surface, the thickness of the glass substrate being 0.3 to 5.0 mm, and the glass substrate having a SiO content of 55 to 88 mol % expressed in mole % on an oxide basis. ２ , 0 to 25 mol% Al ２ O ３ , 0 to 30 mol% B ２ O ３ , 0 to 25 mol % of an alkali metal oxide, and 0 to 25 mol % of an alkaline earth metal oxide, wherein a sodium ion concentration measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) in a region of the glass substrate to a depth of 0.1 μm from the first main surface is 9000 ppm or less.

2. A glass substrate for data recording in which information can be written by a laser, the glass substrate having a first main surface and a second main surface opposite to the first main surface, an outer peripheral end face constituting the outer periphery of the glass substrate being formed between the first main surface and the second main surface, the thickness of the glass substrate being 0.3 to 5.0 mm, and the glass substrate having a SiO content of 55 to 88 mol % expressed in mol % on an oxide basis. ２ , 0 to 25 mol% Al ２ O ３ , 0 to 30 mol% B ２ O ３ , 0.01 to 25 mol % of alkali metal oxide (R ２ 0), and 0 to 25 mol % of an alkaline earth metal oxide, wherein the glass substrate is left in an environment of 85°C and 85% RH, and a haze value (%) measured after 240 hours has passed is 20% or less.

3. The glass substrate contains, in mole percent on an oxide basis, 0.01 to 10 mol % of an alkali metal oxide (R ２ The glass substrate of claim 2 , having a glass composition including:

4. The glass substrate contains 5.0 mol% or less of Na, expressed in mole percent on an oxide basis. ２ The glass substrate according to claim 1 , having a glass composition containing O.

5. Absorption coefficient A of the glass substrate at a wavelength of 355 nm ３５５ 0.8 to 6.0 cm －１ The glass substrate according to any one of claims 1 to 3, wherein 6. Absorption coefficient A of the glass substrate at a wavelength of 1064 nm １０６４ 0.6 to 2.0 cm －１ The glass substrate according to any one of claims 1 to 3, wherein 7. The photoelastic coefficient of the glass substrate is 3.4 × 10 －１２ The glass substrate according to claim 1 , wherein the viscosity is 1 / Pa or less.

8. The glass substrate according to any one of claims 1 to 3, wherein the glass substrate has a Young's modulus of 70 GPa or more.

9. The thermal expansion coefficient of the glass substrate is 45 x 10 －６ The glass substrate according to any one of claims 1 to 3, wherein the temperature is 100°C or lower.

10. The refractive index (R) of the glass substrate is calculated based on the density (D (g / cm ３ 4. The glass substrate according to claim 1 , wherein a value (R / D) obtained by dividing R by D is 0.3 to 0.

65.

11. The internal defects of the glass substrate are 10 / cm ３ The glass substrate according to any one of claims 1 to 3, wherein:

12. The glass substrate according to any one of claims 1 to 3, wherein the maximum retardation value of the glass substrate is 20 nm or less.

13. The glass substrate according to any one of claims 1 to 3, wherein the first main surface has an arithmetic mean roughness of 0.2 to 100 nm.

14. The glass substrate according to any one of claims 1 to 3, wherein the flatness of the first main surface is 30 μm or less.

15. The glass substrate according to any one of claims 1 to 3, wherein the parallelism of the first and second main surfaces is 30 μm or less.

16. The glass substrate according to any one of claims 1 to 3, wherein the arithmetic mean roughness of the outer peripheral edge surface of the glass substrate is 2.0 μm or less.

17. A method for manufacturing a glass substrate for data recording, into which information can be written by a laser, the manufacturing method comprising a surface treatment step of treating the surface of the glass substrate to reduce the sodium concentration, the glass substrate having a first main surface and a second main surface opposite to the first main surface, an outer peripheral end face constituting the periphery of the glass substrate being formed between the first main surface and the second main surface, the thickness of the glass substrate being 0.3 to 5.0 mm, and the glass substrate being made of a glass material having a SiO content of 55 to 88 mol %. ２ , 0 to 25 mol% Al ２ O ３ , 0 to 30 mol% B ２ O ３ %, 0 to 25 mol % of an alkali metal oxide, and 0 to 25 mol % of an alkaline earth metal oxide.

18. The manufacturing method according to claim 17, wherein the sodium concentration reduction treatment is a sulfur treatment or a hot concentrated sulfuric acid treatment.

19. The manufacturing method according to claim 17, wherein the sodium concentration reduction treatment is an ion exchange treatment.

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