Glass substrate

Abstract

The purpose of the present disclosure is to provide a glass substrate suitable for a recording medium inside of which information is inscribed by a laser. The present disclosure relates to a glass substrate for data recording inside of which information can be inscribed by a laser, the glass substrate having a first main surface and a second main surface facing the first main surface. An outer peripheral end surface 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 0.3-5.0 mm. The glass substrate has a glass composition, in mol% based on oxides, of 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. The glass substrate has an absorption coefficient A355 at a wavelength of 355 nm of 0.7 cm−1 or greater and an absorption coefficient A1064 at a wavelength of 1064 nm of 0.6-2.0 cm−1.

Description

Glass substrate

[0001] The present invention relates to 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 this embodiment is to provide a glass substrate suitable for a recording medium in which information is written by a laser.

[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 O ３, 0 to 25 mol % of alkali metal oxide, and 0 to 25 mol % of alkaline earth metal oxide, and the absorption coefficient A of the glass substrate at a wavelength of 355 nm ３５５ is 0.7 cm －１ or more, and the absorption coefficient A １０６４ 0.6 to 2.0 cm －１ The present invention relates to a glass substrate.

[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 to 25 mol % of an alkali metal oxide, and 0 to 25 mol % of an alkaline earth metal oxide, and the photoelastic coefficient of the glass substrate is 3.4 × 10 －１２ / Pa or less.

[0008] According to this embodiment, it is possible to provide a glass substrate suitable for a recording medium in which information is written by a laser.

[0009] FIG. 1 is a perspective view of a glass substrate according to an embodiment of the present invention.

[0010] 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.

[0011] [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 alkali metal oxide, and 0 to 25 mol % of alkaline earth metal oxide, and the absorption coefficient A of the glass substrate at a wavelength of 355 nm ３５５ is 0.7 cm －１ or more, and the absorption coefficient A １０６４ 0.6 to 2.0 cm －１ is.

[0012] From the viewpoint of efficiently writing and reading large amounts of data, it is preferable to process the recording medium into a shape that can be easily rotated, such as a disk shape. The recording method described in Patent Document 1 uses an optical recording medium, specifically, quartz glass. Quartz glass is made of SiO ２ It is a glass made solely of silica, and has high chemical stability and high visible light transmittance. However, because quartz glass is chemically stable, it was found to be unsuitable for processing into disk-shaped glass substrates by polishing or etching.

[0013] Instead of quartz glass, SiO ２ By using glass containing SiO and other substances as a recording medium, the processing rate can be increased in polishing treatment using cerium oxide or silica, or etching treatment using acid such as hydrofluoric acid, and the processability can be improved. ２Simply using it in combination with other substances makes it difficult to focus the laser light, reducing the ease of writing information to the recording medium, i.e., the writability, and further reduces the accuracy of writing using laser light in a specific wavelength band, making it difficult to improve the performance of writing information.

[0014] Therefore, an object of the present embodiment is to provide a glass substrate that is excellent in processability and laser writability.

[0015] The glass substrate having the above-described structure is excellent in processability and in writability with a laser, and also improves the writing performance by increasing the precision during writing.

[0016] <Absorption coefficient> Absorption coefficient A of a glass substrate at a wavelength of 355 nm ３５５ is 0.7 cm －１ or more, and the absorption coefficient A １０６４ 0.6 to 2.0 cm －１ When writing information on a glass substrate, for example, laser light is focused to form altered portions such as multiple recording dots with a refractive index different from that of the surrounding area. In addition, by adjusting the shape, size, orientation and degree of alteration of the altered portions, the altered portions formed on the glass substrate cause birefringence in the light, allowing the information to be read as data. Here, when a laser is irradiated onto the glass substrate, the altered portions are easily formed, improving the writability, and further, forming the altered portions with high precision allows for miniaturization. From this perspective, in the glass substrate, the absorption coefficient A at a wavelength of 355 nm is ３５５ is 0.7 cm －１ or more, and the absorption coefficient A １０６４ 0.6 to 2.0 cm －１ It is stipulated that:

[0017] If the absorption coefficient at a certain wavelength is large, light of that wavelength is well absorbed, and an altered portion is likely to form inside the glass substrate. ３５５ is 0.7 cm －１ or more, and the absorption coefficient A １０６４0.6 to 2.0 cm －１ This makes it possible to obtain a glass substrate on which information can be easily written by using lasers with a wide range of wavelengths, from low wavelength bands to high wavelength bands, in the altered portions, such as recording dots. Furthermore, if the absorption coefficient at a wavelength of 355 nm is small, the processing accuracy by the laser tends to decrease, making it difficult to miniaturize the altered portions.

[0018] Absorption coefficient A ３５５ is preferably 0.70 to 6.50 cm －１ and more preferably 0.70 to 4.00 cm －１ and more preferably 0.75 to 3.00 cm －１ and even more preferably 0.80 to 3.00 cm －１ and particularly preferably 0.95 to 2.00 cm －１ The absorption coefficient A ３５５ By keeping the absorption coefficient A within the above range, the writability with light of 355 nm wavelength tends to improve, and a glass substrate with high processing accuracy with laser light of a predetermined wavelength can be obtained. In other words, by using a glass substrate with high processing accuracy in which the absorption coefficient with laser light of the low wavelength band of 355 nm falls within a predetermined range, recording dots can be formed with high accuracy, and therefore a glass substrate for high-capacity data recording can be obtained. ３５５ When the value is equal to or less than the predetermined value, the affected portion can be formed at an appropriate position in the plate thickness direction.

[0019] Absorption coefficient A １０６４ is preferably 0.62 to 1.80 cm －１ and more preferably 0.64 to 1.60 cm －１ and more preferably 0.66 to 1.40 cm －１ and even more preferably 0.68 to 1.00 cm －１ and particularly preferably 0.68 to 0.80 cm －１ The absorption coefficient A １０６４By having the absorption coefficient A within the above range, for example, the writability with light of 1064 nm wavelength tends to be improved, and a glass substrate with high processing uniformity with laser light of a predetermined wavelength can be obtained. In other words, by using an easily processable glass substrate with an absorption coefficient A within a predetermined range with laser light in the high wavelength band of 1064 nm, recording dots can be easily formed with laser light, and therefore a glass substrate for data recording with high laser processing performance can be obtained. １０６４ When the value is equal to or less than the predetermined value, the affected portion can be formed at an appropriate position in the plate thickness direction.

[0020] 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 １０６４ By setting the wavelength of the recording medium within a predetermined range, the writability with lasers having a wide range of wavelengths tends to improve, and for example, the writability with a laser having a wavelength of 532 nm improves.

[0021] 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 spectrophotometer U2900 manufactured by Hitachi High-Technologies Corporation.

[0022] In this embodiment, unless otherwise specified, the absorption coefficient is a value measured at room temperature (25° C.).

[0023] 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 of３５５ 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.

[0024] [Second Embodiment] A glass substrate according to a second 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 % 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 to 25 mol % of an alkali metal oxide, and 0 to 25 mol % of an alkaline earth metal oxide, and the photoelastic coefficient of the glass substrate is 3.4 × 10 －１２ / Pa or less.

[0025] From the viewpoint of efficiently writing and reading large amounts of data, it is preferable to process the recording medium into a shape that can be easily rotated, such as a disk shape. The recording method described in Patent Document 1 uses an optical recording medium, specifically, quartz glass. Quartz glass is made of SiO ２ It is a glass made solely of silica, and has high chemical stability and high visible light transmittance. On the other hand, because quartz glass is chemically stable, it was found to be unsuitable for processing as a substrate by polishing or etching.

[0026] By using glass containing SiO2 and other substances instead of quartz glass as a recording medium, the hardness is reduced, and the processing rate can be increased in polishing treatment using cerium oxide or silica, or etching treatment using acid such as hydrofluoric acid, improving processability. On the other hand, when reading from a glass substrate on which information has been written by utilizing the birefringence of light in the altered portion, the information is affected by the characteristics of the glass substrate and the external environment, so it is difficult to simply use SiO２ It has been found that the ease of reading information from a recording medium, that is, readability, tends to decrease simply by using a substrate made of a glass composition containing other metal oxides.

[0027] Therefore, an object of the present embodiment is to provide a glass substrate that is excellent in processability and readability.

[0028] The glass substrate having the above-described structure has excellent processability and laser readability.

[0029] <Photoelastic Coefficient> The glass substrate of this embodiment has a photoelastic coefficient of 3.4×10 －１２ / Pa or less. Therefore, birefringence is less likely to occur due to external stress applied to the glass substrate, and written information tends to be easier to read based on the optical information contained in the altered portion. In other words, the readability of the glass substrate tends to improve. When information is written to a glass substrate using a laser, the data is written as an altered portion within the glass substrate. The altered portion has not only three-dimensional position information within the glass substrate, but also size information in the vertical, horizontal, and thickness directions relative to the glass substrate, as well as optical information based on the orientation and orientation of the altered portion. In other words, the altered portion has five-dimensional information combining the above positional information and the above optical information in addition to three-dimensional size information. When reading information from the glass substrate, the written information is read by reading the five-dimensional information of the altered portion. Here, since the glass substrate has a low photoelastic coefficient, birefringence due to external stress is less likely to occur. When reading information derived from the optical information written in the altered portion with light, the influence of birefringence caused by external stress is reduced, preventing read errors and making it easier to read the written information. On the other hand, when the photoelastic coefficient is 3.4 × 10 －１２ A glass substrate with a modulus exceeding 1 / Pa is prone to birefringence due to distortion in the molecular structure or external force, resulting in a decrease in reading accuracy.

[0030] The photoelastic coefficient of the glass substrate is 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 1 is within the above range, the readability of the glass substrate 1 tends to be improved.

[0031] 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 used as the stress on the glass substrate, and the absolute values ​​of the optical path difference and birefringence were used.

[0032] In this embodiment, unless otherwise specified, the photoelastic coefficient is a value measured at room temperature (25° C.).

[0033] 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.

[0034] Preferred aspects of the first and second embodiments will be described below.

[0035] <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 The glass substrate has a glass composition containing 0 to 25 mol % of an alkali metal oxide and 0 to 25 mol % of an alkaline earth metal oxide. This tends to achieve both strength and workability. The glass composition of the glass substrate may consist of these components.

[0036] SiO ２ is a glass network forming component. SiO ２ From 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 80.0 mol %, more preferably 57.5 to 77.5 mol %, and even more preferably 60.0 to 75.0 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.

[0037] 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 2.5 to 20.0 mol %.

[0038] B ２ O ３ is a glass network forming component. ２ O ３ The content is preferably 0.0 to 10.0 mol %, more preferably 0.5 to 7.5 mol %, and even more preferably 1.0 to 5.0 mol %.

[0039] The alkali metal oxides include Li ２ O, Na ２ O.K. ２O. The glass substrate may or may not contain an alkali metal oxide, and when it contains an alkali metal oxide, the content thereof is preferably 0.1 to 30.0 mol %, more preferably 0.5 to 27.5 mol %, and even more preferably 1.0 to 25.0 mol %.

[0040] 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.

[0041] Na as alkali metal oxide ２ It 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 When the O content is within the above range, the processability of the glass substrate tends to be improved.

[0042] 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 %.

[0043] 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 tends to be improved.

[0044] The alkaline earth metal oxide may or may not contain MgO. When MgO is contained, the content thereof is preferably 0.5 to 20.0 mol %, more preferably 1.0 to 17.5 mol %, and even more preferably 2.5 to 15.0 mol %, from the viewpoint of adjusting the Young's modulus and improving the processability of the glass substrate.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The glass composition of the glass substrate 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 %.

[0049] The glass substrate preferably contains one or more materials selected from the group consisting of soda-lime glass, aluminosilicate glass, and alkali-free glass. This tends to improve the writability of the glass substrate. Soda-lime glass is glass containing Si, Na, and Ca. Aluminosilicate glass is glass containing 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.

[0050] 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.

[0051] 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%.

[0052] 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%.

[0053] 1 is a perspective view showing an example of a glass substrate according to this embodiment. The glass substrate 1 has a first main surface 10 and a second main surface 12 opposite the first main surface 10, and an outer peripheral end face 14 constituting the outer periphery of the glass substrate 1 is formed between the first main surface 10 and the second main surface 12. In addition, there is a spindle hole 16 that penetrates from the first main surface 10 to the second main surface 12. Note that the glass substrate 1 does not necessarily have to have the spindle hole 16.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] <Thickness> The thickness of the glass substrate 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 is within the above range, the writability of the glass substrate tends to be improved.

[0058] <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.

[0059] 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.

[0060] 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.

[0061] The Young's modulus of the glass substrate can be measured, for example, in accordance with the method described in JIS R1602:1995.

[0062] <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.

[0063] 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 the ease of use and reading accuracy of the glass substrate at high temperatures tend to improve.

[0064] The thermal expansion coefficient of the glass substrate can be adjusted by changing the glass composition of the glass substrate. ２ O, Na２ O and K ２ Decreasing the O content tends to decrease the thermal expansion coefficient.

[0065] <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.

[0066] <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.

[0067] 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.

[0068] <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.

[0069] The softening point of the glass substrate can be measured, for example, in accordance with the method described in JIS R3103-1:2001.

[0070] <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.

[0071] 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.

[0072] <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.

[0073] 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.

[0074] <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.

[0075] 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.

[0076] <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.

[0077] 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.

[0078] <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.

[0079] <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.

[0080] <Manufacturing Method> The method for manufacturing the glass substrate is not particularly limited, but may include, for example, a method in which raw materials containing the elements to be contained in the glass substrate are melted and mixed, then formed into a desired shape, and slowly cooled. The raw materials containing the elements are not limited to oxides, but may also be carbonates, nitrates, hydroxides, or simple substances.

[0081] <Use> 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, the absorption coefficient A ３５５ and absorption coefficient A １０６4 Since the optical properties of the glass substrate of the second embodiment are within the above-mentioned numerical ranges, it is easy to write information therein using a laser with a wavelength of 355 nm and a laser with a wavelength of 1064 nm. Furthermore, since the photoelastic coefficient of the glass substrate of the second embodiment is within the above-mentioned numerical ranges, it is easy to read information written using a laser. Furthermore, the glass substrates of both embodiments are suitable for use in a recording device. The recording device is a recording device equipped with a glass substrate.

[0082] [Note] 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 alkali metal oxide, and 0 to 25 mol % of alkaline earth metal oxide, and the absorption coefficient A of the glass substrate at a wavelength of 355 nm ３５５ is 0.7 cm －１ or more, and the absorption coefficient A １０６４ 0.6 to 2.0 cm －１ [2] The glass substrate, ３５５ 0.8 to 6.0 cm －１[3] 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 % 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 photoelastic coefficient of the glass substrate is 3.4 × 10 －１２ [4] The glass substrate according to any one of [1] to [3], wherein the Young's modulus of the glass substrate is 70 GPa or more. [5] The thermal expansion coefficient of the glass substrate is 45×10 －６ [6] The glass substrate according to any one of [1] to [4], wherein the refractive index (R) of the glass substrate is set to a value of 0.01 / °C or less. ３ [7] The glass substrate according to any one of [1] to [5], wherein the value (R / D) obtained by dividing the internal defects of the glass substrate by the internal defects of the glass substrate is 0.3 to 0.65. ３ [8] The glass substrate according to any one of [1] to [7], wherein the maximum retardation value of the glass substrate is 20 nm or less. [9] The glass substrate according to any one of [1] to [8], wherein the arithmetic mean roughness of the first main surface is 0.2 to 100 nm.

[10] The glass substrate according to any one of [1] to [9], wherein the flatness of the first main surface is 30 μm or less.

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

[10] , wherein the parallelism of the first and second main surfaces is 30 μm or less.

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

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

[0083] 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).

[0084] The physical properties and shape of the glass substrates of each example were measured. Specifically, the measurements were as follows.

[0085] [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.

[0086] [Photoelastic Coefficient] The photoelastic coefficient of each glass substrate was measured using a birefringence measuring device (WPA200 manufactured by Photonic Lattice, Inc.).

[0087] [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.

[0088] [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.

[0089] [Density] The density was measured by the Archimedes method.

[0090] [Refractive Index] The refractive index (nd) was measured by the refractive index measurement method of JIS B 7071-1:2015.

[0091] [Softening Point] The softening point of the glass substrate was measured by the softening point measuring method specified in JIS R 3103-1:2001.

[0092] [Substrate Thickness] The thickness of the glass substrate of each example was measured with a micrometer.

[0093] [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.

[0094] [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.

[0095] [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.

[0096] [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.

[0097] [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 and interference fringes of a semiconductor laser.

[0098] [Parallelism] The parallelism of the glass substrate of each example was measured using a parallelism measuring device (Verifire™ laser interferometer, manufactured by ZYGO Corporation).

[0099] [Readability Evaluation] The maximum retardation value was measured when a stress of 0.1 MPa was applied to the glass substrate of each example in the tensile direction, and the glass substrate was evaluated based on the following evaluation criteria: <Evaluation Criteria> A: The maximum retardation value of the glass substrate was 20 nm or less B: The maximum retardation value of the glass substrate was more than 20 nm and less than 40 nm C: The maximum retardation value of the glass substrate was more than 40 nm Glass substrates with a maximum retardation value of more than 40 nm will experience birefringence in the glass substrate due to external stress during reading, which can hinder reading of the recording dots and cause reading errors.

[0100] [Evaluation of writability] A femtosecond pulse laser beam (10 J / cm) having a wavelength of 1064 nm was applied to the glass substrate of each example. ２ ) at a speed of 0.5 seconds / cm to cut the glass substrate. The arithmetic mean roughness Ra of the cut surface within a 10 μm square area was measured using an AFM, and the cut surface was photographed using an SEM and evaluated based on the following evaluation criteria. The arithmetic mean roughness Ra is a value defined in accordance with JIS B 0601:2013. <Evaluation Criteria> A: The arithmetic mean surface roughness Ra of the cut surface is 0.2 μm or less, and no scratches such as cracks are observed on the surface of the cut surface. B: The arithmetic mean surface roughness Ra of the cut surface is more than 0.2 μm and less than 0.4 μm, and partial cracks due to cracks are observed. C: The arithmetic mean surface roughness Ra of the cut surface is more than 0.4 μm.

[0101] An altered portion is formed inside the glass substrate due to absorption of the irradiated laser light. The glass substrate is then cut starting from this altered portion. Therefore, a low and uniform arithmetic mean surface roughness Ra of the cut surface means that the glass substrate can be cut with higher precision, that is, the altered portion is more likely to be formed inside the glass substrate, and the altered portion can be formed finely and accurately.

[0102] [Examples 1 to 6, 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.

[0103] The glass substrates of Examples 1 and 2 were obtained by laser cutting from glass plates formed by the float process. The glass substrates of Examples 3, 5, and 6 and Comparative Example 2 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. The glass substrate of Example 4 was obtained. The glass substrate of Comparative Example 1 was obtained by solidifying molten glass to form an ingot, slicing it into a blank, and then cutting it using a laser. 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.

[0104]

[0105]

[0106] 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.

[0107] 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 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 alkali metal oxide, and 0 to 25 mol % of alkaline earth metal oxide, and the absorption coefficient A of the glass substrate at a wavelength of 355 nm ３５５ is 0.7 cm －１ or more, and the absorption coefficient A １０６４ 0.6 to 2.0 cm －１ That is, a glass substrate.

2. The absorption coefficient A ３５５ 0.8 to 6.0 cm －１ The glass substrate according to claim 1 , 3. 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 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, and the photoelastic coefficient of the glass substrate is 3.4 × 10 －１２ / Pa or less.

4. 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.

5. 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.

6. 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.

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

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

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