JPWO2017204143A1 - Glass for data storage medium substrate, glass substrate for data storage medium, and magnetic disk - Google Patents

Abstract

  The present invention provides a glass for a data storage medium substrate, a glass substrate for a data storage medium made of the glass, and a magnetic disk, wherein the glass is easy to recognize in the manufacturing process and it is easy to search for glass fragments generated by cracking or chipping. provide. The present invention relates to a glass for a data storage medium substrate having a specific range of glass composition and a specific range of transmittance at a wavelength of 450 nm and a wavelength of 250 nm.

Description

  The present invention relates to a glass used for a data storage medium such as a magnetic disk or an optical disk, a glass substrate made of the glass, and a magnetic disk.

  In recent years, with the increase in storage capacity of hard disk drives, high recording density has been advanced at a high pace. However, along with the increase in recording density, there is a problem that the miniaturization of the magnetic particles impairs the thermal stability and the crosstalk and the SN ratio of the reproduced signal are lowered. Therefore, thermally assisted magnetic recording technology has attracted attention as a technology for combining light and magnetism.

  In thermally assisted magnetic recording technology, laser light or near-field light is irradiated to the magnetic recording layer, and the external magnetic field is applied and recorded in a state where the coercivity of the locally heated portion is decreased, and recording with a GMR element etc. It is a technology to read the magnetization. According to the thermally assisted magnetic recording technology, since recording can be performed on a high coercive force medium, it is possible to miniaturize the magnetic particles while maintaining the thermal stability.

  In order to form a high coercivity medium as a multilayer film on a substrate by heat assisted magnetic recording technology, it is necessary to heat the substrate sufficiently, and as a glass for a substrate, it has high heat resistance, high Young's modulus and low expansion. An alkali-free glass having the following is proposed (e.g., Patent Document 1).

Japanese Patent Laid-Open Publication No. 2015-28828

  The manufacturing process of the glass substrate for magnetic disk has several steps of polishing and cleaning steps. Also, the removal of the glass is done by human work. Non-alkali glass and low-alkali glass are difficult to be chemically strengthened by ion exchange treatment, or compressive stress due to chemical strengthening is small, so cracking or chipping occurs in manufacturing processes such as polishing processes where high smoothness is required. Likely to happen.

  Therefore, it may be necessary to confirm the condition of the glass for adjustment of the process conditions etc. However, since the glass is colorless and transparent, it is difficult to recognize in the manufacturing process, and once broken, there is broken glass or broken glass. If it occurs, it is difficult to find it in the slurry solution or the like used in the manufacturing process, and the productivity is reduced. In addition, if glass fragments remain in the manufacturing process, such fragments lead to the generation of defects such as scratches on the glass, which lowers productivity.

  Therefore, according to the present invention, a glass for a data storage medium substrate, a glass substrate for a data storage medium made of the glass, and a magnetism, which are easy to recognize glass in a manufacturing process and easy to search for glass fragments generated by cracking or chipping The purpose is to provide a disc.

  The present inventors include an element which emits light upon UV irradiation in an alkali-free glass or a low alkali glass, to control the glass composition in an optimum range, and to set the transmittance at a wavelength of 450 nm and a wavelength of 250 nm to a specific range. The inventors have found that although they are usually colorless and transparent, they emit light at a visible light wavelength by UV irradiation with a wavelength of 250 to 370 nm and can easily visually recognize the glass, thereby completing the present invention.

The present invention, in a molar percentage based on oxides, SiO ₂ 55 to 80%, the _Al 2 _{O 3 6~18%,} the B 2 _{O 3} containing less than 12% or more 0%, MgO, CaO, SrO and _8-26% in total of the content at least one of _{BaO (RO), Li 2 O} , the sum of the content at least one of Na ₂ O and _{K 2} O _{(R 2} O) 10% or less, at least one of a light emitting element SnO ₂ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , WO ₃ , MoO ₃ and CeO ₂ in a total content of 0.03 The glass for a data storage medium substrate, which contains at least 80% of transmittance at a wavelength of 450 nm at a thickness of 0.5 mm and 0.2% or more at a wavelength of 250 nm is provided.

  Further, the present invention provides a glass substrate for data storage medium comprising the glass for data storage medium substrate, and a magnetic disk having a magnetic recording layer formed on the glass substrate for data storage medium.

  The glass for a data storage medium substrate of the present invention is a non-alkali glass that exhibits high heat resistance and also has high Young's modulus, high specific elasticity, and low expansion, and thus is suitable for thermally assisted magnetic recording, a data storage medium Recording density can be further increased. In addition, since the glass for data storage medium substrate of the present invention is an optimal composition capable of emitting fluorescence when irradiated with UV, it can be easily visually recognized by UV irradiation, recognition of the glass in the manufacturing process, The visual search for glass fragments due to breakage or chipping is easy, and the occurrence of defects due to the glass fragments can be significantly suppressed.

  The glass for data storage medium substrates of the present invention (hereinafter sometimes referred to simply as the glass of the present invention) is used as a substrate for data storage media such as a magnetic disk or an optical disk. In addition, unless otherwise stated, a composition is described by the molar percentage on the basis of an oxide.

  Moreover, in the present specification, “-” indicating a numerical range is used in a meaning including the numerical values described before and after it as the lower limit value and the upper limit value, and unless otherwise specified, “-” in the present specification "Is used with the same meaning.

  The glass of the present invention has a transmittance of 80% or more, preferably 85% or more, more preferably 90% or more, still more preferably 90.5% or more, particularly at a wavelength of 450 nm and a thickness of 0.5 mm. Preferably it is 91% or more. The upper limit is not particularly limited, but is usually 95% or less. When the transmittance at a wavelength of 450 nm is 80% or more, the fluorescence emitted by UV irradiation can be prevented from being absorbed by the glass.

As a method for setting the transmittance at a wavelength of 450 nm to 80% or more, for example, the content of a coloring agent such as Fe ₂ O which absorbs the wavelength in the visible range when contained in glass and lowers the transmittance is The percentage by mass may be 1% or less.

  The glass of the present invention has a transmittance of 0.2% or more, preferably 0.5% or more, more preferably 2% or more, still more preferably 4% or more at a wavelength of 250 nm and a thickness of 0.5 mm. Particularly preferably, it is 6% or more, more preferably 8% or more, and most preferably 10% or more. The upper limit is not particularly limited, but is usually 30% or less, more preferably 20% or less, still more preferably 18% or less, particularly preferably 16% or less, more preferably 15% or less, and most preferably 14% or less.

  When the transmittance at a wavelength of 250 nm with a thickness of 0.5 mm is 0.2% or more, it is possible to suppress that the UV light is rapidly attenuated on the glass surface and hard to pass through the inside of the glass. As a result, it is possible to prevent the narrowing of the light emitting region and to suppress the weakening of the visible fluorescence. In addition, it is possible to prevent the fluorescence emitted in the ultraviolet region from being attenuated, and to suppress the light emission due to the glass being excited again by the fluorescence.

Further, by setting the transmittance at a wavelength of 250 nm at a thickness of 0.5 mm to be 30% or less, it is preferable because a large amount of SiO ₂ , B ₂ O ₃ or P ₂ O ₅ may not be contained. If a large amount of SiO ₂ is contained, it becomes difficult to dissolve, and if a large amount of B ₂ O ₃ or P ₂ O ₅ is contained, the weather resistance and heat resistance may be lowered.

Examples of the method for setting the transmittance at a wavelength of 250 nm at a thickness of 0.5 mm to 0.2% or more include the following methods (1) and (2).
(1) When cooling the molten glass, the cooling rate is set to 400 ° C./min or less in the range of Tg + 50 ° C. to Tg + 20 ° C. with respect to the glass transition point Tg.
The transmission at a wavelength of 250 nm with a thickness of 0.5 mm depends on the cooling rate of the glass at a temperature near the glass transition temperature. That is, by reducing the cooling rate of the glass, the structural relaxation of the glass proceeds and the transmittance tends to increase. Further, a temperature distribution occurs during cooling, residual stress remains, and the substrate is warped. In order to prevent it, it is preferable to set it as 400 degrees C / min or less in the range of Tg + 50 degreeC-Tg + 20 degreeC. It is more preferably 300 ° C./minute or less, still more preferably 200 ° C./minute or less, particularly preferably 100 ° C./minute or less, still more preferably 50 ° C./minute or less, and most preferably 10 ° C./minute or less. The lower limit is preferably 0.2 ° C./min or more from the viewpoint of shortening the production time.

  It is considered that a change in the glass structure occurs because the glass slowly cooled at 0.5 ° C./min has a higher density than the glass cooled rapidly. The density of the glass according to the cooling rate is the density Db of the glass after cooling the glass at a temperature of Tg + 30 ° C. for a fixed time at a temperature of Tg ° C./min. It is represented by an increase (Db-Da) / Da x 100 (%), and this is taken as the amount of density change.

  The amount of density change of the glass of the present invention is preferably 0.01% or more, more preferably 0.05% or more, and still more preferably, from the viewpoint of controlling the transmittance at a wavelength of 250 nm within a predetermined range. It is 0.09% or more, more preferably 0.11% or more, and particularly preferably 0.13% or more. The amount of density change of the glass of the present invention is preferably 1% or less, more preferably 0.5% or less, still more preferably 0.4% or less, and still more preferably 0.3% or less And particularly preferably 0.2% or less.

(2) Adjust the composition of the glass as appropriate.
For example, from the viewpoint of reducing the absorption at a wavelength of 250 nm, the content of coloring components such as Fe ₂ O ₃ should be 1 mol% or less, SnO ₂ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ And at least one of WO ₃ , MoO ₃ and CeO ₂ in a total content of not more than 1 mol%, and the total content of SiO ₂ , B ₂ O ₃ or P ₂ O ₅ is 60 mol % Or more or a combination thereof.

  Next, the composition (content of each component) of the glass for a substrate of the present invention will be described on the basis of oxide in terms of mole percentage unless otherwise specified.

SiO ₂ is an essential component that forms the skeleton of glass. The content of SiO ₂ is 55% or more, preferably 60% or more, more preferably 62% or more, and particularly preferably 65% or more. In addition, it is 80% or less, preferably 74% or less, more preferably 73% or less, particularly preferably 72% or less, and still more preferably 71% or less.

By setting the content of SiO ₂ to 55% or more, it is possible to prevent the glass from becoming unstable and the glass transition point and the chemical resistance being lowered. Furthermore, the transmittance at a wavelength of 250 nm can be increased. Further, by setting the content of SiO ₂ to 80% or less, the thermal expansion coefficient does not become too small, and it can be prevented that the melting temperature for producing glass becomes too high.

Al ₂ O ₃ has an effect of enhancing the chemical resistance and the glass transition point of glass and is an essential component. The content of Al ₂ O ₃ is 6% or more, preferably 8% or more, more preferably 10% or more, still more preferably 11% or more, particularly preferably 12% or more, and most preferably Preferably it is 13% or more. Also, it is 18% or less, preferably 17% or less, more preferably 16% or less, still more preferably 15% or less, and particularly preferably 14% or less.

The content of Al ₂ O ₃ by 6% or more, it is possible to obtain the effect. Further, by setting the content to 18% or less, it is possible to prevent the viscosity of the molten glass from becoming too high, and it becomes possible to prevent the molding, particularly the float molding from becoming difficult. Moreover, it can prevent that liquidus temperature becomes high too much.

B ₂ O ₃ can be contained in an amount of less than 12% from the viewpoint of enhancing the dissolution reactivity of the glass, lowering the devitrification temperature, and enhancing the transmittance at a wavelength of 250 nm as described above. However, the content of B ₂ O ₃ is preferably as small as it tends to easily inhibit light emission. The content of B ₂ O ₃ is less than 12%, preferably less than 3%, more preferably less than 1%, still more preferably less than 0.5%, particularly preferably less than 0.2% .

  MgO may be contained from the viewpoint of lowering the viscosity of the molten glass to facilitate melting of the glass and increasing the Young's modulus. The content of MgO is preferably 13% or less, more preferably 11% or less, still more preferably 10% or less, and particularly preferably 8% or less. By setting the content of MgO to 13% or less, inhibition of light emission can be suppressed. Although a minimum is not specifically limited, When containing MgO, it is preferable to contain 1% or more.

  CaO may be contained from the viewpoint of lowering the viscosity of the molten glass, increasing the Young's modulus, or making the glass easy to melt. The content of CaO is preferably 12% or less, more preferably 11% or less, still more preferably 10.5% or less, and particularly preferably 10% or less. Moreover, it is preferable that it is 2% or more, More preferably, it is 2.5% or more, More preferably, it is 3% or more, Especially preferably, it is 3.5% or more. By setting the content of CaO to 12% or less, the inhibition of light emission can be suppressed.

  SrO may be contained from the viewpoint of lowering the viscosity of the molten glass to facilitate melting of the glass. The content of SrO is preferably 10% or less, more preferably 7% or less, still more preferably 5% or less, particularly preferably 4% or less, more preferably 3% or less, Most preferably, it is 2.5% or less. By setting the content of SrO to 10% or less, the specific gravity does not become too heavy, and the decrease in specific elasticity can be suppressed. Although a minimum is not specifically limited, When containing SrO, it is preferable to contain 1% or more.

  BaO may be contained from the viewpoint of raising the glass transition temperature and lowering the viscosity of the molten glass to make the glass easy to melt. The content of BaO is preferably 6% or less, more preferably 5.5% or less, still more preferably 5% or less, and particularly preferably 4.8% or less.

  By setting the content of BaO to 6% or less, the specific gravity can be reduced and the decrease in specific elastic modulus can be prevented. Although a minimum is not specifically limited, When containing BaO, it is preferable to contain 0.5% or more.

  The total content (RO) of the content of MgO, CaO, SrO and BaO is 2% or more, preferably 5% or more, more preferably 8% or more, and still more preferably 10% or more. It is preferably 12% or more, more preferably 14% or more, and most preferably 15% or more. If the total content of MgO, CaO, SrO and BaO is 2% or more, the viscosity of the molten glass can be produced to a sufficient extent. Also, it is 26% or less, preferably 20% or less, more preferably 19% or less, still more preferably 18% or less, particularly preferably 17% or less, more preferably 16.5% or less Most preferably 16% or less. If the total content of MgO, CaO, SrO and BaO is 26% or less, the glass transition point becomes a certain value or more, and there is no possibility of deformation even in the heat treatment in the magnetic disk manufacturing process.

Preferred _{B 2 O 3, MgO, CaO} , as the composition range of SrO and BaO, in (1) and (2) are mentioned below.

(1) 0% or more and less than 3% of B ₂ O ₃ , 0% to 6.5% of MgO, 0% to 12% of CaO, and 0 to 7% of SrO.
Among the alkaline earth metals, MgO, CaO and B ₂ O ₃ tend to inhibit light emission, so the contents of MgO, CaO and B ₂ O ₃ are preferably both low.
More preferably, B ₂ O ₃ is at least 0.5%, more preferably at least 1%, in order to reduce thermal expansion and to facilitate dissolution. Moreover, in order not to reduce a glass transition point or a Young's modulus, 2.5% or less is more preferable, and 2% or less is further more preferable.
The content of MgO is preferably 5.5% or less, more preferably 4.5% or less, particularly preferably 4% or less, still more preferably 3.5% or less, more preferably 3% or less, in order to intensify the light emission by UV irradiation. Most preferred. Moreover, in order to make a Young's modulus high, More preferably, it is 0.5% or more, More preferably, it is 1% or more, Especially preferably, it is 2% or more, More preferably, it is 2.5% or more.
10% or less is more preferable, 8% or less is more preferable, 5% or less is particularly preferable, 4.5% or less is more preferable, and 3.5% or less is more preferable in order to intensify light emission by UV irradiation. Even more preferred is 3% or less. In order to improve the dissolution characteristics, it is more preferably at least 0.5%, still more preferably at least 1%, particularly preferably at least 1.5%, still more preferably at least 2%, most preferably at least 2.5%. is there.
The amount of SrO is more preferably 6.5% or less, further preferably 6% or less, particularly preferably 5.5% or less, still more preferably 5% or less, in order to suppress a decrease in specific elastic modulus and an increase in thermal expansion. 4.5% or less is the most preferable. Further, in order to improve the solubility and increase the Young's modulus, more preferably 0.5% or more, still more preferably 1% or more, particularly preferably 1.5% or more, more preferably 2% or more, most preferably Is 2.5% or more.
BaO is preferably 0.5% or more, more preferably 1% or more, still more preferably 1.5% or more, particularly preferably 2% or more, most preferably 2.5% or more for improving the solubility. is there. Moreover, in order to suppress an increase in specific gravity, a decrease in specific elastic modulus and an increase in thermal expansion, and an increase in mechanical properties, 4.5% or less is more preferable, 4% or less is more preferable, and 3.5% or less is more preferable , 3% or less is particularly preferred.

(2) 0% or more and less than 3% of B ₂ O ₃ , 6.5% to 13% of MgO, 0.5% to 5% of BaO, and 1 to 10% of SrO.
In order to increase the Young's modulus, it is preferable to make MgO 6.5% or more, and it is preferable that the content of SrO be high. Further, in order to prevent the decrease in specific elastic modulus, it is better to reduce the specific gravity, and it is preferable to make BaO 5% or less. Although it is preferable to increase the content of MgO and SrO in order to increase the Young's modulus, devitrification tends to occur if the content is too large, so it is preferable to increase the content of BaO. Moreover, more preferably, 0 to 4.5% of CaO is contained.
More preferably, B ₂ O ₃ is at least 0.5%, more preferably at least 1%, in order to reduce thermal expansion and to facilitate dissolution. Moreover, in order not to reduce a glass transition point or a Young's modulus, 2.5% or less is more preferable, and 2% or less is further more preferable.
MgO is more preferably 7% or more, more preferably 7.5% or more, particularly preferably 8% or more, and more preferably 8.5% or more in order to increase the Young's modulus. Moreover, in order to prevent the fall of the luminescent intensity by UV irradiation, and aggravation of the devitrification characteristic, 12.5% or less is more preferable, 12% or less is more preferable, 11.5% or less is especially preferable, and 11% or less is more Preferably, 10.5% or less is the most preferable.
CaO is more preferably 0.5% or more, particularly preferably 1% or more, more preferably 1.5% or more, and most preferably 2.5% or more in order to improve the dissolution characteristics. Moreover, in order to intensify the light emission by UV irradiation, 4% or less is more preferable, 3.5% or less is especially preferable, and 3% or less is more preferable.
SrO is preferably 2% or more, more preferably 3.5% or more, particularly preferably 4% or more, more preferably 4.5% or more, in order to improve the solubility and increase the Young's modulus. Preferably it is 5% or more. Moreover, in order to suppress an increase in specific gravity, deterioration of brittleness, a decrease in specific elastic modulus and an increase in thermal expansion, 10% or less is preferable, 9% or less is more preferable, 8% or less is more preferable, and 7% or less Particularly preferred.
BaO is more preferably 1% or more, still more preferably 1.5% or more, particularly preferably 2% or more, still more preferably 2.5% or more, most preferably 3% or more for improving the solubility. . Moreover, in order to suppress an increase in specific gravity, a decrease in specific elastic modulus and an increase in thermal expansion, and an increase in mechanical properties, 4.5% or less is more preferable, 4% or less is more preferable, and 3.5% or less is more preferable , 3% or less is particularly preferred.

Since Li ₂ O, Na ₂ O and K ₂ O lower the glass transition point Tg and increase the thermal expansion property, the total content of these three components (R ₂ O) is 10% or less, preferably It is 4% or less, more preferably 3% or less, still more preferably 1% or less, particularly preferably 0.5% or less, more preferably 0.2% or less, most preferably substantially It is preferable not to contain it.

P ₂ O ₅ can be contained at 10% or less from the viewpoint of enhancing the transmittance at a wavelength of 250 nm as described above. However, since P ₂ O ₅ tends to easily inhibit light emission, the smaller the content, the better. The content of P ₂ O ₅ is preferably less than 3%, more preferably less than 1%, still more preferably less than 0.5%, particularly preferably less than 0.2%. Moreover, in glass manufacture, since there exists a possibility of producing the fault derived from the compound of P, it does not contain substantially more preferably.

  In addition, in this specification, "it does not contain substantially" means not intentionally containing in a raw material, and also does not exclude mixing of an unavoidable impurity. Specifically, it means that the content is less than 0.01%.

The glass of the present invention is one of the light emitting elements SnO ₂ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , WO ₃ , MoO ₃ and CeO ₂ in order to emit fluorescence by UV irradiation. The total content of at least one is 0.03% or more, preferably 0.07% or more, more preferably 0.1% or more, still more preferably 0.12% or more, particularly preferably 0.15% or more More preferably, it is 0.2% or more, and most preferably 0.25% or more. Also, it is preferably 1% or less, more preferably 0.8% or less, still more preferably 0.5% or less, particularly preferably 0.4% or less, more preferably 0.3% or less, most preferably 0.35% or less is preferable.

When the total content of SnO ₂ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , WO ₃ , MoO ₃ and CeO ₂ is 0.03% or more, fluorescence emitted due to UV irradiation The strength is sufficient and it is easy to visually recognize glass fragments and glass substrates. On the other hand, by setting the content to 1% or less, absorption by the light emitting element can be suppressed, and in particular, a decrease in transmittance at a wavelength of 250 nm can be prevented.

Fe ₂ O ₃ has absorption in the visible light range, so if it is too large, it may interfere with light emission by UV irradiation. In addition, it may act on the light emitting element to reduce the light emission efficiency, and as a result, the light emission intensity due to UV irradiation may be reduced. Therefore, the content is preferably 1% or less, more preferably 0.5% or less, still more preferably 0.1% or less, particularly preferably 0.05% or less, and most preferably It is 0.03% or less.

On the other hand, when Fe ₂ O ₃ is contained, the glass melt itself easily absorbs the heat radiation at the time of melting the glass, and the glass production becomes easy. In addition, it becomes easy to use inexpensive industrial raw materials. Therefore, it is preferable to contain 0.005% or more, more preferably 0.01%, still more preferably 0.012% or more, particularly preferably 0.014% or more, more preferably 0.016% or more, most preferably Is 0.018% or more.

The value of the total of the content of the light emitting element / the content of Fe ₂ O ₃ is preferably 0.03 or more, more preferably 5 or more, still more preferably 7 or more, and particularly preferably 9 The above, more preferably 12 or more, and most preferably 15 or more. Moreover, it is preferable that it is 500 or less, More preferably, it is 100 or less, More preferably, it is 60 or less, Especially preferably, it is 40 or less, More preferably, it is 30 or less, Most preferably, it is 20 or less.

When the value of the content of the total of the content of the light emitting element / the content of Fe ₂ O ₃ is 0.03 or more, it can be said that sufficient luminescence intensity is obtained for absorption by Fe ₂ O _3. The glass is easily visible. In addition, when the value is 500 or less, the absorption by the light emitting element does not decrease the transmittance particularly at a wavelength of 250 nm, and the emission by UV irradiation can be strengthened.

  The glass of the present invention consists essentially or essentially of the above-mentioned components, but other components as exemplified below may be contained within the range that does not impair the object of the present invention. It is preferable that it is 20% or less, and, as for the sum total of content of components other than the said component, it is more preferable that it is 5% or less.

It may contain up to 5% of the total content of a clarifying agent such as SO ₃ , Cl, As ₂ O ₃ or Sb ₂ O ₃ , a coloring agent such as NiO, Se, Cr ₂ O ₃ or CoO.

  The glass of the present invention preferably has a Young's modulus of 70 GPa or more, more preferably 75 GPa or more, still more preferably 78 GPa or more, particularly preferably 80 GPa or more, more preferably 82 GPa or more, and most preferably 84 GPa or more.

  When the Young's modulus is 70 GPa or more, the substrate is thinned in order to increase the recording capacity of the recording medium, and when the distance between the recording medium and the read head is reduced, the deflection or warpage of the substrate accompanying the thinning of the substrate Can be suppressed. In addition, when the recording medium is subjected to an impact, the substrate can be hardly bent, generation of stress can be suppressed, and the substrate can be hardly broken. The upper limit is not limited but is usually 88 GPa or less.

The glass of the present invention preferably has a thermal expansion coefficient (CTE) at 50 to 350 ° C. of 60 × 10 ⁻⁷ / ° C. or less, more preferably 50 × 10 ⁻⁷ / ° C. or less, still more preferably 45 It is not more than 10 ⁻⁷ / ° C., particularly preferably not more than 40 × 10 ⁻⁷ / ° C. The lower limit is not particularly limited, but is usually 30 × 10 ⁻⁷ / ° C. or more.

When the thermal expansion coefficient (CTE) at 50 to 350 ° C. is 60 × 10 ⁻⁷ / ° C. or less, high heat resistance required for the thermally assisted magnetic recording technology can be obtained, and cracking due to heat can be prevented.

  The glass of the present invention preferably has a glass transition point Tg of 600 ° C. or higher, more preferably 650 ° C. or higher, still more preferably 680 ° C. or higher, particularly preferably 710 ° C. or higher, more preferably 740 ° C. The above, most preferably 760 ° C. or higher.

  When the glass transition point Tg is 600 ° C. or more, the storage density of the data storage medium can be easily increased. That is, in order to increase the storage density, it is effective to increase the coercivity of the magnetic layer which is the magnetic recording layer, and for that purpose, it is preferable to carry out the heat treatment performed at the time of forming the magnetic layer at a higher temperature. The heat treatment can be performed at a desired temperature by setting the glass transition point of the glass used for the data storage medium substrate to 600 ° C. or higher.

The β-OH value of the glass substrate of the present invention is preferably 0.05 mm ⁻¹ or more, more preferably 0.1 mm ⁻¹ or more, still more preferably 0.15 mm ⁻¹ or more, particularly preferably 0.2 mm ^-1 or more. Moreover, 0.7 mm- ¹ or less is preferable, More preferably, it is 0.6 mm- ¹ or less, More preferably, it is 0.5 mm- ¹ or less, Most preferably, it is 0.4 mm- ¹ or less. By setting the β-OH value to 0.7 mm ⁻¹ or less, heat is easily transmitted to the glass and the glass is easily melted. Moreover, the fall of a glass transition point can be suppressed. When producing glass by a general float method, a fusion method, and a press method, it is typically 0.05 mm < ^-1 > or more.

Incidentally, the β-OH value in the present invention is a measure of the hydroxyl group content in glass, and is calculated by the following equation based on the transmittance measured by FT-IR (Fourier transform infrared spectroscopy) .
β-OH value = (1 / X) log ₁₀ (T1 / T2).

Here, X is the thickness of the sample (mm), T1 is the transmittance (%) at a reference wave number 4000 cm ^-1 , T2 is the transmittance at around a hydroxyl group absorption wave number 3500 cm ^-1 (range of 3300 cm ^{-1 to} 3700 cm ^-1 ) Is the minimum value (%) of The higher the β-OH value, the higher the hydroxyl content in the glass.

  The glass substrate for data storage media of the present invention is used as a substrate for data storage media such as a magnetic disk or an optical disk.

  The glass substrate for data storage media in the present invention is typically a circular glass substrate having a thickness of 0.5 to 1.5 mm and a diameter of 20 to 100 mm, and in the case of a glass substrate for magnetic disks, etc. Holes with a diameter of 5 to 25 mm are formed.

  In the magnetic disk of the present invention, at least a magnetic layer, which is a magnetic recording layer, is formed on the main surface of the glass substrate for data storage media of the present invention. Layers may be formed.

  The manufacturing method of the glass of this invention and a glass substrate is not specifically limited, Various methods can be applied. For example, the raw material of each component generally used is prepared so that it may become target composition, and this is heat-melted with a glass melting furnace. The glass is homogenized by bubbling, stirring, addition of a fining agent, etc., and formed into a sheet glass of a predetermined thickness by a method such as the well-known float method, press method, or downdraw method, and adjusted to a predetermined cooling rate. After cooling slowly, processing such as grinding and polishing is performed as necessary, and a glass substrate of a predetermined size and shape is obtained. As a molding method, in particular, a float method suitable for mass production is preferable.

  The raw materials of the respective components were prepared so as to have the composition shown by molar percentage in Table 1 and melted at a temperature of 1550 to 1650 ° C. for 3 to 5 hours using a platinum crucible. Next, the molten glass was poured out, formed into a plate, and annealed. In addition, it was as having shown in Table 1 about the cooling rate of Tg + 50 degreeC-Tg + 20 degreeC.

The glass substrate thus obtained has Young's modulus E (unit: GPa), thermal expansion coefficient CTE (unit: 10 ^-7 / ° C) at 50 to 350 ° C, glass transition point Tg (unit: ° C), β-OH (Unit: mm ⁻¹ ), transmittance at a wavelength of 450 nm (unit:%), transmittance at a wavelength of 250 nm (unit:%), fluorescence intensity at a wavelength of 450 nm, density (unit: g / cm ³ ), cooling rate of 0. The density (unit: g / cm ³ ) at 5 ° C./min, the amount of density change (unit:%), and the presence or absence of light emission by excitation light with a wavelength of 250 nm were measured or evaluated by the following method.

  Glass transition point Tg: Elongation percentage of glass when heated from a room temperature at a rate of 5 ° C./min from quartz glass as a reference sample using a differential thermal expansion meter, the glass is softened and the elongation is no longer observed The temperature, that is, the temperature to the point of deformation was measured, and the temperature corresponding to the inflection point in the thermal expansion curve was taken as the glass transition point.

  Young's modulus E: The measurement was performed by an ultrasonic pulse method on a glass substrate having a thickness of 0.5 mm and a size of 4 cm × 4 cm.

  Thermal expansion coefficient CTE at 50 to 350 ° C .: The thermal expansion coefficient at 50 to 350 ° C. was calculated from the thermal expansion curve obtained in the same manner as the measurement of Tg.

  β-OH value: Both surfaces of a glass substrate having a thickness of 0.5 mm and a size of 2 cm × 2 cm were mirror-polished with cerium oxide, and then a transmission spectrum was measured using FT-IR. Thereafter, the β-OH value was calculated using the above equation.

  Transmittance at a wavelength of 450 nm and transmittance at a wavelength of 250 nm: The transmittance at a thickness of 0.5 mm was measured using a spectrophotometer (manufactured by HITACHI, model number: U-4100). After the measurement light was incident on the glass substrate, the measurement light was measured under the condition that no influence of light emission was caused by transmitting the visible light cut filter (manufactured by Sigma Kouki Co., Ltd., model number: UVTAF-50S-33U) to the emitted light.

  Fluorescence intensity at a wavelength of 450 nm: Measured using a spectrofluorimeter (manufactured by Hitachi High-Technologies Corporation, model number: F4500). The measurement conditions were an excitation wavelength of 250 nm, and the incident side band width was 2.5 nm. A double-sided mirror-polished glass of 50 mm square and 0.5 mm thickness was incident at an incident angle of about 45 °, and fluorescence in the direction of an outgoing angle of about 45 ° was detected. The bandwidth on the detection side was 2.5 nm. The fluorescence wavelength of 400 to 500 nm was scanned at a speed of 1200 nm / min, and the fluorescence intensity at 450 nm was calculated.

  Glass density: Measured using the Archimedes method. The difference in the density of glass depending on the cooling rate is determined by measuring the density Da of the glass produced at each cooling rate by the above method, and then holding each glass at a temperature of Tg + 30 ° C for a fixed time and cooling at 0.5 ° C / min And the density Db of each glass was again measured by the above method. The increase in density (Db−Da) / Da × 100 (%) when cooled at 0.5 ° C./min relative to the density of the glass produced at each cooling rate was taken as the amount of density change.

  Presence or absence of light emission by excitation light of wavelength 250 nm: 1 cm square pieces of glass were placed on black paper. A UV light source (ASONE, model number: Handy UV Lamp SLUV-4) is irradiated from a vertical height of 30 cm from the surface of the glass, and it can be viewed visually at a distance of 1 m by visual observation under an environment of 1 lux. ○, 場合 when not visible.

  The results are shown in Table 1. In Table 1, Examples 1 to 6 are Examples, and Examples 7 to 9 are Comparative Examples.

  As shown in Examples 1 to 6 of Table 1, since the glass of the present invention contains a total of 0.03% or more of light emitting elements, it emits light by UV irradiation and is a glass having high visibility and high heat resistance. , High Young's modulus and low expansibility, which proves to be suitable for thermally assisted magnetic recording.

  On the other hand, in Examples 7 and 9, since the light emitting element was not contained in total by 0.03% or more, no light was emitted by UV irradiation.

In Example 8, since Nb ₂ O ₅ is contained as a light emitting element, the absorption edge of the glass is shifted to the long wavelength side as compared with the case where Nb ₂ O ₅ is not contained. For this reason, compared with Examples 1 and 2 etc. which put SnO ₂ as a light emitting element, the transmittance | permeability of wavelength 250nm becomes low. And, since the cooling rate is as high as 40 ° C./min as compared with Example 3, the transmittance at a wavelength of 250 nm is not 0.2% or more, and it is considered that light emission by UV irradiation was not recognized.

  Although the present invention has been described in detail with reference to particular embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application (Japanese Patent Application No. 2016-104476) filed on May 25, 2016, which is incorporated by reference in its entirety. Also, all references cited herein are taken as a whole.

  The glass for data storage medium substrates of the present invention can be used for data storage media such as magnetic disks or optical disks, their substrates, and their manufacture.

Claims (7)

Containing 55 to 80% of SiO ₂ , 6 to 18% of Al ₂ O ₃ , and 0% to 12% of B ₂ O ₃ in terms of mole percentage on an oxide basis, of MgO, CaO, SrO and BaO ₂ to 26% of at least one in total of its content (RO), 10% or less in total of its content (R ₂ O) of at least one of Li ₂ O, Na ₂ O and K ₂ O, At least one of the light emitting elements SnO ₂ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , WO ₃ , MoO ₃ and CeO ₂ in a total content of at least 0.03% A glass for a data storage medium substrate having a transmittance of 80% or more at a wavelength of 450 nm and a transmittance of 0.2% or more at a wavelength of 250 nm at a thickness of 0.5 mm. A molar percentage based on oxides, _Fe 2 _{O 3} containing 1% or less, a and the value the total content divided by the content of _Fe 2 _{O 3} of the light emitting element is 0.03 to 500 according Item 6. A glass for a data storage medium substrate according to item 1. The glass for a data storage medium substrate according to claim 1 or 2, having a Young's modulus of 70 Gpa or more, a thermal expansion coefficient (CTE) at 50 to 350 ° C of 60 × 10 ^-7 / ° C or less, and a Tg of 600 ° C or more. The composition contains 0% or more and less than 3% of B ₂ O ₃ , 0 to 6.5% of MgO, 0 to 12% of CaO, and 0 to 7% of SrO in terms of mole percentage on an oxide basis. A glass for a data storage medium substrate according to any one of the above. The composition contains 0% or more and less than 3% of B ₂ O ₃ , 6.5 to 13% of MgO, 0.5 to 5% of BaO, and 1 to 10% of SrO in terms of mole percentage on an oxide basis. The glass for data storage media board | substrate of any one of -3.   The glass substrate for data storage media which consists of glass for data storage media board | substrate of any one of Claims 1-5.   A magnetic disk having a magnetic recording layer formed on the glass substrate for data storage medium according to claim 6.