JP7056558B2 - Glass for data storage medium substrate, glass substrate for data storage medium and magnetic disk - Google Patents

Description

The present invention relates to 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 the storage capacity of hard disk drives, the recording density has been increasing at a high pace. However, as the recording density increases, the miniaturization of magnetic particles impairs thermal stability, and there is a problem that the SN ratio of crosstalk and reproduced signals decreases. Therefore, heat-assisted magnetic recording technology is attracting attention as a fusion technology of light and magnetism.

The heat-assisted magnetic recording technology records by irradiating the magnetic recording layer with laser light or near-field light to reduce the coercive force of the locally heated part by applying an external magnetic field, and recording with a GMR element or the like. It is a technique to read the magnetization. According to the heat-assisted magnetic recording technique, it is possible to record on a highly coercive magnetic force medium, so that it is possible to miniaturize magnetic particles while maintaining thermal stability.

In order to form a high coercive force medium into a multilayer film by heat-assisted magnetic recording technology and form a film on the substrate, it is necessary to sufficiently heat the substrate. As a glass for a substrate, it has high heat resistance, high Young's modulus and low expansion. Non-alkali glass having the above has been proposed (for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2015-28828

The manufacturing process of a glass substrate for a magnetic disk has several stages of polishing and cleaning processes. In addition, the removal of the glass involves a human operation. Non-alkali glass and low-alkali glass are difficult to chemically strengthen by ion exchange treatment, or the compressive stress due to chemical strengthening is small, so cracks and chips occur in manufacturing processes such as polishing processes that require high smoothness. Likely to happen.

Therefore, it may be necessary to check the state of the glass in order to adjust the process conditions, but since the glass is colorless and transparent, it is difficult to recognize it in the manufacturing process, and once cracked or chipped, glass fragments will be generated. When it occurs, it is difficult to find it in the slurry solution used in the manufacturing process, and the productivity is lowered. Further, if the glass shards remain in the manufacturing process, the shards lead to the occurrence of defects such as scratches on the glass, and the productivity is lowered.

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

The present inventors include an element that emits light by UV irradiation in non-alkali glass or low-alkali glass to control the glass composition in an optimum range, and set the transmission rate at a wavelength of 450 nm and a wavelength of 250 nm to a specific range. The present invention has been completed by finding that glass is easily visible by emitting light at a visible light wavelength by UV irradiation having a wavelength of 250 to 370 nm, although it is usually colorless and transparent.

The present invention is an oxide-based molar percentage display containing 55 to 80% SiO ₂ , 6 to 18% Al ₂ O ₃ , 0% or more and less than 12% B ₂ O ₃ , MgO, CaO, SrO. And at least one of BaO in total content (RO) of 2 to 26%, and at least one of Li ₂ O, Na ₂ O and K ₂ O in total content (R ₂ O). 10% or less, at least one of the luminescent elements SnO ₂ , TIO ₂ , Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , WO ₃ , MoO ₃ and CeO ₂ with a total content of 0.03 Provided is a glass for a data storage medium substrate, which contains% or more and has a transmittance of 80% or more at a wavelength of 450 nm at a thickness of 0.5 mm and a transmittance of 0.2% or more at a wavelength of 250 nm.

Further, the present invention provides a glass substrate for a data storage medium made of glass for the data storage medium substrate and a magnetic disk in which a magnetic recording layer is formed on the glass substrate for the data storage medium.

The glass for a data storage medium substrate of the present invention is a non-alkali glass having high Young's modulus, high specific elasticity and low expandability while exhibiting high heat resistance, and is therefore suitable for heat-assisted magnetic recording and is a data storage medium. The recording density of can be further increased. Further, since the glass for the data storage medium substrate of the present invention has an optimum composition capable of emitting fluorescence when irradiated with UV, it can be easily visually recognized by UV irradiation, and the glass can be recognized in the manufacturing process. It is easy to visually search for broken glass fragments due to breakage or chipping, and it is possible to remarkably suppress the occurrence of defects caused by the broken glass fragments.

The glass for a data storage medium substrate of the present invention (hereinafter, may be simply referred to as the glass of the present invention) is used for a substrate for a data storage medium such as a magnetic disk or an optical disk. Unless otherwise specified, the composition is expressed as an oxide-based molar percentage.

Further, in the present specification, "-" indicating a numerical range is used to mean that the numerical values described before and after the numerical range are included as the lower limit value and the upper limit value, and unless otherwise specified, the following "-" in the present specification. Is used with the same meaning.

The glass of the present invention has a transmittance of 80% or more at a wavelength of 450 nm at a thickness of 0.5 mm, preferably 85% or more, more preferably 90% or more, still more preferably 90.5% or more, particularly. It is preferably 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, it is possible to prevent the fluorescence emitted by UV irradiation from being absorbed by the glass.

As a method of increasing the transmittance at a wavelength of 450 nm to 80% or more, for example, the content of a colorant such as Fe ₂ O, which absorbs the wavelength in the visible region when contained in glass and causes a decrease in the transmittance, is used. The mass percentage may be 1% or less.

The glass of the present invention has a transmittance of 0.2% or more at a wavelength of 250 nm at a thickness of 0.5 mm, preferably 0.5% or more, more preferably 2% or more, still more preferably 4% or more. It is particularly preferably 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, still more preferably 15% or less, and most preferably 14% or less.

When the transmittance at a wavelength of 250 nm at a thickness of 0.5 mm is 0.2% or more, it is possible to prevent UV light from being rapidly attenuated on the glass surface and difficult to pass through the inside of the glass. As a result, it is possible to prevent the light emitting region from being narrowed and to suppress the visible fluorescence from being weakened. In addition, it is possible to prevent the fluorescence emitted in the ultraviolet region from being attenuated, and to suppress the emission caused by the glass being re-excited by the fluorescence.

Further, by setting the transmittance at a wavelength of 250 nm at a thickness of 0.5 mm to 30% or less, it is not necessary to contain a large amount of SiO ₂ , B ₂ O ₃ or P ₂ O ₅ , which is preferable. 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 decrease.

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 transmittance at a wavelength of 250 nm at a thickness of 0.5 mm depends on the cooling rate of the glass at a temperature near the glass transition point. That is, by reducing the cooling rate of the glass, the structure of the glass is relaxed and the transmittance tends to increase. Therefore, a temperature distribution is generated during cooling, residual stress remains, and the substrate warps. In order to prevent this, the temperature is preferably 400 ° C./min or less in the range of Tg + 50 ° C. to Tg + 20 ° C. It is more preferably 300 ° C./min or less, still more preferably 200 ° C./min or less, particularly preferably 100 ° C./min or less, still more preferably 50 ° C./min or less, and most preferably 10 ° C./min or less. The lower limit is preferably 0.2 ° C./min or more from the viewpoint of shortening the manufacturing time.

Since the density of the glass slowly cooled at 0.5 ° C./min is higher than that of the rapidly cooled glass, it is considered that the glass structure is changed. The density of the glass according to the cooling rate is the density Db of the glass after the glass is held at a temperature of Tg + 30 ° C. for a certain period of time and cooled at 0.5 ° C./min with respect to the density Da of the glass produced at a predetermined cooling rate. It is expressed as an increase (Db-Da) / Da × 100 (%), and this is used as the density change amount.

The amount of change in the density of the glass of the present invention is preferably 0.01% or more, more preferably 0.05% or more, still more preferably 0.05% or more, 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 change in the density 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, still more preferably 0.3% or less. Yes, especially preferably 0.2% or less.

(2) Adjust the composition of the glass as appropriate.
For example, from the viewpoint of reducing 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 , WO ₃ , MoO ₃ and CeO ₂ should be contained in an amount of 1 mol% or less in total, and the total content of SiO ₂ , B ₂ O ₃ or P ₂ O ₅ should be 60 mol. There is either one of% or more or a combination thereof.

Next, the composition (content of each component) of the substrate glass of the present invention will be described in terms of molar percentage according to the oxide standard 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. Further, it is 80% or less, preferably 74% or less, more preferably 73% or less, particularly preferably 72% or less, 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 from being lowered. Further, the transmittance at a wavelength of 250 nm can be increased. Further, by setting the content of SiO ₂ to 80% or less, it is possible to prevent the coefficient of thermal expansion from becoming too small and the melting temperature for producing glass from becoming too high.

Al ₂ O ₃ has the effect of increasing the chemical resistance of glass and the glass transition point, 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, further preferably 11% or more, particularly preferably 12% or more, and most. It is preferably 13% or more. Further, it is 18% or less, preferably 17% or less, more preferably 16% or less, further preferably 15% or less, and particularly preferably 14% or less.

The above effect can be obtained by setting the content of Al ₂ O ₃ to 6% or more. Further, by setting it to 18% or less, it is possible to prevent the viscosity of the molten glass from becoming too high and making molding, particularly float molding, difficult. In addition, it is possible to prevent the liquid phase temperature from becoming too high.

B ₂ O ₃ can be contained in an amount of less than 12% from the viewpoint of increasing the dissolution reactivity of the glass, lowering the devitrification temperature, and increasing the transmittance at a wavelength of 250 nm as described above. However, since B ₂ O ₃ tends to inhibit light emission, it is preferable that the content is small. 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, making it easier to melt 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 MgO content to 13% or less, it is possible to suppress the inhibition of light emission. The lower limit is not particularly limited, but when MgO is contained, it is preferably contained in an amount of 1% or more.

CaO may be contained from the viewpoint of lowering the viscosity of the molten glass, increasing the Young's modulus, or facilitating the melting of the glass. The CaO content is preferably 12% or less, more preferably 11% or less, still more preferably 10.5% or less, and particularly preferably 10% or less. Further, it is preferably 2% or more, more preferably 2.5% or more, further preferably 3% or more, and particularly preferably 3.5% or more. By setting the CaO content to 12% or less, inhibition of luminescence can be suppressed.

SrO may be contained from the viewpoint of lowering the viscosity of the molten glass and making it easier to melt the glass. The content of SrO is preferably 10% or less, more preferably 7% or less, further preferably 5% or less, particularly preferably 4% or less, still more preferably 3% or less, and more preferably 3% or less. Most preferably, it is 2.5% or less. By setting the SrO content to 10% or less, the specific gravity does not become too heavy and the decrease in specific elasticity can be suppressed. The lower limit is not particularly limited, but when SrO is contained, it is preferably contained in an amount of 1% or more.

BaO may be contained from the viewpoint of increasing the glass transition point and lowering the viscosity of the molten glass to facilitate melting of the glass. The BaO content 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 BaO content to 6% or less, the specific gravity can be reduced and the decrease in the specific elastic modulus can be prevented. The lower limit is not particularly limited, but when BaO is contained, it is preferably contained in an amount of 0.5% or more.

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

Preferred composition ranges of B ₂ O ₃ , MgO, CaO, SrO and BaO include the following (1) and (2).

(1) B ₂ O ₃ is contained in an amount of 0% or more and less than 3%, MgO is contained in an amount of 0% to 6.5%, CaO is contained in an amount of 0% to 12%, and SrO is contained in an amount of 0 to 7%.
Among alkaline earth metals, MgO, CaO and B2O3 tend to inhibit light emission. Therefore _, it is preferable that the contents of MgO _, CaO and B2O3 _{are both} low.
B ₂ O ₃ is more preferably 0.5% or more, still more preferably 1% or more, in order to reduce thermal expansion and facilitate dissolution. Further, in order not to reduce the glass transition point and Young's modulus, 2.5% or less is more preferable, and 2% or less is further preferable.
MgO is more preferably 5.5% or less, further preferably 4.5% or less, particularly preferably 4% or less, further preferably 3.5% or less, and 3% or less in order to enhance light emission due to UV irradiation. Most preferred. Further, in order to increase the Young's modulus, it is more preferably 0.5% or more, further preferably 1% or more, particularly preferably 2% or more, still more preferably 2.5% or more.
CaO is more preferably 10% or less, further preferably 8% or less, particularly preferably 5% or less, further preferably 4.5% or less, and 3.5% or less in order to enhance light emission by UV irradiation. Even more preferably, 3% or less is most preferable. In order to improve the dissolution characteristics, it is more preferably 0.5% or more, further preferably 1% or more, particularly preferably 1.5% or more, still more preferably 2% or more, and most preferably 2.5% or more. be.
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. Most preferably 4.5% or less. Further, in order to improve the solubility and increase the Young's modulus, it is more preferably 0.5% or more, further preferably 1% or more, particularly preferably 1.5% or more, still 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, and most preferably 2.5% or more for improving solubility. be. Further, in order to suppress an increase in specific gravity, a decrease in specific elastic modulus, an increase in thermal expansion, and an increase in mechanical properties, 4.5% or less is more preferable, 4% or less is further preferable, and 3.5% or less is further preferable. 3% or less is particularly preferable.

(2) B ₂ O ₃ is contained in an amount of 0% or more and less than 3%, MgO is contained in an amount of 6.5% to 13%, BaO is contained in an amount of 0.5% to 5%, and SrO is contained in an amount of 1 to 10%.
In order to increase Young's modulus, MgO is preferably 6.5% or more, and the content of SrO is preferably high. Further, in order to prevent a decrease in the specific elastic modulus, it is better to reduce the specific gravity, and it is preferable that the BaO is 5% or less. It is preferable to increase the content of MgO and SrO in order to increase the Young's modulus, but it is preferable to increase the content of BaO because if it is too large, devitrification is likely to occur. Further, it more preferably contains 0 to 4.5% of CaO.
B ₂ O ₃ is more preferably 0.5% or more, still more preferably 1% or more, in order to reduce thermal expansion and facilitate dissolution. Further, in order not to reduce the glass transition point and Young's modulus, 2.5% or less is more preferable, and 2% or less is further preferable.
In order to increase Young's modulus, MgO is more preferably 7% or more, further preferably 7.5% or more, particularly preferably 8% or more, still more preferably 8.5% or more. Further, in order to prevent a decrease in emission intensity and deterioration of devitrification characteristics due to UV irradiation, 12.5% or less is more preferable, 12% or less is further preferable, 11.5% or less is particularly preferable, and 11% or less is further preferable. It is preferably 10.5% or less, and most preferably 10.5% or less.
CaO is more preferably 0.5% or more, particularly preferably 1% or more, still more preferably 1.5% or more, and most preferably 2.5% or more in order to improve the dissolution characteristics. Further, in order to enhance the light emission by UV irradiation, 4% or less is further preferable, 3.5% or less is particularly preferable, and 3% or less is further preferable.
SrO is more preferably 2% or more, further preferably 3.5% or more, particularly preferably 4% or more, still more preferably 4.5% or more, most preferably, in order to improve the solubility and increase the Young's modulus. It is preferably 5% or more. Further, in order to suppress an increase in specific gravity, deterioration of brittleness, decrease in specific elastic modulus and increase in thermal expansion, 10% or less is preferable, 9% or less is more preferable, 8% or less is further preferable, and 7% or less is more preferable. Especially preferable.
BaO is more preferably 1% or more, further preferably 1.5% or more, particularly preferably 2% or more, still more preferably 2.5% or more, and most preferably 3% or more for improving the solubility. .. Further, in order to suppress an increase in specific gravity, a decrease in specific elastic modulus, an increase in thermal expansion, and an increase in mechanical properties, 4.5% or less is more preferable, 4% or less is further preferable, and 3.5% or less is further preferable. 3% or less is particularly preferable.

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 (R ₂ O) of these three components is preferably 10% or less. It is 4% or less, more preferably 3% or less, further preferably 1% or less, particularly preferably 0.5% or less, still more preferably 0.2% or less, and most preferably substantially. It is preferable not to contain it.

As described above, P ₂ O ₅ can be contained in an amount of 10% or less from the viewpoint of increasing the transmittance at a wavelength of 250 nm. However, since P ₂ O ₅ tends to inhibit light emission, it is preferable that the content is small. The content of P ₂ O ₅ is preferably less than 3%, more preferably less than 1%, still more preferably less than 0.5%, and particularly preferably less than 0.2%. Further, in the production of glass, since there is a possibility of causing defects derived from the compound of P, it is more preferably substantially not contained.

In addition, in this specification, "substantially not contained" means that it is intentionally not contained in the raw material, and does not exclude the inclusion of unavoidable impurities. 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 fluoresce when irradiated with UV. The total content of at least one species is 0.03% or more, preferably 0.07% or more, more preferably 0.1% or more, still more preferably 0.12% or more, and particularly preferably 0.15% or more. , More preferably 0.2% or more, and most preferably 0.25% or more. Further, 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, still more preferably 0.3% or less, and most preferably. It is preferably 0.35% or less.

Fluorescence emitted by UV irradiation 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. It is strong enough to make it easy to see glass fragments and glass substrates. On the other hand, when it is set to 1% or less, absorption by luminescent elements can be suppressed, and a decrease in transmittance can be prevented especially at a wavelength of 250 nm.

Since Fe ₂ O ₃ is absorbed in the visible light region, if it is too much, it may hinder the light emission due to UV irradiation. In addition, it may act on luminescent elements to reduce the efficiency of luminescence, and as a result, reduce the luminescence intensity due to UV irradiation. Therefore, the content is preferably 1% or less, more preferably 0.5% or less, further 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 heat radiation when the glass is melted, which facilitates glass production. It also makes it easier to use cheap industrial raw materials. Therefore, it is preferably contained in an amount of 0.005% or more, more preferably 0.01%, further preferably 0.012% or more, particularly preferably 0.014% or more, still more preferably 0.016% or more, and most preferably. Is 0.018% or more.

The total content of the luminescent elements / the value of 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 or more. As mentioned above, it is more preferably 12 or more, and most preferably 15 or more. Further, it is preferably 500 or less, more preferably 100 or less, further preferably 60 or less, particularly preferably 40 or less, still more preferably 30 or less, and most preferably 20 or less.

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

The glass of the present invention is substantially or essentially composed of the above-mentioned components, but other components such as those exemplified below may be contained within a range that does not impair the object of the present invention. The total content of components other than the above components is preferably 20% or less, more preferably 5% or less.

A clarifying agent such as SO ₃ , Cl, As ₂ O ₃ or Sb ₂ O ₃ and a coloring agent such as NiO, Se, Cr ₂ O ₃ or CoO may be contained up to 5% in total.

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, still 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 reading head is reduced, the substrate is bent or warped due to the thinning of the substrate. Can be suppressed from increasing. In addition, when the recording medium receives an impact, the substrate can be made difficult to bend, stress can be suppressed, and cracks can be made difficult. The upper limit is not limited, but is usually 88 GPa or less.

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

When the coefficient of thermal expansion (CTE) at 50 to 350 ° C. is 60 × 10 ^-7 / ° C. or less, it is possible to have high heat resistance required for heat-assisted magnetic recording technology, and it is possible to prevent cracking due to heat.

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

When the glass transition point Tg is 600 ° C. or higher, 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 coercive force of the magnetic layer which is the magnetic recording layer, and for that purpose, it is preferable to perform 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 substrate for the data storage medium 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, and particularly preferably 0.2 mm. It is ^-1 or more. Further, 0.7 mm ^-1 or less is preferable, more preferably 0.6 mm ^-1 or less, still more preferably 0.5 mm ^-1 or less, and particularly preferably 0.4 mm ^-1 or less. By setting the β-OH value to 0.7 mm ^-1 or less, heat is easily transferred to the glass and the glass is easily melted. In addition, the decrease in the glass transition point can be suppressed. When glass is manufactured by a general float method, fusion method, or press method, it is typically 0.05 mm ^-1 or more.

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 sample thickness (mm), T1 is the transmittance (%) at the reference wave number 4000 cm ^-1 , and T2 is the transmittance near the 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 group content in the glass.

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

The glass substrate for a data storage medium 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 is usually in the center of a glass substrate for a magnetic disk or the like. A hole having a diameter of 5 to 25 mm is formed.

In the magnetic disk of the present invention, at least a magnetic layer serving as a magnetic recording layer is formed on the main surface of the glass substrate for a data storage medium of the present invention, and if necessary, a base layer, a protective layer, a lubricating layer or unevenness control is formed. Layers and the like may be formed.

The method for producing the glass and the glass substrate of the present invention is not particularly limited, and various methods can be applied. For example, the raw materials of each component usually used are mixed so as to have a target composition, and this is heated and melted in a glass melting kiln. The glass is homogenized by bubbling, stirring, addition of a clarifying agent, etc., molded into a plate glass of a predetermined thickness by a well-known float method, press method, down draw method, etc., and adjusted to a predetermined cooling rate. After slowly cooling, if necessary, processing such as grinding and polishing is performed, and then a glass substrate having a predetermined size and shape is obtained. As the molding method, a float method suitable for mass production is particularly preferable.

The raw materials of each component were prepared so as to have the composition shown in the molar percentage display in Table 1, and dissolved in a platinum crucible at a temperature of 1550 to 1650 ° C. for 3 to 5 hours. Next, the molten glass was poured out, formed into a plate shape, and slowly cooled. The cooling rates of Tg + 50 ° C. to Tg + 20 ° C. were as shown in Table 1.

For the glass substrate thus obtained, Young ratio E (unit: GPa), thermal expansion coefficient CTE at 50 to 350 ° C. (unit: × ^10-7 / ° C.), glass transition point Tg (unit: ° C.), β-OH. (Unit: mm ^-1 ), transmission rate at wavelength 450 nm (unit:%), transmission rate at wavelength 250 nm (unit:%), fluorescence intensity at wavelength 450 nm, density (unit: g / cm ³ ), cooling rate 0. The density at 5 ° C./min (unit: g / cm ³ ), the amount of change in density (unit:%), and the presence or absence of light emission by excitation light having a wavelength of 250 nm were measured or evaluated by the methods shown below.

Glass transition point Tg: Using a differential thermal expansion meter, the elongation rate of the glass when the temperature is raised from room temperature to 5 ° C / min using quartz glass as a reference sample is softened and the elongation is no longer observed. The temperature was measured up to the bending point, that is, the temperature corresponding to the bending point in the thermal expansion curve was defined as the glass transition point.

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

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

β-OH value: Both sides 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 the transmission spectrum was measured using FT-IR. Then, the β-OH value was calculated using the above formula.

Transmittance at a wavelength of 450 nm and transmittance at a wavelength of 250 nm: A 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 light emitted was passed through a visible light cut filter (manufactured by Sigma Kouki Co., Ltd., model number: UVTAF-50S-33U), and the measurement was performed under conditions where the influence of light emission did not appear.

Fluorescence intensity at a wavelength of 450 nm: Measured using a spectrofluorescence fluorometer (manufactured by Hitachi High-Technologies Corporation, model number: F4500). The measurement conditions were an excitation wavelength of 250 nm and a bandwidth on the incident side of 2.5 nm. A 50 mm square, 0.5 mm thick double-sided mirror-polished glass was incident at an incident angle of about 45 °, and fluorescence in an emission 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 that after measuring the density Da of the glass produced at each cooling rate by the above method, each glass is held at a temperature of Tg + 30 ° C for a certain period of time and cooled at 0.5 ° C / min. The density Db of each glass was measured again by the above method. The amount of increase in density (Db-Da) / Da × 100 (%) when cooled at 0.5 ° C./min with respect to the density of the glass produced at each cooling rate was defined as the amount of change in density.

Presence or absence of light emission by excitation light having a wavelength of 250 nm: 1 cm square glass fragments were placed on black paper. When a UV light source (manufactured by ASONE, model number: Handy UV Lamp SLUV-4) is irradiated from a vertical height of 30 cm from the surface of the glass, visually observed in an environment with a brightness of 1 lux, and easily visible at a distance of 1 m. Was marked with ○, and if it was not visible, it was marked with ×.

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 0.03% or more of luminescent elements in total, it emits light by UV irradiation, is highly visible, and has high heat resistance. It was found to be suitable for heat-assisted magnetic recording because of its properties, high Young's modulus and low expansion.

On the other hand, in Examples 7 and 9, since the total amount of luminescent elements was 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 end of the glass is shifted to the longer wavelength side as compared with the case where Nb ₂ O ₅ is not contained. Therefore, the transmittance at a wavelength of 250 nm is lower than that of Examples 1 and 2 in which SnO ₂ is added as a light emitting element. Since the cooling rate was as high as 40 ° C./min as compared with Example 3, it is considered that the transmittance at a wavelength of 250 nm was not 0.2% or more, and no light emission due to UV irradiation was observed.

Although the invention has been described in detail with reference to particular embodiments, it will be apparent to those skilled in the art that various modifications and modifications are possible without departing from the spirit and scope of the invention. This application is based on a Japanese patent application filed on May 25, 2016 (Japanese Patent Application No. 2016-10476), which is incorporated by reference in its entirety. Also, all references cited here are taken in as a whole.

The glass for a data storage medium substrate of the present invention can be used for manufacturing a data storage medium such as a magnetic disk or an optical disk, a substrate thereof, and the like.

Claims (5)

In terms of oxide-based molar percentage display, SiO ₂ is 55 to 80%, Al ₂ O ₃ is 10 to 18%, B ₂ O ₃ is more than 3.0% and less than 12%, and Fe ₂ O ₃ is 1% or less. Then, at least one of MgO, CaO, SrO and BaO is contained in the total content (RO) of 2 to 26%, and at least one of Li ₂ O, Na ₂ O and K ₂ O is contained in the total content (RO). Contains at least one of the luminescent elements SnO ₂ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , WO ₃ , MoO ₃ and CeO ₂ in total (R ₂ O) of 10% or less. The total content is 0.03% or more, the value obtained by dividing the total content of the luminescent element by the content of Fe ₂ O ₃ is 5 or more, and transmission at a wavelength of 450 nm at a thickness of 0.5 mm. Glass for a data storage medium substrate having a rate of 80% or more and a transmission rate of 0.2% or more at a wavelength of 250 nm. The glass for a data storage medium substrate according to claim 1, wherein the value obtained by dividing the total content of the luminescent elements by the content of Fe ₂ O ₃ is 5 to 500. The glass for a data storage medium substrate according to claim 1 or 2 , wherein the Young's modulus is 70 Gpa or more, the coefficient of thermal expansion (CTE) at 50 to 350 ° C. is 60 × 10 ^-7 / ° C. or less, and the Tg is 600 ° C. or more. A glass substrate for a data storage medium comprising the glass for the data storage medium substrate according to any one of claims 1 to 3 . A magnetic disk in which a magnetic recording layer is formed on the glass substrate for a data storage medium according to claim 4 .