WO2018225725A1 - Glass for information recording medium substrate, information recording medium substrate, and glass spacer for information recording medium and recording reproduction device - Google Patents

Abstract

Provided is a glass for an information recording medium substrate, said glass being an an amorphous glass which has, in terms of mol%, an SiO2 content of 55-68%, a B2O3 content of 0-5%, an Al2O3 content of 1-14%, an MgO content of 8-23%, a CaO content of 1-10%, an Li2O content of 5-18%, the total content of Li2O, Na2O and K2O of 5-18%, the total content of ZrO2, TiO2, BaO, SrO and rare earth oxide(s) of 0-5%, the total content of Li2O and MgO of 20-32%, the molar ratio of the total content of Li2O and MgO to the total content of the alkali metal oxides and alkaline earth metal oxides of 0.60-0.95, the molar ratio of the SiO2 content to the total content of the alkali metal oxides of 3-13, a Young's modulus of 86 GPa or more and a specific gravity of 2.75 or less.

Description

Glass for information recording medium substrate, information recording medium substrate, information recording medium, and glass spacer for recording / reproducing apparatus

The present invention relates to a glass for an information recording medium substrate, an information recording medium substrate, an information recording medium, and a glass spacer for a recording / reproducing apparatus.

Conventionally, an aluminum alloy substrate (aluminum substrate) has been mainly used as a substrate for an information recording medium such as a hard disk (information recording medium substrate). However, although the aluminum substrate has high rigidity, it has been pointed out that it is easily deformed, and the smoothness of the substrate surface after polishing is not sufficient. Therefore, in recent years, an information recording medium substrate made of glass has been proposed (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 11-302031

In recent years, with the thinning and high-density recording of information recording media, it has been required to reduce warping and deflection of the information recording medium in a recording / reproducing apparatus such as an HDD (Hard Disk Drive). For example, an HDD has a structure in which a magnetic disk is rotated by pressing a central portion of the magnetic disk with a spindle and a clamp of a spindle motor. If the magnetic disk is warped or bent during this rotation, the magnetic head for writing or reading information is likely to come into contact with the surface of the magnetic disk. When the magnetic head is impacted by contact with the magnetic disk surface, the head is damaged (head crash). In order to reduce warpage and deflection, it is desirable that the glass for the information recording medium substrate has a high rigidity, specifically, a high Young's modulus.

Furthermore, it is desirable to reduce the specific gravity of the glass for the information recording medium substrate. This is because the information recording medium substrate can be reduced in weight by reducing the specific gravity. By reducing the weight of the substrate, the weight of the information recording medium is reduced. For example, in the HDD, the power required for rotating the magnetic disk can be reduced, and the power consumption of the HDD can be suppressed.

Further, the lower the flying height of the magnetic head above the surface of the information recording medium in the recording / reproducing apparatus, the more advantageous for high density recording. However, if the information recording medium is inferior in surface smoothness, the magnetic head comes into contact with a protrusion higher than the flying height existing on the surface of the information recording medium and receives an impact, causing a head crash. Therefore, in order to further increase the recording density by lowering the flying height, it is desirable to increase the surface smoothness of the information recording medium. For this purpose, the surface smoothness of the information recording medium substrate should be increased. desirable.
On the other hand, in the manufacturing process of the information recording medium substrate, a cleaning process is usually performed in order to remove foreign matters attached to the substrate. However, if the chemical durability (for example, acid resistance and / or water resistance) of the glass constituting the substrate is not sufficiently excellent, surface roughening occurs due to the cleaning treatment, and the surface smoothness of the substrate decreases. . Therefore, it is desired that the glass for an information recording medium substrate has excellent chemical durability.

One embodiment of the present invention provides a glass for an information recording medium substrate having high rigidity, low specific gravity, and excellent chemical durability.

One embodiment of the present invention is expressed in mol%,
SiO ₂ content is 55 to 68%,
B ₂ O ₃ content is 0-5%,
Al ₂ O ₃ content is 1 to 14%,
MgO content is 8-23%,
CaO content is 1-10%,
Li ₂ O content is 5-18%,
The total content of Li ₂ O, Na ₂ O and K ₂ O is 5-18%,
The total content of ZrO ₂ , TiO ₂ , BaO, SrO and rare earth oxide is 0-5%,
The total content of Li ₂ O and MgO is 20 to 32%,
Molar ratio of total content of Li ₂ O and MgO to total content of alkali metal oxide and alkaline earth metal oxide {(Li ₂ O + MgO) / (alkali metal oxide + alkaline earth metal oxide) } Is 0.60-0.95,
The molar ratio of SiO ₂ content to the total content of alkali metal oxides (SiO ₂ / alkali metal oxide) is 3 to 13,
And
A glass for an information recording medium substrate, which is an amorphous glass having a Young's modulus of 86 GPa or more and a specific gravity of 2.75 or less,
About.

By having the glass composition, the glass for an information recording medium substrate can have a high rigidity of Young's modulus of 86 GPa or more and a specific gravity of 2.75 or less, and can exhibit excellent chemical durability. .

According to one embodiment of the present invention, it is possible to provide a glass for an information recording medium substrate having high rigidity and low specific gravity and excellent chemical durability. Furthermore, according to one aspect, an information recording medium substrate made of the above glass for information recording medium substrate and an information recording medium including the substrate can be provided. Furthermore, according to one aspect, a glass spacer for a recording / reproducing apparatus can be provided.

[Glass for information recording medium substrate]
One embodiment of the present invention is a glass for an information recording medium substrate (hereinafter, also simply referred to as “glass”) which is an amorphous glass having the above glass composition, a Young's modulus of 86 GPa or more and a specific gravity of 2.75 or less. )

The glass is amorphous glass. Amorphous glass, unlike crystallized glass, is a glass that does not contain a crystalline phase and exhibits a glass transition phenomenon at an elevated temperature. The glass can be an oxide glass. An oxide glass is a glass whose main network forming component is an oxide.

<Glass composition>
In the present invention and the present specification, the glass composition is represented by an oxide-based glass composition. Here, the “oxide-based glass composition” refers to a glass composition obtained by converting all glass raw materials to be decomposed at the time of melting and existing as oxides in the glass. Unless otherwise specified, the glass composition is expressed on a molar basis (mol%, molar ratio).
The glass composition of the present invention and the present specification 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 value is then converted to oxide notation. The analysis value by ICP-AES may include a measurement error of about ± 5% of the analysis value, for example. Therefore, the oxide notation value converted from the analysis value may also contain an error of about ± 5%.
Further, in the present invention and the present specification, the content of the constituent component is 0% or does not contain (does not contain) or does not introduce, which means that the constituent component is not substantially contained, The amount is less than or equal to the impurity level. An impurity level of about or less means, for example, less than 0.01%.

Hereinafter, the glass composition of the glass will be described.

SiO ₂ is a glass network-forming component and has a function of improving glass stability. In addition, SiO ₂ is a component that contributes to improvement of chemical durability. The SiO ₂ content in the glass is 68% or less from the viewpoint of increasing the Young's modulus, and 55% or more from the viewpoint of increasing the chemical durability. The SiO ₂ content is preferably 65% or less, more preferably 64% or less, still more preferably 63% or less, and 62% or less from the viewpoint of improvement of Young's modulus and glass stability. It is more preferable that The SiO ₂ content is preferably 56% or more, more preferably 57% or more, still more preferably 58% or more, and more preferably 59% or more, from the viewpoint of improving chemical durability. It is more preferable that

B ₂ O _{3 is} also a glass network-forming component, a component that contributes to lowering the specific gravity of the glass, and a component that improves meltability. B ₂ O ₃ tends to volatilize during melting and tends to make the glass component ratio unstable. Moreover, there exists a tendency to reduce chemical durability by excessive introduction | transduction. From the above points, the B ₂ O ₃ content in the glass is 0 to 5%. The B ₂ O ₃ content is preferably 3% or less, more preferably 2% or less, still more preferably 1% or less, still more preferably 0.5% or less, and 0% More preferably, it is 3% or less.

Al ₂ O _{3 is} also a glass network forming component and has a function of increasing the Young's modulus of glass and a function of improving chemical durability. From the viewpoint of improving Young's modulus and chemical durability, the Al ₂ O ₃ content in the glass is 1% or more, preferably 3% or more, more preferably 5% or more, 6% More preferably, it is more preferably 7% or more. Further, from the viewpoint of glass melting and / or stability, the Al ₂ O ₃ content in the glass is 14% or less, preferably 13% or less, and more preferably 12% or less. More preferably, it is 11% or less.

The alkaline earth metal oxide is at least one selected from the group consisting of MgO, CaO, SrO and BaO. Among the alkaline earth metal oxides, MgO is a component having a function of increasing the Young's modulus of glass and a function of improving the meltability and / or moldability of the glass. From the viewpoint of obtaining the above functions well, the glass contains MgO as an essential component, and the MgO content is 8% or more, preferably 10% or more, more preferably 11% or more, It is more preferably 12% or more, and further preferably 13% or more. Further, from the viewpoint of glass stability, the MgO content in the glass is 23% or less, preferably 21% or less, more preferably 20% or less, and further preferably 19% or less. 18% or less, more preferably 17% or less.

CaO, like MgO, has a function of increasing the Young's modulus of glass and a function of improving the meltability and / or stability of glass. From the viewpoint of obtaining these functions well, the CaO content in the glass is 1% or more, preferably 2% or more, more preferably 3% or more, and more preferably 4% or more. More preferably, it is more preferably 5% or more. From the viewpoint of improving chemical durability, the CaO content in the glass is 10% or less, preferably 9% or less, more preferably 8% or less, and 7.5% or less. More preferably.

SrO has a function of improving the meltability, formability, and glass stability of glass. On the other hand, SrO is a component that increases the specific gravity and causes a decrease in chemical durability. Considering the above points, the SrO content in the glass is preferably 0 to 5%. A more preferable range of the SrO content is 0 to 3%, a more preferable range is 0 to 2%, and a more preferable range is 0 to 1%, and no SrO is contained, that is, the SrO content is 0%. Most preferred.

BaO also has the function of improving the meltability, moldability and glass stability of glass. On the other hand, BaO is a component that increases the specific gravity and causes a decrease in chemical durability. Considering the above points, the BaO content in the glass is preferably 0 to 5%. A more preferable range of the BaO content is 0 to 3%, a further preferable range is 0 to 2%, and a more preferable range is 0 to 1%, and that no BaO is contained, that is, the BaO content is 0%. Most preferred.

The total content of alkaline earth metal oxides in the glass (MgO + CaO + SrO + BaO) is preferably 15% or more, and from 17% or more, from the viewpoint of improving the Young's modulus of the glass and meltability and / or stability. More preferably, it is 18% or more, more preferably 19% or more. Further, from the viewpoint of further improving the chemical durability of the glass, the total content (MgO + CaO + SrO + BaO) of the alkaline earth metal oxide in the glass is preferably 30% or less, and preferably 28% or less. More preferably, it is 26% or less, more preferably 25% or less.

MgO has a function of increasing the Young's modulus of glass, and is a component that contributes to suppressing an increase in specific gravity compared to other alkaline earth metal oxides. Therefore, MgO is a very useful component for increasing the Young's modulus and decreasing the specific gravity of glass. Therefore, in the glass, the molar ratio {MgO / (MgO + CaO + SrO + BaO)} of the content of MgO to the total content of alkaline earth metal oxides is preferably 0.5 or more. The lower limit of the molar ratio is more preferably 0.55 or more, still more preferably 0.60 or more, and still more preferably 0.65 or more. The upper limit of the molar ratio is preferably 0.95 or less, more preferably 0.90 or less, and still more preferably 0.85 or less, from the viewpoint of glass stabilization. More preferably, it is 0.80 or less.

As described above, MgO and CaO have the function of increasing the Young's modulus of the glass. From the viewpoint of further improving the Young's modulus, the total content of MgO and CaO (MgO + CaO) in the glass is preferably 15 to 35%. About the minimum of the said total amount, it is preferable that it is 17% or more from a viewpoint of the further improvement of a Young's modulus, It is more preferable that it is 19% or more, It is still more preferable that it is 20% or more. The upper limit of the total amount is preferably 30% or less, more preferably 26% or less, and further preferably 25% or less from the viewpoint of maintaining the stability of the glass.

MgO has a greater function to increase the Young's modulus of glass than CaO. Therefore, in the said glass, it is preferable that MgO content shall be more than the same amount as CaO content. In addition, alkaline earth metal oxides can add mixed alkaline earth effect by adding a plurality of kinds rather than adding only a single component to glass, and improve the meltability and / or stability of glass. it can. Therefore, in the glass, the molar ratio of MgO content to MgO content (MgO / CaO) is preferably 1.0 to 20.0. The lower limit of the molar ratio is preferably 1.25 or more, more preferably 1.50 or more, and still more preferably 1.70 or more from the viewpoint of further improving the Young's modulus. The upper limit of the molar ratio is preferably 10.0 or less, more preferably 8.0 or less, still more preferably 6.0 or less, from the viewpoint of maintaining the stability of the glass. Is more preferably 0.0 or less, and even more preferably 4.0 or less.

The alkali metal oxide is an oxide of an alkali metal (Li, Na, K, Rb, Cs, Fr), preferably one or more selected from the group consisting of Li ₂ O, Na ₂ O and K ₂ O. is there. Li ₂ O has a strong effect of improving the meltability and moldability of glass among alkali metal oxides, and is a suitable component for increasing the Young's modulus and imparting a suitable rigidity to the information recording medium substrate. . Li ₂ O is also a component that increases the thermal expansion coefficient. On the other hand, Li ₂ O has a function of lowering the viscosity of the glass, so when introduced excessively, the viscosity at the liquidus temperature tends to decrease and the glass tends to be unstable (devitrified easily). Li ₂ O is also a component that lowers the glass transition temperature. Considering the above functions, the Li ₂ O content in the glass is 5 to 18%. The lower limit of the content of Li 2 _O, preferably at least 6%, more preferably 7% or more, even more preferably 8% or more. Further, the upper limit of the Li ₂ O content is preferably 16% or less, more preferably 14% or less, further preferably 13% or less, and further preferably 12% or less. .

For Na 2 _O, from the viewpoint of improving the improvement of the Young's modulus of the glass and the chemical durability (especially acid resistance), Na 2 _O content in the glass is preferably 10% or less. Also, from the viewpoint of suppressing alkali elution from the substrate surface when glass is used as the substrate, the Na ₂ O content in the glass is preferably 10% or less. Suppressing alkali elution from the substrate surface is preferable because the physical properties of a film such as a recording layer formed on the substrate can be prevented from being affected by the alkali eluted and precipitated from the substrate. Na ₂ O is also a component that improves the meltability and moldability of the glass and increases the thermal expansion coefficient. A preferable range of the Na ₂ O content is 0 to 10%. The upper limit of the Na ₂ O content is more preferably 8% or less, still more preferably 6% or less, still more preferably 5% or less, and even more preferably 4% or less. It is also preferable not to contain (that is, the content is 0%).

For K 2 _O, from the viewpoint of chemical durability further improve and alkaline elution suppression, K _{2 O} content in the glass is preferably 5% or less. K ₂ O has a function of improving the meltability and moldability of glass and is also a component that increases the thermal expansion coefficient. The K ₂ O content in the glass is preferably 0 to 5%, more preferably 0 to 3%, still more preferably 0 to 2%, and more preferably 0 to 1%. It is more preferable that K ₂ O is not contained (that is, the content is 0%).

Li ₂ O, Na ₂ O, and K ₂ O are components that improve the meltability and moldability of the glass and increase the thermal expansion coefficient as described above. From the viewpoint of obtaining the functions of these components satisfactorily, the contents of Li ₂ O, Na ₂ O and K ₂ O in the glass are 5% or more. From the viewpoint of obtaining the functions of these components better, the total content is preferably 6% or more, more preferably 7% or more, and further preferably 8% or more. On the other hand, from the viewpoints of glass heat resistance, suppression of alkali elution, and further improvement in chemical durability, the total content of Li ₂ O, Na ₂ O and K ₂ O in the glass (Li ₂ O + Na ₂ O + K ₂ O). ) Is 18% or less, preferably 16.5% or less, more preferably 15.5% or less, and still more preferably 15.0% or less.

Among the alkali metal oxides and alkaline earth metal oxides, Li ₂ O and MgO are useful components for increasing the Young's modulus of the glass and maintaining the stability of the glass. Therefore, in the glass, the total content of Li ₂ O and MgO (Li ₂ O + MgO) is 20 to 32%. If the said total content is 32% or less, it can suppress that stability of glass falls by the raise of liquidus temperature. The lower limit of the total content of Li ₂ O and MgO (Li ₂ O + MgO) is preferably 21% or more, more preferably 22% or more, and further preferably 22.5% or more. The upper limit of the total content is preferably 30% or less, more preferably 28.5% or less, and further preferably 27.5% or less.

Li ₂ O and MgO are useful components for increasing the Young's modulus of the glass and maintaining the stability of the glass among the alkali metal oxides and alkaline earth metal oxides as described above. Therefore, in order to efficiently exert its action, in the glass, the molar ratio of the total content of Li ₂ O and MgO to the total content of alkali metal oxide and alkaline earth metal oxide {( Li ₂ O + MgO) / (alkali metal oxide + alkaline earth metal oxide)} is 0.60 to 0.95. The lower limit of the molar ratio is preferably 0.65 or more, more preferably 0.70 or more, still more preferably 0.72 or more, from the viewpoint of improving the Young's modulus of the glass. More preferably, it is 74 or more. The upper limit of the molar ratio is preferably 0.90 or less, more preferably 0.85 or less, and 0.82 or less from the viewpoint of improving the meltability and / or stability of the glass. Is more preferable, and 0.80 or less is still more preferable.

The molar ratio of SiO ₂ content to the total content of alkali metal oxides (SiO ₂ / alkali metal oxide) is 3 to 13 in the glass. The upper limit of the molar ratio is 13 or less, preferably 11 or less, more preferably 10 or less, still more preferably 9 or less, from the viewpoint of improving the Young's modulus and improving the meltability of the glass. More preferably, it is 8 or less. Further, the lower limit of the molar ratio is 3 or more from the viewpoint of improving the chemical durability of the glass, preferably 3.5 or more, more preferably 4.0 or more, and 4.2 or more. More preferably, it is 4.5 or more.

ZnO has the function of improving the chemical durability as well as improving the meltability. On the other hand, if ZnO is excessively introduced, the liquidus temperature rises and the glass tends to become unstable. Considering the above points, the ZnO content in the glass is preferably 0 to 10%, more preferably 0 to 5%, still more preferably 0 to 3%, and more preferably 0 to 1%. % Is more preferable, and ZnO may not be contained (that is, the content may be 0%).

ZrO ₂ has a function of improving chemical durability and a function of increasing Young's modulus. However, excessive melting may lower the meltability of the glass and cause the remainder of the raw material to melt. Considering the above points, the ZrO ₂ content in the glass is preferably 0 to 4%, more preferably 0 to 3%, still more preferably 0 to 2%, and more preferably 0 to 1% is more preferable, and it may not be contained (that is, the content may be 0%).

As described above, SiO ₂ and Al ₂ O ₃ are glass network forming components and have a function of improving chemical durability. CaO and ZrO ₂ are common in that they function to increase the Young's modulus. The inventors set the molar ratio of the total content of SiO ₂ and CaO to the total content of Al ₂ O ₃ and ZrO ₂ (SiO ₂ + CaO) / (Al ₂ O ₃ + ZrO ₂ ) within an appropriate range. Has been found to contribute to improving the stability of the glass. From this point, the molar ratio is preferably in the range of 5.0 to 25.0. The lower limit of the molar ratio is more preferably 5.5 or more, still more preferably 6.0 or more, and still more preferably 6.5 or more. The upper limit of the molar ratio is more preferably 20 or less, still more preferably 16 or less, still more preferably 14 or less, and even more preferably 12 or less.

By the way, the phenomenon that the information recording medium (magnetic disk) itself vibrates due to external vibration in the HDD is called fluttering. This fluttering causes a head crash due to a collision between the magnetic head and the surface of the information recording medium. Even if fluttering occurs due to external vibration, if the vibration of the information recording medium itself is settled early, the occurrence of head crash can be suppressed. In this regard, an index called fluttering characteristics is known for glass. The fluttering characteristic d means that fluttering is settled earlier as the value is smaller. The fluttering characteristic d is determined by d = (ρ / E) × (1 / ξ) from the Young's modulus E, density ρ, and transverse vibration internal friction ξ (hereinafter simply referred to as “internal friction”) of the glass constituting the substrate. Is calculated by Therefore, in order to reduce the fluttering characteristic, it is desirable that the internal friction ξ is large, that is, the energy decrease due to vibration absorption is large. In this regard, in the glass, the molar ratio {Al ₂ O ₃ / (Li ₂ O + Na ₂ O)} of the Al ₂ O ₃ content to the total content of Li ₂ O and Na ₂ O is 0.25 to 1. A range of 25 is preferable for suppressing the occurrence of head crash due to fluttering by increasing the internal friction and reducing the fluttering characteristics. From the viewpoint of reducing fluttering characteristics, the molar ratio is preferably 0.4 or more, and more preferably 0.6 or more. From the same viewpoint, the molar ratio is preferably 1.20 or less, and more preferably 1.15 or less.

TiO ₂ functions to improve chemical durability and glass stability and to increase Young's modulus. However, it is a component that causes an increase in the specific gravity of glass. Accordingly, the TiO ₂ content in the glass is preferably 0 to 5%, more preferably 0 to 4%, and still more preferably 0 to 3%.

The rare earth oxide is an oxide of rare earth (Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), preferably La _2. It is at least one selected from the group consisting of O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ . Rare earth oxides, as well as ZrO ₂ , TiO ₂ , SrO and BaO are components that cause an increase in specific gravity. Therefore, from the viewpoint of reducing the specific gravity of the glass, the total content of ZrO ₂ , TiO ₂ , SrO, BaO and rare earth oxide (ZrO ₂ + TiO ₂ + SrO + BaO + rare earth oxide) in the glass is 0 to 5%. The upper limit of the total content is preferably 4% or less, more preferably 3% or less, and still more preferably 2% or less.

La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ and Yb ₂ O ₃ can all improve the Young's modulus of the glass by introducing an appropriate amount. On the other hand, when introduced excessively, the specific gravity of the glass is increased, so the La ₂ O ₃ content, the Y ₂ O ₃ content, the Gd ₂ O ₃ content and the Yb ₂ O ₃ content in the glass are each 1%. Is preferably less than 0.5%, more preferably 0.5% or less, and may be 0%.
The total content of rare earth oxides is preferably 0 to less than 3%, more preferably 0 to less than 2%, and even more preferably 0 to 1%, from the viewpoint of improving Young's modulus and lowering the specific gravity. More preferably, it is not introduced.

Nb ₂ O ₅ , WO ₃ and Ta ₂ O ₅ can all improve the Young's modulus of the glass by introducing an appropriate amount. On the other hand, excessive introduction increases the specific gravity of the glass and increases the material cost. Therefore, the total content of Nb ₂ O ₅ , WO ₃ and Ta ₂ O ₅ is preferably less than 1%, more preferably 0.5% or less, and may be 0%.

Although a small amount of P ₂ O ₅ can be introduced, the chemical durability tends to decrease due to excessive introduction, so the content of P ₂ O _{5 in} the glass is preferably 0 to 2%. Content of P ₂ O _5, 0 to more preferably from _1% to not contain P 2 _{O 5} (i.e. the content of _P 2 _{O 5} is 0%) is more preferable.

The said glass can contain at least 1 type chosen from the group which consists of Sn oxide, Ce oxide, and Sb oxide from a viewpoint of obtaining a clarification effect.
As for the glass containing Sn oxide, the content of Sn oxide (for example, SnO ₂ ) is preferably 0.01% or more and 0.05% or more from the viewpoint of obtaining a fining effect. Is more preferably 0.10% or more, still more preferably 0.15% or more. Further, the content of Sn oxide is preferably less than 1%, and more preferably 0.80% or less. In one aspect, the Sn oxide content may be 0%.
It For glass containing Ce oxide, Ce oxide (e.g., CeO ₂₎ content, from the viewpoint of obtaining a clear effect, preferably at least 0.01%, 0.05% or more Is more preferable, and it is still more preferable that it is 0.10% or more. Further, the Ce oxide content is preferably less than 1%, more preferably 0.80% or less, further preferably 0.50% or less, and 0.30% or less. More preferably. In one aspect, the Ce oxide content may be 0%.
The glass containing Sb oxide content of Sb oxide (e.g. _Sb 2 _{O 3)} is preferably 1 less than percent, more preferably 0.5% or less. In one aspect, the Sb oxide content may be 0%.

The glass is a Fe, in terms of _Fe 2 _{O 3,} it may include a degree of 0.5% or less. The Fe content is preferably 0.2% or less, more preferably 0.1% or less, still more preferably 0.05% or less, in terms of Fe ₂ O ₃ , More preferably, it does not contain Fe.
Moreover, the said glass can contain about 0.5% or less of transition metals, such as Cr, Mn, Fe, Cu, Ni, like Fe. The content of these transition metals is preferably 0.2% or less in terms of oxides, more preferably 0.1% or less, still more preferably 0.05% or less. More preferably, it is not contained.

Since Pb, Cd, As, etc. are substances that adversely affect the environment, it is preferable to avoid introducing them.

In order to obtain a predetermined glass composition, the glass is weighed and mixed with glass raw materials such as oxides, carbonates, nitrates, sulfates, hydroxides, etc., mixed well, and, for example, 1400 It can be produced by molding a homogenized molten glass that is sufficiently blown out by heating, melting, clarification and stirring in the range of ˜1600 ° C. For example, a glass raw material is heated and melted at 1400 to 1550 ° C. in a melting tank, and the obtained molten glass is heated in a clarification tank and maintained at 1450 to 1600 ° C., and then cooled to 1200 to 1400 ° C. It is preferable to flow out and mold.

<Glass characteristics>
The said glass can have the various glass characteristics described below by performing the composition adjustment described above.

(Young's modulus)
In order to meet the above-described requirement for improving the rigidity of the information recording medium, it is desirable that the glass for the information recording medium substrate has high rigidity. In this regard, the glass has a Young's modulus, which is an index of rigidity, of 86 G or more. According to the glass for an information recording medium substrate having a high rigidity exhibiting a Young's modulus of 86 G or more, since the deformation of the substrate in the recording / reproducing apparatus can be suppressed, the warp and the deflection of the information recording medium accompanying the substrate deformation are suppressed. can do. The Young's modulus of the glass is preferably 88 GPa or more, more preferably 90 GPa or more, still more preferably 92 GPa or more, and even more preferably 93 GPa or more. The upper limit of the Young's modulus is, for example, about 120 GPa, but is not particularly limited because the higher the Young's modulus, the higher the rigidity and the better.

(specific gravity)
The specific gravity of the glass is 2.75 or less, preferably 2.72 or less, more preferably 2.70 or less, still more preferably 2.68 or less, and 2.66 or less. More preferably. By reducing the specific gravity of the glass for the information recording medium substrate, the information recording medium substrate can be reduced in weight, and further, the information recording medium can be reduced in weight, thereby reducing the power consumption of the recording / reproducing apparatus such as an HDD. The lower limit of the specific gravity is not particularly limited because the lower the specific gravity, the better.

(Specific modulus)
The specific elastic modulus is obtained by dividing the Young's modulus of glass by the density. Here, the density may be considered as a value obtained by adding a unit of g / cm ³ to the specific gravity of glass. From the viewpoint of providing a substrate that is more difficult to deform, the specific elastic modulus of the glass is preferably 33 MNm / kg or more, more preferably 34 MNm / kg or more, and further preferably 35 MNm / kg or more. More preferably, it is 36 MNm / kg. The upper limit of the specific modulus is not particularly limited because the higher the specific modulus, the better.

(Chemical durability)
The glass can exhibit excellent chemical durability. Examples of the chemical durability evaluation method include acid resistance Da and water resistance Dw, which will be described later in detail. In one aspect, the acid resistance Da is preferably less than 0.20, more preferably 0.10 or less, still more preferably 0.08 or less, and even more preferably 0.06 or less. . In one embodiment, the water resistance Dw is preferably less than 0.05, more preferably 0.04 or less, and still more preferably 0.03 or less. Since Da and Dw are preferably as low as possible, the lower limit is not particularly limited.

(Coefficient of thermal expansion)
A recording / reproducing apparatus incorporating an information recording medium, such as an HDD (Hard Disk Drive), has a structure in which the information recording medium itself is rotated by pressing a central portion with a spindle and a clamp of a spindle motor. Therefore, if there is a large difference in the thermal expansion coefficient between the information recording medium substrate and the spindle material constituting the spindle portion, the thermal expansion / contraction of the spindle and the thermal expansion of the information recording medium substrate with respect to the ambient temperature change during use. -There may be a phenomenon in which the information recording medium is deformed as a result of deviation in heat shrinkage. From the viewpoint of suppressing the occurrence of such a phenomenon, it is desirable that the glass for an information recording medium substrate has an appropriate thermal expansion coefficient. From this point, the average linear expansion coefficient (hereinafter also referred to as “α”) of the glass at 100 to 300 ° C. is preferably in the range of 55 × 10 ⁻⁷ / ° C. to 100 × 10 ⁻⁷ / ° C. A range of 60 × 10 ⁻⁷ / ° C. to 90 × 10 ⁻⁷ / ° C. is more preferable.

(Glass stability)
In one embodiment, the glass can exhibit high glass stability. Examples of the glass stability evaluation method include a 1250 ° C. holding test and a 1200 ° C. holding test described later in detail. It is preferable that the evaluation result is A in the 1250 ° C. holding test, the evaluation result is A in the 1250 ° C. holding test, and more preferably the evaluation result A or B in the 1200 ° C. holding test. A is more preferable. Regarding the glass stability, the better the evaluation result at a lower temperature in the above holding test, the harder the crystals are precipitated in the molten state, and the glass can be molded at a lower molding temperature. As the molding temperature is lowered, the lifetime of the components of the molding apparatus such as the heating element, the furnace body, and the pipe can be extended. In particular, when a substrate blank is produced by press molding, the molding temperature is preferably as low as possible. Further, if the molding temperature can be lowered, the glass viscosity can be increased and molding can be performed, so that volatilization, striae and generation of molding bubbles can be suppressed.

(Glass-transition temperature)
In one embodiment, the glass may have a glass transition temperature (hereinafter also referred to as “Tg”) of 620 ° C. or less. A low Tg of glass is desirable for suppressing deterioration of glass production equipment. Tg can be 615 ° C. or lower or 610 ° C. or lower, for example. Tg can be 500 ° C. or more, for example, but is not particularly limited. In one embodiment, the Tg of the glass may be higher than 620 ° C. (for example, 625 ° C. or higher). A glass having a high Tg can maintain high flatness even when it is exposed to a high temperature, for example, when a magnetic recording layer is formed on a substrate. In one aspect, Tg can be, for example, 630 ° C. or higher, 640 ° C. or higher, or 650 ° C. or higher. In one embodiment, Tg can be, for example, about 770 ° C. or lower, but is not particularly limited. The glass is not limited to a glass for an information recording medium having a magnetic recording layer containing a magnetic material that requires film formation at a high temperature, and may be a glass having a low Tg.

[Information recording medium substrate]
An information recording medium substrate according to an aspect of the present invention is made of the above glass for an information recording medium substrate.

An information recording medium substrate is prepared by heating a glass raw material to prepare a molten glass, and this molten glass is formed into a plate shape by any one of a press molding method, a down draw method, and a float method, and the obtained plate shape It can manufacture through the process of processing glass. For example, in the press molding method, molten glass flowing out from a glass outflow pipe is cut into a predetermined volume to obtain a required molten glass lump, which is press-molded with a press mold to produce a thin disk-shaped substrate blank. . Next, a center hole is provided in the obtained substrate blank, inner and outer peripheral processing, lapping and polishing are performed on both main surfaces. Then, a disk-shaped substrate can be obtained through a cleaning process (for example, acid cleaning and / or alkali cleaning).

In one embodiment, the information recording medium substrate has a uniform surface and internal composition. Here, that the composition of the surface and the inside is homogeneous means that ion exchange is not performed (that is, there is no ion exchange layer). An information recording medium substrate that does not have an ion exchange layer is not subjected to an ion exchange treatment, and thus can greatly reduce manufacturing costs.

In addition, in one aspect, the information recording medium substrate has an ion exchange layer on part or all of the surface. Since the ion exchange layer exhibits compressive stress, the presence or absence of the ion exchange layer can be confirmed by breaking the substrate perpendicular to the main surface and obtaining a stress profile by the Babinet method at the fracture surface. The “main surface” is the surface on which the magnetic recording layer of the substrate is provided or the surface provided. Such a surface is called the main surface because it is the surface with the largest area among the surfaces of the information recording medium substrate. In the case of a disk-shaped information recording medium, the circular surface of the disk (when there is a central hole) Corresponds to (except for the central hole). The presence or absence of the ion exchange layer can also be confirmed by a method of measuring the concentration distribution of alkali metal ions in the depth direction from the substrate surface.

The ion exchange layer can be formed by bringing an alkali salt into contact with the substrate surface at a high temperature and exchanging alkali metal ions in the alkali salt with alkali metal ions in the substrate. For ion exchange (also referred to as “strengthening treatment” or “chemical strengthening”), a known technique can be applied. As an example, paragraphs 0068 to 0069 of WO2011 / 0190010A1 can be referred to.

The information recording medium substrate has, for example, a thickness of 1.5 mm or less, preferably 1.2 mm or less, more preferably 1 mm or less, and the lower limit of the thickness is preferably 0.3 mm. The information recording medium substrate is preferably a magnetic recording medium substrate, and more preferably a disk shape having a central hole.

The information recording medium substrate is made of amorphous glass. According to crystallized glass, the surface of the substrate after processing such as polishing is affected by unevenness due to crystal particles, and the surface smoothness of the substrate tends to be lowered. On the other hand, according to amorphous glass, superior surface smoothness can be realized when processed into a substrate as compared with crystallized glass.

The surface roughness (Ra) of the main surface of the information recording medium substrate is preferably 0.25 nm or less, more preferably 0.20 nm or less, and further preferably 0.15 nm or less.

[Information recording medium]
One aspect of the present invention relates to an information recording medium having an information recording layer on the information recording medium substrate.

A preferred embodiment of the information recording medium is a magnetic recording medium. Disk-shaped magnetic recording media, called magnetic disks, hard disks, etc., record and reproduce internal storage devices (such as fixed disks) such as desktop computers, server computers, notebook computers, and mobile computers, and images and / or audio. It is suitable for an internal storage device of a portable recording / reproducing apparatus, an in-vehicle audio recording / reproducing apparatus, and the like.

A known technique can be adopted for the configuration and manufacturing method of the information recording medium. For example, in one aspect, the magnetic recording medium has at least an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer stacked on the main surface of the information recording medium substrate in order from the side closer to the main surface. It has been configured. For example, an information recording medium substrate is introduced into a vacuum-deposited film forming apparatus, and a magnetic layer is formed from an adhesion layer on the main surface of the information recording medium substrate in an Ar atmosphere by a DC (Direct Current) magnetron sputtering method. The film is formed sequentially. After film formation, a protective layer is formed using C ₂ H ₄ by, for example, CVD (Chemical Vapor Deposition), and a magnetic recording medium is formed by performing nitridation treatment in which nitrogen is introduced into the surface in the same chamber. can do. Thereafter, for example, PFPE (polyfluoropolyether) is applied on the protective layer by a dip coating method, whereby a lubricating layer can be formed.

Recently, by mounting a DFH (Dynamic Flying Height) mechanism on the magnetic head, the gap between the recording / reproducing element portion of the magnetic head and the surface of the information recording medium has been greatly reduced (low flying height). A higher recording density is being achieved. The DFH mechanism is a function in which a heating unit such as a very small heater is provided in the vicinity of the recording / reproducing element unit of the magnetic head, and only the periphery of the element unit is projected toward the medium surface. By doing so, since the distance (flying height) between the magnetic head and the magnetic recording layer of the medium becomes closer, it becomes possible to pick up signals of smaller magnetic particles and achieve further higher recording density. It becomes possible. However, on the other hand, the gap (flying height) between the element portion of the magnetic head and the medium surface is extremely small. If the magnetic head is brought close to the surface of the information recording medium with poor surface smoothness, the magnetic head may come into contact with the surface of the information recording medium and a head crash may occur. Therefore, it is necessary to secure a certain flying height to prevent contact. I don't get it. From the above points, it is desirable to increase the surface smoothness of the information recording medium substrate in order to increase the surface smoothness of the information recording medium. In this regard, a glass excellent in chemical durability is preferable because there is little decrease in surface smoothness after the cleaning treatment. An information recording medium having such a glass substrate is also suitable for a recording / reproducing apparatus equipped with a DFH mechanism in which the flying height is extremely narrowed.

The information recording medium substrate (for example, a magnetic disk substrate) and the information recording medium (for example, a magnetic disk) are not particularly limited in size. For example, since the recording density can be increased, the medium and the substrate can be downsized. Is also possible. For example, a nominal diameter of 2.5 inches can of course be of a smaller diameter (eg, 1 inch, 1.8 inches) or 3 inches, 3.5 inches, etc.

[Glass spacers for recording and playback equipment]
In one embodiment of the present invention, the SiO ₂ content is 55 to 68%, the B ₂ O ₃ content is 0 to 5%, the Al ₂ O ₃ content is 1 to 14%, and the MgO content is expressed in mol%. Is 8 to 23%, CaO content is 1 to 10%, Li ₂ O content is 5 to 18%, the total content of Li ₂ O, Na ₂ O and K ₂ O is 5 to 18%, ZrO ₂ , The total content of TiO ₂ , BaO, SrO and rare earth oxide is 0 to 5%, the total content of Li ₂ O and MgO is 20 to 32%, the total of alkali metal oxide and alkaline earth metal oxide The molar ratio of the total content of Li ₂ O and MgO to the content {(Li ₂ O + MgO) / (alkali metal oxide + alkaline earth metal oxide)} is 0.60 to 0.95, alkali metal oxide The molar ratio of the SiO ₂ content to the total content (SiO ₂ / A The present invention relates to a glass spacer for a recording / reproducing apparatus including amorphous glass having a (Lukari metal oxide) of 3 to 13, a Young's modulus of 86 GPa or more and a specific gravity of 2.75 or less.

The information recording medium can be used for recording and / or reproducing information in a recording / reproducing apparatus. For example, the magnetic recording medium can be used for magnetically recording and / or reproducing information in a magnetic recording / reproducing apparatus. Usually, the recording / reproducing apparatus includes a spacer in order to fix the information recording medium to the spindle of the spindle motor and / or to maintain a distance between the plurality of information recording media. In recent years, it has been proposed to use glass spacers as such spacers. This glass spacer is also desired to have high rigidity, low specific gravity, and excellent chemical durability for the same reason as described above in detail for the glass for the information recording medium substrate. On the other hand, the glass is suitable as a glass spacer for a recording / reproducing apparatus because it has high rigidity and low specific gravity and excellent chemical durability as described above.

The spacer for the recording / reproducing apparatus is a ring-shaped member, and details of the structure and manufacturing method of the glass spacer are well known. In addition, regarding the manufacturing method of the glass spacer, the above description regarding the manufacturing method of the information recording medium substrate glass and the manufacturing method of the information recording medium substrate can also be referred to. For other details such as the glass composition and glass characteristics of the glass spacer for recording / reproducing apparatus according to one aspect of the present invention, information recording medium substrate glass, information recording medium substrate, and information recording according to one aspect of the present invention Reference may be made to the above description regarding the medium.
In addition, the glass spacer for recording / reproducing apparatuses can be made of the glass, or can have a structure in which one or more films such as a conductive film are provided on the surface of the glass. For example, in order to remove static electricity generated when the information recording medium rotates, a conductive film such as a NiP alloy can be formed on the surface of the glass spacer by plating, dipping, vapor deposition, sputtering, or the like. In addition, the glass spacer can increase the surface smoothness by polishing (for example, the average surface roughness is 1 μm or less), thereby strengthening the adhesion between the information recording medium and the spacer and suppressing the occurrence of misalignment. can do.

[Recording and playback device]
One embodiment of the present invention provides:
An information recording medium according to an aspect of the present invention; and a glass spacer according to an aspect of the present invention,
A recording / reproducing apparatus including at least one of
About.

The recording / reproducing apparatus includes at least one information recording medium and at least one spacer, and usually further includes a spindle motor for rotationally driving the information recording medium, and recording and / or information on the information magnetic recording medium. It includes at least one recording / reproducing head for performing reproduction.
The recording / reproducing apparatus according to one aspect of the present invention can include the information recording medium according to one aspect of the present invention as at least one information recording medium, and includes a plurality of information recording media according to one aspect of the present invention. You can also The recording / reproducing apparatus according to one embodiment of the present invention can include the glass spacer according to one embodiment of the present invention as at least one spacer, and can also include a plurality of glass spacers according to one embodiment of the present invention. The physical properties of the information recording medium and the spacer are preferably similar from the viewpoint of suppressing the occurrence of a phenomenon caused by the difference in physical properties between the information recording medium and the spacer. For example, the fact that the difference between the thermal expansion coefficient of the information recording medium and the thermal expansion coefficient of the spacer is small is a phenomenon that can occur due to the difference between the two thermal expansion coefficients, for example, distortion of the information recording medium, This is preferable from the viewpoint of suppressing the occurrence of a decrease in stability during rotation due to a position shift. From this point of view, the recording / reproducing apparatus according to one aspect of the present invention is applied to one aspect of the present invention as at least one information recording medium, and more information recording media when a plurality of information recording media are included. It is preferable to include the glass spacer according to one embodiment of the present invention as the information recording medium, and as at least one spacer and as a larger number of spacers when a plurality of spacers are included. For example, in the recording / reproducing apparatus according to one embodiment of the present invention, the glass constituting the information recording medium substrate included in the information recording medium and the glass constituting the glass spacer have the same glass composition. be able to.

The recording / reproducing apparatus according to one aspect of the present invention may include at least one of the information recording medium according to one aspect of the present invention and the glass spacer according to one aspect of the present invention. Known techniques relating to the apparatus can be applied. In one aspect, the magnetic head includes an energy source (for example, a heat source such as a laser light source, a microwave, etc.) for assisting magnetization reversal (assuming writing of a magnetic signal), a recording element unit, and a reproducing element unit. An energy-assisted magnetic recording head can be used. Such an energy-assisted recording type magnetic recording / reproducing apparatus including an energy-assisted magnetic recording head is useful as a magnetic recording / reproducing apparatus having high recording density and high reliability. When manufacturing an information recording medium (magnetic recording medium) used in a magnetic recording / reproducing apparatus of an energy assist recording system such as a heat assist recording system having a heat assist magnetic recording head having a laser light source or the like, magnetic anisotropy energy In some cases, a magnetic recording layer containing a high magnetic material is formed on an information recording medium substrate. In order to form such a magnetic recording layer, film formation is usually performed at a high temperature, or heat treatment is performed at a high temperature after the film formation. The information recording medium substrate according to one embodiment of the present invention is preferable as an information recording medium substrate that can have high heat resistance that can withstand such high-temperature processing. However, the recording / reproducing apparatus according to one embodiment of the present invention is not limited to the energy-assisted magnetic recording / reproducing apparatus.

Hereinafter, the present invention will be described in more detail with reference to examples. However, this invention is not limited to the aspect shown in the Example.

[Glass No. 1-No. 48]
In order to obtain glasses having the compositions shown in Table 1 (Table 1-1 to Table 1-3), raw materials such as oxides, carbonates, nitrates, and hydroxides were weighed and mixed to obtain blended raw materials. The molten glass obtained by adding this blended raw material to the melting tank and heating and melting it in the range of 1400-1600 ° C is held at 1400-1550 ° C for 6 hours in the clarification tank, and then the temperature is lowered (decreased). The glass was held in the range of 1200 to 1400 ° C. for 1 hour and then a molten glass was formed to obtain a glass (amorphous oxide glass) for the following evaluation.

[Evaluation methods]
(1) Glass transition temperature (Tg), average linear expansion coefficient (α)
The glass transition temperature Tg of each glass and the average linear expansion coefficient α at 100 to 300 ° C. were measured using a thermomechanical analyzer (TMA; Thermomechanical Analysis).

(2) Young's modulus Young's modulus of each glass was measured by an ultrasonic method.

(3) Specific gravity The specific gravity of each glass was measured by the Archimedes method.

(4) Specific modulus The specific modulus was calculated from the Young's modulus obtained in (2) above and the specific gravity obtained in (3).

(5) Water resistance Dw
The powder method water resistance (Dw) of each glass was evaluated by the following method based on the chemical durability (water resistance) measurement method by the powder method defined in the Japan Optical Glass Industry Association standard.
Powder glass having a mass corresponding to specific gravity (particle size: 425 to 600 μm) is placed in a platinum basket and immersed in a quartz glass round bottom flask containing 80 ml of pure water (pH = 6.5 to 7.5). It processed for 60 minutes in the boiling water bath, and calculated | required the weight loss rate (%).

(6) Acid resistance Da
The powder method acid resistance (Da) of each glass was evaluated by the following method according to the measurement method of the powder method water resistance Dw.
Powder glass (particle size: 425 to 600 μm) having a mass corresponding to the specific gravity is placed in a platinum basket, immersed in a quartz glass round bottom flask containing 80 ml of 0.01 mol / L nitric acid aqueous solution, and in a boiling water bath for 60 minutes. The weight loss rate (%) was calculated.

(7) Glass stability 100 g of each glass is put in a platinum crucible, and each crucible is put in a heating furnace whose furnace temperature is set to 1250 ° C. or 1200 ° C., and left for 16 hours while maintaining the furnace temperature. (Retention test). After 16 hours, the crucible was taken out from the heating furnace, the glass in the crucible was transferred onto a refractory and cooled to room temperature, and the presence or absence of crystals in each glass was observed with an optical microscope and evaluated according to the following criteria.
A: A crystal is not confirmed by magnifying observation (magnification 40 to 100 times) with an optical microscope.
B: Crystals are confirmed by magnifying observation (magnification 40 to 100 times) with an optical microscope, but crystals are not confirmed by visual observation.
C: Crystals are confirmed by visual observation.

(8) Liquid phase temperature For each glass, put a glass sample (100 g) into a platinum crucible, put each crucible into a heating furnace set at a predetermined furnace temperature, and maintain the furnace temperature. Left for 16 hours. After 16 hours, the crucible was taken out from the heating furnace, the glass in the crucible was transferred onto a refractory and cooled to room temperature, and the presence or absence of crystals of each glass was observed with an optical microscope. The liquid crystal temperature was defined as the lowest temperature at which no crystal was observed by magnifying observation (magnification 40 to 100 times) with an optical microscope.
The liquidus temperature is an index of devitrification resistance, preferably 1250 ° C. or less, more preferably 1220 ° C. or less, and still more preferably 1200 ° C. or less.

The above results are shown in Table 1 (Table 1-1 to Table 1-3).

From the results shown in Table 1, it was confirmed that all the glass for information recording medium substrates shown in Table 1 had high rigidity, low specific gravity, and excellent chemical durability.

On the other hand, the glass having the composition of Examples 2, 6, 8, and 9 in Table 1 of Patent Document 1 (Japanese Patent Laid-Open No. 11-302031) is referred to as No. 1 above. 1-No. Production was attempted in the same manner as for production of 48 glass, but it was devitrified and glass could not be obtained.

[Production of information recording medium substrate]
(1) Production of Substrate Blank Next, a disk-shaped substrate blank was produced by the following method A or B.
(Method A)
About each glass shown in Table 1, the molten glass of the above-mentioned example which was clarified and homogenized flows out from the outflow pipe at a constant flow rate and is received by the lower mold for press molding, and a predetermined amount of molten glass lump is formed on the lower mold. The molten glass that flowed out was cut with a cutting blade. Then, the lower mold on which the molten glass block was placed was immediately taken out from below the pipe, and was pressed into a thin disk shape having a diameter of 66 mm and a thickness of 1.2 mm using the upper mold and the barrel mold opposed to the lower mold. After the press molded product was cooled to a temperature at which it was not deformed, it was taken out of the mold and annealed to obtain a substrate blank. In the above-described molding, the molten glass flowing out using a plurality of lower molds was successively formed into a disk-shaped substrate blank.
(Method B)
For each glass shown in Table 1, the molten glass of the above-described embodiment, which has been clarified and homogenized, is continuously cast from above into a through hole of a heat-resistant mold provided with a cylindrical through hole, and formed into a cylindrical shape. It was taken out from the lower side of the through hole. The annealed glass was annealed, and then the glass was sliced at regular intervals in a direction perpendicular to the cylinder axis using a multi-wire saw to produce a disk-shaped substrate blank.
Although the above-described methods A and B are employed here, the following methods C and D are also suitable as a method for manufacturing a disk-shaped substrate blank.
(Method C)
The molten glass is poured onto a float bath, formed into a sheet-like glass (forming by a float method), and then annealed, and then a disc-like glass is cut out from the sheet glass to obtain a substrate blank.
(Method D)
The molten glass is formed into a sheet-like glass by the overflow down draw method (fusion method) and annealed, and then the disc-like glass is cut out from the sheet glass to obtain a substrate blank.

(2) Production of glass substrate A through hole is made in the center of the substrate blank obtained by each of the above-mentioned methods, and the outer and inner circumferences are ground, and the main surface of the disk is lapped and polished (mirror polished). Thus, a glass substrate for a magnetic disk having a diameter of 65 mm and a thickness of 0.8 mm was finished. The obtained glass substrate was washed with a 1.7% by mass aqueous solution of silicic acid (H ₂ SiF) and then with a 1% by mass aqueous potassium hydroxide solution, then rinsed with pure water and then dried. When the surface of the board | substrate produced from each glass shown in Table 1 was magnified and observed, surface roughness was not recognized but it was a smooth surface.

[Production of information recording medium (magnetic disk)]
By the following method, an adhesion layer, an underlayer, a magnetic recording layer, a protective layer, and a lubricating layer were formed in this order on the main surface of a glass substrate obtained from each glass shown in Table 1 to obtain a magnetic disk.

First, an adhesion layer, an underlayer, and a magnetic recording layer were sequentially formed in an Ar atmosphere by a DC magnetron sputtering method using a vacuum-deposited film forming apparatus.

At this time, the adhesion layer was formed using a CrTi target so as to be an amorphous CrTi layer having a thickness of 20 nm. Subsequently, a 10 nm thick layer made of CrRu was formed as a base layer by a DC magnetron sputtering method in an Ar atmosphere using a single wafer / stationary facing type film forming apparatus. The magnetic recording layer was formed at a film formation temperature of 400 ° C. using a hard magnetic target made of CoCrPt containing chromium oxide.

Subsequently, a protective layer made of hydrogenated carbon was formed to 3 nm by a CVD method using ethylene as a material gas. Thereafter, a lubricating layer using PFPE (perfluoropolyether) was formed by a dip coating method. The thickness of the lubricating layer was 1 nm.
A magnetic disk was obtained by the above manufacturing process. The obtained magnetic disk is mounted on a hard disk drive (flying height: 8 nm) equipped with a DFH mechanism, and a magnetic signal is recorded at a recording density of 20 gigabits per square inch in a recording area on the main surface of the magnetic disk. As a result, a phenomenon (head crash) in which the magnetic head and the magnetic disk surface collide was not confirmed.

According to one embodiment of the present invention, an information recording medium optimal for high density recording can be provided.

Finally, the above-mentioned aspects are summarized.

According to one aspect, the SiO ₂ content is 55 to 68%, the B ₂ O ₃ content is 0 to 5%, the Al ₂ O ₃ content is 1 to 14%, and the MgO content is expressed in mol%. 8-23%, CaO content 1-10%, Li ₂ O content 5-18%, total content of Li ₂ O, Na ₂ O and K ₂ O 5-18%, ZrO ₂ , TiO ₂ , the total content of BaO, SrO and rare earth oxides is 0-5%, the total content of Li ₂ O and MgO is 20-32%, the total content of alkali metal oxides and alkaline earth metal oxides The molar ratio of the total content of Li ₂ O and MgO to the amount {(Li ₂ O + MgO) / (alkali metal oxide + alkaline earth metal oxide)} is 0.60 to 0.95, Molar ratio of SiO ₂ content to total content (SiO ₂ / Al There is provided a glass for an information recording medium substrate which is an amorphous glass having a potassium metal oxide) of 3 to 13, a Young's modulus of 86 GPa or more and a specific gravity of 2.75 or less.

The glass has high rigidity, low specific gravity, and can exhibit excellent chemical durability.

In one aspect, the molar ratio {(SiO ₂ + CaO) / (Al ₂ O ₃ + ZrO ₂ )} of the total content of SiO ₂ and CaO to the total content of Al ₂ O ₃ and ZrO _{2 in the} glass is: It can range from 5.0 to 25.0.

In one aspect, the total content of MgO and CaO in the glass can be in the range of 15-35%.

In one aspect, the molar ratio (MgO / CaO) of the MgO content to the CaO content of the glass can be in the range of 1.0 to 20.0.

In one embodiment, the molar ratio of MgO content to the total content of alkaline earth metal oxides in the glass (MgO / alkaline earth metal oxide) can be 0.5 or more.

In one embodiment, the molar ratio {Al ₂ O ₃ / (Li ₂ O + Na ₂ O)} of the Al ₂ O ₃ content to the total content of Li ₂ O and Na ₂ O in the glass is 0.25 to 1 .25 range.

In one embodiment, the TiO ₂ content of the glass can range from 0 to 5%.

In one aspect, the ZrO ₂ content of the glass can range from 0 to 3 mol%.

In one embodiment, the SiO ₂ content of the glass can be in the range of 58-65 mol%.

In one aspect, the specific elastic modulus of the glass can be 33 MNm / kg or more.

According to one aspect, an information recording medium substrate comprising the information recording medium is provided.

According to one aspect, an information recording medium having an information recording layer on the information recording medium substrate is provided.

According to one aspect, the SiO ₂ content is 55 to 68%, the B ₂ O ₃ content is 0 to 5%, the Al ₂ O ₃ content is 1 to 14%, and the MgO content is expressed in mol%. 8-23%, CaO content 1-10%, Li ₂ O content 5-18%, total content of Li ₂ O, Na ₂ O and K ₂ O 5-18%, ZrO ₂ , TiO ₂ , the total content of BaO, SrO and rare earth oxides is 0-5%, the total content of Li ₂ O and MgO is 20-32%, the total content of alkali metal oxides and alkaline earth metal oxides The molar ratio of the total content of Li ₂ O and MgO to the amount {(Li ₂ O + MgO) / (alkali metal oxide + alkaline earth metal oxide)} is 0.60 to 0.95, Molar ratio of SiO ₂ content to total content (SiO ₂ / Al There is provided a glass spacer for a recording / reproducing apparatus including amorphous glass having a potassium metal oxide) of 3 to 13, a Young's modulus of 86 GPa or more and a specific gravity of 2.75 or less.

The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
For example, the glass for an information recording medium substrate according to one embodiment of the present invention can be manufactured by adjusting the composition described in the specification for the glass composition exemplified above.
Of course, it is possible to arbitrarily combine two or more of the matters described as examples or preferred ranges in the specification.

Claims (13)

1. In mol% display,
   SiO ₂ content is 55 to 68%,
   B ₂ O ₃ content is 0-5%,
   Al ₂ O ₃ content is 1 to 14%,
   MgO content is 8-23%,
   CaO content is 1-10%,
   Li ₂ O content is 5-18%,
   The total content of Li ₂ O, Na ₂ O and K ₂ O is 5-18%,
   The total content of ZrO ₂ , TiO ₂ , BaO, SrO and rare earth oxide is 0-5%,
   The total content of Li ₂ O and MgO is 20 to 32%,
   Molar ratio of total content of Li ₂ O and MgO to total content of alkali metal oxide and alkaline earth metal oxide {(Li ₂ O + MgO) / (alkali metal oxide + alkaline earth metal oxide) } Is 0.60-0.95,
   The molar ratio of SiO ₂ content to the total content of alkali metal oxides (SiO ₂ / alkali metal oxide) is 3 to 13,
   And
   A glass for an information recording medium substrate, which is an amorphous glass having a Young's modulus of 86 GPa or more and a specific gravity of 2.75 or less.
2. The molar ratio of the total content of SiO ₂ and CaO to the total content of Al ₂ O ₃ and ZrO ₂ {(SiO ₂ + CaO) / (Al ₂ O ₃ + ZrO ₂ )} is 5.0 to 25.0 The glass for an information recording medium substrate according to claim 1, which is a range.
3. The glass for an information recording medium substrate according to claim 1 or 2, wherein the total content of MgO and CaO is in the range of 15 to 35%.
4. The glass for an information recording medium substrate according to any one of claims 1 to 3, wherein a molar ratio of MgO content to CaO content (MgO / CaO) is in the range of 1.0 to 20.0.
5. The information recording according to any one of claims 1 to 4, wherein a molar ratio of MgO content to the total content of alkaline earth metal oxide (MgO / alkaline earth metal oxide) is 0.5 or more. Glass for medium substrate.
6. The molar ratio of Al ₂ O ₃ content to the total content of Li ₂ O and Na ₂ O {Al ₂ O ₃ / (Li ₂ O + Na ₂ O)} is in the range of 0.25 to 1.25. Item 6. The glass for an information recording medium substrate according to any one of Items 1 to 5.
7. TiO ₂ content is in the range of 0-5%, the information recording medium glass substrate according to any one of claims 1 to 6.
8. The glass for an information recording medium substrate according to any one of claims 1 to 7, wherein the ZrO ₂ content is in the range of 0 to 3 mol%.
9. The glass for an information recording medium substrate according to any one of claims 1 to 8, wherein the SiO ₂ content is in the range of 58 to 65 mol%.
10. The glass for an information recording medium substrate according to any one of claims 1 to 9, wherein the specific elastic modulus is 33 MNm / kg or more.
11. An information recording medium substrate comprising the glass for an information recording medium substrate according to any one of claims 1 to 10.
12. An information recording medium having an information recording layer on the information recording medium substrate according to claim 11.
13. In mol% display,
    SiO ₂ content is 55 to 68%,
    B ₂ O ₃ content is 0-5%,
    Al ₂ O ₃ content is 1 to 14%,
    MgO content is 8-23%,
    CaO content is 1-10%,
    Li ₂ O content is 5-18%,
    The total content of Li ₂ O, Na ₂ O and K ₂ O is 5-18%,
    The total content of ZrO ₂ , TiO ₂ , BaO, SrO and rare earth oxide is 0-5%,
    The total content of Li ₂ O and MgO is 20 to 32%,
    Molar ratio of total content of Li ₂ O and MgO to total content of alkali metal oxide and alkaline earth metal oxide {(Li ₂ O + MgO) / (alkali metal oxide + alkaline earth metal oxide) } Is 0.60-0.95,
    The molar ratio of SiO ₂ content to the total content of alkali metal oxides (SiO ₂ / alkali metal oxide) is 3 to 13,
    And
    A glass spacer for a recording / reproducing apparatus comprising amorphous glass having a Young's modulus of 86 GPa or more and a specific gravity of 2.75 or less.