Glass composition for information recording medium and glass plate for information recording medium

Abstract

Provided is a glass composition which has a large Young's modulus and is suitable for an information recording medium represented by a hard disk drive (HDD). The glass composition according to the present invention has a Young's modulus of 98 GPa or more, and contains 17-30 mol% of MgO.

Description

Technical Field

[0001] This invention relates to glass compositions for information recording media, and more specifically, to glass compositions suitable for information recording media used in information recording devices represented by HDDs (Hard Disk Drives). Additionally, this invention relates to glass plates for information recording media. Background Technology

[0002] Information recording devices such as hard disks, represented by HDDs, are constantly demanding increased recording capacity and reduced access time. One means to achieve this is to increase the rotation speed of the information recording medium. However, the substrate of the information recording medium flexes due to rotation. Therefore, if the rotation speed increases, the resonance of the information recording medium increases, which may lead to collisions between the information recording medium and the read / write head, resulting in read errors or head damage. Therefore, in existing substrates, it is impossible to reduce the distance between the read / write head (known as the flight altitude) and the information recording medium to a certain level, which becomes a constraint on increasing recording capacity. In order to reduce substrate flexing and resonance, it is desirable for the substrate to have a high Young's modulus. It is known that although glass varies depending on its composition, it generally has a higher Young's modulus than the aluminum alloy that constitutes the aluminum substrate. Glass compositions developed for use as substrates of information recording media are disclosed, for example, in Patent Document 1.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2012 / 131824 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] The glass composition disclosed in Patent Document 1 has a Young's modulus of about 80 GPa or less, leaving room for improvement. Therefore, the object of the present invention is to provide a glass composition suitable for information recording media.

[0008] Problem-solving methods

[0009] This invention provides a glass composition for an information recording medium, wherein,

[0010] The Young's modulus is above 98 GPa.

[0011] It contains 17–30 mol% MgO.

[0012] The effects of the invention

[0013] According to the present invention, a glass composition suitable for information recording media can be provided. Attached Figure Description

[0014] Figure 1 This is a partial cross-sectional view showing an example of an HDD. Detailed Implementation

[0015] The following describes the details of the present invention, but it is not intended to limit the invention to specific embodiments. In this specification, "substantially free" of a certain component means that the content of such component is less than 0.1 mol%, preferably less than 0.08 mol%, more preferably less than 0.05 mol%. Furthermore, the temperature at which the logarithm (logη) of the liquid phase viscosity η (unit: dPa·s) of the glass composition melt is n is denoted as Tn. Additionally, the upper and lower limits of the content and properties can be arbitrarily combined.

[0016] The present invention provides a glass composition for an information recording medium and a glass plate for an information recording medium in the following manner. The glass composition of the first manner has a Young's modulus of 98 GPa or higher and contains 17 to 30 mol% MgO.

[0017] The glass composition of the second method, according to the first method, contains Al2O3.

[0018] The glass composition of the third method, according to the first or second method, wherein the specific elastic modulus is 36MNm / kg or more.

[0019] The glass composition of the fourth embodiment, according to any one of the first to third embodiments, further comprises 0.2 to 3 mol% of Li₂O and 0.2 to 3 mol% of B₂O₃.

[0020] The glass composition of the fifth method, according to any one of the methods 1 to 4, wherein ΔT, which is the difference between the liquidus temperature (T2) and the devitrification temperature, is 20°C or more.

[0021] The glass composition of the sixth embodiment, according to any one of the first to fifth embodiments, further contains Na2O.

[0022] The glass composition of the seventh embodiment, according to any one of embodiments 1 to 6, wherein, expressed in mole percent, contains:

[0023] SiO2 50~65%

[0024] Al2O 37.5~26%

[0025] MgO 15-30%

[0026] CaO 0-8%

[0027] B2O30~3%

[0028] Li2O 0-3%

[0029] Na2O 0–0.2%,

[0030] The combined content of MgO and CaO ranges from 18% to 35 mol%.

[0031] The molar ratio calculated from Al2O3 / (MgO+CaO) is less than 1.

[0032] The glass composition of method 8, according to any one of methods 1 to 7, wherein, expressed in mole percent, contains:

[0033] SiO2 53-60%

[0034] Al2O3 11-15%

[0035] MgO 18-30%

[0036] CaO 0-5%

[0037] B2O3 0.2–1.5%

[0038] Li2O 0.5~2.5%

[0039] Na2O 0~0.2%,

[0040] The molar ratio calculated from Al2O3 / (MgO+CaO) is 0.3 to 0.5.

[0041] The glass composition of the ninth embodiment, according to any one of embodiments 1 to 7, wherein, expressed in mole percent, contains:

[0042] SiO2 53-60%

[0043] Al2O3 15~26%

[0044] MgO 17-30%

[0045] CaO 0-5%

[0046] B2O3 0.2-3%

[0047] Li2O 0.2–1.5%

[0048] Na2O 0~0.2%,

[0049] The molar ratio calculated from Al2O3 / (MgO+CaO) is 0.5 to 1.0.

[0050] The glass composition of the 10th embodiment, according to any one of the 1st to 7th embodiments, further comprises 50 to 57.8 mol% of SiO2, and the total content of TiO2 and Y2O3 is 3 mol% or less.

[0051] The glass plate of the 11th embodiment contains the glass composition described in any one of the 1st to 10th embodiments.

[0052] [Hard Disk Drive (HDD)]

[0053] The glass composition and glass plate of this embodiment have high Young's modulus and low specific gravity, making them suitable for information recording devices, and particularly suitable for information recording media in HDDs. Figure 1 This is a partial cross-sectional view of an example HDD. HDD10 has: a protective cover forming a sealed enclosure; and multiple platters 1 disposed within the protective cover. Figure 1 The protective cover is only partially shown. Furthermore, the number of discs 1, serving as the information recording medium, is not limited to the four shown. Each disc 1 has: a glass plate made of a glass composition; and magnetic recording layers formed on two main surfaces of the glass plate. Each disc 1 is an annular circular plate with a circular hole in its center. Annular spacers 2 are arranged between adjacent discs 1 to ensure a predetermined interval. The four discs 1 are rotatably supported in their holes by a spindle motor 3. A magnetic head assembly 5 is also disposed inside the protective cover. The magnetic head assembly 5 has: a main body portion disposed on the outer periphery of the four discs 1; and a swing arm portion extending from the main body portion along the main surfaces of the discs 1. The swing arm portion has a magnetic head 6, also called a slider, at its front end. The number of magnetic heads 6 corresponds to the number of the two main surfaces of the discs 1. Figure 1 There are 8 read / write heads configured in the disk. As the disk 1 rotates, the read / write head 6 slightly floats off the main surface of the disk. The deflection of the disk 1 is the cause of damage to the read / write head 6.

[0054] In HDDs, to achieve high capacity, multiple very thin platters are arranged in a small space. With such a dense arrangement, even slight deflection of the rotating platters can easily damage the read / write head. Therefore, a high Young's modulus is desirable for the material constituting the platters. Furthermore, to reduce the load on the small motors that rotate the multiple platters, a low specific gravity is desirable. With the advancement of HDD capacity, the importance of low specific gravity, along with high Young's modulus, has increased. Moreover, from the viewpoint of increasing recording density, it is desirable to use magnetic recording layers capable of handling energy-assisted magnetic recording, represented by heat-assisted magnetic recording (HAMR). High-temperature heat treatment is required during the formation of magnetic recording layers capable of HAMR. In this case, the glass substrate requires heat resistance. As characteristics of the glass composition, Young's modulus and specific gravity, as well as the glass transition temperature (Tg), which serves as an indicator of heat resistance as needed, are all important.

[0055] [Components of the glass composition]

[0056] The following percentages represent the glass content, all in moles.

[0057] (SiO2)

[0058] SiO2 is a component that forms a glass framework and contributes to improved heat resistance. The SiO2 content can be in the range of 50% to 65%. Preferably, the SiO2 content is 52% or more, more preferably 53% or more, particularly preferably 54% or more, and depending on the situation, it can also be 56% or more, and further preferably 57% or more. If the SiO2 content is too high, the Young's modulus will decrease. Therefore, the SiO2 content is preferably 62% or less, 61% or less, more preferably 60% or less, particularly preferably 59% or less, and depending on the situation, it can also be 58% or less, 57.8% or less, and further preferably 57.5% or less.

[0059] (Al2O3)

[0060] Al2O3 helps maintain the heat resistance and water resistance of glass compositions, and is also a component that affects devitrification temperature and viscosity. The content of Al2O3 can range from 7.5% to 26%. Preferably, the content of Al2O3 is 9% or more, more preferably 10% or more, particularly preferably 11% or more, and depending on the situation, it can also be 12% or more, and further 14% or more. If the content of Al2O3 is too high, the liquidus temperature will rise significantly, causing manufacturing problems. Therefore, the content of Al2O3 is preferably 24% or less, more preferably 22% or less, and depending on the situation, it can also be 20% or less, and further 19% or less.

[0061] Especially for mass production considerations, it is preferable that the devitrification temperature of the glass composition is sufficiently low compared to the liquidus temperature. The content of Al₂O₃ suitable for sufficiently lowering the devitrification temperature compared to the liquidus temperature is 11–15%, more preferably 11–14%, and particularly 11.5–13.5%. As described later, to sufficiently lower the devitrification temperature compared to the liquidus temperature, appropriate amounts of Li₂O and / or B₂O₃ can be added. An Al₂O₃ content of 11–15% also contributes to a reduction in specific gravity. The content of Al₂O₃ suitable for sufficiently increasing crack resistance is 15–26%, more preferably 16–22%, and particularly 17–21%.

[0062] <(Al2O3) / (SiO2+Al2O3)>

[0063] Preferably, the molar ratio of Al2O3 to the total content of SiO2 and Al2O3 is set in the range of 0.15 to 0.35. This facilitates achieving both a high Young's modulus and a moderately high liquidus temperature. The molar ratio Al2O3 / (SiO2 + Al2O3) is 0.16 or higher, more preferably 0.18 or higher, and depending on the situation, it can also be 0.20 or higher, or 0.30 or lower. Furthermore, in compositions containing both B2O3 and Li2O, a molar ratio Al2O3 / (SiO2 + Al2O3) with a suitable low specific gravity is 0.25 or lower.

[0064] (MgO)

[0065] MgO contributes to increasing Young's modulus and also affects devitrification temperature and viscosity. The MgO content can range from 17% to 30%. Preferably, the MgO content is 18% or more, particularly preferably 20% or more, and depending on the situation, it can also be 21% or more, and further, 22% or more. If the MgO content is too high, the liquidus temperature will rise significantly. Therefore, the MgO content is preferably 29% or less, and depending on the situation, it can also be 28% or less, and further, 27% or less.

[0066] The content of MgO suitable for sufficiently lowering the devitrification temperature compared to the liquidus temperature is 18-30%, and more preferably 20-28%.

[0067] The content of MgO suitable for significantly increasing crack resistance is 18–30%, further 18–26%, and particularly 22–26%.

[0068] (CaO)

[0069] CaO is any component that helps maintain water resistance and affects devitrification temperature, viscosity, etc. The CaO content can be in the range of 0% to 8%. From the viewpoint of lowering the liquidus temperature, it is preferable to add an appropriate amount of CaO. Therefore, it is preferable to add CaO (content higher than 0%), preferably 0.1% or more, more preferably 0.12% or more, and depending on the situation, it can also be 2% or more, and further more preferably 3% or more. However, too much CaO reduces Young's modulus. Therefore, the CaO content is 7% or less, further preferably 5% or less, particularly 4.5% or less, and depending on the situation, preferably 4% or less. The content of CaO, which is particularly suitable for improving Young's modulus and crack resistance, is less than 1%.

[0070] <Total of MgO and CaO>

[0071] The combined content of MgO and CaO is 18-35%, preferably in the range of 20-30%.

[0072] <(Al2O3) / (MgO+CaO)>

[0073] The preferred molar ratio of Al2O3 to the total content of MgO and CaO is set to be less than 1. This facilitates the coexistence of a high Young's modulus and a moderately high liquidus temperature. The molar ratio Al2O3 / (MgO+CaO) is preferably 0.3 to 0.9, particularly preferably 0.35 to 0.85, and can also be 0.4 to 0.7, and further 0.4 to 0.6, depending on the situation. The molar ratio Al2O3 / (MgO+CaO) can also be 0.3 to 0.5. However, the molar ratio Al2O3 / (MgO+CaO) particularly suitable for improving crack resistance is 0.5 to 1.0, 0.7 or more but less than 1, further 0.7 to 0.9, and particularly 0.8 to 0.9.

[0074] (B2O3)

[0075] B2O3 is any component that forms the framework of glass and affects properties such as devitrification temperature and viscosity. The content of B2O3 can be in the range of 0% to 3%. Adding trace amounts of B2O3 helps to lower the devitrification temperature. Adding trace amounts of B2O3 also helps to lower the specific gravity. Therefore, it is preferable to add B2O3 (content higher than 0%), preferably 0.1% or more, 0.2% or more, particularly preferably 0.3% or more, and depending on the situation, it can also be 0.5% or more, and further 0.7% or more. However, excessive B2O3 reduces Young's modulus. The content of B2O3 is preferably 2.5% or less, more preferably 2% or less, particularly preferably 1.8% or less, and depending on the situation, it can be 1.6% or less, and further 1.5% or less. An example of a preferred range for the content of B2O3 is 0.1% to 1.6%.

[0076] (Li2O)

[0077] Li₂O is a component used to modify the glass framework and can be any component that affects properties such as liquidus temperature, devitrification temperature, and viscosity. The content of Li₂O can be in the range of 0% to 3%. Adding Li₂O within this range is effective in reducing the devitrification temperature. Therefore, it is preferable to add Li₂O (content higher than 0%), preferably 0.1% or more, 0.2% or more, particularly preferably 0.3% or more, and depending on the situation, it can also be 0.5% or more, and further 0.7% or more. If the content of Li₂O is too high, the Young's modulus decreases. Therefore, the content of Li₂O is preferably 2.5% or less, more preferably 2% or less, particularly preferably 1.8% or less, and depending on the situation, it can also be 1.6% or less, and further 1.5% or less. An example of a preferred range for the content of Li₂O is 0.2% to 2.5%, which is higher than the range for the content of Na₂O.

[0078] <Coexistence of B2O3 and Li2O>

[0079] If B2O3 and Li2O coexist (B2O3 > 0%, Li2O > 0%), the liquidus temperature and devitrification temperature of the glass can be easily and appropriately adjusted. The coexistence of B2O3 and Li2O is also advantageous from the viewpoint of reducing the specific gravity of the glass. The combined content of B2O3 and Li2O is preferably 0.1% or more, more preferably higher than 0.5%, particularly preferably 0.7% or more, and may be 1% or more depending on the situation. Furthermore, the combined content is preferably 5.5% or less, more preferably 5% or less, particularly preferably 4%, and may be 3.5% or less depending on the situation. The content of B2O3 and Li2O can be 0.1% to 4%, further 0.2% to 3%, particularly 0.2% to 2.5%. From the viewpoint of reducing specific gravity, the content of B2O3 and Li2O can be 0.1% to 1.3% respectively.

[0080] From the viewpoint of improving properties, it is advantageous to add B2O3 and Li2O in an appropriate ratio. Preferably, the molar ratio of B2O3 / Li2O is 0.2 to 5, more preferably 0.4 to 2.5, particularly preferably 0.5 to 2, and, depending on the circumstances, preferably in the range of 0.8 to 1.25.

[0081] (Na2O)

[0082] Like Li₂O, Na₂O is an arbitrary component that affects properties such as liquidus temperature, devitrification temperature, and viscosity. However, because it has a greater effect on reducing Young's modulus than Li₂O, its content can be 0 to 0.2%. While it is desirable to have virtually no Na₂O, it is limited to 0.2%, and further limited to 0.15%, for the purpose of clarifying the glass melt. For example, it is preferable to add it in a range of above 0% and below 0.1%.

[0083] <Total of the ingredients described above>

[0084] The total content of the seven components described above (SiO2, Al2O3, MgO, CaO, B2O3, Li2O, and Na2O) is preferably 95% or more, more preferably 97% or more, particularly preferably 98% or more, especially preferably 99% or more, and may also be 99.5%, further higher than 99.9%, or even 100%, depending on the circumstances. In an embodiment where the total content of the seven components reaches 100%, in other words, the glass composition consists only of SiO2, Al2O3, MgO, CaO, B2O3, Li2O, and Na2O.

[0085] <Additional ingredients>

[0086] Examples of additional ingredients beyond the seven ingredients described above are shown below. However, additional ingredients are not limited to those listed below, and the display of the content of additional ingredients is also illustrative.

[0087] (K2O)

[0088] Like Li2O, K2O is an arbitrary component that affects properties such as liquidus temperature, devitrification temperature, and viscosity, and plays a role in promoting the clarification of glass melt. However, because it has a greater effect on reducing Young's modulus than Na2O, its content is preferably 0 to 0.1%, more preferably 0 to 0.05%, and particularly preferably set in the range of 0 to 0.03%.

[0089] (SrO)

[0090] SrO can be any component that affects properties such as liquidus temperature, devitrification temperature, and viscosity. However, the addition of SrO can also lead to a decrease in Young's modulus. In addition, excessive SrO hinders the homogeneity of the glass melt. Therefore, the SrO content is preferably set in the range of 0 to 5%. The SrO content is preferably 3% or less, more preferably 1% or less, particularly preferably 0.5% or less, and especially preferably 0.1% or less. Furthermore, the combined content of SrO and CaO is preferably 8% or less, more preferably 6% or less, particularly preferably 5% or less, and, depending on the circumstances, preferably 4% or less.

[0091] (BaO)

[0092] BaO can affect properties such as liquidus temperature, devitrification temperature, and viscosity. However, the addition of BaO significantly reduces Young's modulus. Furthermore, BaO is environmentally unfriendly and requires strict operating conditions. Therefore, it is preferable to have virtually no BaO.

[0093] (Transition metal oxides, etc.)

[0094] Oxides of transition elements (Groups 3 to 11 of the periodic table), known as transition metal oxides, are permitted as additional components. Examples of transition metal oxides include TiO2, ZrO2, Fe2O3, Y2O3, La2O3, and CeO2. ZnO, an oxide of Group 12 elements, is also permitted as an additional component. Although it is desirable to essentially eliminate these oxides, they are sometimes unavoidably mixed in as impurities from raw materials or manufacturing equipment. In addition, depending on the type of oxide, there are cases where trace amounts are added to act as clarifying agents, etc. The content of oxides of Groups 3 to 12 elements, expressed as their totality, is preferably 3% or less, more preferably 1% or less, particularly preferably 0.5% or less, and may be limited to 0.1% or less if necessary. The content of each transition metal oxide is preferably 0.5% or less, particularly preferably 0.3% or less, and especially preferably 0.1% or less.

[0095] The combined content of TiO2 and Y2O3 can be less than 3%, and further less than 2%. The content of TiO2 and Y2O3 can be less than 1% and less than 0.7%, respectively. Suppressing the content of these components is advantageous in terms of manufacturing costs. Suppressing the content of these components is also advantageous from the perspective of reducing their specific gravity.

[0096] In this specification, the content of oxides of transition elements with multiple valences in the glass composition is calculated by converting them into oxides with the highest oxidation state of that metal. For example, iron oxide is usually present in the glass composition as Fe2O3 or FeO. Therefore, iron oxide present as FeO is converted to Fe2O3, and the content of iron oxide is calculated by adding it to iron oxide present as Fe2O3 (conventionally denoted as "T-Fe2O3").

[0097] (Other ingredients)

[0098] Examples of additional components besides those mentioned above include SnO2, Sb2O3, Sb2O5, SO3, Cl, and F. These components can function as clarifying agents. Other examples of additional components include Ga2O3 and P2O5. The content of each component from SnO2 to P2O5 listed in this column is preferably 0.5% or less, particularly preferably 0.3% or less, and especially preferably 0.1% or less.

[0099] <Examples of preferred methods for glass compositions>

[0100] In one embodiment of the invention, the glass composition is substantially free of oxides of rare earth elements. In another embodiment, the glass composition contains 0-0.5% T-Fe₂O₃ and is substantially free of oxides of divalent metals other than MgO, CaO, and FeO. In yet another embodiment, the glass composition is substantially free of alkali metal oxides other than Li₂O and Na₂O. In yet another embodiment, the glass composition is substantially free of TiO₂ and ZrO₂. In yet another embodiment, the glass composition contains nitrides at a rate of 10% by weight or less, preferably substantially free of nitrides. In yet another embodiment, the glass composition is not a crystallized glass. In other words, no diffraction peaks from crystals were detected by X-ray diffraction.

[0101] In one embodiment of the present invention, the total content of the aforementioned seven components (SiO2, Al2O3, MgO, CaO, B2O3, Li2O, and Na2O) and the additional five components (K2O, SrO, TiO2, ZrO2, and T-Fe2O3) in the glass composition is 99% or more, further 99.5% or more, particularly 99.9% or more, especially 99.95% or more, and depending on the situation, 100%. In this embodiment, the content of the additional five components is as follows: K2O: 0-0.05%, SrO: 0-5%, TiO2: 0-0.1%, ZrO2: 0-0.1%, T-Fe2O3: 0-0.5%.

[0102] In one embodiment of the present invention, the total content of the aforementioned seven components (SiO2, Al2O3, MgO, CaO, B2O3, Li2O, and Na2O) and the three additional components (K2O, TiO2, and T-Fe2O3) in the glass composition is 99% or more, further 99.5% or more, particularly 99.9% or more, especially 99.95% or more, and depending on the situation, 100%. In this embodiment, the content of the three additional components is as follows: K2O: 0 to 0.05%, TiO2: 0 to 0.1%, and T-Fe2O3: 0 to 0.5%.

[0103] In one embodiment of the present invention, the glass composition comprises:

[0104] SiO2 53-60%

[0105] Al2O3 11-15%

[0106] MgO 18-30%

[0107] CaO 0-5%

[0108] B2O3 0.2–1.5%

[0109] Li2O 0.5~2.5%

[0110] Na2O 0~0.2%,

[0111] The molar ratio calculated from Al2O3 / (MgO+CaO) is 0.3 to 0.5.

[0112] The molar ratio calculated from Al2O3 / (MgO+CaO) can also be above 0.3 and below 0.5.

[0113] The combined content of MgO and CaO in this glass composition is in the range of 18% to 35%.

[0114] This embodiment is particularly suitable for adjusting the devitrification temperature to a preferred range in relation to liquid phase temperature, etc.

[0115] In one embodiment of the present invention, the glass composition comprises:

[0116] SiO2 53-60%

[0117] Al2O3 15~26%

[0118] MgO 17-30%

[0119] CaO 0-5%

[0120] B2O3 0.2-3%

[0121] Li2O 0.2–1.5%

[0122] Na2O 0~0.2%,

[0123] The molar ratio calculated from Al2O3 / (MgO+CaO) is 0.5 to 1.0, preferably 0.7 to 0.9.

[0124] The combined content of MgO and CaO in this glass composition is in the range of 18% to 35%.

[0125] In this embodiment, the CaO content can be 0–4.5%. This embodiment is particularly suitable for improving crack resistance.

[0126] [Characteristics of the glass composition]

[0127] In information recording devices such as HDDs, it is required to reduce the deflection of the information recording medium. This is because, for example, in HDDs, as mentioned above, the read / write head can come into contact with and be damaged by the deflection of the rotating disk. To reduce deflection, it is desirable for the glass composition of the substrate constituting the disk to have high rigidity, specifically, a high Young's modulus. Additionally, it is desirable for the glass composition of the substrate constituting the disk to have a low specific gravity. The lighter weight of the disk resulting from the lower specific gravity of the glass composition can help reduce the power consumption of the HDD. The high Young's modulus and low specific gravity of the glass composition are particularly important in information recording devices that have made significant progress towards higher capacity, as exemplified by HDDs with multiple platters. As mentioned above, the high Tg of the glass composition is also highly important in relation to the magnetic recording layer corresponding to heat-assisted magnetic recording.

[0128] (proportion)

[0129] In one embodiment of the present invention, the specific gravity of the glass composition is 3.0 or less, 2.8 or less, preferably 2.7 or less, more preferably 2.65 or less, even more preferably 2.64 or less, and particularly preferably 2.63 or less. Glass compositions with such low specific gravity are particularly suitable for information recording media. The lower limit of the specific gravity is not particularly limited, but can be 2.5 or more.

[0130] (Young's modulus)

[0131] In one embodiment of the invention, the Young's modulus of the glass composition is 98 GPa or more, 100 GPa or more, preferably 101 GPa or more, more preferably 103 GPa or more, and, depending on the situation, 104 GPa or more. The upper limit of the Young's modulus is not particularly limited, but can be 110 GPa or less, further 107 GPa or less, and, depending on the situation, 105 GPa or less. The method for measuring the Young's modulus is described in the Examples section. Glass compositions with high Young's modulus are suitable for information recording media.

[0132] (Specific elastic modulus)

[0133] The specific modulus of elasticity can be obtained by dividing Young's modulus by the specific gravity. Glass compositions with a high specific modulus of elasticity are particularly suitable for information recording media. This is because it is desirable for information recording media to exert a low load on drive devices such as motors during high-speed rotation and to exhibit minimal deflection. In one embodiment of the present invention, the specific modulus of elasticity of the glass composition is 36 MNm / kg or more, 36.5 MNm / kg or more, preferably 37 MNm / kg or more, more preferably 38 MNm / kg or more, and particularly preferably 39 MNm / kg or more.

[0134] (Crack resistance load)

[0135] In one embodiment of the invention, the crack resistance of the glass composition is 300g or more, preferably 400g or more, and more preferably 500g or more. Surprisingly, according to one embodiment of the invention, glass compositions with particularly high crack resistance, such as 900g or more, further 1000g or more, and particularly 1200g or more, can be provided. The upper limit of the crack resistance is not particularly limited, but can be 2000g or less. The method for measuring the crack resistance is described in the Examples section. Glass compositions with high crack resistance are suitable for information recording media. In another embodiment of the invention, the glass composition has a crack resistance in the range of 300 to 550g and a devitrification temperature of 1250 to 1350°C.

[0136] (High-temperature viscosity)

[0137] In one embodiment of the invention, the temperature T2 of the glass composition (the temperature at which the logarithm (logη) of the liquid phase viscosity η (in dPa·s) of the glass composition is 2; liquid phase temperature) can be below 1490°C, below 1480°C, further below 1470°C, and, depending on the situation, below 1460°C. A low T2 is suitable for the mass production of information recording media. Similarly, temperature T2.5 is below 1400°C, below 1390°C, further below 1380°C, and, depending on the situation, below 1370°C. Temperature T3 is below 1310°C, below 1300°C, further below 1290°C, and, depending on the situation, below 1280°C.

[0138] (Devitrification temperature)

[0139] In one aspect of the present invention, the devitrification temperature (TL) of the glass composition is 1450°C or lower, preferably 1400°C or lower, more preferably 1380°C or lower, and particularly preferably 1350°C or lower. Glass compositions with high TL are prone to crystal precipitation. Crystals precipitated on the surface of information recording media such as discs can damage the surface smoothness of the medium. A low devitrification temperature is of great importance in glass compositions used in information recording media.

[0140] (Relationship between high-temperature viscosity and devitrification temperature)

[0141] In one embodiment of the present invention, the value (ΔT) of subtracting the devitrification temperature TL of the glass composition from the liquid phase temperature T2 is 20°C or more, preferably 30°C or more, more preferably 50°C or more, and particularly preferably 100°C or more.

[0142] (Glass transition temperature)

[0143] In one embodiment of the invention, the glass transition temperature (glass transition point) Tg of the glass composition is 600°C or higher, 650°C or higher, preferably 700°C or higher, more preferably 725°C or higher, even more preferably 750°C or higher, and particularly preferably 800°C or higher. Glass compositions with high Tg are particularly suitable for information recording media. This is because, as mentioned above, high-temperature processing is required in the process of forming the recording layer, in which case the information recording medium needs to have heat resistance. The upper limit of the glass transition temperature Tg is not particularly limited, for example, 850°C.

[0144] The methods for measuring liquid phase viscosity η, devitrification temperature TL, and glass transition temperature Tg are described in the Example 1 section.

[0145] [Information Recording Medium]

[0146] The glass composition described above is suitable for use as an information recording medium. From another aspect, the present invention provides a glass plate containing the glass composition of the present invention. The glass plate may have a disc-shaped shape. The disc-shaped glass plate may have a hole in its center. The outer diameter of the glass plate may be less than 3.5 inches, less than 2.5 inches, or even less than 1.8 inches. The thickness of the glass plate may, for example, be less than 1 mm, less than 0.8 mm, less than 0.7 mm, less than 0.635 mm, and further less than 0.5 mm.

[0147] The glass sheet can be chemically strengthened glass. Chemical strengthening, as is well known, involves introducing compressive stress onto the glass surface by replacing alkali ions in the glass with alkali ions having larger ionic radii, such as replacing lithium ions with sodium ions or sodium ions with potassium ions. Chemical strengthening of glass sheets is typically carried out by contacting the glass sheet with a molten salt containing alkali ions. Examples of molten salts include potassium nitrate, and mixtures of potassium nitrate and sodium nitrate. When using molten salts containing only potassium nitrate, the temperature of the molten salt is preferably around 460°C to 500°C, considering the thermal decomposition of potassium nitrate and the heat resistance of the glass. The contact time between the glass and the molten salt is preferably, for example, 4 to 12 hours.

[0148] The glass sheet of this embodiment can be mass-produced using the float glass process. As can be understood from the temperature characteristics described above, the glass composition of this embodiment is suitable for mass production using the float glass process. The float glass process, as is well known, includes the following steps: melting glass raw materials in a furnace; and forming a glass sheet from molten glass raw materials introduced into a float glass bath on molten tin within the bath. In one embodiment of the invention, glass raw materials are prepared such that the glass composition constituting the resulting glass sheet has the desired composition described above, thereby manufacturing float glass. In the float glass bath, one main surface is contacted with molten tin and formed, with tin diffusing to this main surface. Therefore, the float glass has a tin-diffused surface layer on one main surface, called the bottom surface, which is absent on the other main surface, called the top surface. Alternatively, in the float glass, the tin concentration on one main surface is higher than the tin concentration on the other main surface.

[0149] Example

[0150] The present invention will be described in more detail below through examples.

[0151] Glass raw materials were blended according to the compositions shown in Tables 1 and 2, and melted in an electric furnace maintained at 1500–1600°C for 4 hours. During melting, the glass was stirred repeatedly with a quartz glass stir bar to ensure homogeneity. The molten glass was then poured into a stainless steel frame to form sheet-like glass. The sheet-like glass was held at its glass transition temperature +20–50°C for at least 2 hours, and then annealed to room temperature for approximately 8 hours to obtain test glass samples. The following properties were measured using these test glass samples.

[0152] (proportion)

[0153] The Archimedes method, using water as the immersion solution, is used to measure the specific gravity (density) of small pieces of glass as a sample.

[0154] (Young's modulus)

[0155] Young's modulus was measured using the ultrasonic pulse method as described in Japanese Industrial Standard (JIS) R 1602-1995. Each test piece was a cuboid measuring 5 mm × 25 mm × 35 mm. Measurements were conducted at room temperature and in atmospheric conditions. The apparatus used was a Panametrics Model 25DL Plus. The specific modulus was obtained by dividing Young's modulus by the specific gravity.

[0156] (Crack resistance load)

[0157] The crack resistance load is measured by pressing a Vickers indenter onto the surface of a mirror-polished sample glass. The apparatus used is a Vickers hardness tester manufactured by Akashi Corporation. The sample glass is processed into a plate shape with parallel planes. Furthermore, the plane on which the indenter is pressed is polished to a mirror finish using a suspension of cerium oxide abrasive. The Vickers indenter is pressed onto this mirror-polished surface for 15 seconds, and after unloading for 5 minutes, the square indentation left on the surface of the sample glass is used to determine whether a crack originates from its apex. Whether a crack occurs is determined by observation using a microscope assembled on the Vickers hardness tester. The microscope has a magnification of 100x. This test is performed 10 times, and the probability of crack occurrence, P, is calculated by dividing the number of apexes where a crack occurred by the total number of measured apexes (40). The above measurements were repeated by changing the load in the order of 50g, 100g, 200g, 300g, 500g, 1000g, and 2000g until P = 100%, and the crack initiation probability P under each load was calculated. This yielded two adjacent loads WH and WL that spanned P = 50%, and their corresponding crack initiation probabilities PH and PL (PH < 50% < PL). A straight line was plotted between the two points (WH, PH) and (WL, PL) with the load and crack initiation probability on the horizontal and vertical axes, respectively. The load at P = 50% was taken as the crack-resistant load.

[0158] (Devitrification temperature TL)

[0159] The glass sample was crushed and passed through a sieve with a mesh size of 2.380 mm. Glass particles remaining on a sieve with a mesh size of 1.000 mm were collected. These particles were then ultrasonically cleaned by immersing them in ethanol and dried in a constant-temperature bath. 30–32 g of these glass particles were placed at approximately a constant thickness onto a platinum boat dish measuring 12 mm wide, 200 mm long, and 10 mm deep as the measurement sample. This platinum boat dish was held in an electric furnace (temperature gradient furnace) with a temperature gradient of 950–1550 °C for 2 hours. The highest temperature of the crystalline phase (devitrification) distributed in the measurement sample was observed and used as the liquidus temperature (TL) for evaluation.

[0160] (T2, T2.5, T3)

[0161] T2, T2.5, and T3 were measured as follows: for the sample glass, the viscosity at each temperature was measured at 25°C intervals using the platinum ball pulling method, and the intermediate viscosity was calculated according to the Fulcher formula.

[0162] (Glass transition temperature Tg)

[0163] A cylindrical sample with a diameter of 5 mm and a length of 18 mm was prepared from the sample glass, and the thermal expansion curve was measured when heated by a TMA device at a rate of 5 °C / min. Based on this curve, the glass transition temperature Tg was obtained.

[0164] The aforementioned properties were measured for each obtained sample. The results are shown in Tables 1-2. As can be understood from Comparative Examples 3-4, the Young's modulus can be increased by adding TiO2, Y2O3, etc. However, as can be understood from Examples 1-10, the increase in Young's modulus brought about by MgO is advantageous in that it can control the specific gravity while increasing the Young's modulus. The Young's modulus of Comparative Examples 1-2 and 5-7 is lower than 98 GPa. In Comparative Examples 1-2, T2 is relatively high, which is somewhat disadvantageous for mass production.

[0165] Table 1

[0166]

[0167] Table 2

[0168]

Claims

1. A glass composition for an information recording medium, wherein, The Young's modulus is above 98 GPa. It contains 17–30 mol% MgO.

2. The glass composition according to claim 1, wherein, It contains Al2O3.

3. The glass composition according to claim 1, wherein the specific elastic modulus is 36MNm / kg or higher.

4. The glass composition according to claim 1, wherein, It also contains 0.2–3 mol% Li₂O and 0.2–3 mol% B₂O₃.

5. The glass composition according to claim 1, wherein, The ΔT obtained by subtracting the devitrification temperature from the liquid phase temperature T2 is above 20℃.

6. The glass composition according to claim 1, wherein, It also contains Na2O.

7. The glass composition according to claim 1, wherein, Expressed as a percentage in moles, it contains: SiO2 50~65% Al2O 37.5~26% MgO 15-30% CaO 0-8% B2O30~3% Li2O 0-3% Na2O 0~0.2%, The combined content of MgO and CaO ranges from 18% to 35 mol%. The molar ratio calculated from Al2O3 / (MgO+CaO) is less than 1.

8. The glass composition according to claim 1, wherein, Expressed as a percentage in moles, it contains: SiO2 53-60% Al2O3 11~15% MgO 18-30% CaO 0-5% B2O3 0.2-1.5% Li2O 0.5~2.5% Na2O 0~0.2%, The molar ratio calculated from Al2O3 / (MgO+CaO) is 0.3 to 0.

5.

9. The glass composition according to claim 1, wherein, Expressed as a percentage in moles, it contains: SiO2 53-60% Al2O3 15~26% MgO 17-30% CaO 0-5% B2O3 0.2-3% Li2O 0.2–1.5% Na2O 0~0.2%, The molar ratio calculated from Al2O3 / (MgO+CaO) is 0.5 to 1.

0.

10. The glass composition according to claim 1, wherein, It also contains 50–57.8 mol% SiO2. The combined content of TiO2 and Y2O3 is less than 3 mol%.

11. A glass plate for an information recording medium, comprising the glass composition according to any one of claims 1 to 10.

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