Glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording and reproducing apparatus, a magnetic recording medium substrate, a magnetic recording medium, a glass spacer for a magnetic recording and reproducing apparatus, and a magnetic recording and reproducing apparatus

Abstract

Provided is a glass for a magnetic recording medium substrate or for a glass spacer to be used in a magnetic recording / reproducing device that is an amorphous glass that has a B2O3 content of 0.10-2.00 mol% inclusive, a Na2O content of 1.00-6.00 mol% inclusive, a CaO content of 0-1.00 mol% inclusive, and a Mgo content of 14.00 mol% or more.

Description

Cross - reference to related applications

[0001] This application claims the priority of PCT / JP2022 / 033744 filed on September 8, 2022, and the entire description thereof is incorporated herein by specific reference as disclosure.

Technical Field

[0002] The present invention relates to glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording and reproducing apparatus, a magnetic recording medium substrate, a magnetic recording medium, a glass spacer for a magnetic recording and reproducing apparatus, and a magnetic recording and reproducing apparatus.

Background Art

[0003] Conventionally, a substrate made of an aluminum alloy (magnetic recording medium substrate) has been used as a substrate for a magnetic recording medium such as a hard disk. However, it has been pointed out that the aluminum alloy substrate is liable to be deformed. Therefore, at present, a glass magnetic recording medium substrate is widely used (see, for example, Japanese Patent Application Laid - Open No. 2002 - 358626, the entire description of which is incorporated herein by specific reference as disclosure).

Summary of the Invention

[0004] The glass for a magnetic recording medium substrate is desired to have high rigidity. This is for the following reasons. A magnetic recording medium is usually mounted inside a hard disk drive (HDD) incorporated in devices such as personal computers. Inside the HDD, a plurality of magnetic recording media (magnetic disks) are attached to the rotating shaft of a spindle motor, and data is written to the magnetic recording layer of the magnetic recording medium rotating at high speed inside the HDD and read from the magnetic recording layer by an actuator incorporated in the HDD. When the magnetic recording medium rotates at high speed for such data writing and reading, large vibrations of the magnetic recording medium can cause the magnetic head to collide with the surface of the magnetic recording medium, resulting in a head crash. For HDDs, the recording capacity can be increased by reducing the thickness of each magnetic recording medium and mounting more magnetic recording media in the HDD. However, generally, the thinner the substrate is to make the magnetic recording medium thinner, the more likely the magnetic recording medium is to vibrate during high-speed rotation. In order to suppress such vibrations, it is desirable to use a glass substrate for the magnetic recording medium that has high rigidity and is less likely to vibrate during high-speed rotation even when thinned. As an index of such rigidity, for example, the specific elastic modulus can be cited.

[0005] In view of the above, one aspect of the present invention aims to provide a glass for a magnetic recording medium substrate having high rigidity, and in one form, aims to provide a glass for a magnetic recording medium substrate having a high specific elastic modulus.

[0006] One aspect of the present invention is as follows. [1] Glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording and reproducing device (hereinafter referred to as "Glass A"), which is an amorphous glass with a B2O3 content of 0.10 mol% or more and 2.00 mol% or less, a Na2O content of 1.00 mol% or more and 6.00 mol% or less, a CaO content of 0 mol% or more and 1.00 mol% or less, and a MgO content of 14.00 mol% or more. [2] Glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording and reproducing device (hereinafter referred to as "Glass A"), which is an amorphous glass with a B2O3 content of 0.10 mol% or more and 2.00 mol% or less, The Na₂O content is 1.00 mol% or more and 6.00 mol% or less, The CaO content is 0 mol% or more and 1.00 mol% or less, The total content of MgO, SrO, CaO, and BaO (MgO + SrO + CaO + BaO) is 14.00 mol% or more, which is an amorphous glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording and reproducing apparatus (hereinafter referred to as "Glass B"). [3] The molar ratio of the Na₂O content to the total content of Li₂O, Na₂O, and K₂O (Na₂O / (Li₂O + Na₂O + K₂O)) is 0.950 or more, the glass according to [1] or [2]. [4] The glass according to any one of [1] to [3], which does not contain Li₂O and K₂O. [5] The total content of SiO₂, B₂O₃, and Al₂O₃ (SiO₂ + B₂O₃ + Al₂O₃) is 70 mol% or more, the glass according to any one of [1] to [4]. [6] The total content of SiO₂ and B₂O₃ (SiO₂ + B₂O₃) is 58 mol% or more, the glass according to any one of [1] to [5]. [7] The total content of SiO₂ and Al₂O₃ (SiO₂ + Al₂O₃) is 70 mol% or more, the glass according to any one of [1] to [6]. [8] The molar ratio of the Na₂O content to the total content of Li₂O, Na₂O, and K₂O (Na₂O / (Li₂O + Na₂O + K₂O)) is 0.350 or more, the glass according to [1] or [2]. [9] The glass according to [1], [2], or [8], which contains Li₂O.

[10] The molar ratio of the Li₂O content to the total content of Li₂O, Na₂O, and K₂O (Li₂O / (Li₂O + Na₂O + K₂O)) is 0.600 or less, the glass according to [1], [2], [8], or [9].

[11] The molar ratio of the SiO₂ content to the Na₂O content (SiO₂ / Na₂O) is 50.0 or less, the glass according to any one of [1], [2], and [8] to

[10] . The glass according to any one of [1] to [7], wherein the molar ratio of the Na2O content to the MgO content (Na2O / MgO) exceeds 0.080. The glass according to any one of [1] to

[12] , wherein the TiO2 content is 4.00 mol% or less. The glass according to any one of [1] to

[13] , wherein the ZnO content is 10.00 mol% or less. The glass according to any one of [1] to

[14] , wherein the specific elastic modulus is 35.0 MNm / kg or more. The glass according to any one of [1] to

[15] , wherein the glass transition temperature is 700 °C or higher. A magnetic recording medium substrate made of the glass according to any one of [1] to

[16] . A magnetic recording medium having the magnetic recording medium substrate according to

[17] and a magnetic recording layer. A glass spacer for a magnetic recording and reproducing apparatus made of the glass according to any one of [1] to

[16] .

[20] The magnetic recording medium according to

[18] , and The glass spacer for a magnetic recording and reproducing apparatus according to

[19] , A magnetic recording and reproducing apparatus including one or more selected from the group consisting of.

[0007] According to one aspect of the present invention, it is possible to provide a glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording and reproducing apparatus having high rigidity. Further, according to one aspect, it is also possible to provide a magnetic recording medium substrate made of the above glass and a magnetic recording medium including this substrate. Furthermore, according to one aspect, it is possible to provide a glass spacer for a magnetic recording apparatus made of the above glass. Still further, according to one aspect, it is possible to provide a magnetic recording and reproducing apparatus.

Embodiments for Carrying Out the Invention

[0008] [Glass] Hereinafter, Glass A and Glass B are collectively referred to simply as "glass". Also, in the following descriptions, unless otherwise specified, the descriptions regarding Glass A can be applied to Glass B, and the descriptions regarding Glass B can be applied to Glass A. Glass A and Glass B are glasses for a magnetic recording medium substrate or a glass spacer for a magnetic recording and reproducing device, and are amorphous glasses. An amorphous glass, unlike a crystallized glass, is a glass that substantially does not contain a crystal phase and exhibits a glass transition phenomenon upon heating. On the other hand, the manufacturing process of crystallized glass is complicated. Also, it is not easy to achieve the high smoothness required for a magnetic recording medium substrate with crystallized glass. Also, Glass A and Glass B can be amorphous oxide glasses. An oxide glass is a glass in which the main network-forming component of the glass is an oxide. Hereinafter, the above glass will be described in more detail.

[0009] In the present invention and this specification, the glass composition is expressed as a glass composition on an oxide basis. Here, the "glass composition on an oxide basis" means a glass composition obtained by converting all glass raw materials into oxides existing in the glass when melted. Also, unless otherwise specified, the glass composition is expressed on a molar basis (mol%, molar ratio). The glass composition in the present invention and this 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. Thereafter, the analysis values are converted into oxide notation. The analysis values by ICP-AES may include a measurement error of about ±5% of the analysis values, for example. Therefore, the values in oxide notation converted from the analysis values may also include an error of about ±5% similarly. In the present invention and in this specification, when the content of a component is 0%, 0.0%, 0.00%, not included, or not introduced, it means that this component is substantially not included, and it refers to the content of this component being at or below the impurity level. Being at or below the impurity level means, for example, less than 0.01%.

[0010] <Glass composition> From the viewpoints of improving chemical durability and rigidity, the B2O3 content of the above glass is 2.00% or less, preferably 1.80% or less, and more preferably 1.50% or less, 1.20% or less, 1.00% or less, 0.80% or less, 0.70% or less, 0.60% or less, 0.50% or less, 0.40% or less in that order. Glass with high chemical durability has high acid resistance and / or alkali resistance, so it is less likely to cause surface roughness during polishing, cleaning, etc., and it is easy to achieve a low surface roughness of the glass surface, which is preferable. The performance that can easily achieve a low roughness by polishing is hereinafter referred to as low roughness polishing performance. From the viewpoints of improving impact resistance, meltability, and thermal stability, the B2O3 content of the above glass is 0.10% or more, preferably 0.20% or more. Glass with high impact resistance is preferable because it is less likely to crack and / or chip during processing such as cutting and grinding. Also, glass with high thermal stability is preferable because it is less likely to devitrify.

[0011] In one form, the above glass can contain one or both of SiO2 and Al2O3.

[0012] From the perspective of improving chemical durability, the SiO2 content of the above glass is preferably 50.00% or more, more preferably 51.00% or more, 52.00% or more, 53.00% or more, 54.00% or more, 55.00% or more, 56.00% or more, 57.00% or more, 58.00% or more, 59.00% or more, 60.00% or more, 61.00% or more, 62.00% or more, 63.00% or more, 64.00% or more in this order. Glass with high chemical durability is preferred because it is less likely to cause surface roughness during polishing and cleaning. On the other hand, from the perspective of further improving rigidity, the SiO2 content is preferably 75.00% or less, more preferably 74.00% or less, 73.0% or less, 72.0% or less, 71.0% or less, 70.0% or less, 69.0% or less, 68.0% or less, 67.0% or less, 66.0% or less, 65.00% or less, 64.00% or less, 63.00% or less, 62.00% or less, 61.00% or less in this order.

[0013] From the perspective of improving thermal stability, the Al2O3 content of the above glass is preferably 20.00% or less, more preferably 19.00% or less, 18.00% or less, 17.00% or less, 16.00% or less in this order. Also, from the perspective of maintaining the temperature required for melting the glass within an appropriate range, it is preferable that the Al2O3 content is within the above range. On the other hand, from the perspective of further improving rigidity, the Al2O3 content is preferably 10.00% or more, more preferably 11.00% or more, 12.00% or more, 13.00% or more in this order.

[0014] In the above glass, the total content of SiO2, B2O3 and Al2O3 (SiO2 + B2O3 + Al2O3) is preferably 70.00% or more, more preferably 71.00% or more, 72.00% or more, 73.00% or more, 74.00% or more, 75.00% or more, 76.00% or more, 77.00% or more, 78.00% or more, 79.00% or more, from the viewpoint of enhancing the thermal stability of the glass. From the viewpoint of further improving the meltability, the total content of SiO2, B2O3 and Al2O3 (SiO2 + B2O3 + Al2O3) of the above glass is preferably 85.00% or less, more preferably 84.00% or less, 83.00% or less, 82.00% or less, 81.00% or less, 80.00% or less, 79.00% or less, 78.00% or less, 77.00% or less, 76.00% or less, 75.00% or less, 74.00% or less, in that order.

[0015] The total content of SiO2 and B2O3 (SiO2 + B2O3) is preferably 58.00% or more, more preferably 59.00% or more, 60.00% or more, 61.00% or more, 62.00% or more, 63.00% or more, 64.00% or more, from the viewpoint of enhancing the thermal stability of the glass. From the viewpoint of further improving the rigidity, the total content of SiO2 and B2O3 (SiO2 + B2O3) of the above glass is preferably 77.00% or less, more preferably 76.00% or less, 75.00% or less, 74.00% or less, 73.00% or less, 72.00% or less, 71.00% or less, 70.00% or less, 69.00% or less, 68.00% or less, 67.00% or less, 66.00% or less, 65.00% or less, 64.00% or less, 63.00% or less, 62.00% or less, in that order.

[0016] In the above glass, from the viewpoint of chemical durability such as acid resistance and alkali resistance, the total content of SiO2 and Al2O3 (SiO2 + Al2O3) is preferably 70.00% or more, more preferably 71.00% or more, 72.00% or more, 73.00% or more, 74.00% or more, 75.00% or more, 76.00% or more, 77.00% or more, 78.00% or more, 79.00% or more in this order. Further, from the viewpoint of the meltability of the glass, the total content of SiO2 and Al2O3 (SiO2 + Al2O3) in the above glass is preferably 85.00% or less, more preferably 84.00% or less, 83.00% or less, 82.00% or less, 81.00% or less, 80.00% or less, 79.00% or less, 78.00% or less, 77.00% or less, 76.00% or less, 75.00% or less, 74.00% or less in this order.

[0017] The above glass contains Na2O as an essential component. Na2O is a component having various functions such as increasing the specific elastic modulus of the glass, improving the meltability, increasing the coefficient of thermal expansion, and lowering the viscosity of the glass during clarification to promote defoaming. Further, among the alkali metal oxides, incorporating Na2O into the glass can contribute to increasing the glass transition temperature compared to the case of adding the same amount of Li2O. The Na2O content of the above glass is 1.00% or more, preferably 1.50% or more, more preferably 2.00% or more, 2.50% or more, 3.00% or more in this order. Further, from the viewpoint of increasing the glass transition temperature, the Na2O content of the above glass is 6.00% or less, preferably 5.50% or less, more preferably 5.00% or less, 4.50% or less, 4.00% or less in this order.

[0018] From the perspective of improving the water resistance of the glass, in the above glass, the molar ratio of the SiO2 content to the Na2O content (SiO2 / Na2O) is preferably 12.0 or more, and more preferably 15.0 or more, 16.0 or more, 17.0 or more, and 18.0 or more in that order. The fact that the glass has excellent water resistance is preferable, for example, in suppressing the roughening of the glass surface and the decrease in smoothness (i.e., the increase in surface roughness) when the super-smoothly polished glass surface comes into contact with water during cleaning or the like. The lower the surface roughness of the glass, the easier it is to improve the orientation of the magnetic particles, and it is also preferable because it is easier to reduce the distance between the magnetic head and the magnetic recording medium (the flying height of the magnetic head). On the other hand, from the perspective of improving the meltability of the glass, the molar ratio (SiO2 / Na2O) is preferably 50.0 or less, more preferably 40.0 or less, and even more preferably 30.0 or less.

[0019] The above glass can also contain alkali metal oxides other than Na2O. Li2O is a component having the same function as the above Na2O, but it is easier to lower the glass transition temperature compared to the case of adding the same amount of Na2O as described above. The Li2O content of the above glass can be, for example, 6.00% or less, 5.00% or less, 4.00% or less, 3.00% or less, 2.00% or less, 1.50% or less, 1.00% or less, 0.50% or less, 0.10% or less. Also, the Li2O content of the above glass can be 0%, 0% or more or more than 0%, more than 0.10%, 0.20% or more, 0.30% or more, 0.40% or more. Also, the Li2O content of the above glass can be more than 0.10% and less than 2.00%, 0.20% or more and 1.5% or less, 0.30% or more and 1.3% or less. In one form, the above glass can be a glass that does not contain Li2O.

[0020] K2O is a component having the same function as the above-mentioned Na2O. However, since its specific gravity is greater than that of Na2O, it is easier to lower the specific elastic modulus compared to the case of adding the same amount of Na2O. The K2O content of the above glass can be, for example, 6.00% or less, 5.00% or less, 4.00% or less, 3.00% or less, 2.00% or less, 1.50% or less, 1.00% or less, 0.50% or less, 0.10% or less. Also, the K2O content of the above glass can be 0%, 0% or more, or more than 0%. In one form, the above glass can be a glass that does not contain K2O. Also, in another form, the above glass can be a glass that contains K2O, for example, a glass that contains 0.10% or more of K2O.

[0021] From the viewpoint of increasing the glass transition temperature and the specific elastic modulus, in the above glass, the molar ratio of the Na2O content to the total content of Li2O, Na2O, and K2O (Na2O / (Li2O + Na2O + K2O)) is preferably 0.350 or more, more preferably 0.400 or more, 0.450 or more, 0.500 or more, 0.550 or more, 0.600 or more, 0.650 or more, 0.700 or more, 0.750 or more, 0.800 or more, 0.850 or more, 0.900 or more, 0.950 or more, 0.960 or more, 0.970 or more, 0.980 or more, 0.990 or more in this order. The molar ratio (Na2O / (Li2O + Na2O + K2O)) of the above glass can be 1.000, or can also be 1.000 or less or less than 1.000. In one form, the above glass can be a glass that does not contain Li2O and K2O. Also, from the viewpoint of improving the water resistance and reducing the roughness of the glass, the molar ratio (Na2O / (Li2O + Na2O + K2O)) is preferably less than 1.000, more preferably 0.950 or less, 0.900 or less in this order.

[0022] From the perspective of improving the water resistance of the glass, in the above glass, the molar ratio of the Li2O content to the total content of Li2O, Na2O, and K2O (Li2O / (Li2O + Na2O + K2O)) is preferably 0.050 or more, and more preferably 0.100 or more. On the other hand, from the perspective of suppressing the decrease in the glass transition temperature, the molar ratio (Li2O / (Li2O + Na2O + K2O)) is preferably 0.600 or less, and more preferably 0.500 or less, 0.400 or less, and 0.300 or less in that order.

[0023] The CaO content of the above glass is 1.00% or less. The CaO content being 1.00% or less contributes to increasing the specific elastic modulus and glass transition temperature of the glass, and furthermore, can also contribute to improving the thermal stability of the glass. From these perspectives, the CaO content is preferably 0.90% or less, and more preferably 0.80% or less, 0.70% or less, 0.60% or less, 0.50% or less, 0.40% or less, 0.30% or less, 0.20% or less, and 0.10% or less in that order. The CaO content of the above glass can be 0%, 0% or more, or more than 0%. In one form, it is preferable that the above glass does not contain CaO.

[0024] Regarding alkaline earth metal oxides, the CaO content of the above glass is as described above. In one form, the above glass can contain one or more alkaline earth metal oxides. Specific examples of alkaline earth metal oxides that can be included in the above glass include MgO, SrO, and BaO. Glass A contains MgO. From the perspective of improving rigidity, the MgO content of Glass A is 14.00% or more, preferably 14.50% or more, more preferably 15.00% or more, 15.50% or more, and 16.00% or more in that order. Also, from the perspective of improving the devitrification resistance of the glass, the MgO content of Glass A is preferably 28.00% or less, more preferably 27.00% or less, 26.00% or less, 25.00% or less, 24.00% or less, 23.00% or less, 22.00% or less, 21.00% or less, 20.00% or less, 19.00% or less, and 18.00% or less in that order. Glass B can contain MgO. For the MgO content of Glass B, the description regarding the MgO content of Glass A can be referred to.

[0025] In Glass B, the total content of MgO, SrO, CaO, and BaO (MgO + SrO + CaO + BaO) is 14.00 mol% or more from the perspective of improving rigidity, preferably 14.50% or more, more preferably 15.00% or more, 15.50% or more, and 16.00% or more in that order. Also, from the perspective of improving the devitrification resistance of the glass, the total content of MgO, SrO, CaO, and BaO (MgO + SrO + CaO + BaO) in Glass B is preferably 28.00% or less, more preferably 27.00% or less, 26.00% or less, 25.00% or less, 24.00% or less, 23.00% or less, 22.00% or less, 21.00% or less, 20.00% or less, 19.00% or less, and 18.00% or less in that order. For the total content of MgO, SrO, CaO, and BaO (MgO + SrO + CaO + BaO) in Glass A, the description regarding the total content of MgO, SrO, CaO, and BaO (MgO + SrO + CaO + BaO) in Glass B can be referred to.

[0026] From the viewpoints of reducing the specific gravity and raw material costs, the SrO content of the above glass is preferably 4.00% or less, more preferably 3.00% or less, 2.00% or less, 1.00% or less, and 0.50% or less in this order. In one form, the SrO content of the above glass can be 0%, or can be 0% or more or more than 0%.

[0027] From the viewpoints of reducing the specific gravity of the glass, improving the Young's modulus, and improving the specific elastic modulus, the BaO content of the above glass is preferably 3.00% or less, more preferably 2.00% or less, 1.00% or less, and 0.50% or less in this order. In one form, the BaO content of the above glass can be 0%, or can be 0% or more or more than 0%.

[0028] The molar ratio of the MgO content to the total content of MgO, CaO, SrO, and BaO (MgO / (MgO + CaO + SrO + BaO)) can be 1.000, 1.000 or less, or less than 1.000. Since MgO has a smaller specific gravity than other alkaline earth metal oxides, it can contribute to increasing the specific elastic modulus. Also, in general glass, the glass transition temperature tends to increase by adding alkaline earth metal oxides with a large specific gravity. On the other hand, according to the study by the present inventors, in the above glass, the glass transition temperature tended to decrease when adding alkaline earth metal oxides with a larger specific gravity than MgO. From the viewpoints of increasing the specific elastic modulus and the glass transition temperature in the above glass, the molar ratio (MgO / (MgO + CaO + SrO + BaO)) is preferably 0.800 or more, more preferably 0.850 or more, 0.900 or more, 0.950 or more, and 1.000 in this order.

[0029] From the viewpoints of reducing the melting viscosity, decreasing the liquidus temperature, and improving the polishing performance of the glass to reduce roughness, the molar ratio of the Na2O content to the MgO content (Na2O / MgO) is preferably more than 0.080. A low melting viscosity of the glass is preferable from the viewpoint of the formability by various forming methods. A glass with a low liquidus temperature is preferable because it has high thermal stability. In addition, the molar ratio (Na2O / MgO) being more than 0.080 can contribute to reducing the specific resistivity of the glass melt. When electric heating is performed during glass melting, a glass with a small specific resistivity is preferable because it can lower the temperature in the furnace and melt it during electric heating. From the above viewpoints, the molar ratio (Na2O / MgO) is more preferably 0.090 or more, and further preferably 0.100 or more, 0.110 or more, 0.120 or more, 0.130 or more, 0.140 or more, 0.150 or more, 0.160 or more in this order. On the other hand, from the viewpoints of increasing the glass transition temperature and the specific modulus of elasticity, the molar ratio (Na2O / MgO) is preferably less than 0.240, and more preferably 0.230 or less, 0.220 or less, 0.210 or less, 0.200 or less, 0.190 or less, or 0.180 or less in this order.

[0030] Regarding TiO2, from the viewpoints of reducing the specific gravity and improving the devitrification resistance, the TiO2 content of the above glass is preferably 4.00% or less, and more preferably 3.00% or less, 2.00% or less, 1.00% or less in this order. The TiO2 content of the above glass can be 0%, or can be 0% or more or more than 0%.

[0031] Regarding ZnO, from the viewpoints of reducing the specific gravity, improving the Young's modulus, and improving the specific modulus of elasticity, the ZnO content is preferably 10.00% or less, and more preferably 8.00% or less, 6.00% or less, 4.00% or less, 2.00% or less, 1.00% or less in this order. The ZnO content of the above glass can be 0%, or can be 0% or more or more than 0%.

[0032] The Fe₂O₃ content of the above glass can be 1 mol% or less, 0.7 mol% or less, 0.5 mol% or less, 0.4 mol% or less, 0.3 mol% or less, 0.1 mol% or less, 0.07 mol% or less, 0.05 mol% or less, 0.04 mol% or less, 0.03 mol% or less, or 0.02 mol% or less, expressed as the content shown by external division. Note that the Fe₂O₃ content is expressed by external division. That is, when the total content of components other than Fe₂O₃ contained in the glass (including additives when including additives in addition to the glass components, it is the total content of the glass components and additives) is taken as 100%, the Fe₂O₃ content is expressed as the molar percentage of the Fe₂O₃ content with respect to 100%. In one form, the above glass can be free of Fe (the Fe₂O₃ content shown by the above external division is 0 mol%).

[0033] The above glass can also contain, or may not contain, one or more metals selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er, or oxides thereof. In the glass composition based on oxides, the inclusion of oxides of one or more metals selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er tends to enhance the thermal stability of the glass. In one form, the content of oxides of one or more metals selected from the group consisting of Zr, Y, La, Ti, Hf, Cu, Co, Mn, Nd, Pr, Nb, V, Cr, Ni, Mo, Ho, and Er (when multiple types are included, it is their total content) can be 0%, 0% or more, or more than 0%, and can also be 5.00% or less, 4.00% or less, 3.00% or less, 2.00% or less, 1.00% or less, 0.50% or less, or 0.10% or less. For example, the Y₂O₃ content can be 0% or more, or more than 0%, and can also be 3.00% or less, 2.00% or less, or 1.00% or less.

[0034] Since F is a component that is likely to volatilize during melting and is also a component that causes veining, it is preferable that the above glass does not contain F. Not containing F is also preferable from the viewpoints of suppressing erosion of the melting furnace, suppressing a decrease in Young's modulus, and suppressing a decrease in specific modulus.

[0035] Since Pb, Cd, and As are substances that have an adverse impact on the environment, it is preferable to avoid introducing them.

[0036] From the viewpoint of obtaining a fining effect, the above glass can contain one or more selected from the group consisting of SnO2, CeO2, and Sb2O3. In one form, the total content of SnO2 and CeO2 can be 0%. In another form, the above glass can contain SnO2 and / or CeO2, and it is preferable that the total content (SnO2 + CeO2) of SnO2 and CeO2 is 0.05 to 2%. When the total content of SnO2 and CeO2 is 0.05% or more, a sufficient fining effect can be obtained, and the remaining bubbles can be reduced. Also, when the total content (SnO2 + CeO2) is 2% or less, it is possible to prevent the molten glass from splashing during glass melting and the productivity from decreasing. Regarding the lower limit of the total content (SnO2 + CeO2), it is preferably 0.10% or more, more preferably 0.20% or more, still more preferably 0.25% or more, even more preferably 0.30% or more, yet even more preferably 0.35% or more, and still even more preferably 0.40% or more. Regarding the upper limit of the total content (SnO2 + CeO2), it is preferably 1.5% or less, more preferably 1.2% or less, still more preferably 1.0% or less, even more preferably 0.70% or less, yet even more preferably 0.65% or less, still even more preferably 0.60% or less, even still more preferably 0.55% or less, and still even still more preferably 0.50% or less.

[0037] SnO₂ has the function of promoting clarification in a state where the melting temperature of the glass is relatively high (in a temperature range of about 1400 to 1600 °C). Among the restrictions on the use of clarifying agents such as Sb₂O₃ and arsenic trioxide that have an adverse impact on the environment, in one form, it is preferable to introduce SnO₂ into the above glass in order to remove bubbles in the glass with a high melting temperature. From the viewpoint of obtaining a clarification effect, the content of SnO₂ is preferably 0.01% or more, more preferably 0.05% or more, still more preferably 0.10% or more, even more preferably 0.15% or more, and yet more preferably 0.20% or more. Also, the content of SnO₂ is preferably 2% or less, more preferably 1.5% or less, still more preferably 1.0% or less, even more preferably 0.8% or less, and yet more preferably 0.5% or less.

[0038] CeO₂ is a component that exhibits a clarifying effect on the glass, similar to SnO₂. Since CeO₂ has the function of taking in oxygen and fixing it as a glass component in a state where the melting temperature of the glass is relatively low (in a temperature range of about 1200 to 1400 °C), in one form, it is preferable to introduce CeO₂ into the above glass as a clarifying agent. From the viewpoint of obtaining a clarification effect, the content of CeO₂ is preferably 0.01% or more, more preferably 0.05% or more, still more preferably 0.08% or more, and even more preferably 0.10% or more. Also, the content of CeO₂ is preferably 2% or less, more preferably 1.5% or less, still more preferably 1.0% or less, even more preferably 0.8% or less, yet more preferably 0.5% or less, and still more preferably 0.3% or less. By coexisting SnO₂ and CeO₂, a clarifying effect in a wide temperature range can be obtained. Therefore, in one form, the above glass preferably contains both SnO₂ and CeO₂.

[0039] From the perspective of reducing environmental impact, it is desirable to refrain from using Sb2O3. The content of Sb2O3 in the above glass is preferably in the range of 0 to 0.5%. More preferably, the content of Sb2O3 is 0.3% or less, still more preferably 0.1% or less, even more preferably 0.05% or less, yet even more preferably 0.02% or less, and particularly preferably it does not contain Sb2O3.

[0040] To obtain a predetermined glass composition, glass raw materials such as oxides, carbonates, nitrates, sulfates, hydroxides, etc. are weighed, formulated, and thoroughly mixed. Then, in a melting vessel, it is heated and melted, for example, in the range of 1400 to 1600 °C, clarified, stirred, and a homogenized molten glass with sufficient defoaming is formed. For example, the glass raw materials are heated and melted at 1400 to 1550 °C in a melting tank, the obtained molten glass is heated up in a clarification tank and held at 1450 to 1600 °C, and then cooled and the glass is discharged and formed at 1200 to 1400 °C, which is preferable.

[0041] Also, according to one aspect of the present invention, the B2O3 content is 0.1 mol% or more and 2.0 mol% or less, the Na2O content is 1.0 mol% or more and 6.0 mol% or less, and the CaO content is 0 mol% or more and 1.0 mol% or less, and it is an amorphous glass that further satisfies any one or more of the following (1) to (10), and is a glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording and reproducing device. can be provided.

[0042] (1) The molar ratio (Na2O / (Li2O + Na2O + K2O)) is 0.950 or more, and the total content (SiO2 + B2O3 + Al2O3) is 70.00% or more.

[0043] (2) It does not contain Li2O and K2O, and the total content (SiO2 + B2O3 + Al2O3) is 70.00% or more.

[0044] (3) The molar ratio (Na2O / (Li2O + Na2O + K2O)) is 0.950 or more, and the total content (SiO2 + B2O3) is 58.00% or more.

[0045] (4) It does not contain Li2O and K2O, and the total content (SiO2 + B2O3) is 58.00% or more.

[0046] (5) The molar ratio (Na2O / (Li2O + Na2O + K2O)) is 0.950 or more, and the total content (SiO2 + Al2O3) is 70.00% or more.

[0047] (6) It does not contain Li2O and K2O, and the total content (SiO2 + Al2O3) is 70.00% or more.

[0048] (7) The molar ratio (Na2O / (Li2O + Na2O + K2O)) is 0.950 or more, and the TiO2 content is 4.00 mol% or less.

[0049] (8) It does not contain Li2O and K2O, and the TiO2 content is 4.00 mol% or less.

[0050] (9) The molar ratio (Na2O / (Li2O + Na2O + K2O)) is 0.950 or more, and the ZnO content is 10.00% or less.

[0051] (10) It does not contain Li2O and K2O, and the ZnO content is 10.00% or less.

[0052] For each of the above glasses, reference can be made to the previous description regarding the compositions of Glass A and Glass B and the following description regarding the physical properties of Glass A and Glass B.

[0053] Also, according to one aspect of the present invention, The B2O3 content is 0.10 mol% or more and 2.00 mol% or less, The total content of Na2O and K2O is 1.00 mol% or more and 6.00 mol% or less, The CaO content is 0 mol% or more and 1.00 mol% or less, The MgO content is 14.00 mol% or more, an amorphous glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording and reproducing apparatus (hereinafter referred to as "glass a"), the B2O3 content is 0.10 mol% or more and 2.00 mol% or less, the total content of Na2O and K2O is 1.00 mol% or more and 6.00 mol% or less, the CaO content is 0 mol% or more and 1.00 mol% or less, the total content of MgO, SrO, CaO and BaO (MgO + SrO + CaO + BaO) is 14.00 mol% or more, an amorphous glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording and reproducing apparatus (hereinafter referred to as "glass b"), can be provided.

[0054] Regarding glass a and glass b, reference can be made to the previous description regarding the compositions of glass A and glass B and the following description regarding the physical properties of glass A and glass B.

[0055] <Glass physical properties> By adjusting the composition as described above, the above glass can have various glass physical properties described below.

[0056] (Specific elastic modulus) By having the composition described above, the above glass can have high rigidity. As an index of the rigidity of the glass, the specific elastic modulus can be mentioned. The specific elastic modulus is calculated by dividing the Young's modulus of the glass by the density. Here, the density refers to the specific gravity of the glass, in g / cm 3It can be considered as a value with the unit of "". The specific elastic modulus of the above glass is preferably 35.0 MNm / kg or more, more preferably 35.5 MNm / kg or more, 36.0 MNm / kg or more, 36.5 MNm / kg or more, and even more preferably 37.0 MNm / kg or more in that order. The specific elastic modulus can be, for example, 45.0 MNm / kg or less, 44.0 MNm / kg or less, 43.0 MNm / kg or less, 42.0 MNm / kg or less, 41.0 MNm / kg or less, 40.0 MNm / kg or less, 39.0 MNm / kg or less, or 38.0 MNm / kg or less. However, since the higher the specific elastic modulus, the higher the rigidity and the more preferable, it is not limited to the values exemplified above. Regarding the above glass, considering the balance with the glass transition temperature, the specific elastic modulus may be 37.0 MNm / kg or less.

[0057] (Young's modulus E) As an index of the rigidity of the glass, Young's modulus can also be mentioned. The Young's modulus of the above glass is preferably 86.0 GPa or more, more preferably 87.0 GPa or more, and even more preferably 88.0 GPa or more, 89.0 GPa or more, 90.0 GPa or more, 91.0 GPa or more, 92.0 GPa or more, and 93.0 GPa or more in that order. The Young's modulus of the above glass can be, for example, 120.0 GPa or less, 110.0 GPa or less, 100 GPa or less, or 95.0 GPa or less. However, since the higher the Young's modulus, the higher the rigidity and the more preferable, it is not limited to the values exemplified above. Regarding the above glass, considering the balance with the glass transition temperature, the Young's modulus may be 94.0 GPa or less, 93.0 GPa or less, or 92.0 GPa or less.

[0058] (Specific gravity d) By reducing the specific gravity of the glass for the magnetic recording medium substrate, the weight of the magnetic recording medium substrate can be reduced, and further, the weight of the magnetic recording medium can be reduced, thereby suppressing the power consumption of the HDD. The specific gravity of the above glass is preferably 2.80 or less, more preferably 2.75 or less, still more preferably 2.70 or less, even more preferably 2.65 or less, and even more preferably 2.60 or less. The specific gravity of the above glass can be, for example, 2.40 or more, but the lower the specific gravity, the more preferable, so it is not limited to the values exemplified above.

[0059] (Glass transition temperature Tg) The magnetic recording medium substrate is usually subjected to high-temperature treatment in the process of forming a magnetic recording layer on the substrate. For example, in order to form a magnetic recording layer containing a magnetic material with high magnetic anisotropy energy, which has been developed in recent years for high-density recording of magnetic recording media, film formation is usually performed at a high temperature, or heat treatment is performed at a high temperature after film formation. It is preferable for the magnetic recording medium substrate to have heat resistance that can withstand such high-temperature treatment in order to prevent the flatness of the substrate from decreasing when exposed to high temperatures. In this regard, the above glass can also exhibit high heat resistance by having the above glass composition. Regarding the glass transition temperature Tg, which is an index of heat resistance, the Tg of the above glass can be, for example, 550 °C or more, preferably 600 °C or more, and more preferably 610 °C or more, 620 °C or more, 630 °C or more, 640 °C or more, 650 °C or more, 660 °C or more, 670 °C or more, 680 °C or more, 690 °C or more, 700 °C or more, 710 °C or more, 720 °C or more, 730 °C or more, 740 °C or more, 750 °C or more in that order. Also, the Tg of the above glass can be, for example, 850 °C or less, 830 °C or less or 810 °C or less, 790 °C or less, 770 °C or less or 750 °C or less, but since the higher the Tg, the more preferable from the viewpoint of heat resistance, it is not limited to the values exemplified above.

[0060] (Thermal stability) The above glass can preferably exhibit high thermal stability. Examples of the method for evaluating thermal stability include the 1300°C 16-hour holding test and the 1320°C 16-hour holding test, which will be described in detail later. In the 1300°C 16-hour holding test, the evaluation result is preferably A or B, and more preferably A. In the 1320°C 16-hour holding test, the evaluation result is preferably A or B, and more preferably A.

[0061] (Liquidus temperature LT) As an index of the thermal stability of the glass, the liquidus temperature (LT) can be mentioned. The LT of the above glass is preferably 1330°C or lower, more preferably 1320°C or lower, and even more preferably 1310°C or lower, 1300°C or lower, 1290°C or lower, 1280°C or lower, 1270°C or lower, 1260°C or lower, 1250°C or lower, 1240°C or lower in this order. A glass with a low liquidus temperature LT is preferable because it is less likely to devitrify. The lower limit of LT can be, for example, 800°C or higher, but is not particularly limited.

[0062] (Coefficient of thermal expansion) An HDD incorporating a magnetic recording medium usually has a structure in which the central part is held by the spindle and clamp of the spindle motor to rotate the magnetic recording medium itself. Therefore, if there is a large difference in the coefficient of thermal expansion between the magnetic recording medium substrate and the spindle material constituting the spindle part, during use, due to the ambient temperature change, there will be a deviation between the thermal expansion and contraction of the spindle and the thermal expansion and contraction of the magnetic recording medium substrate, resulting in a phenomenon where the magnetic recording medium is deformed. When such a phenomenon occurs, the head cannot read the written information, which causes a decrease in the reliability of recording and playback. Therefore, it is desirable to prevent the difference between the coefficient of thermal expansion of the glass for the magnetic recording medium substrate and the coefficient of thermal expansion of the spindle material (such as stainless steel, etc.) from becoming too large. Generally, the spindle material of an HDD has a coefficient of thermal expansion of 70×10 in the temperature range of 100 to 300°C -7It has an average linear expansion coefficient (thermal expansion coefficient) of 30.0×10 -7 / °C or more, and if the average linear expansion coefficient of the glass for the magnetic recording medium substrate at 100 to 300°C is 30.0×10 -7 / °C or more, the difference in the thermal expansion coefficient from the spindle material is small, which can contribute to improving the reliability of the magnetic recording medium. On the other hand, if the thermal expansion coefficient of the glass substrate is too large, the substrate may crack due to heating during film formation. The average linear expansion coefficient α of Glass 2 at 100 to 300°C is preferably 34.0×10 -7 / °C or more, more preferably 35.0×10 -7 / °C or more, 36.0×10 -7 / °C or more, 37.0×10 -7 / °C or more, 38.0×10 -7 / °C or more, 39.0×10 -7 / °C or more, and still more preferably 40.0×10 -7 / °C or less, more preferably 68.0×10 -7 / °C or less, 65.0×10 -7 / °C or less, 63.0×10 -7 / °C or less, 60.0×10 -7 / °C or less, 57.0×10 -7 / °C or less, 55.0×10 -7 / °C or less, 50.0×10 -7 / °C or less in this order.

[0063] The above various physical properties can be obtained by the methods described later for the examples.

[0064] [Magnetic Recording Medium Substrate] The magnetic recording medium substrate according to one aspect of the present invention is made of the above glass.

[0065] The magnetic recording medium substrate can be manufactured through a process of preparing molten glass by heating a glass raw material and then shaping the molten glass into a plate shape by any one of, for example, the press molding method, the down-draw method, or the float method, followed by processing the obtained plate-shaped glass. For example, in the press molding method, the molten glass flowing out from a glass outflow pipe is cut into a predetermined volume to obtain a required molten glass mass, which is then press-molded with a press molding die to produce a thin disk-shaped substrate blank. Next, a center hole is provided in the obtained substrate blank, and machining such as inner and outer peripheral processing, lapping, and polishing is performed on both main surfaces. Then, through a cleaning process including acid cleaning and alkali cleaning, a disk-shaped substrate can be obtained. Regarding the various processes performed to obtain the above magnetic recording medium substrate, known techniques related to the manufacture of magnetic recording medium substrates can be applied.

[0066] In one form, the above magnetic recording medium substrate has a homogeneous composition on the surface and inside. Here, the surface and inside having a homogeneous composition means that ion exchange has not been performed (i.e., it does not have an ion exchange layer). Since a magnetic recording medium substrate without an ion exchange layer is manufactured without performing an ion exchange process, the manufacturing cost can be significantly reduced.

[0067] Also, in one form, the above magnetic recording medium substrate has an ion exchange layer on a part or all of its 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 on the fracture surface. The "main surface" is the surface on which the magnetic recording layer of the substrate is provided or is to be provided. Such a surface is called the main surface because it is the largest surface area among the surfaces of the magnetic recording medium substrate. In the case of a disk-shaped magnetic recording medium, it corresponds to the circular surface of the disk (excluding the center hole if there is one). Also, the presence or absence of the ion exchange layer can be confirmed by a method such as measuring the depth-direction concentration distribution of alkali metal ions from the substrate surface.

[0068] The ion exchange layer can be formed by bringing an alkali salt into contact with the substrate surface at a high temperature and exchanging the alkali metal ions in the alkali salt with the alkali metal ions in the substrate. For ion exchange (also referred to as "strengthening treatment" or "chemical strengthening"), known techniques can be applied. As an example, paragraphs 0068 to 0069 of WO2011 / 019010A1 can be referred to.

[0069] The magnetic recording medium substrate has a thickness of, for example, 1.5 mm or less, preferably 1.2 mm or less, more preferably 1.0 mm or less, still more preferably 0.8 mm or less, even more preferably less than 0.8 mm, yet even more preferably 0.7 mm or less, and still even more preferably 0.6 mm or less. Also, the thickness of the magnetic recording medium substrate is, for example, 0.2 mm or more. The ability to reduce the thickness of the magnetic recording medium substrate is preferable from the viewpoint of improving the recording capacity of the HDD. Further, the magnetic recording medium substrate preferably has a disk shape with a center hole.

[0070] The magnetic recording medium substrate is made of amorphous glass. According to amorphous glass, excellent surface smoothness can be achieved when processing the substrate as compared with crystalline glass.

[0071] Since the magnetic recording medium substrate is made of the glass according to one aspect of the present invention, it can have the glass physical properties described above for the glass.

[0072] [Magnetic Recording Medium] One aspect of the present invention relates to a magnetic recording medium having the magnetic recording medium substrate and a magnetic recording layer.

[0073] The magnetic recording medium is called a magnetic disk, hard disk, etc., and is suitable for various magnetic recording and reproducing devices, for example, internal storage devices (fixed disks, etc.) of desktop personal computers, server computers, notebook personal computers, mobile personal computers, etc., internal storage devices of portable recording and reproducing devices that record and reproduce images and / or sounds, and recording and reproducing devices of in-vehicle audio. In the present invention and this specification, the "magnetic recording and reproducing device" refers to a device capable of performing one or both of magnetic recording of information and magnetic reproduction of information.

[0074] The magnetic recording medium has, for example, a structure in which at least an adhesion layer, a base layer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer are laminated in this order from the side closer to the main surface on the main surface of the magnetic recording medium substrate. For example, the magnetic recording medium substrate is introduced into a film-forming apparatus that has been evacuated, and in an Ar atmosphere by DC (Direct Current) magnetron sputtering method, films are sequentially formed from the adhesion layer to the magnetic layer on the main surface of the magnetic recording medium substrate. For example, CrTi can be used as the adhesion layer, and a material containing, for example, Ru or MgO can be used as the base layer. Incidentally, a soft magnetic layer or a heat sink layer may be added as appropriate. After the above film formation, for example, a protective layer is formed using C2H4 by CVD (Chemical Vapor Deposition) method, and a nitriding treatment for introducing nitrogen to the surface is performed in the same chamber to form a magnetic recording medium. Thereafter, for example, a lubricating layer can be formed by coating PFPE (polyfluoropolyether) on the protective layer by dip coating method.

[0075] For further high-density recording of a magnetic recording medium, the magnetic recording layer preferably contains a magnetic material with high magnetic anisotropy energy. Preferred magnetic materials in this regard include Fe-Pt-based magnetic materials or Co-Pt-based magnetic materials. Here, "based" means containing. That is, the above magnetic recording medium can have a magnetic recording layer containing Fe and Pt, or Co and Pt as the magnetic recording layer. For the magnetic recording layer containing such a magnetic material and its film-forming method, reference can be made to the description in paragraph 0074 of WO2011 / 019010A1 and the examples of the same publication. Also, a magnetic recording medium having such a magnetic recording layer is preferably applied to a magnetic recording apparatus using a recording method called an energy assist recording method. Among the energy assist recording methods, a recording method that assists magnetization reversal by irradiation such as near-field light is called a thermal assist recording method, and a recording method that is assisted by microwaves is called a microwave assist recording method. For details thereof, reference can be made to paragraph 0075 of WO2011 / 019010A1. In addition, a conventional CoPtCr-based material may be used as the magnetic material for forming the magnetic recording layer.

[0076] By the way, in recent years, by mounting a DFH (Dynamic Flying Height) mechanism on a magnetic head, a significant narrowing (lower flying height) of the gap between the recording and reproducing element portion of the magnetic head and the surface of the magnetic recording medium has been achieved, and further high recording density has been attempted. The DFH mechanism is a function of providing a heating portion such as an extremely small heater near the recording and reproducing element portion of the magnetic head and protruding only the periphery of the element portion in the direction of the medium surface. By doing so, the distance (flying height) between the magnetic head and the magnetic recording layer of the medium approaches, so that signals of smaller magnetic particles can also be picked up, and further high recording density can be achieved. In one form, the above magnetic recording medium substrate can be used as the substrate of a magnetic recording medium applied to a magnetic recording and reproducing apparatus equipped with a magnetic head having a DFH mechanism.

[0077] There are no particular restrictions on the dimensions of the above magnetic recording medium substrate (e.g., a glass substrate for a magnetic disk) or the magnetic recording medium (e.g., a magnetic disk). For example, since high recording density is achievable, it is possible to reduce the size of the medium and the substrate. Also, in order to increase the recording capacity per magnetic recording medium, it is possible to increase the size of the medium and the substrate. For example, not only a nominal diameter of 2.5 inches, but also smaller diameters (e.g., 1 inch, 1.8 inches), or 3 inches, 3.5 inches, and even larger sizes can be used.

[0078] [Glass Spacer for Magnetic Recording and Reproducing Apparatus] The glass spacer for a magnetic recording and reproducing apparatus according to one aspect of the present invention (hereinafter, also simply referred to as "glass spacer") is made of the above glass.

[0079] A magnetic recording medium can be used to magnetically record and / or reproduce information in a magnetic recording and reproducing apparatus. A magnetic recording and reproducing apparatus usually includes a spacer in order to fix the magnetic recording medium to the spindle of a spindle motor and / or to maintain the distance between a plurality of magnetic recording media. In recent years, it has been proposed to use a glass spacer as such a spacer. For the same reasons as detailed above for the glass for a magnetic recording medium substrate, it is desired that this glass spacer has high rigidity. In contrast, the glass having the above composition can have high rigidity and is thus suitable as a glass spacer for a magnetic recording and reproducing apparatus.

[0080] The spacer for a magnetic recording and reproducing apparatus is a ring-shaped member, and details such as the configuration and manufacturing method of the glass spacer are known. Also, for the manufacturing method of the glass spacer, reference can be made to the previous descriptions regarding the manufacturing method of the glass for a magnetic recording medium substrate and the manufacturing method of the magnetic recording medium substrate. Also, for other details such as the glass composition and glass physical properties of the above glass spacer, reference can be made to the previous descriptions regarding the above glass, the magnetic recording medium substrate made of the above glass, and the magnetic recording medium having such a magnetic recording medium substrate. Incidentally, the spacer for the magnetic recording and reproducing apparatus can also be made of the above glass spacer, or can also have a configuration in which one or more layers of films such as a conductive film are provided on the surface of the above glass spacer. For example, in order to remove static electricity generated during the rotation of the magnetic recording medium, a conductive film such as a NiP alloy can be formed on the surface of the glass spacer by a plating method, a dipping method, a vapor deposition method, a sputtering method, or the like. Further, the glass spacer can have its surface smoothness improved by polishing (for example, the average surface roughness Ra is 1 μm or less), thereby enhancing the adhesion between the magnetic recording medium and the spacer and suppressing the occurrence of displacement.

[0081] [Magnetic recording and reproducing apparatus] One aspect of the present invention relates to a magnetic recording and reproducing apparatus including one or more selected from the group consisting of the above magnetic recording medium and the above glass spacer.

[0082] The magnetic recording and reproducing apparatus includes at least one magnetic recording medium and at least one spacer, and further usually includes a spindle motor for rotationally driving the magnetic recording medium and at least one magnetic head for recording and / or reproducing information with respect to the magnetic recording medium. The magnetic recording and reproducing apparatus according to one aspect of the present invention described above can include the magnetic recording medium according to one aspect of the present invention as at least one magnetic recording medium, and can also include a plurality of magnetic recording media according to one aspect of the present invention. The magnetic recording and reproducing apparatus according to one aspect of the present invention described above can include the glass spacer according to one aspect of the present invention as at least one spacer, and can also include a plurality of glass spacers according to one aspect of the present invention. A small difference between the thermal expansion coefficient of the magnetic recording medium and the thermal expansion coefficient of the spacer is preferable from the viewpoint of suppressing the occurrence of phenomena that can occur due to the difference in the thermal expansion coefficients of both, for example, distortion of the magnetic recording medium, a decrease in stability during rotation due to displacement of the magnetic recording medium, and the like. From this viewpoint, the magnetic recording and reproducing apparatus according to one aspect of the present invention includes the magnetic recording medium according to one aspect of the present invention as at least one magnetic recording medium, and more magnetic recording media when a plurality of magnetic recording media are included, and includes the glass spacer according to one aspect of the present invention as at least one spacer, and more spacers when a plurality of spacers are included. Further, for example, the magnetic recording and reproducing apparatus according to one aspect of the present invention can be such that the glass constituting the magnetic recording medium substrate included in the magnetic recording medium and the glass constituting the glass spacer have the same glass composition.

[0083] A magnetic recording and reproducing apparatus according to one aspect of the present invention may include at least one of a magnetic recording medium according to one aspect of the present invention and a glass spacer according to one aspect of the present invention, and known techniques related to magnetic recording and reproducing apparatuses can be applied to other aspects. In one aspect, as the magnetic head, an energy assist magnetic recording head having an energy source (such as a heat source like a laser light source, microwaves, etc.) for assisting magnetization reversal (assisting the writing of magnetic signals), a recording element section, and a reproducing element section can be used. Such a magnetic recording and reproducing apparatus using an energy assist recording method including an energy assist magnetic recording head is useful as a magnetic recording and reproducing apparatus having a high recording density and high reliability. Also, when manufacturing a magnetic recording medium used in a magnetic recording and reproducing apparatus using an energy assist recording method such as a heat assist recording method including a heat assist magnetic recording head having a laser light source or the like, a magnetic recording layer containing a magnetic material having a high magnetic anisotropy energy may be formed on a magnetic recording medium substrate. In order to form such a magnetic recording layer, usually, film formation is performed at a high temperature, or heat treatment is performed at a high temperature after film formation. The magnetic recording medium substrate according to one aspect of the present invention can be, in one form, a magnetic recording medium substrate having high heat resistance capable of withstanding such high-temperature treatment. However, the magnetic recording and reproducing apparatus according to one aspect of the present invention is not limited to an energy assist type magnetic recording and reproducing apparatus.

Example

[0084] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the embodiments shown in the examples.

[0085] [Examples 1 to 19] Raw materials such as oxides, carbonates, nitrates, sulfates, and hydroxides were weighed and mixed to obtain a formulated raw material so that the glass having the composition shown in Table 1 could be obtained. The formulated raw material was charged into a melting tank and heated and melted in the range of 1400 to 1600 °C. The molten glass thus obtained was held at 1400 to 1550 °C for 6 hours in a fining tank, and then the temperature was lowered (cooled down) and held in the range of 1200 to 1400 °C for 1 hour, and then the molten glass was formed to obtain a glass (amorphous oxide glass) for the following evaluation.

[0086] <Evaluation of Glass Physical Properties> (1) Glass transition temperature Tg, coefficient of mean linear expansion α The glass transition temperature Tg and the coefficient of mean linear expansion α at 100 to 300 °C of each glass were measured using a thermomechanical analyzer (TMA; Thermomechanical Analysis).

[0087] (2) Young's modulus E The Young's modulus of each glass was measured by the ultrasonic method.

[0088] (3) Specific gravity d The specific gravity of each glass was measured by the Archimedes method.

[0089] (4) Specific elastic modulus The specific elastic modulus was calculated from the Young's modulus obtained in (2) above and the specific gravity obtained in (3).

[0090] (5) 1300 °C 16h holding test 100 g of each glass was placed in a platinum crucible, and each crucible was charged into a heating furnace with the furnace temperature set at 1300 °C and left (holding test) for 16 hours while maintaining the furnace temperature. After 16 hours, the crucible was taken out of the heating furnace, and the glass in the crucible was transferred onto a refractory and cooled to room temperature (20 °C to 25 °C). The presence or absence of crystals in each glass was observed with an optical microscope (magnification 40 to 100 times) and evaluated according to the following criteria. A: No crystals on the glass surface, inside, and at the interface with the bottom of the platinum crucible B: Less than 10 crystals with a diameter of several tens of μm at the interface between the glass surface and the bottom of the platinum crucible per 100 g C: More than 10 crystals with diameters of several tens of μm are present at the interface between the glass surface and the bottom of the platinum crucible per 100 g D: Crystals are present inside the glass E: Crystals are present at the interface between the glass surface, inside the glass, and the bottom of the platinum crucible F: The entire glass has a large number of crystals and is cloudy G: The glass is turbid

[0091] (6) 1320 °C holding test for 16 h Except for setting the furnace temperature to 1320 °C, the holding test and the evaluation of the glass after the holding test were performed by the method described in (5) above

[0092] (7) Liquidus temperature LT The liquidus temperature of the glass shown in the table below was determined by the following method 50 g of glass was weighed into a platinum crucible. With the platinum crucible covered with a platinum lid, it was placed in a heating furnace with an ambient temperature of 1350 °C to completely melt the glass in the crucible. Then, the ambient temperature of the furnace was lowered to a predetermined temperature and held at that temperature for 16 hours. After holding for 16 hours, the platinum crucible was taken out of the furnace and left to cool the glass to room temperature (about 20 °C to 25 °C). The cooled glass was visually observed to check for the presence or absence of crystal precipitation The above operation was carried out in 10 °C increments from 1330 °C to 1200 °C, and the lowest temperature at which no crystal precipitation was observed was taken as the liquidus temperature LT

[0093] (8) Roughness evaluation Using the method described below, glass substrates for magnetic disks having the respective glass compositions shown in the table below were produced. Here, the basic processing conditions such as polishing conditions and cleaning conditions were the same. The arithmetic mean roughness Ra (JIS B0601:2001) of the main surface of the glass substrate for magnetic disks after final cleaning was measured by AFM (atomic force microscope) The Ra measured for each glass is shown as a relative value (ratio) when the Ra value measured for Example 4 is taken as 1.00. The degree of roughness was ranked according to the following criteria. Note that there are no practical problems even with Rank C Rank A: Less than 0.80 Rank B: 0.80 or more and less than 0.90 Rank C: 0.90 or more and 1.00 or less

[0094] The above results are shown in the following table.

[0095]

Table 1

[0096]

Table 2

[0097]

Table 3

[0098]

Table 4

[0099]

Table 5

[0100] <Fabrication of Magnetic Recording Medium Substrate> (1) Fabrication of Substrate Blank A disk-shaped substrate blank was fabricated by the following method A or B. Also, a glass blank for fabricating a glass spacer for a magnetic recording and reproducing apparatus can be obtained by the same method. (Method A) Regarding the glass having the composition shown in Table 1, the clarified and homogenized molten glass was caused to flow out from an outflow pipe at a constant flow rate and received by a lower mold for press molding. The molten glass that had flowed out was cut with a cutting blade so that a predetermined amount of molten glass mass was obtained on the lower mold. Then, the lower mold on which the molten glass mass was placed was immediately carried out from below the pipe, and using an upper mold and a body mold facing the lower mold, it was press-molded into a thin disk shape with a diameter of 99 mm and a thickness of 0.7 mm. After cooling the press-molded product to a temperature at which it does not deform, it was taken out of the mold and annealed to obtain a substrate blank (amorphous oxide glass). In the above-described molding, the molten glass flowing out using a plurality of lower molds was successively molded into disk-shaped substrate blanks. (Method B) Regarding the glass having the composition shown in Table 1, the clarified and homogenized molten glass was continuously cast from above into the through-hole of a heat-resistant mold provided with a cylindrical through-hole, molded into a columnar shape, and taken out from below the through-hole. After annealing the taken-out glass, the glass was sliced at regular intervals in a direction perpendicular to the column axis using a multi-wire saw to produce a disk-shaped substrate blank (amorphous oxide glass). In this example, the above-described Methods A and B were adopted. However, as methods for manufacturing the disk-shaped substrate blank, the following Methods C and D are also suitable. Further, the following Methods C and D are also suitable as methods for manufacturing a glass blank for producing a glass spacer for a magnetic recording and reproducing device. (Method C) It is also possible to pour out the molten glass onto a float bath, mold it into a sheet-shaped glass (molding by the float method), then anneal it, and then cut out a disk-shaped glass from the sheet glass to obtain a substrate blank (amorphous oxide glass). (Method D) It is also possible to mold the molten glass into a sheet-shaped glass by the overflow down-draw method (fusion method), anneal it, and then cut out a disk-shaped glass from the sheet glass to obtain a substrate blank (amorphous oxide glass).

[0101] (2) Production of glass substrate A through-hole was drilled in the center of the substrate blank (amorphous oxide glass) obtained by each of the above methods, and the outer and inner circumferences were ground (while forming chamfered surfaces at the same time), and then the end faces were polished, and the main surfaces of the disks were lapped and polished (mirror polishing) to finish into a glass substrate for magnetic disk with an outer diameter of 97 mm, an inner circular hole diameter of 25 mm, and a thickness of 0.5 mm. Also, by the same method, a glass blank for manufacturing a glass spacer for a magnetic recording and reproducing device can be finished into a glass spacer for a magnetic recording and reproducing device. The glass substrate obtained above was scrubbed and washed, then washed with an aqueous potassium hydroxide solution, and then rinsed with pure water and dried. When the surface of the substrate made of the glass of the example was observed with an atomic force microscope (AFM), no surface roughness or the like was observed, and the surface was smooth (low roughness).

[0102] <Fabrication of Magnetic 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 the glass substrate for magnetic disk fabricated above to obtain a magnetic disk.

[0103] First, using a film-forming apparatus evacuated to a vacuum, an adhesion layer, an underlayer, and a magnetic recording layer were sequentially formed by DC magnetron sputtering in an Ar atmosphere.

[0104] At this time, the adhesion layer was formed using a CrTi target so as to be an amorphous CrTi layer with a thickness of 20 nm. Subsequently, a 10-nm-thick layer made of MgO was formed as the underlayer. Also, the magnetic recording layer was formed using an FePtC or CoPtC target at a film-forming temperature of 200 to 400 °C so as to be a granular layer of FePt or CoPt with a thickness of 10 nm.

[0105] The magnetic disk after the film formation up to the magnetic recording layer was transferred from the film-forming apparatus into a heating furnace and annealed. The temperature in the heating furnace during annealing was in the range of 500 to 700 °C. By this annealing treatment, L 10 Magnetic particles of CoPt-based alloys or FePt-based alloys with a regular structure are formed. Note that it is not limited to the above, and L10 The magnetic recording layer may be heated so that a regular structure is formed. For example, by setting the temperature of the substrate during the formation of a magnetic recording layer of FePt or CoPt to 500 to 700 °C, an L 10 regular structure may be formed.

[0106] Subsequently, a 3-nm protective layer made of hydrogenated carbon was formed by CVD using ethylene as a source gas. Thereafter, a lubricating layer made of PFPE (perfluoropolyether) was formed by dip coating. The film thickness of the lubricating layer was 1 nm. Through the above manufacturing process, a magnetic disk was obtained. The obtained magnetic disk was mounted on a hard disk drive equipped with a DFH mechanism, and magnetic signals were recorded and reproduced at a recording density of 1000 gigabits per square inch in a recording area on the main surface of the magnetic disk. As a result, no phenomenon (crash failure) in which the magnetic head collides with the magnetic disk surface was confirmed.

[0107] In addition, a glass spacer obtained by the above manufacturing process using a glass having the composition shown in Table 1 and having a conductive film of NiP alloy formed on its surface (glass spacer with NiP alloy film) was mounted on a hard disk drive equipped with a DFH mechanism, and magnetic signals were recorded and reproduced at a recording density of 1000 gigabits per square inch in a recording area on the main surface of a magnetic disk separately prepared using a substrate made of a material different from the glass according to one aspect of the present invention. As a result, no phenomenon (crash failure) in which the magnetic head collides with the magnetic disk surface was confirmed.

[0108] Also, using the same glass material according to one aspect of the present invention, the magnetic disk manufactured above and the glass spacer with the NiP alloy film manufactured above are mounted on a hard disk drive equipped with a DFH mechanism, and a magnetic signal is recorded and reproduced at a recording density of 1000 gigabits per square inch in the recording area on the main surface of the magnetic disk. As a result, the phenomenon (crash failure) where the magnetic head collides with the magnetic disk surface was not confirmed. Here, since the glass substrate included in the magnetic disk and the glass spacer are made of the same glass material, the phenomenon that could occur due to the difference in the thermal expansion coefficient described above does not occur.

[0109] According to one aspect of the present invention, a magnetic recording medium suitable for high-density recording can be provided.

[0110] The embodiments disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included. For example, by performing the composition adjustment described in the specification on the glass composition exemplified above, a glass for a magnetic recording medium substrate and a glass spacer for a magnetic recording and reproducing device according to one aspect of the present invention can be produced. Also, it is of course possible to arbitrarily combine two or more of the matters exemplified or described as preferred ranges in the specification.

Claims

1. B ２ O ３ The content is 0.10 mol% or more and 0.80 mol% or less, Na ２ The content of O is 1.00 mol% or more and 6.00 mol% or less, The CaO content is 0 mol% or more and 1.00 mol% or less, the total content of MgO, SrO, CaO and BaO (MgO + SrO + CaO + BaO) is 14.00 mol% or more, the molar ratio of the SiO₂ content to the Na₂O content (SiO₂ / Na₂O) is 50.0 or less, the total content of SiO₂, B₂O₃ and Al₂O₃ (SiO₂ + B₂O₃ + Al₂O₃) is 74.00 mol% or more, and the total content of SiO₂ and Al₂O₃ (SiO₂ + Al₂O₃) is 73.00 mol% or more, an amorphous glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing apparatus.

2. The glass according to Claim 1, wherein the MgO content is 14.00 mol% or more.

3. The B₂O₃ content is 0.10 mol% or more and 2.00 mol% or less, the Na₂O content is 1.00 mol% or more and 6.00 mol% or less, the CaO content is 0 mol% or more and 1.00 mol% or less, the total content of MgO, SrO, CaO and BaO (MgO + SrO + CaO + BaO) is 14.00 mol% or more, and the SiO₂ content exceeds 62.00 mol%, an amorphous glass for a magnetic recording medium substrate or a glass spacer for a magnetic recording / reproducing apparatus.

4. The glass according to Claim 3, wherein the MgO content is 14.00 mol% or more.

5. The glass according to Claim 3, wherein the molar ratio of the SiO₂ content to the Na₂O content (SiO₂ / Na₂O) is 50.0 or less.

6. Na ２ The molar ratio of the content of SiO ２ to the content of O (SiO ２ / Na ２ O) is 50.0 or less, the glass according to claim 4.

7. Li ２ O, Na ２ O and K ２ The molar ratio of Na to the total content of ２ O content (Na ２ O / (Li ２ O + Na ２ O + K ２ O)) is 0.350 or more. The glass according to claim 1.

8. Li ２ The glass according to claim 1, comprising O.

9. Li ２ O, Na ２ O and K ２ The molar ratio of Li to the total content of ２ O (Li ２ O / (Li ２ O + Na ２ O + K ２ O)) is 0.600 or less. The glass according to claim 1.

10. The molar ratio of the Na ２ O content to the MgO content (Na ２ O / MgO) exceeds 0.080, and the glass according to claim 1.

11. The glass according to Claim 1, wherein the specific elastic modulus is 35.0 MNm / kg or more.

12. The glass according to Claim 1, wherein the glass transition temperature is 700 °C or more.

13. A magnetic recording medium substrate made of the glass according to any one of Claims 1 to 12.

14. A magnetic recording medium having the magnetic recording medium substrate according to Claim 13 and a magnetic recording layer.

15. The magnetic recording medium according to Claim 14, and a magnetic head, a magnetic recording / reproducing apparatus including the same.

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