JPWO2014097623A1 - Glass substrate for HDD and information recording medium - Google Patents

Abstract

The glass substrate for HDD of the present invention achieves a recording density of 600 Gb / square inch or more and, as a glass component, expressed as mol%, SiO2: 60 to 70%, Al2O3: 2 to 8%, Li2O: 0.1 7%, Na2O: 4-10%, MgO: 7-14%, CaO: 2-8%, TiO2: 0.1-4%, Nb2O5: 0.1-4%, SiO2 + Al2O3 + B2O3: 65-80% Li2O + Na2O + K2O: 7 to 17%, MgO + CaO + SrO + BaO + ZnO: 10 to 20%, Al2O3 / SiO2: 0.03 to 0.13, (TiO2 + Nb2O5) / SiO2: 0.01 to 0.05.

Description

  The present invention relates to a glass substrate for HDD having a recording density of 630 Gb / square inch or more.

  In recent years, the storage capacity of an information recording apparatus (for example, a hard disk drive HDD) on which an information recording medium is mounted has been improved to achieve 500 GB with one 2.5 inch disk, for example. With the improvement in storage capacity, the quality level required for information recording media (media) used is increasing. In order to improve the storage capacity, it is necessary to reduce the flying height of the read head. In recent years, the flying height has been set as small as several nm. For this reason, if a slight amount of abrasive or foreign matter remains on the surface of the medium, a head crash occurs when the read head collides, which causes a read error. Therefore, as a glass substrate for HDD used for media (hereinafter, sometimes simply referred to as a glass substrate), a glass substrate having a smaller swell and surface roughness Ra than conventional ones has been proposed (Patent Document 1). ).

  However, in such a glass substrate, there is a problem that the reading accuracy is lowered after a magnetic film (magnetic thin film) is formed on the glass substrate, although there are no major problems in smoothness and cleanliness. . As a result of examining this problem, it was found that the SN ratio (signal noise ratio, electromagnetic conversion characteristics) of the magnetic signal varied, and this variation in the SN ratio could be a cause of read / write errors. It was. As a result of further investigation on the cause of the variation in the SN ratio of the magnetic signal, the following has been found.

  That is, generally, after manufacturing, a glass substrate is once sealed and packaged and conveyed, and then taken out to form a magnetic thin film (magnetic film, magnetic layer) on the surface. At that time, in a glass substrate that achieves a recording density of 500 GB or more, cleanliness of the surface of the substrate is particularly important. Therefore, very few particles (foreign matter) on the glass substrate are washed by alkali washing before the magnetic film is formed. Removed. The variation in the S / N ratio of the magnetic signal described above may have an effect that the surface layer of the glass substrate is etched by the alkali cleaning before the magnetic film is formed, and the surface roughness Ra deteriorates accordingly. It has become clear.

Japanese Patent Laid-Open No. 2001-19466

  The present invention has been made in view of such conventional problems, and has alkali cleaning resistance before the formation of the magnetic film, has excellent electromagnetic conversion characteristics even after the formation of the magnetic film, and the frequency of occurrence of read / write errors. An object of the present invention is to provide a glass substrate for HDD with low and high reliability.

The glass substrate for HDD according to one aspect of the present invention has a recording density of 600 Gb / square inch or more and, as a glass component, expressed in mol%, SiO ₂ : 60 to 70%, Al ₂ O ₃ : 2 to 8%, _{B 2 O 3: 0~3%,} Li 2 O: 0.1~7%, Na 2 O: 4~10%, K 2 O: 0~3%, MgO: 7~14%, CaO: 2~ _{8%, SrO: 0~3%,} BaO: 0~3%, ZnO: 0~3%, TiO 2: 0.1~4%, ZrO 2: 0~3%, Y 2 O 3: 0~3 %, La ₂ O ₃ : 0 to 3%, Nb ₂ O ₅ : 0.1 to 4%, Ta ₂ O ₅ : 0 to 3%, CeO ₂ : 0 to 3% and SnO ₂ : 0 to 3% _{wherein, SiO 2 + Al 2 O 3} + B 2 O 3: 65~80%, Li 2 O + Na 2 O + K 2 O: 7~17%, MgO + CaO + _{rO + BaO + ZnO: 10~20%} , Al 2 O 3 / SiO 2: characterized in that it is a _{0.01~0.05: 0.03~0.13, (TiO 2 +} Nb 2 O 5) / SiO 2.

  The objects, features and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

(Glass substrate)
Hereinafter, embodiments of the glass substrate of the present invention will be described in detail. The glass substrate of the present embodiment has a recording density of 600 Gb / square inch or more, and as a glass component, expressed as mol%, SiO ₂ : 60 to 70%, Al ₂ O ₃ : 2 to 8%, B ₂ O _{3. : 0~3%, Li 2 O:} 0.1~7%, Na 2 O: 4~10%, K 2 O: 0~3%, MgO: 7~14%, CaO: 2~8%, SrO : 0 to 3%, BaO: 0 to 3%, ZnO: 0 to 3%, TiO ₂ : 0.1 to 4%, ZrO ₂ : 0 to 3%, Y ₂ O ₃ : 0 to 3%, La ₂ O ₃ : 0 to 3%, Nb ₂ O ₅ : 0.1 to 4%, Ta ₂ O ₅ : 0 to 3%, CeO ₂ : 0 to 3% and SnO ₂ : 0 to 3%, SiO _{2 + Al 2 O 3 + B 2} O 3: 65~80%, Li 2 O + Na 2 O + K 2 O: 7~17%, MgO + CaO + SrO + BaO + _{nO: 10~20%, Al 2 O} 3 / SiO 2: 0.03~0.13%, (TiO 2 + Nb 2 O 5) / SiO 2: and characterized by a 0.01-.05% To do.

SiO ₂ is contained in the glass composition in an amount of 60 to 70%, preferably 61 to 69%. SiO ₂ forms a glass network structure. When the content of SiO ₂ is less than 60%, it is difficult to form glass and the alkali cleaning resistance of the obtained glass substrate tends to decrease. On the other hand, when the content of SiO ₂ exceeds 70%, the viscosity of the glass material at the time of melting tends to be too high, and the handleability tends to decrease.

Al ₂ O ₃ is contained in the glass composition in an amount of 2 to 8%, preferably 3 to 7%. Al ₂ O ₃ forms a glass network structure like SiO ₂ . In addition, Al ₂ O ₃ has the effect of improving the Young's modulus of the obtained glass substrate and the effect of improving the ion exchange performance in the chemical strengthening step described later. When the content of Al ₂ O ₃ is less than 2%, the Young's modulus of the obtained glass substrate tends to decrease, or the ion exchange performance in the chemical strengthening process tends to decrease. On the other hand, when the content of Al ₂ O ₃ exceeds 8%, the alkali cleaning resistance of the resulting glass substrate tends to decrease.

B ₂ O ₃ is an optional component and is contained in the glass composition in an amount of 0 to 3%, preferably 0 to 2%. B ₂ O ₃ forms a glass network structure like SiO ₂ and Al ₂ O ₃ . In addition, B ₂ O ₃ has an effect of reducing the viscosity of the glass material at the time of melting (improving the glass melting property). When the content of B ₂ O ₃ exceeds 3%, the Young's modulus of the obtained glass substrate tends to decrease.

Li ₂ O is contained in the glass composition in an amount of 0.1 to 7%, preferably 0.5 to 6.5%. Li 2 _O is, to improve the Young's modulus of the resulting glass substrate, and improving the glass meltability. When the content of Li ₂ O is less than 0.1%, the glass meltability cannot be sufficiently improved, and the Young's modulus of the obtained glass substrate tends to be lowered. On the other hand, when the content of Li ₂ O exceeds 7%, the alkali cleaning resistance of the obtained glass substrate tends to decrease.

Na ₂ O is contained in the glass composition in an amount of 4 to 10%, preferably 5 to 9%. Na ₂ O improves glass meltability. When the content of Na ₂ O is less than 4%, the glass meltability tends not to be sufficiently improved. On the other hand, when the content of Na ₂ O exceeds 10%, the alkali cleaning resistance of the resulting glass substrate tends to decrease.

K ₂ O is an optional component and is contained in the glass composition in an amount of 0 to 3%, preferably 0 to 2%. K ₂ O improves the glass meltability and the thermal expansion coefficient of the resulting glass substrate. If the K 2 _O content exceeds 3%, there is a tendency for alkali washing resistance of the obtained glass substrate is reduced.

  MgO is contained in the glass composition in an amount of 7 to 14%, preferably 8 to 13%. MgO improves the Young's modulus of the obtained glass substrate and improves the glass melting property. When the content of MgO is less than 7%, the Young's modulus and glass meltability tend not to be sufficiently improved. On the other hand, when the content of MgO exceeds 14%, the liquidus temperature of the glass rises and the devitrification resistance decreases, so vitrification tends to be difficult.

  CaO is contained in the glass composition at 2 to 8%, preferably 3 to 7%. CaO improves the Young's modulus and thermal expansion coefficient of the glass substrate to be obtained, and improves the glass meltability. When the content of CaO is less than 2%, the effect of improving Young's modulus and the effect of improving glass meltability tend to be difficult to obtain. On the other hand, when the content of CaO exceeds 8%, the alkali cleaning resistance of the obtained glass substrate tends to decrease.

  SrO, BaO and ZnO are all optional components, and all are contained in the glass composition in an amount of 0 to 3%, preferably 0 to 2%. SrO, BaO and ZnO all improve the Young's modulus of the glass substrate to be obtained and improve the glass meltability. When the content of any of SrO, BaO, and ZnO exceeds 3%, the alkali cleaning resistance of the resulting glass substrate tends to decrease.

TiO ₂ is contained in the glass composition in an amount of 0.1 to 4%, preferably 0.3 to 3.5%. TiO ₂ improves the glass meltability and improves the alkali cleaning resistance of the resulting glass substrate. When the content of TiO ₂ is less than 0.1%, the glass meltability and the alkali cleaning resistance of the resulting glass substrate tend not to be sufficiently improved. On the other hand, when the content of TiO ₂ exceeds 4%, the liquidus temperature of the molten glass rises, and the devitrification resistance of the resulting glass substrate tends to decrease.

Nb ₂ O ₅ is contained in the glass composition in an amount of 0.1 to 4%, preferably 0.2 to 3%. Nb ₂ O ₅ improves the glass meltability and also improves the alkali cleaning resistance of the resulting glass substrate. When the content of Nb ₂ O ₅ is less than 0.1%, there is a tendency that the glass meltability and the alkali cleaning resistance of the obtained glass substrate cannot be sufficiently improved. On the other hand, when the content of Nb ₂ O ₅ exceeds 4%, the liquidus temperature of the molten glass rises, and the devitrification resistance of the obtained glass substrate tends to decrease.

TiO ₂ and Nb ₂ O ₅ are considered to suppress the elution of metal ions and the like from the surface of the glass substrate during the processing and cleaning of the glass substrate, respectively, and prevent the bond strength of the surface layer of the glass substrate from being weakened. ing. In addition, TiO ₂ and Nb ₂ O ₅ are considered to partly enter part of the glass network structure and improve the alkali cleaning resistance of the resulting glass substrate.

ZrO ₂ , Y ₂ O ₃ , La ₂ O ₃ and Ta ₂ O ₅ are all optional components, and all are contained in an amount of 0 to 3%, preferably 0 to 2% in the glass composition. ZrO ₂ , Y ₂ O ₃ , La ₂ O ₃ and Ta ₂ O ₅ all improve the rigidity of the glass material. When any content of ZrO ₂ , Y ₂ O ₃ , La ₂ O ₃ and Ta ₂ O ₅ exceeds 3%, the devitrification resistance tends to be lowered and vitrification tends to be difficult.

CeO ₂ and SnO ₂ are both optional components, and both are contained in the glass composition in an amount of 0 to 3%, preferably 0 to 2%. CeO ₂ and SnO ₂ both function as fining agents. When any content of CeO ₂ and SnO ₂ exceeds 3%, the devitrification resistance is lowered and vitrification tends to be difficult.

In addition, instead of CeO ₂ and SnO ₂ , As ₂ O ₃ or Sb ₂ O ₃ may be contained as a clarifier, and in addition to these components, a clarification effect is obtained within a range not impairing the object of the present invention. You may contain 0 to 3% of components obtained.

The sum of the contents of SiO ₂ , Al ₂ O ₃ and B ₂ O ₃ (SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ ) is 65 to 80%, preferably 67 to 78% in the glass composition. When the sum of the contents of SiO _2, Al ₂ O ₃ and B ₂ O ₃ is less than 65%, it tends to be difficult to form glass. On the other hand, when the sum of the contents of SiO _2, Al ₂ O ₃ and B ₂ O ₃ exceeds 80%, the viscosity of the glass material at the time of melting tends to be too high (glass meltability is too low).

The sum of the contents of Li ₂ O, Na ₂ O and K ₂ O (Li ₂ O + Na ₂ O + K ₂ O) is 7 to 17%, preferably 9 to 15% in the glass composition. When the sum of the contents of Li ₂ O, Na ₂ O and K ₂ O is less than 7%, the effect of improving the glass meltability tends to be insufficient. On the other hand, when the sum of the contents of Li ₂ O, Na ₂ O and K ₂ O exceeds 17%, the alkali cleaning resistance of the resulting glass substrate tends to decrease.

  The sum of the contents of MgO, CaO, SrO, BaO and ZnO (MgO + CaO + SrO + BaO + ZnO) is 10 to 20%, preferably 12 to 18% in the glass composition. When the sum of the contents of MgO, CaO, SrO, BaO and ZnO is less than 10%, the Young's modulus and glass meltability of the resulting glass substrate tend not to be sufficiently improved. On the other hand, when the sum of the contents of MgO, CaO, SrO, BaO and ZnO exceeds 20%, the alkali cleaning resistance of the resulting glass substrate tends to decrease.

The proportion of _Al 2 _{O 3} content to the content of _{SiO 2 (Al 2 O 3 /} SiO 2) is 0.03 to 0.13, preferably 0.04 to 0.12. When the ratio of the content of Al ₂ O _{3 to} the content of SiO ₂ is less than 0.03, the content of Al ₂ O ₃ is relatively low, so the Young's modulus of the resulting glass substrate tends to decrease. is there. On the other hand, when the ratio of the content of Al ₂ O _{3 to} the content of SiO ₂ exceeds 0.13, the content of Al ₂ O ₃ is relatively high. In this case, since ions easily move in the glass, metal ions and the like are easily eluted from the surface of the glass substrate during processing or cleaning of the glass substrate, and the bonding strength of the surface layer of the glass substrate is weakened. There exists a tendency for the alkali-cleaning tolerance of the glass substrate to fall.

The proportion of the sum of the content of TiO ₂ and NbO ₅ to the content of _{SiO 2 ((TiO 2 + NbO} 5) / SiO 2) is 0.01 to 0.05, preferably at 0.015 to 0.045 . When the ratio of the sum of the content of TiO ₂ and NbO ₅ with respect to the content of SiO ₂ is less than 0.01, the alkali cleaning resistance of the resulting glass substrate tends to decrease. On the other hand, when the ratio of the sum of the content of TiO ₂ and NbO ₅ with respect to the content of SiO ₂ exceeds 0.05, the liquidus temperature of the glass tends to increase and vitrification tends to be difficult.

In the present embodiment, other known oxide components may be appropriately contained as necessary. Examples of such an oxide component include P ₂ O ₅ and GeO _2, and in addition to these components, other oxide components may be included within a range that does not impair the object of the present invention. .

  Since the glass substrate of the present embodiment has the above-described glass composition, it exhibits sufficient alkali cleaning resistance when alkali cleaning is performed before forming the magnetic film, and the glass component is not easily eluted by alkali cleaning. The smaller the amount of glass component eluted from the glass substrate by alkali cleaning (Si elution amount), the better. The amount of Si elution is, for example, 160 ppb or less in an alkali elution test in which a glass substrate is 2.5 inches and a thickness is 0.8 mm, and the glass substrate is immersed in 50 mL of NaOH solution at 0.001 mol / L, pH 11, and 40 ° C. for 30 minutes. Preferably, it is 140 ppb or less. If the Si elution amount in such an alkali elution test is 160 ppb (160 μg / L) or less, it can be said that the glass substrate has excellent alkali cleaning resistance. In addition, since the glass substrate having such excellent alkali cleaning resistance does not easily change the surface roughness Ra by alkali cleaning, it has excellent electromagnetic conversion characteristics even after the formation of the magnetic film, and the frequency of occurrence of read / write errors is low. More reliable.

  Moreover, the Young's modulus of the glass substrate produced from such a glass composition is 80 GPa or more, preferably 84 to 100 GPa. When the Young's modulus of the glass substrate is 80 GPa or more, the media produced using the glass substrate is less likely to cause surface blur due to the air flow generated with the high-speed rotation of the HDD. As a result, the medium can appropriately maintain the flying height of the read head, and the frequency of occurrence of read / write errors can be further reduced. When the Young's modulus is 100 GPa or more, the effect of suppressing the surface blur can be sufficiently obtained, but the workability tends to be lowered.

  As described above, since the glass substrate of the present embodiment has the glass composition described above, it has alkali cleaning resistance before the formation of the magnetic film, has excellent electromagnetic conversion characteristics even after the formation of the magnetic film, and has a frequency of occurrence of read / write errors. Low and reliable.

(Glass substrate manufacturing method)
Hereinafter, a method for producing the glass substrate of the present invention will be described. In addition, the glass substrate of this invention should just have an above-described glass composition, and a manufacturing method is not specifically limited.

  First, as raw materials for the respective components constituting the glass substrate, the corresponding oxides, carbonates, nitrates, hydroxides, and the like are weighed to a desired ratio and mixed sufficiently (prepared raw materials). Next, the blended raw material is charged, for example, into a platinum crucible or the like in an electric furnace heated to 1300 to 1550 ° C., and melted and clarified, and then stirred and homogenized. The obtained molten glass is cast into a preheated mold and is gradually cooled into a glass block.

  The glass block is held for 1 to 3 hours at a temperature near the glass transition point, and then slowly cooled to remove distortion. Thereafter, the glass block is sliced into a disk shape, and is cut out by a core drill with the inner and outer circumferences being concentric to form a glass substrate. Alternatively, the molten glass is press-molded and formed into a disk shape to form a glass substrate.

  The disk-shaped glass substrate thus obtained is further subjected to rough polishing and precision polishing on both surfaces, and then washed with at least one liquid of water, acid, and alkali to obtain a final glass substrate. In the above process, after rough polishing and precision polishing on both sides, chemical strengthening is performed by dipping in a mixed solution of potassium nitrate (50 wt%) and sodium nitrate (50 wt%), and then the chemical strengthening layer is removed. Also good.

  The glass substrate of the present embodiment preferably has a disc shape. In the case of a disk shape, the size is not particularly limited. For example, it can be a small diameter disk of 3.5 inches, 2.5 inches, 1.8 inches, or less, and the thickness is It can be as thin as 2 mm, 1 mm, 0.63 mm, or less.

  A glass substrate obtained by the above manufacturing method is formed with a magnetic thin film (magnetic film) to form an information recording medium (media). At that time, in a glass substrate that achieves a recording density of 500 GB or more, cleanliness of the surface of the substrate is particularly important. Therefore, very few particles (foreign matter) on the glass substrate are washed by alkali washing before the magnetic film is formed. Removed. Examples of the alkali solution used for alkali cleaning include 0.001 mol / L, pH 11, and a 40 ° C. NaOH solution.

  The method of forming the magnetic film is not particularly limited. For example, a method of forming a thermosetting resin in which magnetic particles are dispersed by spin coating on a substrate, a method of forming by sputtering, electroless plating, etc. Conventionally known methods can be employed.

  The magnetic material used for the magnetic film is not particularly limited, and a conventionally known magnetic material can be used. As the magnetic material, for example, a Co-based alloy including Ni having high crystal anisotropy and Ni or Cr added for the purpose of adjusting the residual magnetic flux density can be used in order to obtain a high coercive force. When a recording medium is manufactured, an alloy composed of a transition metal element and a noble metal element, such as a Co—Pt alloy, and an atom of the transition metal element (Co) and the noble metal element (Pt). Alloys with almost the same content, or Co—Ni in which the atomic content of the transition metal element (Co) and the noble metal element (Pt) is almost equal and the atomic content of Ni is 0.1% or more and 50% or less -Pt alloy, Co-Ni-Pt alloy, Co-Cr-Pt alloy, Fe-Pt alloy, Cu and Cu-Ni-Pt alloy having almost the same atomic content of transition metal elements (Co and Ni) and noble metal element (Pt) It is preferable to form a thin film containing an oxide. In this case, a soft magnetic layer (a material having a small coercive force, a Co-based amorphous material, etc.) is preferably laminated below the thin film.

  In order to improve the sliding of the magnetic head, the surface of the magnetic film may be coated with a lubricant. Further, if necessary, the magnetic film may be provided with a base layer and a protective layer. The underlayer and the protective layer are selected according to the type of the magnetic film.

  The technical characteristics of the HDD glass substrate are summarized below.

The glass substrate for HDD according to one aspect of the present invention has a recording density of 600 Gb / square inch or more and, as a glass component, expressed in mol%, SiO ₂ : 60 to 70%, Al ₂ O ₃ : 2 to 8%, _{B 2 O 3: 0~3%,} Li 2 O: 0.1~7%, Na 2 O: 4~10%, K 2 O: 0~3%, MgO: 7~14%, CaO: 2~ _{8%, SrO: 0~3%,} BaO: 0~3%, ZnO: 0~3%, TiO 2: 0.1~4%, ZrO 2: 0~3%, Y 2 O 3: 0~3 %, La ₂ O ₃ : 0 to 3%, Nb ₂ O ₅ : 0.1 to 4%, Ta ₂ O ₅ : 0 to 3%, CeO ₂ : 0 to 3% and SnO ₂ : 0 to 3% _{wherein, SiO 2 + Al 2 O 3} + B 2 O 3: 65~80%, Li 2 O + Na 2 O + K 2 O: 7~17%, MgO + CaO + _{rO + BaO + ZnO: 10~20%} , Al 2 O 3 / SiO 2: characterized in that it is a _{0.01~0.05: 0.03~0.13, (TiO 2 +} Nb 2 O 5) / SiO 2.

  The glass substrate of the present invention having such a glass composition has alkali cleaning resistance before the formation of the magnetic film, has excellent electromagnetic conversion characteristics even after the formation of the magnetic film, has low occurrence frequency of read / write errors, and is reliable. high.

  The glass substrate of the present invention preferably has an Si elution amount of 160 ppb or less in an alkali elution test in which the glass substrate is immersed in an NaOH solution of 0.001 mol / L, pH 11, and 40 ° C. for 30 minutes.

  If the Si elution amount is 160 ppb or less in such an alkali elution test, it can be said that the glass substrate has excellent alkali cleaning resistance. In this case, for example, a very small amount of deposits can be removed by using an alkaline solution having a higher concentration. In addition, since the glass substrate having such excellent alkali cleaning resistance does not easily change the surface roughness Ra by alkali cleaning, it has excellent electromagnetic conversion characteristics even after the formation of the magnetic film, and the frequency of occurrence of read / write errors is low. More reliable.

  The glass substrate of the present invention preferably has a Young's modulus of 80 GPa or more.

  When satisfying such Young's modulus, the media produced using the glass substrate of the present invention is less likely to cause surface blur due to the air flow generated with high-speed rotation of the HDD. As a result, the medium can appropriately maintain the flying height of the read head, and the frequency of occurrence of read / write errors can be further reduced.

Glass substrate of the present invention, as a glass component, in mol% _{display, SiO 2: 61~69%, Al} 2 O 3: 3~7%, B 2 O 3: 0~2%, Li 2 O: 0. 5 to 6.5%, Na ₂ O: 5 to 9%, K ₂ O: 0 to 2%, MgO: 8 to 13%, CaO: 3 to 7%, SrO: 0 to 2%, BaO: 0 to 0 _{2%, ZnO: 0~2%,} TiO 2: 0.3~3.5%, ZrO 2: 0~2%, Y 2 O 3: 0~2%, La 2 O 3: 0~2%, Nb ₂ O ₅ : 0.2 to 3%, Ta ₂ O ₅ : 0 to 2%, CeO ₂ : 0 to 2% and SnO ₂ : 0 to 2%, SiO ₂ + Al ₂ O ₃ + B ₂ O _{3 : 67~78%, Li 2 O +} Na 2 O + K 2 O: 9~15%, MgO + CaO + SrO + BaO + ZnO: 12~18%, Al 2 O 3 / SiO _{2: 0.04~0.12, (TiO 2 +} Nb 2 O 5) / SiO 2: is preferably 0.015 to 0.045.

  A glass substrate having such a glass composition has better alkali cleaning resistance before forming the magnetic film, more excellent electromagnetic conversion characteristics even after the magnetic film is formed, less frequent read / write errors, and more reliable. high.

  Hereinafter, the glass substrate of this invention is explained in full detail according to an Example. In addition, the method of manufacturing the glass substrate of this invention is not limited to the Example shown below at all.

<Examples 1-15, Comparative Examples 1-5>
A predetermined amount of raw material powder was weighed into a platinum crucible and mixed so as to have the glass composition shown in Table 1 or Table 2, and then melted at 1550 ° C. in an electric furnace to obtain a glass melt. After the raw materials were sufficiently dissolved, a platinum stirring blade was inserted into the glass melt and stirred for 1 hour. Thereafter, the stirring blade was taken out and allowed to stand for 30 minutes, and then a glass block was obtained by pouring the glass melt into a jig. Thereafter, the glass block was held in the vicinity of the glass transition point of each glass for 2 hours, and then slowly cooled to remove strain. The obtained glass block was sliced into a 2.5-inch disk having a thickness of about 0.8 mm, and the inner and outer circumferences were concentric and cut out using a cutter. The glass substrate of Examples 1-15 and Comparative Examples 1-5 was produced by performing rough grinding | polishing and precision grinding | polishing with respect to both surfaces of a glass substrate, and washing | cleaning after that.

  About the glass substrate produced in Examples 1-15 and Comparative Examples 1-5, Young's modulus was measured in accordance with the method shown below, alkali washing tolerance was evaluated, and the HDD operation test was done. The results are shown in Table 1 or Table 2.

(Young's modulus)
The Young's modulus E (GPa) was measured according to the dynamic elastic modulus test method of the elastic test method of JIS R 1602 fine ceramics. The dynamic elastic modulus was measured using a dynamic viscoelasticity measuring device (model number: JE-RT, manufactured by Nippon Techno Plus Co., Ltd.).

(Alkali dissolution test)
A 2.5-inch glass substrate (surface roughness Ra: 2 m or less) prepared as described above was immersed in 50 mL of NaOH solution at 0.001 mol / L, pH 11, and 40 ° C. for 30 minutes, and then ICP The amount of Si elution (ppb) in the eluate was analyzed using an emission spectroscopic analyzer (model number: SPS7800, manufactured by SII Nanotechnology Co., Ltd.).

(HDD operation test)
In a polytetrafluoroethylene container, 0.001 mol / L, pH 11 NaOH solution (50 mL) was placed, and the glass substrate was immersed therein for 30 minutes. A magnetic film of Co—Cr alloy was formed on the glass substrate through the film formation process, the disk rotation speed was set to 15000 rpm, and the number of read errors when the head was operated from the inner periphery to the outer periphery in the magnetic recording area was evaluated. . Each evaluation was performed for 100 sheets, and the total number of errors was calculated. The evaluation criteria are shown below.

A: The number of errors was 0 to 2 times.
○: The number of errors was 3 to 5 times.
X: The number of errors was 6 or more.

As shown in Tables 1 and 2, the glass substrates of Examples 1 to 15 each had a Young's modulus of 80 GPa or more, showed excellent alkali durability, and the results of the HDD operation test were also good. Among them, the glass substrates of Examples 1, ₂ , 4 to 9, and 11 to 15 have a ratio of the content of Al ₂ O _{3 to} the content of SiO ₂ (Al ₂ O ₃ / SiO ₂ ) and the content of SiO ₂ . The ratio of the sum of the content of TiO ₂ and NbO ₅ with respect to the amount ((TiO ₂ + Nb ₂ O ₅ ) / SiO ₂ ) was in a preferred range, so the alkali durability was particularly excellent, and the results of the HDD operation test were particularly good Met.

  On the other hand, the glass substrates of Comparative Examples 1 to 5 all had low alkali durability, and the results of HDD operation tests were poor.

Specifically, the glass substrate of Comparative Example 1, many content of _Al 2 _{O 3,} the proportion of _Al 2 _{O 3} content to the content of _{SiO 2 (Al 2 O 3 /} SiO 2) is greater The alkaline durability was low, and the result of the HDD operation test was poor. Glass substrate of Comparative Example 2 is not TiO ₂ is contained, the proportion of the sum of the content of TiO ₂ and NbO ₅ to the content of _{SiO 2 ((TiO 2 + Nb} 2 O 5) / SiO 2) is less Therefore, the alkali durability was low, and the result of the HDD operation test was poor. Since the glass substrate of Comparative Example 3 had a low SiO ₂ content and a high Na ₂ O content, the alkali durability was low and the HDD operation test result was poor. The glass substrate of Comparative Example 4 has a small sum of contents of SiO ₂ , Al ₂ O ₃ and B ₂ O ₃ (SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ ), and is composed of MgO, CaO, SrO, BaO and ZnO. Since the sum of the contents (MgO + CaO + SrO + BaO + ZnO) was large, the alkali durability was low and the result of the HDD operation test was poor. Glass substrate of Comparative Example 5 has a small content of _Al 2 _{O 3,} the proportion of the _Al 2 _{O 3} content to the content of _{SiO 2 (Al 2 O 3 /} SiO 2) is small and is NbO ₅ Since it was not contained, the Young's modulus was less than 80 GPa, the alkali durability was low, and the result of the HDD operation test was poor.

The present invention can be widely used in technical fields such as a glass substrate for HDD having a recording density of 630 Gb / in 2 or more.

Claims (4)

In a glass substrate for HDD having a recording density of 600 Gb / square inch or more,
As a glass component, in mol% display,
_{SiO 2: 60~70%, Al 2} O 3: 2~8%, B 2 O 3: 0~3%, Li 2 O: 0.1~7%, Na 2 O: 4~10%, K 2 O: 0~3%, MgO: 7~14 %, CaO: 2~8%, SrO: 0~3%, BaO: 0~3%, ZnO: 0~3%, TiO 2: 0.1~4 _{%, ZrO 2: 0~3%,} Y 2 O 3: 0~3%, La 2 O 3: 0~3%, Nb 2 O 5: 0.1~4%, Ta 2 O 5: 0~3 %, CeO ₂ : 0 to 3% and SnO ₂ : 0 to 3%,
SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ : 65-80%,
Li ₂ O + Na ₂ O + K ₂ O: 7-17%,
MgO + CaO + SrO + BaO + ZnO: 10 to 20%
_{Al 2 O 3 / SiO 2:} 0.03~0.13,
_{(TiO 2 + Nb 2 O 5} ) / SiO 2: HDD glass substrate is 0.01 to 0.05.   The glass substrate for HDD of Claim 1 whose Si elution amount in the alkali elution test immersed in 0.001 mol / L, pH 11, 40 degreeC NaOH solution for 30 minutes is 160 ppb or less.   The glass substrate for HDD of Claim 1 or 2 whose Young's modulus is 80 GPa or more. As a glass component, in mol% display,
_{SiO 2: 61~69%, Al 2} O 3: 3~7%, B 2 O 3: 0~2%, Li 2 O: 0.5~6.5%, Na 2 O: 5~9%, _{K 2 O: 0~2%, MgO} : 8~13%, CaO: 3~7%, SrO: 0~2%, BaO: 0~2%, ZnO: 0~2%, TiO 2: 0.3 _{~3.5%, ZrO 2: 0~2%} , Y 2 O 3: 0~2%, La 2 O 3: 0~2%, Nb 2 O 5: 0.2~3%, Ta 2 O 5 : 0 to _2%, CeO 2: 0 to 2% and _SnO 2: comprises 0 to 2%,
SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ : 67 to 78%,
_{Li 2 O + Na 2 O +} K 2 O: 9~15%,
MgO + CaO + SrO + BaO + ZnO: 12 to 18%,
_{Al 2 O 3 / SiO 2:} 0.04~0.12,
_{2. The} glass substrate for HDD according to claim 1, which is (TiO ₂ + Nb ₂ O ₅ ) / SiO ₂ : 0.015 to 0.045.