JP5227711B2 - Glass substrate for magnetic disk and manufacturing method thereof - Google Patents

Description

  The present invention relates to a glass substrate for a magnetic disk mounted on a hard disk drive device and a method for manufacturing the same.

  There is a magnetic disk as a magnetic recording medium mounted on a hard disk drive device (HDD device). The magnetic disk is manufactured by depositing a NiP film on a metal substrate made of an aluminum-magnesium alloy or the like, or laminating a magnetic layer or a protective layer on a glass substrate or a ceramic substrate. Conventionally, an aluminum alloy substrate has been widely used as a substrate for a magnetic disk. However, with recent downsizing, thinning, and high-density recording of magnetic disks, surface flatness and A glass substrate having excellent strength with a thin plate has been used (Patent Document 1).

  In recent years, in a magnetic disk mounted on an HDD device, the recording capacity is further expanded in the future, and it is required to further increase the information recording speed and reading speed in the HDD device. In order to satisfy these requirements, it is required to rotate the magnetic disk at a higher speed.

However, if the magnetic disk is rotated at high speed in the HDD device, a strong load is applied to the magnetic disk, and the magnetic disk is required to have high strength (impact resistance). In recent years, HDD devices are used in portable devices such as notebook computers, mobile phones, and portable music players, so that the magnetic disk does not break even when the portable device is dropped. Such impact resistance is required. Thus, there is a need for a magnetic disk (magnetic disk substrate) that satisfies even higher impact resistance than that required at present.
JP-A-9-27150

  The present invention has been made in view of this point, and an object of the present invention is to provide a glass substrate for a magnetic disk that satisfies even higher impact resistance than that currently required, and a method for manufacturing the same.

Glass substrates for magnetic disks of the present invention has a main surface and an end surface, a disk-shaped glass substrate for magnetic disk chemical strengthening processing has been performed, the glass material constituting the glass substrate, SiO ₂ is 57 mass% to 75 mass%, Al ₂ O ₃ is 5 mass% to 20 mass% (however, the total amount of SiO ₂ and Al ₂ O ₃ is 74 mass% or more), ZrO ₂ , HfO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , Y ₂ O ₃ and TiO ₂ total exceeds 0 and is 6% by mass or less, and Li ₂ O exceeds 1% by mass and is 9% by mass or less. Na ₂ O is 5% by mass to 18% by mass (however, the mass ratio Li ₂ O / Na ₂ O is 0.5 or less), K ₂ O is 0 to 6% by mass, and MgO is 0 to 4%. Mass%, CaO is more than 0 and 5 mass% or less (however, M The total amount of O and CaO is not more than 5 wt%, and the content of CaO is greater than the content of MgO), SrO + BaO is 0 to 3 wt%, compressive stress depth is 100-150 .mu.m, The outermost surface stress layer indentation length of the main surface is 49.1 μm or less, and when the angle formed between the main surface and the compressive stress is θ in the stress profile by the Babinet corrector method, the outermost surface portion The stress layer indentation length is not more than a value y of {12 · t · ln (tan θ) + (49.1 / t)}.
Here, the indentation length of the outermost surface stress layer is an indentation when a diamond quadrangular pyramid indenter having a cross-sectional angle of 172 ° 30 ′ and a 130 ° rhombus is pushed into the main surface with a pressing force of 100 g. The length of the longer diagonal line, and the tan θ is a value {(L ₁ + L ₂ ) / (P ₁ + P ₂ )} obtained from the stress value and stress depth obtained by the Babinet corrector method, The t is the substrate thickness.
P ₁ is a compressive stress value, P ₂ is a tensile stress value, L ₁ is a compressive stress depth, and L ₂ is a tensile stress depth.

  According to this configuration, the compressive stress in the surface layer portion (depth of about 1.5 μm from the substrate surface) is high, and the rate of change of the stress value (compressive stress, tensile stress) in the depth direction inside the substrate is small. Higher impact resistance than that required at present (for example, withstanding acceleration of 1500 G to 2000 G in 1/1000 second) can be satisfied.

  In the glass substrate for a magnetic disk of the present invention, the value of y is preferably {16 · t · ln (tan θ) + (49.1 / t)}.

  In the glass substrate for a magnetic disk of the present invention, it is preferable that the glass constituting the glass substrate for a magnetic disk is an aluminosilicate glass containing Zr.

  In the glass substrate for a magnetic disk of the present invention, it is preferable that the surface roughness Ra of the main surface measured with an atomic force microscope is 0.3 nm or less.

  In the glass substrate for magnetic disk of the present invention, it is preferable that the measurement length is 0.8 mm in the circumferential direction of the glass substrate for magnetic disk and the surface roughness Ra of the end face is 0.2 μm or less.

  In the glass substrate for a magnetic disk of the present invention, the compressive stress depth is preferably 50 μm or more.

The method for producing a glass substrate for a magnetic disk according to the present invention is a method for producing a glass substrate for a magnetic disk including a step of subjecting a glass substrate to chemical strengthening, and the glass material constituting the glass substrate has a SiO ₂ of 57. Mass% to 75 mass%, Al ₂ O ₃ is 5 mass% to 20 mass% (however, the total amount of SiO ₂ and Al ₂ O ₃ is 74 mass% or more), ZrO ₂ , HfO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , Y ₂ O ₃ and TiO ₂ are in total more than 0 and 6% by mass or less, Li ₂ O is more than 1% by mass and 9% by mass or less, Na ₂ O is 5% by mass to 18% by mass (however, the mass ratio Li ₂ O / Na ₂ O is 0.5 or less), K ₂ O is 0 to 6% by mass, and MgO is 0 to 4% by mass. %, And CaO exceeds 0 and is 5% by mass or less. And, the total amount of MgO and CaO is not more than 5 wt%, and the content of CaO is greater than the content of MgO), SrO + BaO is 0 to 3 wt%, the chemical strengthening treatment, the compression stress depth 100 to 150 μm, the outermost stress layer indentation length of the main surface of the glass substrate for magnetic disk is 49.1 μm or less, and the stress profile by the Babinet corrector method is between the main surface and the compressive stress. When the angle formed is θ, the outermost stress layer indentation length is less than the value y of {12 · t · ln (tan θ) + (49.1 / t)}. It is characterized by being.
Here, the indentation length of the outermost surface stress layer is an indentation when a diamond quadrangular pyramid indenter having a cross-sectional angle of 172 ° 30 ′ and a 130 ° rhombus is pushed into the main surface with a pressing force of 100 g. The length of the longer diagonal line, and the tan θ is a value {(L ₁ + L ₂ ) / (P ₁ + P ₂ )} obtained from the stress value and stress depth obtained by the Babinet corrector method, The t is the substrate thickness.
P ₁ is a compressive stress value, P ₂ is a tensile stress value, L ₁ is a compressive stress depth, and L ₂ is a tensile stress depth.

  According to this method, the compressive stress in the surface layer portion (depth of about 1.5 μm from the substrate surface) is high, and the rate of change in the stress value (compressive stress, tensile stress) in the depth direction inside the substrate is small. It is possible to obtain a glass substrate for a magnetic disk that satisfies even higher impact resistance than that required at present (for example, withstands acceleration of 1500 G to 2000 G in 1/1000 second).

  In the method for manufacturing a glass substrate for a magnetic disk of the present invention, the value of y is preferably {16 · t · ln (tan θ) + (49.1 / t)}.

  In the method for producing a magnetic disk glass substrate of the present invention, the glass constituting the magnetic disk glass substrate is preferably an aluminosilicate glass containing Zr.

  The magnetic disk of the present invention comprises the glass substrate for a magnetic disk, and a magnetic layer provided directly or via another layer on the main surface of the glass substrate for the magnetic disk. .

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
(Embodiment 1)
The glass substrate for magnetic disks according to the present invention is a glass substrate for magnetic disks mounted on, for example, a hard disk drive (HDD). This magnetic disk is a recording medium capable of performing high-density information signal recording and reproduction by, for example, a perpendicular magnetic recording method. The glass substrate for a magnetic disk is mainly used for a 1.8 inch type magnetic disk or a 2.5 inch type magnetic disk.

The glass substrate for a magnetic disk according to the present invention has an outermost stress layer indentation length of 49.1 μm or less on the main surface, and an angle formed between the main surface and a compressive stress in a stress profile by a Babinet corrector method. the when the theta, the uppermost portion stress layer penetration length is because the value y hereinafter of {12 · t · ln (tanθ ) + (49.1 / t)}, the impact required for current It is possible to satisfy an even higher impact resistance than the property. The outermost stress layer indentation length is long in the indentation when a diamond quadrangular pyramid indenter whose cross-section angle is 172 ° 30 ′ and 130 ° is rhombus is pushed into the main surface with a pressing force of 100 g. The tan θ is the value { (L ₁ + L ₂ ) / (P ₁ + P ₂ ) } determined from the stress value and stress depth determined by the Babinet corrector method, t is the substrate thickness.
P ₁ is a compressive stress value, P ₂ is a tensile stress value, L ₁ is a compressive stress depth, and L ₂ is a tensile stress depth.

In a chemically strengthened glass substrate, a compressive stress layer is formed on the surface layer by exchanging ions of atoms contained in the glass constituting the glass substrate with ions of atoms having an atomic radius larger than that atom. Has been. FIG. 1 shows a stress profile in the glass substrate subjected to the chemical strengthening treatment in this way. FIG. 1 is a diagram showing a stress profile in a glass substrate having a thickness t. In FIG. 1, the right side of the center X-ray is a compressive stress region, and the left side of the X-ray is a tensile stress region. That, P ₁ in FIG. 1 shows the compressive stress value, P ₂ represents a tensile stress value. Further, L ₁ in Figure 1 indicates a compressive stress depth, L ₂ represents a tensile stress depth. In the region of the compressive stress, a high degree of reinforcement larger the compression stress value P _1. In the tensile stress region, the distance (depth) from the substrate surface to the stress profile is a distance at which cracking occurs when the crack reaches the stress profile from the substrate surface. If this depth is large, the glass is difficult to break.

From the viewpoint of impact resistance (hardness to cracking), tan θ is large when θ is the slope of the stress profile (angle formed between the main surface and the compressive stress) from the compressive stress region to the tensile stress region. That is, it is preferable that the distance (depth) from the substrate surface to the stress profile is large. This is because, when tan θ is large, the amount of stress change from the main surface to the inside becomes moderate, and cracks that are likely to be stretched against an impact for a short time (less than two thousandths of a second) can be effectively suppressed. It is. On the other hand, when tan θ is increased in the stress profile, the compressive stress value P ₁ inevitably decreases. In such a situation, the present inventors pay attention to the micro surface layer portion of the substrate surface, and increase the tan θ in the stress profile and reduce the hardness of the substrate surface layer portion even when the compressive stress value P ₁ is small. The inventors have found that the impact resistance can be improved by increasing the height, and have reached the present invention.

  As for the hardness of the substrate surface layer, the longer diagonal line in the indentation when a diamond quadrangular pyramid indenter having a rhombus with a cross-sectional angle of 172 ° 30 ′ and 130 ° is pressed into the main surface of the glass substrate with a pressing force of 100 g. The length (the outermost stress layer indentation length) is evaluated. According to such an evaluation method, the hardness of a thin surface layer having a thickness of about 1 μm to 2 μm on the substrate surface can be indirectly expressed. The method for evaluating the hardness of the surface layer on the substrate surface is not limited to this, and a method capable of indirectly expressing the hardness of a thin surface layer having a thickness of about 1 μm to 2 μm on the substrate surface can be used. In the present invention, the length of the diagonal line with the longer indent in the evaluation method is 49.1 or less.

In addition, when the angle formed between the main surface and the compressive stress in the stress profile by the Babinet corrector method is θ, the outermost stress layer indentation length is expressed as {12 · t · ln (tan θ) + (49 .1 / t) to a value y hereinafter in}. tan θ is a value { (L ₁ + L ₂ ) / (P ₁ + P ₂ ) } obtained from the stress value and stress depth obtained by the Babinet corrector method, and t is the substrate thickness.
At this time, P ₁ is a compression stress value, P ₂ is tensile stress value, L ₁ is a compression stress depth, L ₂ is a tensile stress depth. The characteristic curve y = {12 · t · ln (tan θ) + (49.1 / t)} is a characteristic curve A shown in FIG. Therefore, the glass substrate according to the present invention has a characteristic of a region having an outermost stress layer indentation length of 49.1 or less in this characteristic curve. More preferably, it has the characteristic of the region of y = {16 · t · ln (tan θ) + (49.1 / t)} which is the characteristic curve B shown in FIG. As described above, since tan θ is preferably large from the viewpoint of resistance to cracking, the glass substrate according to the present invention has an outermost stress layer indentation length of 49.1 μm or less in FIG. It is preferable to have the characteristics of the region (lower right region in FIG. 2) on the right side (side where tan θ is larger) than A, preferably the right side (side where tan θ is larger) than the characteristic curve B.

  The stress profile as shown in FIG. 1 can be obtained by the Babinet corrector method. A Babinet corrector is an instrument that includes two opposing quartz wedges with equal angles, and one wedge is moved in the direction of its length by a micrometer screw. Yes. These two wedges have optical axis directions perpendicular to each other, and the optical axis direction of one movable wedge is along the movable direction. This instrument is widely used for the inspection of glass having retardation (retardation), birefringence, or internal stress of crystals.

  In the production of a glass substrate, (1) shape processing step and first lapping step, (2) end shape step (coring step for forming a hole, chamfering at the end (outer peripheral end and inner peripheral end) Chamfering step for forming a surface (chamfered surface forming step)), (3) end surface polishing step (outer peripheral end and inner peripheral end), (4) second lapping step, (5) main surface polishing step (first And a second polishing step) and (6) a chemical strengthening step. In addition, about processes other than a chemical strengthening process, it is performed on the conditions performed normally.

In order to obtain a glass substrate having the above-described characteristics, it is necessary to appropriately set the glass composition and chemical strengthening conditions in the (6) chemical strengthening step. That is, the uppermost portion stress layer penetration length of the main surface 49.1μm or less, an angle between the main surface and the compressive stress in the stress profile by a Babinet compensator method is taken as theta, the uppermost part stress layer penetration length is, to a value y hereinafter of {12 · t · ln (tanθ ) + (49.1 / t)}, is set appropriately glass composition and chemical strengthening conditions.

  Examples of the glass material constituting the glass substrate include aluminosilicate glass. The aluminosilicate glass can realize an excellent smooth mirror surface and can increase the breaking strength by performing chemical strengthening. In particular, it is preferable that the aluminosilicate glass contains Zr. As described above, since the aluminosilicate glass contains Zr, the rigidity (= Young's modulus / specific gravity) of the substrate can be increased.

Specifically, as the aluminosilicate glass, SiO ₂ is 57 mass% to 75 mass%, Al ₂ O ₃ is 5 mass% to 20 mass% (however, the total amount of SiO ₂ and Al ₂ O ₃ is 74 is a mass% or _more), and the _{ZrO 2, HfO 2, Nb 2} O 5, Ta 2 O 5, La 2 O 3, Y 2 O3 _及 beauty TiO ₂ is less than 6 wt% than 0 in total, Li ₂ O exceeds 1 mass% and is 9 mass% or less, Na ₂ O is 5 mass% to 18 mass% (however, the mass ratio Li ₂ O / Na ₂ O is 0.5 or less), and K ₂ O Is 0 to 6% by mass, MgO is 0 to 4% by mass, CaO exceeds 0 and is 5% by mass or less (however, the total amount of MgO and CaO is 5% by mass or less, and The content is larger than the content of MgO), SrO + BaO is 0-3 mass % Can be preferably used.

SiO ₂ is a main component that forms a glass skeleton, and improves glass stability, chemical durability, particularly acid resistance, reduces thermal diffusion of the substrate, and increases the heating efficiency of the substrate by radiation. It is an ingredient. If its content is less than 57%, the devitrification resistance is lowered, and it is difficult to obtain a glass that can be stably produced, and the viscosity is lowered, making it difficult to mold. On the other hand, if it exceeds 75%, it is difficult to melt the glass. Become. From the viewpoint of devitrification resistance, viscosity, moldability, etc., the more preferable content of SiO ₂ is in the range of 63 mass% to 70 mass%, and the more preferable content is in the range of 63 mass% to 68 mass%. .

Al ₂ O ₃ is a component that improves chemical durability and promotes ion exchange. If the content is less than 5% by mass, the above effect is not sufficiently exhibited. The meltability and resistance to devitrification are likely to deteriorate. From the standpoint of balance between chemical durability, ion exchange properties, glass meltability, devitrification resistance, and the like, the more preferable content of Al ₂ O ₃ is in the range of 11% by mass to 20% by mass, and further preferable content The amount ranges from 13% to 18% by weight.

Although SiO ₂ and Al ₂ O ₃ can be substituted for each other, the total content of SiO ₂ and Al ₂ O ₃ is set to 74% by mass or more in order to maintain good glass stability and chemical durability. Is good. A preferable range of the total amount is 76% by mass or more, a more preferable range is 78% by mass or more, a still more preferable range is a range exceeding 79% by mass, and even more preferable is 80% by mass or more.

Alkali metal oxides such as Li ₂ O, Na ₂ O, and K ₂ O increase the meltability of glass and increase the coefficient of thermal expansion, which is suitable for an information recording medium substrate, particularly a magnetic recording medium substrate. It works to grant.

Li ₂ O is the most preferred component as an alkali ion used for ion exchange. When the content is 1% by mass or less, it is difficult to obtain a chemically strengthened glass having a thick compressive stress layer and strength when chemically strengthened. If it exceeds 9% by mass, the chemical durability and devitrification resistance are liable to decrease. From the viewpoints of performance and chemical durability, resistance to devitrification, and the like of the chemically strengthened glass, a more preferable Li ₂ O content is in the range of 1.5% by mass to 7% by mass, and more preferably 2% by mass to It is in the range of 5% by mass.

Na ₂ O is a component for obtaining chemically tempered glass in the same manner as Li ₂ O, and if its content is less than 5% by mass, it is difficult to obtain chemically tempered glass having a desired performance, and 18% by mass. If it exceeds, chemical durability tends to decrease. In terms of the performance and chemical durability of the chemically strengthened glass, the preferable Na ₂ O content is in the range of 7% by mass to 16% by mass, and the more preferable content is in the range of 8% by mass to 15% by mass. Further, as the alkali component, may be used K 2 _O, but the K _{2 O} is because it does not participate in the ion exchange, the content percentages of the order of 0-6% by weight.

However, the ratio of Li ₂ O amount _{(Li 2 O / Na 2 O} ) for Na ₂ O amount is usually 0.5 or less, preferably 0.45 or less, more preferably 0.4 or less, more preferably 0. 38 or less. The glass components that directly contribute to ion exchange during chemical strengthening are Li ₂ O and Na ₂ O, and certain alkali ions that contribute to ion exchange in the molten salt are Na ions and / or K ions. As the number of substrates to be chemically strengthened increases, the Li ion concentration in the molten salt increases. However, when a large amount of glass with (Li ₂ O / Na ₂ O) exceeding 0.5 is processed, the Li ion in the molten salt is increased. The rise in ion concentration becomes significant, and the balance between alkali ions that contribute to ion exchange and alkali ions that do not contribute to ion exchange changes greatly from the start of processing. As a result, the processing conditions optimized at the start of processing deviate from the optimal range as the number of processed sheets increases. In order to solve such a problem, it is preferable to set Li ₂ O / Na ₂ O in the above range.

  MgO and CaO have the effect of improving the meltability of the glass when added in a small amount, but if both are added too much, ion exchange is inhibited, and the thickness of the compressive stress layer of the resulting chemically strengthened glass becomes small. It is not preferable. Therefore, MgO is more preferably 0 to 4% by mass, and CaO is more preferably more than 0% and 5% by mass or less.

  Further, if the total amount of MgO and CaO exceeds 5%, the chemical durability tends to decrease, so the total amount of MgO and CaO is preferably 5% by mass or less, more preferably 4.5% by mass or less, Preferably it is 4 mass% or less. Furthermore, in order to improve the devitrification resistance, the content of CaO is preferably made larger than the content of MgO. From the viewpoint of enhancing chemical durability, it is preferable to coexist MgO and CaO as glass components. The chemical durability can be further enhanced by setting the ratio of MgO amount to CaO amount (MgO / CaO) to preferably 0.1 to 0.9, more preferably 0.3 to 0.7. Further, the glass stability can be improved.

ZrO ₂ , HfO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , Y ₂ O ₃ and TiO ₂ are components that improve chemical durability, particularly alkali resistance, and increase rigidity and toughness. . Therefore, it is preferable that the total content of ZrO ₂ , HfO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , Y ₂ O ₃ and TiO ₂ exceeds 0%. However, if the total content exceeds 6% by mass, the glass stability is lowered, the meltability is lowered, and the specific gravity is increased. Therefore, ZrO ₂ , HfO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , Y ₂ O _3, and TiO ₂ content is preferably more than 0 and 6% by mass or less. A preferable range of the total content is 5.5% by mass or less, a more preferable range is 4% by mass or less, and a further preferable range is 3% by mass or less. The preferable lower limit of the content is 0.1% by mass, the more preferable lower limit is 0.2% by mass, the still more preferable lower limit is 0.5% by mass, the more preferable lower limit is 1% by mass, and the still more preferable lower limit is 1.4% by mass. %.

Among ZrO ₂ , HfO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , Y ₂ O ₃ and TiO ₂ , glass containing TiO ₂ is immersed in water when the glass and water are on the glass surface. Reaction products may adhere and other components are more advantageous with respect to water resistance. Therefore, in order to maintain water resistance, the content of TiO ₂ is preferably 0 to 1% by mass, more preferably 0 to 0.5% by mass, and still more preferably not introduced.

HfO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , and La ₂ O ₃ increase the specific gravity of the glass and increase the mass of the substrate. Therefore, from the viewpoint of reducing the weight of the substrate, HfO ₂ , Nb ₂ O ₅ , Ta ₂ The total content of O ₅ and La ₂ O ₃ is preferably in the range of 0 to 3% by mass, more preferably in the range of 0 to 2% by mass, and in the range of 0 to 1% by mass. More preferably, it is more preferable not to introduce. The preferable content of HfO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , and La ₂ O ₃ is 0 to 3% by mass, more preferably 0 to 2% by mass, still more preferably 0 to 1% by mass, and more Preferably not introduced.

ZrO ₂ has a strong function of improving chemical durability, particularly alkali resistance, and has a function of increasing rigidity and toughness and increasing the efficiency of chemical strengthening. Further, since the raw material cost is lower than that of Y ₂ O ₃ , the content of ZrO ₂ with respect to the total content of ZrO ₂ , HfO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , Y ₂ O ₃ and TiO ₂ is included. The mass ratio of the amount is preferably in the range of 0.8 to 1, more preferably in the range of 0.9 to 1, still more preferably 0.95 to 1, and even more preferably 1. preferable.

ZrO ₂ is an essential component having a function of improving chemical durability, particularly alkali resistance, enhancing rigidity and toughness, and improving the efficiency of chemical strengthening by introducing even a small amount. However, if too much ZrO ₂ is introduced into the thinned substrate, the chemical strengthening efficiency becomes too high, an excessive compressive stress layer is formed, and the substrate is likely to swell. Therefore, the ZrO ₂ content is preferably more than 0% and 5.5% by mass or less. A preferable range of the ZrO ₂ content is 0.1% by mass to 5.5% by mass. The preferable lower limit of the ZrO ₂ content is 0.2% by mass, the more preferable lower limit is 0.5% by mass, the still more preferable lower limit is 1% by mass, the still more preferable lower limit is 1.4% by mass, and the preferable upper limit is 5% by mass. A more preferred upper limit is 4% by mass, and a still more preferred upper limit is 3% by mass.

In addition to reducing the thermal diffusion of the substrate, it is also effective to introduce an additive that absorbs infrared rays into the glass to increase the infrared absorption of the glass. Examples of such infrared absorbing additives include Fe, Cu, Co, Yb, Mn, Nd, Pr, V, Cr, Ni, Mo, Ho, Er, and moisture. Fe, Cu, Co, Yb, Mn, Nd, Pr, V, Cr, Ni, Mo, Ho, and Er exist as ions in the glass, but when these ions are reduced, they precipitate in the glass or on the surface, Since there is a risk of impairing the smoothness of the substrate surface, it is important that the total content be 0 to 1% by mass, preferably 0 to 0.5% by mass, and 0 to 0.2% by mass. % Is more preferable. The amount of Fe introduced is preferably 1% by mass or less, more preferably 0.5% by mass or less, and still more preferably 0.2% by mass or less in terms of Fe ₂ O _3. The content is more preferably 0.1% by mass or less, and still more preferably 0.05% by mass or less. A preferable lower limit is 0.01% by mass, and a more preferable lower limit is 0.03% by mass. A particularly preferred range is 0.03% to 0.02% by mass. When using the above additives, it is desirable to introduce Fe having a large infrared absorption. In any case, since these additives are effective when introduced in a very small amount, glass raw materials containing these additives as impurities, such as silica raw materials, may be used. However, since the amount of impurities is required to be constant, the above points should be noted when selecting raw materials. In addition, Fe is alloyed with platinum or a platinum alloy constituting a part of a glass melting vessel, a stirring rod, and a tube for flowing glass, and damages the vessel, the stirring rod, and the tube. In this case, it is preferable to suppress the addition amount of Fe. In such a case, it is more preferable not to introduce Fe ₂ O ₃ . B ₂ O ₃ functions to improve meltability, but is volatile and may corrode refractories during glass melting, so the content thereof is, for example, less than 2% by mass, preferably 0 to 1. 5% by mass, more preferably 0 to 1% by mass, still more preferably 0 to 0.4% by mass, and more preferably not introduced.

_{Sb 2 O 3, As 2 O} 3, SnO 2, may be introduced as CeO ₂ fining agent. However, As ₂ O ₃ imposes a burden on the environment, it is desirable not to use it especially when a substrate is manufactured through the float process.

  The glass for chemical strengthening having such a glass composition used in the present invention has a specific gravity of usually about 2.3 to 2.8, preferably 2.4 to 2.6, and a glass transition temperature of usually 450 ° C. to It is 600 degreeC, Preferably it is 480 degreeC-520 degreeC.

  The glass material constituting the glass substrate used in the present invention is not limited to those described above, for example, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or And glass ceramics such as crystallized glass.

  As the chemical strengthening solution used for chemical strengthening, although depending on the material constituting the glass, it is preferable to use potassium nitrate, sodium nitrate or the like in consideration of the melting point, price, and the like. The chemical strengthening temperature is preferably 300 ° C. to 450 ° C. in consideration of the melting point of the chemical strengthening solution, the glass transition point of the glass, and the like. The chemical strengthening time is preferably 1 hour to 4 hours in consideration of mass productivity. The chemical strengthening conditions can be appropriately determined depending on the glass material to be used.

By applying such chemical strengthening, the compressive stress in the surface layer (depth of about 1.5 μm from the substrate surface) is increased, and the stress value (compressive stress, tensile stress) in the depth direction inside the substrate is changed. The rate can be reduced. Accordingly, he is uppermost portion stress layer penetration length of the main surface 49.1μm or less, an angle between the main surface and the compressive stress in the stress profile by a Babinet compensator method is taken as theta, the outermost Table unit stress layer penetration length is, it is possible to obtain a glass substrate having a characteristic of a value y hereinafter of {12 · t · ln (tanθ ) + (49.1 / t)}. In this case, the compressive stress depth is preferably 50 μm or more. In addition, after performing ion exchange of Li ⁺ contained in the glass with Na ⁺ as the first stage and then performing chemical strengthening by two-stage ion exchange in which Na ⁺ is ion-exchanged with K ⁺ as the second stage, the above-described characteristics can be efficiently achieved. Can be obtained.

  The glass substrate for a magnetic disk according to the present invention preferably has a surface roughness Ra of the main surface measured by an atomic force microscope (AFM) of 0.3 nm or less. The glass substrate for a magnetic disk according to the present invention preferably has a measurement length of 0.8 mm in the circumferential direction of the glass substrate and a surface roughness Ra of the end face of 0.2 μm or less. Thereby, impact resistance can be further improved.

  A magnetic disk can be produced by providing a magnetic layer directly or via another layer on the glass substrate obtained as described above. Here, as the magnetic layer, a Co—Pt alloy magnetic layer having a high anisotropic magnetic field (Hk) is preferably used. In addition, an underlayer may be appropriately formed between the magnetic disk glass substrate and the magnetic layer from the viewpoint of achieving crystal orientation of the magnetic layer and making the grains uniform and fine. Moreover, it is preferable to provide a protective layer for protecting the magnetic layer on the magnetic layer. Furthermore, it is preferable to form a lubricating layer for reducing the impact from the magnetic head on the protective layer.

  As described above, the magnetic disk glass substrate according to the present invention has a high compressive stress in the surface layer portion (a depth of about 1.5 μm from the substrate surface), and a stress value (compressive stress, tensile strength) in the depth direction inside the substrate. Since the rate of change in stress is small, it is possible to satisfy a higher impact resistance (e.g., withstand acceleration of 1500 G to 2000 G in 1/1000 second) than the impact resistance required at present.

Next, reference examples made to clarify the effects of the present invention will be described.
( Reference example)
First, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper mold, a lower mold, and a body mold to obtain an amorphous plate glass. Next, both main surfaces of the plate glass were lapped to form a disk-shaped glass base material. Next, a hole was formed in the center of the glass base material using a diamond cutter to obtain a disk-shaped glass substrate (coring). The aluminosilicate glass is mainly composed of SiO ₂ : 70 wt%, Al ₂ O ₃ : 10 wt%, Li ₂ O: 5 wt%, Na ₂ O: 7 wt%, ZrO ₂ : 8 wt%. We used what to do.

  Next, the end surface of the glass substrate was subjected to mirror polishing by a brush polishing method. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used. Further, the inner peripheral end portion was mirror polished by a magnetic polishing method. And the glass substrate which finished the mirror polishing process was washed with water. As a result, the diameter of the glass substrate was 65 mm, and the substrate used for the 2.5-inch magnetic disk could be obtained.

  Next, lapping processing was performed on both main surfaces of the obtained glass substrate in the same manner as the above lapping. Next, a first polishing step was first performed as a main surface polishing step. As the abrasive, cerium oxide abrasive grains were used. And the glass substrate which finished this 1st grinding | polishing process is immersed in each washing tank of neutral detergent, pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam drying) sequentially. , Washed.

  Next, a second polishing step for finishing the main surface into a mirror surface was performed on both main surfaces of the glass substrate. As the abrasive, cerium oxide abrasive grains finer than the cerium oxide abrasive grains used in the first polishing step were used. And the glass substrate which finished this 2nd grinding | polishing process is made into neutral detergent (1), neutral detergent (2), pure water (1), pure water (2), IPA (isopropyl alcohol), IPA (vapor drying) ) Were sequentially immersed in each washing tank and washed. Note that ultrasonic waves were applied to each cleaning tank.

  Next, chemical strengthening was performed on the glass substrate after the lapping step and the polishing step described above. For chemical strengthening, a chemical strengthening solution comprising potassium nitrate: sodium nitrate at a weight ratio of 8: 2 is prepared, this chemical strengthening solution is heated to 400 ° C., and a cleaned glass substrate is immersed in the solution for about 4 hours. Was done by. Thus, by immersing in the chemical strengthening solution, Li ions and Na ions were respectively replaced with Na ions and K ions in the chemical strengthening solution in the surface layer of the glass substrate, and the surface layer of the glass substrate was strengthened. At this time, the thickness of the compressive stress layer was 114 μm.

  Such a glass substrate was immersed in a 20 ° C. water bath to be rapidly cooled and maintained for about 10 minutes. And the glass substrate which finished quenching was immersed in the concentrated sulfuric acid heated at about 40 degreeC, and was wash | cleaned. Further, the glass substrate after the sulfuric acid cleaning was cleaned by immersing in a cleaning tank of pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam drying). In addition, ultrasonic waves were applied to each cleaning tank.

For the magnetic disk glass substrate having a thickness of 0.635 mm and an outermost diameter of 65 mm produced in this manner, a diamond quadrangular pyramid indenter having a rhombic cross-section with a ridge angle of 172 ° 30 ′ and a 130 ° is pressed by 100 g. When the length of the longer diagonal line in the indentation (indentation length of the outermost stress layer) was examined by pressing into the main surface with pressure, it was 45.3 μm and 49.1 μm or less. Moreover, when the cut surface of the glass substrate for magnetic disks was measured using the Babinet corrector method, a stress profile as shown in FIG. 1 was obtained. At this time, when the angle formed between the main surface and the compressive stress is θ, the value y of {12 · t · ln (tan θ) + (49.1 / t)} is 53.8 μm. It was more than the indentation length of the surface stress layer. Note that, as described above, tan θ is a value { (L ₁ + L ₂ ) / (P ₁ + P ₂ ) } obtained from the stress value and stress depth obtained by the Babinet corrector method, and t is the substrate. Is the thickness. At this time, P ₁ is a compression stress value, P ₂ is a tensile stress value, L ₁ is a compression stress depth, L ₂ is a tensile stress depth. Thus, this glass substrate has a high compressive stress in the surface layer portion (a depth of about 1.5 μm from the substrate surface), and the rate of change of the stress value (compressive stress, tensile stress) in the depth direction inside the substrate is It was a small one.

  With respect to this magnetic disk glass substrate, impact resistance was evaluated by the Dana impact test method using AVEX-SM-110-MP (trade name, manufactured by Air Brown). In this impact test, a glass substrate for a magnetic disk is assembled in a dedicated impact test jig, and the impact of a sine half-wave pulse is perpendicular to the main surface under the condition of 900 G at 0.2 msec and 1500 G at 1 msec. This was carried out by examining the breakage of the magnetic disk glass substrate. As a result, the glass substrate was not damaged under any conditions.

(Comparative example)
A glass substrate for a magnetic disk was produced in the same manner as in Example except that chemical strengthening was performed under the following conditions. For chemical strengthening, a chemical strengthening solution comprising potassium nitrate: sodium nitrate in a weight ratio of 5: 5 is prepared, this chemical strengthening solution is heated to 340 ° C., and a cleaned glass substrate is immersed in the solution for about 2 hours. Was done by. At this time, the thickness of the compressive stress layer was 80 μm.

  For the magnetic disk glass substrate having a thickness of 0.635 mm and an outermost diameter of 65 mm produced in this manner, a diamond quadrangular pyramid indenter having a rhombic cross-section with a ridge angle of 172 ° 30 ′ and a 130 ° is pressed by 100 g. When the length of the longer diagonal line in the indentation (indentation length of the outermost stress layer) was examined by pressing into the main surface with pressure, it was 49.4 μm and was 49.1 μm or more.

  When the impact resistance of this glass substrate for magnetic disk was evaluated in the same manner as in the Example, no damage occurred under the condition of 900 G at 0.2 msec, but there was damage under the condition of 1500 G at 1 msec. It was.

(Embodiment 2)
In the manufacturing method of the glass substrate for magnetic disks of this Embodiment, there exist four aspects, the manufacturing method 1, the manufacturing method 2, the manufacturing method 3, and the manufacturing method 4 shown below.

[Method 1 of manufacturing glass substrate for magnetic disk]
In the method 1 for manufacturing a glass substrate for a magnetic disk according to the present embodiment, a disk-shaped glass substrate having a circular hole formed in the center is immersed in a chemical strengthening treatment solution, and relatively small ions contained in the glass substrate surface are obtained. Is a method for producing a glass substrate for a magnetic disk, which includes a chemical strengthening treatment step of creating a compressive stress layer on the surface of the glass substrate by ion exchange with relatively large ions contained in the chemical strengthening treatment liquid. The amount of deformation of the circular hole formed in the center of the disk-shaped glass substrate is within 0.05% of the diameter of the circular hole, and the bending strength of the disk-shaped glass substrate is 98 N or higher. It is characterized by strengthening processing.

  In the manufacturing method 1 of the present embodiment, the disk-shaped glass substrate having a circular hole formed in the center is subjected to a chemical strengthening treatment that creates a compressive stress layer on the surface of the glass substrate by ion exchange. A disk glass substrate is produced.

  When this chemical strengthening treatment is performed, the amount of deformation of the circular hole formed in the central part of the disk-shaped glass substrate is within 0.05% of the diameter of the circular hole, and the resistance of the disk-shaped glass substrate is reduced. The chemical strengthening treatment conditions are selected so that the bending strength is 98 N or more.

  If the deformation amount of the circular hole is within 0.05% of the diameter of the circular hole, it is possible to prevent a deviation between the recording / reproducing track position set on the magnetic disk and the recording / reproducing track position where the magnetic head travels. And a glass substrate compatible with high TPI (100 gigabits per square inch or more) can be obtained. The deformation amount of the circular hole is preferably within 0.025% of the circular hole diameter.

  Further, if the bending strength is 98 N or more, it is possible to prevent the glass substrate from being distorted in the hard disk drive. This bending strength is preferably 118 N or more. Moreover, although there is no restriction | limiting in particular in the upper limit, Usually, it is about 147N. The method for measuring the bending strength will be described later.

[Method 2 of manufacturing glass substrate for magnetic disk]
Manufacturing method 2 of the glass substrate for magnetic disks of this Embodiment is a manufacturing method of the glass substrate for donut-shaped magnetic disks which has a circular hole in center part, Comprising: The said 500-1000 glass substrates selected arbitrarily When the circular hole diameter of each glass substrate is measured, the circular hole diameter of each glass substrate is within the range of ± 5 × 10 ⁻⁴ × A with respect to the average circular hole diameter A of the glass substrate, and The bending strength is controlled to be 98 N or more.

In the manufacturing method 2 of the present embodiment, the circular hole diameter of each glass substrate is ± 5 × 10 ⁻⁴ × A with respect to the average circular hole diameter A of 500 to 1000 arbitrarily selected glass substrates. If the value deviates from the range, a deviation occurs between the recording / reproducing track position set on the magnetic disk and the recording / reproducing track position where the magnetic head travels, and a glass substrate compatible with high TPI (100 gigabits per square inch or more) is obtained. It is difficult to achieve the object of the present invention. The circular hole diameter of each glass substrate is preferably within a range of ± 2.5 × 10 ⁻⁴ × A with respect to the average circular hole diameter A.

  In the manufacturing method 2 of the present embodiment, the obtained glass substrate for magnetic disk is a 2.5-inch substrate, and the circular hole diameter of each glass substrate is preferably within A ± 10 μm, and A ± More preferably, it is within 5 μm.

  Moreover, the bending strength of the glass substrate for magnetic disks obtained needs to be 98 N or more. If the bending strength is less than 98 N, the glass substrate is easily distorted in the hard disk drive, and the object of the present invention cannot be achieved. This bending strength is preferably 118 N or more. Moreover, although there is no restriction | limiting in particular in the upper limit, Usually, it is about 147N.

[Method 3 of manufacturing glass substrate for magnetic disk]
In the method 3 for manufacturing a glass substrate for a magnetic disk according to the present embodiment, a relatively small ion contained in the surface of the glass substrate is obtained by immersing a disk-shaped glass substrate having a circular hole at the center in a chemical strengthening treatment solution. Is a method for producing a glass substrate for a magnetic disk, which includes a chemical strengthening treatment step of creating a compressive stress layer on the surface of the glass substrate by ion exchange with relatively large ions contained in the chemical strengthening treatment liquid. The deformation amount of the circular hole formed in the center of the disk-shaped glass substrate is set to be within 0.05% of the diameter of the circular hole, and the bending strength of the disk-shaped glass substrate is 98 N or more. The chemical strengthening treatment is performed by selecting the glass material of the disk-shaped glass substrate and the processing conditions of the chemical strengthening treatment.

  In manufacturing method 3 of the present embodiment, as in manufacturing method 1 described above, a disk-shaped glass substrate having a circular hole formed in the center is created, and a compressive stress layer is created on the surface of the glass substrate by ion exchange. A glass substrate for a magnetic disk is manufactured by performing chemical strengthening treatment.

  Then, when performing this chemical strengthening treatment, the deformation amount of the circular hole formed in the central portion of the disk-shaped glass substrate is set to be within 0.05% of the diameter of the circular hole, and the disk-shaped glass substrate The glass material of the disk-shaped glass substrate and the processing conditions for the chemical strengthening treatment are selected so that the bending strength is 98 N or more.

  The deformation amount of the circular hole is required to be within 0.05% of the diameter of the circular hole and is preferably within 0.025% for the same reason as in manufacturing method 1 described above. Further, the bending strength is required to be 98N or more, and preferably 118N or more, for the same reason as in manufacturing method 1 described above. Moreover, although there is no restriction | limiting in particular in the upper limit, Usually, it is about 147N.

[Method 4 of manufacturing glass substrate for magnetic disk]
In the method 4 for manufacturing a glass substrate for a magnetic disk according to the present embodiment, a relatively small ion contained in the surface of the glass substrate is obtained by immersing a disk-shaped glass substrate having a circular hole at the center in a chemical strengthening treatment solution. Is a method for producing a glass substrate for a magnetic disk, which includes a chemical strengthening treatment step of creating a compressive stress layer on the surface of the glass substrate by ion exchange with relatively large ions contained in the chemical strengthening treatment liquid. The amount of deformation due to the chemical strengthening treatment of the circular hole formed in the center of the disk-shaped glass substrate is grasped in advance for each glass, the deformation amount is within 0.05% of the diameter of the circular hole, and the chemical The glass material is selected so that the bending strength of the disk-shaped glass substrate by the tempering treatment is 98 N or more, and the selected glass material is processed into a disk shape, and the center The circularly holes are formed, characterized by chemical strengthening treatment.

  In manufacturing method 4 of the present embodiment, as in manufacturing method 1 described above, a disk-like glass substrate having a circular hole formed in the center is created, and a compressive stress layer is created on the surface of the glass substrate by ion exchange. A glass substrate for a magnetic disk is manufactured by performing chemical strengthening treatment.

  Then, when performing this chemical strengthening treatment, the amount of deformation due to the chemical strengthening treatment of the circular holes formed in the center of the disk-shaped glass substrate is grasped in advance for each glass, and the amount of deformation is the diameter of the hole. The glass material is selected so that the bending strength of the disk-shaped glass substrate by chemical strengthening treatment is within 0.05% and is 98 N or more, and the selected glass material is processed into a disk shape. A circular hole is formed in the part, and chemical strengthening treatment is performed.

  The deformation amount of the circular hole needs to be within 0.05% of the diameter of the circular hole and is preferably within 0.025% for the same reason as in the manufacturing method 1 described above. Further, the bending strength needs to be 98 N or more, and is preferably 118 N or more, for the same reason as in manufacturing method 1 described above. Moreover, although there is no restriction | limiting in particular in the upper limit, Usually, it is about 147N.

(Chemical strengthening glass)
In the manufacturing methods 1, 3, and 4 of the magnetic disk glass substrate described above, the same glass as used in the first embodiment is used as the glass for chemically strengthening the disk-shaped glass substrate having a circular hole formed in the center. Can do.

(Chemical strengthening treatment)
In the present invention, a disk-shaped glass substrate having a circular hole formed in the center is immersed in the chemical strengthening treatment liquid, and relatively small ions contained in the glass substrate surface are relatively contained in the chemical strengthening treatment liquid. Then, a chemical strengthening treatment is performed to create a compressive stress layer on the surface of the glass substrate by ion exchange with large ions, and a glass substrate for a magnetic disk is manufactured.

  When performing this chemical strengthening treatment, as described above, in the manufacturing method 1, the deformation amount of the circular hole formed in the center of the disk-shaped glass substrate is within 0.05% of the circular hole diameter, In addition, the chemical strengthening treatment conditions are selected so that the bending strength of the disk-shaped glass substrate is 98 N or more. In the manufacturing method 3, the deformation amount of the circular hole formed in the center of the disk-shaped glass substrate Select the glass material of the disk-shaped glass substrate and the processing conditions for the chemical strengthening treatment so that the bending strength of the disk-shaped glass substrate is 98 N or more so as to be within 0.05% of the hole diameter. In the manufacturing method 4, the amount of deformation of the circular hole formed in the center portion of the disk-shaped glass substrate is grasped in advance for each glass, and the amount of deformation is 0.05% of the diameter of the circular hole. Within And a glass material is selected so that the bending strength of the disk-shaped glass substrate by chemical strengthening treatment is 98 N or more, and the selected glass material is processed into a disk shape and a circular hole is formed in the center. And chemical strengthening treatment.

  The chemical strengthening treatment is not particularly limited, and a chemically strengthened disk-shaped glass substrate having a circular hole formed in the center is ionized in a conventionally known method such as a treatment bath containing Na ions and / or K ions. This can be done by exchange processing. It is important to perform this treatment at a temperature below the strain point of the glass and at a temperature at which the molten salt does not decompose, and is usually 350 ° C. to 420 ° C., preferably 360 ° C. to 380 ° C., for 1 hour to 12 hours. To the extent, preferably 2 to 6 hours. As the treatment bath containing Na ions and / or K ions, a treatment bath containing sodium nitrate and / or potassium nitrate is preferably used, but is not limited to nitrates, and sulfates, bisulfates, carbonates Salts, bicarbonates and halides may be used. When the treatment bath contains Na ions, the Na ions exchange with Li ions in the glass, and when the treatment bath contains K ions, the K ions become Li ions and Na ions in the glass. When ion exchange is performed and the treatment bath further contains Na ions and K ions, these Na ions and K ions exchange with Li ions and Na ions in the glass, respectively. By this ion exchange, alkali metal ions in the glass surface layer portion are replaced with alkali metal ions having a larger ion radius, and a compressive stress layer is formed in the glass surface layer portion to chemically strengthen the glass. As described above, since the glass substrate for chemical strengthening used in the present invention has excellent ion exchange performance, the compressive stress layer formed by ion exchange is deep, and its thickness is usually about 10 μm to 150 μm, preferably 50 μm to 120 μm.

  In the magnetic disk glass substrate obtained by such chemical strengthening treatment, the deformation amount of the circular hole formed in the center of the disk-shaped glass substrate is within 0.05%, preferably within 0.025%. And the bending strength of the said glass substrate is 98N or more, Preferably it is 118N or more, The upper limit is about 147N.

In addition, when the circular hole diameter of 500 to 1000 glass substrates arbitrarily selected from the chemically strengthened glass substrate for magnetic disk is measured, the circular hole diameter of each glass substrate is the glass substrate. against the average circular pore diameter a, in the range of ± 5 × ^{10 -4} × a, it is preferably within a range of ± 2.5 × ^{10 -4} × a.

  The glass substrate for magnetic disk having such properties can correspond to a disk whose recorded information has a track density of at least 100 gigabit TPI. Further, the glass substrate for magnetic disk can correspond to a perpendicular magnetic recording system.

Next, the magnetic disk of the present invention will be described.
[Magnetic disk]
The magnetic disk of the present invention is characterized by having at least a magnetic recording layer on the surface of the glass substrate for a magnetic disk obtained by the above-described production methods 1 to 4 of the present invention.

  The magnetic disk of the present invention can be produced by sequentially laminating a normal layer, a magnetic recording layer, a protective layer and a lubricating layer on the magnetic disk glass substrate obtained by the production method of the present invention.

  The magnetic recording layer is not particularly limited, and examples thereof include Co—Cr, Co—Cr—Pt, Co—Ni—Cr, Co—Ni—Pt, Co—Ni—Cr—Pt, and Co—. A magnetic recording layer such as Cr—Ta is preferable. As the underlayer, a Ni layer, a Ni-P layer, a Cr layer, or the like can be adopted. A carbon film or the like can be used as the protective layer, and a perfluoropolyether-based lubricant can be used to form the lubricating layer.

  The glass substrate for a magnetic disk obtained by the method of the present invention is particularly suitable for a perpendicular magnetic recording type magnetic recording medium. In the perpendicular magnetic recording type magnetic recording medium, the magnetic recording layer is composed of a single layer film in which a perpendicular magnetic recording layer is formed on a glass substrate for a magnetic disk, and a double layer film in which a soft magnetic layer and a magnetic recording layer are sequentially stacked. And a three-layer film in which a hard magnetic layer, a soft magnetic layer, and a magnetic recording layer are sequentially laminated can be exemplified as a preferable example. Among them, the two-layer film and the three-layer film are preferable because they are more suitable than the single-layer film for increasing the recording density and maintaining the stable magnetic moment.

(Example)
EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples. Various characteristics in each example were measured according to the following methods.

<Chemical strengthening glass>
(1) Glass transition temperature (Tg) and yield point (Ts)
Using a thermomechanical analyzer, the temperature was increased at a rate of 4 ° C./min.
(2) Average linear thermal expansion coefficient α
The average linear thermal expansion coefficient α at 100 ° C. to 300 ° C. was measured together with the measurement of the glass transition temperature.
(3) Specific gravity A sample of 40 mm × 20 mm × 15 mm was measured by Archimedes method.
(4) Refractive index [nd] and Abbe number [νd]
It measured about the glass cooled at the temperature-fall rate of 30 degreeC per hour.
(5) λ80 and λ5
For a 10 mm-thick polishing sample, the wavelength (nm) at which the transmittance when measuring the spectral transmittance was 80% was determined as λ80, and the wavelength (nm) at which the transmittance was 5% was determined as λ5.

<Glass substrate for magnetic disk>
(6) Circular hole diameter of glass substrate 500 glass substrates for magnetic disks were arbitrarily selected, the circular hole diameter of each glass substrate was determined by the following method, and the average circular hole diameter A was calculated.

  The circular hole diameter (inner diameter) of the glass substrate was measured using an inner diameter measuring apparatus shown in FIG. This inner diameter measuring device will be described below.

  FIG. 3 is a perspective view of a laser displacement meter 100 common to all embodiments of the glass substrate inner diameter measuring apparatus according to the present invention. The laser displacement meter 100 includes a line laser light source 110 that irradiates a line laser 112 that is line light, a substrate holder 130 that supports a glass substrate 200 in which a circular hole 210 is formed in the center, and the line laser 112 that is a glass substrate 200. Based on the holder lifting / lowering unit 140 that lifts and lowers the substrate holder 130 so as to pass through the circular hole 210, the light receiving unit 120 that receives the line laser 112 that has passed during the lifting / lowering, and the line laser 112 received by the light receiving unit 120. An inner diameter measurement unit 150 that measures the inner diameter of the hole 210 and a cassette 160 that stores a plurality of glass substrates 200 are included.

  Then, the glass substrate 200 is moved up and down by the holder lifting / lowering unit 140, and the line laser 112 is irradiated to the glass substrate 200 that is moving up and down. At this time, the light receiving unit 120 measures the distance of the circular hole 210 based on the received line laser 112. And among the measured distance, let the maximum value be the internal diameter of the glass substrate 200. In this way, the inner diameter of the glass substrate 200 is measured.

(7) Folding strength of glass substrate The bending strength of the glass substrate was measured using a bending strength tester (Shimadzu Autograph DDS-2000) shown in FIG. Specifically, when a load was applied on the glass substrate, the load when the glass substrate broke was determined as the bending strength.

(8) Thickness of compressive stress layer The cross section of the glass substrate for magnetic disks was grind | polished and the thickness of the compressive stress layer was measured with the polarization microscope.

Examples 1 to 6 and Comparative Example 1
A mixture of about 2 kg using silica powder, aluminum hydroxide, alumina, lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, zirconium oxide, iron oxide, etc. so as to have the oxide composition shown in Table 1. Was prepared, melted and clarified in a platinum crucible at 1450 ° C. to 1550 ° C., cast into an iron mold, and annealed to prepare a glass for chemical strengthening. The physical properties are shown in Table 1.

  Next, 150 pieces of doughnut-shaped 2.5 inch disk-shaped glass substrates each having a circular hole with a diameter of 20 mm at the center were prepared using each of the glass for chemical strengthening. Details are shown below.

(1) Shape processing process The glass of the composition as described in Examples 1-6 was shape | molded with the direct press method, and it was set as the disk-shaped glass substrate of the amorphous state. And the hole was made in the center part of the glass substrate using the grindstone, and it was set as the disk-shaped glass substrate which has a circular hole in the center part. Further, chamfering was performed on the outer peripheral end surface and the inner peripheral end surface.

(2) End face polishing step Subsequently, the surface roughness of the end face (inner circumference, outer circumference) of the glass substrate by brush polishing while rotating the glass substrate is about 1.0 μm at the maximum height (Rmax), arithmetic average roughness The thickness (Ra) was polished to about 0.3 μm.

(3) Grinding step Subsequently, the surface of the glass substrate was ground using # 1000 abrasive grains so that the flatness of the main surface was 3 μm, Rmax was about 2 μm, and Ra was about 0.2 μm. Here, the flatness is a distance (height difference) in the vertical direction (direction perpendicular to the surface) between the highest portion and the lowest portion of the substrate surface, and was measured by a flatness measuring device. Moreover, Rmax and Ra measured the rectangular area | region of 5 micrometers x 5 micrometers with atomic force microscope (AFM) (Digital Instruments company nanoscope).

(4) Pre-polishing step Subsequently, the pre-polishing step was performed using a polishing apparatus capable of polishing both main surfaces of 100 to 200 glass substrates at a time. A hard polisher was used for the polishing pad. A polishing pad previously containing zirconium oxide and cerium oxide was used.

  The polishing liquid in the preliminary polishing step was prepared by mixing cerium oxide polishing abrasive grains having an average particle diameter of 1.1 μm with water. The abrasive grains having a grain diameter exceeding 4 μm were previously removed. When the polishing liquid was measured, the maximum value of the abrasive grains contained in the polishing liquid was 3.5 μm, the average value was 1.1 μm, and the D50 value was 1.1 μm.

In addition, the load applied to the glass substrate was 784 to 980 mN / cm ^2, and the removal thickness of the surface portion of the glass substrate was 20 μm to 40 μm.

(5) Mirror Polishing Step Subsequently, the mirror polishing step was performed using a planetary gear type polishing apparatus that can polish both main surfaces of 100 to 200 glass substrates at a time. A soft polisher was used for the polishing pad.

  The polishing liquid in the mirror polishing step was prepared by adding sulfuric acid and tartaric acid to ultrapure water, and further adding colloidal silica particles having a grain diameter of 40 nm. At this time, the sulfuric acid concentration in the polishing liquid was set to 0.15% by mass, and the pH value of the polishing liquid was set to 2.0 or less. The concentration of tartaric acid was 0.8% by mass, and the content of colloidal silica particles was 10% by mass.

  In the mirror polishing process, the pH value of the polishing liquid did not vary and could be kept substantially constant. In this example, the polishing liquid supplied to the surface of the glass substrate was collected using a drain, cleaned by removing foreign substances with a mesh filter, and then reused by supplying it to the glass substrate again.

  The polishing speed in the mirror polishing process is 0.25 μm / min, and it has been found that an advantageous polishing speed can be realized under the above-described conditions. The polishing speed was determined by dividing the amount of reduction in glass substrate thickness (processing allowance) required for finishing to a predetermined mirror surface by the required polishing time.

(6) Cleaning step after mirror polishing treatment Subsequently, the glass substrate was immersed in an aqueous NaOH solution having a concentration of 3% by mass to 5% by mass to perform alkali cleaning. Cleaning was performed by applying ultrasonic waves. Furthermore, it wash | cleaned by immersing one by one in each washing tank of neutral detergent, a pure water, a pure water, isopropyl alcohol, and isopropyl alcohol (steam drying). When the surface of the glass substrate after cleaning was observed with an AFM (Nanoscope manufactured by Digital Instruments) (measurement of a rectangular area of 5 μm × 5 μm), adhesion of colloidal silica abrasive grains was not confirmed. Also, no foreign matter such as stainless steel or iron was found. Moreover, the increase in the roughness of the substrate surface before and after the cleaning was not observed.

(7) Chemical strengthening treatment step Subsequently, a washed glass substrate preheated to 300 ° C in a chemically strengthened salt obtained by mixing potassium nitrate (60% by mass) and sodium nitrate (40% by mass) and heating to 375 ° C. Was subjected to chemical strengthening treatment by dipping for about 4 hours. By this treatment, lithium ions and sodium ions on the surface of the glass substrate are respectively replaced with sodium ions and potassium ions in the chemically strengthened salt, and the glass substrate is chemically strengthened. The thickness of the compressive stress layer formed on the surface of the glass substrate was about 100 μm to 150 μm. After carrying out the chemical strengthening, the glass substrate was immersed in a 20 ° C. water bath, quenched, and maintained for about 10 minutes.

(8) Cleaning step after chemical strengthening Subsequently, the glass substrate after the rapid cooling was immersed in sulfuric acid heated to about 40 ° C. and cleaned while applying ultrasonic waves. After washing the glass substrate using a fluorosilicate acid _(H 2 SiF) aqueous solution of 0.5% (Vol%), it was cleaned glass substrate by using a 1 wt% aqueous potassium hydroxide. And manufacture of the glass substrate for magnetic discs was completed.

(9) Inspection process of glass substrate for magnetic disk Subsequently, the glass substrate for magnetic disk was inspected. When the roughness of the surface of the magnetic disk glass substrate was measured with an AFM (atomic force microscope) (measuring a rectangular area of 5 μm × 5 μm), the maximum peak height (Rmax) was 1.5 nm, and the arithmetic average roughness (Ra ) Was 0.15 nm. Further, the surface was in a clean mirror state, and there was no foreign matter that hindered the flying of the magnetic head or foreign matter that caused thermal asperity failure. Moreover, the increase in the roughness of the substrate surface before and after the cleaning was not observed.

  In the above description, acid cleaning and alkali cleaning are performed after chemical strengthening, but acid cleaning and alkali cleaning may be performed in the cleaning after the mirror polishing process.

（注）ガラス組成において、（Ｈ）、（Ｃ）及び（Ｎ）は、それぞれ原料として、水酸化物、炭酸塩、硝酸塩を意味する。 Further, regarding the glass substrate for magnetic disk of each example, the average diameter A of the circular holes is obtained, and the circular hole diameter of each glass substrate deviates from the range of ± 5 × 10 ⁻⁴ × A with respect to the average circular hole diameter A. The percentage (%) of what to do was determined. Moreover, the thickness and average bending strength of the average compressive-stress layer of the glass substrate for magnetic disks of each example were calculated | required. These results are shown in Table 1.

(Note) In the glass composition, (H), (C) and (N) mean hydroxide, carbonate and nitrate as raw materials, respectively.

  Next, using the magnetic disk glass substrate prepared in Example 1, a magnetic disk was prepared as shown below, and a hard disk drive test was performed. FIG. 5 schematically shows the film configuration (cross section) on the substrate 12.

  First, the adhesion layer 14 and the soft magnetic layer 16 were sequentially formed in an Ar atmosphere by a DC magnetron sputtering method using a film forming apparatus that was evacuated.

  At this time, the adhesion layer 14 was formed using a CrTi target so as to be an amorphous CrTi layer of 20 nm. The soft magnetic layer 16 was formed using a CoTaZr target so as to be a 200 nm amorphous CoTaZr (Co: 88 atomic%, Ta: 7 atomic%, Zr: 5 atomic%) layer.

  When the magnetic disk 10 having been formed up to the soft magnetic layer 16 was taken out of the film forming apparatus and the surface roughness was measured in the same manner, it was a smooth mirror surface with Rmax of 2.1 nm and Ra of 0.20 nm. When the magnetic properties were measured with a VSM (vibrating sample type magnetometer), the coercive force (Hc) was 2 Oersted and the saturation magnetic flux density was 810 emu / cc, indicating a suitable soft magnetic property.

  Subsequently, using a single wafer / stationary facing film forming apparatus, in an Ar atmosphere, the underlayer 18, the granular structure miniaturization promoting layer 20, the granular structure ferromagnetic layer 32, the magnetic coupling control layer 34, and the exchange energy A control layer 36 and a protective film 24 were sequentially formed. In this embodiment, the underlayer 18 has a two-layer structure having a first layer and a second layer.

  In this step, first, a 10 nm thick layer made of amorphous NiTa (Ni: 40 atomic%, Ta: 10 atomic%) is formed on the disk substrate as the first layer of the underlayer 18. A Ru layer having a thickness of 10 to 15 nm was formed as a layer.

Next, the miniaturization promoting layer 20 having an hcp crystal structure of 2 to 20 nm was formed using a target made of nonmagnetic CoCr—SiO ₂ . Further, a ferromagnetic layer 32 having an hcp crystal structure of 15 nm was formed using a hard magnetic target made of CoCrPt—SiO ₂ . The composition of the target for forming the ferromagnetic layer 32 is Co: 62 atomic%, Cr: 10 atomic%, Pt: 16 atomic%, and Si: 12 atomic%. Further, a magnetic coupling control layer 34 made of a Pd layer was formed, and an exchange energy control layer 36 made of a [CoB / Pd] n layer was formed.

  Next, a protective film 24 made of hydrogenated carbon was formed by a CVD method using ethylene as a material gas. Since the film hardness is improved by using hydrogenated carbon, it is possible to protect the magnetic recording layer 22 against an impact from the magnetic head.

  Thereafter, a lubricating layer 26 made of PFPE (perfluoropolyether) was formed by a dip coating method. The film thickness of the lubricating layer 26 is 1 nm. Through the above manufacturing process, a perpendicular magnetic recording type magnetic disk 10 which is a perpendicular magnetic recording medium was obtained. When the obtained surface roughness was measured in the same manner as described above, it was a smooth mirror surface with Rmax of 2.2 nm and Ra of 0.21 nm.

  The obtained magnetic disk 10 was mounted on a 2.5 inch type load / unload type hard disk drive. The magnetic head mounted on the hard disk drive is a Dynamic Flying Height (abbreviation: DFH) type magnetic head. The flying height of this magnetic head with respect to the magnetic disk is 8 nm.

  When a recording / reproducing test was performed on the recording / reproducing area on the main surface of the magnetic disk with this hard disk drive at a recording density of 200 gigabits per square inch, good recording / reproducing characteristics were exhibited. In addition, no crash or thermal asperity failures occurred during the test.

  Next, a load unload (hereinafter referred to as LUL) test was performed using a hard disk drive.

  The LUL test is performed with a 2.5 inch hard disk drive rotating at 5400 rpm and a magnetic head with a flying height of 8 nm. The magnetic head described above was used. The shield part is made of a NiFe alloy. A magnetic disk is mounted on the magnetic disk device, and the LUL operation is continuously performed by the above-described magnetic head, and the number of times the LUL is durable is measured.

  After the LUL durability test, the surface of the magnetic disk and the surface of the magnetic head are observed with the naked eye and an optical microscope to check whether there are any abnormalities such as scratches and dirt. This LUL durability test is required to endure without failure for the number of LUL times of 400,000 times or more, and it is particularly preferable to endure 600,000 times or more. Note that it is said that in an environment where HDDs (hard disk drives) that are normally used are used, in order to exceed the number of LULs over 600,000, it is necessary to use them for about 10 years.

  When this LUL test was performed, the magnetic disk 10 was durable and passed 600,000 times or more. Further, after the LUL test, the magnetic disk 10 was taken out and inspected, but no abnormalities such as scratches and dirt were detected. No precipitation of alkali metal components was observed.

  The present invention is not limited to the above embodiment, and can be implemented with appropriate modifications. Embodiments 1 and 2 can be implemented in appropriate combination. In addition, the number, size, processing procedure, and the like of the members in the above embodiment are merely examples, and various changes can be made within the range where the effects of the present invention are exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

It is a figure which shows the stress profile in a glass substrate. It is a figure which shows the relationship between outermost layer stress indentation length and tan (theta). It is a perspective view which shows the structure of the internal diameter measuring apparatus which measures the internal diameter of the glass substrate for magnetic discs in this invention. It is drawing which shows schematic structure of the bending strength tester which measures the bending strength of the glass substrate for magnetic discs in this invention. It is a figure which shows an example of a structure of the magnetic disc which concerns on one Embodiment of this invention.

Claims (9)

A disk-shaped glass substrate for a magnetic disk having a main surface and an end surface and subjected to a chemical strengthening treatment,
Glass material constituting the glass substrate is a SiO ₂ is 57 wt% to 75 wt%, _Al 2 _{O 3} is 5% by mass to 20% (provided that the total amount of SiO ₂ and _Al 2 _{O 3} is 74 ZrO ₂ , HfO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , Y ₂ O ₃ and TiO ₂ in total exceed 0 and less than 6% by mass, and Li ₂ O exceeds 1% by mass and is 9% by mass or less, Na ₂ O is 5% by mass to 18% by mass (however, the mass ratio Li ₂ O / Na ₂ O is 0.5 or less), and K ₂ O is 0 to 6% by mass, MgO is 0 to 4% by mass, CaO exceeds 0 and is 5% by mass or less (however, the total amount of MgO and CaO is 5% by mass or less, and CaO is contained) The amount is larger than the content of MgO), SrO + BaO is 0 to 3% by mass ,
The compressive stress depth is 100 to 150 μm;
The outermost surface stress layer indentation length of the main surface is 49.1 μm or less, and when the angle formed between the main surface and the compressive stress is θ in the stress profile by the Babinet corrector method, the outermost surface portion A glass substrate for a magnetic disk, wherein the stress layer indentation length is not more than a value y of {12 · t · ln (tan θ) + (49.1 / t)}.
Here, the indentation length of the outermost surface stress layer is an indentation when a diamond quadrangular pyramid indenter having a cross-sectional angle of 172 ° 30 ′ and a 130 ° rhombus is pushed into the main surface with a pressing force of 100 g. The length of the longer diagonal line, and the tan θ is a value {(L ₁ + L ₂ ) / (P ₁ + P ₂ )} obtained from the stress value and stress depth obtained by the Babinet corrector method, The t is the substrate thickness.
P ₁ is a compressive stress value, P ₂ is a tensile stress value, L ₁ is a compressive stress depth, and L ₂ is a tensile stress depth.   The glass substrate for a magnetic disk according to claim 1, wherein the value of y is {16 · t · ln (tan θ) + (49.1 / t)}.   The glass substrate for a magnetic disk according to claim 1 or 2, wherein the glass constituting the glass substrate for a magnetic disk is an aluminosilicate glass containing Zr.   The glass substrate for a magnetic disk according to any one of claims 1 to 3, wherein a surface roughness Ra of the main surface measured by an atomic force microscope is 0.3 nm or less.   5. The glass substrate for a magnetic disk according to claim 1, wherein a measurement length is 0.8 mm in the circumferential direction of the glass substrate for a magnetic disk and a surface roughness Ra of the end surface is 0.2 μm or less. A method of manufacturing a glass substrate for a magnetic disk including a step of subjecting a glass substrate to chemical strengthening treatment,
Glass material constituting the glass substrate is a SiO ₂ is 57 wt% to 75 wt%, _Al 2 _{O 3} is 5% by mass to 20% (provided that the total amount of SiO ₂ and _Al 2 _{O 3} is 74 ZrO ₂ , HfO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , Y ₂ O ₃ and TiO ₂ in total exceed 0 and less than 6% by mass, and Li ₂ O exceeds 1% by mass and is 9% by mass or less, Na ₂ O is 5% by mass to 18% by mass (however, the mass ratio Li ₂ O / Na ₂ O is 0.5 or less), and K ₂ O is 0 to 6% by mass, MgO is 0 to 4% by mass, CaO exceeds 0 and is 5% by mass or less (however, the total amount of MgO and CaO is 5% by mass or less, and CaO is contained) The amount is larger than the content of MgO), SrO + BaO is 0 to 3% by mass ,
The chemical strengthening treatment has a compressive stress depth of 100 to 150 μm, the outermost stress layer indentation length of the main surface of the glass substrate for magnetic disk is 49.1 μm or less, and the stress profile by the Babinet corrector method When the angle between the main surface and the compressive stress is θ, the outermost stress layer indentation length is less than or equal to the value y of {12 · t · ln (tan θ) + (49.1 / t)} Therefore, a method for producing a glass substrate for a magnetic disk, which is performed under sufficient conditions.
Here, the indentation length of the outermost surface stress layer is an indentation when a diamond quadrangular pyramid indenter having a cross-sectional angle of 172 ° 30 ′ and a 130 ° rhombus is pushed into the main surface with a pressing force of 100 g. The length of the longer diagonal line, and the tan θ is a value {(L ₁ + L ₂ ) / (P ₁ + P ₂ )} obtained from the stress value and stress depth obtained by the Babinet corrector method, The t is the substrate thickness.
P ₁ is a compressive stress value, P ₂ is a tensile stress value, L ₁ is a compressive stress depth, and L ₂ is a tensile stress depth. The method for producing a glass substrate for a magnetic disk according to claim 6, wherein the value of y is {16 · t · ln (tan θ) + (49.1 / t)}. The method for producing a glass substrate for magnetic disk according to claim 6 or 7, wherein the glass constituting the glass substrate for magnetic disk is aluminosilicate glass containing Zr. A glass substrate for a magnetic disk according to any one of claims 1 to 5 , and a magnetic layer provided directly or via another layer on the main surface of the glass substrate for a magnetic disk. Magnetic disk.

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