JP2008140498A - Manufacturing method of glass substrate for recording medium, glass substrate for recording medium and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a glass substrate for a recording medium free from a fissure, a crack and deformation and having satisfactory strength. <P>SOLUTION: In the manufacturing method of the glass substrate for the recording medium having a chemical strengthening step for bringing the glass substrate into contact with a chemical strengthening liquid and replacing alkali metal ions on the surface of the glass substrate with alkali metal ions contained in the chemical strengthening liquid and each having an ion diameter larger than that of the alkali metal ion on the surface of the glass substrate to perform chemical strengthening, the chemical strengthening step has a chemical strengthening liquid immersion step for immersing the glass substrate in the chemical strengthening liquid and a water immersion step for immersing the glass substrate taken out from the chemical strengthening liquid in water after the glass substrate is made to wait for 1 sec or longer in atmosphere. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a glass substrate for recording medium, a glass substrate for recording medium, and a recording medium.

  Conventionally, as a recording medium substrate, aluminum alloys are used for stationary information devices such as desktop computers and servers, and glass substrates are generally used for portable information devices such as notebook computers and mobile computers. It had been. Since the aluminum alloy is easily deformed and has insufficient hardness, the smoothness of the substrate surface after polishing cannot be said to be sufficient. Further, when the recording head mechanically contacts the magnetic disk, there is a problem that the magnetic film is easily peeled off from the substrate. Therefore, glass substrates with little deformation, good smoothness, and high mechanical strength will be widely used not only for portable devices but also for home-use devices such as stationary information devices and other televisions in the future. It is predicted.

  In order to improve the mechanical strength of the glass substrate for recording media, chemical strengthening treatment has been widely performed. In this chemical strengthening treatment, a glass substrate is immersed in a chemical strengthening solution stored in a chemical strengthening treatment tank, and alkali metal ions on the surface of the glass substrate are replaced with alkali metal ions having an ion diameter larger than the metal ions. Thus, compressive strain is generated and mechanical strength is improved. As the chemical strengthening solution, a molten nitric acid salt such as potassium nitrate or sodium nitrate heated and melted is generally used.

  While improving said mechanical strength, the flatness of a glass substrate is calculated | required. This is because, when the flatness of the glass substrate for recording medium is insufficient, abnormal vibration occurs or it becomes difficult to follow the magnetic head when the glass substrate for recording medium is incorporated in a recording apparatus and rotated. This is because the problem arises.

  As a method for producing a glass substrate for a recording medium that is chemically strengthened using such a chemical strengthening solution, for example, there are the following.

There is a method for manufacturing a glass substrate for a recording medium including the following manufacturing steps (1) and (2) (see Patent Document 1).
(1) A glass substrate is immersed in a heated chemical strengthening solution (same as the chemical strengthening solution), and the glass substrate is chemically strengthened by ion exchange of alkali metal ions on the surface of the glass substrate with alkali metal ions in the chemical strengthening solution. Chemical strengthening treatment process.
(2) By bringing the glass substrate in a state where heat is applied in the chemical strengthening treatment step of (1) into contact with the solvent, the ionic bond of the crystalline substance of the salt adhered on the glass substrate is changed between the polarity of the solvent and the heat. A salt crystal washing process for washing salt crystals by reducing or separating them using energy.
JP-A-10-226539

  In Patent Document 1, it is preferable to pull up the glass substrate from the chemical strengthening treatment liquid and slowly cool it to a predetermined temperature. By slowly cooling the glass substrate, damage due to thermal distortion can be avoided. As a specific example, the glass substrate taken out from the chemical strengthening treatment liquid heated to 400 ° C. is transferred to the first annealing chamber at 300 ° C. and held for about 10 minutes, and then the second annealing chamber at 200 ° C. And then immersed in a 90 ° C. warm water temperature as a solvent. In this way, the temperature difference between the glass substrate and the hot water in which it is immersed is relaxed. The slow cooling chambers at 300 ° C. and 200 ° C. are expensive equipments and require a long time for slow cooling, and thus there is a problem that chemical strengthening of the glass substrate cannot be performed efficiently. In addition, the inventors' experiments have shown that there are cases where there is no problem even if the chemical strengthening treatment liquid is taken out into the atmosphere without providing the slow cooling chamber as described above and then immersed in water.

  The present invention has been made in view of the above problems, and its object is to provide a method for manufacturing a glass substrate for recording medium having sufficient mechanical strength and good deformation, a glass substrate for recording medium, and a recording medium. Is to provide a medium.

  Said subject is solved by the following structures.

1. A chemical strengthening step in which the glass substrate is brought into contact with a chemical strengthening solution and the alkali metal ions on the surface of the glass substrate are replaced with alkali metal ions having a larger ion diameter than the alkali metal ions contained in the chemical strengthening solution. In a method for producing a glass substrate for a recording medium having
The chemical strengthening step includes
A chemical strengthening solution immersion step of immersing the glass substrate in the chemical strengthening solution;
And a water immersion step of immersing the glass substrate taken out of the chemical strengthening solution in water after waiting for 1 second or more in the atmosphere.

  2. A glass substrate for a recording medium, which is produced by the method for producing a glass substrate for a recording medium according to 1.

  3. 3. A recording medium comprising a magnetic film on a surface of the glass substrate for recording medium according to 2.

  According to this invention, after taking out the glass substrate immersed in the chemical strengthening liquid, it waits for 1 second or more in air | atmosphere, and is immersed in water. By exposing the glass substrate to the atmosphere as it is for 1 second or more, the temperature of the entire glass substrate is homogenized, and then immersion in water suppresses uneven chemical strengthening and suppresses deformation and strength reduction due to uneven chemical strengthening. .

  Accordingly, it is an object of the present invention to provide a method for producing a good glass substrate for recording medium having no deformation and sufficient strength.

  Although the present invention will be described based on the illustrated embodiment, the present invention is not limited to the embodiment.

(Manufacturing process)
The manufacturing method of the glass substrate for recording media is demonstrated. FIG. 1 is a flowchart showing an example of a manufacturing process of a recording medium glass substrate. First, a glass material is melted (glass melting process), molten glass is poured into a lower mold, and press molding is performed with an upper mold to obtain a disk-shaped glass substrate precursor (press molding process). Note that the disk-shaped glass substrate precursor may be produced by cutting a sheet glass formed by, for example, a downdraw method or a float method with a grinding stone, without using press molding.

  In the press-molded glass substrate precursor, if necessary, a hole is formed in the central portion with a core drill or the like (coring step). In the first lapping step, both surfaces of the glass substrate are polished, and the overall shape of the glass substrate, that is, the parallelism, flatness, and thickness of the glass substrate are preliminarily adjusted.

  Next, the outer peripheral end surface and inner peripheral end surface of the glass substrate are ground and chamfered to finely adjust the outer diameter and roundness of the glass substrate, the inner diameter of the hole, and the concentricity between the glass substrate and the hole ( Inner and outer diameter machining process). Thereafter, the inner peripheral end face of the glass substrate is polished to remove fine scratches (inner peripheral end face processing step).

  Next, both surfaces of the glass substrate are polished again, and the parallelism, flatness, and thickness of the glass substrate are finely adjusted (second lapping step). And the outer periphery end surface of a glass substrate is grind | polished and a fine crack etc. are removed (outer periphery end surface processing process).

  Next, after the glass substrate is washed, the glass substrate is immersed in a chemical strengthening solution described later to form a chemical strengthening layer on the glass substrate (chemical strengthening step). Thereafter, polishing is performed to precisely finish the surface of the glass substrate (polishing process). Then, cleaning and inspection are performed to obtain a glass substrate for a recording medium as a product. In addition, although there exists a polishing process which grind | polishes after the chemical strengthening process which forms a chemical strengthening layer, the intensity | strength of the glass substrate before and behind this grinding | polishing process hardly changes.

  The contents of the chemical strengthening step are shown in the flowchart of FIG. The cleaned glass substrate is preheated and then immersed in a chemical strengthening solution (chemical strengthening solution immersion step). The glass substrate taken out from the chemical strengthening solution is cooled in the cooling step, washed with water (water immersion step), and dried.

(Chemical strengthening liquid immersion process)
In the chemical strengthening solution immersion step, the glass substrate is immersed in a chemical strengthening solution in which the chemical strengthening agent is melted, and the alkali metal ions on the surface of the glass substrate are ion-exchanged with the alkali metal ions of the chemical strengthening solution.

As the chemical strengthening agent, conventionally known ones can be used, and examples thereof include potassium nitrate (KNO ₃ ), sodium nitrate (NaNO ₃ ), potassium carbonate (K ₂ CO ₃ ) and the like. These can be used alone or in combination of two or more. To use.

  A predetermined amount of the chemical strengthening agent is put into a chemical strengthening treatment tank, and is melted by heating to become a chemical strengthening liquid. The heating temperature of the chemical strengthening solution is preferably in the range of 280 to 660 ° C., more preferably in the range of 300 to 450 ° C. from the viewpoint of ion exchange rate and Tg of the glass substrate. By setting this high temperature side (upper limit) to a range of 300 ° C. to 450 ° C. lower than the glass transition temperature Tg, the reaction rate of ion exchange is not too slow, and the shape of the glass substrate is not affected.

  The time for immersing the glass substrate in the chemical strengthening solution is preferably in the range of 0.1 hour to several tens of hours. Moreover, as shown in this example, it is preferable to preheat the glass substrate before immersing it in the chemical strengthening solution. When the glass substrate is heated in advance, the temperature of the chemical strengthening solution does not decrease excessively when immersed in the chemical strengthening solution, and chemical strengthening can be performed efficiently.

  The thickness of the reinforcing layer is preferably in the range of about 5 μm to 15 μm from the viewpoint of improving the strength of the glass substrate and shortening the time of the polishing process.

(Standby for glass substrate)
Before dipping the glass substrate taken out from the chemical strengthening solution into the atmosphere in water, which is a water dipping process, the glass substrate is allowed to stand by for 1 second or longer. It is better to wait for 30 seconds or more. If a standby period is provided in the atmosphere before being immersed in water, the strength of the glass substrate does not decrease. The reason for this is not clear, but is presumed as follows. For example, in a glass substrate taken out from the chemical strengthening solution of about 300 ° C. into the atmosphere, the temperature of the surface of the glass substrate rapidly decreases due to heat dissipation due to the temperature difference compared to the temperature inside the glass substrate. However, when the surface temperature of the glass substrate decreases to some extent, the difference between the atmosphere and the surface temperature of the glass substrate is relaxed, and the decrease in the surface temperature of the glass substrate is suppressed and slowed down. On the other hand, the temperature inside the glass substrate decreases and catches up with the surface temperature of the glass substrate. Therefore, the temperature of the whole glass substrate becomes uniform. Such homogenization of the temperature of the whole glass substrate has reached an effective state after 1 second or more has passed in the atmosphere after the glass substrate is taken out from the chemical strengthening solution. More preferably, 30 seconds or more should elapse. After at least 30 seconds, the temperature of the entire glass substrate becomes more effective and uniform. The upper limit of the waiting period is not particularly limited, and may be determined as appropriate based on manufacturing efficiency.

  If the glass substrate is immersed in water with the glass substrate temperature homogenized as described above, there is little temperature unevenness throughout the glass substrate, so chemical strengthening is not particularly excessive or insufficient in the entire glass substrate, but in a well-balanced and homogeneous state. The strengthening liquid can be removed. As a result, since non-uniformity of the strengthening after removal of the chemical strengthening liquid does not occur, it is presumed that the chemically strengthened layer is uniformly formed, the compressive strain is uniform, the deformation is difficult to occur, the flatness is good, and the mechanical strength is also good. The

  For example, when the glass substrate is taken out from the chemical strengthening liquid at about 300 ° C. into the atmosphere at about 30 ° C. for 1 second and the temperature elapses for about 1 second, the temperature of the glass substrate becomes about 200 ° C. Become. After taking out the glass substrate taken out from the chemical strengthening tank into the atmosphere without providing a high temperature annealing chamber at 300 ° C. and 200 ° C., it is immersed in water with an appropriate waiting period as described above. A good glass substrate can be obtained without being damaged.

(Water immersion process)
After taking out from the chemical strengthening solution, after the waiting time has elapsed, it is immersed in water to remove the chemical strengthening solution. In the chemical strengthening solution immersion step, for example, after being immersed in a chemical strengthening solution at about 300 ° C., the glass substrate taken out is kept in the atmosphere for 1 second and immersed in water, so that the glass substrate is cracked or cracked. There is no.

  The higher the temperature of the water in which the glass substrate is immersed, the more efficiently the chemical strengthening solution and the crystalline crystals of the salt forming the chemical strengthening solution can be removed from the glass substrate in a shorter time. From the viewpoint of practical production, the temperature of water is preferably 35 ° C. or higher and 100 ° C. or lower under atmospheric pressure.

  By immersing the glass substrate in water, the chemical strengthening liquid on the surface of the glass substrate can be removed without unevenness. For this reason, the chemical strengthening liquid does not partially exist on the glass substrate, the chemical strengthening does not proceed partially, and the chemical strengthening is not uneven. Thus, the glass substrate can have a uniform strength.

  Here, if warpage occurs due to deformation or the like, the flatness of the glass substrate deteriorates, but the flatness allowed as a deformation amount that does not cause a problem is less than 6 μm. For example, flatness tester FT-900 (manufactured by NIDEK) using a laser oblique incidence interferometer can be used for measuring the flatness.

(Glass substrate)
The glass substrate to be chemically strengthened is not particularly limited, but soda lime glass mainly composed of silicon dioxide, sodium oxide, calcium oxide; silicon dioxide, aluminum oxide, R ₂ O (R = K, Na, Li). Aluminosilicate glass as main component; borosilicate glass; lithium oxide-silicon dioxide glass; lithium oxide-aluminum oxide-silicon dioxide glass; R′O-aluminum oxide-silicon dioxide glass (R ′ = Mg, Ca, Sr or Ba) can be used, and these glass materials may be added with zirconium oxide, titanium oxide or the like.

  The size of the glass substrate is not limited, and the method of the present invention can be applied to a small-diameter disk of 2.5 inches, 1.8 inches, 1 inch, 0.85 inches or less, and the thickness thereof. Can be applied to a thin type such as 2 mm, 1 mm, 0.63 mm, or less.

  In the glass substrate provided for the chemical strengthening step, the roughness of the main surface and the end face portion is not particularly limited, but the surface roughness of the main surface of the glass substrate is Rmax (maximum height) of 10 nm or less, Ra (center) The line average roughness) is preferably 1.0 nm or less. The surface roughness of the end face is preferably in the range of Rmax from 0.01 μm to 1 μm and Ra in the range of 0.001 μm to 0.8 μm. If the surface-polished glass substrate is chemically strengthened, the reinforcing layer can be formed uniformly.

(Strength test method)
FIG. 3A is a schematic diagram illustrating an example of the shape of the glass substrate 10 for recording medium. The glass substrate 10 is a disk-shaped glass substrate having an outer diameter φ1 = 65 mm, an inner diameter φ2 = 20 mm, and a plate thickness d = 0.635 mm, and is a glass substrate used for a normal 2.5-inch hard disk.

  FIG. 3B is a schematic diagram of an annular bending test machine 20 used in a test called an annular bending strength test for measuring the breaking strength of the glass substrate 10 for recording medium shown in FIG. is there.

  The annular bending test machine 20 places an evaluation sample of the recording medium glass substrate 10 on a support base 23 to support the outer periphery 8 in an annular shape, and supports the iron ball 22 in the hole 4 of the recording medium glass substrate 10. A pressure-destructive test is performed by placing a force on the inner periphery 9 of the recording medium glass substrate 10 with the load 21 through the iron ball 22 through the inner periphery 9. This method is the same as a method generally used in the industry as a strength test of a recording medium for hard disk.

  The support base 23 has a cylindrical shape having an outer diameter φ5 = 70 mm, an inner diameter φ6 = 63 mm, and a height h = 50 mm. The recording medium glass substrate 10 is placed on the upper portion of the cylinder, and the outer periphery 8 is supported in an annular shape.

  The iron ball 22 is an iron ball having a diameter of φ4 = 28.57 mm, and has a mass of about 100 grams, which is negligible compared to the force applied by the load 21. The iron ball 22 abuts on the inner periphery 9 of the recording medium glass substrate 10 and applies a force, thereby applying a bending stress to the recording medium glass substrate 10 supported on the outer periphery 8 by the support base 23. The pressing speed of the load 21 is about 0.5 mm / min. If the push-down force that destroys the glass substrate for recording medium 10 is 100 N or more, it is assumed that the recording medium glass substrate 10 has good strength.

(recoding media)
Next, a recording medium using the recording medium glass substrate described so far will be described. When this information recording glass substrate is used, durability and high recording density are realized. Hereinafter, a recording medium will be described with reference to the drawings.

  FIG. 4 is a perspective view of a magnetic disk as an example of a recording medium. In this magnetic disk D, a magnetic film 2 is directly formed on the surface of a circular recording medium glass substrate 1. As a method for forming the magnetic film 2, a conventionally known method can be used. For example, a method in which a thermosetting resin in which magnetic particles are dispersed is spin-coated on a substrate, or a method by sputtering or electroless plating is used. A method is mentioned. The film thickness by spin coating is about 0.3 μm to 1.2 μm, the film thickness by sputtering is about 0.04 μm to 0.08 μm, and the film thickness by electroless plating is 0.05 μm to 0.1 μm. From the viewpoint of thinning and densification, film formation by sputtering and electroless plating is preferable.

The magnetic material used for the magnetic film is not particularly limited and conventionally known materials can be used. However, in order to obtain a high coercive force, Ni having high crystal anisotropy is basically used, and Ni or A Co-based alloy to which Cr is added is suitable. Specific examples include CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, and CoNiPt containing Co as a main component, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, and CoCrPtSiO. The magnetic film may have a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa) that is divided by a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) to reduce noise. In addition to the above magnetic materials, granular materials such as ferrite, iron-rare earth, non-magnetic films made of SiO ₂ , BN, etc. in which magnetic particles such as Fe, Co, FeCo, CoNiPt are dispersed, etc. Also good. Further, the magnetic film may be either an inner surface type or a vertical type recording format.

  In addition, a lubricant may be thinly coated on the surface of the magnetic film in order to improve the sliding of the magnetic head. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.

  Furthermore, you may provide a base layer and a protective layer as needed. The underlayer in the magnetic disk is selected according to the magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. In the case of a magnetic film containing Co as a main component, Cr alone or a Cr alloy is preferable from the viewpoint of improving magnetic characteristics. Further, the underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

Examples of the protective layer that prevents wear and corrosion of the magnetic film include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be formed continuously with an in-line type sputtering apparatus, such as an underlayer and a magnetic film. In addition, these protective layers may be a single layer, or may have a multilayer structure including the same or different layers. Note that another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, tetraalkoxysilane is diluted with an alcohol-based solvent on a Cr layer, and then colloidal silica fine particles are dispersed and applied, followed by baking to form a silicon dioxide (SiO ₂ ) layer. It may be formed.

  The magnetic disk has been described above as one embodiment of the recording medium. However, the recording medium is not limited to this, and the glass substrate of the present invention can be used for a magneto-optical disk, an optical disk, and the like.

  As a glass substrate to be chemically strengthened, an aluminosilicate glass substrate having an outer diameter φ1 = 65 mm, an inner diameter φ2 = 20 mm, and a plate thickness d = 0.635 mm manufactured until after the outer peripheral end face processing along the manufacturing process of FIG. Chemical strengthening was performed along FIG. Moreover, the below-mentioned flatness of all the prepared glass substrates before chemical strengthening was 2 micrometers or less.

The above 30 glass substrates were heated in advance to 350 ° C. and then immersed in a chemical strengthening solution for 15 minutes. As the chemical strengthening solution, a chemical strengthening agent having a mass ratio of 1: 9 of NaNO ₃ and KNO ₃ was added to the chemical strengthening tank and heated to 330 ° C.

  After being immersed in the chemical strengthening solution, the product was taken out from the chemical strengthening tank to the atmosphere, and each of the 30 glass substrates was waited for 0.5 to 120 seconds, immersed in water at 35 ° C. for 5 minutes, and then dried.

  After drying, the glass substrate was evaluated for cracks, cracks, deformation (flatness), and strength. The cracks and cracks were confirmed visually and using a magnifying glass. The flatness was measured using a flatness tester FT-900 (manufactured by NIDEK) as a p-v value on the surface of the glass substrate excluding 1 mm on the outside and 1 mm on the inside. The strength was evaluated by an annular bending strength test. The cracks and cracks were not listed in Table 1 because they were all good because they could not be observed on all glass substrates.

The flatness (p-v value) in Table 1 indicates the maximum value of the glass substrate. The symbols for determining the flatness indicate the following.
○: The flatness of the total number of glass substrates was less than 6 μm.
X: The flatness of the total number of glass substrates was 6 μm or more.

The number of cracks in Table 1 indicates the number of cracks when the pressing force is less than 100 N in the annular bending strength test. Further, the symbols for determining the strength indicate the following. From the viewpoint of production yield, 16 or more glass substrates on which cracks occurred were regarded as unqualified (x symbol).
A: There were no broken glass substrates at less than 100N.
A: The number of glass substrates broken at less than 100 N was 1 or more and 7 or less.
Δ: The number of glass substrates broken at less than 100 N was 8 or more and 15 or less.
X: The number of glass substrates broken at less than 100 N was 16 or more.

  From the above results, it is better to immerse in a chemical strengthening solution, take it out into the atmosphere, wait for 1 second or more and then immerse in water, and more preferably 30 seconds or more.

It is a flowchart which shows the example of the manufacturing process of the glass substrate for recording media. It is a flowchart which shows the content of the chemical strengthening process process in FIG. (A) shows the figure which shows the example of the shape of the glass substrate for recording media typically, (b) is an annular bending test machine for measuring the fracture strength of the glass substrate for recording media shown in (a). It is a figure which shows the example of a structure typically. It is a perspective view containing the partial cross section of a magnetic disc.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 10 Glass substrate for recording media 2 Magnetic film 4 Hole part 8 Outer periphery 9 Inner periphery 20 Ring bending test machine 21 Load 22 Iron ball 23 Support stand D Magnetic disk

Claims (3)

A chemical strengthening step in which the glass substrate is brought into contact with a chemical strengthening solution and the alkali metal ions on the surface of the glass substrate are replaced with alkali metal ions having a larger ion diameter than the alkali metal ions contained in the chemical strengthening solution. In a method for producing a glass substrate for a recording medium having
The chemical strengthening step includes
A chemical strengthening solution immersion step of immersing the glass substrate in the chemical strengthening solution;
And a water immersion step of immersing the glass substrate taken out of the chemical strengthening solution in water after waiting for 1 second or more in the atmosphere. A glass substrate for a recording medium manufactured by the method for manufacturing a glass substrate for a recording medium according to claim 1. A recording medium comprising a magnetic film on a surface of the glass substrate for a recording medium according to claim 2.

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