JP2005285276A - Manufacturing method of glass substrate for magnetic disk, manufacturing method of magnetic disk and magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for a magnetic disk having excellent impact resistance without causing thermal asperity even when the substrate is constructed as a magnetic disk used in high recording density of 40 gigabit/1 inch<SP>2</SP>or greater, to provide the magnetic disk, to provide a glass substrate for a magnetic disk capable of realizing stable operation even when the substrate is constructed as a small-sized magnetic disk having e.g. ≤30 mm outside diameter so that the small-sized magnetic disk can be mounted on portable information instruments of e.g. a cellular phone, a digital camera, a portable MP3 player, a PDA, etc. and car instruments of e.g. a car-navigation system etc. and to provide the magnetic disk. <P>SOLUTION: The manufacturing method of the glass substrate for the magnetic disk has a mirror surface working step for performing mirror surface working of an end surface part of a glass disk. In the mirror surface working step, a polishing means is made to come in slide contact with the end surface part to subject the surface of the end surface part to mirror surface polishing and then the end surface part is subjected to chemical treatment while a mirror surface state is maintained to remove a crack existing on a surface layer part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing a glass substrate for a magnetic disk used for a magnetic disk used in a hard disk drive (HDD) that is a magnetic disk device, and a method of manufacturing a magnetic disk.

  2. Description of the Related Art In recent years, information technology, particularly magnetic recording technology, has been required to undergo dramatic technological innovation with the development of the so-called IT industry. Unlike other magnetic recording media such as magnetic tapes and flexible disks, the magnetic disk mounted on a hard disk drive (HDD), which is a magnetic disk device used as a computer storage, is rapidly increasing in information recording density. Has been continued. The information capacity that can be stored in the personal computer device has been dramatically increased, supported by such an increase in the information recording density of the magnetic disk.

  Such a magnetic disk is configured by forming a magnetic layer or the like on a substrate such as an aluminum alloy substrate or a glass substrate. In a hard disk drive, an information signal is recorded as a magnetization pattern on a magnetic layer and reproduced by the magnetic head while flying over the magnetic disk rotated at high speed.

  In recent years, a high-strength and high-rigidity glass substrate has attracted attention as a magnetic disk substrate. In addition, since a smooth surface is obtained on a glass substrate, the flying height of a magnetic head that performs recording and reproduction while flying over the magnetic disk can be reduced, and a magnetic disk with a high information recording density can be obtained. Can be obtained.

  However, the glass substrate also has a side face that it is a brittle material and may be damaged. For this reason, various glass substrate strengthening methods have been proposed. For example, it is known that sufficient strength can be obtained by performing a predetermined chemical strengthening process on a glass substrate.

  For example, as described in Patent Document 1, for the purpose of increasing the mechanical strength of the glass substrate, a technique for removing scratches present on the end surface portion of the glass substrate by an etching process has been proposed.

  On the other hand, in a hard disk drive, in recent years, a magnetoresistive element is used in a reproducing portion of a magnetic head in order to increase an information recording capacity by improving an S / N ratio (Signal Noise Ratio) of a recording / reproducing signal. It has been. In a magnetic head provided with such a magnetoresistive effect reproducing element, a thermal asperity failure is likely to occur. Therefore, in the magnetic disk, it is necessary to finish not only the main surface of the disk substrate but also the end face part in a predetermined mirror surface state.

  For example, Patent Document 2 discloses a disk substrate that can prevent generation of particles that cause thermal asperity by setting the surface roughness (Ra) of an end surface portion of a glass substrate to less than 1 μm, for example. Has been described.

JP-A-7-230621 JP-A-10-154321

  Recently, the information recording density of magnetic disks has increased to reach over 40 gigabits per square inch. For this reason, it may be required to suppress thermal asperity failure to a level higher than the conventional level.

  Further, as a result of recording / reproducing at such a high information recording density, even a relatively small magnetic disk can store practically sufficient information. For this reason, in addition to a hard disk drive (HDD) for personal computers that records and reproduces in a stationary environment such as a desk, small hard disk drives for mobile devices have begun to be actively developed. For this reason, in order to improve reliability, improvement in impact resistance is required for the components constituting the hard disk drive.

  Specifically, for example, by using a small glass disk substrate having an outer diameter of 30 mm or less or a disk thickness of 0.4 mm or less, for example, in-car use such as a car navigation system, PDA (personal digital assistant: personal digital) Assistant) applications, portable “MP3” player applications, mobile phone applications, and other mobile hard disk drives (HDD) based on portability are being studied.

  In the case of these hard disk drives for mobile use, it is necessary to design parts on the premise of carrying impacts and dropping impacts not only when stopping but also when recording and reproducing. Accordingly, it has become necessary to make a design with significantly improved impact resistance as compared with a glass substrate for conventional applications. Specifically, it is necessary to design impact resistance so that the glass substrate is not damaged even when a gravitational acceleration of 3000 G is applied.

  However, the glass substrate manufactured by the technique described in Patent Document 1 can obtain a desired mechanical strength as a magnetic disk of a hard disk drive for a personal computer device, but it can be a hard disk for a “mobile device”. It has been found that the magnetic disk of the drive has insufficient impact resistance and may be damaged.

  Therefore, the present invention eliminates the shock resistance shortage that is particularly serious in the hard disk drive for the “mobile device” as described above, and realizes a glass substrate for a magnetic disk capable of realizing a high information recording density. It has been proposed.

  That is, the present invention does not cause a thermal asperity failure even when it is configured as a magnetic disk that is used for a high recording density such as 40 gigabits per square inch or more, and has an impact resistance. It is a first object of the present invention to provide a magnetic disk glass substrate and a magnetic disk excellent in the above.

  In addition, the present invention is very portable, for example, so-called mobile phones, digital cameras, portable “MP3 players”, portable information devices such as PDAs, or in-vehicle devices such as “car navigation systems”. For example, even if it is configured as a small magnetic disk with an outer diameter of 30 mm or less so that it can be mounted on equipment, sufficient impact resistance can be obtained, and stable operation can be realized without any thermal asperity failure. A second object is to provide a glass substrate for a magnetic disk and a magnetic disk.

  As a result of advancing research to solve the above problems, the present inventors have mirror-polished the end face of a glass disk finished into a disk shape by grinding in a manufacturing process of a glass substrate for a magnetic disk, and then appropriately It has been found that the above-mentioned problems can be solved by performing a chemical treatment.

  That is, the present invention has the following configuration.

[Configuration 1]
The method for manufacturing a glass substrate for a magnetic disk according to the present invention is a method for manufacturing a glass substrate for a magnetic disk having a mirror surface processing step of mirror-processing the end surface portion of the glass disk, and the mirror surface processing step of the end surface portion includes an end surface portion. The polishing means is brought into contact with the surface, and the polishing means and the glass disk are moved relative to each other to mirror-polish the surface of the end face, and then the end face is chemically treated while maintaining the mirror surface state of the surface. It is characterized by performing a process of removing cracks existing in the surface layer portion.

  That is, in this method of manufacturing a glass substrate for magnetic disk, the mirror surface processing step of the end surface portion of the glass disk is composed of two sub-processes, a “mirror polishing” step and a “chemical treatment” step. In the “mirror polishing” step, the surface of the end surface portion is made into a mirror surface state, and in the “chemical treatment” step, cracks existing in the surface layer portion of the end surface portion are removed. Here, the “surface layer portion” is a region up to a minute depth below the surface of the end surface portion. In addition, the process of removing the crack is a process of removing the crack by changing the shape to a shape that is not substantially a crack shape by blunting the sharp shape of the bottom of the crack even if the concave defect itself is not removed. Including.

[Configuration 2]
The present invention uses a polishing brush or a polishing pad as a polishing means in the method for manufacturing a glass substrate for a magnetic disk described in Configuration 1, and between these polishing brush or the polishing pad and the end face of the glass disk. While supplying the polishing slurry, mirror polishing of the surface of the end face is performed.

[Configuration 3]
The present invention is characterized in that in the method for manufacturing a glass substrate for a magnetic disk according to Configuration 1 or 2, glass having a depth of 50 nm to 800 nm at the end face is removed in the chemical treatment. is there.

  Since the amount of glass removed by this chemical treatment is a small amount of 1 μm or less, this chemical treatment does not disturb the mirror surface state already formed by the mirror polishing process.

[Configuration 4]
The present invention provides the method for manufacturing a glass substrate for a magnetic disk according to any one of the structures 1 to 3, wherein the chemical treatment is a treatment in which a dissolution rate for the glass constituting the glass disk is 10 nm / min to 800 nm / min. The liquid is performed by bringing the liquid into contact with an end surface portion of the glass disk.

  In the chemical treatment according to the present invention, a processing solution having a predetermined dissolving ability with respect to the glass constituting the glass disk, in other words, a processing solution having a predetermined dissolution rate is used, so that the mirror surface state already formed by the mirror polishing process is disturbed. There is nothing to do.

  In addition, although the solubility with respect to glass changes with the kind of glass, a composition and density | concentration of a process liquid, environmental temperature, etc., when this invention performs this chemical treatment, the melt | dissolution rate with respect to glass is 10 nm per minute. The solubility is such that the minute becomes 800 nm.

[Configuration 5]
The present invention is characterized in that in the method for manufacturing a glass substrate for a magnetic disk according to any one of Structures 1 to 4, a chemical strengthening process is performed on the glass disk after the chemical process.

[Configuration 6]
The present invention is the method for producing a glass substrate for a magnetic disk according to any one of the structures 1 to 5, wherein the glass constituting the glass disk is an aluminosilicate glass.

[Configuration 7]
The present invention provides a method for manufacturing a glass substrate for a magnetic disk according to any one of Structures 1 to 6, wherein the hard disk drive uses a 1-inch hard disk drive or a magnetic disk smaller than the 1-inch hard disk drive. A glass substrate for a magnetic disk to be mounted is manufactured.

[Configuration 8]
A magnetic disk manufacturing method according to the present invention uses a magnetic disk glass substrate manufactured by the method for manufacturing a magnetic disk glass substrate according to any one of Structures 1 to 7, and uses the magnetic disk glass substrate. On the main surface, at least a magnetic layer is formed.

  The glass disk in the present invention includes a donut-shaped form in which a circular hole is formed in the center part in addition to the disk-shaped form. In a donut-shaped glass disk, the present invention can be applied not only to the outer peripheral end face part but also to the inner peripheral end face part.

  Further, the mirror surface referred to in the present invention is not a pear-like surface but a flat and smooth surface, and when defined by the numerical value of the surface roughness, the surface having an arithmetic average roughness (Ra) of 100 nm or less. say. The definition of the surface roughness is based on Japanese Industrial Standard (JIS) B0601, and refers to the surface roughness measured by an atomic force microscope (AFM), for example.

  In the above-described mirror polishing process of the end face, that is, a mechanical polishing method, it is possible to obtain an excellent mirror surface quality that can prevent thermal asperity failure, while generating extremely fine cracks on the polishing surface. It has been.

  During polishing, the glass is reduced as the polishing progresses, and the surface is gradually polished to a mirror surface state, but fine cracks generated on the polished surface are gradually extended to the surface layer (under the surface). May end up.

  Therefore, the end surface portion after mirror polishing has a mirror surface, but a fine crack may remain on the surface layer portion.

  In the present invention, by removing such cracks, a glass substrate for a magnetic disk having sufficient impact resistance even when used for a hard disk drive for a “mobile device” has been successfully produced.

  That is, the present inventor has developed from various viewpoints in order to raise the impact resistance of the glass substrate for magnetic disks to a level suitable for a hard disk drive for “mobile devices”. For example, carefully examine the factors considered as factors that reduce the impact resistance such as the composition and rigidity of the glass material, the method of chemical strengthening treatment, the polishing method, scratches and their causes, and conduct the impact resistance test. Repeated.

  As a result, the present inventors have surprisingly found that there is one of the causes in the mirror polishing process of the end face part, which has not been considered as a factor that lowers impact resistance. Conventionally, the end surface portion is finished in a mirror-like state with no scratches by this process, so this process has not been considered to cause a problem regarding impact resistance.

  It is extremely difficult to develop a method other than a mechanical polishing method that can provide excellent mirror surface quality for a magnetic disk glass substrate with a high recording density of 40 gigabits per square inch or more. It was. Therefore, in the present invention, while assuming a mechanical mirror polishing step, a chemical treatment is performed after the mirror polishing step to remove fine cracks in the surface layer portion formed in the mirror polishing step.

  In the present invention, in order to remove the fine cracks in the surface layer portion while maintaining the mirror surface state of the end surface portion formed by the mirror polishing step, the dissolving ability of the treatment liquid for performing the chemical treatment is suppressed. It is necessary to. This is because if the solubility of the treatment liquid is excessive, the surface roughness of the end face becomes coarse, which may cause a thermal asperity failure.

  According to the examination results by the present inventor, since the cracks generated in the mirror polishing process are fine, even if the treatment liquid has only a very weak dissolving ability, the cracks are reduced to a level where there is no problem in impact resistance. It is considered that the sharp shape at the bottom can be blunted.

  In other words, in the present invention, the sharp shape of the bottom (tip) of the crack is blunted (for example, the sharp shape is transformed into a rounded shape without completely removing the concave defect itself by etching or the like). Therefore, if the crack shape is removed, it is considered that a glass substrate for a magnetic disk having sufficient impact resistance can be provided.

  In the present invention, for example, the end surface of a glass disk finished into a disk shape by grinding is mirror-polished, and then subjected to appropriate chemical treatment, so that it is particularly serious in a hard disk drive for “mobile devices”. Thus, it is possible to realize a glass substrate for a magnetic disk that can solve the shortage of shock resistance and can realize a high information recording density.

  That is, the present invention does not cause a thermal asperity failure even when it is configured as a magnetic disk that is used for a high recording density such as 40 gigabits per square inch or more, and has an impact resistance. It is possible to provide a magnetic disk glass substrate and a magnetic disk excellent in the above.

  In addition, the present invention is very portable, for example, so-called mobile phones, digital cameras, portable “MP3 players”, portable information devices such as PDAs, or in-vehicle devices such as “car navigation systems”. For example, even if it is configured as a small magnetic disk with an outer diameter of 30 mm or less so that it can be mounted on equipment, sufficient impact resistance can be obtained, and stable operation can be realized without any thermal asperity failure. A glass substrate for a magnetic disk and a magnetic disk can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  The method for producing a glass substrate for a magnetic disk according to the present invention comprises grinding a main surface of a plate glass to obtain a glass base material, cutting the glass base material to cut out the glass disk (cutting), The end face is ground, then mirror polishing and chemical treatment are performed, then at least the main surface of the glass disk is subjected to polishing treatment and chemical strengthening treatment to produce a glass substrate for a magnetic disk. is there.

  This plate-like glass can be manufactured using a known manufacturing method such as a press method, a float method, or a fusion method, using, for example, molten glass as a material. Of these, plate glass can be produced at low cost by using the pressing method.

  The glass used in the present invention is preferably amorphous glass. Preferred examples of the glass material include aluminosilicate glass. Further, such an aluminosilicate glass can obtain a predetermined mirror surface quality in the mirror polishing of the end surface portion, and can preferably cause the treatment liquid to act in the chemical treatment. In particular, aluminosilicate glass containing lithium is preferable.

The composition ratio of such aluminosilicate glass, a SiO _2, 58 to 75 wt%, the _Al 2 _{O 3,} 5 to 23 wt%, the Li ₂ O, 3 to 10 wt%, a Na ₂ O, It is preferable to contain 4 to 13% by weight as a main component.

Furthermore, the composition ratio of the aluminosilicate glass is as follows: SiO ₂ is 62 to 75 wt%, Al ₂ O ₃ is 5 to 15 wt%, Li ₂ O is 4 to 10 wt%, Na ₂ O is 4 wt%. to 12 wt%, the ZnO _2, 5.5 to 15 wt%, with containing as a main component, the weight ratio of Na ₂ O and _{ZnO 2 (Na 2 O / ZnO} 2) is 0.5 to 2.0 The weight ratio of Al ₂ O ₃ to ZnO ₂ (Al ₂ O ₃ / ZnO ₂ ) is preferably 0.4 to 2.5.

Further, in order to eliminate the protrusions on the surface of the glass disk caused by the undissolved material of ZnO ₂ , in terms of mol%, SiO ₂ is 57 to 74%, ZnO ₂ is 0 to 2.8%, Al the ₂ O _3, 3 to 15%, the LiO _2, 7 to 16%, a Na ₂ O, it is preferable to use a glass containing 4 to 14%.

  Such an aluminosilicate glass is particularly preferable for the present invention because the bending strength is increased and the Knoop hardness is excellent by applying a chemical strengthening treatment.

  The end surface portion of the glass disk obtained by cutting (cutting) as described above is shaped into a predetermined shape by grinding. For grinding, a grinding wheel such as a diamond wheel is used. By this grinding process, a predetermined chamfered surface (chamfer surface) is formed on the end surface portion.

  The mirror polishing of the end face is performed by a mechanical polishing method. This is because the mechanical polishing method can obtain a flat and smooth mirror surface state as compared with the etching method, and thus can satisfactorily prevent thermal asperity failure.

  Usually, a glass disk is made into a disk shape (or donut shape) by a cutting or grinding process. At this time, since grinding is performed using a rough grindstone of about # 100 to # 500, scratches are generated on the end face portion. If there is such a scratch, the strength of the glass disk cannot be maintained, but this scratch can be reliably removed by mirror polishing.

  In the mirror polishing of the end face part in the present invention, the polishing slurry is supplied to the end face part, and the polishing brush or the polishing pad and the glass disk are brought into contact with the surface of the end face part with the polishing brush or the polishing pad. It is preferable to perform relative polishing and mirror polishing.

  By performing mirror polishing in this way, excellent mirror surface quality can be realized at the end surface portion. As the free abrasive grains contained in the polishing slurry, fine abrasive grains having an average particle diameter of 0.05 μm to 2 μm are used. As the abrasive grains, cerium oxide abrasive grains can be used. As the polishing means, either a polishing brush or a polishing pad can be suitably used. However, when a chamfered surface is formed on the end surface portion, the chamfered surface can be surely used by using the polishing brush. This is preferable because it can be mirror-polished.

  And it is necessary to perform the chemical treatment in the present invention so as not to disturb the mirror surface quality obtained by mirror polishing. This is because if the mirror surface quality is disturbed, a thermal asperity failure may occur. Specifically, it is necessary to perform chemical treatment so that the surface roughness of the end face after chemical treatment does not exceed 100 nm in terms of arithmetic average roughness (Ra). Within this range, a treatment liquid capable of dissolving the glass constituting the glass disk may be brought into contact with the end face of the glass disk. For example, the processing liquid may be supplied to the end surface portion of the glass disk, or the glass disk may be immersed in the processing liquid.

  Specifically, the chemical treatment conditions may be such that the removal allowance of the glass removed by the chemical treatment is within the range of 50 nm to 800 nm. Further, the chemical treatment can be performed by bringing the treatment liquid having a dissolution rate (melting ability) into the glass constituting the glass disk into contact with the end surface of the glass disk, for example, from 10 nm / min to 800 nm / min.

  As the treatment liquid in this chemical treatment, a liquid containing a substance capable of dissolving the glass constituting the glass disk, such as hydrofluoric acid, ammonium fluoride, or sodium fluoride can be used. In particular, it is preferable to use hydrofluoric acid or sodium fluoride.

  As a material for the treatment rod for performing the chemical treatment, any material that has excellent corrosion resistance and low dust generation may be used. By selecting a material excellent in corrosion resistance as the material of the treatment tank, damage and dust generation can be suppressed, and thermal asperity failure and head crash can be suppressed. From this point of view, a quartz material is particularly preferable, but a stainless material, particularly a martensitic or austenitic stainless material having excellent corrosion resistance is also preferable. Quartz material is excellent in corrosion resistance, but is expensive, so it may be selected appropriately in consideration of profitability.

  Next, the main surface of the glass disk is mirror-finished. By performing mirror polishing on the main surface, cracks on the main surface of the glass disk are removed, and the surface roughness of the main surface is, for example, 5 nm or less for Rmax and 0.5 nm or less for arithmetic average roughness (Ra). The If the main surface of the glass disk has such a mirror surface, even if the flying height of the magnetic head is 10 nm in a magnetic disk manufactured using this glass disk, for example, a so-called crash failure And thermal asperity failure can be prevented. Further, if the main surface of the glass disk is such a mirror surface, in the chemical strengthening process described later, the chemical strengthening process can be performed uniformly in the fine region of the glass disk, and delayed fracture due to micro cracks can be performed. Can be prevented.

  This main surface mirror polishing is performed, for example, by pressing a surface plate having a polishing cloth (for example, a polishing pad) affixed to the main surface of a glass disk and supplying a polishing liquid to the main surface of the glass disk. This is done by relatively moving the disk and the surface plate to polish the main surface of the glass disk. At this time, the polishing liquid may contain polishing abrasive grains. Colloidal silica abrasive grains can be used as the abrasive grains. As the abrasive grains, abrasive grains having an average abrasive grain size of 10 nm to 200 nm may be used.

  Further, in the present invention, since the end surface portion of the glass disk is mirror-polished, the generation of particles can be suppressed. In a magnetic disk manufactured using this magnetic disk glass substrate, a so-called thermal asperity failure is achieved. This is because it can be prevented well. In addition, when the end surface portion is a mirror surface, delayed fracture due to microcracks can be prevented when chemical strengthening treatment is performed. As a mirror surface state of the end surface portion, a mirror surface having an arithmetic average roughness (Ra) of 100 nm or less is preferable.

  The chemical strengthening treatment in the present invention is not particularly limited as long as a known chemical strengthening treatment method is used. The chemical strengthening treatment of the glass disk is performed, for example, by bringing the glass disk into contact with a heated chemically strengthened molten salt, and ions on the surface layer of the glass disk are ion-exchanged with ions of the chemically strengthened salt.

  Here, as the ion exchange method, a low temperature type ion exchange method, a high temperature type ion exchange method, a surface crystallization method, a dealkalization method on the glass surface, etc. are known. It is preferable to use a low-temperature ion exchange method in which ion exchange is performed in a temperature region not exceeding.

  The low-temperature ion exchange method here refers to an increase in the volume of the ion exchange part by substituting alkali ions in the glass with alkali ions having a larger ion radius than the alkali ions in the temperature range below the annealing point of the glass. This refers to a method of generating a compressive stress on the glass surface layer and strengthening the glass surface layer.

  The heating temperature of the molten salt when performing the chemical strengthening treatment is preferably 280 ° C. to 660 ° C., particularly 300 ° C. to 400 ° C., from the viewpoint that ion exchange is performed satisfactorily. .

  The time for bringing the glass disk into contact with the molten salt is preferably several hours to several tens of hours.

  In addition, before making a glass disc contact with molten salt, it is preferable to heat a glass disc to 100 degreeC thru | or 300 degreeC as preheating. In addition, the glass disk after the chemical strengthening treatment is subjected to cooling, a cleaning process, and the like to be a product (a glass substrate for a magnetic disk).

  In the present invention, the material of the treatment rod for performing the chemical strengthening treatment is not particularly limited as long as it is excellent in corrosion resistance and has a low dust generation property. Chemically strengthened salt and chemically strengthened molten salt are oxidative and the processing temperature is high, so by selecting materials with excellent corrosion resistance, damage and dust generation are suppressed, resulting in thermal asperity failures and head crashes. It is necessary to suppress. From this point of view, a quartz material is particularly preferable as a material for the treatment rod, but a stainless material, or a martensitic or austenitic stainless material having particularly excellent corrosion resistance can also be used. In addition, although quartz material is excellent in corrosion resistance, since it is expensive, it can select suitably in consideration of profitability.

  As the material of the chemically strengthened salt in the present invention, it is preferable to use a nitrate containing an alkali metal element, for example, a nitrate containing potassium nitrate, sodium nitrate or the like. This is because such a chemically strengthened salt can realize predetermined rigidity and impact resistance as a glass substrate for a magnetic disk when chemically strengthening glass, particularly aluminosilicate glass.

  The magnetic disk glass substrate according to the present invention manufactured as described above is particularly suitable as a thin magnetic disk glass substrate having a disk thickness of less than 0.5 mm, particularly a disk thickness of 0.1 mm to 0.4 mm. is there. The magnetic disk glass substrate is particularly suitable as a small-diameter magnetic disk glass substrate having a disk diameter (outer diameter) of 30 mm or less. This is because such a thin, small-diameter small-sized magnetic disk is mounted on a “1-inch hard disk drive” or a hard disk drive smaller than the “1-inch hard disk drive”. That is, this glass substrate for magnetic disk is suitable as a glass substrate for magnetic disk mounted on a “1 inch type hard disk drive” or a hard disk drive smaller than “1 inch type hard disk drive”.

  In addition, the diameter of the glass substrate for magnetic disks for manufacturing the magnetic disk mounted in the “1-inch hard disk drive” is about 27.4 mm, and the disk thickness is 0.381 mm. Further, the diameter of the glass substrate for magnetic disk for manufacturing the magnetic disk to be mounted on the “0.85 inch type hard disk drive” is about 21.6 mm.

  Such a small magnetic disk glass substrate is characterized in that the disk thickness is thinner than a conventional magnetic disk glass substrate. If the disk thickness is thin, there is a problem that the compressive stress generated by the chemical strengthening process is reduced. However, in the present invention, the end face part is processed as described above, so the compressive stress is reduced. However, sufficient impact resistance can be obtained. From this viewpoint as well, the present invention is suitable for mounting on a hard disk drive for “mobile devices”.

  In other words, in the present invention, it is preferable that the manufactured magnetic disk glass substrate is manufactured so as not to be damaged even when an acceleration of 3000 G is applied. By manufacturing in this way, it is possible to obtain a glass substrate for magnetic disk that is excellent in impact resistance and suitable for a hard disk drive for “mobile devices”.

  In the present invention, the surface roughness of the main surface of the magnetic disk glass substrate is preferably a mirror surface that allows the magnetic head to float safely and does not cause thermal asperity failure. Specifically, the surface roughness of the main surface is preferably a mirror surface having an arithmetic average roughness (Ra) of 0.5 nm or less and a maximum height (RMax) of 5 nm or less.

  In the magnetic disk according to the present invention, the magnetic layer formed on the magnetic disk glass substrate can be made of, for example, a cobalt (Co) ferromagnetic material. In particular, it is preferably formed as a magnetic layer made of a cobalt-platinum (Co—Pt) -based ferromagnetic material or a cobalt-chromium (Co—Cr) -based ferromagnetic material that provides a high coercive force. As a method for forming the magnetic layer, a sputtering method (DC magnetron sputtering method) can be used.

  Moreover, it is preferable to insert an underlayer or the like as appropriate between the glass substrate and the magnetic layer. As the material of these underlayers, an Al—Ru alloy, a Cr alloy, or the like can be used.

  Further, a protective layer for protecting the magnetic layer from the impact of the magnetic head can be provided on the magnetic layer. As this protective layer, a hard amorphous carbon layer or a hydrogenated carbon protective layer can be preferably used. As a method for forming the protective layer, for example, a plasma CVD method can be used.

  Furthermore, by forming a lubricating layer made of a PFPE (perfluoropolyether) compound on this protective layer, interference between the magnetic head and the magnetic disk can be reduced. This lubricating layer can be formed, for example, by coating by a dip method.

  Hereinafter, the present invention will be specifically described by giving examples and comparative examples. In addition, this invention is not limited to the structure of these Examples.

[Example 1 (Example of manufacturing method of glass substrate for magnetic disk)]
The manufacturing method of the glass substrate for magnetic disks in the present embodiment described below includes the following steps (1) to (6).

(1) Rough grinding process (2) End face grinding process (3) Fine grinding process (4) End face mirror finishing process (4-1) End face mirror polishing process (4-2) End face chemical treatment process (5) ) Main surface mirror finishing process (6) Chemical strengthening process First, an amorphous aluminosilicate glass was cut out (cut) to prepare a disk-shaped glass base material. This aluminosilicate glass contains lithium. The composition of this aluminosilicate glass is SiO ₂ 63.6% by weight, Al ₂ O ₃ 14.2% by weight, Na ₂ O 10.4% by weight, Li ₂ O 5.4% by weight. %, ZnO ₂ 6.0 wt%, and Sb ₂ O ₃ 0.4 wt%.

(1) Rough grinding step Using the above disk-shaped glass base material, a disk-shaped glass disk having a diameter of 28.7 mm and a thickness of 0.6 mm was obtained.

  Specifically, first, using alumina abrasive grains of particle size # 400, setting the load to about 100 kg, and rotating the sun gear and the internal gear, both surfaces of the glass disk housed in the carrier are improved in surface accuracy. It was ground to 0 to 1 μm and surface roughness (Rmax) of about 6 μm.

(2) End face grinding process (shape machining process)
This end face part grinding process is a process of creating an outer peripheral side end face part and an inner peripheral side end face part on a glass disk using a grinding wheel.

  In this end face portion grinding process, using a cylindrical grindstone, a hole with a diameter of 6 mm was formed in the center portion of the glass disk, and the outer peripheral end face portion was ground to a diameter of 27.5 mm. A predetermined chamfering process was performed on the outer peripheral end surface portion and the inner peripheral end surface portion. The grinding wheel used in this shape processing step has abrasive grains of # 400. The surface roughness of the end face of the glass disk was about 4 μm in Rmax. At this stage, the surface of the end face was in a state of small scratches due to processing with a grinding wheel.

(3) Fine grinding step Next, the grain size of the abrasive grains is changed to # 1000, and the main surface of the glass disk is ground, so that the surface roughness of the main surface is about 2 μm for Rmax and about 0.2 μm for Ra. did.

  By performing this fine grinding process, the fine uneven | corrugated shape formed in the main surface can be reduced.

  The glass disk after such a fine grinding process was immersed in each washing tank of neutral detergent and water to which ultrasonic waves were applied in order to perform ultrasonic cleaning.

(4) End face part mirror finishing process (4-1) End face part mirror polishing process Next, the end face part (inner peripheral end face part and outer circumference) of the end face part of the glass disk while rotating the glass disk by brush polishing. The surface roughness of the end face portion was mirror-polished to about 30 nm with Ra.

  That is, while the abrasive slurry is sprayed and supplied to the end surface portion of the glass disk, the abrasive brush with a shaft provided with the nylon resin bristles is brought into contact with the end surface portion of the glass disk, and the rotating shaft of the polishing brush and the glass disk Were rotated in opposite directions to perform brush polishing of the end face portion and perform mirror polishing. At this time, cerium oxide abrasive grains having an average particle diameter of 1 μm were used as free abrasive grains contained in the polishing slurry. In this end face part mirror polishing process, in order to surely remove the scratches generated in the end face part due to the grinding process in the shape processing process, the removal allowance of the glass is set to about 20 μm to 50 μm, for example. By this end face part mirror polishing process, the surface of the end face part was in a mirror state, and its surface roughness was 30 nm in Ra.

(4-2) End face portion chemical treatment step Next, the end face portion was chemically treated. Specifically, a hydrofluoric acid aqueous solution (0.5% by weight) was used as a treatment liquid, and a glass disk was immersed in this treatment liquid for 2 minutes. A treatment tank made of a martensitic corrosion-resistant stainless alloy material was used.

  In this chemical treatment, when the dissolution capacity of the treatment liquid with respect to the aluminosilicate glass constituting the glass disk is expressed by the dissolution rate, it is 50 nm per minute. Moreover, the machining allowance of the glass removed in this chemical treatment is 100 nm.

  After this chemical treatment, the end face of the glass disk was analyzed and found to be in a mirror state. That is, the end surface portion of the glass disk was processed into a state in which particles such as particles could be prevented by this end surface mirror processing step. Moreover, the surface roughness of the end face portion was 40 nm in Ra, and the change in the surface roughness was slight before and after the chemical treatment.

  In addition, it was 27.4 mm when the diameter of the glass disc was measured after the end surface part mirror surface process.

(5) Main surface mirror finishing process The main surface mirror polishing of the glass disk was performed using a double-side polishing apparatus. In a double-side polishing machine, a glass disk held by a carrier is brought into close contact with an upper and lower surface plate to which a polishing pad is attached, the carrier is engaged with a sun gear and an internal gear, and the glass disk is sandwiched between upper and lower surface plates. Press. Thereafter, by supplying and rotating polishing slurry between the polishing pad and the main surface of the glass disk, the glass disk revolves while rotating on the surface plate, and both surfaces are polished simultaneously. The holding hole of the polishing carrier was formed of a member that did not damage the end face of the glass disk.

  As the free abrasive contained in the polishing slurry, cerium oxide abrasive was used. A high-quality mirror finish was achieved by gradually reducing the average particle size. When the main surface of the glass disk which finished the main surface mirror polishing was analyzed, it was in a mirror state. The surface roughness was about 0.5 nm for Ra and about 5 nm for RMax.

(6) Chemical strengthening process The glass disk was chemically strengthened. For chemical strengthening, a nitrate for chemical strengthening prepared by mixing potassium nitrate and sodium nitrate is prepared, heated to 340 ° C to 380 ° C to form a molten salt, and the glass disk is immersed for about 2 hours to 4 hours to perform ion exchange. A chemical strengthening treatment was performed.

  The glass substrate after chemical strengthening was washed and dried.

  A glass substrate for a magnetic disk was manufactured as described above. It was confirmed that a glass substrate for a magnetic disk for mounting on a “1 inch type” hard disk drive having an outer diameter of 27.4 mm and an inner diameter of 7 mm was manufactured.

[Inspection and test results]
The main surface and the end surface of the glass substrate for magnetic disk were visually inspected, and further, a precise inspection using light reflection, scattering and transmission was performed. As a result, no defects such as protrusions, scratches, cracks, or foreign matters were found on the main surface and the end surface of the magnetic disk glass substrate. No foreign matter causing thermal asperity failure was found at all.

  Further, the end face part on the outer peripheral side and the end face part on the inner peripheral side of the obtained magnetic disk glass substrate obtained through the above-described steps are subjected to an optical microscope, an electron microscope, an atomic force microscope (AFM). And analyzed precisely. As a result, the surface was clean and the surface roughness was 40 nm in terms of Ra. No scratches or fine cracks were observed.

  Further, the surface roughness of the main surface of this magnetic disk glass substrate was measured with an atomic force microscope (AFM), and it was an ultra-smooth mirror surface with Rmax 2.5 nm and Ra 0.30 nm. It was confirmed.

  The numerical value of the surface roughness is calculated according to Japanese Industrial Standard (JIS) B0601 for the surface shape measured by AFM (Atomic Force Microscope).

  The obtained magnetic disk glass substrate has an inner diameter of 7 mm, an outer diameter of 27.4 mm, and a plate thickness of 0.381 mm. The glass disk substrate for magnetic disks used in “1-inch type” hard disk drives has the predetermined dimensions. I confirmed that there was.

[Strength measurement and impact resistance test]
The obtained glass substrate for magnetic disk was subjected to strength measurement. A steel ball having a diameter of 10 mm is placed on the inner diameter part of the glass substrate for magnetic disk, and the steel ball is pushed down at a speed of 3 mm per minute while holding the outer periphery. It was measured. As a result, it was not broken until a load of 2.2 kgf was applied. For the strength measurement, “Autograph AG-I5kN” manufactured by Shimadzu Corporation was used.

Next, an impact resistance test of the glass substrate for magnetic disk was performed. Various impacts were applied to the obtained glass substrate for magnetic disk, and impact resistance was analyzed by converting the impact when the glass substrate for magnetic disk was broken into mass acceleration. As a result, it was not damaged even at an acceleration of 5000 G (1 G is 9.8 m / sec ² ), and it was durable.

[Example 2 (Example of magnetic disk manufacturing method)]
Next, a magnetic disk was manufactured through the following steps.

  On both main surfaces of the glass substrate for a magnetic disk obtained by the above-described process, using a stationary facing DC magnetron sputtering apparatus, an Al—Ru alloy seed layer, a Cr—W alloy underlayer, Co—Cr—Pt A magnetic layer of Ta alloy and a hydrogenated carbon protective layer were sequentially formed. The seed layer has an effect of refining the magnetic grains of the magnetic layer, and the undercoat layer has an effect of orienting the easy axis of magnetization of the magnetic layer in the in-plane direction.

  This magnetic disk is a non-magnetic substrate for a magnetic disk, a magnetic layer formed on the magnetic disk glass substrate, a protective layer formed on the magnetic layer, and formed on the protective layer. And at least a lubricated layer.

  A nonmagnetic metal layer (nonmagnetic underlayer) including a seed layer and an underlayer is formed between the magnetic disk glass substrate and the magnetic layer. In this magnetic disk, the layers other than the magnetic layer are all made of a nonmagnetic material. In this embodiment, the magnetic layer, the protective layer, the protective layer, and the lubricating layer are formed in contact with each other.

  That is, first, an Al—Ru (aluminum-ruthenium) alloy (Al: 50 at%, Ru: 50 at%) is used as a sputtering target, and is made of a 30 nm thick Al—Ru alloy on a magnetic disk glass substrate. A seed layer was formed by sputtering. Next, using a Cr—W (chromium-tungsten) alloy (Cr: 80 at%, W: 20 at%) as a sputtering target, a base layer made of a 20 nm thick Cr—W alloy is sputtered on the seed layer. Was formed. The seed layer has a function of refining the magnetic grains of the magnetic layer, and the underlayer has a function of orienting the easy axis of magnetization of the magnetic layer in the in-plane direction.

  Next, as a sputtering target, a sputtering target made of a Co—Cr—Pt—B (cobalt-chromium-platinum-boron) alloy (Cr: 20 at%, Pt: 12 at%, B: 5 at%, balance Co) is used. A ferromagnetic layer made of a Co—Cr—Pt—B alloy having a thickness of 15 nm was formed on the base layer by sputtering.

  Next, a protective layer made of amorphous hydrogenated carbon was formed on the magnetic layer by plasma CVD, and a lubricating layer made of PFPE (perfluoropolyether) was formed by dipping. The protective layer functions to protect the magnetic layer from the impact of the magnetic head. In this way, a magnetic disk was obtained.

  Using the obtained magnetic disk, it is mounted on a “1-inch hard disk drive” that requires an information recording density of 40 gigabits or more per square inch, and the magnetic head has a magnetoresistive effect element as a reproducing element. As a result, it was possible to perform recording and reproduction without any particular problem. That is, no crash failure or thermal asperity failure occurred.

  Further, when a glide inspection was performed using a glide head with a flying height of 5 nm using the obtained magnetic disk, no colliding foreign matter was detected, and a stable flying state could be maintained.

  Furthermore, when this magnetic disk was subjected to a load / unload durability test, it showed good durability.

  In the present invention, the diameter (size) of the glass substrate for magnetic disk is not particularly limited. However, the present invention exhibits excellent utility particularly when a small glass substrate for a magnetic disk is manufactured. The small size here is, for example, a glass substrate for a magnetic disk having a diameter of 30 mm or less.

  That is, for example, a small magnetic disk having a diameter of 30 mm or less is used in a storage device in an in-vehicle device such as a so-called “car navigation system” or a portable device such as a so-called “PDA” or a mobile phone terminal. This is because higher durability and impact resistance are required as compared with a normal magnetic disk in a used device.

Example 3
In Example 1 described above, the glass substrate for a magnetic disk and the magnetic disk were manufactured by changing the processing conditions of the (4-2) end face chemical treatment step in various ways. The processing conditions are shown in [Table 1] below.

  The glass substrate for magnetic disk in Example 3 was inspected and tested in the same manner as in Example 1. As a result, both the end face and the main surface caused defects such as protrusions, scratches, cracks, foreign matters, and thermal asperity failures. No foreign matter was found. Further, when the surface states of the end face part and the main surface were similarly investigated, the surface state was the same as that of the magnetic disk glass substrate of Example 1, and no scratches or fine cracks existed.

  When the strength test was performed in the same manner as in Example 1, it was not broken until a load of 2.2 kgf to 2.4 kgf was applied.

  The impact resistance test was performed in the same manner as in Example 1. However, as in Example 1, the impact resistance test was not broken even at an acceleration of 5000 G, and excellent impact resistance was exhibited.

  Further, when a magnetic disk was manufactured in the same manner as in Example 2 using the glass substrate for magnetic disk obtained in Example 3, no crash failure or thermal asperity failure occurred as in the result of Example 2. Therefore, it was possible to perform recording and reproduction without problems. The results of the glite inspection and the load / unload durability test were also excellent results similar to those of Example 2.

[Comparative example]
(Comparative Example 1)
In the end surface chemical treatment step in Example 1, when the immersion time in the processing liquid was extended and the glass removal amount (removal) was set to 3000 nm, the surface of the end surface portion became a pear-like surface state.

  Further, when a magnetic disk was manufactured using this magnetic disk glass substrate, a thermal asperity failure occurred.

  This is considered to be caused by the fact that the surface state of the end face is not mirror-like but pear-like.

(Comparative Example 2)
As Comparative Example 2-1, a glass substrate for magnetic disk that does not perform the end face chemical treatment step in Example 1 was manufactured.

  Moreover, the glass substrate for magnetic discs which does not perform the end surface part mirror polishing process in Example 1 as Comparative Example 2-2 was manufactured.

  Further, as Comparative Example 2-3, the order of the end surface mirror polishing step and the end surface chemical treatment step in Example 1 was changed, and first, the end surface chemical treatment was performed, and then the end surface mirror polishing was performed. A glass substrate for a magnetic disk was manufactured.

  As a result, in Comparative Example 2-1, the surface state of the end face was a mirror surface, but in the impact resistance test, it was confirmed that it was damaged at 3000G. This is considered to be caused by minute cracks remaining in the surface layer portion of the end face portion.

  Moreover, in Comparative Example 2-2, since the end surface part mirror polishing process was not passed, the surface of the end surface part became a pear-like surface state. Further, when a magnetic disk was manufactured using this magnetic disk glass substrate, a thermal asperity failure occurred. This is considered to be caused by the fact that the surface state of the end face is not mirror-like but pear-like.

  Furthermore, in Comparative Example 2-3, the surface state of the end face was a mirror surface, but in the impact resistance test, it was confirmed that it was damaged at 3000G. This is considered to be caused by minute cracks remaining in the surface layer portion of the end face portion.

Claims (8)

A method of manufacturing a glass substrate for a magnetic disk having a mirror surface processing step of mirror-finishing an end surface portion of a glass disk,
The mirror-finishing step of the end face part is made by bringing a polishing means into contact with the end face part, and mirror-polishing the surface of the end face part by relatively moving the polishing means and the glass disk, and then mirror-finishing the surface. A method for producing a glass substrate for a magnetic disk, comprising: chemically treating the end face portion while maintaining the state, and removing a crack existing in the surface layer portion. As the polishing means, a polishing brush or a polishing pad is used, and while polishing slurry is supplied between the polishing brush or the polishing pad and the end face of the glass disk, the surface of the end face is mirror polished. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein: 3. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the glass is removed to a depth of 50 nm to 800 nm at an end face in the chemical treatment. The chemical treatment is performed by bringing a treatment liquid having a dissolution rate with respect to the glass constituting the glass disk into contact with an end surface portion of the glass disk at a rate of 10 nm to 800 nm per minute. The manufacturing method of the glass substrate for magnetic discs as described in any one of Claims 3. The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 4, wherein a chemical strengthening process is performed on the glass disk after the chemical process. The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 5, wherein the glass constituting the glass disk is aluminosilicate glass. A glass substrate for a magnetic disk mounted on a 1-inch hard disk drive or a hard disk drive using a magnetic disk smaller than the 1-inch hard disk drive is manufactured. The manufacturing method of the glass substrate for magnetic discs as described in any one of these. Using the magnetic disk glass substrate produced by the method for producing a magnetic disk glass substrate according to any one of claims 1 to 7,
A method for producing a magnetic disk, comprising: forming at least a magnetic layer on a main surface of the glass substrate for a magnetic disk.