JP5706250B2 - Glass substrate for HDD - Google Patents

Description

  The present invention relates to a glass substrate for HDD.

  A magnetic information recording apparatus records information on an information recording medium by using magnetism, light, magneto-optical, and the like. A typical example is a hard disk drive device. A hard disk drive device is a device that magnetically records information on a magnetic disk as an information recording medium having a recording layer formed on a substrate by a magnetic head. As a base material of such an information recording medium, a so-called substrate, a glass substrate is preferably used.

  Further, recent hard disk drive devices have been required to have excellent strength and smoothness with respect to glass substrates used in the hard disk due to the improved recording density.

  As a method for improving the strength of the glass substrate, chemical strengthening treatment by ion exchange is generally known, and as a method for improving smoothness, there is a method of using polishing and grinding multiple times for the glass substrate. Known (Patent Document 1). High smoothness refers to a state where the flatness, swell, and roughness of the glass substrate are good and no end face sagging occurs.

  The chemical strengthening treatment is safe from the viewpoint of operation particularly in the case of a low temperature type, and may be from the viewpoint of the smoothness of the substrate. Specifically, the strength is improved by heating nitrate, etc., immersing the glass substrate in the melt, and exchanging alkali metal ions on the surface of the glass substrate with alkali metal ions having a larger ion diameter than the alkali metal ions. The method of letting it be mentioned. Although the chemical strengthening step can improve the strength of the glass substrate, the smoothness of the substrate is adversely affected by the compressive stress layer applied at the same time.

  That is, the flatness and the undulation shape of the glass substrate are deteriorated due to the non-uniform balance of the compressive stress layer. As a method of avoiding such a problem, the smoothness is not affected by polishing the recording surface of the glass substrate after the chemical strengthening treatment and removing a part of the compressive stress layer.

  However, in recent years, when a glass substrate from which the above-described compressive stress layer has been partially removed is used for a high-density hard disk of 500 GB / P (2.5 inch platter) or more, there has been a problem in smoothness. Specifically, the flying height, called the GA value, with which the head can stably read and write on the magnetic disk has become unstable.

Patent No. 4209316

  The present invention has been made in view of the prior art, and an object to be solved is to provide a glass substrate for HDD having excellent strength and high smoothness.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies by paying attention to the thickness of the compressive stress layer formed by the chemical strengthening process applied to the glass substrate for HDD. As a result, the smoothness in the vicinity of the outer end when mounted on a hard disk can be eliminated by making the compressive stress layers of the inner end, outer end and main surface of the HDD glass substrate have different thicknesses. I found it. That is, the outer end compressive stress layer is made thinner than the inner end compressive stress layer and thicker than or equal to the main surface compressive stress layer, thereby providing high strength and high smoothness at the same time. It has been found that a glass substrate for HDD can be obtained.

  That is, the present invention is a glass substrate for HDD having a central hole, to which a compressive stress layer is applied by a chemical strengthening process, and compressive stress in the inner end portion, outer end portion and main surface portion of the HDD glass substrate. When the depth of the layer is x (μm), y (μm), and z (μm), the condition of x> y ≧ z is satisfied.

  In the glass substrate for HDD, it is preferable that the depth of the compressive stress layer in the main surface portion is 30 μm or more.

  ADVANTAGE OF THE INVENTION According to this invention, the glass substrate for HDD excellent in intensity | strength and provided with high smoothness can be provided.

It is a manufacturing process figure explaining the process in manufacture of the glass substrate for HDD. It is a figure which shows the whole structure of a glass substrate precursor. It is sectional drawing of the glass substrate for HDD in each process step of the manufacturing method of the glass substrate for HDD. It is a figure which shows the example of the magnetic recording medium provided with the magnetic film on the front main surface of the glass substrate for HDD.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

  The glass substrate for HDD according to the present embodiment is a glass substrate for HDD having a central hole to which a compressive stress layer is provided by a chemical strengthening process, and includes an inner end portion, an outer end portion, and a main end portion of the HDD glass substrate. When the depth of the compressive stress layer in the surface portion is x (μm), y (μm), and z (μm), the condition x> y ≧ z is satisfied.

  In order to create a glass substrate for HDD in the present embodiment, for example, as shown in FIG. 1, a disk processing step including a glass melting step, a pressing step and a coring step, an inner / outer diameter precision processing step, Examples include an inner diameter polishing step, a first lapping step, a second lapping step, a chemical strengthening step, an outer diameter polishing step, a first polishing step, a second polishing step, and a cleaning step. That is, if the outer diameter polishing step is performed after the chemical strengthening step, the depths of the compressive stress layers at the outer end portion and the inner end portion can be made different. Further, in the polishing step, if the main surface is polished deeper than the depth of the compressive stress layer at the outer end, the depth of the compressive stress layer is increased in the order of the inner end, the outer end, and the main surface. can do.

  In addition, since it is preferable to make a lapping process into 2 processes, it is divided into the 1st lapping process and the 2nd lapping process, respectively. Further, the polishing step (also referred to as a polishing step) is preferably two steps, which are divided into a first polishing step and a second polishing step, respectively.

  For example, the order of the second polishing step and the cleaning step may be switched as long as the conditions regarding the depth of the compressive stress layer in each part of the present invention can be satisfied. Furthermore, it may be a method including steps other than these, for example, a chemical treatment step using hydrofluoric acid.

  Moreover, about a washing | cleaning process, you may carry out after a rough | crude grinding | polishing process, after a precision grinding | polishing process, and you may carry out once after a rough grinding | polishing process and a precision grinding | polishing process, respectively.

  FIG. 2 shows the overall configuration of the glass substrate precursor 1 after the disk processing step. As shown in FIG. 2, the glass substrate precursor 1 has a donut-shaped disk shape in which a center hole 5 is formed. 10t is an outer peripheral end surface, 20t is an inner peripheral end surface, 7a is a front main surface, and 7b is a back main surface.

  FIG. 3A is a view showing a cross section of the glass substrate precursor 1 of FIG. 2 along the line II-II, and FIG. 3A is the glass after the disk processing step (a) of FIG. It corresponds to a substrate precursor.

  Next, the inner and outer diameter precision machining steps are used to grind the inner and outer diameter corners, and so-called chamfering is performed on the glass substrate precursor 1 (FIG. 3B). The chamfered glass substrate precursor 1 is subjected to an inner diameter polishing step, a first lapping step, and a second lapping step in order, and then a chemical strengthening step is performed on the entire surface (FIG. 3C). . Thus, when a chemical strengthening process is performed to the whole surface of the glass substrate precursor 1, intensity | strength can be uniformly provided with respect to the surface.

  In the conventional method for manufacturing a glass substrate for HDD, since the inner diameter polishing step and the outer diameter polishing step were provided before the chemical strengthening step, the depth of the compressive stress layer at the outer end portion and the inner end portion was the same. . And the compressive-stress layer was shaved off by performing the polishing process with respect to the main surface of the glass substrate after a chemical strengthening process.

  By removing the compressive stress layer on the main surface in this way, a glass substrate having no problem to some extent with respect to flatness, waviness and roughness can be obtained. However, in recent years, hard disks with a high density of 500 GB / P or more have been widely used, and even with a substrate from which only the compressive stress layer on the main surface has been removed, there is still a problem in smoothness. This is because the compressive stress layer at the outer end is the cause and the smoothness near the outer end of the main surface is deteriorated. In other words, because the compressive stress layer at the outer edge is too strong, the stress balance of the recording surface is lost, the shape near the outer edge (smoothness) deteriorates, and the flying height of the head is not stable when mounted on a hard disk. This leads to deterioration of the GA value.

  In order to avoid the above problems, the compressive stress layer applied to the outer end portion is scraped off by providing an outer diameter polishing step after the chemical strengthening step (FIG. 3D).

  As described above, in order to further improve the smoothness of the main surface of the glass substrate precursor 1 provided with a difference in depth between the compressive stress layers on the inner end face and the outer end face, a polishing step is applied to the main surface. The compressive stress layer on the surface is removed by polishing (FIG. 3E).

  As described above, by providing the outer diameter polishing step after the chemical strengthening step, the depth of the compressive stress layer at the inner end portion can be made larger than the compressive stress layer at the outer end portion. Further, in the subsequent polishing step, if polishing is performed so that the compressive stress layer on the main surface becomes smaller than the compressive stress layer on the outer end portion, the inner end portion, outer end portion and main surface portion of the HDD glass substrate When the depth of the compressive stress layer in x is x (μm), y (μm), and z (μm), respectively, it is possible to insert the compressive stress layer deeply so as to satisfy the condition of x> y ≧ z. As a result, the smoothness in the vicinity of the outer edge on the main surface can be enhanced while applying the compressive stress layer by the chemical strengthening step, so that the HDD glass substrate can be simultaneously filled with high strength and high smoothness.

  In addition, the thickness of the compressive stress layer can be appropriately set to an optimum value according to a target design value, for example, impact resistance, outer periphery smoothness, or central portion smoothness.

  Hereinafter, the above-described manufacturing steps will be described in detail.

<Disk processing process>
In the disk processing step, a glass material having a predetermined composition is melted, press-molded, and penetrated into the center so that the inner and outer circumferences are concentric circles as shown in FIG. This is a step of processing into a disk-shaped glass substrate precursor 1 in which holes 5 are formed.

(Glass melting process)
First, a glass material is melted as a glass melting step. As a material of the glass substrate, for example, soda lime glass mainly composed of SiO ₂ , Na ₂ O, CaO; mainly composed of SiO ₂ , Al ₂ O ₃ , R ₂ O (R = K, Na, Li) Aluminosilicate glass; borosilicate glass; Li ₂ O—SiO ₂ glass; Li ₂ O—Al ₂ O ₃ —SiO ₂ glass; R′O—Al ₂ O ₃ —SiO ₂ glass (R ′ = Mg) , Ca, Sr, Ba) and the like can be used. Among these, aluminosilicate glass and borosilicate glass are particularly preferable because they are excellent in impact resistance and vibration resistance.

(Pressing process)
Next, as a pressing step, molten glass is poured into a lower mold and press-molded with an upper mold to obtain a disk-shaped glass substrate precursor. The disc-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.

  There is no limitation on the size of the glass substrate. For example, there are glass substrates of various sizes such as an outer diameter of 2.5 inches, 1.8 inches, 1 inch, and 0.8 inches. Further, the thickness of the glass substrate is not limited, and there are glass substrates having various thicknesses such as 2 mm, 1 mm, and 0.63 mm.

(Coring process)
The press-molded glass substrate precursor is pierced at the center in the coring process. In the drilling, a hole is drilled in the center by grinding with a core drill or the like equipped with a diamond grindstone or the like in the cutter part.

<Inner and outer diameter precision machining process>
Next, as the inner / outer diameter fine machining step, the inner / outer diameter processing is performed by grinding the outer peripheral end surface and the inner peripheral end surface of the glass substrate with a grinding wheel such as a drum-shaped diamond.

<Inner diameter polishing process>
A plurality of glass substrates that have undergone the inner / outer diameter fine processing step are stacked and stacked, and in this state, the inner peripheral surface is polished using an end surface polishing machine.

<First lapping process>
Next, as a first lapping step, both surfaces of the glass substrate are polished to preliminarily adjust the overall shape of the glass substrate, that is, the parallelism, flatness and thickness of the glass substrate.

  Moreover, it is preferable to use fixed abrasive grains in the first lapping step. Since the grinding process has a large machining allowance, the use of fixed abrasive grains can remove the stress layer on the main surface with high productivity.

<Second wrapping process>
Further, both surfaces of the glass substrate are polished again to finely adjust the parallelism, flatness and thickness of the glass substrate.

  As the polishing machine for polishing the front and back surfaces of the glass substrate in the first and second lapping processes, a known polishing machine called a double-side polishing machine can be used. The double-side polishing machine includes a disk-shaped upper surface plate and a lower surface plate that are arranged vertically so as to be parallel to each other, and rotate in opposite directions. A plurality of diamond pellets for polishing the main surface of the glass substrate are attached to the opposing surfaces of the upper and lower surface plates. Between the upper and lower surface plates, there are a plurality of carriers that rotate in combination with an internal gear provided in an annular shape on the outer periphery of the lower surface plate and a sun gear provided around the rotation axis of the lower surface plate. The carrier is provided with a plurality of holes, and a glass substrate is fitted into the holes. The upper and lower surface plates, the internal gear and the sun gear can be operated by separate driving.

  The polishing operation of the polishing machine is such that the upper and lower surface plates rotate in opposite directions, and the carrier sandwiched between the surface plates via the diamond pellets rotates with the surface plate holding a plurality of glass substrates. Revolves in the same direction as the lower surface plate relative to the center of rotation. In such an operating polishing machine, the glass substrate can be polished by supplying a polishing liquid between the upper surface plate and the glass substrate, and the lower surface plate and the glass substrate.

When using this double-side polishing machine, the weight of the surface plate applied to the glass substrate and the number of rotations of the surface plate are adjusted as appropriate according to the desired polishing state. The weight in the first and second lapping steps is preferably 60 g / cm ² to 120 g / cm ² . Further, it is preferable that the rotation speed of the surface plate is about 10 to 30 rpm, and the rotation speed of the upper surface plate is about 30 to 40% slower than the rotation speed of the lower surface plate. Increasing the load on the surface plate and increasing the rotation speed of the surface plate increases the amount of polishing, but if the load is increased too much, the surface roughness will not be good, and if the rotation speed is too high, the flatness will be good. Not. Further, when the load is small and the rotation speed of the surface plate is slow, the polishing amount is small and the production efficiency is lowered.

  When the second lapping process is completed, defects such as large waviness, chipping and cracks are removed, and the surface roughness of the main surface of the glass substrate is about 2 to 4 μm for Rmax and about 0.2 to 0.4 μm for Ra. Is preferable. By setting it as such a surface state, it can polish efficiently by a 1st polishing process through the following chemical strengthening process.

  In the first lapping step, roughly large undulations, chips and cracks are efficiently removed so that the second lapping step can be performed efficiently. For this reason, it is preferable to use diamond pellets of # 800 mesh to # 1200 mesh which are coarser than # 1300 mesh to # 1700 mesh used in the second wrapping. The surface roughness at the time when the first lapping process is completed is preferably such that Rmax is 4 to 8 μm and Ra is about 0.4 to 0.8 μm.

  In addition, as a method for polishing the glass substrate, a method in which a pad is attached to the polishing surfaces of the upper and lower surface plates and a polishing liquid containing an abrasive is supplied for polishing can be used. Examples of the abrasive include cerium oxide, zirconium oxide, aluminum oxide, manganese oxide, colloidal silica, and diamond. These are dispersed in water and used as a slurry. The pad is divided into a hard pad and a soft pad, but can be appropriately selected and used as necessary. Examples of the hard pad include pads made of hard velor, urethane foam, pitch-containing suede, etc., and examples of the soft pad include pads made of suede, velor, etc.

  A polishing method using a pad and a polishing agent can cope with rough polishing to precision polishing by changing the particle size of the polishing agent and the type of the pad. Therefore, in the first lapping step and the second lapping step, the abrasive material, abrasive particle size, and pad are appropriately combined so that the above-mentioned surface roughness can be obtained by efficiently removing large undulations, chips, cracks, etc. Can respond.

  Moreover, it is preferable to perform the washing | cleaning process for removing the abrasive | polishing agent and glass powder which remained on the surface of the glass substrate after the 1st and 2nd lapping process.

  It should be noted that the polishing machines used in the first lapping process and the second lapping process have the same configuration, but it is preferable to perform polishing using different polishing machines prepared exclusively for the respective processes. This is because the dedicated diamond pellets are pasted, so that the replacement is a large-scale operation, and complicated operations such as resetting the polishing conditions are required, resulting in a reduction in manufacturing efficiency.

<Chemical strengthening process>
Following the second lapping step, a compressive stress layer is formed on the surface of the glass substrate precursor as a chemical strengthening step. Specific examples include a method of immersing a glass base plate in a chemical strengthening treatment liquid. By this method, a compressive stress layer can be formed on the surface of the glass base plate, for example, in a region of 5 μm from the glass base plate surface. And by forming a compressive stress layer, impact resistance, vibration resistance, heat resistance, etc. can be improved.

  In other words, by immersing the glass base plate in the heated chemical strengthening treatment liquid, alkali metal ions such as lithium ions and sodium ions contained in the glass base plate are converted into alkali metal ions such as potassium ions having a larger ion radius. This is performed by the ion exchange method for substitution. Due to the strain caused by the difference in ion radius, compressive stress is generated in the ion-exchanged region, and the surface of the glass base plate is strengthened.

  As the salt used in the treatment liquid in the chemical strengthening step, a known salt can be used. Examples of the salt include nitrate, carbonate, sulfate and the like. Further, ions to be ion-exchanged include sodium and potassium. Of these, potassium nitrate is the best. Since potassium nitrate has a low melting point, it is easy to handle, and ion exchange can be performed without variation by exchange of potassium ions.

In the chemical strengthening step, by immersing the glass substrate in a heated chemical strengthening solution, alkali metal ions such as lithium ions and sodium ions contained in the glass substrate are converted into alkali ions such as potassium ions having a larger ion radius. This is performed by the ion exchange method for substitution. Compressive stress is generated in the ion-exchanged region due to the distortion caused by the difference in ion radius, and the surface of the glass substrate is strengthened.

The chemical strengthening treatment liquid is heated to a temperature higher than the temperature at which the above components melt. On the other hand, when the heating temperature of the chemical strengthening treatment liquid is too high, the temperature of the glass substrate is excessively increased, and the glass substrate may be deformed. For this reason, the heating temperature of the chemical strengthening treatment liquid is preferably lower than the glass transition point (Tg) of the glass substrate, more preferably lower than the glass transition point −50 ° C.

<Chemical treatment process>
The manufacturing method of the glass substrate for HDD of this invention may be equipped with a chemical treatment process with hydrofluoric acid.

  Moreover, it is preferable that this chemical treatment process is performed before the 2nd chemical strengthening process mentioned later. Cracks on the surface of the glass substrate can be removed by a chemical treatment step using hydrofluoric acid, and the strength can be further increased.

<Outside diameter polishing process>
A plurality of glass substrates having been subjected to the above steps are stacked and stacked, and in this state, the outer peripheral surface is polished using an end surface polishing machine.

<Polishing process>
Next, a polishing process as a polishing process is performed.

  In the polishing process, the surface of the glass substrate is precisely finished, and the shape of the outer peripheral end of the main surface is polished to a predetermined shape. The polishing step may be one step, but two steps are preferable.

(First polishing process)
First, in the first polishing step, the surface roughness is improved and finally the shape of the present invention is efficiently improved so that the surface roughness finally required in the second polishing step can be efficiently obtained. Polishing can be obtained.

  The polishing method uses a polishing machine having the same configuration as the polishing machine used in the first and second lapping processes except that a pad and a polishing liquid are used instead of the diamond pellets and the grinding liquid used in the lapping process.

  The pad is preferably a hard pad having a hardness A of about 80 to 90, for example, urethane foam. When the pad hardness becomes soft due to heat generated by polishing, the shape change of the polished surface increases, so it is preferable to use a hard pad. The abrasive is preferably cerium oxide having a particle size of 0.6 μm to 2.5 μm and dispersed in water to form a slurry. The mixing ratio of water and abrasive is preferably about 1: 9 to 3: 7. The abrasive is preferably free abrasive. By polishing the main surface using loose abrasive grains, the smoothness of the main surface of the glass substrate can be improved.

The weight applied to the glass substrate by the surface plate is preferably 90 g / cm ² to 110 g / cm ² . The load applied to the glass substrate by the surface plate greatly affects the shape of the outer peripheral edge. As the weight is increased, the inner side of the outer peripheral end portion tends to decrease and increase toward the outer side. Further, when the weight is reduced, the outer peripheral end portion tends to be close to a plane and the surface sagging increases. The weight can be determined while observing these trends.

  In order to improve the surface roughness, it is preferable that the rotation speed of the surface plate is 25 rpm to 50 rpm, and the rotation speed of the upper surface plate is 30% to 40% slower than the rotation speed of the lower surface plate.

  The polishing amount is preferably 30 to 40 μm depending on the above polishing conditions. If it is less than 30 μm, scratches and defects cannot be removed sufficiently. On the other hand, when the thickness exceeds 40 μm, the surface roughness can be in the range of 2 to 60 nm for Rmax and 2 to 4 nm for Ra, but the polishing is performed more than necessary and the production efficiency is lowered.

(Second polishing step)
The second polishing step is a step of further precisely polishing the surface of the glass substrate after the first polishing step. The pad used in the second polishing step is a soft pad having a hardness of about 65 to 80 (Asker-C) softer than the pad used in the first polishing step, and it is preferable to use, for example, urethane foam or suede. As the abrasive, cerium oxide or the like similar to that in the first polishing step can be used, but it is preferable to use an abrasive having a finer particle size and less variation in order to make the surface of the glass substrate smoother. An abrasive having an average particle diameter of 40 nm to 70 nm is dispersed in water to form a slurry and used as a polishing liquid. The mixing ratio of water and abrasive is preferably about 1: 9 to 3: 7.

The weight applied to the glass substrate by the surface plate is preferably 90 g / cm ² to 110 g / cm ² . The weight applied to the glass substrate by the surface plate greatly affects the shape of the outer peripheral edge as in the first polishing step, but the shape cannot be changed as efficiently as the first polishing step because the polishing rate is slow. The change in the shape of the outer peripheral end due to the increase / decrease of the weight is the same as in the first polishing step, and when the weight is increased, the inner side of the outer peripheral end tends to fall and rise outward. Further, when the weight is reduced, the outer peripheral end portion tends to be close to a plane and the surface sagging increases. In order to obtain the shape of the outer peripheral edge, the weight can be determined while observing such a tendency. The rotation speed of the surface plate is preferably 15 rpm to 35 rpm, and the rotation speed of the upper surface plate is preferably 30% to 40% slower than the rotation speed of the lower surface plate.

  As described above, the polishing conditions in the second polishing step are adjusted to obtain the shape of the outer peripheral edge, and the surface roughness is set to the range of Rmax from 2 nm to 6 nm and Ra from 0.2 nm to 0.4 nm. be able to.

  The polishing amount is preferably 2 to 5 μm. When the polishing amount is within this range, minute defects such as minute roughness and undulation generated on the surface and minute scratches generated in the process so far can be efficiently removed.

<Washing process>
The cleaning step is a step of cleaning the glass base plate that has been subjected to the rough polishing step.

  The glass base plate after the rough polishing by the rough polishing step is preferably cleaned by a cleaning step. The washing process is not particularly limited. Specifically, for example, the following washing steps are mentioned.

  First, the glass base plate is washed with an alkaline detergent having a pH of 13 or more, and the glass base plate is rinsed. Next, the glass base plate is washed with an acid detergent having a pH of 1 or less, and the glass base plate is rinsed. Moreover, it is preferable to use a rinse tank after each washing. In some cases, a surfactant, a dispersing agent, a chelating agent, a reducing material, and the like may be added to these detergents. Moreover, it is preferable to apply an ultrasonic wave to each washing tank and to use deaerated water for each detergent. Finally, the glass base plate is taken out, rinsed with pure water, and IPA dried.

The glass substrate after the rough polishing is cleaned so that the amount of cerium oxide on the surface of the glass substrate is 0.125 ng / cm ² or less. When the amount of cerium oxide on the surface of the glass base plate is too large, there is a tendency that the flatness of the glass base plate cannot be improved.

<Inspection process>
In the inspection process, inspections such as scratches, cracks and adhesion of foreign substances are performed.

  The glass substrate judged to be a non-defective product in the inspection process is stored in a glass substrate storage cassette and vacuum packed in a clean environment so that no foreign matter adheres to the surface. Shipped.

  Next, a magnetic recording medium using the glass substrate produced as described above will be described.

  Hereinafter, a magnetic recording medium will be described with reference to the drawings.

  FIG. 2 is a perspective view of a magnetic disk as an example of a magnetic recording medium. In the magnetic disk D, a magnetic film 2 is directly formed on the surface of a circular glass substrate 1 for an information recording medium. 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 to 1.2 μm, the film thickness by sputtering is about 0.04 to 0.08 μm, and the film thickness by electroless plating is 0.05 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 a conventionally known material can be used. However, in order to obtain a high coercive force, Ni having a 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. Addition to the above magnetic material, ferrite, iron - rare-earth or be in a non-magnetic film made of _{SiO 2, BN Fe, Co,} FeCo, etc. granular structure magnetic particles are dispersed, such CoNiPt 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 the Cr layer, and then colloidal silica fine particles are dispersed and applied, and then baked to form a silicon dioxide (SiO ₂ ) layer. It may be formed.

  By using the magnetic recording medium based on the glass substrate for information recording medium of the present invention obtained as described above, the operation of the magnetic head during high-speed rotation can be stabilized.

  The glass substrate for an information recording medium of the present invention is not limited to a magnetic recording medium, and can be used for a magneto-optical disk or an optical disk.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

  Using a 2.5-inch aluminosilicate glass, the steps described in the following examples or comparative examples were applied to produce a glass substrate. The plate thickness of the glass substrate was adjusted so that the thickness of the substrate was 0.8 mm after the surface polishing 2.

<Example 1>
After applying the coring process to the aluminosilicate glass, the inner and outer diameter precision machining process, the inner diameter polishing process, the first lapping process, the second lapping process, the chemical strengthening process, the outer diameter polishing process, the first polishing process, the first The glass substrate was manufactured in the order of 2 polishing steps.

  In the chemical strengthening step, the substrate was immersed for 2 hours in a treatment solution in which a salt prepared by mixing potassium nitrate and sodium nitrate in a ratio of 1: 1 was heated to 450 ° C. and melted.

  Further, 20 μm of the outer peripheral compressive stress layer was removed in the outer diameter polishing step.

  The main surface polishing was performed in two stages. In the first polishing step, the main surface was polished with cerium oxide with a removal allowance of 40 μm, and the stress layer on the main surface was removed. In the second polishing step, polishing was performed with a particle size of colloidal silica of 20 nm to finish the roughness of the substrate. The machining allowance was 5 μm.

<Comparative example 1>
After applying the coring process to the aluminosilicate glass, the inner and outer diameter precision machining process, the inner diameter polishing process, the first lapping process, the second lapping process, the outer diameter polishing process, the chemical strengthening process, the first polishing process, the first The glass substrate was manufactured in the order of 2 polishing steps.

  In the chemical strengthening step, the substrate was immersed for 20 minutes in a processing solution in which a salt prepared by mixing potassium nitrate and sodium nitrate in a ratio of 1: 1 was heated to 450 ° C.

  The main surface polishing was performed in two stages. In the first polishing process, the main surface was polished with cerium oxide with a removal of 30 μm, and the stress layer on the main surface was removed. In the second polishing step, polishing was performed with a particle size of colloidal silica of 20 nm to finish the roughness of the substrate. The machining allowance was 5 μm.

<Comparative example 2>
After applying the coring process to the aluminosilicate glass, the inner and outer diameter precision machining process, the first lapping process, the second lapping process, the outer diameter polishing process, the chemical strengthening process, the inner diameter polishing process, the first polishing process, the first The glass substrate was manufactured in the order of 2 polishing steps.

  In the chemical strengthening step, the substrate was immersed for 3 hours in a treatment solution obtained by heating a salt prepared by mixing potassium nitrate and sodium nitrate in a ratio of 1: 1 to 450 ° C.

  Also, 20 μm of the inner compressive stress layer was removed in the inner diameter polishing step.

  The main surface polishing was performed in two stages. In the first polishing step, the main surface was polished with cerium oxide with a removal allowance of 40 μm, and the stress layer on the main surface was removed. In the second polishing step, polishing was performed with a particle size of colloidal silica of 20 nm to finish the roughness of the substrate. The machining allowance was 5 μm.

<Comparative Example 3>
After applying the coring process to the aluminosilicate glass, the inner and outer diameter precision machining process, the inner diameter polishing process, the first lapping process, the second lapping process, the outer diameter polishing process, the first polishing process, the second polishing process, The glass substrate was manufactured in the order of the chemical strengthening process.

  The main surface polishing was performed in two stages. In the first polishing step, the main surface was polished with cerium oxide with a removal allowance of 40 μm, and the stress layer on the main surface was removed. In the second polishing step, polishing was performed with a particle size of colloidal silica of 20 nm to finish the roughness of the substrate. The machining allowance was 5 μm.

  In the chemical strengthening step, the substrate was immersed for 3 hours in a treatment solution obtained by heating a salt prepared by mixing potassium nitrate and sodium nitrate in a ratio of 1: 1 to 450 ° C.

<Comparative example 4>
After applying the coring process to the aluminosilicate glass, the inner and outer diameter precision machining process, the inner diameter polishing process, the first lapping process, the second lapping process, the chemical strengthening process, the outer diameter polishing process, the first polishing process, the first The glass substrate was manufactured in the order of 2 polishing steps.

  In the chemical strengthening step, the substrate was immersed for 3 hours in a treatment solution obtained by heating a salt prepared by mixing potassium nitrate and sodium nitrate in a ratio of 1: 1 to 450 ° C.

  Further, the outer diameter stress layer was all removed by outer diameter polishing.

  The main surface polishing was performed in two stages. In the first polishing step, the main surface was polished with cerium oxide with a removal allowance of 40 μm, and the stress layer on the main surface was removed. In the second polishing step, polishing was performed with a particle size of colloidal silica of 20 nm to finish the roughness of the substrate. The machining allowance was 5 μm.

<Comparative Example 5>
After applying the coring process to the aluminosilicate glass, the inner and outer diameter precision machining process, the inner diameter polishing process, the first lapping process, the second lapping process, the outer diameter polishing process, the chemical strengthening process, the first polishing process, the first The glass substrate was manufactured in the order of 2 polishing steps.

  In the chemical strengthening step, the substrate was immersed for 3 hours in a treatment solution obtained by heating a salt prepared by mixing potassium nitrate and sodium nitrate in a ratio of 1: 1 to 450 ° C.

  The main surface polishing was performed in two stages. In the first polishing step, the main surface was polished with a removal of 15 μm using cerium oxide, and the stress layer on the main surface was removed. In the second polishing step, polishing was performed with a particle size of colloidal silica of 20 nm to finish the roughness of the substrate. The machining allowance was 5 μm.

(Measurement of compressive stress layer)
The compressive stress layer was measured using a polarimeter.

(Smoothness evaluation)
The smoothness was evaluated as follows by measuring the surface roughness Ra (256 × 256 scan on 1 × 1 μm square). Evaluated by. The apparatus used was a Veeco Dimension Icon.

  The measurement part measured the main surface inside 5 mm from the outer peripheral end part.

◎: Less than 2.0 mm ○: 2.0 mm or more and less than 2.2 mm ×: 2.2 mm or more

(Drop impact resistance test)
Each substrate was formed into a film and then incorporated into a hard disk drive to conduct an impact resistance test. In this cracking test, the substrate was assembled in a drive and dropped to perform a test while changing the load, and the set value of the load at which the substrate was not cracked was measured.

(Outer periphery GA value evaluation)
A magnetic film was formed on the magnetic disk glass substrate produced in each example and each comparative example, and the media was prepared and then mounted on a GA tester. The head flying stability (glide avalan value (GA value)) was measured. GA value is measured by rotating the media as if it were a drive, and the head gradually falls on it, and the height at which the head floating becomes unstable is the GA value. The value is evaluated as follows: did.

  The rotation speed was 7200 rpm. The GA value at this time was measured at the r32 point. r32 is a point 32 mm from the center of the substrate. By measuring the GA value of r32, the influence of the flatness in the vicinity of the outer end can be understood. The results are shown in the “GA value” column of Table 1. The lower the GA value, the better the head floating stability, and the higher the flatness and smoothness of the magnetic disk glass substrate.

A: Less than 3.0 mm O: 3.0 mm or more and less than 3.5 mm X: 3.5 mm or more Test results of Example 1 and Comparative Examples 1 to 4 are shown in Table 1.

  As is apparent from the results in Table 1, Example 1 was manufactured so that the depth of the compressive stress layer increased in the order of the inner end portion, the outer end portion, and the main surface portion. And the glass substrate for HDD excellent in the smoothness of the center part was able to be obtained. In Comparative Example 1, since the stress layer depth at the inner end portion and the outer diameter portion is small and the same depth, the drop impact resistance is insufficient. Moreover, since the compressive-stress layer of the inner end part was larger than the outer end part, the comparative example 2 was inferior to the smoothness of an outer peripheral part, and resulted in inferior impact resistance compared with Example 1. Moreover, since the comparative example 3 which provided the compressive-stress layer uniformly was not processed after chemical strengthening, it resulted in being inferior to the smoothness of an outer peripheral part and a center part. In Comparative Example 4, since all of the outer diameter compressive stress layer was removed, the outer diameter portion was weak against impact, so there was no problem with smoothness, but the result was inferior in impact resistance compared to Example 1. It was.

<Example 2-1>
After applying the coring process to the aluminosilicate glass, the inner / outer diameter precision machining process, inner diameter polishing process, chemical strengthening process, first lapping process, second lapping process, outer diameter polishing process, chemical strengthening process (second time ), A glass substrate was manufactured in the order of the first polishing step and the second polishing step.

  In the chemical strengthening step, the substrate was immersed for 3 hours in a treatment solution obtained by heating a salt prepared by mixing potassium nitrate and sodium nitrate in a ratio of 1: 1 to 450 ° C. The first chemical strengthening step and the second chemical strengthening step were performed under the same conditions.

  Further, 30 μm of the outer peripheral compressive stress layer was removed in the outer diameter polishing step.

  The main surface polishing was performed in two stages. In the first polishing step, the main surface was polished with cerium oxide with a removal allowance of 40 μm, and the stress layer on the main surface was removed. In the second polishing step, polishing was performed with a particle size of colloidal silica of 20 nm to finish the roughness of the substrate. The machining allowance was 5 μm.

<Example 2-2>
After applying the coring process to the aluminosilicate glass, the inner and outer diameter precision machining process, the inner diameter polishing process, the first lapping process, the second lapping process, the chemical strengthening process, the outer diameter polishing process, the first polishing process, the first The glass substrate was manufactured in the order of 2 polishing steps.

  In the chemical strengthening step, the substrate was immersed for 2 hours in a treatment solution in which a salt prepared by mixing potassium nitrate and sodium nitrate in a ratio of 1: 1 was heated to 450 ° C. and melted.

  Further, the outer peripheral compressive stress layer was removed by 45 μm in the outer diameter polishing step.

  The main surface polishing was performed in two stages. In the first polishing step, the main surface was polished with cerium oxide with a removal allowance of 40 μm, and the stress layer on the main surface was removed. In the second polishing step, polishing was performed with a particle size of colloidal silica of 20 nm to finish the roughness of the substrate. The machining allowance was 5 μm.

  Since Examples 2-1 and 2-2 were designed and manufactured so that the depth of the compressive stress layer was increased in the order of the inner end portion, the outer end portion, and the main surface portion, the impact resistance was excellent. The glass substrate for HDD excellent in the smoothness of the outer periphery and the center part was able to be obtained.

DESCRIPTION OF SYMBOLS 1 Glass substrate precursor 2 Magnetic film 5 Inner hole 7a Front main surface 7b Back main surface 10t Outer peripheral end surface 20t Inner peripheral end surface D Magnetic disk

Claims (3)

A glass substrate for HDD having a central hole, to which a compressive stress layer is applied by a chemical strengthening process,
When the depth of the compressive stress layer in the inner end portion, outer end portion and main surface portion of the glass substrate for HDD is x (μm), y (μm) and z (μm), respectively, x> y ≧ z The glass substrate for HDD characterized by satisfy | filling conditions. The glass substrate for HDD according to claim 1 , wherein the drop impact resistance is 1100 to 1300G . The glass substrate for HDD according to claim 1 or 2, wherein the surface roughness Ra is less than 2.2 mm.

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