JP2009076167A - Method of manufacturing glass substrate for information recording medium, glass substrate for information recording medium and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of efficiently manufacturing a glass substrate for information recording medium, which has high smoothness, to provide the glass substrate for information recording medium manufactured by the method, and to provide an information recording medium using the glass substrate for information recording medium. <P>SOLUTION: As for the surface of the glass substrate after a polishing process, an arithmetic average roughness Ra is ≤0.2 nm, a waviness Wa is ≤0.5 nm and a fine waviness μWa is ≤0.2 nm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  Conventionally, there is a magnetic disk as an information recording medium used for a computer or the like. As a magnetic disk substrate, an aluminum substrate has been generally used. However, in recent years, with the demand for a reduction in the flying height of the magnetic head for improving the recording density, the surface smoothness is superior to that of an aluminum substrate and the surface defects are few, so that the flying height of the magnetic head can be reduced. The proportion of using glass substrates as magnetic disk substrates is increasing.

  Such a glass substrate for an information recording medium such as a magnetic disk is manufactured by subjecting a glass substrate called a blank material to polishing. As for a glass substrate (blank material), a method of manufacturing by press molding, a method of cutting and manufacturing a plate glass manufactured by a float method, and the like are known. If the glass substrate is cut into a certain shape, the surface has large irregularities, and it is necessary to polish the surface. Also, a technique for polishing with higher accuracy is required because of the demand for higher density.

In Patent Document 1, the outer surface of the magnetic disk molding glass substrate other than the upper and lower main surfaces is a molding free surface, thereby reducing the number of processing steps, suppressing the generation of foreign matters, and the average surface roughness of the main surface. A processing method with good smoothness has been proposed by setting Ra to 0.5 nm or less, maximum height Ry to 5.0 nm or less, microwaviness Wa to 0.5 nm or less, and flatness to 3 μm or less.
Japanese Patent Laid-Open No. 2002-100025

  However, even if the technique proposed in Patent Document 1 is used, a glass having a very high level of smoothness that is required in response to the recent demand for reduction in the flying height of the magnetic head for improving the recording density. It is very difficult to manufacture the substrate efficiently, and when the produced magnetic disk is mounted, read / write failure occurs due to insufficient smoothness.

  The present invention has been made in view of the technical problems as described above, and an object of the present invention is to provide a method for producing a glass substrate for an information recording medium that can be produced efficiently and with high smoothness. It is providing the glass substrate for information recording media manufactured by the method, and the magnetic recording medium using the glass substrate for information recording media.

  In order to solve the above problems, the present invention has the following features.

1.
In the manufacturing method of the glass substrate for information recording media which has the grinding | polishing process of grind | polishing the surface of a glass substrate,
Information recording characterized in that arithmetic mean roughness Ra of the surface of the glass substrate after the polishing step is 0.2 nm or less, waviness Wa is 0.5 nm or less, and microwaviness μWa is 0.2 nm or less. A method for producing a glass substrate for a medium.

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

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

  According to the present invention, the arithmetic average roughness Ra of the surface of the glass substrate after the polishing step is 0.2 nm or less, the waviness Wa is 0.5 nm or less, and the microwaviness μWa is 0.2 nm. Therefore, it is possible to provide a method for manufacturing a glass substrate for an information recording medium that can be manufactured efficiently and with high smoothness. In addition, it is possible to provide a glass substrate for an information recording medium that can respond to a request for reducing the flying height of the magnetic head by the manufacturing method and a magnetic recording medium using the glass substrate for an information recording medium.

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

  FIG. 1 shows the overall configuration of a glass substrate for information recording medium (hereinafter also referred to as a glass substrate) 1 according to the present invention. As shown in FIG. 1, the glass substrate 1 has a donut-shaped disk shape with a hole 5 formed in the center. 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. 2 is a diagram showing an example of a magnetic recording medium D (also referred to as a magnetic disk) having the magnetic film 2 on the front main surface 7a of the glass substrate 1 shown in FIG. The magnetic film 2 can also be provided on the back main surface 7b.

  FIG. 3 shows a manufacturing process diagram of an embodiment of a method for manufacturing a glass substrate for an information recording medium according to the present invention.

  In the present embodiment, in the polishing process, which is the final polishing process, the arithmetic average roughness Ra of the surface of the glass substrate after the polishing process is 0.2 nm or less, the waviness Wa is 0.5 nm or less, and the microwaviness μWa Is 0.2 nm.

  An enlarged view of the cross section of the glass substrate is shown in FIGS. A solid line 11 in FIG. 4A is a measurement cross-sectional curve showing the surface shape of the glass substrate. A broken line 12 is a waviness curve representing the waviness of the surface of the glass substrate. FIG. 4B is an enlarged view of a part of FIG. 4A, and shows the minute undulation 13 generated on the undulation curve 12.

  The waviness height Wa of the waviness curve 12 in FIG. 4A is measured using a multi-function disk interferometer (manufactured by Optiflat Phase Shift Technology. Inc.), and the entire surface of the glass substrate is measured. The measurement principle is a method of measuring a subtle shape change of the surface by irradiating the surface of the glass substrate with white light and measuring an intensity change of interference between the reference light and the measurement light having different phases. The obtained measurement data was cut off with a period of 5 mm or more to obtain a waviness Wa.

  The height μWa of the micro undulation generated on the undulation of FIG. 4B is measured by a three-dimensional surface structure analysis microscope (manufactured by ZYGO; trade name NEWVIEW 200). The wavelength was measured in the range of 30 to 200 μm, 1 μm square was measured at four locations, and the average value was defined as microwaviness μWa.

  A surface roughness is generated on the curve of the minute waviness. The surface roughness is defined in JIS B0601 as the arithmetic average roughness Ra of the surface, and can be measured by an atomic force microscope (AFM), and is defined as the arithmetic average roughness Ra.

  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.

(Manufacturing process of glass substrate for information recording medium)
The manufacturing process of the glass substrate for information recording media will be described in detail with reference to the manufacturing process diagram of FIG.

  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.

  First, a glass material is melted (glass melting step), molten glass is poured into a lower mold, and press molding is performed with an upper mold to obtain a disk-shaped glass substrate precursor (press molding process). 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.

The material of the glass substrate is not particularly limited as long as it can be chemically strengthened by ion exchange. For example, soda lime glass mainly composed of SiO ₂ , Na ₂ O, CaO; aluminosilicate glass mainly composed of SiO ₂ , Al ₂ O ₃ , R ₂ O (R = K, Na, Li); 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) Etc. can be used. Among these, aluminosilicate glass and borosilicate glass are particularly preferable because they are excellent in impact resistance and vibration resistance.

  The press-molded glass substrate precursor is drilled in the center with a core drill or the like having a diamond grindstone or the like in the cutter (coring process).

  Next, 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 (first lapping step).

  Next, the inner and outer diameters are processed by grinding the outer peripheral end surface and the inner peripheral end surface of the glass substrate with, for example, a grinding wheel such as a drum-shaped diamond (inner / outer diameter processing step).

  Next, on the inner peripheral end surface of the glass substrate, the corners of the chamfered portion are curved by brush polishing using a polishing liquid, and fine scratches and the like are removed (inner peripheral end surface processing step).

  Next, both surfaces of the glass substrate are polished again to finely adjust the parallelism, flatness and thickness of the glass substrate (second lapping step).

  Then, the outer peripheral end surface of the glass substrate is subjected to brush polishing using a polishing liquid so that the corner portion of the chamfered portion is curved, and fine scratches and the like are removed (outer peripheral end surface processing step).

  The order from the first lapping step after the coring processing to the outer peripheral end surface processing step is not limited to that shown in FIG. 3 and can be changed as appropriate according to the situation. For example, the lapping process may be performed first, and then the inner / outer diameter machining process, the inner circumference, and the outer circumference end face machining process may be performed. Further, after the first lapping step and the inner / outer diameter machining step, a second lapping step, an inner circumference and an outer circumference end face machining step may be performed.

  A polishing machine that polishes the glass substrate in the first and second lapping steps will be described. As the polishing machine, 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. The diamond pellet can be substituted by a resin sheet in which diamond abrasive grains are embedded. 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 with respect to the center of rotation. In such an operating polishing machine, the glass substrate can be polished by supplying a grinding 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 wrapping steps is preferably 600 kg / m ² to 1200 kg / m ² . Further, the rotation speed of the surface plate is preferably about 10 to 30 rpm, and the rotation speed of the upper surface plate is preferably about 30 to 40% slower than the lower surface rotation speed. 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.

  Upon completion of the second lapping step, 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 μm to 4 μm for Rmax and about 0.1 μm 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 about # 800 mesh to # 1200 mesh coarser than # 1300 mesh to # 2200 mesh used in the second wrapping. The surface roughness at the time when the first lapping step is completed is preferably such that Rmax is 4 μm to 8 μm and Ra is about 0.3 μm to 0.8 μm.

  The inner peripheral and outer peripheral end faces of the glass substrate are polished by brush polishing in the inner peripheral and outer peripheral end face processing steps. The brush is preferably made of nylon, polypropylene or the like having a diameter of about 0.2 to 0.3 mm. The polishing liquid is preferably cerium oxide having a particle size of about several μm. As a result of brush polishing, it is preferable that the surface roughness of the inner and outer end faces is such that Rmax is 0.2 μm to 0.4 μm and Ra is about 0.02 μm to 0.04 μm. The shape of the end surface of the glass substrate that has undergone the inner and outer diameter processing steps and the inner and outer peripheral end surface processing steps is such that the corner formed by the main surface and the end surface is removed, and the position is about 0.2 mm to 0.5 mm from the outer peripheral end surface. From the main surface.

  Here, Ra (center line average roughness) and Rmax (maximum height) are defined in JIS B0601: 2001. These can be measured by an atomic force microscope (AFM) or the like. These rules and measurement methods also apply to Ra and Rmax described below.

  In the above example, the diamond pellet and the grinding liquid are used when polishing the glass substrate. However, it is also possible to apply a polishing method by attaching a pad to the polishing surface of the upper and lower surface plates and supplying the polishing liquid. . 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 a pad made of hard velor, urethane foam, pitch-containing suede, etc., and examples of the soft pad include a pad 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.

  Following the outer end surface polishing step, an annealing step is performed. In the annealing step, the glass substrate is placed in an electric heating furnace and held at a temperature of 200 ° C. or higher and 400 ° C. or lower for 20 to 120 minutes. The rate of temperature increase and the rate of temperature decrease are not particularly specified, but it is preferable that the temperature is raised to a predetermined temperature in about 10 to 30 minutes and the cooling is performed over a period of about 10 to 30 minutes. By this annealing step, the stress strain generated in the glass substrate in the previous processing steps can be released. In addition to the air, the annealing step is preferably performed in an oil such as silicone oil that hardly deteriorates at an annealing temperature, in an inert gas such as argon gas or helium gas, or in nitrogen gas. When annealing is performed in such an atmosphere, ionized substances do not enter the glass substrate surface, so that the flatness of the glass substrate surface can be maintained.

  Next, a polishing process as a polishing process is performed.

  In the polishing step, the surface of the glass substrate is polished so as to obtain the surface shape of the present invention. The polishing step may be one step, but two steps are preferable. By performing the polishing process after the annealing process, stress strain is released inside the glass, cracks are not generated during the polishing process, and the incidence of defective products is reduced.

  First, in the first polishing step, the surface roughness is improved and the shape of the present invention is finally 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 suede 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 70 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 used in the form of a slurry by dispersing cerium oxide or the like having a particle size of 0.2 μm to 1.5 μm in water. The mixing ratio of water and abrasive is preferably about 1: 9 to 3: 7.

Weighted on the glass substrate by platen, it can be adjusted arbitrarily, preferably the 1100 kg / m ² from 900 kg / m ² in terms of productivity. 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.

  Moreover, in order to improve surface roughness, the rotational speed of the surface plate can be arbitrarily adjusted, but from the viewpoint of productivity, the rotational speed of the upper surface plate is set to 30% from the lower surface plate rotational speed from 25 rpm to 50 rpm. It is preferable to slow down by 40%.

  The polishing amount is preferably 30 μm 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 polishing is performed more than necessary, and the production efficiency is lowered.

  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 size of 10 nm to 50 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 can be arbitrarily adjusted, but 900 kg / m ² to 1100 kg / m ² is preferable from the viewpoint of productivity. 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. Although the rotation speed of the surface plate can be adjusted arbitrarily, it is preferable to set the rotation speed of the upper surface plate to 30 to 40% slower than the rotation speed of the lower surface plate, from the viewpoint of productivity.

  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.

  By adjusting the polishing conditions in the first and second polishing steps as described above, the arithmetic average roughness Ra of the surface of the glass substrate of the present invention is 0.2 nm or less, the waviness Wa is 0.5 nm or less, and further minute A glass substrate for information recording media having a waviness μWa of 0.2 nm can be obtained.

  Further, it can be said that the smaller the arithmetic average roughness Ra, the waviness Wa and the minute waviness μWa are, the better from the viewpoint of smoothness.

  After completion of the second polishing step, the glass substrate is cleaned and inspected to complete the information recording medium glass substrate.

  In addition, in the manufacturing method of the glass substrate for information recording media, you may have various processes other than the above. For example, it has a heat shock process for confirming the reliability of the strength of the glass substrate, a cleaning process for removing foreign substances such as abrasives and chemical strengthening treatment liquid remaining on the surface of the glass substrate, various inspection / evaluation processes, etc. May be.

  Further, in the second polishing step, it is preferable not to use the polishing machine used in the first polishing process as it is, but to perform polishing using another polishing machine having the same configuration but prepared for each process. . This is because, if the polishing machine used in the first polishing process is used as it is, the polishing accuracy in the second polishing process decreases due to the abrasive remaining in the first polishing process, and the polishing conditions are reset. This is because work is required and manufacturing efficiency is lowered.

  Next, the magnetic recording medium provided on the glass substrate for information recording medium 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 μm to 1.2 μm, the film thickness by sputtering is about 0.04 μm to 0.08 μm, and the film thickness by electroless plating is 0.05 μm to 0.1 μm. From the viewpoint of thinning and densification, film formation by sputtering and electroless plating is preferable.

The magnetic material used for the magnetic film is not particularly limited, and 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 a Cr layer, and then colloidal silica fine particles are dispersed and applied, followed by baking to form a silicon dioxide (SiO ₂ ) layer. It may be formed.

  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 substrates and magnetic disks of Examples 1 to 4 and Comparative Examples 1 to 3 were produced as follows.
(Production of glass substrate)
Aluminosilicate glass (Tg: 500 ° C.) was used as a glass material, and a molten glass was press-molded to produce a blank material. A glass substrate having an outer diameter of 65 mm and an inner diameter of 20 mm was obtained through an inner and outer peripheral processing step and a lapping step. The thickness of the glass substrate was 0.64 mm.
(Annealing process)
As an annealing process, an electric heating furnace was used in an air atmosphere, and 100 glass substrates were respectively produced at the annealing temperature and annealing time shown in Table 1. The temperature rising time from room temperature was 30 minutes, and the temperature lowering time to room temperature was 1 hour.
(Polishing process)
As the first polishing process, a urethane pad manufactured by Nitta Haas was used, and cerium oxide was used as the abrasive.

  As the second polishing step, a suede pad manufactured by FILWEL was used, and cerium oxide and colloidal silica were used as the abrasive.

As polishing conditions for the first polishing step and the second polishing step, the hardness of the pad (hardness A, Asker-C), the particle size of the abrasive (μm, nm), the rotation speed (rpm), and the load (kg / m ² ) Table 1 shows these conditions.
(Washing process)
As a cleaning process, brush scrubbing with a roll scrubbing machine and cup scrubbing machine was performed, followed by cleaning with an ultrasonic cleaner.
(Measurement of surface roughness, waviness and micro waviness)
Arithmetic average roughness of the surface of the glass substrate produced using an atomic force microscope, an interferometer for multi-functional disc (manufactured by Optiflat Phase Shift Technology. Inc.) and a three-dimensional surface structure analysis microscope (manufactured by ZYGO; trade name NEWVIEW 200) The thickness Ra, the waviness Wa and the minute waviness μWa were measured. The measurement results are shown in Table 1.
(Production of magnetic disk)
On the surface of the obtained glass substrate, magnetic particles CoPt were sputtered to form a 0.05 μm magnetic film, thereby producing an air conditioned disk.
(Evaluation of magnetic disk)
The produced magnetic disks of Examples 1 to 4 and Comparative Examples 1 to 3 were each mounted on a magnetic disk device, and the occurrence of read / write failure when reading and writing was evaluated. In the case of x, the case where no reading / writing failure occurred at all was marked as ◯. The evaluation results are shown in Table 1.

  Looking at Examples 1 and 2 and Comparative Example 1 in Table 1, when the waviness Wa is 0.5 nm, the minute waviness μWa is 0.2 nm, and the arithmetic average roughness Ra of the surface exceeds 0.2 nm, read / write failure Has occurred. Further, when Examples 1 to 3 and Comparative Example 2 are compared, when the waviness Wa is 0.5 nm, the arithmetic average roughness Ra of the surface is 0.2 nm, and the fine waviness μWa exceeds 0.2 nm, read / write failure occurs. is doing. Further, when Examples 1 to 4 and Comparative Example 3 are compared, if the microwaviness μWa is 0.2 nm, the arithmetic average roughness Ra of the surface is 0.2 nm, and the waviness Wa exceeds 0.5 nm, read / write failure occurs. Yes. Thus, the arithmetic mean roughness Ra of the surface of the glass substrate after the polishing step of the present invention is 0.2 nm or less, the waviness Wa is 0.5 nm or less, and the microwaviness μWa is 0.2 nm. It can be seen that it is possible to manufacture a glass substrate for an information recording medium that does not cause read / write defects. In addition, it has been found that the read / write failure is caused by the jump of the head due to the unevenness of the glass substrate surface. From the above, according to the present invention, it is possible to provide a method for producing a glass substrate for information recording medium that can be produced with high smoothness and efficiency, and read and write using the glass substrate for information recording medium by the production method. It can be seen that a magnetic disk free from defects can be provided.

It is a figure which shows the whole structure of the glass substrate for information recording media. 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 information recording media. It is a manufacturing process figure explaining the process in manufacture of the glass substrate for information recording media. It is an expanded sectional view of the board | substrate for demonstrating the wave | undulation and micro wave | undulation of a glass substrate surface, and surface roughness.

Explanation of symbols

1 Glass substrate for information recording media (glass substrate)
2 magnetic film 5 hole 7a front main surface 7b back main surface 10t outer peripheral end surface 11 measurement cross-section curve 12 waviness curve 13 micro waviness curve 20t inner peripheral end surface D magnetic disk

Claims (3)

In the manufacturing method of the glass substrate for information recording media which has the grinding | polishing process of grind | polishing the surface of a glass substrate,
Information recording characterized in that arithmetic mean roughness Ra of the surface of the glass substrate after the polishing step is 0.2 nm or less, waviness Wa is 0.5 nm or less, and microwaviness μWa is 0.2 nm or less. A method for producing a glass substrate for a medium. A glass substrate for an information recording medium manufactured by the method for manufacturing a glass substrate for an information recording medium according to claim 1. A magnetic recording medium comprising a magnetic film on the surface of the glass substrate for information recording medium according to claim 2.

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