JP2009087483A - Manufacturing method of 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 manufacturing method of a glass substrate for an information recording medium by which an unpolished part is eliminated, the generation of cracks and chips is eliminated in a short polishing time and surfaces of an inner peripheral end surface and an outer peripheral end surface can be efficiently made smooth, to provide the glass substrate for the information recording medium manufactured by the manufacturing method, and to provide a magnetic recording medium. <P>SOLUTION: In the manufacturing method of the glass substrate for the information recording medium having an end surface treatment step for polishing end surfaces of the glass substrate by using a polishing brush or a polishing pad and a polishing liquid, the polishing liquid contains a hydrogen fluoride based solvent. <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 front and back surfaces, the inner and outer peripheral surfaces, and the outer peripheral surface are uneven, and it is necessary to polish the surface. Is required.

In order to solve such a problem, in Patent Document 1 and Patent Document 2, as a method of efficiently and accurately polishing the surface of the inner and outer peripheral end surfaces of the glass substrate, a polishing brush is used in a state where a plurality of glass substrates are laminated. There has been proposed a polishing apparatus for polishing by rotating contact.
JP-A-11-28649 Japanese Patent Laid-Open No. 11-33886

  However, even in the methods described in Patent Document 1 and Patent Document 2, a portion where the polishing brush and the inner and outer peripheral end surfaces cannot contact with each other is generated, a polishing residue is generated, and the polishing time is as long as several tens of minutes. There was a problem that a yield occurred and the yield was poor.

  The present invention has been made in view of such problems, and has smooth polishing of the inner peripheral end surface and the outer peripheral end surface with no polishing residue, no cracking, and no occurrence of cracks. An object of the present invention is to provide a method for producing a glass substrate for information recording medium, a glass substrate for information recording medium produced by the production method, and a magnetic recording medium.

  Said subject is solved by the following structures.

1.
In the method for producing a glass substrate for an information recording medium, comprising an end face processing step of polishing the end face of the glass substrate using a polishing brush or a polishing pad and a polishing liquid,
The method for producing a glass substrate for an information recording medium, wherein the polishing liquid contains a hydrofluoric acid solvent.

2.
2. The method for producing a glass substrate for an information recording medium according to 1, wherein the hydrofluoric acid solvent has a concentration of hydrofluoric acid of 2 to 6% by mass.

3.
3. The method for producing a glass substrate for an information recording medium according to 2, wherein the hydrofluoric acid solvent contains sulfuric acid having a concentration of 5 to 10% by mass.

4).
A glass substrate for an information recording medium, which is produced by the production method according to any one of 1 to 3.

5).
5. A magnetic recording medium comprising a magnetic film on the surface of the glass substrate for information recording medium according to 4.

  According to the present invention, the polishing of the end face of the glass substrate is performed using a polishing liquid containing a polishing brush or a polishing pad and a hydrofluoric acid solvent, so that even a portion where the brush cannot be contacted due to the etching effect of hydrofluoric acid is polished. The surface state of the glass substrate end face having no residue and high smoothness can be produced in a short time. In addition, since it is not necessary to make the brush contact excessively and polish for a long time, there is no occurrence of cracks and cracks. Therefore, the manufacturing method of the glass substrate for information recording media which can smooth the surface state of an inner peripheral end surface and an outer peripheral end surface efficiently can be provided.

  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 (hereinafter also referred to as a magnetic disk) D provided with a 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 this embodiment, in the process of polishing the inner peripheral end face and the outer peripheral end face of the glass substrate, polishing is performed by rotating a polishing brush or a polishing pad in contact with a polishing liquid containing hydrofluoric acid. By polishing while applying a polishing liquid containing hydrofluoric acid in this way, compared to the conventional method of polishing the end face of a glass substrate using a fine abrasive material over a long period of time, hydrofluoric acid. The etching effect can be used, and end face polishing can be performed in a short time. Moreover, even if it is a location where polishing members, such as a brush, do not reach, a smooth glass end surface can be processed by slightly etching the surface. Furthermore, by increasing the polishing rate of the glass end face, it can be processed in a short time, and the chance of occurrence of cracks and cracks can be reduced.

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.
(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 press molding step, molten glass is poured into the lower mold and press molded with the 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 made in the center by grinding with a core drill or the like provided with a diamond grindstone or the like in the cutter part.
(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.
(Inner / outer diameter machining process)
Next, as the inner / outer diameter processing step, 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 a grinding wheel such as a drum-shaped diamond.
(Inner peripheral end face machining process)
After finishing the inner and outer diameter processing steps, the inner peripheral surface is then polished.

  FIG. 4 shows a schematic view of the inner peripheral end surface polishing machine 50. The inner peripheral end surface polishing machine 50 alternately stacks the spacers 3 and the glass substrates 1 one by one, and polishes the inner peripheral end surface of the laminate 4 as shown in FIG. The spacer 3 has an inner diameter slightly larger than the inner diameter of the glass substrate, and has an outer diameter slightly smaller than the outer diameter of the glass substrate.

  The material of the spacer 3 is preferably a resin having a specific gravity of 1 or less, and the thickness is not particularly limited, but a value slightly larger than the diameter of the brush used for polishing is preferable. For example, if the brush diameter is 0.2 mm, a thickness of about 0.3 mm is preferable.

  In the inner peripheral end face processing step, the inner periphery of the glass substrate 1 is polished using an inner peripheral end face polishing machine 50 as shown in FIG. The laminated body 4 polishes the inner periphery with the rotating brush 51 of the inner peripheral end surface polishing machine 50. The rotating brush 51 reciprocates up and down in order to polish the inner periphery of the glass substrate 1 while rotating. At this time, the polishing liquid 61 is supplied from the polishing nozzle 60.

  The polishing liquid 61 contains a hydrofluoric acid solvent, an additive, and an abrasive.

  The concentration of hydrofluoric acid in the hydrofluoric acid solvent is preferably 2 to 6% by mass. When the concentration of hydrofluoric acid is 2 to 6% by mass, the processing time is short due to the etching effect of hydrofluoric acid, and the smoothness of the surface and the accuracy of the outer diameter are also in a favorable range.

  As the solvent, an organic solvent such as IPA can be used in addition to water.

  Furthermore, it is preferable that sulfuric acid is added to the hydrofluoric acid solvent so that the concentration of sulfuric acid is 5 to 10% by mass. By doing in this way, surface smoothness and outer diameter dimensional accuracy can be further improved. This is presumably because the smoothness of the surface and the etching rate can be appropriately adjusted by adding sulfuric acid having a smaller etching effect to a hydrofluoric acid solvent having a strong etching effect.

  As the abrasive, cerium oxide having a particle size of about several μm is used, but other abrasives such as iron oxide, magnesium oxide, zirconium oxide, manganese oxide, and colloidal silica can also be used. As an average particle diameter of an abrasive | polishing agent, 1-4 micrometers is preferable. If it is less than 1 μm, the polishing agent has a weak force to grind the glass substrate, and polishing is often performed with the tip of the rotating brush in direct contact with the end surface of the glass substrate, so the chamfered shape of the glass substrate should be controlled. However, when the thickness exceeds 4 μm, the particle size of the abrasive is large, so that the surface roughness becomes large.

  As the additive, a small amount of a known dispersion stabilizer for obtaining the dispersion stability of the abrasive can be added and used.

  Each compounding ratio is preferably 10 to 50 parts by mass of the abrasive with respect to 100 parts by mass of the hydrofluoric acid solvent.

  As the bristles of the rotating brush 51, it is preferable to use nylon, polypropylene or the like of about φ0.2 to φ0.3 mm, but instead of nylon fiber, vinyl chloride fiber, pig hair, piano wire, stainless steel fiber, etc. It may be used. When using a polishing pad, for example, a soft polisher made of suede or velor, or a hard polisher such as hard velor, urethane foam, or pitch impregnated suede can be used.

  A preferable rotation speed of the rotary brush 51 is 1000 to 30000 rpm. The laminated body 4 may be fixed, or may be rotated in the direction opposite to the rotating brush 51. The rotating brush 51 may move up and down with rotation.

  The replenishment amount of the polishing liquid 61 may be determined as appropriate, but is preferably 5 to 200 ml / s. If the amount is too small, the effect of the polishing liquid 61 is reduced. If the amount is too large, the cost is increased and the cost is increased.

  Also, the polishing liquid 61 may be replenished from the side of the rotary brush 51 as shown in FIG. 4 and moved up and down to enter the inside of the laminate 4. An introduction pipe for the polishing liquid 61 may be provided inside the shaft so as to be ejected outside through the bristles of the brush.

In this way, the inner peripheral end face of the glass substrate is polished, so that there is no cracking, grinding, or polishing residue, and the surface roughness of the inner peripheral end face can be smoothed in a short time.
(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 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 lapping steps is preferably 60 g / cm ² to 120 g / cm 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.

  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 μm to 4 μm for Rmax and about 0.2 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 # 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 step is completed is preferably such that Rmax is 4 μm to 8 μm and Ra is about 0.4 μm 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 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.
(Outer peripheral end face machining process)
Next, as the outer peripheral end surface processing step, the outer peripheral end surface of the glass substrate is made into a curved surface with a corner portion of the chamfered portion by brush polishing using the polishing liquid 61, and fine scratches and the like are removed.

  FIG. 5 shows an outer peripheral end surface polishing machine 70. A laminated body 4 in which the spacers 3 and the glass substrates 1 are alternately stacked one by one is held in the outer peripheral end surface polishing machine 70. The spacer 3 has an outer diameter slightly smaller than the outer diameter of the glass substrate, and has a hole diameter slightly larger than the hole diameter of the glass substrate.

  As the material of the rotating brush 71, the polishing pad, and the spacer 3, the same materials as those used in the inner peripheral end face processing step can be used.

  In the outer peripheral end face processing step, the laminate 4 is held and rotated in a state of being laminated by the work shaft 41, and the outer circumference is polished by the rotating brush 71. At this time, the polishing liquid 61 is supplied from the polishing nozzle 60. The polishing liquid 61 is the same as that used in the inner peripheral end face machining step.

  A preferable rotation speed of the rotary brush 71 is 1000 to 30000 rpm. You may make it rotate the rotation direction of the laminated body 4 in the reverse direction to the rotating brush 51. FIG. The rotating brush 71 may move up and down with rotation.

  In this way, the polishing of the outer peripheral end face of the glass substrate is carried out, and there is no cracking, shaving or polishing residue, and the surface roughness of the outer peripheral end face can be smoothed in a short time.

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

  As a result of brush polishing on the inner and outer end faces of the glass substrate, 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. It is preferable to do this. The shape of the end surface of the glass substrate that has undergone the inner / outer diameter processing step 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, especially about 0.2 mm to 0.5 mm from the outer peripheral end surface. It will be in a state of sagging from the main surface from the position.

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.
(Chemical strengthening process)
Next to the outer peripheral end face processing step, as a chemical strengthening step, the glass substrate is immersed in a chemical strengthening solution to form a chemically strengthened layer on the glass substrate. By forming the chemical strengthening layer, impact resistance, vibration resistance, heat resistance and the like can be improved.

  In the chemical strengthening process, 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 replaced with alkali metal ions such as potassium ions having a larger ion radius. It is performed by the ion exchange method. 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.

  There is no restriction | limiting in particular in a chemical strengthening liquid, A well-known chemical strengthening liquid can be used. In general, a molten salt containing potassium ions or a molten salt containing potassium ions and sodium ions is generally used. Examples of the molten salt containing potassium ions and sodium ions include potassium and sodium nitrates, carbonates, sulfates, and mixed molten salts thereof. Among these, from the viewpoint that the melting point is low and deformation of the glass substrate can be prevented, it is preferable to use nitrate.

  The chemical strengthening 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 solution 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 solution is preferably lower than the glass transition point (Tg) of the glass substrate, and more preferably lower than the glass transition point −50 ° C.

  Prior to immersion in the chemical strengthening solution, the glass substrate is heated to a predetermined temperature before being immersed in the chemical strengthening solution in order to prevent generation of cracks and fine cracks due to thermal shock when immersed in the heated chemical strengthening solution. You may have the preheating process heated to.

  The thickness of the chemically strengthened layer is preferably in the range of about 5 μm to 15 μm in view of improving the strength of the glass substrate and shortening the time of the polishing process. When the thickness of the reinforcing layer is within this range, a glass substrate having good impact resistance, which is flatness and mechanical strength, can be obtained.

The shapes of the outer peripheral end portions of the front main surface 7a and the back main surface 7b after the chemical strengthening step are almost the same as those before the chemical strengthening step, and the above-mentioned chemical strengthening layer of about 5 μm to 15 μm is almost equal to the entire surface of the glass substrate. It will be in the state of being put on.
(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, 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 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 used in the form of a slurry by dispersing cerium oxide or the like having a particle size of 0.6 to 2.5 μm in water. 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 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 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 it exceeds 40 μm, the surface roughness can be in the range of Rmax from 2 nm to 60 nm and Ra from 2 nm to 4 nm.

  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.
(Cleaning and inspection process)
After completion of the second polishing process, 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 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, 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 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 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 1 to 9 and Comparative Example 1 were prepared and evaluated as follows.
(1) Melting and Pressing Process Aluminosilicate glass having a Tg of 480 ° C. was used as a glass material, and the molten glass was press-molded to produce a blank material (outer diameter 68 mm, thickness 1.3 mm).
(2) Coring step Next, a circular hole (diameter 18 mm) was opened in the center of the glass substrate using a cylindrical diamond grindstone.
(3) 1st lapping process Both surfaces of the glass substrate were grind | polished using the grinder (made by HAMAI).

As polishing conditions, diamond pellets of # 1000 mesh were used, the load was 100 g / cm ² , the upper platen was rotated at 30 rpm, and the lower platen was rotated at 10 rpm.

The thickness of the obtained glass substrate was 0.9 mm, and the surface roughness was Rmax of 1.5 μm and Ra of 1.0 μm.
(4) Inner / outer processing step Inner / outer diameter processing was performed with a drum-shaped diamond grindstone to obtain an inner diameter of 20 mm and an outer diameter of 65 mm.
(5) Inner peripheral end face processing step The glass substrate 1 and the spacer 3 obtained by finishing the inner and outer processing steps were alternately stacked one by one, and a laminate 4 composed of 100 glass substrates and 100 spacers was created. This laminated body 4 was set in the inner peripheral end surface polishing machine 50 of FIG. 4, and the inner peripheral end surface was polished. The spacer 3 at this time was made of polypropylene and had a thickness of 0.3 mm, an inner diameter of 21 mm, and an outer diameter of 64 mm.

  Nylon fibers having a diameter of 0.2 mm were used for the brush bristles of the polishing machine. The rotation speed of the rotating brush was 10,000 rpm. As the polishing liquid 61, one containing the hydrofluoric acid solvent of Examples 1 to 9 shown in Table 1 and one not containing the hydrofluoric acid solvent of Comparative Example 1 were prepared. Specifically, in Examples 1 to 4, water was used as a solvent and a hydrofluoric acid solvent having a predetermined concentration was used. Moreover, what added the sulfuric acid of Examples 5-9 added the sulfuric acid which becomes a predetermined density | concentration to the 4 mass% hydrofluoric acid aqueous solution, and made it the hydrofluoric acid type solvent.

  A dispersant was used as the additive, and cerium oxide having a particle size of 3 μm was used as the abrasive. Each compounding ratio was as follows.

Examples 1-9
Hydrofluoric acid solvent 100 parts by weight Abrasive 40 parts by weight Additive 1 part by weight Comparative Example 1
Water 100 parts by mass Polishing agent 40 parts by mass Additive 1 part by mass These were mixed in a mixer to obtain polishing liquid 61.

  The polishing liquid 61 was polished for 5 minutes while flowing 50 ml / sec.

The surface roughness of the inner peripheral end face of the obtained glass substrate was measured, and its Rmax and Ra are shown in Table 1.
(6) Second lapping step Next, both surfaces of the glass substrate were polished using a polishing machine (manufactured by HAMAI).

As polishing conditions, diamond pellets of # 1500 mesh were used, the load was 100 g / cm ² , the upper platen was rotated at 30 rpm, and the lower platen was rotated at 10 rpm.

As for the surface roughness of the obtained glass substrate, Rmax was 3 μm and Ra was 0.3 μm.
(7) Outer peripheral end surface processing step The glass substrate and spacer obtained by finishing the second lapping step were alternately stacked one by one to create a laminate composed of 100 glass substrates and 100 spacers. This laminated body was grind | polished the outer peripheral end surface using the outer peripheral end surface grinder 70 shown in FIG. The spacer used at this time was made of polypropylene and had a thickness of 0.3 mm, an inner diameter of 21 mm, and an outer diameter of 64 mm. Nylon fibers having a diameter of 0.2 mm were used for the brush bristles of the polishing machine. The polishing liquid 61 used was the same as the inner peripheral end face processing step, and Examples 1 to 9 and Comparative Example 1 shown in Table 1 were used. The rotating brush 71 was rotated at 10,000 rpm, and the polishing liquid 61 was polished for 5 minutes while flowing 50 ml / sec.

The surface roughness of the outer peripheral end face of the obtained glass substrate was measured, and its Rmax and Ra are shown in Table 1.
(8) Chemical strengthening step Next, a chemical strengthening step was performed by immersing the glass substrate in a chemical strengthening solution. As the chemical strengthening liquid, a mixed molten salt of potassium nitrate (KNO ₃ ) and sodium nitrate (NaNO ₃ ) was used. The mixing ratio was 1: 1 by mass ratio. The temperature of the chemical strengthening solution was 400 ° C. and the immersion time was 40 minutes.
(9) Polishing Step Next, as a first polishing step, a polishing machine (manufactured by HAMAI) was used, and urethane foam having a hardness A of 80 degrees was used for the pad. As the abrasive, cerium oxide having an average particle diameter of 1.5 μm was dispersed in water and used as a slurry. The mixing ratio of water and abrasive was 2: 8. The load was 100 g / cm ² , the upper platen was rotated at 30 rpm, and the lower platen was rotated at 10 rpm. The polishing amount was 30 μm.

  As for the surface roughness of the obtained glass substrate, Rmax was 30 nm and Ra was 3 nm.

Next, as a second polishing process, a polishing machine (manufactured by HAMAI) was used, and urethane foam having a hardness A of 70 degrees was used for the pad. As the abrasive, cerium oxide having an average particle diameter of 60 nm was dispersed in water and used as a slurry. The mixing ratio of water and abrasive was 2: 8. The load was 90 g / cm ² , the upper platen was rotated at 30 rpm, and the lower platen was rotated at 10 rpm. The polishing amount was 3 μm.

  As for the surface roughness of the obtained glass substrate, Rmax was 5 nm and Ra was 0.3 nm.

  After completion of the second polishing process, the glass substrate was cleaned and inspected.

Inspecting the surface of the inner and outer peripheral end faces of the produced glass substrate, a scanning laser disk surface inspection apparatus was used to count the number of minute scratches on the inner and outer peripheral end faces, and the average value of 100 sheets was calculated. Further, the amount of change in the inner and outer diameters of the glass substrate was also measured, and the average value of 100 sheets was calculated.
(Evaluation)
The level of the inner and outer peripheral end face roughness values was evaluated as follows.

  Evaluation of Rmax: ◎ is 0.3 μm or less, ◯ is 0.3 μm or more and 0.6 μm or less is ○, 0.6 μm or more is 0.8 μm or less is Δ, and 0.8 μm or more is ×. When Rmax exceeds 0.8 μm, a problem occurs in terms of dust generation, and it cannot be used.

  Ra evaluation: ◎ for 0.1 μm or less, ◯ for more than 0.1 μm and 0.2 μm or less, Δ for more than 0.2 μm and 0.5 μm or less, and × for those exceeding 0.5 μm. When Ra exceeds 0.5 μm, a problem occurs in terms of dust generation as described above, and it cannot be used.

  Evaluation of change in inner and outer diameters: 5 μm or less x 5 μm to 10 μm or less Δ, 5 μm to 30 μm or less ○, 30 μm to 50 μm or less ◎, 30 μm to 50 μm or less ◎, 30 μm ◎, 50 μm or less, ◎, 70 μm or less, ○, 70 μm or more, 80 μm or less, Δ, 80 μm or more, ×. If the inner / outer diameter change amount is 5 μm or less, there is a problem that the machining allowance is insufficient and the surface is not uniform, and if it exceeds 80 μm, there is a problem that the processing progresses too quickly and is difficult to control. I can't.

  The number of scratches on the inner and outer peripheral end faces: 10 or less was marked with ◎, 10 and over 50 were marked with ◯, 50 and over 100 were marked with △, and over 100 were marked with ×. When the number of scratches exceeds 100, the amount of ions oozing out onto the substrate surface increases, and surface degradation occurs during use as a recording medium, making it impossible to use.

  Moreover, the polishing residue of 100 inner and outer peripheral end faces was observed using an electron microscope, and “X” indicates that there is polishing residue even at one place, and “◯” indicates that there is no polishing residue.

  The evaluation results are shown in Table 1.

  From the results shown in Table 1, when using a hydrofluoric acid solvent in the polishing liquid as in Examples 1 to 16 as compared with Comparative Example 1, there are few scratches even in a short polishing time of 5 minutes, no polishing residue, and smoothness. It can be seen that the surface state of the inner and outer peripheral end faces of the glass substrate can be obtained with high values (Rmax, Ra values of Δ level or more). In addition, from the results of Examples 1 to 16, the hydrofluoric acid concentration is 2 to 6% by mass, and the smoothness is higher (Rmax and Ra values are higher than or equal to the ○ level), and the change in the inner and outer dimensions is within an appropriate range (O Level or higher), which is more preferable. Furthermore, from the results of Examples 5 to 16, when sulfuric acid was added to the hydrofluoric acid solvent and the sulfuric acid concentration was adjusted to 5 to 10%, the smoothness was further improved (Rmax and Ra values were レ ベ ル level), and the external dimension change was also improved. It can be seen that it can be adjusted to a preferred range (（level). Moreover, about Examples 1-16, the crack and the hook were not recognized.

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 a schematic diagram which shows the state currently grind | polished using an inner peripheral end surface grinder. It is a schematic diagram which shows the state currently grind | polished using the outer periphery end surface grinder.

Explanation of symbols

1 Glass substrate for information recording media (glass substrate)
DESCRIPTION OF SYMBOLS 2 Magnetic film 3 Spacer 4 Laminate 5 Hole 7a Front main surface 7b Back main surface 10t Outer peripheral end surface 20t Inner peripheral end surface 41 Work shaft 50 Inner peripheral end surface grinder 51, 71 Rotating brush 60 Polishing nozzle 61 Polishing liquid 70 Outer peripheral end surface grinder D Magnetic disk

Claims (5)

In the method for producing a glass substrate for an information recording medium, comprising an end face processing step of polishing the end face of the glass substrate using a polishing brush or a polishing pad and a polishing liquid,
The method for producing a glass substrate for an information recording medium, wherein the polishing liquid contains a hydrofluoric acid solvent. The method for producing a glass substrate for an information recording medium according to claim 1, wherein the hydrofluoric acid solvent has a hydrofluoric acid concentration of 2 to 6 mass%. The method for producing a glass substrate for an information recording medium according to claim 2, wherein the hydrofluoric acid solvent contains sulfuric acid having a concentration of 5 to 10% by mass. A glass substrate for an information recording medium, which is manufactured by the manufacturing method according to any one of claims 1 to 3. A magnetic recording medium comprising a magnetic film on a surface of the glass substrate for information recording medium according to claim 4.

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