JP5536481B2 - Manufacturing method of glass substrate for information recording medium and manufacturing method of information recording medium - Google Patents

Description

  The present invention relates to a method for manufacturing a glass substrate for an information recording medium and an information recording medium used for an information recording medium having a recording layer using properties such as magnetism, light, and magnetomagnetism.

  Among information recording media having a recording layer utilizing properties such as magnetism, light, and magnetomagnetism, a typical example is a magnetic disk. Conventionally, aluminum substrates have been widely used as magnetic disk substrates. 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.

  In such a method for producing a glass substrate for an information recording medium such as a magnetic disk, for the purpose of improving the impact resistance and vibration resistance of the glass substrate and preventing the substrate from being damaged by impact and vibration, In general, a substrate is strengthened by applying a chemical strengthening treatment to the surface. Chemical strengthening treatment is usually performed by immersing a glass substrate in a chemical strengthening treatment liquid, and ion exchange between alkali metal ions such as sodium ions contained in the glass substrate and alkali metal ions such as potassium ions contained in the chemical strengthening treatment liquid. By an ion exchange method in which an ion exchange layer is formed on the surface of the glass substrate. Such an ion exchange layer has a high compressive stress and strengthens the glass substrate.

  However, when chemical strengthening treatment is performed, substrate warpage due to the effect of compressive stress on the surface of the glass substrate and generation of fine irregularities on the surface due to erosion of the chemical strengthening treatment liquid occur, and the information recording medium such as a magnetic disk is used. The magnetic head may collide.

  For such a problem, in Patent Document 1, as a method of removing the warp and fine irregularities of the surface of the glass substrate after the chemical strengthening step and ensuring the necessary smoothness, after performing the chemical strengthening treatment, A method of polishing the surface has been proposed.

  Moreover, in patent document 2, the location which chemically strengthens is limited to the outer peripheral and inner peripheral end surface of a glass substrate, and the generation | occurrence | production of the fine unevenness | corrugation by the curvature of the front and back of a glass substrate or the erosion of a chemical strengthening process liquid is prevented. For this purpose, a method has been proposed in which a chemical strengthening process is performed in a state where the main surfaces of the front and back surfaces of a glass substrate are covered with a metal spacer.

JP 2000-207730 A JP 2008-198285 A

  However, as the recording density is improved, the flying height between the substrate and the magnetic head is reduced, and the level of flatness required for the glass substrate for information recording media is increasing. In the method of polishing the main surface chemically treated as described in Patent Document 1 to ensure the required level of flatness, it is necessary to sufficiently remove the chemically strengthened layer on the main surface. However, the chemically strengthened surface is hard, so that there is a problem that it takes a long polishing time and the productivity is poor.

  Moreover, in the state which covered the main surface of the front and back of a glass substrate with the metal spacers as described in patent document 2, the spacer cannot adhere to the main surface, and a slight gap may occur. The chemical strengthening liquid permeates into the gap to generate partial stress distortion, and the substrate warps. Further, in the method of chemically strengthening after final polishing of the main surface as described in Patent Document 2, when handling the glass substrate before and after the chemical strengthening step, the main surface is scratched to generate micro defects. Probability is high. Such a scratch or warp on the main surface after the chemical strengthening process has caused a problem that a reading error or a head crash by the magnetic head occurs.

  The present invention has been made in view of the technical problems as described above, and an object of the present invention is to have a chemically strengthened inner peripheral end face and outer peripheral end face, and have desired flatness and surface roughness. An object of the present invention is to provide a method for producing a glass substrate for information recording medium having few surface defects on the main surface and a method for producing an information recording medium using the glass substrate for information recording medium by the production method.

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

1. In the method of manufacturing a glass substrate for information recording medium manufactured using a glass substrate having a main surface having a center hole, an inner peripheral end surface, and an outer peripheral end surface,
At least one pre-polishing step of polishing the main surface;
After the pre-polishing step, a plurality of the glass substrate and a spacer having a Young's modulus of 2 to 300 MPa that substantially covers the main surface of the glass substrate are alternately stacked, and the main surface and the spacer are in close contact with each other. An adhesion process for forming a body;
A chemical strengthening step of immersing the laminate in a chemical strengthening treatment liquid and forming an ion exchange layer on an inner peripheral end surface and an outer peripheral end surface of the glass substrate by ion exchange,
A post-polishing step of polishing the main surface of the glass substrate after the chemical strengthening step;
The manufacturing method of the glass substrate for information recording media characterized by the above-mentioned.

  2. 2. The method for producing a glass substrate for an information recording medium according to the item 1, wherein the spacer has a Young's modulus of 4 to 100 MPa.

  3. 3. The method for producing a glass substrate for an information recording medium according to 1 or 2, wherein the polishing amount of the main surface polished in the post-polishing step is 0.5 to 10 μm.

4). When the outer diameter of the glass substrate before the chemical strengthening step is C and the inner diameter is D,
The outer diameter E of the spacer is C-10 mm <E <C-0.1 mm,
The inner diameter F of the spacer is D + 0.1 mm <F <D + 10 mm,
4. The method for producing a glass substrate for an information recording medium according to any one of 1 to 3, wherein:

  5. 5. The method for producing a glass substrate for an information recording medium according to any one of 1 to 4, wherein the spacer has a thickness of 0.1 to 5 mm.

  6). 6. An information recording comprising a recording layer formed on a main surface of a glass substrate for information recording medium manufactured by the method for manufacturing a glass substrate for information recording medium described in any one of 1 to 5 above. A method for manufacturing a medium.

  7). 7. The method for manufacturing an information recording medium according to 6, wherein the recording layer is a magnetic layer.

  According to the present invention, a method for producing a glass substrate for an information recording medium having a sufficiently chemically strengthened inner peripheral end face and outer peripheral end face, having desired flatness and surface roughness, and having few surface defects on the main surface, and The manufacturing method of the information recording medium using the glass substrate for information recording media by this manufacturing method 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 the schematic for demonstrating the laminated body in the contact | adherence process, and its manufacturing method. It is the schematic for demonstrating the laminated body in the contact | adherence process, and its manufacturing method.

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

  FIG. 1 is a diagram showing an example of the overall configuration of a glass substrate for information recording medium (hereinafter also referred to as a glass substrate) 1. As shown in FIG. 1, the glass substrate 1 has a donut-like 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) G provided with 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 production process diagram of one embodiment of the method for producing a glass substrate for an information recording medium of the present invention. Details of the manufacturing process diagram will be described later.

  A feature of the method for producing a glass substrate for information recording medium of the present invention is that the main surface is polished in the method for producing a glass substrate for information recording medium having a main surface having a center hole, an outer peripheral end face, and an inner peripheral end face. At least one pre-polishing step, and after the pre-polishing step, a plurality of glass substrates and spacers having Young's modulus of 2 to 300 MPa that substantially cover the main surface of the glass substrate are alternately overlapped, and the main surface and the spacer Of the glass substrate after the chemical strengthening step, the chemical strengthening step of forming an ion exchange layer on the glass substrate by ion exchange, And a post-polishing step of polishing the main surface.

  Thus, before the chemical strengthening step, at least one or more pre-polishing steps for polishing the main surface, and after the pre-polishing step, the glass substrate and a Young's modulus of 2 to 300 MPa that substantially covers the main surface of the glass substrate. A plurality of spacers alternately stacked to form a laminated body in which the main surface and the spacers are in close contact with each other, so that even if some warping remains after the polishing step, an elastic spacer can be obtained. Deformation occurs along the main surface, and the main surface and the spacer are sufficiently adhered in the adhesion process. As a result, the chemical strengthening treatment liquid does not enter between the main surface and the spacer in the subsequent chemical strengthening process, and new warping or roughening of the surface may occur after the chemical strengthening process. Absent. In addition, after the chemical strengthening process, the post-polishing process is performed to make the main surface of the glass substrate have the desired surface roughness and flatness, thereby eliminating minute scratches generated by handling after the adhesion process or the chemical strengthening process. be able to. In the post-polishing step after this chemical strengthening step, the main surface of the glass substrate is less warped and rough, and since it is not chemically strengthened, it can be easily polished to a predetermined surface roughness and flatness. The productivity can be improved as compared with the conventional method. The magnetic disk using the glass substrate manufactured by such a manufacturing method is excellent in smoothness and flatness of the main surface, so that the flying height of the magnetic head can be further reduced and the density has been increased in recent years. Can meet the demands of.

  Moreover, as a material of the spacer used for this invention, what is necessary is just a spacer whose Young's modulus is 2-300 MPa.

  In particular, the Young's modulus is preferably 4 to 100 MPa. By making the Young's modulus within this range, even if the glass substrate before the chemical strengthening step is slightly warped, it can be along the main surface of the glass substrate, and a part of the spacer is at the inner peripheral edge or outer peripheral edge. It is preferable without fear of covering a part.

  Examples of the material that can be used as the spacer include urethane rubber, silicon rubber, chloroprene rubber, and butadiene rubber as rubber materials. Among these, it is preferable to use silicon rubber from the viewpoint of excellent durability and chemical strengthening treatment liquid.

  The Young's modulus used in the present invention was measured by a general method. Both ends of a bar having a uniform cross section A are pulled with a force P, the normal stress generated in the bar is σ = P / A, and the strain when a bar of length L is extended by u by this force P is ε = u / L From these values, the Young's modulus was calculated as E = σ / ε.

  Moreover, it is preferable that the grinding | polishing amount of the main surface grind | polished at the post-polishing process performed after a chemical strengthening process is 0.5-10 micrometers. By making the polishing amount after the chemical strengthening step within this range, the fine defects generated on the surface of the glass substrate can be sufficiently eliminated when performing the adhesion step and the chemical strengthening step, and more than necessary. Therefore, productivity is also improved, which is preferable.

  Moreover, the shape of the spacer used for the laminated body may be any shape as long as it covers the main surface of the glass substrate before the chemical strengthening step and can be chemically strengthened without covering the inner peripheral end surface and the outer peripheral end surface. What is necessary is just to have an inner diameter slightly larger than the inner diameter of the glass substrate and an outer diameter slightly smaller than the outer diameter of the glass substrate. In particular, when the outer diameter of the glass substrate before the chemical strengthening step is C and the inner diameter is D, the outer diameter E of the spacer is C-10 mm <E <C-0.1 mm, and the inner diameter F of the spacer is D + 0. It is preferable that 1 mm <F <D + 10 mm.

  By setting the inner diameter and outer shape of the spacer within this range, the inner peripheral end face and the outer peripheral end face can be chemically strengthened, the main surface of the glass substrate can be sufficiently covered, and the stress on the main surface caused by the chemical strengthening liquid can be reduced. You can make it more ridiculous.

  Moreover, it is preferable that the thickness of a spacer is 0.1-5 mm. By making the spacer thickness within this range, the warpage of the glass surface before chemical strengthening can be absorbed sufficiently by the spacer, and the volume when the laminate is produced can be reduced, so the chemical strengthening bath can be made compact. it can.

The manufacturing method of the glass substrate for information recording media of this invention is demonstrated in detail using the manufacturing-process figure 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.
(Molding process)
Next, as a molding step, molten glass is poured into a lower mold and press-molded with an upper mold to obtain a disk-shaped glass substrate. Note that the disk-shaped glass substrate may be manufactured by cutting a sheet glass formed by, for example, a downdraw method or a float method with a grinding wheel, 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.
(First lapping process)
Next, as a first lapping step, both surfaces of the press-molded glass substrate are polished to preliminarily adjust the parallelism, flatness and thickness of the glass substrate.
(Coring process)
Next, in the coring process, a hole is made in the center of the glass substrate after the first lapping 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 / 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.
(Second wrapping process)
Further, as the second lapping step, 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 using a planetary gear mechanism 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 preferably Ra from about 0.2 μm to 0.4 μm, The flatness of the main surface is preferably 7 to 10 μm.

  By maintaining such a surface state, it is possible to efficiently perform polishing in the next first polishing step.

  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 about Ra of 0.4 μm to 0.8 μm, and the flatness of the main surface is preferably 10 to 15 μm.

  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.

In addition, the surface roughness used by this invention is the value which measured the range of 1 micrometer x 1 micrometer using the atomic force microscope (Digital Instruments company nanoscope). The flatness used in the present invention is a value measured by a flatness measuring device, and is a difference in height (PV value) between the highest position and the lowest position on the surface of the glass substrate.
(End polishing process)
The outer peripheral surface and the inner peripheral surface of the glass substrate after the second lapping step are polished using an end surface polishing machine.
(First polishing process)
Next, a first polishing process is performed. In the first polishing step, the surface roughness is improved and finally the main surface roughness is improved so that the surface roughness finally required in the second polishing step performed after the next chemical strengthening step can be efficiently obtained. Polishing is performed so that the shape of the invention can be obtained efficiently.

  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 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. In addition, the at least 1 or more process of grind | polishing the main surface performed before the next contact | adherence process is called a pre-polishing process.
(Adhesion process)
Next, as the adhesion process, the glass substrate after the first polishing process and a spacer having a Young's modulus of 2 to 300 MPa that almost covers the main surface of the glass substrate are alternately overlapped so that the main surface and the spacer adhere to each other. A laminated body is formed. Since the material, shape, Young's modulus, etc. of the spacer have been described above, they are omitted here.

  A laminated body and its manufacturing method are demonstrated using FIG. 4, FIG. FIG. 4 is a view showing a state in which a predetermined number of sheets are stacked by alternately inserting the spacers 4 and the glass substrate 1 into the jig 31 attached to the lower base plate 3. FIG. 5 shows that the spacer 4 and the glass substrate 1 stacked in FIG. 4 are further arranged on the uppermost part of the glass substrate 1, and the spacer and the glass substrate 1 stacked between the lower base plate 3 and the upper base plate 32 are sandwiched. It is the figure which showed the laminated body 100 of the state which extracted 31. FIG.

First, the jig 31 is fitted into the base plate 3. The outer shape of the jig 31 is slightly smaller than the inner diameter of the glass substrate 1. The spacers 4 and the glass substrate 1 are alternately stacked while positioning with the outer shape of the jig 31. After the predetermined number of spacers 4 and the glass substrate 1 are stacked, the upper base plate 32 is stacked after the spacers 4 are finally stacked as shown in FIG. Next, the lower base plate 3 and the upper base plate 32 are fastened with bolts 34 and nuts 35 so that the spacer 4 and the main surface of the glass substrate 1 are brought into close contact with each other. Next, the jig 31 is extracted, and the laminate 100 is produced. A plurality of the bolts 34 may be arranged at positions away from the outer peripheral surface of the glass substrate 1 so that the pressure that causes the spacer 4 and the glass substrate 1 to be in close contact with each other is applied almost evenly on the main surface of the glass substrate 1.
(Chemical strengthening process)
Next, as a chemical strengthening step, the laminate formed in the adhesion step is immersed in a chemical strengthening solution to form a chemically strengthened layer on the inner peripheral end surface and the outer peripheral end surface of the glass substrate. It is possible to improve impact resistance, vibration resistance, heat resistance, etc. by forming a chemically strengthened layer on the inner and outer peripheral end faces, and to prevent warping and surface roughening due to chemical strengthening of the main surface. it can.

  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 inner peripheral end surface and the outer peripheral end surface of the glass substrate are strengthened.

  There is no restriction | limiting in particular in a chemical strengthening process liquid, A well-known chemical strengthening process 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 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.

  In addition, in order to prevent the occurrence of cracks and fine cracks in the glass substrate due to thermal shock when immersed in the heated chemical strengthening treatment liquid, the glass substrate is placed in a preheating tank prior to immersion in the chemical strengthening treatment liquid. You may have the preheating process heated to predetermined temperature.

The thickness of the chemically strengthened layer is preferably in the range of about 5 μm to 15 μm from the viewpoint of improving the strength of the glass substrate. When the thickness of the reinforcing layer is within this range, a glass substrate having good mechanical strength and impact resistance can be obtained.
(Second polishing step)
Next, a second polishing process is performed after the chemical strengthening process.

  The second polishing step is a step of further precisely polishing the surface of the glass substrate after the chemical strengthening step, and is performed by the same polishing method as 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 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.

  By adjusting the polishing conditions in the second polishing step as described above, the target flatness can be 3 μm or less and the surface roughness Ra can be 0.1 nm.

The polishing amount in the second polishing step is preferably 2 μm 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. In addition, the process of grind | polishing the main surface of a glass substrate after a chemical strengthening process is called a post-polishing process.
(Washing process)
Next, scrub cleaning is performed as a cleaning process after the second polishing process. In particular, it is not limited to scrub cleaning, and any cleaning method that can clean the surface of the glass substrate after the polishing step may be used.

If necessary, the glass substrate that has been scrubbed is subjected to ultrasonic detergent cleaning and drying treatment. In the drying process, the cleaning liquid remaining on the glass substrate surface is removed using IPA or the like, and the substrate surface is dried. For example, a water rinse cleaning process is performed on the glass substrate after scrub cleaning for 2 minutes to remove the residue of the cleaning liquid. Next, an IPA (isopropyl alcohol) cleaning process is performed for 2 minutes to remove water on the substrate. Finally, an IPA (isopropyl alcohol) vapor drying step is performed for 2 minutes, and the liquid IPA adhering to the substrate is removed while being removed by the IPA vapor. The substrate drying process is not limited to this, and a method generally known as a glass substrate drying method such as spin drying or air knife drying may be used.
(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 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, 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 non-magnetic film (for example, Cr, CrMo, CrV, etc.) to reduce noise. In addition to the above magnetic materials, granular materials such as ferrite, iron-rare earth, and non-magnetic films made of SiO ₂ , BN, etc. in which magnetic particles such as Fe, Co, FeCo, CoNiPt are dispersed, etc. Also good. Further, the magnetic film may be either an inner surface type or a vertical type recording format.

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

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

Examples of the protective layer that prevents wear and corrosion of the magnetic film include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be formed continuously with an in-line type sputtering apparatus, such as an underlayer and a magnetic film. In addition, these protective layers may be a single layer, or may have a multilayer structure including the same or different layers. Note that another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, tetraalkoxysilane is diluted with an alcohol-based solvent on 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 1-5)
The manufacturing process of FIG. 3 was used as a manufacturing process of the glass substrate for information recording media used in Examples 1-5.
(1) Glass melting and forming process Using an aluminosilicate glass having a Tg of 480 ° C as a glass material, the molten glass was press-molded to produce 100 blank materials (outer diameter 68 mm, thickness 1.3 mm).
(2) 1st lapping process Both surfaces of the glass substrate were grind | polished using the grinder (made by HAMAI).

As the polishing conditions, diamond pellets of # 1200 mesh were used, the load was 100 g / cm ² , the upper surface plate was rotated at 30 rpm, and the lower surface plate was rotated at 10 rpm. The polishing amount was 100 μm.

The average flatness of 100 glass substrates obtained was 15 μm, and the surface roughness Ra was 0.50 μm.
(3) Coring process Next, the circular hole (diameter 18mm) was opened in the center part of the glass substrate using the cylindrical diamond grindstone.
(4) Inner / Outer Diameter 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) Second lapping step Both surfaces of the glass substrate were polished using a polishing machine (manufactured by HAMAI).

As the polishing conditions, diamond pellets of # 1200 mesh were used, the load was 100 g / cm ² , the upper surface plate was rotated at 30 rpm, and the lower surface plate was rotated at 10 rpm.

The average flatness of 100 glass substrates obtained was 10 μm, and the surface roughness Ra was 0.25 μm.
(6) End surface processing step 100 glass substrates obtained by finishing the inner and outer processing steps were stacked, and the inner and outer end surfaces were polished using an end surface polishing machine.

Nylon fibers having a diameter of 0.2 mm were used for the brush bristles of the polishing machine. As the polishing liquid, cerium oxide having a particle diameter of 3 μm was used. As for the surface roughness of the inner peripheral end face of the obtained glass substrate, Ra was 0.03 μm.
(7) First 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 surface plate was rotated at 30 rpm, and the lower surface plate was rotated at 10 rpm. The polishing amount was 30 μm.

The average flatness of 100 glass substrates obtained was 4 μm, and the surface roughness Ra was 0.7 nm.
(8) Contact process Silicone rubber was used as the spacer. By adjusting the rubber height, the silicone rubbers having Young's modulus of Examples 1 to 5 in Table 1 were used as spacers. The spacer used in each example had an inner diameter of 25 mm, an outer diameter of 60 mm, and a thickness of 0.5 mm. In each example, a laminate in which 100 glass substrates and 101 spacers were alternately laminated was prepared by the method shown in FIGS.
(9) Chemical strengthening step Next, a chemical strengthening step was performed by immersing the glass substrate in a chemical strengthening treatment solution. A mixed molten salt of potassium nitrate (KNO ₃ ) and sodium nitrate (NaNO ₃ ) was used as the chemical strengthening treatment liquid. The mixing ratio was 1: 1 by mass ratio. The temperature of the chemical strengthening treatment liquid was 400 ° C. and the immersion time was 40 minutes.
(10) Second Polishing Step Next, as the second polishing step, 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 surface plate was rotated at 30 rpm, and the lower surface plate was rotated at 10 rpm. The polishing amount of the main surface in the second polishing step was 5 μm.
(11) Cleaning step After the second polishing step, scrub cleaning was performed. As the cleaning liquid, a chemical liquid in which KOH and NaOH were mixed at a ratio of 100: 100 was diluted with ultrapure water (DI water), and a cleaning liquid to which a nonionic surfactant was added to enhance the cleaning performance was used. The cleaning liquid was supplied by spraying. Next, in order to remove the cleaning liquid remaining on the glass substrate surface, a water rinse cleaning step was performed for 2 minutes and an IPA (isopropyl alcohol) cleaning step was performed for 2 minutes in an ultrasonic bath, and then the surface was dried with IPA vapor.

  Thus, 100 glass substrates of Examples 1 to 5 were prepared. The average flatness, surface roughness, and number of minute defects of 100 glass substrates after the cleaning step were measured and evaluated as follows. Table 1 shows the evaluation results.

  In addition, the measurement of a micro defect performed the number of defects of (phi) 0.1 micrometer or more over the main surface whole surface using the optical surface defect measuring apparatus (OSA), and computed the average number of defects of 100 sheets.

  When the average value of the flatness of 100 sheets is 2.0 μm or less, “◯” is given, and when 2.0 μm is exceeded, 3.5 μm or less is “Δ”, and when the average value is more than 3.5 μm, “x” is given. If the average value of the flatness of 100 sheets exceeds 3.5 μm, the probability of head crushing in the case of a magnetic disk becomes high, resulting in a problem of poor product yield.

  In addition, the average value of the surface roughness Ra of 100 sheets was evaluated as “◯” when 0.1 nm or less, Δ when exceeding 0.3 nm and Δ when exceeding 0.3 nm. If the average value of the surface roughness Ra of 100 sheets exceeds 0.3 nm, the probability of head crushing in the case of a magnetic disk becomes high, resulting in a poor product yield.

In addition, the average number of microdefects having a diameter of 0.1 μm or more was 100, and 10 or less was evaluated as ◯, 10 was exceeded, 20 or less was evaluated as Δ, and 20 or more were evaluated as ×. If the average number of micro defects of φ0.1 μm or more exceeds 20, the probability of head crashes when using a magnetic disk increases, and the yield as a product becomes poor.
(Examples 6 to 9)
Examples 6 to 9 were carried out except that the polishing amount (5 μm) of the main surface in the second polishing step after the chemical strengthening step in Example 3 was adjusted to the polishing amount in Table 1 by adjusting the polishing time. In the same manner as in Example 3, 100 glass substrates were produced and evaluated. The evaluation results are shown in Table 1.
(Comparative Example 1)
In Comparative Example 1, a glass substrate was produced and evaluated in the same manner as in Example 1 except that a laminate was produced without using a spacer in Example 3. In addition, the clearance gap was recognized between the glass substrates of the laminated body produced at the contact | adherence process of the comparative example 1. FIG. The evaluation results are shown in Table 1.
(Comparative Example 2)
In Comparative Example 2, a glass substrate was produced and evaluated in the same manner as in Example 1 except that a laminate was produced using stainless steel as the spacer material in Example 1. The Young's modulus of stainless steel was 200 GPa. Note that a slight gap was observed between the spacer of the laminate produced in the adhesion process of Comparative Example 2 and the glass substrate. The evaluation results are shown in Table 1.
(Comparative Example 3)
In Comparative Example 3, a glass substrate was prepared and evaluated in the same manner as in Example 1 except that the second polishing step after the chemical strengthening step was not performed in Example 3. The evaluation results are shown in Table 1.

From the results of Table 1, when Examples 1 to 9 and Comparative Examples 1 to 3 are compared, the glass substrate manufacturing method includes a spacer as an elastic body and a polished glass substrate before the glass substrate chemical strengthening step. And alternately stacking layers to form a laminate, and chemically strengthening using the laminate produced in the adhesion step, followed by polishing the main surface of the glass substrate, the desired flatness It can be seen that a glass substrate having a high degree of surface roughness and a small number of minute defects can be obtained. Moreover, it turns out that 4-100 Mpa is preferable as a Young's modulus of the spacer which has elasticity from the result of Examples 1-5. Moreover, it turns out that 0.5-10 micrometers is preferable as a grinding | polishing amount grind | polished by the post-polishing process after a chemical strengthening process from the result of Example 3 and Examples 6-9.
(Production of magnetic recording media)
Next, a magnetic film was provided on 100 glass substrates of Examples 1 to 9 and Comparative Examples 1 to 3, respectively, to obtain a magnetic recording medium. From the glass substrate side, the magnetic film consists of a Ni—Al base layer (thickness of about 100 nm), a Co—Cr—Pt recording layer (thickness 20 nm), and a protective film (DLN 5 nm) made of DLC (Diamond Like Carbon). Were sequentially laminated.

  The produced magnetic recording medium was loaded in a hard disk drive, read and written by each recording method, and whether or not a head crash occurred during that time was evaluated. At this time, the writing density of the in-plane recording method was 50 Gbit / in 2 and the writing density of the vertical recording method was 0.5 Tbit / in 2. Of the 100 magnetic recording media of Examples 1 to 9, the occurrence of head crashes was 5 or less, and good results were obtained. Of the 100 magnetic recording media of Comparative Examples 1 to 3, the number of head crashes was 6 or more, which was a practically problematic level.

1 Glass substrate for information recording media (glass substrate)
2 Magnetic film 3 Lower base plate 4 Spacer 5 Hole 7a Front main surface 7b Back main surface 10t Outer end face 20t Inner end face 31 Jig 32 Upper base plate 34 Bolt 35 Nut 100 Laminate G Magnetic disk

Claims (6)

In the method of manufacturing a glass substrate for information recording medium manufactured using a glass substrate having a main surface having a center hole, an inner peripheral end surface, and an outer peripheral end surface,
At least one pre-polishing step of polishing the main surface;
After the front polishing step, the glass substrate, by superposing a plurality alternating with spacer Young's modulus 2~300MPa for covering the, the main surface of the glass substrate, stacked to the main surface and the spacer is in close contact An adhesion process for forming a body;
A chemical strengthening step of immersing the laminate in a chemical strengthening treatment liquid and forming an ion exchange layer on an inner peripheral end surface and an outer peripheral end surface of the glass substrate by ion exchange,
A post-polishing step of polishing the main surface of the glass substrate after the chemical strengthening step;
Only including,
When the outer diameter of the glass substrate before the chemical strengthening step is C and the inner diameter is D,
The outer diameter E of the spacer is C-10 mm <E <C-0.1 mm,
The inner diameter F of the spacer is D + 0.1 mm <F <D + 10 mm,
A method for producing a glass substrate for an information recording medium, comprising:   The method for producing a glass substrate for an information recording medium according to claim 1, wherein the spacer has a Young's modulus of 4 to 100 MPa.   The method for producing a glass substrate for an information recording medium according to claim 1 or 2, wherein the polishing amount of the main surface polished in the post-polishing step is 0.5 to 10 µm. The method for producing a glass substrate for an information recording medium according to any one of claims 1 to 3, wherein the spacer has a thickness of 0.1 to 5 mm . A recording layer is formed on the main surface of the glass substrate for information recording medium manufactured by the method for manufacturing a glass substrate for information recording medium according to any one of claims 1 to 4. A method for manufacturing a recording medium. 6. The method of manufacturing an information recording medium according to claim 5, wherein the recording layer is a magnetic layer.

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