JP2009048688A - 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 having excellent productivity and capable of easily separating a spacer and moving to a next step without scratching the surface. <P>SOLUTION: A layered body is immersed in a water vessel, the glass substrate on an uppermost part of the layered body is separated from the layered body by using a separating means and at least a part of the glass substrate separated by using the separating means is rocked in the water vessel. Thus, the spacer is removed from the surface of the separated glass substrate. <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.

With respect to such a problem, in Patent Document 1, as a method of efficiently and accurately polishing the surface of the inner and outer peripheral end surfaces of a glass substrate, a plurality of glass substrates are interposed with thin disc-shaped resin spacers. Then, a method has been proposed in which the main surfaces are separated from each other and laminated, and a polishing brush or a polishing pad is rotationally contacted for polishing.
JP 2001-162510 A

  However, in the method described in Patent Document 1, when a plurality of glass substrates are integrated via a spacer and end face processing of the inner periphery or outer periphery is performed, then processing in the next step, for example, chemical strengthening, is performed. It is necessary to remove. The spacer used is usually made of resin and has a thickness of one hundred microns to several hundred microns. Since the spacer is pressed during end face processing, it cannot be easily removed from the glass substrate. For this reason, the separation and removal are generally performed manually, and there is a problem in that it takes time and cost and may damage the surface.

  The present invention has been made in view of such problems, and a plurality of glass substrates are laminated through spacers, and after the end surfaces of the glass substrates are polished, the spacers are easily separated. An object of the present invention is to provide a method for producing a glass substrate for an information recording medium with excellent productivity, which can be transferred to the next step without scratching the surface.

  Said subject is solved by the following structures.

1.
In a method for producing a glass substrate for an information recording medium, the method includes a step of polishing a glass substrate that is a laminated body by laminating a plurality of glass substrates with a spacer interposed therebetween, and polishing an end surface of the glass substrate that has become the laminated body.
After polishing the end face of the glass substrate, the laminate is immersed in a water tank, and the glass substrate at the top of the laminate is separated from the laminate by a separating means,
By swinging at least a part of the glass substrate separated by the separation means in the water tank,
A method for producing a glass substrate for an information recording medium, wherein the spacer is removed from the surface of the glass substrate separated by the separating means.

2.
2. The method for producing a glass substrate for an information recording medium according to 1, wherein the glass substrate separated by the separating means is taken out of the water surface of the water tank and then immersed in the water tank again.

3.
The water tank includes an inlet for allowing water to flow in, and an outlet for allowing the water in the tank to overflow with water flowing from the inlet.
Having another water tank for receiving water overflowing from the outlet;
The spacer removed from the glass substrate separated by the separating means,
3. The method for producing a glass substrate for an information recording medium according to 1 or 2, wherein the water overflows from the outlet to the other water tank.

4).
The water tank includes an ultrasonic vibrator,
4. The method for producing a glass substrate for an information recording medium according to any one of 1 to 3, wherein the water in the water tank is vibrated by the ultrasonic vibrator.

5).
5. The method for producing a glass substrate for an information recording medium according to 4, wherein the vibration frequency of the ultrasonic vibrator is modulated.

6).
6. The method for producing a glass substrate for an information recording medium according to 4 or 5, wherein the vibration amplitude of the ultrasonic vibrator is modulated.

7).
A glass substrate for an information recording medium, which is produced by the production method according to any one of 1 to 6.

8).
8. A magnetic recording medium comprising a magnetic film on the surface of the glass substrate for information recording medium according to 7.

  According to the present invention, after polishing the end surface of the glass substrate of the laminated body in which a plurality of glass substrates are overlapped via a spacer, the laminated body is immersed in a water tank, and the uppermost glass substrate of the laminated body is laminated. The spacer adhered to the glass substrate separated from the laminate is removed by swinging at least a part of the separated glass substrate in a water tank. Since the spacer can be easily removed from the glass substrate by such a method for manufacturing a glass substrate for an information recording medium, a manufacturing method with high productivity can be provided as compared with a conventional manual method.

  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 the present embodiment, first, in order to polish the outer peripheral end face of the glass substrate, a plurality of glass substrates are overlapped with a spacer interposed therebetween to form a laminated body. Next, after polishing the outer peripheral end surface of the glass substrate which became this laminated body, this laminated body is immersed in a water tank. The uppermost glass substrate of the laminated body that has been immersed is held by a separating means, and is pulled up to separate from the laminated body. Next, the spacer adhered to the surface of the glass substrate separated from the laminate is removed by swinging at least a part of the separated glass substrate in the water tank. By repeating this operation, the glass substrates can be separated one by one from the laminate, and the spacers can be reliably removed.

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)
A plurality of glass substrates that have undergone the inner and outer diameter processing steps are stacked and stacked, and in this state, the inner peripheral surface is polished using an inner peripheral end surface polishing machine.
(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 an outer peripheral end surface processing step, the outer peripheral end surface of the glass substrate is made to have a curved corner portion of the chamfered portion by brush polishing using a polishing liquid, and fine scratches are removed.

  FIG. 4 shows a configuration diagram of the laminate 4. FIG. 4A shows a view from the side of the laminate 4, and FIG. 4B shows the overlap state of the spacer 3 and the glass substrate 1 as seen from the top.

  After performing the second lapping process of polishing both surfaces of the glass substrate 1 in the process of FIG. 3, the spacers 3 and the glass substrate 1 are alternately stacked one by one to form a laminate 4 as shown in FIG. And this laminated body 4 is moved to an outer peripheral end surface processing process. 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.

  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 outer peripheral end face processing step, the outer periphery of the glass substrate 1 is polished using an outer peripheral end face polishing machine 50 as shown in FIG. The laminated body 4 is held and rotated in a state of being laminated by the work shaft 41, and the outer periphery is polished by the rotating brush 51. At this time, the polishing liquid 61 is supplied from the polishing nozzle 60.

  The laminated body 4 which finished the outer peripheral end surface polishing step is moved to a spacer separation device 70 for separating the spacer 3 shown in FIG.

  A method for separating and removing the spacer 3 according to the present invention will be described.

  The spacer separation device 70 includes a water tank 71 for immersing the laminate 4 of the glass substrate 1 and the spacer 3, a water inlet 81, an outlet 82, and another water that receives the overflowing water from the outlet 82. An arm having a water tank 72, a pipe 74 for returning and circulating water from another water tank 72 to the water tank 71, a pump 73, and an arm 75 as a separating means for separating the uppermost glass substrate 1 of the laminate 4. A head 76, a rotating unit 78 that rotates the arm head 76, and a moving shaft 77 that moves the arm head 76 are provided.

  First, the laminated body 4 which has finished the outer peripheral end face processing is immersed in the water tank 71. Thereafter, the uppermost glass substrate 1 of the laminate 4 is chucked by the arm 75, and the arm head 76 is pulled up by the moving shaft 77 to separate the glass substrate 1 from the laminate 4. The spacer 3 that is in close contact with the surface of the glass substrate 1 may be separated during the separation, but most of the spacers 3 are in close contact with the upper surface and / or the lower surface of the glass substrate 1. In this state, the moving shaft 77 is swung left and right as shown in FIG. By swinging, the spacer 3 in close contact with the surface of the glass substrate 1 is easily peeled off. In FIG. 6, it swings left and right in water, but as shown in FIG. 7, it may swing in a circular arc shape around the rotating portion 78, and further, as shown in FIG. The arm head 76 may be rotated by 90 ° by rotating 78 to make the glass substrate 1 perpendicular to the water surface, and then may be swung up and down by the moving shaft 77. A part of the glass substrate may be swung in water. Further, it is preferable that the glass substrate is once taken out of the water surface of the water tank and then immersed in the water tank again. Thus, once it goes out of the water surface of a water tank and returns to a water tank again, the spacer 3 which contact | adhered becomes easier to separate and remove.

  By doing so, the spacer 3 is reliably separated from the surface of the glass substrate 1 and is made of a resin having a specific gravity lower than that of water, so that it floats on the surface of the water tank 71.

  Since the water tank 71 has a supply of water and an outlet 82 for overflow so that water always flows in from the inlet 81 and overflows, the spacer 3 floating on the surface of the water tank 71 has overflowing water and Together, it falls into another water tank 72. The spacers 3 dropped in another water tank 72 are collected and used again to make the laminate 4 for the outer peripheral end surface polishing process. Moreover, the water that has fallen into another water tank 72 is returned to the water tank 71 by the pump 73 and circulated.

  Further, if an ultrasonic vibrator is attached to the water tank 71 so that the water in the water tank 71 vibrates, the spacer 3 is more easily separated and removed from the surface of the glass substrate 1. Furthermore, if the water in the water tank 71 is vibrated while changing the amplitude or frequency of the ultrasonic vibrator, the spacer 3 is more easily separated.

  FIG. 9 is a schematic view showing a state in which the ultrasonic transducer 90 is attached to the water tank 71. The ultrasonic transducer 90 is composed of a PZT element or the like, and generates ultrasonic vibrations when a voltage having a predetermined frequency is applied by the ultrasonic oscillator 91. The ultrasonic oscillator 91 shown in FIG. 9 includes a frequency modulation circuit 92 and an amplitude modulation circuit 93, and can perform frequency modulation and amplitude modulation. In the case of performing frequency modulation, an electric signal having a frequency of several hundred KHz to several MHz is oscillated inside the ultrasonic oscillator 91, and this electric signal is frequency-modulated by a frequency modulation circuit 92 as shown in FIG. The electric signal is converted into an electrical signal, and the power is amplified and sent to the ultrasonic transducer 90. When amplitude modulation is performed, an electric signal having a frequency of several hundred KHz to several MHz is oscillated inside the ultrasonic oscillator 91, and this electric signal is amplitude-modulated by an amplitude modulation circuit 93 as shown in FIG. The electric signal is converted into an electrical signal, and the power is amplified and sent to the ultrasonic transducer 90. When the frequency and the amplitude are modulated simultaneously, an electric signal having a frequency of several hundred KHz to several MHz is oscillated inside the ultrasonic oscillator 91, and this electric signal is generated by the frequency modulation circuit 92 as shown in FIG. As shown in FIG. 10 (c), an electric signal whose frequency and amplitude are modulated at the same time is generated by changing the electric signal into a frequency-modulated electric signal as shown in FIG. After amplification, it is sent to the ultrasonic transducer 90.

  By thus modulating the vibration state of the ultrasonic vibrator 90 and vibrating the water in the water tank, the spacer 3 can be further easily separated and removed from the surface of the separated glass substrate 1.

  As a separating means for separating the glass substrate 1 from the upper part of the laminated body 4, in addition to the arm 75, separation may be performed by adsorbing the uppermost glass substrate 1 surface with a vacuum pad. In this case, when the spacer 3 is in close contact with the upper portion, only the spacer 3 is sucked and removed by the vacuum pad. Thereafter, the surface of the uppermost glass substrate 1 is again adsorbed with a vacuum pad, and the above-described swinging is performed, whereby the spacer 3 adhered to the lower surface side of the glass substrate 1 can be removed.

  The glass substrates separated from the laminate 4 and separated and removed from the spacers 3 are placed one by one on the process cassette by the moving shaft 77.

  Next, the glass substrate 1 placed on the process cassette is moved to the next chemical strengthening step.

  By using such a spacer separating device 70, it is possible to quickly perform the place where the manual separation has been performed conventionally, and the occurrence of scratches or the like due to manual labor is reduced, and the productivity is improved.

  The separation of the spacer 3 by the spacer separating device 70 is not limited to after the outer peripheral end face processing step, but may be used after the inner peripheral end face processing step. After the laminate 4 is prepared, the spacer 3 may be used in an operation that needs to be separated.

  The order from the first lapping step after the coring processing to the outer peripheral end surface processing step is not limited to that shown in FIG. 5 and can be changed as appropriate according to the situation. For example, the lapping process may be performed first, and then the inner / outer diameter machining process, the inner circumference, and the outer circumference end face machining process may be performed. Further, after the first lapping step and the inner / outer diameter machining step, a second lapping step, an inner circumference and an outer circumference end face machining step may be performed.

  The end surfaces of the inner and outer peripheries of the glass substrate are polished using an end surface polishing machine in the inner and outer peripheral end surface processing steps, and are subjected to polishing by brush polishing. The brush is preferably made of nylon, polypropylene or the like having a diameter of about 0.2 to 0.3 mm. The polishing liquid is preferably cerium oxide having a particle size of about several μm. In the processing step of the inner peripheral end surface, the glass substrate 1 is polished in a stacked state without using a spacer, but the inner peripheral end surface processing may be performed as a laminate through the spacer. In this case, it is necessary to separate the glass substrate and the spacer by the spacer separating device 70 before moving to the next second lapping step. The reason why the spacer 3 is used in the outer peripheral end surface processing step is to smooth the edge between the chamfered portion and the front and back surfaces of the glass substrate when the edge is chamfered in the outer peripheral processing.

  As a result of brush polishing, it is preferable that the surface roughness of the inner and outer end faces is such that Rmax is 0.2 μm to 0.4 μm and Ra is about 0.02 μm to 0.04 μm. The shape of the end surface of the glass substrate that has undergone the inner / 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 treatment liquid, alkali metal ions such as lithium ions and sodium ions contained in the glass substrate are converted into alkali ions such as potassium ions having a larger ion radius. This is performed by the ion exchange method for substitution. Compressive stress is generated in the ion-exchanged region due to the distortion caused by the difference in ion radius, and the surface of the glass substrate is strengthened.

  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 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 treatment liquid remaining on the surface of the glass substrate, various inspection / evaluation processes, etc. May be.

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

  Next, 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.

(Example 1)
(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 # 1200 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 100 glass substrates obtained by finishing the inner / outer processing steps were stacked, and the inner peripheral end face was polished using an inner peripheral end face 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. The surface roughness of the inner peripheral end surface of the obtained glass substrate was 0.3 μm for R and 0.03 μm for Ra.
(6) Second lapping process Both surfaces of the glass substrate were polished using a polishing machine (manufactured by HAMAI).

As polishing conditions, diamond pellets of # 1200 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. The outer peripheral end face of this laminate was polished using an outer peripheral end face polishing machine 50 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. As the polishing liquid, cerium oxide having a particle diameter of 3 μm was used.

  After polishing by the outer peripheral end surface polishing machine 50, the spacers were separated using the spacer separation device 70 shown in FIG. 6, and the glass substrates were placed one by one in the process cassette. The glass substrate 1 was swung in water by moving the distance of 10 cm in the horizontal direction in 1 second, stopping for 1 second, and then moving the distance of 10 cm in the reverse direction in 1 second for 5 cycles.

  By doing in this way, the spacer closely_contact | adhered to the upper surface and lower surface of the glass substrate 1 can be isolate | separated easily, The glass substrate 1 which could be isolate | separated was pulled up from the water tank 71, and was mounted in the process cassette. This operation was repeated until there was no glass substrate 1 constituting the laminate 4, and 100 glass substrates could be placed on the process cassette.

As for the surface roughness of the outer peripheral end surface of the obtained glass substrate, Rmax was 0.3 μm and Ra was 0.03 μm.
(8) Chemical strengthening step Next, a chemical strengthening step was performed by immersing the glass substrate in a chemical strengthening treatment solution. As the chemical strengthening treatment 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 treatment liquid 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.

For the inspection of the produced glass substrate, a scanning laser disk surface inspection device was used to evaluate minute scratches and adhesion of minute objects on the substrate surface. Micro scratches and adhesion of fine objects were not observed on 100 glass substrates.
(Example 2)
In Example 2, the same procedure as in Example 1 was performed except that the spacer separating apparatus 70 in the outer peripheral end face machining step of Example 1 was performed using the one shown in FIG. The glass substrate 1 was oscillated by moving a distance of 20 cm in the vertical direction in 2 seconds, stopping for 1 second, and then moving the distance of 20 cm in the reverse direction in 1 second for 5 cycles. The glass substrate 1 was once completely exposed to the air from the water surface of the water tank 1. The conditions were the same except that the glass substrate was swung for spacer separation as shown in FIG.

  100 glass substrates prepared were evaluated in the same manner as in Example 1. However, neither fine scratches nor fine deposits were observed.

  After polishing the end face of the glass substrate in this way, the laminate is immersed in a water tank, and the surface of the uppermost glass substrate of the laminate is separated from the laminate by a separating means, and at the same time, at least a part of the glass substrate 1 is placed in the water tank. The spacer that is in close contact with the glass substrate can be easily separated and removed by swinging at, and the production of a glass substrate for an information recording medium having excellent productivity without damaging the surface of the glass substrate. Could provide a way.

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 block diagram of a laminated body. It is a schematic diagram which shows the state currently grind | polished using the outer periphery end surface grinder. It is a schematic diagram which shows the state which is rocking | fluctuating a glass substrate horizontally by the spacer separation apparatus which concerns on this invention. It is a schematic diagram which shows the state which is rock | fluctuating the glass substrate in circular arc shape by the spacer separation apparatus which concerns on this invention. It is a schematic diagram which shows the state which is rock | fluctuating the glass substrate up and down by the spacer separation apparatus which concerns on this invention. The schematic diagram of the state which attached the ultrasonic vibrator to the water tank is shown. It is a schematic diagram which shows the electric signal oscillated with an ultrasonic oscillator.

Explanation of symbols

1 Glass substrate for information recording media (glass substrate)
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 Outer peripheral end surface polishing machine 51 Rotating brush 60 Polishing nozzle 61 Polishing liquid 70 Spacer separator 71 Water tank 72 Separate Water tank 73 Pump 74 Pipe 75 Arm 76 Arm head 77 Moving shaft 78 Rotating part 81 Inlet 82 Outlet 90 Ultrasonic vibrator 91 Ultrasonic oscillator 92 Frequency modulation circuit 93 Amplitude modulation circuit D Magnetic disk

Claims (8)

In a method for producing a glass substrate for an information recording medium, the method includes a step of polishing a glass substrate that is a laminated body by laminating a plurality of glass substrates with a spacer interposed therebetween, and polishing an end surface of the glass substrate that has become the laminated body.
After polishing the end face of the glass substrate, the laminate is immersed in a water tank, and the glass substrate at the top of the laminate is separated from the laminate by a separating means,
By swinging at least a part of the glass substrate separated by the separation means in the water tank,
A method for producing a glass substrate for an information recording medium, wherein the spacer is removed from the surface of the glass substrate separated by the separating means. 2. The method for producing a glass substrate for an information recording medium according to claim 1, wherein the glass substrate separated by the separating means is taken out of the water surface of the water tank and then immersed in the water tank again. The water tank includes an inlet for allowing water to flow in, and an outlet for allowing the water in the tank to overflow with water flowing from the inlet.
Having another water tank for receiving water overflowing from the outlet;
The spacer removed from the glass substrate separated by the separating means,
The method for producing a glass substrate for an information recording medium according to claim 1, wherein the glass substrate is caused to flow down to the other water tank together with water overflowing from the outlet. The water tank includes an ultrasonic vibrator,
The method for manufacturing a glass substrate for an information recording medium according to any one of claims 1 to 3, wherein water in the water tank is vibrated by the ultrasonic vibrator. 5. The method for manufacturing a glass substrate for an information recording medium according to claim 4, wherein the vibration frequency of the ultrasonic vibrator is modulated. 6. The method for manufacturing a glass substrate for an information recording medium according to claim 4, wherein the vibration amplitude of the ultrasonic transducer is modulated. A glass substrate for an information recording medium, which is manufactured by the manufacturing method according to claim 1. A magnetic recording medium comprising a magnetic film on the surface of the glass substrate for information recording medium according to claim 7.

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