WO2012086256A1

WO2012086256A1 - Method of manufacturing glass substrate for recording medium

Info

Publication number: WO2012086256A1
Application number: PCT/JP2011/068061
Authority: WO
Inventors: 葉月中江
Original assignee: コニカミノルタオプト株式会社
Priority date: 2010-12-24
Filing date: 2011-08-08
Publication date: 2012-06-28

Abstract

The invention relates to a manufacturing method of a glass substrate for a recording medium using a glass substrate precursor, comprising a step of forming a chemically toughened layer on the surface of the glass substrate precursor, and a step of removing the chemically toughened layer from the recording surface of the glass substrate precursor using a first polishing solution, wherein the first polishing solution comprises water and a first polishing material, the first polishing material comprises CeO₂, and the effective amount of CeO₂ in the step of removing the chemically toughened layer is between 0.05 to 0.5 µg/cm².

Description

Method for producing glass substrate for recording medium

The present invention relates to a method for producing a glass substrate for a recording medium.

2. Description of the Related Art Information recording apparatuses that record information on a recording medium by using magnetism, light, or magnetomagnetism are known. A typical example of such an information recording apparatus is a hard disk drive (HDD) apparatus. A hard disk drive device is a device that magnetically records information on a magnetic disk as an information recording medium having a recording layer formed on a substrate by a magnetic head. As a substrate for such an information recording medium, that is, a so-called substrate, a glass substrate is suitably used (hereinafter, such a glass substrate is also referred to as “glass substrate for recording medium”).

In such a hard disk drive, when recording information on a magnetic disk (glass substrate for recording medium), the magnetic head is levitated with respect to the magnetic disk without contacting the magnetic disk. It is known that the recording density can be improved by reducing the flying height of the magnetic head. Therefore, in order to increase the recording density by reducing the flying height of the magnetic head, the glass substrate for recording medium is required to have high smoothness and high cleanliness.

Such a glass substrate for a recording medium is manufactured by polishing a plurality of times using a glass base plate (hereinafter also referred to as “glass substrate precursor”). Specifically, JP 2009-076167 A (Patent Document 1) discloses a method for manufacturing a glass substrate for a recording medium.

In Patent Document 1, in a method for producing a glass substrate for an information recording medium having a polishing step for polishing the surface of a glass substrate, the arithmetic average roughness Ra of the surface of the glass substrate after the polishing step is 0.2 nm or less, undulation A method for producing a glass substrate for an information recording medium is disclosed, characterized in that Wa is 0.5 nm or less and microwaviness μWa is 0.2 nm or less.

JP 2009-076167 A

In recent hard disk drives, magnetic heads equipped with a DFH (dynamic flying height) mechanism are used, and the flying height of the magnetic head is further reduced, so that the smoothness of the glass substrate for recording media is further increased. Therefore, the glass substrate obtained by the manufacturing method described in Patent Document 1 is also required to be further improved.

According to the research of the present inventors, it has been found that it is important to control the waviness of the glass substrate for recording medium as the smoothness of the glass substrate for recording medium, and there exists a waviness of 10,000 μm to 5000 μm. It has become clear that there is a possibility that the glass substrate for recording medium and the magnetic head come into contact with each other, and this contact may cause reading / writing failure of information or damage the magnetic head. And when further research was conducted, it was found that the waviness mainly occurred in the process of removing the chemically strengthened layer using an abrasive for the glass substrate precursor in the manufacturing process of the glass substrate for recording medium. found. That is, the glass substrate precursor is formed with a chemically strengthened layer to reinforce its surface, but the chemical strengthened layer is sufficiently effective only by being formed on the outer peripheral end surface or inner peripheral end surface of the glass substrate precursor. As a result, it has been found that the recording surface may be removed, and undulation occurs during the removal process.

The present invention has been made on the basis of the above-described knowledge, and its object is to produce a glass substrate for a recording medium in which the above-described swell generated during the production process is reduced as much as possible. Is to provide.

The present invention relates to a method for producing a glass substrate for a recording medium using a glass substrate precursor, a step of forming a chemical strengthening layer on the surface of the glass substrate precursor, and using a first polishing liquid, Removing the chemical strengthening layer from the recording surface of the glass substrate precursor, wherein the first polishing liquid contains water and a first abrasive, and the first abrasive contains CeO ₂ , An effective amount of CeO ₂ in the step of removing the chemical strengthening layer is 0.05 to 0.5 μg / cm ² .

Here, the present invention may include a step of polishing the recording surface of the glass substrate precursor using a second polishing liquid different from the first polishing liquid after the step of removing the chemical strengthening layer. The concentration of the first abrasive in the first polishing liquid is preferably 1 to 9% by mass.

The present invention also includes a step of grinding the surface of the glass substrate precursor before the step of forming the chemical strengthening layer, and after the step of grinding the surface of the glass substrate precursor, the glass substrate precursor. The surface of the body preferably has an arithmetic average roughness Ra of 0.1 μm or less. The first abrasive has a maximum value of 3.5 μm or less and a cumulative 50 volume% diameter D50 of 0.5 to 1.5 μm in a particle size distribution measured by a laser diffraction scattering method. Preferably, the first polishing liquid preferably contains 60% by mass or more of CeO ₂ with respect to the total solid content.

Since the glass substrate for a recording medium manufactured by the manufacturing method of the present invention has as few wavinesses as possible, when it is used with a hard disk drive device or the like, information read / write failure occurs or the magnetic head is It can be prevented from being damaged.

Hereinafter, the present invention will be described in more detail.
<Method for producing glass substrate for recording medium>
The present invention relates to a method for producing a glass substrate for a recording medium using a glass substrate precursor, and a step of forming a chemical strengthening layer on the surface of the glass substrate precursor (hereinafter referred to as “chemical strengthening layer forming step”). And a step of removing the chemical strengthening layer from the recording surface of the glass substrate precursor using the first polishing liquid (hereinafter also referred to as “chemical strengthening layer removing step”).

The method for producing a glass substrate for a recording medium of the present invention can include other steps as long as it includes the chemical strengthening layer forming step and the chemical strengthening layer removing step. As such other processes, for example, a glass substrate precursor preparation process for preparing a glass substrate precursor can be exemplified.

<Glass substrate for recording medium>
The glass substrate for a recording medium produced by the present invention is used as a substrate for an information recording medium in an information recording apparatus such as a hard disk drive device, and its size and shape are not particularly limited. For example, the outer diameter is 2.5 inches, 1.8 inches, 1 inch, 0.8 inches, etc., and the thickness is 2 mm, 1 mm, 0.65 mm, 0.8 mm, etc. be able to. Further, a hole for setting in the information recording apparatus may be formed in the disc-shaped central portion.

<Glass substrate precursor preparation process>
A glass substrate precursor preparation process is a process performed before performing the chemical strengthening layer formation process of this invention, and is a process of preparing the glass substrate precursor for performing a chemical strengthening layer formation process.

Such a glass substrate precursor preparation step includes, for example, the following steps. First, a glass material is melted (glass melting step), molten glass is poured into a lower mold, and press molding is performed with an upper mold to obtain a disk-shaped glass substrate precursor (press molding process). Note that the disk-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 such a press molding process.

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

Next, the glass substrate precursor press-molded as described above is perforated at the center with a core drill or the like having a diamond grindstone or the like in the cutter (coring process). Hereinafter, the end face of the hole is referred to as an inner circumference.

Next, both surfaces of the glass substrate precursor with holes formed therein are ground to preliminarily adjust the overall shape of the glass substrate precursor, that is, the parallelism, flatness and thickness of the glass substrate precursor (first lapping step) ).

Subsequently, the inner and outer diameters are processed by grinding the outer peripheral end surface and the inner peripheral end surface of the glass substrate precursor with, for example, a grinding wheel such as a drum-shaped diamond (inner / outer diameter processing step). Next, the inner peripheral end face of the glass substrate is made to have a curved corner at the chamfered portion by brush polishing using a polishing liquid, and fine scratches and the like are removed (inner peripheral end face processing step).

Subsequently, both surfaces of the glass substrate precursor are ground again to finely adjust the parallelism, flatness and thickness of the glass substrate (second lapping step). Then, the outer peripheral end surface of the glass substrate is subjected to brush polishing using a polishing liquid so that the corners of the chamfered portion are curved surfaces, and fine scratches are removed (outer peripheral end surface processing step).

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

Here, a grinding machine for grinding the glass substrate precursor in the first and second lapping steps will be described. As the grinding machine, a known grinding machine called a double-side grinding machine can be used. The double-sided grinding 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. On the opposing surfaces of the upper and lower surface plates, the recording surface of the glass substrate precursor (the surface of the glass substrate precursor having a large area excluding the outer peripheral end surface and the inner peripheral end surface, the main surface or simply A plurality of diamond pellets for grinding the surface (also called the surface) are attached. 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 the glass substrate precursor is fitted into the holes and arranged. The upper and lower surface plates, the internal gear and the sun gear can be operated by separate driving.

The so-called lapping process including the first lapping process and the second lapping process is a process of processing the glass substrate precursor to a predetermined plate thickness. Specifically, for example, a step of grinding (lapping) both surfaces of the glass substrate precursor can be mentioned. By doing so, the parallelism, flatness, and thickness of the glass substrate precursor can be adjusted. Further, this lapping step may be performed once or twice or more. For example, in the case of performing twice, in the first lapping step (first lapping step), the parallelism, flatness and thickness of the glass substrate precursor are preliminarily adjusted, and in the second lapping step (second lapping step), Finely adjust the parallelism, flatness and thickness of the glass substrate precursor.

More specifically, examples of the first lapping step include a step in which the entire surface of the glass substrate precursor has a substantially uniform surface roughness. For example, a mechanical method using loose abrasive polishing by a surface grinder can be applied. At that time, for example, when the arithmetic average roughness Ra of the glass substrate precursor surface is measured at a plurality of locations, the difference between the minimum value and the maximum value of Ra obtained should be about 0.01 to 0.4 μm. Is preferred.

The second lapping step is preferably a step in which the arithmetic average roughness Ra of the glass substrate precursor surface is 0.1 μm or less and the flatness is 7 μm or less. From the viewpoint of obtaining the effects of the present invention, the surface roughness Ra is 0.1 μm or less, and it is preferable that the surface roughness Ra is as low as possible. However, if the surface roughness Ra is too low, the surface becomes too smooth. Since the processing becomes difficult in the lapping process, it is considered that 0.01 μm is the limit.

In order to obtain the surface quality of such a glass substrate precursor, for example, a method of grinding with a fixed abrasive polishing pad set in a lapping apparatus can be applied. As the fixed abrasive polishing pad, for example, a commercially available one can be used, such as a three-dimensional fixed abrasive with a surface pattern such as Trizacto (diamond tile size 2 μm, manufactured by Sumitomo 3M Co., Ltd.) 2 μm. Can be used.

When the second lapping process is completed, defects such as large waviness, chipping, and cracks are removed, and the surface roughness of the recording surface of the glass substrate precursor has a maximum height Rmax of 1.0 μm and an arithmetic average roughness Ra. Is preferably 0.1 μm or less. More preferably, Ra is 0.05 μm or less. By having such a surface state, polishing (removal of the chemical strengthening layer) can be efficiently performed in the chemical strengthening layer removing step through the chemical strengthening layer forming step described later.

Therefore, the present invention includes a step of grinding the surface of the glass substrate precursor (that is, the lapping step described above) before the step of forming a chemical strengthening layer described later, and the surface of the glass substrate precursor is ground. After the process (when the lapping process includes the first lapping process and the second lapping process as described above), the surface of the glass substrate precursor has an arithmetic average roughness Ra of 0.1 μm. The following is preferable.

On the other hand, it is preferable that the inner peripheral and outer peripheral end faces of the glass substrate precursor are polished by brush polishing in the inner peripheral and outer peripheral end face processing steps. The brush is preferably made of nylon, polypropylene or the like having a diameter of about 0.2 to 0.3 mm. The polishing liquid preferably contains cerium oxide (CeO ₂ ) having a particle size of about several μm. As a result of brush polishing, the surface roughness of the inner and outer peripheral end faces is preferably 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 precursor that has undergone the inner and outer diameter processing steps and the inner and outer peripheral end surface processing steps is such that the corner formed by the main surface and the end surface is removed, and 0.2 mm to 0.5 mm from the outer end surface It will be in a state of sagging from the main surface from a certain position.

Here, the arithmetic average roughness Ra (centerline average roughness) and the maximum height Rmax are defined in JIS B0601: 2001. These can be measured by an atomic force microscope (AFM) or the like. These rules and measurement methods are common to the other Ra and Rmax in this specification unless otherwise specified.

It should be noted that the grinding machines used in the first lapping process and the second lapping process have the same configuration, but it is preferable to perform grinding using separate grinding machines prepared exclusively for each process. 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 grinding conditions are required, resulting in a decrease in manufacturing efficiency.

<Chemical strengthening layer formation process>
The chemical strengthening layer forming step of the present invention is a step of forming a chemical strengthening layer on the surface of the glass substrate precursor prepared through the glass substrate precursor preparing step. Such a process usually reinforces the surface of the glass substrate precursor using a chemical strengthening treatment liquid. Such a chemically strengthened layer forming step can be employed without any particular limitation to a conventionally known method known as a chemical strengthening step in the method for producing a glass substrate for recording medium.

Specifically, for example, a step of immersing the glass substrate precursor in a chemical strengthening treatment liquid can be exemplified. Thereby, a chemical strengthening layer is formed in the area | region of several micrometers from the surface, Preferably about 5 micrometers in the surface and end surface of a glass substrate precursor. In the present invention, “the surface of the glass substrate precursor” in the expression “to form the chemical strengthening layer on the surface of the glass substrate precursor” includes a recording surface, an inner peripheral end surface, and an outer peripheral end surface. .

More specifically, in such a chemical strengthening layer forming step, the alkali metal ions such as lithium ions and sodium ions contained in the glass substrate precursor are immersed by immersing the glass substrate precursor in a heated chemical strengthening treatment liquid. It is carried out by an ion exchange method that substitutes alkali metal ions such as potassium ions having a larger ion radius. Compressive stress is generated in the ion-exchanged region due to the strain caused by the difference in ion radius, and the surface of the glass substrate precursor is strengthened in the region. Examples of such chemical strengthening treatment liquid include nitrate. Specifically, a salt obtained by mixing sodium nitrate and potassium nitrate is heated, and the glass substrate precursor is immersed in the molten liquid. The glass substrate precursor is preferably washed with a neutral detergent and pure water and dried after being treated with such a chemical strengthening treatment solution.

The interface between the chemically strengthened layer and the non-chemically strengthened region is determined based on whether or not ions introduced by ion exchange are present, and is usually SEM-EDX (scanning electron microscope-energy dispersive type). The cross section of the glass substrate precursor is measured using X-ray spectroscopy, and the point where the ratio of sodium and potassium is the same as the glass composition is taken as the interface. For this reason, the determination as to whether or not the chemical strengthening layer has been removed by the process described later is also based on the same measurement, and in the absence of ions introduced by ion exchange, the chemical strengthening layer has been removed. to decide.

Such a chemically strengthened layer has an effect of improving impact resistance, vibration resistance, heat resistance and the like. However, such an effect can be obtained by forming a chemical strengthening layer only on the end face (that is, the outer peripheral end face and the inner peripheral end face) of the glass substrate precursor. The reinforcing layer is removed from the surface (that is, the recording surface) of the glass substrate precursor. This is because, by removing the chemical strengthening layer from the recording surface in this way, it is possible to obtain an advantage of not generating scratches or dents that occur during processing.

<Chemical strengthening layer removal process>
The chemical strengthening layer removing step of the present invention is a step of removing the chemical strengthening layer from the recording surface of the glass substrate precursor using the first polishing liquid. Here, the first polishing liquid contains water and a first abrasive, and the first abrasive contains CeO ₂ (cerium oxide). In the present invention, the effective CeO ₂ amount in the chemical strengthening layer removing step is 0.05 to 0.5 μg / cm ² . Thereby, it succeeded in reducing the wave | undulation of the glass substrate for recording media as much as possible.

Such a chemical strengthening layer removing step removes the chemical strengthening layer from the recording surface of the glass substrate precursor, precisely finishes the recording surface of the glass substrate precursor, and has a desired shape of the outer peripheral edge of the recording surface. It has the effect of finishing into a shape. Furthermore, this chemical strengthening layer removing step improves the surface roughness and efficiently obtains the final shape so that the surface roughness finally required in the polishing step described later can be efficiently obtained. It also has the effect of adjusting its shape so that it can be made.

Specifically, the chemical strengthening layer removing step is performed by polishing the recording surface of the glass substrate precursor on which the chemical strengthening layer is formed, using a pad holding the first polishing liquid. The layer is removed. Here, the first polishing liquid contains at least water and a first abrasive, and the first abrasive contains at least CeO ₂ . The first abrasive may contain other abrasives as long as it contains CeO ₂ in this way. Examples of such other abrasives include zirconium silicate, zirconia, alumina, colloidal silica, and the like.

Further, the concentration of the first abrasive in the first polishing liquid is preferably 1 to 9% by mass, and more preferably 3 to 7% by mass. If the amount is less than 1% by mass, sufficient polishing action cannot be obtained. If the amount exceeds 9% by mass, the effective CeO ₂ amount exceeds the above range, and undulation may occur.

The first polishing liquid may preferably include CeO ₂ 60 wt% or more based on the total solid content, more preferably it contains more than 90 wt%. When CeO ₂ is less than 60% by mass, a sufficient polishing action cannot be obtained. In this respect, the higher the concentration of CeO ₂ , the better. However, since the one containing CeO ₂ at a high concentration is expensive, it is economical. Disadvantageous. In addition, although the solid content contained in a 1st polishing liquid is normally occupied with a 1st abrasive | polishing agent, surfactant, a dispersing agent, a chelating agent, etc. may be contained.

The first abrasive has a maximum value of 3.5 μm or less and a cumulative 50 volume% diameter D50 of 0.5 to 1.5 μm in a particle size distribution measured by a laser diffraction scattering method. preferable. The maximum value is more preferably 2.5 μm or less, and the cumulative 50 volume% diameter D50 is more preferably 0.5 to 1.2 μm. If the maximum value exceeds 3.5 μm, scratches may occur on the recording surface, which may not be preferable. Further, if the cumulative 50 volume% diameter D50 is less than 0.5 μm, the processing is difficult to perform and the production efficiency is deteriorated, and if it exceeds 1.5 μm, the roughness after processing becomes rough, which is not preferable.

Further, the effective CeO ₂ amount in the chemical strengthening layer removing step is an index indicating the degree or strength of the action of the first abrasive on the recording surface of the glass substrate precursor in the step, which is 0.05. By controlling in the range of ˜0.5 μg / cm ² , the undulation generated on the glass substrate can be reduced as much as possible. The effective CeO ₂ amount is more preferably 0.1 to 0.4 μg / cm ² . The effective amount of CeO ₂ is less than 0.05 [mu] g / cm ^2, or could not be sufficiently removed chemically strengthened layer, it becomes impossible to obtain a sufficient polishing effect. On the other hand, when the effective CeO ₂ amount exceeds 0.5 μg / cm ² , undulation occurs in the glass substrate. The above knowledge was obtained for the first time by the inventor's research and constitutes the greatest feature of the present invention. Such an effective CeO ₂ amount can be achieved by controlling the first abrasive concentration in the first polishing liquid and the CeO ₂ content in the total solid content as described above.

Here, in the present invention, the effective CeO ₂ amount refers to a numerical value measured as follows. First, the glass substrate precursor immediately after the chemical strengthening layer removing step is immersed in a mixed solution of 50 ml of nitric acid and 10 ml of 35 mass% hydrogen peroxide solution for 30 minutes at a liquid temperature of 80 ° C. Usually, a rinsing step for cleaning the glass substrate precursor is performed after the chemical strengthening layer removing step is completed. For the measurement, the glass substrate before such cleaning (that is, immediately after the chemical strengthening layer removing step) is performed. It is necessary to use a precursor.

Then, after the immersion for 30 minutes, the glass substrate precursor is taken out of the mixed solution, and then the mass of Ce contained in the mixed solution is measured using an inductively coupled plasma mass spectrometer (ICP-MS). To do. As the inductively coupled plasma mass spectrometer (ICP-MS), “7700s” (trade name) manufactured by Agilent Technologies can be used. Then, from the mass of the measured Ce, it calculates the CeO ₂ mass in the recording surface of the glass substrate precursor during chemical strengthening layer removing step. Then, it is the effective amount of CeO ₂ as determined from the area of the mass and the glass substrate precursor of the recording surface of the calculated CeO ₂ (both sides).

Hereinafter, the chemical strengthening layer removing step of the present invention will be further described.
First, the pad for holding the first polishing liquid is a hard pad having a hardness A of about 80 to 90. For example, a pad made of urethane foam is preferably used. When the hardness of the pad becomes soft due to the heat generated by polishing, the shape change of the polished surface increases, so it is preferable to use a hard pad.

Such a chemically strengthened layer removing step can be normally performed using a polishing apparatus having a structure similar to that of the grinding machine described above. However, the weight applied to the glass substrate precursor by the surface plate of the polishing apparatus. Is preferably 90 g / cm ² to 110 g / cm ² . The load applied to the glass substrate precursor 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 such a tendency.

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.

It is preferable to employ the above polishing conditions and set the polishing amount to 30 μm to 40 μm (that is, to remove the region from the surface to a depth of 30 μm to 40 μm so that the chemical strengthening layer can be completely removed). If it is less than 30 μm, scratches and defects may not be sufficiently removed. On the other hand, when the thickness exceeds 40 μm, it is possible to obtain a surface roughness in which Rmax is in the range of 2 to 60 nm and Ra is in the range of 2 to 4 nm. Thereby, the chemical strengthening layer on the recording surface of the glass substrate precursor can be completely removed.

In addition, it is preferable to add the dispersing agent which has polycarboxylic acid as a main component to a 1st polishing liquid, and to improve the dispersibility of a 1st polishing agent. The dispersant containing polycarboxylic acid as a main component is preferably about 0.25 to 5 parts by mass with respect to 1 part by mass of the first abrasive. This is because the concentration is sufficient to enhance dispersibility. The main component polycarboxylic acid preferably has an average molecular weight of about 1000 to 2000. This is to prevent the viscosity from affecting. Other dispersing agents can be used as long as the same dispersibility can be obtained. For example, a sulfonic acid-based or phosphonic acid-based dispersant can be used.

The effective CeO ₂ amount is not only the concentration of the first abrasive and the content of CeO ₂ with respect to the total solid content, but also the load on the glass substrate precursor, the rotational speed of the polishing apparatus, and the difference between the upper and lower surfaces of the rotational speed. It is also possible to make adjustments by appropriately adjusting the above. For example, if the load on the glass substrate precursor is increased, the effective CeO ₂ amount tends to increase, and the effective CeO ₂ amount tends to increase even if the rotational speed of the polishing apparatus is increased. Even if the difference is increased, the effective CeO ₂ amount tends to increase.

<Polishing process>
In the present invention, after the chemical strengthening layer removing step, the recording surface of the glass substrate precursor is polished using a second polishing liquid different from the first polishing liquid (hereinafter also referred to as “polishing step”). It is preferable to contain.

Such a polishing step is a step of further precisely polishing the recording surface of the glass substrate precursor after the chemical strengthening layer removing step. Specifically, it is a step of polishing the recording surface of the glass substrate precursor from which the chemical strengthening layer has been removed, using a pad holding a second polishing liquid different from the first polishing liquid.

Here, as the second polishing liquid, one containing water and a second abrasive can be used. As the second abrasive, CeO ₂ (cerium oxide) can be contained in the same manner as the first abrasive, but in order to make the recording surface of the glass substrate precursor more smooth, the grains are smaller than the first abrasive. It is preferable to use an abrasive having a finer diameter and less variation. The average particle size of the second abrasive is preferably about 20 nm. And it can be set as a 2nd polishing liquid by disperse | distributing such a 2nd abrasive | polishing agent in water, and making it a slurry form. In such a second polishing liquid, the mixing ratio of water and the second abrasive is preferably about 1: 9 to 3: 7. In the second abrasive, components other than CeO ₂ can include the same components as those mentioned for the first abrasive.

The pad for holding the second polishing liquid is a soft pad having a hardness of about 65 to 80 (Asker-C) that is softer than the pad used in the chemical strengthening layer removing step. For example, the pad is made of urethane foam or suede. It is preferable to use a pad made of metal.

Such a polishing step can usually be performed using a polishing apparatus similar to the above, but the weight applied to the glass substrate by the surface plate of the polishing apparatus should be 90 g / cm ² to 110 g / cm ^2. preferable. The load applied to the glass substrate by the surface plate greatly affects the shape of the outer peripheral edge as in the chemical strengthening layer removal process, but the shape cannot be changed as efficiently as the chemical strengthening layer removal process 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 chemical strengthening layer removing step. 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 desired shape of the outer peripheral edge, it is preferable to determine the weight 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.

Thus, by adjusting the polishing conditions in this polishing step, the shape of the outer peripheral edge of the present invention is obtained, and the surface roughness of the recording surface is Rmax 2 nm to 6 nm and Ra is 0.2 nm to 0.4 nm. It can be a range.

The polishing amount is preferably 1 μm to 5 μm (that is, polished and removed from the surface to a depth of 1 μm to 5 μm). By setting the polishing amount within this range, it is possible to efficiently remove minute defects such as minute roughness and undulation generated on the surface, and minute scratches generated in the steps so far.

In the polishing process, it is preferable not to use the polishing apparatus used in the chemical strengthening layer removing process as it is, but to perform polishing using another polishing apparatus having the same configuration but prepared for each process. This is because, if the polishing apparatus used in the chemical strengthening layer removal process is used as it is, the polishing accuracy in the polishing process decreases due to the first abrasive remaining in the chemical strengthening layer removal process, or the polishing conditions are reset. This is because complicated work is required and the production efficiency is lowered.

The glass substrate for recording medium of the present invention can be produced by washing the glass substrate precursor with acid or alkali after the completion of such a polishing step and subsequently conducting inspection.

<Other processes>
The method for producing a glass substrate for recording medium of the present invention may have various steps other than those described above. For example, heat shock process for confirming strength reliability of glass substrate for recording media, cleaning process for removing foreign substances such as abrasives and chemical strengthening treatment liquid remaining on the surface of glass substrate, various inspection / evaluation processes, etc. You may have.

<Magnetic recording medium>
A magnetic recording medium using the glass substrate for recording medium of the present invention will be described below by taking a magnetic disk as an example.

First, in such a magnetic disk, a magnetic film is directly formed on the surface of a disk-shaped recording medium glass substrate. As a method for forming the magnetic film, 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 glass substrate for a recording medium, sputtering, electroless Examples include a method of forming by plating. 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. In addition to the above-mentioned magnetic materials, there may be a granular structure in which magnetic particles such as Fe, Co, FeCo, CoNiPt are dispersed in a non-magnetic film made of ferrite, iron-rare earth, SiO ₂ , BN, or the like. 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.

Further, if necessary, an underlayer or a protective layer may be provided. The underlayer is formed between the glass substrate for recording medium and the magnetic film, and the protective layer is formed on the magnetic film.

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. 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 continuously formed with an underlayer, a magnetic film, and the like by an in-line sputtering apparatus. Further, such a protective layer may be a single layer, or may be a multilayer structure composed of 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, instead of the protective layer, a dispersion liquid in which colloidal silica fine particles are dispersed in a solution obtained by diluting tetraalkoxysilane with an alcohol solvent is applied on the Cr layer, and further fired to obtain silicon dioxide ( A SiO ₂ ) layer may be formed.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

<Examples 1 to 10 and Comparative Examples 1 to 3>
Using aluminosilicate glass (Tg: 500 ° C.) as the glass material, the glass melting step (melting at 1500 ° C.), the press molding step (the molten glass is poured into a flat mold, and the mold melts. Glass blanks with a thickness of 1.00 mm were obtained by sandwiching glass and press forming), coring process (through holes were formed in the center of the surface of the glass blanks using a diamond core drill, and donut-shaped perforated blanks 1st lapping step (Blank material is ground with a double-side grinding machine holding a plate with diamond pellets, and the parallelism, flatness, and thickness are pre-adjusted),・ Outer diameter processing step (grinding using # 325 grindstone and chamfering with # 500 grindstone, outer diameter of blanks material Method, roundness, inner diameter of the hole, etc.), inner peripheral end surface processing step (polishing the inner peripheral end surface with a nylon polishing brush and cerium oxide to make a mirror surface), second lapping step (The conditions were changed as will be described later), outer diameter end surface processing step (outer end portion is polished with a nylon polishing brush and cerium oxide and mirrored like the inner peripheral portion) A glass substrate precursor having a thickness of 65 mm, an inner diameter of 20 mm, and a thickness of 0.8 mm was obtained.

The surface of the glass substrate precursor is subjected to a second lapping step (that is, a step of grinding the surface of the glass substrate precursor that is performed before the step of forming the chemical strengthening layer) under the conditions of diamond tile (Diamond Tile). The surface of the glass substrate precursor can be lapped by using a three-dimensional fixed abrasive with a surface pattern. Specifically, lapping can be performed using Tri-act (registered trademark) of 3M. The diamond tile used here had a concentration of 100 and a particle size of 2 μm. By changing the degree of concentration of the diamond tile or changing the particle size, the surface of the glass substrate precursor before the chemical strengthening layer forming step is changed to the arithmetic average roughness described in Table 1 ("Initial Ra" section). It adjusted so that it might become Ra. In this case, Ra tends to decrease when the concentration of diamond tiles is increased, and Ra tends to decrease even if the particle size is decreased.

Next, the glass substrate precursor prepared as described above is immersed in a chemical strengthening treatment liquid at 400 ° C. for 60 minutes, which is composed of a 1: 1 composition of sodium nitrate and potassium nitrate. A chemically strengthened layer was formed on the 10 μm region of the surface.

Next, the concentration of the first abrasive (corresponding to the total amount of solids) containing water and the first abrasive becomes the concentration described in Table 1 (section “First Abrasive Concentration”), and is based on the total amount of solids the content of CeO ₂ was prepared first polishing liquid such that the content described in Table 1 (the "CeO ₂ content"). When the first abrasive was measured by a laser diffraction scattering method (using a particle size distribution measuring device (trade name: “SALD-2200”, manufactured by Shimadzu Corporation)) and the particle size distribution was measured, the maximum value was 3. The cumulative 50% by volume diameter D50 was 1.0 μm.

And using this 1st polishing liquid, the chemical strengthening layer was removed from the recording surface of the glass substrate precursor in which the chemical strengthening layer was formed above.

Specifically, the first polishing liquid obtained above is held on a urethane pad (trade name: “MH-C15A”, manufactured by Nita Haas Co., Ltd., hardness A: 85), and a polishing apparatus (manufactured by Speed Fem Co.) is used. By using, the chemical strengthening layer was removed from the recording surface of the glass substrate precursor by polishing under the following polishing conditions.

The polishing conditions were a load of 100 g / cm ² , a rotation speed of the upper surface plate of 30 rpm, a rotation speed of the lower surface plate of 24 rpm, and a polishing amount of 32 μm.

Thereafter, a recording substrate glass substrate was manufactured by polishing the recording surface of the glass substrate precursor under the following polishing conditions using a second polishing liquid different from the first polishing liquid.

The composition of the second polishing liquid is as follows. That is, it contains water and a second abrasive, and the second abrasive consists of colloidal silica having a particle size of 20 nm, a dispersant mainly composed of polycarboxylic acid, HEDP (chelating agent), and citric acid. The polishing conditions were a load of 110 g / cm ² , an upper surface plate rotation speed of 30 rpm, a lower surface plate rotation speed of 30 rpm, and a polishing amount of 1.5 μm.

Then, the glass substrate for a recording medium thus obtained was measured effective amount of CeO ₂ and swell. The results are shown in Table 1. The effective CeO ₂ amount was measured by the measurement method described above before the polishing step with the second polishing liquid. The waviness Wa was evaluated according to the following criteria by measuring at a wavelength of 10 mm to 0.1 mm using OptiFlat (manufactured by Phase Shift Technology).

<Evaluation of swell>
A: Waviness Wa is less than 5 mm B: Waviness Wa is 5 mm or more and less than 7 mm C: Waviness Wa is 7 mm or more and less than 9 mm D: Waviness Wa is more than 9 mm Show.

As is apparent from Table 1, it was confirmed that the undulation was reduced by setting the effective CeO ₂ amount in the range of 0.05 to 0.5 μg / cm ² . Therefore, it is clear that the waviness of the glass substrate for recording medium manufactured according to the manufacturing method of the present invention is reduced.

Although the embodiments and examples of the present invention have been described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Claims

A method for producing a glass substrate for a recording medium using a glass substrate precursor,
Forming a chemically strengthened layer on the surface of the glass substrate precursor;
Using the first polishing liquid, removing the chemical strengthening layer from the recording surface of the glass substrate precursor,
The first polishing liquid contains water and a first abrasive,
The first abrasive comprises CeO 2 ;
A method for producing a glass substrate for a recording medium, wherein an effective amount of CeO 2 in the step of removing the chemical strengthening layer is 0.05 to 0.5 μg / cm 2 .
The recording medium according to claim 1, further comprising a step of polishing the recording surface of the glass substrate precursor using a second polishing liquid different from the first polishing liquid after the step of removing the chemical strengthening layer. A method for producing a glass substrate.
The method for producing a glass substrate for a recording medium according to claim 1 or 2, wherein the concentration of the first abrasive in the first polishing liquid is 1 to 9% by mass.
Before the step of forming the chemical strengthening layer, the step of grinding the surface of the glass substrate precursor,
4. The recording medium according to claim 1, wherein after the step of grinding the surface of the glass substrate precursor, the surface of the glass substrate precursor has an arithmetic average roughness Ra of 0.1 μm or less. A method for producing a glass substrate.
2. The first abrasive has a maximum value of 3.5 μm or less and a cumulative 50 volume% diameter D50 of 0.5 to 1.5 μm in a particle size distribution measured by a laser diffraction scattering method. 5. A method for producing a glass substrate for a recording medium according to any one of items 1 to 4.
6. The method for producing a glass substrate for a recording medium according to claim 1, wherein the first polishing liquid contains 60% by mass or more of CeO 2 with respect to the total solid content.