JP2000203888A - Production of glass substrate for information recording medium, production of information recording medium, production of glass substrate for magnetic disc and production of magnetic disc - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a flying height and to prevent a head crash and an thermal asperity by bringing a glass substrate into contact with a chemically strengthening treatment solution containing a chemically strengthening salt and substituting ion in the substrate with ion having a larger ion diameter in the treatment solution. SOLUTION: A glass substrate such as aluminosilicate glass is immersed in and brought into contact with a chemically strengthening treatment solution containing a chemically strengthening salt cleaned by removing particles in a region not exceeding a glass transition temperature to give a glass substrate strengthened by substituting lithium ion, etc. in the substrate with ion having a larger ion diameter such as sodium ion. The chemically strengthening salt comprises sodium nitrate, potassium nitrate or their mixture, etc. is filtered in a dissolved state in water by a filter, etc. to remove particles. The amount of particles having >=0.2 μm particle diameter is adjusted to <=12,000 particles/ml. The obtained chemically strengthening salt is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an information recording medium used as a recording medium for information processing equipment, a method for manufacturing a substrate thereof, and a method for manufacturing a magnetic disk.

[0002]

2. Description of the Related Art A magnetic disk is one of such information recording media. A magnetic disk is formed by forming a thin film such as a magnetic layer on a substrate, and an aluminum or glass substrate has been used as the substrate. However, in recent years, in response to the pursuit of higher recording density, the ratio of glass substrates that can make the distance between the magnetic head and the magnetic recording medium (the flying height of the magnetic head) narrower than that of aluminum has Are getting higher and higher.

[0003] The glass substrate which is increasing in such a manner,
It is generally manufactured by chemically strengthening it to increase its strength so as to withstand the impact when it is mounted on a magnetic disk driver. Further, the glass substrate surface is polished with high precision to achieve a high recording density so that the flying height of the magnetic head can be reduced as much as possible. On the other hand, not only the glass substrate but also the magnetic head has changed from a thin film head to a magnetic resistance (MR head), responding to a high recording density.

[0004]

As described above, high flatness of the surface of a magnetic disk is indispensable for a low flying height required for a high recording density. In addition, when an MR head is used, high flatness is required on the surface of the magnetic recording medium due to the problem of thermal asperity. The thermal asperity is such that when a protrusion is present on the surface of a magnetic disk, the protrusion is influenced by the MR head, and
This is a phenomenon in which heat is generated in the R head, and the resistance value of the head fluctuates due to the heat, causing a malfunction in electromagnetic conversion. Even if the surface of the magnetic disk has high flatness, if there are protrusions on the surface of the magnetic disk that cause thermal asperity, these protrusions may cause a head crash, or the head crash may cause the magnetic disk to be damaged. It also has an adverse effect on magnetic disks, such as peeling off of the constituent magnetic films.

As described above, the demand for a high flatness of the magnetic disk surface is increasing day by day for the purpose of reducing the flying height and preventing the head crash, and also for preventing the occurrence of thermal asperity. In order to obtain such high flatness of the magnetic disk surface, a substrate surface with high flatness is ultimately required. However, if the substrate surface is no longer polished with high precision, the high recording density of the magnetic disk can no longer be obtained. We have reached the stage where we cannot realize the realization. That is,
Even if polishing is performed with high precision, high flatness cannot be obtained if foreign matter adheres to the substrate. Of course, foreign matter has been conventionally removed, but foreign matter on the substrate, which has been conventionally allowed, is considered to be a problem at today's high-density level.

[0006] Examples of such foreign matter include extremely fine iron powder and stainless steel pieces which cannot be removed by ordinary washing. For example, the chemical strengthening process is performed in a state in which particles such as iron powder adhere to the glass substrate, or in a state in which particles such as iron powder in the chemical strengthening solution adhere to the glass substrate in the chemical strengthening solution. It was found that the oxidation reaction occurring in the chemical strengthening process and the heat applied in this process formed a convex portion (protrusion) as if the iron were melted on the glass substrate. When a thin film such as a magnetic film is laminated on a glass substrate on which such projections (projections) are formed, projections are formed on the surface of the magnetic disk, thereby reducing flying height, preventing head crash, and improving thermal asperity. It was found to be a hindrance factor for the prevention of sickness. A detailed investigation of the cause of such fine iron powder adhering to the glass substrate revealed that the atmosphere in the chemical strengthening chamber where the chemical strengthening treatment was performed contained iron powder, and in particular, the chemical strengthening salt itself contained many iron powders. Was found to be included. Specifically, when the number of iron powders was examined for each factor, chemical strengthening salts (such as sodium nitrate and potassium nitrate)
It was found that the iron powder contained in the chemically strengthened salt itself before the preparation of the chemically strengthened treatment liquid by mixing was overwhelming. Furthermore, it has been found that the chemical strengthening salt itself contains many other particles that adhere to the glass substrate for the information recording medium in the chemical strengthening step and adversely affect the information recording medium. The applicant of the present application has previously developed a technology for removing iron powder and the like contained in the atmosphere in the chemical strengthening chamber where the chemical strengthening process is performed, thereby preventing the mixing of the iron powder and the like into the chemical strengthening treatment solution. An application has already been filed (Japanese Unexamined Patent Publication No.
No. 785). In addition, iron powder mixed into the chemical strengthening solution from the atmosphere in the chemical strengthening room is filtered through a chemical strengthening solution such as a micro sieve (wire mesh with holes formed by etching), which has excellent high-temperature corrosion resistance. A technology for removal has been developed and an application has already been filed (Japanese Patent Laid-Open No. Hei 10-194786).
issue). Here, the former method is effective in removing iron powder and the like contained in the atmosphere in the chemical strengthening chamber where the chemical strengthening process is performed. Although the latter method has a certain effect,
As described above, since the number of iron powders contained in the chemical strengthening salt itself before the chemical strengthening treatment liquid is prepared is overwhelming, the effect is not sufficient as a countermeasure for iron powder removal. Further, the latter method is not sufficient as a measure for removing other particles which adhere to the glass substrate for the information recording medium and adversely affect the information recording medium in the chemical strengthening step.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a glass substrate for an information recording medium capable of effectively suppressing the adhesion of particles which adhere to the glass substrate for the information recording medium and adversely affect the information recording medium in the chemical strengthening step. And Another object of the present invention is to provide a method for manufacturing a glass substrate for an information recording medium, which can effectively suppress the formation of projections due to adhesion of fine iron powder or the like to a glass substrate in a chemical strengthening step. Furthermore, the present invention can effectively suppress the adhesion of particles that adhere to the glass substrate for the information recording medium and adversely affect the information recording medium in the chemical strengthening step, and therefore produce a high-quality information recording medium with few defects. The purpose of the present invention is to provide a manufacturing method. Another object of the present invention is to provide a method of manufacturing a magnetic disk capable of achieving a reduction in flying height, prevention of head crash, and prevention of thermal asperity.

[0008]

According to the present invention, as a result of research and development for achieving the above-mentioned object, Japanese Patent Laid-Open No.
According to the method described in No. 4786, the formation of the above-mentioned projections (projections) cannot be sufficiently suppressed, and the projections (projections) can be formed even with iron powder of 1 μm or less (for example, 0.2 μm). I found it. And it was found that removing iron powder contained in the chemical strengthening salt itself in advance was very effective. In addition, it has been found that it is very effective to remove particles that adversely affect the information recording medium contained in the chemical strengthening salt itself beforehand, and have completed the present invention.

That is, the present invention has the following configuration.

(Structure 1) By bringing a glass substrate into contact with a chemical strengthening treatment solution containing a chemical strengthening salt, some ions contained in the glass substrate can be converted into a treatment solution having an ion diameter larger than the ions. In the method for manufacturing a glass substrate for an information recording medium, comprising a chemical strengthening step of strengthening the glass substrate by substituting ions, the chemical strengthening salt is a factor of thermal asperity so as to prevent generation of thermal asperity. A method for producing a glass substrate for an information recording medium, characterized in that the amount of particles to be formed is suppressed.

(Structure 2) By bringing a glass substrate into contact with a chemical strengthening treatment solution containing a chemical strengthening salt, a part of ions contained in the glass substrate can be removed from the processing solution having an ion diameter larger than the ions. In a method for manufacturing a glass substrate for an information recording medium, comprising a chemical strengthening step of strengthening the glass substrate by substituting ions, the amount of particles having a particle size of 0.2 μm or more contained in the chemical strengthening salt is 120.
A method for producing a glass substrate for an information recording medium, characterized in that the number is not more than 00 pieces / ml.

(Structure 3) Structure 2 is characterized in that particles occupying a particle size of 2 μm or more account for 25% or less of particles contained in the chemical strengthening salt.
The method for producing a glass substrate for an information recording medium according to the above.

(Structure 4) The content of particles having a particle diameter of 2 μm or more contained in the chemically strengthened salt is 4000 particles / m 2.
4. The method for producing a glass substrate for an information recording medium according to Configuration 2 or 3, wherein the glass substrate is at most 1.

(Structure 5) The method for manufacturing a glass substrate for an information recording medium according to any one of structures 1 to 4, wherein the particles include iron particles.

(Structure 6) The method for manufacturing a glass substrate for an information recording medium according to any one of Structures 1 to 5, wherein the glass substrate for an information recording medium is a glass substrate for a magnetic disk.

(Arrangement 7) An arrangement wherein the glass for a magnetic disk is a glass substrate for a magnetic disk used in combination with a magnetoresistive head (MR head) or a large magnetoresistive head (GMR head). 7. The method for producing a glass substrate for an information recording medium according to item 6.

(Structure 8) Manufacturing of an information recording medium characterized in that at least a recording layer is formed on a glass substrate obtained by the method of manufacturing a glass substrate for an information recording medium according to any one of Structures 1 to 7. Method.

(Structure 9) A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer on a glass substrate obtained by the method for manufacturing a glass substrate for an information recording medium according to any one of Structures 1 to 7. .

(Structure 10) A step of preparing a glass substrate, a correlation between the amount of particles contained in the chemical strengthening salt itself and the glide height is determined in advance, and the correlation of the particles having desired glide characteristics is determined from the correlation. A step of determining the amount as a reference set value, a step of determining that the amount of particles contained in the chemically strengthened salt itself is equal to or less than a predetermined reference set value, and, when exceeding the reference set value, included in the chemically strengthened salt itself. A step of reducing the amount of particles to a predetermined reference value or less; a step of preparing a chemical strengthening treatment liquid by mixing a chemical strengthening salt in which the amount of particles is equal to or less than a predetermined reference setting value; By contacting a glass substrate, a part of ions contained in the glass substrate is replaced with ions in a processing solution having a larger ion diameter than the ions. Method of manufacturing a glass substrate for a magnetic disk and having a chemical strengthening process to enhance more glass substrate.

(Structure 11) A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer on the main surface of the magnetic disk glass substrate obtained by Structure 10.

[0021]

According to the above configuration 1, since the amount of particles that cause thermal asperity contained in the chemical strengthening salt itself is suppressed, minute iron powder or the like in the chemical strengthening treatment liquid is deposited on the glass substrate. It is possible to effectively suppress the formation of the above-mentioned convex portion by adhering. Therefore, it is possible to manufacture a magnetic disk capable of achieving low flying height, prevention of head crash, and prevention of thermal asperity.

According to the above configuration 2, the amount of particles having a particle size of 0.2 μm or more contained in the chemical strengthening salt itself is reduced to 120.
Since it is not more than 00 particles / ml, it is possible to effectively suppress the adhesion of particles that adhere to the glass substrate for the information recording medium and adversely affect the information recording medium in the chemical strengthening treatment liquid. In particular, it is possible to effectively prevent fine iron powder and the like in the chemical strengthening treatment liquid from adhering to the glass substrate and forming the above-mentioned convex portions. Here, the reason why the particle size is set to 0.2 μm or less is that particles smaller than the particle size are considered to have no influence on the formation of the convex portions that cause thermal asperity. When the amount of particles having a particle size of 0.2 μm or more contained in the chemical strengthening salt exceeds 12000 particles / ml, fine iron powder or the like in the chemical strengthening treatment liquid adheres to the glass substrate to form the above-described convex portion. There is a tendency that the ratio is high and the number of protrusions increases, and the height of protrusions and the density of protrusions increase. Further, the rate of causing thermal asperity and head crash increases, which is not preferable.
Similarly, when the amount of particles having a particle size of 0.2 μm or more contained in the chemical strengthening salt exceeds 12000 particles / ml, the particles adhere to the glass substrate for the information recording medium in the chemical strengthening treatment liquid and adversely affect the information recording medium. This is not preferable because the number of particles attached increases. From the same viewpoint as above, the amount of particles having a particle size of 0.2 μm or more contained in the chemical strengthening salt is preferably 8000 particles / ml or less,
It is more preferably at most 00 / ml. This is because by reducing the amount of particles contained in the chemical strengthening salt, the amount of particles contained in the chemical strengthening salt is directly reflected in the occurrence of protrusions and the adhesion of particles in the chemical strengthening treatment liquid. This is because it is possible to reduce the probability of generation of the convex portion and the number of adhered particles. The density of the projections is desirably 0.002 / mm ² or less, and more desirably 0.0003 / mm ² or less. The amount of particles contained in the chemically strengthened salt was measured by a predetermined method shown below. That is, 10 g of each of the chemical strengthening salts (for example, potassium nitrate and sodium nitrate) is dissolved alone in 90 ml of ultrapure water (water that is sufficiently clean and does not contain particles that affect the measurement), and the solution is used for liquid. Using a particle counter (manufactured by Rion or PMS) of 5 ml three times in a row,
The number of particles contained per 1 ml (total number of particles in each particle size (total number of particles existing in each particle size range arbitrarily determined)) is obtained and converted, and the average value is calculated as the number of particles. did.

According to the above configuration 3, in the particles contained in the chemical strengthening salt, a large particle size (specifically, a particle size of 2 μm or more) which has a great influence on the formation of the projections (projections).
By setting the ratio of particles occupying 25% or less, it is possible to effectively prevent the formation of projections (projections). From the same viewpoint, this value is preferably set to 20% or less, more preferably 15% or less.

According to the above configuration 4, since the amount of particles having a particle size of 2 μm or more contained in the chemical strengthening salt itself is set to 4000 particles / ml or less, it is possible to more effectively prevent the formation of projections and the like. This is because particles having a particle size of 2 μm or more have a greater effect than particles having a particle size of less than 2 μm, and the particle size of, for example, iron particles, which is a cause of thermal asperity, is approximately It is due to being 2 μm or more.

In the above configuration 5, the particles include iron particles. This is because, when particles contained in the chemical strengthening salt itself were analyzed, O, Na, Mg, Al, Si, Cl, Fe, C
r etc. were detected. In particular, when the particles are Fe (iron) and the particles (iron) adhere to the glass substrate in the chemical strengthening treatment solution, the oxidation reaction occurring in the chemical strengthening process and the heat applied in this process cause the heat on the glass substrate. A protrusion (protrusion) is formed as if the iron were melted, and this protrusion has a high probability of causing thermal asperity or head crash. In the case of relatively large particles, the particles melt to form convex portions (projections),
In the case of relatively small particles, it was confirmed by a microscope that the particles were aggregated and melted to form convex portions (projections). Therefore, in the case of a magnetic disk, a remarkable effect appears particularly by controlling the amount of iron (particles) contained in the chemically strengthened salt. When the particles contain iron, iron oxide, SUS, and the like are included in the iron particles as well as iron. Further, as the material of the particles on which the convex portions (projections) are formed by the above-described oxidation reaction and heating, a metal (for example, Cr, Al, or the like) can be considered.

According to the sixth aspect, when the glass substrate for an information recording medium is a glass substrate for a magnetic disk, the formation of the above-mentioned convex portion which causes a head crash can be effectively suppressed. Therefore, it is possible to manufacture a magnetic disk capable of achieving a low flying height and preventing a head crash.

According to the above configuration 7, when the glass for a magnetic disk is a glass substrate for a magnetic disk used in combination with a magnetoresistive head, the above-mentioned convexity which causes thermal asperity and head crashes. The formation of the portion can be effectively suppressed, and as a result, a low flying height can be realized. When a magnetoresistive head is used, a low flying height is particularly required.
Especially effective.

According to the above configuration 8, since the glass substrate obtained by the method for manufacturing a glass substrate for an information recording medium according to any one of the above configurations 1 to 7 is used, the information is stored in the chemical strengthening treatment liquid. Particles that adhere to the recording medium glass substrate and adversely affect the information recording medium can be effectively suppressed, and a high-quality information recording medium with few defects can be obtained.

According to the ninth aspect, since the glass substrate obtained by the method for manufacturing a glass substrate for an information recording medium according to any one of the first to seventh aspects is used, the fine particles in the chemical strengthening treatment liquid are used. It is possible to effectively suppress the formation of the above-mentioned protrusions due to the adhesion of iron powder and the like to the glass substrate. Therefore, it is possible to obtain a magnetic disk in which the flying height is reduced, the head crash is prevented, and the thermal asperity is prevented.

According to the above configuration 10, the correlation between the amount of particles contained in the chemical strengthening salt itself and the glide height is determined in advance, and the amount of the particles having desired glide characteristics is determined from this correlation as a reference set value. The step of determining that the amount of particles contained in the chemical strengthening salt itself is equal to or less than a predetermined reference set value, and determining the amount of particles contained in the chemical strengthening salt itself if the amount exceeds the reference set value. And the step of setting the amount of particles to be equal to or less than the predetermined reference set value. Therefore, it is possible to reduce the occurrence of projections and the attachment of particles in the chemical strengthening process. The reference set value can be set according to the allowable level of the defect required for the information recording medium. Further, the reference set value is determined, for example, by disposing a magnetic head facing a main surface of a magnetic disk (or glass substrate) and moving the magnetic head relative to the magnetic disk (or glass substrate) at a predetermined glide height. To determine desired glide characteristics, in other words, by determining the reference set value based on the result of a glide test, it is possible to effectively reduce head crash, thermal asperity, etc. Can be prevented. The desired glide characteristics are
For example, a characteristic in which the incidence of hits and crashes is 0% when the glide height is 1.2 μ inch or less.

According to the above configuration 11, at least a magnetic layer is formed on the main surface of the glass substrate for a magnetic disk according to the above configuration 10, thereby preventing low flying height and head crash, and preventing thermal asperity. Can be manufactured.

A method for manufacturing a glass substrate for an information recording medium according to the present invention will be described. In the present invention, in order to remove particles contained in the chemical strengthening salt itself, for example, the particles are removed by a capturing means such as a filter in a state where the chemical strengthening salt is dissolved in water. By selecting the performance (minimum trapping particle size) and type of the filter, the amount of particles contained in the chemically strengthened salt can be reduced to a desired amount (for example, the amount of particles having a particle size of 0.2 μm or more can be reduced to 1200).
0 or less or 4000 or less). Also, using multiple filters with different minimum trapping particle diameters, it is possible to remove particles with a large particle diameter using a filter with a large minimum trapping particle diameter, and then remove particles with a small particle diameter with a filter with a small minimum trapping particle diameter. it can. In the present invention, it is not necessary to use a reagent in which all components other than the chemical strengthening salt are purified to high purity, and in particular, a chemically strengthened salt that has been cleaned by removing only particles that adversely affect iron powder and the information recording medium is used. If it is used, it is enough and cheap. Of course, such a highly purified reagent can be used, but is expensive. Further, the chemical strengthening salt used in the present invention preferably does not contain an additive for preventing caking. This is because it is considered that the additive for preventing caking contains a large amount of particles.

In the present invention, when particles contained in the chemically strengthened salt itself were analyzed, it was found that O, Na, Mg, A
1, Si, Cl, Fe, Cr and the like were detected. In particular, when the particles are Fe (iron) and the particles (iron) adhere to the glass substrate in the chemical strengthening treatment solution, the oxidation reaction occurring in the chemical strengthening process and the heat applied in this process cause the heat on the glass substrate. A protrusion (protrusion) is formed as if the iron were melted, and this protrusion has a high probability of causing thermal asperity or head crash. Therefore,
In the case of a magnetic disk, a remarkable effect appears particularly by controlling the amount of iron (particles) contained in the chemical strengthening treatment solution.

As the chemical strengthening method, low-temperature chemical strengthening in which ion exchange is performed in a region not exceeding the glass transition temperature is preferable. As the alkali molten salt used as the chemical strengthening treatment solution, potassium nitrate, sodium nitrate, or a nitrate obtained by mixing them can be used. Aluminosilicate glass, soda lime glass,
Borosilicate glass and the like. Examples of the glass substrate for an information recording medium include a glass substrate for a magnetic recording medium, a glass substrate for an optical recording medium, and a glass substrate for a magneto-optical recording medium. The present invention has a remarkable effect particularly with respect to a magnetic disk for a magnetoresistive head and its substrate.

Next, a method for manufacturing the magnetic recording medium (magnetic disk) of the present invention will be described. In the present invention, a magnetic recording medium is manufactured by forming at least a magnetic layer on the glass substrate for a magnetic recording medium of the present invention.

According to the present invention, the adhesion of particles that cause thermal asperity or head crash can be effectively suppressed. Therefore, when manufacturing a magnetic recording medium having a magnetic layer or the like formed on a glass substrate, In addition, it is difficult for a convex portion formed by particles that cause thermal asperity to be formed on the main surface of the glass substrate, and it is possible to prevent thermal asperity and head crash at a higher level. Since no projection is formed, a low glide height of, for example, 1.2 μ inch or less can be realized. In particular, the function of the magnetoresistive head can be fully exploited for a magnetic recording medium that performs reproduction with the magnetoresistive head. In addition, the performance of a CoPt-based magnetic recording medium or the like that can be suitably used for a magnetoresistive head can be sufficiently brought out. Further, there is no possibility that a defect such as a magnetic layer is generated by a particle which causes thermal asperity to cause an error.

The magnetic recording medium usually has a predetermined flatness and surface roughness, and has an underlayer, a magnetic layer, a protective layer, It is manufactured by sequentially laminating a lubricating layer.

The underlayer in the magnetic recording medium is selected according to the magnetic layer.

As the underlayer, for example, Cr, Mo, T
a, an underlayer made of at least one material selected from nonmagnetic metals such as Ti, W, V, B, Al, and Ni. In the case of a magnetic layer containing Co as a main component,
From the viewpoint of improving the magnetic properties, it is preferable that the material is Cr alone or a Cr alloy. The underlayer is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked.
For example, Cr / Cr, Cr / CrMo, Cr / CrV,
NiAl / Cr, NiAl / CrMo, NIAl / Cr
V and the like.

The material of the magnetic layer in the magnetic recording medium is not particularly limited.

As the magnetic layer, for example, CoPt, CoCr, CoNi, CoNiCr, C
oCrTa, CoPtCr, CoNiPt, CoNi
CrPt, CoNiCrTa, CoCrPtTa, Co
A magnetic thin film such as CrPtSiO may be used. In the magnetic layer, the magnetic film is formed of a non-magnetic film (for example, Cr, CrMo, Cr).
V, etc. to reduce noise (for example, CoPtCr / CrMo / CoPtCr, CoC
rPtTa / CrMo / CoCrPtTa).

As a magnetic layer corresponding to a magnetoresistive head (MR head) or a large magnetoresistive head (GMR head), a Co-based alloy is prepared by adding Y, Si, a rare earth element, Hf, G
An impurity element selected from e, Sn, and Zn, or an element containing an oxide of these impurity elements is also included.

The magnetic layer has a structure in which magnetic particles such as Fe, Co, FeCo, and CoNiPt are dispersed in a nonmagnetic film made of ferrite, iron-rare earth, or SiO2 or BN. And the like. Further, the magnetic layer may have any of an inner surface type and a perpendicular type recording format.

The protective layer in the magnetic recording medium is not particularly limited.

As the protective layer, for example, a Cr film, a Cr alloy film, a carbon film, a hydrogenated carbon film, a zirconia film,
A silica film is exemplified. These protective films are an underlayer,
It can be formed continuously with an in-line type sputtering device together with a magnetic layer and the like. Further, these protective films may have a single-layer structure or a multi-layer structure composed of the same or different films. Note that another protective layer may be formed on the protective layer or in place of the protective layer. For example, in place of the above protective layer, colloidal silica fine particles are dispersed and applied to a Cr film after diluting tetraalkoxylan with an alcohol-based solvent, and then baked to form a silicon oxide (SiO2) film. May be.

The lubricating layer in the magnetic recording medium is not particularly limited.

The lubricating layer is prepared, for example, by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon and dip coating, spin coating, or the like on the medium surface.
It is formed by applying by a spray method and performing heat treatment as needed.

[0048]

EXAMPLES The present invention will be described below more specifically based on examples.

Embodiment 1

(1) Roughing Step First, a glass substrate made of aluminosilicate glass having a diameter of 96 mmφ and a thickness of 3 mm cut out from a sheet glass formed by a downdraw method with a grinding wheel is used.
Grinding with a relatively rough diamond wheel
It was molded to a diameter of 1.5 mm and a thickness of 1.5 mm. In this case, instead of the down-draw method, the molten glass may be directly pressed using an upper mold, a lower mold, and a body mold to obtain a disk-shaped glass body. Further, it may be formed by a float method. As aluminosilicate glass, in terms of mol%, SiO2 is 57 to 74%, ZnO2 is 0 to 2.8%,
Al2O3 3-15%, LiO2 7-16%, Na2O
(For example, in terms of mol%, SiO 2: 67.0%, Zn
O2: 1.0%, Al2 O3: 9.0%, LiO2: 12.0
%, Na2O: glass for chemical strengthening containing 10.0% as a main component).

Next, both surfaces of the glass substrate were ground one by one with a diamond grindstone having a finer grain size than the grindstone. The load at this time was about 100 kg. As a result, the surface roughness of both surfaces of the glass substrate can be reduced to Rmax (JIS
B 0601) (about 10 μm). Next, a hole was made in the center of the glass substrate using a cylindrical grindstone, and the outer peripheral end face was also ground to make the diameter 95 mmφ.
After that, the outer peripheral end surface and the inner peripheral surface were subjected to predetermined chamfering. At this time, the surface roughness of the glass substrate end face is Rma
x was about 4 μm.

(2) Sanding (Lapping) Step Next, the glass substrate was sanded. This sanding step aims at improving dimensional accuracy and shape accuracy.
The sanding process was performed using a lapping device, and was performed twice while changing the grain size of the abrasive grains to # 400 and # 1000. More specifically, first, by using alumina abrasive grains having a grain size of # 400, setting the load L to about 100 kg, and rotating the internal rotation gear and the external rotation gear, both surfaces of the glass substrate housed in the carrier can be subjected to surface accuracy. 0 to 1 μm, surface roughness (Rma
x) Lapping was performed to about 6 μm. Next, lapping was performed by changing the particle size of the alumina abrasive grains to # 1000, to obtain a surface roughness (Rmax) of about 2 μm. The glass substrate that had been subjected to the sanding process was washed by sequentially immersing it in a neutral detergent and water washing tank.

(3) Mirror Finishing Step Next, the surface roughness of the end face of the glass substrate is set to 1 μm in Rmax and Rmax while rotating the glass substrate by brush polishing.
Polished to about 0.3 μm with a. The surface of the glass substrate that had been subjected to the end surface mirror finishing was washed with water.

(4) First Polishing Step Next, a first polishing step was performed. This first polishing step is intended to remove scratches and distortion remaining in the above sanding step, and was performed using a polishing apparatus. For details, use a hard polisher (cerium pad M) as polisher (polishing powder).
HC15: manufactured by Speed Fam) under the following polishing conditions. Polishing liquid: cerium oxide + water Load: 300 g / cm ² (L = 238 kg) Polishing time: 15 minutes Removal amount: 30 μm Lower platen rotation speed: 40 rpm Upper platen rotation speed: 35 rpm Inner gear rotation speed: 14 rpm Outside Gear rotation speed: 29 rpm The glass substrate after the first polishing step is washed with a neutral detergent, pure water, pure water, IPA (isopropyl alcohol), IPA.
(Steam drying) and sequentially immersed in each washing tank to wash.

(5) Second Polishing Step Next, using the polishing apparatus used in the first polishing step, the polisher was changed from a hard polisher to a soft polisher (Polyak: manufactured by Speedfam), and the second polishing step was performed. Carried out. The polishing conditions were the same as in the first polishing step, except that the load was 100 g / cm ² , the polishing time was 5 minutes, and the removal amount was 5 μm. The glass substrate after the second polishing step was immersed in each of a washing tank of a neutral detergent, a neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying) to be washed.

(6) Step of Preparing Chemically Reinforced Treatment Solution Next, particles contained in the chemically strengthened salt itself were removed to prepare sufficiently purified potassium nitrate and sodium nitrate, respectively. Specifically, potassium nitrate and sodium nitrate were respectively dissolved in ultrapure water, and particles contained in the chemical strengthening salt itself were removed using a liquid filter. Particles contained in each of the potassium nitrate and sodium nitrate were measured using a liquid particle counter. More specifically, potassium nitrate and sodium nitrate each alone are dissolved in 90 ml of ultrapure water (water that is sufficiently clean and does not contain particles that affect the measurement), and the solution is dissolved in a particle counter for liquid (particle size 0). .2 μm or more and 2.0 μm
Those with a particle size of less than Rion use a particle counter of 2.0 μm or more.
Is measured three times in succession by 5 ml each time, and the number of particles contained per 1 ml (total number of particles in each particle size) is calculated and converted, respectively.
The average value thereof was taken as the number of particles. As a result, there were more particles contained in sodium nitrate than particles contained in potassium nitrate. The amount of particles contained in sodium nitrate is 0.2 μm
1912 particles / ml, particle size 0.3 μm
m or more and less than 0.5 μm: 1192 particles / ml, particle size: 0.5
161 / ml with a particle size of 1.0 μm or more and less than 1.0 μm, and a particle size of 1.0
10 μm / ml with a particle diameter of 2.0 μm or more and less than 2.0 μm
310 or more / m and less than 3.0 μm, particle size 3.0 μm
m or more and less than 4.0 μm: 111 particles / ml, particle size: 4.0 μm
m / m <5.0 μm 60 particles / ml, particle size 5.0 μm
The number of particles having a particle diameter of not less than 6.0 μm is 36 particles / ml, the particle diameter of not less than 6.0 μm is 169 particles / ml, and the particles having a particle diameter of 2.0 μm or more is 686 particles / ml and the particle diameter is 0.2 μm or more.
The particles having a particle diameter of 2.0 μm or more accounted for 17.3% of the particles having a particle diameter of 2.0 μm or more. there were. 60% and 40% (total 73.5 kg) of the potassium nitrate and sodium nitrate were mixed and dissolved, respectively, to obtain a chemically strengthened treatment liquid.

(7) Chemical strengthening step The chemical strengthening treatment liquid obtained in the above step (6) is heated to 400 ° C. in a chemical strengthening treatment tank, and the cleaned glass substrate preheated to 300 ° C. is heated for about 3 hours. The immersion was performed. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, the immersion was performed in a state where a plurality of glass substrates were housed in a holder so as to be held at the end faces. in this way,
By immersion treatment in the chemical strengthening treatment liquid, lithium ions and sodium ions in the surface layer of the glass substrate are replaced by sodium ions and potassium ions in the chemical strengthening treatment liquid, respectively, and the glass substrate is strengthened. The thickness of the compressive stress layer formed on the surface layer of the glass substrate is about 100 to 200.
μm. The chemically strengthened glass substrate is
It was immersed in a water bath at 0 ° C., rapidly cooled, and maintained for about 10 minutes. The quenched glass substrate was immersed in sulfuric acid heated to about 40 ° C., and washed while applying ultrasonic waves.

The surface roughness Ra of the glass substrate obtained through the above steps was 0.5 to 1 nm. Further, when the glass surface was observed with an optical microscope, no projections causing thermal asperity or head crash were found.

(8) Magnetic Disk Manufacturing Process NiAl (Ni: 50 at%, Al: 50 at%) was formed on both surfaces of the glass substrate for a magnetic disk obtained through the above-described process by using an in-line sputtering apparatus.
Seed layer (film thickness 40 nm), CrMo (Cr: 94a)
t%, Mo: 6 at%) underlayer (film thickness 25 nm), Co
CrPtTa (Co: 75 at%, Cr: 17 at%,
Pt: 5 at%, Ta: 3 at%) Magnetic layer (film thickness 27 n)
m), a hydrogenated carbon protective layer (thickness: 10 nm) is formed sequentially, and a liquid lubricant layer (1 nm thick) made of perfluoropolyether is formed on the protective layer by a dipping method to form an MR head. A magnetic disk was obtained.

A glide test was performed on the obtained magnetic disk (glide height: 1.2 μ inch, peripheral speed: 8 m /
s) (1500 sheets), no hit (the head hits a protrusion on the magnetic disk surface) or crash (the head hits a protrusion on the magnetic disk surface) was not observed. In addition, it was confirmed that no defect was generated in the film such as the magnetic layer due to the particles causing the thermal asperity.

A reproduction test was performed on the magnetic disk of this embodiment after the glide test by using a magnetoresistive head. A malfunction of reproduction due to thermal asperity was observed for all of a plurality of samples (500 sheets). I couldn't.

Examples 2 to 4 and Comparative Example 1 Next, chemically strengthened salts having different amounts of particles were prepared.
A glass substrate for a magnetic disk and a magnetic disk were prepared and evaluated in the same manner as in Example 1 except that a chemical strengthening treatment liquid was prepared. In Comparative Example 1, a chemically strengthened salt that had not been cleaned was used. The amount of particles of the chemical strengthening salt (sodium nitrate) (particle size of 2.0 μm or more, particle size of 0.2 μm or more and less than 2.0 μm, the total thereof), the height (average value) of the projections, and the density of the projections ( Average value),
And glide test results (failure rate) of magnetic disks (5
000 sheets) are shown in Table 1. In Examples 2 to 4 and Comparative Example 1, the ratio of particles having a particle size of 2.0 μm or more to the total particles having a particle size of 0.2 μm or more was 18.2% (Example 2). , 15.0
% (Example 3), 22.1% (Example 4), 25.3%
(Comparative Example 1).

[0063]

[Table 1]

As can be seen from Table 1, the use of a chemically strengthened salt that has been cleaned (and consequently, the amount of particles contained in the chemical strengthening treatment liquid is reduced) allows the glass substrate surface to be effectively treated. It can be seen that the number of convex portions formed can be reduced, and the result of a reproduction test using a magnetoresistive head in the glide test is also good. In particular, when the amount of particles having a particle diameter of 0.2 μm or more is 4000 particles / ml or less (the amount of particles having a particle diameter of 2.0 μm or more is 700 particles / ml or less), no convex portion is formed, and thus glide This is preferable because no failure occurs in the test. On the other hand, the amount of particles having a particle size of 0.2 μm or more contained in the chemically strengthened salt is 12000 particles / m 2.
In particular, when the ratio of particles having a particle diameter of 2.0 μm or more exceeds 25%, the ratio of the formation of the projections increases during the chemical strengthening step, and the height of the projections also exceeds 30 nm. , The density of the projections is also 0.002 / m
m ² , the defect rate (the ratio of hits and head crashes) in the 1.2 μ inch-high glide test is high, and the reproduction test (500 sheets) was performed. In addition, the probability of malfunction of reproduction due to thermal asperity also increased. Further, in Comparative Example 1 chemically strengthened with a chemically strengthened treatment solution that had not been cleaned, the particle size of the chemically strengthened salt was 0.2 μm.
The amount of particles of m or more is 19320 particles / ml. In the chemical strengthening step, the rate of formation of the projections becomes extremely high, and the height of the projections is 100 nm and the density of the projections is 0.007. / Mm ² , the defect rate in a 1.2 μ inch high glide test (5000 sheets) was as high as 10%, and a reproduction test (500 sheets) was performed, but the probability of malfunction of reproduction due to thermal asperity was high. Was. When the protrusions formed in Examples 3 and 4 and Comparative Example 1 were analyzed and observed, the components of the protrusions contained iron, and those having solid particles adhered thereto, and those in the chemical strengthening process. And a convex portion in which particles (iron) were melted by the applied heat and the applied heat was observed.

Further, based on the results of the glide test shown in Table 1, the amount of particles contained in the chemical strengthening salt itself is predetermined and determined as a reference set value so that desired glide characteristics can be obtained. It can be seen that a magnetic disk can be manufactured by forming a glass substrate for a magnetic disk which can provide the glide characteristics of above, and further by forming at least a magnetic layer on the glass substrate. That is, for example, to obtain a chemically strengthened magnetic disk glass substrate satisfying a glide height of 1.2 μ inch,
The amount of particles contained in the chemical strengthening salt itself before being made into the chemical strengthening treatment liquid was changed to the chemical strengthening treatment liquid (molten salt) using particles having a particle size of 0.2 μm or more with 4000 particles / ml or less. ) And chemically strengthened using this chemical strengthening solution. In the above embodiment,
Although the glide height is described as an example of 1.2 μ inch, the present invention is not limited to this. As described above, the correlation between the glide height and the amount of particles contained in the chemical strengthening salt itself is determined in advance, and a desired value is obtained. The amount of particles contained in the chemically strengthened salt itself may be controlled so as to obtain the glide height of.

Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the above embodiments. For example,
The present invention can be applied to any glass substrate for an information recording medium manufactured through a chemical strengthening step, and a glass substrate for an optical disk, a glass substrate for a magneto-optical disk, and the like can be widely applied to various glass substrates for an information recording medium. In this case, in a glass substrate for an optical disk or a glass substrate for a magneto-optical disk, if the density of the convex portions is large, the recording / reproduction is adversely affected. Therefore, focusing on the density of the convex portions, the amount of particles contained in the chemical strengthening salt itself is focused on. Should be controlled.

[0067]

As described above, according to the present invention, since the amount of particles contained in the chemical strengthening salt itself is controlled, it adheres to the glass substrate for the information recording medium in the chemical strengthening treatment liquid, and the information recording medium Particles, which adversely affect the surface, can be effectively suppressed. In particular, it is possible to effectively suppress the formation of a convex portion that causes thermal asperity and head crash due to adhesion of minute iron powder and the like in the chemical strengthening treatment liquid to the glass substrate. Therefore, a high-quality information recording medium with few defects can be obtained.
As a result, a magnetic disk which can prevent the deterioration of the reproduction function due to asperity can be obtained. Further, a low flying height of 1.2 μ inch or less can be realized.

Claims (11)

[Claims] 1. A method in which a glass substrate is brought into contact with a chemical strengthening treatment solution containing a chemical strengthening salt to convert some of the ions contained in the glass substrate into ions in the treatment solution having an ion diameter larger than the ions. In the method for manufacturing a glass substrate for an information recording medium, comprising a chemical strengthening step of strengthening the glass substrate by substituting, the chemical strengthening salt is a factor of thermal asperity so as to prevent generation of thermal asperity A method for producing a glass substrate for an information recording medium, wherein the amount of particles is suppressed. 2. A method in which a glass substrate is brought into contact with a chemical strengthening treatment solution containing a chemical strengthening salt to convert some of the ions contained in the glass substrate into ions in the treatment solution having an ion diameter larger than the ions. A method for producing a glass substrate for an information recording medium, comprising a chemical strengthening step of strengthening the glass substrate by substituting, wherein the amount of particles having a particle size of 0.2 μm or more contained in the chemical strengthening salt is 12000 particles / ml or less. A method for producing a glass substrate for an information recording medium, the method comprising: 3. The method for producing a glass substrate for an information recording medium according to claim 2, wherein the proportion of particles having a particle size of 2 μm or more in particles contained in the chemical strengthening salt is 25% or less. . 4. The glass substrate for an information recording medium according to claim 2, wherein the content of particles having a particle size of 2 μm or more contained in the chemically strengthened salt is 4000 particles / ml or less. Method. 5. The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein the particles include iron particles. 6. The glass substrate for an information recording medium is a glass substrate for a magnetic disk.
6. The method for manufacturing a glass substrate for an information recording medium according to any one of claims 1 to 5. 7. The magnetic disk glass may be a magnetoresistive head (MR head) or a large magnetoresistive head (GMR head).
7. The method for producing a glass substrate for an information recording medium according to claim 6, wherein the glass substrate is a glass substrate for a magnetic disk used in combination with the head. 8. An information recording medium according to claim 1, wherein at least a recording layer is formed on a glass substrate obtained by the method for producing a glass substrate for an information recording medium according to claim 1. Production method. 9. A method for manufacturing a magnetic disk, comprising: forming at least a magnetic layer on a glass substrate obtained by the method for manufacturing a glass substrate for an information recording medium according to claim 1. Description: Method. 10. A step of preparing a glass substrate, a correlation between the amount of particles contained in the chemical strengthening salt itself and a glide height is determined in advance, and the amount of the particles having a desired glide characteristic is determined from the correlation. A step of determining that the amount of particles contained in the chemical strengthening salt itself is equal to or less than a predetermined reference setting value, and determining the amount of particles contained in the chemical strengthening salt itself when the amount exceeds the reference setting value. A step of reducing the amount to be equal to or less than a predetermined reference set value; a step of preparing a chemical strengthening treatment liquid by mixing a chemical strengthening salt having an amount of particles equal to or less than the predetermined reference setting value; By contacting
A chemical strengthening step of strengthening the glass substrate by replacing some of the ions contained in the glass substrate with ions in a processing solution having a larger ion diameter than the ions, A method for manufacturing a glass substrate. 11. A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer on the main surface of the glass substrate for a magnetic disk obtained according to claim 10.