JP2001006168A - Fabrication method of glass substrate for information recording medium, and fabrication method of information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent fine iron particles or the like in a chemical strengthening treatment liquid from being attached on a glass substrate so as to suppress formation of a raised portion which would cause thermal asperity or head crash. SOLUTION: In a fabrication method of a glass substrate for an information recording medium comprising the step of chemically strengthening the substrate by contacting the glass substrate with a chemical strengthening treatment liquid containing a chemical strengthening salt, a chemical strengthening salt, for example, with concentrations of Fe and Cr to be detected by an ICP emission analysis method or a fluorescent X-ray analysis method are equal to or less than 500 ppb, respectively, 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 and the like, and a method for manufacturing a substrate thereof.

[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 substrate or a 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,
In general, the magnetic disk drive is manufactured by being chemically strengthened to increase the strength so as to withstand an impact when the magnetic disk drive is mounted. 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, a high flatness is required on the surface of the magnetic recording medium due to the problem of thermal asperity. This thermal asperity is such that when a protrusion is present on the surface of a magnetic disk, the protrusion is affected by the MR head and the MR
This is a phenomenon in which heat is generated in the 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. And the oxidation reaction that occurs during the chemical strengthening process, and the heat applied in this process causes iron to adhere firmly to the glass substrate, causing protrusions (projections)
Was formed. Such protrusions (projections)
When a thin film such as a magnetic film is laminated on a glass substrate on which is formed, a convex portion is formed on the surface of the magnetic disk, which causes a reduction in flying height, prevention of head crash and prevention of thermal asperity. I knew it was there. 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. In addition, the present invention is not limited to the above-described glass substrate for an information recording medium, but also includes a glass substrate for an electronic device (a glass substrate for a photomask, a glass substrate for a phase shift mask, and a glass substrate for an information recording medium. ), Glass substrates used for optical elements, or optical glass products, ion exchange of ions contained in the glass with ions contained in the ion exchange treatment liquid to chemically strengthen,
Alternatively, the refractive index distribution is adjusted. Even in such a glass substrate, if particles such as iron powder and stainless steel pieces (Cr, etc.) are contained in the ion exchange treatment liquid, the efficiency of ion exchange is reduced, and the above-mentioned convex portions are formed. (For example, a desired characteristic cannot be obtained by blocking the light at the convex portion).

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. In addition, the present invention can effectively suppress the adhesion of particles that adversely affect the glass substrate for an electronic device, the glass substrate for an optical element, an optical glass product, or the like in the ion exchange treatment step, and therefore, the electron with less defects It is an object of the present invention to provide a manufacturing method capable of manufacturing devices, optical elements, optical glass products, and the like.

[0008]

Means for Solving the Problems The present inventor has conducted research and development in order to achieve the above-mentioned object. As a result, iron powder (including iron oxide and stainless steel) of 1 μm or less (for example, 0.2 μm) was obtained.
It has been found that even with these methods, a projection (projection) may be formed. And it is very effective to remove particles such as iron powder contained in the chemical strengthening salt itself in advance,
To this end, it has been found that quantitative analysis of iron and chromium contained in the chemical strengthening salt itself is very effective, and the present invention has been completed.

That is, the present invention has the following configuration.

(Structure 1) A method of manufacturing a glass substrate for an information recording medium, comprising the step of chemically strengthening a glass substrate by bringing the glass substrate into contact with a chemical strengthening treatment solution containing the chemical strengthening salt. As Fe detected by ICP emission analysis or X-ray fluorescence analysis,
A method for manufacturing a glass substrate for an information recording medium, wherein a chemically strengthened salt having a Cr concentration of 500 ppb or less is used.

(Structure 2) As the chemically strengthened salt, ICP
F detected by luminescence analysis or X-ray fluorescence analysis
3. The method for producing a glass substrate for an information recording medium according to Configuration 1, wherein a chemically strengthened salt having a concentration of each of e and Cr of 100 ppb or less is used.

(Structure 3) As the chemically strengthened salt, ICP
F detected by luminescence analysis or X-ray fluorescence analysis
3. The method for producing a glass substrate for an information recording medium according to Configuration 1, wherein a chemically strengthened salt having a concentration of each of e and Cr of 20 ppb or less is used.

(Structure 4) A solution in which the chemical strengthening salt is dissolved in a solvent is filtered by a filter, the particles captured by the filter are dissolved in an acid, and based on a calibration curve previously obtained from measurement of a sample having a known concentration. The glass substrate for an information recording medium according to any one of the constitutions 1 to 3, wherein a quantitative analysis of an element contained in the chemically strengthened salt and its concentration is performed by ICP emission spectroscopy or X-ray fluorescence analysis. Manufacturing method.

(Structure 5) A method of manufacturing a glass substrate for an information recording medium, comprising the step of chemically strengthening the glass substrate by bringing the glass substrate into contact with a chemical strengthening treatment solution containing the chemical strengthening salt. The particle size is 0.2 μm as determined from the difference between the amount of particles in the sample in which the chemically strengthened salt is dissolved in the reference solution (blank) and the amount of particles in the reference solution, measured using a liquid particle counter. The amount of the above particles is 120,000
What is claimed is: 1. A method for producing a glass substrate for an information recording medium, comprising using a chemical strengthening salt of not more than 1 / g.

(Structure 6) A method for producing a glass substrate for an information recording medium, comprising the step of chemically strengthening the glass substrate by bringing the glass substrate into contact with a chemical strengthening treatment solution containing the chemical strengthening salt. As, when a secondary electron image or a backscattered electron image is observed by a secondary electron detector or a backscattered electron detector with a scanning electron microscope (SEM),
When particles contained in 1 g of the chemically strengthened salt are trapped by a filter having a trapping minimum particle diameter of 0.2 μm and a diameter of 13 mmφ, the amount of particles having a particle diameter of 0.2 μm or more becomes 90%.
A method for producing a glass substrate for an information recording medium, comprising using a chemically strengthened salt of not more than 0 / mm ² .

(Structure 7) A glass substrate for an information recording medium according to Structure 6, wherein the amount of the particles having a particle diameter of 0.2 μm or more is 500 or less / mm ² or less. Production method.

(Structure 8) The glass substrate for an information recording medium according to Structure 6, wherein a chemically strengthened salt having an amount of the particles having a particle diameter of 0.2 μm or more is 30 particles / mm ² or less is used. Production method.

(Structure 9) A method for manufacturing a glass substrate for an information recording medium, comprising the step of chemically strengthening the glass substrate by bringing the glass substrate into contact with a chemical strengthening treatment solution containing the chemical strengthening salt. A method for producing a glass substrate for an information recording medium, comprising using a chemically strengthened salt which does not become black, gray or reddish brown when the chemically strengthened salt is analyzed by a colorimetric method.

(Structure 10) A method of manufacturing a glass substrate for an information recording medium, comprising the step of chemically strengthening a glass substrate by bringing the glass substrate into contact with a chemical strengthening treatment solution containing the chemical strengthening salt. A solution obtained by dissolving in a solvent is filtered by a filter, and when the particles are captured by the filter, a chemically strengthened salt having a color density of the filter below a certain standard is used for an information recording medium. A method for manufacturing a glass substrate.

(Structure 11) A method for testing a chemically strengthened salt, wherein the method according to any one of Structures 1 to 10 is used.

(Structure 12) The method for manufacturing a glass substrate for an information recording medium according to any one of structures 1 to 10, wherein the glass substrate for an information recording medium is a glass substrate for a magnetic disk.

(Configuration 13) A glass substrate for a magnetic disk is a magnetoresistive head (MR head) or a huge (large) head
13. The method for manufacturing a glass substrate for an information recording medium according to Configuration 12, wherein the method is a glass substrate for a magnetic disk used in combination with a magnetoresistive head (GMR head).

(Structure 14) An information recording medium characterized in that at least a recording layer is formed 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 10. Production method.

(Structure 15) Manufacturing of a magnetic disk characterized in that at least a magnetic layer is formed 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 10. Method.

(Structure 16) A method for producing an optical glass product, comprising the step of contacting a glass member with an ion-exchange treatment liquid to perform an ion-exchange treatment between ions in the glass member and ions in the ion-exchange treatment liquid. Claims 1 to 3, 5 to 1 as salts used in the ion exchange treatment liquid.
A method for producing an optical glass product, comprising using a salt satisfying the conditions described in any one of (1) to (3).

(Structure 17) The optical glass product is a glass substrate for an electronic device or a glass substrate for an optical element,
The method for producing an optical glass product according to Configuration 16, wherein the ion exchange treatment liquid is a chemical strengthening treatment liquid containing a chemical strengthening salt.

[0027]

According to the above constitutions 1-3, as a chemically strengthened salt,
By using a chemical strengthening salt in which the concentrations of Fe and Cr detected by ICP emission analysis or X-ray fluorescence analysis are each 500 ppb or less, minute iron powder and the like in the chemical strengthening treatment liquid adhere to the glass substrate. Thus, the formation of the above-mentioned convex portion can be effectively suppressed. Therefore, it is possible to manufacture a magnetic disk capable of achieving low flying height, prevention of head crash, and prevention of thermal asperity. Fe and Cr concentrations are 500ppb each
Is exceeded, the ratio of the projections formed during the chemical strengthening process becomes very high, the height of the projections and the density of the projections become large, and the defect rate in the glide test of 1.2 μ inches high And the probability of malfunction of reproduction due to thermal asperity increases. From a similar perspective, F
The concentrations of e and Cr are each preferably 250 ppb or less, more preferably 100 ppb or less, 20 ppb or less, 10 ppb or less, 5 ppb or less, and 1 ppb or less.
In the ICP emission spectroscopy, an element to be analyzed contained in a sample is vaporized and excited by inductively coupled plasma generated by inductively coupling high-frequency power, and the emission intensity at the obtained atomic spectrum line is reduced. This is a method of performing quantitative analysis or the like by measuring (JIS K0116).

According to the above configuration 4, the solution in which the chemical strengthening salt is dissolved in the solvent is filtered by the filter, the particles captured by the filter are dissolved in the acid, and the calibration curve previously obtained from the measurement of the sample having the known concentration is obtained. Based on ICP emission spectroscopy or X-ray fluorescence analysis, based on quantitative analysis of the elements and their concentrations contained in the chemically strengthened salt, metal-based particles such as iron and chromium are dissolved in acid, Quantitative analysis can be performed by ICP emission spectroscopy or the like, which is highly efficient. Here, the known concentration samples refer to standard samples having several different concentrations, and the calibration curve is obtained from the standard samples having different concentrations.

According to the above configuration 5, the reference liquid (blank) is used.
The amount of particles in the sample obtained by dissolving the chemically strengthened salt in
Since the amount of particles obtained from the difference from the amount of particles in the reference liquid is used as a determination target, an accurate and small measurement value of the amount of particles can be obtained, and a correct determination can be made based on this. Furthermore, the amount of particles having a particle size of 0.2 μm or more contained in the chemical strengthening salt itself was reduced to 1200.
Since the number is not more than 00 particles / g, 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 more is that particles smaller than the particle size are considered to have no influence on the formation of the convex portions causing thermal asperity. When the amount of particles having a particle size of 0.2 μm or more contained in the chemical strengthening salt exceeds 120,000 particles / g, 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 chemically strengthened salt exceeds 120,000 particles / g, 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 / g or less,
The number is more preferably 0 / g or less. 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. In addition,
The density of the projections is desirably 0.002 / mm ² or less,
0.0003 / mm ² or less is more desirable.

According to the above constitutions 6 to 8, 1 g of a chemically strengthened salt is obtained when a secondary electron image or a reflected electron image is observed by a secondary electron detector or a reflected electron detector with a scanning electron microscope (SEM). When the particles contained in the chemically strengthened salt are trapped by a filter having a trapping minimum particle size of 0.2 μm and a diameter of 13 mmφ, the amount of particles (iron powder, stainless steel pieces, etc.) having a particle size of 0.2 μm or more is 900 / Mm ²
By using the following chemical strengthening salt, 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 portion. Therefore, it is possible to manufacture a magnetic disk capable of achieving low flying height, prevention of head crash, and prevention of thermal asperity. Since the amount of particles per unit area captured by the filter is inversely proportional to the area of the filter, conversion may be performed if the area of the filter is different. For example, if the area of the filter is doubled, the amount of captured particles is halved.
m or more particles (iron powder, stainless steel pieces, etc.)
The same result as above can be obtained by using a chemically strengthening salt having an amount of 450 or less per mm ² . The amount of particles (iron powder, stainless steel pieces, etc.) is 900 / mm ²
Is exceeded, the ratio of the projections formed during the chemical strengthening process becomes very high, the height of the projections and the density of the projections become large, and the defect rate in the glide test of 1.2 μ inches high And the probability of malfunction of reproduction due to thermal asperity increases. The amount of particles (iron powder, stainless steel pieces, etc.) is 500 / mm ²
Below, 300 pieces / mm ² or less, 100 pieces / mm ² or less, 3
The number is preferably 0 / mm ² or less, more preferably 10 / mm ² or less.

According to the above configuration 9, as the chemically strengthened salt,
When the chemically strengthened salt is analyzed by a colorimetric method, by using a chemically strengthened salt that does not become black, gray or reddish brown, fine iron powder or the like in the chemically strengthened treatment liquid adheres to the glass substrate and is described above. The formation of the convex portion can be effectively suppressed. Therefore, it is possible to manufacture a magnetic disk capable of achieving low flying height, prevention of head crash, and prevention of thermal asperity. When the chemically strengthened salt is analyzed by a colorimetric method, when the color becomes black, gray or reddish brown, during the chemical strengthening step, the ratio of the convex portions formed becomes extremely high, and the height and convexity of the convex portions are increased. As a result, the defect density in the glide test with a height of 1.2 μ inch is high, and the probability of malfunction of reproduction due to thermal asperity is also increased.

According to the above configuration 10, by chemically filtering the solution of the chemical strengthening salt with a filter, causing the filter to capture particles, and using the chemical strengthening salt having a color density of a certain level or less on the filter. It is possible to effectively suppress the formation of the above-mentioned protrusions due to the attachment of the minute iron powder and the like in the strengthening treatment liquid to the glass substrate. Therefore, low flying height and head crash prevention, thermal
A magnetic disk capable of preventing asperity can be manufactured. When the color density of the filter is darker than a certain standard, the ratio of the projections formed becomes extremely high during the chemical strengthening step, and the height of the projections and the density of the projections increase. The defect rate in a glide test with a height of .2 μ inches is high, and the probability of malfunction of reproduction due to thermal asperity also increases.

According to the above configuration 11, the analysis method according to any one of the configurations 1 to 10 can be used as a method for testing a chemically strengthened salt.

According to the above configuration 12, when the glass substrate for an information recording medium is a glass substrate for a magnetic disk,
It is possible to effectively suppress the formation of the above-described convex portion that causes a head crash. Therefore, it is possible to manufacture a magnetic disk capable of achieving a low flying height and preventing a head crash.

According to the thirteenth aspect, if the magnetic disk glass is a magnetic disk glass substrate used in combination with a magnetoresistive head, the above-mentioned convexity which causes thermal asperity and head crashes is obtained. The formation of the portion can be effectively suppressed, and as a result, a low flying height can be realized. The use of a magnetoresistive head is particularly effective because it requires a particularly low flying height.

According to the above configuration 14, the above configurations 1 to 1
0, since the glass substrate obtained by the method for manufacturing a glass substrate for an information recording medium according to any one of 0 is used,
Particles that adhere to the glass substrate for an information recording medium in the chemical strengthening treatment liquid 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 above configuration 15, the above configurations 1 to 1
0, since the glass substrate obtained by the method for manufacturing a glass substrate for an information recording medium according to any one of 0 is used,
It is possible to effectively suppress the formation of the above-mentioned protrusions due to the attachment of the minute iron powder or the like in the chemical strengthening treatment liquid 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-mentioned constitutions 16 and 17, the salt used in the ion-exchange treatment liquid, which satisfies the condition described in any one of constitutions 1 to 3 and 5 to 10, is used. In this case, the efficiency of ion exchange is reduced, and particles (iron powder, stainless steel pieces, etc.) can be effectively prevented from adhering to the surface of the optical glass product. Therefore, high-quality electronic devices, optical elements, and optical glass products can be obtained. If such foreign matter adheres to the surface of the optical glass product, it is not preferable because light-blocking foreign matter blocks light and transmissive foreign matter refracts and scatters light. As optical glass products, for example,
Examples include an optical element, an electronic device, a gradient index lens, and an optical fiber, and also include a glass substrate for an electronic device and a glass substrate for an optical element.

The particles referred to in the present invention include iron particles. This is because when the particles contained in the chemical strengthening salt itself were analyzed, O, Na, M
g, Al, 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. Is firmly adhered to the surface, forming a projection (projection), and this projection has a high probability of causing thermal asperity or head crash. In the case of a relatively large particle, the particle adheres firmly to form a projection (projection), and in the case of a relatively small particle, the particle aggregates and adheres firmly to form a projection (projection). Was confirmed under a microscope. Therefore, in the case of a magnetic disk, a remarkable effect appears particularly by controlling the amount of particles such as iron contained in the chemically strengthened salt. Note that iron particles include iron oxide, iron oxide, stainless steel, and the like, as well as iron. Further, as other materials of the particles on which the convex portions (projections) are formed by the above-described oxidation reaction and heating, Ti, Al, Cl, Ce, glass pieces, and the like can be considered.

The method for producing a glass substrate for an information recording medium according to the present invention will be described. The present invention is characterized in that the amount and concentration of particles such as iron contained in the chemical strengthening salt itself are analyzed by the above-described analysis method, and the chemical strengthening salt having a standard value or less is used. As described above, it is determined by analysis that the amount of particles contained in the chemically strengthened salt itself is equal to or less than a predetermined reference value, and by preparing the chemically strengthened salt having a value equal to or less than the reference value, the amount of particles is reduced to a predetermined amount. It is possible to prepare a chemically strengthened treatment solution having a value not more than the value. Therefore, it is possible to reduce the occurrence of projections and the attachment of particles in the chemical strengthening process. The reference value is
It can be set according to the allowable level of defects required for the information recording medium. Further, the reference 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. It is determined that the desired glide characteristics are obtained, in other words, by determining the reference value based on the result of the glide test, head crash and thermal asperity are effectively prevented. it can. Here, the desired glide characteristic means, for example, such a characteristic that a hit or crash occurrence rate is 0% at a glide height of 1.2 μ inch or less.

In order to remove particles contained in the chemically strengthened salt itself based on the above analysis results, for example, the particles are removed by a capturing means such as a filter in a state where the chemically strengthened 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 controlled to a desired amount and concentration. 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.

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. Examples of the alkali molten salt used as the chemical strengthening treatment solution include potassium nitrate, sodium nitrate, a nitrate mixed with them, potassium sulfate, sodium sulfate, a sulfate mixed with them, NaBr, K
Br, a salt thereof or the like can be used.
Examples of the glass substrate include aluminosilicate glass, soda lime glass, and borosilicate glass. 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, 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 and the like.

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

As the underlayer (including the seed layer), for example, Cr, Mo, Ta, Ti, W, V, B, Al, Ni
And an underlayer made of at least one or more materials selected from nonmagnetic metals. In the case of a magnetic layer containing Co as a main component, it is preferable to use Cr alone or a Cr alloy from the viewpoint of improving magnetic properties. 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 / CrM
o, Cr / CrV, NiAl / Cr, NiAl / CrM
o, multilayer underlayers such as NIAl / CrV 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
Magnetic thin films such as CrPtB and CoCrPtSiO can be used. In the magnetic layer, the magnetic film is formed of a non-magnetic film (for example, Cr,
Multi-layer configuration (for example, CoPtCr / CrMo / CoP) in which noise is reduced by dividing by CrMo, CrV, etc.
tCr, CoCrPtTa / CrMo / CoCrPtT
a)).

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, SiO2, BN, or the like. 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 formed, 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.

[0056]

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

Example 1 and Comparative Example 1 (1) Roughing Step First, a glass substrate made of aluminosilicate glass cut into a disk shape having a diameter of 96 mmφ and a thickness of 3 mm using a grinding wheel from a sheet glass formed by a downdraw method. To
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. Thus, the surface roughness of both surfaces of the glass substrate can be reduced to Rmax (JISB).
(Measured at 0601) to about 10 μm. Next, a hole was made in the center of the glass substrate using a cylindrical grindstone, and the outer peripheral end surface was also ground to a diameter of 95 mmφ. Then, the outer peripheral end surface and the inner peripheral surface were subjected to predetermined chamfering.
At this time, the surface roughness of the end face of the glass substrate was 4 at Rmax.
It was about 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 adjusted to 1 μm by 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 Outer gear rotation speed : 29 rpm The glass substrate after the above first polishing step was 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 (Polytex: manufactured by Speed Fam), 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) Preparation and Analysis Step of Chemically Enhanced Salt Next, a part is taken from each raw material bag (lot) of potassium nitrate and sodium nitrate, which are the raw materials of the newly purchased chemically strengthened salt. A sample was prepared as follows.
First, particles contained in the chemically strengthened salt itself were removed to prepare fully purified samples of potassium nitrate and sodium nitrate (Example 1). Purification was performed by dissolving potassium nitrate and sodium nitrate in ultrapure water, respectively, and filtering with a liquid filter. In addition, samples of potassium nitrate and sodium nitrate which had not been subjected to any cleaning treatment and were merely collected from each raw material bag were produced (Comparative Example 1). Fe and Cr contained in these potassium nitrate and sodium nitrate were measured using ICP emission spectroscopy as follows. Although various particles are present in the chemically strengthened salt, the analysis here focuses on metal-based particles (iron powder, stainless steel pieces, etc.) that are difficult to remove when attached and cause defects. Was. Therefore, all the jigs used were made of glass or plastic in order to prevent dust generation of these particles from the jigs and filter holders used.

A portion of potassium nitrate and a portion of sodium nitrate were collected from a sufficiently cleaned sample (Example 1) and a sample not cleaned at all (Comparative Example 1).
After drying at 0 ° C. for one day or more, about 200 g was weighed. This sample was dissolved in hot water obtained by heating ultrapure water, and the obtained solution was filtered using a hydrophilic PTFE (polytetrafluoroethylene) membrane filter (minimum trapping particle size: 0.2 μm). . This membrane filter is immersed in an aqueous acid solution (hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, a mixed acid of these, etc.) containing 2 ml of aqua regia (hydrochloric acid 3: nitric acid 1) to dissolve the collected substance captured on the filter. . Pure water is added to the obtained aqueous acid solution, and the volume is adjusted to 50 ml.

For the analysis, an ICP emission spectrometer (SPS-1200VR, manufactured by Seiko Instruments Inc.) was used. First, solutions of four concentrations with known concentrations were prepared for Fe and Cr, respectively, and these elements were quantified by the above-mentioned ICP emission spectrometer by the absolute calibration method. The measurement conditions are shown below.

[0066]

[Table 1]

Using the sample obtained above, the above IC
With a P emission spectrometer, under the same measurement conditions as above,
Elemental quantification was performed. The measured concentration was determined from the calibration curve determined above. The conversion from the measured concentration to the sample concentration was obtained from the following relational expression (1).

Content in sample [ppb] = ICP measurement value [mg / l] × 10 ⁹ [ppb] × flask volume [ml] / 1000 [ml / l] / sample weight [mg] (1)

The measurement results were less than 500 ppb in Example 1 and more than 500 ppb in Comparative Example 1. Table 2 shows the results. It was confirmed that there was variation between lots.

[0070]

[Table 2]

(7) Chemical strengthening step Potassium nitrate and sodium nitrate were used at 60% and 40%, respectively, using the chemically strengthened salt analyzed in the above step (6).
(Total 73.5 kg) were mixed and dissolved to obtain a chemically strengthened treatment liquid. The obtained chemically strengthened treatment solution is transferred to a chemical strengthening treatment tank for 4 hours.
The cleaning was performed by immersing the cleaned glass substrate heated to 00 ° C. and preheated to 300 ° C. for about 3 hours. 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. As described above, by immersing 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 was about 100 to 200 μm. The glass substrate that had been chemically strengthened was immersed in a water bath at 20 ° 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. Also, when the glass surface was observed with an optical microscope, in Example 1,
No convexity causing thermal asperity or head crash was found. However, in Comparative Example 1, a convexity causing thermal asperity or head crash was observed.

(8) Magnetic Disk Manufacturing Process NiAl (Ni: 50 at%, Al: 50 at%) is formed on both surfaces of the magnetic disk glass substrate 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.

(Evaluation) A glide test was performed on the obtained magnetic disk (glide height: 1.2 μ inch, peripheral speed:
8m / s) (1500 sheets),
No hit (the head hits a protrusion on the surface of the magnetic disk) or crash (the head hits a protrusion on the surface of the magnetic disk) 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 example, which had completed the glide test, using a magnetoresistive head. No reproduction malfunction due to thermal asperity was observed for all of the plurality of samples (500 sheets). .

In Comparative Example 1, a glass substrate for a magnetic disk and a magnetic disk were prepared in the same manner as in Example 1 except that a chemically strengthened treatment solution was prepared by using a chemically strengthened salt that had not been cleaned. The same evaluation was performed. In Comparative Example 1, in which the chemical strengthening treatment was performed without cleaning, the concentration of Fe and Cr contained in the chemically strengthened salt was 500 p.
In the chemical strengthening step, the rate of formation of the projections becomes extremely high, and the height of the projections and the density of the projections are large.
(00 sheets) was as high as 10%, and a reproduction test (500 sheets) was conducted. As a result, the probability of a malfunction in reproduction due to thermal asperity was high.

Examples 2 to 5 Next, in the course of salt purification, several kinds of chemically strengthened salts were prepared in which the amounts of Fe and Cr were adjusted, and the same as in Example 1 except that these chemically strengthened salts were used. Thus, a glass substrate for a magnetic disk was produced. In addition, F contained in each salt
The amounts of e and Cr were measured in the same manner as in Example 1. Example 2: KNO ₃ : 3.4 ppb (Fe), 0.5 ppb (Cr) NaNO ₃ : 3.3 ppb (Fe), 0.8 ppb (Cr) Example 3: KNO ₃ : 74.2 ppb (Fe), 12.5 ppb (Cr) NaNO ₃ : 13.0 ppb (Fe), 3.3 ppb (Cr) Example 4; KNO ₃ : 195.5 ppb (Fe), 10.3 ppb (Cr) NaNO ₃ : 36.2 ppb (Fe), 5.7 ppb (Cr) Example 5; KNO ₃ : 478.2 ppb (Fe), 22.6 ppb (Cr) NaNO ₃ : 87.9 ppb (Fe), 45.5 ppb (Cr) When the surface of the obtained glass substrate was observed with an optical microscope, thermal asperity and head crash were observed. No protruding portion was found, but the chemically strengthened salt (K
It was confirmed that as the amounts of Fe and Cr contained in NO ₃ and NaNO ₃ ) increased, the height of the projections, the incidence of the projections, and the density of the projections tended to increase. However, the height of the protrusion was smaller than the height of the protrusion of Comparative Example 1, and was not a height that would cause thermal asperity or head crash.

Example 6 A glass substrate for a magnetic disk and a magnetic disk were manufactured in the same manner as in Example 1 except that the measurement was performed using a total reflection X-ray fluorescence analyzer instead of the ICP emission analysis method in Example 1. Was prepared and the same evaluation was performed. Hereinafter, the analysis method and the analysis conditions will be described. X-ray fluorescence analysis uses X
By irradiating the sample with strong primary X-rays obtained from a tube, the wavelength and intensity of the generated intrinsic X-rays are measured, the contained elements are identified, and a calibration curve considering the matrix effect is obtained using standard reagents. It is a method of preparing and quantifying contained elements.
Here, the incident angle of general X-rays is about 30 ° to 90 °, but may be about 30 ° to a critical angle which is the maximum incident angle at which the total reflection phenomenon of incident X-rays appears. The latter has higher sensitivity in principle, and it is more preferable to set the incident angle to about １ ／ to の of the critical angle. In the present embodiment, the analysis is performed by a total reflection X-ray fluorescence analyzer (TREX61 manufactured by Technos Co., Ltd.).
0) was used. The measurement conditions are shown below. Target: Tungsten (W) (other targets may be used) Spectral crystal: Monochromator Detector: Si (Li) SSD Atmosphere: Vacuum Voltage: 30 kV Current: 200 mA Measurement time: 500 sec Incident angle: 0.05 ° First , Fe and Cr were respectively prepared at four concentrations of known concentrations, and quantification of these elements was carried out under the above conditions by the absolute calibration curve method using the above total reflection X-ray fluorescence analyzer. In the measurement procedure, a known amount of the above solution is dropped on a clean silicon wafer, dried, and then the dried residue is irradiated with primary X-rays to measure the intensity of the intrinsic X-rays of Fe and Cr. In addition, it does not necessarily need to be in a dried state, and may be in a liquid state. Next, potassium nitrate and sodium nitrate were partially collected from the sufficiently cleaned sample prepared in Example 1 and dried at 110 ° C. for one day or more, and then about 200 g was weighed. This sample was dissolved in warm water heated with ultrapure water, the resulting solution was dropped on a silicon wafer, dried, and the residue was analyzed in the same manner as described above. As a result, almost the same quantitative results as those measured by the ICP emission spectrometry of Example 1 were obtained. However, the sensitivity was higher than the ICP emission spectrometry, and the analysis could be performed easily. In addition, a glass substrate for a magnetic disk manufactured in the same manner as in Example 1 except that a chemically strengthened salt analyzed using a total reflection X-ray fluorescence analyzer was used. No protrusion was found, and no malfunction of reproduction due to thermal asperity was recognized for the magnetic disk.

Example 7 and Comparative Example 2 A glass substrate for a magnetic disk and a magnetic disk were prepared in the same manner as in Example 1 and Comparative Example 1 except that the analysis of the chemically strengthened salt was performed using SEM. Was evaluated. The analysis was performed as follows.

Although various particles are present in the chemically strengthened salt, the analysis is performed by paying particular attention to metal-based particles (iron powder, stainless steel pieces, etc.) which are difficult to remove when adhered and cause defects. Therefore, all the jigs used were made of glass or plastic in order to prevent dust generation of these particles from the jigs and filter holders used. The jig to be used is cleaned in advance using pure water in a clean room. The vial bottle is made of Bencott (Nabebayashi Co., Ltd.) with a neutral detergent.
Wash the mouth and cap twice, and rinse off the detergent well. Thereafter, a 0.2 μm membrane filter unit was attached to the syringe, and a filter holder (diameter 13 mm,
(With a membrane filter with a minimum capture particle size of 0.2 μm) and filtered (hereinafter referred to as “predetermined pure water”)
Then rinse the vial well. For ceramic tweezers, rinse the tip with pure water. The filter holder is rinsed well with the specified pure water. At this time, the attached spacer for fixing the filter is also fitted into the filter holder and rinsed together. Place the jig after cleaning on a clean bencot so that the particles do not adhere again. As shown in FIG. 1, the cleaned filter holders A and B
In between, use ceramic tweezers, spacer 2
And a membrane filter 1 having a diameter of 13 mm and a minimum capture particle diameter of 0.2 μm are set. At that time, the holder is securely stopped so that the liquid does not leak from between the filter holders A and B.

The A side of the filter holder was attached to a 50 ml syringe (without a needle), and the sample (from the completely cleaned sample prepared in Example 1 and Comparative Example 1 and the sample not cleaned at all) , Potassium nitrate, and sodium nitrate were partially collected, dried at 110 ° C. for one day or more, weighed about 200 g, and the sample was dissolved in hot water heated with ultrapure water. Pour into it. In addition, after sucking up a sample with a syringe (without a needle), it may be mounted on the A side of the filter holder. Do not use the injection needle because it is made of metal and may generate dust. Press the syringe piston to inject the sample into the folder and perform the filtering. At this time, the piston is pressed so as not to push the piston at once, but to such an extent that the extract drops. In addition, if air bubbles are present in the filter holder A, not only a large pressing force is required, but also there is unevenness in the collection of foreign matters, so the presence or absence of air bubbles is checked. After the filtering, 10 ml of predetermined pure water is flushed three times and flushed.
Remove potassium and sodium from the filter. If a large amount of these remains on the filter, SEM observation becomes difficult due to charge-up, and EDX
Even during analysis (energy dispersive X-ray spectroscopy), accurate analysis cannot be performed due to the interference. Note that flushing can be easily performed using warm pure water. The filter is placed in a desiccator containing a desiccant for about 24 hours to remove moisture.

The membrane filter obtained above is placed on a carbon sample stage and trimmed with carbon dootite. At that time, a gap of about 2 mm is left without applying dootite on the entire circumference. By doing so, air that has entered between the membrane filter and the double-sided tape can be evacuated by evacuation during vapor deposition described below. Evaporation is platinum palladium 10
This is performed for 30 seconds at mA to obtain a sample for SEM analysis. Thereby, observation and analysis can be performed without problems at an acceleration voltage of 15 kV. Using the sample for SEM analysis obtained above, SEM observation is performed. The conditions are as follows: acceleration voltage 15 kV,
Observe using a WD 15 mm, backscattered electron detector or secondary electron detector. At this time, SE having a backscattered electron detector
With the use of the M device, the filter with a large amount of carbon appears black due to the atomic number effect, which looks brighter as the atomic number increases, and metal and glass appear sharply white, which is extremely convenient for visual inspection and photo judgment, and the counting accuracy is high. Get higher. In the case of a secondary electron beam image, it is difficult to distinguish between the filter and the foreign matter. The stage was moved to a place where the particles were conspicuous, and photographs of the entire image (100 times) and an enlarged image (500 times) were taken. FIG. 2 shows an overall image (100 ×) of KNO _{3 according} to Example 2, and FIG. 3 shows an enlarged image (500 ×).
Shown in FIG. 4 shows an overall image (100 ×) of KNO _{3 according} to Comparative Example 2, and FIG. 5 shows an enlarged image (500 ×). From these photographs, the amount of particles per unit area can be determined. If the entire screen is charged up with particles at the time of observation, it is considered that flushing was inadequate. Next, EDX analysis (energy dispersive X
Ray spectroscopy) (ESCA (X-ray photoelectron spectroscopy), SIMS
(Secondary ion mass spectrometry may be used). The conditions are analyzed using an acceleration voltage of 15 kV, a WD of 15 mm, and a backscattered electron detector. Particles of 10 points are randomly selected from within a 500-fold field of view and subjected to elemental analysis. This makes it clear what kind of element the particles contained in the chemically strengthened salt are made of.

As a result of these measurements, in Example 2, the amount of particles (iron powder, stainless steel pieces, etc.) having a particle size of 0.2 μm or more was 30 particles / mm ² or less (25 particles / mm ² ). In Example 2, the amount of particles (iron powder, stainless steel pieces, etc.) having a particle size of 0.2 μm or more was 900 particles / mm ^2.
It was super (915 / mm ² ).

(Evaluation) The surface of the glass before the formation of the magnetic film was observed with an optical microscope. As a result, in Example 2, no convexity causing thermal asperity or head crash was found. In No. 2, a protrusion causing thermal asperity and head crash was recognized. Glide test on the obtained magnetic disk (glide height: 1.2 μ inch, peripheral speed: 8 m / s)
(1500 sheets), no hits or crashes were found in Example 2. In addition, thermal
It was also confirmed that no defects occurred in the film such as the magnetic layer due to the particles that caused asperity.
A reproduction test was performed on the magnetic disk of this example, which had completed the glide test, using a magnetoresistive head. No reproduction malfunction due to thermal asperity was observed for all of the plurality of samples (500 sheets). .

On the other hand, in Comparative Example 2, the defect rate in the glide test (5000 sheets) having a height of 1.2 μ inch was as high as 10%, and the reproduction test (500 sheets) was performed. The probability of was high.

Examples 8 to 10 Next, in the course of salt purification, several kinds of chemically strengthened salts were prepared in which the amounts of Fe and Cr were adjusted, and the same as in Example 1 except that these chemically strengthened salts were used. Thus, a glass substrate for a magnetic disk was produced. In addition, F contained in each salt
The amounts of e and Cr were measured in the same manner as in Example 7. Example 8: 87 particles / mm ² (particles having a particle size of 0.2 μm or more) Example 9: 292 particles / mm ² (particles having a particle size of 0.2 μm or more) Example 10: 485 particles / mm ² (particle size When the surface of the obtained glass substrate was observed with an optical microscope, no protrusions causing thermal asperity or head crash were observed.
NO ₃ , NaNO ₃ ) as the amount of particles (particles having a particle size of 0.2 μm or more) increases.
It was confirmed that the height of the projections, the incidence rate of the projections, and the density of the projections tended to increase. However, the height of the protrusion was smaller than the height of the protrusion of Comparative Example 2, and was not a height that would cause thermal asperity or head crash.

Example 11 and Comparative Example 3 The filters obtained in Example 7 and Comparative Example 2 were visually observed after filtering, coloration and the like were compared, and the coloration and the like were correlated with the SEM analysis results and the like. By
This is an effective means that can determine the quality of the chemically strengthened salt. Specifically, for example, the membrane filter is taken out from the filter holder, and the water is completely removed with Kimwipe (manufactured by Nabebayashi Co., Ltd.). At this time, if salt crystals can be visually confirmed on the membrane filter, it is considered that flushing was inadequate, and the process is repeated from the beginning. Next, only the membrane filter is sandwiched between transparent adhesive sheets (for example, a pouch made by Meiko Shosha Co., Ltd.) and sealed. This is because if the paper is sealed together with the paper, the color will be changed later.
Next, the sealed membrane filter is placed on white paper and sealed again. Since the membrane filter is colored brown, white paper is used for the base for easy comparison. As a result of correlation with the SEM analysis result, when the color of the filter after filtering is darker than a certain standard, it causes a product defect. In the case of almost no coloring or light coloring, no product failure occurred.

Example 12 and Comparative Example 4 A glass substrate for a magnetic disk and a magnetic disk were prepared in the same manner as in Example 1 and Comparative Example 1, except that the analysis of the chemically strengthened salt was carried out by colorimetry. The same evaluation was performed. The analysis was performed as follows. From the fully-cleaned sample prepared in Example 1 and Comparative Example 1 and a sample that has not been cleaned at all, potassium nitrate and sodium nitrate were partially collected and dried at 110 ° C. for one day or more, About 200 g was weighed, this sample was dissolved in warm water heated with ultrapure water, and the obtained solution was subjected to a hydrophilic PTFE (polytetrafluoroethylene) membrane filter (minimum trapping particle size: 0.2 μm , Diameter: 13 mmφ). This membrane filter is immersed in an aqueous acid solution (hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, a mixed acid of these, etc.) containing 2 ml of aqua regia (hydrochloric acid 3: nitric acid 1) to dissolve the collected substance captured on the filter. . Pure water was added to the resulting acid aqueous solution, and the volume was adjusted to 50 ml. The solution with the constant volume was analyzed by a colorimetric method. In the colorimetric method, it is necessary to use one that is not black, gray or reddish brown when the chemically strengthened salt is analyzed by the colorimetric method. As a result of correlation with the IPC analysis result,
Black or gray contains a lot of stainless steel, red-brown contains a lot of rust (iron oxide), and when these colors appear, stainless steel and iron oxide are also 500 ppb in concentration.
The above included, causing product failure. In the case of almost colorless or pale skin color, no product failure occurred.

Example 13 A glass substrate for a magnetic disk and a magnetic disk were prepared in the same manner as in Example 1 and Comparative Example 1 except that the analysis of the chemically strengthened salt was performed using a particle counter, and the same evaluation was performed. went. The analysis was performed as follows.

For sample preparation, put in a clean vial
5.000 g of chemically strengthened salt (potassium nitrate newly purchased) was added, and 50 ml of ultrapure water filtered through a 0.2 μm filter was added thereto, followed by capping. The vial is immersed in warm water at 50 ° C. to dissolve the chemically strengthened salt. It was confirmed that the chemical strengthening salt did not recrystallize when the temperature of the solution was lowered to room temperature.

On the other hand, as a submerged particle counter, a light scattering type automatic particle counter (KL-2 manufactured by RION) is used.
0 type), and 10 ml of IPA (isopropyl alcohol) was flowed 5 times from the sample injection port of the particle counter.
Flashing. Then, add 0. 0 to the washed beaker.
Prepare a reference solution (background) gently containing 600 ml of ultrapure water filtered through a 2 μm filter. Then, 10 ml of this reference solution was flowed five times in the same manner as above,
A is completely discharged.

Subsequently, 10 ml of the reference liquid is allowed to flow five times in the same manner as described above, the number of particles is counted, and the number of particles in the reference liquid is determined for each particle diameter from the average of the latter three times. On this occasion,
When the 0.2 μm count is 200 or more in the latter three counts, or when the total count of five times is 300 or more, a reference solution is prepared again and counting is performed again.

To 500 ml of the reference solution, 1.0 ml of the solution of the chemically strengthened salt prepared above is added, and the mixture is stirred slowly.
This sample is allowed to flow five times in the same manner as described above, and the number of particles is counted.

From the number of increase in the number of particles = the number of particles in the sample liquid−the number of particles in the reference liquid, the number of increase in the number of particles in 10 ml is obtained. The number of impurity particles in 1 g of the chemically strengthened salt is obtained from the following equation.

Increased number of particles in 10 ml / [(5 g / 50 m
l) × (1ml / 500ml) × 10ml]

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 191 when the particle size is 0.2 μm or more and less than 0.3 μm.
119 particles / g, particle size 0.3 μm or more and less than 0.5 μm
2 particles / g, particle size of 0.5 μm or more and less than 1.0 μm is 161
Particles / g, 10 particles / g
g, 310 particles / 2.0 μm or more and less than 3.0 μm /
g, particle size: 3.0 μm or more and less than 4.0 μm
g, particle size of 4.0 μm or more and less than 5.0 μm is 60 particles / g,
A particle size of 5.0 μm or more and less than 6.0 μm is 36 particles / g, a particle size of 6.0 μm or more is 169 particles / g, and a particle size of 2.0 μm
The above particles are 686 particles / g, and the particles having a particle size of 0.2 μm or more and less than 2.0 μm are 3275 particles / g.
The total amount of particles having a particle size of 0.2 μm or more is 396.
1 particle / g, of which particles having a particle size of 2.0 μm or more accounted for 17.3%.

(Evaluation) The surface of the glass before the formation of the magnetic film was observed with an optical microscope. As a result, no protrusions causing thermal asperity or head crash were found. Glide test on the obtained magnetic disk (glide height: 1.2 μ inch, peripheral speed: 8 m / s)
(1500 sheets), no hits or crashes were found. 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 example, which had completed the glide test, using a magnetoresistive head. No reproduction malfunction due to thermal asperity was observed for all of the plurality of samples (500 sheets). .

Examples 14 to 16 and Comparative Example 5 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 13 except that a chemical strengthening treatment liquid was prepared. In Comparative Example 5, a chemically strengthened salt that had not been cleaned was used. Amount of particles of chemical strengthening salt (sodium nitrate) (particle size 2.0μ)
m or more, particle diameter of 0.2 μm or more and less than 2.0 μm, the sum of them), the height of the protrusions (average value), the density of the protrusions (average value), and the glide test result (defective rate) of the magnetic disk (5,000 sheets) are shown in Table 3. Examples 14 to
In Comparative Example 16 and Comparative Example 5, 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 1).
4), 15.0% (Example 15), 22.1% (Example 16), and 25.3% (Comparative Example 5).

[0098]

[Table 3]

As can be seen from Table 3, the use of the cleaned chemical strengthening salt (and consequently, the reduction of the amount of particles contained in the chemical strengthening treatment liquid) effectively applied to the glass substrate surface. 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 size of 0.2 μm or more is 4000 particles / g or less (the amount of particles having a particle size of 2.0 μm or more is 700 particles / g or less), no projections are formed, and thus glide This is preferable because no failure occurs in the test. On the other hand, the particle size of the chemical strengthening salt is not more than 0.1.
When the amount of the particles having a particle diameter of 2 μm or more exceeds 120,000 particles / g, particularly when the ratio of the particles having a particle diameter of 2.0 μm or more exceeds 25%, the ratio of the formation of the projections increases in the chemical strengthening step. At the same time, the height of the projections exceeds 30 nm, and the density of the projections is 0.002 / mm.
Since the ratio exceeds 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. The probability of malfunction of reproduction due to thermal asperity has also increased. In Comparative Example 5 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 193,200 particles / g. 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. The projections formed in Examples 15 to 16 and Comparative Example 5 were analyzed and observed. The components of the projections contained iron, and those having solid particles attached thereto,
Oxidation reaction in the chemical strengthening step and the heat applied thereto caused projections such as particles (iron) strongly adhered.

Further, based on the results of the glide test shown in Table 3, 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 is reduced by using a chemical strengthening salt in which the amount of particles having a particle size of 0.2 μm or more is 4000 particles / g or less. (Molten salt) is obtained and chemically strengthened using this chemical strengthening solution. In the above embodiment, the glide height was 1.2 μ inch as an example. However, 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. In advance, the amount of particles contained in the chemically strengthened salt itself may be controlled so as to obtain a desired glide height.

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 size and pore size of the filter used for the analysis are not limited to those described above. The filter size can be appropriately selected depending on the analysis method, for example, in the range of 10 mmφ to 50 mmφ in diameter, and the pore size of the filter is in the range of 0.1 to 2 μm, for example. Further, the elemental quantitative analysis can be performed in the same manner as described above by using the fluorescent X-ray analysis method instead of the ICP emission analysis method in Example 1. However, the ICP emission analysis method is excellent in terms of sensitivity and reproducibility. Further, by using a plurality of analysis methods in combination, the reliability of the analysis can be improved, and the quality of the product can be improved from the improvement of the analysis accuracy.

The present invention can be applied to any glass substrate for an information recording medium manufactured through a chemical strengthening process, and a glass substrate for an optical disk, a glass substrate for a magneto-optical disk, and the like can be widely applied to glass substrates for various information recording media. Can be applied. 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. Should be controlled.

[0104]

As described above, in the present invention, the amount of particles contained in the chemical strengthening salt itself is analyzed, and only the chemically strengthening salt that has passed the analysis is used. Particles that adhere to the information recording medium glass substrate and adversely affect the information recording medium 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, and in particular, a magnetic disk capable of achieving a low flying height, preventing a head crash, and preventing a decrease in the reproduction function due to thermal asperity can be obtained. Further, a low flying height of 1.2 μ inch or less can be realized.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a filter holder used in an embodiment.

FIG. 2 is a SEM photograph showing an analysis result of a chemically strengthened salt according to another example of the present invention.

FIG. 3 is a SEM photograph showing an analysis result of a chemically strengthened salt according to another example of the present invention.

FIG. 4 shows SE showing the analysis results of the chemically strengthened salt according to the comparative example.
It is an M photograph.

FIG. 5 shows SE showing the analysis result of a chemically strengthened salt according to a comparative example.
It is an M photograph.

[Explanation of symbols]

 1 Membrane filter 2 Spacer A Filter holder B Filter holder

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuki Sasaki 2-7-5 Nakaochiai, Shinjuku-ku, Tokyo Inside the Hoya Co., Ltd. (72) Inventor Yumi Mukai 2-7-5 Nakaochiai, Shinjuku-ku, Tokyo No. F-term in Hoya Corporation (reference) 4G059 AA08 AB03 AB09 AB11 AC16 AC18 HB02 HB13 HB14 HB15 HB23 5D112 AA02 BA03 GA26

Claims (17)

[Claims] 1. A method for manufacturing a glass substrate for an information recording medium, comprising the step of chemically strengthening a glass substrate by bringing the glass substrate into contact with a chemical strengthening treatment solution containing the chemical strengthening salt, A method for producing a glass substrate for an information recording medium, comprising using a chemically strengthened salt having a Fe and Cr concentration of 500 ppb or less, respectively, as detected by ICP emission analysis or X-ray fluorescence analysis. 2. The chemical strengthening salt according to claim 1, wherein the concentration of each of Fe and Cr detected by ICP emission analysis or X-ray fluorescence analysis is 100 ppb or less. The method for producing a glass substrate for an information recording medium according to the above. 3. The chemical strengthening salt according to claim 1, wherein the concentration of each of Fe and Cr detected by ICP emission analysis or X-ray fluorescence analysis is 20 ppb or less. The method for producing a glass substrate for an information recording medium according to the above. 4. A solution obtained by dissolving a chemically strengthened salt in a solvent is filtered through a filter, particles captured by the filter are dissolved in acid, and ICP emission is determined based on a calibration curve previously obtained from measurement of a sample of known concentration. The glass substrate for an information recording medium according to any one of claims 1 to 3, wherein a quantitative analysis of an element contained in the chemically strengthened salt and its concentration is performed by a spectroscopic analysis method or a fluorescent X-ray analysis method. Manufacturing method. 5. A method for producing a glass substrate for an information recording medium, comprising a step of chemically strengthening a glass substrate by bringing the glass substrate into contact with a chemical strengthening treatment solution containing the chemical strengthening salt, wherein: Particles having a particle size of 0.2 μm or more determined from the difference between the amount of particles in the sample obtained by dissolving the chemically strengthened salt in the reference solution (blank) and the amount of particles in the reference solution, measured using a liquid particle counter. A method for producing a glass substrate for an information recording medium, comprising using a chemically strengthened salt having an amount of particles of 120,000 particles / g or less. 6. A method for producing a glass substrate for an information recording medium, comprising a step of chemically strengthening a glass substrate by bringing the glass substrate into contact with a chemical strengthening treatment solution containing the chemical strengthening salt, When a secondary electron image or a backscattered electron image is observed with a secondary electron detector or a backscattered electron detector using a scanning electron microscope (SEM), particles contained in 1 g of the chemically strengthened salt are captured. When captured by a filter having a diameter of 13 mmφ, the particle size is 0.2 μm
A method for producing a glass substrate for an information recording medium, comprising using a chemically strengthened salt having an amount of the above particles of 900 particles / mm ² or less. 7. A glass substrate for an information recording medium according to claim 6, wherein a chemical strengthening salt having an amount of particles having a particle diameter of 0.2 μm or more of 500 particles / mm ² or less is used. Method. 8. The glass substrate for an information recording medium according to claim 6, wherein a chemically strengthened salt having an amount of particles having a particle size of 0.2 μm or more of 30 particles / mm ² or less is used. Method. 9. A method for producing a glass substrate for an information recording medium, comprising a step of chemically strengthening a glass substrate by bringing the glass substrate into contact with a chemical strengthening treatment solution containing the chemical strengthening salt, A method for producing a glass substrate for an information recording medium, comprising using a chemically strengthened salt that does not become black, gray or reddish brown when the chemically strengthened salt is analyzed by a colorimetric method. 10. A method for manufacturing a glass substrate for an information recording medium, comprising the step of chemically strengthening a glass substrate by bringing the glass substrate into contact with a chemical strengthening treatment solution containing the chemical strengthening salt, A glass substrate for an information recording medium, characterized by using a chemically strengthened salt having a color density of the filter equal to or less than a certain standard when a solution dissolved in the filter is filtered by a filter and particles are captured by the filter. Manufacturing method. 11. A method for testing a chemically strengthened salt, comprising using the analysis method according to any one of claims 1 to 10. 12. The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein the glass substrate for an information recording medium is a glass substrate for a magnetic disk. 13. A magnetic disk glass substrate used in combination with a magnetoresistive head (MR head) or a giant (large) magnetoresistive head (GMR head). Claim 1
2. The method for producing a glass substrate for an information recording medium according to item 2. 14. 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. 15. 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. 16. A method for producing an optical glass product, comprising: a step of subjecting a glass member to an ion exchange treatment liquid to perform an ion exchange treatment on ions in the glass member and ions in the ion exchange treatment liquid. Claims 1 to 3 as salts used in the exchange treatment solution
A method for producing an optical glass product, comprising using a salt satisfying the conditions described in any one of 3, 5, and 10. 17. The method according to claim 16, wherein the optical glass product is a glass substrate for an electronic device or a glass substrate for an optical element, and the ion exchange treatment liquid is a chemical strengthening treatment liquid containing a chemical strengthening salt. A method for producing the optical glass product according to the above.