JPH09124345A - Production of both glass substrate for magnetic disk and magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high flatness by dipping a glass substrate in a chemical strengthening solution, chemically strengthening the substrate, then pulling up the resultant glass substrate, cooling the pulled up substrate to a higher temperature than a crystallizing temperature of a molten salt, subsequently quenching the substrate at a specific rate and then washing the substrate surface. SOLUTION: A disklike glass substrate such as an aluminosilicate is preheated at about 200-350 deg.C and then dipped in a chemical strengthening solution prepared by heating a mixture, etc., of KNO3 /NaNO3 at 300-650 deg.C for about 1-20hr and the ion exchange of the substrate surface is then carried out to chemically strengthen the glass substrate. The strengthened glass substrate is then pulled up from the chemical strengthening solution and annealed to 300-350 deg.C which is higher than the crystallizing starting temperature of a molten salt at about 2-100 deg.C/min rate. The annealed substrate is further brought into contact with a refrigerant at 100-0 deg.C for 10-60min and quenched at 1600-400 deg.C/min rate for preventing the crystallization of the deposited molten salt. The quenched substrate is subsequently dipped and washed in a strong acid such as sulfuric acid warmed at about 40 deg.C, then washed with water to afford the chemically strengthened glass substrate. A ground layer, a magnetic layer, a protecting layer and a lubricating layer are successively laminated to the prepared glass substrate to produce a magnetic disk.

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 a glass substrate for a magnetic disk used for a hard disk and a method for manufacturing a magnetic disk.

[0002]

2. Description of the Related Art An aluminum substrate has been widely used as a glass substrate for a magnetic disk, but with the demand for downsizing the magnetic disk, thinning the plate, and lowering the flying height of the magnetic head, the size of the aluminum substrate is smaller than that of the aluminum substrate. Since it is easy to make a thin plate, the flatness is high, and the flying height of the magnetic head is easily made low, the ratio of using a glass substrate is increasing.

As described above, when the glass substrate is used as a magnetic disk substrate, the surface of the glass substrate is coated on the surface of the glass substrate for the purpose of improving impact resistance and vibration resistance and preventing the substrate from being damaged by impact or vibration. It is common to carry out a chemical strengthening treatment by a low temperature ion exchange method.

As a method for manufacturing a magnetic disk using this type of chemically strengthened glass substrate, for example, Japanese Patent Laid-Open No. 5-32
The method described in Japanese Patent No. 431 is widely known. The method described in this publication is one in which a glass substrate is immersed in a mixed solution of potassium nitrate and sodium nitrate heated to 400 ° C. to be chemically strengthened, and an underlayer and a magnetic layer are formed on this chemically strengthened glass substrate. .

[0005]

However, as in the above-mentioned conventional method, a magnetic disk manufactured by pulling up a glass substrate from a chemical strengthening solution, washing it, and then forming an underlayer and a magnetic layer on the glass substrate. However, there is a problem that abnormal protrusions often occur on the surface of the magnetic disk.
In this way, if an abnormal protrusion is generated on the surface of the magnetic disk, it causes a head crash with the magnetic head and cannot be used as a product.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method of manufacturing a glass substrate for a magnetic disk without abnormal projections and a method of manufacturing a magnetic disk.

The present inventor has investigated the cause of the generation of abnormal protrusions on the surface of the magnetic disk. As a result, a molten salt (for example, a precipitated molten salt) is deposited on the glass substrate pulled from the chemically strengthening solution.
It was found out that the deposited molten salt could not be removed even by washing, and the deposited molten salt became a foreign substance, causing abnormal protrusions on the magnetic disk surface. As a result of further research based on this finding, it was found that the deposition state of the molten salt deposited on the substrate differs depending on the cooling process after the chemical strengthening. Specifically, when the molten salt is slowly adhered to the substrate when slowly cooled like natural heat radiation, the rapidly molten precipitated molten salt is fragile and can be easily removed by washing, and the present invention has been completed. .

[0008]

In order to achieve the above object, a method of manufacturing a glass substrate for a magnetic disk according to the present invention comprises immersing a glass substrate in a heated chemical strengthening solution to remove ions in the surface layer of the glass substrate from the chemical strengthening solution. The step of chemically strengthening the glass substrate by ion exchange with the ions inside, the step of slowly pulling up the glass substrate from the chemical strengthening solution to a predetermined temperature (a temperature higher than the temperature at which the crystallization of the molten salt begins), and the glass substrate surface It is configured to include a step of rapidly cooling the glass substrate at a rate that prevents crystallization of the molten salt deposited on the glass substrate and a step of cleaning the surface of the glass substrate.

The method for manufacturing a glass substrate for a magnetic disk according to the present invention is the same as the method for manufacturing a glass substrate for a magnetic disk, wherein the glass substrate is rapidly cooled at 1600 ° C.
/ Min to 400 ° C / min, chemical strengthening solution 350
C. to 650.degree. C. to chemically strengthen it, pull up the glass substrate, gradually cool it to 300 to 350.degree. C., contact it with a refrigerant of 100.degree. C. to 0.degree. C. to quench it, and bring the glass substrate into contact with the refrigerant. The time is 10 minutes to 60 minutes, or in the chemical strengthening step, the glass substrate is held by the end face to perform the chemical strengthening.

Furthermore, the method for producing a magnetic disk of the present invention has a structure in which at least a magnetic layer is formed on a glass substrate for a magnetic disk obtained by using the above method for producing a glass substrate for a magnetic disk.

[0011]

In the present invention, the molten molten salt adhering to the glass substrate can be weakened by rapidly cooling the glass substrate pulled up from the chemical strengthening solution, and the molten molten salt can be easily removed by washing. Therefore, it is possible to manufacture a glass substrate for a magnetic disk without abnormal protrusions.

Further, when the glass substrate is housed in a holding means for holding it at its end face and immersed in the chemical strengthening solution, the precipitated molten salt generated between the end face of the glass substrate and the holding member also becomes fragile. It is possible to prevent damage to the end surface of the glass substrate when taking it out from the holding member.

Further, the chemically strengthened glass substrate has compressive stress on the surface and tensile stress on the inside. Therefore, if there are fine scratches on the surface, the glass substrate will be damaged by rapid cooling. Can be identified.

Further, according to the method for manufacturing a magnetic disk of the present invention, since the glass substrate for a magnetic disk having no abnormal protrusions or fine scratches on the surface is used, it is caused by the abnormal protrusions or fine scratches. High-quality magnetic disks with few defects can be manufactured with high yield.

Hereinafter, the present invention will be described in detail.

In the method for producing a glass substrate for a magnetic disk of the present invention, first, the glass substrate is immersed in a heated chemical strengthening solution, and the ions in the surface layer of the glass substrate are ion-exchanged with the ions in the chemical strengthening solution to make the glass substrate. To strengthen chemically.

Here, as the ion exchange method, a low temperature type ion exchange method, a high temperature type ion exchange method, a surface crystallization method, a dealkalization method of the glass surface and the like are known, but from the viewpoint of the glass transition point, It is preferable to use a low temperature type ion exchange method.

In the low temperature type ion exchange method, alkali ions in the glass are replaced with alkali ions having a larger ionic radius than that in a temperature range below the glass transition temperature Tg.
This is a method in which a strong compressive stress is generated in the glass surface layer by increasing the volume of the ion exchange section, thereby strengthening the glass surface.

As the chemical strengthening solution, potassium nitrate (K
Molten salts such as NO ₃ ), sodium nitrate (NaNO ₃ ) and potassium carbonate (K ₂ CO ₃ ), and molten salts of a mixture of these salts (KNO ₃ + NaNO ₃ , KNO ₃ + K ₂ CO ₃ ); Alternatively, Cu, Ag, Rb, C
Examples thereof include a molten salt of a mixture of salts of ions such as s. Note that the chemical strengthening solution may be a solution of the above salt instead of the molten salt.

The heating temperature is set at 3 from the viewpoint of the glass transition point.
It is preferably 50 ° C to 650 ° C, particularly 350 ° C to 480 ° C, and further preferably 350 ° C to 450 ° C.

The immersion time is preferably about 1 to 20 hours from the viewpoint of bending strength and stress strain layer.

The thickness of the compressive stress layer formed on the surface layer of the glass substrate is set at 6 from the viewpoint of improving the shock resistance and vibration resistance.
The thickness is preferably about 0 to 300 μm.

Before immersing the glass substrate in the molten salt, it is preferable to preheat the glass substrate to 200 to 350 ° C. for the purpose of preventing cracking.

In the chemical strengthening step, it is preferable to hold the glass substrate at the end face to carry out the chemical strengthening. this is,
This is for chemically strengthening the entire surface of the glass substrate.

In the present invention, after the chemical strengthening, the glass substrate is pulled out from the chemical strengthening solution and gradually cooled to a predetermined temperature (a temperature higher than the temperature at which the crystallization of the molten salt starts).

The lower limit temperature in gradual cooling cannot be generally stated because it depends on the type of chemical strengthening solution used (type of molten salt to be precipitated), but it is controlled to a temperature higher than the temperature at which crystallization of molten salt begins. It is preferable to perform cooling.

The glass substrate is slowly cooled at a rate of 2 ° C./min.
100 ° C./min, particularly 5 ° C./min to 60 ° C./min, and more preferably 10 ° C./min to 50 ° C./min.

In the present invention, after the slow cooling, the glass substrate is rapidly cooled at a rate that prevents the crystallization of the molten salt deposited on the surface of the glass substrate.

The rate of quenching the glass substrate is 1600 ° C.
/ Min-200 ° C / min, especially 1200 ° C / min-300 ° C
/ Min, more preferably 800 ° C / min to 400 ° C / min.

From the viewpoint of heat shock, it is preferable to quench the glass substrate by bringing it into contact with a refrigerant at 100 ° C. to 0 ° C.

From the viewpoint of cleanability, the time for contacting the glass substrate with the cooling medium is preferably about 10 to 60 minutes.

Examples of the refrigerant include water, hot water, a solution, a liquid refrigerant such as liquid nitrogen, a gas refrigerant such as nitrogen gas, water vapor, and cooling air, as well as air blowing.

In the present invention, after the rapid cooling, the surface of the glass substrate is washed to remove the precipitated molten salt attached to the glass substrate.

The washing method is not particularly limited as long as it is a method suitable for removing the precipitated molten salt. As the cleaning method, for example, a glass substrate is added to an acid such as heated sulfuric acid, phosphoric acid, nitric acid, hydrofluoric acid, hydrochloric acid, a mixed acid of these acids, or a mixture of these acids with a salt of these acids. Examples include a method of immersing and cleaning. In this case, cleaning may be performed while applying ultrasonic waves. In addition, after acid cleaning, commercially available cleaning agents (neutral detergents, surfactants, alkaline cleaning agents, etc.)
Known cleaning treatments such as cleaning with, scrub cleaning, pure water cleaning, solvent cleaning, and solvent drying may be performed. Moreover, in each cleaning, heating or ultrasonic application may be performed.

The glass substrate is not particularly limited as long as it is an ion-exchangeable glass substrate. Further, the size, thickness, etc. of the glass substrate are not particularly limited.

The material of the glass substrate is, for example, sodium ion (Na ⁺ ) such as aluminosilicate glass, soda lime glass, soda aluminosilicate glass.
And a multi-component glass containing ion-exchangeable ions such as lithium ion (Li ⁺ ) and the like. Aluminosilicate glass is particularly preferable because it has high strength after chemical strengthening, a deep compressive stress layer, and excellent shock resistance and vibration resistance.

As the aluminosilicate glass, Si is used.
O ₂ : 62 to 75% by weight, Al ₂ O ₃ : 5 to 15% by weight,
Li ₂ O: 4 to 10% by weight, Na ₂ O: 4 to 12% by weight,
ZrO _2: 5.5 to 15 with containing by weight% as the main component, the weight ratio of Na ₂ O / ZrO ₂ is 0.5 to 2.
0, and a glass for chemical strengthening in which the weight ratio of Al ₂ O ₃ / ZrO ₂ is 0.4 to 2.5 is preferable. By chemically strengthening such an aluminosilicate glass, it has excellent heat resistance, does not precipitate Na even in a high temperature environment, maintains flatness, and has excellent Knoop hardness.

The method for manufacturing a glass substrate for a magnetic disk according to the present invention is also used as a method for treating an end surface of a glass substrate for a magneto-optical disk or an electro-optical disk substrate such as an optical disk which does not like abnormal protrusions or fine scratches. it can.

Next, a method of manufacturing the magnetic disk of the present invention will be described.

In the method for producing a magnetic disk of the present invention, at least a magnetic layer is formed on the glass substrate for a magnetic disk obtained by using the method for producing a glass substrate for a magnetic disk described above.

In the present invention, a glass substrate having no abnormal protrusions or fine scratches on its surface is used, so that it is of high quality as a magnetic disk. In other words, by using a glass substrate with a much better surface condition than before, bed crashes due to abnormal protrusions do not occur in the case of magnetic disks, and defects due to scratches on the magnetic layer etc. It does not cause an error.

A magnetic recording medium is usually manufactured by sequentially laminating an underlayer, a magnetic layer, a protective layer and a lubricating layer on a glass substrate for a magnetic disk.

As the underlayer in the magnetic recording medium,
For example, non-magnetic thin films such as Cr, Mo, Ta, Ti, W, and Al can be mentioned. Al / Cr / CrMo, Al / Cr
A multi-layered underlayer such as / Cr may be used.

As the magnetic layer, for example, a magnetic thin film containing Co as a main component such as CoPtCr or CoNiCrTa can be used. CoPtCr / CrMo / CoPtCr or the like, which is obtained by dividing the magnetic layer with a nonmagnetic film to reduce noise. It may have a multilayer structure. The magnetic layer may be either a horizontal magnetic recording layer or a vertical magnetic recording layer.

Examples of the protective layer include a Cr film, a Cr alloy film, a carbon film, a zirconia film, and a silica film. These protective films can be continuously formed with an underlayer, a magnetic layer, and the like by an in-line type sputtering apparatus. Further, these protective films may have a single-layer structure or a multi-layer structure composed of the same or different films. Another protective layer may be further formed on the protective layer. For example, tetraalkoxylane is diluted with an alcohol-based solvent and applied on the protective layer, followed by firing to obtain silicon oxide (Si
An O ₂ ) film may be formed.

The lubricating layer is prepared by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon, and applying it to the surface of the medium by a dipping method, a spin coating method or a spraying method, and if necessary. It is formed by heat treatment.

[0047]

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

Example 1

The manufacturing method of the glass substrate for magnetic disk is as follows.
It is roughly divided into (1) grinding and polishing steps, (2) chemical strengthening step, (3) cooling step, and (4) cleaning step. (1) Grinding and polishing steps First, a sheet glass made of aluminosilicate glass is formed by a downdraw method. As the aluminosilicate glass, SiO ₂ : 63% by weight, Al ₂ O ₃ :
A glass for chemical strengthening containing 14% by weight, Li ₂ O: 6% by weight, Na ₂ O: 10% by weight and ZrO ₂ : 7% by weight as main components was used.

Then, the glass is cut out from the sheet glass into a disk shape by using a grinding wheel. Next, the front surface and the back surface are ground by sanding. Then, the center portion of the glass substrate is perforated in a disk shape, and the inner and outer peripheral surfaces perforated with a grindstone are polished to determine the outer and inner diameter dimensions, and the inner and outer peripheral surfaces are chamfered. Then, as the last of the polishing process, the front and back surfaces are subjected to precision polishing to finish. Thus, a disk-shaped glass substrate was obtained.

(2) Chemical Strengthening Step Next, the glass substrate that has undergone the grinding and polishing steps is washed and then chemically strengthened. Chemical strengthening is performed using potassium nitrate (6
0%) and sodium nitrate (40%) are mixed to prepare a chemical strengthening solution, which is heated to 400 ° C.
It was performed by immersing the cleaned glass substrate 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 end faces.

As described above, the lithium ion and the sodium ion on the surface layer of the glass substrate are converted into the sodium ion in the chemical strengthening solution by the immersion treatment in the chemical strengthening solution.
The glass substrate is strengthened by being replaced with potassium ions. The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 to 200 μm.

(3) Cooling Step The glass substrate that has undergone the chemical strengthening is gradually cooled in the first and second annealing chambers. First, the glass substrate is pulled up from the chemical strengthening solution, transferred to a first annealing chamber heated to 300 ° C., and kept in this for about 10 minutes to gradually cool the glass substrate to 300 ° C. Then, the glass substrate is transferred from the first slow cooling chamber to the second slow cooling chamber heated to 200 ° C., and the glass substrate is gradually cooled from 300 ° C. to 200 ° C. By gradually cooling in two stages in this way, the glass substrate can be released from damage due to thermal strain. Next, the glass substrate that had been gradually cooled was immersed in a water bath at 20 ° C. to be rapidly cooled and maintained for about 20 minutes.

(4) Washing Step The glass substrate that had been subjected to the cooling step was immersed in sulfuric acid heated to about 40 ° C. and washed while applying ultrasonic waves.

When the surface of the glass substrate for a magnetic disk manufactured through the above steps was illuminated with a halogen lamp at 150,000 lux and visually inspected, no foreign matter causing a problem was found.

(5) Magnetic Disk Manufacturing Step A Cr underlayer, a CrMo underlayer, a CoPtCr magnetic layer, and a C protective layer are formed on both surfaces of the glass substrate for a magnetic disk obtained through the above-mentioned steps by using an in-line type sputtering device. The layers were sequentially deposited to obtain a magnetic disk.

A glide test was carried out on the obtained magnetic disk. No hits (the head scratched the projections on the magnetic disk surface) or crashes (the head collided with the projections on the magnetic disk surface) were not observed. . It was also confirmed that no defect occurred in the film such as the magnetic layer.

[0058] soda-lime glass in place of Examples 2-3 aluminosilicate glass (Example 2), except for the use of soda aluminosilicate glass (Example 3) in the same manner as in Example 1, a glass for a magnetic disk A substrate and a magnetic disk were obtained.

As a result, the depth of the compressive stress layer was shallower than that of aluminosilicate glass, but there was no problem in practical use.

Example 4 Al (film thickness 50 Å) / Cr (100) was formed on both surfaces of the magnetic disk glass substrate obtained in Example 1.
0 angstrom) / CrMo (100 angstrom) underlayer, CoPtCr (120 angstrom) / CrMo (50 angstrom) / Co
A magnetic layer made of PtCr (120 Å),
A Cr (50 Å) protective layer was formed by an in-line type sputtering apparatus.

The above substrate was dipped in an organic silicon compound solution (mixture of water, IPA and tetraethoxysilane) in which fine silica particles (grain size 100 Å) were dispersed,
A protective layer made of SiO ₂ is formed by firing, and a dip treatment is performed on the protective layer with a lubricant made of perfluoropolyether to form a lubricating layer.
A magnetic disk for an R head was obtained.

When a glide test was conducted on the obtained magnetic disk, no hits or crashes were observed. It was also confirmed that no defect occurred in the film such as the magnetic layer.

EXAMPLE 5 Al / Cr / Cr was used as the underlayer and CoNiCr was used as the magnetic layer.
A magnetic disk for a thin film head was obtained in the same manner as in Example 4 except that Ta was used.

It was confirmed that the magnetic disk was the same as in Example 4.

Example 6 A magnetic disk for a thin film head was obtained in the same manner as in Example 1 except that the chemical strengthening solution was heated to 500 ° C. and the glass substrate preheated to 350 ° C. was chemically strengthened.

It was confirmed that the magnetic disk was the same as in Example 1.

Comparative Example 1 A glass substrate for a magnetic disk and a magnetic disk were obtained in the same manner as in Example 1 except that the glass substrate that had been gradually cooled was naturally cooled without quenching.

When the surface of the glass substrate for a magnetic disk was visually inspected in the same manner as in Example 1, about 100 to 10 foreign substances were found. Further, when a glide test was performed on the obtained magnetic disk, hits and crashes were recognized in about 20% of the number of tested sheets.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not necessarily limited to the above embodiment.

For example, in the washing step, a commercially available surfactant or detergent (including alkali type) may be used instead of the neutral detergent.

Further, as a polishing agent, cerium oxide (Ce
O ₂ ), colloidal silica (SiO ₂ ), alumina (γ-
Al ₂ O ₃ ), bran (Fe ₂ O ₃ ), chromium oxide (Cr
₂ O ₃ ), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ) and the like can also be used. The soft polisher may be made of suede or velour, and the hard polisher may be hard velor, urethane foam, pitch-impregnated suede or the like.

[0072]

As described above, according to the method of manufacturing a glass substrate for a magnetic disk of the present invention, the molten salt deposited on the glass substrate can be easily removed by washing,
It is possible to manufacture a glass substrate for a magnetic disk having high flatness without abnormal protrusions.

Further, since the molten salt precipitated between the end surface of the glass substrate and the holding member also becomes brittle, damage to the end surface of the glass substrate can be prevented when the glass substrate is taken out from the holding member.

Further, if there are fine scratches on the surface, they will be damaged by rapid cooling, so that defective products can be easily identified.

Further, according to the method of manufacturing a magnetic disk of the present invention, since the glass substrate for a magnetic disk having no abnormal protrusions or fine scratches on the surface is used, it is caused by the abnormal protrusions or fine scratches. High-quality magnetic disks with few defects can be manufactured with high yield.

Claims (6)

[Claims] 1. A step of immersing a glass substrate in a heated chemical strengthening solution to ion-exchange the ions in the surface layer of the glass substrate with ions in the chemical strengthening solution to chemically strengthen the glass substrate, and a step of removing the glass substrate from the chemical strengthening solution. A step of gradually cooling the molten salt to a temperature higher than the temperature at which crystallization of the molten salt begins, a step of rapidly cooling the glass substrate at a rate that prevents crystallization of the molten salt that precipitates on the glass substrate surface, and a step of cleaning the glass substrate surface A method of manufacturing a glass substrate for a magnetic disk, comprising: 2. A glass substrate is rapidly cooled at a rate of 1600.
C./min. To 400.degree. C./min.
A method for manufacturing a glass substrate for a magnetic disk as described above. 3. The chemical strengthening solution is heated to 350 ° C. to 650 ° C. for chemical strengthening, and the glass substrate is pulled up to 300 to 35.
The method for producing a glass substrate for a magnetic disk according to claim 1 or 2, wherein the glass substrate is gradually cooled to 0 ° C and brought into contact with a refrigerant at 100 ° C to 0 ° C to rapidly cool the glass substrate. 4. The time for contacting the glass substrate with the refrigerant is
It is 10 minutes-60 minutes, The manufacturing method of the glass substrate for magnetic discs of any one of Claims 1-3 characterized by the above-mentioned. 5. The chemical strengthening step is characterized in that the glass substrate is held at the end face to carry out the chemical strengthening.
5. The method for manufacturing a glass substrate for a magnetic disk according to any one of items 4 to 4. 6. At least a magnetic layer is formed on a glass substrate for a magnetic disk obtained by using the method for manufacturing a glass substrate for a magnetic disk according to any one of claims 1 to 5. Method for manufacturing magnetic disk.