JPH11328665A - Magnetic disk glass substrate and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a high strength without using a chemical reinforcement method, decreasing the danger that moisture and organic components are left in a protecting film and prevent a magnetic film from being deteriorated in performance at the time of forming a magnetic disk by etching an inner circumferential end face of a doughnut-shaped glass plate and coating the inner circumferential end face with the protecting film having a specific hardness to a pencil scratch. SOLUTION: A protecting film coating an etched inner circumferential end face is set to have a pencil scratch hardness of not smaller than 5H, preferably not smaller than 6H, particularly preferably not smaller than 8H. The etching process can eliminate deep flaws present at inner and outer circumferential end faces which control a bending strength of a doughnut-shaped glass plate, particularly, deep flaws of the inner circumferential end face which more strongly controls the bending strength. A depth of the etching is preferably 15-40 μm. The protecting film preferably uses a silica layer obtained by setting a coat composition including polysilazane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-strength glass substrate for a magnetic disk and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, aluminum alloy substrates have been mainly used as substrates for magnetic disks used in magnetic disk storage devices and the like. As a result, glass substrates having a hard material itself and excellent flatness and smoothness have begun to be used. However, a glass substrate for a magnetic disk made of glass, which is a brittle material, may be broken during handling or use, which is one of the problems.

One of the factors that govern the mechanical strength of a doughnut-shaped glass substrate for a magnetic disk is a flaw existing on the inner peripheral end surface of the glass substrate where a maximum tensile stress occurs during use of the magnetic disk. However, in a glass substrate for a magnetic disk, the inner and outer peripheral end surfaces (hereinafter, collectively referred to as inner and outer peripheral end surfaces) have surface roughnesses of the main surfaces (inner and outer surfaces) which require extremely high flatness and smoothness. The surface is generally rougher than the surface except for the peripheral end surface). The reason for this is that the inner and outer peripheral end faces are cut out from the glass plate in the first place in a circular shape, and the center part is perforated.They are not involved in magnetic recording. And what cannot be done.

In order to reduce the depth of the scratches on the inner and outer peripheral surfaces and increase the mechanical strength, finishing of the inner and outer peripheral surfaces with abrasive grains finer than # 500 mesh is also performed. There are still quite deep scratches on the surface. In order to further improve the finish of the inner and outer peripheral end faces, that is, to further reduce the roughness, multi-stage processing using finely-grained abrasive grains is required. However, this multi-step processing has the problem that productivity and cost are significantly worsened.

Conventionally, in order to further increase the mechanical strength of a glass substrate for a magnetic disk, a chemical strengthening method called an ion exchange method is generally used rather than improving the finish of the inner and outer peripheral end faces. The ion exchange method refers to a method in which a glass is immersed in a molten salt containing K, for example, a molten potassium nitrate, and a Na ion on the glass surface and a K ion of the molten potassium nitrate are ion-exchanged to form a compression layer on the glass surface to form a glass. This is a method of increasing the strength of the hologram. However, the effect of improving the strength by the chemical strengthening method is that a predetermined ratio of Na
Or only for glasses containing Li.

The depth and the magnitude of the compressive stress value of the surface compressive stress layer introduced on the glass surface by such a chemical strengthening method vary to some extent depending on conditions such as the temperature of the molten salt and the immersion time. By increasing the immersion time, higher strength can be achieved. However, in practice, it depends more heavily on the composition of the glass itself.
That is, generally, in order to obtain a deep compressive stress layer and obtain high strength, it is necessary to increase the content of Na or Li in the glass composition.

On the other hand, in a magnetic disk, a very thin metal or alloy magnetic film is formed on the surface of a glass substrate. When an alkali metal component such as Na in glass increases, the alkali metal component causes the magnetic film to be damaged. There is a problem of corrosion.

As a countermeasure against this problem, it is conceivable to form an underlayer under the magnetic film to prevent an alkali metal component from entering the magnetic film. However, in this case, it is necessary to make the underlayer sufficiently thick. In particular, in the case of glass containing a large amount of an alkali metal component, the thickness of the underlayer must be considerably increased. Also, when this underlayer is formed on the surface of a doughnut-shaped glass substrate by a sputtering method, a vacuum evaporation method, or the like, it is difficult to form an underlayer having a sufficient thickness on the inner and outer peripheral end faces. The membrane becomes more susceptible to corrosion.

In order to prevent such a corrosion of the magnetic film by the alkali metal component, it is preferable to use glass having a low alkali metal content. On the other hand, L in glass
When the amount of i or Na is small, the depth of the compressive stress layer on the glass surface generated by ion exchange becomes small, and becomes smaller than the depth of the flaw existing on the glass surface. Therefore, there is a problem that the effect of the chemical strengthening is small and sufficient strength cannot be obtained.

Further, the glass substrate for a magnetic disk is also excellent in that the rigidity of the glass substrate is high and the thickness thereof can be reduced. However, when the thickness of the glass substrate is small, if the depth of the surface compressive stress layer formed by the chemical strengthening method becomes excessively large, a large tensile stress is generated at the center in the thickness direction of the glass substrate, and the strength is rather reduced. There is a risk of lowering.

Further, in the chemical strengthening method, glass is immersed in a molten salt at 450 ° C. or higher, so that the glass surface is contaminated with the molten salt, and polishing must be performed after chemical strengthening to remove the molten salt. Did not. In addition, 45
Due to the high temperature of 0 ° C. or more, the flatness of the glass substrate might be deteriorated.

On the other hand, hydrofluoric acid etching is widely known as a surface treatment method for general glass products. However, hydrofluoric acid etching is conventionally not preferable for glass substrates for magnetic disks. The reason is that an excessive etching process forms high protrusions on the surface of the glass substrate. That is, in the magnetic disk storage device, since the magnetic head flies at a height of 10 to 50 nm away from the surface of the magnetic disk rotating at high speed, a high protrusion caused by excessive etching causes a head crash, and the recording surface of the magnetic disk It causes total destruction.

As a glass substrate for solving the above-mentioned problems, Japanese Patent Application Laid-Open No. 2-301017 discloses a glass substrate having a thickness of 0.2 to 50 .mu.
A glass substrate for an information recording disk in which a continuous film of an oxide of m or a continuous film containing an oxide as a main component is formed is disclosed.

The above-described continuous film of oxide or a continuous film containing oxide as a main component is made of Si, Ti, Al, and Zr.
It is preferable to include at least one of the above. In addition, the circular processed glass disk is etched with hydrofluoric acid or buffered hydrofluoric acid,
It is described that providing the continuous film after leaching with sulfuric acid, nitric acid or the like is more effective in removing the scratch itself.

Further, in forming the continuous film,
It is described that it is necessary to use a so-called wet process in which a solidified film is formed by applying a solution or slurry, followed by drying and heat treatment. Also, a 2 μm thick SiO 2 is prepared by using colloidal silica dispersed in ethanol and a sol solution obtained by hydrolyzing ethyl silicate with an aqueous nitric acid solution.
Forming embodiment _two continuous film was formed on a glass disk surface, the SiO ₂ continuous film containing some organic groups having a thickness of 5μm using a monomethyl trimethoxysilane and water glass-based colloidal silica and acid to the glass disc surface Examples have been described.

However, the continuous film disclosed in Japanese Patent Application Laid-Open No. 2-301017 tends to remain with water and organic substances. When a glass substrate having such a continuous film formed on its surface is put into a vacuum process in the magnetic disk manufacturing process, gas generation occurs due to moisture and organic substances remaining in the continuous film, which degrades the performance of the magnetic film. May be caused. Further, in order to form the continuous film, it is necessary to adjust the pH and viscosity of the coating solution with high accuracy, and there is a problem in workability.

[0017]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-strength glass substrate for a magnetic disk and a method for manufacturing the same, which solve the above-mentioned problems.

[0018]

According to the present invention, there is provided a donut-shaped glass plate, the inner peripheral end surface of which is etched, and the etched inner peripheral end surface has a pencil scratch value of 5H or more. A glass substrate for a magnetic disk covered with a protective film having hardness and a donut-shaped glass plate are subjected to an etching treatment, and then the inner peripheral end surface of the donut-shaped glass plate has a hardness of a pencil scratch value of 5H or more. A method for producing a glass substrate for a magnetic disk covered with a protective film.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The glass substrate for a magnetic disk according to the present invention has a donut shape, that is, a disk shape with a perforated center, and its dimensions are shown in mm. A) Inner diameter 20, outer diameter 65, plate Thickness 0.635, b) inner diameter 25, outer diameter 84, plate thickness 0.635, c) inner diameter 25, outer diameter 95, plate thickness 0.8,
There are various types such as d) inner diameter 25, outer diameter 84, plate thickness 1.0, or e) inner diameter 25, outer diameter 95, plate thickness 1.0, and there is no particular limitation.

The donut-shaped glass plate in the present invention is a glass plate having a shape of a disk having a predetermined radius, and a shape having a shape in which a circle having the same center as the center of the disk is perforated.

In the glass substrate for a magnetic disk of the present invention, the inner peripheral end surface of the donut-shaped glass plate is etched, and the inner peripheral end surface is covered with a protective film having a hardness of not less than a pencil scratch value of 5H. ing. This makes it difficult for the inner peripheral end surface to be damaged.

For the etching treatment, a general glass etching method such as a wet etching method using an etching solution, a dry etching method using an etching gas, or the like can be used. Among them, a wet etching method using an etching solution such as a hydrofluoric acid solution, a fluorosulfuric acid solution, or hydrofluoric acid can be preferably used, and a method using a fluorosulfuric acid solution can be particularly preferably used. Note that this etching treatment is performed in a range where a high protrusion is not formed on the surface of the glass substrate.

Prior to the etching process, the inner and outer peripheral end faces, particularly the inner peripheral end face of the donut-shaped glass plate are # 200 to # 200.
It is preferable to perform the finishing process using abrasive grains of about # 1000 mesh.

By the etching treatment, deep scratches existing on the inner and outer peripheral end faces that govern the bending strength of the donut-shaped glass plate,
In particular, deep flaws on the inner peripheral end face that more strongly governs bending strength can be removed. The etching depth of the etching treatment is preferably 15 to 40 μm. If it is less than 15 μm, the removal of deep flaws, especially on the inner peripheral end face, becomes insufficient, and the mechanical strength may be reduced. If it exceeds 40 μm, high projections may be formed on the surface of the glass substrate.

The hardness of the protective film covering the inner peripheral end face is a pencil scratch value of 5H or more. If it is 4H or less, scratches generated due to handling of the glass substrate for a magnetic disk after coating with the protective film penetrate the protective film and reach the inner peripheral end face,
Mechanical strength may be reduced. It is preferably at least 6H, more preferably at least 7H, particularly preferably at least 8H. In addition, the pencil scratch value is JIS K54.
According to 8.4.2 (hand-drawing method) of No. 00, the protective film was scratched with a pencil and examined.

As the protective film, it is preferable to use a silica layer obtained by curing a coating composition containing polysilazane (hereinafter referred to as a curable coating composition). Polysilazane is an inorganic polymer that is soluble in an organic solvent. Therefore, organic groups are less likely to remain in the silica layer, and as a result, gas is less likely to be generated in a vacuum process in a magnetic disk manufacturing process. In addition, there is little possibility that moisture will remain in the silica layer. From the above, performance degradation of the magnetic film due to gas generation in the vacuum process is unlikely to occur.

The curable coating composition usually contains a solvent in addition to polysilazane. Further, a catalyst and other additives may be contained in addition to the solvent. Polysilazane is (-Si-
A polymer having two or more units of N-), and in this chemical formula, the remaining two bonds of Si atoms (tetravalent) and the remaining one bond of N atoms (trivalent) are H atoms, respectively. Or an organic group (such as an alkyl group). In addition, not only a polymer having a linear structure consisting of the repeating unit alone, but also one or both of the remaining two bonds of the Si atom and the bond of the nitrogen atom are bonded to form a cyclic structure. You may. The polymer may be composed of a repeating cyclic structure alone, or may be a linear polymer partially having a cyclic structure.

These polysilazanes include, for example, polysilazanes described in JP-A-9-31333 and the documents cited therein, and such polysilazanes can be used as polysilazanes in the present invention. Modified polysilazane described in JP-A-9-31333 and the literature cited therein can also be used as the polysilazane in the present invention.

Polysilazane is decomposed in the presence of oxygen, and N atoms are replaced by O atoms to form silica. Silica formed from polysilazane is more dense than silica formed from hydrolyzable silane compounds. For example,
Silica formed from perhydropolysilazane is denser and has better surface properties such as abrasion resistance than silica formed from a tetrafunctional hydrolyzable silane compound (eg, tetraalkoxysilane).

Examples of the polysilazane include polysilazane (perhydropolysilazane) substantially free of an organic group, polysilazane in which a hydrolyzable group such as an alkoxy group is bonded to a Si atom, and an organic group such as an alkyl group in a Si atom or an N atom. And polysilazane bonded thereto (hereinafter, the latter two are referred to as organic type polysilazane).

The polysilazane is composed of a polymer having a chain, cyclic or crosslinked structure, or a mixture of polymers having a plurality of these structures in the molecule. The polysilazane preferably has a number average molecular weight of 200 to 50,000. When the number average molecular weight is less than 200, it is difficult to form a uniform silica layer even when cured. In addition, the number average molecular weight is 50
If it exceeds 000, it becomes difficult to dissolve in a solvent, and the curable coating composition may become viscous.

Examples of the solvent for dissolving polysilazane include hydrocarbon solvents such as aliphatic hydrocarbons, alicyclic hydrocarbons and aromatic hydrocarbons, halogenated hydrocarbon solvents, ethers such as aliphatic ethers and alicyclic ethers. Can be used. Specifically, pentane, hexane, isohexane, methylpentane, heptane, isoheptane, octane, isooctane, cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, benzene, toluene, xylene, hydrocarbons such as ethylbenzene, methylene chloride, chloroform Halogenated hydrocarbons such as carbon tetrachloride, bromoform, ethylene chloride, ethylidene chloride, trichloroethane, and tetrachloroethane; and ethers such as ethyl ether, isopropyl ether, ethyl butyl ether, butyl ether, dioxane, dimethyl dioxane, tetrahydrofuran, and tetrahydropyran. is there.

When these solvents are used, a plurality of types of solvents may be mixed and used for adjusting the solubility of polysilazane and the evaporation rate of the solvent.

The amount of the solvent used varies depending on the method of applying the curable coating composition, the structure of polysilazane, the average molecular weight, and the like, but it is preferable that the solid content be 0.5 to 80% by weight.

A catalyst is usually used to lower the curing temperature of the polysilazane. By selecting the type and amount of the catalyst, curing can be performed at a lower temperature, and in some cases, at room temperature. In addition, the atmosphere in which the curing is performed is preferably an atmosphere in which oxygen such as air is present.

When the polysilazane is cured, its N atom becomes O
Substitution into atoms produces silica. By curing in an atmosphere in which sufficient oxygen exists, a dense silica layer is formed. Further, treatment with water or steam is also effective for curing at a low temperature (see JP-A-7-223867).

As the catalyst, it is preferable to use a catalyst capable of curing polysilazane at a lower temperature. As such a catalyst, for example, a metal catalyst composed of fine particles of a metal such as gold, silver, palladium, platinum and nickel (Japanese Patent Laid-Open No.
-19686), amines and acids (JP-A-9-3)
1333). Examples of the amines include an alkylamine, a dialkylamine, a trialkylamine, an arylamine, a diarylamine, and a cyclic amine. Examples of the acids include organic acids such as acetic acid and inorganic acids such as hydrochloric acid.

The particle diameter of the fine particles of the metal catalyst is preferably smaller than 0.1 μm, and more preferably smaller than 0.05 μm in order to ensure the transparency of the cured product.
In addition, since the specific surface area increases as the particle size decreases and the catalytic ability increases, it is preferable to use a catalyst having a smaller particle size in terms of improving the catalytic performance. Amines and acids can be blended with the polysilazane solution, and the curing of amines and acids (including aqueous solutions) and their vapors (including vapors from aqueous solutions) can be accelerated by contact with the polysilazane. Can be.

When a catalyst is used in combination with polysilazane, the amount of the catalyst is preferably 0.01 to 10 parts by weight, more preferably 0.05 to 10 parts by weight, per 100 parts by weight of polysilazane.
-5 parts by weight. If the amount is less than 0.01 part by weight, a sufficient catalytic effect cannot be expected. If the amount is more than 10 parts by weight, aggregation of the catalysts tends to occur, which may impair transparency.

The curable coating composition may further contain, if necessary, stabilizers such as an ultraviolet absorber, a light stabilizer, an antioxidant, a leveling agent, an antifoaming agent, a thickener, an antisettling agent, and a dispersant. A surfactant such as an antistatic agent may be appropriately blended.

The thickness of the silica layer obtained by curing the curable coating composition is preferably 0.05 to 10 μm. If it exceeds 10 μm, no further improvement in scratch resistance can be expected, and the silica layer becomes brittle, so that even a slight deformation of the glass substrate for a magnetic disk tends to cause cracks or the like in this silica layer. If the thickness is less than 0.05 μm, the effect of improving the scratch resistance may be insufficient.
The more preferable thickness of the silica layer obtained by curing the curable coating composition is 0.1 to 6 μm, particularly preferably 0.1 to 4 μm.

The method of manufacturing a glass substrate for a magnetic disk according to the present invention comprises performing the above-mentioned etching treatment on a donut-shaped glass plate, and then coating the inner peripheral end surface with a protective film having a hardness of 5H or more. It is a feature. In addition, the etching process referred to in the present invention means that at least the inner peripheral end face is etched.

The coating of the protective film is preferably performed by applying a coating solution using a coating method and curing the coating solution by baking or the like. When using a coating method, it is essential to apply a coating liquid to the inner peripheral end face. It is more preferable to apply to the outer peripheral end face. In this case, the case where the coating liquid protrudes from the inner peripheral end face or the inner peripheral end face and exists on the main surface is also included.

Examples of the coating method include the following. (1) A brush application method using a brush. (2) Supply the coating liquid to the porous surface of the roller brush made of foamed plastic or the like,
While rotating at 0 to 60 rpm, the coating liquid is transferred and brought into contact with the inner peripheral end surface or the outer peripheral end surface of the donut-shaped glass plate.
Roller coating method to apply. In this case, it is preferable that the donut-shaped glass plate is also vacuum-adsorbed and rotated at 30 to 50 rpm. (3) Donut-shaped glass plate is vacuum-adsorbed to 10 to 200
A direct coating method in which a predetermined amount of a coating liquid is supplied and applied by a dispenser to an inner peripheral end surface or an outer peripheral end surface thereof while rotating at rpm.

The glass that can be used for the glass substrate for a magnetic disk of the present invention is not particularly limited, but glass having the following characteristics is preferable for improving the weather resistance. Water resistance: When the glass is immersed in water at 80 ° C. for 24 hours, the weight loss (elution amount) of the glass due to elution of components from the glass is 0.02 mg / cm ² or less.

Acid resistance: In 0.1 N hydrochloric acid aqueous solution at 80 ° C.
Dissolution of components from glass when glass is immersed for 24 hours
0.06mg /
cm ^TwoLess than.

Alkali resistance: When glass was immersed in a 0.1 N sodium hydroxide aqueous solution at 80 ° C. for 24 hours,
Loss of glass (elution amount) due to elution of components from glass is 1 mg / cm ² or less, more preferably 0.18 m
g / cm ² or less.

In the present invention, since the use of the chemical strengthening method is not essential, there is no lower limit of the content of alkali metals such as Na and Li from the viewpoint of enabling chemical strengthening. Examples of the glass that can be used for the glass substrate for a magnetic disk of the present invention include alkali-free glass, glass having an alkali metal oxide content of 1 to 20% by weight, such as soda lime silica glass and crystallized glass. .

[0049]

EXAMPLES (Example 1) The composition expressed in% by weight is SiO ₂ :
_{56%, B 2 O 3:} 6%, Al 2 O 3: 11%, Fe 2 O 3:
0.05%, Na ₂ O: 0.1%, MgO: 2%, Ca
A donut-shaped glass plate having an outer diameter of 95 mm, an inner diameter of 25 mm, and a thickness of 1.1 mm made of glass A having O: 3%, BaO: 15%, and SrO: 6.5% was prepared. The elution amount (unit: mg / cm ² ) in each test of water resistance, acid resistance, and alkali resistance of the glass was 0.01,
0.03 and 0.67.

The inner and outer peripheral end faces of the donut-shaped glass plate are #
Finish polishing is performed using diamond abrasive grains of 500 mesh under. The concentricity of the inner and outer circumferences (distance between the center of the inner circumferential circle and the center of the outer circumferential circle) is 25 μm or less and the roundness is 25 μm each
m or less. Next, lap polishing was performed using alumina abrasive grains having an average particle diameter of 9 μm, and the thickness was about 0.9 μm.
mm. This glass plate was further immersed in a hydrofluoric acid solution containing 5% each of hydrofluoric acid and sulfuric acid for 15 minutes to perform an etching treatment with an etching depth of about 20 μm.

Next, a xylene solution of an organic type polysilazane having a number average molecular weight of 1000 and containing a catalyst (trade name “L710” manufactured by Tonen Co., Ltd.) is mainly placed on the inner and outer peripheral end faces of the etched glass plate. (Solid content 20% by weight) was applied by brush. After this, 50-60
After drying in a thermostat at 10 ° C. for 10-20 minutes, 400 ° C.
For 1 hour in an electric furnace. The thickness of the coating thus formed varies depending on the location,
μm.

Thereafter, the glass plate with the coating was polished with cerium oxide having an average particle size of 2.5 μm to a thickness of about 0.81 mm. At this time, the coating protruding from the inner and outer peripheral end faces was also removed at the same time. As a result of examining the pencil scratch value of the inner peripheral end face of the glass substrate obtained by coating only the inner and outer peripheral end faces with the coating film obtained as described above, it was 8H.

(Example 2) It is made of glass A and has an outer diameter of 95 m.
m, inner diameter 25.015 to 25.035 mm, thickness 0.
An 85 mm donut-shaped glass plate was prepared. This donut-shaped glass plate was subjected to finish polishing, lap polishing, and etching treatment in the same manner as in Example 1.

The same coating liquid as in Example 1 was applied to the inner peripheral end face of the etched donut-shaped glass plate by a direct coating method, and fired in the same manner as in Example 1. As a result of examining the pencil scratch value of the inner peripheral end face of the donut-shaped glass plate having the inner peripheral end face covered with the coating film, the value was 8H.

This donut-shaped glass plate (coated product) was subjected to the following damage test simulating use in a magnetic disk drive. The number of samples is 5. For comparison, a scratch test was also performed on a donut-shaped glass plate (uncoated product) that had been subjected to etching but not applied. The number of uncoated samples is also 5. result,
That is, Table 1 shows the breaking stress (unit: kgf / mm ² ).

The minimum value of the breaking stress of the coated product according to the embodiment of the present invention is 16.1 kgf / mm ² , whereas the uncoated product as the comparative example is 13.4, which is clearly the value of the coated product. The strength is higher.

Scratch test: a stainless steel cylinder (diameter: 24.96 mm, fixed on a stainless steel disk)
The test sample was inserted into the disk at a height of 8 mm, and the sample was dropped from a height (initial position) 7 mm away from the disk surface. After repeating this 50 times, the sample was inverted and dropped 50 times more.

The fracture stress of the sample thus injured was measured using a strength tester (trade name: A, manufactured by Shimadzu Corporation).
(UTOGRAPH). That is, a stainless steel ball having a diameter of 36 mm is set on the inner periphery of the sample, and the sample is broken by applying a pressure of 30 mm / min through the ball to break the sample. The breaking stress was calculated.

[0059]

[Table 1]

(Example 3) The composition expressed by weight% is Si
O ₂ : 61.2%, Al ₂ O ₃ : 11.5%, Na ₂ O: 1
_{6%, K 2 O: 2.1} %, Li 2 O: 2.9%, MgO:
0.8%, CaO: 2.9%, TiO 2: 0.5%, Z
_{rO 2: 1.9%, SO 3} : made of 0.2%, a glass B, an outer diameter of 95 mm, an inner diameter of 25.015 to 25.
A donut-shaped glass plate having a thickness of 035 mm and a thickness of 0.85 mm was prepared.

Samples (coated and uncoated) were prepared in the same manner as in Example 2 except that the glass of the donut-shaped glass plate was glass B instead of glass A.
A wound test was performed. Breaking stress (unit: kgf / m
Table 2 shows the measurement results of m ² ). In addition, the pencil scratch value of the inner peripheral end face of the coated product according to the example of the present invention was 8H.

The minimum value of the breaking stress of the coated product according to the example of the present invention was 18.2 kgf / mm ² , whereas the uncoated product as the comparative example was 13.1. The strength of the coated product of the embodiment is higher.

[0063]

[Table 2]

[0064]

According to the present invention, it is possible to provide a high-strength glass substrate for a magnetic disk which does not require chemical strengthening and a method for manufacturing the same. In particular, in the present invention, there is little possibility that moisture or organic components remain in the protective film, and there is no possibility that the performance of the magnetic film is deteriorated at the time of manufacturing the magnetic disk.

The coating solution of the present invention, that is, the coating composition containing polysilazane has a low viscosity and is excellent in workability.
Furthermore, in the present invention, there are few restrictions on the coating conditions such as the temperature and pH of the coating liquid, and the workability is also excellent in this respect. As described above, since there are few restrictions on workability, there are few restrictions on the protective film forming apparatus, and the apparatus can be selected widely.

Claims (4)

[Claims] 1. A donut-shaped glass plate whose inner peripheral end face is etched and the etched inner peripheral end face is covered with a protective film having a hardness of not less than a pencil scratch value of 5H. Glass substrates for magnetic disks. 2. The glass substrate for a magnetic disk according to claim 1, wherein the protective film is a silica layer obtained by curing a coating composition containing polysilazane. 3. A donut-shaped glass plate is etched,
Then, a method for manufacturing a glass substrate for a magnetic disk, wherein the inner peripheral end surface of the donut-shaped glass plate is covered with a protective film having a hardness of 5H or more in pencil scratching value. 4. A coating composition containing polysilazane is applied to the inner peripheral end face of the doughnut-shaped glass plate subjected to the etching treatment,
The method for producing a glass substrate for a magnetic disk according to claim 3, wherein the protective film is cured to form a protective film having a pencil scratch value of 5H or more, and then the main surface of the donut-shaped glass plate is polished.