JP2605292B2 - Method of manufacturing magnetic disk substrate - Google Patents

Description

The present invention relates to a method for manufacturing a magnetic disk substrate.

2. Description of the Related Art A magnetic recording medium (hereinafter, referred to as a medium) and a recording / reproducing magnetic head (hereinafter, referred to as a head) in which a magnetic film and a protective film are formed on a disk-shaped substrate are main components of a hard disk drive. Has formed. At the start of operation, the head and the medium are in contact with each other, and during rotation of the medium, the head flies above the surface of the medium due to air resistance. At the end of the operation, the head contacts the medium again. This method is called the contact start stop (CSS) method. When the surface of the medium is smooth, the head is attracted to the medium (this phenomenon is called a head stick).
This may cause a head crash.

If fine irregularities are previously formed on the surface of the medium by a mechanical method or the like, the coefficient of friction between the head and the medium is reduced, and the occurrence of a head stick can be prevented.

Aluminum alloy is widely used as the material of the substrate of the magnetic disk, but glass has higher rigidity than aluminum, so even if the thickness of the substrate is reduced, the high flatness required for the media can be maintained. Therefore, miniaturization of the drive device is expected.

When glass is used for the substrate, it is difficult to form irregularities on the magnetic film, and it is necessary to form irregularities on the substrate.

As a method of forming the irregularities, the method of applying mechanical scratches to the substrate surface is more effective when the substrate material is glass than when the aluminum alloy or the nickel-phosphorus alloy on the aluminum alloy is scratched. Has a small degree of plastic flow, and generates innumerable microcracks on the surface. Therefore, the moisture or the cleaning liquid occluded in the cracks may adversely affect the magnetic film (corrosion).

As a method of forming irregularities on a glass surface, a method of chemically treating the glass surface with a chemical is widely known. Most of the industrially practical methods are methods of immersing glass in an aqueous solution of hydrofluoric acid or a fluorine compound. In this method, the height of the peaks of the irregularities on the glass surface is in the range of 50 to 1000 ° required for the medium, more preferably 100 to 4 mm.
It is difficult to adjust the thickness to the range of 00 °, and it is suitable for forming irregularities exceeding 1000 ° in Rmax as generally seen in non-glare or frosted glass.

When an acid gas such as CO ₂ or SO ₂ is brought into contact with the surface of a glass containing an alkali or alkaline earth metal, fine particles such as Na ₂ CO ₃ , NaHCO ₃ and CaSO ₄ are generated on the surface of the glass, The glass surface after removal of Na, Ca, etc.
A layer rich in iO ₂ and having a slightly lower refractive index is formed. This is a phenomenon called burn, and the product is not glass. Irregularities on the glass surface after removal of this product by pickling do not reach the roughness required for the media because the SiO ₂ skeleton structure is generally left.

[Problems to be Solved by the Invention] An object of the present invention is to provide a method for manufacturing a glass substrate for a magnetic disk having improved CSS characteristics and static friction characteristics, and to form irregularities on the surface of the glass substrate. The present invention provides a novel method that has not been known before.

[Means for Solving the Problems] The present invention has been made to solve the above problems, and 0.01 to 10 mol of hydrogen fluoride is contained in air, nitrogen gas, or a mixture of air and nitrogen gas. % By contacting a mixed gas containing 5% by weight with a glass substrate maintained at a temperature in the range of 5 ° C. to 90 ° C. to form irregularities on the surface of the glass base plate to obtain a magnetic disk substrate. A method of manufacturing a substrate is provided.

The glass used in the present invention may be any silicate glass having SiO ₂ as a skeleton component, as described later using a chemical reaction formula. Here, the glass plate before the formation of the unevenness on the surface is referred to as a base plate, and the disc-shaped glass formed with the unevenness and used for a medium is referred to as a substrate to be distinguished.

The base plate may be a soda-lime silicate glass, a borosilicate glass, or any other glass containing SiO ₂ and containing approximately 45% or more of SiO ₂ by weight of the constituent oxide.

The irregularities formed on the surface of the substrate according to the present invention have a maximum height (Rmax) of the surface roughness of the irregularities of 250 μm in order to satisfy the CSS characteristics and the static friction characteristics required for the magnetic disk. Is preferably 1000 ° or less, and 50 ° or more at a reference length of 50 μm. The surface roughness here conforms to JIS B 0601 [Surface roughness]. Use a stylus type surface roughness meter with a nominal radius of 2.5 μm for the stylus, needle load 25 mg, sufficiently slow scanning speed The one obtained by the measurement will be adopted.

Substrates whose Rmax does not reach 50 ° can be manufactured by, for example, adjusting the time for exposing the base plate to hydrogen fluoride gas to be short, but when used as a medium, the static friction characteristics deteriorate. However, it is not sufficient as a substrate for a magnetic disk.

On the other hand, the irregularities formed on the surface of the substrate according to the present invention are:
In order to satisfy the magnetic characteristics required for magnetic disks,
Preferably, Rmax is at least 1000 ° or less. Here, the magnetic characteristics refer to a modulation error, a missing bit, a bit shift, an S / N ratio, and the like.In general, these magnetic characteristics are better if the substrate is smoother as long as the CSS characteristics and the static friction characteristics are not deteriorated. Become good.

Therefore, the unevenness suitable for the substrate is such that the maximum height (Rmax) of the surface roughness composed of the unevenness is 1000 ° or less at a reference length of 250 μm when the above-mentioned method for measuring the surface roughness is used, and It is preferably 50 ° or more at 50 μm, more preferably 700 ° or less at a reference length of 250 μm, and more preferably 400 ° or less at a reference length of 250 μm.

It is desirable that the maximum height (Rmax) be in the range indicated by the above numerical values over the entire surface of the substrate, but within a range that does not hinder the achievement of the above object of the present invention.
Mountains less than 50Å or more than 1000Å may be present.

As a method of providing this roughness, for example, in the case of an aluminum magnetic disk, it is generally achieved by performing polishing using abrasive grains of aluminum oxide.
In the case of glass containing 45 wt% or more of SiO ₂ , it is possible to form uniform unevenness having no in-plane direction on the surface of the base plate by a chemical method using hydrogen fluoride. Here, “having no directivity” means that the irregularities formed on the substrate surface by the method of the present invention correspond to the reference length (JI
S-B0601), when taken in the radial direction of the disk surface, in the circumferential direction or in any direction of the disk surface, it always has almost the same roughness curve.

Hereinafter, the present invention will be described with reference to FIG. 1 and FIG. However, the present invention is not limited by these figures.

In FIG. 1, an aqueous solution of hydrofluoric acid is placed in a tank 21.
20 and the temperature of the aqueous solution was kept constant. The reaction tank 2 was installed in a separately provided constant temperature water tank 3, and the temperature was kept constant.

On the other hand, a motor 6 and a shaft 7 are fixed to the lid 4. The glass substrate 1 previously held at a predetermined temperature was mounted on the shaft 7 via a clamp 8 and set at a predetermined position in a reaction tank. Next, the valves 33 and 34 were opened, and nitrogen gas was introduced into the reaction tank at a rate of 20 l / min through the pipes 30 and 31 and held for 3 to 8 minutes until the glass plate 1 reached a predetermined temperature. Next, after rotating the base plate at about 1300 RPM, by closing the valve 34 and opening the valves 35 and 36, nitrogen gas was introduced into the aqueous solution 20 of hydrofluoric acid, and the obtained HF, H ₂ O and A mixed gas of N ₂ was introduced into the reactor.
This mixed gas containing hydrogen fluoride partially reacts with the glass to form irregularities on the glass surface, while generating a transparent silicon tetrafluoride gas SiF ₄ or a hydrosilicic acid H ₂ SiF ₆ A mist was generated in the form of white smoke, exited the reaction tank through the outlet 10, and was sent to a hydrogen fluoride waste gas abatement facility through a hood (not shown). After the reaction was allowed to proceed for a predetermined time, the valves 35 and 36 were closed, and then the valve 34 was opened to purge HF in the reaction tank with nitrogen gas. Then, the glass was taken out of the tank with the handle 9 of the lid.

When this glass was viewed with reflected light such as an indoor fluorescent lamp, a reaction product having a reflection color tone determined according to the degree of the reaction was attached to the surface. It was found that when the thickness of the reaction product was small, the reflected light exhibited a blue interference color, and as the thickness increased, the yellowish color became stronger and a red interference color was exhibited.
As the reaction proceeded further, the reaction product did not show any interference color, and showed the original white color of the reaction product.

After the reaction, the glass disk taken out of the tank was removed from the motor shaft, and scrubbed in pure water to wash the reaction product. Next, after performing ultrasonic cleaning and drying, surface irregularities were measured with a stylus type surface roughness meter.

Table 1 shows the results of Examples using a soda lime silicate glass containing about 71 wt% of SiO ₂ as a glass base plate and having an outer diameter of 130 mm. The plate was roughly polished and polished on both sides to a thickness of about 1.905 mm, and then washed and dried. The HF concentration in the mixed gas in the table is a value obtained by analyzing a sample gas collected by the absorption method by a wet analysis method according to JIS K0105, and the glass temperature is the glass stopped in the tank. Is the indicated temperature of the thermocouple attached to the surface, and the surface roughness is the roughness of the irregularities formed by rotating the disk at about 1300 RPM by a motor under the same conditions. In addition, the surface roughness and the pitch of the peak are measured values of a representative sample. Here is the mountain pitch
The distance between adjacent peaks on the roughness curve obtained by the above-mentioned method.

The processing time in the table refers to the time from when the above-described valves 35 and 36 are opened to when the glass is taken out of the reaction tank.
As can be easily understood, the length of this time varies depending on the length of the pipe 31 connecting the tank 21 containing hydrofluoric acid and the reaction tank 2 and the capacity of the reaction tank 2.

From Table 1, it is possible to form irregularities suitable for the magnetic disk substrate over a wide range by appropriately selecting the processing time for the glass temperature and the HF concentration in the mixed gas. However, if the temperature of the substrate is too high, Rmax does not increase, and there is a tendency for smooth etching.If the temperature of the substrate is too low, Rmax increases, and large irregularities exceeding 1000 ° are likely to occur. It became clear from the result of the experiment.

In another embodiment, about 72% of SiO ₂ is used as a glass substrate,
Table 2 shows an example of the results obtained by treating a disk made of aluminoborosilicate glass containing about 7% of alkali and having an outer diameter of 130 mm and a thickness of about 1.905 mm in the same manner as the previous example. Compared with the case of the soda-lime silicate glass of the previous embodiment, it was found that the glass temperature should be raised by about 15 ° C. at the same HF concentration in order to obtain the above-mentioned irregularities suitable for the magnetic disk substrate.

As still another embodiment, about 55.5 wt% of SiO ₂
Table 3 shows a part of the results obtained using borosilicate glass containing 0.05 wt% of alkali. The outer diameter and thickness of the disk are the same as those in the above examples. In this glass, the HF concentration is 0.03 mol
%, A glass substrate having a temperature of 60 ° C. and a processing time of 3 minutes provided irregularities suitable for a disk substrate.

As another example, irregularities were formed on a base plate of soda-lime silicate glass containing about 72.5 wt% of SiO ₂ using the equipment shown in FIG. The cylinder 41 in FIG. 2 contains 99.99 wt% of hydrogen fluoride 40, which is maintained at 19.5 ° C. or higher, which is the boiling point of HF, by the infrared heater 42. The flow rate was detected by a manometer 63 provided in the pipe 60 around which the ribbon heater 64 was wound. This hydrogen fluoride gas was mixed with the conditioned air supplied by the pipe 61 in the mixing tank 50, and the mixed gas thus obtained was introduced into the same reaction tank 2 as in FIG. Table 4 shows part of the experimental results when the concentration of moisture in the conditioned air was changed. In the region where the moisture in the air is less than this, the change of Rmax is not large by changing the concentration of the moisture, but the moisture is 3 mol% (30%).
℃ For equivalent to moisture R _H = 72% in air) of becomes a frost in 1 minute treatment time under the conditions of the experiment, it incapable of forming irregularities suitable for magnetic disk was found.

The irregularities formed by Example 2 in Table 1 had a peak height of about 300 ° Rmax and a pitch of about 3 μm. On this substrate, a Co-based magnetic film is formed by sputtering, and a carbon protective film is further formed thereon.
The head stick property, S / N ratio and missing pulse were evaluated. Here, the CSS characteristic is to measure how many times the friction characteristic or the magnetic characteristic deteriorates when the head is stopped and worn intensively at a specific point in the disk, but the CSS characteristic is Static friction coefficient after test
The test was rejected when it exceeded 0.5 or when the output after the test fell below 90%, and the test was passed even after repeating the test 70,000 times. In addition, water penetrated between the head and the medium, and the degree of damage to the magnetic film at the time of startup was observed. The S / N ratio (signal / noise ratio) was as good as 35 dB. Further, missing pulse (a read-out waveform drop when reading after writing information due to minute defects on the media surface)
Was as good as 2 cores / plane or less when the threshold value was 70%.

As described above, the present invention is a new method for manufacturing a glass magnetic disk substrate which greatly improves the conventional problems, but the glass substrate is not a plate smoothed by polishing, but an unpolished plate having a fired surface. May be a polished smooth plate, or a surface obtained by processing the surface of a smooth plate, for example, a surface having a groove formed in the surface of a smooth plate mechanically in a concentric or other shape. You may.

Further, the disk base plate may be rotated in the reaction vessel or may be stationary, and the method of introducing the mixed gas containing hydrofluoric acid into the reaction vessel is provided on the wall of the reaction vessel. Alternatively, the gas may be blown from one or a plurality of openings, or equipment configured to blow the mixed gas directly to the surface of the glass base plate from a slit provided in the vicinity of the glass base plate may be used. Furthermore, without providing a special reaction tank, a plurality of glass base plates are continuously flowed by a transport machine such as a conveyor,
A method in which the mixed gas is continuously sprayed onto a base plate by a slit or the like at one location of the transport machine, and exhaust gas including a generated gas generated by a reaction and the unreacted mixed gas is removed by a local exhaust device by suction. Can also be used.

[Action] The mechanism of the reaction considered in the present invention will be described for an example in which a soda-lime silicate glass having the following chemical composition is used for the base plate: SiO ₂ : 73%, Al ₂ O ₃ : 1.5%, CaO: 8% , MgO: 4%, Na ₂ O
+ K ₂ O: 13.5%.

When a hydrogen fluoride gas is brought into contact with a glass surface having such a composition, SiO _2, which is a skeleton structure of the glass, is converted into a SiF ₄ gas according to the formula (1) and removed from the surface.

SiO ₂ + 4HF → SiF ₄ (gas) + 2H ₂ O (1) The SiF ₄ thus generated reacts with the hydrogen fluoride gas to be hydrofluoric acid. That is, SiF ₄ (gas) + 2HF → H ₂ SiF ₆ (liq) (2) As a result, a phenomenon in which mist of hydrosilicofluoric acid is generated in the form of white smoke is observed from the surface of the glass during the reaction. .

When SiO ₂ is removed from the glass surface, the remaining components lose their skeleton, and when the surrounding water is low, a protective film of powder is formed on the glass surface. This film is a silicofluoride made by the formula (3) to the formula (4) and has a very sparse structure.
O ₂ can continue to erode.

_{Na 2 O, CaO, MgO,} Al 2 O 3 etc + HF → NaF, CaF 2, MgF 2, AlF 3 etc + H 2 O ... (3) Na 2 F, CaF 2, MgF 2, AlF 3 + SiF 4 → Na 2 SiF 6 , CaSiF ₆ , MgSiF ₆ , etc ... (4) The layer of this reaction product is inconspicuous at the beginning of the reaction. Although it is presented, when the reaction proceeds further, it becomes a thick layer of pure white. However, a carrier gas (for example, humidified air,
Or H ₂ O or nitrogen gas) in the water due to the OH group adsorbed on the glass surface from the beginning (silanol group),
The water generated by the formulas (1) and (3) is accumulated, and if the reaction proceeds too much, it turns into a wet slurry, which is eroded by the same mechanism as the hydrofluoric acid solution. The height of the mountain is more than 2000 mm, sometimes 100,000 mm, and the pitch of the mountain is 10
A so-called coarse frost exceeding 0 μm is produced.
Such a frost is not suitable as a substrate for a magnetic disk because magnetic characteristics such as deterioration of S / N ratio, beat shift, and increase of modulation error are deteriorated because Rmax is too large. In particular, Example 4 in Table 4 above
As in the conditions shown, if the water is high in the mixed gas and blown up from the entire surface immediately glass when leading the mixed gas containing HF large amount mist H ₂ SiF ₆ is the reaction product initially To a wet slurry. As can be seen in this example, the moisture in the gas mixture containing HF is relative humidity.
It is preferred to keep it below 70%.

[Effects of the Invention] As described above, according to the present invention, a mixture containing 0.01 to 10 mol of hydrogen fluoride in air, nitrogen gas, or a mixture of air and nitrogen gas, which has not been known, is known. Whether the gas is brought into contact with the surface of the glass plate kept at a temperature of 5 ° C. to 90 ° C. to easily form fine irregularities on the surface which are uniformly distributed without any directivity in the surface. A magnetic disk medium using the glass substrate thus obtained has sufficiently satisfied the performance required for the medium.

In particular, the present invention is to form irregularities having a surface roughness suitable for a substrate of a magnetic disk by bringing a vapor of hydrogen fluoride into contact with the surface of glass containing at least 45 wt% of SiO ₂ . A method of forming the above irregularities on the glass surface by using the above-mentioned mixed gas has not been conventionally known. This method has many advantages over the method of immersing glass in an aqueous solution of a fluorine compound such as hydrofluoric acid to form irregularities on the surface.

First, in the immersion method, since the glass itself dissolves in the solution of the fluorine compound, the concentration of HF in the solution decreases as the number of discs processed increases, and at the same time, the reaction product enters the solution. As a result of the increase, it is difficult to control the concentration of the liquid, but according to the method of the present invention, since the reaction product does not mix with the HF of the source, the control of the HF concentration is extremely simple, Has great advantages.

Second, according to the method of the present invention, the progress of the reaction is as follows:
Since the interference color of the reaction product deposited on the glass surface can be regarded as a temporal change, the interference color can be measured from outside using a colorimeter or the like to help process control. it can.

Third, the equipment for processing the same number of disks can be used for a long time even if it is used in a reaction tank without coating with stainless steel in the present invention, so that simple equipment can be used. This is because the product produced by the reaction between stainless steel and hydrogen fluoride remains as a protective layer on the surface of stainless steel in the case of the present invention.

Fourth, as shown in the previous examples, when the disk is rotated and treated with hydrogen fluoride vapor while rotating, the resulting irregularities on the glass surface can have extremely uniform roughness within the surface.

When the glass substrate manufactured by the method of the present invention is used as a part of a structure of a medium, the substrate itself has appropriate irregularities required by the medium. It is not necessary to form irregularities again.

Further, the unevenness of the substrate surface formed by the method of the present invention,
A glass composition containing approximately 45 wt% or more of SiO ₂ can be optimized by changing the manufacturing conditions according to the composition, and it is characterized by unevenness having a surface roughness suitable for the magnetic disk substrate. The optimization of the obtaining conditions is easier than the conventional method of immersing in a hydrofluoric acid solution or the like to obtain irregularities. Furthermore, the shape of this unevenness has no directivity in the plane, and the so-called surface roughness in the direction perpendicular to the surface is almost uniform over the entire surface of a nominal 51/4 inch disk with an outer diameter of 130 mm. It has a characteristic Rmax.

As a result, a thin film magnetic film having a large magnetization and squareness ratio can be formed on the unevenness by a method such as sputtering to a thickness of 1000 mm or less, and since the Rmax is uniform in the plane, the magnetic head floating The height can be reduced to within 1000 mm, and as a result, a high-density magnetic disk with a small pit shift and modulation error and a high S / N ratio can be manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an embodiment of a manufacturing apparatus used for carrying out the present invention, and FIG. 2 is an explanatory view of an embodiment of another manufacturing apparatus. 1 ... glass plate 2 ... reaction tank 3 ... constant temperature water tank 20
... hydrofluoric acid solution, 21 ... tank, 22 ... constant temperature water tank, 23 ... heat exchanger, 30, 31 ... piping, 40 ... hydrogen fluoride, 50 ... mixing tank, 60, 61, 62 …… Piping.

Claims (5)

(57) [Claims] 1. A glass plate kept in a temperature range of 5 ° C. to 90 ° C. with a mixed gas containing 0.01 to 10 mol% of hydrogen fluoride in air, nitrogen gas or a mixture of air and nitrogen gas. A method for manufacturing a magnetic disk substrate, wherein irregularities are formed on the surface of the glass base plate to obtain a magnetic disk substrate. 2. The maximum height (Rm) of the surface roughness comprising the irregularities.
2. The method for manufacturing a magnetic disk substrate according to claim 1, wherein ax) is 1000 ° or less at a reference length of 250 μm and 50 ° or more at a reference length of 50 μm. 3. The glass base plate is a soda-lime silicate glass,
2. The method for manufacturing a magnetic disk substrate according to claim 1, wherein the substrate is made of one of alkali-containing borosilicate glass and alkali-free borosilicate glass. 4. The magnetic disk according to claim 1, wherein the air, nitrogen gas, or a mixture of air and nitrogen gas is humidified to a relative humidity of 70% or less. Substrate manufacturing method. 5. A mixed gas containing 0.01 to 10 mol% of hydrogen fluoride in the air, nitrogen gas, or a mixture of air and nitrogen gas, wherein the liquid temperature is 5 to 40 ° C.
It is obtained by blowing air, nitrogen gas, or a mixed gas of the above air and nitrogen gas conditioned to a relative humidity of 70% or less into hydrofluoric acid containing wt% hydrogen fluoride. 2. The method for manufacturing a magnetic disk substrate according to claim 1, wherein the method comprises: