JPH1111973A - Flattening method of sheet glass and production of magnetic recording medium by using the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin glass substrate having high flatness without scratches by suspending or dispersing an inorg. powder in a solvent which does not produce a decomposed gas to prepare a soln., applying the prepared soln. on the surface of a sheet glass formed by down loading method, laminating the glass sheets, interposing the glass sheets between compressing plates with high flatness, and heating and slowly cooling the sheets while pressurizing. SOLUTION: The inorg. powder to be applied preferably consists of MgCO3 and/or CaCO3 and contains boron nitride. The particle size is uniform and preferably about 20 to 30 μm. The powder is uniformly applied preferably by rotating a sponge roller impregnated with a soln. in which the inorg. material is suspended along the surface of the sheet glass. The concn. of the soln. is preferably controlled to a low level so as to form a single molecular layer. Moreover, the sponge roller impregnated with water is preferably brought into contact with the sheet glass under pressure. By this flattening method of sheet glass, a succeeding polishing process can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for flattening a glass sheet and a method for manufacturing a magnetic recording medium using the glass substrate.

[0002]

2. Description of the Related Art Conventionally, thin glass substrates have been used as substrates for magnetic disks (hard disks), optical disks, liquid crystal displays and the like.

Usually, these thin glass substrates are manufactured by processing a flat glass plate obtained by a manufacturing method such as a down-draw method or a float method into predetermined dimensions and then polishing the surface. Here, the downdraw method is generally a method of manufacturing a sheet glass by flowing down molten glass and drawing vertically downward. More specifically, for example, the molten glass flows down along the front and back surfaces of the molded body having a wedge-shaped cross section, merges at the lower end of the molded body to form a plate, and is cooled and solidified while being pulled downward by a tension roller. (An example of a down-draw method) for producing a sheet glass is known (JP-A-5-163).
No. 032).

[0004] Sheet glass made by this down-draw method is thinner than sheet glass made by other methods, and is therefore used as a thin glass substrate for a magnetic disk or a thin glass substrate for a liquid crystal display. Due to the characteristics of the forming method, the flatness of the sheet is worse than that of the sheet glass made by the float method or the like. Therefore, when thin glass made by the down-draw method is used for these applications, heat treatment (heating and slow cooling) is required to remove distortion and correct (rectify) the flatness and improve the flatness. .

Specifically, as shown in FIGS. 4 (a) and 4 (b), the method is as follows: a thin plate is placed between a ground or polished compression plate (flat aluminum plate for flatness correction) 10 having good flatness. The glass 11 is sandwiched one by one, and heating or gradual cooling is performed by sandwiching paper or carbon paper 12 as a release agent on both surfaces of the thin glass 11. 13 are fins for preventing deformation of the compression plate 10

In the case where a plurality of thin glass sheets are heat-treated in order to increase the efficiency, if the heat treatment is performed as it is, the thin glass sheets are thermally fused and cannot be used. It is necessary to prevent heat fusion between the two. For this reason, put paper between thin glass,
A method using paper cinders as a release agent or a method using carbon paper as a release agent has been used (JP-A-6-247730, etc.).

Here, in the method of sandwiching paper between thin glass sheets, carbon dioxide generated when the paper burns is sealed between the glass sheets, so that the flatness of the glass deteriorates and the required accuracy cannot be satisfied. In addition, the handling and cleaning of the cinders require labor. In addition, when taking out the thin glass from the heating furnace after the heat treatment, the ember of the paper is scattered around and the working environment is deteriorated, so that the handling is complicated, and further, the tar component generated from the paper adheres to the surface of the thin glass. The cleaning process is time-consuming and labor-intensive.

Also, in the method of sandwiching carbon paper between thin glass sheets, the thickness of the carbon paper and its elasticity make it impossible to improve the accuracy of flatness to the required accuracy, and carbon paper is expensive. Therefore, the cost is high. More specifically, because the carbon paper thickness is 0.5 mm or more and thicker than paper,
The flatness of the glass sheet is absorbed by the elastic force and the correction of the flatness becomes insufficient, so that the accuracy of the flatness is not improved. In addition, carbon paper has insufficient strength and is easily broken, and is expensive, resulting in high costs.

Furthermore, when paper or carbon paper is sandwiched between thin glass sheets, dust in the air is entrained, which causes rubbing and flaws, leading to a reduction in yield.

In addition, a method is considered in which fine powder of an inorganic substance such as BN is sprayed as it is and used as a release agent. In this case, the fine powder is uniformly sprayed (coated) on the surface of the thin glass. It is difficult to do so, and the accuracy of flatness is not improved. In addition, the fine powder scatters around and deteriorates the working environment. From these facts, it is considered that they are not suitable as release agents for preventing heat fusion in heat treatment for flattening glass substrates for information recording media and liquid crystal glass substrates, which require high flatness accuracy. Was.

Due to such a problem, it has been conventionally difficult to efficiently heat-treat a plurality of thin glass sheets with a required degree of flatness and without causing scratches or fusion of foreign substances. Met.

For this reason, conventionally, thin sheets of glass are sandwiched one by one between compression plates having good flatness to ensure the required flatness of accuracy, while sacrificing efficiency, or heat treatment is performed at the expense of accuracy. In addition, heat treatment was performed by sandwiching paper or carbon paper between thin glass sheets, and cleaning had to be performed while suffering from burning.

[0013]

As described above, in the conventional method, the thin glass sheets can be formed without causing flaws or fusion of foreign matters while preventing heat fusion between the laminated thin glass sheets. It has been difficult to efficiently heat-treat a plurality of sheets to obtain the required accuracy flatness.

Further, the conventional thin glass substrate is expensive due to securing the required accuracy flatness at the expense of efficiency, or uses thin glass manufactured at the expense of accuracy. Therefore, a considerable amount of polishing is required to ensure the required flatness of accuracy, and there is a problem that the cost is high.

Further, the conventional magnetic disk is expensive due to the use of the above-mentioned expensive substrate, and has scratches and foreign substances which cannot be completely removed by the polishing process on the substrate, and the surface condition is poor. When a disc is used, there is a problem that a head crash occurs or a defect occurs in a film such as a magnetic layer to cause an error.

The present invention has been made in view of the above problems, and a first object of the present invention is to prevent generation of scratches and fusion of foreign matters while preventing heat fusion between laminated thin glass sheets. It is an object of the present invention to provide a method for flattening a glass sheet which can efficiently heat-treat a plurality of thin glass sheets without heat and obtain a required degree of flatness. A second object is to provide an inexpensive thin glass substrate with high flatness, and a third object is to provide a magnetic recording that does not cause a head crash and does not cause a defect in a film such as a magnetic layer. Is to provide a medium.

[0017]

In order to achieve the above object, a flattening method for a flat glass according to the present invention is characterized in that one or a plurality of flat glasses formed by a downdraw method are stacked on both sides of a compressed flat plate having high flatness. In a method of flattening a plate glass by heating and gradually cooling while pressing the plate glass, a solution in which a powder of an inorganic substance is suspended or dispersed in a solvent on at least one main surface of the plate glass, and the plate glass is heated. It is configured to apply a solution that does not decompose at a temperature and emit a reaction gas.

Further, the method for flattening a glass sheet according to the present invention comprises:
In the flattening method for a flat glass according to the present invention, the inorganic material powder is MgCO ₃ and / or CaCO ₃ ; the inorganic material powder contains boron nitride (BxNy); A solution obtained by suspending or dispersing the powder in a solvent is impregnated into a sponge roller in which a sponge having a uniform thickness is wound around a shaft, and the sponge roller is rotated along the surface of the plate glass while being pressed against the plate glass. A configuration in which the powder of the inorganic substance is uniformly applied to the plate glass, or a plurality of sponge rollers each having a sponge having a uniform thickness wound around a shaft member, and the plurality of sponge rollers are sequentially rotated while being pressed against the plate glass. At this time, a solution obtained by suspending or dispersing the powder of the inorganic substance in a solvent by a sponge roller that first comes into contact with the glass sheet is applied to the glass sheet. As well as fabrics, it is constituted that the sponge roller in contact with subsequent glass sheet is rotated while pressed against the turn plate glass sponge roller impregnated with the water previously impregnated with water.

Further, the coating apparatus of the present invention has a plurality of sponge rollers in which a sponge having a uniform thickness is wound around a shaft, and means for rotating the plurality of sponge rollers while sequentially pressing them against a sheet glass, First, the sponge roller that comes into contact with the glass sheet has means for impregnating a solution obtained by suspending or dispersing an inorganic substance powder in a solvent, and the sponge roller that comes into contact with the glass sheet thereafter has means for impregnating with water. There is a configuration.

Further, in the method of manufacturing a magnetic recording medium of the present invention, the main surface of the glass sheet which has been subjected to the flattening method of the present invention is polished, chemically strengthened by ion exchange, and then at least the magnetic layer is formed. It is configured to be formed.

[0021]

According to the present invention, a solution in which a powder of an inorganic substance such as MgCO ₃ or CaCO ₃ is suspended or dispersed in a solvent is applied to a glass sheet with a sponge roller or the like, so that the surface of the glass is uniformly and thinly coated. The substance can be applied.

In other words, powders of inorganic substances such as MgCO ₃ and CaCO ₃ are easily suspended and do not require the use of an organic suspending or dispersing agent. Decomposes at the heating temperature (normally around the strain point) to generate a reaction gas, and this gas does not deteriorate the accuracy of flatness.

Further, these inorganic substance powders can prevent heat fusion between laminated thin glass sheets, and do not cause generation of scratches and fusion of foreign substances. Powders of these inorganic substances can be applied uniformly and thinly on the glass surface, and a coating of an inorganic compound that prevents thermal fusion of the glass is applied in a state where the flatness of the glass sheet is not prevented (thickness of several microns). ), It is possible to obtain the required flatness with the required accuracy. Further, the powder of these inorganic substances can be completely removed by washing or light polishing, so that there is no adverse effect on subsequent products.

Further, it has been found that the powders of these inorganic substances can be applied to the glass surface with a sponge roller in an extremely thin and uniform manner. Since the sponge roller is used, the apparatus is simple, and costs and labor are not required.

Hereinafter, the present invention will be described in detail.

In the present invention, one or more sheets of sheet glass formed by the down-draw method are stacked and sandwiched on both sides with a high flatness compression plate, and the sheet glass is heated and gradually cooled while applying pressure to flatten the sheet glass. Become

Here, the sheet glass formed by the down-draw method may be a sheet glass formed by a conventionally known down-draw method including the detailed manufacturing conditions, or may be the same as a sheet glass formed by the down-draw method. It may be a sheet glass having properties.

The material, size, thickness and the like of the sheet glass are not particularly limited. Examples of the material of the plate glass include aluminosilicate glass, sodaaluminosilicate glass, sodalime glass, and chain silicate glass.

The number of laminated sheets of glass is suitably about 2 to 50 from the viewpoint of the thermal conductivity of the glass. In addition,
The sheet glass can be flattened one by one without being laminated.

As a material of the compression plate having high flatness, a material having heat resistance and high heat conductivity is preferable.
A C plate, a carbon plate, or a metal plate such as an aluminum plate is preferable. In addition, a quartz plate or a heat-resistant glass plate having a low thermal conductivity may be used, but in this case, the slow cooling schedule needs to be gradual, and the same result can be obtained by increasing the slow cooling time.

The flatness of the surface of the compression plate which is in contact with the glass plate is preferably higher than the flatness required for the glass plate.
The following flatness is preferable. Further, it is preferable to increase the thickness of the compression plate in order to prevent deformation of the compression plate and maintain its flatness. For example, the thickness is preferably 10 mm or more for a SiC plate, 15 mm or more for a carbon plate, and 20 mm or more for an aluminum plate. Fins for preventing deformation of the compression plate may be provided on the back surface of the compression plate.

In order to apply a load to the sheet glass, for example, a compression plate / laminated sheet glass / compression plate may be stacked in this order, and a load plate having a predetermined weight may be placed thereon.

The heating and gradual cooling are performed by controlling the heating temperature and the heating time in the heat treatment furnace so that a predetermined heating gradual cooling schedule (heating, temperature holding, gradual cooling, cooling) is performed according to the glass material and the like. . In this case, the heating temperature needs to be higher than the strain point of the glass, and is preferably higher than the dislocation temperature of the glass. Further, the holding time is a time during which the glass is deformed by utilizing the flatness and load of the compression plate to make the whole sufficiently uniform to remove distortion and sufficiently correct the flatness of the plate glass.

In the present invention, in flattening the above-mentioned laminated glass sheets, at least one surface of the glass sheets is a solution in which a powder of an inorganic substance is suspended or dispersed in a solvent, and It is characterized by applying a solution which does not decompose at the heating temperature and emits a reaction gas. In this case, at least the coating surface is interposed between the laminated glass sheets. The application surface is also provided between the sheet glass and the compression plate. Of course, the above solution may be applied to each surface (both surfaces) of each sheet glass to be laminated.

Here, as the inorganic substance powder, MgC
_O3, CaCO _3, and the like. These inorganic substance powders may be used alone or in a combination of two or more. In addition, the powder of these inorganic substances,
Boron nitride (BxNy) or the like may be added for use. These inorganic substances form a carbonate coating on the surface of the glass and prevent the glass from being thermally fused. Further, these carbonate films can be easily washed and removed by water washing after the heat treatment. It is preferable that the particle diameter of the inorganic substance powder is uniform and the particle diameter is small. Specifically, the particle diameter of the inorganic substance powder is preferably in the range of about 20 to 30 μm. In addition, the concentration of the solution in which the powder of the inorganic substance is suspended or dispersed in the solvent,
It is preferable to make it thin so that a monomolecular layer is formed. The coating thickness of the solution needs to be a thickness that does not hinder the correction of the flatness of the glass, and specifically, is preferably about several microns. When the application of the aqueous solution becomes uneven, heat fusion of the glass occurs at that portion. Also,
If an organic substance such as a surfactant is added to the solution, it reacts with oxygen in the air during the heat treatment to generate carbon dioxide gas, and this gas deteriorates the accuracy of flatness, which is not preferable. Water is preferred as the solvent. The solution contains
Other components such as alcohol that does not generate carbon dioxide gas during the heat treatment may be added.

As a method of applying a solution containing a water-soluble inorganic substance and a surfactant to each surface of each sheet glass, a method of applying the solution using a sponge after absorbing the solution into a sponge is preferable. In this case, it is particularly preferable to apply the composition using a sponge roller. By using a sponge roller, the apparatus is simplified, cost and labor are not required, thin and uniform application can be achieved as compared with the spray method, and there is no danger of dust generation as compared with the spray method. Application by a sponge roller impregnates a solution in which a powder of an inorganic substance is suspended or dispersed in a solvent into a sponge roller in which a sponge having a uniform thickness is wound around a hard shaft, and the sponge roller is pressed against a sheet glass. It is preferable to apply the composition by rotating it along the surface of the glass sheet.
Furthermore, a plurality of sponge rollers were prepared, and when these plurality of sponge rollers were sequentially rotated while being pressed against the sheet glass, the powder of the inorganic substance was suspended or dispersed in the solvent by the sponge roller that first came into contact with the sheet glass. It is particularly preferable to apply the solution to the glass sheet and then impregnate the sponge roller that comes into contact with the glass sheet, and rotate the sponge roller impregnated with the water while sequentially pressing the glass sheet against the glass sheet. By using a sponge roller impregnated with water in this way, it is possible to apply even more thinly and evenly. It is difficult to apply other coating methods, for example, using a spray gun, or immersing a sheet glass in a solution to apply thin and uniform.

The flattening method of the present invention is suitably used for the production of a glass substrate for a magnetic disk or a glass substrate for an LCD, which will be described later. However, the present invention is not limited to this. It can be used as a method for flattening the surface of glass substrates and other general glass plates.

Next, the glass sheet produced by the method for flattening the glass sheet of the present invention is usually cut into a predetermined size and shape, chamfered, and, if necessary, polished and chemically treated. Various glass substrates are obtained through a strengthening process and the like.

The flat glass manufactured by the above flat glass flattening method can be used as various glass substrates requiring high surface smoothness without polishing or by simple polishing. Can, therefore,
It can be made much cheaper than before.

Specifically, a magnetic disk substrate manufactured by polishing a glass plate having a thickness of 3 mm or more and polishing it by about 2 mm since it was conventionally difficult to manufacture using a thin glass substrate is described above. Using thin sheet glass manufactured using the flat glass flattening method, after cutting into a predetermined size and shape, it is possible to make a glass substrate for a magnetic disk simply by performing light surface polishing, making polishing easy. And at very low cost. In addition, if the size and shape of the thin glass to be manufactured using the above-described flat glass flattening method are set to the size of the LCD substrate in advance, the LCD surface can be lightly polished without cutting.
The glass substrate can be easily polished and very inexpensive.

Next, another invention of the present invention will be described. According to another aspect of the present invention, there is provided a magnetic recording medium characterized in that after a main surface of a sheet glass subjected to the above-mentioned method for flattening a sheet glass is chemically reinforced by ion exchange, at least a magnetic layer is formed. It is a manufacturing method of.

The flat glass which has been subjected to the flat glass flattening method described above has a much higher flatness and surface state than conventional ones. Therefore, there is no flaw or fusion of foreign matter which cannot be completely removed by the polishing process on the substrate, and the surface condition is good. Therefore, when a magnetic disk is used, head crash does not occur, and the film such as the magnetic layer has a defect. Does not occur and does not cause an error.

Further, the magnetic recording medium according to the present invention is manufactured using the above-mentioned inexpensive glass substrate, and the polishing process can be simplified. Specifically, compared to the case where a magnetic disk substrate manufactured by polishing about 2 mm from a glass plate having a thickness of 3 mm or more as in the past is used, light polishing is performed from a glass plate having a thickness of just over 1 mm. Thus, a magnetic disk substrate of about 1 mm or less can be obtained, so that the polishing time is short and the cost is low.

The magnetic recording medium generally has a predetermined flatness and surface roughness, and is provided with an underlayer, a magnetic layer, a protective layer, and a lubricating layer on a magnetic disk glass substrate having a surface chemically strengthened. It is manufactured by sequentially laminating.

The underlayer in the magnetic recording medium is appropriately selected according to the magnetic layer. As the underlayer, for example, C
An underlayer made of at least one material selected from non-magnetic metals such as r, Mo, Ta, Ti, W, V, B, and Al is exemplified. 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 / CrMo, Cr
/ CrV, CrV / CrV, Al / Cr / CrMo, A
A multi-layer underlayer such as 1 / Cr / Cr is exemplified.

The material of the magnetic layer is not particularly limited. As the magnetic layer, specifically, for example, C containing Co as a main component is used.
oPt, CoCr, CoNi, CoNiCr, CoCr
Ta, CoPtCr, CoNiPt, CoNiCrP
t, CoNiCrTa, CoCrPtTa, CoCrP
A magnetic thin film such as tSiO is used. Further, the magnetic layer is divided by a non-magnetic film (for example, Cr, CrMo, CrV, or the like) to reduce the noise to obtain a multilayer structure (for example, CoP).
tCr / CrMo / CoPtCr, CoCrTaPt /
CrMo / CoCrTaPt). Also,
As the magnetic layer, in addition to the above-described Co-based material, for example, magnetic particles such as Fe, Co, CoFe, and CoNiPt are dispersed in a nonmagnetic film made of, for example, a ferrite-based material, an iron-rare earth-based material, or SiO ₂ or BN. Granular structure and the like. The magnetic layer may be either an inner surface type or a vertical type.

The unevenness forming layer is provided for the purpose of controlling the unevenness of the medium surface. There is no particular limitation on the method of forming the unevenness forming layer, the material, and the like. Further, the formation position of the unevenness forming layer is not particularly limited. In the case of a magnetic recording medium for a non-contact recording type magnetic disk device, the unevenness forming layer forms unevenness due to the unevenness of the unevenness forming layer on the medium surface. It is formed for the purpose of preventing adsorption to a medium and improving CSS durability. In the case of a magnetic recording medium for a contact-type recording type magnetic disk device, it is not necessary to provide a concavo-convex forming layer because the medium surface is preferably as flat as possible to avoid damage to the magnetic head and the magnetic recording medium. . There are various known materials and methods for forming the unevenness forming layer, and there is no particular limitation.
As the material of the unevenness forming layer, Al, Ti, Cr, Ag,
Nb, Ta, Bi, Si, Zr, Cu, Ce, Au, S
Metals such as n, Pd, Sb, Ge, Mg, In, W, and Pb and alloys thereof, or oxides, nitrides, and carbides of these metals and alloys can be used. From the viewpoint of easy formation, etc., Al alone, Al alloy, Al oxide (Al
It is desirable to use a metal containing Al as a main component, such as ₂ O ₃ ) or Al nitride (eg, AlN). Asperity forming layer,
It may be a continuous texture film or may be composed of discretely distributed island-like projections.

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 or stationary facing sputtering apparatus. Further, these protective films may be a single layer, or may be a multilayer structure composed of the same or different films. Another protective layer may be formed on the protective layer or in place of the protective layer. For example, instead of the above-mentioned protective layer, colloidal silica fine particles may be dispersed and applied while diluting tetraalkoxylan with an alcohol-based solvent, and then baked to form a silicon oxide (SiO ₂ ) film. . In this case, it functions as both the protective layer and the unevenness forming layer.

Although various proposals have been made for a lubricating layer, generally, a perfluoropolyether (PF) is generally used.
A liquid lubricant composed of PE) or the like is applied to the surface of the medium by a dipping method (immersion method), a spin coating method, a spray method, or the like, and is formed by performing a heat treatment as needed.

[0050]

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

Example 1 MgCO _{3 having a} particle size of 20 to 30 μm as a powder of an inorganic substance
And a solution obtained by suspending the suspension in water was thinly applied to the surface of a sheet glass (made of aluminosilicate glass) 1 using a sponge roller applying apparatus shown in FIG. The sponge roller 6a was impregnated with the above solution, and the sponge rollers 6b and 6c were each impregnated with water.

Next, as shown in FIG. 2, 15 sheets of the glass sheet 1 coated with the aqueous solution were laminated, and the laminated glass sheet (group) 2 was ground and polished to a flatness of 10 μm or less. 25 mm) 3. Furthermore, a thick plate made of SiC (thickness: 25 m) having the same smoothness as the thick plate 3 is placed on the laminated glass plate 2 placed on the thick plate 3.
m) 4 was placed. On this thick plate 4, a steel material 5 of 10 kg for applying a load was placed.

The laminated glass sheet 2 set as described above was heated and gradually cooled according to the slow cooling schedule shown in FIG. 3 to flatten the flat glass sheet.

After the glass was sufficiently cooled by slow cooling, the surface of the glass plate taken out of the furnace was covered with a white film as the alkali turned into a carbonate, and the glass plates did not fuse with each other. In addition, no gas was generated during the heat treatment. Further, the white film could be easily removed by washing with water, and no scratch was generated on the glass surface.

As a result, a flat glass of 300 × 300 × 1.1 mm having a flatness of 100 μm or less was obtained.
When a 66 mmφ magnetic disk substrate was cut out from the glass sheet, a flatness of 15 μm or less (average 7 μm or less) was obtained.

Further, it was examined how much the warpage (warpage) of the sheet glass was improved by the above-mentioned flattening treatment by heating and slow cooling. As a result, the reference length (the length of the sample) a
The value of the warpage rate (%) = b / a, which indicates the ratio of the warpage amount b with respect to the temperature, is about 1/1 by the flattening process by heating and slow cooling.
It was found that it was improved to about 0. Further, when the bending ratio (%) was examined in the same manner, the same tendency was found. In addition, it is known that the warpage of the sheet glass has an adverse effect on the strength of the glass substrate, and a reduction in the warpage rate (%) or the like can prevent a decrease in the glass strength.

The glass transition temperature of the used glass sheet was 500 ° C.
Was sufficient. Further, it was necessary to keep the holding time for 5 hours or more so that the whole was uniform. The temperature required for the planarization process is above the strain point,
In the case of this glass, it was necessary to heat it to a temperature of 400 ° C. or higher, and it was necessary to increase the holding time as the temperature was lowered to 500 ° C. or lower. At a heating temperature of 450 ° C., a holding time of 10 hours was required.

[0058] As Examples 2-4 inorganic material instead of MgCO _3, CaCO ₃ (Example 2), which was added boron nitride (BxNy) in MgCO ₃ (Example 3), boron nitride CaCO ₃ ( Example 1 except that the compound (BxNy) was added (Example 4).
In the same manner as described above, the flat glass was flattened. This result was almost the same as in Example 1.

Example 5 A flat glass sheet was treated in the same manner as in Example 1 except that the sponge rollers 6b and 6c impregnated with water were not used. As a result, the accuracy of the flatness was lower than that of Example 1, and the accuracy range was large and the stability was not high.

Comparative Example 1 A flat glass was treated in the same manner as in Example 1 except that a commercially available surfactant was added to the aqueous solution.

As a result, the reaction gas was released from the surfactant, and the warpage became worse.

In order to make the above-mentioned glass plate of 300 × 300 × 1.1 mm into a glass substrate for LCD, considerable polishing was required. Since the glass plate was thin and large in size, there were not a few cases where it was broken in the polishing step. In addition, it was difficult to manufacture a glass substrate for a magnetic disk from 1.1 mm thin glass by polishing because the flatness was poor and considerable polishing was required.

Comparative Example 2 A flat glass was treated in the same manner as in Example 1 except that paper (interleaf paper) was sandwiched between glass plates instead of applying the aqueous solution to the glass surface.

As a result, carbon dioxide gas came out of the paper, and the warpage became worse.

In order to make the above-mentioned glass plate of 300 × 300 × 1.1 mm into a glass substrate for LCD, considerable polishing was required, and since it was thin and large in size, there were not a few cases where it was broken in the polishing step. In addition, it was difficult to manufacture a glass substrate for a magnetic disk from 1.1 mm thin glass by polishing because the flatness was poor and considerable polishing was required.

As is clear from Examples 1 to 5 and Comparative Examples 1 and 2, according to the flattening method of the present invention, much higher flatness and surface condition can be obtained as compared with the conventional method. . Further, since the cleaning process is easy, the pre-process up to the polishing process can be shortened, and the production efficiency can be increased. Further, the polishing is easy and very inexpensive.

Example 6 A glass substrate for a magnetic disk of 66 mmφ having a flatness of 5 μm or less (average of 2 μm or less) manufactured in Example 1 was used.
After the chamfering, a polishing process using cerium oxide (CeO ₂ ) was performed through a sanding process of # 400 and # 1000 abrasive grains, and a finishing process was performed to a surface roughness Rmax of about 20 Å through a cleaning process.

Next, the glass substrate for a magnetic disk was subjected to a low-temperature ion exchange treatment to chemically strengthen it. At the time of this ion exchange, in the flattening treatment of the conventional sheet glass, flaws and fusion of foreign substances that cannot be completely removed by polishing in the previous step remain, and uniform chemical strengthening may not be performed. A more uniform chemical strengthening was achieved. In addition, damage due to uneven stress was prevented. Next, on both sides of the substrate, Al
(Film thickness 50 Å) / Cr (1000 Å) / CrMo (100 Å) underlayer, CoPtCr (120 Å) / CrMo (50 Å) / CoPtC
r (120 angstroms) magnetic layer, Cr
(50 Å) A protective layer was formed by an in-line type sputtering apparatus.

The above substrate is immersed in an organic silicon compound solution (a mixed solution of water, IPA and tetraethoxysilane) in which fine silica particles (particle size: 100 Å) are 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 7.
A magnetic disk for an MR head was obtained.

When a flying test of the magnetic head was performed on the magnetic disk, it was confirmed that head crash did not occur. Further, since no defect was generated on the substrate surface, it was confirmed that no defect was generated in the film such as the magnetic layer. The magnetic disk is inexpensive as compared with the conventional one and has no defects on the substrate surface. Was.

Example 7 The underlayer was made of Al / Cr / Cr, and the magnetic layer was made of CoNiCr.
A magnetic disk for a thin film head was obtained in the same manner as in Example 6 except that Ta was used. The same thing as Example 5 was confirmed for the above magnetic disk.

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

For example, following the flattening method of the present invention, a flattening treatment of the flat glass can be performed.
This re-flattening treatment can be performed for various purposes such as further improvement of flatness, correction when flatness is insufficient, and re-processing when flatness is poor due to various factors. In this case, as the flattening treatment of the plate glass, a conventionally well-known flattening process of the plate glass or the flattening method of the plate glass of the present invention can be selected and performed as necessary. In the case where a conventionally known flattening process for plate glass is performed, since the flattening process of the present invention is in a state where heat fusion hardly occurs, a release agent such as paper or carbon paper is used. Usually, it is not necessary to use them, but of course, these release agents can be used. In the re-flattening treatment of the sheet glass, the sheet glass may be treated singly or a plurality of sheets may be laminated.

[0074]

As described above, according to the method for flattening a glass sheet of the present invention, it is possible to prevent heat fusion between laminated thin glass sheets and to prevent generation of scratches and fusion of foreign matter. A plurality of thin glass sheets can be stacked and efficiently heat-treated to obtain a highly accurate flatness.

The thin glass substrate obtained by the present invention has less warpage, has excellent flatness, and is inexpensive.

Further, in the magnetic recording medium manufactured according to the present invention, since the glass substrate has excellent flatness and there is no fusion of foreign matter on the substrate surface, head crash can be prevented. Further, since no defect occurs on the substrate surface, no defect occurs in the film such as the magnetic layer. Furthermore, since it is manufactured using an inexpensive glass substrate and the polishing process can be further simplified, it can be manufactured at a much lower cost than before.

[Brief description of the drawings]

FIG. 1 is a side view showing a solution application device in an embodiment.

FIG. 2 is a perspective view for explaining a heat treatment method in an example.

FIG. 3 is a diagram showing a heated and slowly cooled schedule in an example.

4A and 4B are views for explaining a conventional heat treatment method, wherein FIG. 4A is a front view and FIG. 4B is a side view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sheet glass 2 Sheet glass laminated 3 Thick plate (compression plate) 4 Thick plate (compression plate) 5 Steel material 6 Sponge roller 7 Solution (coating liquid)

Claims (7)

[Claims] 1. A method of flattening a sheet glass by pressing and heating and gradually cooling the sheet glass while pressing both sides of a single or a plurality of sheet glasses formed by a down-draw method while sandwiching the sheet glass with a high flatness compression plate, A solution obtained by suspending or dispersing an inorganic substance powder in a solvent on at least one main surface of the sheet glass, and applying a solution that does not decompose at the heating temperature of the sheet glass and emit a reaction gas. Flattening method for sheet glass. 2. The method according to claim 1, wherein the powder of the inorganic substance is MgCO ₃ and / or CaCO ₃ . 3. The method according to claim 1, wherein the powder of the inorganic substance is boron nitride (Bx
3. The method according to claim 2, wherein Ny) is contained. 4. A solution in which a powder of the inorganic substance is suspended or dispersed in a solvent is impregnated in a sponge roller in which a sponge having a uniform thickness is wound around a shaft, and the sponge roller is pressed against the sheet glass while pressing the sheet glass. The flattening method for a flat glass according to any one of claims 1 to 3, wherein the powder of the inorganic substance is uniformly applied to the flat glass by rotating along the surface. 5. A method in which a plurality of sponge rollers each having a sponge having a uniform thickness wound around a shaft member are used, and when the plurality of sponge rollers are sequentially rotated while being pressed against the sheet glass, the sponge roller is first brought into contact with the sheet glass. A solution prepared by suspending or dispersing an inorganic substance powder in a solvent is applied to a glass sheet, and then the sponge roller that comes into contact with the glass sheet is impregnated with water, and the water-impregnated sponge roller is sequentially pressed against the glass sheet. 5. The flattening method for a flat glass according to claim 1, wherein the flat glass is rotated while rotating. 6. A sponge having a plurality of sponge rollers each having a sponge having a uniform thickness wound around a shaft member, and a means for rotating the plurality of sponge rollers while sequentially pressing them against a sheet glass, wherein the sponge first contacts the sheet glass. Roller has a means for impregnating a solution in which a powder of an inorganic substance is suspended or dispersed in a solvent, and a sponge roller which comes into contact with the glass sheet thereafter has means for impregnating with water. Coating equipment. 7. A magnetic material comprising: polishing a main surface of a glass sheet subjected to the method for flattening a glass sheet according to claim 1; strengthening the main surface by ion exchange; and then forming at least a magnetic layer. Manufacturing method of recording medium.