JP5978394B2 - Manufacturing method of plate glass, manufacturing method of glass substrate for information recording medium, and manufacturing method of information recording medium - Google Patents

Description

The present invention relates to a method for manufacturing an information recording medium, a method for manufacturing a glass substrate for an information recording medium , and a plate glass , which are mounted on an information recording apparatus such as a hard disk drive (HDD) as a part of the information recording medium. It relates to the manufacturing method .

  In recent years, as the storage capacity of HDDs has increased dramatically, it has become indispensable to reduce the recording area of a medium that is spent on one bit. In proportion to this, the size of magnetic particles for recording must be reduced. However, the energy for maintaining the direction of magnetization recorded in one direction is reduced by miniaturization, and it is easily affected by thermal energy. In order to stabilize the magnetization direction, there is a need to change the medium from a CoCr-based alloy, which is currently widely used as a magnetic material, to an Fe—Pt-based magnetic material having a high coercive force.

  However, in the film formation of the Fe—Pt magnetic material, the arrangement of Fe and Pt atoms becomes irregular and a high coercive force cannot be obtained. In order to obtain a high coercive force by ordering, it is essential to perform a high-temperature heat treatment at about 600 ° C. on the glass substrate after film formation.

  In order to obtain such a glass substrate, a glass substrate manufacturing method using a float method is generally used. For example, in Japanese Patent Laid-Open No. 7-53223 (Patent Document 1), Japanese Patent Application Laid-Open No. 2001-357515 (Patent Document 2), and Japanese Patent Application Laid-Open No. 2003-36528 (Patent Document 3), information using the float method is used. A method for manufacturing a glass substrate for a recording medium is disclosed.

Japanese Patent Laid-Open No. 7-53223 JP 2001-357515 A JP 2003-36528 A

  As described above, since it is indispensable to perform high-temperature heat treatment at about 600 ° C. on the Fe—Pt magnetic material, the temperature of Tg, which is an index of heat resistance of the glass substrate, is increased to 600 ° C. or more. A high-temperature heat treatment at about 600 ° C. is performed during the film formation of the Fe—Pt magnetic material on the glass substrate.

  As a result, although there is no problem in heat resistance, a new problem has arisen that the magnetic properties are deteriorated only on one side of the information recording medium (magnetic disk). As a result of diligent research by the inventors, as a result of component analysis of error portions of the information recording medium (magnetic disk), it was discovered that Sn was contained.

  Furthermore, as a result of investigation of the cause by the inventors, when a high-Tg material for heat-assisted recording is used, the temperature during the float bath process during the float process is high, and the temperature during molding is high. It was found that tin (tin) tends to evaporate and the tin content on the lower surface of the glass increases.

  With the recording density of conventional magnetic disks, tin content in the glass substrate has not been a problem, but high-temperature heat treatment is required when forming a Fe—Pt alloy or the like to be a magnetic layer for heat-assisted recording. During the high temperature heat treatment, tin diffusion on the lower surface of the glass substrate proceeds. As a result, it was revealed that the diffusion of tin reaches the magnetic film, and the SNR (signal-noise ratio or signal-to-noise ratio) quality on the bottom surface of the magnetic disk becomes unstable. Although it is possible to remove the tin diffusion layer in the lapping process in advance, it is not preferable because flatness and parallelism deteriorate.

Accordingly, the present invention has been made to solve the above-described problems, and when used as an information recording medium, the method for manufacturing the information recording medium and the glass for the information recording medium capable of stabilizing the SNR quality. It aims at providing the manufacturing method of a board | substrate , and the manufacturing method of plate glass .

In the plate glass manufacturing method in accordance with the present invention, the dissolution tank, refining tank, float bath, and in the order of gradual cooling line, a glass raw material and molten glass in the melting tank, the molten glass, the refining bath, the float bath, and is passed through the slow cooling line, using the float process of molding into a sheet glass, a method for producing a plate glass, comprising the following steps.

  In the float bath, the molten glass floats on the surface of molten tin melted by heating, and the molten glass has a viscosity logη = 4.0 (dPa · s) of 1100 ° C. or higher, and the clarification tank The internal temperature is equal to or higher than the liquid phase temperature of the molten glass, and includes a step of cooling the molten glass in the float bath at a temperature lowering rate of 50 ° C./min or higher.

  The step of cooling the molten glass starts cooling the molten glass from a position at which the molten glass flows into the float bath from a cooling start position at least 50 cm ahead of the flow direction of the molten glass. The viscosity of the molten glass at the cooling start position is log η = 3.6 (dPa · s) or less, and the viscosity of the molten glass is log η = 4.0 (dPa · s) or less. Cool at a rate of 50 ° C./min or more.

In another aspect of the method for producing plate glass according to the present invention, in the order of the melting tank, the clarification tank, the float bath, and the cooling line, the glass raw material is made into molten glass in the melting tank, and the molten glass is A plate glass manufacturing method using a float method in which the clarification tank, the float bath, and the cooling line are passed through and formed into a sheet glass, and includes the following heights.
In the float bath, the molten glass floats on the surface of molten tin melted by heating, and the molten glass has a viscosity logη = 4.0 (dPa · s) of 1100 ° C. or higher, and the clarification tank The internal temperature of the molten glass is equal to or higher than the liquidus temperature of the molten glass, and includes a step of cooling the molten glass at a temperature lowering rate of 50 ° C./min or more in the float bath, and the step of cooling the molten glass includes: The molten glass is cooled at a rate of 50 ° C./min or more until the viscosity becomes log η = 3.6 (dPa · s) to log η = 4.0 (dPa · s).
In another form, the process of cooling the said molten glass sprays gas on the said molten glass.

  In another form, the process of cooling the said molten glass makes a solid contact the said molten glass.

In another embodiment, the step of cooling the molten glass controls the temperature of the molten tin in the float bath.
In another embodiment, the plate glass is for a glass substrate for information recording media.

In another form, the glass substrate for information recording media is a glass substrate for heat assist.
In the manufacturing method of the glass substrate for information recording media based on this invention, at least grinding | polishing process is given to the main surface of the plate glass obtained by the manufacturing method of the plate glass in any one of the above-mentioned.
The method for producing an information recording medium according to the present invention includes a process of forming an annular glass substrate from the plate glass obtained by the method for producing an information recording medium glass substrate.

According to the present invention, there are provided an information recording medium manufacturing method, an information recording medium glass substrate manufacturing method , and a plate glass manufacturing method capable of stabilizing SNR quality when used as an information recording medium. It is possible to do.

It is a perspective view which shows an information recording device. It is a top view which shows the glass substrate 1 manufactured by the manufacturing method of the glass substrate for information recording media based on embodiment. It is arrow sectional drawing along the III-III line in FIG. It is a top view which shows the information recording medium 10 provided with the glass substrate 1 as an information recording medium. It is arrow sectional drawing along the VV line in FIG. It is a flowchart which shows the manufacturing method of a glass substrate. It is a schematic diagram which shows the float glass process in a glass substrate shaping | molding process. It is a figure which shows the shaping | molding process of the glass substrate in the float bath used for the float glass process in embodiment. It is a figure which shows the shaping | molding process of the glass substrate in the float bath used for the float glass process in other embodiment. It is a figure which shows the shaping | molding process of the glass substrate in the float bath used for the float glass process in other embodiment. It is a figure which shows the viscosity curve of a molten glass raw material. It is a figure which shows the evaluation result of the HDD operation test in Example 1-8 and Comparative Example 1-4.

  Embodiments and examples based on the present invention will be described below with reference to the drawings. In the description of the embodiments and the examples, when the number, amount, and the like are referred to, the scope of the present invention is not necessarily limited to the number, amount, and the like unless otherwise specified. In the description of the embodiment and each example, the same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated.

[Embodiment]
(Information recording device 30)
First, the information recording device 30 will be described with reference to FIG. FIG. 1 is a perspective view showing the information recording apparatus 30. The information recording apparatus 30 includes the glass substrate 1 manufactured by the method for manufacturing a glass substrate for information recording medium (hereinafter also simply referred to as a glass substrate) in the embodiment as the information recording medium 10.

  Specifically, the information recording device 30 includes an information recording medium 10, a housing 20, a head slider 21, a suspension 22, an arm 23, a vertical shaft 24, a voice coil 25, a voice coil motor 26, a clamp member 27, and a fixing screw. 28. A spindle motor (not shown) is installed on the upper surface of the housing 20.

  An information recording medium 10 such as a magnetic disk is rotatably fixed to the spindle motor by a clamp member 27 and a fixing screw 28. The information recording medium 10 is rotationally driven by this spindle motor at, for example, several thousand rpm. Although details will be described later with reference to FIGS. 4 and 5, in the information recording medium 10, a compression stress layer 12 (see FIG. 5) and a magnetic recording layer 14 (see FIGS. 4 and 5) are formed on the glass substrate 1. To be manufactured.

  The arm 23 is attached to be swingable about the vertical axis 24. A suspension 22 formed in a leaf spring (cantilever) shape is attached to the tip of the arm 23. A head slider 21 is attached to the tip of the suspension 22 so as to sandwich the information recording medium 10.

  A voice coil 25 is attached to the side of the arm 23 opposite to the head slider 21. The voice coil 25 is clamped by a magnet (not shown) provided on the housing 20. A voice coil motor 26 is constituted by the voice coil 25 and the magnet.

  A predetermined current is supplied to the voice coil 25. The arm 23 swings around the vertical axis 24 by the action of electromagnetic force generated by the current flowing through the voice coil 25 and the magnetic field of the magnet. As the arm 23 swings, the suspension 22 and the head slider 21 also swing in the direction of the arrow AR1. The head slider 21 reciprocates on the front and back surfaces of the information recording medium 10 in the radial direction of the information recording medium 10. A magnetic head (not shown) provided on the head slider 21 performs a seek operation.

  While the seek operation is performed, the head slider 21 receives a levitation force due to an air flow generated as the information recording medium 10 rotates. Due to the balance between the levitation force and the elastic force (pressing force) of the suspension 22, the head slider 21 travels with a constant flying height with respect to the surface of the information recording medium 10. By the traveling, the magnetic head provided on the head slider 21 can record and reproduce information (data) on a predetermined track in the information recording medium 10. The information recording apparatus 30 on which the glass substrate 1 is mounted as a part of the members constituting the information recording medium 10 is configured as described above.

(Glass substrate 1)
FIG. 2 is a plan view showing glass substrate 1 manufactured by the method for manufacturing a glass substrate for information recording medium according to the present embodiment. 3 is a cross-sectional view taken along the line III-III in FIG.

  As shown in FIGS. 2 and 3, the glass substrate 1 (glass substrate for information recording medium) used as a part of the information recording medium 10 (see FIGS. 4 and 5) has a main surface 2, a main surface 3, It has the inner peripheral end surface 4, the hole 5, and the outer peripheral end surface 6, and is formed in a disk shape as a whole. The hole 5 is provided so as to penetrate from one main surface 2 toward the other main surface 3. A chamfer 7 is formed between the main surface 2 and the inner peripheral end surface 4 and between the main surface 3 and the inner peripheral end surface 4. Between the main surface 2 and the outer peripheral end surface 6 and between the main surface 3 and the outer peripheral end surface 6, a chamfered portion 8 (chamfer portion) is formed.

The size of the glass substrate 1 is, for example, 0.8 inch, 1.0 inch, 1.8 inch, 2.5 inch, or 3.5 inch. It is possible to make the size smaller than this or larger than this. The thickness of the glass substrate is, for example, 0.30 mm to 2.2 mm from the viewpoint of preventing breakage. In the present embodiment, the glass substrate has an outer diameter of about 64 mm, an inner diameter of about 20 mm, and a thickness of about 0.8 mm. The thickness of the glass substrate is a value calculated by averaging the values measured at a plurality of arbitrary points to be pointed on the glass substrate. From the viewpoint of increasing the hardness of the glass substrate, the Vickers hardness of the glass substrate 1 is preferably 610 kg / mm ² or more.

(Information recording medium 10)
FIG. 4 is a plan view showing an information recording medium 10 provided with a glass substrate 1 as an information recording medium. FIG. 5 is a cross-sectional view taken along the line VV in FIG.

  As shown in FIGS. 4 and 5, the information recording medium 10 includes a glass substrate 1, a compressive stress layer 12, and a magnetic recording layer 14. The compressive stress layer 12 is formed so as to cover the main surfaces 2 and 3, the inner peripheral end face 4, and the outer peripheral end face 6 of the glass substrate 1. The magnetic recording layer 14 is formed so as to cover a predetermined region on the main surfaces 2 and 3 of the compressive stress layer 12. By forming the compressive stress layer 12 on the inner peripheral end face 4 of the glass substrate 1, a hole 15 is formed inside the inner peripheral end face 4. The information recording medium 10 is fixed to a spindle motor provided on the housing 20 (see FIG. 1) using the holes 15.

  In the information recording medium 10 shown in FIG. 5, the magnetic recording layer 14 is formed on both the compressive stress layer 12 formed on the main surface 2 and the compressive stress layer 12 formed on the main surface 3 (both sides). Is formed. The magnetic recording layer 14 may be provided only on the compression stress layer 12 (one side) formed on the main surface 2, or on the compression stress layer 12 (one side) formed on the main surface 3. It may be provided.

  The magnetic recording layer 14 is formed by spin-coating a thermosetting resin in which magnetic particles are dispersed on the compressive stress layer 12 on the main surfaces 2 and 3 of the glass substrate 1 (spin coating method). The magnetic recording layer 14 may be formed by a sputtering method or an electroless plating method performed on the compressive stress layer 12 on the main surfaces 2 and 3 of the glass substrate 1.

  The film thickness of the magnetic recording layer 14 is about 0.3 μm to 1.2 μm in the case of spin coating, about 0.04 μm to 0.08 μm in the case of sputtering, and about 0.05 μm to about in the case of electroless plating. 0.1 μm. From the viewpoint of thinning and high density, the magnetic recording layer 14 is preferably formed by sputtering or electroless plating.

  As a magnetic material used for the magnetic recording layer 14, an Fe—Pt magnetic material is used as a magnetic layer material suitable for heat-assisted recording.

  In order to improve the sliding of the magnetic head, the surface of the magnetic recording layer 14 may be thinly coated with a lubricant. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon.

  The magnetic recording layer 14 may be provided with an underlayer or a protective layer as necessary. The underlayer in the information recording medium 10 is selected according to the type of magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni.

  The underlayer provided on the magnetic recording layer 14 is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

  Examples of the protective layer for preventing wear and corrosion of the magnetic recording layer 14 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, or a silica layer. These protective layers can be formed continuously with an in-line type sputtering apparatus together with the underlayer and the magnetic film. These protective layers may be a single layer, or may have a multilayer structure composed of the same or different layers.

  Another protective layer may be formed on the protective layer or instead of the protective layer. For example, instead of the protective layer, colloidal silica fine particles are dispersed and coated on a Cr layer with tetraalkoxylane diluted with an alcohol solvent, and then fired to form a silicon oxide (SiO2) layer. May be.

(Glass substrate manufacturing method)
Next, the manufacturing method S100 of the glass substrate (glass substrate for information recording media) in this Embodiment is demonstrated using the flowchart figure shown in FIG. A glass substrate manufacturing method S100 in the present embodiment includes a plate-like glass molding step S10, a cutting step S20, an end surface polishing step S30, a rough polishing step S40, a cleaning step S50, a chemical strengthening step S60, a precision polishing step S70, and A scrub cleaning step S80 is provided.

  A magnetic thin film forming step S200 is performed on the glass substrate obtained through the scrub cleaning step S80. Through the magnetic thin film forming step S200, the information recording medium 10 (see FIGS. 4 and 5) is obtained. Hereinafter, the detail of each process S10-S80 which comprises manufacturing method S100 of a glass substrate is demonstrated in order.

(Plate-shaped glass molding step S10)
First, in the glass sheet forming step S10, a glass sheet is manufactured using a float glass method using a molten glass material as a material. Details of the float method of the present embodiment will be described later.

  Corresponding oxides, carbonates, nitrates, hydroxides, and the like are used as raw materials for the respective components constituting the molten glass, and are weighed to a desired ratio and thoroughly mixed with powders to prepare raw materials. For example, the blended raw material is put into a melting tank heated to 1600 ° C., melted and clarified, float-molded, and gradually cooled to form a plate glass.

  As a material of the glass substrate, for example, amorphous glass or crystallized glass can be used. It is also possible to subject the glass substrate to chemical strengthening treatment. In that case, it is possible to provide a glass substrate for an information recording medium excellent in strength quality on the surface of the glass substrate.

(Cutting step S20)
Referring to FIG. 6 again, in the cutting step S20, an inner hole is formed in the center of the glass substrate using a cylindrical diamond drill, and an annular glass substrate is formed (coring process). . Thereafter, the inner peripheral end face and the outer peripheral end face are ground with a diamond grindstone and subjected to predetermined chamfering (forming, chamfering). You may make it transfer to an end surface grinding | polishing process after performing the lapping process which lapping (grinding) the main surface after a cutting-out process.

(End face polishing step S30)
In the end surface polishing step S30, the inner peripheral end surface and the outer peripheral end surface of the glass substrate 1 are polished using a polishing brush having a spiral brush bristle material. While supplying the polishing slurry between the polishing brush and each end surface of the glass substrate 1, the polishing brush is rotated in contact with each end surface. With the glass substrate 1 immersed in the polishing liquid, the polishing brush may be rotated in contact with each end face.

(Rough polishing step S40)
The glass substrate 1 whose inner peripheral end face and outer peripheral end face are polished has its main surfaces 2 and 3 polished roughly in a plurality of times. For example, the main surfaces 2 and 3 are polished in two steps of the first and second rough polishing steps. By gradually increasing the finishing accuracy of the glass substrate 1, the glass substrate 1 having a highly smooth and flat surface can be obtained. When rough polishing is performed in two steps, the first rough polishing step is mainly intended to remove scratches and distortions remaining on the main surfaces 2 and 3, and the second rough polishing step is performed on the main surfaces 2 and 3. Is intended to be finished in a mirror shape.

(Washing step S50)
After the rough polishing step S40, the glass substrate 1 is subjected to a cleaning process using an acidic cleaning liquid. The purpose of this cleaning treatment is to remove from the surface of the glass substrate 1 any one of cerium oxide, zirconium oxide, or zirconium silicate that has been used as a polishing slurry in the rough polishing step S40 that is the previous step.

  Specifically, the glass substrate 1 after rough polishing is removed from the polishing pad used in the rough polishing step S40, and then the surface of the glass substrate 1 is etched using a cleaning liquid containing sulfuric acid and hydrofluoric acid. Wash. The polishing slurry such as cerium oxide, zirconium oxide, or zirconium silicate adhering to the surface of the glass substrate 1 is appropriately removed by a strongly acidic cleaning liquid such as sulfuric acid and / or hydrofluoric acid. Thereafter, the glass substrate 1 is cleaned using an acidic cleaning solution.

  The cleaning liquid used in the cleaning step S50 varies depending on the chemical resistance of the glass substrate 1, but a concentration of about 1% to 30% is preferable for sulfuric acid, and 0.2% to 5% for hydrofluoric acid. A concentration of about is preferred. Cleaning using these cleaning liquids may be performed while applying ultrasonic waves in a cleaning machine in which an aqueous solution is stored. The frequency of the ultrasonic wave used at this time is preferably 78 kHz or higher.

(Chemical strengthening step S60)
After the cleaning step S50, the glass substrate 1 is chemically strengthened. As the chemical strengthening liquid, for example, a mixed liquid of potassium nitrate (50 wt%) and sodium sulfate (50 wt%) can be used. The chemical strengthening liquid is heated to, for example, 300 ° C. to 480 ° C. The cleaned glass substrate 1 is preheated to 300 ° C. to 480 ° C., for example. The glass substrate 1 is immersed in the chemical strengthening solution for 3 hours to 4 hours, for example. The chemical strengthening process may be performed after the precision polishing process.

  When dipping, the plurality of glass substrates 1 can be held in their respective holders so that the entire main surfaces 2 and 3 of the glass substrate 1 are chemically strengthened. preferable. By immersing the glass substrate 1 in the chemical strengthening solution, alkali metal ions (lithium ions and sodium ions) on the surface layer of the glass substrate 1 are chemically strengthened salts (sodium ions) having a relatively large ion radius in the chemical strengthening solution. And potassium ions). Thereby, a compressive stress layer having a thickness of, for example, 50 μm to 200 μm is formed on the surface layer of the glass substrate 1.

  By forming the compressive stress layer, the surface of the glass substrate 1 is strengthened, and the glass substrate 1 has good impact resistance. The glass substrate 1 subjected to the chemical strengthening treatment is appropriately washed. For example, the glass substrate 1 is further cleaned using pure water or IPA (isopropyl alcohol) after being cleaned with sulfuric acid. Thereafter, the chemically strengthened layer may be removed.

(Precision polishing step S70)
After the chemical strengthening step S60, a precision polishing process is performed on the glass substrate 1. The precision polishing step S70 is intended to finish the main surface of the glass substrate 1 in a mirror shape. In the precision polishing step S70, as in the above-described rough polishing step S40, the glass substrate 1 is precisely polished using a double-side polishing machine (see FIG. 11).

  The precision polishing step S70 and the rough polishing step S40 are different in the composition of the polishing abrasive grains contained in the polishing liquid (slurry) used and the polishing pad used. In the precision polishing step S70, the grain size of the abrasive grains in the polishing liquid supplied to the main surfaces 2 and 3 of the glass substrate 1 on which the compressive stress layer is formed is smaller than that in the rough polishing step S40. Soften the hardness.

  An example of the polishing pad used in the precision polishing step S70 is a soft foam resin polisher. The precision polishing step S70 uses loose abrasive grains, and includes a first polishing step with abrasive grains mainly composed of Ce and a second polishing step of polishing with abrasive grains mainly composed of Si.

(Scrub cleaning step S80)
After the precision polishing step S70, a scrub cleaning process is performed on the glass substrate 1. Specifically, the glass substrate 1 after the precision polishing is removed from the polishing pad used in the precision polishing step S70, and then the cleaning liquid is supplied to the surface of the glass substrate 1 while the compression stress layer is formed. Scrub cleaning is performed on the surface using a scrub cleaning device.

  The glass substrate 1 may be temporarily stored in water after being removed from the polishing pad of the double-side polishing machine. By storing in water, it is possible to reduce the amount of foreign matter such as polishing wrinkles or loose abrasive grains adhering to the glass substrate 1 after precision polishing while preventing the surface of the glass substrate 1 from drying after precision polishing. After the glass substrate 1 is stored in water for a predetermined time, the glass substrate 1 is set in a scrub cleaning device and scrub cleaning is performed on the glass substrate 1.

  For scrub cleaning, for example, a cleaning liquid such as a detergent or pure water is used. The pH of the cleaning solution used for scrub cleaning is preferably 9.0 or more and 12.2 or less. Within this range, the ζ potential can be easily adjusted and scrub cleaning can be performed efficiently. As scrub cleaning, both scrub cleaning with a detergent and scrub cleaning with pure water may be performed. By using a detergent and pure water, the glass substrate 1 can be more appropriately cleaned. The glass substrate 1 may be further rinsed with pure water between scrub cleaning with a detergent and scrub cleaning with pure water.

  After the scrub cleaning, the glass substrate 1 may be further subjected to ultrasonic cleaning. After scrub cleaning with detergent and pure water, ultrasonic cleaning with chemical solution such as sulfuric acid aqueous solution, ultrasonic cleaning with pure water, ultrasonic cleaning with detergent, ultrasonic cleaning with IPA, and / or steam drying with IPA, etc. Further, it may be performed.

  The manufacturing method S100 of the glass substrate 1 in the present embodiment is configured as described above. By using manufacturing method S100 of glass substrate 1, glass substrate 1 of this embodiment shown in Drawing 2 and Drawing 3 can be obtained.

(Magnetic thin film forming step S200)
A magnetic recording layer using an Fe—Pt magnetic material is formed on the main surfaces 2 and 3 (or one of the main surfaces 2 and 3) of the glass substrate 1 that has been subjected to the scrub cleaning process. Thereby, the information recording medium 10 shown in FIGS. 4 and 5 can be obtained.

(Float method)
Hereinafter, the float method in the present embodiment will be described with reference to FIGS. FIG. 7 is a schematic diagram showing the float method in the glass substrate molding step, and FIG. 8 is a diagram showing the glass substrate molding step in the float bath used in the float method.

  Referring to FIG. 7, in the float process, dissolution tank 1100, clarification tank 1200, float bath 1300, and decooling line 1400 are provided in this order. The glass raw material introduced into the melting tank 1100 becomes molten glass at a temperature of about 1600 ° C. or higher and is fed into the clarification tank 1200.

  In the clarification tank 1200, the molten glass sent into the clarification tank 1200 lowers the temperature to about 1300 ° C to 1200 ° C. While proceeding while being pushed in this state, bubbles in the molten glass are absorbed and disappeared in the molten glass.

  The molten glass lowered to about 1100 ° C. flows into the float bath 1300. The float bath 1300 is formed into a glass plate shape. The float bath 1300 stores molten metal (tin dissolved in a liquid state) like a pool. The interior of the float bath 1300 is filled with an atmospheric gas (such as a mixed gas of nitrogen and hydrogen) so that tin does not participate, and the temperature is controlled using an electric heater or the like.

  The molten glass that has flowed into the float bath 1300 advances while spreading over the liquid surface of tin so that oil floats on the water surface. Since the specific gravity of the molten glass (for example, 2.5) is lighter than that of tin (for example, 6.5), the molten glass can float on the surface of tin. The surface (lower surface) in contact with tin of the molten glass becomes a flat surface (horizontal plane) reflecting the horizontal surface of tin. The upper surface of the molten glass becomes a horizontal plane due to gravity. As a result, the molten glass is molded into a parallel flat plate glass while being cooled to about 600 ° C.

  The plate glass conveyed to the cooling line 1400 is cooled while being conveyed slowly so that distortion due to a temperature difference does not occur inside the glass. The plate glass cooled by the cooling line 1400 is cut into a plate glass having a predetermined size in the next step.

  In the present embodiment, when the molten glass is molded in the float bath 1300, the viscosity of the molten glass is based on a viscosity of about log η = 4.0 (dPa · s). When the molten glass has the above-mentioned viscosity and the temperature is 1100 ° C. or higher, the molten tin is rapidly evaporated and the diffusion rate into the molten glass is increased.

  Therefore, at least 50 ° C. from log η = 3.6 (dPa · s) to log η = 4.0 (dPa · s) with respect to the high-temperature molten glass flowing into the float bath 1300 at the liquidus temperature (TL) or higher. It becomes possible to suppress the diffusion of molten tin into the molten glass by cooling (rapid cooling) at / min or more. The temperature of the clarification tank 1200 is the liquidus temperature TL or higher. This is because, at the liquidus temperature TL or lower, crystallization of the molten glass proceeds in the clarification tank 1200 and the glass substrate becomes opaque (devitrification occurs).

  With reference to FIG. 8, the cooling with respect to the molten glass with respect to the float bath 1300 is demonstrated. As described above, molten tin 2000 is stored inside the float bath 1300 like a pool. The molten glass 100 pushed out from the clarification tank 1200 is poured out from the inlet 1310 of the float bath 1300 onto the surface of the molten tin 2000.

Cooling of the molten glass with respect to the float bath 1300 is at least 50 cm (dimension L 1 in the drawing) or more from the position (inlet 1310) where the molten glass 100 flows into the float bath 1300 with respect to the flow direction of the molten glass. The cooling of the molten glass 100 is started from the cooling start position. If it is less than 50 cm, the molten glass 100 does not spread sufficiently in the float bath 1300 (in the vertical direction in the drawing), which may adversely affect the control of the thickness of the molten glass 100.

  In this embodiment mode, the molten glass is cooled by blowing a gas using the blower 3100. A gas temperature of about 25 ° C. to 30 ° C. is sufficient, but a gas cooled to a predetermined temperature using a cooling device may be used. As the gas, in order not to disturb the atmospheric gas filled in the float bath 1300, the same mixed gas of nitrogen and hydrogen as the atmospheric gas may be used.

  As shown in FIG. 9, as another cooling means, a cooling roller 320 may be disposed at the cooling start position, and the molten glass may be cooled by bringing the cooling roller 320 into contact with the surface of the molten glass. By bringing a solid such as the cooling roller 320 into contact with the surface of the molten glass, the molten glass can be efficiently cooled. The cooling roller 320 may be made of SUS, ceramic, or refractory material. By circulating the refrigerant inside the cooling roller 320, the molten glass can be cooled more efficiently.

  As shown in FIG. 10, as another cooling means, a weir 2100 and a weir 2200 are provided at a position at a constant interval (L2) from the cooling start position (L1), and a region surrounded by the weir 2100 and the weir 2200 is melted. The molten glass 100 may be cooled by controlling the temperature of the tin 2000 to a temperature lower than other regions by using the temperature control means 2300. Control of the temperature of molten tin 2000 includes temperature management of molten tin 2000 using a cooling means, or temperature management by managing the amount of molten tin 2000.

(Example)
HDD operation tests were performed using magnetic recording media manufactured using the glass substrate manufacturing methods of Examples 1-8 and Comparative Examples 1-4 shown below.

The glass substrate was produced by changing the cooling start viscosity, the cooling end viscosity, and the cooling rate of the molten glass in the float bath 1300. In any of the examples and comparative examples, the glass composition is 63 wt% for SiO ₂ , ₂ wt% for Al ₂ O _{3, 3} wt% for Na ₂ O, 9 wt% for K ₂ O, 5 wt% for MgO, and 10 wt% for CaO. %, ZrO ₂ 8 wt% glass was used.

  The liquidus temperature (TL) of this glass was 1180 ° C. as a result of a 3-hour devitrification test. Tg (glass transition point) was 670 ° C. The viscosity was measured by a platinum ball pulling method, and the viscosity curve shown in FIG. 11 was obtained. The temperature at log η = 4.0 (dPa · s) was about 1125 ° C.

  The temperature in the clarification tank 1200 of the previous process of the float bath 1300 was 1250 degreeC. The cooling start position (L1) in the float bath 1300 was 50 cm, the glass viscosity at that position was log η = 3.4 (dPa · s), and the temperature was 1200 ° C. The molten tin temperature of the float bath was 600 ° C.

Example 1
In Example 1, the viscosity of the molten glass at the cooling start position (L1) is log η = 3.6 (dPa · s).

  For cooling the molten glass 100, a blower 3100 shown in FIG. 8 was used. The temperature of the cooling gas was about 25 to 30 ° C., and the same gas as the atmospheric gas in the float bath 1300 was used.

  The molten glass has a cooling end viscosity of log η = 4.0 (dPa · s) and a temperature decrease rate of 50 ° C./min.

(Example 2)
In Example 2, the viscosity of the molten glass at the cooling start position (L1) is log η = 3.4 (dPa · s). Cooling of the molten glass 100 is the same as in the first embodiment.

  The molten glass has a cooling end viscosity of log η = 4.0 (dPa · s) and a temperature decrease rate of 50 ° C./min.

(Example 3)
In Example 3, the viscosity of the molten glass at the cooling start position (L1) is log η = 3.6 (dPa · s). Cooling of the molten glass 100 is the same as in the first embodiment.

  The viscosity of the molten glass after cooling is log η = 4.2 (dPa · s), and the cooling rate is 50 ° C./min.

Example 4
In Example 4, the viscosity of the molten glass at the cooling start position (L1) is log η = 3.6 (dPa · s). Cooling of the molten glass 100 is the same as in the first embodiment.

  The molten glass has a cooling end viscosity of log η = 4.0 (dPa · s) and a temperature decrease rate of 100 ° C./min.

(Example 5)
In Example 5, the viscosity of the molten glass at the cooling start position (L1) is log η = 3.4 (dPa · s). Cooling of the molten glass 100 is the same as in the first embodiment.

  The molten glass has a cooling end viscosity of log η = 4.2 (dPa · s) and a temperature lowering rate of 200 ° C./min.

(Example 6)
In Example 6, the viscosity of the molten glass at the cooling start position (L1) is log η = 3.4 (dPa · s).

  For cooling the molten glass 100, a cooling roller 320 shown in FIG. 9 was used. SUS304 was used for the cooling roller 320. The temperature of the cooling roller 320 was 600 ° C.

  The molten glass has a cooling end viscosity of log η = 4.2 (dPa · s) and a temperature drop rate of 250 ° C./min.

(Example 7)
In Example 7, the viscosity of the molten glass at the cooling start position (L1) is log η = 3.6 (dPa · s).

  The method of controlling the temperature of the molten tin 2000 shown in FIG. 10 was used for cooling the molten glass 100. The total length of the float bath 1300 was about 10 m, a weir 2100 was provided at a position of L1 = 1 m, and a weir 2200 was provided at a position of L2 = 4 m. The temperature of the molten tin 2000 in the region surrounded by the weir 2100 and the weir 2200 was controlled to 500 ° C. The temperature of the molten tin 2000 in the other region is 600 ° C.

  The viscosity of the molten glass after cooling is log η = 4.2 (dPa · s), and the cooling rate is 50 ° C./min.

(Comparative Example 1)
In Comparative Example 1, the viscosity of the molten glass at the cooling start position (L1) is log η = 3.6 (dPa · s). Cooling of the molten glass 100 is the same as in the first embodiment.

  The molten glass has a cooling end viscosity of log η = 3.9 (dPa · s) and a temperature lowering rate of 50 ° C./min.

(Comparative Example 2)
In Comparative Example 2, the viscosity of the molten glass at the cooling start position (L1) is log η = 3.7 (dPa · s). Cooling of the molten glass 100 is the same as in the first embodiment.

  The molten glass has a cooling end viscosity of log η = 4.0 (dPa · s) and a temperature decrease rate of 50 ° C./min.

(Comparative Example 3)
In Comparative Example 3, the viscosity of the molten glass at the cooling start position (L1) is log η = 3.6 (dPa · s). Cooling of the molten glass 100 is the same as in the first embodiment.

  The molten glass has a cooling end viscosity of log η = 4.0 (dPa · s) and a temperature decrease rate of 40 ° C./min.

(Comparative Example 4)
In Comparative Example 4, the viscosity of the molten glass at the cooling start position (L1) is log η = 5.5 (dPa · s). Cooling of the molten glass 100 is the same as in the first embodiment.

  The molten glass has a cooling end viscosity of log η = 6.8 (dPa · s) and a temperature lowering rate of 200 ° C./min.

  A magnetic recording medium was manufactured based on the flowchart shown in FIG. 6 using the glass substrates obtained in Examples 1-8 and Comparative Example 1-4. As the magnetic material used for the magnetic recording layer, an Fe—Pt alloy was used as a magnetic layer material suitable for heat-assisted recording, and heat treatment was performed at 600 ° C. for 1 hour to complete the magnetic recording medium.

<Measurement of the number of read errors>
The number of read errors when the magnetic recording medium manufactured using the glass substrate obtained in Example 1-8 and Comparative Example 1-4 is mounted on the information recording apparatus shown in FIG. 1 and operated at 15000 rpm. Measurements were made and evaluated. The result is shown in FIG.

  Evaluation was performed on 100 sheets in each example and each comparative example, and the total number of reading errors is shown in FIG. When the number of errors is 0 to 2, the evaluation is “A”, when the number of errors is 3 to 5, the evaluation is “B”, and when the number of errors is 6 or more, the evaluation is “F”. As a result of analyzing the location where the error occurred by SEM-EDX (energy dispersive X-ray spectroscopy), tin (Sn) was confirmed by all the magnetic disks where the error occurred.

  From the evaluation results of Example 1 to Example 8 shown in FIG. 12, the viscosity of the molten glass at the cooling start position is log η = 3.6 (dPa · s) or less, and the viscosity of the molten glass is log η = 4. It was confirmed that it was good to cool at a rate of 50 ° C./min or more until it became 0 (dPa · s) or less.

  In Comparative Example 1, since the final viscosity was too low, log η = 3.9 (dPa · s), the diffusion of tin (Sn) proceeded even after the cooling was completed. In Comparative Example 2, since the starting viscosity was too high, log η = 3.7 (dPa · s), the diffusion of tin (Sn) had already progressed. In Comparative Example 3, the rate of temperature decrease was as low as 40 ° C./min, and thus the diffusion of tin (Sn) could not be sufficiently suppressed. In Comparative Example 4, since the starting viscosity was too high, log η = 5.5 (dPa · s), the diffusion of tin (Sn) had already progressed.

  As mentioned above, according to the manufacturing method of the glass substrate for information recording media in this Embodiment, by suppressing the diffusion of tin (Sn) on the lower surface of the molten glass in the float bath process in the float process, It is possible to improve the SNR quality of magnetic recording media.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 glass substrate, 2, 3 main surface, 4 inner peripheral end surface, 5,15 holes, 6 outer peripheral end surface, 10
Information recording medium, 12 Compressive stress layer, 14 Magnetic recording layer, 20 Housing, 21 Head slider, 22 Suspension, 23 Arm, 24 Vertical axis, 25 Voice coil, 26 Voice coil motor, 27 Clamp member, 28 Fixing screw, 30 Information recording apparatus, 100 molten glass, 320 cooling roller, 1100 melting tank, 1200 clarification tank, 1300 float bath, 1400 cooling line, 2000 molten tin, 3100 blower, 2100, 2200 weir, 2300 temperature control means.

Claims (9)

In the order of melting tank, clarification tank, float bath, and cooling line, the glass raw material is made into molten glass in the melting tank, and the molten glass passes through the clarification tank, the float bath, and the cooling line. Let it be a plate glass manufacturing method using a float method to be molded into a plate glass,
In the float bath, the molten glass floats on the surface of molten tin melted by heating,
The molten glass has a temperature at a viscosity log η = 4.0 (dPa · s) of 1100 ° C. or higher,
The internal temperature of the clarification tank is equal to or higher than the liquidus temperature of the molten glass,
In the float bath, including the step of cooling the molten glass at a temperature drop rate of 50 ° C./min or more,
The step of cooling the molten glass includes
From the position where the molten glass flows into the float bath, the cooling of the molten glass is started from the cooling start position at least 50 cm ahead of the flow direction of the molten glass,
The viscosity of the molten glass at the cooling start position is log η = 3.6 (dPa · s) or less, and the viscosity of the molten glass is log η = 4.0 (dPa · s) or more. Cool at a rate of 50 ° C / min or more,
A manufacturing method of plate glass. In the order of melting tank, clarification tank, float bath, and cooling line, the glass raw material is made into molten glass in the melting tank, and the molten glass passes through the clarification tank, the float bath, and the cooling line. Let it be a plate glass manufacturing method using a float method to be molded into a plate glass,
In the float bath, the molten glass floats on the surface of molten tin melted by heating,
The molten glass has a temperature at a viscosity log η = 4.0 (dPa · s) of 1100 ° C. or higher,
The internal temperature of the clarification tank is equal to or higher than the liquidus temperature of the molten glass,
In the float bath, including the step of cooling the molten glass at a temperature drop rate of 50 ° C./min or more,
The step of cooling the molten glass includes
Cooling at a rate of 50 ° C./min or more until the viscosity of the molten glass is log η = 3.6 (dPa · s) to log η = 4.0 (dPa · s),
A manufacturing method of plate glass.   The method for producing a plate glass according to claim 1 or 2, wherein the step of cooling the molten glass blows a gas to the molten glass.   The method for producing a plate glass according to claim 1 or 2, wherein the step of cooling the molten glass brings a solid into contact with the molten glass.   The method for producing a plate glass according to claim 1 or 2, wherein the step of cooling the molten glass controls the temperature of the molten tin in the float bath.   The said plate glass substrate is a manufacturing method of the plate glass of any one of Claims 1-5 which is an object for glass substrates for information recording media.   The said glass substrate for information recording media is a manufacturing method of the plate glass of Claim 6 which is a glass substrate for information recording media for heat assist recording. A method for producing a glass substrate for an information recording medium, comprising a step of forming an annular glass substrate from a plate glass obtained by the method for producing a plate glass according to any one of claims 1 to 7.   A method for producing an information recording medium, comprising forming at least a magnetic film on a surface of the glass substrate for information recording medium obtained by the method for producing a glass substrate for information recording medium according to claim 8.

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