JPWO2013046584A1 - Manufacturing method of HDD glass blanks and manufacturing method of HDD glass substrate - Google Patents

Abstract

One aspect of the present invention has a central hole, the radius of the central hole is r0, and the radius of the glass blank is r1, and recording is performed on the entire circumference at a position of radius r = r0 + (r1−r0) / 2. The glass blank for HDD, wherein the maximum amount of retardation when linearly polarized light is incident in a direction perpendicular to the surface is 20 nm / mm or less.

Description

  The present invention relates to a glass blank for HDD, a method for manufacturing a glass blank for HDD, a glass substrate for HDD, and a method for manufacturing a glass substrate for HDD.

  A magnetic information recording apparatus records information on an information recording medium by using magnetism, light, magneto-optical, and the like. A typical example is a hard disk drive (HDD) device. A hard disk drive device is a device that magnetically records information on a magnetic disk as an information recording medium having a recording layer formed on a substrate by a magnetic head. As a base material of such an information recording medium, a so-called substrate, a glass substrate is preferably used.

  In addition, the HDD device records information on the magnetic disk while rotating at a high speed about a few nanometers with respect to the magnetic disk without contacting the magnetic head. Further, 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. Since the size of the magnetic particles is also miniaturized in proportion to this, the read / write function of the micro area is improved, and the distance between the head and the media is further reduced, so there are problems such as read / write errors and head crashes. Has become more severe.

  Furthermore, the use of HDDs in recent years, such as carrying notebook PCs and portable HDDs, has increased, and accordingly, it has become indispensable to ensure even higher shock resistance on glass substrates.

  On the other hand, as a method for producing a glass substrate used in the HDD, a glass intermediate formed body called glass blanks is produced by a direct press method in which molten glass is pressed with a mold, and the glass blanks are ground and ground. A method of finishing the glass substrate by polishing or the like is mentioned. The glass substrate manufactured by this direct pressing method is known to be excellent in parallelism and flatness, but even with such a glass substrate, the above-mentioned problem with respect to impact resistance has not been solved. It was.

  In Patent Document 1, the position of the shear mark (cutting marks) formed on the front and back surfaces of the glass blanks is localized in the center to improve the shape accuracy of the glass blanks, thereby enabling the labor saving of the outer peripheral surface processing. There is disclosed a method for producing a disk-shaped glass which has been formed into a shape and has improved roundness and flatness. However, it is difficult to suppress the residual strain inside the glass blanks after press molding only by localizing the shear mark at the center, and the internal stress resulting from the residual strain remains even after processing the glass substrate. Therefore, there was room for improvement in terms of impact resistance.

JP 2009-67636 A

  The present invention has been made in view of the prior art, and the problem to be solved is a glass for HDD excellent in impact resistance for mounting on a hard disk drive having a high recording density equipped with a DFH mechanism. It aims at providing blanks, a glass substrate for HDD, and those manufacturing methods.

One aspect of the present invention has a center hole, where r _{0 is} the radius of the center hole and r ₁ is the radius of the glass blank, and the position of radius r = r ₀ + (r ₁ −r ₀ ) / 2 The glass blank for HDD is characterized in that the maximum value of retardation when linearly polarized light is incident in the direction perpendicular to the recording surface is 20 nm / mm or less.

  Another aspect of the present invention is a method for manufacturing the glass blanks for HDD, comprising a molten glass supply step and a press molding step, wherein in the molten glass supply step, on a lower mold surface of a press machine die In the press molding step, the heat conductivity of the press machine die is 120 W / m · K or more and the press time is 0.05 to It is a manufacturing method of the glass blanks for HDD characterized by performing butt-forming for 0.20 second.

  In another aspect of the present invention, an HDD glass substrate is manufactured by subjecting an HDD glass blank obtained by the above manufacturing method to a grinding step and a polishing step to manufacture an HDD glass substrate. Is the method.

Another aspect of the present invention is a glass substrate for HDD manufactured by the above manufacturing method, which has a central hole, wherein the radius of the central hole is r ₀ ′ and the radius of the glass substrate is r ₁ ′. The maximum amount of retardation when linearly polarized light is incident in the direction perpendicular to the recording surface over the entire circumference at the position of radius r ′ = r ₀ ′ + (r ₁ ′ −r ₀ ′) / 2. Is a glass substrate for HDD, characterized by being 1 nm / mm or less.

  Objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

FIG. 1 is a diagram illustrating an example of a molding die for glass blanks and a press machine. FIG. 2 is a perspective view of a rotary table on which a glass blank forming press is disposed. FIG. 3 is a schematic diagram for explaining a molten glass supply step for supplying molten glass to a lower mold of a glass blank forming mold. FIG. 4 is a schematic view showing a pressurizing step of pressurizing the molten glass with a glass blanks molding die. FIG. 5 is a schematic view of glass blanks after the coring step. FIG. 6 is a view showing an example of a glass substrate for HDD manufactured by the method for manufacturing a glass substrate for HDD according to the present embodiment. FIG. 7 is a schematic cross-sectional view showing an example of a polishing apparatus used in a rough polishing step and a precision polishing step in the method for manufacturing a glass substrate for HDD according to the present embodiment. FIG. 8 is a partial cross-sectional perspective view showing a magnetic disk which is an example of a magnetic recording medium using the glass substrate for HDD manufactured by the method for manufacturing the glass substrate for HDD according to the present embodiment.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies by paying attention to the circumferential distortion of glass blanks produced by the direct press method.

  As a result, it has been found that by having the following configuration, a glass blank for HDD and a glass substrate for HDD excellent in impact resistance can be obtained, and the present invention has been completed.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

<Glass blanks for HDD>
The glass blank for HDD according to the present embodiment has a center hole, and when the radius of the center hole is r ₀ and the radius of the glass blank is r ₁ , the radius r = r ₀ + (r ₁ −r ₀ ). The maximum retardation amount when linearly polarized light is incident in the direction perpendicular to the recording surface is 20 nm / mm or less over the entire circumference at the position / 2. The glass blank is an intermediate formed body of a glass substrate for HDD, and is called a glass base or a glass base plate. Moreover, the glass blanks represent a state after the direct pressing process is performed and before the grinding process and the polishing process are performed on the main surface.

(Measurement of retardation amount)
In the glass blank according to the present embodiment, the amount of retardation when linearly polarized light is incident in the direction perpendicular to the recording surface over the entire circumference at a position of radius r = r ₀ + (r ₁ −r ₀ ) / 2 from the center. Is a maximum value of 20 nm / mm or less, preferably 12 nm / mm or less. If the maximum value of the retardation amount is larger than 20 nm / mm, the shape of the glass substrate to be obtained becomes unstable. Therefore, if the HDD is accidentally dropped or an impact is applied during carrying, there is a risk of cracking. There is.

The retardation amount (Re) is an index representing strain (internal strain) of glass blanks or glass substrates, and is represented by the following formula.
Re = (nx−ny) × d
However, nx represents the refractive index of the direction x with the largest refractive index in the plane direction of glass blanks (or glass substrate), ny represents the refractive index in the y direction orthogonal to the x direction, and d represents the glass blanks. (Or glass substrate) thickness (nm unit).

  If there is distortion (stress variation) inside the glass blank or glass substrate, the refractive index varies depending on the direction at each place on the glass blank or glass substrate, so the internal strain can be measured by measuring the amount of retardation. .

As a measuring method, the amount of retardation in the entire circumference at the position of radius r = r ₀ + (r ₁ −r ₀ ) / 2 of the glass blank is linearly polarized on the glass blank using PA-100 (Photonics Lattice). It is possible to measure by observing the change of the polarization state after passing.

  In addition, by suppressing the amount of retardation to be small, distortion of the recording medium generated by the clamp can be reduced in a clamp method that presses linearly in a circumferential direction, which is generally used in a normal HDD. The impact property can be further improved.

  As described above, if the retardation amount is created within a predetermined range at the time of forming the glass blanks, the retardation amount of the glass substrate for HDD manufactured using the same can be naturally reduced, resulting in internal distortion. Therefore, impact resistance can be improved.

  Conventionally, in order to improve the distortion of the glass substrate, it has been dealt with by correcting the shape in the grinding / polishing process, but there are cases where it is difficult to sufficiently eliminate the distortion remaining inside. When attempting to reduce the distortion of the glass substrate, there has been a problem that the machining allowance increases, resulting in a reduction in thickness from a desired thickness or an increase in processing cost. Therefore, it is possible to control the distortion of the glass substrate as a result by controlling the amount of retardation before the grinding / polishing step, that is, in the state of glass blanks.

  The glass blank manufacturing method according to the present embodiment includes a molten glass supply step and a press molding step, and in the molten glass supply step, the shape of the glass gob supplied on the lower mold surface of the press machine die is axially symmetric. In the press molding step, butt molding is performed in which the thermal conductivity of the press die is 120 W / m · K or more and the press time is 0.05 to 0.20 seconds. It is mentioned as a preferable method.

  Moreover, it is preferable that the glass blanks which concern on this embodiment are manufactured by what is called a direct press method. The direct press method is generally manufactured by supplying molten glass and press molding while cooling the molten glass. In the production of the glass blank according to the present embodiment, in addition to the above steps, if necessary, a heat treatment is performed to correct the flatness of the glass blank and remove internal strain.

  FIG. 1 is a schematic view of a mold and a press for producing glass blanks according to the present embodiment by press molding. The press 1 for forming glass blanks is supplied with molten glass, and includes a lower mold 5 and a lower part 7 having a first molding surface 6 for pressurizing the supplied molten glass, and a lower mold 5. It has an upper die 3 and a press machine upper part 2 provided with a second molding surface 4 for pressurizing molten glass with one molding surface 6.

  FIG. 2 is a perspective view showing a mechanism in which glass blanks are press-molded by the press lower part 7 and the press upper part 2 arranged on the rotary table. The press machine lower part 7 is embedded in the rotary table 9 side by side in the circumferential direction. The rotary table 9 is provided so as to be able to be driven to rotate around the rotary shaft 8 at a specific speed v (m / s).

  Further, the lower mold 5 of the mold is installed on the lower part 7 of the press machine, but the molten glass 23 is supplied to the lower mold 5 by the outflow nozzle 21 at a predetermined position on the turntable. The lower mold 5 supplied with the molten glass 23 is transported by the rotary table together with the lower part 7 of the press machine, and the upper mold 3 installed on the upper part 2 of the press machine at another position is lowered to the position of the lower mold 5 to be melted. Pressurize the glass.

  A plurality of heaters are installed inside the mold. The heater is preferably arranged in one or more rounds and concentrically so as to be arranged at a uniform angle in the circumferential direction in terms of easy temperature control of the mold. Note that a plurality of heaters may or may not be arranged in the press machine lower part 7 in the same manner as the press machine upper part 2, but depending on the pressurizing time to be pressed, It is preferable that they are arranged.

  Therefore, the manufacture of the glass blanks in the present embodiment is mainly performed by a molten glass supply step for supplying molten glass to the first molding surface 6 formed on the lower mold 5 and a second molding surface formed on the upper mold 3. 4 and a press molding step of obtaining glass blanks by cooling while pressing the molten glass supplied to the first molding surface 6.

(Molten glass supply process)
A molten glass supply process is a process of supplying molten glass to the 1st shaping | molding surface formed in the lower mold | type. FIG. 3 is a schematic diagram showing the lower mold 5 and the molten glass 23 in the molten glass supply process. First, the molten glass 23 flows out from the outflow nozzle 21 and is supplied to the lower mold 5 (FIG. 3A).

  Thereafter, when the molten glass reaches a predetermined amount, the molten glass 23 is cut by the blade 22, and the molten glass 23 is separated (FIG. 3B). The molten glass 23 supplied in the molten glass supply step comes into contact with the center portion of the first molding surface 6, and cooling starts mainly by heat radiation from there.

  Here, the heat of the glass is rapidly taken away by the cutting by the blade 22, the viscosity of the separation portion increases, and a cutting mark (hereinafter referred to as a shear mark) tends to remain in the press-molded product as a separation mark. That is, since the shear mark is generated when the molten glass flow is sandwiched by the blade 22, the upper surface of the sandwiched molten glass lump (hereinafter referred to as glass gob) has a protruding shape. This protrusion shape causes a reduction in the axial symmetry of the surface temperature of the glass gob, and as a result, internal distortion tends to occur.

  Therefore, in the method for manufacturing glass blanks according to the present embodiment, it is preferable to make the shear mark generated in the glass gob as small as possible and to localize the shear mark in the center of the glass gob. By doing in this way, it becomes easy to make the temperature distribution of the glass gob before a press molding process close to axial symmetry.

  In order to localize the position of the shear mark in the center, for example, as shown in FIG. 3 (a), the blade 22 has a V-shaped pair of cutting blades facing each other. What is provided may be used. By using a pair of blades having a V-shape, the molten glass flow is not constricted in one direction even when sandwiched between the blades, and the glass flow is cut while being thinned. As a result, the shear mark can be reduced.

  The inner angle of the V shape of the blade 22 is preferably in the range of 50 ° to 120 °, for example, and more preferably in the range of 70 ° to 110 °. The planar view shape of the portion where the pair of blades intersect can be an arc shape or a shape approximating an arc shape, and if the angle is constant, the size of the shear mark is reduced by reducing the radius of the arc. can do. Thus, the size of the shear mark can be adjusted by adjusting the angle and the radius of the arc.

  If the V-shaped cabinet is 50 ° or more, there is a problem that when the molten glass flow is sandwiched between blades, the molten glass flow does not go into the back of the V-shape, that is, does not go into the arcuate part and deteriorates the cut surface. It is preferable because it is difficult.

  The lower mold 5 needs to be temperature controlled, and is heated to a predetermined temperature in advance. The temperature of the lower mold 5 is preferably a temperature range from Tg to Tg ± 100 (° C.) when the glass transition temperature is Tg (° C.). In the case of Tg-100 (° C.) or higher, it is possible to reduce the occurrence of problems such as deterioration of flatness of the glass substrate, generation of wrinkles on the transfer surface, and damage due to thermal shock. Moreover, when it is below Tg + 100 (degreeC), while suppressing fusion | melting with glass, deterioration of a metal mold | die can be suppressed and it is preferable.

  Further, when a heater is also installed in the upper part 2 of the press machine, the temperature of the upper die 3 needs to be controlled. Regarding the specific temperature, heating is performed in the same range as the temperature of the lower mold 5 described above.

  The heating means of the lower mold 5 and the upper mold 3 can be obtained by embedding a heater in the press machine in contact therewith and adjusting the set temperature of the heater to a predetermined temperature. In addition, a cartridge heater and a burner are preferably used as the mold overheating means. Among these, the cartridge heater is particularly preferable because it is not affected by the atmosphere and the temperature control of the mold is simpler.

  The method for reducing the amount of retardation of the glass blanks is not limited to the method of arranging the plurality of heaters in the circumferential direction inside the press machine, and the method of directly controlling the temperature of the blanks by changing the mold material in the circumferential direction. And a method of managing the pressure applied to the press machine in the circumferential direction.

(Press molding process)
In the press molding process, the glass blanks 10 are cooled by pressurizing the molten glass supplied to the first molding surface 6 on the first molding surface 6 and the second molding surface 4 formed on the upper mold 3. It is the process of obtaining.

  FIG. 4 is a schematic diagram showing the glass blanks molding die 1 and the glass blanks 10 in the press molding process. It is preferable that the lower mold 5 to which the molten glass 23 is supplied in the molten glass supply process rotates the rotary table at a speed of 0.3 m / s or less to a position facing the upper mold 3. By setting the speed of the rotary table to 0.3 m / s or less, the glass gob does not lose its shape, and it is possible to remarkably suppress eccentricity of circumferential distortion after press molding, thereby reducing internal distortion. .

  Thereafter, the molten glass is pressurized with the first molding surface 6 of the lower mold 5 and the second molding surface 4 of the upper mold 3. The molten glass spreads by pressurization and contacts the periphery of the first molding surface 6. The molten glass is cooled and solidified by dissipating heat from the contact surface with the first molding surface 6 and the second molding surface 4 to form glass blanks 10.

  Here, the thermal conductivity of the press die composed of the lower die 5 and the upper die 3 is preferably 120 W / m · K or more, and more preferably 150 W / m · K or more. This is because the high temperature glass gob comes into contact with the central portion of the mold during press molding, so that the temperature can be made uniform quickly from the central portion where the temperature has risen to the outside. If the thermal conductivity is 120 W / m · K or more, only the temperature at the center rises, and the phenomenon that the difference in the cooling rate between the center and the outside of the glass blank is increased is suppressed, and the residual strain is reduced. Can do. The thermal conductivity of the press die is preferably 350 W / m · K or less, and more preferably 300 W / m · K or less. When the heat conductivity is 350 W / m · K or less, the heat conduction to the lower mold peripheral member is not so large, the deterioration of the peripheral member can be suppressed, and the peripheral member is made of a material having high heat resistance. Since it is not limited, it is preferable.

  For example, a tungsten-based material or a ceramic material can be suitably used for the press die having the above-described thermal conductivity.

  The pressing time at this time is preferably 0.05 to 0.20 seconds, and more preferably 0.08 to 0.17 seconds. If the press time is 0.05 seconds or more, the temperature of the upper surface of the glass blanks can be lowered to the vicinity of the glass transition point when the upper surface of the glass blanks and the mold are brought into contact with each other. It becomes difficult to cause deterioration. Moreover, if press time is less than 0.20 second, it will become easy to suppress fusion | bonding with glass and a metal mold | die, and to suppress the generation | occurrence | production of the adhesion trace at the time of press molding.

  As a pressurizing means for applying a load to the lower mold 5 and the upper mold 3 to pressurize the molten glass, a known pressurizing means can be appropriately selected and used. For example, an air cylinder, a hydraulic cylinder, an electric cylinder using a servo motor, and the like can be given.

  Here, the plate | board thickness of the press-molded glass blanks needs to be equal. In order to make the plate thickness uniform, any molding method may be used as long as the plate thickness can be controlled, but it is preferable to use butt molding. By using butt molding, it becomes easy to apply a press pressure evenly in the in-plane direction of the glass blanks, and it becomes easy to strictly control the plate thickness. And generation | occurrence | production of the location from which plate | board thickness differs in glass blanks is suppressed, and it becomes possible to also reduce the distortion resulting from the difference in the subsequent cooling rate.

  Next, the upper mold 3 is separated from the glass blanks 10, and the glass substrate is taken out from the lower mold 5 with an adsorbing member or the like.

(Heat treatment process)
A heat treatment step may be performed for the purpose of correcting the flatness and removing internal strain. The heat treatment is performed by using a setter (alumina, zirconia, etc.), and alternately stacking with glass blanks and putting them in a heat treatment furnace. The heat treatment of the glass blank needs to be performed in a temperature range of Tg to Tg + 100 (° C.). When the temperature is equal to or higher than Tg (° C.), the flatness of the glass blank can be sufficiently corrected, and when the temperature is equal to or lower than Tg + 100 (° C.), the deterioration of the shape of the glass blank is reduced. This is preferable because it is possible to reduce the possibility of occurrence of adhesion marks due to fusion with the setter. A particularly preferable temperature range for correcting the flatness and removing the internal strain is Tg to Tg + 70 ° C.

(Coring process)
The coring step is a step of forming a glass blank (perforated blanks material) 10 by forming an inner hole (center hole) using a diamond core drill at the center of the surface of the blanks material obtained by the above-described step. That is. The center of the glass blanks is determined by this coring process. In this invention, a glass blank shall mean the glass molding before finishing the coring process and performing the grinding process of a main plane.

In FIG. 5, the top view which looked at the glass blanks obtained by the said process from one surface is shown. In the present invention, the radius from the center of the glass molded product is r ₁ and the radius of the inner hole is r ₀ . Then, the entire circumference of the position of r ₀ + (r ₁ −r ₀ ) / 2 measured in the retardation amount measuring method described above is indicated by a one-dot chain line.

  The glass blanks obtained by the manufacturing method as described above have a maximum retardation amount of 20 nm / mm or less at the position, and are excellent in impact resistance.

<Glass substrate for HDD>
The glass substrate for HDD according to the present embodiment has a radius r ′ = r ₀ ′ + (r ₁ ′ −r ₀ ′) where r ₀ ′ is the radius of the central hole and r ₁ ′ is the radius of the glass substrate. ) / 2, the maximum amount of retardation when linearly polarized light is incident in the direction perpendicular to the recording surface is preferably 1 nm / mm or less. When the maximum value of the retardation amount is larger than 1 nm / mm, the shape of the obtained glass substrate becomes unstable like the above-mentioned HDD glass blanks, so that the HDD is accidentally dropped or an impact is applied during carrying. If this happens, cracking may occur.

  Moreover, the manufacturing method of the glass substrate for HDD which concerns on this embodiment is performed by giving the grinding process and the grinding | polishing process to the glass blank for HDD obtained by the manufacturing method mentioned above, It is characterized by the above-mentioned.

  The grinding process may be performed once or a plurality of times. The polishing process includes a rough polishing process for removing scratches and distortions remaining in the grinding process, and a precision polishing process for finishing the main surface of the glass substrate into a smooth mirror surface.

  Moreover, in the manufacturing method of the glass substrate which concerns on this embodiment, processes other than the said grinding process and a grinding | polishing process may be provided, for example, it is preferable to provide a chemical strengthening process. By providing the chemical strengthening step, the impact resistance of the glass substrate according to the present embodiment can be further improved.

  Moreover, you may provide the washing | cleaning process which removes the abrasives adhering by the grinding | polishing process, the end surface grinding | polishing process which chamfers the outer peripheral end surface and inner peripheral end surface of a glass substrate precursor, etc.

  By forming a magnetic film on the glass substrate for HDD obtained by the above manufacturing method, a magnetic recording medium is obtained and mounted on the HDD.

  FIG. 6 is a diagram showing an example of a glass substrate for HDD manufactured by the method for manufacturing a glass substrate for HDD according to the present embodiment. 6A is a perspective view, and FIG. 6B is a cross-sectional view. The glass substrate 30 for HDD is a disk-shaped glass substrate in which a center hole 33 is formed, and has a main surface 31, an outer peripheral end surface 34, and an inner peripheral end surface 35. Chamfered portions 36 and 37 are formed on the outer peripheral end surface 34 and the inner peripheral end surface 35, respectively.

<Grinding process>
The grinding step is a step of processing the glass substrate into a predetermined plate thickness. Specifically, the process etc. which grind | polish (lapping) the both surfaces of the said glass blanks using an acidic grinding liquid are mentioned. By processing in this way, the parallelism, flatness and thickness of the glass substrate can be adjusted. Moreover, this grinding process may be performed once or twice or more. For example, when it is performed twice, the parallelism, flatness and thickness of the glass substrate are preliminarily adjusted in the first grinding step (first grinding step), and the glass substrate in the second grinding step (second grinding step). It is possible to finely adjust the parallelism, flatness and thickness of the film.

  More specifically, examples of the first grinding step include a step of making the glass substrate have a substantially uniform flatness.

  In addition, examples of the second grinding step include a step of grinding the main surface of the roughened glass substrate using a fixed abrasive polishing pad. In this second grinding step, for example, a roughened glass substrate is set in a grinding apparatus, and a three-dimensional fixed abrasive with a surface pattern such as diamond tile is used, so that the glass substrate The surface can be ground.

  When the second grinding step is performed, polishing performed in a rough polishing step described later can be efficiently performed. Further, the surface roughness Ra of the glass substrate used in the polishing process performed by the second grinding process is preferably 0.10 μm or less, and more preferably 0.05 μm or less.

  The grinding step is usually performed after manufacturing glass blanks, but may be performed after the coring step or may be performed a plurality of times.

<Rough polishing process>
The rough polishing step (primary polishing step) is a step of rough polishing the surface of the glass substrate on which the grinding step has been performed. This rough polishing is intended to remove scratches and distortions remaining in the above-described grinding process, and is performed using the following polishing method.

  The surface to be polished in the rough polishing step is a main surface and / or an end surface. The main end surface is a surface parallel to the surface direction of the glass substrate. The end surface is a surface composed of an inner peripheral end surface and an outer peripheral end surface. Moreover, an inner peripheral end surface is a surface which has an inclination with respect to the surface of the inner peripheral side perpendicular to the surface direction of the glass substrate and the surface direction of the glass substrate. Further, the outer peripheral end surface is a surface that is inclined on the outer peripheral side, the surface perpendicular to the surface direction of the glass substrate and the surface direction of the glass substrate.

  The polishing apparatus used in the rough polishing step is not particularly limited as long as it is a polishing apparatus used for manufacturing a glass substrate. Specifically, a polishing apparatus 11 as shown in FIG. FIG. 7 is a schematic cross-sectional view showing an example of the polishing apparatus 11 used in the rough polishing step and the precision polishing step in the method for manufacturing a glass substrate for HDD according to this embodiment.

  A polishing apparatus 11 as shown in FIG. 7 is an apparatus capable of simultaneous grinding on both sides. The polishing apparatus 11 includes an apparatus main body 11a and a polishing liquid supply unit 11b that supplies a polishing liquid to the apparatus main body 11a.

  The apparatus main body 11a includes a disk-shaped upper surface plate 12 and a disk-shaped lower surface plate 13, and they are arranged vertically spaced apart so that they are parallel to each other. Then, the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13 rotate in directions opposite to each other.

  A polishing pad 15 for polishing both the front and back surfaces of the glass blanks 10 is attached to each of the opposing surfaces of the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13. The polishing pad 15 used in the rough polishing step is not particularly limited as long as it is a polishing pad used in the rough polishing step. Specifically, for example, a hard polishing pad made of polyurethane or the like can be used.

  A plurality of rotatable carriers 14 are provided between the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13. The carrier 14 is provided with a plurality of base plate holding holes 51, and the glass blanks 10 can be fitted into the base plate holding holes 51 and disposed. For example, the carrier 14 may include 100 base plate holding holes 51 so that 100 glass blanks 10 can be fitted and arranged. Then, 100 glass blanks 10 can be processed by one process (1 batch).

  The carrier 14 sandwiched between the surface plates 12 and 13 via the polishing pad holds the plurality of glass blanks 10 and rotates in the same direction as the lower surface plate 13 with respect to the center of rotation of the surface plates 12 and 13 while rotating. Revolve to. The disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13 can be operated by separate driving. In the polishing apparatus 11 operating in this way, the polishing slurry 16 is supplied between the upper surface plate 12 and the glass blanks 10 and between the lower surface plate 13 and the glass blanks 10, thereby the glass blanks 10. Rough polishing can be performed.

  The polishing slurry supply unit (polishing liquid supply unit) 11 b includes a liquid storage unit 110 and a liquid recovery unit 120. The liquid reservoir 110 includes a liquid reservoir main body 110a and a liquid supply pipe 110b having a discharge port 110e extending from the liquid reservoir main body 110a to the apparatus main body 11a. The liquid recovery part 120 was extended to the liquid recovery part main body 120a, the liquid recovery pipe 120b extended from the liquid recovery part main body 120a to the apparatus main body part 11a, and the polishing slurry supply part 11b from the liquid recovery part main body 120a. And a liquid return pipe 120c.

  Then, the polishing slurry 16 put in the liquid storage unit main body 110a is supplied from the discharge port 110e of the liquid supply pipe 110b to the apparatus main body part 11a, and from the apparatus main body part 11a via the liquid recovery pipe 120b, the liquid recovery part main body 120a. To be recovered. The recovered polishing slurry 16 is returned to the liquid storage part 110 via the liquid return pipe 120c and can be supplied again to the apparatus main body part 11a.

  Further, the polishing pad 15 used here is a foam of synthetic resin such as urethane or polyester containing a cerium oxide abrasive.

Next, the polishing agent used in the polishing step performed before the chemical strengthening step uses a material having a high CeO ₂ content and a small amount of alkaline earth metal, thereby increasing the polishing rate and polishing the glass substrate. Can improve the smoothness. Also for the polishing pad, as in the case of the above-mentioned abrasive, by using a material containing a large amount of CeO ₂ and a small amount of alkaline earth metal, the polishing rate is increased and the smoothness of the polished glass substrate is improved. It can be raised sufficiently.

When polishing with a polishing liquid in which the abrasive is dispersed in water, the polishing liquid is in a state where the acidic abrasive is dispersed in a solvent such as water, and the content of CeO ₂ It is preferable that it is 3-15 mass% with respect to the said polishing liquid whole quantity. If it is such a range, the glass substrate for HDD excellent in impact resistance can be manufactured, Furthermore, a grinding | polishing speed can be raised more and the glass substrate for HDD with higher smoothness can be manufactured.

<Precision polishing process (secondary polishing process)>
The precision polishing process is a mirror polishing process that finishes a smooth mirror surface having a surface roughness (Rmax) of about 6 nm or less, for example, while maintaining the flat and smooth main surface obtained in the rough polishing process. The precision polishing step is performed, for example, by using a polishing apparatus similar to that used in the rough polishing step and replacing the polishing pad from a hard polishing pad to a soft polishing pad. The surface to be polished in the precision polishing step is the main surface, similar to the surface to be polished in the rough polishing step.

  Further, as the abrasive used in the precision polishing step, an abrasive that causes fewer scratches even if the abrasiveness is lower than the abrasive used in the rough polishing step is used. Specifically, for example, a polishing agent containing silica-based abrasive grains (colloidal silica) having a particle diameter lower than that of the polishing agent used in the rough polishing step. The average particle diameter of the silica-based abrasive is preferably about 20 nm. And the polishing slurry liquid containing the said abrasive | polishing agent is supplied to a glass substrate, a polishing pad and a glass substrate are slid relatively, and the surface of a glass substrate is mirror-polished.

  The surface roughness Ra of the glass substrate for HDD after the precision polishing treatment is preferably 0.1 to 5 mm. If it is in such a range, while having the smoothness required as a glass substrate for a magnetic recording medium, the head is prevented from adsorbing on an excessively smooth magnetic disk, and the head is configured as a hard disk drive device. Can be stably levitated.

<Chemical strengthening process>
In addition to the above steps, the chemical strengthening step is preferably performed once or a plurality of times, and the chemical strengthening step may be performed after any of the coring step, the grinding step, and the polishing step. If the chemical strengthening process performed in the manufacturing method which concerns on this embodiment is a well-known method, it will not specifically limit. Specifically, for example, a step of immersing a glass substrate in a chemical strengthening treatment liquid and the like can be mentioned. By doing so, a chemical strengthening layer can be formed in the surface of a glass substrate, for example, a 5 micrometer area | region from the glass substrate surface. And by forming a chemical strengthening layer, impact resistance, vibration resistance, heat resistance, etc. can be improved.

  More specifically, in the chemical strengthening step, by immersing the glass substrate in a heated chemical strengthening treatment liquid, alkali metal ions such as lithium ions and sodium ions contained in the glass substrate are potassium ions having a larger ionic radius. It is carried out by an ion exchange method for substituting with alkali metal ions. Due to the strain caused by the difference in ion radius, compressive stress is generated in the ion-exchanged region, and the surface of the glass substrate is strengthened.

  In addition, the chemical strengthening process in the present embodiment may be performed after the coring process, after the lapping process, after the rough polishing process, or after the precision polishing process, and may be performed a plurality of times depending on the composition of the glass. Good.

In the present embodiment, it is considered that the reinforcing layer is suitably formed by this chemical strengthening step by using the glass composition having the above glass composition as the glass substrate that is a raw material of the glass substrate. Specifically, among the Li ₂ O, Na ₂ O, and K ₂ O, which are alkali components of the glass substrate, the content of Na ₂ O is large, and the sodium ions of this Na ₂ O are added to the chemical strengthening treatment liquid. It is thought that it is easily exchanged for contained potassium ions.

  The chemical strengthening treatment liquid is not particularly limited as long as it is a chemical strengthening treatment liquid used in the chemical strengthening step in the method for producing a glass substrate for hard disk. Specifically, for example, a melt containing potassium ions, a melt containing potassium ions and sodium ions, and the like can be given.

  Examples of these melts include melts obtained by melting potassium nitrate, sodium nitrate, potassium carbonate, sodium carbonate, and the like. Among these, it is preferable to use a combination of a melt obtained by melting potassium nitrate and a melt obtained by melting sodium nitrate from the viewpoint of low melting point and preventing deformation of the glass substrate. At that time, a melt obtained by melting potassium nitrate and a melt obtained by melting sodium nitrate are preferably mixed in approximately the same amount.

<Washing process>
In the method for manufacturing a glass substrate according to the present embodiment, a cleaning step may be performed in addition to the above steps. The cleaning step is a step of cleaning the glass substrate that has been subjected to the rough polishing step.

  The glass substrate after the rough polishing by the rough polishing step is preferably cleaned by a cleaning step. For example, the glass substrate is washed with an alkaline detergent having a pH of 13 or more, and the glass substrate is rinsed. Next, the glass substrate is washed with an acid detergent having a pH of 1 or less, and the glass substrate is rinsed. Finally, the glass substrate is cleaned using a hydrofluoric acid (HF) solution. For polishing using cerium oxide, it is most efficient to perform cleaning in the order of alkali cleaning, acid cleaning, and HF cleaning. This is because the abrasive is first dispersed and removed with an alkaline detergent, then the abrasive is dissolved and removed with an acid detergent, and finally the glass substrate is etched with HF to remove the abrasive deeply stuck in the glass substrate. is there.

  The cleaning step is preferably performed in separate tanks for alkali cleaning, acid cleaning, and HF cleaning. This is because when these washings are performed in a single tank, efficient washing may not be possible. In particular, when the acid detergent and HF are put in the same tank, the etching rate of HF decreases at a place where there is a large amount of abrasive, and therefore there is a tendency that the inside of the substrate cannot be uniformly etched. Moreover, it is preferable to use a rinse tank after each washing. In some cases, a surfactant, a dispersing agent, a chelating agent, a reducing material, and the like may be added to these detergents. Moreover, it is preferable to apply an ultrasonic wave to each washing tank and to use deaerated water for each detergent.

(Magnetic recording medium)
FIG. 8 is a partial cross-sectional perspective view showing a magnetic disk as an example of a magnetic recording medium using a glass substrate for HDD manufactured by the manufacturing method according to the present embodiment. The magnetic disk D includes a magnetic film 102 formed on the main surface of a circular HDD glass substrate 101. For the formation of the magnetic film 102, a known method is used. For example, a formation method (spin coating method) in which a magnetic film 102 is formed by spin-coating a thermosetting resin in which magnetic particles are dispersed on the HDD glass substrate 101, or a magnetic property by sputtering on the HDD glass substrate 101. Examples thereof include a forming method for forming the film 102 (sputtering method) and a forming method for forming the magnetic film 102 on the glass substrate 101 for HDD by electroless plating (electroless plating method).

  In such a magnetic recording medium based on the HDD glass substrate 101 in this embodiment, the HDD glass substrate 101 has the impact resistance as described above, so that information recording and reproduction can be performed with high reliability over a long period of time. It can be carried out.

  In the above description, the HDD glass substrate 101 in this embodiment is used as a magnetic recording medium. However, the present invention is not limited to this, and the HDD glass substrate 101 in this embodiment is a magneto-optical disk. It can also be used for optical discs and the like.

  As described above, the present specification discloses various modes of technology, of which the main technologies are summarized below.

One aspect of the present invention has a center hole, where r _{0 is} the radius of the center hole and r ₁ is the radius of the glass blank, and the position of radius r = r ₀ + (r ₁ −r ₀ ) / 2 The glass blank for HDD is characterized in that the maximum value of retardation when linearly polarized light is incident in the direction perpendicular to the recording surface is 20 nm / mm or less.

  According to such a structure, the glass blanks for HDD which can manufacture the glass substrate for HDD with a small retardation amount can be provided. Therefore, the glass substrate for HDD manufactured using this glass blank for HDD is excellent in impact resistance since the internal strain is reduced as a result. From the above, it is possible to provide glass blanks for HDDs capable of producing a glass substrate excellent in impact resistance.

  Another aspect of the present invention is a method for manufacturing the glass blanks for HDD, comprising a molten glass supply step and a press molding step, wherein in the molten glass supply step, on a lower mold surface of a press machine die In the press molding step, the heat conductivity of the press machine die is 120 W / m · K or more and the press time is 0.05 to It is a manufacturing method of the glass blanks for HDD characterized by performing butt-forming for 0.20 second.

  According to such a structure, the glass blanks for HDD which can manufacture the glass substrate excellent in impact resistance can be manufactured.

  In another aspect of the present invention, an HDD glass substrate is manufactured by subjecting an HDD glass blank obtained by the above manufacturing method to a grinding step and a polishing step to manufacture an HDD glass substrate. Is the method.

  According to such a structure, the glass substrate excellent in impact resistance can be manufactured.

  Moreover, in the manufacturing method of the said glass substrate for HDD, it is suitable to further provide a chemical strengthening process.

  According to such a configuration, a glass substrate with better impact resistance can be manufactured.

Another aspect of the present invention is a glass substrate for HDD manufactured by the above manufacturing method, which has a central hole, wherein the radius of the central hole is r ₀ ′ and the radius of the glass substrate is r ₁ ′. The maximum amount of retardation when linearly polarized light is incident in the direction perpendicular to the recording surface over the entire circumference at the position of radius r ′ = r ₀ ′ + (r ₁ ′ −r ₀ ′) / 2. Is a glass substrate for HDD, characterized by being 1 nm / mm or less.

  According to such a structure, the glass substrate excellent in impact resistance can be provided.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

(Example 1)
First, a glass raw material having a glass composition as shown in Table 1 is melted, clarified and homogenized molten glass flows out from the nozzle, and the molten glass flow is received at the center of the lower mold surface of the press mold and flows out. The middle part of the molten glass flow was cut between a pair of blades. Thus, an amount of glass gob corresponding to the press-molded product was obtained at the center of the lower mold surface.

  A blade having a V shape in plan view was selected, and the inner angle of the V shape was set to 80 °. An arc shape was used as a planar view shape of the portion where the V-shaped crosses.

  Next, an upper mold facing the lower mold is used with the molten glass gob supplied to the center of the lower mold forming surface, and a tungsten-based material having a thermal conductivity of 150 W / m · K is used for the upper mold and the lower mold. It was. The pressing time was 0.07 seconds, and butt molding was performed so that the thickness of the blanks after molding was uniform. In addition, a shear mark remained in the center of the molded glass. The diameter of the shear mark was about 10 mm, and the shear mark was localized at the center of the disk-shaped glass molded product.

  Thereafter, the amount of retardation of the glass blanks subjected to the heat treatment step and the coring step was measured.

The retardation amount is obtained by applying the distortion in the entire circumference at the position of radius r = r ₀ + (r ₁ −r ₀ ) / 2 from the central hole of the glass blank to the glass blank using PA-100 (Photonics Lattice). The measurement was performed by passing linearly polarized light and observing the change in the polarization state after the passage. And from this point, it evaluated by the maximum value of the retardation amount at the time of measuring 1 round concentrically.

  The glass blanks after measuring the retardation amount were further subjected to a grinding step, a polishing step, and a cleaning step, and the amount of retardation of the glass substrate produced was measured.

(Example 2)
Glass blanks were produced by the same production method as in Example 1 except that the thermal conductivity of the mold in the press molding step was 180 W / m · K, and the amount of retardation was measured. Moreover, the amount of retardation of the glass substrate which performed the processing process similar to Example 1 was measured.

(Example 3)
Glass blanks were produced by the same production method as in Example 1 except that the press time in the press molding step was 0.10 seconds, and the amount of retardation was measured. Moreover, the glass substrate retardation amount which performed each process similar to Example 1 was measured.

Example 4
Glass blanks were produced by the same production method as in Example 1 except that the thermal conductivity of the mold in the press molding step was 250 W / m · K, and the amount of retardation was measured. Moreover, the amount of retardation of the glass substrate which performed the processing process similar to Example 1 was measured.

(Comparative Example 1)
Glass blanks were produced by the same production method as in Example 1 except that the thermal conductivity of the mold in the press molding step was 100 W / m · K, and the amount of retardation was measured. Moreover, the amount of retardation of the glass substrate which performed the processing process similar to Example 1 was measured.

(Comparative Example 2)
Glass blanks were produced by the same production method as in Example 1 except that the press time in the press molding step was 0.04 seconds, and the amount of retardation of the glass blanks was measured. Moreover, the amount of retardation of the glass substrate which performed the processing process similar to Example 1 was measured.

(Comparative Example 3)
Glass blanks were produced by the same production method as in Example 1 except that the thermal conductivity of the mold in the press molding step was 30 W / m · K and the press time was 0.03 seconds, and the amount of retardation was measured. . Moreover, the amount of retardation of the glass substrate which performed the processing process similar to Example 1 was measured.

  The result is shown in Table 2 about the maximum value of each retardation amount of the above Examples 1-4 and Comparative Examples 1-3.

(Evaluation method)
A magnetic film was formed on the glass substrates of Examples 1 to 4 and Comparative Examples 1 to 3 and mounted on the HDD, and the impact resistance in a drop test was evaluated. In the evaluation method, when 100 HDDs were dropped from the height of 1500 G three times each, the magnetic disk that was not cracked was evaluated as acceptable. Moreover, the same evaluation was performed also about what performed the chemical strengthening process with respect to the glass substrate of Examples 1-4 and Comparative Examples 1-3. Table 2 shows the above test evaluation.

From the results shown in Table 2, Examples 1 to 4 in which the thermal conductivity of the mold in the press molding process is 120 W / m · K or more and the press time is 0.05 to 0.20 seconds are the center when glass blanks are created. The maximum value of the retardation amount in the entire circumference at the position of radius r = r ₀ + (r ₁ −r ₀ ) / 2 was 20 nm or less. Moreover, the maximum value of the retardation amount in the entire circumference of the same position of the glass substrate was 1 nm or less. Further, the drop test pass rate was 90% or more, and it was revealed that the drop resistance was excellent.

  On the other hand, about the comparative example 1 with a low heat conductivity of a metal mold | die and the comparative example 2 with a short press time, the maximum value of each retardation amount of a glass blank and a glass substrate becomes a big thing compared with the said Examples 1-4. Also, the impact resistance was inferior. Furthermore, in Comparative Example 3 having a low thermal conductivity and a short pressing time, the maximum value of the retardation amount was further increased, and the impact resistance was further deteriorated.

  ADVANTAGE OF THE INVENTION According to this invention, the glass blanks for HDD excellent in impact resistance, the manufacturing method of the glass blanks for HDD, the glass substrate for HDD, and the manufacturing method of the glass substrate for HDD are provided.

Claims (5)

The recording surface has a central hole, the radius of the central hole is r ₀ , and the radius of the glass blank is r _{1. The} recording surface has a radius r = r ₀ + (r ₁ −r ₀ ) / 2. The glass blank for HDD, wherein the maximum value of the retardation amount when linearly polarized light is incident in the vertical direction is 20 nm / mm or less. It is a manufacturing method of the glass blanks for HDD of Claim 1,
It has a molten glass supply process and a press molding process,
In the molten glass supply step, the shape of the glass gob supplied on the lower mold surface of the press die is controlled so as to have axial symmetry,
The HDD is characterized in that in the press molding step, butt molding is performed in which a press machine has a thermal conductivity of 120 W / m · K or more and a press time is 0.05 to 0.20 seconds. Manufacturing method of glass blanks.   A method for producing a glass substrate for HDD, comprising subjecting the glass blank for HDD obtained by the production method according to claim 2 to a grinding step and a polishing step to produce a glass substrate for HDD.   The manufacturing method of the glass substrate for HDD of Claim 3 further equipped with a chemical strengthening process. A glass substrate for HDD manufactured by the manufacturing method according to claim 3 or 4,
It has a central hole, and when the radius of the central hole is r ₀ ′ and the radius of the glass substrate is r ₁ ′, the position of radius r ′ = r ₀ ′ + (r ₁ ′ −r ₀ ′) / 2 A glass substrate for HDD, wherein the maximum retardation amount when linearly polarized light is incident in a direction perpendicular to the recording surface is 1 nm / mm or less over the entire circumference.

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