JP6104668B2 - Method for manufacturing glass substrate for information recording medium and carrier - Google Patents

Description

  The present invention relates to a method for producing a glass substrate for an information recording medium.

  2. Description of the Related Art Information recording apparatuses that record information on an information recording medium by using magnetism, light, photomagnetism, or the like are known. A typical example of such an information recording apparatus is a hard disk drive apparatus. A hard disk drive device is a device that magnetically records (writes) information on a magnetic disk (hard disk) as an information recording medium having a recording layer formed on a substrate, and reproduces (reads) the recorded information. is there. As a base material of such an information recording medium, a so-called substrate, a glass substrate is preferably used.

  Further, the hard disk drive device is configured to float the magnetic head with respect to the magnetic disk instead of contacting the magnetic disk when information is recorded on or read from the magnetic disk. It is known that the recording density can be improved by reducing the flying height of the magnetic head. In recent years, the storage capacity of a magnetic disk has been increased by reducing the flying height of the magnetic head to about several nanometers and increasing the recording density of the magnetic disk. For these reasons, in order to further reduce the flying height of the magnetic head and increase the recording density, it is required that the glass substrate for the information recording medium has high smoothness.

  Such a glass substrate for information recording media is manufactured by cutting a glass base plate (glass blanks) obtained from molten glass and then polishing it. Specifically, a rough polishing process is first performed on the cut glass base plate with a polishing liquid containing cerium oxide as an abrasive, and further polished with a polishing liquid containing colloidal silica as an abrasive. Examples include a method of performing a precision polishing step. Thus, the glass substrate for information recording media with high smoothness was obtained by performing grinding | polishing process in multiple times.

  In addition, in order to further satisfy the demand for increasing the storage capacity of the magnetic disk, not only the recording density is increased, but also the magnetic disk is passed through the magnetic head to the vicinity of the end of the magnetic disk. It is considered to be able to record information.

  As described above, when the magnetic disk is used up to the vicinity of the end of the magnetic disk, even if the magnetic disk is obtained using the glass substrate having improved smoothness as described above, the end of the magnetic disk When the magnetic head passed through the area, problems were likely to occur. Specifically, the vicinity of the end of the magnetic disk tends to be less uniform in thickness, flatness, etc. than the center, and this causes the flying posture of the magnetic head to pass near the end. Disturbance and fluttering characteristics were likely to deteriorate. Further, in order to increase the speed of information recording and reproduction, it has been studied to increase the rotation speed of the magnetic disk. As described above, when the rotational speed of the magnetic disk is increased, the above-described deterioration of fluttering characteristics becomes remarkable. For these reasons, when the magnetic disk is to be used up to the vicinity of the end of the magnetic disk, it is required that the shape disorder in the vicinity of the end of the glass substrate for information recording medium is small. That is, the uniformity of the thickness, flatness, etc. of the glass substrate for information recording media is required to be high up to the vicinity of the end.

  As a method for manufacturing a glass substrate in consideration of suppressing the shape disturbance up to the vicinity of the end portion, a method described in Patent Document 1 can be given.

  Patent Document 1 discloses a surface temperature measured on the inner peripheral end side of an upper surface plate of a double-side polishing apparatus when both main planes of a glass base plate are simultaneously polished in a polishing step for polishing both main planes of a glass base plate. A method for producing a glass substrate for a magnetic recording medium is described in which the absolute value of the difference Δtp (tp1−tp2) between tp1 and the surface temperature tp2 measured on the outer peripheral end side is 3 ° C. or less.

JP 2011-243252 A

  According to Patent Document 1, a glass substrate for a magnetic recording medium that is excellent in parallelism (plate thickness uniformity within the same glass substrate surface) and has a small plate thickness deviation between glass substrates polished in the same lot is manufactured with high productivity. It is disclosed that it can be done.

  However, when a magnetic disk is manufactured using the glass substrate for a magnetic recording medium obtained by the method described in Patent Document 1 and used near the end of the magnetic disk, fluttering characteristics may deteriorate. It was. When the rotational speed of the magnetic disk was increased, the deterioration was remarkable.

  The present invention has been made in view of such circumstances, and the production of a glass substrate for an information recording medium capable of obtaining an information recording medium having a uniform plate thickness up to the vicinity of an end and excellent fluttering characteristics. It aims to provide a method.

  Patent Document 1 discloses a method for adjusting the difference Δtp between the surface temperature measured on the inner peripheral end side of the upper surface plate and the surface temperature measured on the outer peripheral end side when both main surfaces of the glass base plate are polished simultaneously. Is illustrated as follows. Specifically, as a means for setting the absolute value of Δtp to 3 ° C. or less, a method of controlling the temperature of the polishing liquid supplied during polishing, a method of controlling the balance of the amount of polishing liquid supplied in the surface plate radial direction, Examples thereof include a method for suppressing frictional heat generated when the polishing surface of the upper surface plate and the polishing surface of the lower surface plate when the glass base plate is polished are strongly rubbed on the outer peripheral end side or the inner peripheral end side.

  According to the study of the present inventor, the reason described in Patent Document 1 was inferred as follows as the reason why a glass substrate having sufficiently excellent fluttering characteristics cannot be obtained. The inventor firstly adjusts the temperature difference of the polishing liquid before and after polishing the glass base plate by a polishing liquid supply method such as adjustment of the temperature and supply amount of the polishing liquid. I guessed that. If so, even if the temperature difference of the polishing liquid before and after the polishing of the glass base plate is adjusted by the polishing liquid supply method, both main surfaces of the glass base plate are simultaneously adjusted due to the difference in the supply amount of the polishing liquid. The present inventor has inferred that a difference occurs in the frictional force applied to the end of the glass base plate when polished. Further, the present inventor may cause unevenness in the temperature of the polishing liquid in the adjustment by the method of supplying the polishing liquid, and the temperature of the glass base plate during polishing may be different depending on the position of the glass base plate in the carrier. I guessed. At that time, it was inferred that, for example, thermal deformation of a surface plate or a carrier that supports the polishing pad may occur non-uniformly. And this inventor guessed that the glass substrate which was sufficiently excellent in fluttering characteristics will not be obtained because the end shape varies due to the difference in frictional force and temperature unevenness as described above. .

  Therefore, as a result of intensive studies on the carrier that holds the glass base plate at the time of polishing, not the method of supplying the polishing liquid, the present inventor has conceived the present invention as follows, focusing on the thermal conductivity of the carrier. Arrived.

  In the method for manufacturing a glass substrate for an information recording medium according to one aspect of the present invention, a glass base plate held by a carrier is sandwiched between two polishing pads, and a polishing liquid is supplied onto the glass base plate. And a polishing step of polishing both main surfaces of the glass base plate simultaneously by relatively moving the glass base plate and the polishing pad, and the carrier has a thermal conductivity of 2 W / m · K or more. It is characterized by being.

  According to such a configuration, it is possible to provide a method for manufacturing a glass substrate for an information recording medium capable of obtaining an information recording medium having a uniform plate thickness up to the vicinity of the end portion and having excellent fluttering characteristics.

  This is considered to be due to the following. Since the thermal conductivity of the carrier for holding the glass base plate is higher than that of conventional carriers, the temperature difference due to the position of the glass base plate in the carrier can be generated without adjusting the amount of polishing liquid supplied to the carrier. It is thought that it can be suppressed. This is considered to suppress the occurrence of non-uniform thermal deformation of the surface plate or carrier that supports the polishing pad. That is, it is considered that the occurrence of the difference in frictional force and the uneven temperature as described above can be sufficiently suppressed. From these facts, it is considered that the obtained glass substrate can sufficiently suppress the occurrence of variation in shape even in the vicinity of the end portion and has sufficiently excellent fluttering characteristics.

  From the above, according to the above configuration, it is considered that an information recording medium having a uniform plate thickness up to the vicinity of the end portion and excellent in fluttering characteristics can be obtained.

  In the method for manufacturing the glass substrate for information recording medium, it is preferable that the carrier has a thermal conductivity of 5 W / m · K or more.

  According to such a configuration, it is possible to obtain an information recording medium having a more uniform plate thickness up to the vicinity of the end portion and excellent in fluttering characteristics. This is considered to be because the generation of a temperature difference due to the position of the glass base plate in the carrier can be further suppressed.

  In the method for manufacturing the glass substrate for information recording medium, it is preferable that the carrier contains a resin and carbon fiber, and the thermal conductivity is adjusted by the content of the carbon fiber.

  According to such a structure, since it can grind | polish using the carrier containing resin similar to the conventional carrier, the thermal conductivity of a carrier is high, exhibiting the effect show | played by grinding | polishing using the conventional carrier. The above-described effects exhibited by the above can be exhibited.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the glass substrate for information recording media which can obtain the information recording medium which plate | board thickness is uniform to the edge part vicinity, and was excellent in fluttering characteristics can be provided.

It is a schematic sectional drawing which shows an example of the grinding | polishing apparatus used at the grinding | polishing process in the manufacturing method of the glass substrate for information recording media which concerns on one Embodiment of this invention. It is a schematic sectional drawing which shows an example of the apparatus main body with which the grinding | polishing apparatus used at the grinding | polishing process used in the manufacturing method of the glass substrate for information recording media which concerns on one Embodiment of this invention is provided. It is a top view which shows the glass base plate used with the manufacturing method of the glass substrate for information recording media which concerns on one Embodiment of this invention. 1 is a partial cross-sectional perspective view showing a magnetic disk as an example of an information recording medium using an information recording medium glass substrate manufactured by a method for manufacturing an information recording medium glass substrate according to an embodiment of the present invention. It is drawing for demonstrating the method to measure the fluttering characteristic of the glass substrate for information recording media manufactured by the manufacturing method of the glass substrate for information recording media which concerns on one Embodiment of this invention.

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

  The manufacturing method of the glass substrate for information recording media which concerns on this embodiment is equipped with the following grinding | polishing processes. That is, the manufacturing method of the information recording medium glass substrate according to the present embodiment is not particularly limited as long as it includes the following polishing step.

  In the polishing step, the glass base plate held by a carrier is sandwiched between two polishing pads, and the glass base plate and the polishing pad are relative to each other in a state where a polishing liquid is supplied onto the glass base plate. And moving both the main surfaces of the glass base plate simultaneously. A carrier having a thermal conductivity of 2 W / m · K or more is used as the carrier.

  By providing the polishing step as described above, it is possible to manufacture a glass substrate for an information recording medium capable of obtaining an information recording medium having a uniform plate thickness up to the vicinity of the end portion and excellent fluttering characteristics. This is considered to be due to the following.

  First, since the thermal conductivity of the carrier for holding the glass base plate is higher than that of the conventional carrier, the temperature difference due to the position of the glass base plate in the carrier can be adjusted without adjusting the amount of polishing liquid supplied to the carrier. It is thought that generation | occurrence | production can be suppressed. This is considered to suppress the occurrence of non-uniform thermal deformation of the surface plate or carrier that supports the polishing pad. That is, it is considered that the above-described difference in frictional force applied to the glass base plate and generation of temperature unevenness can be sufficiently suppressed. From these facts, it is considered that the obtained glass substrate can sufficiently suppress the occurrence of variation in shape even in the vicinity of the end portion and has sufficiently excellent fluttering characteristics.

  Moreover, the manufacturing method of the glass substrate for information recording media which concerns on this embodiment will not be specifically limited if the said grinding | polishing process is provided as mentioned above. Specifically, the polishing step is not particularly limited except that the polishing step is as described above, and any conventional manufacturing method may be used. Moreover, in the conventional general manufacturing method, it is common to perform multiple times of polishing including a rough polishing step and a precision polishing step as a polishing step for polishing the main surface. In the method for manufacturing a glass substrate for an information recording medium according to the present embodiment, the polishing step may be any polishing step, but according to the present embodiment as a precision polishing step that requires more smoothness and the like. A polishing step is preferably performed, and any polishing step is more preferably performed according to the present embodiment. By doing so, the variation in shape can be suppressed over the entire surface, and a glass substrate with better fluttering characteristics can be obtained. The variation in shape is, for example, a variation in the thickness of the glass substrate. If the method for manufacturing a glass substrate for information recording media according to the present embodiment is used, a glass substrate in which the variation in thickness is suppressed can be obtained. It is done. In addition, the plate | board thickness of a glass substrate can be measured using a micrometer, a laser displacement meter, a laser interferometer, etc., for example.

  Further, the fluttering characteristic referred to in the present embodiment means an amplitude amount (surface runout) at the time of high-speed rotation of the glass substrate, and is defined by a relational expression such as the following formula (I).

式（Ｉ）中、Ｆはフラッタリング特性（単位：ｎｍ）であり、ａはガラス基板の外半径を示し、νはガラス基板のポアソン比を示し、Ｅはガラス基板のヤング率を示し、ξはガラス基板の減衰係数を示し、ｈはガラス基板の厚みを示し、λ^４はモデル関数パラメータである。この場合、ガラス基板の外半径および厚みを一定にすれば、ポアソン比は化学組成による差があまりなく、フラッタリング特性Ｆは、最右辺により関係付けられる。

In formula (I), F is a fluttering characteristic (unit: nm), a represents the outer radius of the glass substrate, ν represents the Poisson's ratio of the glass substrate, E represents the Young's modulus of the glass substrate, ξ Indicates the attenuation coefficient of the glass substrate, h indicates the thickness of the glass substrate, and λ ⁴ is a model function parameter. In this case, if the outer radius and thickness of the glass substrate are made constant, the Poisson's ratio does not vary greatly depending on the chemical composition, and the fluttering characteristic F is related to the rightmost side.

  That is, since the fluttering characteristic is the amount of amplitude at the time of high-speed rotation of the glass substrate as described above, it is preferable to reduce this. It has been considered that it is generally advantageous to increase the Young's modulus and the damping coefficient as in the above formula, but the flying height is getting lower on the substrate aiming at higher density, so it is more precise. Fluttering characteristics are required.

  In this embodiment, when the glass substrate for information recording medium, for example, the glass substrate for HDD, has a diameter of 60 to 70 mm and a thickness of 0.7 to 0.9 mm, fluttering characteristics at a rotational speed of 15000 rpm are 120 nm or less, more preferably 50 nm or less, and even more preferably 48 nm or less. Similarly, fluttering characteristics at a rotation speed of 10,000 rpm are preferably less than 100 nm, and more preferably less than 50 nm. Similarly, the fluttering characteristic at a rotation speed of 7000 rpm is preferably 40 nm or less, more preferably 20 nm or less, and further preferably 18 nm or less. As a result, when the HDD glass substrate is set in a hard disk drive or the like and rotated at a high speed, the head and the HDD glass substrate can be prevented from coming into contact with each other, and inconveniences such as damage to the head can be prevented. it can.

  Here, the polishing process in the method for manufacturing the glass substrate for information recording medium according to the present embodiment will be described.

  The carrier used in this polishing step has a thermal conductivity of 2 W / m · K or more, preferably 5 W / m · K or more, and more preferably 10 W / m · K or more. When the thermal conductivity of the carrier is too low, the occurrence of variation in shape near the end cannot be sufficiently suppressed, and fluttering characteristics tend not to be sufficiently improved. This is considered to be because it becomes impossible to sufficiently suppress the difference in friction force applied to the glass base plate and the occurrence of temperature unevenness on the glass base plate. Further, the higher the thermal conductivity of the carrier, the better. However, for example, if the carrier is configured to contain carbon fibers and a resin as described later, 100 W from the standpoint of maintaining the shape. The limit is about / m · K. Therefore, the upper limit of the carrier thermal conductivity is 100 W / m · K. The thermal conductivity here can be measured, for example, by a laser flash method or the like.

  The carrier is not particularly limited as long as it has a thermal conductivity of 2 W / m · K or more and can be used as a carrier in the polishing process. The shape of the carrier and the like are not particularly limited, but the specific shape may be a shape described later. Examples of the material of the carrier include the following. As the carrier, for example, a carrier containing a resin and carbon fiber and adjusted so that the thermal conductivity is within the above range depending on the content of the carbon fiber is preferably used. The resin is preferably a curable resin such as a thermosetting resin from the viewpoint of heat resistance. Specific examples of the resin include an epoxy resin. Examples of carbon fibers include PAN-based carbon fibers and pitch-based carbon fibers. Further, the carrier may contain components other than the resin and the carbon fiber. For example, as components other than resin and carbon fiber, carbon that is not fibrous, that is, carbon powder, glass fiber, and the like can be given. For example, if it is carbon powder, it can graphitize by the heat processing at the time of hardening a resin component at the time of carrier manufacture, for example, and it can contribute to the improvement of the intensity | strength and thermal conductivity of a carrier. Moreover, if it is glass fiber, it can contribute to the intensity | strength improvement of a carrier, without having a big influence on thermal conductivity. The carbon fiber content can be appropriately adjusted depending on the type of resin or carbon fiber, the required thermal conductivity, or the like. When there are too few carbon fibers, there exists a tendency which cannot fully raise the heat conductivity of a carrier. In addition, when the carbon fiber is too much, the thermal conductivity of the carrier is expected to be sufficiently increased, but the resin content is relatively reduced, and the glass substrate which is a function as a carrier is retained. It tends to be difficult to ensure sufficient strength. Further, the content of the resin can be appropriately adjusted according to the kind of the resin and the carbon fiber, the required thermal conductivity, and the like, similarly to the content of the carbon fiber.

  In addition, it is considered that the method for manufacturing the glass substrate for information recording medium according to the present embodiment can suppress the occurrence of a temperature difference due to the position of the glass base plate due to the high thermal conductivity of the carrier. It is not necessary to adjust the temperature and supply amount of the liquid. Specifically, in the polishing step, the polishing liquid at a constant temperature may be supplied at a constant supply amount. In addition, it is preferable to supply the polishing liquid at a constant temperature at a constant supply amount in order to suppress the occurrence of a difference in frictional force applied to the glass base plate due to the difference in the supply amount of the polishing liquid.

  Next, a polishing apparatus used in the polishing process will be described.

  The polishing apparatus used in this polishing step is not particularly limited as long as it is a polishing apparatus used for manufacturing a glass substrate for an information recording medium. Specifically, there is a polishing apparatus 1 as shown in FIG. FIG. 1 is a schematic cross-sectional view showing an example of a polishing apparatus used in a polishing step in the method for manufacturing a glass substrate for information recording medium according to the present embodiment.

  A polishing apparatus 1 as shown in FIG. 1 is an apparatus capable of simultaneously polishing both surfaces of a main surface of a glass base plate. The polishing apparatus 1 includes an apparatus main body (polishing main body) 11 and a polishing liquid supply unit 16 that supplies a polishing liquid (polishing slurry) to the apparatus main body 11.

  As shown in FIGS. 1 and 2, the apparatus main body 11 includes two surface plates 12 and 13 arranged to face each other. FIG. 2 is a schematic cross-sectional view showing an example of the apparatus main body provided in the polishing apparatus used in the polishing step in the method for manufacturing the glass substrate for information recording medium according to the present embodiment. The positional relationship between the respective surface plates is not limited to the upper and lower sides. For example, of the two surface plates, the surface plate disposed on the upper side is the upper surface plate 12, and the surface plate disposed on the lower side is This is referred to as the lower surface plate 13. That is, the apparatus main body 11 includes a disk-shaped upper surface plate 12 and a disk-shaped lower surface plate 13, and they are arranged at intervals in the vertical direction 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 base plate 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.

  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 formed with a plurality of base plate holding holes 14a, and the glass base plate 10 can be placed in the base plate holding holes 14a. As the carrier 14, for example, 100 base plate holding holes 14 a may be formed, and 100 glass base plates 10 may be fitted and arranged. If it does so, 100 glass base plates can be processed by one process (1 batch). Specifically, the shape of the carrier 14 is as shown in FIG. As the carrier 14 used in the polishing step, a carrier that satisfies the above-described configuration, that is, a carrier having a thermal conductivity of 2 W / m · K or more is used. Further, the thickness of the carrier 14 is thinner than the thickness of the glass base plate 10.

  The carrier 14 sandwiched between the surface plates 12 and 13 through the polishing pad 15 is the same as the lower surface plate 13 with respect to the center of rotation of the surface plates 12 and 13 while rotating while holding the glass base plate 10. Revolve in the direction. 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 1 operating in this manner, the polishing liquid 17 is supplied between the upper surface plate 12 and the glass base plate 10 and between the lower surface plate 13 and the glass base plate 10, respectively. The glass base plate 10 can be polished.

  Further, the polishing liquid supply unit 16 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 11. The liquid recovery part 120 was extended from 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 11, and the polishing liquid supply part 16 from the liquid recovery part main body 120a. And a liquid return pipe 120c.

  Then, the polishing liquid 17 put in the liquid reservoir main body 110a is supplied to the apparatus main body 11 from the discharge port 110e of the liquid supply pipe 110b, and the liquid recovery section main body 120a from the apparatus main body 11 through the liquid recovery pipe 120b. To be recovered. The recovered polishing liquid 17 is returned to the liquid storage part 110 via the liquid return pipe 120c, and can be supplied to the apparatus main body part 11 again.

  Here, the case where the recovered polishing liquid is used in a circulating manner (circulation use) has been described. However, a new polishing liquid is always used without recovering the polishing liquid used for polishing. It may be a case where a polishing liquid is used (flowing use). The reason for using the polishing liquid by pouring is that if polishing sludge (polishing waste, glass sludge) generated by polishing is present in the polishing liquid, it may cause scratches on the surface of the glass substrate.

  In addition, as described above, the method for manufacturing the glass substrate for an information recording medium according to the present embodiment preferably performs the polishing process according to the present embodiment as a rough polishing process and separately performs a precision polishing process. Such a precision polishing process is not particularly limited as long as it is a general precision polishing process in the method for producing a glass substrate for information recording medium. The precision polishing step maintains a flat and smooth main surface obtained in the rough polishing step (the polishing step), for example, and a smooth mirror surface having a surface roughness (Rmax) of the main surface of about 0.3 nm or less. This is a mirror polishing process that finishes. This precision polishing step may be performed using, for example, a polishing apparatus similar to that used in the above polishing step. Note that the surface to be polished in the precision polishing step is the main surface, similar to the surface to be polished in the polishing step.

Further, the polishing pad used in the polishing step is a processing tool for polishing both main surfaces of the glass substrate, and particularly if it is used in the polishing step when manufacturing the glass substrate for information recording medium, It is not limited. Specifically, for example, a hard polishing pad such as a hard urethane pad is used as a polishing pad used in the rough polishing process, and a soft polishing such as a suede pad is used as a polishing pad used in the precision polishing process. It is possible to use a pad. Moreover, it is also conceivable to use a soft polishing pad such as a suede pad as the polishing pad in both the rough polishing process and the precision polishing process. The suede pad is a suede type soft foamed resin pad whose surface (polishing layer) is made of a soft foamed resin such as soft foamed polyurethane. The suede pad is a polishing pad in which bubbles are open to the surface (pad surface), and there are relatively many soft walls separating the bubbles. And the hardness of the pad surface of a polishing pad is Asker C hardness, It is preferable that it is 60-90, It is more preferable that it is 70-84, It is further more preferable that it is 75-84. Moreover, it is preferable that the diameter (open diameter) of the bubble open | released by the pad surface is 20-80 micrometers. Moreover, it is preferable that the density of the polishing layer arrange | positioned on the surface of a polishing pad is 0.55-0.62 g / m < ³ >. Further, a so-called non-buffing polishing pad in which the pad surface of the polishing pad is not buffed is preferable. As the polishing pad used in the polishing process, specifically, a polyurethane suede pad is used, and for example, NP178 (Asker C hardness 82) manufactured by Filwel is used. Moreover, as a hard polishing pad, the polishing pad etc. whose hardness exceeds 90 by Asker C hardness are mentioned, for example, More specifically, a hard urethane pad etc. are mentioned.

  Further, the polishing liquid used in the polishing step is not particularly limited as long as the polishing liquid used in the polishing step is appropriately selected and used. Specifically, as a polishing liquid used in the rough polishing process, a polishing liquid generally used in the rough polishing process can be used. More specifically, the polishing liquid used in the rough polishing step includes a polishing liquid containing cerium oxide as an abrasive. Moreover, as a polishing liquid used in the precision polishing process, a polishing liquid generally used in the precision polishing process can be used. More specifically, examples of the polishing liquid used in the precision rough polishing step include a polishing liquid containing silica-based abrasive grains such as colloidal silica as an abrasive.

  Moreover, as a manufacturing method of the glass substrate for information recording media which concerns on this embodiment, the said grinding | polishing process should just be provided, but the other process may be provided. For example, a method including a disk machining process, a grinding process (lapping process), an internal / external grinding process, an end surface polishing process, a chemical strengthening process, a polishing process (polishing process), and a cleaning process can be used. And each said process may be performed in this order, and a chemical strengthening process may be performed after a grinding | polishing process. Furthermore, a method including steps other than these may be used. Moreover, a grinding | polishing process performs the said grinding | polishing process.

  The disk processing step is a step of processing the raw glass into a disk-shaped glass base plate 10 in which a through hole 10a is formed at the center so that the inner periphery and the outer periphery are concentric circles as shown in FIG. is there. Specifically, a glass melting step in which raw glass is melted in a melting furnace to form molten glass, a forming step in which the molten glass is formed into a disc-shaped glass base plate, and the formed disc-shaped glass base plate The coring process which forms the through-hole 10a in the center part of this, and processes to the disk shaped glass base plate 10 as shown in FIG. 3 is provided. FIG. 3 is a top view showing the glass base plate used in the method for manufacturing the glass substrate for information recording medium according to the present embodiment.

The glass melting step is not particularly limited as long as raw glass can be melted in a melting furnace to obtain molten glass. The starting glass is not particularly limited, for _example, SiO 2, _Na 2 O, and soda-lime glass composed mainly of _{CaO, SiO 2, Al 2 O} 3, and ^R ₁ in 2 O (wherein, ^{R 1} is , K, Na, or Li.) Aluminosilicate glass, borosilicate glass, Li ₂ O—SiO ₂ glass, Li ₂ O—Al ₂ O ₃ —SiO ₂ containing an oxide represented by Glass, R ² O—Al ₂ O ₃ —SiO ₂ glass (wherein R ² represents Mg, Ca, Sr, or Ba). More specifically, for example, a glass composition, SiO ₂ is 55 to 75 wt%, _Al 2 _{O 3} is 5 to 18 wt%, Li ₂ O is 1 to 10 mass%, Na ₂ O is 3 to 15 mass %, K ₂ O is 0.1 to 5% by mass, MgO is 0.1 to 5% by mass, and CaO is 0.1 to 5% by mass. Among these, aluminosilicate glass and borosilicate glass are preferable in that they are excellent in impact resistance and vibration resistance. Moreover, it does not specifically limit as a melting method of raw material glass, Usually, the method of fuse | melting the said glass raw material at high temperature by well-known temperature and time is employable.

  The forming step is not particularly limited as long as the molten glass can be formed into a disk-shaped glass base plate. Specifically, the press process etc. which form a disk shaped glass base plate by press molding molten glass are mentioned. The forming step is not limited to the pressing step, and may be a step of, for example, cutting a sheet glass formed by a downdraw method or a float method with a grinding stone to produce a disk-shaped glass base plate. The float method is, for example, a method in which a molten liquid obtained by melting a glass material is poured onto molten tin and solidified as it is. Since the obtained glass base plate is a free surface of glass and the other surface is an interface between glass and tin, the smoothness is high, for example, the arithmetic average roughness Ra is 0.001 μm. The following mirror surface is provided. Moreover, as a thickness of a glass base plate, a 0.95 mm thing is mentioned, for example. In addition, the surface roughness of a glass base plate or a glass substrate, for example, Ra or Rmax, can be measured using a general surface roughness measuring machine.

  Moreover, the said coring process is a process of giving the coring process which forms the through-hole 10a in the center part of the disk shaped glass base plate formed at the said formation process. By doing so, the disk-shaped glass base plate 10 in which the through-hole 10a was formed in the center part as shown in FIG. 3 is obtained. The coring process is not particularly limited as long as it is a drilling process that forms a through hole in the center of the glass base plate. For example, a method of forming a through hole in the center of the glass base plate by grinding with a core drill equipped with a diamond grindstone or the like, a cylindrical diamond drill, or the like can be used. By doing so, a through hole is formed in the center of the glass base plate, and an annular glass base plate is obtained in plan view.

  By the disk processing step, for example, the outer diameter r1 is 2.5 inches (about 64 mm), 1.8 inches (about 46 mm), 1 inch (about 25 mm), 0.8 inches (about 20 mm), etc., and the thickness is Disc-shaped glass base plates of 2 mm, 1 mm, 0.63 mm, etc. are obtained. Further, when the outer diameter r1 is 2.5 inches (about 64 mm), for example, the inner diameter r2 is processed to 0.8 inches (about 20 mm).

  The grinding step (lapping step) is a step of processing the glass base plate to a predetermined plate thickness. Specifically, for example, a step of grinding (lapping) both surfaces of the glass base plate can be mentioned. By doing so, the parallelism, flatness and thickness of the glass base plate are adjusted. Further, this lapping step may be performed once or twice or more. For example, when it is performed twice, the parallelism, flatness and thickness of the glass base plate are preliminarily adjusted in the first lapping process (first lapping process), and glass is used in the second lapping process (second lapping process). Finely adjust the parallelism, flatness and thickness of the base plate. Moreover, when performing a grinding process twice, you may perform a 1st lapping process and a 2nd lapping process continuously, but perform the inside-and-outside grinding process mentioned later and an end surface grinding | polishing process between these processes. Also good.

  The grinding apparatus used in the grinding process is not particularly limited as long as it can be used as a grinding apparatus used in the grinding process in the method for producing a glass substrate for information recording medium. Specifically, it is the same as the polishing apparatus used in the polishing step, and includes a resin sheet (grinding sheet) using diamond as a fixed abrasive instead of the polishing pad.

  In addition, examples of the first lapping step include a step in which the entire surface of the glass base plate has a substantially uniform surface roughness. Moreover, as a grinding sheet used at a 1st lapping process, it is preferable to use that whose average particle diameter of a fixed abrasive is 6-12 micrometers, for example. In the first lapping step, when the arithmetic average roughness Ra of the glass base plate is measured at a plurality of locations, the difference between the minimum value and the maximum value of Ra obtained is about 0.01 to 0.4 μm. It is preferable to do.

  In addition, examples of the second wrapping step include a step in which a glass base plate from which defects such as large undulations, chips, and cracks are removed can be obtained. Moreover, as a grinding sheet used at a 2nd lapping process, it is preferable to use that whose average particle diameter of a fixed abrasive is 0.5-4 micrometers, for example, and it is preferable to use a 1-2 micrometers thing. Moreover, it is preferable that Rmax of the obtained glass base plate shall be 0.5-2 micrometers in the said 2nd lapping process. Moreover, it is preferable that Ra shall be 0.1-0.5 micrometer. If the surface of the glass base plate after the second lapping step is too rough, it is difficult to obtain a glass substrate having sufficiently high smoothness even if the polishing step is performed. In addition, the glass base plate after the second lapping step is preferably as smooth as possible, that is, as Ra is small, but in the lapping step, about 0.01 μm is the limit, and 0.01 μm is the limit. This is considered to be the lower limit value of the arithmetic average roughness Ra of the glass base plate after the second lapping step.

  The inner / outer grinding step is a step of grinding the outer peripheral end surface and the inner peripheral end surface of the glass base plate. Specifically, the process etc. which grind the outer peripheral end surface and inner peripheral end surface of a glass base plate with grinding wheels, such as a drum-shaped diamond grindstone, are mentioned.

  The said end surface grinding | polishing process is a process of grind | polishing the outer peripheral end surface and inner peripheral end surface of a glass base plate. Specifically, a plurality of glass base plates subjected to the inner and outer grinding steps, for example, about 100, are stacked and laminated, and in this state, the outer peripheral end surface and the inner peripheral end surface are polished using an end surface polishing machine. And the like.

  The said chemical strengthening process is not specifically limited, Specifically, the process etc. which immerse a glass base plate in a chemical strengthening liquid (strengthening process liquid) and form a chemical strengthening layer in a glass base plate are mentioned. By performing such a process, a chemical strengthening layer can be formed in the surface of a glass base plate, for example, a 5 micrometer area | region from the glass base plate 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 base plate in a heated chemical strengthening treatment liquid, alkali metal ions such as lithium ions and sodium ions contained in the glass base plate are potassium having a larger ion radius. It is carried out by an ion exchange method for substituting alkali metal ions such as 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 base plate is strengthened. That is, it is considered that the reinforcing layer is suitably formed on the glass base plate by this chemical strengthening step.

  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 a magnetic information recording medium. 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 base plate. 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.

  The said washing | cleaning process is a process of wash | cleaning a glass base plate. It is preferable that the washing process is appropriately performed after each process. Moreover, scrub cleaning is mentioned as a final-cleaning process which wash | cleans the glass substrate grind | polished by the said grinding | polishing process among the said washing | cleaning processes, for example. Scrub cleaning is a wet physical cleaning method in which the scrub member and the glass substrate are relatively moved while the scrub member is pressed against the glass substrate while supplying a cleaning liquid to the surface of the glass substrate. . By doing so, dirt on the surface of the glass substrate can be scraped off. The apparatus for scrub cleaning (scrub cleaning apparatus) is not particularly limited as long as it is an apparatus capable of scrub cleaning an information recording medium glass substrate. Specifically, a roll scrub cleaning device in which the scrub member is a cylindrical roll scrub, a cup scrub cleaning device in which the scrub member is a cup type, and the like can be given.

  In addition, the glass base plate or the glass substrate before the cleaning step such as the final cleaning step is kept in contact with the liquid in order to prevent foreign matter from adhering to the surface. It is preferable.

  Further, as the final cleaning step, it is preferable to perform ultrasonic cleaning after scrub cleaning.

  In addition, after the final cleaning, the glass substrate is dried. Examples of the drying method include drying with IPA vapor, spin drying, and hot water drying.

  Next, a magnetic recording medium using the glass substrate for information recording medium manufactured by the method for manufacturing the glass substrate for information recording medium according to the present embodiment will be described.

  FIG. 4 is a partial cross-sectional perspective view showing a magnetic disk as an example of a magnetic recording medium using the glass substrate for information recording medium manufactured by the method for manufacturing the glass substrate for information recording medium according to the present embodiment. This magnetic disk D includes a magnetic film 102 formed on the main surface of a circular glass substrate 101 for an information recording medium. For the formation of the magnetic film 102, a known method is used. For example, a formation method (spin coating method) for forming the magnetic film 102 by spin-coating a thermosetting resin in which magnetic particles are dispersed on the glass substrate 101 for information recording medium, Examples thereof include a forming method for forming the magnetic film 102 by sputtering (sputtering method) and a forming method for forming the magnetic film 102 on the glass substrate 101 for information recording medium by electroless plating (electroless plating method). The thickness of the magnetic film 102 is about 0.3 to 1.2 μm when the spin coating method is used, and is about 0.04 to 0.08 μm when the sputtering method is used. In some cases, the thickness is about 0.05 to 0.1 μm. From the viewpoint of thinning and densification, film formation by sputtering is preferable, and film formation by electroless plating is preferable.

The magnetic material used for the magnetic film 102 can be any known material and is not particularly limited. The magnetic material is preferably, for example, a Co-based alloy based on Co having high crystal anisotropy in order to obtain a high coercive force, and Ni or Cr added for the purpose of adjusting the residual magnetic flux density. More specifically, CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, CoCrPtSiO, and the like whose main component is Co can be given. The magnetic film 102 has a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa, etc.) divided by a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) in order to reduce noise. May be. Magnetic material used for the magnetic layer 102, in addition to the magnetic material, ferrite or iron - may be a rare earth, also, Fe in a non-magnetic film made of _SiO 2, BN, etc., Co, FeCo, CoNiPt and the like A granular material having a structure in which the magnetic particles are dispersed may be used. In addition, for recording on the magnetic film 102, either an inner surface type or a vertical type recording format may be used.

  In order to improve the sliding of the magnetic head, the surface of the magnetic film 102 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 freon-based solvent.

Furthermore, an underlayer or a protective layer may be provided on the magnetic film 102 as necessary. The underlayer in the magnetic disk D is appropriately selected according to the magnetic film 102. 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. For example, in the case of the magnetic film 102 containing Co as a main component, the material of the underlayer is preferably Cr alone or a Cr alloy from the viewpoint of improving magnetic characteristics. Further, the underlayer is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked. Examples of such an underlayer having a multilayer structure include multilayer underlayers such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, and NiAl / CrV. Examples of the protective layer that prevents wear and corrosion of the magnetic film 102 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be continuously formed with the underlayer and the magnetic film 102 by an in-line sputtering apparatus. These protective layers may be a single layer, or may be a multi-layer structure composed of the same or different layers. Note that another protective layer may be formed on the protective layer or instead of the protective layer. For example, instead of the protective layer, a SiO ₂ layer may be formed on the Cr layer. Such a SiO ₂ layer is formed by dispersing and applying colloidal silica fine particles in a tetraalkoxysilane diluted with an alcohol-based solvent on the Cr layer and further baking.

  In such a magnetic recording medium based on the information recording medium glass substrate 101 according to the present embodiment, the information recording medium glass substrate 101 is formed with the above-described composition. Can be done by sex.

  In addition, although the case where the glass substrate 101 for information recording media in this embodiment was used for a magnetic recording medium (magnetic disk) was demonstrated above, it is not limited to this, For information recording media in this embodiment The glass substrate 101 can also be used for magneto-optical disks, optical disks, and the like.

  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, as a raw material _{glass, SiO 2, Al 2 O 3} , R 2 O (R = K, Na, Li) using aluminosilicate glass as a main component was carried out a disk working process. Specifically, the raw glass was melted by a known method, and the obtained molten glass was press-molded to obtain a disk-shaped glass base plate having an outer diameter of 67 mm. Moreover, it shape | molded so that the thickness of this glass base plate might be set to 1.0 mm.

  Next, both main surfaces of the obtained glass base plate were ground using a double-side grinding machine. Then, the coring process was given to the glass base plate which gave the grinding process, and the through-hole was formed in the center part of the glass base plate. Specifically, a circular center hole (through hole) having a diameter of about 19.6 mm was formed in the center of the ground glass plate using a core drill equipped with a cylindrical diamond grindstone.

  Next, an inner and outer grinding step was performed on the glass base plate. Specifically, the outer peripheral end face and the inner peripheral end face of the glass base plate were ground using a drum-shaped diamond grindstone so that the outer diameter of the glass base plate was 65 mm and the inner diameter was 20 mm. Then, the end surface process was performed with respect to the glass base plate. Specifically, with 100 glass base plates stacked, the outer peripheral end surface and the inner peripheral end surface of the glass base plate were polished using an end surface polishing machine. Nylon fiber having a diameter of 0.2 mm was used as the brush hair of the polishing machine. As the polishing liquid, a slurry containing cerium oxide having an average primary particle diameter of 3 μm as abrasive grains was used. Thereafter, both surfaces of the glass base plate were processed using a diamond sheet with a double-side grinding machine.

  The glass base plate thus obtained was subjected to a polishing process. Specifically, both main surfaces of the glass base plate were polished using a polishing apparatus as shown in FIGS. Specifically, for the glass substrate subjected to the polishing step, first, as shown in Table 1, as a carrier, a known method is used except that a carrier having a thermal conductivity of 2 W / m · K is used. A rough polishing step was performed. A rough polishing step was performed. Then, as shown in Table 1, as a carrier for the glass substrate that has been subjected to the rough polishing step, a precision polishing step is performed by a known method except that a carrier having a thermal conductivity of 2 W / m · K is used. gave.

  The carrier was prepared by blending epoxy resin and carbon fiber at various blending ratios. Thereafter, the thermal conductivity of the produced carrier was measured by a laser flash method, and a carrier having a desired thermal conductivity was selected. In this way, carriers having various thermal conductivities were produced.

  Next, a final cleaning process was performed on the glass substrate subjected to the precision polishing process. Specifically, scrub cleaning was first performed. At that time, a liquid obtained by adding a nonionic surfactant to increase the cleaning ability was used as the cleaning liquid. Thereafter, in order to remove the cleaning liquid remaining on the surface of the lath substrate, a water rinse cleaning process was performed in an ultrasonic bath for 2 minutes, and an IPA cleaning process was performed in an ultrasonic bath for 2 minutes. Finally, the surface was dried with IPA vapor. By doing so, a glass substrate was obtained.

[Example 2 and Example 3]
Example 2 and Example 3 are the same as Example 1 except that the carrier having the thermal conductivity shown in Table 1 is used as the carrier in the polishing step.

[Comparative Example 1]
Comparative Example 1 is the same as Example 1 except that a conventionally used carrier is used as the carrier in the polishing step. Specifically, a carrier obtained by blending an epoxy resin and glass fiber, that is, a carrier made of glass epoxy was used as the carrier.

[Comparative Example 2]
Comparative Example 2 is the same as Comparative Example 1 except that the temperature of the surface plate is adjusted. In Examples 1 to 3 and Comparative Example 1, the temperature of the surface plate was not adjusted.

[Evaluation]
The said Example and the comparative example were evaluated with the following method.

(Thickness difference)
In each of the examples and comparative examples, the thickness of a plurality of locations of the obtained glass substrate was measured using a micrometer manufactured by Mitutoyo Corporation. Specifically, the thickness of about 10 locations at various locations such as the vicinity of the inner peripheral side end portion, the central portion, and the outer peripheral end portion of the glass substrate was measured. The difference between the maximum value and the minimum value was calculated. The difference was evaluated as a plate thickness difference.

(Fluttering characteristics)
The fluttering characteristics were measured by a method as shown in FIG. Specifically, the measurement method is as follows.

  First, in each Example and Comparative Example, the obtained glass substrate (measurement object) 40 was rotated at a high speed (10000 rpm) in the direction of the arrow A by the air spindle motor 41. Laser light was irradiated from the laser vibrometer 42 toward the vicinity of the outer peripheral end of the rotated measurement object 40. And the reflected light reflected by the surface P of the measuring object 40 was detected with the laser vibrometer 42, and the wavelength of the reflected light was measured. At this time, since this wavelength changes due to vibration in the vertical direction of the measurement object 40 (axial direction of the spindle), the change in wavelength during one rotation of the measurement object was measured. That is, the measured change amount of the wavelength corresponds to the shake amount in the vicinity of the outer peripheral end portion of the measurement object 40. Fluttering characteristics were evaluated based on the amount of change in wavelength corresponding to the amount of shake.

  When the change in wavelength was less than 50 nm, it was evaluated as “◎”, when it was 50 nm or more and less than 100 nm, it was evaluated as “◯”, and when it was 100 nm or more, it was evaluated as “x”.

  The evaluation results are shown in Table 1 together with the thermal conductivity of the carrier.

表１から、熱伝導率が２Ｗ／ｍ・Ｋ以上のキャリアを用いた場合（実施例１〜３）は、熱伝導率が２Ｗ／ｍ・Ｋ未満のキャリアを用いた場合と比較して、板厚差が小さく、フラッタリング特性に優れたガラス基板が得られることがわかった。

From Table 1, when using a carrier having a thermal conductivity of 2 W / m · K or more (Examples 1 to 3), compared to using a carrier having a thermal conductivity of less than 2 W / m · K, It was found that a glass substrate having a small thickness difference and excellent fluttering characteristics can be obtained.

  Even if a carrier with a thermal conductivity of less than 2 W / m · K is used, the plate thickness difference can be reduced by adjusting the temperature of the surface plate, but the fluttering characteristics are excellent. A glass substrate could not be obtained.

  From these facts, it is understood that the carrier preferably has a thermal conductivity of 2 W / m · K or more, and from Examples 2 and 3, it is preferably 5 W / m · K or more. .

DESCRIPTION OF SYMBOLS 1 Polishing apparatus 10 Glass base plate 10a Through-hole 11 Apparatus main body part 12 Upper surface plate 13 Lower surface plate 14 Carrier 14a Base plate holding hole 15 Polishing pad 16 Polishing liquid supply part 17 Polishing liquid 40 Measuring object 41 Air spindle motor 42 Laser Vibrometer 101 Glass substrate for information recording medium 102 Magnetic film 110 Liquid reservoir 110a Liquid reservoir main body 110b Liquid supply pipe 110e Discharge port 120 Liquid recovery section 120a Liquid recovery section main body 120b Liquid recovery pipe 120c Liquid return pipe

Claims (4)

The glass base plate held by the carrier is sandwiched between two polishing pads, and the glass base plate and the polishing pad are relatively moved while the polishing liquid is supplied onto the glass base plate. , Comprising a polishing step for simultaneously polishing both main surfaces of the glass base plate,
Thermal conductivity of the carrier state, and are more 2W / m · K,
The method for producing a glass substrate for an information recording medium , wherein the carrier contains a resin and carbon fiber, and the thermal conductivity is adjusted by the content of the carbon fiber .   The method for producing a glass substrate for an information recording medium according to claim 1, wherein the carrier has a thermal conductivity of 5 W / m · K or more. A substrate having holes for holding a substrate, the substrate placed in the holes for holding the substrate is sandwiched between two polishing pads, and a polishing liquid is supplied onto the substrate, and the substrate and the substrate A carrier used when polishing both main surfaces of the base plate by moving the polishing pad relative to each other,
The carrier contains a resin and carbon fiber,
A carrier having a thermal conductivity of 2 W / m · K or more. The carrier according to claim 3, wherein the carrier has a thermal conductivity of 5 W / m · K or more.

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