JP2012014751A - Glass plate heat treatment setter and manufacturing method of glass substrate for information recording medium using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass plate heat treatment setter capable of enhancing smoothness and reducing surface defects and a manufacturing method of glass substrate for information recording medium using the same.SOLUTION: A glass plate heat treatment setter ST according to the invention is used for heat treatment of a lamination body which is formed by stacking plural lamination pairs, each of which includes a glass plate heat treatment setter ST and a glass plate to be treated placed thereon. The glass plate heat treatment setter ST is a plate-like member having an upper surface SFa and a lower surface SFb facing each other in parallel and an edge ED formed from the upper surface SFa to the lower surface SFb, in which surface roughness of the edge ED is smaller than the surface roughness of the upper surface SFa and the lower surface SFb.

Description

  The present invention relates to a glass plate heat treatment setter, and more particularly to a glass plate heat treatment setter capable of reducing defects generated in a glass plate. And this invention relates to the manufacturing method of the glass substrate for information recording media which manufactures the glass substrate for information recording media using this setter for glass plate heat processing.

  Glass substrates are used as various substrates due to their physical properties. For example, glass substrates are used as flat display panel substrates and information recording medium substrates. For example, when used as a substrate for this information recording medium, a recording layer using magnetism, light, magneto-magnetism, etc. is formed on a glass substrate to form an information recording medium, typically used for a hard disk drive. There is a magnetic disk to be played. In recent years, the magnetic disk used in this hard disk drive has been required to reduce the flying height of the magnetic head in order to improve the recording density, and has an excellent surface smoothness instead of the conventional aluminum substrate. In particular, glass substrates are often used because of the small number of defects.

  Glass substrates used for such various applications are often manufactured through a heat treatment process. In the heat treatment step of applying a predetermined heat treatment to the glass substrate, a glass substrate heat treatment setter is generally used to transport the glass substrate into a heating furnace and support the glass substrate during the heat treatment. This setter for heat treatment of a glass substrate is generally made of a heat-resistant material with little thermal expansion and contraction in accordance with the heat treatment in order to suppress warpage occurring during the heat treatment, and has a flat and smooth mounting surface. A plate-shaped body provided. The glass substrate to be heat-treated is placed on the placement surface of the setter for heat-treating glass substrate, conveyed into a heating furnace, and heat-treated.

  Such a glass substrate heat treatment setter is disclosed in, for example, Patent Document 1. The setter for heat treatment of a glass substrate disclosed in Patent Document 1 is a setter for heat treatment of a rectangular flat glass substrate that is fed to a heating furnace by a conveying means in a state where the glass substrate is placed on the surface, As the contour shape of the longitudinal cross section perpendicular to the direction along the side edge of the end portion moves from the start end position to the outer side, respectively, with the start end positions of the front and back surfaces parallel to each other as boundaries. It consists of asymptotic lines consisting of straight lines that gradually approach the central portion in the thickness direction, and convex curved lines that continue to the outer ends of these asymptotic lines, and the angle θ between the front and back surfaces and each asymptotic line is 10 It is ˜30 °, and the convex curve line is smoothly connected to the outer end of each asymptotic line, and the length of each asymptotic line is longer than the length of the convex curve line. . According to Patent Document 1, such a setter for heat treatment of a glass substrate is caused by the end of the setter on which the glass substrate is placed abutting or colliding with a conveying means for guiding the setter to a heating furnace. Thus, it is possible to suppress as much as possible the problem of chipping or cracking at the end of the setter.

Japanese Patent No. 4399720

  By the way, for example, in a recording head floating type information recording apparatus that floats a recording head from the recording surface of an information recording medium such as a hard disk drive and reads / writes data to / from the recording layer, the recording layer of the information recording medium and the recording layer In order to avoid defects such as head crashes and data write errors and read errors with the levitated recording head, smoothness and low surface defect on the surface of the recording layer are required, and as a result, the recording A glass substrate for an information recording medium that forms a surface is also required to have improved smoothness and reduced surface defects.

  In particular, in the case of hard disk drives, in recent years, in order to improve the recording density, the flying height between the magnetic head and the surface of the magnetic recording layer is required to be an extremely short interval of, for example, several nm to several tens of nm. For this reason, the glass substrate for information recording media is also required to have high smoothness and low surface defect that can cope with it.

  The present invention has been made in view of the above circumstances, and its object is to provide a setter for heat treatment of a glass plate capable of further improving smoothness and reducing surface defects, and an information recording medium using the setter. It is providing the manufacturing method of a glass substrate.

  As a result of various investigations and examinations, the present inventor has found that the surface roughness of the setter for glass substrate heat treatment used in the heat treatment step (annealing) performed at a relatively early stage in the manufacturing process of the glass substrate for information recording medium. Was found to be the cause of surface defects in the finally obtained glass substrate for information recording media, and the above object was found to be achieved by the present invention described below. That is, the setter for glass plate heat treatment according to one aspect of the present invention is a laminate in which a plurality of pairs of laminates in which a glass plate to be treated and a setter for glass plate heat treatment on which the glass plate is placed are further laminated. The glass plate heat treatment setter used to perform a predetermined heat treatment in the state of the laminated body, wherein the upper surface and the lower surface that are parallel to each other and the end surface that extends from the upper surface to the lower surface The surface roughness of the end surface is smaller than the surface roughness of the upper surface and the surface roughness of the lower surface.

  In the glass plate heat treatment setter having such a configuration, when the glass plate and the glass plate heat treatment setter are in contact with each other when forming the laminate, or after the heat treatment, the glass plate and the glass plate heat treatment setter are removed from the laminate. When the glass plate and the setter for heat treatment of glass plate come into contact with each other, the surface roughness of the end surface of the setter for heat treatment of glass plate is smaller than the surface roughness of the upper and lower surfaces. Further, the occurrence of defects in the glass plate is reduced, and the generation of chipping on the glass plate and the setter for heat treatment of the glass plate due to contact is also reduced. For this reason, the setter for heat treatment of a glass plate having such a configuration can improve smoothness and reduce surface defects with respect to a predetermined glass substrate generated from the glass plate, for example, a glass substrate for information recording media. it can.

  According to another aspect, in the setter for glass plate heat treatment described above, the Ra value of the surface roughness of the end face is 0.005 μm ≦ Ra ≦ 0.4 μm.

  The glass plate heat-treating setter having such a configuration can improve the smoothness and reduce the surface defects with respect to a predetermined glass substrate generated from the glass plate, as will be apparent from examples described later. .

  According to another aspect, in the above-described setter for glass plate heat treatment, the upper surface, the end surface, and the lower surface always have a differential line with a contour line of a longitudinal section including a normal direction of the upper surface. It is characterized by being continuously connected.

  The setter for glass plate heat treatment having such a configuration has no singular point having a differential coefficient in the contour line and has no so-called corner on the surface thereof, so that it is more smooth than a predetermined glass substrate generated from the glass plate. Can be improved and surface defects can be reduced.

  According to another aspect, in the setter for glass plate heat treatment described above, the end surface satisfies 0.15 t ≦ R ≦ 0.5 t, where t is the thickness from the upper surface to the lower surface. It is formed by R chamfering.

  The glass plate heat-treating setter having such a configuration can improve the smoothness and reduce the surface defects with respect to a predetermined glass substrate generated from the glass plate, as will be apparent from examples described later. .

  Moreover, in the manufacturing method of the glass substrate for information recording media which comprises at least the heat processing process which performs predetermined heat processing to the several glass plate of the process target concerning other one aspect | mode, the said heat processing in the manufacturing method of the glass substrate for information recording media. The step forms a laminate by alternately laminating the plurality of glass plates and a plurality of glass plate heat treatment setters for placing the glass plates, with the glass plate heat treatment setter as the bottom layer. An alternating lamination step, a heating step for heating the laminate, and a lamination separation step for separating the plurality of glass plates and the plurality of glass plate heat treatment setters from the laminate after the heating step, respectively. The glass plate heat treatment setter is any one of the glass plate heat treatment setters described above.

  Since the manufacturing method of the glass substrate for information recording media having such a configuration uses any of the above-described glass plate heat treatment setters in the heat treatment step, it is further reduced that the glass plate heat treatment setter causes defects in the glass plate. In addition, the generation of chipping on the glass plate and chipping on the setter for heat treatment of the glass plate due to the contact is reduced. For this reason, the manufacturing method of the glass substrate for information recording media having such a configuration improves the smoothness and reduces surface defects with respect to a predetermined glass substrate generated from a glass plate, for example, a glass substrate for information recording media. Can be achieved.

  The setter for heat treatment of a glass plate and a method for producing a glass substrate for an information recording medium using the same according to the present invention are improved in smoothness and reduced in surface defects with respect to a glass substrate for an information recording medium produced from a glass plate. Can be achieved.

It is a figure for demonstrating the setter for glass plate heat processing in embodiment. It is a figure for demonstrating the heat processing process using the setter for glass plate heat processing of embodiment. It is a flowchart which shows the manufacturing method of the glass substrate for information recording media using the setter in this embodiment. It is a partial cross section perspective view showing a magnetic disk which is an example of a magnetic recording medium using the glass substrate for information recording media of an embodiment. It is a figure which shows the cross-sectional shape of each setter in 1st new 5th Example.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted suitably.

(Embodiment)
Drawing 1 is a figure for explaining a setter for glass plate heat treatment in an embodiment. FIG. 1A is a cross-sectional view showing a setter for heat treatment of a glass plate according to an embodiment and an enlarged cross-sectional view in which an end is enlarged, and FIG. 1B is an enlarged cross-sectional view of an end for comparison. . Drawing 2 is a figure for explaining the heat treatment process using the setter for glass plate heat treatment of an embodiment.

  In the present embodiment, the setter ST for heat treatment of a glass plate, when subjecting a glass plate to be treated to a predetermined heat treatment, carries the glass plate into a furnace and heats the glass plate in the furnace. It is used to support the glass plate when unloading the glass plate.

  Such a glass plate heat treatment setter ST has a predetermined thickness and a predetermined shape as shown in FIG. 1 (A), and an upper surface SFa and a lower surface SFb facing each other, and a lower surface from the upper surface SFa. It is a plate-shaped body provided with end surface ED which reaches surface SFb. The upper surface SFa and the lower surface SFb are parallel to each other. That is, the end surface ED starts from the peripheral portion of the upper surface SFa where the upper surface SFa is not parallel to the lower surface FSb, and is the peripheral portion of the lower surface SFb where the lower surface SFb is not parallel to the upper surface FSa. End. The predetermined thickness and the predetermined shape may be any thickness and arbitrary shape suitable for this purpose because the setter ST for heat treatment of the glass plate supports the glass plate to be processed. The predetermined shape is, for example, preferably a shape similar to the shape of the glass plate in plan view and slightly larger than the glass plate. In the present embodiment, the glass plate is processed into a glass substrate for an information recording medium, and thus has a disk shape in plan view. Therefore, the predetermined shape of the setter ST for heat treatment of a glass plate of the present embodiment is In plan view, it has a slightly larger disk shape. One or both of the upper surface SFa and the lower surface SFb is a mounting surface on which a glass plate is mounted, and is flat and has a predetermined surface roughness.

  And since the setter ST for glass plate heat treatment is used for heat treatment, a heat-resistant material with little thermal expansion and contraction according to the heat treatment (for example, heat-resistant glass such as alumina-based ceramics or Pyrex (registered trademark)). Formed with.

  Here, in the setter ST for heat treatment of a glass plate of the present embodiment, the surface roughness of the end surface ED is smaller than the surface roughness of the upper surface SFa and the surface roughness of the lower surface SFb. That is, the end surface ED in the setter ST for heat treatment of a glass plate of the present embodiment is not rougher than the upper surface SFa and the lower surface SFb as shown in FIG. 1 (B), and as shown in FIG. It is smoother than the upper surface SFa and the lower surface SFb. The surface roughness is represented by, for example, an Ra value that is an arithmetic average roughness defined in JIS B 0601. The end surface ED in the setter ST for heat treatment of glass plate according to this embodiment is polished by using known conventional means so as to be smaller than the surface roughness of the upper surface SFa and the surface roughness of the lower surface SFb. Can be formed.

  Then, in a predetermined heat treatment step of performing a predetermined heat treatment on a plurality of glass plates to be processed, the setter ST for glass plate heat treatment of the present embodiment is used as shown in FIG. 2, for example.

  In the heat treatment step shown in FIG. 2 inherited from a predetermined previous step performed before the heat treatment step, first, an alternate lamination step is performed, then a heating step is performed, and then a lamination separation step is performed. And when this heat treatment process is completed, it is taken over to a predetermined post-treatment process performed after the heat treatment process.

  In the alternate lamination process, a plurality of glass plates G to be processed and a plurality of glass plate heat treatment setters ST for placing the glass plates G are alternately laminated with the glass plate heat treatment setter ST as the lowermost layer. Thus, the laminated body LS is formed. When manufacturing the glass substrate for information recording media, this glass plate G is glass which is not processed as a glass substrate for information recording media, and is called a blank material.

  More specifically, as shown on the left side of FIG. 2, a glass plate stack in which a plurality of glass plates (blank materials) G are previously stacked is prepared, and a plurality of glass plate heat treatment setters ST are previously stacked. A setter stack for plate heat treatment is prepared. Next, one glass plate heat treatment setter ST is first picked up from the glass plate heat treatment setter stack by the robot arm RA and placed at a predetermined position. The robot arm RA is configured to pick up, move, and release the glass plate heat treatment center ST and the glass plate G. The robot arm RA, for example, attaches and detaches the work by applying a suction force to the work (here, the glass plate heat treatment center ST and the glass plate G) attached to the tip and a link mechanism capable of moving the tip. And a workpiece attaching / detaching portion that can be configured. The suction force can be generated, for example, by drawing air with a pump or the like. Next, one glass plate G is picked up from the glass plate stack by the robot arm RA and arranged so as to be stacked on the glass plate heat treatment setter ST arranged at the predetermined position. Next, the next glass plate heat treatment setter ST is picked up by the robot arm RA from the glass plate heat treatment setter stack and laminated on the glass plate G laminated on the glass plate heat treatment setter ST. Placed. Next, similarly, the next one glass plate G is picked up from the glass plate stack by the robot arm RA and arranged so as to be laminated on the glass plate heat treatment setter ST laminated on the glass plate G. The Similarly, a laminate LS in which the setters ST for glass plate heat treatment and the glass plates G are alternately stacked one by one, a predetermined number of glass plates G are stacked, and the setter ST for glass plate heat treatment is sandwiched between the lowermost layer and the lower layer. Is formed.

  The heating process heats the stacked body LS formed by the alternate stacking process. More specifically, for example, as shown in the center of FIG. 2, the stacked body LS formed by the alternate stacking step is transported into a heating furnace such as an electric furnace, and then, for a predetermined time, for a predetermined time. It is heated at the temperature, and when the heating is finished, it is taken out from the heating furnace. For example, in the case of manufacturing a glass substrate for information recording media, the heating process releases the residual stress generated during press forming, which is the previous process of the heat treatment process, eliminates warping, and crystallizes amorphous glass. Is promoted.

  The lamination separation step separates the laminated body LS after the heating step into a plurality of glass plates G and a plurality of glass plate heat treatment setters ST. More specifically, as shown on the right side of FIG. 2, the laminate LS unloaded from the heating furnace is picked up one by one from the top by the robot arm RA. In addition to being placed in a predetermined place for the plate G, when the setter ST for heat-treating the glass plate is taken up, it is placed in a predetermined place for the setter for heat-treating the glass plate. Thereby, the stacked body LS is separated into a plurality of glass plates G and a plurality of glass plate heat treatment setters ST, respectively.

  In such a glass plate heat treatment setter ST of this embodiment, for example, as shown by P1 on the left side of FIG. 2, the glass plate G and the glass plate heat treatment setter ST are in contact with each other when the laminate LS is formed. In some cases, as indicated by P2 on the right side of FIG. 2, the glass plate G and the glass plate heat treatment setter ST are in contact with each other when the glass plate G and the glass plate heat treatment setter ST are separated from the laminate LS after the heat treatment. In this case, since the surface roughness of the end surface of the glass plate heat treatment setter ST is smaller than the surface roughness of the upper and lower surfaces SFa and SFb, the glass plate heat treatment setter ST is less likely to cause defects in the glass plate G. Moreover, the generation | occurrence | production of the chip of the glass plate G accompanying the contact and the chip of the setter ST for glass plate heat processing are also reduced. For this reason, the setter ST for heat treatment of a glass plate having such a configuration is improved in smoothness and surface defects with respect to a final predetermined glass substrate generated from the glass plate G, for example, a glass substrate for information recording media. Reduction can be achieved.

<Method for producing glass substrate for information recording medium>
Next, the manufacturing method of the glass substrate for information recording media using setter ST in this embodiment is demonstrated. FIG. 3 is a flowchart showing a method for manufacturing a glass substrate for an information recording medium using the setter in the present embodiment.

(Glass melting process)
In the production of the information recording medium glass substrate shown in FIG. 3, first, a glass melting step of melting a glass material is performed (S11). As the material of the glass substrate for information recording medium, for example, soda lime glass mainly composed of SiO ₂ , Na ₂ O, CaO, SiO ₂ , Al ₂ O ₃ , R ′ ₂ O (R ′ is K, Na, Aluminosilicate glass or borosilicate glass mainly composed of one or more elements selected from Li), Li ₂ O—SiO ₂ glass, Li ₂ O—Al ₂ O ₃ —SiO ₂ glass, and , RO—Al ₂ O ₃ —SiO ₂ glass (R is one element selected from Mg, Ca, Sr, and Ba). Among these, aluminosilicate glass and borosilicate glass are particularly preferable because they are excellent in impact resistance and vibration resistance.

(Molding process)
Next, the shaping | molding process which shape | molds the predetermined | prescribed glass plate G (blank material B) from the glass raw material fuse | melted at the glass melting process is performed (S12). In this molding step, first, the glass melted in the glass melting step is poured into the lower die, and then this is press-molded by the upper die. Thereby, for example, a disc-shaped blank material B is obtained. In addition, this disc-shaped blank B may be produced by cutting out a sheet glass formed by, for example, a downdraw method or a float method with a grinding stone, without using press molding. The magnitude | size of the blank material B may be a desired dimension (size), and is not specifically limited. The blank material B may have various sizes such as, for example, an outer diameter of 2.5 inches, 1.8 inches, 1 inch, and 0.8 inches. Moreover, the thickness of the blank material B may also be a desired dimension, and is not specifically limited. The blank material B may have various thicknesses such as 2 mm, 1 mm, and 0.63 mm.

(Heat treatment process)
Next, a heat treatment step for heating the blank material B obtained in the molding step at a predetermined temperature is performed (S13). In this heat treatment step, a plurality of blank materials (press glass substrate or cut glass substrate) B and a plurality of setters ST of the present embodiment are alternately laminated one by one, and this alternately laminated laminate LS is heated at high temperature. It is transported into the furnace and passed through a high temperature electric furnace. Thereby, the warp of the blank material B is eliminated, and the glass crystallization of the blank material B is promoted, and the glass substrate GS is generated.

(First lapping process)
Next, the 1st lapping process which polishes the glass substrate GS heat-processed at the heat processing process is performed (S14). In the first lapping step, both surfaces (upper surface and lower surface) of the glass substrate GS are polished. This preliminarily adjusts the parallelism, flatness and thickness of the glass substrate GS.

(Coring process)
Next, in order to create a glass substrate for an information recording medium, a coring process step of opening a through hole in the glass substrate GS that has undergone the first lapping step is performed (S15). In this coring process, a through hole (hole) is formed by grinding, for example, with a core drill or the like at the center of the glass substrate GS after the first lapping process. This core drill is a tool provided with a diamond grindstone or the like in a cutter portion.

(Inner / outer diameter machining process)
Next, an inner / outer diameter processing step for processing the inner and outer diameters of the coring-processed glass substrate is performed (S16). In this inner and outer diameter processing step, the inner and outer diameters are processed by grinding the outer peripheral end surface of the glass substrate GS and the inner peripheral end surface of the through hole opened by coring with a grinding wheel such as a drum-shaped diamond. . Accordingly, the inner diameter (inner diameter) and the outer diameter (outer diameter) are adjusted to predetermined dimensions.

(Second wrapping process)
Next, a second lapping process for further polishing the glass substrate GS having the inner and outer diameters processed is performed (S17). In the second lapping step, both surfaces of the glass substrate GS are polished again. Thereby, the parallelism, flatness and thickness of the glass substrate GS are finely adjusted to predetermined dimensions.

  In the first and second lapping processes, a known polishing machine called a double-side polishing machine using a planetary gear mechanism can be used as a polishing machine that polishes the front and back surfaces of the glass substrate GS. This double-side polishing machine includes a disk-shaped upper surface plate and a lower surface plate that are arranged vertically so as to be parallel to each other, and rotate in opposite directions. A plurality of diamond pellets for polishing the main surface of the glass substrate GS are attached to the opposing surfaces of the upper and lower surface plates facing each other. Between the upper surface plate and the lower surface plate, there are a plurality of carriers that rotate in combination with an internal gear provided in an annular shape on the outer periphery of the lower surface plate and a sun gear provided around the rotation axis of the lower surface plate. . The carrier is provided with a plurality of holes, and a plurality of glass substrates GS are respectively fitted into the plurality of holes. Each of the upper surface plate, the lower surface plate, the internal gear, and the sun gear can be operated by separate driving.

  In the polishing operation of the polishing machine, the upper surface plate and the lower surface plate rotate in opposite directions, and the carrier sandwiched between the upper surface plate and the lower surface plate via the diamond pellets holds a plurality of glass substrates GS. In this state, it revolves in the same direction as the lower surface plate with respect to the rotation center of the upper surface plate and lower surface plate while rotating. In the polishing machine operating in this way, the glass substrate GS is polished by supplying the grinding liquid between the upper surface plate and the glass substrate GS and between the lower surface plate and the glass substrate GS, respectively.

When using this double-side polishing machine, the weight applied by the upper and lower surface plates applied to the glass substrate GS and the number of rotations of the upper and lower surface plates are appropriately adjusted according to the desired polishing state. The weight in the first and second lapping steps is preferably 60 g / cm ² to 120 g / cm ² . Further, the number of rotations of the upper and lower surface plates is set to about 10 to 30 rpm, and the number of rotations of the upper surface plate is preferably made 30 to 40% slower than the number of rotations of the lower surface plate. By increasing the load on the upper and lower surface plates and increasing the rotational speed of the upper and lower surface plates, the polishing amount increases, but if the load is increased too much, the surface roughness will not be good and the rotational speed will be high. If it passes, flatness will not become favorable. Further, when the load is small and the rotation speed of the upper and lower surface plates is slow, the polishing amount is small and the production efficiency is lowered.

  When the second lapping process is completed, defects such as large undulations, chips and cracks are removed, and the surface roughness of the main surface of the glass substrate GS is preferably about 0.2 μm to 0.4 μm in Ra value. The flatness of the main surface is preferably 7 to 10 μm. By maintaining such a surface state, it is possible to efficiently perform polishing in the next first polishing step.

  Here, the surface roughness in this application is the value which measured the range of 1 micrometer x 1 micrometer using the atomic force microscope (Digital Instruments company nanoscope). The flatness in the present application is a value measured by a flatness measuring device, and is a difference in height (PV value) between the highest position and the lowest position on the surface of the glass substrate GS.

  In the first lapping step, roughly large undulations, chips and cracks are removed so that the second lapping step can be performed efficiently. For this reason, the diamond pellet used in the first lapping step is preferably about # 800 mesh to # 1200 mesh, which is coarser than # 1300 mesh to # 1700 mesh. The surface roughness at the time when the first lapping step is completed preferably has an Ra value of about 0.4 μm to 0.8 μm, and the flatness of the main surface is preferably 10 to 15 μm.

  Moreover, it is preferable to perform a washing | cleaning process in order to remove the abrasive | polishing agent and glass powder which remained on the surface of the glass substrate GS after a 1st lapping process and a 2nd lapping process.

(End polishing process)
Next, an end surface polishing step for polishing the end surface of the glass substrate GS after the second lapping step is performed (S18). In this end surface polishing process, the outer peripheral surface and the inner peripheral surface of the glass substrate GS after the second lapping step are polished by, for example, an end surface polishing machine.

(First polishing process)
Next, a first polishing process is performed on the glass substrate GS that has undergone the end face polishing process (S19). In the first polishing step, the surface roughness is improved and the final surface roughness required in the second polishing step performed after the next chemical strengthening step can be efficiently obtained. Polishing is performed so that the shape can be obtained efficiently. The polishing in the first polishing process is the same as the polishing machine used in the first and second lapping processes except that a pad and a polishing liquid are used instead of the diamond pellets and the grinding liquid used in the lapping process. A construction grinder is used.

  The pad used in the first polishing step is preferably a hard pad having a hardness A of about 80 to 90, and for example, urethane foam is used. Since the change in the shape of the polishing surface increases when the hardness of the pad becomes soft due to heat generated by polishing, it is preferable to use a hard pad. The abrasive is preferably a slurry obtained by dispersing cerium oxide having a particle size of 0.6 to 2.5 μm in water. The mixing ratio of water and abrasive in this abrasive is preferably about 1: 9 to 3: 7.

In the first polishing step, the weight applied to the glass substrate by the upper and lower surface plates is preferably 90 g / cm ² to 110 g / cm ² . The weight applied to the glass substrate by the upper and lower surface plates greatly affects the shape of the outer peripheral edge. When this weight is increased, the inner side of the outer peripheral end portion tends to decrease and increase toward the outer side. Moreover, when this weight is reduced, the outer peripheral end portion tends to become closer to a plane and the surface sagging increases. The weight is determined while observing such a tendency.

  Further, in order to improve the surface roughness, the rotation speed of the upper and lower surface plates is preferably 25 rpm to 50 rpm, and the rotation speed of the upper surface plate is made 30% to 40% slower than the rotation speed of the lower surface plate. .

  The polishing amount is preferably 30 to 40 μm depending on the polishing conditions. If it is less than 30 μm, scratches and defects cannot be sufficiently removed, which is not preferable. Further, in the case of exceeding 40 μm, the surface roughness can be in the range of Rmax from 2 nm to 60 nm and Ra from 2 nm to 4 nm. However, it is preferable because polishing is performed more than necessary and manufacturing efficiency is reduced. Absent.

(Chemical strengthening process)
Next, a chemical strengthening step for forming a chemically strengthened layer on the glass substrate GS that has undergone the first polishing step is performed (S20). In this chemical strengthening step, the glass substrate GS after the first polishing step is immersed in the chemical strengthening solution. Thereby, a chemically strengthened layer is formed on the inner peripheral end face and the outer peripheral end face of the glass substrate GS. By forming a chemically strengthened layer on the inner and outer peripheral end faces, impact resistance, vibration resistance, heat resistance, etc. are improved, and warpage and surface roughening due to chemical strengthening of the main surface are prevented. The

  In this chemical strengthening step, a so-called ion exchange method is performed. More specifically, by immersing the glass substrate GS in a heated chemical strengthening solution, alkali metal ions such as lithium ions and sodium ions contained in the glass substrate GS are replaced with potassium ions having a larger ion radius. It is replaced by the alkali metal ion. Compressive stress is generated in the ion-exchanged region due to strain caused by the difference in ion radius, and the inner peripheral end surface and the outer peripheral end surface of the glass substrate GS are strengthened.

  There is no restriction | limiting in particular in this chemical strengthening liquid, A well-known chemical strengthening process liquid can be used. As the chemical strengthening liquid, a molten salt containing potassium ions or a molten salt containing potassium ions and sodium ions is usually used. Examples of the molten salt containing potassium ion or sodium ion include potassium, sodium nitrate, carbonate, sulfate, and mixed molten salts thereof. Among these, nitrate is preferable from the viewpoint that the melting point is low and deformation of the glass substrate can be prevented.

(Second polishing step)
Next, a second polishing process is performed on the glass substrate GS that has undergone the chemical strengthening process (S21). This second polishing step is a step of further precisely polishing the surface of the glass substrate GS after the chemical strengthening step, and is performed by the same polishing method as the first polishing step. The pad used in the second polishing process is preferably a soft pad having a hardness of about 65 to 80 (Asker-C), which is softer than the pad used in the first polishing process, such as urethane foam or suede. As the abrasive, cerium oxide or the like similar to that in the first polishing step can be used, but in order to make the surface of the glass substrate GS smoother, an abrasive having a finer particle size and less variation is preferably used. The polishing liquid is a slurry in which an abrasive having an average particle size of 40 nm to 70 nm is dispersed in water, and preferably the mixing ratio of water and abrasive is approximately 1: 9 to 3 : About 7.

The weight applied to the glass substrate GS by the upper and lower surface plates is preferably 90 g / cm ² to 110 g / cm ² . The number of rotations of the upper and lower surface plates is preferably 15 rpm to 35 rpm, and preferably the number of rotations of the upper surface plate is 30% to 40% slower than the number of rotations of the lower surface plate.

  By adjusting the polishing conditions in the second polishing step, the target flatness can be 3 μm or less, and the surface roughness Ra value can be 0.1 nm.

  The polishing amount in the second polishing step is preferably 2 μm to 5 μm. By setting the polishing amount within this range, it is possible to efficiently remove minute defects such as minute roughness and undulation generated on the surface, and minute scratches generated in the previous steps.

(Washing process)
Next, a cleaning process for cleaning the glass substrate GS that has undergone the second polishing process is performed (S22). The glass substrate GS after the cleaning step is, for example, an information recording medium glass substrate 101 used as an information recording medium substrate. In this cleaning process, the cleaning method is not particularly limited as long as the cleaning method can cleanly clean the surface of the glass substrate GS after the second polishing process. For example, scrub cleaning is performed in this cleaning process.

  The glass substrate GS that has been subjected to scrub cleaning is subjected to ultrasonic detergent cleaning and drying treatment as necessary. The drying process is a process of removing the cleaning liquid remaining on the surface of the glass substrate GS using IPA (isopropyl alcohol) or the like and drying the substrate surface. For example, the glass substrate GS after scrub cleaning is subjected to a water rinse cleaning process for 2 minutes, and the residue of the cleaning liquid is removed. Next, an IPA cleaning process is performed for 2 minutes to remove water on the substrate. Finally, the IPA vapor drying process is performed for 2 minutes, and the liquid IPA adhering to the substrate is dried while being removed by the IPA vapor. The substrate drying process is not limited to this, and may be a generally known method for drying the glass substrate GS such as spin drying or air knife drying.

(Inspection process)
And the test | inspection process which performs a predetermined test | inspection with respect to the glass substrate GS which passed through the washing | cleaning process is performed (S23). In this inspection process, inspections such as visual scratches, cracks, and adhesion of foreign substances are performed. Adhesion of foreign matter that cannot be discerned visually is inspected by using an optical surface analyzer (OSA (Optical Surface Analyzer), manufactured by KLA-TENCOL, OSA6100).

  The glass substrate GS determined to be a non-defective product in this inspection process is stored in a glass substrate storage cassette and vacuum-packed in a clean environment so that foreign matter or the like does not adhere to the surface. Shipped as a glass substrate 101 for use.

<Magnetic recording medium>
Next, a magnetic recording medium using the glass substrate for information recording medium of this 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 of the embodiment. The magnetic disk D includes a magnetic film 102 formed on the 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 method of 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, or a magnetic film by sputtering on the glass substrate 101 for information recording medium. Examples thereof include a forming method for forming 102 and a forming method for forming the magnetic film 102 on the glass substrate 101 for information recording medium by electroless plating. The thickness of the magnetic film 102 is about 0.3 μm to 1.2 μm in the case of the spin coating method, and about 0.04 μm to 0.08 μm in the case of the sputtering method, and is based on the electroless plating method. In some cases, the thickness is about 0.05 μm 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.

  Such a magnetic recording medium based on the information recording medium glass substrate 101 according to the present embodiment has a high smoothness and a low surface defect as described above. The magnetic head can be stably operated during rotation.

  In the above description, the case where the glass substrate 101 for information recording medium in the present embodiment is used as a magnetic recording medium has been described. However, the present invention is not limited to this, and the glass substrate 101 for information recording medium in the present embodiment is It can also be used for magneto-optical disks and optical disks.

(Examples and Comparative Examples)
Next, first to fifth examples and comparative examples will be described. FIG. 5 is a diagram showing a cross-sectional shape of each setter in the first and fifth embodiments. 5A is the setter of the first embodiment, FIG. 5B is the setter of the second embodiment, and FIG. 5C is the setter of the third embodiment. (D) is the setter of the fourth embodiment, and FIG. 5 (E) is the setter of the fifth embodiment.

<First to fifth embodiments>
Glass substrates GSa to GSe corresponding to the first to fifth examples were produced by the manufacturing method shown in FIG. 3 using the setters STa to STe in the first to fifth examples. Each manufacturing process (S11-S23) is as follows.

(Glass melting step S11 and molding step S12)
In the glass melting step S11 and the molding step S12, an aluminosilicate glass having a glass transition temperature Tg of 480 ° C. is used as a glass material. By press molding the molten glass, the outer diameter is φ68 mm and the thickness is 1. The blank material B which is 3 mm was produced.

(Heat treatment step S13)
In the heat treatment step S13, a laminate in which a total of 50 blanks B and the setters ST of the example were alternately laminated was conveyed into an electric furnace at about 430 ° C., and heat treatment was performed for 2 hours. Five types of setters STa to STe of the first to fifth embodiments were prepared as the setter ST of the embodiment. In the setters STa to STe of the first to fifth embodiments, after sintering and forming alumina into a schematic shape, both surfaces are ground with a # 3000 grindstone and end faces are ground with a # 4000 grindstone. After that, by polishing with an alumina brush, the outer diameter was 70 mm and the thickness was 2 mm. The surface roughness of both surfaces in the setters STa to STe of the first to fifth examples had an Ra value of 0.5 μm, and the surface roughness of these end portions had an Ra value of 0.4 μm. The Ra value of the surface roughness is an arithmetic average roughness defined in JIS B 0601, and was measured under the condition that the measurement cutoff value is 0.8 mm and the measurement length is 4 mm.

  The cross-sectional shape of the end of the setter STa of the first embodiment is a C chamfer of C0.5, as shown in FIG.

  The cross-sectional shape of the end of the setter STa of the second embodiment is an R chamfer of R0.2 (R0.2, thickness t = 2 mm; t / 2,. 1t).

  As shown in FIG. 5C, the cross-sectional shape of the end portion of the setter STa of the third embodiment is an R chamfer of R0.3 (R0.3, thickness t = 2 mm; t / 2,. 15t).

  As shown in FIG. 5D, the cross-sectional shape of the end portion of the setter STa of the fourth embodiment is an R chamfer of R0.7 (R0.7, thickness t = 2 mm; t / 2,. 35t).

  The cross-sectional shape of the end of the setter STa of the fifth embodiment is an R chamfer of R1 (R1, thickness t = 2 mm; t / 2, 0.5t) as shown in FIG.

(First wrapping step S14)
In the first lapping step S14, both surfaces of the glass substrate GS were polished using a polishing machine (manufactured by HAMAI). Polishing conditions, using a # 1200 mesh as diamond pellets, load and 100 g / cm ^2, and 30rpm rotation rate of the upper stool and was 10rpm rotation rate of the lower stool. The polishing amount was 100 μm.

  The average flatness with respect to 100 glass substrates GS obtained in this way was 15 μm, and the surface roughness Ra value was 0.50 μm.

(Coring process S15)
In the coring step S15, a circular hole having a diameter of 18 mm was formed in the center of the glass substrate GS using a cylindrical diamond grindstone.

(Inner / outer diameter machining step S16)
In the inner / outer diameter processing step S16, inner diameter processing and outer diameter processing were performed with a drum-shaped diamond grindstone, the inner diameter of the glass substrate GS was set to 20 mm, and the outer diameter was set to 65 mm.

(Second wrapping step S17)
In the second lapping step S17, both surfaces of the glass substrate GS were polished using a polishing machine (manufactured by HAMAI). Polishing conditions, using a # 1200 mesh as diamond pellets, load and 100 g / cm ^2, and 30rpm rotation rate of the upper stool and was 10rpm rotation rate of the lower stool.

  The average flatness with respect to 100 glass substrates GS thus obtained was 10 μm, and the surface roughness Ra value was 0.25 μm.

(End face polishing step S18)
In the end surface polishing step S18, 100 glass substrates GS were stacked, and the inner peripheral end surface and the outer peripheral end surface were polished using an end surface polishing machine. Nylon fibers having a diameter of 0.2 mm were used for the brush bristles of the polishing machine. As the polishing liquid, cerium oxide having a particle diameter of 3 μm was used. The Ra roughness of the surface roughness of the inner peripheral end face of the glass substrate GS thus obtained was 0.03 μm.

(First polishing step S19)
In the first polishing step S19, a polishing machine (manufactured by HAMAI) was used, and urethane foam having a hardness A of 80 degrees was used for this pad. As the abrasive, cerium oxide having an average particle diameter of 1.5 μm dispersed in water to form a slurry was used. The mixing ratio of water and abrasive was 2: 8. The polishing conditions were a load of 100 g / cm ² , a rotation speed of the upper surface plate of 30 rpm, and a rotation speed of the lower surface plate of 10 rpm. The polishing amount was 30 μm. The average flatness with respect to 100 glass substrates GS obtained in this manner was 4 μm, and the surface roughness Ra value was 0.7 nm.

(Chemical strengthening step S20)
In the chemical strengthening step S20, the glass substrate GS was immersed in the chemical strengthening solution. As this chemical strengthening liquid, a mixed molten salt of potassium nitrate (KNO ₃ ) and sodium nitrate (NaNO ₃ ) was used. The mixing ratio was 1: 1 by mass ratio. Moreover, the temperature of the chemical strengthening solution was 400 ° C., and the immersion time was 40 minutes.

(Second polishing step S21)
In the second polishing step S21, a polishing machine (manufactured by HAMAI) was used, and urethane foam having a hardness A of 70 degrees was used for this pad. As the abrasive, cerium oxide having an average particle diameter of 60 nm was dispersed in water to form a slurry. The mixing ratio of water and abrasive was 2: 8. The polishing conditions were a load of 90 g / cm ² , a rotation speed of the upper surface plate of 30 rpm, and a rotation speed of the lower surface plate of 10 rpm. The polishing amount of the main surface was 5 μm.

(Washing step S22)
In the cleaning step S22, scrub cleaning was performed. As a cleaning solution, a cleaning solution in which a chemical solution in which KOH and NaOH were mixed at 100: 100 was diluted with ultrapure water (DI water) and a nonionic surfactant was added to improve the cleaning capability was used. The cleaning liquid was supplied by spraying. Then, in order to remove the cleaning liquid remaining on the surface of the glass substrate GS, a water rinse cleaning process is performed for 2 minutes, an IPA (isopropyl alcohol) cleaning process is performed for 2 minutes in an ultrasonic bath, and then the surface is dried by IPA vapor. It was done.

<First and second comparative examples>
The information recording medium glass substrates GSf and GSg corresponding to the first and second comparative examples are the above-described information recording medium glass substrates GSa to GSe corresponding to the first to fifth embodiments, except for the heat treatment step S13. Created by each process.

  The heat treatment step S13 in the first and second comparative examples was performed using the setters STf and STg in the first and second comparative examples.

  In the heat treatment step S13 in the comparative example, a laminate in which the blank material B and the setter ST of the comparative example were alternately laminated in total was transported into an electric furnace at about 430 ° C., and heat treatment was performed for 2 hours. As the setter ST of the comparative example, two types of setters STf and STg of the first and second comparative examples were prepared. The setter STf of the first comparative example was formed by sintering alumina into a rough shape, grinding both surfaces with a # 3000 grindstone, and grinding the ends with a # 1000 grindstone. It was prepared with a diameter of 70 mm and a thickness of 2 mm. The surface roughness of both surfaces in the setter STf of the first comparative example had a Ra value of 0.5 μm, and the surface roughness of the end portion had a Ra value of 0.6 μm. Further, the setter STg of the second comparative example is formed by sintering alumina into a schematic shape, and then grinding both surfaces and ends with a # 3000 grindstone so that the outer diameter is 70 mm and the thickness is 2 mm. Created. The surface roughness of both surfaces and end portions in the setter STg of the second comparative example had a Ra value of 0.5 μm. The Ra value of the surface roughness is an arithmetic average roughness defined in JIS B 0601, and was measured under the condition that the measurement cutoff value is 0.8 mm and the measurement length is 4 mm.

  The cross-sectional shape of the end portions of the setters STf and STg of the first and second comparative examples is C chamfering of C0.5.

<Results of Examples and Comparative Examples>
Thus, 100 glass substrates GSa to GSe corresponding to the first to fifth embodiments according to the method of manufacturing the glass substrate for information recording medium using the setters STa to STe in the first to fifth embodiments, respectively. 100 glass substrates GSf and GSg corresponding to the first and second comparative examples are prepared and manufactured by the method of manufacturing the glass substrate for information recording medium using the setters STf and STg in the first and second comparative examples. It was created one by one. Each of the 100 glass substrates after the cleaning step S22 is evaluated using an optical surface defect measuring apparatus (OSA), and the results of the average number of defects are shown in Table 1.

  Comparing the first to fifth embodiments with the first and second comparative examples, as understood from Table 1, the surface roughness of the end portion is smaller than the surface roughness of the upper and lower surfaces of the setter ST. However, the final glass substrate GS produced through the steps S11 to S22 has a small number of defects. When comparing each of the first to fifth embodiments, the final glass substrate GS has a smaller number of defects when the cross-sectional shape of the end portion of the setter ST is R chamfered than C chamfered. The number of defects is smaller in the R chamfering of R0.3 or more than in the R chamfering of the end portion in ST of R0.2. Accordingly, the cross-sectional shape of the setter ST is such that the contour line representing the contour is continuously connected so that it always has a differential coefficient (continuous so that there is no singular point where the differential coefficient becomes discontinuous). The final glass substrate GS is preferable because the number of defects is small.

  Therefore, from the first to fifth examples and the first and second comparative examples, the setter ST for glass plate heat treatment described above is applied to a predetermined glass substrate GS generated from the glass plate G (blank material B). In order to further improve the smoothness and reduce the surface defects, the following first to third aspects are preferable.

  In the first aspect, the Ra value of the surface roughness of the end surface ED is 0.005 μm ≦ Ra ≦ 0.4 μm. Note that if the Ra value is less than 0.005 μm, it is difficult to realize it, and even if it is realized, the cost increases, which is not preferable.

  In the second aspect, the end surface ED is formed by R chamfering where 0.15 t ≦ R ≦ 0.5 t, where t is the thickness from the upper surface SFa to the lower surface SFb. If 0.5 t is exceeded, the end of the end surface ED has a sharp shape, and the end surface ED has a convex portion. When the end surface ED comes into contact with the glass plate G, the convex portion may damage the glass plate G. This is not desirable.

  In the third aspect, the upper surface SFa, the end surface ED, and the lower surface SFb are continuously connected so that the contour line of the longitudinal section including the normal direction of the upper surface SFa always has a differential coefficient. The setter ST for heat treatment of a glass plate having such a configuration has no singular point having no differential coefficient in the contour line and has no so-called corner on the surface thereof, and therefore, for a predetermined glass substrate GS generated from the glass plate G, Smoothness can be improved and surface defects can be reduced.

  Subsequently, the magnetic recording medium using the glass substrates GSa to GSe corresponding to the first to fifth examples and the glass substrates GSf and GSg corresponding to the first and second comparative examples as the glass substrate 101 for the information recording medium. Was created and a hard disk drive was created. More specifically, first, the magnetic film 102 is formed on 100 glass substrates GSa to GSe corresponding to the first to fifth embodiments and 100 glass substrates GSf and GSg corresponding to the first and second comparative examples. Was formed, and a magnetic recording medium was prepared. From the glass substrate GS side, the magnetic film 102 has an underlayer of about 100 nm made of Ni—Al, a recording layer of 20 nm made of Co—Cr—Pt, and a thickness made of DLC (Diamond Like Carbon). It was formed by sequentially laminating 5 nm protective films.

  A hard disk drive using each of the magnetic recording media thus produced was created, read and write tests were performed using a predetermined recording method, and the presence or absence of head crashes occurring during that time was evaluated. The writing density in the in-plane recording method was 50 Gbit / in 2 and the writing density in the perpendicular recording method was 0.5 Tbit / in 2. In the first to fifth examples, the occurrence of head crashes in each of 100 magnetic recording media was 5 or less, which was a satisfactory result. On the other hand, in the first and second comparative examples, there were six or more head crashes in 100 magnetic recording media, which was at a practically problematic level.

  In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not covered by the claims. To be construed as inclusive.

G Glass plate B Blank material GS Glass substrate D Magnetic disk 101 Glass substrate 102 for information recording medium Magnetic film

Claims (5)

Forming a laminated body by further laminating a plurality of paired laminated bodies in which a glass plate to be treated and a glass plate heat treatment setter on which the glass plate is placed are laminated, and performing a predetermined heat treatment in the state of the laminated body The setter for heat treatment of glass plate used for,
A plate-like body comprising an upper surface and a lower surface that are parallel to each other and an end surface that extends from the upper surface to the lower surface,
The glass plate heat treatment setter characterized in that the surface roughness of the end face is smaller than the surface roughness of the upper surface and the surface roughness of the lower surface. The glass plate heat treatment setter according to claim 1, wherein the Ra value of the surface roughness of the end face is 0.005 μm ≦ Ra ≦ 0.4 μm. The upper surface, the end surface, and the lower surface are continuously connected such that a contour line of a longitudinal section including a normal direction of the upper surface always has a differential coefficient. Item 3. A setter for heat-treating a glass sheet according to Item 2. The end face is formed by R chamfering that satisfies 0.15t ≦ R ≦ 0.5t, where t is a thickness from the upper surface to the lower surface. The setter for glass plate heat treatment according to any one of 3. In the method for producing a glass substrate for information recording medium, comprising at least a heat treatment step for performing a predetermined heat treatment on a plurality of glass plates to be treated, and producing a glass substrate for information recording medium,
The heat treatment step includes
Alternating lamination step of forming a laminate by alternately laminating the plurality of glass plates and a plurality of glass plate heat treatment setters for placing the glass plates, with the glass plate heat treatment setter as the lowest layer. When,
A heating step of heating the laminate;
From the laminated body after the heating step, the plurality of glass plates, and a plurality of glass plate heat treatment setters, respectively, a lamination separation step,
The glass plate heat treatment setter is the glass plate heat treatment setter according to any one of claims 1 to 4. A method for producing a glass substrate for an information recording medium.

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