JP2006225181A - Glass substrate, method of manufacturing glass substrate, glass substrate for magnetic recording medium and method of manufacturing glass substrate for magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for a magnetic recording medium which has prescribed flatness attained by grinding and polishing. <P>SOLUTION: The glass substrate 1 has recessed surfaces 1a, 1b. The glass substrate is formed to have thickness d1 which is the thickest in the outer peripheral part 3 and gradually thinning toward the center part 2 and the thinnest in the center part 2 ((the thickness d1 of the outer peripheral part 3)≥(the thickness d2 of the center part 2)) that means the glass substrate is shaped so that the outer peripheral part 3 is projected compared to the center part 2 and the surface 1a and the surface 1b are warped in the opposed direction. In the grinding of both surfaces, the outer peripheral part 3 is gradually ground to be made flat. The outer peripheral part 3 being in contact with a grind stone of a grinder increases the contact area with the grind stone by the grinding to stably grind the glass substrate 1. The flatness of the the glass substrate is improved after grinding and sufficiently satisfies that required for the glass substrate for the magnetic recording medium. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a glass substrate for a magnetic recording medium used for a substrate of a magnetic disk recording apparatus, and more particularly to a glass substrate for a magnetic recording medium that can be easily flattened by polishing.

  An aluminum alloy or glass disk is used as a substrate in a magnetic disk recording device used in a computer or the like, for example, a hard disk. A metal magnetic thin film is formed on this substrate, and information is recorded by magnetizing the metal magnetic thin film with a magnetic head.

  Conventionally, aluminum alloys have been mainly used as substrates for magnetic recording media. However, in recent years, magnetic disk recording devices have also been adopted in portable personal computers such as notebook computers, and in order to increase the response speed of magnetic disk recording devices, magnetic recording media can be operated at high speeds of 10,000 [rpm] or more. Need to rotate. Accordingly, a substrate for a high-strength magnetic recording medium has been required, and a glass substrate has been used to satisfy these needs. As this glass substrate, an amorphous glass substrate, a crystallized glass substrate, or a chemically strengthened glass substrate is used.

  Here, the manufacturing method of the glass substrate for magnetic recording media is demonstrated easily. First, a method for manufacturing an amorphous glass substrate will be described. First, a glass material is melted (glass melting step), the molten glass is poured into a planar mold, and the molten glass is sandwiched between the molds to be press-molded to produce a disk-shaped glass substrate (press molding) Process). A glass substrate of a semi-finished product that is produced by this press molding process and subjected to the grinding / polishing process described below is referred to as a “blank material”. A hole is made in the center of the blank material, and a doughnut-shaped glass substrate (perforated blank material) is produced.

The doughnut-shaped glass substrate (perforated blanks material) is ground on both surfaces, and the parallelism, flatness, and thickness of the substrate are preliminarily adjusted (first lapping step). The glass substrate whose parallelism is preliminarily adjusted is ground and chamfered on the outer peripheral end surface and the inner peripheral end surface of the hole, and the outer diameter and roundness of the glass substrate, the inner diameter of the hole, and the like are finely adjusted. (End grinding process). The process of cutting with diamond is called a grinding process. The glass substrate whose outer diameter is finely adjusted, the outer peripheral end surface and the inner peripheral end surface are polished, and the end surface is mirror-finished (end surface polishing step). Note that the step of cutting using CeO ₂ is referred to as a polishing step. The glass substrate whose end face is polished is ground again on both surfaces, and the parallelism, flatness, and thickness of the glass substrate are finely adjusted (second lapping step). The glass substrate whose degree of parallelism and the like has been finely adjusted is polished on both surfaces, the surface irregularities are made uniform (polishing step), and finally cleaned. In this way, a glass substrate for a magnetic recording medium as a final product is produced.

  Moreover, when producing a crystallized glass substrate, after an above-mentioned press molding process, an amorphous glass substrate (blanks material) is pinched | interposed with the board | plates made from a ceramic, and it is made to crystallize (crystallization process). After the annealing process, the above-described first lapping process to polishing process are performed.

  Moreover, when producing a chemically strengthened glass substrate, the glass substrate (blanks material) obtained by melting and pressing is subjected to the treatment up to the polishing step, and then mixed with sodium nitrate, potassium nitrate, and the like. By immersing in molten salt, a compressive stress layer is formed on the surface to increase the fracture strength. Thereafter, a cleaning process is performed.

  A magnetic recording medium is manufactured by laminating a magnetic layer or the like on the surface of the glass substrate thus manufactured. Further, the flatness of the glass substrate for a magnetic recording medium as a final product is required to be 8 [μm] or less, preferably 5 [μm] or less, which is a general standard. This flatness is represented by the Max-Min value of the amount of displacement from the virtual reference plane.

  A magnetic head for reading magnetic recording information recorded on a magnetic recording medium is configured to move in a state of floating from the surface of the magnetic recording medium. If the flatness of the magnetic recording medium is high (bad), the magnetic recording medium and the magnetic head collide when the magnetic head moves, and there is a possibility that problems such as damage to the magnetic head and damage to the magnetic recording medium may occur.

  Further, when a magnetic recording medium having a magnetic film formed thereon is assembled and fixed in a hard disk drive, if the flatness is high (poor), the magnetic recording medium may be broken.

  In order to suppress the occurrence of such defects, the glass substrate (blank material) obtained by press molding is subjected to grinding (first lapping step), and after the first lapping step, the flatness is set to 8 [ Attempts to make the surface of the glass substrate parallel and flat have been made (for example, Patent Document 1).

  Further, in order to mass-produce a large number of glass substrates for magnetic recording media with the above flatness, it is necessary to reduce the variation in flatness between the substrates and to reduce the standard deviation. In recent years, a glass substrate having a flatness of 3 [μm] or less and a standard deviation of 0.2 [μm] or less is required.

  As described above, the semi-finished glass substrate (blank material) is produced by pressing the glass material melted in the press molding process with a mold. Thereafter, a first lapping process is performed. The press time in the press molding process is a few seconds, and the glass material is rapidly cooled from a high temperature state heated to 1000 degrees C to normal temperature.

  Usually, the flatness of the glass substrate (blanks material) after a press molding process is 100-150 [micrometers]. Since crystallized glass needs to be subjected to heat treatment for 10 to 30 hours at a high temperature of several hundred degrees Celsius by sandwiching a blanks material with a flat plate such as ceramic in the heat treatment (crystallization step) described above, In addition, the flatness becomes secondary and the flatness becomes about 50 [μm].

  By performing the crystallization process in this way, it becomes possible to improve the flatness, but since the crystallization process is necessary as compared with the amorphous glass substrate, the number of processes increases and the cost also increases. End up. Further, even when the crystallization process is performed, the flatness is only about 50 [μm].

  Therefore, an amorphous glass substrate (blanks material) with a flatness of 100 to 150 [μm] immediately after the press molding process and a crystallized glass (blanks material) with a flatness of about 50 [μm] are used in the first lapping process. It is necessary to grind and process the flatness to 8 [μm] or less, preferably 5 [μm] or less.

JP 2003-63831 A

  Usually, in a 1st lapping process, the board | substrate with which the uneven | corrugated state of the surface is similar is selected from several glass substrates (blanks material), and the glass substrate (blanks material) of substantially the same shape is made into a processing unit (50-150 sheets). In summary, polishing corresponding to the uneven state is performed. Then, the initial polishing conditions (pressure and rotational speed) are optimized (low pressure and low rotational speed). Furthermore, after completion of the first lapping step, the glass substrate is further selected based on the flatness, and the flatness is further improved in the second lapping step. Conventionally, since it is necessary to sort the substrates in this way, there has been a problem that it takes more time than necessary to take the product and time and effort.

  Also, in the press molding process, it is possible to improve the flatness by slowing down the press speed, but for that purpose it is necessary to heat the mold and slow down the speed of solidifying the glass. Will be disturbed.

  Further, in order to crystallize the amorphous glass substrate, it is necessary to perform a heat treatment at a high temperature of about 700 degrees, so that the cost increases.

  The present invention solves the above-mentioned problem, and by making the surface concave, the thickness on the outer peripheral portion side is increased compared to the vicinity of the central portion of the glass substrate, so that a desired plane can be relatively easily obtained by grinding. It aims at providing the glass substrate from which a degree is obtained, and the manufacturing method of the glass substrate.

  The invention according to claim 1 is a glass substrate before being polished and ground to produce a glass substrate for a magnetic recording medium by being polished and ground, and has a disk shape, The glass substrate is characterized in that at least one surface is concave, and the radius of curvature r of the concave surface is 2 to 12 [m].

The invention according to claim 2 is the glass substrate before being polished and ground to produce a glass substrate for a magnetic recording medium by being polished and ground, and has a disk shape, A glass substrate characterized in that at least one surface is concave, the radius of the disk is R, and the radius of curvature of the concave surface is r, r / R ² is 3 to 10 [1 / m]. is there.

  The invention according to claim 3 is a glass substrate before the grinding and grinding to produce a glass substrate for a magnetic recording medium by being polished and ground, and the molten glass material is formed into a convex shape. It is a glass substrate manufactured by sandwiching and pressing with a pressing mold.

  Invention of Claim 4 is a manufacturing method of the glass substrate before the said grinding | polishing and said grinding for manufacturing the glass substrate for magnetic recording media by grinding | polishing and grinding, Comprising: The molten glass raw material is used. A glass substrate production method comprising producing a glass substrate by sandwiching and pressing between convex pressing dies.

  The invention according to claim 5 polishes and grinds both surfaces of the glass substrate according to any one of claims 1 to 3 or the glass substrate produced by the method for producing a glass substrate according to claim 4. It is a glass substrate for magnetic recording media manufactured by this.

  The invention described in claim 6 polishes and grinds both surfaces of the glass substrate according to any one of claims 1 to 3 or the glass substrate manufactured by the method for manufacturing a glass substrate according to claim 4. This is a method for producing a glass substrate for a magnetic recording medium.

  The glass substrate of the present invention is a glass substrate used for a magnetic recording medium by grinding and polishing both surfaces, and is a glass substrate (blanks material) in a previous stage where grinding is performed. Since this glass substrate (blank material) has a concave surface on one or both sides, the edge of the disk-shaped substrate has the greatest thickness and gradually becomes thinner toward the center.

  In order to precondition the parallelism, flatness, and thickness of the substrate, both sides of the glass substrate are ground. This grinding process corresponds to the first lapping step. When both surfaces of the glass substrate are ground, the glass is ground from the thickest edge and gradually ground toward the center. Grind until both sides of the substrate are flat. Since the outer peripheral side of the glass substrate is in contact with the grindstone and is ground from the outer peripheral side, it is possible to perform stable grinding. In other words, since the outer periphery is the circumference of the glass substrate, the area of the portion that contacts the grinding wheel of the polishing machine becomes relatively large, and the surface can be ground without causing local stress concentration on the glass substrate. It becomes. As a result, the flatness of the surface after grinding can be made relatively low (good), and the flatness requirement required for the glass substrate for magnetic recording media as the final product can be satisfied. Become.

  Thus, by gradually grinding from the edge toward the center, the flatness of the ground glass substrate becomes low (good). For example, a 2.5-inch magnetic recording medium used for mobile The standard of flatness required for a glass substrate can be sufficiently satisfied. Further, by using the glass substrate of the present invention regardless of the size of the magnetic recording medium, the flatness can be easily lowered (good).

  In addition, although amorphous glass substrates, such as a borosilicate glass and an aluminosilicate glass, are used for the glass substrate of this invention, it does not specifically limit to those materials.

In consideration of the grinding time, it is desirable that the radius of curvature r of the concave surface is 2 [m] or more, or r / R ² is 3 [1 / m] or more, and the glass substrate of the present invention can be manufactured. Considering the range, it is desirable that the radius of curvature r of the concave surface is 12 [m] or less, or r / R ² is 10 [1 / m] or less.

  According to the present invention, since the outer peripheral side of the glass substrate is in contact with the grindstone and is ground from the outer peripheral side, it is possible to perform stable grinding, and the flatness of the surface after grinding can be made relatively low. It becomes. As a result, it is possible to satisfy the flatness requirement required for a glass substrate for a magnetic recording medium as a final product.

  For example, when a 2.5 inch substrate is used, the flatness after grinding can be reduced to about 5 μm, and a glass substrate for a magnetic recording medium having a low (good) flatness can be produced. When the glass substrate for magnetic recording medium is used, a magnetic recording medium whose surface is hardly damaged can be manufactured.

  Furthermore, according to the present invention, it is not necessary to slow down the speed of solidifying the glass in the press molding process, and it is not necessary to crystallize in order to obtain flatness, so the productivity of the glass substrate (blanks material) is increased. It is possible to improve and reduce production costs.

  Hereinafter, a glass substrate for a magnetic recording medium according to an embodiment of the present invention will be described with reference to FIGS.

[First Embodiment]
First, a glass substrate for a magnetic recording medium according to a first embodiment of the present invention will be described with reference to FIGS.

(Constitution)
The structure of the glass substrate 1 for magnetic recording media according to the first embodiment will be described with reference to FIG. FIG. 1 shows the structure of a glass substrate for a magnetic recording medium according to the first embodiment of the present invention. FIG. 1 (a) is a perspective view of the glass substrate 1, and FIG. 1 (b) is FIG. It is sectional drawing of the glass substrate 1 shown to a).

  The glass substrate 1 according to the present embodiment has a disk shape and is used as a substrate for a magnetic recording medium such as a hard disk. A glass substrate 1 shown in FIG. 1 is a glass substrate (blanks material) as a semi-finished product at a stage before the first lapping step. By performing the above-described first lapping process to polishing process on the glass substrate (blank material), a glass substrate for a magnetic recording medium as a final product before the magnetic film is formed can be obtained.

  The glass substrate 1 is made of amorphous glass, and as shown in FIG. 1A, the front surfaces 1a and 1b (the front surface 1b is the back surface of the front surface 1a) are concave. This structure will be further described with reference to FIG. This cross-sectional view shows a cross section of the diameter of the glass substrate 1. In addition, although the surface 1a is shown by Fig.1 (a), the surface 1b which is the opposite surface is also concave.

  As shown in FIG. 1 (b), the surfaces 1a and 1b are concave and curved, so that the glass substrate 1 has the thickest thickness d1 of the outer peripheral portion 3 and gradually increases toward the central portion 2. And the thickness d2 of the center portion 2 is formed to be the thinnest (thickness d1 of the outer peripheral portion 3 ≧ thickness d2 of the center portion 2). That is, the outer peripheral portion 3 has a shape protruding from the center portion 2, and the surface 1a and the surface 1b are warped in opposite directions. Moreover, although the surface 1a and the surface 1b of this glass substrate 1 have the same curvature, a curvature may differ. For example, the curvature of the surface 1b may be larger than the curvature of the surface 1a, and the curvature of the surface 1b may be larger than that of the surface 1a. The reverse is also possible. Here, the radius of the glass substrate 1 is R (diameter is 2R).

  In the present embodiment, the surfaces 1a and 1b are schematically formed smoothly, but this is for the sake of convenience. In an actual glass substrate, the surface is “swelled”. And “micro swell”. Even in a glass substrate in which such “swells” or the like occur, the thickness gradually decreases from the outer peripheral portion 3 toward the central portion 2 as compared with the central portion 2 when viewed macroscopically. The outer peripheral part 3 should just protrude. That is, it is only necessary that the warpage of the surfaces 1a and 1b of the glass substrate 1 is larger than the size of the “swell” so that the “swell” can be ignored.

(Grinding process: lapping process)
Next, a process for producing a glass substrate for a magnetic recording medium as a final product using the glass substrate 1 of the present embodiment will be described with reference to FIGS. FIG. 2 is a cross-sectional view of the substrate sequentially illustrating the steps of grinding the glass substrate according to the first embodiment of the present invention. FIG. 3 is a perspective view schematically showing a state in which the glass substrate is ground. This step corresponds to the above-described first lapping step, and the parallelism, flatness, and thickness of the substrate are adjusted by grinding both surfaces of the glass substrate 1 (blanks material). In addition, before giving a 1st lapping process, a hole is made in the center part of the glass substrate 1 (blanks material), and a doughnut-shaped glass substrate (perforated blanks material) is produced, but in FIG. For convenience, the illustration of the central hole is omitted.

  In the first lapping step, as shown in FIG. 3, the processing carrier 11 is usually sandwiched between the grindstone 13 a of the upper mold 12 a and the grindstone 13 b of the lower mold 12 b, and the glass plate 1 is held on the carrier 11. By rotating the carrier 11 as indicated by an arrow A, each glass plate 1 can be ground to a predetermined thickness.

  Next, how the glass substrate 1 is ground will be described. As shown in FIG. 2 (a), first, the glass substrate 1 (blanks material) is sandwiched from both sides by the grindstones 13a and 13b, and both surfaces 1a and 1b of the glass substrate 1 are ground in this state. In this state, the outer peripheral portions 3 of the surfaces 1a and 1b of the glass substrate 1 are in contact with the grindstones 13a and 13b.

  When grinding continues, the outer peripheral portion 3 of the glass substrate 1 is gradually scraped, and the shaved portion becomes flat. Since the outer peripheral portion 3 is in contact with the grindstones 13a and 13b of the polishing machine, the contact area with the grindstones 13a and 13b is increased, and the glass substrate 1 can be ground without causing local stress concentration. That is, since the outer peripheral part 3 becomes the circumference of the disk-shaped glass substrate 1, a contact part with the grindstones 13a and 13b increases. And as shown in FIG.2 (b), the glass substrate 4 with which the outer peripheral part 6 was planarized is produced.

  As the grinding continues further, it is gradually cut from the outer peripheral portion 6 toward the central portion 5, and is ground to the central portion 8 as shown in FIG. 2 (c) and is ground until both surfaces are flattened. . Then, as shown in FIG. 2D, grinding is continued until a desired thickness is obtained, and a glass substrate 10 for a magnetic recording medium is manufactured.

  Thus, by grinding the glass substrate 1 (blank material) whose both surfaces are concave, the flatness of the glass substrate 10 after grinding becomes good. For example, 2.5-inch magnetic recording used for mobiles. It becomes possible to sufficiently satisfy the standard of flatness required for the glass substrate for the medium.

  In addition, when the glass substrate (blanks material) which has both surfaces convex is ground, since the surface is convex, the center of the surface and the grindstones 13a and 13b are in contact with each other, and the contact area is reduced. As a result, the glass substrate cannot be ground without causing local stress concentration, and it becomes difficult to reduce (good) the flatness. By setting the surface to be concave like the glass substrate 1 according to this embodiment, the glass substrate 1 can be stably ground, and the flatness can be lowered (good).

  The above processing corresponds to the first lapping step, and the glass substrate 10 obtained by grinding is further subjected to an end surface grinding step, an end surface polishing step, a second lapping step, and a polishing step as a final product. A glass substrate for a magnetic recording medium is obtained. And a magnetic recording medium is produced by forming a magnetic film on this glass substrate for magnetic recording media.

  In addition, even if the glass substrate has “swells” on the surfaces 1a and 1b, the effect of the present invention can be achieved. Even if “undulation” occurs, the outer peripheral portion 3 protrudes more than the central portion 2, so that the outer peripheral portion 3 is thicker than the central portion 2, and the outer peripheral portion 3 moves toward the central portion 2. Therefore, the outer peripheral portion 3 having a large area comes into contact with the grindstones 13a and 13b. As a result, since the glass substrate 1 is stably ground, the flatness of the surface after grinding is relatively good.

(Production method)
Next, the manufacturing method of the glass substrate 1 which concerns on this embodiment is demonstrated, referring FIG. FIG. 4 is a cross-sectional view of the substrate sequentially illustrating the glass substrate manufacturing method according to the first embodiment of the present invention. This manufacturing method corresponds to the press molding step described above. As shown in FIG. 4A, molds 14a and 14b having convex surfaces are prepared.

  Next, as shown in FIG. 4B, the molten glass material 15 is sandwiched between a mold 14a and a mold 14b and press-molded to produce a disk-shaped glass substrate 1. Thus, the glass substrate 1 of this embodiment is obtained by press-molding using the metal mold | die which has a convex surface.

  According to the glass substrate 1 according to the present embodiment, it is not necessary to slow down or crystallize the glass in the press molding process, thereby improving the productivity of the glass substrate and reducing the production cost. It becomes possible to do.

  Further, the glass substrate 1 described above is concave on both sides, but the present invention is not limited to this. For example, as shown in the cross-sectional view of the substrate shown in FIG. 5A, only one side (one side) is concave. There may be. Even if only one surface is concave, the flatness of the glass substrate after grinding is good. The glass substrate 20 shown to Fig.5 (a) has a disk shape similarly to the above-mentioned glass substrate 1, The surface 20a is a concave surface. Further, in FIG. 5A, the surface 20b is illustrated as being flat, but this is for convenience of explanation, and the flatness is actually increased due to “swell” or the like. Thus, the glass substrate 20 is formed so that the outer peripheral portion 22 has the largest thickness, the thickness gradually decreases toward the stop portion 21, and the central portion 21 has the smallest thickness.

  The glass substrate 20 is held on the carrier 11 shown in FIG. 3, and the upper and lower surfaces of the glass substrate 20 are ground by the grindstones 13a and 13b. Even the glass substrate 20 having such a structure can achieve the effects of the present invention. Similarly to the glass substrate 1 described above, when both surfaces of the glass substrate 20 are ground, the outer peripheral portion 22 comes into contact with the grindstones 13a and 13b.

  First, as shown to Fig.5 (a), the glass substrate 20 (blanks material) is inserted | pinched with the grindstones 13a and 13b from both surfaces, and both surfaces 20a and 20b of the glass substrate 20 are ground in this state. In this state, the outer peripheral portion 22 of the surface 20a of the glass substrate 20 is in contact with the grindstone 13a.

  If grinding is continued, the outer peripheral portion 22 and the surface 20b of the surface 20a of the glass substrate 20 are gradually scraped, and the shaved portion becomes flat. Since the outer peripheral portion 22 is in contact with the grindstone 13a on the surface 20a, the contact area with the grindstone 13a is increased, and the glass substrate 20 can be ground stably. Therefore, as shown in FIG. 5B, the glass substrate 23 in which the outer peripheral portion 25 of the surface 23a is flattened is manufactured.

  As the grinding continues further, the surface 23 a is gradually scraped from the outer peripheral portion 25 toward the central portion 24. Then, as shown in FIG. 5 (c), the surface is ground until both surfaces become flat, and as shown in FIG. 5 (d), the grinding is continued until a desired thickness is obtained, and a glass substrate for a magnetic recording medium is obtained. 28 is produced.

  Thus, the flatness of the glass substrate 28 after grinding becomes good by grinding both surfaces of the glass substrate 20 (blanks material) whose one surface is concave.

[Second Embodiment]
Next, a glass substrate according to a second embodiment of the present invention will be described with reference to FIG. The glass substrate according to the first embodiment is concave on one side or both sides and has a curved surface, but may not be curved.

(Constitution)
The configuration of the glass substrate 60 according to the second embodiment will be described with reference to FIG. FIG. 6 is a sectional view of a glass substrate according to the second embodiment of the present invention.

  The glass substrate 60 according to the present embodiment has a disk-like shape as in the first embodiment, and the surfaces 60a and 60b are recessed in the glass substrate 60, but unlike the first embodiment. It is not curved.

  As shown in FIG. 6, the surfaces 60 a and 60 b are recessed inside the glass substrate 60, and the outer peripheral portion 62 projects from the central portion 61. The thickness of the central portion 61 is the smallest, the thickness gradually increases toward the outer peripheral portion 62, and the thickness of the outer peripheral portion 62 is the thickest (the thickness of the outer peripheral portion d6 ≧ the thickness of the central portion. d7). And the inclination from the center part 61 to the outer peripheral part 62 is a straight line.

  Even the glass substrate 60 having such a structure can exhibit the effects of the present invention. As in the first embodiment, when both surfaces of the glass substrate 60 are ground, the outer peripheral portion 62 comes into contact with the grindstones 13a and 13b. When grinding is continued, the glass substrate 60 is gradually scraped from the outer peripheral portion 62 toward the central portion 61, and the shaved portion becomes flat. And it grinds to the center part 61 and grinds until both surfaces become flat. Then, grinding is continued until a desired thickness is obtained, and a glass substrate for a magnetic recording medium is manufactured.

  Thus, even if both surfaces are not curved concave surfaces, the flatness of the ground glass substrate is improved by the outer peripheral portion projecting from the central portion. Moreover, although both surfaces of the glass substrate 60 in the present embodiment are recessed, only one surface may be recessed and the one surface may be flat as in the first embodiment. Even when only one surface is depressed, the contact portion with the grindstone increases on that one surface, so that stable grinding is possible.

  Moreover, in this embodiment, although the inclination of the inclination of both surfaces is the same, it may be different. For example, as shown in the cross-sectional view of the glass substrate in FIG. 7A, the outer peripheral portion 72 compared to the central portion 71 even when the inclination of the surface 70 a is steep compared to the inclination of the surface 70 b of the glass substrate 70. Therefore, the contact portions with the grindstones 13a and 13b are increased, and stable grinding can be performed.

  Furthermore, in the present embodiment, the thickness of the central portion 61 is the smallest and the thickness of the outer peripheral portion 62 is the thickest. However, as shown in the cross-sectional view of the glass substrate in FIG. The vicinity of the central portion of 80 may not be formed obliquely. As shown in the figure, since the outer peripheral portion 82 protrudes in comparison with the inner portion, the outer peripheral portion 82 comes into contact with the grindstones 13a and 13b, so that the glass substrate 80 and the grindstones 13a and 13b come into contact with each other (area). Therefore, a glass substrate for a magnetic recording medium that can be stably ground and has good flatness can be produced. In FIG. 7B, the vicinity of the central portion 81 is illustrated as being flat. However, this is for convenience of explanation, and the flatness is actually increased due to “swell” or the like.

  Furthermore, the present invention is not limited to the embodiment described above. The surface of the glass substrate may be either a curved surface or a straight line, and the effect of the present invention can be achieved as long as the outer peripheral side protrudes from the center so as to increase the contact portion with the grindstone when grinding. It becomes possible. Therefore, although the case where the outermost edge part protrudes most is a preferable form, you may be a case where the protruded part is located inside the outermost part.

  In other words, since the end of the glass substrate has a circumferential length, the contact portion (area) is larger when the outer peripheral side is in contact with the grindstone than when the central portion is in contact with the grindstone, and the glass substrate is stable. Thus, it becomes possible to produce a glass substrate for a magnetic recording medium that is ground and has good flatness.

[Example]
Next, specific examples of the present invention will be described.

Example 1
First, as Example 1, a specific example of the glass substrate 1 according to the first embodiment will be described. The dimensions of the glass substrate 1 as Example 1 are as follows.
Size: Diameter (2R) = 67 [mm]
Thickness of the central part 2: d2 = 0.95 [mm]
The thickness of the outer peripheral part 3: d1 = 1.25 [mm]
Radius of curvature r of surface 1a and surface 1b: r = 3737 [mm] (= 3.737 [m])
R / R ² of the surface 1a and the surface 1b = 3.33 [1 / m]
The glass substrate 1 is composed of an amorphous glass substrate of borosilicate glass.

By grinding both surfaces of the glass substrate 1 of the first embodiment in the first lapping step, the glass substrate 10 having both flat surfaces is produced. The grinding conditions in the first lapping step will be described.
Polishing machine: 16B type double-side polishing machine manufactured by Speed Fam Co., Ltd. Abrasive: “Diamond Pellet (DP)” made by baking and molding diamond into a pellet shape “Diamond Plate” pasted on a polishing plate
Tiremond pellets are manufactured by Mitsui Grinding Wheel Co., Ltd., and the diamond particle size is 10 to 30 [μm] (average 15 [μm]).
Processing pressure: 100 to 300 [g / cm ² ] (normally 200 [g / cm ² ])
Rotation speed: 5-50 [rpm] (normally 30 [rpm])

  The both surfaces of the glass substrate 1 were ground on the above conditions, and the flatness of the glass substrate 1 before processing and the glass substrate 10 after processing was evaluated. The flatness is evaluated by “optical interference method” using optical interference (Newton ring) between the reference plane and the object to be measured, when there is sufficient reflection on the substrate and it can be optically performed. On the other hand, when reflection is low and optical measurement is difficult, the dial gauge method is used as an alternative to the “light interference method”.

  For example, when evaluating flatness on the order of several microns, use the “light interference method” using Newton rings, and when the reflection is low at a flatness of several tens of microns, use the dial gauge method. went. In the optical interference method, an optical interferometer manufactured by Nidick was used, and in the dial gauge method, an in-house measuring jig using a Mitutoyo dial gauge was used. Evaluation of the flatness of the glass substrate 1 was performed by a method of measuring a displacement amount of the central portion with a dial gauge with reference to the outer peripheral portion. It should be noted that the glass substrate 10 after the first lapping process was performed by “optical interference method”.

(Evaluation results for the glass substrate 1 before grinding)
Evaluation number: 300
Flatness: 0.165 [mm]
Standard deviation: 0.025 [mm]
(Evaluation results for glass substrate 10 after grinding)
Evaluation number: 300
Flatness: 0.0035 [mm] (= 3.5 [μm])
Standard deviation: 0.00023 [mm] (= 0.23 [μm])
As described above, when the glass substrate according to the present embodiment is used, it is possible to obtain a glass substrate with good flatness in the first lapping step. Thus, for example, it is possible to satisfy the flatness standard required for a glass substrate used for a 2.5-inch hard disk.

  If the flatness cannot be optically evaluated, a stylus roughness meter or the like may be used. In that case, the scanning is performed from the end of the glass substrate 1 or the glass substrate 10 to the opposite end, and the unevenness is measured in a linear shape. Then, the Max-Min value with respect to the reference may be obtained, and the maximum displacement amount may be used as the flatness for evaluation.

Moreover, the manufacturing conditions of the glass substrate which concerns on Example 1 are demonstrated concretely. In order to manufacture the glass substrate according to the present embodiment, a mold having a convex surface is prepared. The glass substrate according to Example 1 can be obtained by press-molding with a glass material melted by this mold. Below, an example of the kind of glass and a metal mold | die is shown.
Type of glass: Borosilicate glass, aluminosilicate glass Mold with convex surface: curvature radius of convex surface is 2500 [mm] (= 2.5 [m]), center part is 0.15 [mm] compared to outer peripheral part Only protruding.

(Example 2)
Next, as Example 2, another specific example of the glass substrate 1 according to the first embodiment will be described. The dimensions of the glass substrate 1 of Example 2 are as follows.
Size: Diameter (2R) = 67 [mm]
Thickness of the central part 2: d2 = 0.95 [mm]
The thickness of the outer peripheral part 3: d1 = 1.05 [mm]
Radius of curvature r of surface 1a and surface 1b: r = 11222 [mm] (= 111.22 [m])
R / R ² of the surface 1a and the surface 1b = 10.0 [1 / m]
The glass substrate 1 is composed of an amorphous glass substrate of borosilicate glass.

  Both surfaces of this glass substrate are ground under the same conditions as in Example 1 (first lapping step). Then, the flatness of the glass substrate after grinding is evaluated under the same conditions (optical interference method or dial gauge method) as in Example 1.

(Evaluation results for the glass substrate 1 before grinding)
Evaluation number: 300
Flatness: 0.045 [mm]
Standard deviation: 0.0027 [mm]
(Evaluation results for glass substrate 10 after grinding)
Evaluation number: 300
Flatness: 0.0031 [mm] (= 3.1 [μm])
Standard deviation: 0.00013 [mm] (= 0.13 [μm])
As described above, also in Example 2, it is possible to obtain a glass substrate having a flatness of 5 [μm] or less in the same manner as in Example 1, and it is possible to satisfy the standard of flatness.

(Example 3)
Next, as Example 3, another specific example of the glass substrate 1 according to the first embodiment will be described. The dimensions of the glass substrate 1 of Example 3 are as follows.
Size: Diameter (2R) = 67 [mm]
Thickness of the central part 2: d2 = 0.95 [mm]
The thickness of the outer peripheral part 3: d1 = 1.25 [mm]
Radius of curvature r of surface 1a and surface 1b: r = 5611 [mm] (= 5.611 [m])
R / R ² of the surface 1a and the surface 1b = 5.00 [1 / m]
The glass substrate 1 is composed of an amorphous glass substrate of borosilicate glass.

  Both surfaces of this glass substrate are ground under the same conditions as in Example 1 (first lapping step). Then, the flatness of the glass substrate after grinding is evaluated under the same conditions (optical interference method or dial gauge method) as in Example 1.

(Evaluation results for the glass substrate 1 before grinding)
Evaluation number: 300
Flatness: 0.098 [mm]
Standard deviation: 0.0022 [mm]
(Evaluation results for glass substrate 10 after grinding)
Evaluation number: 300
Flatness: 0.0032 [mm] (= 3.2 [μm])
Standard deviation: 0.00010 [mm] (= 0.10 [μm])
As described above, also in Example 2, it is possible to obtain a glass substrate having a flatness of 5 [μm] or less in the same manner as in Example 1, and it is possible to satisfy the standard of flatness.

  In Example 1 to Example 3 described above, an example in which a glass substrate having a diameter (2R) of 67 [mm] is used has been described. In the following Example 4 to Example 6, an example in which a glass substrate having a diameter (2R) of 49 [mm] is used will be described.

Example 4
Next, as Example 4, a specific example of the glass substrate 1 according to the first embodiment will be described. The dimensions of the glass substrate 1 as Example 4 are as follows.
Size: Diameter (2R) = 49 [mm]
Center part 2 thickness: d2 = 0.98 [mm]
The thickness of the outer peripheral part 3: d1 = 1.25 [mm]
Radius of curvature r of surface 1a and surface 1b: r = 2000 mm (= 2 [m])
R / R ² of the surface 1a and the surface 1b = 3.33 [1 / m]
The glass substrate 1 is composed of an amorphous glass substrate of borosilicate glass.

  Both surfaces of this glass substrate are ground under the same conditions as in Examples 1 to 3 (first lapping step). And the flatness of the glass substrate after grinding is evaluated on the same conditions (optical interference method or dial gauge method) as Examples 1-3.

(Evaluation results for the glass substrate 1 before grinding)
Evaluation number: 350
Flatness: 0.152 [mm]
Standard deviation: 0.034 [mm]
(Evaluation results for glass substrate 10 after grinding)
Evaluation number: 350
Flatness: 0.0028 [mm] (= 2.8 [μm])
Standard deviation: 0.00011 [mm] (= 0.11 [μm])
As described above, the glass substrate having a flatness of 5 [μm] or less can be obtained in the fourth embodiment as well as the first to third embodiments, and the flatness criterion can be satisfied.

(Example 5)
Next, as Example 5, a specific example of the glass substrate 1 according to the first embodiment will be described. The dimensions of the glass substrate 1 as Example 5 are as follows.
Size: Diameter (2R) = 49 [mm]
Center part 2 thickness: d2 = 0.98 [mm]
Thickness of outer peripheral part 3: d1 = 1.18 [mm]
Radius of curvature r of surface 1a and surface 1b: r = 3000 [mm] (= 3 [m])
R / R ² of the surface 1a and the surface 1b = 5.00 [1 / m]
The glass substrate 1 is composed of an amorphous glass substrate of borosilicate glass.

  Both surfaces of this glass substrate are ground under the same conditions as in Examples 1 to 4 (first lapping step). And the flatness of the glass substrate after grinding is evaluated on the same conditions (optical interference method or dial gauge method) as Examples 1-4.

(Evaluation results for the glass substrate 1 before grinding)
Evaluation number: 350
Flatness: 0.103 [mm]
Standard deviation: 0.024 [mm]
(Evaluation results for glass substrate 10 after grinding)
Evaluation number: 350
Flatness: 0.0024 [mm] (= 2.4 [μm])
Standard deviation: 0.00009 [mm] (= 0.09 [μm])
As described above, also in Example 5, it is possible to obtain a glass substrate having a flatness of 5 [μm] or less in the same manner as in Examples 1 to 4, and the flatness standard can be satisfied.

(Example 6)
Next, as Example 6, a specific example of the glass substrate 1 according to the first embodiment will be described. The dimensions of the glass substrate 1 as Example 6 are as follows.
Size: Diameter (2R) = 49 [mm]
Center part 2 thickness: d2 = 0.98 [mm]
Thickness of the outer peripheral portion 3: d1 = 1.08 [mm]
Radius of curvature r of surface 1a and surface 1b: r = 6000 [mm] (= 6 [m])
R / R ² of the surface 1a and the surface 1b = 10.0 [1 / m]
The glass substrate 1 is composed of an amorphous glass substrate of borosilicate glass.

  Both surfaces of this glass substrate are ground under the same conditions as in Examples 1 to 5 (first lapping step). Then, the flatness of the glass substrate after grinding is evaluated under the same conditions (optical interference method, dial gauge method) as in Examples 1-5.

(Evaluation results for the glass substrate 1 before polishing)
Evaluation number: 350
Flatness: 0.054 [mm]
Standard deviation: 0.0052 [mm]
(Evaluation results for the polished glass substrate 10)
Evaluation number: 350
Flatness: 0.0021 [mm] (= 2.1 [μm])
Standard deviation: 0.00008 [mm] (= 0.08 [μm])
As described above, also in Example 6, it is possible to obtain a glass substrate having a flatness of 5 [μm] or less as in Examples 1 to 5, and it is possible to satisfy the standard of flatness.

  By making the surface 1a and the surface 1b concave as in the first to sixth embodiments shown above, the flatness after polishing and grinding can be made 5 [μm] or less, and the required plane It is possible to meet the degree standard. Further, the flatness can be made 5 [μm] or less regardless of the size of the glass substrate 1. In addition, said Example is an example of this invention, This invention is not limited to said Example, If at least 1 surface is the concave surface among the surface 1a or the surface 1b, the effect | action of this invention and It is possible to produce an effect.

Further, according to the first to sixth embodiments, the curvature radius r is set to 2000 [mm] (= 2 [m]) or more (or r / R ^{2 is set} to 3 [1 / m] or more). Since the glass substrate can be ground without increasing the grinding time, the manufacturing time can be shortened. Furthermore, in consideration of the range in which the glass substrate can be manufactured, it is desirable that the radius of curvature r is 12000 [mm] (= 12 [m]) or less (or r / R ² is 10 [1 / m] or less). . Even if the curvature radius r is smaller than 2 [m] (r / R ² is 3 [1 / m]), it is possible to achieve the effects of the present invention by extending the grinding time.

That is, in the glass substrate 1 according to the embodiment of the present invention, the curvature radius r of the surface 1a and the surface 1b is 2 to 12 [m] (or r / R ² is 3 to 10 [1 / m]). It is desirable. When the curvature radius r is in the range of 2 to 12 [m], the glass substrate 1 can be manufactured, and the larger the curvature radius r, the shorter the grinding time.

(Example 7)
Next, as Example 7, a specific example of the glass substrate 60 according to the second embodiment will be described. The dimensions of the glass substrate 60 as Example 7 are as follows.
Size: Diameter (2R) = 67 [mm]
Thickness of the central portion 61: d7 = 0.98 [mm]
The thickness of the outer peripheral part 62: d6 = 1.18 [mm]
The glass substrate 60 is made of an amorphous glass substrate of borosilicate glass.

  Both surfaces of this glass substrate are ground under the same conditions as in Examples 1 to 6 (first lapping step). Then, the flatness of the glass substrate after grinding is evaluated under the same conditions (optical interference method or dial gauge method) as in Example 1 to Example 6.

(Evaluation results for the glass substrate 60 before grinding)
Evaluation number: 300
Flatness: 0.1 [mm]
Standard deviation: 0.0033 [mm]
(Evaluation results for glass substrate after grinding)
Evaluation number: 300
Flatness: 0.0031 [mm] (= 3.1 [μm])
Standard deviation: 0.00023 [mm] (= 0.23 [μm])
As described above, also in Example 7, it is possible to obtain a glass substrate having a flatness of 5 [μm] or less in the same manner as in Examples 1 to 6, and the flatness standard can be satisfied.

(Comparative example)
Next, comparative examples for Examples 1 to 7 will be described below. Although the glass substrate of Example 1- Example 7 is shape | molded using the metal mold | die which has a convex surface, the glass substrate of a comparative example is shape | molded using the metal mold | die with a flat surface. In other words, the glass substrates of Examples 1 to 7 are molded using a convex mold so that the surface is intentionally concave, but the glass substrate of this comparative example has been conventionally used. It is molded using a flat mold.

The dimensions of the glass substrate as a comparative example are as follows.
Evaluation number: 100 Size: Diameter (2R) = 67 [mm]
Average thickness of the central part and the outer peripheral part: 1.25 [mm]
The difference in thickness between the central portion and the outer peripheral portion (the thickness of the outer peripheral portion−the thickness of the central portion) in 100 glass substrates is as follows.
Average value of 100 sheets: 0.03 [mm]
Maximum value: 0.12 [mm]
Minimum value: -0.11 [mm] (the central part is thicker than the outer peripheral part)
Standard deviation: 0.06 [mm]
Thus, if it molds using a flat metallic mold, the thickness of a glass substrate will not become uniform, but thickness will differ partially.

  Both surfaces of the glass substrate of this comparative example are ground in the first lapping step. The grinding conditions in the first lapping step are the same as those in the first embodiment. And the flatness of the glass substrate after grinding is evaluated on the same conditions as Examples 1-7.

(Evaluation results for glass substrate after grinding)
Evaluation number: 100 Flatness (average value): 0.0042 [mm] (= 4.2 [μm])
Standard deviation: 0.0015 [mm] (= 1.5 [μm])
The average value of the flatness is 5 [μm] or less. However, in 23 out of 100 glass substrates, the flatness is larger than 5 [μm], which is a good result as in the example of the present invention. Was not obtained.

  From the above results, when a glass substrate is molded using a flat mold, the entire glass substrate is deformed like a swell, and since the swell is ground from the largest part of the swell, the part is ground. It is considered that a large stress is concentrated, and as a result, the flatness after grinding is increased (deteriorated).

It is a figure which shows the structure of the glass substrate which concerns on 1st Embodiment of this invention. It is sectional drawing of the board | substrate which shows the process of grinding the glass substrate which concerns on 1st Embodiment of this invention in order. It is a perspective view which shows the state which grinds a glass substrate typically. It is sectional drawing of the board | substrate which shows the manufacturing method of the glass substrate which concerns on 1st Embodiment of this invention in order. It is sectional drawing of the board | substrate which shows the process of grinding the glass substrate which concerns on 1st Embodiment of this invention in order. It is sectional drawing of the glass substrate which concerns on 2nd Embodiment of this invention. It is sectional drawing of the glass substrate which concerns on 2nd Embodiment of this invention.

Explanation of symbols

1, 10, 20, 28, 60, 70, 80 Glass substrate 1a, 1b, 20a, 20b, 60a, 60b, 70a, 70b, 80a, 80b Surface 2, 21, 61, 71, 81 Center part 3, 22, 62, 72, 82 Outer peripheral portion 13a, 13b Grinding wheel 14a, 14b Mold 15 Melted glass material

Claims (6)

The glass substrate before being ground for producing a glass substrate for a magnetic recording medium by being polished and ground,
Having a disk-like shape, at least one surface being concave,
The radius of curvature r of the concave surface is 2 to 12 [m].
A glass substrate characterized by being: The glass substrate before being ground for producing a glass substrate for a magnetic recording medium by being polished and ground,
Having a disk-like shape, at least one surface being concave,
Let R be the radius of the disk,
If the radius of curvature of the concave surface is r,
r / R ² is 3 to 10 [1 / m]
A glass substrate characterized by: The glass substrate before being ground for producing a glass substrate for a magnetic recording medium by being polished and ground,
A glass substrate manufactured by sandwiching and pressing a molten glass material with a convex pressing mold. A method of manufacturing a glass substrate before being ground for manufacturing a glass substrate for a magnetic recording medium by polishing and grinding,
A method for producing a glass substrate, comprising producing a glass substrate by sandwiching and pressing a molten glass material with a convex pressing mold.   It is produced by polishing and grinding both surfaces of the glass substrate according to any one of claims 1 to 3 or the glass substrate produced by the method for producing a glass substrate according to claim 4. A glass substrate for magnetic recording media. A glass substrate according to any one of claims 1 to 3, or a glass substrate produced by the method for producing a glass substrate according to claim 4, wherein both surfaces of the glass substrate are polished and ground. A method for producing a glass substrate.

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