JP2008130179A - Glass substrate for information recording medium, manufacturing method of glass substrate for information recording medium and information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for an information recording medium having high strength and high flatness in combination and capable of maintaining high flatness even when being used in a condition of large temperature variation, a manufacturing method of the glass substrate for the information recording medium, and the information recording medium using the glass substrate for the information recording medium. <P>SOLUTION: Outer and inner peripheral end surfaces of the glass substrate have a high thermal conductivity layer having thermal conductivity higher than thermal conductivity of an inner part of the glass substrate, formed on their uppermost layers, wherein the high thermal conductivity layer on the outer and inner peripheral end surfaces at a center part in the thickness direction of the glass substrate has thickness of 5 to 20 μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a glass substrate for an information recording medium used for an information recording medium having a recording layer utilizing properties such as magnetism, light, and magnetomagnetism, a method for producing a glass substrate for an information recording medium, and an information recording medium.

  Among information recording media having a recording layer utilizing properties such as magnetism, light, and magnetomagnetism, a typical example is a magnetic disk. Conventionally, aluminum substrates have been widely used as magnetic disk substrates. However, in recent years, with the demand for a reduction in the flying height of the magnetic head for improving the recording density, the surface smoothness is superior to that of an aluminum substrate and the surface defects are few, so that the flying height of the magnetic head can be reduced. The proportion of using glass substrates as magnetic disk substrates is increasing.

  In such a method for producing a glass substrate for an information recording medium such as a magnetic disk, for the purpose of improving the impact resistance and vibration resistance of the glass substrate and preventing the substrate from being damaged by impact and vibration, In general, a substrate is strengthened by applying a chemical strengthening treatment to the surface. Chemical strengthening treatment is usually performed by immersing a glass substrate in a chemical strengthening treatment liquid, and ion exchange between alkali metal ions such as sodium ions contained in the glass substrate and alkali metal ions such as potassium ions contained in the chemical strengthening treatment liquid. By an ion exchange method in which a reinforcing layer is formed on the surface of the glass substrate. Such a reinforcing layer has a high compressive stress, and the glass substrate is strengthened.

  After the chemical strengthening treatment, the main surface subjected to the chemical strengthening treatment is often polished to remove erosion or fine scratches from the chemical strengthening treatment liquid to ensure necessary smoothness. However, since a part of the reinforcing layer formed on the main surface of the glass substrate is removed by this polishing process, the balance of stress between the main surface on the front side and the main surface on the back side of the glass substrate is lost, and the glass substrate becomes There existed a problem that curvature and flatness will deteriorate.

Thus, in order to prevent the flatness of the glass substrate from being deteriorated by polishing the main surface subjected to the chemical strengthening treatment, a polishing treatment is performed after the chemical strengthening to remove the reinforcing layer on the main surface of the disk substrate. There has been proposed a disk substrate in which a reinforcing layer having a thickness of 30 μm or more and 200 μm or less is left only on the peripheral end surface portion (see, for example, Patent Document 1).
JP 2000-207730 A

  However, as the recording density is improved, the level of flatness required for the glass substrate for information recording media becomes higher, and the main surface that has been chemically strengthened as described in Patent Document 1 is polished to the main surface. Even when the reinforcing layer formed on the surface is removed, there is a problem that such a request cannot be sufficiently met.

  In recent years, the use of magnetic disks has expanded, and in many cases, magnetic disks are employed not only in devices installed in offices, but also in portable devices and in-vehicle devices that are carried around. Thus, when placed in an environment with a large temperature change, the flatness of the magnetic disk may be further deteriorated, which is a serious problem.

  The present invention has been made in view of the technical problems as described above, and an object of the present invention is to have high strength and high flatness, and to maintain high flatness even when used in an environment with a large temperature change. An information recording medium glass substrate, a method for producing the information recording medium glass substrate, and an information recording medium using the information recording medium glass substrate are provided.

  In order to solve the above problems, the present invention has the following features.

  1. A disk-shaped glass substrate having a central hole, the glass substrate for an information recording medium having a main surface, an outer peripheral end surface, and an inner peripheral end surface, wherein the outer peripheral end surface and the inner peripheral end surface are heat conduction inside the glass substrate. The outermost surface has a high thermal conductivity layer having a thermal conductivity higher than the rate, and the thickness of the outer peripheral end surface and the inner peripheral end surface of the high thermal conductivity layer is 5 μm at the center in the thickness direction of the glass substrate. A glass substrate for an information recording medium, characterized in that it is ˜20 μm.

  2. 2. The glass substrate for an information recording medium according to 1, wherein a portion of the main surface excluding a boundary region between the outer peripheral end face and the inner peripheral end face does not have the high thermal conductivity layer. .

  3. The high thermal conductivity layer is a layer in which at least a part of alkali metal ions contained in the glass substrate is replaced with another alkali metal ion having a large ion radius. The glass substrate for information recording media as described.

  4). In the method for manufacturing a glass substrate for an information recording medium including a chemical strengthening step of immersing a disk-shaped glass substrate having a center hole in a chemical strengthening treatment liquid and chemically strengthening the glass substrate by ion exchange, the chemical strengthening step includes: Forming a high thermal conductivity layer having a thermal conductivity higher than the thermal conductivity inside the glass substrate on an outer peripheral end surface and an inner peripheral end surface of the glass substrate; The method for producing a glass substrate for an information recording medium, wherein the high thermal conductivity layer formed on the peripheral end surface has a thickness of 5 μm to 20 μm at a central portion in the thickness direction of the glass substrate.

  5. By the chemical strengthening step, a high thermal conductivity layer having a thermal conductivity higher than the thermal conductivity inside the glass substrate is formed on the main surface of the glass substrate, and the high thermal conductivity layer is formed. Polishing the main surface, and having a post-strengthening polishing step of removing the high thermal conductivity layer from a portion of the main surface excluding a boundary region between the outer peripheral end surface and the inner peripheral end surface. 4. A method for producing a glass substrate for an information recording medium according to 4.

  6). An information recording medium, wherein at least a recording layer is formed on the glass substrate for an information recording medium described in any one of 1 to 3 above.

  According to the present invention, even if the temperature of the glass substrate changes due to the presence of the high thermal conductivity layer having higher thermal conductivity than the inside on the outer peripheral end surface and the inner peripheral end surface of the glass substrate, It is possible to maintain the balance of stress at the end face and the inner peripheral end face. Accordingly, a glass substrate for an information recording medium that has both high strength and high flatness and can maintain high flatness even when used in an environment with a large temperature change, a method for manufacturing the glass substrate for information recording medium, and the information recording An information recording medium using the glass substrate for medium can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Glass substrate for information recording media)
1 and 2 are diagrams showing an example of a glass substrate for an information recording medium of the present invention. FIG. 1A is a perspective view showing the entire glass substrate 10, and FIG. 1B is a sectional view thereof. FIG. 2 is an enlarged cross-sectional view of the vicinity of the outer peripheral end face 14 of the glass substrate 10. The glass substrate 10 is a disk-shaped glass substrate having a central hole 13 and has a main surface 11 on which a recording layer is formed. Chamfered portions 16 and 17 are provided on the outer peripheral end surface 14 and the inner peripheral end surface 15, respectively.

  The outer peripheral end face 14 and the inner peripheral end face 15 of the glass substrate 10 have a high thermal conductivity layer 18 having a thermal conductivity higher than the thermal conductivity inside the glass substrate 10 on the outermost surface. The high thermal conductivity layer 18 immerses the glass substrate in a heated chemical strengthening treatment solution, and replaces alkali metal ions such as sodium ions contained in the glass substrate with alkali metal ions such as potassium ions having a larger ion radius. Can be formed. Due to the distortion caused by the difference in ionic radius between sodium ions and potassium ions, the thermal conductivity of the high thermal conductivity layer 18 which is an ion exchanged region is higher than the non-ion exchanged region 19 inside the glass substrate 10. . FIG. 2 is a view in the vicinity of the outer peripheral end face 14, but the inner peripheral end face 15 also has a high thermal conductivity layer 18 in the same manner as the outer peripheral end face 14.

  The present inventor has intensively studied to solve the conventional problem that the flatness deteriorates due to the temperature change of the glass substrate, and the thermal conductivity of the outer peripheral end face 14 and the inner peripheral end face 15 of the glass substrate 10 is glass. It was found that the flatness of the substrate 10 is greatly affected. As a result of further investigation, the outer peripheral end face 14 and the inner peripheral end face 15 have a high thermal conductivity layer having a thermal conductivity higher than the thermal conductivity inside the glass substrate 10 on the outermost surface, and glass Even if the temperature of the glass substrate is changed by setting the thickness D of the high thermal conductivity layer 18 of the outer peripheral end surface 14 and the inner peripheral end surface 15 to 5 μm to 20 μm at the central portion in the thickness direction of the substrate, the outer peripheral end surface 14. And it was found that the stress balance in the inner peripheral end face 15 can be maintained.

  Here, the thermal conductivity inside the glass substrate 10 is the thermal conductivity of the glass substrate 10 other than the region where the thermal conductivity is increased by chemical strengthening, that is, the region 19 not ion-exchanged in the chemical strengthening process. Rate. The thermal conductivity inside the glass substrate 10 varies depending on the type of glass, but is usually about 1 to 2 W / (m · K).

  The thermal conductivity of the high thermal conductivity layer 18 is not particularly limited as long as it is higher than the thermal conductivity inside the glass substrate 10, but from the viewpoint of securing the strength of the glass substrate 10, the thermal conductivity inside the glass substrate 10. The ratio is preferably 1.001 times or more. Further, since the thermal conductivity is increased by ion exchange, the upper limit is the thermal conductivity when all replaceable ions are replaced. Usually, the upper limit is about 1.1 times the thermal conductivity inside the glass substrate 10.

  The thickness D of the high thermal conductivity layer 18 on the outer peripheral end face 14 and the inner peripheral end face 15 is 5 μm to 20 μm. If the thickness D is less than 5 μm, the strength of the glass substrate is lowered. On the other hand, if it is thicker than 20 μm, it becomes impossible to maintain the balance of stresses on the outer peripheral end face 14 and the inner peripheral end face 15 when the temperature of the glass substrate changes. Since the high thermal conductivity layer 18 is a layer whose thermal conductivity has been increased by ion exchange in the chemical strengthening process, the thickness D can be measured by measuring the ion concentration distribution of sodium ions, potassium ions, and the like. . The thickness D of the high thermal conductivity layer 18 is the distance from the outermost surface such as the outer peripheral end surface to the depth at which the ion concentration becomes a constant value. The ion concentration can be measured with an EPMA (Electron Probe Micro Analyzer), a time-of-flight secondary ion mass spectrometer (Time of FLIGHT (TOF) -SIMS), or the like.

  The main surface 11 of the glass substrate 10 may or may not have a high thermal conductivity layer similar to the outer peripheral end face. However, if the thickness of the high thermal conductivity layer existing in the main surface 11 excluding the boundary region 11a between the outer peripheral end surface 14 and the inner peripheral end surface 15 is different between the front and back surfaces, the temperature of the glass substrate changes. In this case, it is not preferable because the stress balance cannot be maintained. Further, in some cases, much time and labor may be required to make the thicknesses of the high thermal conductivity layers accurately match between the front main surface and the back main surface. Therefore, it is preferable that the same high thermal conductivity layer as the outer peripheral end face does not exist in the main surface 11 of the glass substrate 10 except for the boundary region 11a between the outer peripheral end face 14 and the inner peripheral end face 15. . Here, the boundary region 11a is a boundary region between the main surface 11 and the outer peripheral end surface 14 and between the main surface 11 and the inner peripheral end surface 15, and has a high thermal conductivity such as the outer peripheral end surface 14 as shown in FIG. An area where the layer is visible from the main surface side. As for the range of the boundary region 11a, the distance L from the outer peripheral end surface 14 (inner peripheral end surface 15) is generally equal to or less than the thickness t of the glass substrate 10.

The material of the glass substrate is not particularly limited as long as it is a glass capable of ion exchange by being immersed in a chemical strengthening treatment solution. For example, soda lime glass mainly composed of SiO ₂ , Na ₂ O, CaO; aluminosilicate glass mainly composed of SiO ₂ , Al ₂ O ₃ , R ₂ O (R = K, Na, Li); borosilicate Glass; Li ₂ O—SiO ₂ glass; Li ₂ O—Al ₂ O ₃ —SiO ₂ glass; R′O—Al ₂ O ₃ —SiO ₂ glass (R ′ = Mg, Ca, Sr, Ba) Etc. can be used. Among these, aluminosilicate glass and borosilicate glass are particularly preferable because they are excellent in impact resistance and vibration resistance.

  There is no limitation on the size of the glass substrate. For example, glass substrates having various sizes such as 2.5 inches, 1.8 inches, 1 inch, and 0.8 inches in outer diameter can be used. Moreover, there is no limitation also on the thickness of a glass substrate. For example, glass substrates having various thicknesses such as 2 mm, 1 mm, 0.64 mm, 0.4 mm, and 0.25 mm can be used. Among them, a glass substrate having a thickness of 1 mm or less is a glass substrate whose flatness is particularly likely to deteriorate, but the application of the present invention can effectively prevent the flatness from being deteriorated.

(Manufacturing process of glass substrate for information recording medium)
FIG. 3 is a flowchart showing an example of the manufacturing process of the glass substrate for information recording medium in the present invention.

  The glass substrate for an information recording medium of the present invention undergoes a chemical strengthening step and, if necessary, a post-strengthening polishing step after passing through pre-steps such as a blank material manufacturing step, an inner and outer peripheral processing step, a lapping step, and a first polishing step. It is manufactured by.

  Pre-processes such as a blank material manufacturing process, an inner and outer peripheral processing process, a lapping process, and a first polishing process can be performed by a method that is usually used as a method for manufacturing a glass substrate for an information recording medium. The blank material production process is a process for forming a blank material that is the basis of a glass substrate for an information recording medium, and a method for producing a molten glass by press molding or a method for producing a sheet glass by cutting is known. ing. The inner and outer peripheral machining step is a step of performing drilling of the center hole, grinding for ensuring the shape and dimensional accuracy of the outer peripheral end surface and the inner peripheral end surface, polishing of the inner and outer peripheral end surfaces, and the like. The lapping process is a process of lapping for satisfying the flatness, thickness, parallelism, etc. of the surface on which the recording layer is formed. It is a step of polishing the main surface of the glass substrate before the chemical strengthening step, and is a step of removing scratches and irregularities on the surface of the glass substrate and improving smoothness.

  The order of each of these pre-processes is not limited to that shown in FIG. 3, and can be appropriately changed according to the situation. Moreover, a process can also be abbreviate | omitted as needed, without performing all the processes. For example, the inner and outer peripheral processing steps may be performed after performing the blank manufacturing step and the lapping step. Further, the lapping process may be divided into two processes, a first half process and a second half process, and the inner and outer peripheral machining processes may be performed after the first half process of the lapping process, and then the second half process of the lapping process may be performed. Further, after the lapping process, the chemical strengthening process can be performed as it is without the first polishing process.

  In addition, in the manufacturing method of the glass substrate for information recording media of this invention, you may have various processes other than the above. For example, an annealing process for relaxing internal distortion of the glass substrate, a heat shock process for confirming the reliability of the strength of the glass substrate, and removing foreign substances such as abrasives and chemical strengthening treatment liquid remaining on the surface of the glass substrate. You may have a washing process, various inspection and evaluation processes, etc.

(Chemical strengthening process)
The chemical strengthening step involves immersing the glass substrate in a heated chemical strengthening solution to replace alkali metal ions such as sodium ions contained in the glass substrate with alkali metal ions such as potassium ions having a larger ion radius. This is done by the exchange method. Compressive stress is generated in the ion-exchanged region due to the strain caused by the difference in ion radius, and the glass substrate is strengthened.

  In the present invention, ion exchange is performed so that the thicknesses of the high thermal conductivity layers on the outer peripheral end face and the inner peripheral end face are 5 μm to 20 μm at the center in the thickness direction of the glass substrate. The thickness of such a high thermal conductivity layer is determined by the temperature of the chemical strengthening treatment liquid and the immersion time in addition to the type of the chemical strengthening treatment liquid. Therefore, the thickness of the high thermal conductivity layer can be set in the above range by appropriately setting these conditions. In general, the higher the temperature of the chemical strengthening treatment liquid and the longer the immersion time, the thicker the high thermal conductivity layer, and the lower the temperature of the chemical strengthening treatment solution and the shorter the immersion time, the thinner the high thermal conductivity layer. Become.

  There is no restriction | limiting in particular in the chemical strengthening process liquid used for this invention, The well-known chemical strengthening process liquid used for manufacture of the glass substrate for information recording media can be used. In general, a molten salt containing potassium ions or a molten salt containing potassium ions and sodium ions is generally used. Examples of the molten salt containing potassium ions and sodium ions include potassium and sodium nitrates, carbonates, sulfates, and mixed molten salts thereof. Among these, from the viewpoint that the melting point is low and deformation of the glass substrate can be prevented, it is preferable to use nitrate.

  The chemical strengthening treatment liquid is heated to a temperature higher than the temperature at which the above components melt. On the other hand, if the heating temperature of the chemical strengthening treatment liquid is too high, the temperature of the glass substrate is excessively increased, and the glass substrate may be deformed. For this reason, the heating temperature of the chemical strengthening treatment liquid is preferably lower than the glass transition point (Tg) of the glass substrate, more preferably lower than the glass transition point −50 ° C.

  In addition, in order to prevent the occurrence of cracks and fine cracks in the glass substrate due to thermal shock when immersed in the heated chemical strengthening treatment liquid, the glass substrate is placed in a preheating tank prior to immersion in the chemical strengthening treatment liquid. You may have the preheating process heated to predetermined temperature. Moreover, it is preferable to perform the washing | cleaning process for fully removing the chemical strengthening process liquid adhering to the glass substrate after a chemical strengthening process.

(Polishing post-strengthening process)
The post-strengthening polishing step is a step of polishing the main surface of the glass substrate after the chemical strengthening step. In the present invention, this is not necessarily an essential step. However, from the viewpoint of balancing the stress on the front and back of the glass substrate, in the post-strengthening polishing step, the portion of the main surface of the glass substrate excluding the boundary region between the outer peripheral end surface and the inner peripheral end surface is formed in the chemical strengthening step. It is preferable to remove the formed high thermal conductivity layer.

  As a polishing method, a known method used as a method for producing a glass substrate for an information recording medium can be used as it is. For example, a pad is pasted on the opposing surface of two rotatable surface plates placed opposite to each other, a glass substrate is placed between the two pads, and the glass substrate surface is rotated simultaneously with the pad contacting the glass substrate surface. It can carry out by the method of supplying an abrasive | polishing agent to. Further, it is also preferable to perform polishing in a plurality of steps such as a rough polishing step and a precision polishing step by changing the particle size of the abrasive and the type of pad.

  Examples of the abrasive include cerium oxide, zirconium oxide, aluminum oxide, manganese oxide, colloidal silica, and diamond. Among these, it is preferable to use cerium oxide which has high reactivity with glass and can obtain a smooth polished surface in a short time.

  The pad is divided into a hard pad and a soft pad, but can be appropriately selected and used as necessary. Examples of the hard pad include pads made of hard velor, urethane foam, pitch-containing suede, etc., and examples of the soft pad include pads made of suede, velor, etc.

(Information recording medium)
An information recording medium can be obtained by forming at least a recording layer on the glass substrate for information recording medium of the present invention. The recording layer is not particularly limited, and various recording layers utilizing properties such as magnetism, light, and magnetomagnetism can be used. In particular, for the production of an information recording medium (magnetic disk) using the magnetic layer as a recording layer. Is preferred.

  The magnetic material used for the magnetic layer is not particularly limited, and a known material can be appropriately selected and used. Examples thereof include CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, and CoCrPtSiO containing Co as a main component. The magnetic layer may be divided by a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) to have a multilayer structure in which noise is reduced.

As the magnetic layer, in addition to the above-mentioned Co-based material, ferrite or iron - and material of the rare earth-based, Fe, Co, CoFe, magnetic particles such CoNiPt are dispersed in a non-magnetic film made of SiO _2, BN A granular structure can also be used. The magnetic layer may be either an in-plane type or a vertical type.

  As a method for forming the magnetic film, a known method can be used. For example, a sputtering method, an electroless plating method, a spin coating method, and the like can be given.

The magnetic disk may further be provided with an underlayer, a protective layer, a lubricating layer, and the like as necessary. Any of these layers can be used by appropriately selecting a known material. Examples of the material for the underlayer include Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. Examples of the material for the protective layer include Cr, Cr alloy, C, ZrO ₂ , and SiO ₂ . Moreover, as a lubrication layer, the thing etc. which apply | coated the liquid lubricant which consists of perfluoro polyether (PFPE) etc., and heat-processed as needed are mentioned, for example.

(pre-process)
Aluminosilicate glass was used as the glass material, and the blank glass was produced by press molding the molten glass. The glass substrate having an outer diameter of 65 mm, an inner diameter of 20 mm, and a thickness of 0.64 mm was obtained through an inner and outer peripheral processing step, a lapping step, and a first polishing step. The flatness (PV value) of the glass substrate was less than 1 μm on both sides. The flatness was measured by measuring interference fringes using a flat plate finished to a level of 0.1 μm or less.

(Chemical strengthening process and post-strengthening polishing process)
A mixed molten salt of potassium nitrate (KNO ₃ ) and sodium nitrate (NaNO ₃ ) was prepared as a chemical strengthening treatment liquid. The mixing ratio was 1: 1 by mass ratio. The temperature of the chemical strengthening treatment liquid was 400 ° C.

  Twenty glass substrates were set on a conveying jig, and the entire conveying jig was immersed in a chemical strengthening treatment liquid. As shown in Table 1 below, chemical strengthening treatment was performed under conditions where the immersion time was changed from 10 minutes to 150 minutes. After immersing for a predetermined time, the glass substrate was taken out together with the conveying jig, the remaining chemical strengthening treatment liquid was washed by an ultrasonic cleaner, and the glass substrate was taken out from the conveying jig.

  Thereafter, the main surface was polished to remove the ion exchange layer formed on the main surface. As the abrasive, cerium oxide was used.

(Measurement of the thickness of the high thermal conductivity layer)
Two glass substrates are extracted for each condition, the distribution of sodium ion ion concentration on the outer peripheral end surface and inner peripheral end surface of the glass substrate is measured, and the distance from the end surface to the position where the ion concentration is constant is determined as the high thermal conductivity layer. It was set as the thickness. The ion concentration of sodium ions was measured by EPMA. The thickness of the high thermal conductivity layer was the average of the measured value of the outer peripheral end face and the measured value of the inner peripheral end face.

(Measurement of flatness)
Next, five glass substrates were extracted for each condition, and the flatness (PV value) was measured. The flatness was measured by measuring interference fringes in the same manner as the substrate before the chemical strengthening treatment. The flatness is preferably small, and if it exceeds 5 μm, there is a problem in performance as a magnetic disk. Here, the case where the average value of the five flatnesses was 5 μm or less was evaluated as good (evaluation ○), and the case where the average value exceeded 5 μm was regarded as problematic (evaluation x).

(Measurement of strength by ring bending strength test)
Furthermore, ten glass substrates were extracted for each condition, and the strength of the glass substrate was measured by an annular bending strength test.

  FIG. 4 is a schematic diagram of the annular bending test machine 20 used in this example. The annular bending test machine 20 places a glass substrate 30 on a support base 23 to support an outer periphery 31 in an annular shape, places an iron ball 22 on an inner periphery 33 of the glass substrate 30, and loads 21 via the iron ball 22. A destructive test is performed by applying a load to the inner periphery 33 of the glass substrate 30. This method is the same as a method generally used in the industry as a strength test of an information recording medium for hard disks.

  The support base 23 has a cylindrical shape with an inner diameter d = 63 mm. The iron ball 22 is an iron ball having a diameter of 28.57 mm and has a mass of about 100 grams, which is negligible compared to the load applied by the load 21. The iron ball 22 abuts on the inner periphery 33 of the glass substrate 30 and applies a force, thereby applying a bending stress to the glass substrate 30 supported on the outer periphery 31 by the support base 23. The pressing speed of the load 21 is 0.5 mm / min.

  According to the conventional experience of the present inventor, when the breaking strength is less than 100 N, the yield reduction due to breakage such as cracking or chipping of the glass substrate for information recording medium becomes remarkable. Therefore, here, the case where the breaking strength is 100 N or more in all of the 10 glass substrates measured is the best (evaluation ◎), and the case where the glass substrate having the breaking strength of 100 N or more is 7 or more is good (evaluation ○ ), The case where there were less than 7 glass substrates having a breaking strength of 100 N or more was evaluated as having a problem (evaluation x).

(Evaluation results)
The evaluation results are shown in Table 1. The symbols in the comprehensive judgment column have the following meanings.
○: Both flatness and fracture strength are evaluated as “good” or “good”.
X: When either flatness or breaking strength is evaluated x.

  It was confirmed that both the strength and flatness of the glass substrate were good when the thickness D of the high thermal conductivity layer existing on the outer peripheral end face and the inner peripheral end face was 5 μm to 20 μm (Examples 1 to 4).

  In the comparative examples (Comparative Examples 1 and 2) in which the thickness D of the high thermal conductivity layer existing on the outer peripheral end face and the inner peripheral end face is less than 5 μm, the evaluation of the breaking strength is x, and the outer peripheral end face and the inner peripheral end face In the comparative examples (Comparative Examples 3 and 4) in which the thickness D of the existing high thermal conductivity layer exceeds 20 μm, the evaluation of the flatness is x, and in any case, it is possible to obtain a good glass substrate for an information recording medium. could not.

It is a figure which shows an example of the glass substrate for information recording media of this invention, Fig.1 (a) is a perspective view which shows the whole glass substrate 10, and FIG.1 (b) is the sectional drawing. It is an expanded sectional view of the outer periphery end surface 14 vicinity of the glass substrate 10 for information recording media of this invention. It is a flowchart which shows an example of the manufacturing process of the glass substrate for information recording media in this invention. It is a schematic diagram of the annular bending test machine 20 used in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Glass substrate 11 Main surface 11a Boundary region 13 Center hole 14 Outer peripheral end surface 15 Inner peripheral end surface 18 High thermal conductivity layer

Claims (6)

A disk-shaped glass substrate having a central hole, and a glass substrate for an information recording medium having a main surface, an outer peripheral end surface and an inner peripheral end surface,
The outer peripheral end surface and the inner peripheral end surface have a high thermal conductivity layer having a higher thermal conductivity than the thermal conductivity inside the glass substrate on the outermost surface,
The glass substrate for an information recording medium, wherein a thickness of the high thermal conductivity layer on the outer peripheral end surface and the inner peripheral end surface is 5 μm to 20 μm at a central portion in the thickness direction of the glass substrate. The glass for an information recording medium according to claim 1, wherein a portion of the main surface excluding a boundary region between the outer peripheral end face and the inner peripheral end face does not have the high thermal conductivity layer. substrate. The high thermal conductivity layer is a layer in which at least a part of alkali metal ions contained in the glass substrate is replaced with another alkali metal ion having a large ion radius. The glass substrate for information recording media described in 1. In the method for producing a glass substrate for an information recording medium comprising a chemical strengthening step of chemically strengthening the glass substrate by ion exchange by immersing a disk-shaped glass substrate having a center hole in a chemical strengthening treatment liquid,
The chemical strengthening step is a step of forming a high thermal conductivity layer having a thermal conductivity higher than the thermal conductivity inside the glass substrate on an outer peripheral end surface and an inner peripheral end surface of the glass substrate,
The glass substrate for an information recording medium, wherein the high thermal conductivity layer formed on the outer peripheral end surface and the inner peripheral end surface of the glass substrate has a thickness of 5 μm to 20 μm at a central portion in the thickness direction of the glass substrate. Manufacturing method. By the chemical strengthening step, a high thermal conductivity layer having a thermal conductivity higher than the thermal conductivity inside the glass substrate is formed on the main surface of the glass substrate,
After strengthening to polish the main surface on which the high thermal conductivity layer is formed and remove the high thermal conductivity layer from a portion of the main surface excluding a boundary region between the outer peripheral end face and the inner peripheral end face The method for producing a glass substrate for an information recording medium according to claim 4, further comprising a polishing step. An information recording medium comprising at least a recording layer formed on the glass substrate for an information recording medium according to any one of claims 1 to 3.

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