JPWO2008062657A1 - Manufacturing method of glass substrate for information recording medium, glass substrate for information recording medium, and information recording medium - Google Patents

Abstract

A method for producing a glass substrate for information recording medium that has both high strength and high smoothness by chemical strengthening and can be efficiently produced, a glass substrate for information recording medium produced by the production method, and the glass substrate for information recording medium An information recording medium using the above is provided.

Description

  The present invention relates to a method for producing 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 glass substrate for information recording medium produced by the production method, and The present invention relates to an information recording medium using the glass substrate for 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. In the chemical strengthening treatment, a glass substrate is usually immersed in a chemical strengthening treatment solution, and alkali metal ions such as lithium ions and sodium ions contained in the glass substrate are alkali metal ions such as potassium ions having a larger ion radius than these ions. It is performed by an ion exchange method in which a compressive stress layer is formed on the surface of the glass substrate by ion exchange.

However, it is known that the smoothness of the glass substrate is deteriorated by performing such chemical strengthening treatment. As one measure for solving this, a method has been proposed in which after the surface of the glass substrate is subjected to ion exchange treatment, the polishing treatment is performed so that the thickness reduction due to polishing is larger than 0.7 μm on one surface. (For example, refer to Patent Document 1).
JP-A-8-124153

  However, as proposed in Patent Document 1, the method of polishing again the surface of the chemically strengthened glass substrate as it is cannot obtain the required smoothness or obtain the smoothness. However, there was a problem that much time and labor were required for that purpose.

  In particular, with the recent demand for reduction in the flying height of the magnetic head for improving the recording density, the glass substrate for information recording media is required to have a very high level of smoothness with a surface roughness Ra of 0.3 nm or less. However, it has been very difficult to efficiently manufacture such a glass substrate having high smoothness.

  The present invention has been made in view of the technical problems as described above, and an object of the present invention is to provide a glass for an information recording medium that has high strength and high smoothness by chemical strengthening and can be efficiently manufactured. It is providing the manufacturing method of a board | substrate, the glass substrate for information recording media manufactured by this manufacturing method, and the information recording medium using this glass substrate for information recording media.

In order to solve the above problems, the present invention has the following features.
1.
Information recording including a chemical strengthening step of chemically strengthening the glass substrate by immersing the glass substrate in a chemical strengthening treatment liquid and replacing alkali metal ions contained in the glass substrate with alkali metal ions contained in the chemical strengthening treatment liquid. In the method for producing a glass substrate for a medium,
The chemical strengthening step;
A homogenization step of increasing the surface roughness Ra of the surface of the glass substrate;
A second polishing step for polishing the surface;
A method for manufacturing a glass substrate for an information recording medium, wherein the steps are performed in this order.
2.
The homogenizing step is a step of etching the surface of the chemically strengthened glass substrate with a solution. The manufacturing method of the glass substrate for information recording media as described in 2 ..
3.
The surface roughness Ra of the surface is
It is 0.3 to 0.5 nm before the chemical strengthening step, 0.6 to 2 nm after the homogenizing step, and 0.3 nm or less after the second polishing step. Or 2. The manufacturing method of the glass substrate for information recording media as described in 2 ..
4).
1. To 3. An information recording medium glass substrate produced by the method for producing an information recording medium glass substrate according to any one of the above.
5).
4). An information recording medium, wherein at least a recording layer for recording information is formed on the glass substrate for information recording medium described in 1.
6).
4. The recording layer is a magnetic layer made of a magnetic material. The information recording medium described in 1.

  According to the present invention, after chemically strengthening the glass substrate, the surface of the glass substrate is subjected to a step of uniformly roughening the surface of the chemically strengthened glass substrate and increasing the surface roughness Ra of the surface. A glass substrate having high smoothness can be obtained efficiently by polishing the entire surface after the entire surface is made uniform. Therefore, a method for producing a glass substrate for information recording medium that has both high strength and high smoothness by chemical strengthening and can be efficiently produced, a glass substrate for information recording medium produced by the production method, and the information recording medium use An information recording medium using a glass substrate can be provided.

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 figure which shows an example of the glass substrate for information recording media of this invention. It is a figure which shows another example of the glass substrate for information recording media of this invention. It is an image figure of the roughness curve of the surface of the glass substrate before and behind a chemical strengthening process. It is an image figure of the roughness curve of the surface of the glass substrate after a homogenization process. It is an image figure of the roughness curve of the surface of the glass substrate after a 2nd grinding | polishing process.

Explanation of symbols

10, 10a, 10b Glass substrate 11, 11a, 11b Surface 13 Center hole 14 Outer peripheral end surface 15 Inner peripheral end surface

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

(Glass substrate for information recording media)
FIG. 2 is a view showing an example of the glass substrate for information recording medium of the present invention. 2A is a perspective view, and FIG. 2B is a cross-sectional view. The glass substrate 10 is a disk-shaped glass substrate having a central hole 13 and has a 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.

  Moreover, the glass substrate 10 has the area | region 18 strengthened chemically and the area | region 19 which is not chemically strengthened. The chemically strengthened region 18 is obtained by immersing a glass substrate in a heated chemical strengthening treatment solution, so that alkali metal ions such as lithium ions and sodium ions contained in the glass substrate have a larger ion radius than potassium ions. The glass substrate is strengthened by generating compressive stress in the chemically strengthened region 18 due to distortion caused by the difference in ion radius.

  FIG. 3 is a view showing another example of the glass substrate for information recording medium of the present invention. FIG. 3A is a cross-sectional view showing the glass substrate 10a when the amount of polishing in the second polishing step (polishing step after chemical strengthening treatment) is increased, and FIG. 3B is a diagram in the second polishing step. It is sectional drawing which shows the glass substrate 10b at the time of further enlarging polishing amount. In the glass substrate 10a of FIG. 3A, the depth of the chemically strengthened region remaining on the surface 11a is the depth of the chemically strengthened region remaining on the outer peripheral end surface 14 and the inner peripheral end surface 15 by polishing the surface 11a. It is shallower than that. Further, in the glass substrate 10b of FIG. 3B, since the polishing amount of the surface 11b is larger, a region 19 that is not chemically strengthened is directly exposed on the surface 11b, and the chemically strengthened region 18 is an outer peripheral end face. 14 and the inner peripheral end face 15 only.

  Thus, in the glass substrate for an information recording medium of the present invention, there is no particular limitation on whether or not a strengthened region remains on the surface, or the thickness of the strengthened region, etc., and at least the outer peripheral end surface 14 and the inner surface It suffices if the reinforced region 18 exists on the peripheral end face 15.

The material of the glass substrate 10 is not particularly limited as long as it can be chemically strengthened by ion exchange. For example, soda lime glass mainly composed of SiO ₂ , Na ₂ O and CaO; aluminosilicate glass mainly composed of SiO ₂ , Al ₂ O ₃ and 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.

In particular, considering the balance between solubility characteristics and mechanical strength for information recording media, various physical characteristics, and stability, a material mainly composed of SiO ₂ is more preferable. Furthermore, the content of SiO ₂ is more preferably in the range of 45 to 85% by mass.

  There is no limitation on the size of the glass substrate 10. 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. Further, the thickness of the glass substrate 10 is not limited. For example, glass substrates 10 having various thicknesses such as 2 mm, 1 mm, and 0.63 mm can be used.

(Manufacturing process of glass substrate for information recording medium)
FIG. 1 is a flowchart showing an example of a manufacturing process of a glass substrate for an information recording medium in the present invention.

  The glass substrate for an information recording medium of the present invention is subjected to a preparatory process such as a blank material manufacturing process of S1, an inner and outer peripheral processing process of S2, a lapping process of S3, a first polishing process of S4, a chemical strengthening process of S5, It manufactures by performing the equalization process of S6, and the 2nd grinding | polishing process of S7 in order. The manufacturing method of the glass substrate for information recording media of this invention has the characteristics in the equalization process of S6 and the 2nd grinding | polishing process of S7 among these processes.

  Pre-processes such as a blank material manufacturing process, an inner and outer peripheral processing process, and a lapping 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 producing 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.

  The order of each of these pre-processes is not limited to that shown in FIG. 1, and can be appropriately changed depending on the situation. For example, the inner and outer peripheral machining steps may be performed after the blank material 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.

  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 strain of the glass substrate 10, a heat shock process for confirming the reliability of the strength of the glass substrate 10, and foreign matters such as abrasives and chemical strengthening treatment liquid remaining on the surface of the glass substrate 10 It may have a cleaning process for removing, various inspection / evaluation processes, and the like.

(First polishing process)
A 1st grinding | polishing process is a process of grind | polishing the surface of the glass substrate 10 before a chemical strengthening process, and is a process of removing the flaw and unevenness | corrugation of the surface of the glass substrate 10, and improving smoothness. As a polishing method, a known method can be used as it is as a method for producing a glass substrate for an information recording medium. For example, a pad is pasted on the opposing surfaces of two rotatable surface plates arranged opposite to each other, a glass substrate 10 is disposed between the two pads, and the glass substrate 10 is rotated while contacting the pad with the surface of the glass substrate 10. This can be done by supplying an abrasive to the surface of the substrate 10.

  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.

  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. Moreover, it is preferable to perform the washing | cleaning process for removing the abrasive | polishing agent which remained on the surface of the glass substrate 10 after a 1st grinding | polishing process.

  In the present invention, the surface roughness Ra of the surface of the glass substrate 10 after the first polishing step is not particularly limited, but in order to finally obtain the glass substrate 10 having high smoothness, The surface roughness Ra of the surface of the glass substrate 10 is preferably in the range of 0.3 to 0.5 nm. In the subsequent chemical strengthening step, the phenomenon that the smoothness of the surface of the glass substrate 10 deteriorates unevenly occurs, but when Ra after the first polishing step exceeds 0.5 nm, the degree of the deterioration becomes remarkable. It gets bigger. Therefore, in order to finally obtain a glass substrate 10 having high smoothness, the amount of increase in Ra in the homogenization process must be increased, and more time and labor than necessary for the second polishing process are required. come. Further, even if Ra is less than 0.3 nm, there is no influence on the effect of the present invention to finally obtain a glass substrate 10 having high smoothness, but it takes more time and effort for the first polishing step than necessary. turn into.

  In addition, surface roughness Ra means arithmetic mean height Ra prescribed | regulated by JISB0601: 2001. The surface roughness Ra can be measured by an atomic force microscope (AFM) or the like.

(Chemical strengthening process)
In the chemical strengthening step, by immersing the glass substrate 10 in a heated chemical strengthening treatment liquid, alkali metal ions such as lithium ions and sodium ions contained in the glass substrate 10 are converted into alkali metals such as potassium ions having a larger ion radius. This is performed by an ion exchange method in which ions are substituted. Compressive stress is generated in the ion-exchanged region due to the distortion caused by the difference in ion radius, and the surface of the glass substrate 10 is strengthened.

  There is no restriction | limiting in particular in a chemical strengthening process liquid, A well-known chemical strengthening process liquid 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 10 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 10 is excessively increased and the glass substrate 10 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 10, and more preferably lower than the glass transition point −50 ° C.

  Conventionally, it has been known that the smoothness of the glass substrate 10 is deteriorated by performing the chemical strengthening treatment. The present inventor has found that the deterioration of smoothness due to the chemical strengthening treatment does not occur when the surface of the glass substrate 10 is uniformly roughened, but occurs when relatively large irregularities, particularly convex portions, occur unevenly. I found it. Such unevenness is considered to be caused by a crystal such as a nitrate that is a chemical strengthening treatment liquid being firmly attached or by erosion by the chemical strengthening treatment liquid.

  FIG. 4 is an image diagram of the surface roughness curve of the glass substrate 10 before and after the chemical strengthening step. The horizontal axis in FIG. 4 is the distance L (μm) of the surface 11 of the glass substrate 10 and the vertical axis is the height H (nm) of the surface 11. FIG. 4A shows a state before the chemical strengthening step, and FIG. 4B shows a state after the chemical strengthening step. Before the chemical strengthening step, the first polishing step is uniformly polished, the roughness curve is uniform, and no large abnormality is observed. However, after the chemical strengthening step, no significant change is observed in the average roughness, but it is recognized that relatively large irregularities exist unevenly.

  Even if the surface of the glass substrate 10 is further polished in this state, it is difficult to finish the entire surface with high smoothness because it is affected by unevenness that exists unevenly. The present inventor does not perform the polishing directly after the chemical strengthening step, but performs the polishing after performing the uniformizing step for increasing the surface roughness Ra by uniformly roughing the surface of the glass substrate 10 once. The present inventors have found that the entire surface of the glass substrate 10 can be efficiently finished with high smoothness without being affected by uneven unevenness generated in the strengthening process.

  In addition, in order to prevent generation | occurrence | production of the crack of the glass substrate 10 by a thermal shock at the time of being immersed in the heated chemical strengthening process liquid, and generation | occurrence | production of a fine crack, a glass substrate is used in a preheating tank prior to immersion in a chemical strengthening process liquid. You may have the preheating process which heats 10 to predetermined temperature.

(Uniformization process)
The homogenizing step is a step of increasing the surface roughness Ra by roughening the surface of the chemically strengthened glass substrate 10. As described above, after the chemical strengthening step, the surface of the glass substrate 10 is once uniformly roughened, and the polishing is performed after the uniformizing step of increasing the surface roughness Ra, thereby causing non-uniformity generated in the chemical strengthening step. The entire surface of the glass substrate 10 can be efficiently finished with high smoothness without being affected by unevenness. That is, after removing the protruding portion on the surface of the glass substrate 10 as shown in FIG. 4B, uniform irregularities as shown in FIG. 5 are formed on the surface of the glass substrate 10.

  The homogenization step is not particularly limited as long as the surface of the chemically strengthened glass substrate 10 can be roughened to increase the surface roughness Ra of the surface. For example, a method of polishing using a polishing agent having a particle size larger than that of the polishing agent used in the second polishing step, a method of etching with a solution, a method of sandblasting, and the like can be mentioned. Among these, from the viewpoint that the entire surface of the glass substrate 10 can be efficiently roughened, a method of performing etching with a solution is preferable.

As the solution used for etching, hydrofluoric acid, silicic hydrofluoric acid, ammonium fluoride, an acidic aqueous solution containing at least one of them, or a strong alkaline aqueous solution containing NaOH or KOH as a main component is appropriately selected and used. be able to.
When using acidic aqueous solutions, add acid chemicals such as hydrochloric acid, nitric acid, sulfuric acid, acetic acid, oxalic acid, citric acid, surfactants, etc. as necessary, taking dissolution rate, homogeneity, stability, etc. into consideration. It is preferable to adjust the characteristics of the solution. Also in the case of using a strong alkaline aqueous solution, it is preferable to adjust the characteristics of the solution by adding a surfactant and adjusting the characteristics of the solution. Thus, the etching reactivity with respect to the glass containing SiO ₂ as a main component can be enhanced by adjusting the characteristics of the solution.
More preferably, by using an acidic aqueous solution containing at least one of silicic acid, ammonium fluoride, and at least one of them, the etching reactivity with respect to the glass mainly composed of SiO ₂ can be greatly increased, and the surface roughness is increased. This can be easily controlled.
In addition, it is also preferable to heat and use the solution for efficient etching.

FIG. 5 is an image diagram of the roughness curve of the surface of the glass substrate 10 after the homogenization step. The horizontal axis in FIG. 5 is the distance L (μm) of the surface 11 of the glass substrate 10, and the vertical axis is the height H (nm) of the surface 11.
As shown in FIG. 5, the unevenness | corrugation which generate | occur | produced in the chemical strengthening process has decreased, and it has been in the state where the whole was uniformly roughened. Although there is no restriction | limiting in particular about surface roughness Ra of the surface of the glass substrate 10 after a homogenization process, In order to obtain the glass substrate 10 which finally has high smoothness efficiently, the glass substrate 10 after a homogenization process The surface roughness Ra of the surface is preferably in the range of 0.6 to 2 nm. When the surface roughness Ra is less than 0.6 nm, the unevenness generated in the chemical strengthening process cannot be sufficiently removed, and it may be difficult to finally obtain the glass substrate 10 having high smoothness. If the surface roughness Ra exceeds 2 nm, the second polishing step takes more time and effort than necessary.

  In addition, it is also preferable to provide the washing | cleaning process for fully removing a chemical strengthening process liquid, a solution, etc. before and after a homogenization process.

(Second polishing step)
The second polishing step is a step of polishing the surface of the glass substrate 10 whose surface has been uniformly roughened by the homogenizing step. As a polishing method, a known method can be used as it is as a method for manufacturing the glass substrate 10 for an information recording medium. For example, it is possible to polish by the same method as in the first polishing step using the same polishing agent and pad as in the first polishing step.
Or you may grind | polish using texturing. Texture processing is a tape polishing method using a fine polishing slurry such as diamond, and is a general method for manufacturing a glass substrate for an information recording medium.

  By the second polishing process, the chemically strengthened region on the surface of the glass substrate 10 is reduced. There is no restriction on whether or not the strengthened region remains on the surface of the glass substrate 10 after the second polishing step, or the thickness of the remaining strengthened region.

FIG. 6 is an image diagram of the roughness curve of the surface of the glass substrate 10 after the second polishing step. The horizontal axis in FIG. 6 is the distance L (μm) of the surface 11 of the glass substrate 10, and the vertical axis is the height H (nm) of the surface 11.
As described above, the surface 11 of the glass substrate 10 after the second polishing step is uniform and has high smoothness. The surface roughness Ra of the surface of the glass substrate 10 after the second polishing step is not particularly limited, but from the viewpoint of reducing the flying height of the magnetic head for improving the recording density, the glass after the second polishing step. The surface roughness Ra of the surface of the substrate 10 is preferably 0.3 nm or less.

(Information recording medium)
An information recording medium can be obtained by forming at least a recording layer on the glass substrate 10 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. 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, etc., if 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.

(Examples 1-4)
Aluminosilicate glass was used as the glass material, and the blank glass was produced by press molding the molten glass. After the inner and outer peripheral processing steps and the lapping step, a first polishing step was performed to obtain a glass substrate 10 having an outer diameter of 65 mm, an inner diameter of 20 mm, and a thickness of 0.635 mm. In the first polishing step, cerium oxide was used as an abrasive. The surface roughness Ra of the surface of the glass substrate 10 after the first polishing step was 0.4 nm. The surface roughness Ra was measured using an atomic force microscope (AFM).

Next, the glass substrate 10 was immersed in a chemical strengthening treatment solution to perform a chemical strengthening step. As the chemical strengthening treatment 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. The temperature of the chemical strengthening treatment liquid was 400 ° C. and the immersion time was 40 minutes.

  After the chemical strengthening treatment step, the glass substrate 10 was immersed in a solution to perform a homogenization step. Hydrofluoric acid was used for the solution. The temperature of the solution was 25 ° C. Glass substrates 10 having surface roughness Ra of 0.6 nm (Example 1), 1 nm (Example 2), 2 nm (Example 3), and 3 nm (Example 4) were obtained by variously changing the immersion time. Ten sheets were produced.

  Then, the 2nd grinding | polishing process was performed and the surface roughness Ra was measured. As in the first polishing step, cerium oxide was used as an abrasive. Of the 10 glass substrates 10 under each condition, 5 sheets with a polishing time of 5 minutes in the second polishing step and 5 sheets with a polishing time of 15 minutes were used. The evaluation was best when the surface roughness Ra was 0.3 nm or less under the condition of polishing time 5 minutes (evaluation ◎), and the surface roughness Ra was 0.3 nm or less under the condition of polishing time 15 minutes. The case was good (evaluation ○), and the case where the surface roughness Ra did not become 0.3 nm or less even under the condition of the polishing time of 15 minutes was regarded as problematic (evaluation x). In addition, the surface roughness Ra used the average value of the measured value of 105 glass substrates.

  The results are shown in Table 1. In Examples 1, 2, and 3 in which the surface roughness Ra after the second polishing step is in the range of 0.6 to 2 nm, the surface roughness Ra becomes 0.3 nm or less under the condition of the polishing time of 5 minutes. And it was very good. In Example 4 in which the surface roughness Ra after the second polishing step was 3 nm, the surface roughness Ra was 0.3 nm or less under the condition of the polishing time of 15 minutes, and the glass substrate 10 having good smoothness was obtained. I was able to.

(Comparative Example 1)
A glass substrate 10 was produced under the same conditions as in Example 1 except that the homogenization step was not performed, and the surface roughness Ra after the second polishing step was measured. The results are also shown in Table 1. Since the homogenization process was not performed, the surface roughness Ra did not become 0.3 nm or less even when the polishing time in the second polishing process was 15 minutes, and a glass substrate 10 having good smoothness could not be obtained. .

Claims (6)

Information recording including a chemical strengthening step of chemically strengthening the glass substrate by immersing the glass substrate in a chemical strengthening treatment liquid and replacing alkali metal ions contained in the glass substrate with alkali metal ions contained in the chemical strengthening treatment liquid. In the method for producing a glass substrate for a medium,
The chemical strengthening step;
A homogenization step of increasing the surface roughness Ra of the surface of the glass substrate;
A second polishing step for polishing the surface;
A method for manufacturing a glass substrate for an information recording medium, wherein the steps are performed in this order. The method for producing a glass substrate for an information recording medium according to claim 1, wherein the homogenizing step is a step of etching the surface of the chemically strengthened glass substrate with a solution. The surface roughness Ra of the surface is
3. The method according to claim 1, wherein the thickness is 0.3 to 0.5 nm before the chemical strengthening step, 0.6 to 2 nm after the homogenization step, and 0.3 nm or less after the second polishing step. The manufacturing method of the glass substrate for information recording media of 1 term | claim or 2nd term | claim. A glass substrate for an information recording medium manufactured by the method for manufacturing a glass substrate for an information recording medium according to any one of claims 1 to 3. An information recording medium, wherein at least a recording layer for recording information is formed on the glass substrate for information recording medium according to claim 4. 6. The information recording medium according to claim 5, wherein the recording layer is a magnetic layer made of a magnetic material.