JP2007217204A - Glass substrate for magnetic recording medium and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for a magnetic recording medium, having improved fracture strength and improved adhesion to a metal layer to be formed on the surface thereof. <P>SOLUTION: The disk glass substrate 1 for a magnetic recording medium is characterized in that a nonchemically strengthened layer 2 (tensile stress layer) is formed in its inside, a chemically strengthened layer 3c (compression stress layer) is formed around the end face 1c of the inner periphery, and a chemically strengthened layer 3d is formed around the end face 1d of the outer periphery. Chemically strengthened layers are formed on neither of the main surfaces (upper surface 1a and lower surface 1b). The fracture strength of the glass substrate can be improved because the chemically strengthened layers formed around the end faces of the substrate can give a balance between the tensile stress and the compression stress in the inside of the substrate. Further, the adhesion strength between a nickel alloy layer formed on the upper surface 1a or the lower surface 1b and the glass substrate can be improved because chemically strengthened layers are formed on neither of the upper surface 1a nor of the lower surface 1b. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a glass substrate used for a magnetic recording medium and a manufacturing method thereof.

  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 are also used 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 rotated at a high speed of 10,000 [rpm] or more. It is necessary to let 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, 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 a general donut-shaped 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 perform press molding to produce a disk-shaped glass substrate (press molding) Process). A hole is made in the center of the glass substrate to produce a donut-shaped glass substrate.

  Both surfaces of the doughnut-shaped glass substrate are ground and polished, 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 is ground and polished again, and the parallelism, flatness, and thickness of the glass substrate are finely adjusted (second lapping step). The glass substrate with finely adjusted parallelism and the like is polished on both surfaces, the surface irregularities are made uniform (polishing step), and finally washed to become a glass substrate for a magnetic recording medium.

  Usually, for the glass substrate, in order to increase its breaking strength, crystallized glass in which a crystal phase is generated is used, or chemically strengthened glass subjected to chemical strengthening after completion of the polishing process.

  In the case of producing a crystallized glass substrate, the glass substrate that has been subjected to the press molding step is sandwiched between ceramic plates and heat-treated to be crystallized (crystallization step). After the crystallization process, the above-described first lapping process to polishing process are performed.

  In the case of producing a chemically strengthened glass substrate, the glass substrate obtained by melting and press-molding is processed up to the polishing step, and then mixed in a molten salt such as sodium nitrate or potassium nitrate. By immersing, a compressive stress layer is formed on the surface to increase the fracture strength (for example, Patent Document 1). Thereafter, the cleaning process is performed.

  Then, a magnetic recording medium is manufactured by forming a magnetic material on the surface of the crystallized glass substrate or the chemically strengthened glass substrate by a sputtering method or the like. In addition, the magnetic head for reading the magnetic recording information recorded on the magnetic recording medium is configured to move in a state of floating from the surface of the magnetic recording medium.

  By the way, the magnetic recording density has been increasing at a tremendous rate in recent years, and there is a competition to achieve an annual rate of 100%, that is, a magnetic recording density that is doubled every year. As measures for improving the recording density on the magnetic recording medium side, there are an improvement by conventional in-plane magnetic recording and a method of adopting perpendicular magnetic recording.

  In order to improve by in-plane magnetic recording, a method is adopted in which a texture is applied to the surface of the glass substrate to reduce the flying height of the magnetic head and improve the electromagnetic conversion characteristics. Texture processing is performed to form circumferential fine grooves called “texture” on the surface of the glass substrate (for example, Patent Document 2). By performing this texture processing, the magnetic head floats on the magnetic recording medium and seeks. In this case, the magnetic recording medium and the magnetic head can be prevented from coming into contact with each other and rubbed, and the in-plane magnetization direction can be oriented in the circumferential direction which is the recording direction. By orienting in the circumferential direction, high density recording becomes possible as a so-called “anisotropic medium”.

  The grooves formed on the substrate surface by this texturing need to be concentric with a width of 1 [μm] or less and a depth of about 0.1 [nm]. A magnetic body is arranged along the concentric grooves to form one bit. The processed magnetic body has anisotropy along a concentric circle, and the N pole and the S pole can be easily separated, so that the S / N ratio of electromagnetic conversion characteristics can be increased.

  The texture processing is performed by sliding the tape member on the surface of the glass substrate while dropping the diamond slurry on the surface of the glass substrate. The texture processing apparatus is not particularly limited, and a so-called texture machine is used. The control of this texture processing also depends on the fine waviness and surface average roughness of the glass substrate.

  On the other hand, it is possible to texture the aluminum alloy substrate more easily than the glass substrate. When producing a magnetic recording medium using an aluminum alloy substrate, a nickel-phosphorus (Ni-P) alloy layer is generally formed on the aluminum alloy substrate by an electroless plating method, and further smoothed by polishing. Texture processing is performed. In other words, the aluminum alloy substrate is textured on the nickel alloy layer, and the crystallized glass substrate and the chemically strengthened glass substrate can be easily formed if the nickel alloy layer is formed on the surface. It is considered possible to apply texture processing.

  On the other hand, in a perpendicular magnetic recording medium that is highly expected as a high-density technology, it is necessary to arrange magnetic materials perpendicularly to the substrate surface. For this purpose, it is necessary to form a soft magnetic layer between the magnetic material and the substrate. is there. Since the soft magnetic layer needs to have a thickness of about 100 μm, the sputtering method for forming the magnetic material takes an enormous amount of time, which is an obstacle to realizing mass production. A typical alloy of the soft magnetic layer is a nickel-cobalt (Ni-Co) alloy. Therefore, if a nickel alloy can be formed on a crystallized glass substrate or a chemically strengthened glass substrate by an electroless plating method that is faster than the sputtering method and easy to process in large quantities, mass production of perpendicular magnetic recording media is possible. it is conceivable that.

JP 2003-157522 A JP 2002-251716 A

  However, it is difficult to form nickel alloy layers such as nickel-phosphorus alloy layers and nickel-cobalt alloy layers with high adhesion strength on crystallized glass substrates and chemically tempered glass substrates. However, sufficient adhesion strength is not obtained.

  As for the technique of forming a nickel alloy film on a crystallized glass substrate or a chemically strengthened glass substrate by an electroless plating method, an attempt has been made mainly to devise a pretreatment method before plating treatment. However, even if the pretreatment method is devised in this way, the adhesion strength of the nickel alloy layer can be increased to the extent that it can withstand the processing pressure of the polishing in the polishing process for smoothing performed after the plating process. However, the nickel alloy layer is peeled off during the polishing process, making mass production difficult.

  In the electroless plating method, a base metal having a higher ionization tendency than a target metal is deposited as a seed crystal on a substrate surface, and then the substrate is immersed in a plating solution containing the target metal ion. As a result, the target metal ion-exchanges with the seed crystal metal, and the target metal plating proceeds to form the target metal on the substrate surface.

  Conventionally, in order to increase the adhesion strength of the nickel alloy layer, it has been important that the seed crystal has firmly penetrated the surface of the glass substrate. To that end, based on the idea that the surface should be moderately uneven The invention has been made to roughen the substrate surface. For example, crystallized glass is advantageous for roughening the surface of a glass substrate because a crystal phase and an amorphous phase are mixed, and therefore, crystallized glass is said to be easy to plate. .

  However, it is considered that the substrate that can cope with the further high-density recording required in the future needs to have a smooth surface. Therefore, roughening the surface of the glass substrate to form a nickel alloy layer hinders further high-density recording. Also, even if an attempt is made to smooth the surface by polishing the surface on which the nickel alloy layer is formed by plating, the unevenness of the base (glass substrate) affects the surface, so it cannot be smoothed sufficiently, and high-density recording There is a problem that the surface cannot be smoothed to a level required for the above.

  SUMMARY OF THE INVENTION The present invention solves the above-described problem, and an object thereof is to provide a glass substrate for a magnetic recording medium that can increase the adhesion strength with a metal layer formed on the substrate surface while increasing the fracture strength. And

  The inventor according to this application pays attention to the fact that when a metal layer is formed on a glass substrate that has not been chemically strengthened, the adhesion strength of the metal layer is increased, and after performing a chemical strengthening treatment on the glass substrate By removing the chemical strengthening layer on the main surface and forming a metal layer on the main surface from which the chemical strengthening layer has been removed, the adhesion strength between the glass substrate and the metal layer is increased while increasing the breaking strength of the glass substrate. I found that I can do it.

  When a metal layer is formed on a glass substrate that has not been subjected to chemical strengthening treatment, the adhesion strength between the glass substrate and the metal layer is increased, but since the chemical strengthening treatment is not performed, the fracture strength is reduced.

  Then, the inventor who concerns this application removed the chemical strengthening layer formed in the main surface, after performing the chemical strengthening process with respect to the glass substrate. Thereby, it turned out that a chemical strengthening layer remains in the end surface of a glass substrate, and the fracture strength of a glass substrate can be maintained with the chemical strengthening layer formed in the end surface. Since the chemically strengthened layer formed on the main surface is removed, the adhesion strength between the glass substrate and the metal layer can be increased when a metal layer is formed on the main surface.

  Hereinafter, specific embodiments of the present invention will be described.

  1st form of this invention is a disk-shaped glass substrate for magnetic recording media which has an end surface around the surface and the said surface, Comprising: The chemical strengthening layer is formed over the predetermined range inside from the said end surface. This is a glass substrate for a magnetic recording medium.

  A second aspect of the present invention is a glass substrate for a magnetic recording medium according to the first aspect, wherein a metal layer is formed on the surface.

  According to a third aspect of the present invention, there is provided the glass substrate for a magnetic recording medium according to the second aspect, wherein the metal layer is composed of a nickel alloy deposited by an electroless plating method. Is.

  According to a fourth aspect of the present invention, there is provided a chemical strengthening treatment step for subjecting a surface of a disk-shaped glass substrate and the periphery of the surface to a chemical strengthening treatment, and a chemical formed on the surface by polishing the surface. And a removing step for removing the reinforcing layer. A method for producing a glass substrate for a magnetic recording medium.

  A fifth aspect of the present invention is a method for manufacturing a glass substrate for a magnetic recording medium according to the fourth aspect, further comprising a metal layer forming step of forming a metal layer on the polished surface. To do.

  A sixth aspect of the present invention is a method for manufacturing a glass substrate for a magnetic recording medium according to the fifth aspect, wherein in the metal layer forming step, a metal layer made of a nickel alloy is polished after the polishing by an electroless plating method. It is formed on the surface of this.

  According to the present invention, it is possible to increase the adhesion strength with the metal layer formed on the surface of the substrate while increasing the breaking strength of the glass substrate for a magnetic recording medium.

[Configuration of glass substrate for magnetic recording medium]
A schematic configuration of a glass substrate for a magnetic recording medium according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a schematic configuration of a glass substrate for a magnetic recording medium according to an embodiment of the present invention. FIG. 1 (a) is a perspective view of the substrate, and FIG. 1 (b) is a sectional view of the substrate.

  As shown in FIG. 1A, the glass substrate 1 for a magnetic recording medium according to this embodiment has a disk shape, and a hole is formed at the center.

  As shown in the AA cross-sectional view of FIG. 1B, the glass substrate 1 for magnetic recording medium has a non-chemical strengthening layer 2 (tensile stress layer) inside, and the inner peripheral end face 1c has chemical inside. A reinforcing layer 3c is formed, and a chemical reinforcing layer 3d is formed inside the outer peripheral end face 1d. In this embodiment, the chemical strengthening layer is not formed on the upper surface 1a and the lower surface 1b which are main surfaces. For example, aluminosilicate glass is used as the glass substrate.

  Thus, by providing a chemical strengthening layer on the inner peripheral end face 1c and the outer peripheral end face 1d without providing a chemical strengthening layer on the upper surface 1a and the lower face 1b, which are the main surfaces, the compressive stress due to the chemical strengthening layer formed on the end face Further, it is possible to achieve a balance with the tensile stress due to the non-chemically strengthened layer existing inside, and as a result, it is possible to increase the breaking strength of the glass substrate 1 for magnetic recording media. In particular, if the compressive stress of the upper surface 1a and the lower surface 1b, which is the main surface, increases, the glass substrate may be destroyed. Therefore, the breaking strength of the glass substrate 1 for magnetic recording media is increased.

  Then, a nickel alloy layer is formed on the upper surface 1a of the magnetic recording medium glass substrate 1 by electroless plating. Since no chemically strengthened layer is formed on the upper surface 1a, the adhesion strength between the magnetic recording medium glass substrate 1 and the nickel alloy layer can be increased. Even when the nickel alloy layer is formed on the lower surface 1b, since the chemically strengthened layer is not formed on the lower surface 1b, the adhesion strength between the magnetic recording medium glass substrate 1 and the nickel alloy layer can be increased. It becomes possible.

[Method for producing glass substrate for magnetic recording medium]
Next, the manufacturing method of the glass substrate for magnetic recording media which concerns on this embodiment is demonstrated.

  First, a semi-finished glass substrate (blank material) is produced (step S01). Then, a glass substrate (perforated blanks material) in the previous stage to be subjected to the grinding / polishing process is produced (step S02). Next, the perforated blanks material is ground and a glass substrate (hereinafter referred to as RTP glass substrate) before polishing (Ready To Polish: RTP) is produced (step S03). Thereafter, a chemical strengthening process is performed on the RTP glass substrate (step S04). After performing the chemical strengthening treatment, the main surface of the glass substrate is polished to remove the chemical strengthening layer formed on the main surface, thereby producing a glass substrate for a magnetic recording medium (step S05). Thereafter, the glass substrate for magnetic recording medium is washed (step S06). Through these steps, the glass substrate 1 for magnetic recording media according to this embodiment is manufactured. Then, a nickel alloy layer is formed on the cleaned glass substrate for magnetic recording medium by electroless plating (step S07). Hereinafter, specific processing contents in each step will be described.

<Step S01: Blanks Material Production Process>
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 and press-molded to produce a disk-shaped glass substrate (press formation) Process). The semi-finished glass substrate produced by this press molding process is referred to as “blank material”.

<Step S02: Production of perforated blanks>
A hole with an inner diameter of 6 [mm] is opened with a diamond core drill in the center of the blanks after the crystallization treatment. Through this process, a donut-shaped perforated blank material having an outer diameter of 66 [mm], an inner diameter of 19 [mm], and a plate thickness of 1.1 [mm] is obtained.

<Step S03: Grinding, RTP glass substrate manufacturing process>
The perforated blanks produced in step S03 is ground by a double-side grinding machine holding a plate on which diamond pellets are attached, and the thickness is processed to 0.8 [mm]. Then, it is processed into an outer diameter of 65 [mm] and an inner diameter of 20 [mm] by a processing apparatus capable of processing the inner diameter and the outer diameter simultaneously. Thereafter, the perforated blank material is further ground with the double-side grinding machine until the thickness becomes 0.67 [mm]. The glass substrate that has been subjected to the grinding process is referred to as an RTP glass substrate.

<Step S04: Chemical Strengthening Process>
A chemical strengthening process is performed on the RTP glass substrate using a mixed solution (molten salt) obtained by mixing sodium nitrate and potassium nitrate. Hereinafter, the mixing ratio and temperature of the mixed liquid (molten salt) are shown.
Mixed liquid (molten salt): Sodium nitrate and potassium nitrate were mixed at a weight ratio of 3: 1.
Temperature of mixed liquid (molten salt): 380 ° C

  A chemical strengthening layer (compressive stress layer) was formed by immersing the RTP glass substrate in the liquid mixture (molten salt) at 380 ° C. for a predetermined time. By performing the chemical strengthening treatment, sodium ions and potassium ions diffuse into the glass and exchange (ion exchange) with lithium ions in the glass substrate. This ion exchange generates a compressive stress on the surface of the glass substrate due to the difference in atomic radius.

<Step S05: Polishing Process>
Next, the main surface of the glass substrate that has been subjected to grinding is polished. In this polishing, polishing is performed in two steps using a double-side polishing machine. Hereinafter, conditions of the first polishing process and the second polishing process will be described.

(Conditions for the first polishing process)
As a polishing machine, a 16B type polishing machine manufactured by Speed Fam Co., Ltd. was used. The number of sheets processed at one time is 100 sheets. Polishing cloth made of polyurethane foam (Roder MHC14) is attached to the upper and lower plates of the polishing machine. As the abrasive, an abrasive slurry containing cerium oxide as a main component (E-21 made by Mitsui Metals) in water and adjusted to a slurry concentration of about 100 g / L was used.

The glass on which the first chemical strengthening process has been completed with a double-side polishing machine while circulating the polishing slurry under the polishing processing conditions of pressure 150 [kg / cm ² ], rotation speed 20 [rpm], and polishing time of about 30 minutes. The substrate was polished. By polishing the glass substrate, about 15 [μm] on one side and about 30 [μm] on both sides were polished.

(Conditions for second polishing process)
The polishing machine used was the polishing machine used in the first polishing process (16B type polishing machine manufactured by Speedfam). Kanebo's suede polishing cloth was used by adhering it to the upper and lower plates. As the abrasive, a fine slurry (V2104 manufactured by Showa Denko) containing cerium oxide as a main component was included in water and the slurry was adjusted to a slurry concentration of about 100 g / L.

A glass substrate on which a first polishing process has been completed with a double-side polishing machine while circulating the polishing slurry under a polishing process condition of a pressure of 80 [g / cm ² ], a rotation speed of 50 [rpm], and a polishing time of about 10 minutes. Polished. By polishing the glass substrate, about 2 [μm] on one side and about 4 [μm] on both sides were polished.

  By carrying out the first polishing process and the second polishing process in the polishing process in step S05, the thickness of the glass substrate was set to about 0.635 [mm].

  Here, the chemical strengthening process in step S04 and the polishing process in step S05 will be described with reference to FIG. FIG. 2 is a cross-sectional view of a substrate for explaining a method for manufacturing a glass substrate for a magnetic recording medium according to an embodiment of the present invention.

(Step S04)
First, a chemical strengthening process is performed on the RTP glass substrate to form a chemically strengthened layer 3 (compressive stress layer) on the entire surface of the glass substrate, as shown in FIG. This glass substrate has a non-chemically strengthened layer 2 (tensile stress layer) inside, and the periphery thereof is chemically strengthened to form a chemically strengthened layer 3 (compressive stress layer).

(Step S05)
Next, by polishing the chemical strengthening layer (compressive stress layer) formed on the main surface (upper surface 1a and lower surface 1b) of this glass substrate, as shown in FIG. 2B, the glass substrate for magnetic recording medium 1 is produced. Here, the chemical strengthening layer (compressive stress layer) formed on the main surface (upper surface 1a and lower surface 1b) by this polishing process is completely removed, and the chemical strengthening layer is not left on the main surface (upper surface 1a and lower surface 1b). . Since only the main surface of the glass substrate is polished and the inner peripheral end face 1c and the outer peripheral end face 1d are not polished, the chemically strengthened layer 3c remains on the inner peripheral end face 1c, and the outer peripheral end face 1d is chemically strengthened internally. Layer 3d remains.

  As described above, the chemical strengthening layer (compressive stress layer) formed on the main surface (upper surface 1a and lower surface 1b) is polished and removed, and the chemical strengthening layer remains on the inner peripheral end surface 1c and the outer peripheral end surface 1d. Since the compressive stress and tensile stress inside the glass substrate can be balanced, the breaking strength of the glass substrate can be increased.

<Step S06: Cleaning Process>
Next, the glass substrate after the polishing treatment is washed. Here, scrub cleaning is performed with a sponge brush made of PVA, and then cleaning is performed using a detergent in an ultrasonic immersion bath. And the glass substrate after washing | cleaning is dried in the vapor | steam of IPA.

<Step S07: Plating process>
A nickel alloy layer is formed by an electroless plating method on the glass substrate for magnetic recording media produced through the above steps. Since the chemical strengthening layer is not formed on the main surface (upper surface 1a and lower surface 1b) of the glass substrate 1 for magnetic recording media, the adhesion strength between the substrate and the nickel alloy layer can be increased. The formation method of the nickel alloy layer is the same as a known method, but after the degreasing, sensitization, and activation processes are performed, electroless plating is performed to form the nickel alloy layer.

In step S07, general nickel alloy plating described in “Surface Technology Vol. 44 No. 10, 1993 (Adhesiveness between Glass and Electroless Nickel Plating)” was applied. Here, the degreasing process, the sensitization process, the activation process, and the electroless plating will be described in detail.
Degreasing treatment: The glass substrate for magnetic recording medium was immersed in an alkaline detergent PK-LCG22 (5% aqueous solution, 50 ° C.) manufactured by Parker Corporation for 15 minutes, and then washed with water.
Sensitization treatment: The sample was immersed in a 0.1 g / L aqueous solution of stannous chloride (SnCl) for 5 minutes, and then washed with water.
Activation treatment: It was immersed in a 0.1 g / L aqueous solution of the reagent palladium chloride (PdCl) for 5 minutes, and then washed with water.
Electroless plating: After performing the above degreasing, sensitization and activation treatments, it was immersed in a nickel-phosphorous plating solution manufactured by Uemura Kogyo to form a 20 μm nickel-phosphorous alloy layer.
Baking: After electroless plating, baking was performed at 150 ° C. for 2 hours.

<Measurement of thickness of chemically strengthened layer>
Here, a method for measuring the thickness of the chemically strengthened layer will be described. When a chemically strengthened glass substrate is divided and the cross section of the glass substrate is observed with a polarizing microscope, the difference in internal stress can be observed with the degree of coloring. In addition, when ion analysis is performed in the depth direction with an EPMA (Electron Probe Micro Analyzer), the ion distribution of sodium and potassium can be quantitatively evaluated. The sodium ion concentration gradually decreases from the outermost surface toward the inside, but does not decrease any more when the sodium ion concentration decreases to the base contained in the glass composition. The thickness that reaches this constant value from the surface is taken as the thickness of the chemically strengthened layer.

<Evaluation of adhesion strength>
A peel test (JIS K5400 8.15) was performed on the glass substrate for magnetic recording medium on which the nickel alloy layer was formed in step S07, and the adhesion strength of the nickel alloy layer was evaluated.

<Evaluation of fracture strength>
A glass substrate obtained by the process up to Step 06 was mounted on a ramp load type Toshiba hard disk device on which a 2.5-inch substrate is mounted, and the glass substrate was dropped from a height of 2 m onto an iron plate. Then, a drop test was performed on 10 glass substrates, and the breaking strength was evaluated based on the number of broken glass substrates.

[Example]
Next, a specific example and a comparative example for the example will be described.

Example 1
The conditions of the glass substrate used in Example 1 are shown below.
Glass type: aluminosilicate glass (IG-93 made by Ishizuka Glass)

The chemical strengthening process was performed on the RTP glass substrate manufactured through the processes from Step S01 to Step S03 (Step S04). At this time, the glass substrate was immersed for 40 minutes in a 380 ° C. mixed solution (molten salt) in which sodium nitrate and potassium nitrate were mixed at a weight ratio of 3: 1. As a result, it was chemically strengthened from the surface of the glass substrate to a depth of 25 [μm]. Thereafter, the main surface (upper surface 1a and lower surface 1b) of the glass substrate was polished to remove the chemical strengthening layer formed on the upper surface 1a and the lower surface 1b, thereby manufacturing the glass substrate 1 for magnetic recording medium (step S05). Thereafter, the glass substrate 1 for magnetic recording medium was washed (step S06). The surface roughness Ra of the glass substrate 1 for magnetic recording media was 5 mm. This surface roughness Ra is an arithmetic average roughness Ra of “surface roughness” according to JIS B0601. Below, the dimension of the glass substrate after the process of step S05 is given is shown.
Outer diameter: 65 [mm]
Inner diameter: 20 [mm]
Thickness: 0.635 [mm]
Thickness of the chemical strengthening layer formed on the inner peripheral end face 1c and the outer peripheral end face 1d: 25 [μm]
The chemical strengthening layer on the main surface (upper surface 1a and lower surface 1b) of the glass substrate is removed.

<Evaluation of adhesion strength>
A nickel-phosphorus alloy layer is formed by applying an electroless plating method to the glass substrate 1 for magnetic recording medium from which the chemical strengthening layer on the main surface (upper surface 1a and lower surface 1b) has been removed (step S07). The adhesion strength between the layer and the glass substrate surface was evaluated.
Evaluation results: The above peel test (JIS K5400 8.15) was carried out, and it was found that the adhesion strength between the nickel alloy layer and the glass substrate was high.

<Evaluation of fracture strength>
The glass substrate 1 for magnetic recording media produced up to step S06 was mounted on a hard disk device, and the above drop test was performed. Here, a drop test was performed on ten glass substrates.
Number of cracks: 0 (out of 10)
Thus, it was found that the breaking strength of the glass substrate was high.

  As described above, according to the glass substrate of Example 1, it is possible to form a nickel alloy layer having sufficiently high adhesion strength with the substrate surface while increasing the fracture strength required for the magnetic recording medium. .

  In addition, even if the surface roughness Ra of the glass substrate is 5 mm, the adhesion strength between the nickel alloy layer and the glass substrate can be increased, so that the surface smoothness required for high density recording is maintained and the adhesion is maintained. A nickel alloy layer having high strength can be formed on the glass substrate. In other words, in order to increase the adhesion strength between the nickel alloy layer and the glass substrate, there is no need to form irregularities on the surface of the glass substrate to roughen the surface, and the surface of the glass substrate is smoothed while the nickel alloy layer and the glass substrate are smoothed. It is possible to increase the adhesion strength.

  Next, a comparative example for the above embodiment will be described.

(Comparative Example 1)
The conditions of the glass substrate used in Comparative Example 1 are shown below.
Glass type: aluminosilicate glass

The chemical strengthening process was performed on the RTP glass substrate manufactured through the processes from Step S01 to Step S03 (Step S04). In Comparative Example 1, the glass substrate was immersed for 40 minutes in a mixed solution (molten salt) at 380 ° C. in which sodium nitrate and potassium nitrate were mixed at a weight ratio of 3: 1. As a result, it was chemically strengthened from the surface of the glass substrate to a depth of 25 [μm]. After performing the chemical strengthening treatment, the glass substrate was washed (step S06). In this comparative example, the chemical strengthening layer remains on the main surface (upper surface and lower surface) without polishing the main surface (upper surface and lower surface). Below, the dimension of the glass substrate after a chemical strengthening process is given is shown.
Outer diameter: 65 [mm]
Inner diameter: 20 [mm]
Thickness: 0.635 [mm]
Thickness of the chemically strengthened layer formed on the surface of the glass substrate: 25 [μm]
Since the main surface (upper surface and lower surface) is not polished, the chemical strengthening layer remains not only on the inner peripheral end surface and the outer peripheral end surface but also on the main surface (upper surface and lower surface).

<Evaluation of adhesion strength>
A nickel-phosphorus alloy layer was formed by applying an electroless plating method to this glass substrate, and the adhesion strength between the nickel alloy layer and the glass substrate surface was evaluated.
Evaluation results: The above peel test (JIS K5400 8.15) was carried out, and it was found that the adhesion strength between the nickel alloy layer and the glass substrate was low.

<Evaluation of fracture strength>
The glass substrate manufactured up to step S06 was mounted on a hard disk device, and the drop test was performed. Here, a drop test was performed on ten glass substrates.
Number of cracks: 0 (out of 10)
Thus, it was found that the breaking strength of the glass substrate was high.

  As described above, according to the glass substrate according to Comparative Example 1, since the chemical strengthening treatment was performed over the entire surface of the substrate, the fracture strength could be increased, but the surface subjected to the chemical strengthening treatment was applied. Since the nickel alloy layer was formed, the adhesion strength between the nickel alloy layer and the substrate surface could not be increased.

(Comparative Example 2)
The conditions of the glass substrate used in Comparative Example 2 are shown below.
Glass type: aluminosilicate glass

In Comparative Example 2, the chemical strengthening process of Step S04 was not performed, but the processes of Steps S01 to S03, S05, and S06 were performed to produce a glass substrate having a surface roughness Ra = 5 mm. Below, the dimension of the glass substrate which concerns on this comparative example 2 is shown.
Outer diameter: 65 [mm]
Inner diameter: 20 [mm]
Thickness: 0.635 [mm]

<Evaluation of adhesion strength>
The glass substrate was subjected to electroless plating to form a nickel-phosphorus alloy layer (step S07), and the adhesion strength between the nickel alloy layer and the glass substrate surface was evaluated.
Evaluation results: The above peel test (JIS K5400 8.15) was carried out, and it was found that the adhesion strength between the nickel alloy layer and the glass substrate was high.

<Evaluation of fracture strength>
The glass substrate according to Comparative Example 2 was mounted on a hard disk device, and the drop test was performed. Here, a drop test was performed on ten glass substrates.
Number of cracks: 8 (out of 10)
Thus, it was found that the fracture strength of the glass substrate was low.

  As described above, according to the glass substrate of Comparative Example 2, since the chemical strengthening treatment was not performed, the adhesion strength between the nickel alloy layer and the substrate surface could be increased, but the fracture strength required for the magnetic recording medium Was not obtained.

  The result of putting together Example 1 and Comparative Examples 1 and 2 is shown in the table of FIG. It can be seen that the glass substrate according to Example 1 satisfies the conditions required for the magnetic recording medium, and the glass substrates according to Comparative Examples 1 and 2 do not satisfy the conditions. In the table | surface of FIG. 3, the pass of comprehensive evaluation satisfy | fills the said conditions, and it has shown that the rejection does not satisfy | fill the conditions. Therefore, by removing the chemically strengthened layer on the main surface of the glass substrate, it is possible to increase the adhesion strength between the substrate surface and the nickel alloy layer while maintaining the fracture strength required for the magnetic recording medium.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows schematic structure of the board | substrate for magnetic recording media based on embodiment of this invention, Fig.1 (a) is a perspective view of a board | substrate, FIG.1 (b) is AA sectional drawing of a board | substrate. It is sectional drawing of the board | substrate for demonstrating the manufacturing method of the board | substrate for magnetic recording media which concerns on embodiment of this invention. It is a table | surface which shows the evaluation result of adhesion strength and fracture strength.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate for magnetic recording media 1a Upper surface 1b Lower surface 1c Inner peripheral end surface 1d Outer peripheral end surface 2 Non-chemical strengthening layer (tensile stress layer)
3 Chemical strengthening layer (compressive stress layer)

Claims (6)

A disk-shaped glass substrate for a magnetic recording medium having a surface and an end surface around the surface,
A glass substrate for a magnetic recording medium, wherein a chemically strengthened layer is formed over a predetermined range from the end face to the inside.   The glass substrate for a magnetic recording medium according to claim 1, wherein a metal layer is formed on the surface.   The glass substrate for a magnetic recording medium according to claim 2, wherein the metal layer is made of a nickel alloy deposited by an electroless plating method. A chemical strengthening treatment step for subjecting the surface of the disk-shaped glass substrate and the periphery of the surface to a chemical strengthening treatment;
By removing the chemical strengthening layer formed on the surface by polishing the surface,
The manufacturing method of the glass substrate for magnetic recording media characterized by the above-mentioned.   The method for producing a glass substrate for a magnetic recording medium according to claim 4, further comprising a metal layer forming step of forming a metal layer on the polished surface.   6. The method for manufacturing a glass substrate for a magnetic recording medium according to claim 5, wherein in the metal layer forming step, a metal layer made of a nickel alloy is formed on the polished surface by an electroless plating method.

Images