JPS63306529A - Substrate for magnetic disk - Google Patents

Abstract

PURPOSE:To improve heat resistance, weatherability and recording density by providing two intermediate layers formed of a ceramics material on both faces of a central layer formed of a composite of nonmetallic heat resistant fiber materials and ceramics material and coating glass layers on the outside surfaces thereof. CONSTITUTION:The central layer has a specified thickness and is constituted of the composite of one or >=two kinds of the nonmetallic heat resistant fiber materials selected from inorg. fibers, inorg. whiskers, carbon fibers and carbon whiskers and the ceramics. The intermediate layers having a specified thickness are formed of the ceramics material on both faces thereof. The surface layers 3 formed by glass coating are disposed on both faces of such substrate base. The heat resistance and weatherability are thereby improved and the high- density recording is enabled.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to a magnetic disk substrate.

[Prior Art] In recent years, with the rapid progress of magnetic disk devices and the increase in the recording density of magnetic disks as magnetic recording media, the following
As shown in (2) to (3), there is a demand for improved characteristics of magnetic disk substrates.

■Firstly, in order to increase the density of magnetic disks, the surface roughness of the substrate must be as small as possible and have few defects. ■In order to improve the tracking performance of the magnetic head, The substrate must have a surface shape with small undulations and no microprotrusions; ■As a substrate for supporting magnetic media, it must have good surface treatment properties, no magnetism, and chemical properties with excellent heat resistance and weather resistance. , ■ Since there is a risk of contact with the magnetic head, it must have excellent hardness and strength to ensure durability, and ■ It must have good flying characteristics and good CSS resistance.
(contact, start, stop) characteristics are required.

By the way, aluminum alloys have conventionally been used for magnetic disk substrates, but in order to satisfy the above-mentioned requirements (■ to ■), the following measures (A) to (C) have been considered. . In other words, (A) highly purifying the aluminum alloy base material of the substrate, (B) forming an alumite film on the surface of the aluminum alloy substrate to improve polishing workability and friction resistance, (C) aluminum alloy substrate For example, a plating film such as N1-P may be formed on the surface to improve polishing workability.

However, each of the above methods has the following problems. First, as shown in (A), it is extremely difficult to further purify the aluminum alloy base material due to the manufacturing process. Furthermore, high-purity aluminum alloys are difficult to handle in terms of corrosion resistance and cleanliness.

Further, even if the aluminum alloy base material is highly purified, there are limits to its hardness and rigidity as a metal material, and furthermore, it has poor workability for improving shape accuracy such as flatness and smoothness.

Furthermore, in (B), since the aluminum of the substrate itself serves as a material to form the alumite film, intermetallic compounds are likely to be incorporated into the alumite film and cause defects.

Furthermore, a thin film magnetic medium (γ-Fe2O3) is placed on the surface of the substrate.
In the heat treatment process for forming the film, cracks and deformation of the substrate are likely to occur due to the large difference in thermal expansion coefficient between the substrate and the film.

Furthermore, when a plating film is formed as shown in (C), there is a problem that it becomes easily charged by heat treatment.

As described above, it is extremely difficult to satisfy the above-mentioned requirements (1) to (2) using metallic materials.

Therefore, for example, JP-A-56-19527, 60-2
No. 2733, No. 66-138730, No. 60-15183
No. 7, No. 60-229224, No. 60-229233,
61-13434, 61-42730, 61-10
No. 5725, 61-122910.61-123034
No. 61-131229, No. 61-132576, etc., propose the use of ceramics or a composite of ceramics and glass as a magnetic disk substrate.

Generally, ceramic materials are far superior to aluminum alloy materials in terms of heat resistance, friction resistance, weather resistance, insulation, mechanical strength, and chemical stability.

For example, aluminum alloy material has a Vickers hardness of 1
00 kg/cut, whereas ceramic materials have a Vickers hardness of 600 kg/cut or more. Furthermore, the bending strength of aluminum alloy materials is about 1000 kg/co!, while that of ceramic materials is 2000 kg/co! That's all.

For this reason, ceramic materials are used in a wide range of applications in various fields.

[Problems to be solved by the invention] However, ceramic materials and glass materials are mainly composed of ionic bonds and covalent bonds, and lack ductility, and when external force is applied, they do not behave like metals. Ceramic materials and glass materials, which do not undergo plastic deformation, undergo brittle fracture when an external force exceeding the fracture stress is applied.

Therefore, if the disk substrate in the disk drive device reaches breaking stress for some reason, there is a risk of serious damage not only to the substrate but also to the disk drive device itself.

In addition, a magnetic disk is manufactured by forming a thin film magnetic medium on the surface of this magnetic disk substrate, but due to the demand for thinner and higher purity media, the ceramic surface that constitutes the substrate has to be made even more non-porous. It is necessary to eliminate distortion.

The present invention has been made in view of such circumstances, and
A magnetic disk substrate that has high strength, does not cause brittle fracture, has excellent flatness and smoothness, and has excellent heat resistance and weather resistance, making it possible to improve the recording density and speed of media. The purpose is to provide.

[Means for Solving the Problems] The magnetic disk substrate according to the present invention has a central layer formed of a composite of a nonmetallic heat-resistant fiber material and a ceramic material, and a ceramic material on both sides of the central layer. It is characterized by being a laminate having two intermediate layers formed and two surface layers formed by coating the outer surfaces of the intermediate layers with a glass material, respectively.

[Function] In the present invention, the magnetic disk substrate includes a center layer,
This is a 5-layer laminate including two intermediate layers laminated on both sides of this central layer and two surface layers laminated on the outside of this intermediate layer. The center layer is formed of a composite of a nonmetallic heat-resistant fiber material and a ceramic material. Such nonmetallic heat-resistant fiber materials include inorganic fibers, inorganic whiskers,
There are carbon fibers or carbon whiskers, and a combination of two or more of these types may be used.The substrate is laminated with two intermediate layers made of ceramic materials sandwiching such a center layer, which increases the strength of the substrate. In addition to having a high level of resistance, it is also difficult to cause brittle fracture.

Furthermore, since the surface layer is formed of a glass material, the flatness and smoothness of the substrate are excellent.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a sectional view of a main part of a magnetic disk substrate according to an embodiment of the present invention.

The center layer 1 has a certain thickness and is composed of a composite of ceramics and one or more nonmetallic heat-resistant fiber materials selected from inorganic fibers, inorganic whiskers, carbon fibers, and carbon whiskers. There is. On both sides of the center layer 1, intermediate layers 2 having a constant thickness are formed of a ceramic material. Surface layers 3 formed by glass coating are disposed on both sides of the substrate support constructed in this manner.

In addition to glass fiber, the inorganic fibers in the center layer 1 include alumina, zirconia, mullite, silica, SiC, and Si3.
Examples include ceramic fibers such as N4 or potassium titanate. Further, whiskers of these inorganic materials may be used to form a composite with ceramics, or carbon fibers or their whiskers may also be used.

The fibers used for the center layer 1 are preferably those that can be composited with the ceramic material constituting the intermediate layer 2 and that provide good adhesion at the interface between the fiber layer and the ceramic material layer. By providing the center layer 1 made of a composite of the fiber layer and the ceramic material layer, brittle fracture of the disk substrate is prevented.

Therefore, from the viewpoint of preventing brittle fracture, it is preferable for the center layer 1 made of this composite to be thick; however, if the composite layer is too thick, the mechanical strength of the disk substrate will decrease, and the ceramic material layer ( The unevenness of the composite layer (center layer 1) at the interface with the intermediate layer 2) appears on the surface of the glass coating film (surface layer 3), making it impossible to obtain good surface smoothness. For this reason, it is preferable that the center layer 1 formed of a composite has a thickness of 20 to 80% of the total thickness of the disk substrate, and if this center layer 1 is smaller than 20% of the total thickness of the disk substrate. This is because, while the effect of improving the toughness of the disk cannot be obtained, if it exceeds 80%, good surface smoothness cannot be obtained.

This center layer can be formed into a sheet by a paper making method, a press molding method, a sheet molding method, an impregnation method, or the like.

Note that if the content of inorganic fibers, carbon fibers, or their whiskers is 3% by volume, the effect of preventing brittle fracture cannot be obtained by adding fibers. For this reason, it is preferable that the content of fibers and/or whiskers in the composite constituting the center layer 1 be 3% by volume or more.

The intermediate layer 2 can be made of any ceramic material such as A4120S, ZrO2, 5iC1 or 5ilN4. The intermediate layer 2 needs to have good adhesion at the interface with the center layer 1 formed of a composite with fibers and form a strong laminate. The intermediate layer 2 made of this ceramic material improves the rigidity and mechanical strength of the magnetic disk substrate, and provides good surface smoothness.

The intermediate layer 2 made of this ceramic material is as follows (a)
It can be formed on the center layer 1 of the composite by the methods shown in (C).

(a) First, a sheet made of a ceramic material is formed in advance by a tape molding method, a calender roll method, or an extrusion molding method, and this ceramic sheet is pressed onto both sides of the composite layer of the center layer 1 by a press method. , or thermocompression bonding. After that, the ceramic sheet and the composite layer are subjected to CIP.
The ceramic sheets are integrated by a method such as a cold isostatic pressing method, and then fired to make the ceramic sheets dense.

(b) Layers made of a ceramic material are formed on both sides of the composite layer of the center layer 1 by a powder pressing method, a CIP method, etc., and then this laminate is fired to densify the ceramic layer.

(c) Apply a vapor deposition method, sputtering method, ion sputtering method, CVD method or sol-
A ceramic thin film is formed using a gel method or the like.

This intermediate layer 2 is preferably a sintered body as dense as possible in order to increase the rigidity and mechanical strength of the magnetic disk substrate and improve the surface smoothness. It is preferable that the total porosity of the ceramic material constituting the porosity is in the range of 0 to 3%.

Note that the thicker the intermediate layer 2, the better the surface smoothness of the magnetic disk substrate, but if the intermediate layer 2 is too thick,
The bulk specific gravity of the magnetic disk substrate becomes too large, resulting in poor CSS resistance during high-speed rotation (contact, start, stop)
In addition to impeding its properties, brittle fracture becomes more likely to occur. Therefore, the thickness of the intermediate layer 2 is set to 2 as in the embodiment described later.
The total thickness of the layers is preferably 7 to 80%, preferably 20 to 40%, of the total thickness of the substrate.

When the intermediate layer 2 made of a ceramic material is thinner than the above range, the unevenness of the interface between the central layer 1 and the intermediate layer 2 made of a ceramic material may cause the surface layer 3 formed of a glass coating film to become uneven. As a result, good surface smoothness cannot be obtained.

In addition, if the intermediate layer 2 is thicker than the above range, the overall thickness is specified in the standards for magnetic disk substrates, so the thickness of the center layer will be correspondingly thinner, resulting in brittle failure. It becomes easier.

The crystal grain size of the ceramic material forming the intermediate layer 2 is
In order to reduce defects such as pinholes and bubbles on the surface of the glass coating film constituting the surface layer 3 described later, the maximum crystal grain size is 100 μm or less, and the average crystal grain size is 50 μm or less.
If the crystal grain size exceeds these values and is coarse and 17 μm or less, the number of defects on the glass coating surface will be 300 or more, making high-density recording difficult, as will be described later.

There are some pores on the surface of the intermediate layer 2 formed of this ceramic material. Therefore, in order to improve the surface smoothness of the substrate, a surface layer 3 is formed by covering the intermediate layer 2 with a glass coating film.

The thickness of the glass coating film constituting the surface layer 3 is 3
The thickness is preferably from 10 to 300 μm, preferably from 10 to 300 μm.

If the thickness of the glass coating film is less than 3 μm, micropores on the surface of the underlying ceramic layer will appear on the surface of the glass coating film, and the surface smoothness of the substrate will deteriorate.

On the other hand, when the thickness of the glass coating film exceeds 500 μm, air bubbles generated during vitrification are incorporated into the glass coating film, and when the surface of the glass coating film is polished, the air bubbles become pinholes. appears, making it impossible to perform high-density recording.

The surface layer 3 made of a glass coating film can be formed by applying a powder slurry or paste that can have a glass composition by printing or painting, and then heating and melting it to vitrify it.

Further, it is also possible to form a powder that can have a glass composition into a sheet by a tape forming method or the like, apply this sheet to the surface of the intermediate layer 2, and then heat it to vitrify it.

Furthermore, a granulated powder having a glass composition is applied to the intermediate layer 2 by a thermal spraying method.
may be coated.

Furthermore, after coating the surface of the intermediate layer 2 with a sol that can have a glass composition, it may be vitrified by gelling it and heat-treating it.

At this time, the coefficient of thermal expansion of the surface layer 3 formed of the glass coating film is 15X10-7 in the temperature range of 0 to 1000°C with respect to the coefficient of thermal expansion of the underlying ceramic intermediate layer 2.
If the difference is greater than /℃, the strain generated within the glass coating film will increase, and there is a risk that cracks and fissures will occur in the glass coating film of the magnetic recording medium due to the thermal shock applied during the production of the magnetic recording medium. There is. Therefore, the difference in thermal expansion coefficient between the surface M3 and the intermediate layer 2 is between O and 100
It is preferable to keep the temperature within the range of 0°C to 15×10-77°C or less.

Next, the results of measuring the characteristics of the magnetic disk substrate according to the embodiment of the present invention will be explained together with the grounds for adopting the above-mentioned constituent elements and numerical limitations.

Made of SiC whiskers and Si3N4, thickness 600mm
A μm composite was produced by the HIP method (hot isostatic pressing method). This composite becomes the center layer, and the amount of whiskers added is 1% by volume, 3% by volume, 5% by volume, and 9% by volume.
The content was varied by volume%, 15% by volume, and 20% by volume.

When the transverse strength (3-point bending method) and critical stress intensity factor +c (notched beam method) of the composite thus prepared were measured, the effect of whisker addition appeared at 3% by volume or more, and 9% by volume. and KIC of 25 and 3 at 15% by volume.
It showed a high toughness value of 0 MN/m"2.

・On the other hand, at 20% by volume, the bending strength is 1500kg
It has decreased to /-. Therefore, the amount of SiC whiskers added was selected to be 15% by volume.

Next, the thickness of the center layer of the composite with this blending ratio is determined by the diameter of 3
, 10% (127 μm) of the thickness 1.27 mm specified by the standard for 5-inch magnetic disk substrates.
, 20% (254 μm).

50% (635 μm), 80% (1016 μm).

Samples each set to 90% (1143 μm) were prepared, an intermediate layer of SiC was formed on both sides, and a surface layer of barium glass whose thermal expansion coefficient difference with SiC was 3X10-7/°C was further formed. A magnetic disk substrate was created using the following steps.

The thickness of the surface glass layer is 30 μm per layer, and the remaining part is made of a single layer of SiC, with a thickness of 1.27 μm.
It was used as a substrate for a magnetic disk of mm.

The thickness of each part of each sample (including two layers each for the intermediate layer and the surface layer) is shown in Table 1 below.

Table 1 However, in Table 1, the % column indicates the ratio to the total thickness of the substrate.

The surface of each sample was polished under the same conditions, and the surface roughness was measured using a contact type surface roughness measuring device. Further, the KIC of the magnetic disk substrate was measured in the same manner as described above. These results are shown in Table 2 below.

Table 2 As a result, if the thickness of the center layer exceeds 80% of the entire substrate according to the evaluation described below, the unevenness of the center layer will appear on the surface, making it undesirable as a magnetic disk substrate for high-density recording. Furthermore, it was found that if the amount is less than 20%, the effect of improving toughness by adding fibers cannot be obtained.

Next, in order to determine the optimal range of the thickness of the intermediate layer as a substrate for a magnetic disk, substrates were prepared in which the thickness of the intermediate layer was varied variously as shown in Table 3 below.

Table 3 The surfaces of each sample were polished in the same manner as described above, and the surface roughness and KIC were measured. The results are shown in Table 4 below.

Table 4: When the thickness of the intermediate layer is less than 7% of the total thickness,
The surface roughness decreases, making it unsuitable for high-density recording as described later. On the other hand, if the thickness of the intermediate layer exceeds 80% of the total thickness, the fracture toughness X+C decreases and the effect of adding fibers cannot be obtained.

Next, a magnetic disk substrate was prepared in which the thickness of the center layer was 635 μm, the thickness of the glass layer was varied as shown on the horizontal axis in FIG. 2, and the remaining part was an intermediate layer. Then, the number of defects such as bubbles and pinholes generated on this magnetic disk substrate was measured. The results are shown in FIG.

As described later, when the number of defects is 300 or less, high-density recording is possible. Moreover, as is clear from FIG. 2, when the thickness of the glass coating film is 300 μm or less, the number of defects is 300 or more, and the sample N11L
Magnetic disk substrates were prepared in which the maximum crystal grain size and the average crystal grain size of the crystal grains were varied in relation to the substrate No. 3.

Then, the number of defects generated on the surface of this magnetic disk substrate was measured. FIGS. 3 and 4 show the relationship between the number of defects and the maximum crystal grain size and average crystal grain size, respectively.

As is clear from FIGS. 3 and 4, when the maximum crystal grain size is 100 μm or less and when the average crystal grain size is 50 μm or less,
When the number of defects is less than m, the number of defects is less than 300. Therefore, for high-density recording, the maximum crystal grain size must be 1100I.
i or less, the average crystal grain size is preferably 50 μm or less.

Next, a magnetic film was formed on each sample magnetic disk substrate to create a magnetic disk. First, an α-Fe203 film (thickness 0.21μ
m), then reduced at 330°C in a hydrogen atmosphere to form a Fe3O4 film, and further oxidized in air at 330°C to convert into a γ-Fe2O3 film to create a high-density magnetic disk. did. The performance of the thus obtained magnetic disk as a magnetic disk was tested by flying the head under the condition that the flying height was 0.2 μm.

When we inspected the magnetic disks of each sample for signal errors during writing and reading, we found that sample N[L
1 to 4, sample Nn, '7 to 11, sample N[
The substrates of L12 to 16, Sample N [L 19 to 23, and Sample N [L26 to 29] have extremely low error occurrence compared to other substrates, and are not confirmed to be suitable for high-density recording. .

[Effects of the Invention] According to the present invention, five layers are provided, including a central layer made of a composite of fibers or whiskers and ceramics, an intermediate layer made of a ceramic material, and a surface layer covered with a glass material. Since it is made into a layer laminate, the obtained magnetic disk substrate has high strength, excellent heat resistance and weather resistance,
Furthermore, the flatness and smoothness are excellent, and the number of substrate defects, which is one of the causes of errors in magnetic disks, is reduced.

Therefore, C3S (contact, start, stop) resistance is extremely excellent, and the magnetic disk substrate does not undergo brittle fracture even when external force is applied, so the reliability of the device is high.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing an example of the present invention, Fig. 2 is a graph showing the relationship between the thickness of the glass coating film and the number of defects, and Fig. 3 is a graph showing the relationship between the maximum crystal grain size of the intermediate layer and the number of defects. FIG. 4 is a graph showing the relationship between the average grain size and the number of defects.

Claims (9)

[Claims] (1) A central layer made of a composite of a non-metallic heat-resistant fiber material and a ceramic material, two intermediate layers made of ceramic materials on both sides of this central layer, and an outer surface of this intermediate layer. 1. A magnetic disk substrate characterized in that it is a laminate having two surface layers each coated with a glass material. (2) The magnetic disk substrate according to claim 1, wherein the thickness of the center layer is 20 to 80% of the thickness of the entire laminate. (3) The magnetic disk substrate according to claim 1, wherein the thickness of the intermediate layer is 7 to 80% of the thickness of the entire laminate. (4) The magnetic disk substrate according to claim 1, wherein the surface layer has a thickness of 3 to 500 μm. (5) The ceramic material constituting the intermediate layer has a maximum crystal grain size of 100 μm or less and an average crystal grain size of 50 μm or less.
The magnetic disk substrate according to claim 1, wherein the magnetic disk substrate has a diameter of μm or less. (6) The ceramic material constituting the central layer has a maximum crystal grain size of 100 μm or less and an average crystal grain size of 50 μm or less.
The magnetic disk substrate according to claim 1 or 5, wherein the magnetic disk substrate has a diameter of μm or less. (7) the coefficient of thermal expansion of the glass material constituting the surface layer;
The difference between the coefficient of thermal expansion of the ceramic material constituting the intermediate layer is 15×10^- in the temperature range of 0 to 1000°C.
The magnetic disk substrate according to claim 1, characterized in that the temperature is ^7/°C or less. (8) The nonmetallic heat-resistant fiber is one or more materials selected from inorganic fibers, inorganic whiskers, carbon fibers, and carbon whiskers. Substrate for magnetic disks. (9) The magnetic disk substrate according to claim 8, wherein the content of fibers and/or whiskers in the composite constituting the center layer is 3% by volume or more.