JPH04295614A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a practically very excellent magnetic recording medium which is extremely excellent in weather resistance, durability, and magnetic characteristic and uses a glass substrate. CONSTITUTION:This magnetic recording medium is formed by providing a magnetic layer 5 on a glass substrate 1 on which an electroless plated layer 2 having a thickness of >=1000Angstrom and metallic layers having large numbers of small projections on the surfaces are successively formed and the surface roughness of the recording medium is adjusted to <=400Angstrom in crest height.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium using a glass substrate, which has excellent weather resistance, durability, and magnetic properties.

0002

2. Description of the Related Art The density of magnetic disk drives is increasing at a very rapid rate. One way to increase the density is to reduce the flying distance between the magnetic disk medium and the head, and recently it has been required to reduce the flying distance to 0.1 μm or less. For this purpose, it is desirable that the magnetic disk substrate be smoother, and glass substrates are attracting attention because of their excellent smoothness, hardness, and fewer surface defects. For example, in Japanese Patent Publication No. 43-4621, a magnetic film is formed on a glass substrate by a plating method,
Furthermore, Japanese Patent Laid-Open No. 171031/1983 proposes a magnetic recording medium in which a Co--Pt magnetic film is formed on a glass substrate by sputtering.

[0003] However, there are some practical problems.
Not commonly used. One of the problems is the problem of weather resistance under high humidity. In other words, glass substrates have poor water resistance and are easily eroded by water, unlike ordinary aluminum substrates with Ni-P electroless plating.
In addition, the alkali components of the glass substrate may be eluted to the surface, for example, in the book "Glass Surface Design" (Kindai Editing Co., Ltd.) P.
．． 43 and P. 156. As a practical countermeasure, in order to prevent the elution of alkaline components from liquid crystal glass substrates, it is industrially implemented to form a thin layer of silicon oxide film by applying an organic silicon solution, and to prevent the elution of alkaline components. A smaller amount of borosilicate glass is used than soda-lime silicate glass. However, these are disadvantageous in terms of cost, and borosilicate glass is expensive.

[0004] When a glass substrate is used as a substrate for a magnetic recording medium, corrosion occurs on the inner and outer peripheries of the magnetic disk in a humid environment, and many proposals have been made to improve this problem. For example, JP-A No. 63-269319 proposes applying epoxy resin or the like to the magnetic recording layer and the exposed portion of the glass at the periphery of the magnetic disk, and JP-A No. 64-42025 proposes the composition of the glass substrate. It has been proposed to change the composition of However, changing the composition is a change in manufacturing conditions, which causes manufacturing problems such as an increase in melting temperature, and also increases costs. Furthermore, the application of resin or organic silicon solution adversely affects the flatness of the magnetic disk. Recently, due to the increase in the capacity of magnetic disks, the head flies at a low level and flies to the outermost periphery of the magnetic disk, which is undesirable because it may cause a head crash.

Another major problem is durability. When a magnetic disk device is not recording or reproducing, the head does not fly but is in contact with the medium. Glass substrates have good smoothness and excellent specularity on the substrate surface. On the other hand, magnetic recording media that use mirror-finished glass substrates as they are have an increased contact area between the head and the medium, making it difficult for the device to use. When the disk is driven or stopped, the frictional force and attraction force between the disk medium and the disk medium increase, which causes sticking between the disk medium and the head, or a head crash. In particular, with the recent spread of small magnetic disk drives, motor torque has become smaller and power consumption has been reduced.
Reduction of static friction force is required.

[0006] In order to solve this problem,
No. 36035 proposes etching a glass substrate to form continuous irregularities at a certain period, and Japanese Patent Application Laid-Open Nos. 62-256214 and 62-2562 also propose
No. 15 and Japanese Unexamined Patent Publication No. 62-256216 propose forming a continuous aluminum uneven layer by sputtering. However, JP-A-62-2562
No. 14, JP-A-62-256215, JP-A-62-2
No. 56216 solved the problem of disk media rotation failure due to so-called sticking, but the static friction coefficient was 3.
This has more than doubled, and the reduction in motor torque and power consumption described above is still insufficient. Furthermore, as a problem in terms of magnetic properties, J. Appl. Ph
ys. 67(9), 1, 1990, P4701, etc., when a base Cr layer and a magnetic layer are formed directly on a glass substrate by sputtering, the coercive force decreases due to the influence of moisture on the glass substrate. There is a problem.

[0007]

[Problems to be Solved by the Invention] The present invention solves the problem of corrosion of magnetic films due to alkaline components eluted from substrates such as ordinary glass substrates, soda lime glass, aluminosilicate glass, etc., and the problem of corrosion of magnetic films due to the influence of moisture on glass substrates. This is intended to solve the problem of deterioration of magnetic properties as well as the durability problem caused by increased frictional force and adsorption force with the head.

[0008]

[Means for Solving the Problems] The gist of the present invention is as follows:
A magnetic recording medium has a magnetic layer formed on a glass substrate on which an electroless plating layer with a thickness of 0 Å or more and a metal layer having a large number of microscopic protrusions are sequentially formed, and has a medium surface roughness with a peak height of 400 Å or less. Exists.

The present invention will be explained in detail below. The magnetic recording medium of the present invention has a magnetic layer provided on a glass substrate on which an electroless plating layer with a thickness of 1000 Å or more and a metal layer having a large number of fine protrusions are sequentially formed, and the peak height is 40 Å.
It has a medium surface roughness of 0 Å or less. There are no particular restrictions on the type of glass substrate, but ordinary soda lime glass, aluminosilicate glass, and lithium-based glass (for example, "ML-5" manufactured by Nippon Electric Glass Co., Ltd.) as crystallized glass can be used. I can do it. Usually, from a cost perspective, inexpensive chemically strengthened soda lime glass or aluminosilicate glass is mirror-polished. The surface roughness of the mirror-polished glass substrate was measured using a contact roughness meter, with a center line average roughness of Ra 10 Å and a maximum height Rmax of 150 Å.
It is preferable to have the following finish.

[0010] Because the substrate surface is smooth as described above, the adhesion between the substrate and the electroless plating layer is poor, and the normal electroless plating method can only form an electroless plating film with a thickness of about 300 Å. The electrolytic plating film is not sufficient to be used as a film for preventing alkaline component elution from the substrate due to the film thickness and coverage. In order to prevent elution of alkali components and corrosion of the magnetic film layer, a film thickness of 1000 Å or more is required.

Therefore, the following preferred method is exemplified as a method for obtaining an electroless plating layer with good adhesion and a thickness of 1000 Å or more even when a commercially available plating bath is used. First, a mirror-polished glass substrate is degreased and cleaned with a normal neutral detergent, then activated with a standard SnCl2 bath and PdCl2 bath, and then thickened with a normal electroless plating bath. After forming the first electroless plating film with a thickness of 300 Å or less, it was heated to 150 Å in a clean dryer.
Heat treatment is carried out at a temperature of ~400°C. After heat treatment again,
After washing with a neutral detergent, a second layer of electroless plating film is formed in an electroless plating bath to a total film thickness of 1000 Å or more,
Further, heat treatment is performed at a temperature of 150 to 400°C. In addition, in the formation of the second layer electroless plating film,
This may be interrupted and the heat treatment described above at 150 to 400°C may be performed as appropriate.

The electroless plating bath may be non-magnetic Ni--P plating similar to conventional aluminum substrates, or may be copper plating. Further, the type of each plating layer may be changed. However, a non-magnetic film is preferable. If the thickness of the first layer exceeds 300 Å, partial peeling will occur during plating or washing with water. The thickness of the first layer is preferably about 200 to 300 Å. The total plating film thickness is 1000 Å for weather resistance.
The above is necessary. Although there is no particular upper limit to the film thickness, it is preferably 1 μm or less from the viewpoint of adhesion. Above all, 1500Å or more5
000 Å or less is more preferable.

[0013] The preferred heat treatment temperature is 150°C to 400°C.
℃ range. Below 150℃, there is little effect, and 40℃
When the temperature exceeds 0° C., diffusion of potassium ions in the chemically strengthened layer of the glass substrate occurs, resulting in a decrease in strength. Heat treatment time is 30
Minutes or more, preferably 30 minutes to 60 minutes. It is preferable to perform electroless plating by, for example, holding the disk at the inner periphery of the disk and immersing it in an electroless plating bath while rotating, so that an electroless plating film is uniformly formed over the entire surface of the substrate.

In addition, if the glass substrate is not a mirror-polished substrate but has a roughened substrate surface, for example by chemical etching or crystallization treatment, the adhesion of the electroless plating layer will improve, so the first step electroless plating will improve the adhesion of the electroless plating layer. Accordingly, 1
A film thickness of 000 Å or more can be obtained. Furthermore, by subjecting this to the above-described heat treatment, the adhesion can be further improved. In this way, by providing a non-magnetic electroless plating layer with high adhesion and a predetermined film thickness, it is possible to not only elute alkaline components from the glass substrate under high humidity, but also to prevent the elution of alkaline components from the substrate during sputtering film formation, which will be described later. The influence of moisture can also be shielded, and a recording medium with good magnetic properties can be obtained.

Next, the substrate treated as described above is placed in a sputtering apparatus, and a metal layer having a large number of fine protrusions is formed by sputtering. Since the shape of this protrusion is carried over even after the formation of the underlying layer, magnetic layer, protective layer, and lubricant film layer, the peak height of the protrusion shape should be controlled so that the final media surface has a peak height Rmax of 400 Å or less. This results in a magnetic recording medium with excellent durability. The composition of the metal layer having many fine protrusions is Ag, Al, Pb, Sn.
, Sb, and other low-melting point metals tend to form protrusions, and alloys thereof, such as Al-Cu alloys, may also be used.

The ease with which protrusions are formed is estimated to be due to the balance between the surface energy of the substrate, the surface energy of the sputtered material, and the interfacial energy between the sputtered material and the substrate, but it is not possible to quantify it. The details are unknown. Cr, which is generally used as an underlayer for magnetic layers,
Even if the Ti film is several hundred Å thick, it becomes a substantially smooth continuous film and no protrusions are formed. The ease with which protrusions are formed is strongly influenced by the film formation method, sputtering conditions, especially substrate temperature, and film thickness. The size (diameter) of each protrusion is preferably 2000 Å or less, preferably 200 to 1000 Å, and more preferably 30 Å or less.
It is 0 to 600 Å. If the thickness exceeds 2000 Å, the reproduction noise of the medium may decrease, similar to when the surface is roughened.

Furthermore, from the viewpoint of durability, it is preferable that the protrusions are distributed in an island-like manner without being in close contact with each other, and that the area of contact with the head is reduced to the necessary minimum. An island-like structure is likely to be formed in the initial stage of film formation, but as another method, in order to reduce the nucleation density, Cr, Ti, etc. It is preferable to provide a sputtered layer of 1, because the formation of the metal layer is controlled and island-shaped protrusions are formed. It is desirable that the distance between the protrusions be at least half the size (diameter) of the protrusion shapes.

The sputtering atmosphere may be under normal conditions and may be selected from a range of argon partial pressure of 1 to 10 mTorr. The higher the substrate temperature, the rougher the protrusion shape becomes.
0°C is preferred. Further, the thicker the film, the larger the height of the peaks and the rougher the film becomes.

Although it is difficult to define the film thickness due to the shape having protrusions, in terms of film thickness during sputtering film formation at room temperature, the film thickness is 300 Å or less, preferably 30 to 200 Å. The height of the peaks on the medium surface is 400 Å or less as Rmax,
Among these, 70 to 300 Å is preferable. If it is smaller than 50 Å, the effect of improving durability will be small. On the other hand, if it exceeds 400 Å, the flying distance between the head and the medium will not become small, and the reproduction noise of the medium will increase, which is not preferable. It is desirable that all the peaks have a height of 400 Å or less over the entire surface of the substrate, but 10 of the protrusion shapes measured per unit length are within the range that does not interfere with achieving the purpose of the present invention. %
As long as the height of the peak exceeds 400 Å, it is acceptable.

The glass substrate provided with the metal layer having a large number of fine protrusions in this manner is placed in a sputtering apparatus, and if necessary, an undercoat layer is formed by sputtering, and then a magnetic layer is provided. Moreover, a protective layer and/or a lubricating layer can be provided on the magnetic layer, if necessary. The undercoat layer formed by sputtering is a Cr layer, a Ti layer, or the like, and is used to improve the magnetic properties of the magnetic layer. The thickness of the undercoat layer is usually
The thickness is approximately 500 to 3000 Å. The magnetic layer composition is Co-Cr, Co-Cr-X, Co-N by sputtering method.
A Co-based alloy magnetic film containing Co as a main component represented by i-X, Co-W-X, etc. can be used. Here, X is L
i, Si, B, Ca, Ti, V, Cr, Ni, As, Y
, Zr, Nb, Mo, Ru, Rh, Ag, Sb, Hf,
Ta, W, Re, Os, Ir, Pt, Au, La, Ce
, Pr, Nd, Pm, Sm, and Eu. The thickness of the magnetic layer is usually about 300 to 1000 Å. In addition, Co-
When using Ni-Pt alloy, Co-PT alloy, etc., Cr
There is no need to provide a subbing layer such as. As the protective film, a carbonaceous film, a zirconia film, etc., or an organic silicon film may be applied by sputtering. As the lubricant layer, a liquid lubricant film such as fluorine-based perfluoropolyether or a solid lubricant film such as fatty acid is used.

Furthermore, by forming a conductive electroless plating film on the glass substrate, the electrical resistance between the substrate and the substrate holder becomes approximately 10Ω or less during the subsequent sputtering film formation, so that normal sputtering conditions can be avoided. In addition to film formation, it is possible to apply a negative bias potential to the substrate in the same way as with conventional aluminum substrates coated with Ni-P electroless plating films, and undercoat while applying a negative bias potential. The layer and/or the magnetic layer can be deposited by sputtering and a high coercive force can be obtained. As a bias application method, in addition to this substrate bias method, it is also possible to provide an intermediate electrode between the target and the substrate, and apply a positive potential to the substrate with respect to the electrode.

[0022]

[Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. Example 1 After chemically strengthening, the surface had a center line average roughness of Ra8 Å,
Mirror-finished to maximum height Rmax 100Å, outer diameter 95φ
After degreasing a soda lime glass substrate with a diameter of 25 mm and a thickness of 1.27 mm using a neutral detergent and washing it with ion-exchanged water, a 0.3 g/l SnCl2 aqueous solution (bath temperature 50°C) was prepared.
After rinsing with water, immersing in a 0.1 g/l PdCl2 aqueous solution (bath temperature 50°C) for 1 minute to perform activation treatment, and rinsing with water.
Co., Ltd., Enplate NI-4828), pH 4.5
An electroless Ni-P plating film was formed to a thickness of 300 Å at a bath temperature of 77° C. (first stage electroless plating). After washing with water, heat treatment was performed at 200° C. for 1 hour in a clean dryer. After that, it was degreased again with a neutral detergent, washed with ion-exchanged water, and then immersed in the electroless Ni-P plating bath again to obtain a total film thickness of 1500 Å.
An electroless Ni-P plating film was formed (second stage electroless plating). After washing with water, heat treatment was performed at 200° C. for 1 hour in a clean dryer. The electroless plating process was performed while rotating the substrate so that a plating layer was formed on the entire surface of the substrate.

[0023] After loading this substrate into a DC magnetron sputtering device and evacuation to 1 x 10-6 Torr,
The substrate temperature was raised to 150℃ and the argon partial pressure was increased to 5×10−3.
Approximately 1 in terms of film thickness during sputtering film formation at room temperature under Torr
A layer of Al having a large number of fine protrusions with a thickness of 50 Å was deposited by sputtering. Subsequently, the temperature of the substrate was raised to 200°C, and a Cr underlayer was formed at a temperature of 170°C under an argon partial pressure of 5 x 10-3 Torr.
0 Å, CoNi30Cr7 at% magnetic layer of 600 Å
A carbon protective layer of 300 Å was continuously formed by sputtering. Furthermore, a 20 Å perfluoropolyether was applied as a lubricating layer on top of this to produce a magnetic recording medium. The peak height Rmax on the medium surface at this time was 300 Å, and observation using a scanning electron microscope showed that the protrusions were almost close to each other. Figure 1 shows a schematic diagram.

In order to evaluate the obtained magnetic recording medium, 3
．． Durability test (CSS) using a 5-inch magnetic disk drive
Measure the coefficient of static friction between the head and the medium at the beginning and after 20,000 times of the test (a test in which the magnetic head is brought into contact with the surface of the magnetic recording medium and the magnetic recording medium is started and stopped rotating in a stationary state); A weather resistance test was carried out in a clean constant temperature and humidity chamber at 85° C. and a relative humidity of 80% for 504 hours, and the coercive force of the medium was measured using a sample vibrating magnetometer (VSM). The results are shown in Table 1.

Comparative Example 1 A magnetic recording medium was produced in the same manner as in Example 1 except that the electroless Ni--P plating layer was not formed.
We conducted an evaluation. The results are shown in Table 1. Comparative Example 2 A magnetic recording medium was fabricated in the same manner as in Example 1, except that the layer having many fine Al projections was not provided, and then evaluated. The results are shown in Table 1.

Example 2 Electroless Ni--P was treated in the same manner as in Example 1.
On top of the plating layer, a DC magnetron sputtering device was used to initially apply an argon partial pressure of 3×1 at a substrate temperature of 150°C.
A Cr layer with a thickness of about 1000 Å was formed at 0-3 Torr, and a layer of Al having a large number of fine protrusions was formed on it at a thickness of about 80 Å in terms of room temperature.
A magnetic recording medium was prepared in the same manner as in Example 1 except that the film was formed to a thickness of Å, and then evaluated. The results are shown in Table 1. It should be noted that in this layer of Al having a large number of fine protrusions, the protrusions were not closely spaced, and the protrusions were distributed in an island-like manner with an interval of about 700 to 1400 Å. Figure 2 shows a schematic diagram. Note that the peak height Rmax on the medium surface was 300 Å.

Example 3 In Example 2, a negative bias potential of -200 V was applied to the substrate during the formation of the Cr underlayer, which is the underlayer of the magnetic layer, on the Al layer having many fine protrusions, and during the formation of the magnetic layer. A magnetic recording medium was fabricated in the same manner except that the film was formed by sputtering while applying . The results are shown in Table 1. The height of the peaks on the medium surface was Rmax 300 Å.

Example 4 In Example 3, the composition of the magnetic layer was changed to CoCr12Ta2.
A magnetic recording medium was fabricated in the same manner except that it was set to at%, and then evaluated. The results are shown in Table 1. The height of the peaks on the medium surface at this time was Rmax 300 Å.

Example 5 A magnetic recording medium was prepared in the same manner as in Example 2, except that the layer having minute protrusions was made of Ag, and then evaluated. The results are shown in Table 1. The layer having many fine projections of Ag is distributed in an island-like manner as in Example 2, and the height of the peaks on the medium surface at this time is Rm.
ax was 350 Å.

[0030]

[Table 1]

[0031]

According to the present invention, it is possible to provide a magnetic recording medium using a glass substrate which is excellent in durability, weather resistance, and magnetic properties and is practically excellent.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing a cross section of a magnetic recording medium obtained in Example 1.

FIG. 2 is a diagram schematically showing a cross section of a magnetic recording medium obtained in Example 2.

[Explanation of symbols]

1 Soda lime glass substrate 2
Electroless plating layer 3 Metal layer 4 having many fine protrusions
Base layer for magnetic layer 5 Magnetic layer 6 Protective layer 7 Lubricating layer 8 Soda lime glass substrate 9
Electroless plating layer 10 Underlayer 11 for controlling a metal layer having a large number of fine protrusions Metal layer 12 having a large number of fine protrusions in the form of scattered islands 12 Underlying layer for magnetic layer 13 Magnetic layer 14 Protective layer 15 Lubricant layer

Claims (3)

[Claims] Claim 1: A magnetic layer is provided on a glass substrate on which an electroless plating layer with a thickness of 1000 Å or more and a metal layer having a large number of fine protrusions are sequentially formed, and the medium surface roughness has a peak height of 400 Å or less. A magnetic recording medium with 2. The magnetic recording medium according to claim 1, wherein the metal layer having a large number of fine protrusions is distributed in an island shape. 3. The magnetic recording medium according to claim 2, characterized in that an underlayer for controlling the formation of the metal layer is provided between the electroless plating layer and the metal layer having a large number of fine protrusions. magnetic recording media.