JPH03224131A - magnetic recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to magnetic recording media, and particularly relates to magnetic recording media that have the characteristics necessary for practical use such as wear resistance, running stability, durability, and environmental resistance. The present invention relates to a ferromagnetic metal thin film magnetic recording medium.

[Conventional technology] In recent years, with the increase in the amount of information in the field of information processing technology and the increase in the quality of videos and images in the field of video processing technology, the demand for magnetic recording media capable of high-density recording has increased. ing. Therefore, research and development are actively being carried out to meet this demand.

Among them, Co-Ni, Co-C are used as magnetic recording layers.
Metal thin film magnetic recording media, in which ferromagnetic metal thin films such as r, Go-Ni-P, etc. are formed by vapor deposition, sputtering, wet plating, etc., have improved compared to coating-type magnetic recording media commonly used today. It is seen as a promising medium suitable for high-density recording, and some have even been put into practical use. Among these, perpendicular magnetic recording media are attracting attention. When a signal is recorded on this medium, the residual magnetization is oriented in a direction perpendicular to the film surface of the medium, so that the shorter the wavelength of the signal, the less the demagnetizing field and the better reproduction output can be obtained.

In metal thin film magnetic recording media, unlike conventional coated media, the entire thin film contributes to magnetic recording, so it is highly efficient to use as a magnetic recording layer. Furthermore, since the medium surface has good flatness, it is possible to minimize spacing loss.

In this way, if the advantages of metal thin film type magnetic recording media can be utilized, a recording medium can be obtained that far exceeds coating type magnetic recording media in both output and C/N ratio.

Furthermore, by adopting narrower tracks and shorter wavelengths as a recording method, it becomes possible to perform high-density recording at least several times as much as in coating-type magnetic recording media.

However, the magnetic recording layer, which is made of a thin metal film, is easily damaged by contact with the magnetic head, and if it is damaged, running properties may deteriorate, resulting in a decrease in output, or in severe cases, it may become impossible to run. There is. This problem has been the biggest problem preventing the practical use of metal thin film magnetic recording media.

Another problem in practical application is that depending on the type of metal used, it may corrode if exposed to air for a long period of time. For example, a Co--Ni metal thin film corrodes in a short period of time in an environment of high temperature and humidity or where the air contains salt.

Conventionally used coated magnetic recording media are made by mixing magnetic powder with a binder and coating it on a base film.The surface is originally finely roughened, so the friction is small, but the binder contains abrasion resistant material. By adding substances with excellent properties and lubricity, problems related to sliding with the magnetic head have been solved and overall reliability has been improved.

On the other hand, in metal thin film media, a protective layer is formed on the surface of the metal magnetic layer by the methods listed below, and the protective layer provides functions such as ■wear resistance, ■lubricity, and ■environmental resistance. Attempts have been made to solve the above problems by applying them to magnetic recording media.

■Providing wear resistance: An inorganic protective layer made of a hard material is formed on the metal thin film magnetic recording layer.

For example, 5iO1SiO□, SiN, Al□03,
A thin film of TiO□, diamond-like carbon, or the like is formed by vacuum evaporation, sputtering, plasma CVD, or the like.

■Providing lubricity i) A protective layer made of a lubricating material is formed on the metal thin film magnetic recording layer or the above-mentioned inorganic protective layer.

For example, a thin film of an inorganic material such as Mo52, WS2, diamond-like carbon, or amorphous carbon is formed by vacuum evaporation, sputtering, plasma CVD, or the like. Alternatively, a layer of an organic material such as a fluororesin, a silicone oil surfactant, a saturated fatty acid, or an ester oligomer is formed by a liquid coating method, a vacuum evaporation method, a sputtering method, or the like.

ii) Forming fine irregularities on the surface of the magnetic recording medium to reduce the number of real contact points and lower the coefficient of friction.

■Providing environmental resistance: Forms a corrosion-resistant protective layer.

[Problems to be Solved by the Invention] Here, when examining the durability standards for floppy disks that require high reliability, it is found that floppy disks for data recording can withstand more than 3 million passes at room temperature and at high temperatures (approximately 50
℃) and low temperature (approximately 10℃) for over 1 million passes, as a guideline for practical use with video floppy disks.
Normal temperature, high temperature and high humidity (40℃, 85%RH), low temperature (-5
Both are required to have continuous running durability of 48 hours (approximately 10 million buses) or more at temperatures (°C).

However, with the metal thin film magnetic recording media equipped with the protective layer that has been tried in the past, scratches and deposits occur on the media surface and head surface after running several hundred to several hundred thousand passes. However, the playback output is significantly reduced, and it cannot be said that it has reached a practical level.

The cause of this problem has conventionally been considered to be the hardness, adhesion, abrasion resistance, and corrosion resistance of the protective layer.

The present invention solves the above-mentioned problems that have been an impediment to the practical application of metal thin film type magnetic recording media. The present invention provides a magnetic recording medium equipped with a protective film that has excellent overall durability such as storage durability.

[Means for Solving the Problems] The present inventors have basically developed a material that has high hardness, long-term storage durability,
Focusing on silicon oxide, which has excellent environmental resistance, we conducted extensive studies on the relationship between the film quality and durability of a silicon oxide thin film, which is several hundred thick, and found that the adhesion of the silicon oxide protective film ,
The inventors have discovered that wear resistance and durability depend on the internal stress of the silicon oxide protective film, leading to the present invention.

The present invention provides a magnetic recording medium in which a magnetic recording layer made of a thin ferromagnetic metal film and a protective layer made of a thin film mainly composed of silicon oxide are formed in this order on at least one surface of a non-magnetic substrate, wherein the protective layer The internal stress (compressive stress) of I
The magnetic recording medium is characterized in that it has a magnetic flux of dyn/cm2 or less.

According to the present invention, wear resistance is improved by using a thin film mainly composed of silicon oxide and having an internal stress of I x 10'dyn/cm'' or less as a protective layer of a magnetic recording layer made of a ferromagnetic metal thin film. It has now become possible to provide a practical level metal thin film magnetic recording medium with excellent durability and environmental resistance.

Generally, when a silicon oxide thin film (mainly SiO□) is formed, its internal stress is compressive stress immediately after the film is formed, but its value changes significantly toward tensile stress under high temperature and high humidity conditions. For example, compressive stress is 5×10” dyn/cm2
The internal stress of the 5iOa sputtered film is 70℃, 85%R
Under the high temperature and high humidity conditions of H, less than half (~2×
1OI0dyn/Cm2). It was confirmed by a scratch test that the adhesion and wear resistance of the SiO□ film also changed as the internal stress changed at this time. That is, the present inventors have discovered that changes in internal stress change the adhesion and wear resistance of the protective film. The amount of change in the internal stress increases as the compressive stress value immediately after the SiO□ film is formed, and the adhesion and wear resistance of the 5iOz film are
It became clear that the larger the amount of change in internal stress, the greater the deterioration. Therefore, the smaller the internal stress immediately after the silicon oxide protective film is formed, the better.
n/cm" or less, it was found that there was no problem in the adhesion or abrasion resistance of the protective film under high temperature and high humidity conditions, leading to the present invention.

FIG. 1 is a sectional view of the magnetic recording medium of the present invention showing the basic structure thereof.

The non-magnetic substrate 1 may be made of materials commonly used as substrates for magnetic recording media, such as aluminum alloy, glass, or polymer films, but especially those with a glass transition temperature of 20
Preferably, the film is a heat-resistant polymer film having a temperature of 0° C. or higher, such as polyimide, polysulfone, polyamideimide, polyetheretherketone, aramid, and the like. The front or back surface of the non-magnetic substrate 1 may have a large number of fine protrusions as necessary in order to improve the slipperiness of the film and the running stability of the magnetic recording medium.

A ferromagnetic metal thin film 2 is formed as a magnetic recording layer on at least one surface of a nonmagnetic substrate 1, and a thin film 3 containing silicon oxide as a main component is formed thereon as a protective layer.

For the magnetic recording layer 2, for example, a ferromagnetic alloy film, a ferromagnetic oxide film, a ferromagnetic nitride film, etc. containing Fe, Co, and Ni as main components can be used. These magnetic recording layers can be formed by a vacuum deposition method, an ion blating method, a physical vapor deposition method such as a sputtering method, a plating method, or the like. Among them, carbon formed by vacuum evaporation or sputtering and consisting of 15 to 23% by weight of Cr and the balance of CO.
The present invention is particularly effective when an o-Cr perpendicularly magnetized film is used as the magnetic recording layer.

The protective layer 3 consists of a thin film mainly composed of silicon oxide,
The internal stress of the film is a compressive stress of 1 x 109 dyn/cm" or less. If it exceeds I x 10" dyn/cm, the amount of change in internal stress under high temperature and high humidity conditions will be too large, and the adhesion strength of the film will deteriorate. Wear characteristics deteriorate.

The amount of silicon oxide contained as a main component in the protective layer is
It is preferably 80% by weight or more, more preferably 85% by weight or more, based on the protective layer.

The protective layer 3 can be formed by vacuum evaporation method, ion blating method,
It can be formed by a physical vapor deposition method such as a sputtering method, or a liquid coating method.

When forming by physical vapor deposition, Si, SiO, or SiO2 is used as a vapor deposition source. When forming the protective layer by physical vapor deposition, the value of the packing density of the protective layer is controlled by gas pressure, oxygen partial pressure, substrate temperature, input power, film thickness, etc. In order to reduce the internal stress of the protective layer, i) reduce the packing density of the protective layer, ii) increase the oxygen partial pressure ratio (up to about 15%), 1ii) increase the total pressure (for example, Ar + 0□). Possible methods include:

On the other hand, in the liquid coating method, the internal stress of the protective layer can be controlled by adjusting the concentration, curing temperature, curing time, film thickness, etc.

In addition, in order to improve the adhesion between the metal thin film and the protective layer, improve wear resistance, etc., B, C1N, P,
S, A1. Ti, ■, Cr, Zn, Ge, Z
r, Nb, Mo, Ta, Mg, Hf, Au,
It may contain at least one element selected from the group consisting of Pt or a compound thereof. Among these, B, Al2O3, TiO□, B2O5, B206,
MgO and the like are preferred. The amount added is such that the adhesion and protective function (wear characteristics) of the protective layer are not deteriorated, and is usually 10 to 20% by weight.

Furthermore, by forming the organic lubricating layer 4 on the protective layer 3, it is possible to reduce the coefficient of friction and further improve wear resistance and durability under harsh environmental conditions such as high temperature, high humidity, or low temperature.

As the material for the organic lubricant layer 4, commonly used polar or non-polar liquid lubricants or solid lubricants can be used. Specifically, fluororesin, silicone oil,
These include surfactants, saturated fatty acids, ester oligomers, etc. The organic lubricant layer 4 can be formed by a liquid coating method such as dipping or spin cord, or a physical vapor deposition method such as vacuum deposition or sputtering.

The thickness of the magnetic recording layer 2 is not particularly limited, although it is sufficient to have a thickness of about 0.1 to 1.0 μm.

The thickness of the protective layer 3 is preferably 500 Å or less, and 300 Å or less.
The most preferable value is Å or less. The lower limit of the thickness of the protective layer 3 may be such that the function of the protective layer 3 is not impaired, for example, 50 Å or more, preferably 100 Å or more.

The thickness of the organic lubricant layer 4 is preferably 100 Å or less, more preferably 30 Å or less.

Although the presence of the protective layer 3 and the organic lubricant layer 4 may cause spacing loss, the spacing loss can be sufficiently reduced by setting the film thickness as described above.

A back coat layer 6 is coated on the back surface of the non-magnetic substrate 1 as necessary for the purpose of lubrication. The back coat layer 6 is
It can be formed by dispersing inorganic fine particles such as carbon black, graphite, CaCO5, etc. in a binder such as polyester resin, polyurethane resin, urethane resin, etc.
-The composition used for boat fishing may be used.

The structure of this medium can also be applied to a double-sided magnetic recording medium in which a magnetic recording layer 2.2' and a protective layer 33' are formed on both sides of a nonmagnetic substrate, as shown in FIG.

Further, the magnetic recording layer 2 may be a single layer or a multilayer.

Further, in the lower part of the magnetic recording layer 2, A1. Ge,
A thin film such as Cr, Ti, or 5i(h) or a high magnetic permeability layer such as a Fe--Ni film or a Co--Zr film may be provided as the intermediate layer 5 as a backing layer of a perpendicularly magnetized film.

The surface roughness of a magnetic recording medium is not particularly limited, but considering spacing loss and dropout, the height of the protrusions is When taking the statistical distribution of , the projection height corresponding to 001% from the highest is 6
00 Å or less, more preferably 300 Å or less, and the protrusion density is in the range of 1×10′ to 1×10 8 pieces/mm 2 , more preferably 1×10 6 to 1×10 7 pieces/mm 2 .

Here, the surface roughness and protrusion density of the magnetic recording medium are measured by the shadowing method, which is a non-contact measurement method, as disclosed in Japanese Patent Application Laid-Open No. 63-188818.

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to the following examples.

[Example〕 Real 1u Kaijo FIG. 2 is a schematic diagram showing the configuration of the medium of this embodiment.

Polyimide film substrate 1 (Ubilex S type manufactured by Ube Industries, thermal expansion coefficient 1.2X 10-5cm/c
m/℃, tensile modulus 1020 kg/mm2. The surface roughness is approximately 10,000 μm from the highest protrusion per area to 0. The protrusion height corresponding to O1% is 300 people,
A Co-Cr perpendicularly magnetized film of 2°2' was applied to both sides of the protrusion density 5 x 106 pieces/mm2 using a facing target sputtering device.
Then, a silicon oxide thin film 3.3' was formed using an RF magnetron sputtering device.

FIG. 3 shows a schematic diagram of a facing target type sputtering apparatus used in the present invention. A long polyimide film substrate 1 having a thickness of 30 μm and a width of 100 mm was subjected to heat treatment in a vacuum prior to forming a magnetic layer. Specifically, 19 in a vacuum
The long polyimide film substrate 1 is conveyed in contact with the rotating drum 11 whose temperature has been raised to 0°C, and the ultimate vacuum degree is 2 x 1O-
The heat treatment was performed while maintaining the pressure at 3 Pa or less. At that time, the tension of the polyimide film base 1 was 1.5 kg, and the conveyance speed was 6
cm/min. After heat treatment, the ultimate vacuum level is 5
After evacuation to below X 10-'Pa, a Co--Cr perpendicular magnetization film was formed. The dimensions of the target 13 are 5 inches (127 mm) x 5 inches (152,4 mm) x 6
mm, the distance from the center between the targets to the rotating drum surface is 120 mm, the composition of the target is Co 80 w
t%-Cr 20 wt%. The film forming conditions were: argon pressure 0.2 Pa, input power 2.5 kW, film forming speed 0.
．． 1 ALm/min, the rotating drum temperature was 190°C, the tension of the polyimide film substrate 1 was 1.5 kg, and the thickness of the formed Co-Cr film was 0.4 μm. After forming the magnetic layer 2 on one side under the above conditions, a Co--Cr magnetic layer 2' was formed on the back side under the same film forming conditions to prevent curling.

FIG. 4 shows a schematic diagram of the RF magnetron sputtering apparatus used in the present invention. 8 inch (203,2mm)φ S
Using the iO□ target, the temperature of the rotating drum 11 is 2.
After forming a silicon oxide thin film 3 with a thickness of 200 at 00°C, Ar+O□ pressure of 0.3 Pa, 026%, input power of 2 kW, and film formation rate of 0.05 μm/min, a film was also applied to the back side to prevent curling. A silicon oxide thin film 3' was formed under the same conditions.

When the internal stress of the silicon oxide thin film formed at this time was measured using the method described below, it was found to be lX 109 dyn/a.
It was "m".

Measuring method for internal stress: A silicon oxide thin film is formed on a Si wafer under the same conditions as when forming the silicon oxide thin film above, and the warpage of the substrate is measured from the interference fringes on the film surface using Zygo. was calculated using the following formula.

E: Young's modulus b of the substrate (Si wafer): 〃 Thickness ν: 〃 Poisson's ratio d: Thickness of the silicon oxide thin film γ: Radius of curvature of the substrate Next, as a lubricant layer 4 on the protective layer 3, an ester-based Oligomer (manufactured by Asahi Glass Co., Ltd., trade name 5TL117) was coated to a thickness of 20 people.

Next, on the protective layer 3' which is the back side, a back coating liquid (manufactured by Toyo Ink Co., Ltd., trade name: TPB) containing carbon black and CaCO5 fine particles in a polyester binder is applied.
-3091 black), and back coat layer 6 was coated with 0
．． It was formed to have a thickness of 5 μm.

The magnetic recording medium produced as described above was 2 inches in diameter (
50.8 mm), insert it into a floppy disk jacket, and insert it into a recording/playback device (Fujix
P-3) for recording and playback at high temperature and high humidity (40℃, 8℃).
A durability test was conducted under conditions (5% RH). The durability test is
A 7 MHz signal was recorded and fluctuations in its reproduction output were measured. The time when the reproduction output attenuates to the initial value -3 dB is defined as the durability time.

The results are shown in FIG. The durability of this medium was 30 to 70 hours (10 samples). In other words, this medium meets the environmental durability standards for video floppy disks (40°C,
It can be said that a practical level has been reached at 85% RH for 48 hours or more.

A magnetic recording medium was fabricated in the same manner as in Example 1, except that the silicon oxide thin film 3.3', which is the protective layer for X-rays, was formed under conditions where the oxygen partial pressure was 8%.

The internal stress of the silicon oxide thin film 3 formed at this time was 8
X 108 dyn/cm2.

The results of measuring the durability of the obtained floppy disk are shown in FIG. The durability of this medium is 50 to 80 hours (
10 samples). In other words, it was found that the magnetic recording medium of the present invention sufficiently satisfies the durability standards of video floppy disks and is of a practical level.

A magnetic recording medium was produced in the same manner as in Example 1, except that the silicon oxide thin film 3.3' serving as the protective layer was formed under the same conditions as in Example 1, except that the oxygen partial pressure was 10%.

The internal stress of the silicon oxide thin film 3 formed at this time was 6
X 108 dyn/cm2.

The results of measuring the durability of the obtained floppy disk are shown in FIG. The durability of this medium was 70 to 100 hours (10 samples). In other words, it was found that the magnetic recording medium of the present invention sufficiently satisfies the durability standards of video floppy disks and is of a practical level.

A magnetic recording medium was produced in the same manner as in Example 1, except that the film formation conditions for the silicon oxide thin film 3.3', which is the mosquito protection layer, were argon pressure of 0.5 Pa and no oxygen gas introduced. .

The internal stress of the silicon oxide thin film 3 formed at this time is 2
X 10'dyn/cm2.

The results of measuring the durability of the obtained floppy disk are shown in FIG. The durability of this medium is 10 to 30 hours (
10 samples). That is, the magnetic recording medium of the present invention has a durability slightly lower than the durability standards of video floppy disks. Scratches occurred on the media surface after the environmental durability test.
There was powder adhering to the area around the scratch.

A magnetic recording medium was produced in the same manner as in Example 1, except that the silicon oxide thin films 3 and 3', which serve as protective layers, were formed under the same conditions as in Example 1, with an argon pressure of 0.3 Pa and no introduction of oxygen gas. .

The internal stress of the silicon oxide thin film 3 formed at this time was 3
X 10'dyn/cm".

The results of measuring the durability of the obtained floppy disk are shown in FIG. The durability of this media is 4 to 16 hours (1
0 specimens). That is, the magnetic recording medium of the present invention does not meet the durability standards of video floppy disks. Scratches occurred on the media surface after the environmental durability test.
There was powder adhering to the area around the scratch.

For comparison, the silicon oxide thin film 3.3', which is a protective layer, was formed under the following conditions: argon pressure 0.3 Pa, no oxygen gas introduced, and input power 4.
A magnetic recording medium was produced in the same manner as in Example 1 except that the power was 5 kW.

The internal stress of the silicon oxide thin film 3 formed at this time was 5
X 10”dyn/cm2.

The results of measuring the durability of the obtained floppy disk are shown in FIG. The durability of this medium is 0.1 to 2 hours (
10 samples). That is, the magnetic recording medium of the present invention does not meet the durability standards of video floppy disks. Scratches occurred on the media surface after the environmental durability test, and powder was attached around the scratches.

[Effects of the Invention] As explained above, in a magnetic recording medium having a magnetic recording layer made of a ferromagnetic metal thin film, a protective layer is formed on the magnetic recording layer and has an internal stress of I x 10 "dyn/cm" or less. Forming a thin film mainly composed of silicon oxide has the effect of dramatically improving wear resistance, durability, and long-term storage durability to a practical level.

[Brief explanation of drawings]

1 and 2 are partial sectional views showing the basic structure of the metal thin film magnetic recording medium of the present invention, FIG. 3 is a schematic diagram of a facing target sputtering device, and FIG. 4 is a RF magnetron sputtering device. FIG. 5 is a diagram showing the relationship between the internal stress of the silicon oxide protective layer and the durability of the magnetic recording medium. 1; Non-magnetic substrate 2.2' - Magnetic recording layer 3.3 made of ferromagnetic metal thin film
': Protective layer mainly composed of silicon oxide 4: Lubricating layer
5: Intermediate layer 6: Back coat layer 7: Unwinding roller 8, free roller 9: Winding roller 10: Free roller 11: Rotating drum 12/mask 13:
Opposing target 14: Magnetron target

Claims (1)

[Claims] (1) In a magnetic recording medium in which a magnetic recording layer made of a thin ferromagnetic metal film and a protective layer made of a thin film mainly composed of silicon oxide are formed in this order on at least one surface of a nonmagnetic substrate, the protective layer A magnetic recording medium having an internal stress of 1×10^9 dyn/cm^2 or less.