JP2005149609A - Magnetic recording medium and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a highly reliable magnetic tape medium which is excellent in electromagnetic conversion characteristics, archive characteristics, traveling durability and storage durability by forming a film of a magnetic layer by means of a vapor deposition device for manufacturing usual magnetic tapes. <P>SOLUTION: A film is formed on a long sheet substrate 1 comprising a polymer film by means of a vacuum vapor deposition process by using an iron-cobalt alloy as a vapor deposition source, and a magnetic layer 2 is formed, which comprises a thin film whose main component is a cobalt-containing maghemite which contains cobalt of 2-20 wt.%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a tape-like magnetic recording medium, and in particular, high-density recording is realized in a system using a magnetoresistive head (MR head) or a giant magnetoresistive head (GMR head). In addition, the present invention provides a magnetic recording medium excellent in storage stability.

  In recent years, in magnetic recording media, in order to handle a large amount of data, there is an increasing demand for higher density recording. In particular, recently, in order to achieve higher density recording, a magnetic head used for reproducing a recording signal is replaced with a magnetoresistive head (MR head) or a giant magnetoresistive instead of a conventional induction head. High-sensitivity magnetic heads such as effect type magnetic heads (GMR heads) have been applied, and are applied not only to hard disks but also to so-called magnetic tapes.

As such a high density type magnetic recording medium, a so-called metal thin film type magnetic recording medium having a magnetic layer made of a Co—CoO thin film formed by a so-called sputtering method or a vacuum evaporation method has been proposed. However, in response to the application of the high-sensitivity magnetic head as described above, it is required to reduce the thickness of the magnetic layer in order to further improve the recording density, thereby realizing high coercivity and low noise.
In addition to the high density recording, the demand for so-called archiving properties that can be stored without causing deterioration of signal quality over a long period of time is becoming stricter.

  Metal thin-film magnetic tapes have been put to practical use as next-generation high-density magnetic recording media, but they have the problem that they are inferior to coated magnetic tapes in terms of corrosion resistance, and data has been stored for a long time. However, there is still a problem to be solved with respect to the characteristics (archivability) of storage over a long period of time.

On the other hand, as a magnetic recording medium that achieves both high density recording and archiving properties, a perpendicular recording medium for a hard disk having a structure in which a magnetic layer of a cobalt-containing maghemite thin film is formed by a sputtering method has been proposed (for example, Patent Documents). (See 1 and 2)
Such cobalt-containing maghemite thin films have excellent storage stability, high film hardness and durability compared to metal thin film magnetic layers, and have a fine particle size because they are formed by sputtering. As compared with the conventional vapor deposition type magnetic tape, there is an advantage that noise can be further reduced.

JP 11-1110731 A JP 11-328651 A

However, when manufacturing magnetic tapes by sputtering, the existing magnetic tape manufacturing equipment, such as coating and vapor deposition equipment, cannot be used, so there were manufacturing problems such as the need to introduce new equipment. .
Accordingly, in view of such problems in the present invention, while taking advantage of the magnetic layer made of a cobalt-containing maghemite thin film, a tape-like magnetic recording medium having a structure in which a magnetic layer is formed on a substrate made of a plastic film, A magnetic layer made of cobalt-containing maghemite thin film is formed using existing magnetic tape manufacturing equipment (not shown) to solve problems such as archiving, recording signal stability, and low noise. Aimed.

  In the present invention, a thin film mainly composed of cobalt-containing maghemite having a cobalt content of 2 to 20% by weight formed on a long substrate made of a polymer film by a vacuum deposition method. A magnetic recording medium having a magnetic layer is provided.

  Also, the method for producing a magnetic recording medium of the present invention comprises forming a film on a long substrate made of a polymer film using an iron-cobalt alloy as a vapor deposition source by a vacuum vapor deposition step, and having a cobalt content of 2 to 2. A magnetic layer composed of a thin film mainly composed of 20% by weight of cobalt-containing maghemite is formed.

  According to the present invention, by forming a thin film containing cobalt-containing maghemite as a main component by a vacuum vapor deposition process, the tape-shaped tape having excellent electromagnetic conversion characteristics, archiving properties, durability, stability and high reliability. A magnetic recording medium could be obtained.

Specific embodiments of the magnetic recording medium of the present invention will be described, but the present invention is not limited to the following examples.
A schematic sectional view of an example of the magnetic recording medium 10 of the present invention is shown in FIG.
The magnetic recording medium 10 has a magnetic layer 2 formed on one main surface of a long and non-magnetic substrate 1, and a protective layer 3 and a lubricant layer 4 are sequentially formed on the magnetic layer 2. It has a configuration.

As the substrate 1, any material conventionally used as a substrate for magnetic tape, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyamide, polyimide, etc., can be applied.
On the magnetic layer forming surface side of the substrate 1, it is desirable that 5 to 30 nm high protrusions are formed at a rate of 5 × 10 ^{6 to} 3 × 10 ⁷ pieces / mm ² . Thereby, the running durability due to sliding with the magnetic head can be sufficiently ensured, and the decrease in output due to the spacing can be suppressed.
Moreover, you may provide a base layer and an intermediate | middle layer as needed. For example, there are an adhesive layer that improves the bonding force (adhesive force) between the substrate 1 and the magnetic layer 2 described later, a functional layer that relieves stress, a layer that imparts smoothness to the surface, a layer that improves magnetic properties, and the like. Can be mentioned.

The magnetic layer 2 is made of a thin film mainly composed of cobalt-containing maghemite (Co-γFe ₂ O ₃ ), and the content of cobalt is 2 to 20% by weight.
When the cobalt content is less than 2% by weight, a sufficient coercive force Hc cannot be secured. When the cobalt content exceeds 20% by weight, rust is generated when stored for a long time in a high-temperature and high-humidity environment. This is to cause a decline.

  The magnetic layer 2 is an in-plane orientation film of a cobalt-containing maghemite thin film, and the coercive force Hc in the in-plane direction is 1500 Oe (119.4 kA / m) or more in order to realize low noise and high resolution. Need to keep. However, if it exceeds 3000 Oe (239 kA / m), in a system using a high-sensitivity magnetic head such as an MR head or a GMR head, signals cannot be recorded sufficiently and the reproduction output is lowered. As described above, the coercive force Hc is preferably 1500 to 3000 Oe (119.4 kA / m to 239 kA / m).

It is desirable to form a protective layer 3 on the magnetic layer in order to improve running durability and weather resistance and to prevent wear and damage due to sliding with the magnetic head.
Any protective layer 3 may be used as long as it is used as a protective layer for a conventionally known metal magnetic thin film type magnetic recording medium. In particular, in order to reduce the wear of the magnetic head, a DLC (diamond-like carbon) thin film formed by plasma CVD is suitable. _{Other, CrO 2, Al 2 O 3} , BN, Co _{oxide, MgO, SiO 2, Si 3} O 4, SiN, SiC, SiN x -SiO 2, ZrO 2, TiO 2, TiC , and the like.
However, since the cobalt-containing maghemite thin film constituting the magnetic layer has high hardness, practical strength can be ensured without forming the protective layer 3.

Furthermore, it is desirable to improve the runnability of the magnetic recording medium by forming the lubricant layer 4 on the outermost surface on the magnetic layer forming surface side. As the lubricant, any of those usually used as a lubricant for metal magnetic thin film type magnetic recording media can be applied. For example, a perfluoropolyether lubricant is suitable.
A back layer (not shown) may be provided on the surface of the substrate 1 opposite to the magnetic layer forming surface. Examples of the back layer include those containing carbon as a main component, and may be formed by either a wet process or a dry process.

Next, a method for manufacturing the magnetic recording medium of the present invention will be described.
First, a substrate 1 made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyamide, polyimide or the like is prepared.
Next, a film is formed on one main surface of the substrate 1 by vacuum vapor deposition using an iron cobalt alloy as a vapor deposition source and introducing oxygen gas into the vapor deposition atmosphere.
At this time, the cobalt content in the iron-cobalt alloy is 2 to 20% by weight, and the cobalt content of the finally obtained cobalt-containing maghemite is 2 to 20% by weight.

  As the vacuum evaporation method, any of the vacuum evaporation methods such as resistance heating evaporation, induction heating evaporation, electron beam evaporation, ion beam evaporation, ion plating, laser beam evaporation, arc discharge evaporation can be applied. From the viewpoint of productivity, the electron beam evaporation method is most suitable.

The thin film obtained by the vacuum deposition method as described above is mainly composed of magnetite, and may not provide a sufficient coercive force Hc. In such a case, it is necessary to oxidize the cobalt-containing magnetite to form a cobalt-containing maghemite film.
As a method of oxidizing a cobalt-containing magnetite film to form a cobalt-containing maghemite film, a method of contacting a can kept at a high temperature in the atmosphere and carrying it for a long time (in-air annealing treatment) is generally used. Since it is necessary to keep the temperature of the substrate at about 200 to 300 ° C. and to heat it for a long time, the substrate to be used is limited to polyimide or polyamide.
As other methods, plasma oxidation treatment that can be performed even at a low temperature of 200 ° C. or lower, UV-ozone treatment that irradiates ultraviolet rays in an oxygen-containing gas atmosphere, or the like may be used. It is possible to use a PET film or a PEN film as the substrate.

  Note that in the thin film formed by the vacuum deposition process, when the ratio of maghemite is high and a practically sufficient coercive force Hc can be obtained, the above-described oxidation treatment process can be omitted.

Next, the protective layer 3 is formed on the magnetic layer 2. The protective layer 3 can be formed by a sputtering method, a CVD (Chemical Vapor Deposition) method, or the like. Specifically, when a DLC (diamond-like carbon) thin film is formed by plasma CVD, a conventionally known material such as a hydrocarbon-based, ketone-based, or alcohol-based material is applied as the carbon compound of the film-forming material. be able to. Further, at the time of plasma generation, argon, hydrogen or the like may be introduced as a gas for promoting the decomposition of the carbon compound. Protective layer 3, _{other, CrO 2, Al 2 O 3} , BN, Co _{oxide, MgO, SiO 2, Si 3} O 4, SiN, SiC, from _{SiN x -SiO 2, ZrO 2,} TiO 2, TiC or the like It is good also as a thin film. The thickness of the protective layer 3 is preferably 1 to 10 nm.

Furthermore, the lubricant layer 4 is formed on the outermost surface on the magnetic layer forming surface side by applying a lubricant.
Further, a back layer is formed on the surface of the substrate 1 opposite to the surface on which the magnetic layer is formed, if necessary, by a conventionally known method such as a wet process or a dry process.

Hereinafter, the magnetic recording medium of the present invention will be described by producing sample magnetic tapes as specific examples and comparative examples.
[Example 1]
An aramid film was prepared as the substrate 1.
Using an electron beam evaporation system, using iron + cobalt alloy (Co content 2% by weight) as the evaporation source, setting the distance between the evaporation source and the substrate to 300 mm, introducing oxygen gas and reactive vacuum evaporation to contain cobalt-containing magnetite A film having a thickness of 50 nm was formed on the substrate 1.
Next, plasma oxidation treatment with oxygen plasma was performed to form the magnetic layer 2 as a cobalt-containing maghemite thin film.
The composition of the magnetic layer 2 was analyzed with an ICP emission spectroscopic analyzer.

[Examples 2 to 5], [Comparative Example 1]
A magnetic layer 2 mainly composed of a cobalt-containing maghemite thin film was formed using a base 1 and an iron + cobalt alloy as shown in Table 1 below.
In Example 5, plasma oxidation treatment with oxygen plasma was not performed after the reactive vacuum deposition process.

[Comparative Example 2]
An aramid film was prepared as the substrate 1.
Using an electron beam vapor deposition apparatus, Co was used as a vapor deposition source, the distance between the vapor deposition source and the substrate was set to 300 mm, oxygen gas was introduced, and a Co—CoO magnetic layer 2 was formed to a thickness of 50 nm by reactive vacuum vapor deposition.

Next, the coercive force Hc of the magnetic layer was measured with a VSM (vibrating sample magnetometer).
Moreover, corrosion resistance was evaluated by the method shown below.
Corrosion resistance was estimated from the magnetization deterioration rate of the magnetic layer after the corrosion test. For the magnetization deterioration rate, the sample was allowed to stand for 6 days in an environment of a temperature of 65 ° C. and a relative humidity of 90%, and Ms ₀ (saturation magnetization) before being left and magnetization Ms ₁ after being left alone were measured. It calculated using.
In addition, it was judged that it was practically acceptable if the magnetization deterioration rate (%) was 15% or less.
Magnetization degradation rate (%) = ((Ms ₀ −Ms ₁ ) / Ms ₀ ) × 100 (1)
The following table shows the measurement results of the deposition source composition of the sample magnetic tape, the material of the substrate, the composition of the magnetic layer formed, the oxidation treatment method, the coercive force Hc, and the magnetization deterioration rate (%) of the magnetic layer after the corrosion test. It is shown in 1.

As shown in Table 1, all the magnetic tapes of Examples 1 to 5 in which the cobalt content of the cobalt-containing maghemite was 2 to 20% by weight had a coercive force Hc of 119.4 kA / m or more, which was excellent. Magnetic properties were obtained.
In addition, the magnetization deterioration rate (%) of the magnetic layer after the corrosion test was extremely low, and it was found that the magnetic layer had excellent storage stability even under severe use environment.

  In Example 5, the plasma oxidation treatment using oxygen plasma was not performed, and the magnetic layer was formed only by the reactive vacuum vapor deposition process. However, the inclusion of maghemite after film formation compared to film formation by sputtering. Since the amount can be increased, a practically sufficient coercive force Hc can be secured.

In Comparative Example 1, since the cobalt content of the magnetic layer was too low, a practically sufficient coercive force Hc could not be obtained.
In Comparative Example 2, the Co—CoO magnetic layer 2 formed by reactive vacuum deposition had a high magnetization deterioration rate after the corrosion test, and practically sufficient storage stability was not obtained.

1 is a schematic sectional view of a magnetic recording medium of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base | substrate, 2 ... Magnetic layer, 3 ... Protective layer, 4 ... Lubricant layer, 10 ... Magnetic recording medium

Claims (4)

On a long substrate made of a polymer film, it has a magnetic layer made of a thin film mainly composed of cobalt-containing maghemite,
The magnetic recording medium according to claim 1, wherein the thin film containing cobalt-containing maghemite as a main component is formed by a vacuum vapor deposition method and has a cobalt content of 2 to 20% by weight.   The magnetic recording medium according to claim 1, wherein the magnetic layer has a coercive force Hc of 119.4 kA / m or more.   A thin film mainly composed of cobalt-containing maghemite having a cobalt content of 2 to 20% by weight on a long substrate made of a polymer film, using an iron-cobalt alloy as a deposition source, and performing a vacuum deposition process. A method for producing a magnetic recording medium comprising forming a magnetic layer. The method of manufacturing a magnetic recording medium according to claim 3, wherein an oxidation treatment is performed after the vacuum deposition step.

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