JPH08180364A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To provide a magnetic recording medium having superior output characteristics over a wide wavelength range by prescribing the favorable range of the numerical value of each parameter expressing the output characteristics of the magnetic layer of a magnetic recording medium using magnetic powder of hexagonal ferrite. CONSTITUTION: A magnetic layer is formed on a nonmagnetic substrate by coating with a magnetic coating material contg. magnetic powder of hexagonal ferrite to obtain the objective magnetic recording medium for a digital magnetic recording system by which a 1st group of recording wavelengths including >=5μm wavelength and a 2nd group of recording wavelengths which are shorter wavelengths than each wavelength in the 1st group, are recorded on the magnetic layer and reproduced. The magnetic layer satisfies formulae I, II when the coercive force of the magnetic layer in the longitudinal direction of the coated face of the substrate is represented by HcL (Oe), the max. residual magnetization in the longitudinal direction is represented by MrL (emu/cc) and the max. residual magnetization in a direction perpendicular to the coated face is represented by MrP (emu/cc).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording medium such as a magnetic tape containing hexagonal ferrite as magnetic powder, and particularly to an external storage device of a computer, a digital image or a digital voice. The present invention relates to a magnetic recording medium used in a digital magnetic recording system such as a digital signal recording / reproducing apparatus.

[0002]

2. Description of the Related Art Conventionally, a magnetic recording medium for recording a magnetic signal on a magnetic layer formed on a non-magnetic support has been used as a particularly effective means for compactly storing a large amount of information.
It is widely used in various fields such as a data recording device, an audio recording device and a video recording device. Generally, the main magnetic recording medium is a thin film type in which a magnetic layer consisting of a metal magnetic thin film is formed on a non-magnetic support by vapor deposition or sputtering, or a magnetic layer is formed on a non-magnetic support by applying a magnetic paint. Examples include molds.

Above all, a magnetic paint prepared by dispersing a magnetic powder composed of ferromagnetic particles such as cobalt-containing iron oxide, pure iron or hexagonal ferrite in a resin binder is applied on a non-magnetic support such as a polyethylene terephthalate film. The coating type magnetic recording medium in which the magnetic layer is formed by coating on the substrate is widely used because it has excellent mass productivity, durability, corrosion resistance, and high reliability as compared with the thin film type magnetic recording medium. .

Further, today, with the rapid increase in the amount of information to be recorded, these magnetic recording media are required to have a larger capacity. In order to meet this demand, the particle diameter of the magnetic powder is made small, and the coercive force (Hc) thereof is made as high as possible in the range where magnetic recording by a normal magnetic head is possible to achieve high recording density. It has been attempted to improve the recording / reproducing output by various means such as increasing the filling rate of the powder particles in the resin binder or improving the surface roughness of the medium. In particular, hexagonal ferrite magnetic powder has been attracting attention as a magnetic powder that meets the purpose of increasing the capacity and recording density of such magnetic recording media. Hexagonal ferrite magnetic powder is used as a magnetic recording medium for digital magnetic recording systems. Is also being applied.

By the way, in the digital signal recording system, conventionally, a servo signal for head tracking control is recorded on a magnetic recording medium together with a signal of information data to be recorded. Servo signals in the helical scan data 8 mm cartridge tape subsystem, CTL signals in the D-2 format digital VTR, ATF signals in the digital audio tape recorder, etc. are typical examples of such tracking signals. In the current system, most of the wavelengths of information data signals are in a relatively short recording wavelength band of about 0.4 to 4 μm, and in order to easily distinguish them from these signals, servo signals are usually 20
Those having a recording wavelength in the long wavelength region around μm are selected.

Since the tracking signal is not a signal for directly storing data, its characteristics are often neglected. However, considering that it is a signal for controlling running of the magnetic head at the time of data reproduction, it is long for a magnetic recording medium for digital recording. It can be said that wavelength output is as important as short wavelength output.

Therefore, a magnetic recording medium for a digital signal recording system is required to exhibit good recording / reproducing characteristics in both the long and short recording wavelength regions. That is, it is strongly demanded that the recording / reproducing characteristics are further improved in a wide wavelength range as compared with the conventional magnetic recording media for analog signal recording systems such as audio tapes and VTR tapes.

[0008]

The hexagonal ferrite magnetic powder is hexagonal plate-like fine particles and has uniaxial anisotropy in which the easy axis of magnetization is perpendicular to the plate surface. A medium in which this is used, for example, in a short wavelength region of a recording wavelength of about 1 μm or less, a higher reproduction output can be obtained as compared with a magnetic recording medium using acicular magnetic powder having a similar coercive force. On the other hand, it has been found that a high reproduction output cannot be obtained in the long wavelength region.

Conventionally, in order to solve the above technical problem of obtaining a high output in a wide recording wavelength range, in many cases, the saturation magnetization of the magnetic powder used is increased or the orientation ratio of the magnetic layer is increased. Alternatively, a method such as adjusting the coercive force of the magnetic powder is adopted. However, those methods
This is a situation in which the relationship between the output of a specific wavelength and the individual magnetic characteristics is obtained, and then optimization is performed by trial and error.

Generally, a digital magnetic recording apparatus records a signal of each wavelength with a constant current. Therefore, if the coercive force is increased, the short wavelength signal output is improved, but the long wavelength signal output is decreased. Conversely, if the coercive force is decreased, the long wavelength signal output is improved, but the short wavelength signal output is decreased.
In this way, it is extremely difficult to obtain a high output in a wide recording wavelength range only by adjusting the individual magnetic characteristics.

The present invention has been made in view of the above technical problems, and proposed a parameter expressing the output characteristics of the magnetic layer, and by defining the parameter, hexagonal ferrite magnetic powder was used. A magnetic recording medium,
It is an object of the present invention to provide a magnetic recording medium for a digital magnetic recording system, which has excellent output characteristics over a wide wavelength range from a long wavelength to a short wavelength.

[0012]

According to the present invention, a magnetic layer is formed on a non-magnetic support by coating a magnetic coating material containing hexagonal ferrite magnetic powder, and the magnetic layer has at least one type of 5 μm or more. For a digital magnetic recording system that records and reproduces a first recording wavelength group consisting of a plurality of wavelengths and a second recording wavelength group consisting of a plurality of types of wavelengths shorter than each wavelength of the first recording wavelength group. In the recording medium, the coercive force in the longitudinal direction with respect to the coated surface of the magnetic layer is HcL (Oe), the maximum remanent magnetization is also MrL (emu / cc), and the maximum remanent magnetization perpendicular to the coated surface is MrP (emu). / Cc), the following two relational expressions HcL × (MrP ÷ MrL) ≦ 800 1100 ≦ HcL ≦ 1700 are satisfied.

The maximum remanent magnetization MrP in the vertical direction is a value after demagnetizing field correction.

In the present invention, the value of HcL × (MrP ÷ MrL) may be 80 O or less, but more preferably 250 or more and 500 or less. HcL × (MrP ÷
When MrL) is larger than 800, the long-wavelength output starts to decrease, which is not preferable. In the present invention, HcL
Is a premise for exhibiting a good short wavelength output in the range of 1100 Oe or more and 1700 Oe or less, but the range of 1300 Oe or more and 1500 Oe or less is more preferable. As described above, when magnetic recording is performed with a constant current, the lower the coercive force in the in-plane direction, the larger the long wavelength output. From the viewpoint of long wavelength output only, there is no lower limit to the coercive force. However, looking at short wavelength output, if the coercivity is below 1100 Oe,
The output begins to drop due to the effect of recording demagnetization. Therefore, a coercive force of less than 1100 Oe is not preferable.

The coercive force in the in-plane direction is 1700 Oe.
Beyond the above, it becomes impossible to sufficiently magnetize the medium even when using an alloy-based magnetic head having a high writing capability such as Sendust. As a result, the reproduction output is lowered and the erasing rate is deteriorated, which is not preferable.

The maximum remanent magnetization MrL in the longitudinal direction, the maximum remanent magnetization MrP in the vertical direction, and the coercive force HcL in the longitudinal direction of the magnetic layer formed by applying the magnetic coating material containing hexagonal ferrite magnetic powder are used. It can be controlled by changing the shape and magnetic characteristics of the hexagonal ferrite magnetic powder, or by changing the orientation magnetic field strength during medium preparation.

The control of the particle shape of the magnetic powder is performed as follows at the time of manufacturing. For example, in the case of producing Ba ferrite particles by the glass crystallization method, the higher the crystallization temperature, the larger the average particle diameter of the obtained crystals. Further, if Ba is excessively added to the glass composition as a raw material, the plate ratio becomes large. Usually, when crystallization is carried out at 800 ° C. for 5 hours, the average particle diameter becomes 50 nm, and when 2 to 3 wt% of Ba is excessively added to the glass component, the plate ratio becomes 6
It can be ~ 7.

Further, in controlling the magnetic properties of the magnetic powder, the saturation magnetization changes depending on the thickness or plate ratio of the particles, and as the thickness becomes thicker, the saturation magnetization also increases, but by applying a spinel layer to the surface of the particles, etc. , Can be further increased.

Ferromagnetic particles usable as magnetic powder in the present invention include, for example, the following general formula BaO.n (Fe _{1 -m} M _m ) ₂ O ₃ (where M is Zn, Co, Ti, Ni). , Mn, I
n, Cu, Ge, Nb, Sn, Mg, Ta, Cr, M
a hexagonal crystal such as Ba ferrite represented by one or more elements selected from o, W, Zr, Hf, V, m is 0 to 0.2, and n is a number in the range of 5 to 10). Examples include fine ferrite particles.

These hexagonal ferrite fine particles are hexagonal plate-like crystals, and their particle shape is usually expressed by the ratio of the particle diameter, which is the length of the diagonal line of the plate surface, to the length and thickness of the diagonal line of the hexagonal plate surface. It is expressed as a certain plate ratio. The particle shape also affects the magnetic properties of the magnetic powder. The magnetic properties of the magnetic powder are affected not only by such a particle shape but also by the magnitude of the orientation strength during medium preparation.

In the magnetic recording medium of the present invention, the average particle size is 0.03 μm, with the particle size being the length of the diagonal line of the plate surface.
Hexagonal ferrite fine particles in the range of 0.1 μm are suitable.

Further, it is preferable that the ratio of the length of the diagonal line of the hexagonal plate surface to the thickness, that is, the plate ratio is in the range of 2 to 7. In the case of a magnetic powder having a plate-like ratio of less than 2, it is difficult to orient the magnetic field after forming the magnetic layer, regardless of the direction, whether vertical or in-plane. Therefore, the reproduction output of the manufactured magnetic recording medium is reduced in the entire wavelength range. Further, in the case of a magnetic powder having a plate ratio of more than 7, re-aggregation is likely to occur when it is made into a coating, and dispersion becomes difficult.

In the present invention, the magnetic layer may be made of any material such as a thermoplastic resin, a thermosetting resin, a reactive resin, an electron beam curing resin, etc., as long as it is generally blended as a resin binder for a magnetic paint. Things can be mixed. Among them, vinyl chloride resin, polyurethane, to which a functional group such as a functional group such as metal sulfonate is added.
Resins such as polyester are particularly preferred.

Further, in addition to the above magnetic powder and resin binder, the magnetic layer may contain a lubricant such as fatty acid or fatty acid ester, an abrasive such as alumina particles, and an antistatic agent such as carbon as additives. .

The magnetic recording medium of the present invention is manufactured as follows according to a conventional method. That is, it is manufactured by adding a solvent to a composition comprising the above magnetic powder, a resin binder, and various additives, kneading and dispersing to prepare a magnetic coating material, and coating this on a non-magnetic support.

Here, as the material constituting the non-magnetic support, various materials such as polyolefins, celluloses, polycarbonate, etc. can be used in addition to polyesters such as polyethylene terephthalate or polyethylene naphthalate.

[0027]

In the present invention, HcL × (MrP ÷ MrL) is introduced as a parameter for long-wavelength output, and coercive force HcL in the in-plane direction of the magnetic layer is selected as a parameter for short-wavelength output to determine the proper range of both. By stipulating,
A magnetic recording medium for a digital magnetic recording system having excellent long-wavelength output and short-wavelength output is provided.

A characteristic of the present invention is that even in a magnetic recording medium using hexagonal ferrite, which is said to have many perpendicular magnetization components, long wavelength output is recorded in the longitudinal direction with respect to the coated surface. It is assumed that the parameter H
This is because cL × (MrP ÷ MrL) was introduced, the correspondence between this and long-wavelength output was found, and it was combined with the condition for achieving both short-wavelength output.

That is, in the parameter HcL × (MrP ÷ MrL) related to the long wavelength output, the part of the coercive force HcL is
It was introduced with a focus on the fact that the lower the coercive force, the greater the long-wavelength output. Further, the ratio of the maximum remanent magnetization MrP in the vertical direction to the maximum remanent magnetization MrL in the longitudinal direction (MrP / Mr
The part (L) represents the degree of easiness of remaining magnetization in the longitudinal direction. As (MrP ÷ MrL) is smaller than 1, that is, as the maximum remanent magnetization in the longitudinal direction is larger than that in the perpendicular direction, the magnetization in the longitudinal direction is likely to remain, so that it is considered to be recorded longitudinally. The long wavelength output becomes large.

On the other hand, the coercive force HcL in the longitudinal direction of the magnetic layer is used as a parameter for the short wavelength output. As described above, when the coercive force in the longitudinal direction of the magnetic layer is less than 1100 Oe, the short wavelength output starts to decrease due to the effect of demagnetization. Also, the coercive force in the longitudinal direction is 1
If it exceeds 700 Oe, the medium cannot be magnetized sufficiently even if a magnetic head having a high writing capability is used, so that the characteristics of the medium deteriorate such as a reduction in reproduction output and a deterioration in erasing rate. Therefore, 1100 ≦ HcL ≦ 1700 is introduced as a preferable range of the coercive force in the longitudinal direction.

In the present invention, the relationship between the value of HcL × (MrP ÷ MrL) and the long-wavelength output and the short-wavelength output when HcL is in such a range is investigated, and a good long-wavelength output and a good output are obtained. Parameter HcL × (MrP that can achieve both short wavelength output
The range of ÷ MrL could be derived. And HcL ×
It has been found that by setting (MrP ÷ MrL) to be 800 or less, it is possible to achieve both a good long-wavelength output and a good short-wavelength output required for a digital magnetic recording medium. When HcL × (MrP ÷ MrL) exceeds 800, the long wavelength output starts to decrease.

[0032]

EXAMPLES The magnetic recording medium of the present invention will be described in detail with reference to Examples and Comparative Examples.

Examples 1 to 5 The following material compositions using Ba ferrite magnetic powder were mixed and kneaded, diluted, and stirred and dispersed according to a conventional method to prepare a magnetic coating material.

[0034] The obtained magnetic paint was applied on the surface of a polyethylene terephthalate base film having a thickness of 9 μm using a reverse coater. At this time, the coating amount was adjusted so that the thickness of the coating layer after drying was 2 μm, and the coating speed was 120 m / min. The thickness of the magnetic layer was controlled to be constant in order to keep the calendering processability constant and to make the surface roughness of each medium uniform.

After the magnetic coating material was applied, the coating film was passed through a magnetic field before it was dried for magnetic field orientation treatment, followed by drying and then surface smoothing treatment with a calendar.
Calendar conditions are linear pressure of 300 kg / cm ² and temperature of 80 ° C.
And After the magnetic layer was formed, it was cured in a constant temperature bath at a temperature of 60 ° C. to obtain a raw material of the magnetic recording medium. Then, this raw fabric was cut into a width of 8 mm and stored in a tape cassette to obtain magnetic recording media of Examples 1 to 5 of the present invention.

The manufactured magnetic recording media of Examples 1 to 5 were used.
, The maximum remanent magnetization MrL in the longitudinal direction, the maximum remanent magnetization MrP in the perpendicular direction, and the coercive force HcL in the longitudinal direction with respect to the coated surface of these magnetic layers are used as magnetic powder B.
The shape and magnetic properties of the a ferrite fine particles were controlled by changing them by the adjustment in the manufacturing process as described above.

In Examples 1 to 5, the average particle size was 4
5-60 nm, plate ratio 3.5-5.0, saturation magnetization 6
0 to 65 emu / g, and coercive force of 1100 to 140
At the same time as using different magnetic powders within the range of 0 Oe, the orientation magnetic field strength at the time of medium preparation was 4 kOe to 6 kOe.
The maximum remanent magnetization and coercive force of the magnetic layer were controlled by variously changing the range.

Comparative Example 1 A magnetic recording medium of Comparative Example 1 was prepared in the same manner as in Example 1 except that Ba ferrite powder having a saturation magnetization of 55 emu / g was used as the magnetic powder and the orientation magnetic field strength at the time of producing the medium was 4 kOe. Was produced.

Comparative Examples 2 to 8 As magnetic powder, B having a coercive force of 1000 to 1050 Oe
a Oriented magnetic field strength at the time of medium preparation is set to 2 by using ferrite powder
Comparative Example 2
A magnetic recording medium No. 8 was manufactured.

Comparative Examples 9 and 10 As the magnetic powder, Ba ferrite powder having a saturation magnetization of 55 to 60 emu / g and a coercive force of 1000 to 1050 Oe was used, and the orientation magnetic field strength during the production of the medium was set to 2 kOe to 4 kOe. Magnetic recording media of Comparative Examples 9 and 10 were produced in the same manner as in the example.

Next, the magnetic characteristics and output characteristics of the magnetic recording media of Examples 1 to 5 and Comparative Examples 1 to 10 described above were examined. Further, two parameters HcL and HcL × (MrP ÷ MrL), which are features of the present invention, were calculated. The evaluation results and the calculation results are shown in Table 1 together.

In measuring the magnetic characteristics, a maximum magnetic field of 10 kgaus was applied using a vibrating sample magnetometer (VSM). The maximum remanent magnetization MrP in the perpendicular direction is a value after demagnetizing field correction. In the evaluation of the reproduction output characteristics, as a typical tracking signal of the digital magnetic recording system, the servo signal output of the helical scan data 8 mm cartridge subsystem (recording wavelength 2
In the present invention, a signal of 4 MHz was selected as a representative of short wavelength recording signals, and the output thereof was measured as a measurement value of 0 μm).

[0043]

[Table 1] In addition, in FIG. 1, these Examples 1-5 and Comparative Examples 1-
Servo signal output of 10 magnetic recording media (approximately 20 μ
m) and the parameter HcL × (MrP ÷ MrL) are shown. Further, FIG. 2 shows the relationship between the 4 MHz output of these 15 magnetic recording media and the parameter HcL.

As is clear from Table 1 and FIGS. 1 and 2, in the present invention, two parameters HcL and HcL ×
By introducing (MrP ÷ MrL) and setting the preferable range thereof, a magnetic recording medium in which short-wavelength output and long-wavelength output are well balanced can be obtained.

[0045]

According to the present invention, by proposing a parameter expressing the output characteristic of the magnetic layer in the magnetic recording medium using the hexagonal ferrite magnetic powder, and defining the preferable range of the numerical value of the parameter, There is easily provided a magnetic recording medium for a digital magnetic recording system, which has excellent output characteristics over a wide wavelength range from a long wavelength to a short wavelength.

[Brief description of drawings]

FIG. 1 shows magnetic recording media of Examples and Comparative Examples,
It is a figure which shows the relationship between a servo signal output and parameter HcLx (MrP / MrL).

FIG. 2 shows magnetic recording media of Examples and Comparative Examples,
It is a figure which shows the relationship between the signal output of 4 MHz, and parameter HcL.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiko Igarashi 1-13-1, Nihonbashi, Chuo-ku, Tokyo TDC Corporation (72) Osamu Inoue 1-13-1-1, Nihonbashi, Chuo-ku, Tokyo -Dk Co., Ltd. (72) Inventor ▲ Kuwa ▼ Takayoshi Shima 1-13-1, Nihonbashi, Chuo-ku, Tokyo

Claims (2)

[Claims] 1. A magnetic layer is formed on a non-magnetic support by applying a magnetic paint containing hexagonal ferrite magnetic powder,
In this magnetic layer, a first recording wavelength group consisting of at least one wavelength of 5 μm or more and a second recording wavelength group consisting of a plurality of wavelengths shorter than each wavelength of the first recording wavelength group are provided. In a magnetic recording medium for recording and reproducing for a digital magnetic recording system, a coercive force in the longitudinal direction with respect to the coated surface of the magnetic layer is HcL (O
e), the maximum remanent magnetization in the longitudinal direction with respect to the coated surface is MrL (e
mu / cc) and the maximum remanent magnetization in the direction perpendicular to the coated surface is MrP (emu / cc), the following two relational expressions HcL × (MrP ÷ MrL) ≦ 800 1100 ≦ HcL ≦ 1700 are established. A magnetic recording medium characterized by the above. 2. The magnetic recording medium according to claim 1, wherein the following two relational expressions 250 ≦ HcL × (MrP ÷ MrL) ≦ 500 1300 ≦ HcL ≦ 1500 are satisfied.