JPH08263824A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To ensure high reproduction output in a short wavelength region by mixing acicular magnetic powder with platy magnetic powder having an axis of easy magnetization in a direction perpendicular to the plate surface, obliquely orienting the resultant powdery mixture and forming a magnetic layer. CONSTITUTION: Since acicular magnetic powder has an axis of easy magnetization in the direction of the major axis, when a metallic roll 1 is pressed against the surface of a magnetic layer contg. the magnetic powder at the time of calendering, the magnetic powder falls in the intrasurface direction and the angle of the axis of easy magnetization is reduced. Such acicular magnetic powder is mixed with platy magnetic powder having an axis of easy magnetization in a direction perpendicular to the plate surface and the resultant powdery mixture is obliquely oriented. The angle of an axis of easy magnetization of the surface of a magnetic layer contg. the mixture after calendering is increased as compared with the case of only the acicular magnetic powder and the objective medium having higher output in a short wavelength region than a medium contg. only the acicular magnetic powder is obtd.

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,
More specifically, it relates to a magnetic recording medium having a high reproduction output in a short wavelength region.

[0002]

2. Description of the Related Art Magnetic recording media such as magnetic tapes produced by coating magnetic powder on a substrate together with a binder resin or the like are generally acicular magnetic powders oriented in the longitudinal direction from the viewpoint of recording and reproducing characteristics. It has been widely used.

However, when the recording wavelength is shortened to increase the recording density, the loss of self-demagnetization, recording demagnetization, etc. in the magnetic recording medium oriented in the longitudinal direction becomes large, and the reproduction output remarkably decreases at the short wavelength. There is a problem of doing.

As a method of reducing the loss of self-demagnetization or recording demagnetization at a short wavelength, it is generally effective to increase the coercive force of the magnetic recording medium. However, in terms of structure, another method is to thin the magnetic layer, or It is known that, instead of the conventional longitudinal orientation, a method of orienting in a diagonal direction from the in-plane longitudinal direction to the out-of-plane vertical direction is effective.

[0005]

However, among the above methods, the method of orienting the acicular magnetic powder at a high angle in an oblique direction is difficult due to the shape of the magnetic powder and the influence of the demagnetizing field. In the calendar treatment for smoothing the magnetic layer surface after being obliquely oriented, the magnetic layer surface is pressed by a heated metal roll, and thus the obliquely oriented needle-shaped magnetic powder falls toward the in-plane direction, There is a drawback in that the easy magnetization axis angle decreases from the in-plane longitudinal direction to the out-of-plane vertical direction.

In order to improve the reproduction output at a short wavelength, it is desirable that the magnetic layer is obliquely oriented at a higher angle as it gets closer to the surface of the magnetic layer. The inclination of the powdery magnetic powder from the oblique direction to the in-plane direction is larger at the surface.

According to the present invention, it is difficult to obliquely orient the needle-like magnetic powder from the in-plane longitudinal direction to the out-of-plane vertical direction, which is possessed by the above-mentioned prior art, and the magnetic layer surface is formed by the calendar treatment after the oblique orientation. Effectively eliminates the disadvantage that the magnetic easy axis angle decreases from the in-plane longitudinal direction to the out-of-plane perpendicular direction due to the magnetic powder falling in the in-plane direction closer to it, and thus magnetic recording with excellent electromagnetic conversion characteristics. The purpose is to provide a medium.

[0008]

The above-mentioned object includes needle-like magnetic powder and magnetic powder having a plate-like shape and having an easy axis of magnetization in the direction perpendicular to the plate surface, and the easy axis of magnetization extends from the in-plane longitudinal direction. This is achieved by the first means having a magnetic layer that is oblique to the outer vertical direction.

In the first means, the coercive force Hc1 of the acicular magnetic powder and the coercive force Hc2 of the plate-shaped magnetic powder having the easy axis of magnetization in the direction perpendicular to the plate surface are given by | 1-Hc2 / Hc1 It is achieved by the second means that satisfies the relationship | ≦ 0.05.

Further, in the first and second means, a third means is provided in which the easy axis of magnetization of the magnetic layer is in the range of 5 to 60 degrees from the in-plane longitudinal direction to the out-of-plane vertical direction. It

[0011]

As described above, the present invention mixes acicular magnetic powder with magnetic powder having a plate-like shape and having an easy axis of magnetization in the direction perpendicular to the plate surface and inclining from the in-plane longitudinal direction to the out-of-plane vertical direction. By orienting and forming the magnetic layer, a high reproduction output can be obtained in the short wavelength region.

The principle of the present invention will be described below with reference to the drawings.

FIG. 1 shows the orientation of the magnetic powder before and after the calendering process and the direction of the easy axis of magnetization when the acicular magnetic powder is oriented so as to be inclined from the in-plane longitudinal direction to the out-of-plane vertical direction.

In the figure, 1 is a metal roll, 2 is a magnetic layer, 3 is the direction of needle-like magnetic powder before calendaring, 4 is the direction of needle-like magnetic powder after calendaring, and 5 is needle-like before calendaring. The direction of the easy axis of magnetization of the magnetic powder, and 6 is the direction of the easy axis of the needle-shaped magnetic powder after the calendar treatment.

Since the acicular magnetic powder has an easy axis of magnetization in the major axis direction, when the metal roll 1 is pressed against the surface of the magnetic layer by calendering, the magnetic powder falls in the in-plane direction, and the easy axis of magnetization is It will be smaller than before calendar processing.

On the other hand, in the case of a magnetic powder having a plate-like shape and having an easy axis of magnetization in the direction perpendicular to the plate surface, the magnetic powder is subjected to the pressure of the metal roll 1 as in the case of the acicular magnetic powder, as shown in FIG. Although it falls down, since the easy magnetization axis is perpendicular to the plate surface, the easy magnetization axis angle becomes larger after the calendering process than before the calendering process.

In FIG. 2, 7 is the direction of the plate-like magnetic powder before the calendering process, 8 is the direction of the plate-like magnetic powder after the calendering process, and 9 is the direction of the easy axis of magnetization of the plate-like magnetic powder before the calendering process. Reference numeral 10 indicates the direction of the easy axis of magnetization of the plate-like magnetic powder after the calendar treatment.

Then, the acicular magnetic powder is mixed with a plate-shaped magnetic powder having an easy axis of magnetization in the direction perpendicular to the plate surface and obliquely oriented so that the angle of easy axis of magnetization of the surface of the magnetic layer after calendering is acicular. It becomes larger than the case of magnetic powder alone,
It is possible to obtain a medium having a higher output than the case where the acicular magnetic powder alone has a short wavelength.

If the coercive force of the acicular magnetic powder used for mixing is different from that of the plate-shaped magnetic powder having an easy axis of magnetization in the direction perpendicular to the plate surface, the steepness of magnetization reversal is impaired. Playback output drops. Therefore, the coercive force Hc1 of the acicular magnetic powder and the coercive force Hc2 of the plate-shaped magnetic powder having an easy axis of magnetization in the direction perpendicular to the plate surface satisfy the relationship | 1-Hc2 / Hc1 | ≦ 0.05. Is desirable.

Further, the easy axis angle of magnetization from the longitudinal direction of the plane suitable for high density recording to the perpendicular direction of the plane varies depending on the recording / reproducing characteristics required by the recording apparatus side. With respect to the direction, the easy magnetization axis angle is inclined in the range of 5 to 60 degrees from the longitudinal direction in the plane to the direction perpendicular to the plane outside along the direction of the head magnetic field on the trailing edge side of the head. Is desirable. When the axis of easy axis of magnetization is further inclined to approach the vertical orientation, the long-wavelength output remarkably decreases, and the recording demagnetization increases even at the short wavelength, and the reproduction output lowers as compared with the longitudinal orientation.

[0021]

EXAMPLE A magnetic recording medium such as a magnetic tape according to the present invention is a γ-Fe ₂ O ₃ powder, Fe ₃ O ₄ powder, Co.
Γ-Fe ₂ O ₃ powder containing, Fe ₃ O ₄ powder containing Co, C
rO ₂ powder, Fe powder, Co powder, Co-Ni alloy powder, Fe-Ni alloy powder, Co-Ni-P alloy powder, C
Various magnetic powders such as o-Ni-Fe alloy powder and Ba ferrite powder are mixed and dispersed with a binder resin, an organic solvent and other necessary components to prepare a magnetic paint, and this magnetic paint is used as a non-magnetic material such as a polyester film. A magnetic layer is formed by a method of coating and drying on a substrate or a non-magnetic layer, and then the magnetic recording medium stock thus obtained is cut into a predetermined width.

Here, as the binder resin, vinyl chloride-
Vinyl acetate-based copolymers, polyvinyl butyral resins, fibrin-based resins, polyurethane-based resins, polyester-based resins, isocyanate compounds, etc. that are commonly used in magnetic recording media are used, and as the organic solvent,
Conventionally widely used organic solvents such as methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, ethyl acetate, dioxane, benzene, toluene and xylene are used alone or in combination of two or more.

An embodiment of the present invention will be described below with reference to FIGS.

(Example 1) (Magnetic coating) Needle-like magnetic powder (metal magnetic powder: major axis diameter 0.21 μm, acicular ratio 5, coercive force 172 Oe, saturation magnetization 126 emu / g) 68 parts by weight Plate Magnetic powder (Ba ferrite magnetic powder: plate ratio 4, particle size 500Å, coercive force 1750 Oe, saturation magnetization 58 emu / g) 12 parts by weight vinyl chloride resin 10 parts by weight urethane resin 6 parts by weight alumina 8 parts by weight carbon black 1.6 parts by weight myristic acid 1.6 parts by weight-n-butyl stearate 1.2 parts by weight 2-butanone 70 parts by weight cyclohexanone 70 parts by weight toluene 70 parts by weight This composition is mixed and dispersed in a ball mill for about 72 hours. Adjust the magnetic paint and apply this magnetic paint so that the dry thickness is about 2.8 μm, and make the easy magnetization axis angle of the magnetic layer after drying about 30 degrees. And it dried made an oblique orientation to so that. Next, calendering was performed to leave a part of the raw sheet, and then calendering was performed to form a magnetic layer.

Next, a back coating layer coating composition having the following composition is applied to the back surface of the polyester base film having a magnetic layer having a calendered surface so as to have a dry thickness of about 0.7 μm, and the back coating layer is dried. To form a magnetic tape stock.

(Backcoat layer coating material) Barium sulfate 80 parts by weight Nitrocellulose (Nitrocellulose HIGI manufactured by Asahi Kasei Corporation) 27 parts by weight Urethane elastomer (Estan 5702 manufactured by Goodrich Chemical Co.) 19 parts by weight Trifunctional low molecular weight isocyanate compound ( Nippon Polyurethane Industry Co., Ltd. Coronate L) 8 parts by weight Alumina 10 parts by weight Carbon black 10 parts by weight Myristic acid 3 parts by weight Stearic acid-n-butyl 3 parts by weight 2-butanone 50 parts by weight Cyclohexanone 300 parts by weight Toluene 300 parts by weight Methyl ethyl ketone 300 Parts by Weight Next, a magnetic tape stock having a magnetic layer and a back coat layer formed thereon was cut into a width of 8 mm with a slitter to prepare a magnetic tape.

(Comparative Example 1) A calender was prepared in the same manner as in Example 1 except that the magnetic powder contained in the composition of the magnetic coating material of Example 1 was 80 parts by weight only for the metal powder which was needle magnetic powder. A magnetic tape having a processed raw sheet and a calendered magnetic layer was prepared.

FIG. 3 shows the results of measurement of the easy axis angle of magnetization of the magnetic layer before and after the calendar treatment in Example 1 and Comparative Example 1 with a torque meter. Here, the magnetization easy axis angle in FIG. 3 is the magnetization easy axis angle in which the influence of the shape anisotropy of the sample is removed by measuring the saturation magnetization using a sample vibrating magnetometer and calculating the energy due to the demagnetizing field.

As is apparent from this figure, the magnetic layer in which the metal powder of Example 1 and Ba ferrite powder were mixed and obliquely oriented was compared with the magnetic layer in Comparative Example 1 in which only the metal powder was obliquely oriented, by the calendar treatment. The easy axis of magnetization is large in the front and back,
In addition, the reduction angle of the easy axis of magnetization due to the calendar processing is also small.

Further, the magnetic tapes produced in Example 1 and Comparative Example 1 were incorporated into a commercially available Hi8VTR cassette deck, and the commercially available Hi8VTR was modified so that the electromagnetic conversion characteristics could be measured, and the reproduction output at a recording wavelength of 0.5 μm was obtained. Was measured.

Recording at the optimum current that maximizes the reproduction output,
The reproduction output is read by using a spectrum analyzer. B.
W at 10 KHz, V. B. The results of measurement with W set to 30 Hz are shown in FIG. The reproduction output was compared by a relative value based on the reproduction voltage of the tape in which only the metal powder of Comparative Example 1 was obliquely oriented.

As is apparent from this figure, the tape in which the metal powder of Example 1 and Ba ferrite powder were mixed and obliquely oriented had a larger reproduction output and a higher reproduction output than the tape in Comparative Example 1 in which only the metal powder was obliquely oriented. Excellent as a density recording medium.

(Comparative Example 2) In the composition of Example 1 above, B
Sample tapes 1 to 1 were prepared in the same manner as in Example 1 except that Ba ferrite magnetic powders A, B, C, and D having different coercive forces shown below were used as the a ferrite magnetic powders.
4 was produced.

Ba ferrite magnetic powder A: coercive force 1580 Oe, plate ratio 5, particle size 450 Å, saturation magnetization 57 emu / g) Ba ferrite magnetic powder B: coercive force 1650 Oe, plate ratio 4, particle size 500 Å, saturation magnetization 58 emu / G) Ba ferrite magnetic powder C: coercive force 1790 Oe, plate ratio 4, particle size 500 Å, saturation magnetization 58 emu / g) Ba ferrite magnetic powder D: coercive force 1840 Oe, plate ratio 5, particle size 450 Å, saturation magnetization 57 emu / G) Sample tapes 1 produced in Example 1 and Comparative Example 2
In order to obtain the coercive force distribution of No. 4, SFD was measured with a sample vibration type magnetometer. This SFD has a coercive force Hc when the MH major loop due to the magnetization M and the magnetic field H is differentiated by H.
The curve has a pulse in the vicinity, but is defined as ΔH / Hc, where ΔH is the pulse width at half the peak value of this pulse.

Also, the sample tapes 1 to 4 produced in Example 1 and Comparative Example 2 were incorporated into a commercially available Hi8VTR cassette deck, and reproduction was performed at a recording wavelength of 0.5 μm using a Hi8VTR modified so that the electromagnetic conversion characteristics could be measured. The output was measured. The measurement conditions were recorded at the optimum current that maximized the reproduction output, and the reproduction output was measured using a spectrum analyzer. B. W at 10 KHz, V. B. W to 30Hz
And

FIG. 5 shows the measurement results of the reproduction output based on the SFD and the reproduction voltage of Example 1.

As is clear from this figure, when the coercive force of the mixed metal powder and the Ba ferrite powder is greatly different, the SFD corresponding to the coercive force distribution of the medium becomes large and a steep magnetization transition region cannot be formed. Especially, the reproduction output at a short wavelength is reduced. Therefore, it is desirable that the coercive force Hc1 of the needle-like magnetic powder used for mixing and the coercive force Hc2 of the plate-like magnetic powder having an easy axis of magnetization in the direction perpendicular to the plate surface are as close to each other as possible, and Hc1 and Hc2. Preferably satisfies the relationship | 1-Hc2 / Hc1 | ≦ 0.05. Incidentally, | 1-Hc2 / Hc1 | is 0.02 in the first embodiment.
And satisfies the above conditions.

(Comparative Example 3) Sample tapes 1 to 6 were produced in the same manner as in Example 1 except that the magnetic paint produced in the same manner as in Example 1 was oriented at various angles.

FIG. 6 shows the results of measuring the easy axis angles of magnetization of the sample tapes 1 to 6 produced as described above and the tape of Example 1 with a torque meter.

Here, the easy axis angle of magnetization in FIG. 6 is obtained by measuring the saturation magnetization using a sample vibrating magnetometer and calculating the energy due to the demagnetizing field to eliminate the influence of the shape anisotropy of the sample. And

Each of the above tapes was incorporated into a commercially available Hi8VTR cassette deck, and the reproduction output at a recording wavelength of 0.5 μm was measured using a Hi8VTR modified so that the electromagnetic conversion characteristics could be measured. Recording was performed at the optimum current that maximizes the reproduction output, and the reproduction output was recorded using a spectrum analyzer. B. W at 10 KHz, V. B. The result of measurement with W set to 30 Hz is also shown in FIG.

As is apparent from this figure, the reproduction output at the recording wavelength of 0.5 μm is improved as compared with the longitudinal orientation when the easy axis angle is from the longitudinal direction to about 60 degrees. From the above, it is preferable for the medium for high density recording that the easy axis of magnetization is in the range of 5 to 60 degrees.

[0043]

As described above, the magnetic recording medium according to the present invention contains magnetic powder having a needle-like shape on a substrate and magnetic powder having a plate-like shape and having an easy axis of magnetization in the direction perpendicular to the plate surface, and is magnetized. Since the easy axis has a magnetic layer that is oblique from the in-plane longitudinal direction to the out-of-plane vertical direction, it has a high reproduction output in the short wavelength region and has an industrial value as a high-density recording medium. It will be very expensive.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing directions of acicular magnetic powder and an easy axis of magnetization before and after calendering.

FIG. 2 is a conceptual diagram showing the directions of the plate-like magnetic powder and the easy axis of magnetization before and after calendaring.

FIG. 3 is a comparative characteristic diagram of easy magnetization axis angles in Example 1 and Comparative Example 1.

FIG. 4 is a comparative characteristic diagram of reproduction outputs in Example 1 and Comparative Example 1.

5 is a comparison characteristic diagram of SFD and reproduction output in Example 1 and Comparative Example 2. FIG.

FIG. 6 is a comparison characteristic diagram of an easy axis angle of magnetization and a reproduction output in Example 1 and Comparative Example 3.

[Explanation of symbols]

 1 metal roll 2 magnetic layer 3 orientation of needle-shaped magnetic powder before calendaring 4 orientation of needle-shaped magnetic powder after calendaring 5 direction of easy axis of magnetization of needle-shaped magnetic powder before calendaring 6 needle-shaped after calendaring Direction of easy axis of magnetization of magnetic powder 7 Direction of plate-like magnetic powder before calendar processing 8 Direction of plate-like magnetic powder after calendar processing 9 Direction of easy axis of magnetization of plate-like magnetic powder before calendar processing 10 After calendar processing Direction of easy axis of magnetization of plate-like magnetic powder

Claims (3)

[Claims] 1. An acicular magnetic powder and a magnetic powder having a plate-like shape and having an easy axis of magnetization in a direction perpendicular to a plate surface, wherein the easy axis of magnetization is oblique from an in-plane longitudinal direction to an out-of-plane vertical direction. A magnetic recording medium having a magnetic layer according to claim 1. 2. The coercive force Hc1 of a needle-shaped magnetic powder and the coercive force Hc2 of a plate-shaped magnetic powder having an easy axis of magnetization in the direction perpendicular to the plate surface are | 1-Hc2 / Hc1 | A magnetic recording medium characterized by satisfying a relationship of ≦ 0.05. 3. The magnetic recording medium according to claim 1, wherein the easy axis of magnetization of the magnetic layer is in the range of 5 to 60 degrees from the in-plane longitudinal direction to the out-of-plane vertical direction.