KR0138505B1 - Magnetic recording medium - Google Patents

Abstract

The present invention relates to a magnetic recording medium having a magnetic layer formed by dispersing hexagonal ferrite powder in a resin binder on a nonmagnetic support, wherein the hexagonal ferrite powder is represented by the following general formula:

AO2 (M10) Fe16 _- xM2 _X O ₂₄

(Wherein A represents at least one element selected from Ba, Sr, Ca, and Pb, M1 represents Zn, Ni, and M2 represents two element orientations of Co-Ti, Zn-Ti or Co, Ti, Zn) Hexagonal ferrite powder with an average platelet ratio of 2.0 to 5.0 is disclosed, and a hexagonal ferrite powder has a small temperature dependence of coercivity. On the other hand, as a result of controlling the average plate ratio of hexagonal ferrite powder with little elution of metal ions into the magnetic layer within a predetermined range, the coercive force of the magnetic recording medium is stable even under various conditions of use or long-term use and storage. It is characterized in that a magnetic recording medium having high reliability, high output high S / N, and optimum for high density recording can be obtained.

Description

Magnetic recording medium

1 is a schematic diagram showing a cross section of a magnetic recording medium according to one embodiment of the present invention;

2 shows the temperature dependence of the magnetic powder coercive force (Hc), and shows the relationship between the coercive force (Hc) of the magnetic powder and the temperature (T),

3 shows the temperature dependence of the magnetic recording medium coercive force Hc, and shows the relationship between the coercive force Hc and the temperature T of the magnetic recording medium;

4 is a view showing a state in which the coercive force (Hc) of the magnetic component changes over time,

5 is a view showing a state in which the coercive force Hc of the magnetic component changes over time.

* Description of the symbols for the main parts of the drawings *

11 film 21 magnetic layer

31: magnetic layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium suitable for high density recording showing stable magnetic properties even under various use environment conditions.

In recent years, magnetic recording media have been widely used as recording media for recording a large amount of information in the field of audio, video, computers, and the like. In addition, there is a further demand for improving the recording density of magnetic recording media.

As one of the methods for meeting such a demand for improving the recording density, it has been attempted to manufacture a magnetic recording medium using magnetic powder having ultrafine particles perpendicular to the particle plate on the particle plate. Examples of the magnetic powder having a biaxial axis for magnetization perpendicular to the particle plate-like surface include hexagonal ferrite powders represented by barium ferrite and the like.

Since the hexagonal ferrite powder is perpendicular to the particle plate surface, the hexagonal ferrite powder is more easily oriented in the vertical direction than the conventional acicular magnetic component. In addition, the ultrafine hexagonal ferrite powder can improve the filling rate of the magnetic powder in the magnetic layer. In this regard, hexagonal ferrite powder is most suitable for high density recording magnetic components.

On the other hand, as the recording capacity increases, the field of use of magnetic recording media such as, for example, a propi disk is further expanded, and the importance and value of information to be recorded are also increasing. In addition, magnetic recording media, which have been mostly used in a conventional temperature and humidity environment, are being used under various environmental conditions in recent years with the supply of devices such as personal word processors and personal computers. For this reason, the demands on the durability of the magnetic recording medium and the reliability of data storage are becoming more stringent. In addition, the stability of the magnetic characteristics of the magnetic recording medium is required. In particular, the stability of the coercive force Hc, which is a main characteristic thereof, is strictly required.

In order to improve the stability of the magnetic recording medium coercive force Hc, it is necessary to consider two kinds of changes in the coercive force Hc. One is the general change in the coercive force (Hc) that occurs as a result of changes in environmental temperature. The other is a permanent change in the coercive force (Hc) that occurs when stored for a long time in an abnormal environment such as high temperature and high humidity.

Hereinafter, in this specification, the temporary change of the coercive force Hc according to the change of the environmental temperature of the electron is the temperature change of the coercive force δHc, and the permanent change of the coercive force Hc in the abnormal environment is referred to as the environmental change ΔHc of the coercive force. It is called.

As means for reducing the temperature change (δHc) of the coercive force, for example, Japanese Patent Laid-Open No. 63-139017, Japanese Patent Laid-Open No. 63-144118 or Japanese Patent Laid-Open No. 56-60001 The described technology and the like have been proposed. Among them, Japanese Patent Laid-Open No. 63-139017 or Japanese Patent Laid-Open No. 63-144118 discloses a technique of coating a spinel-type ferrite on a plate-shaped hexagonal ferrite surface. Also, Japanese Patent Laid-Open No. 56-60001 discloses a hexagonal ferrite magnetic powder containing a magnet ferrite crystal structure phase and a spinel crystal structure phase as a W structure. By using these conventional techniques, it is possible to reduce the temperature change δHc of the magnetic powder coercive force.

Such a permanent change in the coercive force Hc, ie, the environmental change ΔHc, generated when the magnetic recording medium is stored for a long time in an environment other than the conventional temperature and humidity is not known or discussed at all. The environmental change ΔHc generated in such coercive force Hc is completely different from the temporary change (temperature change δHc) generated according to the temperature condition.

The environmental change ΔHc generated in the coercive force Hc is permanent, and the changed coercive force Hc does not return to its original state. Therefore, when the magnetic recording medium is used for a long time, the presence of the environmental change ΔHc of the coercive force becomes a big problem in recording / reproducing.

The present invention aims to stabilize the coercive force (Hc) of a magnetic recording medium. More specifically, it is an object of the present invention to provide a magnetic recording medium suitable for high-density recording as well as controlling the temperature change δHc of the coercive force, as well as minimizing the environmental change ΔHc. The present invention provides a magnetic recording medium having a magnetic layer formed by dispersing hexagonal ferrite powder in a resin binder on a nonmagnetic support, wherein the hexagonal ferrite powder is represented by the following general formula:

AO2 (M10) Fe16 _- xM2 _X O ₂₄

(Wherein A represents at least one element selected from Ba, Sr, Ca, and Pb, M1 represents Zn, Ni, and M2 represents a combination of two elements, Co-Ti and Zn-Ti, or Co-Ti- Zn represents one of three or more element combinations, and X represents a number of 0.6 to 3.0.)

It is represented by and is an hexagonal ferrite powder whose average plate ratio is the range of 2.0-5.0.

Prior to describing the magnetic recording medium of the present invention in detail, a change in the magnetic powder or the coercive force Hc of the magnetic recording medium will be described here. As described above, the change in the coercive force Hc as the temperature change δHc represents the degree of the coercive force Hc that is temporarily changed by the temperature condition as is known in the art. 2 is a diagram showing the temperature dependency of magnetic powder. In FIG. 2, the coercive force (Hc) of two kinds of magnetic powders (a) and (b) of different compositions is shown to change with temperature. In FIG. 2, the curve a shows the coercive force Hc of the magnetic powder a, and the curve b similarly shows the coercive force Hc of the magnetic powder b. As shown in FIG. 2, the magnetic powder coercive force has a difference in temperature variation (δHc) depending on the composition of the magnetic powder.

FIG. 3 is a diagram showing the temperature dependence of the magnetic recording medium coercive force Hc manufactured using the two kinds of magnetic powders (a) and (b) shown in FIG.

It can be understood from FIGS. 2 and 3 that the magnetic powder tends to coincide almost with the temperature change δHc and the change of the magnetic recording medium δHc. Therefore, in order to reduce the temperature change δHc of the magnetic recording medium, it is understood that magnetic powder whose temperature change δHc is stable may be used.

On the other hand, in the magnetic powder or the magnetic recording medium, with respect to the temperature change δHc of such coercive force, the permanent change of the coercive force Hc generated according to the environmental condition stored or used as described above with the environmental change ΔHc. It shows the degree of change.

4 shows the environmental change (ΔHc) of the magnetic powder (a) coercive force. 5 shows the environmental change (ΔHc) of the magnetic recording medium coercive force produced using the magnetic powder (a). 4 and 5, it can be seen that there is no correlation between the environmental change ΔHc of the magnetic powder coercive force and the environmental change ΔHc of the magnetic recording medium coercive force.

In this regard, in order to obtain a magnetic recording medium in which the coercive force environment ΔHc is stable, it is thought that attention should be paid not only to the composition of the magnetic powder but also to the factors present in the magnetic recording medium. As a result of the consideration of various factors in the magnetic recording medium, the main causes of the increase in the environmental change (△ Hc) of the magnetic recording medium coercive force are the dissolution of metal ions and impurities into the magnetic layer and the shape of the magnetic particles. I could find it.

When the amount of metal ions eluted from the magnetic powder in the magnetic layer is large, the reactor of the curing agent does not sufficiently react with the resin binder but reacts with the metal ions eluted from the magnetic powder. Therefore, since the resin binder cannot be bonded three-dimensionally, the magnetic powder is present in a highly unstable state in the magnetic layer. In addition, since the magnetic powder in the magnetic layer is slightly moved, it causes a slight change in the aggregated state, so that the environmental change ΔHc of the coercive force Hc is generated by the change of the environmental conditions.

In addition, the type of magnetic particles was often examined, and it was found that the average plate ratio particularly affected the environmental change (ΔHc) of the magnetic recording medium coercive force (Hc). In the hexagonal ferrite powder, the plate-like ratio is represented by the ratio (D / t) of the diameter (D) of the magnetic particle plate surface on the hexagonal plate surface to the plate thickness (t).

This invention is made | formed based on the above consideration. In the magnetic recording medium of the present invention, magnetic powder has a stable coercive temperature change (? Hc), little metal ion dissolution into the magnetic layer, and a magnetic powder having a predetermined average platelet ratio. With this arrangement, it is possible to obtain a magnetic recording medium which is stable together with the temperature change δHc and the environmental change ΔHc of the coercive force Hc and which is suitable for high density recording.

Hereinafter, the magnetic recording medium of the present invention will be described in detail.

The magnetic powder according to the present invention is a magnetic powder of W composition having a magnet frumbite composition and a spinel composition at a predetermined ratio. This magnetic powder has a temperature change (δHc) because the change in the coercive force (Hc) generated in the magnet prumbite composition due to the change in temperature condition is canceled by the change in the coercive force (Hc) generated in the spinel composition due to the change in temperature condition. ) Is stable.

In the magnetic recording medium of the present invention, since the magnetic powder is used, the change in the coercive force Hc, that is, the temperature change δHc, is stable with temperature conditions.

In addition, the magnetic powder according to the present invention is composed of a combination of two kinds of elements of Co-Ti, Zn-Ti, or three kinds of elements of Co-Ti-Zn, which have a particularly low ion dissolution into the magnetic layer. will be. Elution of metal ions into the magnetic layer can be suppressed by substitution by these substituted components in a predetermined range amount, and control of coercive force (Hc) or particle diameter and improvement of saturation magnetization are also possible.

In addition, when the amount of substitution of the substitution component is less than 0.6, there is an abnormal increase in the coercive force (Hc), making it difficult to obtain a magnetic powder suitable for the magnetic recording medium. On the other hand, if the amount of substitution is greater than 3.0, there is a risk of elution of the substitution component in the magnetic layer, and at the same time, it becomes difficult to obtain a suitable coercive force (Hc).

Therefore, as substitution amount of the said substitution component, the range of 0.6-3.0, and the thing of more preferable 0.8-2.2 are suitable. Within this range, it is easy to control the coercive force suitable for the high density magnetic recording medium, that is, 600 to 2000 Oe.

In particular, it is possible to achieve higher density recording by controlling the coercive force in the range of 850 to 2000 Oe.

And, the average particle diameter of the hexagonal ferrite powder according to the present invention is preferably 0.02 ~ 0.8㎛. If the average particle diameter is larger than 0.8 mu m, the S / N of the magnetic recording medium decreases and high density recording is difficult to achieve. In addition, when the average particle diameter is smaller than 0.02 mu m, it is difficult to disperse highly in the magnetic layer, which makes it difficult to achieve high density recording.

In the magnetic powder according to the present invention, the range of the average platelet ratio is 2.0 to 5.0, more preferably 2.8 to 4.4, so that the individual magnetic particles are stably maintained in the magnetic layer in a three-dimensional bonding state. Therefore, the environmental change ΔHc of the coercive force Hc is stabilized.

Further, the film thickness of the magnetic recording medium magnetic layer of the present invention is preferably in the range of 0.3 to 0.7 mu m in consideration of overwrite characteristics and the like. By using such a thin magnetic layer, a better effect can be obtained. In the magnetic recording medium of the present invention, in order to achieve higher density recording, it is preferable that the square ratio (after diamagnetic field correction) in the vertical direction with respect to the film surface of the magnetic layer is set to 0.7 or more. By setting the square ratio in the vertical direction to 0.7 or more, the magnetic field in the vertical direction can be used more effectively with respect to the membrane surface.

Therefore, high reproduction output can be ensured in the short wavelength recording area. Therefore, the square ratio in the vertical direction is 0.7 or more because it is preferable for a magnetic recording medium such as a propi disk having a high demand for high density recording.

The magnetic recording medium of the present invention may have a square ratio (after diamagnetic field correction) of 0.7 or more in the in-plane direction. By setting the square ratio in the in-plane direction to 0.7 or more, the reproduction output when the recording wavelength is in the long wavelength range of 4.0 to 5.0 µm can be increased. Therefore, the square ratio in the in-plane direction is 0.7 or more because it is preferable for magnetic tapes such as recording color signals in the long wavelength region.

In this invention, it is possible to use the various well-known thing conventionally used as a resin binder. For example, a polyurethane resin, a polyester resin, a polycarbonate resin, a polyacrylic resin, an epoxy resin, a phenol resin, a vinyl chloride resin, a vinyl acetate resin or a mixture thereof, a copolymer, or the like is used.

As described above, when the square ratio in the vertical direction or the in-plane direction is set to 0.7 or more, it is preferable to use soft resins and hard resins in combination among these resins as resin binders. Among these resins, for example, a polyurethane resin such as N-2301 (trade name: Nippon Polyurethane Co., Ltd.) or a urethane-modified resin may be mentioned as the soft resin. As the hard resin, for example, VAGH (trade name: vinyl hydrochloride-vinyl acetate copolymer such as manufactured by U.S. Union Carbide Co., Ltd., or cellulose-based resin such as nitro cellulose may be used. The balance between the role of the binder and the role of retaining the aligned particles and the role of contributing to the orientation can be improved, and the durability of the magnetic recording medium can be easily secured.

In the magnetic recording medium of the present invention, various known ones conventionally used can be used as lubricants. For example, lauric acid, parmitic acid, stearic acid, etc. are mentioned. Moreover, various surfactant, such as a dispersing agent, such as lecithin, can be used as needed. In the magnetic recording medium of the present invention, for example, inorganic powder having a hardness of 5 or more, such as TiO ₂ , Cr ₂ O ₃ , Al ₂ O ₃ , SiC, ZrO ₂ , can be used. It is preferable to add and mix about 0.5-10 weight part of these inorganic powders with an average particle diameter of about 0.1-2.0 micrometers with respect to 100 weight part of magnetic powders. In the present invention, as a method of obtaining hexagonal ferrite powder, a conventionally known method, i.e., a glass crystal method, a coprecipitation method, a hydrothermal synthesis method or the like can be used. Among them, the glass crystallization method is easy to obtain hexagonal ferrite powder having an average particle diameter of 0.02 to 0.8 mu m, which is suitable for high density magnetic recording, and is a suitable method. Table 1 shows the composition and properties of the hexagonal ferrite powder that can be used in producing the magnetic recording medium of the present invention.

Sample Number Hexagonal Ferrite Composition Plate ratio D / t Particle size (㎛) Coercivity Hc (Oe) Temperature change of coercive force δHc (Oe / ℃) A M1 M2 Zn Ni Co Ti Zn 123456789 B aB aB aB aB aB aB aB aB a 01.01.01.01.01.01.01.01.0 01.01.01.01.01.01.01.01.0 0. 930. 900. 32 ---- 0. 420.960.300.100 50 ------------One. 000. 42 ------------ 0. 50 3.93.13.93.34.12.84.73.21.8 3.93.13.93.34.12.84.73.21.8 0. 0520. 0500. 0530. 0490. 0500. 0480. 0510. 0550.050 620730181073075071019002500770 -0. 20-0. 2-0. 6-0. 5 + 0. 1-0. 8 + 1. 2 + 1. 0

All of these magnetic components shown in Table 1 can be manufactured as follows by the glass crystallization method. For example, in the preparation of the hexagonal ferrite powder shown in the magnetic powder sample 4, _first , various materials such as BaO, fE ₂ , O ₃ , CoO, ZnO, NiO, and TiO ₂ are desired for B ₂ O ₃ · BaO glass. A predetermined amount was mixed in order to obtain a magnetic component. Then, the mixture was heated and melted at 1350 ° C., and then dropped on both rolls to quench and roll to obtain an amorphous body. By heating this amorphous body at 800 degreeC for 4 hours, the hexagonal ferrite crystal by which the predetermined amount of substituted elements were substituted in the matrix was deposited. The crystal thus obtained was washed with dilute acetic acid followed by pure water and dried again to obtain hexagonal Ba ferrite powder.

Hereinafter, a magnetic recording medium was produced using the magnetic components shown in Table 1 below. A magnetic recording medium which is an embodiment of the present invention will be described.

Example 1

In manufacturing the magnetic recording medium of the present invention, first, the following materials were uniformly mixed and dispersed using a sand grinder to prepare a magnetic paint.

Magnetic paint material

1100 parts by weight of magnetic powder sample

4 parts by weight of Al ₂ O ₃ powder (average particle diameter: 0.3 μm)

1 part by weight of phosphate ester

10 parts by weight of polyurethane resin

(Average particle weight 45000)

5 parts by weight of vinyl chloride-vinyl acetate copolymer resin

(Average particle amount 32000)

4 parts by weight of fatty acid ester

Methyl ethyl ketone 60 parts by weight

60 parts by weight of cyclohexanone

Toluene 60 parts by weight

The obtained coating material was filtered through a filter to remove impurities or ordinary large particles. To the magnetic paint thus obtained, 3 parts by weight of an isocyanate compound was further added as a curing agent and stirred.

Then, as shown in FIG. 2, the polyester film 11 of 80 micrometers in thickness was used as a nonmagnetic support body, and also the said magnetic paint was apply | coated uniformly and the magnetic layer 21 was provided. In application | coating, the application | coating amount was adjusted so that the thickness of the magnetic layer 21 after drying and calendering process might be set to 3 micrometers using the reverse scoter. After performing drying and calendering process and smoothing the surface, the coating film was fully hardened in the high temperature cure tank of 60 degreeC.

In addition, on the surface on the opposite side where the magnetic layer 21 of the polyester film 11 was provided, the magnetic coating was similarly applied, dried and calendered. And it hardened similarly and the magnetic layer 31 was formed.

As mentioned above, the film in which the magnetic layer 21 and the magnetic layer 31 were formed on both surfaces was dripped on the 3.5-inch size disk. A metal center core was installed at the center of the disc, and the rotation was freely accommodated in the jacket to make a 3.5 inch profile disk. In this manner, a magnetic recording medium of embodiment (1) according to the present invention in the shape of a disc was obtained.

Examples 2-7

Magnetic recording media Examples 2 to 7 were obtained in the same manner as Example 1 except for using the magnetic powder samples 2 to 7 shown in Table 1 as the magnetic powder. The change in magnetic powder sample and the number of the examples of the magnetic recording medium manufactured using the same are corresponded.

Example 8

A magnetic recording medium was produced in the same manner as in Example 1 except that the magnetic powder sample (2) was used as the magnetic powder and the magnetic coating was applied and then subjected to the alignment process by passing through a 6 kOe vertically oriented magnetic field facing the S and N poles.

Example 9

A magnetic recording medium was produced in the same manner as in Example 8 except that 9 parts by weight of polyurethane resin (average molecular weight 24000) and 4 parts by weight of vinyl chloride-vinyl acetate copolymer resin (average molecular weight 32000) were used.

Example 10

A magnetic recording medium was obtained in the same manner as in Example 9 except that the magnetic powder sample C (3) was used as the magnetic component.

Next, the various characteristics of the magnetic recording medium according to Examples 1 to 10 thus produced were evaluated. The evaluation results are shown in Table 2. In addition, evaluation of each item shown in Table 2 was performed as follows.

The output and S / N were measured by an optimum output current at a recording density of 35 KFRPI using a MIG (Metal-In-GaP) head having a gap length of 0.4 mu m and a track width of 35 mu m. Moreover, the rotation speed of the disk was 300 rpm, and the track used for evaluation was 79 track which is the innermost.

The change in the coercive force of the magnetic recording medium (ΔHc) is based on the initial coercive force of Hc ', when the coercive force is Hc after being left for one week in a high temperature and high humidity environment at a temperature of 60 ° C, a humidity of 90%, and {(Hc-Hc' ) / Hc '} × 100. In the case of Hc'Hc, + is attached and in the case of Hc'Hc,-is indicated.

The durability was evaluated in three types of environments: high temperature and high humidity environment, and cycle environment in addition to low temperature and low humidity environment. The low temperature and low humidity environment is 5 ° C and 10% humidity, and the high temperature and high humidity environment is 60 ° C and 90% humidity. In addition, the cycle environment is to exchange the environment of temperature 5 ℃, 10% humidity and the environment of temperature 60 ℃, 90% humidity in a 24-hour cycle. The disc was driven in these three kinds of environments. In the track 12 defined in JIS, it was determined that the disk had reached the end of durability based on the time when a 70% output reduction was recognized for the initial output or when surface damage was obtained by visual inspection. The result determined in this way was shown by the number of running passes (full pass) until a target.

Sample Number Square ratio SQR Output (dB) S / N (dB) Environmental change of coercivity △ Hc (%) Durability (retrieved) Low temperature and low humidity High temperature and high humidity cycle Example 1 2 3 4 5 6 7 8 9 10 0. 550. 530. 560. 550. 570. 540. 570. 750. 820. 83 0 + 0. 4 + 4. 8 + 1. 0 + 1. 1 + 0. 4 + 5. 2 + 3. 6 + 4. 5 + 8. 6 0 + 1. 5 + 4. 0 + 2. 0 + 1. 5 + 1. 0 + 5. 8 + 3. 8 + 4. 6 + 8. 0 +0. 3 + 0. 5 + 0. 3 + 0. 4 + 0. 2 + 0. 6-0. 2 + 0. 5 + 0. 2 + 0. One 1500 or more 1500 or more 1500 or more 1500 or more 1500 or more 1500 or more 1500 or more 1500 or more 1500 or more 1500 or more 1200 or more 1050 or more 1200125011001400130015009501210920870 More than 1500 More than 1500 More than 1860 13001 030 980 Comparative example 12 0.540.55 +3. 5 + 0. 9 +2. 1 + 1. 0 +0. 8 + 3. 8 7001500 or more 300900 6001000

Next, a comparative example was produced in the same manner as in Example 1 except that a ferrite composition or a plate-shaped ratio was not used in the present invention as the magnetic powder. The composition and properties of the magnetic powder whose ferrite composition or plate ratio is not accompanied by the present invention are shown in Table 1 as magnetic powder samples (8, 9) in advance.

Comparative Examples 1 and 2

Magnetic recording media Comparative Examples 1 and 2 were produced in the same manner as in Example 1, except that the magnetic powder samples (8) and (9) were used as the magnetic powder. The numbers of magnetic powder samples and the numbers of comparative examples of magnetic green media produced by using the same correspond to each other in the above order. Next, various characteristics of the magnetic recording media of Comparative Examples 1 and 2 thus produced were evaluated in the same manner as in the examples. The evaluation result is shown in Table 2 with the evaluation result of an Example.

As can be seen from Table 2, in the PROPY disk according to the embodiment of the present invention, the output and S / N are excellent, as well as the environmental change of coercive force (ΔHc) is considerably small. In addition, it can be seen that durability is shown not only in the environment of normal temperature and humidity but also in a high temperature, high humidity environment, and a cycle environment. In addition, as apparent from Table 1, the absolute value of the temperature change (? Hc) of the magnetic powder coercive force used in the examples is a small value of 1.0 (Oe / ° C) or lower. Since the temperature change δHc of the magnetic recording medium coercive force tends to substantially coincide with the temperature change δHc of the magnetic powder coercive force, according to the present invention, it is possible to stabilize the temperature change δHc of the magnetic recording medium coercive force.

In addition, although the said Example showed the case where a single layer magnetic layer was provided in each of both surfaces of a nonmagnetic support body, this invention is not limited to this. Of course, you may arrange | position a single layer magnetic layer to one side of a nonmagnetic support body, or may have a layer structure with another magnetic layer. It goes without saying that a layer such as a conductive layer or an adhesive layer may be disposed between the nonmagnetic support and the magnetic layer. In the above-described embodiment, the profile disk is taken as an example, but it is natural that a magnetic tape or the like may be used.

As described above, in the present invention, the hexagonal ferrite powder is selected as the hexagonal ferrite powder and the coercive ferrite powder with little coercive force temperature and little metal ions in the magnetic layer is eluted. The control is performed within a predetermined range. As a result, it is possible to obtain a magnetic recording medium excellent in magnetic properties with little change in the coercive force of the magnetic recording medium with temperature (ΔHc) and with the environment (ΔHc). Further, the magnetic recording medium of the present invention has a high output and high S / N, and thus is a magnetic recording medium which is particularly preferable for high density recording.

Claims (11)

A magnetic recording medium having a hexagonal ferrite powder dispersed in a resin binder formed on a nonmagnetic support, wherein the hexagonal ferrite powder is represented by the following general formula: AO2 (M10) Fe16 _- xM2 _X O ₂₄ (A is at least one element selected from Ba, Sr, Ca, and Pb, M1 represents Zn, Ni, and M2 represents a combination of two kinds of elements of Co-Ti, Zn-Ti, or Co-Ti-Zn. Any one of the three types of combinations, X represents a number from 0.6 to 3.0, respectively) A magnetic recording medium having a mean plate ratio of 2.0 to 5.0, wherein the magnetic layer has a coercive force of 850-2000 Oe. The method of claim 1, And a mean plate ratio of the hexagonal ferrite powder is in the range of 2.8 to 4.4. The method of claim 2, The hexagonal ferrite powder is a magnetic recording medium, characterized in that the Ba ferrite powder. The method of claim 1, Magnetic recording medium, characterized in that the average particle diameter of the hexagonal ferrite powder is in the range of 0.02 ~ 0.8㎛. The method of claim 1, And wherein a perpendicular angular ratio of the magnetic layer is 0.7 or more. The method of claim 1, A magnetic recording medium according to claim 1, wherein the ratio of the inner surface direction of the magnetic layer is 0.7 or more. The method of claim 5, A magnetic recording medium suitable for recording / reproducing in a short wavelength region. The method of claim 6, A magnetic recording medium suitable for recording / reproducing in a long wavelength region. The method of claim 5, And the resin binder is a polyurethane-based or polyurethane-modified resin and a vinyl chloride-vinyl acetate copolymer or nitro cellulose. The method of claim 6, And the resin binder is a polyurethane resin or a polyurethane modified resin and a vinyl chloride-vinyl acetate copolymer or nitro cellulose. In a magnetic recording medium having a magnetic layer in which hexagonal ferrite powder is dispersed in a resin binder, on a nonmagnetic support, The hexagonal ferrite powder is characterized in that the temperature dependence of the coercivity is less, the elution of metal ions to the magnetic layer is less, the average plate ratio is controlled to a predetermined range.