JPH06290924A - Magnetic powder and high density magnetic recording medium made of same - Google Patents

Abstract

PURPOSE:To provide magnetic powder which can be densely filled and lessened in noise and a magnetic recording medium which is formed of the above magnetic powder, enhanced in output power, and lessened in noise and wherein data can be densely recorded. CONSTITUTION:Magnetic powder is so compressed by a pressure of 400kgf/cm<2> as to range from 2.5 to 3.5g/cm<3> in filling density and has a grain diameter distribution whose geometrical standard deviation is smaller than 1.5, and a magnetic recording medium formed of this magnetic powder is more enhanced in filling density as compared with one where conventional magnetic powder is used, improved in output power, and lessened in noise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic powder used for high density magnetic recording and a magnetic recording medium using the magnetic powder.

[0002]

2. Description of the Related Art A magnetic recording medium manufactured by coating is
It is composed of a support base made of a non-magnetic material such as polyethylene terephthalate, and a magnetic layer formed on the support base and containing magnetic powder and a binder resin as main components.

Magnetic powders used in magnetic recording media are conventionally γ-Fe2 O3, Co-deposited γ-Fe2 O3,
Needle-shaped magnetic powder such as Co-doped γ-Fe2 O3, Co-deposited Fe3 O4, and metallic Fe is used, and an in-plane recording method using magnetization in the longitudinal direction of the magnetic layer film surface is adopted. Was there.

However, in this in-plane recording method, the influence of the demagnetizing field becomes stronger as the recording density increases,
It was not suitable for high density recording / reproduction.

Therefore, in recent years, a perpendicular magnetic recording system has been proposed which uses magnetization in the direction perpendicular to the magnetic layer film surface. This perpendicular magnetic recording system, with the increase in recording density,
Since its magnetization is more stable, it can be said to be the most suitable recording method for high density recording.

As a magnetic recording medium suitable for such a perpendicular magnetic recording system, a Co--Cr alloy or the like is deposited on a supporting substrate using a vacuum technique such as a vacuum evaporation method or a sputtering method, or a plate surface. It is known that a hexagonal ferrite powder having an easy axis of magnetization in a direction perpendicular to is applied together with a binder resin.

A magnetic recording medium using a vacuum technique has various problems such as weather resistance, mass productivity, and manufacturing cost. On the other hand, a coating type magnetic recording medium has a conventional manufacturing facility. It is very promising and attracts attention because it can be used and is excellent in mass production.

The hexagonal ferrite powder used in such a coating type magnetic recording medium is, for example, M type Ba.
Fe ₁₂ O ₁₉ , W-type BaMe ₂ Fe ₁₆ O ₂₇ (Me is a divalent metal element), or hexagonal ferrite powder in which some of those atoms are replaced with other elements, or M-type and W-type Examples thereof include composite powder, M-type and spinel composite powder, and the like.

Various methods such as a glass crystallization method, a hydrothermal synthesis method, and a coprecipitation / flux method have been proposed as methods for producing such magnetic powder.

[0010]

By the way, there is a demand for higher density recording on a magnetic recording medium so that a large amount of information can be recorded / reproduced. Then, in order to obtain such a magnetic recording medium, it is required to increase the output and reduce the noise by highly filling the magnetic powder.

However, heretofore, a magnetic powder capable of high filling and realizing low noise has not been obtained.

The present invention has been made to solve the above-mentioned problems, and in particular, magnetic powder capable of high filling and low noise, and high output and low noise by using this magnetic powder. It is an object of the present invention to provide a magnetic recording medium which can be achieved and which enables high density recording.

[0013]

The magnetic powder of the present invention has a pressure compression characteristic of the powder, and the magnetic powder is filled in a closed container,
Pressurized at a pressure of 400 kgf / cm ² , the packing density of the magnetic powder after removing the pressure is in the range of 2.5 to 3.5 g / cm ³ , and the geometric standard deviation of the particle size distribution of the magnetic powder is 1.5 or less. It is characterized by being.

The magnetic recording medium of the present invention is a magnetic recording medium comprising a support and a magnetic layer formed on the support, wherein the magnetic layer is substantially composed of magnetic powder and a binder. Here, the magnetic powder contained in the magnetic layer has a pressure compression characteristic of the powder of 400 kgf / cm2 when the magnetic powder is filled in a closed container.
Pressurized with ² pressure, the packing density of magnetic powder after removal of the pressure is in the range of 2.5 ~3.5g / cm ^3, and a geometric standard deviation of the particle size distribution is 1.5 or less, and the magnetic layer The value of the saturation magnetization (Ms) per unit volume of is 95% or more with respect to the value of the theoretical saturation magnetization (Ms '). Here, the theoretical saturation magnetization (Ms') is the original constituent component only. It is the value of the saturation magnetization calculated in the case where the magnetic layer is configured, that is, the value of the saturation magnetization when there is no gap between the magnetic powder and the binder in the magnetic layer.

The magnetic recording medium of the present invention is a magnetic recording medium provided with a support and a magnetic layer containing magnetic powder formed on the support, wherein the magnetic powder is a powder. As a compression property, the packing density of compressed magnetic powder after filling in a closed container and pressurizing at a pressure of 400 kgf / cm ² and removing the pressure is in the range of 2.5-3.5 g / cm ³ , Moreover, the geometric standard deviation of the particle size distribution is 1.5 or less, and the vertical squareness ratio showing the orientation of the magnetic powder in the magnetic layer is 0.80 or more.

The present inventors have conducted sincere research to solve the above-mentioned technical problems, and as a result, as described above, the magnetic powder was
400 kg filled in a closed container as a pressure compression property of powder
Pressurized at a pressure of f / cm ² and the packing density after pressure removal is 2.5
Magnetic recording capable of high filling, high output and low noise, and high density recording when the geometric standard deviation of particle size distribution is 1.5 or less within a range of up to 3.5 g / cm ^3. It has been found that a medium is obtained.

In the present invention, as the magnetic powder, M-type BaFe ₁₂ O ₁₉ and W-type BaMe ₂ Fe ₁₆ O ₂₇ (M
e represents a divalent metal element. ), Or a hexagonal ferrite in which some of those atoms are substituted with other elements, a composite powder of M type and W type, a composite type hexagonal ferrite of M type and spinel, and the like. The basic constituents of this hexagonal ferrite are BaO, SrO, CaO, Pb.
Fe ₂ O ₃ and at least one selected from O, and Co, Ni, Cu, Zn, Ti, Mg, N as components for controlling coercive force and improving characteristics such as saturation magnetization.
At least one selected from b, Sn, Zr, V, Cr, Mo, Al, Ge and W can be used.

Among them, AO.n (Fe _12-xy M1 _x M2
_A hexagonal ferrite represented by the chemical formula _y O _18-δ ) is preferable. In the formula, A is at least one element selected from Ba, Sr and Ca, M1 is at least one element selected from divalent, M2 is at least one element selected from 4 to 6 and δ is [ x + (3-m) y] / 2 (where m is the average valence of M2), n is a number from 0.8 to 3.0, x or y is at least 0 and x is 3 or less, and y is The number represented by 2 or less) is preferable. It is particularly effective to use at least one element selected from Co, Zn and Ni as M1.

As an index showing the characteristics of the magnetic powder, the size of the magnetic powder, the plate-like ratio of the hexagonal ferrite powder (the average diameter D of the particles / the average thickness t of the particles), the specific surface area of the powder, etc. Although conventionally considered, the inventors have focused on the particle size distribution of the magnetic powder and the compression property of the particles.

As the powder of the magnetic powder, it is necessary that the geometric standard deviation of the particle size distribution of the magnetic powder is 1.5 or less, that is, the magnetic powder has a very uniform particle size distribution. However, it was found that even if the particle size distribution was uniform with the geometric standard deviation of 1.5 or less, low noise and high filling could not always be achieved.

Here, the geometric standard deviation showing the particle size distribution is calculated based on the particle size value obtained from the electron micrograph of the magnetic powder.

That is, the particle size is plotted on the horizontal axis of the lognormal probability paper,
The integrated value is taken on the vertical axis, and it is determined from the obtained straight line based on the following equation.

Geometric standard deviation = (84.3% diameter under cumulative sieving) / 50% particle size As an index showing the characteristics of magnetic powder, there is a packing density under pressure, which was held in November 1992, for example. '92 Intern
The “Charging characteristics of barium ferrite powder for magnetic recording media” described on pages 130-131 of the Proceedings of the “Ational Conference on Color Materials” shows the importance of the packing density of magnetic powder under pressure. It is shown.

Therefore, the inventors of the present invention further studied in addition to the geometric standard deviation of the particle size distribution of the magnetic powder described above,
The relationship between the packing density after applying pressure to the magnetic powder and the pressure applied was investigated. As a result, at a relatively low pressure of 300 kgf / cm ² or less, the compressive force received by the magnetic powder is smaller than the effective compressive force of the magnetic powder received in the process such as calendering,
Therefore, the correlation with the actual state of existence of the magnetic powder becomes small.

Also, as described in the above-mentioned literature, 500 kgf
It has been found that the magnetic powder may have a shape or size that is different from the actual state of existence of the magnetic powder, because the magnetic powder may be partially damaged at a density of more than / cm ² .

As a result of intensive studies on the relationship between the pressure and the magnetic powder, the present inventors have found that the packing density of the compressed powder after pressing at a pressure of 400 kgf / cm ² indicates the magnetic property in the magnetic recording medium. I newly discovered the fact that it is highly correlated with the existence of powder.

The magnetic layer is formed of a composite material such as an inorganic particle such as an abrasive, a polymer material such as a lubricant or a binder resin, in addition to the magnetic powder, and is manufactured by being compressed by calendering or the like. This is especially true for magnetic powders.
It is considered to be very similar to the state after pressurizing with a pressure of 0 kgf / cm ² , and it is considered to correlate well with the true state of the magnetic powder in the magnetic layer.

Further, it is essential for achieving the above-mentioned low noise and high filling that the packing density of the powder compressed under pressure is not simply high, but particularly within the range of 2.5 to 3.5 g / cm ^3. It was confirmed by the experiment that the above requirement is satisfied.

The reason why the density of the magnetic powder compressed under pressure is limited to the above range is that the density is 3.5 g even if the geometric standard deviation of the particle size distribution of the magnetic powder is 1.5 or less. /
In the case of magnetic powder larger than cm ³ , that is, in the case of particles in which magnetic powders are very easily compressed by pressure compression, the dispersibility may be reduced due to the strong cohesive force between particles and noise may be reduced. In addition, the surface property cannot be improved, and it becomes difficult to obtain a high output.
On the contrary, when the density of the powder compressed under pressure is less than 2.5 g / cm ³ , that is, when the powder is a magnetic powder in which particles are hard to aggregate with each other under pressure, it is possible to achieve high packing in the magnetic recording medium. It is considered to be difficult and the output is lowered.

The packing density of the magnetic powder compressed under pressure in this specification is calculated as follows.
First, 50 mg of magnetic powder is placed in a stainless steel container with a diameter of 4 mm.
The magnetic powder density is calculated from the thickness measured after putting in and pressurizing it with a pressure of 400 kgf / cm ² .

As described above, in the present invention, the magnetic powder is M-type BaFe ₁₂ O ₁₉ or W-type BaMe.
₂ Fe ₁₆ O ₂₇ (here, Me represents a divalent metal element), or hexagonal ferrite in which some of those atoms are replaced with other elements, or M-type and W-type composite powder, M Examples include mixed type hexagonal ferrite of type and spinel,
Among them, the chemical formula, AO · n (Fe _12-xy M1 _x M2 _y O
_{A hexagonal} ferrite represented by _18-δ ) is preferable. In the formula, A is at least one element selected from Ba, Sr, and Ca, M1 is at least one element selected from the group of divalent Co, Ni, and Zn, and M2 is at least selected from 4 to 6 valences. One element, δ is [x + (3-m) y]
/ 2 (where m is the average valence of M2) and n is 0.8
It is preferable that the number is 3.0 or less, and x or y is at least 0, x is 3 or less, and y is 2 or less.

The use of the magnetic powder in the present invention is not particularly limited, but it is required to be magnetically stable particularly when it is used for a magnetic recording medium. Therefore, the average particle size of the magnetic powder is preferably about 20 to 300 nm, and the specific surface area of the hexagonal ferrite powder is preferably within the range of ²⁰ to 60 m ² / g.
This is because when the specific surface area is smaller than 20 m ² / g, noise is increased, and when the specific surface area exceeds 60 m ² / g, the dispersibility is impaired or the magnetic properties are deteriorated.
Particularly preferably, the specific surface area of the hexagonal ferrite powder is within the range of 30 to 50 m ² / g.

The plate-like ratio is particularly preferably in the range of 2 to 5 in consideration of the deterioration of properties and the orientation of the magnetic powder due to stacking. On the other hand, if the coercive force is too high, the head magnetic field is saturated during recording, and if it is too low, it becomes impossible to retain the recording signal. Therefore, it is preferable to adjust the coercive force to 200 to 2500 Oe.

As the method for obtaining the magnetic powder in the present invention, various methods such as the well-known glass crystallization method, hydrothermal synthesis method, coprecipitation / flux method, etc. can be used.

In order to control both the geometric standard deviation and the pressure packing density within the scope of the present invention, the glass component and the material component are melted together and the melt is quenched to amorphize. Further, it is preferable to use a glass crystallization method including a method of removing the glass component after further firing, and sodium (Na) is further used as the glass component.
Is preferably used for controlling the pressure packing density.

However, it goes without saying that it is important to properly control the melting temperature and the firing temperature, and it is important to select the material components. Both packing densities can be controlled within the scope of the invention. The magnetic recording medium of the present invention uses the above-mentioned magnetic powder, and particularly, the saturation magnetization (Ms) per unit volume is relative to the theoretical saturation magnetization (Ms') of the medium (Ms / Ms).
High output and low noise can be achieved by configuring the magnetic layer so that ′) is 95% or more. The saturation magnetization (Ms) per unit volume is the saturation magnetization that is actually measured when the magnetic recording medium is used, and the theoretical saturation magnetization (Ms') is only the original constituent elements of the magnetic layer. It is the saturation magnetization calculated when it is constructed. The reason why the actual saturation magnetization (Ms) differs from the theoretical saturation magnetization (Ms ′) is that the magnetic layer actually has a portion other than the constituent elements such as voids inside. That is, the fact that the actual saturation magnetization is 95% or more of the theoretical saturation magnetization means that the magnetic recording medium of the present invention has very few voids inside,
Therefore, it means that the filling rate of the magnetic powder inside is extremely improved.

The magnetic recording medium of the present invention uses the above-mentioned magnetic powder and has a squareness ratio in the vertical or longitudinal direction (after demagnetization compensation) of 80% or more, so that a high band or a low band is obtained. The characteristics in the band can be greatly improved. In order to obtain such a high orientation, it is effective to apply a magnetic coating material and then dry it while applying an orientation magnetic field.

As the binder resin used together with the magnetic powder in the magnetic layer of the magnetic recording medium of the present invention, various conventionally known binder resins can be used, but polar groups such as sulfone group, hydroxyl group and carboxyl group are particularly sufficient. The material contained in (1) acts very effectively in order to sufficiently disperse the fine magnetic powder.

As a matter of course, together with the binder resin, conventionally known additives such as an abrasive and an antistatic agent typified by carbon can be added simultaneously with the magnetic powder.

[0040]

[Function] As described above, the magnetic powder is packed in a closed container as a compression and compression property of the powder and pressurized at a pressure of 400 kgf / cm ² , and the packing density after pressure removal is 2.5- 3.5 g /
cm ³ and geometric standard deviation of particle size distribution is 1.5
In the following cases, the magnetic layer can be highly filled, so that high output and low noise can be achieved, and a magnetic recording medium capable of high density recording can be obtained.

[0041]

EXAMPLES The present invention will be described in detail below with reference to examples.

Example 1 As a starting material, B ₂ O _{3 was used.}
31.35 mol%, BaO 26.68 mol%, Li ₂ O. 5.0
mol%, Na ₂ O 5.0 mol%, Fe ₂ O ₃ 27.33 mol%,
2.21 mol% CoO, 1.50 mol% ZnO, Nb ₂ O ₅
0.93 mol% was thoroughly dry mixed and calcined at 720 ° C. After mixing this calcined material more thoroughly, it is heated to 1250 ° C by high frequency heating.
Melted in. Next, the melt was sufficiently stirred, then dropped between twin rolls and rapidly cooled. And 730 to this quenched rolled product
Ba ferrite was generated by heat treatment at ℃. Finally, the heat-treated material was washed, Ba ferrite was extracted and dried to obtain the desired magnetic powder. Here, extraction of Ba ferrite is carried out by adding 1 water of acetic acid to 1 of heat-treated substance
The mixture was placed in a stainless steel container at a weight ratio of 50, stirred for 24 hours while applying ultrasonic waves, and then repeatedly washed with water until the pH was saturated.

The obtained magnetic powder had a packing density of 2.8 g / cm ³ after being pressed at 400 kgf / cm ² , and a geometric standard deviation.
1.42, the specific surface area by the BET method was 37 m ² / g, the coercive force by the vibrating sample magnetometer was 1350 Oe, and the saturation magnetization was 60 emu / g.

Example 2 B ₂ O ₃ was used as a starting material.
31.35 mol%, BaO 21.01 mol%, Na ₂ O 15.68 mo
l%, Fe ₂ O ₃ 27.21 mol%, CoO 2.30 mol%,
ZnO (1.50 mol%) and Nb ₂ O ₅ (0.95 mol%) were thoroughly dry-mixed and then calcined at 740 ° C. Subsequent heat treatment temperature is 750 ℃
Magnetic powder was obtained by the same steps as in Example 1 except that

The obtained magnetic powder had a packing density of 3.2 g / cm ³ after being pressed at 400 kgf / cm ² and a geometric standard deviation.
1.4, specific surface area 32 m ² / g, coercive force 1270 Oe, saturation magnetization
It was 62 emu / g.

Comparative Example 1 B ₂ O ₃ was used as a starting material.
31.35 mol%, BaO 35.68 mol%, K ₂ O 1.0 mol%,
27.33 mol% Fe ₂ O ₃ , 2.21 mol% CoO, ZnO
Of 1.50 mol% and Nb ₂ O ₅ of 0.93 mol% were thoroughly dry-mixed and calcined at 740 ° C. Thereafter, magnetic powder was obtained by the same steps as in Example 1 except that the heat treatment temperature was 780 ° C.

The magnetic powder obtained had a packing density of 2.3 g / cm ³ after being pressed at 400 kgf / cm ² and a geometric standard deviation.
1.48, specific surface area 36 m ² / g, coercive force 1330 Oe, saturation magnetization 61
It was emu / g.

Comparative Example 2 B ₂ O ₃ was used as a starting material.
31.35 mol%, BaO 24.68 mol%, K ₂ O 9.0 mol%,
V ₂ O ₅ 1.0 mol%, Fe ₂ O ₃ 27.33 mol%, CoO
2.21 mol%, ZnO 1.50 mol%, Nb ₂ O ₅ 0.93
Mol% was thoroughly dry mixed and then calcined at 740 ° C. Thereafter, magnetic powder was obtained by the same steps as in Example 1 except that the heat treatment temperature was 750 ° C.

The obtained magnetic powder had a packing density of 2.7 g / cm ³ after being pressed at 400 kgf / cm ² and a geometric standard deviation.
1.83, specific surface area 30 m ² / g, coercive force 1100 Oe, saturation magnetization
It was 62 emu / g.

Comparative Example 3 B ₂ O ₃ was used as a starting material.
31.35 mol%, BaO 36.68 mol%, Fe ₂ O ₃ 27.33
mol%, CoO 2.21 mol%, ZnO 1.50 mol%, Nb
0.93 mol% of ₂ O ₅ was thoroughly dry mixed and calcined at 740 ° C. Thereafter, magnetic powder was obtained by the same steps as in Example 1 except that the heat treatment temperature was 780 ° C.

The magnetic powder obtained had a packing density of 2.3 g / cm ³ after being pressed at 400 kgf / cm ² and a geometric standard deviation.
1.55, specific surface area 33 m ² / g, coercive force 1250 Oe, saturation magnetization 62
It was emu / g.

(Comparative Example 4) Magnetic powder was obtained by the same steps as in Example 1 except that the heat treatment temperature was 780 ° C.

The obtained magnetic powder had a packing density of 3.9 g / cm ³ after being pressed at 400 kgf / cm ² and a geometric standard deviation.
1.47, specific surface area 17 m ² / g, coercive force 1220 Oe, saturation magnetization 62
It was emu / g.

Table 1 shows the characteristics of the above magnetic powder.

Table 1 Packing density Geometric standard deviation Specific surface area Coercive force Saturation magnetization g / cm ³ m ² / g Oe emu / g Example 1 2.8 1.42 37 1350 60 Example 2 3.2 1.4 32 1270 62 Comparative Example 1 2.3 1.48 36 1330 61 Comparative Example 2 2.7 1.83 30 1100 62 Comparative Example 3 2.3 1.55 33 1250 62 Comparative Example 4 3.9 1.47 17 1220 62 From Table 1, Examples 1 and 2 and Comparative Examples 1, 2, 3, and 4 show coercive force and saturation. Both the magnetization and the magnetic properties are satisfactory as magnetic powder. However, the characteristic values of the powder are quite different. That is, although the specific surface areas of the powders are similar to each other, it can be seen that the compression properties of Comparative Examples 1 and 3 are 2.3, which are hard to be compressed under pressure. On the other hand, in Comparative Example 2, the geometric standard deviation value is considerably larger than that of other magnetic powders, and it can be seen that the particle size varies.

Using the magnetic powders obtained in each of the above Examples and Comparative Examples, magnetic paints were prepared with the following composition.

(Coating Composition) 100 parts by weight of magnetic powder of each specific example and comparative example 7 parts by weight of sulfonated vinyl chloride vinyl acetate copolymer resin 7 parts by weight Dispersant (lecithin) 1 part by weight Abrasive (Al 2 O 3) 5 parts by weight Lubricant ( Stearic acid / butyl stearate) 4 parts by weight Curing agent (coronate) 4 parts by weight Methyl ethyl ketone 40 parts by weight Toluene 30 parts by weight Cyclohexanone 30 parts by weight Each of the above coating compositions is kneaded with a sand grinder for 5 hours to form a magnetic paint. Using this magnetic coating, a magnetic coating was applied on a polyethylene terephthalate film with a thickness of 9 μm so that the thickness after drying and calendering would be 3 μm, and 6 kOe of 6 kOe perpendicular to the film surface. 8 mm with a magnetic layer formed by applying a magnetic field to dry and calendering
A magnetic tape was formed by cutting into a width.

The saturation magnetization (Ms) and the perpendicular squareness ratio (after demagnetization compensation) of the magnetic tape thus obtained were measured with a vibrating sample magnetometer (VSM). Then, the filling property of the magnetic powder in the unit volume was calculated from the ratio of the saturation magnetization (Ms) per unit volume and the theoretical saturation magnetization (Ms ′) calculated. For example, the theoretical saturation magnetization Ms ′ in the case of the first embodiment of the present invention is 172 emu / c from the above configuration.
m is ^3.

In addition to the surface property of each magnetic tape, the output of the magnetic tape in the 9 MHz band and the noise of 8 MHz were measured.

Table 2 shows various characteristics of the magnetic tapes using the magnetic powders obtained in the specific examples 1 and 2 and the comparative examples 1 to 4 described above.

Table 2 Characteristics of magnetic recording medium Magnetic powder Surface property Vertical Ms 'Ms Ms / Ms' Reproduction output noise (Rz) nm Squareness ratio (emu / cm ³ ) (%) (dB) (dB) Example 1 22 0.84 172 168 98 2.5 -0.5 Example 2 24 0.85 177 170 96 2.5 -0.5 Comparative Example 1 26 0.78 175 151 86 0.5 0.5 Comparative Example 2 35 0.73 177 150 85 0.0 2.0 Comparative Example 3 30 0.76 177 156 88 0.0 0.0 Comparative Example 4 40 0.68 177 149 84 -2.0 3.0 From the examples and comparative examples described above, the magnetic powder of the present invention achieves higher filling in the magnetic layer and secures higher output than the magnetic powder of the comparative example. It can be seen that excellent surface properties are obtained, which results in low noise.

Further, a characteristic feature of this embodiment is that the magnetic recording medium using the magnetic powder of the present invention can achieve high packing property and orientation, which allows, for example, vertical perpendicularity easily. A magnetic recording medium capable of magnetic recording can be obtained relatively easily.

[0063]

As described above, according to the magnetic powder of the present invention, a high filling is achieved as compared with the conventional magnetic powder, which not only makes it possible to secure a high output, but also a sufficiently low value. Noise is achieved. Further, since it is not possible to easily achieve high orientation as compared with the conventional one, it is very effective in increasing the density.

[0064]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Etsuji Ogawa 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Incorporated Toshiba Research and Development Center

Claims (8)

[Claims] 1. A magnetic powder for high-density magnetic recording, wherein the magnetic powder is filled in a closed container and pressurized at a pressure of 400 kgf / cm ² ,
The packing density of the magnetic powder after removing the pressure is in the range of 2.5 gr / cm ³ to 3.5 g / cm ³ , and the geometric standard deviation of the particle size distribution of the magnetic powder is 1.5 or less. 2. The magnetic powder according to claim 1 is mainly composed of hexagonal ferrite represented by the following chemical formula: AO.n (Fe12-xy M1x M2y O18-δ), wherein A is Ba, Sr. , Ca, at least one element selected from the group of Ca, M1 is at least one element selected from the group of divalent metal elements, and M2 is at least one element selected from the group of tetravalent to hexavalent metal elements. Is an element, n,
x, y and δ are numbers that respectively satisfy the following equation, 0.
8 ≤ n ≤ 3.0, 0 ≤ x ≤ 3, 0 ≤ y ≤ 2, and δ = {x + (3-m) y} / 2, where m is the average valence of the M2 metal element. . 3. A magnetic powder characterized in that the magnetic powder according to claim 1 or 2 is mainly composed of hexagonal ferrite having a specific surface area of 20 to 60 m ² / g. 4. A magnetic powder characterized in that the magnetic powder according to claim 1 is mainly composed of hexagonal ferrite having a specific surface area of 30 to 50 m ² / g. 5. A magnetic recording medium comprises a non-magnetic support and a magnetic layer formed on the support, and the magnetic layer consists essentially of magnetic powder and a binder, wherein the magnetic The powder was packed in a closed container and pressed at a pressure of 400 kgf / cm ² , and the packing density of the magnetic powder after removing the pressure was 2.5 gr.
/ cm ³ to 3.5 g / cm ³ , and the geometric standard deviation of the particle size distribution of the magnetic powder is 1.5 or less. 6. The magnetic recording medium according to claim 5,
The filling ratio of the magnetic powder contained in the magnetic layer is 95% or more, where the filling ratio is from the constituent components of the magnetic layer having the saturation magnetization Ms measured for the magnetic layer per unit volume. It is a ratio to the theoretically calculated saturation magnetization Ms ′. 7. The magnetic recording medium according to claim 5, wherein the magnetic powder contained in the magnetic layer has a perpendicular squareness ratio of 0.
8 or more. 8. The magnetic recording medium according to claim 5, wherein the magnetic powder is mainly represented by the following chemical formula 6.
Composed of tetragonal ferrite: AO.n (Fe12-xy M1x M2y O18-δ), where A is at least one element selected from the group of Ba, Sr, and Ca, and M1 is a group of divalent metal elements At least one element selected from the group M2 is at least one element selected from the group of tetravalent to hexavalent metal elements, n,
x, y and δ are numbers that respectively satisfy the following equation, 0.
8 ≤ n ≤ 3.0, 0 ≤ x ≤ 3, 0 ≤ y ≤ 2, and δ = {x + (3-m) y} / 2, where m is the average valence of the M2 metal element. .