JP2002289415A - Magnetic recording spindle-shaped alloy magnetic particle powder and magnetic recoding medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-density magnetic recording medium which is superior in output characteristics in a short wavelength range, capable of reducing noises remarkably, and excellent in stock stability and spindle-shaped alloy magnetic particulate powder having Fe and Co as main components which is included in the magnetic recording medium. SOLUTION: The spindle-shaped alloy magnetic particulate powder contains 20 to 50 atom% cobalt in terms of Co to all Fe, has an average major axis (L) of 0.03 to 0.10 μm, and contains Fe and Co as main components. The spindle- shaped alloy magnetic particulate powder containing Fe and Co as main components has a coercive force of 159.2 to 238.7 kA/m (2000 to 3000 Oe), a crystal size of 100 to 160 Å, and a volume change of activation (Vact) of 0.01 to 0.07 E-4 μm<3> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-density magnetic recording medium having excellent output characteristics in a short wavelength region, significantly reducing noise, and excellent storage stability, and Fe contained in the magnetic recording medium. And a spindle-shaped alloy magnetic particle powder containing Co and Co as main components.

[0002]

2. Description of the Related Art In recent years, magnetic recording / reproducing devices for audio, video, and computers have been reduced in size and weight, recorded for a long time, and increased in storage capacity. Demands for high-density recording are increasing.

[0003] In particular, in the field of computer tapes, with the rapid increase in performance of computers, there is a strong demand for improvements in storage capacity in order to reduce the size and increase the capacity.

[0004] That is, it is required that the magnetic recording medium has high density, high output characteristics and improved frequency characteristics, especially excellent output characteristics in a short wavelength region. To this end, noise caused by the magnetic recording medium is required. , And have a high coercive force Hc.

In recent years, introduction of a magnetoresistive (MR) head as a reproducing head for a computer tape has been studied instead of the inductive magnetic head used so far. MR heads are much easier to obtain reproduction output than inductive magnetic heads, and are expected to achieve higher density recording.

In particular, in an MR head, impedance noise associated with an induction coil does not occur, and noise associated with a system such as equipment noise is greatly reduced. N can be achieved. Therefore, there is a stronger demand than ever before to reduce noise in magnetic recording media.

In addition, in order to increase the recording density, particularly to reduce the recording wavelength, it is desired that the magnetization transition region is narrow and the digital signal reproduction waveform is sharp from the viewpoint of high output and noise suppression. For this purpose, it is desired that the magnetization reversal width is small and the magnetization can be rotated simultaneously with respect to the magnetic field.

These characteristics of the magnetic recording medium are closely related to the magnetic particle powder used in the magnetic recording medium, and in recent years, the coercive force is higher than that of the conventional iron oxide magnetic particle powder. Attention has been focused on metal magnetic particle powder containing iron as a main component and having a large saturation magnetization σs, and computer tapes are used in external storage systems such as DDS, DLT, and TRAVAN.

Therefore, there is a strong demand for further improvement of the characteristics of metallic magnetic particles containing iron as a main component in order to satisfy the requirements for the magnetic recording medium.

That is, in order to obtain a magnetic recording medium having a high coercive force, a small noise, and a small magnetization reversal width, metal magnetic particles containing iron as a main component are fine particles, and have a small crystallite size. It is strongly required to have a high coercive force, excellent dispersibility, and a magnetization reversal mechanism close to simultaneous rotation.

First, with respect to the formation of fine particles of metal magnetic particles, Japanese Unexamined Patent Publication No. 2000-251243 discloses a method in which a magnetic material used is compared with the length of a signal recording area. Since it is not possible to create a clear magnetization transition region, recording becomes substantially impossible.Therefore, fine particles of a magnetic material have been used for many years in order to increase the recording density used. " As described above, in order to obtain a magnetic recording medium with high output in a short wavelength region and reduced noise, it is necessary to make the metal magnetic particles finer, that is,
It is necessary to reduce the major axis diameter.

Regarding the crystallite size of the metal magnetic particles, Japanese Patent Application Laid-Open No. 7-126704 discloses a method of reducing the X-ray particle size of the metal magnetic particles as small as possible in order to reduce the noise level due to the recording medium. as is also an effective means ...... "becomes according to, in order to obtain a magnetic recording medium with less noise, that magnetic metal particles containing iron as a main component has a smaller crystallite size D ₁₁₀ Highly required.

Further, in order to further reduce the noise of the magnetic recording medium, it is not sufficient to simply reduce the major axis diameter and the crystallite size of the metal magnetic particle powder, and to further clarify the factors relating to the noise reduction. Is strongly required.

In particular, recently, research has been conducted on an activation volume obtained by measuring a time change of magnetization due to thermal fluctuation magnetic aftereffect, and by optimizing the activation volume, a magnetic field is obtained. Attempts have been made to reduce the noise of the recording medium.

[0015] Further, it is required that the magnetization reversal mode of the metal magnetic particle powder be close to simultaneous rotation.

However, to obtain metal magnetic particle powder which is fine particles, has a small crystallite size, has a high coercive force, and whose main component is Fe and Co whose magnetization reversal mode is nearly simultaneous rotation, requires the manufacturing method. Very difficult due to the law.

Hereinafter, this fact will be described in detail.

That is, generally, iron-based metal magnetic particle powder is passed through an aqueous solution containing an iron-containing precipitate obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline solution, through an oxygen-containing gas such as air. Spindle-like goethite particle powder obtained by performing an oxidation reaction by heating, spindle-like hematite particle powder obtained by heating and dehydrating the goethite particle powder, or spindle-like particle powder containing a heterogeneous element other than iron in these particle powders Is used as a starting material, and the starting material is reduced by heating under a reducing gas atmosphere.

First, regarding the relationship between the crystallite size and the coercive force, Japanese Patent Application Laid-Open No. 4-61302 discloses that, as the crystallite size decreases, the coercive force tends to decrease. There is a strong demand for magnetic particles having a small crystallite size while maintaining the coercive force of the powder as high as possible. " The magnetic force has an inverse correlation, and it is very difficult to make both the crystallite size of the metal magnetic particle powder smaller and have a high coercive force.

In consideration of the oxidation stability of the magnetic metal particles, it is necessary to increase the heating reduction temperature as much as possible to sufficiently increase the reduction rate. In addition, the starting material tends to cause shape breakage, which results in a decrease in coercive force. Furthermore, since the conditions such as the atmosphere and temperature in the heat reduction step are very severe, the spindle-shaped metal magnetic particles tend to cause sintering between the particles and the particles.

When the starting material is fine particles having a particle size of 0.15 μm or less, the destruction of the particle shape in the heat reduction step tends to be more remarkable. The shape-destructed metal magnetic particle powder cannot obtain a high coercive force due to a decrease in shape anisotropy, and the particle size distribution decreases. In addition, the reduction in the particle size causes a rapid decrease in oxidation stability.
In addition, even when producing a magnetic recording medium, kneading with a binder in a vehicle, an increase in interparticle force in a dispersion process,
Alternatively, due to an increase in magnetic cohesion, the dispersibility is reduced, the squareness ratio when a magnetic coating film is formed is reduced, and an excellent SFD is obtained.
It is difficult to obtain a magnetic recording medium having

Further, the magnetization reversal mode of the metal magnetic particle powder can be brought close to the simultaneous rotation by increasing single crystallization of the metal magnetic particle powder, but as a result, the crystallite size increases. It has been difficult to achieve both the reversal of the magnetization reversal mode of the metal magnetic particle powder near simultaneous rotation and the reduction of the crystallite size of the metal magnetic particle powder.

By improving the characteristics of the magnetic metal particle powder, it is possible to obtain a magnetic recording medium satisfying high output and low noise, as disclosed in JP-A-8-171718 and JP-A-9-917.
No. 22522, JP-A-9-22523, JP-A-9-106535, JP-A-10-302243
No., etc.

[0024]

The present invention relates to fine particles having a high coercive force and an appropriate saturation magnetization value, despite having a small crystallite size, in particular of less than 160 °, and
Spindle-shaped alloy magnetic particle powders whose magnetization reversal mode is close to simultaneous rotation are the most demanded at present, but spindle-shaped alloy magnetic particle powders that sufficiently satisfy the above-mentioned characteristics have not yet been provided.

That is, in Japanese Patent Application Laid-Open No. Hei 8-171718, the ratio Hc / HK of the coercive force Hc of the magnetic recording medium to the anisotropic magnetic field HK is specified. Therefore, it is hardly enough to reduce noise. In addition, characteristics of metal magnetic particles required for noise reduction are not sufficiently considered.

JP-A-9-22522 and JP-A-9-22523 specify the number of crystallites of the metal magnetic particle powder, and JP-A-9-106535 discloses the number of crystallites. Although the number of crystallites and the crystal ratio of are specified, and the magnetization reversal mode is mentioned, it cannot satisfy the requirements in terms of noise reduction, and the magnetization reversal mode is not sufficient from the viewpoint of simultaneous rotation. It is difficult.

Japanese Patent Application Laid-Open No. 10-302243 specifies the magnetization reversal volume of a magnetic recording medium obtained from the frequency dependence of the coercive force, but is not satisfactory in terms of noise reduction. . Further, there is no reference to the characteristics of the metal magnetic particles required for noise reduction.

Also, IEICE Technical Report, MR97-22, 29-
34 (1997-07) (The Institute of Electronics, Information and Communication Engineers)
Describes the relationship between the activation volume and the actual volume of a magnetic recording medium using metal magnetic particle powder, but the activation volume is large and it is hardly sufficient to reduce noise. In addition, characteristics of metal magnetic particles required for noise reduction are not sufficiently considered.

Also, Journal of magne
tism and magnetic material
ls, 193, 314-317 (1999) describes the activation volume of metal magnetic particle powder.
It is difficult to say that the crystallite size is large and noise can be sufficiently reduced.

Therefore, the present invention provides a fine particle having a high coercive force and an appropriate saturation magnetization value, despite having a small crystallite size, particularly 160 ° or less,
It is a technical object to obtain a spindle-shaped alloy magnetic particle powder having a small rotation hysteresis integral value.

[0031]

The above technical objects can be achieved by the present invention as described below.

That is, the present invention mainly comprises Fe and Co containing 20 to 50 atomic% of cobalt in terms of Co with respect to all Fe and having an average major axis diameter (L) of 0.03 to 0.10 μm. Spindle-shaped alloy magnetic particle powder as a component, 159.2
２238.7 kA / m (2000-3000 Oe), crystallite size is 100-160 ° and activation volume (Vact) is 0.01-0.07E-4 μm ³
A spindle-shaped alloy magnetic particle powder for magnetic recording, characterized in that:

Further, the present invention mainly comprises Fe and Co containing 20 to 50 atomic% of cobalt in terms of Co with respect to all Fe and having an average major axis diameter (L) of 0.03 to 0.10 μm. And the coercive force of the spindle-shaped alloy magnetic particles containing Fe and Co as the main components is 159.2 to 238.7 kA / m (2000 to 300
0 Oe), the crystallite size is 100 to 160 °, and the activation volume (Vact) is 0.01 to 0.07.
E-4 μm ³ , the rotation hysteresis integral (Rh)
Spindle-shaped alloy magnetic particles having a value of 1.0 or less.

Further, the present invention mainly comprises Fe and Co containing 20 to 50 atomic% of cobalt in terms of Co with respect to all Fe and having an average major axis diameter (L) of 0.03 to 0.10 μm. And the coercive force of the spindle-shaped alloy magnetic particles containing Fe and Co as the main components is 159.2 to 238.7 kA / m (2000 to 300
0 Oe) and the saturation magnetization is 100 to 150 Am ²
/ Kg, crystallite size is 100-160 °, activation volume (Vact) is 0.01-0.07E
A -4μm ^3, a spindle-shaped alloy magnetic particles rotating hysteresis integration (Rh) value is equal to or less than 1.0.

Further, the present invention is a magnetic recording medium characterized in that a magnetic layer mainly composed of any of the spindle-shaped alloy magnetic particles and a binder is formed on a non-magnetic support.

Next, the configuration of the present invention will be described in more detail.

First, the spindle-shaped alloy magnetic particles according to the present invention will be described.

The spindle-shaped alloy magnetic particles according to the present invention comprise:
Co in an amount of 20 to 50 atomic%, preferably 2
0 to 45 atomic% is contained. If the Co content is less than 20 atomic%, the oxidation stability cannot be sufficiently improved, and a large coercive force cannot be obtained. If it exceeds 50 atomic%, the saturation magnetization value and the coercive force decrease. Unnecessary addition is not preferable from the viewpoint of cost.

The average major axis diameter of the spindle-shaped alloy magnetic particles according to the present invention is 0.03 to 0.10 μm. When the average major axis diameter is less than 0.03 μm, the saturation magnetization value and the oxidation stability are rapidly reduced, and at the same time, it is difficult to obtain a high coercive force. Further, a change over time in recording due to thermal fluctuations cannot be ignored, which is not preferable as a recording material. 0.10μ
If it exceeds m, high output and low noise in a target short wavelength region cannot be sufficiently achieved. In addition, it is not preferable from the viewpoint of a decrease in coercive force. Preferably 0.03 to
0.098 μm, more preferably 0.03 to 0.095
μm.

The average minor axis diameter of the spindle-shaped alloy magnetic particles according to the present invention is preferably 0.008 to 0.020 μm. When the average short axis diameter exceeds 0.020 μm, the coercive force and the anisotropic magnetic field decrease, which is not preferable. Further, it is difficult to obtain alloy magnetic particle powder satisfying all of the crystallite size, the activation volume, and the integral value of the rotation hysteresis. Average short axis diameter is 0.00
When the thickness is less than 8 μm, the saturation magnetization value and the oxidation stability decrease rapidly, and at the same time, it becomes difficult to obtain a high coercive force. Further, a change over time in recording due to thermal fluctuations cannot be ignored, which is not preferable as a recording material.

The axial ratio (average major axis diameter / average minor axis diameter) is preferably 3 to 8.

The crystallite size _{D 110} of spindle-shaped alloy magnetic particles according to the present invention is 100～160A. 160
If Å is exceeded, the desired noise reduction in the short wavelength region cannot be sufficiently achieved. If it is less than 100 °, the saturation magnetization value and the oxidation stability are sharply reduced, and at the same time, it is difficult to obtain a high coercive force. Further, a change over time in recording due to thermal fluctuations cannot be ignored, which is not preferable as a recording material. Preferably it is 100 to 155 °.

The activation volume (Vact) of the spindle-shaped alloy magnetic particles according to the present invention is 0.01 to 0.07E-4 μm.
³ . Preferably 0.015 to 0.07E-4 μm
³ . When it exceeds 0.07E-4 μm ³ , low noise in a target short wavelength region is not sufficiently achieved.
If it is less than 0.01E-4 μm ³ , the saturation magnetization value and the oxidation stability sharply decrease, and at the same time, it becomes difficult to obtain a high coercive force. Further, a change over time in recording due to thermal fluctuations cannot be ignored, which is not preferable as a recording material.

The rotational hysteresis integral (Rh) value of the spindle-shaped alloy magnetic particles according to the present invention is 1.0 or less, preferably 0.95 or less. When the rotation hysteresis integral (Rh) value exceeds 1.0, high output and low noise in a short wavelength region cannot be achieved.

B of the spindle-shaped alloy magnetic particles according to the present invention
ET specific surface area is preferably 40~75m ² / g, more preferably 45~75m ² / g. When it is more than 75 m ² / g, it is difficult to disperse at the time of coating, which is not preferable. If it is less than 40 m ² / g, metal magnetic particle powder satisfying all of the crystallite size, activation volume and major axis diameter cannot be obtained.

The spindle-shaped alloy magnetic particles according to the present invention comprise:
The coercive force Hc is 159.2 to 238.7 kA / m (200
0 to 3000 Oe). When it exceeds 238.7 kA / m, the recording head is saturated, and a high output in a target short wavelength region cannot be obtained. 159.2 kA /
If it is less than m, a sufficiently high output cannot be obtained in a short wavelength region. Preferably, 167.1 to 222.8 kA / m (21
00-2800 Oe).

Saturation of the spindle-shaped alloy magnetic particles according to the present invention
Sum magnetization value s is 100 to 150 Am ²/ Kg (100 ~
150 emu / g), more preferably 100 emu / g.
~ 145Am²/ Kg (100-145 emu / g)
is there. 150 Am²/ Kg, noise increases
Is not preferred from the viewpoint of Especially the MR head for the reproducing head
When used, excessive remanent magnetization may occur, causing unnecessary noise
Since this causes an increase, C / N decreases, which is not preferable.
100 Am²/ Kg or less, the metal magnetic particles powder
Causes decrease in coercive force and expansion of coercive force distribution, preferably
Absent.

The squareness ratio (σr / σs) of the spindle-shaped alloy magnetic particles according to the present invention is preferably 0.52 to 0.55.

The anisotropic magnetic field (Hk) of the spindle-shaped alloy magnetic particles according to the present invention is 477.5 to 636.6 kA / m.
(6000-8000 Oe), preferably 517.3-
636.6 kA / m (6500 to 8000 Oe). It is difficult to obtain metal magnetic particles more than 636.6 kA / m (8000 Oe) industrially. 47
When it is less than 7.5 kA / m (6000 Oe), a high output in a short wavelength region cannot be obtained.

The oxidation stability Δσs of the saturation magnetization value of the spindle-shaped alloy magnetic particles according to the present invention is preferably 15% or less,
It is more preferably at most 13%, still more preferably at most 10%.

Next, the magnetic recording medium according to the present invention will be described.

The magnetic recording medium according to the present invention comprises a non-magnetic support and a magnetic recording layer formed on the non-magnetic support and containing the spindle-shaped alloy magnetic particles according to the present invention and a binder resin. .

As the non-magnetic support, polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, and the like which are currently widely used for magnetic recording media are used.
Synthetic resin films such as polyimide, aluminum, and metal foils and plates such as stainless steel and various types of paper can be used, and the thickness thereof varies depending on the material, but is usually preferably 1.0 to 300 μm, more preferably 2.0 ~
50 μm.

In the case of a magnetic disk, polyethylene terephthalate is usually used as the nonmagnetic support, and its thickness is usually 50 to 300 μm. In the case of magnetic tape, in the case of polyethylene terephthalate, the thickness is
Usually, the thickness is 3 to 100 μm, in the case of polyethylene naphthalate, the thickness is usually 3 to 50 μm, and in the case of polyamide, the thickness is usually 2 to 10 μm.

As the binder resin, vinyl chloride-vinyl acetate copolymers, urethane resins, vinyl chloride-vinyl acetate-
Maleic acid copolymer, urethane elastomer, butadiene-acrylonitrile copolymer, polyvinyl butyral, cellulose derivatives such as nitrocellulose, polyester resin, synthetic rubber resin such as polybutadiene, epoxy resin, polyamide resin, polyisocyanate, electron beam curable acrylic Urethane resins and the like and mixtures thereof can be used.

Further, each binder resin has --OH, --COO
A polar group such as H, —SO ₃ M, —OPO ₂ M ₂ , and —NH ₂ (where M is H, Na, or K) may be included.

The thickness of the magnetic recording layer formed on the non-magnetic support is in the range of 0.01 to 5.0 μm. 0.
When the thickness is less than 01 μm, it is not preferable because uniform coating is difficult and uneven coating is likely to occur. If it exceeds 5.0 μm, it becomes difficult to obtain desired electromagnetic conversion characteristics due to the influence of a demagnetizing field.

The mixing ratio of the composite magnetic particle powder and the binder resin in the magnetic recording layer is such that the composite magnetic particle powder is 5 to 2,000 parts by weight based on 100 parts by weight of the binder resin.

In the magnetic recording layer, known lubricants, abrasives, antistatic agents and the like used for the magnetic recording medium are required. If necessary, about 0.1 to 50 parts by weight with respect to 100 parts by weight of the binder resin. May be included.

The magnetic recording medium obtained by using the spindle-shaped alloy magnetic particles according to the present invention has a coercive force Hc of 15%.
9.2 to 238.7 kA / m (2000 to 3000 O
e), the squareness ratio (Br / Bm) is 0.82 or more, preferably 0.85 or more, and the SFD is 0.60 or less;
Preferably 0.50 or less, the degree of orientation is 2.0 or more,
Preferably, it is 2.3 or more, and the oxidation stability ΔBm is 8%.
And preferably less than 5%, and the surface roughness Ra is 8n
m, preferably 5 nm or less.

In the magnetic recording medium according to the present invention, a non-magnetic underlayer containing non-magnetic particles and a binder resin may be formed between the non-magnetic support and the magnetic recording layer.

As the non-magnetic particle powder for the non-magnetic underlayer,
Usually, a nonmagnetic inorganic powder used for a nonmagnetic underlayer for a magnetic recording medium can be used. Specifically, hematite, hydrous iron oxide, titanium oxide, zinc oxide, tin oxide, tungsten oxide, silicon dioxide, α-alumina,
β-alumina, γ-alumina, chromium oxide, cerium oxide, silicon carbide, titanium carbide, silicon nitride, boron nitride, calcium carbonate, barium carbonate, magnesium carbonate, strontium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, titanium Barium acid or the like can be used alone or in combination, particularly, hematite,
Hydrous iron oxide, titanium oxide and the like are preferred.

In order to improve the dispersibility in the vehicle during the production of the non-magnetic paint, if necessary, the surface of the non-magnetic particle powder is treated with aluminum hydroxide, aluminum oxide, silicon hydroxide, The surface may be treated with an oxide of silicon or the like, and if necessary, to improve various characteristics such as light transmittance, surface electric resistance, mechanical strength, surface smoothness, and durability of the obtained magnetic recording medium. , A inside the particle
l, Ti, Zr, Mn, Sn, Sb and the like may be contained.

The non-magnetic particle powder includes particles of various shapes, such as spherical, granular, octahedral, hexahedral, polyhedral, etc., needle-like, spindle-like, rice-granular, etc. There are plate-like particle powders and the like. Considering the surface smoothness of the obtained magnetic recording medium, the particle shape of the nonmagnetic particle powder is preferably acicular.

The non-magnetic particles usually have an average particle diameter of 0.01 to 0.3 μm, and the particle shape is granular, acicular or plate-like.

When the particle shape is acicular, the axial ratio is usually 2 to 20, and when the particle shape is plate-like, the plate ratio (average plate surface diameter / average thickness) is 2 to 50. .

The nonmagnetic underlayer has a coating thickness of 0.2 to 1
A range of 0.0 μm is preferred. If it is less than 0.2 μm, it becomes difficult to improve the surface roughness of the non-magnetic support.

The binder resin used for forming the magnetic recording layer can be used as the binder resin in the nonmagnetic underlayer.

The mixing ratio of the non-magnetic particle powder and the binder resin in the non-magnetic underlayer is 5 to 2000 parts by weight of the non-magnetic particle powder with respect to 100 parts by weight of the binder resin.

It is to be noted that a known lubricant, an abrasive, an antistatic agent and the like used for a magnetic recording medium are required for the non-magnetic underlayer, if necessary, about 0.1 to 50 parts by weight with respect to 100 parts by weight of the binder resin. May be included.

The magnetic recording medium having a nonmagnetic underlayer according to the present invention has substantially the same characteristics as the magnetic recording medium having no nonmagnetic underlayer. In the magnetic recording medium having a nonmagnetic underlayer according to the present invention, particularly, the surface can be easily smoothed by a calender, and the running durability is improved because a lubricant is supplied from the nonmagnetic underlayer.

Next, a method for producing the spindle-shaped alloy magnetic particles according to the present invention will be described.

The spindle-shaped alloy magnetic particles according to the present invention comprise:
Spindle-shaped goethite particle powder containing 20 to 50 atomic% of cobalt in terms of Co with respect to all Fe and having an average major axis diameter of 0.05 to 0.15 μm or obtained by heating and dehydrating the spindle-shaped goethite particle powder. In a production method of obtaining spindle-shaped alloy magnetic particle powder using spindle-shaped hematite particle powder as a starting material, the starting material is mixed with an inert gas atmosphere at 300 to 6%.
The temperature is raised to a temperature range of 00 ° C., and after switching to a reducing gas atmosphere, heat reduction is performed in a temperature range of 300 to 600 ° C. to obtain spindle-shaped alloy magnetic particles. The spindle-shaped alloy magnetic particle powder is subjected to surface oxidation in an oxygen-containing inert gas atmosphere at a temperature in the range of 80 to 200 ° C. to reduce the saturation magnetization of the spindle-shaped alloy magnetic particle powder to 100.
A second step of -135 Am ² / kg; the spindle-shaped alloy magnetic particle powder passing through the second step is heated at a temperature higher than the reduction temperature of the first step by 50 ° C. or more in an inert gas atmosphere and at 400 ° C.
A third step of raising the temperature to a temperature range of 400 to 700 ° C., then switching to a reducing gas atmosphere, and then performing heat reduction again at a temperature range of 400 to 700 ° C. and spindle-shaped alloy magnetic particles via the third step The powder can be obtained by performing surface oxidation again in a temperature range of 40 to 160 ° C. in an inert gas atmosphere containing 5 to 10 g / m ³ of water vapor and oxygen.

The starting material of the present invention contains 20 to 50 atomic% of cobalt in terms of Co with respect to all Fe,
Spindle-shaped goethite particles having an average major axis diameter of 0.05 to 0.15 μm or 20 to 80% in terms of Co with respect to all Fe obtained by heating and dehydrating the spindle-shaped goethite particles.
Contains 50 atomic% of cobalt and has an average major axis diameter of 0.05
Spindle-shaped hematite particle powder having a size of about 0.13 μm is used.

The starting material in the present invention is spindle-shaped particles, which do not contain dendritic particles and have an excellent size distribution.

The spindle-shaped goethite particles can be obtained by using one or more of sodium carbonate, ammonium hydrogencarbonate, and aqueous ammonia and a mixed solution thereof with sodium hydroxide as an aqueous alkaline solution. . In consideration of the reduction of the amount of Na and the magnetic properties, it is preferable to use ammonium bicarbonate and / or aqueous ammonia.

The spindle-shaped goethite particles according to the present invention may be coated on their surfaces with a Co compound, an Al compound and a sintering inhibitor.

As the sintering inhibitor, compounds of rare earth elements can be used, and one or more of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium and the like are preferable. In particular, yttrium is preferred.

In order to improve the effect of preventing sintering, or if necessary, other elements such as Si, B, Mg, B
One or more compounds of the element selected from a, Sr and the like may be used. These compounds not only have the effect of preventing sintering but also have the function of controlling the reduction rate, and thus may be used in combination as necessary.

The spindle-shaped goethite particles according to the present invention have an average minor axis diameter of 0.010 to 0.024 μm and a total
Contains 5 to 15 atomic% of aluminum in terms of Al and 5 to 15 atomic% of rare earth element in terms of rare earth element, has an axial ratio (average major axis diameter / average minor axis diameter) of 4 to 8, BET
The specific surface area value is preferably from 100 to 250 m ² / g.

The spindle-shaped hematite particles can be prepared by mixing the spindle-shaped goethite particles in an oxidizing atmosphere at 150-35.
Dehydrate by heating in the temperature range of 0 ° C.
It is preferable to obtain by performing heat treatment in a temperature range of more than 0 ° C and less than 700 ° C.

The spindle-shaped hematite particles according to the present invention have an average minor axis diameter of 0.010 to 0.023 μm, and
Contains 5 to 15 atomic% of aluminum in terms of Al and 5 to 15 atomic% of rare earth element in terms of rare earth element, has an axial ratio (average major axis diameter / average minor axis diameter) of 4 to 8, BET
The specific surface area value is preferably from 50 to 120 m ² / g.

Further, the spindle-shaped hematite particle powder after the heat treatment may be washed to remove impurity salts such as Na ₂ SO ₄ contained from the reaction for producing the spindle-shaped goethite particle powder. In this case, by washing under the condition that the coated sintering inhibitor does not elute,
It is preferable to remove impurities.

In the present invention, when the starting particle powder is charged into a reducing device, the starting particle powder is granulated by an ordinary method to obtain an average particle diameter of 1: 1.
It is preferable to use granules having a size of 5 mm.

As the reducing device in the present invention, a reducing device having a fixed layer formed thereon is preferable. Specifically, a stationary reducing device (batch type) or a fixed layer is formed on a belt and the belt is transferred. A mobile reduction device (continuous type) for reducing while reducing is preferable.

In the present invention, the fixed layer has a height of 30 cm.
The following is preferred. If it exceeds 30 cm, a large amount of C
At the same time, the reduction promoting action is remarkable because of containing o, and at the same time, the problem that the coercive force of the upper part of the fixed layer is reduced due to the increase of the partial pressure of steam due to the rapid reduction of the lower part of the fixed layer, The characteristics deteriorate. Considering industrial productivity, 3 to 30 cm is more preferable. Incidentally, a batch method (Japanese Patent Application Laid-Open No. 54-62915, Japanese Patent Application Laid-Open
4609) and the continuous type (JP-A-6-93312, etc.) have different productivity. Therefore, in the case of a batch type fixed bed reduction apparatus, the thickness is preferably more than 8 cm and 30 cm or less.

In the present invention, the atmosphere during the period in which the temperature is raised to the heat reduction temperature in the first step and the third step is an inert gas atmosphere. As the inert gas atmosphere, nitrogen gas, helium gas, argon gas and the like are preferable, and nitrogen gas is particularly preferable. In an atmosphere other than the inert gas, reduction occurs at a time when the temperature changes with time, and the reduction temperature during generation of metal magnetic particles cannot be kept constant, so that uniform particle growth hardly occurs and a high coercive force cannot be obtained. .

The temperature raising rate in the first and third steps is not particularly limited, but is preferably 2 to 100 ° C./min.

Further, the gas superficial velocity of the inert gas at the time of raising the temperature in the first step and the third step is not particularly limited, as long as the starting material granular material is not scattered or broken. Good.

The switching from the inert gas atmosphere at the time of raising the temperature in the first step and the third step to the reducing gas atmosphere in the heating and reducing step differs depending on the type of the reducing apparatus, and is industrially a batch type. In such a case, a method in which the pressure in the reduction device is controlled in a stepwise manner while controlling the pressure is preferable. In the case of a continuous system, a method in which a heating zone and a reduction zone are divided is preferable. In any case, it is preferable to perform the switching in a short time, and it is preferable to perform the switching within at least 10 minutes.

The atmosphere in the first and third heating and reducing steps of the present invention is a reducing gas, and hydrogen is preferably used as the reducing gas.

The heat reduction temperature in the first step in the present invention is 300 to 600 ° C., preferably 350 to 550.
° C. It is preferable that the heat reduction temperature is appropriately selected from the above temperature range according to the type and amount of the compound used for the coating treatment of the starting material. When the heat-reduction temperature is lower than 300 ° C., the progress of the reduction is very slow and not industrial, and the obtained spindle-shaped alloy magnetic particles have a low saturation magnetization value. If the temperature exceeds 600 ° C., the reduction reaction proceeds rapidly, causing shape destruction of the particles and sintering between the particles and between the particles, and the coercive force decreases.

The superficial velocity of the reducing gas in the first step of the present invention is preferably 40 to 150 cm / s. If the gas superficial velocity is less than 40 cm / s, the speed at which the steam generated by the reduction of the starting material is carried out of the system becomes very slow, so that the coercive force and SFD at the upper part of the layer are reduced, and the overall coercive force is high. Can not be obtained. If it exceeds 150 cm / s,
Although the desired spindle-shaped alloy magnetic particle powder can be obtained, it is not preferable because problems such as a high reduction temperature being required, or a granulated material being scattered and broken are likely to occur.

In the second step of the present invention, a surface oxidation treatment is performed in an atmosphere of an inert gas containing oxygen. As the inert gas atmosphere, nitrogen gas, helium gas, argon gas and the like are preferable, and nitrogen gas is particularly preferable. The oxygen content is preferably 0.1 to 5 vol%, and it is preferable to gradually increase the oxygen content to a predetermined amount.

The reaction temperature of the second step in the present invention is 8
It is 0-200 degreeC, Preferably it is 80-180 degreeC. If the temperature is lower than 80 ° C., it is difficult to form a surface oxide layer having a sufficient thickness. When the temperature is higher than 200 ° C., the shape of the particles is changed, particularly, a large amount of oxide is generated, so that the short axis is extremely expanded, and in some cases, the shape is easily broken, which is not preferable.

Spindle-shaped alloy magnetic particle powder after completion of the second step
At the end, the saturation magnetization value is 85 to 135 Am²/ Kg (85-
135 emu / g), preferably 90 to 130 A
m²/ Kg (90-130 emu / g).
Preferably 95-130 Am²/ Kg (95-130 em
u / g). Saturation magnetization value is 85 Am²Less than / kg
In this case, since the surface oxide layer becomes too thick, the third step
Spindle-shaped alloy magnet with large coercive force even after heat reduction
Powder cannot be obtained. 135 Am ²/ Kg
In the case of exceeding, the formation of the surface oxide layer was insufficient.
Therefore, a dense surface oxide layer cannot be formed.

In the case where the whole particles are oxidized in the second step, the shape of the particles changes, especially the short-axis growth occurs.
Since a large amount of oxide is generated, the short axis is extremely expanded, and in some cases, the skeleton is destroyed. Even if the oxide is reduced again, the shape is already collapsed, so that the coercive force does not improve.

In the present invention, the heat reduction temperature in the third step is a temperature higher than the heat reduction temperature in the first step by 50 ° C. or more, and is in a temperature range of 400 to 700 ° C. When the temperature is not higher than 50 ° C. than the heat reduction temperature in the first step, and 4
When the temperature is lower than 00 ° C., the progress of the reduction is very slow and not industrial, and it is difficult to reduce the surface oxide layer formed in the second step and to densify the whole particles. When the temperature exceeds 700 ° C., the shape of the particles is broken, and sintering between the particles is caused, so that the coercive force is reduced. The heat reduction temperature in the third step is preferably 450 to 650 ° C.

The gas superficial velocity of the reducing gas in the third heat reduction step of the present invention is preferably 40 to 150 cm / s as in the first step.

In the third step, an annealing treatment may be performed after the reduction step.
The temperature is preferably 700 ° C., and the atmosphere is preferably a hydrogen gas or an inert gas, and particularly preferably a nitrogen gas.

In the fourth step of the present invention, 5 to 10 g /
performing a surface oxidation treatment in an inert gas atmosphere containing water vapor and oxygen m ^3. When the content of water vapor is less than 5 g / m ³ , it is difficult to form a dense and thin surface oxide layer,
The improvement of the coercive force is hardly sufficient. If the content of water vapor exceeds 10 g / m ³ , the desired effect can be obtained, so that it is meaningless to include more than necessary.
The content of water vapor is preferably 2 to 8 g / m ³ . Further, the oxygen content is preferably 0.1 to 5 vol%, and is preferably gradually increased to a predetermined amount. As the inert gas, nitrogen gas, helium gas, argon gas and the like are preferable, and nitrogen gas is particularly preferable.

In the present invention, the reaction temperature in the fourth step is 40.
-160 ° C, preferably 40-140. The reaction temperature in the fourth step is preferably lower than the surface oxidation treatment temperature in the second step. If the temperature is lower than 40 ° C,
It is not preferable because the formation of the surface oxide layer is insufficient. 160
When the temperature exceeds ℃, the surface oxide layer becomes thick and the saturation magnetization decreases, which is not preferable.

[0103]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows.

The average major axis diameter, average minor axis diameter, and axis ratio of the spindle-shaped goethite particles, spindle-shaped hematite particles, and spindle-shaped alloy magnetic particles in the present invention are all numerical values measured from electron micrographs. The average value was shown.

In the present invention, the contents of Co, Al, rare earth element and other metal elements in the spindle-shaped goethite particles, the spindle-shaped hematite particles and the spindle-shaped alloy magnetic particles in the present invention are defined as inductively coupled plasma emission. The measurement was carried out using a spectrophotometer SPS4000 (manufactured by Seiko Denshi Kogyo KK).

The BET specific surface area value of each particle powder was shown by a value measured by a BET method using “Monosorb MS-11” (manufactured by Cantachrome Co., Ltd.).

The crystallite size D ₁₁₀ (the X-ray crystal particle diameter of the spindle-shaped alloy magnetic particles) was measured using an “X-ray diffractometer” (Rigak
u) (Measurement conditions: target Cu, tube voltage 40 kV,
Using a tube current of 40 mA), the size of the crystal particles measured by the X-ray diffraction method was determined using the (110)
It represents the thickness of a crystal grain in a direction perpendicular to each of the crystal planes, and is represented by a value calculated from the diffraction peak curve for each crystal plane using the following Scherrer equation.

D ₁₁₀ = Kλ / βcos θ where β = half-width (in radians) of a true diffraction peak corrected for mechanical width due to the apparatus. K = Scherrer constant (= 0.9), λ = wavelength of X-ray (Cu Kα-ray 0.1542 nm), θ = diffraction angle (corresponding to the diffraction peak of (110) plane).

The magnetic properties of the spindle-shaped alloy magnetic particles are as follows.
Using a “vibrating sample magnetometer” (manufactured by Toei Industry Co., Ltd.)
The measurement was performed with an external magnetic field of 795.8 kA / m (10 kOe).

Δσs, which is an evaluation of the oxidation stability of the saturation magnetization value of the powder, and ΔBm, which is an evaluation of the weather resistance of the saturation magnetic flux density Bm of the magnetic coating film, are obtained by placing the powder in a thermostat at a temperature of 60 ° C. and a relative humidity of 90%. After the accelerated aging test in which the body or the magnetic coating film piece was allowed to stand for one week, the saturation magnetization value of the powder and the saturation magnetic flux density of the magnetic coating film were measured, respectively, and σs and Bm measured before the test was started.
Δs and ΔBm were calculated by dividing the difference (absolute value) between σs ′ and Bm ′ one week after the accelerated aging test by σs and Bm before the start of the test, respectively. Δσs and ΔBm are 0
% Indicates that the oxidation stability is excellent.

Rotational hysteresis integrated value Rh (rotational hysteresis) of the spindle-shaped alloy magnetic particles powder
The s integral and the anisotropic magnetic field Hk were determined as follows using a torque magnetometer (manufactured by Digital Measurement Systems).

First, the spindle-shaped alloy magnetic particles powder in the demagnetized state is filled in a capsule, and 19.9 kA from 19.9 kA / m (250 Oe) to 795.8 kA / m (10 kOe).
/ M (in the state where an external magnetic field is applied in increments of 250 Oe), the rotational angle of the magnetic field is reciprocated from 0 to 360 ° to 0 (in increments of 5.63 °), and the hysteresis loss Wr of the magnetic torque in each magnetic field is obtained The rotation hysteresis integral value Rh was determined from the following equation by plotting the reciprocal (1 / H) of each applied magnetic field, and a tangent line was drawn on the Wr-1 / H curve on the high applied magnetic field side to have a maximum gradient. The intersection of the tangent and the reciprocal (1 / H) axis of the applied magnetic field is shown as an anisotropic magnetic field Hk.

Rh = ∫ (Wr / Ms) d (1 / H) Ms: saturation magnetization value (emu / cm ³ )

Activation Volume Va of Spindle-Shaped Alloy Magnetic Particle Powder
ct (Activation Volume) was determined as follows using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.).

First, the spindle-shaped alloy magnetic particles were packed in a capsule and magnetized with an external magnetic field of 795.8 kA / m (10 kOe). Then, at 300 K, the applied magnetic field was maintained from 200 Oe to 3600 Oe on a demagnetization curve in steps of 200 Oe. Then, the change in magnetization due to thermal fluctuation magnetic aftereffect was measured for 1000 seconds, and the attenuation of the magnetization was defined as ΔM. Immediately after that, the applied magnetic field is increased by 200 Oe, and the attenuation of magnetization after 1000 seconds is measured in the same manner. Next, the applied magnetic field is set to 200
Oe is reduced, and the reversible magnetic susceptibility χrev is obtained. The total differential susceptibility χtot was determined by dividing the difference in magnetization value when the time change of the magnetization after 1000 seconds was reduced by 200 Oe.

The irreversible susceptibility χirr from 200 Oe to 3600 Oe was obtained by subtracting the reversible susceptibility χrev from the total differential susceptibility χtot. Since the activation volume of the spindle-shaped alloy magnetic particles has a gradual magnetic field dependence, the value of the coercive force Hc was used as a representative value.
Next, the activation volume Vact was determined by Expressions 1 and 2.

(Equation 1) Sv = △ M / (χirr · Int) (Equation 2) Vact = kB · T / Ms · Sv kB: Boltzmann constant Sv: Magnetic aftereffect constant

The true density of the spindle-shaped alloy magnetic particles was measured by a constant volume expansion method using “Multi Volume Densitometer 1305” (manufactured by Micromeritex).

<Manufacture of Magnetic Tape> Next, a magnetic tape was prepared and coated by the following method to prepare a magnetic tape.

"Coating composition" Spindle-shaped alloy magnetic particles powder 100 parts by weight <Binder> Vinyl chloride-based copolymer resin 10 parts by weight (trade name: MR104 Nippon Zeon Co., Ltd.) Polyurethane-based resin 10 parts by weight (trade name) : UR-8200 Toyobo Co., Ltd. 10 parts by weight of α-alumina (trade name: AKP-50 Sumitomo Chemical Co., Ltd.) 3 parts by weight of carbon black (trade name: 3250 Mitsubishi Chemical Corporation) <Lubricant> Myristic acid 1 part by weight butyl stearate 2 parts by weight <Curing agent> Isocyanate-based curing agent 5 parts by weight (trade name: E-31 Takeda Pharmaceutical Co., Ltd.) <Solvent> Methyl ethyl ketone 114 parts by weight Toluene 68 parts by weight Cyclohexanone 46 parts by weight

[Coating method] A solvent was added to the alloy magnetic particle powder, vinyl chloride copolymer resin, α-alumina and carbon black, mixed, kneaded with a pressure kneader, and then diluted by adding a solvent. After further adding a urethane-based copolymer resin, dispersing with a sand mill, adding a lubricant and a solvent,
It was adjusted to an appropriate solid content and filtered with a filter. Then, a hardening agent was added while stirring the paint before application to prepare a magnetic paint.

"Coating Method" A dry magnetic layer having a thickness of 1.2 μm was formed on a polyethylene terephthalate film having a thickness of 7 μm.
And subjected to an orientation treatment using a solenoid magnet, dried, and subjected to a surface smoothing and curing treatment using a calender.

Subsequently, a backcoating paint composed of carbon black, a vinyl chloride copolymer resin and a polyurethane resin was applied to the surface opposite to the magnetic layer and dried to form a backcoat layer. Thereafter, the tape was slit into a width of 8 mm to form a magnetic tape.

The obtained magnetic tape was measured for magnetostatic properties, surface roughness and electromagnetic conversion properties by the following methods.

The magnetic properties of the magnetic tape were measured using a vibrating sample magnetometer (model: VSM-3S-15, manufactured by Toei Kogyo KK) with an external magnetic field of 795.8 kA / m (10 kOe).

The surface roughness Ra of the magnetic tape was obtained by measuring the center line average roughness using a stylus type surface roughness meter (model: Surfcom-575A, manufactured by Tokyo Seimitsu Co., Ltd.).

The electromagnetic conversion characteristics of the magnetic tape were measured using a fixed head type electronic measuring device (model: drum tester BX-3168,
(BELBEX). A magnetic tape is wound around a drum, and a relative speed between the tape and the head is 3.3 m /.
sec. Then, the drum was rotated so that a short-wave signal of 10 kHz was recorded at the optimum recording current of each tape, and the output level of 10 kHz was measured by a spectrum analyzer. Next, the difference between the noise level at 9 kHz (recording frequency-1 kHz) and the output level at 10 kHz was determined as C / N. The output level and C / N level are shown as relative values (dB) with respect to the reference tape. As the reference tape, the tape obtained in Comparative Example 1 was used.

<Production of spindle-shaped goethite particles> 30 mol of ammonium hydrogen carbonate and 45 mol of aqueous ammonia
Into a reaction tower equipped with a stirrer equipped with bubble dispersion blades, while rotating the stirrer at a rate of 600 revolutions per minute, while passing nitrogen gas at a flow rate of 60 l / min. Adjust to Next, 16 l of an aqueous ferrous sulfate solution containing 20 mol as Fe ²⁺ (a mixed alkali aqueous solution with respect to ferrous sulfate is 1.875 in terms of a prescribed conversion).
It corresponds to the equivalent. ) Was put into a bubble column and aged for 25 minutes. Then, 4 l of an aqueous solution of cobalt sulfate containing 4.0 mol of Co ²⁺ (corresponding to 20 atom% in terms of Co with respect to the total Fe) was added, and the mixture was further aged for 3 hours. After that, the reaction was carried out while passing air at a flow rate of 2 l / min until 30% of the total Fe ²⁺ was oxidized.

Then, 1 liter of an aqueous solution of aluminum sulfate containing 1.6 mol of Al ³⁺ (corresponding to 8 atomic% in terms of Al with respect to all Fe) was added, and an oxidation reaction was further performed until the reaction was completed. The pH at the end of the reaction was 7.63.

The obtained slurry containing goethite particles was separated by filtration using a press filter, washed with ammonia water adjusted to pH = 10.5 using ammonia, and then further washed with ion-exchanged water. And made it into a press cake.

The spindle-shaped goethite particles obtained by drying and pulverizing a part of the cake by a conventional method have an average major axis diameter of 0.11 μm, an average minor axis diameter of 0.019 μm, and an axial ratio of 5 μm. 0.8, a size distribution (standard deviation / average major axis diameter) of 0.16, a BET specific surface area of 192 m ² / g, and a Co content of 19.8 atomic% based on the total Fe of the particles as a whole;
The Al content was 8 atomic% based on the total Fe.

<Production of Spindle-Shaped Hematite Particle Powder> After the obtained press cake of the spindle-shaped goethite particle powder is sufficiently dispersed in water, an yttrium nitrate aqueous solution (total Fe
) And an aqueous solution of cobalt acetate (23 at.% Based on the total Fe) were added and stirred sufficiently. Then, while stirring, an aqueous solution of ammonium bicarbonate was added to adjust the pH of the aqueous solution to 7.2, and then filtered and washed with a filter press to obtain a press cake. The obtained press cake was extruded with a molding plate having a hole diameter of 3 mm using an extruder and granulated, and then dried at 120 ° C. to obtain a spindle-shaped goethite particle powder coated with a Y compound and a Co compound. A granulated product was obtained. The content of Co in the obtained spindle-shaped goethite particles was 37 atomic% based on the total Fe,
Is 8 atomic% based on the total Fe, and the Y content is
11 atomic% with respect to e

The granules of the spindle-shaped goethite particles coated with the Y and Co compounds were dehydrated in air at 300 ° C.
Thereafter, the mixture was heated and dehydrated at 600 ° C. in the same atmosphere to obtain a granulated product of spindle-shaped hematite particles.

<Production of Spindle-Shaped Alloy Magnetic Particle Powder> Next, 100 g (average diameter: 2.6 mm) of the obtained granulated spindle-shaped hematite particle powder was put into a batch-type fixed bed reduction apparatus having an inner diameter of 72 mm. After raising the bed height to 5.5 cm, the nitrogen gas was heated to 400 ° C. while flowing at a gas superficial velocity of 50 cm / s, and then switched to hydrogen gas and passed at a gas superficial velocity of 50 cm / s. While 400
The mixture was heated and reduced at ℃ until the exhaust gas dew point reached -30 ℃ to obtain spindle-shaped alloy magnetic particles (first step).

Thereafter, the gas was switched again to nitrogen gas and the temperature was changed to 80 ° C.
Then, the product temperature is maintained at 80 ° C., and then air is mixed to gradually increase the oxygen concentration to 0.35 vol% until the product temperature becomes [holding temperature + 1] ° C. (maximum product temperature 140 ° C.).
(C, treatment time: 2 hours) A surface oxidation treatment was performed to form a surface oxidation layer on the particle surface (second step).

After the completion of the second step, the saturation magnetization value of the spindle-shaped alloy magnetic particles is 108.1 Am ^{2 /} kg (108.1 e).
mu / g). Next, under an inert gas atmosphere,
The temperature was raised to 0 ° C., and the gas was switched to hydrogen gas with a superficial gas velocity of 60 cm / s, and heat reduction was performed again until the exhaust gas dew point reached −30 ° C. (third step).

Thereafter, the gas was switched again to nitrogen gas and the temperature was changed to 50 ° C.
Until the product temperature is maintained at 50 ° C. and then 6 g of steam
/ M ³ and air, and gradually increase the oxygen concentration to 0.35 vol% until the product temperature becomes [holding temperature + 1] ° C. (maximum product temperature 110 ° C., processing time 1.25 hours) Oxidation treatment was performed to form a stable surface oxide layer on the particle surface to obtain a molded product of spindle-shaped alloy magnetic particles (fourth step).

The obtained spindle-shaped alloy magnetic particles had an average major axis diameter of 0.073 μm, an average minor axis diameter of 0.017 μm,
It has an average particle volume of 0.166 × 10E-4 μm ³ , a BET specific surface area of 61.3 m ² / g, a crystallite size D ₁₁₀ of 134 °, a spindle shape, a uniform particle size, and no dendritic particles. Was. Further, the Co content in the particles was 37 atomic% based on the total Fe, the Al content was 8 atomic% based on the total Fe, and the Y content was 11 atomic%.

The magnetic properties of the spindle-shaped alloy magnetic particles are as follows. The coercive force Hc is 187.1 kA / m (2351 O / m).
e), the saturation magnetization value σs is 130.0 Am ² / kg (13
0.0 emu / g) and squareness ratio (σr / σs) of 0.54
3. The oxidation stability Δσs of the saturation magnetization value is 7.
5% (measured value -7.5%), was a true density of 5.8 g / cm ^3. The rotation hysteresis integral value Rh is 0.7
9. Anisotropic magnetic field Hk is 536 kA / m (6730 Oe)
Met.

The activation volume Vact of the spindle-shaped alloy magnetic particles was 0.043 × E-4 μm ³ (0.04
3 × 10 ⁻⁴ μm ³ ).

The magnetic properties of the magnetic tape prepared using the spindle-shaped alloy magnetic particle powder obtained above are as follows.
95.4 kA / m (2456 Oe), squareness ratio (Br / B
m) is 0.876, the degree of orientation OR is 2.81, the SFD is 0.351, the surface roughness Ra is 3.3 nm, and the oxidation stability Δ
Bm was 3.8% (actually measured value -3.8%) as an absolute value.

The electromagnetic conversion characteristics of the obtained magnetic tape were such that the output level at 10 kHz was +2.8 dB and the C / N level was +5.7 dB. Further, the waveform of the reproduced signal at 10 kHz was sharp, and the half width of the reproduced signal was smaller than that of Comparative Example 1.

[0143]

The most important point in the present invention is that Fe and Co
By specifying the crystallite size and activation volume of the spindle-shaped alloy magnetic particle powder containing the magnetic recording medium, a magnetic recording medium with reduced noise can be obtained.

In the present invention, in the above production method,
The activation volume and the crystallite size are controlled to be small by the reduction and surface oxidation in the first and second steps.
The reduction and surface oxidation of the process minimizes the growth of the activation volume and crystallite size, while maintaining a small crystallite size and activation volume by forming a dense surface oxide layer, and The present inventor estimates that a high coercive force and a small rotational hysteresis integrated value have all been achieved.

In the present invention, the activation volume and the crystallite size can be controlled to be small, so that noise can be reduced. Further, since the rotation hysteresis integral value is small, the width of magnetization reversal is small, and the magnetization reversal mode can be approximated to simultaneous rotation. Furthermore, since the particles are fine, and have a high coercive force and a large anisotropic magnetic field, a high output can be achieved.

The spindle-shaped alloy magnetic particles according to the present invention comprise:
Since the above characteristics are satisfied, the magnetic recording medium using the spindle-shaped alloy magnetic particles according to the present invention has excellent output characteristics in a short wavelength region, noise is significantly reduced, and the width of magnetization reversal is reduced. Can be. In addition, the spindle-shaped alloy magnetic particle powder obtained by the production method has no sintering between particles and can form a dense surface oxide layer,
The magnetic recording medium using the alloy magnetic particle powder has excellent surface smoothness and long-term storage stability because of its excellent dispersibility and oxidation stability.

[0147]

Next, examples and comparative examples will be described.

A goethite particle powder shown in Table 1 was prepared.
Hematite particle powder shown in Table 2 was obtained using the goethite particle powder.

Goethite particles 1 and hematite particles 1;
Spindle-shaped goethite particles and spindle-shaped hematite particles were obtained in the same manner as in the embodiment of the invention except that the number of revolutions of the stirrer, the aging time, the amount of air flow, and the amount of the Y compound added were changed.

Goethite particles 2 and hematite particles 2 <Preparation of spindle-shaped goethite particles powder>
5 mol and 20 mol of an aqueous sodium hydroxide solution (sodium hydroxide is 28.30 in terms of a prescribed conversion with respect to the mixed alkali).
This corresponds to 6 mol%. ) Containing mixed alkaline aqueous solution 3
0 l is charged into the bubble column, and the temperature is adjusted to 47 ° C. while passing nitrogen gas at a flow rate of 50 l / min. Next, 20 l of an aqueous ferrous sulfate solution containing 20 mol as Fe ²⁺ (a mixed alkali aqueous solution with respect to ferrous sulfate corresponds to 1.75 equivalents in terms of a prescribed conversion) was charged into a bubble column, and aged for 30 minutes. 4 l of an aqueous solution of cobalt sulfate containing 4.0 mol of Co ²⁺ (corresponding to 20 atom% in terms of Co with respect to the total Fe) was added, and the mixture was aged for 4 hours and 30 minutes, and then air was blown at a flow rate of 90 l / min. , 40 of all Fe ²⁺
The reaction was run until the% oxidized.

Next, 1 liter of an aqueous solution of aluminum sulfate containing 2.4 mol of Al ³⁺ (12% in terms of Al with respect to all Fe)
It corresponds to atomic%. ) To perform the oxidation reaction,
The cake was washed with deionized water to obtain a press cake.

A spindle-shaped goethite particle powder obtained by drying and pulverizing a part of the cake by a conventional method has an average major axis diameter of 0.109 μm and an average minor axis diameter of 0.0160 μm.
m, the axial ratio is 7.0, the size distribution (standard deviation / average major axis diameter) is 0.19, the BET specific surface area value is 181 m ² / g,
The Co content of the whole particles was 20.0 atomic% based on the total Fe, and the Al content was 12 atomic% based on the total Fe (goethite particle powder 2).

<Production of Spindle-Shaped Hematite Particle Powder> Next, the obtained press cake of spindle-shaped goethite particle powder was sufficiently dispersed in water, and then an aqueous yttrium nitrate solution (8 atomic% based on the total Fe) and sulfuric acid were added. An aqueous cobalt solution (8 atomic% based on the total Fe) was added and stirred sufficiently. Then, while stirring, an aqueous solution of sodium carbonate was added to adjust the pH of the aqueous solution to 9.5, and then filtered and washed with a filter press to obtain a press cake. The obtained press cake was extruded with a molding plate having a hole diameter of 3 mm using an extruder, and then dried at 120 ° C. to obtain a Y compound and Co.
A molded product of spindle-shaped goethite particles coated with the compound was obtained. Co in the obtained spindle-shaped goethite particle powder
Was 28 atomic% based on the total Fe, the Al content was 12 atomic% based on the total Fe, and the Y content was 8 atomic% based on the total Fe.

The molded product of the spindle-shaped goethite particles coated with the Y and Co compounds was dehydrated in air at 300 ° C.
Thereafter, the mixture was heated and dehydrated at 600 ° C. in the same atmosphere to obtain a molded product of spindle-shaped hematite particles.

In the obtained spindle-shaped hematite particles, the content of Co in the particles was 28 atomic% based on the total Fe,
The content of 1 was 12 atomic% with respect to the total Fe, and the content of Y was 8 atomic% with respect to the total Fe (hematite particle powder 2).

Tables 1 and 2 show various properties of the obtained goethite particle powder and hematite particle powder.

Goethite particles 3 and hematite particles 3;
Addition time and amount of Co compound, air ventilation, Al
Spindle-shaped hematite particles were obtained in the same manner as the goethite particles 2 and the hematite particles 2 except that the amount of the compound added was changed.

Tables 1 and 2 show various properties of the obtained goethite particle powder and hematite particle powder.

Goethite particles 4 and 5 and hematite particles 4 and 5: The above-mentioned invention was the same except that the addition time and amount of the Co compound, the number of rotations of the stirrer, the aging time, the air flow rate, and the addition amount of the Y compound were changed. Goethite particle powder and hematite particle powder were obtained in the same manner as in the embodiment.

The properties of the obtained goethite particle powder and hematite particle powder are shown in Tables 1 and 2.

[0161]

[Table 1]

[0162]

[Table 2]

Examples 1 to 3 and Comparative Examples 1 and 2 Spindle-shaped alloy magnetic particles were obtained in the same manner as in the embodiment of the invention except that the types of starting materials and the respective production conditions were variously changed. .

The production conditions at this time are shown in Table 3, and various properties of the obtained spindle-shaped alloy magnetic particles are shown in Tables 4 and 5.

[0165]

[Table 3]

[0166]

[Table 4]

[0167]

[Table 5]

Production of Magnetic Tape Using the spindle-shaped alloy magnetic particles shown in Tables 4 and 5, magnetic tapes were obtained in the same manner as in the embodiment of the invention. Table 6 shows properties and electromagnetic conversion properties of the obtained magnetic tape.

[0169] Magnetic tape of Example 3: Magnetic tape having a non-magnetic underlayer; magnetic paint was prepared in the same manner as in the above embodiment of the present invention. The non-magnetic paint for the non-magnetic underlayer was formed into a paint by the following composition and method, and the magnetic paint and the non-magnetic paint were applied as follows to prepare a magnetic tape. Coating composition: 100 parts by weight of nonmagnetic acicular hematite powder (average major axis diameter: 0.16 μm, average minor axis diameter: 0.026 μm, axial ratio: 6.2, BET: 49.1 m ² / g, Al content <Binder> 7.5 parts by weight of vinyl chloride copolymer resin (trade name: MR104 Nippon Zeon Co., Ltd.) 7.5 parts by weight of polyurethane resin (trade name: UR-8200 Toyobo Co., Ltd.) <Lubricant> 2.5 parts by weight of myristic acid 2.5 parts by weight of butyl stearate <Curing agent> 5 parts by weight of isocyanate-based curing agent (trade name: E-31 Takeda Pharmaceutical Co., Ltd.) <Solvent> 93 parts by weight of methyl ethyl ketone Toluene 55 parts by weight Cyclohexanone 36 parts by weight

A solvent was added to the hematite particle powder and the vinyl chloride copolymer resin, mixed, kneaded with a pressure kneader, and then diluted by adding a solvent. Further, a urethane-based copolymer resin was added and dispersed in a sand mill, and then a lubricant and a solvent were added to adjust to an appropriate solid content, and the mixture was filtered with a filter. Then, a hardening agent was added while stirring the coating before application to prepare a non-magnetic coating.

Coating method: The magnetic paint and the non-magnetic paint were dried on a polyethylene terephthalate film having a thickness of 7 μm by 0.15 μm each when the magnetic layer thickness and the non-magnetic layer thickness were dried.
m and 1.1 μm were simultaneously applied, subjected to an orientation treatment using a solenoid magnet, dried, and subjected to surface smoothing and curing treatment using a calender. Subsequently, a paint for a back coat consisting of carbon black, a vinyl chloride-based copolymer resin, and a polyurethane-based resin was applied to the surface opposite to the magnetic layer and the nonmagnetic layer, and dried to form a back coat layer. Thereafter, the tape was slit into a width of 8 mm to form a magnetic tape.

[0172]

[Table 6]

[0173]

The spindle-shaped alloy magnetic particles according to the present invention have a small major axis diameter, an activation volume and a small crystallite size, satisfy high coercive force and excellent oxidation stability, and have a small integral value of rotational hysteresis. Therefore, a high-density magnetic recording medium suitable for high output and low noise can be obtained.

Since the magnetic recording medium according to the present invention uses the spindle-shaped alloy magnetic particle powder according to the present invention, it is suitable as a high density recording, high output and low noise digital magnetic recording medium.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 5/714 H01F 1/06 H (72) Inventor Akinori Yamamoto 1-4-1 Meijishinkai Toda Kogyo, Otake City, Hiroshima Prefecture Inside the Otake Creative Center Co., Ltd. (72) Inventor Yasutaka Ota 1-1-1, Shinoki, Onoda-shi, Onoguchi-shi, Yamaguchi F-term in the Onoda Plant of Toda Kogyo Co., Ltd. 4K018 AA10 AA24 AA25 BA04 BA13 BD02 5D006 BA02 BA04 BA08 5E040 AA11 AA14 CA06 HB17 NN06 NN12

Claims (4)

[Claims] 1. An average major axis diameter (L) containing 20 to 50 atomic% of cobalt in terms of Co with respect to all Fe is 0. 1
A spindle-shaped alloy magnetic particle powder mainly composed of Fe and Co having a coercive force value of 159.2 to 0.10 μm, wherein the spindle-shaped alloy magnetic particle powder mainly composed of Fe and Co has a coercivity value of 159.2 to 159.2 μm.
238.7 kA / m (2000 to 3000 Oe), a crystallite size of 100 to 160 °, and an activation volume (Vact) of 0.01 to 0.07E-4 μm ^3. Spindle-shaped alloy magnetic particle powder for recording. 2. An average major axis diameter (L) containing 20 to 50 atomic% of cobalt in terms of Co with respect to all Fe is 0.
A spindle-shaped alloy magnetic particle powder mainly composed of Fe and Co having a coercive force value of 159.2 to 0.10 μm, wherein the spindle-shaped alloy magnetic particle powder mainly composed of Fe and Co has a coercivity value of 159.2 to 159.2 μm.
238.7 kA / m (2000-3000 Oe), crystallite size of 100-160 °, activation volume (Vact) of 0.01-0.07E-4 μm ³ , and rotation hysteresis integral ( Rh) a spindle-shaped alloy magnetic particle powder having a value of 1.0 or less. 3. An average major axis diameter (L) containing 20 to 50 atomic% of cobalt in terms of Co with respect to all Fe is 0.
A spindle-shaped alloy magnetic particle powder mainly composed of Fe and Co having a coercive force value of 159.2 to 0.10 μm, wherein the spindle-shaped alloy magnetic particle powder mainly composed of Fe and Co has a coercivity value of 159.2 to 159.2 μm.
238.7 kA / m (2000-3000 Oe), a saturation magnetization value of 100-150 Am ² / kg, a crystallite size of 100-160 °, and an activation volume (Vact) of 0.01- A spindle-shaped alloy magnetic particle powder having a rotational hysteresis integral (Rh) value of not more than 1.0, which is 0.07E-4 μm ³ . 4. The method according to claim 1, wherein the non-magnetic support is provided on a non-magnetic support.
A magnetic recording medium comprising a magnetic layer mainly composed of the spindle-shaped alloy magnetic particle powder according to any one of claims 1 to 4 and a binder.