JP3425458B2 - Method for producing hematite particles - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an improvement in a method for producing monodisperse spindle type hematite particles having a very small particle size distribution, which is useful as a pigment, a paint, a catalyst, a raw material of ferrite, a raw material of iron oxide for magnetic recording and the like. The present invention relates to a magnetic recording medium for high density recording, which uses a ferromagnetic powder for magnetic recording made of this material.

[0002]

2. Description of the Related Art In magnetic recording technology, a medium can be repeatedly used, signals can be easily digitized, and a system can be constructed by combining with peripheral equipment.
Since it has excellent features not found in other recording methods, such as the ability to easily modify signals,
It has been widely used in various fields including computer applications.

In order to meet the demands for downsizing equipment, improving the quality of recording / reproducing signals, lengthening the recording time, increasing the recording capacity, etc., the recording density of the recording medium should be further improved. Has always been desired.

For example, in audio and video applications, in order to cope with the practical use of a digital recording method for improving the sound quality and image quality and the development of a recording method compatible with high-definition TV, it is more important than the conventional system. A magnetic recording medium capable of recording and reproducing a short wavelength signal has been required.

Further, even for a floppy disk having a magnetic layer on a flexible non-magnetic support which is an external storage medium of a personal computer, the spread of personal computers in recent years, the sophistication of application software, and the increase in processing information have been increased. Due to trends, there has been a strong demand for higher capacity of 10 Mbytes or more.

The magnetic recording medium is used in the form of a tape, a disk, a card or the like according to the application by forming a magnetic layer on a non-magnetic support. In the magnetic layer, a coating liquid in which ferromagnetic powder is dispersed is applied and dried on a non-magnetic support, so-called coating type magnetic layer mainly composed of ferromagnetic powder and binder resin, and vapor deposition or sputtering. There is a so-called metal thin film type magnetic layer composed of a ferromagnetic metal thin film obtained by vacuum film formation on a non-magnetic support by the vacuum film formation method.

From the viewpoint of recording density, the latter metal thin film type magnetic layer is excellent, and has been studied for practical use for a long time, and has been put into practical use for 8 mm video applications. The system is about to be used.

However, the metal thin film type magnetic recording medium has problems in characteristics such as durability, running property and corrosion resistance.
The original excellent characteristics are not fully utilized to deal with the problem. Further, the manufacturing cost is high and there is a problem in economic efficiency. On the other hand, a so-called coating type magnetic recording medium having a magnetic layer mainly composed of a ferromagnetic powder and a binder resin is superior to the metal thin film type in terms of running property, durability and corrosion resistance, and has long been used. Although it has been put to practical use for various purposes, with respect to the electromagnetic conversion characteristics, many efforts have been made to improve the recording density, not to the metal thin film type, but there has been a limit.

From the viewpoint of improving the magnetic characteristics of the magnetic layer, improving the dispersibility of the ferromagnetic powder, and improving the surface property of the magnetic layer for the purpose of achieving high density recording of the coating type magnetic recording medium. Have studied and proposed various methods.

For example, a method of using a ferromagnetic metal powder or a hexagonal ferrite as a ferromagnetic powder in order to improve magnetic properties is disclosed in JP-A-58-122623 and JP-A-61-7.
4137, Japanese Patent Publication No. 62-49656, Japanese Patent Publication No. 60-50323, US462953, U
S46666770, US4543198, etc. are disclosed.

Further, in order to enhance the dispersibility of the ferromagnetic powder, various surface active agents (for example, JP-A-52-15660).
6, JP-A-53-15803, JP-A-53
It is disclosed in Japanese Patent Laid-Open No. 116114. ) Or various reactive coupling agents (see, for example, JP-A-4
9-59608, JP-A-56-58135, JP-B-62-28489 and the like. ) Is proposed.

Further, in order to improve the surface property of the magnetic layer,
A method (for example, disclosed in Japanese Patent Publication No. 60-44725) of improving the surface forming treatment method of the magnetic layer after coating and drying has been proposed.

The above-mentioned ferromagnetic metal powder and hexagonal ferrite are excellent as ferromagnetic powders for high density recording media, but in reality, the electromagnetic conversion characteristics of metal thin film type magnetic recording media are inferior. . In particular, hexagonal ferrite has a problem that its saturation magnetization is small and the magnetic flux density of the magnetic layer cannot be increased. Further, its dispersibility is poor, and it is difficult to obtain a magnetic layer having excellent surface properties.

As a method for reducing the self-demagnetization loss and recording demagnetization loss of the magnetic layer to improve the recording density, the magnetic layer is made as thin as a ferromagnetic metal thin film type magnetic recording medium, and its magnetic property is reduced. A magnetic recording medium provided with a relatively thick non-magnetic layer as a lower layer in order to secure the flatness and strength of the layer is disclosed in Japanese Patent Laid-Open No.
7-198536, JP 62-154225, JP 63-187428, JP 4-3.
No. 25915, Japanese Patent Application Laid-Open No. 4-325916, Japanese Patent Application Laid-Open No. 4-325917, etc., the electromagnetic conversion characteristics are similar to those of a ferromagnetic metal thin film type magnetic recording medium with excellent output particularly in a high range. However, further attempts to improve the electromagnetic conversion characteristics have been limited due to the following problems related to the particle shape of the ferromagnetic powder.

That is, when the magnetic characteristics of the coating type medium using the metal thin film type and the fine particle metal (ferromagnetic metal) powder are compared, the SFD (Swit) of the coating type medium using the metal powder is compared.
It has been recently revealed that the ching field (Destination Field) has a large numerical value and is inferior in characteristics to metal thin films, while Nakamura et al. conducted simulations to improve the electromagnetic conversion characteristics of metal thin film media. It has been pointed out that the short wavelength output is improved by improving the distribution of the magnetic field (Journal of Applied Magnetics, Vol. 115, 155-158 (199).
1)). The anisotropic magnetic field distribution has a strong correlation with the SFD, and if the anisotropic magnetic field distribution is large, the SFD (Hc distribution) will be large.

It is known that the ferromagnetic metal powder has a large effect on shape anisotropy with respect to Hc (coercive force), and the wider the particle size distribution of the ferromagnetic powder is, the more H is increased.
It is known that the distribution of c also becomes wider. For this reason, goethite, which is a needle-shaped particle that is a raw material of the ferromagnetic metal powder,
Attempts to reduce the particle size distribution of rapid crosite, hematite, etc., are constantly being made. When the fine ferromagnetic metal powder is used to reduce the roughness of the surface of the tape and improve the short wavelength output, variations in the major axis length and the minor axis length have a great influence on the Hc distribution.

As described above, in order to further improve the characteristics and improve the recording density of the conventional magnetic recording medium, the ferromagnetic metal powder should have a small particle size and the particle size and shape should be as uniform as possible. Is desired. Particles that are well separated and have a very small particle size distribution are called monodisperse particles. Studies are underway to synthesize monodisperse particles to study particle size and catalytic performance and particle-particle interactions (eg, surface,
29,978 (1991), 23,177 (198).
4)). The method for synthesizing monodisperse spindle-type hematite is
M. Ozaki et al. Colloid Inte
rface Sci. 102 146-151 (198)
4). As a first method, they use 0.
02 mol ferric chloride and 1.0 × 10 ^{−4 to} 4.0 × 10
A liquid containing ⁴ mol of NaH ₂ PO ₄ or NaH ₂ PO ₂ was kept at 100 ± 2 ° C. for 2 days to give a particle length of 0.1
Particles with a needle ratio of 2 to 0.55 μm and a needle ratio of 2 to 5.5 are synthesized. As a second method, sodium hydroxide is added to ferric nitrate to form ferric hydroxide, and washing with distilled water is repeated,
5 to 20 in 200 cm ^{3 of} 0.02 mol of ferric hydroxide
0.1 of 1N HCl and 0.5～2.5Cm ³ of cm ³
M NaH ₂ PO ₄ was added, and the whole was diluted with distilled water to 500c.
m ³ and hold at 100 ± 2 ℃ for 2 days, particle length 0.2
Particles having a particle size of 7 to 0.33 μm and an acicular ratio of 3 to 6 are synthesized. In the first method, the second chloride was added to increase the yield.
It has been reported that if the concentrations of iron and NaH ₂ PO ₄ or NaH ₂ PO ₂ are increased, βFeOOH is mixed and a single-phase monodisperse spindle hematite cannot be obtained. In the second method, when ferric nitrate is increased and sodium hydroxide is added to synthesize ferric hydroxide in order to increase the yield, gelation often occurs. Therefore, washing with water cannot be sufficiently performed, and it becomes difficult to obtain a single-phase hematite due to the influence of remaining impurities.

M. Ozaki et al. Reduced the obtained monodisperse spindle hematite with hydrogen at 340 to 400 ° C. for 1 to 3 hours and then flowing air to oxidize at 240 ° C. for 1 to 2 hours to obtain γFe ₂ O
_The result set to ₃ is J. Colloid Interfac
e Sci. 107 199-203 (1985). In addition, the inventors of the present invention previously found that the extremely rich Fe (O
H) ₃ gel (about 1 mol / liter) is used as a starting material, and an intermediate product βFeOOH is used to generate a pseudo cube (average particle size of about 2).
(μm) monodisperse spindle type hematite particles were synthesized (J.
Colloid Interface Sci. 15
2, 587 (1992)).

M. According to the method of Ozaki et al., ΓFe ₂ O ₃ is obtained from monodisperse spindle hematite. However, since the concentration of the reaction solution for producing monodisperse spindle hematite is low, the yield of monodisperse spindle hematite is small and it is economically large-scale. Can not be synthesized. J. Colloid Interf
ace Sci. According to the method of 152 587 (1992), spindle-type hematite cannot be obtained and fine particles cannot be obtained.

The inventors of the present invention have found that a method for producing monodisperse spindle type hematite particles by converting ferric hydroxide in the presence of hematite fine particle nuclei crystals and SO ₄ ²⁻ or phosphate radical ion is produced. It has been disclosed earlier. Further, it was found that the magnetic powder and the magnetic recording medium using the monodisperse spindle type hematite thus obtained as a starting material have excellent electromagnetic conversion characteristics (Japanese Patent Application Nos. 5-103753 and 5-5).
No. 158161).

[0021] However, when enlarging the aim production scale industrialization, is difficult to maintain the uniformity of the particle shape when heat-treating the f hematite particles for crystallite size monodispersed spindle-shaped hematite particles obtained are small It was found that the obtained ferromagnetic powder was inferior in Hc and Hc distribution.

Even when the production scale is expanded aiming at industrialization, fine, monodisperse spindle-type hematite particles that are not easily affected by the production scale are produced, and this is used as a ferromagnetic powder. It is desired to obtain a high recording density magnetic recording medium which is excellent in practical properties such as durability and storability and is economical, has good electromagnetic conversion properties, and can be applied even if it is a coating type and is comparable to a metal thin film type magnetic recording medium. ing.

[0023]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. Even when the production scale is expanded for industrialization, the control of the crystallite size is less likely to be affected by the production scale. And a method for industrially producing shape-controlled monodisperse spindle hematite particles, particularly monodisperse spindle hematite particles having an average particle size of 1 μm or less and an acicular ratio of 2 to 8, A dispersion spindle type hematite particle is used as a ferromagnetic powder, and a magnetic recording medium suitable for high density recording using the ferromagnetic powder is provided.

[0024]

The present inventors have found that it is difficult to maintain the uniformity of particle shape when heat treating spindle-type hematite on an industrial production scale.
The cause of inferior c and Hc distribution was earnestly studied. As a result, they have found that the crystallite size of hematite particles varies greatly depending on the types of anions that coexist in ferric hydroxide and nuclei. Specifically, the salt of ferric partially neutralized, as an additive to further anion hematite ultrafine particles as seed crystals into the ferric gel suspension hydroxide state ferric ion free coexist It was found that the crystallite size of hematite obtained when the sulfate ion was added was extremely small, 250 angstrom.

As a result of paying attention to the factors which control the crystallite size of hematite, when hematite is grown by adding a nuclear crystal to hydrolyze it and the coexisting anions are strongly adsorbed to hematite, the crystal of hematite is strong. It was found that the child size was small, and the present invention was reached. As a result of changing the adsorption strength to hematite by changing the coexisting anions at the time of hydrolysis and measuring the crystallite size of the generated hematite, it was difficult to increase the crystallite size because the sulfate ion had a strong adsorption power. On the contrary, it was found that the crystallites could be enlarged if the anions such as nitrate ion, perchlorate ion and phosphate root ion were present in the raw material. In other words, the present invention has been found that the crystallite size can be controlled by the coexisting anion when hydrolyzing.

[0026] That object of the present invention, in the presence of phosphate root ions ferric hydroxide generated from ferric salt comprising at least one of ferric nitrate and ferric perchlorate monodisperse spinning production method ,, wherein monodisperse spindle-shaped hematite particles to be deposited on nuclei crystal hematite fine particles
Following the method for producing the cone-type hematite particles, the obtained monodisperse spindle-type hematite particles are reduced to magnetite, and the magnetite is oxidized to produce FeO _x (1.33 <x
≦ 1.5), the method for producing a ferromagnetic iron oxide, and the production of monodisperse spindle hematite particles as described
Following the method, by reducing the resulting monodispersed spindle-shaped hematite particles after a magnetite, and more can be achieved in the manufacture how the ferromagnetic metal powder which comprises reducing the magnetite.

The present invention provides at least a specific anion for controlling the crystallite size and shape of monodisperse spindle-type hematite particles, ie, the ferric iron-derived anion (ie, the anion derived from ferric hydroxide used to form ferric hydroxide). , Nitrate and / or perchlorate) and phosphate roots , and optionally
The present invention is characterized by using a shape-controlling anion composed of more chlorine ions, and converts ferric hydroxide into monodisperse spindle-type hematite in the coexistence of nucleation crystals composed of hematite fine particles.

That is, the present invention controls the crystallite size and the shape and size of the hematite particles produced by selecting the type of shape-controlling anion to prepare the desired monodisperse spindle hematite particles. But you can
The control mechanism is explained by the difference in the adsorption strength to the grown hematite particles as described above, and it is considered that the crystallite size is reduced when an anion having a strong adsorption strength is used. Therefore, in the present invention, monodisperse spindle hematite particles having a desired crystallite size can be prepared by selecting or combining shape-controlling anions having a predetermined adsorption strength.

As a result, the present invention can synthesize monodisperse spindle type hematite particles having a large crystallite size,
It is possible to maintain the particle shape even by heat treatment on an industrial scale when making a ferromagnetic powder. By using the ferromagnetic powder thus obtained in the magnetic layer of a magnetic recording medium, electromagnetic conversion A high density magnetic recording medium having excellent characteristics can be provided.

In the present invention, the timing of the mutual contact of ferric hydroxide, the nuclei crystal, and the shape controlling anion is not particularly limited, and any combination can be selected. Generally, a ferric iron salt containing nitrate ions and / or perchlorate ions is added with an alkali (preferably partially neutralized) to form a secondary hydroxide.
An example can be given in which a nucleus crystal dispersion is added to and mixed with a system in which a gel suspension of iron is produced, and then phosphate radical ions and , if desired, chloride ions are added. The ferric hydroxide produced in the above system may be washed with water to intentionally remove nitrate ions and / or perchlorate ions, or a treatment for changing the anion concentration may be provided.

In the present invention, as the nitrate ion and / or the perchlorate ion, only those produced when the ferric salt is hydrolyzed with an alkali to produce ferric hydroxide may be used. However, it may be additionally added in the form of another salt. In addition, phosphate ion ,
Chloride ions, if desired, are also commonly used in the form of salts, such as alkali metal salts. The salt that releases these shape control anions is also referred to as a shape control agent.

The alkali for producing ferric hydroxide is not particularly limited, but alkali metal hydroxide, especially sodium hydroxide is preferable. The ferric salt is preferably partially neutralized with an alkali, and the alkali is 2.4 to 3 mol, preferably 2.8, per mol of the ferric salt.
Used in the range of up to 2.95 mol. The phosphate root ion is
Usually refers to the form of PO ₄ ^3- , but it is HPO ₄ ^2- , H ₂ PO
₄ ^- including such ^- but well, also ^{_{HPO 3 2-, H 2 PO 2}} .

In the present invention, the phosphate ion concentration is 0.
001 to 0.01 mol / liter (hereinafter referred to as M),
The range is preferably 0.002 to 0.01M, and particularly preferably 0.03 to 0.008M. In the present invention, the ferric hydroxide concentration is 0.05 to 2M, preferably 0.07 to 1.5M, and particularly preferably 0.08 to 1.3.
It is the range of M.

For example, the concentration range of ferric hydroxide gel obtained by partially neutralizing ferric nitrate and ferric perchlorate with alkali is
If the viscosity of the gel, which is considered to be limited in the solubility of the iron salt, is too high, stirring becomes difficult. A uniform monodisperse spindle type hematite can be obtained when the concentration is low, but the lower limit of the concentration is determined from the economical point of view because the yield decreases as the concentration decreases. The amount of alkali added such as NaOH when preparing ferric hydroxide gel is Fe ³⁺
ΒFeO, which is an intermediate product, if it is not less than the equivalent of the ion
OH is not obtained and the hematite produced is not monodispersed.

The nuclei crystal used in the present invention is not particularly limited as long as it consists of hematite fine particles, but preferably has the following properties. The nuclear crystals are preferably obtained by converting ferric hydroxide, and have a particle size of 30 to 200Å, preferably 50 to 150Å,
It is particularly preferably 70 to 120Å, and a pseudo spheroidal shape is preferable. If the particle size is too small, the effect as nuclei is poor, and if it is too large, fine particle monodisperse spindle hematite cannot be obtained. It is effective to make the particle size distribution of nuclei uniform, and it is desirable to crush the hematite particles, which are the conversion product of ferric hydroxide, by mechanical force to remove coarse particles before use. When nucleation crystals are added to ferric hydroxide gel in which ferric nitrate and / or ferric perchlorate is partially neutralized with an alkali to cause a conversion reaction, if the reaction rate is too high, new nucleation occurs. Dispersed particles may not be obtained. It is necessary to set the temperature, pressure and time within the range where monodisperse particles can be obtained.

The monodisperse spindle-type hematite particles thus obtained are subjected to powder X-ray diffraction to calculate the crystallite size from the (110) plane using Scherrer's formula to evaluate the method of the present invention. You can The crystallite size of the hematite obtained in the present invention is in the range of about 350 to about 2000Å. In the present invention, the crystallite size can be controlled by selecting reaction conditions such as selection of the shape control anion as described above, and in order to perform heat treatment on an industrial scale, the crystallite size is 400 to It is preferably 1800 Å, more preferably 450 to 1500 Å. If the crystallite size is smaller than 350Å, the shape will be destroyed by heat treatment, and when the crystallite size is 2000Å or more, oxygen is removed from the particles by reduction, and voids are generated, which grows and deteriorates the magnetic properties, which is preferable. Absent.
The average major axis length of the hematite particles obtained by the present invention observed by a transmission electron microscope is 0.1 to 1.0 μm, preferably 0.1 to 0.6 μm, particularly preferably 0.1 to 1.0 μm.
0.5 μm, the acicular ratio is 2 to 10, preferably 2.5 to 8, and particularly preferably 3 to 7,
The variation (%) of the major axis length (standard deviation of major axis length / average major axis length) is 10% or less, preferably 8% or less, particularly preferably 5% or less.

The present inventors have found that the monodisperse spindle type hematite fine particles obtained as described above can be used to obtain a ferromagnetic powder for magnetic recording having excellent magnetic properties. In producing the ferromagnetic iron oxide powder, the obtained monodisperse spindle type hematite particles are reduced to magnetite, and then the magnetite is oxidized to produce FeO.
x (1.33 <x ≦ 1.5) can be obtained.

Here, it is effective to subject the hematite to a sintering prevention treatment before reducing or oxidizing the hematite particles. As the sintering inhibitor, silica, phosphoric acid, aluminum-
Silica or a combination thereof can be used.

The amount of the sintering inhibitor used is preferably 0.05 to 3.0% by weight, more preferably 0.1 to 1.5% by weight, based on hematite. If the amount of the sintering inhibitor is too small, the shape retention effect during reduction and oxidation will be poor, and if it is too large, the saturation magnetization will be small and the magnetic properties of the obtained ferromagnetic powder will be deteriorated. In the present invention, the ferromagnetic powder having good magnetic properties is obtained as described above because the monodisperse spindle hematite particles obtained in the present invention have a large crystallite size, and thus the obtained monodisperse spindle hematite is obtained. By reducing particles in hydrogen to form magnetite, and simply oxidizing or reducing the particles, a ferromagnetic powder having excellent magnetic properties such as Hc and saturation magnetization (σ _S ) can be obtained. There is an advantage in that it is not necessary to increase the crystallite size by annealing the dispersed spindle type hematite particles prior to the reduction or by annealing the reduced spindle type hematite particles after the reduction. If necessary, annealing treatment may be performed after the reduction or oxidation of the hematite particles.

When annealing is performed prior to the reduction, the annealing temperature is preferably 450 to 800 ° C, more preferably 500 to 750 ° C. The annealing time is preferably about 1 to 5 hours, and it is desirable to select it in relation to the processing temperature. If the annealing is performed for a long time at a high temperature, the particle shape will change. As a method of reducing the particles, a well-known hydrogen gas reduction method, a method of using a reducing gas generated when an organic substance is thermally decomposed in an inert gas, and the like can be used. In the case of annealing after making magnetite, it is desirable to perform the treatment at a slightly lower temperature than that in the case of treating with hematite, and it is preferable to perform the treatment at 400 to 600 ° C.

After reduction, air is flowed at 200 to 300 ° C. to obtain γ.
Fe ₂ O ₃ and Fe Ox by adjusting the degree of oxidation
It can be set to (1.33 <x ≦ 1.5). As a method of adjusting the degree of oxidation, it can be adjusted by lowering the oxygen concentration in the oxidizing gas, or by setting the temperature during oxidation to 60 to 150 ° C. After making magnetic iron oxide,
Any surface treatment can be applied, for example, Co
Well-known methods can be used to deposit the compounds. These methods are described, for example, in JP-A-49-7439.
No. 9, 50-37667. Japanese Patent Publication Sho 49-49475
It is described in each publication.

FeOx (1.33 obtained by the present invention
The crystallite size of (110) by X-ray diffraction measurement of <x ≦ 1.5) is 200 to 500 Å, preferably 200 to 4
00Å, particularly preferably 250 to 350Å, and the average major axis length measured by a transmission electron microscope is 0.1 to 0.8.
μm, preferably 0.15 to 0.6 μm, particularly preferably 0.15 to 0.5 μm, and the acicular ratio is 2 to
The range is 10, preferably 2.5 to 8, and particularly preferably 3 to 7. The Hc of the FeOx is 200 to 40.
0 Oe, preferably 250 to 400 Oe, particularly preferably 300 to 400 Oe, and σ _S is 70 to 79 em.
u / g, preferably 72 to 79 emu / g, and particularly preferably 75 to 79 emu / g.

Next, in order to convert the monodisperse spindle type hematite obtained according to the present invention into a ferromagnetic metal powder, it is preferable to treat with a sintering inhibitor, and as the sintering inhibitor, Al, Si, Al-Si, B, Ca and combinations thereof can be used. The amount of the sintering inhibitor to be treated is preferably 1 to 20 atom% with respect to iron, and more preferably 3 to 15 atom%. The method for applying the sintering inhibitor is to disperse the hematite particles that have been sufficiently washed with water, add an aqueous solution of a compound containing an element used for preventing sintering, and adsorb it, or deposit on the particle surface by neutralization treatment, etc. Then, it is preferable to wash with water to remove impurities. It is also preferable to alloy after the reduction by depositing a metal element before treatment with a sintering inhibitor in order to improve magnetic properties and weather resistance. The elements used for the deposition treatment are:
In addition to the above, Co, Ni, Mn, Cu, Sn, Cr, S
b, Nd, Y, La, Sc, Ba, Sr and the like, which may be used alone or in combination.

The amount of metal used for alloying is generally 0.1 to 30% by weight, preferably 0.5 to 30% by weight, depending on the alloyable composition region. When it becomes a non-magnetic alloy, the addition amount cannot be too large, but Co, N
The addition amount of the transition metal such as i can be changed in the range of 0.1 to 30% by weight, preferably 2 to 30% by weight. Co is a preferable additive element because it has an effect of enhancing saturation magnetization and improving weather resistance. On the other hand, Ni and Cu are elements that promote reduction and can be reduced at a low temperature and are effective in terms of shape retention effect. When the metal element is deposited, it is also an effective means to anneal it prior to the reduction in order to evenly distribute the element in the particles. The annealing temperature is 400 to 800 ° C., preferably 500.
It can be selected in the range of ˜750 ° C. for 1 to 5 hours, preferably 2 to 3 hours.

As a method of reducing the hematite particles, a well-known hydrogen gas reduction method, a method of using a reducing gas produced when an organic substance is thermally decomposed in an inert gas, and the like can be used. In the case of annealing after making magnetite, it is desirable that the treatment is carried out at a slightly lower temperature than that in the case of treating with hematite, and it is preferable to carry out the treatment at 400 to 600 ° C, preferably 400 to 550 ° C.

Pure hydrogen is used to reduce hematite to metal, and the temperature is 350 to 550 ° C., preferably 400 to 550 ° C.
Reduction is carried out at 500 ° C. for 2 to 12 hours, preferably 3 to 8 hours. The progress of the reduction can be determined by monitoring the water content in the hydrogen gas after the reduction with a dew point meter or the like. In order to use the obtained ferromagnetic metal powder as a raw material for a magnetic recording medium, it is necessary to oxidize and stabilize the surface of the obtained ferromagnetic metal powder. For this reason, after the reduction, the surface is gradually oxidized by flowing a gas whose oxygen concentration is controlled or by passing an oxygen-containing gas in an organic solvent. At this time, it is necessary to monitor the calorific value with a thermometer to prevent sudden oxidation, and it is desirable that the water content in the gas used for gradual oxidation be as low as possible. In addition, before the slow oxidation, JP-A-61-2232 is used.
It is also effective to gradually oxidize the ferromagnetic alloy powder after the treatment with the compound described in JP-A No. 7, since the saturation magnetization σ _S of the ferromagnetic alloy powder can be increased.

X of the ferromagnetic metal powder obtained by the present invention
The crystallite size of (110) by line diffraction measurement is 100.
To 250 Å, preferably 120 to 200 Å, particularly preferably 120 to 160 Å, and the average major axis length observed by a transmission electron microscope is 0.05 to 0.5 μm, preferably 0.06 to 0.25 μm, and particularly 0. 0.06 to 0.15 μm
And the acicular ratio is 2 to 10, preferably 2.5.
-8, particularly preferably 3-7. The Hc of the ferromagnetic metal powder is 1500 to 2000 Oe, preferably 1550 to 1900 Oe, and particularly preferably 165.
0 to 1900 Oe and σ _S is 115 to 160 em
u / g, preferably 120 to 155 emu / g, and particularly preferably 125 to 155 emu / g.

The ferromagnetic powder of the present invention can be used in a magnetic layer of a coating type magnetic recording medium having an arbitrary layer structure in which a ferromagnetic powder and a magnetic layer mainly containing a binder resin are provided on a non-magnetic support. You can Since the ferromagnetic powder of the present invention is used, even if the magnetic layer has a single layer, the SFD is superior to that of the conventional magnetic recording medium using the ferromagnetic metal powder. Are better.

Further, a non-magnetic layer having non-magnetic powder dispersed in a binder is provided on a non-magnetic support, and a magnetic layer having the ferromagnetic powder of the present invention dispersed in the binder is provided thereon in a dry thickness. 1μ
The structure provided below m can provide a magnetic recording medium having an increased single wavelength output and higher performance than the case of a single layer. As a method of forming two or more coating layers on a non-magnetic support, the first coating layer on the non-magnetic support (refers to the layer closest to the non-magnetic support, regardless of whether it is a magnetic layer or a non-magnetic layer). Wet-on coating of the second coating layer (usually a magnetic layer, but may be a non-magnetic layer; also referred to as the upper layer) while the lower layer is still wet.
Wet method (simultaneous multilayer coating method, JP-A-61-139)
No. 929, Japanese Patent Laid-Open No. 61-54992, and the like. ), That is, when the upper magnetic layer is formed while the first coating layer is in a wet state,
It is easy to make the upper magnetic layer thin, and coating defects can be reduced. Furthermore, it is preferable because the adhesion between the layers can be increased.

When two or more coating layers are provided in the magnetic recording medium of the present invention, it is extremely preferable to use the above-mentioned ferromagnetic powder as the uppermost layer. The reason for this is to maximize the high-density magnetic recording performance, and the content is primarily the addition of non-magnetic powder such as carbon, which is necessary for the practical characteristics of the magnetic recording medium, only to the lower layer to provide the required electrical conductivity. This is because it is possible to increase the saturation magnetic flux density per unit volume of the uppermost layer of the magnetic recording medium, which is important for short-wavelength magnetic recording. Because it can be finished. Further, the amount of relatively expensive ferromagnetic powder obtained by reducing monodisperse spindle type hematite as a material can be reduced, which is economically advantageous.

The magnetic recording medium of the present invention has a high Hc, a high SQ and a low SFD, but when the lower layer is a non-magnetic layer and the upper layer is a magnetic layer, Hc is 1500 to 2000.
Oe, preferably in the range 1600 to 1900 Oe, SQ 0.80 to 0.92, preferably 0.85.
˜0.92, SFD is 0.25-0.4
5, preferably 0.25 to 0.40, and particularly preferably 0.25 to 0.36.

The binder resin for the magnetic layer in the magnetic recording medium of the present invention may be a conventionally known thermoplastic resin, thermosetting resin, reactive resin or a mixture thereof. The thermoplastic resin has a glass transition temperature of -1.
00 to 150 ° C, number average molecular weight of 1000 to 200
000, preferably 10,000 to 100,000, and the degree of polymerization is about 50 to 1,000.

Examples of such binder resin include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, There are polymers or copolymers containing vinyl butyral, vinyl acetal, vinyl ether, etc. as constituent units, polyurethane resins, and various rubber resins.

As the thermosetting resin or the reaction type resin, a phenol resin, an epoxy resin, a polyurethane curing type resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, a silicone resin, Examples thereof include epoxy-polyamide resin, a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, and a mixture of polyurethane and polyisocyanate.

In order to obtain more excellent dispersion effect of the ferromagnetic powder and durability of the magnetic layer in the above-mentioned binder resin, COOM, SO ₃ M, OSO ₃ M, P = O (OM) is added as necessary.
₂ , OP = O (OM) ₂ , (wherein M is a hydrogen atom or an alkali metal base), OH, NR ₂ , N ⁺ R
It is preferable to use one in which at least one polar group selected from ₃ (R is a hydrocarbon group), an epoxy group, SH, CN and the like is introduced by copolymerization or an addition reaction.
The amount of such a polar group is 10 ^{-1 to} 10 ^-8 mol / g, preferably 10 ^{-2 to} 10 ^-6 mol / g.

The binder resin used in the magnetic recording medium of the present invention is in the range of 5 to 50% by weight based on the ferromagnetic powder,
It is preferably used in the range of 10 to 30% by weight. It is preferable to use a combination of these in the range of 5 to 100% by weight when using a vinyl chloride resin, 2 to 50% by weight when using a polyurethane resin, and 2 to 100% by weight of polyisocyanate.

The filling degree of the ferromagnetic powder in the magnetic layer can be calculated from the maximum saturation magnetization σ _S and the maximum magnetic flux density Bm of the used ferromagnetic powder, that is, (Bm / 4πσs),
In the present invention, the value is preferably 1.7 g / cc.
Or more, more preferably 1.9 g / cc or more, and most preferably 2.1 g / cc or more.

In the present invention, when polyurethane is used, the glass transition temperature is −50 to 100 ° C., the elongation at break is 100 to 2000%, and the stress at break is 0.05 to 10 k.
The g / cm ² and the yield point are preferably 0.05 to 10 kg / cm ² .

The polyisocyanate used in the present invention includes tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate and naphthylene.
Isocyanates such as 1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate and triphenylmethane triisocyanate, and also
Products of these isocyanates and polyalcohols, polyisocyanates produced by condensation of isocyanates, and the like can be used. Commercially available trade names of these isocyanates are Coronate L, Coronet HL, manufactured by Nippon Polyurethane Co., Ltd.
Coronate 2030, Coronet 2031, Millionaire
To MR Millionate MTL, Takeda Yakuhin, Takenet D-102, Takenet D-110N, Takenet D-
200, Takenet D-202, Sumitomo Bayer Co., Ltd., Desmodul L, Desmodule IL, Desmodule N, Desmodule HL, etc., which are used alone or by utilizing the difference in curing reactivity. You can use one or more combinations.

The magnetic layer of the magnetic recording medium of the present invention usually has various functions such as a lubricant, an abrasive, a dispersant, an antistatic agent, a dispersant, a plasticizer and a fungicide. The material to have is contained according to the purpose.

As the lubricant used in the magnetic layer of the present invention, dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxy polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy poly Siloxane (alkyl has 1 to 5 carbon atoms, alkoxy has 1 to 4 carbon atoms), phenyl polysiloxane, fluoroalkyl polysiloxane (alkyl has 1 to 5 carbon atoms)
Silicon oil such as); conductive fine powder such as graphite; inorganic powder such as molybdenum disulfide and tungsten disulfide; plastic fine powder such as polyethylene, polypropylene, polyethylene vinyl chloride copolymer, polytetrafluoroethylene; α- Olefin polymer; unsaturated aliphatic hydrocarbon that is liquid at room temperature (compound in which n-olefin double bond is bonded to terminal carbon, carbon number about 20); monobasic fatty acid having 12 to 20 carbon atoms and carbon number Fatty acid esters, fluorocarbons and the like composed of 3 to 12 monohydric alcohols can be used.

Of these, fatty acid esters are more preferable.
The alcohol used as the raw material of the fatty acid ester is ethanol, butanol, phenol, benzyl alcohol,
2-Methylbutyl alcohol, 2-hexyldecyl alcohol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, dipropylene glycol monobutyl ether, diethylene glycol monobutyl ether, monoalcohols such as s-butyl alcohol, ethylene glycol, diethylene glycol, neopentyl glycol. And polyhydric alcohols such as glycerin and sorbitan derivatives. Similarly, as fatty acids, acetic acid, propionic acid, octanoic acid, 2-ethylhexanoic acid, lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, arachidic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, palmitoleic acid. And aliphatic carboxylic acids or mixtures thereof.

Specific examples of the fatty acid ester include butyl stearate, s-butyl stearate, isopropyl stearate, butyl oleate, amyl stearate, 3-methylbutyl stearate, 2-ethylhexyl stearate, 2-hexyldecyl. Stearate, butyl palmitate, 2-ethylhexyl myristate,
Mixture of butyl stearate and butyl palmitate, butoxyethyl stearate, 2-butoxy-1-propyl stearate, dipropylene glycol monobutyl ether acylated with stearic acid, diethylene glycol dipalmitate, hexamethylene diol myristic acid And various ester compounds such as glycerin oleate and the like.

Further, in order to reduce the hydrolysis of fatty acid ester that often occurs when the magnetic recording medium is used under high humidity, branched / straight chain, cis / trans and other isomeric structures of raw material fatty acid and alcohol, and branched position Is made. These lubricants are added in the range of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

The following compounds may be used as the lubricant. That is, silicone oil, graphite, molybdenum disulfide, boron nitride, fluorinated graphite, fluoroalcohol, polyolefin, polyglycol, alkyl phosphate, tungsten disulfide and the like.

As the abrasive used in the magnetic layer of the present invention, generally used materials are fused alumina, silicon carbide,
Chromium oxide (Cr ₂ O ₃ ), corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite) are used.
These abrasives have a Mohs hardness of 6 or more. Specific examples are AKP-10 and AKP-1 manufactured by Sumitomo Chemical Co., Ltd.
2, AKP-15, 20, AKP-30, AKP-5
0, AKP-1520, AKP-1500, HIT-5
0, HIT60A, HIT-100, Nippon Kagaku Kogyo KK, G5, G7, S-1, chromium oxide K, Uemura Kogyo UB40B, Fujimi Abrasives WA8000, WA10.
000, Toda Kogyo TF140, TF180 and the like. Those having an average particle size of 0.05 to 3 μm are effective, and preferably 0.05 to 1.0 μm.
Is.

These abrasives are added in an amount of 1 to 20 parts by weight, preferably 1 to 15 parts by weight, based on 100 parts by weight of the ferromagnetic powder. If it is less than 1 part by weight, sufficient durability cannot be obtained, and if it is more than 20 parts by weight, the surface property and filling degree are deteriorated. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint.

The magnetic layer of the magnetic recording medium of the present invention may contain conductive particles as an antistatic agent in addition to the nonmagnetic powder. However, in order to maximize the saturation magnetic flux density of the uppermost layer, it is preferable to add as little as possible to the uppermost layer and to add it to a coating layer other than the uppermost layer. As the antistatic agent, it is particularly preferable to add carbon black in order to reduce the surface electric resistance of the entire medium. The carbon black that can be used in the present invention may be a furnace for rubber, thermal for rubber, black for color, conductive carbon black, acetylene black or the like. Specific surface area of 5 to 500 m ² / g, DBP
Oil absorption is 10 to 1500ml / 100g, particle size is 5
mμ to 300 mμ, pH 2 to 10 and water content 0.
It is preferably 1 to 10% and the tap density is 0.1 to 1 g / cc. A specific example of the carbon black used in the present invention is BLACKPEARL manufactured by Cabot Corporation.
S2000, 1300, 1000, 900, 800, 7
00, VULCAN XC-72, manufactured by Asahi Carbon Co., Ltd., #
80, # 60, # 55, # 50, # 35, Mitsubishi Kasei Kogyo Co., Ltd., # 3950B, # 3250B, # 2400B, #
2300, # 900, # 1000, # 30, # 40, #
10B, Columbia Carbon Co., CONDUCTEX
SC, RAVEN 150, 50, 40, 15, Ketjen Black EC, Ketjen Black ECDJ-500, Ketjen Black ECDJ, manufactured by Lion Agzo.
-600 and the like are listed. The carbon black may be surface-treated with a dispersant or the like, the carbon black may be oxidized, or may be grafted with a resin, or a part of the surface may be graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint. When carbon black is used in the magnetic layer, it is preferably used in an amount of 0.1 to 30% by weight based on the ferromagnetic powder. Further, the nonmagnetic layer preferably contains 3 to 20% by weight based on the total amount of the nonmagnetic powder.

Generally, carbon black not only functions as an antistatic agent, but also functions to reduce the coefficient of friction, impart light-shielding properties, improve film strength, etc., and these differ depending on the carbon black used. Therefore, these cards used in the present invention
Of course, it is possible to change the type, amount, and combination of the bonblacks, and to use the bonblacks properly according to the purpose based on the above-mentioned various characteristics such as particle size, oil absorption, electric conductivity, and pH. The carbon black that can be used can be referred to, for example, in "Carbon Black Handbook" edited by Carbon Black Association.

When the non-magnetic layer is formed below the magnetic layer of the magnetic recording medium of the present invention, the non-magnetic layer is a layer in which non-magnetic powder is dispersed in a binder resin. Various non-magnetic powders can be used for the non-magnetic layer. For example,
α-alumina, β-alumina, γ- with an alpha conversion rate of 90% or more
Alumina, silicon carbide, chromium oxide, cerium oxide, α
-Iron oxide, corundum, silicon nitride, titanium carbide,
Titanium oxide, silicon dioxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate and the like are used alone or in combination. The particle size of these non-magnetic powders is preferably 0.01 to 2μ, but if necessary, non-magnetic powders having different particle sizes may be combined, or a single non-magnetic powder may be used to broaden the particle size distribution to obtain the same effect. You can also The non-magnetic powder used may be surface-treated in order to increase the interaction with the binder resin used and improve the dispersibility. The surface-treated product may be treated with an inorganic substance such as silica, alumina or silica-alumina, or may be treated with a coupling agent. Tap density is 0.3 to 2 g / cc, water content is 0.1 to 5% by weight, pH is 2 to 11, specific surface area is 5 to 100 m ² /
g is preferred. The shape of the non-magnetic powder is needle-like, spherical,
Either a dice shape or a plate shape may be used. Specific examples of the non-magnetic powder used in the present invention include A manufactured by Sumitomo Chemical Co., Ltd.
KP-20, AKP-30, AKP-50, HIT-5
0, Nippon Kagaku Kogyo KK, G5, G7, S-1, Toda Kogyo TF-100, TF-120, TF-140, Ishihara Sangyo TT055 series, ET300W, Titanium Kogyo STT30, magnetic oxidation Examples include hematite particles, which are an intermediate material for iron.

When the lower magnetic layer is formed under the upper magnetic layer of the magnetic recording medium of the present invention, the ferromagnetic powder is iron oxide ferromagnetic powder, cobalt modified iron oxide ferromagnetic powder,
Various materials can be used in which CrO ₂ , hexagonal ferrite, and various metal ferromagnetic powders are dispersed in resin.

Regarding the coating method for forming two or more coating layers on the non-magnetic support, the concrete method of the above-mentioned wet-on-wet method is as follows: (1) Gravure generally used in magnetic paints The lower layer is first coated by coating, roll coating, blade coating, or extrusion coating, and while the layer is still in a wet state, for example, Japanese Patent Publication No. 1-486186, JP-A-6-186186.
No. 0-238179 and Japanese Unexamined Patent Publication No. 2-265672, a method of coating an upper layer by a non-magnetic support pressure type extrusion coating apparatus,

(2) With a coating head having two built-in slits for passing the coating liquid as disclosed in JP-A-63-88080, JP-A-2-17971 and JP-A-2-265672. , A method of applying the lower layer coating solution and the upper layer coating solution almost simultaneously,

(3) A method of coating the upper layer and the lower layer almost at the same time by using the extrusion coating apparatus with a backup roll disclosed in Japanese Patent Laid-Open No. 2-174965.

When applying by the wet-on-wet method, the flow characteristics of the coating liquid for the magnetic layer and the coating liquid for the non-magnetic layer should be as close to each other as possible so that the interface between the coated magnetic layer and the non-magnetic layer is not disturbed. It is possible to obtain a magnetic layer having a uniform thickness and less variation in thickness. Since the flow characteristics of the coating liquid strongly depend on the combination of the powder particles and the binder resin in the coating liquid,
In particular, it is necessary to pay attention to the selection of the non-magnetic powder used for the non-magnetic layer.

The non-magnetic support of the present magnetic recording medium is usually
1 to 100 μm, preferably 3 to 20 μm, and the nonmagnetic layer is 0.5 to 10 μm, preferably 1 to 5 μm
m. The thickness of the uppermost layer is 1 μm or less, preferably 0.1 to 0.5 μm. Further, forming other layers other than the magnetic layer and the non-magnetic layer according to the purpose,
This is allowed as long as the magnetic layer is the uppermost layer and the non-magnetic layer is the lower layer. For example, an undercoat layer for improving adhesion may be provided between the non-magnetic support and the lower layer. This thickness is 0.01 to 2 μm, preferably 0.05 to 0.5 μm. In addition, a backcoat layer may be provided on the side opposite to the side of the nonmagnetic support magnetic layer. This thickness is 0.1 to 2 μm, preferably 0.3
To 1.0 μm. Known intermediate layers and back coat layers can be used. In the case of a disk-shaped magnetic recording medium, the above layer constitution can be provided on one side or both sides.

The non-magnetic support used in the present invention is not particularly limited, and those commonly used can be used. Examples of materials that form the non-magnetic support include polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, polyimide, polysulfone, polyethersulfone, and other synthetic resin films, and aluminum foil. , And metal foils such as stainless steel foil.

In order to effectively achieve the object of the present invention, the surface roughness of the non-magnetic support is 0.03 μm or less, preferably 0.02 μm, as the center line average surface roughness Ra (cutoff value 0.25 mm). Hereafter, it is more preferably 0.01 μm or less. Further, it is preferable that these non-magnetic supports not only have a small center line average surface roughness but also that they have no coarse protrusions of 1 μm or more. Further, the surface roughness shape can be freely controlled depending on the size and amount of the filler added to the non-magnetic support, if necessary. Examples of these fillers include oxides and carbonates of Ca, Si, Ti and the like, and fine organic resin powders of acrylic and the like. The F-5 value in the web running direction of the non-magnetic support used in the present invention is preferably 5 to 50 kg / m.
m ² , the F-5 value in the web width direction is preferably 3 to 30.
It is generally kg / mm ² , and the F-5 value in the longitudinal direction of the web is generally higher than the F-5 value in the width direction of the web, but this is not the case especially when it is necessary to increase the strength in the width direction. .

The heat shrinkage ratio of the support in the web running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less at 80 ° C. for 30 minutes. The rate is preferably 1% or less, more preferably 0.5% or less. Breaking strength is 5 to 10 in both directions
0 kg / mm ² , elastic modulus is 100 to 2000 kg / m
m ² is desirable.

The organic solvent used in the present invention may be any ratio of ketones such as acetone, methylethylketone, methylisobutylketone, diisobutylketone, cyclohexanone, isophorone, tetrahydrofuran, and the like, and methanol.
Alcohols such as alcohol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, etc., methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycoacetate -Esters such as glycol, dimethyl ether, glycol monoethyl ether, glycol ethers such as dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, Chlorinated hydrocarbons such as carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, N,
Those such as N-dimethylformamide and hexane can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted substances, by-products, decomposition products, oxides, and water in addition to the main components.
The content of these impurities is preferably 30% or less, more preferably 10% or less. The type and amount of the organic solvent used in the present invention may be changed between layers if necessary. The surface property is improved by using a highly volatile solvent for the first layer,
Examples include the use of a solvent having a high surface tension (cyclohexanone, dioxane, etc.) for the first layer to improve the coating stability, and a solvent having a high solubility parameter for the second layer to increase the filling degree. Of course, it is not limited to these examples.

The magnetic recording medium of the present invention is kneaded and dispersed by using an organic solvent together with the above-mentioned ferromagnetic powder, a binder resin and, if necessary, other additives, and a magnetic coating material is coated on a non-magnetic support, It is obtained by orienting and drying if necessary.

The process for producing the magnetic paint or the non-magnetic paint for the magnetic recording medium of the present invention comprises at least a kneading process, a dispersing process, and a mixing process provided before and after these processes, if necessary. Each process may be divided into two or more stages. Ferromagnetic powder or non-magnetic powder used in the present invention, binder, carbon black,
All raw materials such as abrasives, antistatic agents, lubricants and solvents may be added at the beginning or in the middle of any step. In addition, individual raw materials may be divided and added in two or more steps. For example, polyurethane may be divided and added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion.

Various kneading machines are used for kneading and dispersing the magnetic paint or the non-magnetic paint. For example, two roll mill, three roll mill, ball mill, pebble mill,
Tron mill, sand grinder, Segbari (Szeg
vari), attritor, high-speed impeller disperser, high-speed stone mill, high-speed impact mill, disper, kneader, high-speed mixer, homogenizer, ultrasonic disperser and the like can be used.

In order to achieve the object of the present invention, it is needless to say that the conventionally known manufacturing technique can be used as a part of the steps, but in the kneading step, a continuous kneader or a pressure kneader is used. High Br of the magnetic recording medium of the present invention can be obtained by using a material having a strong kneading force such as a dam. When a continuous kneader or a pressure kneader is used, all or a part of the ferromagnetic powder and the binder (however, 30% or more of the total binder is preferable) and 15 to 500 per 100 parts by weight of the ferromagnetic powder. Kneading is performed within the range of parts by weight. Details of these kneading treatments are described in JP-A-1-10.
6338 and JP-A-64-79274. In the present invention, it is possible to produce more efficiently by using the simultaneous multi-layer coating method as shown in JP-A-62-212933.

The residual solvent contained in the magnetic layer of the magnetic recording medium of the present invention is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less, and the residual solvent contained in the magnetic layer is contained in the non-magnetic layer. It is preferably less than the residual solvent contained.

The porosity of the magnetic layer in both the lower layer and the uppermost layer is preferably 30% by volume or less, more preferably 10% by volume or less. The porosity of the nonmagnetic layer is preferably larger than that of the magnetic layer, but may be small as long as the porosity of the nonmagnetic layer is 5% by volume or more.

It is easily estimated that the magnetic recording medium of the present invention can change the physical properties of the lower layer and the uppermost layer according to the purpose. For example, the elastic modulus of the uppermost layer is increased to improve running durability, and at the same time, the elastic modulus of the lower layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

By such a method, the magnetic layer coated on the support is optionally subjected to a treatment for orienting the ferromagnetic powder in the layer, and then the formed magnetic layer is dried. If necessary, the surface is smoothed or cut into a desired shape to manufacture the magnetic recording medium of the present invention. The above-mentioned composition for the uppermost layer and the composition for the lower layer are dispersed together with a solvent, and the obtained coating liquid is coated on a non-magnetic support and oriented and dried to obtain a magnetic recording medium.

The elastic modulus of the magnetic layer at 0.5% elongation is preferably 100 to 2000 k in both the web coating direction and the width direction.
g / mm ² , breaking strength is preferably 1 to 30 kg / c
m ² , the elastic modulus of the magnetic recording medium is preferably 100 to 1500 kg / mm ² in both the web coating direction and the width direction, the residual spread is preferably 0.5% or less, and the heat shrinkage rate at any temperature of 100 ° C. or less is desirable. Is 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less.

The magnetic recording medium of the present invention may be a tape for video or audio use, or a floppy disk or magnetic disk for data recording.
It is particularly effective for a medium for digital recording in which the loss of a signal due to the occurrence of drop-out is fatal.
Furthermore, by setting the lower layer to be a non-magnetic layer and the thickness of the uppermost layer to be 1 μm or less, it is possible to obtain a high density, large capacity magnetic recording medium having high electromagnetic conversion characteristics.

[0091]

EXAMPLES The novel features of the present invention will be specifically described in the following examples, but the present invention is not limited thereto. . Hereinafter, examples of the present invention will be specifically described in comparison with comparative examples. Preparation of nuclear crystals (Preparation of nuclear crystals) 500 ml of 2M FeCl ₃ aqueous solution and 500 m of 5.94N NaOH aqueous solution in a sealable 2 liter glass container.
1 with stirring for 5 minutes, and after addition is complete, add 20 more
After stirring for a minute, the container was completely stoppered.

It was placed in an oven preheated to 100 ° C. and kept for 48 hours. After 48 hours, quench with running water, collect the reaction solution and centrifuge at 15000 rp.
The mixture was centrifuged at m for 15 minutes and the supernatant was discarded. Distilled water was added to this to redisperse it, and the mixture was centrifuged again and the supernatant was discarded.
Thus, the washing with water was repeated 4 times using the centrifuge. Hematite particles that have been washed with water (average particle size of about 0.
The precipitate (1 μm) was filtered and dried. 50g of this dry powder
To the beaker was added 5 ml of distilled water to pulverize for 30 minutes with a raikai machine, and the beaker was washed with 700 ml of distilled water, followed by ultrasonic dispersion for 30 minutes. This dispersion was aliquoted and spun at 10,000 rpm for 30
After centrifuging for minutes, the supernatant liquid in which the pseudo fine spheroidal ultrafine hematite particles (average particle diameter of about 100Å) were dispersed was taken out to obtain a nuclear crystal liquid. The iron concentration (concentration of hematite converted to iron atoms) in the nucleating liquid was 2000 rpm.

Examples 1-1 to 4 and Comparative Examples 1-1 to 1-2: Crystallite size control of monodisperse spindle type hematite particles In a reaction vessel equipped with a stirrer, 180 mol of 2 mol / l ferric nitrate.
Add 1 and cool to bring the temperature of the solution to 5 ° C. 180 ml of a 4.8 mol / l sodium hydroxide solution was added to 1 while stirring.
Add slowly over 0 minutes. After the addition, stirring was continued for further 5 minutes, 180 ml of the nuclear crystal solution was added, and the mixture was stirred for 10 minutes. 60 ml of each of the obtained liquids was sampled, and a predetermined amount of an aqueous solution of a shape control agent (which releases phosphate radical ions and optionally chloride ions) and / or water having various concentrations shown in Table 1 was added. After that, it was kept in an oven preheated to 100 ° C. for 48 hours.

After holding for a predetermined time, it was rapidly cooled with running water, and the reaction solution was centrifuged at 18000 rpm for 15 minutes in a centrifugal separator, and the supernatant was discarded. Distilled water was added to this to redisperse it, and the mixture was centrifuged again and the supernatant was discarded. Thus, the washing with water was repeated three times using the centrifuge. Next, 1 M aqueous ammonia was added and redispersed, and the mixture was centrifuged and the supernatant was discarded. Distilled water was added to this to redisperse it, and the mixture was centrifuged again and the supernatant was discarded. Thus, the washing with water was repeated three times using the centrifuge. The product was freeze dried. The monodisperse spindle type hematite particles thus obtained (sample: actual 1-
1 to 4 , ratios 1-1 to 2) are observed by a transmission electron microscope, and variations in average major axis length, acicular ratio (major axis / minor axis) and major axis length (standard deviation of major axis length / average length) The axial length) was calculated. Further, the crystallite size of (110) was determined by the powder X-ray diffraction method.
The results are shown in Table 1. Comparative Example 1-3 2M FeCl ₃ aqueous solution 1 in a 1 liter glass beaker
To 50 ml, 150 ml of 4.8N NaOH aqueous solution was added with stirring for 5 minutes, and after the addition was completed, the mixture was stirred for 10 minutes, and 40 ml of the obtained ferric hydroxide gel was added to 200 ml.
It was taken out in a ml-capable container. 20 ml of nucleation liquid
Add with stirring and after an additional 5 minutes 0.12M Na
20 ml of ₂ SO ₄ aqueous solution was added and stirred for 5 minutes. It was put in an oven which had been heated to 100 ° C. in advance and kept for 48 hours. Particles obtained by washing with water in the same manner as above were used in Example 1.
Evaluation was made in the same manner as in -1, and the obtained results are shown in Table 1.

Comparative Example 1-4 In Example 1-1, 180 ml of water was used instead of the nucleating solution.
Was treated in the same manner except that was used.

[0096]

[Table 1]

From Table 1, it can be seen that monodisperse spindle type hematite particles having a predetermined crystallite size, a predetermined shape and a particle size can be obtained by setting the shape control anion to a predetermined value. It can be seen that Comparative Examples 1-2 and 3 have smaller crystallite sizes than the other examples. Ratio 1-4 is
It can be seen that the particles become large without the nuclei.
In the sample column, "actual" indicates an example, and "ratio" indicates a comparative example (the same applies hereafter).

Examples 2-1 to 5 and Comparative Example 2 180 m of 2 mol / l ferric nitrate in a reaction vessel equipped with a stirrer.
Add 1 and cool to bring the temperature of the solution to 5 ° C. 180 ml of a 4.8 mol / l sodium hydroxide solution was added to 1 while stirring.
Add slowly over 0 minutes. After the addition, stirring was continued for further 5 minutes, and 60 ml of the obtained liquid was collected. Add nucleating solution to each as shown in Table 2, then add 0.0
10 ml of 48 M NaH ₂ PO ₄ and 0.48 M NaC
After adding 10 ml, the mixture was kept in an oven preheated to 100 ° C. for 72 hours.

After holding for a predetermined time, it was rapidly cooled with running water, and the reaction solution was centrifuged at 18,000 rpm for 15 minutes by a centrifugal separator, and the supernatant was discarded. Distilled water was added to this to redisperse it, and the mixture was centrifuged again and the supernatant was discarded. Thus, the washing with water was repeated three times using the centrifuge. Next, 1 M aqueous ammonia was added and redispersed, and the mixture was centrifuged and the supernatant was discarded. Distilled water was added to this to redisperse it, and the mixture was centrifuged again and the supernatant was discarded. Thus, the washing with water was repeated three times using the centrifuge. The product was freeze dried. The monodisperse spindle type hematite particles thus obtained were evaluated in the same manner as in Example 1 and the results are shown in Table 2.

[0100]

[Table 2]

From Table 2, it can be seen that monodisperse spindle-type hematite particles having a predetermined crystallite size, a predetermined shape and a particle size can be obtained depending on the shape-controlling anion and the concentration of nuclei. Examples 3-1 to 5 and Comparative Example 3 1 mol / l ferric perchlorate 18 was added to a reaction vessel equipped with a stirrer.
0 ml is added and 180 ml of 2.7 mol / l sodium hydroxide solution is slowly added over 10 minutes while stirring. After the addition, stirring was further continued for 5 minutes, 60 ml was sampled, a predetermined amount of the nuclei crystal solution was added, and the mixture was stirred for 10 minutes. Then, 10 ml of 0.048 M NaH ₂ PO _{4 and} 10 ml of 0.48 M NaCl were added and the mixture was kept in an oven preheated to 100 ° C. for 48 hours.

After holding for 48 hours, it was rapidly cooled with running water, and the reaction solution was centrifuged at 18000 rpm for 15 minutes in a centrifugal separator, and the supernatant was discarded. Distilled water was added to this to redisperse it, and the mixture was centrifuged again and the supernatant was discarded. Thus, the washing with water was repeated three times using the centrifuge. Next, 1 M aqueous ammonia was added and redispersed, and the mixture was centrifuged and the supernatant was discarded.
Distilled water was added to this to redisperse it, and the mixture was centrifuged again and the supernatant was discarded. In this way, wash with water using a centrifuge.
Repeated times. The product was freeze dried.

The monodisperse spindle-type hematite particles thus obtained were observed with a transmission electron microscope, and variations in average major axis length, acicular ratio (major axis / minor axis), and major axis length (minor axis length) were observed. The standard deviation / average major axis length) was determined. Further, the crystallite size of (110) was determined by the powder X-ray diffraction method. The results are shown in Table 3.

[0104]

[Table 3]

From Table 3, it can be seen that monodisperse spindle type hematite particles having a predetermined crystallite size, a predetermined shape and a particle size can be obtained depending on the shape control anion and the concentration of the nuclei. Examples 4-1 and 2 and Comparative Examples 4-1 and 4-2 Comparative Examples 1-3, Example 2-2, Example 3-2, and Comparative Example 1
The monodisperse spindle type hematite (starting material) obtained under the condition of No. -4 was transferred to an electric furnace, the temperature of the electric furnace was kept at 400 ° C., and nitrogen gas was allowed to flow at 2 liters / minute for 30 minutes. 380
After the temperature reached ℃, it was changed to hydrogen gas, hydrogen gas was flowed at 2 liters / minute, and reduction was carried out for 1 hour. After completion of the reduction, the temperature was switched to nitrogen gas and the temperature of the electric furnace was lowered to 240 ° C. Next, the nitrogen gas was switched to air, and air was flowed at 2 liters / minute for 1 hour to oxidize and produce γFe ₂ O ₃ . The magnetic properties of the obtained ferromagnetic powder were measured with a vibrating sample magnetometer (VSM-5 type manufactured by Toei Industry Co., Ltd.) at a measurement magnetic field strength of 10 kOe.
In addition, the specific surface area cantersorb (manufactured by Canterchrome)
Was measured for 30 minutes at 250 ° C. Further, the obtained particles were observed with a transmission electron microscope to determine the average major axis length and the acicular ratio (major axis / minor axis). Obtained γFe ₂ O
The crystallite size of (110) was calculated from the X-ray diffraction measurement of ₃ . The results are shown in Table 4.

[0106]

[Table 4]

From Table 4, Examples 4-1 and 4-2 are Comparative Example 4
It can be seen that the magnetic characteristics are superior to those of Comparative Example -1 and Comparative Example 4-2. Examples 5-1 and 2 and Comparative Examples 5-1 and 2 Comparative Examples 1-3, Example 2-2, Example 3-2, and Comparative Example 1
The monodisperse spindle type hematite (starting material) obtained under the condition of No. 4 was dispersed in distilled water so that the hematite concentration was 2%, cobalt sulfate was set to 100 atom% of Fe in hematite, and Co was 10 atom. %, And the mixture was thoroughly stirred and mixed. While monitoring the pH of this suspension, aqueous ammonia was added to the suspension to adjust the pH to 8.0 and a Co compound was deposited on the surface of the hematite. An aqueous solution of sodium aluminate and sodium silicate was added to this solution as Fe in hematite.
Is added to the suspension such that Al is 5 atom% and Si is 1 atom%, and carbon dioxide gas is bubbled through the suspension while monitoring the pH of the suspension to adjust the pH to 7. 0 and Co
Al and Si compounds were deposited on the surface of the deposited monodisperse spindle hematite. The suspension was filtered and washed with distilled water to remove impurities. The surface-treated spindle-type hematite obtained had a diameter of 3
After passing through a mm molding plate, it was molded into a cylindrical shape and dried.

500 g of the surface-treated monodisperse spindle hematite was placed in a static reduction furnace and annealed in nitrogen at 500 ° C. for 1 hour. Next, the temperature was set to 450 ° C., the hydrogen gas was changed to 50 liter / min, and the hydrogen gas was reduced for 5 hours. After completion of the reduction, the atmosphere was changed to nitrogen gas and cooled to room temperature. Using a gas mixer, mix an oxygen-containing gas with nitrogen gas, adjust the oxygen concentration in nitrogen to 0.1% by volume, contact for 5 hours, and then monitor the temperature of the upper part of the ferromagnetic metal powder to exceed 50 ° C. The oxygen concentration was increased to 21% while gradually refining the ferromagnetic powder while keeping this state for 5 hours. Magnetic properties of the obtained ferromagnetic metal powder were measured with a vibrating sample magnetometer (VSM-5 type manufactured by Toei Industry Co., Ltd.) at a magnetic field strength of 10 kOe. The specific surface area is 250 ° C. using Cantersorb (manufactured by Canterchrome).
It was dehydrated for 30 minutes and measured. Further, the obtained ferromagnetic metal powder was observed with a transmission electron microscope to determine the average major axis length and the acicular ratio (major axis / minor axis). X of the obtained ferromagnetic metal powder
The crystallite size of (110) was calculated from the line diffraction measurement.
The results are shown in Table 5.

[0109]

[Table 5]

[0110]

[0111]

[0112]

[0113]

[0114]

[0115]

According to the present invention, when the ferric hydroxide is converted to hematite particles, the specific fine particle hematite and the shape controlling anion that coexist with ferric hydroxide are selected, so that the major axis length is extremely small. Since the crystallite size of the monodisperse spindle-type hematite particles can be controlled as desired, in particular, to be large, the magnetic properties of the ferromagnetic iron oxide and the ferromagnetic metal powder obtained from the raw material can be significantly improved. be able to. In addition, the present invention has an advantage that the shape of the ferromagnetic powder to be obtained can be easily controlled because the acicular ratio of the monodisperse spindle type hematite particles can be controlled as desired, and thus magnetic recording according to various purposes can be achieved. It can provide a very effective means for manufacturing a medium.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C01G 49/00-49/08

Claims (5)

(57) [Claims] 1. A nuclear ferric nitrate and based on the hematite particles of the presence of phosphate root ions ferric hydroxide generated from ferric salt comprising at least one of ferric perchlorate A method for producing monodisperse spindle type hematite particles which are precipitated on a crystal. 2. The phosphate ion concentration is 0.001 to 0.0
The method for producing monodisperse spindle-type hematite particles according to claim 1, which is 1 mol / liter. 3. The monodispersion according to claim 1, wherein ferric hydroxide is present in a gel suspension state in which the ferric salt according to claim 1 is partially neutralized with an alkali. A method for producing spindle-shaped hematite particles. 4. A single-min according to any one of claims 1 to 3
Following the method for producing dispersed spindle-type hematite particles , the obtained monodispersed spindle-type hematite particles are reduced to magnetite, and the magnetite is oxidized to produce FeO _x (1.33).
<X ≦ 1.5), a method for producing a ferromagnetic iron oxide. 5. The monodisperse product according to claim 1.
A method for producing a ferromagnetic metal powder, which comprises reducing the obtained monodisperse spindle-type hematite particles to magnetite, and then reducing the magnetite , following the method for producing the spindle-type hematite particles.