JPH06203365A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetically and chemically stable magnetic recording medium having high coercive force and low light transmissivity. CONSTITUTION:A substrate is coated with a resin compsn. contg. magnetic iron oxide particles made of spinel type composite particles obtd. by crystal growth of CoFe2O4 on the surfaces of Fe3O4 particles as nuclear crystal grains to obtain the objective magnetic recording medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having a high coercive force, a low light transmittance and an excellent magnetic and chemical stability. .

[0002]

2. Description of the Related Art In recent years, with the progress of miniaturization and weight reduction of magnetic recording / reproducing devices, there is an increasing need for higher performance of magnetic recording media such as magnetic tapes and magnetic disks. That is, it is required to have a high recording density, a low light transmittance, and excellent magnetic and chemical stability.

The magnetic recording medium is generally manufactured by coating a resin composition containing magnetic particle powder on a substrate, and various characteristics of the magnetic recording medium are closely related to the magnetic particle powder used. Known to be.

First, in order to improve the recording density characteristics of the magnetic recording medium, it is necessary to increase the coercive force of the magnetic recording medium. For that purpose, the magnetic particle powder used has a coercive force as high as possible. Required to have. This fact is shown, for example, in the Institute of Electronics and Communication Engineers, Technical Report of the Institute of Electronics and Communication Engineers, MR77-36 (issued in 1978), 37th.
As described on the page, "In order to increase the recording density of the magnetic tape, it is necessary to increase the coercive force of the magnetic powder used in the tape."

Next, stopping the running of a magnetic recording medium such as a magnetic tape, particularly a video tape, is carried out by detecting a portion of the magnetic recording medium having a high light transmittance with a video deck. In recent years, with the improvement of the recording density characteristics of magnetic recording media, there has been a tendency toward thinning of magnetic recording media and ultrafine particles of magnetic particle powder dispersed in a recording layer. When the light transmittance of the whole layer becomes large, there arises a problem that it becomes difficult for the video deck to detect it. In order to solve this problem, carbon is added to the magnetic recording layer to reduce the light transmittance. Therefore, it is essential to add carbon to the magnetic recording layer in the current video tape.

However, the addition of carbon black, which is not involved in magnetism, conflicts with the performance improvement of the magnetic recording medium, and in addition, when kneading with the magnetic particle powder to form a coating composition, carbon black is used. It has been pointed out that the presence of the particle powder hinders the dispersion of the magnetic particle powder in the vehicle, and reduces the orientation and filling properties of the magnetic particle powder in the coating film.

Since the carbon black particle powder is a bulky powder having a bulk density of about 0.1 g / cm ^3, it is difficult to handle and the workability is poor, and the carcinogenicity, safety and hygiene are high. Some problems have been pointed out.

Therefore, in order to reduce the light transmittance of the magnetic recording medium, it has been attempted to reduce the amount of carbon black particle powder by using black magnetic particle powder as much as possible. Is strongly demanded.

Further, the magnetic recording medium is required to have excellent magnetic and chemical stability, and for that purpose, the magnetic particle powder used is excellent in magnetic and chemical stability. Is required.

This fact is based on, for example, Japanese Patent Publication No. 55-658.
No. 0, "In recent years, recording signals have tended to shift to a shorter wavelength region more and more, and this tendency is remarkable especially for video cassettes, that is, at the same time as high density recording, high output characteristics, especially improvement of frequency characteristics. Magnetic stability is required.The characteristics of magnetic materials suitable for satisfying the above requirements for magnetic recording media are magnetic stability and high coercive force (H
c). ".

As described above, the magnetic particle powder used in the magnetic recording medium is strongly required to have a high coercive force, exhibit a black color, and be magnetically and chemically stable. There is.

Conventionally, so-called Co-doped magnetic iron oxide particles and so-called Co have been used as magnetic particle powders having high coercive force.
Adhesive magnetic iron oxide particles are known. In the former case, a Co salt is added in advance in the production reaction of magnetite particles, or a Co salt is added in advance in the production reaction of goethite particles as a starting material to produce Co-containing goethite particles, and then reduction is performed. It can be obtained by forming Co-containing magnetite particles or by further oxidizing it to Co-containing maghemite particles if necessary. The latter is
It can be obtained by coating magnetite particles obtained by reducing goethite particles as a starting material or maghemite particles obtained by further oxidizing if necessary as precursor particles and coating the particle surface of the precursor particles with a Co compound.

As is well known, the Co-doped magnetic iron oxide particle powder is magnetically and chemically unstable.

Co-deposited magnetic iron oxide particles are Co
Compared with doped type magnetic iron oxide particles, it has relatively excellent magnetic and chemical stability.In particular, when the precursor particles are magnetite particles, the stability is higher than when the precursor particles are maghemite particles. Since it has a magnetic force and a large saturation magnetization and is relatively stable against pressure, the Co-adhered magnetite particle powder is expected to be used as a magnetic iron oxide particle powder for magnetic recording.

However, it is known that the Co-adhered magnetite particle powder is magnetically and chemically unstable due to the fact that the particles generally contain Fe ²⁺ . This phenomenon is described in JP-B-55-6580, "Cobalt-containing acicular magnetite particle powder has a large coercive force and saturation magnetic flux density, and its use as a magnetic material for magnetic recording is expected. On the other hand, since it has Fe ²⁺ , it has a drawback that the change of coercive force with time is large. "And" ... Cobalt-containing acicular magnetite particle powder is oxidized when taken out into the air. And Fe ²⁺ becomes less than the stoichiometric amount,
This causes vacancies in the crystal lattice. When such a cobalt-containing acicular magnetite particle powder is left at room temperature, cations (Fe ²⁺ , Co
²⁺ ) moves to a stable position and the coercive force gradually increases with time. When the cobalt-containing acicular magnetite particle powder is left at room temperature, the coercive force changes with time because of the problem of the coordination of ions in the crystal lattice. When left at room temperature, F through the vacancy
e ²⁺ , Co ²⁺ move to a stable position, and as a result, the coercive force changes with time ... ”.

That is, when the Co-adhered magnetite particle powder is heated to a constant temperature, the coercive force value before and after heating fluctuates, the thermal history of the coercive force value loses reversibility, or is left for a certain period of time. , The coercive force fluctuates over time, the saturation magnetization decreases over time (hereinafter referred to as magnetic instability), and Fe ²⁺ decreases over time (hereinafter referred to as chemical instability). .) And other phenomena occur.

As a result, in the magnetic recording medium obtained by using Co-adhered magnetite particle powder, the coercive force value before and after heating fluctuates when heated to a constant temperature, and the thermal history of the coercive force value is reversible. Disappear, or when left for a certain period of time, the coercive force and squareness (Br / Bm) increase with time, the saturation magnetic flux density Bm decreases with time, and
A phenomenon occurs in which the light transmittance increases with time.

The degree of blackness of the Co-deposited magnetite particle powder is "Powder and powder metallurgy" Vol. 26, No. 7, No. 23.
9 to 240, "The degree of blackness of the sample depends on the Fe (II) content and the average particle size.
The powder of m is a bluish black powder and is most suitable as a black pigment. The Fe (II) content is 10% or more, a slight difference in blackness is recognized, but all the samples are black. When the Fe (II) content is reduced to 10% or less, each sample changes from black to reddish brown. As described comprising ", it is influenced mainly by Fe ²⁺ content, Fe ²⁺
It is known that the blackness tends to increase as the content increases, and the Co-coated magnetite particle powder in which Fe ²⁺ is reduced by leaving it for a certain period has a small blackness. When the adherent type magnetite particle powder is used, a magnetic recording medium having a sufficiently low light transmittance cannot be obtained.

Various attempts have been hitherto made to improve the magnetic and chemical instability of Co-deposited magnetite particles, and for example, FeO _x (x = 1.33 to
Fe _{3 is present on the} surface of the iron oxide nucleation particles consisting of 1.5).
A preliminary coating made of O ₄ or a non-stoichiometric compound and a method for forming a coating of Co hydroxide on the preliminary coating (Japanese Patent Laid-Open No. Sho 63-63
-74920).

[0020]

A magnetic recording medium having a high coercive force, a low light transmittance, and a magnetically and chemically stable magnetic recording medium is currently most demanded. A magnetic recording medium that fully satisfies these characteristics has not been obtained.

That is, the magnetic iron oxide particle powder described in the above-mentioned Japanese Patent Laid-Open No. 63-74920 is intended to minimize the temperature dependence of the coercive force. It is not intended to impart reversibility to history, improve coercive force and magnetic stability of saturation magnetization, or improve chemical stability of Fe ^2+.
2+ content is low and the degree of blackness is poor, and the magnetic recording medium produced by using such magnetic iron oxide particle powder has a light transmittance due to the characteristics of the magnetic iron oxide particle powder used. Was large and the magnetic and chemical stability was poor.

Therefore, a technical object of the present invention is to obtain a magnetic recording medium having a high coercive force, a small light transmittance, and being magnetically and chemically stable.

[0023]

The above technical problems can be achieved by the present invention as follows.

That is, in the present invention, Fe ₃ O ₄ particles are used as nucleation particles on the substrate, and CoFe ₂ particles are formed on the surface of the nucleation particles.
A magnetic recording medium coated with a resin composition containing magnetic iron oxide particle powder composed of spinel type composite particles in which O ₄ is crystal-grown.

Next, various conditions for carrying out the present invention will be described.

The magnetic iron oxide particle powder according to the present invention has CoF on the crystal plane of the Fe ₃ O ₄ particles, as will be shown in the examples below.
e ₂ O ₄ is a spinel type composite particle in which crystals are grown.

It is important that the nuclei crystal grains in the present invention have a composition of Fe ₃ O ₄ . If nucleate particles having a large number of vacancies in the crystal lattice are used, magnetic iron oxide particle powder excellent in magnetic and chemical stability cannot be obtained, and the blackness is lowered.

Spinel type compound particles used in the [0028] present invention, it is essential that the particle surface has a composition of CoFe ₂ O _4, and if not the composition of the CoFe ₂ O ₄ is
It is not possible to obtain the magnetic iron oxide particle powder excellent in magnetic and chemical stability, which is the object of the present invention.

The amount of CoFe ₂ O ₄ in the present invention is 10 to 80% by weight based on the spinel type composite particles. 10
If it is less than wt%, magnetically and chemically stable spinel type composite particle powder cannot be obtained. If it exceeds 80% by weight, CoF in the spinel type composite particles
The amount of e ₂ O ₄ increases and the blackness decreases.

The spinel type composite particle powder of the present invention has a coercive force of 100 when the nucleation particles are granular particles.
.About.3000 Oe and the nucleation particles are needle-shaped particles or spindle-shaped particles, a coercive force of 400 to 3000 Oe.
have e.

Fe ₃ O ₄ which is the nucleation particle in the present invention
The particle powder is obtained by air-oxidizing an iron-containing precipitate produced by the reaction of an aqueous ferrous salt solution with an aqueous alkali solution such as an alkali hydroxide or an alkali carbonate, or by ferric oxide hydroxide powder or ferric oxide. Granular Fe produced from an aqueous solution by a wet method by heating a suspension having a pH of 6 or more containing particle powder and ferrous hydroxide at a temperature of 40 ° C. or more.
₃ O ₄ particle powder, 20 needle-shaped rapid crosite particles
The acicular maghemite particles obtained by heating and dehydrating in the temperature range of 0 to 500 ° C. are dispersed in an alkaline suspension containing a ferrous hydroxide colloid, and the suspension is 40 to 40 in a non-oxidizing atmosphere. Iron-containing precipitate formed by reaction of acicular magnetite particle powder or ferrous salt aqueous solution produced from an aqueous solution by a wet method by heating and stirring in a temperature range of 100 ° C. and an aqueous alkaline solution such as an alkali hydroxide or an alkali carbonate. Needle-shaped or spindle-shaped Fe ₃ O ₄ particles obtained by a so-called dry method, in which acicular and spindle-shaped hydrous ferric oxide particles obtained by air-oxidizing a substance are heated and reduced in a reducing atmosphere. Any of the powders can be used.

In order to prevent or suppress the oxidation of Fe ²⁺ in Fe ₃ O ₄ particles, it is preferable to directly use the magnetite particles produced in the aqueous solution by the wet method. The granular magnetite particle powder may have any shape such as a spherical shape, a hexahedron, an octahedron, and the size thereof may be a particle having an average particle diameter of 0.01 to 0.5 μm.

The acicular or spindle-shaped Fe ₃ O ₄ particle powder has an average major axis diameter of 0.01 to 0.3 μm, which is generally used as magnetic iron oxide particles for magnetic recording, and an axial ratio (long axis diameter / Minor axis diameter) 2 or more, especially 5 to 20 particles can be used.

For crystal growth of CoFe ₂ O ₄ ,
It is important to prevent the Fe ₃ O ₄ particle powder used as the nucleation particles from being oxidized by oxygen in the air. In the case of the above wet method, the reaction solution in which the Fe ₃ O ₄ particle powder is formed is or crystal growth of CoFe ₂ O ₄ used as it is, in case of the dry method, CoFe ₂ after removal once the vessel was purged with inert gas such as nitrogen
O ₄ crystal growth may be performed.

[0034] To the CoFe ₂ O ₄ on the surface of the particles of the Fe ₃ O ₄ particles is grown in the present invention, the hydroxide of the mixed solution or Co ²⁺ and Fe ²⁺ containing Co ²⁺ and Fe ²⁺ Fe ²⁺ is prepared in advance in a proportion of 2 mol or more and less than 3 mol with ^respect to 1 mol of Co ²⁺ , and
A mixed solution containing ²⁺ and Fe ²⁺ or a suspension containing hydroxides of Co ²⁺ and Fe ²⁺ is mixed in an alkaline dispersion so that the concentrations of Co ion and Fe ion are Co ²⁺ and Fe ²⁺ . Total is 0.
It is important to add it while controlling it to be in the range of more than 005M and less than 0.5M.

[0035] Without the suspension containing hydroxides of Co ²⁺ and Fe ²⁺ mixed solution or the composition adjusted include compositions adjusted Co ²⁺ and Fe ²⁺ are crystals CoFe ₂ O ₄ I can't grow.

The mixed solution containing Co ²⁺ and Fe ²⁺ is Co
By mixing the aqueous salt solution and the aqueous ferrous salt solution, C
The suspension containing hydroxides of o ²⁺ and Fe ²⁺ is produced by the reaction of the aqueous Co salt solution and the aqueous ferrous salt solution with alkali hydroxide.

As the Co salt aqueous solution, cobalt sulfate, cobalt chloride or the like can be used.

As the aqueous ferrous salt solution, ferrous sulfate, ferrous chloride or the like can be used.

As the alkali hydroxide, sodium hydroxide, potassium hydroxide or the like can be used.

The order of adding the aqueous Co salt solution and the aqueous ferrous salt solution and the alkali hydroxide may be either first or simultaneous.

Mixed solution containing Co ²⁺ and Fe ²⁺ or Co
Co ²⁺ and Fe in suspension containing ²⁺ and Fe ²⁺ hydroxides
Ratio of the ^2+, Co ²⁺ 1 mole Fe ²⁺ is less than 3 mol 2 mol or more. When Fe ²⁺ is less than 2 mol, unreacted Co (OH) ₂ remains in the reaction mother liquor and is mixed in the magnetic iron oxide particles even if the oxidation reaction is carried out for a long time. It is not possible to obtain the magnetic iron oxide particle powder excellent in magnetic and chemical stability, which is the object of the invention. Three
Even when the amount is more than the molar amount, the magnetic iron oxide particle powder as the object of the present invention can be obtained, but Fe ^{2+ which} is not involved in the formation of CoFe ₂ O ₄ becomes Fe ₃ O ₄ and Fe ₃ which is a nuclear crystal particle.
It is meaningless to add more than necessary because it is generated on the particle surface of O ₄ particles.

Co in the alkaline dispersion of the present invention
Ion and Fe ions are added at concentrations of Co ²⁺ and Fe
The sum of ²⁺ is more than 0.005M and less than 0.5M.
When it is 0.005 M or less, the crystal growth of CoFe ₂ O ₄ is insufficient, and the magnetic iron oxide particles excellent in magnetic and chemical stability, which is the object of the present invention, cannot be obtained.
When it is 0.5 M or more, CoFe ₂ O ₄ is formed on the nucleation particles.
Although it is possible to grow crystals of CoFe ₂ O ₄ , it takes a long time to grow the crystals of CoFe ₂ O ₄ , and CoFe ₂ O ₄ is separately fractionated and precipitated, which is not preferable.

The crystal growth of CoFe ₂ O ₄ in the present invention is carried out by passing an oxygen-containing gas through an alkaline dispersion liquid having a pH of 10 or higher at a temperature of 50 ° C. or higher and a boiling point or lower. When the oxygen-containing gas is not aerated, CoFe ₂ O
₄ is not generated, and the magnetic iron oxide particle powder excellent in magnetic and chemical stability, which is the object of the present invention, cannot be obtained.

When the temperature in the alkaline dispersion liquid is lower than 50 ° C., CoFe ₂ O ₄ is not produced, and magnetic iron oxide particles which are the object of the present invention and are excellent in magnetic and chemical stability are obtained. I can't. Since the present invention is a reaction in an aqueous solution, its upper limit value is the boiling point.

The magnetic recording medium according to the present invention can be obtained by applying a coating composition containing a binder resin and magnetic particle powder on a substrate to form a coating film by a conventional method.

Lubricants, abrasives, antistatic agents and the like which are usually used may be added to the above coating composition.

Examples of the binder resin in the present invention include vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate maleate urethane elastomer, butadiene acrylonitrile copolymer, polyvinyl butyral, which are currently widely used in the production of magnetic recording media. Cellulose derivatives such as nitrocellulose, synthetic rubber resins such as polyester resins and polybutadiene, epoxy resins, polyamide resins, isocyanate polymers, electron beam curable acrylic urethane resins, and the like and mixtures thereof can be used.

As the base material in the present invention, at present,
Polyethylene terephthalate, polyethylene, polypropylene, which are widely used in the manufacture of magnetic recording media,
It is possible to use synthetic resin films such as polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, polyimide, polysulfone, and metal foils and plates such as aluminum and stainless steel, and various papers.

[0049]

First, the most important point in the present invention is Fe ₃
O ₄ particles were used as nucleation particles, and Co particles were formed on the surface of the nucleation particles.
The magnetic recording medium produced using the spinel-type composite particle powder in which Fe ₂ O ₄ is crystal-grown has a high coercive force and exhibits a black color,
Moreover, it is a fact that it has a high coercive force due to its excellent magnetic and chemical stability, has a low light transmittance, and is excellent in magnetic and chemical stability. .

The magnetic recording medium according to the present invention has a temperature range of -35 ° C.
The thermal history of coercive force in the temperature range of 150 ° C. is reversible.

The magnetic recording medium according to the present invention has a temperature of 60.
Even when left for a long time under the condition of ° C and humidity of 90%, the coercive force, the saturation magnetic flux density, and the square-shaped characteristics maintain their initial values, and the magnetic stability is extremely excellent.

In the magnetic recording medium according to the present invention, the Fe ²⁺ content of the spinel type composite particles maintains the initial value, and the chemical stability is excellent. Is fully maintained.

[0053] Magnetic magnetic recording medium according to the present invention, the present inventors about the reason for excellent chemical stability, Fe ₃
O ₄ was used as nucleation particles, and CoFe was formed on the surface of the nucleation particles.
_{Since the} spinel-type composite particles in which ₂ O ₄ is crystal-grown are stable against oxidation due to the fact that the particle surface of the spinel-type composite particles does not substantially contain Fe ²⁺ , the nucleation crystal particles are Oxidation of Fe ²⁺ in Fe ₃ O ₄ is prevented or suppressed, and as a result, vacancy does not occur in the crystal lattice and F
I think that it is because the movement of e ²⁺ and Co ²⁺ does not occur.

[0054]

The present invention will be described below with reference to Examples and Comparative Examples. The major axis diameter and the axial ratio (major axis diameter / minor axis diameter) of the particles in the following Examples and Comparative Examples are all shown as the average value of the numerical values measured from electron micrographs. Further, the amount of Co in the magnetic iron oxide particle powder is shown by a value measured by ICAP plasma emission spectroscopy, and Fe ²⁺ and Fe ³⁺ are shown by values measured by a redox titration method. The magnetic characteristics were measured by applying an external magnetic field up to 10 KOe using a "vibrating sample magnetometer VSM-3S-15" (manufactured by Toei Industry Co., Ltd.).

Regarding the thermal history of the coercive force before and after heating the magnetic particle powder and the magnetic recording medium, the measurement sample for the vibrating sample type magnetometer was covered with a quartz protective tube, and the inside of the protective tube was made a nitrogen atmosphere. After heating to ℃, room temperature (25
50 ℃, 70 ℃, 90 in the process of lowering the temperature to
The value of the coercive force obtained by holding the above-mentioned measurement sample for 1 minute at each temperature of ℃, 110 ℃, 130 ℃ and 150 ℃ was obtained by plotting on the diagram showing the relationship between temperature and coercive force.

In the figure, ◯ indicates the coercive force value at each temperature during the temperature raising process, and Δ mark indicates the coercive force value at each temperature during the temperature lowering process. It means that the history of the coercive force is more reversible as the marks ◯ and Δ overlap, and the history of the coercive force is more irreversible as the marks ◯ and Δ are further apart.

The initial amount of Fe ^{2+ in} the magnetic iron oxide particle powder is
The magnetic iron oxide particle powder obtained by drying at 60 ° C. for 24 hours in high-purity nitrogen is shown as the measured value. In addition, Fe over time
The change in the amount of ²⁺ indicates the measured value in the iron oxide particle powder after standing in the air at a temperature of 60 ° C. and a humidity of 90%.

The change in hue with time is shown by the measured values of L ^* value (brightness), a ^* value and b ^* value under the same conditions. The L ^* value (brightness), a ^* value, and b ^* value were measured by the Hunter's Lab space using a multi-source spectrophotometric colorimeter MSC-IS-2D (manufactured by Suga Test Instruments Co., Ltd.). L
^* Value, a ^* value, and b ^* value are measured respectively, and the International Commission on Illumination (Commission International
le de l'Eclairage, CIE) 197
6 (L ^* , a ^* , b ^* ) The values are shown according to the uniform perceptual color space.

A sample piece for hue measurement was prepared by kneading 0.5 g of magnetic iron oxide particles powder and 0.5 cc of castor oil with a Hoover-type Mahler to form a paste, and adding 4.5 g of clear lacquer to this paste to knead to form a paint. It was obtained by coating on cast coated paper with a 6 mil applicator.

The light transmittance is measured by a photoelectric spectrophotometer UV-21.
00 (manufactured by Shimadzu Corporation) was used to measure the light transmittance at λ = 900 nm. It is standardized in JIS X 6121 that the light transmittance is 1% or less.

<Production of Nuclear Crystal Particles> Nuclear crystal particle A 22 L of 1.8-N NaOH aqueous solution heated to 90 ° C.
While blowing air at 100 liters per minute, 1.72-
10 L of a ferrous sulfate aqueous solution of M was added and the reaction was carried out for 2 hours to obtain a suspension containing a black precipitate. After completion of the reaction, a part of the slurry liquid was sampled from the reaction liquid to measure the characteristics of the black particle powder. The obtained black particle powder was Fe ₃ O _{4 as} a result of the redox titration method and had an average particle diameter of 0.15.
μm, magnetic characteristics: coercive force of 150 Oe, saturation magnetization of 8
It was 5.2 emu / g.

Nuclear Crystal Particle B 1300 g of needle-like hematite particles having a major axis diameter of 0.20 μm and a minor axis diameter of 0.03 μm were put into a 10 l retort reduction vessel, and H ₂ gas was added at a rate of 2 l / min while being driven and rotated. And then reduced at a reduction temperature of 400 ° C. to obtain acicular magnetite particle powder. When a part of this was sampled, this black particle powder showed Fe ₃
O ₄ with major axis diameter 0.20 μm, minor axis diameter 0.03 μm
As for the magnetic characteristics, the coercive force was 420 Oe and the saturation magnetization was 81.2 emu / g.

Nuclear Crystal Particles C 1300 g of needle-like hematite particles having a major axis diameter of 0.30 μm and a minor axis diameter of 0.042 μm were put into a 10 l retort reduction vessel, and H ₂ gas was added at a rate of 2 l / min while being driven and rotated. And then reduced at a reduction temperature of 400 ° C. to obtain acicular magnetite particle powder. When a part of this was sampled, this black particle powder showed Fe ₃
It is O _4, major axis diameter 0.30μm, minor axis diameter 0.042μ
The coercive force was 420 Oe and the saturation magnetization was 81.2 emu / g.

<Production of Spinel Type Composite Particle Powder> Examples 1 to 5 Comparative Examples 1 to 4; Example 1 Granular Fe ₃ O ₄ particle powder of the nucleation particles A (average particle size of 0.
15 μm, coercive force 150 Oe, saturation magnetization 85.2 em
u / g) The above suspension 3 in which 1294 g is mixed and dispersed.
While 2l was continuously blown with air at a rate of 100l / min, 3.033l of an 18-N NaOH aqueous solution was added to obtain an alkaline dispersion having a pH of 14.1. This alkaline dispersion was heated to 90 ° C. and separately adjusted 1.68-
M (Fe ²⁺ to Co ²⁺ 1 mole corresponds to 2 moles.) Mixed solution of FeSO ₄ and 0.840-M CoSO ₄ of the 10 l to the alkaline dispersion Co ²⁺ and Fe
²⁺ was added while controlling the total concentration of Co ²⁺ and Fe ²⁺ to be 0.05 M, and the synthesis reaction of the composite particles was controlled to 60%.
(The coating amount of CoFe ₂ O ₄ corresponds to 60.0% by weight based on the produced spinel-type composite particles.).
After completion of the reaction, black particles were obtained by filtration, washing with water and drying by a conventional method.

The resulting black particle powder had an average particle size of 0.
It has a coercive force Hc of 840 O.
e, the saturation magnetization σs was 78.5 emu / g. The amount of Fe ²⁺ was 13.2 wt%, and the hue was L ^* value of 22.0, a ^* value of −0.07, and b ^* value of −1.15.
Met.

As shown in FIG. 1, the thermal history of the coercive force in the temperature range of −35 to 150 ° C. is reversible, and as shown in Table 1, the coercive force in the environment of temperature 60 ° C. and humidity 90%. Also, it was confirmed that the saturation magnetization hardly changed and the magnetic stability was excellent.

It should be noted that in FIG. 1, the thermal history of the coercive force when the temperature is raised from 25 ° C. to 150 ° C. and then to room temperature, and 10 ° C. in the process of further cooling to −35 ° C. and then heating to 25 ° C. , -20 ° C and -35 ° C, the history of coercive force obtained by measuring after holding the measurement sample for 1 minute is also shown. In addition, the Fe ²⁺ content and hue in an environment of temperature 60 ° C and humidity 90% are also shown in Table 1.
Also, as shown in Table 2, there was almost no change, and it was confirmed that it was chemically stable.

As a result of X-ray diffraction, only a peak showing a spinel type crystal structure was observed in this black particle powder, and the results of composition analysis of Co ²⁺ , Fe ²⁺ and Fe ³⁺ measured by the following method. It was confirmed that the composition of the particle surface was CoFe ₂ O ₄ and the nucleation crystal particles were Fe ₃ O ₄ .
In addition, the composition analysis was conducted by adding 10 g of the above black particle powder to 100 ml.
Suspended in water, placed in a reaction vessel and heated to 60 ° C., 200 ml of 1-N HCl solution was added with stirring to dissolve Co ²⁺ , Fe ²⁺ and Fe ³⁺
This was done by measuring the amount. That is, 6 points of measurement samples are prepared, and the moment when HCl is added is set to t = 0, 1, 5, 1
Samples were taken out one by one at each time of 0, 30, 60, and 120 minutes, and the amounts of Co ²⁺ , Fe ²⁺ and Fe ³⁺ in the filtrate obtained by filtering out black particles were measured. analyzed. As a result, Fe ²⁺ was not detected in the liquid of t = 1, and C
The ratio of o ²⁺ : Fe ³⁺ was 1: 2. From this, it was confirmed that the surface of the black particles had a CoFe ₂ O ₄ composition. The black particles filtered out of the suspension at t = 120 were washed with pure water to remove water-soluble salts, and then the black particles were subjected to compositional analysis. As a result, Co ²⁺ was not detected and Fe 2
³⁺ : Fe ²⁺ was 2: 1. From this, it was confirmed that the nucleation portion of the black particles obtained had a Fe ₃ O ₄ composition.

Example 2 1. Instead of 3.033 l of 18-N NaOH aqueous solution
Using 767 l, an alkaline suspension having a pH of 14.1 was prepared, and the concentration of CoSO ₄ was changed to 0.840 M to 0.60.
M (Fe ²⁺ corresponds to 2.8 moles relative to 1 mole of Co ²⁺ ), the amount of air blown in is 80 l / min, the temperature of the alkaline dispersion liquid is 95 ° C., and Co ²⁺ and Fe ² The synthesis reaction of the composite particles was carried out in the same manner as in Example 1 except that the ⁺ concentration was controlled so that the total sum of Co ²⁺ and Fe ²⁺ was 0.03M (CoFe ₂ O ₄ Corresponds to 57.6% by weight with respect to the produced spinel-type composite particles).

The obtained black particle powder had an average particle size of 0.
19 μm, and the magnetic characteristic is a coercive force Hc of 484 O
e, the saturation magnetization s was 85.6 emu / g. Further, the amount of Fe ²⁺ was 15.9 wt%, and the hue had an L ^* value of 21.5, an a ^* value of −0.04, and a b ^* value of −1.07.
Met.

Further, as indicated by the straight line a in FIG. 2, the thermal history of the coercive force before and after heating is reversible, and as shown in Table 1, the coercive force and saturation under the environment of temperature 60 ° C. and humidity 90%. It was confirmed that the magnetization hardly changed and the magnetic stability was excellent. Temperature 60 ℃, humidity 90
It was confirmed that the Fe ²⁺ content and the hue under the environment of% hardly changed as shown in Tables 1 and 2 and were chemically stable.

As a result of X-ray diffraction, only a peak showing a spinel type crystal structure was observed in this black particle powder,
Moreover, as a result of analyzing the composition in the same manner as in Example 1, the composition on the surface of the particles was CoFe ₂ O ₄ , and the nucleation portion was Fe _3.
It was found to be O ₄ .

Example 3 Needle-like Fe ₃ O _{4 of} the nucleation particles B (long axis 0.20 μm, short axis 0.03 μm, in place of granular Fe ₃ O ₄ as nucleation particles,
Coercive force Hc420 Oe, saturation magnetization 81.2 emu /
g) 1200 g of 1200 g of 1200 g of NaOH.
PH 13.2 using 0.827 l instead of 715 l.
6 in an alkaline suspension, and the concentration of CoSO ₄ is 0.8.
40M instead of 0.178M, FeSO ₄ concentration 1.
0.356M instead of 68M (Fe per 1 mol of Co ^2+
2+ corresponds to 2 moles. ), And Co ²⁺ and Fe
The concentration of ²⁺ was synthesized reactions to composite particles in the same manner as in Example 1 except for adding while controlling so as to 0.01M in total of Co ²⁺ and Fe ²⁺ (CoFe ₂ O ₄ Corresponds to 25.5% by weight based on the produced spinel type composite particles.).

The obtained black particle powder has a major axis diameter of 0.2.
1 μm, minor axis diameter 0.032 μm, magnetic characteristics coercive force Hc 967 Oe, saturation magnetization 77.1 emu
/ G. The amount of Fe ²⁺ was 15.5 wt%, and the hue was L ^* value 23.0, a ^* value 0.11, b ^*.
The value was -0.84.

As shown by the straight line b in FIG. 2, the thermal history of the coercive force before and after heating is reversible, and as shown in Table 1,
It was confirmed that the coercive force and the saturation magnetization under the environment of the temperature of 60 ° C. and the humidity of 90% hardly changed, and the magnetic stability was excellent. Also, temperature 60 ℃, humidity 90
It was confirmed that the Fe ²⁺ content and the hue under the environment of% hardly changed as shown in Tables 1 and 2 and were chemically stable.

As a result of X-ray diffraction, only a peak showing a spinel type crystal structure was observed in this black particle powder,
Moreover, as a result of analyzing the composition in the same manner as in Example 1, the composition on the surface of the particles was CoFe ₂ O ₄ , and the nucleation portion was Fe _3.
It was found to be O ₄ .

Example 4 1. Instead of 0.827 l of 18-N aqueous NaOH solution.
An alkaline suspension having a pH of 13.8 was prepared using 420 l, and the concentration of CoSO ₄ was changed to 0.178 M to 0.35.
6M, 0.7% instead of FeSO ₄ concentration of 0.356M
12M (corresponding to 2 moles of Fe ²⁺ to 1 mole of Co ²⁺ ), the amount of air blown is 120 l / min, the temperature in the alkaline dispersion is 95 ° C., and Co ²⁺ and Fe ²⁺
Was added while controlling so that the total concentration of Co ²⁺ and Fe ²⁺ would be 0.15M, and the synthesis reaction of the composite particles was performed in the same manner as in Example 3 (CoFe ₂ O ₄ coating). The amount corresponds to 40.7% by weight based on the generated spinel type composite particles.).

The obtained black particle powder has a major axis diameter of 0.2.
3 μm, minor axis diameter 0.033 μm, magnetic characteristics coercive force 1467 Oe, saturation magnetization 73.4 emu /
It was g. The amount of Fe ²⁺ was 12.1 wt%, and the hue was L ^* value of 21.2, a ^* value of 0.06, and b ^*.
The value was -0.96.

As indicated by the straight line c in FIG. 2, the thermal history of the coercive force before and after heating is reversible, and as shown in Table 1,
It was confirmed that the coercive force and the saturation magnetization under the environment of the temperature of 60 ° C. and the humidity of 90% hardly changed, and the magnetic stability was excellent. Also, temperature 60 ℃, humidity 90
It was confirmed that the Fe ²⁺ content and the hue under the environment of% hardly changed as shown in Tables 1 and 2 and were chemically stable. As a result of X-ray diffraction, only a peak showing a spinel type crystal structure was observed in this black particle powder, and the composition was analyzed in the same manner as in Example 1. As a result, the composition of the particle surface was CoFe ₂ O ₄ It was confirmed that the nucleation part was Fe ₃ O ₄ .

Example 5 Needle-like Fe ₃ O _{4 of} nucleation grains C (long axis 0.30 μm, short axis 0.042 μm, coercive force Hc430 Oe, saturation magnetization 8)
2.3 emu / g), and using 1.120 l instead of 0.827 l of 18-N NaOH aqueous solution, pH 1
As an alkaline suspension of 3.7, the concentration of CoSO ₄ was changed to 0.178M, and the concentration of FeSO ₄ was changed to 0.356M, which was 0.534M (1 mole of Co ²⁺ to Fe ^2+). There corresponds to 2 moles.), the air blowing amount 80 l / min, the temperature of the alkaline dispersion and 90 ° C., and the sum of the concentrations of Co ²⁺ and Fe ²⁺ is Co ²⁺ and Fe ²⁺ Reaction was performed in the same manner as in Example 3 except that the addition was carried out while controlling so that the concentration became 0.10 M (CoFe ₂ O ₄
Corresponds to 34.0% by weight based on the produced spinel type composite particles. ).

The obtained black particle powder has a major axis diameter of 0.3.
2 μm, minor axis diameter 0.045 μm, magnetic characteristics coercive force 1020 Oe, saturation magnetization 79.1 emu /
It was g. Further, the amount of Fe ²⁺ was 16.0 wt%, and the hue was L ^* value of 18.8, a ^* value of 0.01, and b ^*.
The value was -1.12.

As indicated by the straight line d in FIG. 2, the thermal history of the coercive force before and after heating is reversible, and as shown in Table 1,
It was confirmed that the coercive force and the saturation magnetization under the environment of the temperature of 60 ° C. and the humidity of 90% hardly changed, and the magnetic stability was excellent. Also, temperature 60 ℃, humidity 90
It was confirmed that the Fe ²⁺ content and the hue under the environment of% hardly changed as shown in Tables 1 and 2 and were chemically stable.

As a result of X-ray diffraction, only a peak showing a spinel type crystal structure was observed in this black particle powder,
Moreover, as a result of analyzing the composition in the same manner as in Example 1, the composition on the surface of the particles was CoFe ₂ O ₄ , and the nucleation portion was Fe _3.
It was found to be O ₄ .

Comparative Example 1 18-N NaOH aqueous solution was replaced by 3.033 l of 1.
Using 833 liters of NaOH to make an alkaline dispersion of pH 13.9 and 1.2M FeSO ₄ and 0.24
M aqueous solution of CoSO ₄ (1 mole of Co ²⁺ for Fe
²⁺ corresponds to 5 mol. ) 10 l, the liquid temperature in the alkaline suspension is 80 ° C., and the amount of air blown is 120 l.
/ Min and, and except that a mixed solution of FeSO ₄ and CoSO ₄ concentrations of Co ²⁺ and Fe ²⁺ was added while controlling so as to 0.03M in total of Co ²⁺ and Fe ²⁺ Performs the synthetic reaction of the composite particles for 2 hours in the same manner as in Example 1 (the coating amount of CoFe ₂ O ₄ corresponds to 42.5% by weight based on the produced spinel composite particles), and then by a conventional method. It was filtered, washed with water, and dried to obtain a black particle powder.

The obtained black particle powder had an average particle diameter of 0.20 μm and had magnetic properties of a coercive force Hc of 650.
The Oe and the saturation magnetization were σs 85.2 emu / g.
The amount of Fe ²⁺ is 12.2 wt%, and the hue is L ^*.
Value 19.39, a ^* value 0.45, b ^* value -1.0
It was 2.

As shown in FIG. 3, the thermal history of the coercive force before and after heating is irreversible, and as shown in Table 1, the coercive force and the saturation magnetization under the environment of temperature 60 ° C. and humidity 90% are large. The width was changed and it was confirmed that it was magnetically unstable. Further, as shown in Table 1, the Fe ²⁺ content is also greatly reduced, and as a result, the hue is also significantly changed as shown in Table 2, indicating that it is chemically unstable. Was recognized.

As a result of X-ray diffraction, this black particle powder showed a spinel type crystal structure, and the composition analysis was carried out in the same manner as in Example 1. As a result, it was found that Co ²⁺ , Fe
²⁺ and Fe3 ⁺ were detected. From this, it was confirmed that the particle surface of the black particles was a spinel substance having Co ²⁺ , Fe ²⁺ and Fe ^{3+, and} was a composition given by the general formula Co _x Fe _1-x Fe ₂ O ₃ . .

COMPARATIVE EXAMPLE 2 18-N NaOH aqueous solution was replaced by 3.033 l of 3.
344 l NaOH was used to make an alkaline dispersion of pH 14.2 and 1.68 M FeSO ₄ and 1.1
Mixed aqueous solution of 2M CoSO ₄ (F 2 for 1 mol of Co ²⁺
e ²⁺ corresponds to 1.5 mol. ) 10 l, the liquid temperature in the alkaline suspension was 80 ° C, and the amount of air blown was 10
0 l / min and, and, a mixed solution of FeSO ₄ and CoSO _4, while controlling the concentrations of Co ²⁺ and Fe ²⁺ is 0.15M in total of Co ²⁺ and Fe ²⁺ A synthesis reaction was performed in the same manner as in Example 1 except that the addition was performed. When the reaction mother liquor was sampled at 2 hours, 4 hours, and 8 hours after the start of air blowing and the product was observed by an electron microscope, the mixture of hexagonal plate-like particles was confirmed in all the samples. . The hexagonal plate-like particles were Co (OH) _{2 as} a result of electron diffraction.

[0089] Comparative Example 3 Co ²⁺ and Fe concentration of ²⁺ in the same manner as in Example 1 except for adding while controlling so as to 0.6M by the sum of Co ²⁺ and Fe ²⁺ synthesis reaction I went. After the completion of the reaction, the particles obtained by washing with water and drying were observed by an electron microscope. As a result, particles smaller than Fe ₃ O ₄ particles, which are nucleation particles, and particles that grew greatly were observed, and the particles were separated separately. Were found to be mixed.

[0090] Comparative Example 4 Co ²⁺ and Fe concentration of ²⁺ in the same manner as in Example 1 except for adding while controlling so that the 0.001M in total of Co ²⁺ and Fe ²⁺ synthesis reaction I went. After the reaction,
As a result of electron microscopic observation of the particles obtained by washing with water and drying, particles smaller than Fe ₃ O ₄ particles which are nucleation particles and particles grown large were observed, and particles separated separately were mixed. It was recognized that

Tables 1 and 2 show various properties of the spinel-type composite particle powder at this time.

[0092]

[Table 1]

[0093]

[Table 2]

<Production of Magnetic Tape> Examples 6 to 10 Comparative Example 5; Example 6 100 parts by weight of the spinel-type composite particle powder obtained in Example 1, VAGH (vinyl chloride-vinyl acetate-vinyl alcohol copolymer) : U.S.C. company) 14 parts by weight, myristic acid 1 part by weight, toluene 30 parts by weight, methyl ethyl ketone 30 parts by weight, and Al ₂ O ₃ powder 1 part by weight, and after kneading with a kneader for 90 minutes, Toluene 4 was added to the kneaded product.
5 parts by weight and 45 parts by weight of methyl ethyl ketone were added to dilute, and then mixed and dispersed by a sand grinder for 3 hours.

Polyurethane resin (Product name: Nipolan 2304: manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the above-mentioned mixed dispersion.
Methyl ethyl ketone solution containing 14 parts by weight of solid content of
After adding 0 part by weight and mixing for 30 minutes, 3 parts by weight of Coronate L (trifunctional low molecular weight isocyanate compound: manufactured by Nippon Polyurethane Industry Co., Ltd.) was mixed with the filtered product to produce a magnetic coating material. did.

The above magnetic coating material was applied onto a polyester base film having a thickness of 14 μm and then dried to form a magnetic layer having a thickness of 4 μm, which was then cut into 1/2 inch width to prepare a magnetic tape. .

The magnetic characteristic of the above magnetic tape is that the coercive force is 9
12 Oe, saturation magnetic flux density Bm was 1452 Gauss, and squareness ratio (Br / Bm) was 0.702. Moreover, the light transmittance was as small as 0.32.

As shown in FIG. 4, the thermal history of the coercive force in the temperature range of −35 to 150 ° C. is reversible, and as shown in Tables 3 and 4, under the environment of temperature 60 ° C. and humidity 90%. It was confirmed that the magnetic coercive force, the saturation magnetic flux density, and the squareness ratio were almost unchanged, and the magnetic stability was excellent. Then, as shown in Table 4, it was confirmed that the light transmittance hardly changed and the chemical stability was excellent.

In FIG. 4, along with the thermal history of the coercive force when the temperature is raised from 25 ° C. to 150 ° C. and then to room temperature, 10 ° C. in the process of further cooling to −35 ° C. and then heating to 25 ° C. , -20 ° C and -35 ° C, the history of coercive force obtained by measuring after holding the measurement sample for 1 minute is also shown.

Examples 7 to 10 and Comparative Example 5 A magnetic tape was manufactured in the same manner as in Example 6 except that the kind of magnetic particle powder was changed variously.

Various characteristics of the magnetic tape at this time are shown in Tables 3 and 4 and FIGS. 5 and 6. In FIG. 5, straight lines a to d
Are magnetic recording media obtained in Examples 7 to 10, respectively. FIG. 6 shows the magnetic recording medium obtained in Comparative Example 5.

[0102]

[Table 3]

[0103]

[Table 4]

[0104]

The magnetic recording medium according to the present invention has a high coercive force, a small light transmittance, and excellent magnetic and chemical stability as shown in the above-mentioned embodiments. Therefore, it is suitable for high performance, especially for high recording density, high sensitivity and high output.

[Brief description of drawings]

1 shows -3 of the spinel type composite particles obtained in Example 1. FIG.
The thermal history of coercive force in the temperature range of 5 ° C to 150 ° C is shown.

FIG. 2 shows the thermal history of coercive force in the temperature range of 25 ° C. to 150 ° C. of the spinel type composite particles obtained in Examples 2 to 5. In FIG. 2, straight lines a to d are spinel-type composite particles obtained in Examples 2 to 5, respectively.

FIG. 3 shows 25 spinel-type composite particles obtained in Comparative Example 1.
The thermal history of coercive force in the temperature range of ℃ to 150 ℃ is shown.

FIG. 4 shows the magnetic recording medium obtained in Example 6 at −35 ° C.
The thermal history of coercive force in the temperature range of 150 ° C. is shown.

FIG. 5 shows 2 of the magnetic recording media obtained in Examples 7 to 10.
The thermal history of coercive force in the temperature range of 5 ° C to 150 ° C is shown. In FIG. 5, straight lines a to d are magnetic recording media obtained in Examples 7 to 10, respectively.

6 is a graph of the magnetic recording medium obtained in Comparative Example 5 at 25 ° C. to 1;
The thermal history of coercive force in the temperature range of 50 ° C. is shown.

Claims (1)

[Claims] 1. A magnetic iron oxide particle powder comprising spinel-type composite particles in which Fe ₃ O ₄ particles are used as nucleation particles and CoFe ₂ O ₄ is crystal-grown on the surface of the nucleation particles on a substrate. A magnetic recording medium coated with a resin composition containing.