DE112019004072T5 - MAGNETIC POWDER AND METHOD FOR MANUFACTURING THEREOF, AND MAGNETIC RECORDING MEDIUM - Google Patents

Abstract

A method for producing a magnetic powder comprises: performing a reduction process on particles containing ε-iron oxide (in which at least a part of the Fe sites is replaced by a metal oxide M), and forming triiron tetraoxide (in which at least a part of the Fe sites is replaced by the metal oxide M) at least in a part of the surface of the particles, whereby magnetic particles are obtained.

Description

TECHNICAL AREA

The present disclosure relates to a magnetic powder and a method for producing the same, and a magnetic recording medium.

GENERAL STATE OF THE ART

Conventionally, as a magnetic recording medium, there is known a recording type magnetic recording medium in which a recording layer is formed by applying a magnetic coating material containing a magnetic powder, a binder and an organic solvent on a non-magnetic support and drying the magnetic coating material. Such a recording type recording medium is widely used as a high density recording medium such as a backup data cartridge.

In recent years, particles of magnetic powder contained in a recording layer have been made fine particles to correspond to a recording medium having a high recording density. However, when the particles are made into finer particles, the magnetic powder is affected by external heat in an environment where a magnetic tape is used, an influence of so-called thermal disturbance of magnetization is noticeable, and a phenomenon that the recorded magnetization disappears occurs on. In order to avoid the influence of the thermal disturbance of magnetization, it is necessary to increase a coercive force of the magnetic powder.

However, when the coercive force is increased, it is difficult for a recording head to reverse magnetization, that is, to record an information signal. Further, when the particles are made into finer particles, a saturation magnetization value σ _{s of} the magnetic powder may decrease, and a noise ratio (hereinafter referred to as "CNR") may be greatly deteriorated, in combination with a decrease in performance due to the recording with high density.

In order to solve these problems, for example, Patent Document 1 proposes a method for producing a magnetic powder that forms a shell part containing α-Fe by reducing a surface area of an ε-iron oxide particle.

LITERATURE LIST

PATENT DOCUMENT

Patent Document 1: PCT International Patent Application Laid-Open No. 2016/092744

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

It is an object of the present technology to provide a magnetic powder capable of high performance, excellent thermal stability and ease of recording, and a method for producing the same, and a magnetic recording medium.

SOLUTIONS TO THE PROBLEMS

In order to solve the above-described problems, a first disclosure is a method for producing a magnetic powder, the method comprising: reducing a particle containing ε-iron oxide (comprising ε-iron oxide in which some of the Fe sites are replaced by a metal element M) to form triiron tetraoxide (comprising triiron tetraoxide in which some of the Fe Places are replaced by the metal member M) on at least a part of a surface of the particle, thereby obtaining a magnetic particle.

A second disclosure is a magnetic powder comprising a magnetic particle comprising: a particle containing ε-iron oxide (comprising ε-iron oxide in which some of the Fe sites are replaced with the metal element M); and triiron tetraoxide (comprising triiron tetraoxide in which some of the Fe sites are replaced with the metal element M) formed on at least a part of a surface of the particle.

A third disclosure is a magnetic recording medium comprising a recording layer containing the magnetic powder according to the second disclosure.

A fourth disclosure is a method for producing a magnetic powder, the method comprising: transforming a first particle containing ferrous oxide (comprising ferrous oxide in which the metal element M replaces some of the Fe sites are), into a second particle containing γ-iron oxide (comprising γ-iron oxide in which some of the Fe sites are replaced by the metal element M), and then transforming part of the second particle into ε-iron oxide (comprising ε-iron oxide in which some of the Fe sites are replaced with the metal element M) to obtain a magnetic particle.

A fifth disclosure is a magnetic powder comprising a magnetic particle comprising: a particle containing ε-iron oxide (comprising ε-iron oxide in which some of the Fe sites are replaced with the metal element M); and γ-iron oxide (including γ-iron oxide in which some of the Fe sites are replaced with the metal element M) formed on at least a part of the surface of the particle.

A sixth disclosure is a magnetic recording medium comprising a recording layer containing the magnetic powder according to the fifth disclosure.

EFFECTS OF THE INVENTION

According to the present disclosure, high performance, excellent thermal stability and ease of recording can be obtained. It should be noted that the effects described herein are not necessarily limited, and may be or different from any of the effects described in the present disclosure.

Figure list

• 1 Fig. 13 is a sectional view of a magnetic powder according to a first embodiment of the present disclosure.
• 2 Fig. 13 is a sectional view of a magnetic powder according to a second embodiment of the present disclosure.
• 3 Fig. 13 is a sectional view of a magnetic recording medium according to a third embodiment of the present disclosure.
• 4th Fig. 13 is a flow chart for explaining a method for producing magnetic powders according to Examples 1 to 8 and 11 to 15.
• 5 FIG. 13 is a flow chart for explaining a method for producing magnetic powders according to Examples 9 and 10. FIG.

MODE FOR CARRYING OUT THE INVENTION

1. 1 Erste Ausführungsform (Beispiel eines magnetischen Pulvers)
2. 2 Zweite Ausführungsform (Beispiel eines magnetischen Pulvers)
3. 3 Dritte Ausführungsform (Beispiel eines magnetischen Aufzeichnungsmediums)

Embodiments of the present disclosure are described in the following order.

1. 1 First embodiment (example of magnetic powder)
2. 2 Second embodiment (example of magnetic powder)
3. 3 Third embodiment (example of magnetic recording medium)

<First embodiment>

[Design of Magnetic Powder]

A magnetic powder according to a first embodiment of the present disclosure includes a magnetic particle 10 having a core-shell type structure as in 1 illustrated. The magnetic particle 10 includes a core part 11 , which contains ε-iron oxide (comprising ε-iron oxide in which some of the Fe Places are replaced by the metal element M), and a shell part 12th that is on the periphery of the core part 11 and contains triiron tetraoxide (including triiron tetraoxide in which some of the Fe sites are replaced by the metal element M). The core part 11 and the shell part 12th preferably form an exchange link. At an interface between the core part 11 and the shell part 12th the compositions and / or states and the like of the core part may differ 11 and the shell part 12th change discontinuously or continuously. The magnetic particle 10 has a substantially cubic shape or a substantially spherical shape, for example. The magnetic powder according to the first embodiment is suitable for use as a recording layer (magnetic layer) of a high-density magnetic recording medium.

(Mean particle radius r)

The magnetic particle 10 preferably has a mean particle radius r of 4 nm r 20 nm. If the mean particle radius r of the magnetic particle 10 4 nm r is satisfied, it is possible to suppress a decrease in dispersibility of the magnetic powder when a coating material forming a recording layer is prepared using the magnetic powder, and therefore the electromagnetic conversion characteristics (for example, CNR) of a magnetic Recording medium can be further improved. When the mean particle radius r of the magnetic particle 10 When r 20 nm is satisfied, it is possible to suppress an increase in noise of a magnetic recording medium when a recording layer is formed using the magnetic powder. Therefore, the electromagnetic conversion characteristics (for example, CNR) of the magnetic recording medium can be further improved. Further, when a recording layer forming coating material containing the magnetic powder is used to form a coating film, it is possible to suppress deterioration in the surface property of the coating film. It should be noted that in the present disclosure, not only in a case where the magnetic particle 10 has a substantially spherical shape, but also in a case where the magnetic particle 10 has a substantially cubic shape, in terms of mean particle radius r of the magnetic particle 10 and mean particle diameter D thereof can be used.

The above mean particle radius r of the magnetic particle 10 is determined as follows. First, the magnetic powder is imaged using a transmission electron microscope (TEM). An apparatus (TEM) and imaging conditions used for imaging are described below.
Device (TEM): H9000NAR manufactured by Hitachi, Ltd.
Accelerating voltage: 200 kV
Total magnification: 500,000 times

Next will be 500 magnetic particles 10 whose shapes can be clearly confirmed are randomly selected from the depicted TEM photograph, and an area S of each of the magnetic particles 10 is determined. Next, assuming the shape of the magnetic particle 10 is spherical, a radius r _{A of} each of the magnetic particles 10 calculated from the following formula to obtain a particle size distribution of the magnetic powder. $${\text{r}}_{\text{A.}}={\left(\text{S /}\mathrm{\pi }\right)}^{1\text{/}2}$$

Next, a median diameter (50% diameter, D50) is determined from the determined particle size distribution and defined as the mean particle radius r.

(Ratio R _{1 of} the standard deviation σ of the particle size distribution to the mean particle diameter D)

A ratio R ₁ (= (σ / D) × 100) of a standard deviation σ of the particle size distribution of the magnetic particle 10 to the mean particle diameter D of the magnetic particle 10 preferably satisfies R ₁ 40%. When the ratio R ₁ satisfies R ₁ 40%, the particle size variation of the magnetic particle is 10 small, and the variation in the magnetic characteristics of the magnetic powder can be suppressed. A lower limit of the ratio R ₁ is not particularly limited, but for example, R ₁ satisfies 5% R ₁ .

The above ratio R ₁ is determined as follows. First, the area S of each particle is determined in a manner similar to the method for calculating the mean particle radius r of the magnetic particle 10 definitely. Next, assuming the shape of the magnetic particle 10 is spherical, a diameter D _{A of} each particle is calculated from the following formula to obtain a particle size distribution of the magnetic powder. $${\text{D.}}_{\text{A.}}=2\text{x}{\left(\text{S /}\mathrm{\pi }\right)}^{1\text{/}2}$$

Next, a median diameter (50% diameter, D50) is determined from the determined particle size distribution and defined as the mean particle diameter D. In addition, the standard deviation σ is determined from the determined particle size distribution. Next, the ratio R ₁ (= (σ / D) × 100) is calculated using the determined mean particle diameter D and the determined standard deviation σ of the particle size distribution.

(Saturation magnetization value σ _s )

A saturation magnetization value, σ _s , of the magnetic particle 10 preferably satisfies 30 emu / g σ _s 60 emu / g. In a case where the saturation magnetization value σ _s 30 emu / g ≤ σ _s, met, when a recording layer using the magnetic powder is manufactured, a higher performance can be obtained and, therefore, better electromagnetic conversion characteristics can be obtained (for example, CNR) become. If σ _s satisfies σ _s ≤ 60 emu / g, it is possible that the ratio of the shell part is too large 12th to the core part 11 to suppress, that is, too large a ratio of a soft magnetic material to a hard magnetic material, and therefore a decrease in the coercive force Hc can be suppressed.

The above saturation magnetization value σ _s is determined as follows. First, a magnetic powder sample having a predetermined shape is prepared. The magnetic powder sample can be made freely within a range that does not affect the measurement, such as compaction into a measuring capsule or binding to a tape measure. Next, an MH loop of the magnetic powder sample is obtained using a vibrating sample magnetometer (VSM), and then the saturation magnetization value σ _{s is determined} from the obtained MH loop. It should be noted that the above measurement of the MH loop is carried out in the vicinity of 25 ° C. Further, a highly sensitive vibrating sample magnetometer “VSM-P7-15” manufactured by Toei Industry Co., Ltd. is used for the above measurement of the MH loop. The measurement conditions are set to the measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field level: 40 bits, time constant of the locking device: 0.3 s, waiting time: 1 s, and MH mean value: 20.

(Core part)

The core part 11 preferably contains an ε-Fe ₂ O ₃ crystal which is a hard magnetic material (comprising an ε-Fe ₂ O ₃ crystal in which some Fe sites are replaced by the metal element M) as a main phase, and more preferably contains a single-phase ε-Fe ₂ O ₃ crystal. The metal element M is at least one of Al, Ga, and In, for example. However, when a molar ratio between M and Fe is expressed by M: Fe = x: (2 - x), 0 x <1 is satisfied. Here, the compositional formula of ε-iron oxide is expressed by Fe ₂ O ₃ , but ε-iron oxide may have a non-stoichiometric composition.

In the present disclosure, unless otherwise specified, the ε-Fe ₂ O ₃ crystal includes, in addition to a pure ε-Fe ₂ O ₃ crystal in which an Fe site is not replaced by another element, a crystal in some Fe sites are replaced by a trivalent metal element M, and a space group is the same as the pure ε-Fe ₂ O ₃ crystal (that is, the space group is Pna2 ₁ ).

(Shell part)

The shell part 12th covers at least part of the periphery of the core part 11 . Specifically, the shell part 12th partly the periphery of the core part 11 cover or may cover the entire periphery of the core part 11 cover. The shell part 12th preferably covers the entire surface of the core part 11 from the standpoint of creating an exchange coupling between the core part 11 and the shell part 12th sufficient to improve the magnetic characteristics.

The shell part 12th preferably contains an Fe ₃ O ₄ crystal which is a soft magnetic material (comprising an Fe ₃ O ₄ crystal in which some of the Fe sites are replaced with the metal element M) as a main phase, and more preferably contains a single phase Fe ₃ O ₄ crystal. However, when a molar ratio between M and Fe is expressed by M: Fe = x: (3-x), 0 x <1.5 is satisfied. Here is the Compositional formula of triiron tetraoxide expressed by Fe ₃ O ₄ , however, triiron tetraoxide may have a non-stoichiometric composition.

In the present disclosure, unless otherwise specified, the Fe ₃ O ₄ crystal includes, in addition to a pure Fe ₃ O ₄ crystal in which an Fe site is not replaced by another element, a crystal in which some of the Fe Digits are replaced by the trivalent metal element M, and a space group is the same as the pure Fe ₃ O ₄ crystal.

The shell part 12th For example, by reducing a surface area of a particle (hard magnetic particle), the ε-iron oxide can be obtained as a precursor particle of the magnetic particle 10 contains.

(Mean volume V _{s of} the shell part and ratio R _{2 of} the mean volume V _{s of} the shell part to the mean volume V of the magnetic particle)

A mean volume V _{s of} the shell part 12th preferably satisfies 90 nm ³ V2, and a ratio R ₂ (= (V _s / V) × 100) of the mean volume V _{s of} the shell part 12th to an average volume V of the magnetic particle 10 preferably satisfies 16% R ₂ 62%. When the mean volume V _s satisfies 90 nm ³ V _s and the ratio R ₂ satisfies 16% R ₂ , it is possible to suppress too small a saturation magnetization value σ _s and the saturation magnetization value σ _s within a range of, for example 30 emu / g ≤ σ _s . Therefore, when a recording layer is formed using the magnetic powder, higher performance can be obtained, and therefore better electromagnetic conversion characteristics (for example, CNR) can be obtained. At this time, when the mean volume V _s satisfies 90 nm ³ V ₂ and the ratio R ₂ R ₂ 62% satisfies, it is possible _{to suppress too large a saturation magnetization value σ s} and the saturation magnetization value σ _s within a range, for example of σ _s ≤ 60 emu / g. It is also possible that the ratio of the shell part is too large 12th to the core part 11 to suppress, that is, too large a ratio of a soft magnetic material to a hard magnetic material, and therefore a decrease in the coercive force Hc can be suppressed.

The above mean volume V _s and the ratio R ₂ are determined as follows. First, the magnetic powder is imaged using a TEM. An apparatus (TEM) and imaging conditions used for imaging are described below.
Device (TEM): H9000NAR manufactured by Hitachi, Ltd.
Accelerating voltage: 200 kV
Total magnification: 500,000 times

$${\text{r}}_{\text{Ah}}={\left({\text{S}}_{\text{h}}\text{/}\mathrm{\pi }\right)}^{1\text{/}2}$$

Next will be 500 magnetic particles 10 whose shapes can be clearly confirmed are randomly selected from the depicted TEM photograph, and an area S of each of the magnetic particles 10 is determined, and an area S _{h of} the core part 11 is determined. Next, assuming that the magnetic particle 10 and the core part 11 are spherical, a radius r _{A of} each of the magnetic particles 10 and a radius r _{Ah of} each core part 11 calculated from the following formulas to get particle distributions of the magnetic particle 10 and the core part 11 to obtain. $${\text{r}}_{\text{A.}}={\left(\text{S /}\mathrm{\pi }\right)}^{1\text{/}2}$$

$${\text{r}}_{\text{Ah}}={\left({\text{S.}}_{\text{H}}\text{/}\mathrm{\pi }\right)}^{1\text{/}2}$$

$${\text{V}}_{\text{h}}=\left(4\text{/}3\right)\times \mathrm{\pi }\times {\text{r}}_{\text{h}}{}^3$$

Next, a median diameter (50% diameter, D50) is determined from the particle distribution of the magnetic particle 10 determined and as the mean particle radius r of the magnetic particle 10 Are defined. Furthermore, a median diameter (50% diameter, D50) is determined from the particle distribution of the core part 11 and defined as the mean radius r _{h of} the core part 11 Are defined. Next, assuming the shapes of the magnetic particle 10 and the core part 11 are spherical, the mean volume V of the magnetic particle 10 and the mean volume V _{h of} the core part 11 determined from the following formulas. $$\text{V}=\left(\mathrm{4th}\text{/}3\right)\times \mathrm{\pi }\times {\text{r}}^3$$

$${\text{V}}_{\text{H}}=\left(\mathrm{4th}\text{/}3\right)\times \mathrm{\pi }\times {\text{r}}_{\text{H}}{}^3$$

Then, using the determined mean volume V of the magnetic particle 10 and the determined mean volume V _{h of} the core part 11 the mean volume V _{s of} the shell part 12th determined from the following formula. $${\text{V}}_{\text{s}}=\text{V}-{\text{V}}_{\text{H}}$$

Finally, using the determined mean volume V of the magnetic particle 10 and the determined mean volume V _{s of} the shell part 12th the ratio R ₂ (= (V _s / V ₁ ) × 100) of the mean volume V _{s of} the shell part 12th to the mean volume V of the magnetic particle 10 calculated.

[Method of making magnetic powder]

Hereinafter, a method for producing a magnetic powder according to the first embodiment of the present disclosure will be described. This method of manufacturing magnetic powder includes: reducing a particle containing ε-iron oxide (including ε-iron oxide in which some of the Fe sites are replaced with the metal element M) (hereinafter referred to as “ε-iron oxide particles”) ) to the shell part 12th containing triiron tetraoxide (comprising triiron tetraoxide in which some of the Fe sites are replaced by the metal element M) on at least a part of a surface of the ε-iron oxide particle, thereby forming the magnetic particle 10 having a core-shell type structure is obtained.

First, an ε-iron oxide particle powder is produced. The ε-iron oxide particle preferably contains an ε-Fe ₂ O ₃ crystal (comprising an ε-Fe ₂ O ₃ crystal in which some Fe sites are replaced by the metal element M) as a main phase, and more preferably contains a single-phase ε-Fe ₂ O ₃ crystal.

Then, the ε-iron oxide particle powder is transported into a heating furnace, and then the inside of the heating furnace is replaced with a neutral gas or an inert gas. As the neutral gas, for example, at least one selected from the group consisting of nitrogen (N ₂ ), dry hydrogen (dry H ₂ ) and an ammonia (NH ₃ ) decomposition gas can be used. As the inert gas, for example, one selected from the group consisting of argon (Ar) and helium (He) can be used.

Next, the ε-iron oxide particle powder is reduced by a vapor phase reduction method. More specifically, the ε-iron oxide particle powder is heated while a reducing gas is introduced into the heating furnace. Hence the shell part 12th containing an Fe ₃ O ₄ crystal (comprising an Fe ₃ O ₄ crystal in which some Fe sites are replaced with the metal element M) is formed on at least a part of a surface of the ε-iron oxide particle. As the reducing gas, for example, at least one selected from the group consisting of hydrogen (H ₂ ), carbon monoxide (CO) and a hydrocarbon-based gas (CH ₄ , C ₃ H ₈ , C ₄ H ₁₀ and the like) can be used will.

In a case where a reducing gas having an H ₂ concentration of 4% is used, the heating time during heating is preferably 10 minutes or more and one hour or less. When the heating time 10 Minutes or more, the periphery of ε-Fe ₂ O _{3 can be} effectively reduced to Fe ₃ O _4. At this time, when the heating time is one hour or less, ε-Fe ₂ O ₃ can be _{reduced to Fe 3} O ₄ while effectively suppressing the disappearance of ε-Fe ₂ O _3.

The heating temperature during heating is preferably 250 ° C or more and 600 ° C or less. When the heating temperature is 250 ° C. or more, ε-Fe ₂ O _{3 can be} effectively reduced to Fe ₃ O _4. At this time, when the heating temperature is 600 ° C. or less, it is possible to _{effectively suppress the transformation of ε-Fe 2} O ₃ into another crystal by heat.

Thereafter, the furnace is cooled to room temperature, and then the obtained magnetic powder is carried out of the furnace. Therefore, a magnetic powder is obtained which is the in 1 contains illustrated magnetic particles.

[Effect]

The magnetic powder according to the first embodiment includes the magnetic particle 10 that is the core part 11 containing ε-iron oxide (comprising ε-iron oxide in which some of the Fe sites are replaced with a metal element), and the shell part 12th contains on at least part of the periphery of the core part 11 and contains triiron tetraoxide (including triiron tetraoxide in which some of the Fe sites are replaced by a metal element). By forming a recording layer of a magnetic recording medium using this powder, it is possible to obtain a magnetic recording medium having high performance, excellent thermal stability and ease of recording.

In the method for producing a magnetic powder according to the first embodiment, a surface area of an ε-iron oxide particle prepared in advance is directly reduced, and therefore the particle diameter of the ε-iron oxide particle to be a precursor particle is approximately the same as the particle diameter of the magnetic particle obtained by reduction 10 . Therefore, by setting the particle diameter of the ε-iron oxide particle to be a precursor particle, the magnetic particle can be made 10 can be produced with a desired particle diameter. Therefore, it is possible to suppress the occurrence of variations in the particle size distribution.

In the technique described in Patent Document 1, it is difficult for the ε-iron oxide (hard magnetic material) and α-Fe (soft magnetic material) to coexist, and an oxide film is required on one face. Therefore, a process is complicated and it is difficult to set a three-layer structure (three-layer structure including a single-layer core part and a two-layer shell part). Therefore, it is difficult to manufacture a magnetic particle having a core-shell type structure. In the magnetic particle according to the first embodiment, triiron tetraoxide (soft magnetic material) having an oxidation resistance is formed on a surface of an ε-iron oxide particle (hard magnetic particle). Therefore, a process is simple, and it is easy to set a two-layer structure (two-layer structure comprising a single-layer core part and a single-layer shell part). Therefore, the magnetic particle 10 with a core-shell type structure can be easily manufactured.

<Second embodiment>

[Design of Magnetic Powder]

A magnetic powder according to a second embodiment of the present disclosure includes a magnetic particle 20th having a core-shell type structure as in 2 illustrated. The magnetic particle 20th includes a core part 21 containing ε-iron oxide (comprising ε-iron oxide in which some Fe sites are replaced with a metal element), and a shell part 22nd containing γ-iron oxide (including γ-iron oxide in which some Fe sites are replaced with the metal element).

(Core part)

The core part 21 can, for example, by transforming the inside of a particle containing γ-iron oxide (including γ-iron oxide in which some Fe sites are replaced by the metal element) as a precursor particle of the magnetic particle 20th can be obtained in ε-iron oxide. The core part 21 is similar to the core part 11 in the first embodiment except for the points described above.

(Shell part)

The shell part 22nd preferably contains a γ-Fe ₂ O ₃ crystal which is a soft magnetic material (comprising a γ-Fe ₂ O ₃ crystal in which some of the Fe sites are replaced by the metal element M) as a main phase, and more preferably contains a single-phase γ- Fe ₂ O ₃ crystal. However, when a molar ratio between M and Fe is expressed by M: Fe = x: (2 - x), 0 x <1 is satisfied. Here, the compositional formula of γ-iron oxide is expressed by γ-Fe ₂ O ₃ , but γ-iron oxide may have a non-stoichiometric composition. The shell part 12th can be obtained, for example, by transforming a particle containing ferrous oxide (comprising ferrous oxide in which some of the Fe sites are replaced with the metal element M) as precursor particles by firing.

In the present disclosure, unless otherwise specified, the γ-Fe ₂ O ₃ crystal comprises, in addition to a pure γ-Fe ₂ O ₃ crystal in which an Fe site is not replaced by another element is a crystal in which some of the Fe sites are replaced with the trivalent metal element M, and a space group is the same as the pure γ-Fe ₂ O ₃ crystal. The shell part 22nd is similar to the shell part 12th in the first embodiment except for the points described above.

[Method of making magnetic powder]

Hereinafter, a method for producing a magnetic powder according to the second embodiment of the present disclosure will be described. This method of manufacturing magnetic powder comprises: firing a particle containing ferrous oxide (comprising ferrous oxide in which some of the Fe sites are replaced with a metal element) (hereinafter referred to as “FeO particles "Referred to"), transforming the FeO particle into a particle containing γ-iron oxide (comprising γ-iron oxide in which some of the Fe sites are replaced by a metal element) (hereinafter referred to as "γ-iron oxide particles"), and then transforming the inside of the γ-iron oxide particle into ε-iron oxide to make the magnetic particle 20th with a core-shell type structure.

First, an FeO particle powder is produced. The FeO particle powder preferably contains an FeO crystal (comprising an FeO crystal in which some of the Fe sites are replaced with a metal element M) as a main phase, and more preferably contains a single phase FeO crystal. However, when a molar ratio between M and Fe is expressed by M: Fe = x: (1 - x), 0 x <1 is satisfied. Here, the compositional formula of ferrous oxide is expressed by FeO, but ferrous oxide may have a non-stoichiometric composition.

In the present disclosure, unless otherwise specified, the FeO crystal includes, in addition to a pure FeO crystal in which one Fe site is not replaced by another element, a crystal in which some of the Fe sites are replaced by a divalent metal element M. are replaced, and a space group is the same as the pure FeO crystal.

The FeO particle powder is then transported to a furnace. Thereafter, the temperature of the furnace is raised, the FeO particle powder is fired, the FeO particle is transformed into a γ-iron oxide particle, and then the inside of the γ-iron oxide particle is transformed into an ε-iron oxide. The γ-iron oxide particle preferably contains a γ-Fe ₂ O ₃ crystal (comprising a γ-Fe ₂ O ₃ crystal in which some of the Fe sites are replaced by the metal element M) as a main component, and more preferably contains single-phase Fe ₃ O _4th The ε-iron oxide contained inside the γ-iron oxide particle preferably contains an ε-Fe ₂ O ₃ crystal (comprising an ε-Fe ₂ O ₃ crystal in which some of the Fe sites are replaced by the metal element M. ) as the main phase, and preferably contains single-phase ε-Fe ₂ O ₃ .

The burning time is preferably 10 hours or more and 200 hours or less. When the burn time 10 Hours or more, the inside of the γ-iron oxide particle can be effectively transformed into ε-iron oxide. At this time, when the burning time is 200 hours or less, the disappearance of γ-iron oxide can be effectively suppressed.

The firing temperature is preferably 950 ° C. or more and 1,400 ° C. or less. When the firing temperature is 950 ° C. or more, the inside of the γ-iron oxide particle can be effectively transformed into ε-iron oxide. At this time, when the firing temperature is 1400 ° C or less, the disappearance of γ-iron oxide can be effectively suppressed.

Before the entire γ-iron oxide particle is transformed into ε-iron oxide, the furnace is cooled to room temperature and the obtained magnetic powder is carried out of the furnace. Therefore, a magnetic powder is obtained which is the in 2 illustrated magnetic particles 20th contains.

[Effect]

The magnetic powder according to the second embodiment can produce an effect similar to the magnetic powder according to the first embodiment. Further, the method for manufacturing magnetic powder according to the second embodiment can produce an effect similar to the method for manufacturing magnetic powder according to the first embodiment.

<Third embodiment>

[Design of the magnetic recording medium]

A magnetic recording medium 30th according to a third embodiment of the present disclosure is a so-called tape-shaped magnetic recording medium and comprises, as in FIG 3 illustrates a long substrate 31 , a base layer (non-magnetic layer) 32 disposed on a major surface of the substrate 31 and a recording layer (magnetic layer) 33 formed on the base layer 32 is arranged. It should be noted that the base layer 32 is arranged as necessary and can be omitted. The magnetic recording medium may further have a back coating layer 34 having on the other major surface of the substrate 31 arranged as necessary.

(Saturation magnetization value Ms)

A saturation magnetization value M _{s of} the recording layer 33 preferably satisfies 50 emu / cc M _s 110 emu / cc. When the saturation magnetization value M _{s s} satisfies 50 emu / cc ≤ M, a higher performance can be obtained, and therefore better electromagnetic conversion characteristics can be obtained (for example, CNR). At this time, when the saturation magnetization value M _s satisfies M _s 110 emu / cc, it is possible to suppress occurrence of saturation of a reproducing head, and therefore generation of noise can be suppressed. Therefore, the electromagnetic conversion characteristics (for example, CNR) of the magnetic recording medium can be further improved.

The above saturation magnetization value Ms is determined as follows. First there are three long magnetic recording media 30th overlapped and bound with double-sided tape, and then punched with a φ6.39mm punch to make a measurement sample. At this time, marking is made with an arbitrary ink without magnetism such that the longitudinal direction (moving direction) of the magnetic recording medium 10 can be recognized. Then, using a VSM, an MH loop is made of the entire measurement sample (the entire magnetic recording medium 30th ) measured according to a perpendicular direction (direction of thickness) of the measurement sample. Next, the coating film (the base layer 32 , the recording layer 33 , the backside coating layer 34 and the like) using acetone, ethanol and the like. Wiped off, leaving only the substrate 31 remains behind. Then the obtained three substrates 31 overlapped and bound with double-sided tape, and then punched with a φ6.39mm die to make a background correction sample (hereinafter referred to simply as the "correction sample"). Then, using a VSM, an MH loop of the correction sample (substrate 31 ) corresponding to a perpendicular direction (direction of thickness) of the substrate 31 measured.

When measuring the MH loop of the test sample (of the entire magnetic recording medium 30th ) and the MH loop of the correction sample (substrate 311), a highly sensitive vibrating sample magnetometer "VSM-P7-15 Type" manufactured by Toei Industry Co., Ltd. is used. The measurement conditions are set to the measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field level: 40 bits, time constant of the locking device: 0.3 s, waiting time: 1 s, and MH mean value: 20.

After the MH loop of the measurement sample (of the entire magnetic recording medium 10 ) and the MH loop of the correction sample (base layer 11 ), the MH loop of the correction sample (substrate 31 ) from the MH loop of the entire measurement sample (of the entire magnetic recording medium 30th ) is subtracted to make background correction and an MH loop after background correction is obtained. A measurement / analysis program in the package with the "VSM-P7-15 Type" is used to calculate the background correction. The saturation magnetization value ms (emu) is determined from the obtained MH loop. It should be noted that each of the above measurements of the MH loops are made at 25 ° C. When the MH loop is in a perpendicular direction of the magnetic recording medium 30th is measured, no “demagnetization correction” is carried out.

Next, there are carbon layers on one surface of the magnetic recording medium 30th on the side of the recording layer 33 and on a surface of the magnetic recording medium 30th on the side of the back layer 34 formed by a vapor deposition method, and then a tungsten layer is further formed on the surface of the magnetic recording medium 30th on the side of the recording layer 33 formed by the vapor deposition process. These layers are formed to protect a sample as it is thinned, as described below. Next will be the magnetic recording medium 30th on which the above layers are formed, processed to be thinned by a focused ion beam (FIB) method. The thinning is carried out in a length direction (lengthwise direction) of the magnetic recording medium 30th performed. That is, by the thinning, a cross section becomes parallel to both the longitudinal direction of the magnetic recording medium 30th as well as the direction of the thickness thereof.

The above cross section of the obtained thinned sample is observed through a TEM to obtain a TEM image. It should be noted that the magnification and the accelerating voltage can be appropriately set according to the type of the device. The apparatus and observation conditions used for the observation are described below.
Device: TEM (H9000NAR, manufactured by Hitachi, Ltd.)
Accelerating voltage: 300 kV
Total magnification: 100,000 times

Next, using the obtained TEM image, the thickness of the recording layer is determined 33 a 10 or more dots in a lengthwise direction of the magnetic recording medium 30th measured. Thereafter, the measured values are simply averaged (arithmetically averaged) by an average thickness d of the recording layer 33 to determine. It should be noted that the measurement points are selected at random from a test piece.

Next, a volume v (= S xd) (cc) of the measurement sample is determined using an area S of the measurement sample used for the measurement of the MH loop and the average thickness d of the recording layer 33 is used. Then, the saturation magnetization value m _s (emu / cc) using the specific volume v (cc) and the saturation magnetization value ms (emu) is calculated.

(Coercive force H _c in the vertical direction)

An upper limit value of the coercive force H _c in a perpendicular direction is 3000 Oe or less, more preferably 2900 Oe or less, and still more preferably 2850 Oe or less. A large coercive force H _c is preferred because it is less affected by the thermal disturbance and the demagnetizing field. However, when the coercive force H _c exceeds 3000 Oe, saturation recording with a recording head is difficult and, as a result, there may be parts that cannot be recorded and noise may increase. Therefore, the electromagnetic conversion characteristics (for example, CNR) can be deteriorated.

A lower limit value of the coercive force H _c in the vertical direction is preferably 2200 Oe or more, more preferably 2400 Oe or more, and still more preferably 2600 Oe or more. When the coercive force H _{c is} 2200 Oe or more, it is possible to suppress a decrease in the electromagnetic conversion characteristics (for example, CNR) in a high temperature environment due to the thermal disturbance and the demagnetizing field.

The above coercive force H _c is determined as follows. First, in a manner similar to the above-described method for calculating a saturation magnetization value M _s , an MH loop is obtained after background correction. Next, the coercive force H _{c is determined} from the obtained MH loop.

(Substrate)

The substrate 31 , which serves as a carrier, is a flexible, long and non-magnetic substrate. The non-magnetic substrate is a film, and the film has a thickness of, for example, 3 µm or more and 8 µm or less. Examples of a material of the substrate 31 include a polyester such as polyethylene terephthalate, a polyolefin such as polyethylene or polypropylene, a cellulose derivative such as cellulose triacetate, cellulose diacetate or cellulose butyrate, a vinyl-based resin such as polyvinyl chloride or polyvinylidene chloride, a plastic such as polycarbonate, polyimide or polyamideimide, a light metal, such as an aluminum alloy or a titanium alloy, a ceramic such as alumina glass, and the like.

(Recording layer)

The recording layer 33 For example, the magnetic powder according to the first embodiment contains a binder and conductive particles. The recording layer 33 may further contain an additive such as a lubricant, an abrasive, or a rust preventive as necessary.

As the binder, a resin having a structure in which a polyurethane-based resin is given a crosslinking reaction, a vinyl chloride-based resin, and the like are preferred. However, the binder is not limited to these resins, and other resins may be appropriately mixed according to physical properties and the like required for the magnetic recording medium. Usually, a resin to be mixed is not particularly limited as long as it is generally used in an application type of the magnetic recording medium.

Examples of the resin to be mixed include polyvinyl chloride, polyvinyl acetate, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinylidene chloride copolymer, a vinyl chloride-acrylonitrile copolymer, an acrylate-acrylonitrile copolymer, an acrylate-vinyl chloride-vinylidene chloride copolymer, a vinyl chloride Acrylonitrile copolymer, an acrylate-acrylonitrile copolymer, an acrylate-vinylidene chloride copolymer, a methacrylate-vinylidene chloride copolymer, a methacrylate-vinyl chloride copolymer, a methacrylate-ethylene copolymer, polyvinyl fluoride, a vinylidene chloride-acrylonitrile copolymer, an acrylonitrile -Butadiene copolymer, a polyamide resin, polyvinyl butyral, a cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate and nitrocellulose), a styrene-butadiene copolymer, a polyester resin, an amino resin, a synthetic rubber and the like.

Further, examples of a thermosetting resin or a reactive resin include a phenol resin, an epoxy resin, a urea resin, a melamine resin, an alkyl resin, a silicone resin, a polyamine resin, a urea-formaldehyde resin and the like.

Further, in order to improve the dispersibility of the magnetic powder, a polar functional group such as -SO ₃ M, -OSO ₃ M, -COOM or P = O (OM) ₂ can be introduced into any of the above-described binders. Here, in the formulas, M represents a hydrogen atom or an alkali metal such as lithium, potassium or sodium.

In addition, examples of the polar functional group include a side chain type group having an end group of -NR1R2 or -NR1R2R3 ⁺ X ^- , and a main chain type group of> NR1R2 ⁺ X ^- . Here, in the formulas R1, R2 and R3 each represent a hydrogen atom or a hydrocarbon group, and X ^- represents an ion of a halogen element such as fluorine, chlorine, bromine or iodine, or an inorganic or organic ion. Further, examples of the polar functional group include -OH, -SH, -CN, an epoxy group, and the like.

The recording layer 33 furthermore aluminum oxide (α-, β- or γ-aluminum oxide), chromium oxide, silicon oxide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (titanium oxide of the rutile type or anatase type) and the like.

The average thickness of the recording layer 33 is preferably 30 nm or more and 120 nm or less, and more preferably 50 nm or more and 70 nm or less. It should be noted that a method of calculating the average thickness of the recording layer 33 as described above.

(Base layer)

The base layer 32 is a non-magnetic layer containing a non-magnetic powder and a binder as main components. The base layer 32 may further contain at least one of additives such as conductive particles, a lubricant, a hardener, or a rust preventive as necessary.

The non-magnetic powder can be an inorganic substance or an organic substance. Furthermore, the non-magnetic powder may be carbon black or the like. Examples of the inorganic substance include a metal, a metal oxide, a metal carbonate, a metal sulfate, a metal nitride, a metal carbide, a metal sulfide and the like. Examples of the shape of the non-magnetic powder include various shapes such as a needle shape, a spherical shape, a cubic shape and a plate shape, but they are not limited thereto. The binder is similar to that of the recording layer described above 33 .

The mean thickness of the base layer 32 is preferably 0.6 µm or more and 2.0 µm or less, and more preferably 0.8 (µm or more and 1.4 µm or less. Note that a method of calculating the average thickness of the base layer 32 is similar to the method described above for calculating the average thickness of the recording layer 33 .

[Method of manufacturing the magnetic recording medium]

Next, an example of a method of manufacturing a magnetic recording medium having the configuration described above will be described. First, by kneading and dispersing a non-magnetic powder, a binder and the like in a solvent, a coating material which forms a base layer is prepared. Next, by kneading and dispersing the magnetic powder according to the first embodiment, a binder and the like in a solvent, a coating material which forms a recording layer is prepared. For the preparation of the coating material forming the recording layer and the coating material forming the base layer, for example, the following solvents, dispersing devices and kneading devices can be used.

Examples of the solvent used for preparing the above-described coating materials include a ketone based solvent such as acetone, methyl ethyl ketone, methyl isobutyketone or cyclohexanone, an alcohol based solvent such as methanol, ethanol or propanol, a solvent based on an ester, such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate or ethylene glycol acetate, a solvent based on an ether, such as ethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran or dioxane, a solvent based on an aromatic hydrocarbon such as benzene, Toluene or xylene, a halogenated hydrocarbon-based solvent such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform or chlorobenzene, and the like. These solvents may be used singly or may be suitably used in admixture thereof.

Examples of a kneading device used for producing the above-described coating materials include a twin-screw continuous kneading machine, a twin-screw continuous kneading machine capable of multi-stage dilution, a kneader, a pressure kneader, a roll kneader and Like. However, they are not particularly limited to these devices. Further, examples of a dispersing device used for preparing the above-described coating materials include a roller mill, a ball mill, a horizontal sand mill, a vertical sand mill, a pin mill, a pin mill, a tower mill, a bead mill (for example, "DCP Mill", manufactured by Eirich Co., Ltd., etc.), a homogenizer, an ultrasonic wave dispersing machine and the like, however, are not particularly limited to these devices.

Next, the coating material forming the base layer is applied to a main surface of the substrate 31 applied and dried to the base layer 32 to build. Next, by applying the coating material forming the recording layer on the base layer 32 and drying the coating material constituting the recording layer, the recording layer 33 on the base layer 32 educated. It should be noted that during drying, the magnetic powder has a magnetic field orientation in the direction of the thickness of the substrate 31 for example, can be subjected by a solenoid coil. Next, a lubricant layer can be provided on the recording layer 33 may be formed as necessary or the back coat layer 34 can be on the other major surface of the substrate 31 are formed.

Next is the substrate 31 on which the base layer 32 and the recording layer 33 are formed, wound around a large diameter core and hardened. Next is the substrate 31 on which the base layer 32 and the recording layer 33 are formed, calendered and then cut into a predetermined width. As a result, it becomes the target magnetic recording medium 30th Receive.

[Effect]

In the magnetic recording medium 30th according to the third embodiment of the present disclosure, the recording layer contains 33 the magnetic powder according to the first embodiment, and therefore it is possible to use the magnetic recording medium 30th with high performance, excellent thermal stability and ease of recording.

EXAMPLES

Hereafter, the present disclosure is specifically described with examples, but the present disclosure is not limited to only these examples.

[Examples 1 to 4, 8, 11, 12 and 15]

Hereinafter, a method for producing a magnetic powder is described with reference to FIG 4th described. First, in step S11, an ε-Fe ₂ O ₃ particle powder was weighed out, placed on a quartz boat, and placed in a tube furnace. At that time, as the ε-Fe ₂ O ₃ particle powder, an ε-Fe ₂ O ₃ particle powder having an average particle radius substantially the same as an average particle radius r of a finally obtained magnetic powder (see Table 1) was produced. After the ε-Fe ₂ O ₃ particle powder was put into the tube furnace, the inside of the tube furnace was replaced once by an N ₂ atmosphere in step S12. Thereafter, in step S13, the temperature of the tube furnace was raised to a predetermined temperature (350 ° C.).

After the temperature was raised, 240 ml of a reducing gas having an H ₂ concentration of 4% was supplied and heating to 350 ° C. was performed in step S14. More specifically, heating was performed for 24 minutes while the reducing gas having an H ₂ concentration of 4% was supplied at 10 ml / min. Therefore, an area of an ε-Fe ₂ O ₃ particle was reduced and transformed into Fe ₃ O ₄ . Here, the supply amount of the reducing gas of 240 ml means the total amount of the reducing gas supplied during the reduction. Thereafter, in step S15, the inside of the tube furnace was again replaced with an N ₂ atmosphere. In step S16, the tube furnace was cooled to room temperature. From the above, a core-shell type magnetic particle having an Fe ₃ O ₄ layer on one face thereof was obtained. Finally, in step S17, the obtained magnetic powder was collected.

[Examples 5 to 7, 13 and 14]

Magnetic powders were obtained in a manner similar to Example 2, except that in the step S14, as illustrated in Table 1, the total amount of the reducing gas with an H ₂ concentration of 4% was changed to 80 ml (Example 13), 160 ml (Example 5), 320 ml (Example 6), 400 ml (Example 7) and 480 ml (Example 14).

[Examples 9 and 10]

Hereinafter, a method for producing a magnetic powder is described with reference to FIG 5 described. First, in step S21, an FeO particle powder was weighed, placed on a quartz boat, and placed in a furnace. At that time, as the FeO particle _{powder, an Fe 2} O ₃ particle powder having an average particle radius substantially the same as an average particle radius r of a finally obtained magnetic powder (see Table 1) was prepared. After the FeO particle powder was put into the furnace, the furnace was heated to a predetermined temperature (1100 ° C.) in step S22.

After the temperature was raised, as illustrated in Table 1, baking was carried out at 1100 ° C. for 50 hours (Example 9) or at 1100 ° C. for 70 hours (Example 10) in step S23. Therefore, an FeO particle was transformed into a γ-iron oxide particle, and then the inside of the γ-iron oxide particle was transformed into ε-iron oxide. It should be noted that the firing was done in an air atmosphere. Thereafter, in step S24, the furnace was cooled to room temperature before the entire γ-iron oxide particle was transformed into ε-iron oxide. From the above, a core-shell type magnetic particle having a γ-iron oxide layer on one surface thereof was obtained. Finally, in step S25, the obtained magnetic powder was collected.

[Evaluation of Magnetic Powder]

The magnetic powders obtained as described above were evaluated as follows.

(Mean particle radius r)

A mean particle radius r was determined in a manner similar to the above-described method for calculating the mean particle radius r of the magnetic particle described in the first embodiment.

(Mean radius r _{h of} the core part)

A mean radius r _{h of} a core part was determined in a manner similar to the above-described method for calculating the mean radius r _{h of} the core part 11 described in the first embodiment (described in the method for calculating the ratio R ₂ ).

(Ratio R _{1 of} the standard deviation σ of the particle size distribution to the mean particle diameter D)

A ratio R _{1 of} a standard deviation σ of the particle size distribution to the mean particle diameter D was determined in a manner similar to the above-described method for calculating the ratio R _{1 of} the standard deviation σ of the particle size distribution to the mean particle diameter D described in the first embodiment.

(Mean volume V of the magnetic particle)

A mean volume V of a magnetic particle was determined in a manner similar to the above-described method for calculating the mean volume V of a magnetic particle described in the first embodiment (described in the method for calculating the ratio R ₂ ).

(Mean volume V _{h of} the core part)

A mean volume V _{h of} the core part was determined in a manner similar to the above-described method for calculating the mean volume V _{h of} the core part described in the first embodiment (described in the method for calculating the ratio R ₂ ).

(Mean volume V _{s of} the shell part)

A mean volume V _{s of} the shell part was determined in a manner similar to the above-described method for calculating the mean volume V _{s of} the shell part described in the first embodiment (described in the method for calculating the ratio R ₂ ).

(Ratio R _{2 of} the mean volume V _{s of} the shell part to the mean volume V of the magnetic particle)

A ratio R _{2 of} the mean volume V _{s of} the shell part to the mean volume V of the magnetic particle was determined in a manner similar to the method described above for calculating the ratio R _{2 of} the mean volume V _{s of} the shell part to the mean volume V of the magnetic particle, described in the first embodiment.

(Saturation magnetization value σ _s )

A saturation magnetization value σ _s was determined in a manner similar to the above-described method for calculating the saturation magnetization value σ _{s of} the magnetic particle described in the first embodiment.

[Evaluation of the magnetic tape]

Magnetic tapes were manufactured using the magnetic powders obtained as described above, and the following evaluation was made. It should be noted that the magnetic tapes used for the evaluation were manufactured as follows.

(Step of preparing the coating material constituting the recording layer)

A coating material constituting the recording layer was prepared as follows. First, a first composition having the following formulation was kneaded with an extruder. Next, the kneaded first composition and a second composition having the following formulation were added to a stirring tank equipped with a disper, and were premixed. Thereafter, the mixture was further subjected to sand mill mixing and was subjected to filter treatment to prepare a coating material constituting the recording layer.

(First composition)

Magnetic powder: 100 parts by mass
Resin based on vinyl chloride (cyclohexanone solution 30% by mass): 10 parts by mass
(Degree of polymerization: 300, Mn = 10000, OSO ₃ K = 0.07 mmol / g and secondary OH = 0.3 mmol / g were contained as polar groups)
Alumina powder: 5 parts by mass
((α-Al ₂ O ₃ , mean particle diameter: 0.2 µm)
Soot: 2 parts by mass
(Manufactured by Tokai Carbon Co., Ltd., trade name: Seast TA)

Note that the magnetic powders of Examples 1 to 15 (see Table 1) were used as the magnetic powder.

(Second composition)

Resin based on vinyl chloride: 1.1 parts by mass (resin solution: resin content 30% by mass, cyclohexanone 70% by mass)
n-butyl stearate: 2 parts by mass
Methyl ethyl ketone: 121.3 parts by mass
Toluene: 121.3 parts by mass
Cyclohexanone: 60.7 parts by mass

Finally, 4 parts by mass of polyisocyanate (trade name: Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) as a curing agent and 2 parts by mass of myristic acid were added to the recording layer-forming coating material prepared as described above.

(Step of producing the coating material forming the base layer)

A coating material constituting the base layer was prepared as follows. First, a third composition having the following formulation was kneaded with an extruder. Next, the kneaded third composition and a fourth composition having the following formulation were added to a stirring tank equipped with a disper, and were premixed. Thereafter, the mixture was further subjected to sand mill mixing and was subjected to filter treatment to prepare a coating material constituting the base layer.

(Third composition)

Acicular iron oxide powder: 100 parts by mass
((α-Al ₂ O ₃ , mean length of the long axis: 0.15 µm)
Resin based on vinyl chloride: 55.6 parts by mass (resin solution: resin content 30% by mass, cyclohexanone 70% by mass)
Carbon black: 10 parts by mass
(Mean particle diameter: 20 nm)

(Fourth composition)

Polyurethane-based resin UR8200 (manufactured by Toyobo Co., Ltd.): 18.5 parts by mass
n-butyl stearate: 2 parts by mass
Methyl ethyl ketone: 108.2 parts by mass
Toluene: 108.2 parts by mass
Cyclohexanone: 18.5 parts by mass

Finally, 4 parts by mass of polyisocyanate (trade name: Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) as a curing agent and 2 parts by mass of myristic acid were added to the base layer forming coating material prepared as described above.

(Step of preparing the backing layer forming coating material)

A coating material forming the back layer was prepared as follows. The following raw materials were mixed in a stirring tank equipped with a disperser, and were subjected to filter treatment to prepare a backing layer coating material.

Carbon black (manufactured by Asahi Carbon Co., Ltd., trade name: # 80): 100 parts by mass
Polyester polyurethane: 100 parts by mass
(Trade name: N-2304 made by Nippon Polyurethane Industry Co., Ltd.)
Methyl ethyl ketone: 500 parts by mass
Toluene: 400 parts by mass
Cyclohexanone: 100 parts by mass

(Film formation step)

Using the coating materials prepared as described above, a magnetic tape was prepared as follows. First, a long PEN film (base film) with an average thickness of 4.0 µm was produced as a support. Next, the coating material forming the base layer was applied to a main surface of the PEN film and dried to form a base layer having an average thickness of 1.1 µm on the PEN film. Next, by applying the recording layer forming coating material on the base layer and drying the recording layer forming coating material, a recording layer having an average thickness of 0.1 µm was formed on the base layer. Note that the magnetic powder was subjected to magnetic field orientation in the direction of the thickness of the PEN film by a solenoid coil when the coating material constituting the recording layer was dried.

Then, the coating material forming the back layer was applied to the other major surface of the PEN film and dried to form a back layer having an average thickness of 0.4 µm. Then, the PEN film on which the base layer, the recording layer and the back layer were formed was cured. Thereafter, the film was calendered to flatten a surface of the recording layer.

(Cutting step)

The magnetic tape obtained as described above was cut into a width of 1/2 inch (12.65 mm). Therefore, a long magnetic tape with an average thickness of 5.6 µm was obtained.

(Saturation magnetization value Ms of the magnetic tape)

A saturation magnetization value Ms of a magnetic tape was determined in a manner similar to the above-described method for calculating the saturation magnetization value Ms of the magnetic tape described in the third embodiment.

(Coercive force H _{c of} the magnetic tape)

The coercive force H _{c of} a magnetic tape was determined in a manner similar to the above-described method for calculating the coercive force H _{c of} a magnetic tape described in the third embodiment.

(CNR)

First, a reproduction signal of a magnetic tape was detected using a loop tester (manufactured by MicroPhysics, Inc.). The detection conditions of the reproduction signal are described below.
Head: GMR head
Speed: 2 m / s
Signal: single recording frequency (10 MHz)
Recording current: optimal recording current

Next, the reproduction signal was picked up by a spectrum analyzer. A mean value of reproduction output at 10 MHz and a mean value of noise at 10 MHz ± 1 MHz were measured, and a difference therebetween was defined as CNR. The results are illustrated in Table 1 as relative values with the CNR of Example 15 being 0 dB.

Table 1 illustrates the evaluation results of the magnetic powders of Examples 1 to 15 and the evaluation results of the magnetic tapes produced using the magnetic powders of Examples 1 to 15.

The above evaluation results show the following.

By reducing a surface of an ε-iron oxide particle by means of a vapor phase reduction method, a magnetic particle with a core-shell structure can be obtained.

By burning an FeO particle, transforming the FeO particle into a γ-iron oxide particle, and then transforming the inside of the γ-iron oxide particle into ε-iron oxide, a magnetic particle having a core-shell structure can be obtained.

The magnetic particle preferably has a mean particle radius r of 4 nm r 20 nm from the standpoint of improving the CNR.

The ratio R ₁ (= (σ / D) x 100) of a standard deviation σ of the particle size distribution of the magnetic particle to the mean particle diameter D of the magnetic particle preferably satisfies R ₁ 40% from the standpoint of improving the CNR.

The mean volume Vs of the shell part preferably satisfies 90 nm ³ Vs, and the ratio R ₂ (= (V _{s /} V) × 100) of the mean volume V _{s of} the shell part to the mean volume V of the magnetic particle preferably satisfies 16% R ₂ ≤ 62% from the standpoint of improving the CNR.

The saturation magnetization value σ _{s of} the magnetic particle preferably satisfies 30 emu / g σ _s 60 emu / g from the standpoint of improving the CNR.

The saturation magnetization value Ms of the recording layer preferably satisfies 50 emu / cc M _s 110 emu / cc from the standpoint of improving the CNR.

The magnetic particle particularly preferably satisfies all of the above-described numerical ranges of the mean particle radius r, the ratio R1, the ratio R2 and the saturation magnetization value σ _s from the standpoint of improving the CNR.

[Modification]

Hereafter, the first to third embodiments of the present disclosure have been specifically described. However, the present disclosure is not limited to the above-described first to third embodiments, but various modifications can be made based on the technical idea of the present disclosure.

For example, the configurations, the methods, the steps, the shapes, the materials, the numerical values, and the like given as an example in the above-described first to third embodiments are only examples, and a configuration, a method is a Step, a shape, a material, a numerical value and the like other than these can be used as necessary. Further, the chemical formulas of the compounds and the like are representative and are not limited to the described valences and the like as long as the compounds have common names of the same compound.

Further, the configurations, the methods, the steps, the shapes, the materials, the numerical values and the like in the above-described first to third embodiments can be combined with each other as long as they do not depart from the gist of the present disclosure.

Further, in the above-described method for producing a magnetic powder according to the first embodiment, the case was described where the ε-iron oxide particle powder is reduced by a vapor phase reduction method, but the ε-iron oxide particle powder can also be reduced by a liquid phase reduction method be reduced.

Further, in the above-described method for producing a magnetic powder of the second embodiment, the case where the inside of the γ-iron oxide particle is transformed into ε-iron oxide has been described, but a part of that of the γ-iron oxide particle other than the inside thereof can be transformed into ε-iron oxide by adjusting the firing conditions.

Further, in the above-described manufacturing method of the third embodiment, the case where the recording layer 33 the magnetic powder according to the first Embodiment includes the recording layer 33 however, may also contain the magnetic powder according to the second embodiment, or may contain both the magnetic powder according to the first embodiment and the magnetic powder according to the second embodiment.

• (1) Verfahren zur Herstellung eines magnetischen Pulvers, wobei das Verfahren umfasst:
  • Reduzieren eines Partikels, das ε-Eisenoxid enthält (umfassend ε-Eisenoxid, in dem einige der Fe Stellen durch ein Metallelement ersetzt sind), um Trieisentetraoxid zu bilden (umfassend Trieisentetraoxid, in dem einige der Fe Stellen durch das Metallelement ersetzt sind), auf mindestens einem Teil einer Oberfläche des Partikels, wodurch ein magnetisches Partikel erhalten wird.
• (2) Verfahren zur Herstellung eines magnetischen Pulvers nach (1), wobei das magnetische Partikel einen mittleren Partikelradius r von 4 nm ≤ r ≤ 20 nm aufweist.
• (3) Verfahren zur Herstellung eines magnetischen Pulvers nach (1) oder (2), wobei ein Verhältnis Ri (= (σ/D) x 100) einer Standardabweichung σ der Partikelgrößenverteilung des magnetischen Partikels zu einem mittleren Partikeldurchmesser D des magnetischen Partikels R₁ ≤ 40 % erfüllt.
• (4) Verfahren zur Herstellung eines magnetischen Pulvers nach einem von (1) bis (3), wobei das magnetische Partikel eine Struktur vom Kern-Schale-Typ aufweist.
• (5) Verfahren zur Herstellung eines magnetischen Pulvers nach (4), wobei ein Schalenteil des magnetischen Partikels ein mittleres Volumen V_s von 90 nm³ ≤ V_s aufweist, und ein Verhältnis R₂ (= (Vs/V) × 100) des mittleren Volumens V_s des Schalenteils zu einem mittleren Volumen V des magnetischen Partikels 16 % ≤ R₂ ≤ 62 % erfüllt.
• (6) Verfahren zur Herstellung eines magnetischen Pulvers nach einem von (1) bis (5), wobei das magnetische Partikel einen Sättigungsmagnetisierungswert σ_s, von 30 emu/g ≤ σ_s ≤ 60 emu/g aufweist.
• (7) Magnetisches Pulver, umfassend ein magnetisches Partikel, umfassend:
  • ein Partikel, das ε-Eisenoxid enthält (umfassend ε-Eisenoxid, in dem einige der Fe Stellen durch ein Metallelement ersetzt sind); und
  • Trieisentetraoxid (umfassend Trieisentetraoxid, in dem einige der Fe Stellen durch das Metallelement ersetzt sind), das auf mindestens einem Teil einer Oberfläche des Partikels gebildet ist.
• (8) Magnetisches Aufzeichnungsmedium, umfassend eine Aufzeichnungsschicht, die das magnetische Pulver nach (7) enthält.
• (9) Magnetisches Aufzeichnungsmedium nach (8), wobei die Aufzeichnungsschicht einen Sättigungsmagnetisierungswert Ms von 50 emu/cc ≤ M_s ≤ 110 emu/cc aufweist.
• (10) Verfahren zur Herstellung eines magnetischen Pulvers, wobei das Verfahren umfasst:
  • Transformieren eines ersten Partikels, das Eisen(II)-Oxid enthält (umfassend Eisen(II)-Oxid, in dem einige der Fe Stellen durch ein Metallelement ersetzt sind), in ein zweites Partikel, das γ-Eisenoxid enthält (umfassend γ-Eisenoxid, in dem einige der Fe Stellen durch das Metallelement ersetzt sind), und dann Transformieren eines Teils des zweiten Partikels in ε-Eisenoxid (umfassend ε-Eisenoxid, in dem einige der Fe Stellen durch das Metallelement ersetzt sind), um ein magnetisches Partikel zu erhalten.
• (11) Verfahren zur Herstellung eines magnetischen Pulvers nach (10), wobei ein Teil des zweiten Partikels ein Inneres des zweiten Partikels ist.
• (12) Verfahren zur Herstellung eines magnetischen Pulvers nach (11), wobei das magnetische Partikel eine Struktur vom Kern-Schale-Typ aufweist.
• (13) Magnetisches Pulver, umfassend ein magnetisches Partikel, umfassend:
  • ein Partikel, das ε-Eisenoxid enthält (umfassend ε-Eisenoxid, in dem einige der Fe Stellen durch ein Metallelement ersetzt sind); und
  • γ-Eisenoxid (umfassend γ-Eisenoxid, in dem einige der Fe Stellen durch das Metallelement ersetzt sind), das auf mindestens einem Teil der Oberfläche des Partikels gebildet ist.
• (14) Magnetisches Aufzeichnungsmedium, umfassend eine Aufzeichnungsschicht, die das magnetische Pulver nach (13) enthält.

Furthermore, the present disclosure may take the following interpretations:

• (1) A method for producing a magnetic powder, the method comprising:
  • Reducing a particle containing ε-iron oxide (comprising ε-iron oxide in which some of the Fe sites are replaced with a metal element) to form triiron tetraoxide (including triiron tetraoxide in which some of the Fe sites are replaced with the metal element) at least a part of a surface of the particle, thereby obtaining a magnetic particle.
• (2) The method for producing a magnetic powder according to (1), wherein the magnetic particle has an average particle radius r of 4 nm r 20 nm.
• (3) The method for producing a magnetic powder according to (1) or (2), wherein a ratio Ri (= (σ / D) x 100) of a standard deviation σ of the particle size distribution of the magnetic particle to an average particle diameter D of the magnetic particle R ₁ ≤ 40% fulfilled.
• (4) The method for producing a magnetic powder according to any one of (1) to (3), wherein the magnetic particle has a core-shell type structure.
• (5) The method for producing a magnetic powder according to (4), wherein a shell part of the magnetic particle has an average volume V _s of 90 nm ³ V _s , and a ratio R ₂ (= (Vs / V) × 100) des mean volume V _{s of} the shell part to a mean volume V of the magnetic particle 16% R ₂ 62% fulfilled.
• (6) The method for producing a magnetic powder according to any one of (1) to (5), wherein the magnetic particle has a saturation magnetization _{value σ s} of 30 emu / g σ _s 60 emu / g.
• (7) A magnetic powder comprising a magnetic particle comprising:
  • a particle containing ε-iron oxide (including ε-iron oxide in which some of the Fe sites are replaced with a metal element); and
  • Triiron tetraoxide (comprising triiron tetraoxide in which some of the Fe sites are replaced with the metal element) formed on at least a part of a surface of the particle.
• (8) A magnetic recording medium comprising a recording layer containing the magnetic powder according to (7).
• (9) The magnetic recording medium according to (8), wherein the recording layer has a saturation magnetization _{value Ms of 50 emu / cc M s} 110 emu / cc.
• (10) A method of manufacturing magnetic powder, the method comprising:
  • Transforming a first particle containing ferrous oxide (comprising ferrous oxide in which some of the Fe sites are replaced by a metal element) into a second particle containing γ-iron oxide (comprising γ-iron oxide in which some of the Fe sites are replaced with the metal element), and then transforming a part of the second particle into ε-iron oxide (including ε-iron oxide in which some of the Fe sites are replaced with the metal element) to become a magnetic particle Receive.
• (11) The method for producing a magnetic powder according to (10), wherein a part of the second particle is an inside of the second particle.
• (12) The method for producing a magnetic powder according to (11), wherein the magnetic particle has a core-shell type structure.
• (13) A magnetic powder comprising a magnetic particle comprising:
  • a particle containing ε-iron oxide (comprising ε-iron oxide in which some of the Fe sites are replaced with a metal element); and
  • γ-iron oxide (comprising γ-iron oxide in which some of the Fe sites are replaced with the metal element) formed on at least a part of the surface of the particle.
• (14) A magnetic recording medium comprising a recording layer containing the magnetic powder according to (13).

List of reference symbols

10, 20

magnetic particle

11, 21

Core part

12, 22

Shell part

30th

magnetic recording medium

31

Substrate

32

Base layer

33

Recording layer

34

Back coating layer

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2016/092744 [0006]

Claims (14)

A method of making a magnetic powder, the method comprising: Reducing a particle containing ε-iron oxide (comprising ε-iron oxide in which some of the Fe sites are replaced with a metal element) to form triiron tetraoxide (including triiron tetraoxide in which some of the Fe sites are replaced with the metal element) at least a part of a surface of the particle, thereby obtaining a magnetic particle. Method for producing a magnetic powder according to Claim 1 , wherein the magnetic particle has an average particle radius r of 4 nm r 20 nm. Method for producing a magnetic powder according to Claim 1 , wherein a ratio R ₁ (= (σ / D) × 100) of a standard deviation σ of the particle size distribution of the magnetic particle to an average particle diameter D of the magnetic particle _{satisfies R 1} 40%. Method for producing a magnetic powder according to Claim 1 wherein the magnetic particle has a core-shell type structure. Method for producing a magnetic powder according to Claim 4 , wherein a shell part of the magnetic particle has an average volume V _s of 90 nm ³ ≤ V _s , and a ratio R ₂ (= (V _{s /} V) × 100) of the mean volume V _{s of} the shell part to an average volume V des magnetic particle 16% ≤ R ₂ ≤ 62% satisfied. Method for producing a magnetic powder according to Claim 1 , wherein the magnetic particle has a saturation magnetization _{value σ s} , of 30 emu / g σ _s 60 emu / g. A magnetic powder comprising a magnetic particle comprising: a particle containing ε-iron oxide (including ε-iron oxide in which some of the Fe sites are replaced with a metal element); and Triiron tetraoxide (comprising triiron tetraoxide in which some of the Fe sites are replaced with the metal element) formed on at least a part of a surface of the particle. A magnetic recording medium comprising a recording layer containing the magnetic powder Claim 7 contains. Magnetic recording medium according to Claim 8 wherein the recording layer has a saturation magnetization _{value M s} of 50 emu / cc M _s 110 emu / cc. A method of making a magnetic powder, the method comprising: Transforming a first particle containing ferrous oxide (comprising ferrous oxide in which some of the Fe sites are replaced by a metal element) into a second particle containing γ-iron oxide (comprising γ-iron oxide in which some of the Fe sites are replaced with the metal element), and then transforming a part of the second particle into ε-iron oxide (including ε-iron oxide in which some of the Fe sites are replaced with the metal element) to become a magnetic particle Receive. Method for producing a magnetic powder according to Claim 10 wherein a part of the second particle is an interior of the second particle. Method for producing a magnetic powder according to Claim 11 wherein the magnetic particle has a core-shell type structure. A magnetic powder comprising a magnetic particle comprising: a particle containing ε-iron oxide (including ε-iron oxide in which some of the Fe sites are replaced with a metal element); and γ-iron oxide (comprising γ-iron oxide in which some of the Fe sites are replaced with the metal element) formed on at least a part of the surface of the particle. A magnetic recording medium comprising a recording layer containing the magnetic powder Claim 13 contains.

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