JPH09128740A - Magnetic recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having excellent electromagnetic conversion characteristics, such as frequency characteristics, and preservable stability and with which the recording of a higher density is possible. SOLUTION: This medium has a base 2 and a magnetic layer 3 on this base 2 and this magnetic layer 2 contains ferromagnetic metallic powder and a binder. The surface roughness of the magnetic layer 3 is <=10nm, the coercive force thereof is larger than 1500Oe, the squareness ratio thereof is >=0.85 and the residual magnetic flux density thereof is >=2600 gauss. The attenuation factor ΔBs (the change rate of the saturation magnetic flux density Bs' after resting for 30 days under the environment of 60 deg.C and 90% relative humidity to the saturation magnetic flux density Bs of the magnetic layer before the resting and is the value expressed by ΔBs=(1-Bs'/Bs)×100) of the raturation magnetic flux density is <=10%. This process for producing the magnetic recording medium includes a state for forming a coating material for kneading a coating material compsn. prepd. by using the specific ferromagnetic metallic powder and the binder in such a manner that the solid content attains >=70wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium excellent in electromagnetic conversion characteristics such as frequency characteristics and storage stability and capable of high density, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, magnetic recording media have been widely used in the form of tapes, disks, drums or sheets. Such a magnetic recording medium is usually manufactured by applying a magnetic paint mainly composed of a magnetic powder and a binder onto a support such as a polyester film or a polyaramid film.

However, in recent years, high density recording has been demanded, and the conventional magnetic recording medium has electromagnetic conversion characteristics such as frequency characteristics which are required in accordance with the demand for high density recording. However, there is a problem that storage stability is poor, such as deterioration of the electromagnetic conversion characteristics during storage. In order to solve such a problem, a magnetic recording medium made of an alloy of Fe and Co added as a ferromagnetic metal powder has been proposed. This magnetic recording medium has a saturation magnetization of the ferromagnetic metal powder. Decay rate (Δσs)
Although the above problem has been improved and the above problems have been improved to some extent, a magnetic recording medium having excellent electromagnetic conversion characteristics such as frequency characteristics and storage stability is not yet satisfied to the above extent. This is the current situation.

Therefore, an object of the present invention is to provide a magnetic recording medium which is excellent in electromagnetic conversion characteristics such as frequency characteristics and storage stability and which can be highly densified, and a manufacturing method thereof.

[0005]

As a result of intensive studies to solve the above problems, the present inventors have found that the magnetic layer has a surface roughness, a coercive force, a squareness ratio, a residual magnetic flux density and a saturation in a specific range. It has been found that a magnetic recording medium having a magnetic flux density attenuation rate is excellent in electromagnetic conversion characteristics such as frequency characteristics and storage stability and can be highly densified.

The present invention has been made based on the above findings, and has a support and a magnetic layer provided on the support, wherein the magnetic layer includes a ferromagnetic metal powder and a binder. In the medium, the magnetic layer has a surface roughness of 10n.
m or less, coercive force of more than 1500 Oe, squareness ratio of 0.85 or more, residual magnetic flux density of 2600 gauss or more, and saturation magnetic flux density attenuation rate ΔBs (temperature 60 ° C., relative humidity 90%). Is the rate of change of the saturation magnetic flux density Bs ′ after standing for 30 days in the above environment with respect to the saturation magnetic flux density Bs of the magnetic layer before standing, ΔBs = (1−Bs ′
/ Bs) × 100) is 10% or less.

Further, the present invention is a method for manufacturing the above magnetic recording medium, which uses a ferromagnetic metal powder and a binder,
The method includes a step of preparing a coating composition so that the solid content is 70% by weight or more, and kneading the coating composition to obtain a magnetic coating, wherein the ferromagnetic metal powder has a major axis of 0. 0
5 to 0.3 μm, a crystallite size of 140 Å or more, a saturation magnetization of 120 emu / g or less, and a saturation magnetization attenuation rate Δσs (temperature 60 ° C, relative humidity 90%, left for 7 days. Is the rate of change of the saturation magnetization σs ′ after the annealing with respect to the saturation magnetization σs before leaving, Δσs = (1−σ
The present invention provides a method for producing a magnetic recording medium, characterized in that a ferromagnetic metal powder having a value represented by s ′ / σs) × 100) of 10% or less is used.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic recording medium of the present invention will be described below in detail. First, a preferred configuration of the magnetic recording medium of the present invention will be described with reference to FIG.

The magnetic recording medium 1 of the present invention shown in FIG. 1 comprises a support 2 and a magnetic layer 3 provided on the support 2. A back coat layer 4 is provided on the back surface of the support 2 as necessary.

In the magnetic recording medium of the present invention, a non-magnetic layer may be provided between the magnetic layer and the support, if necessary, in addition to the support, the magnetic layer and the back coat layer. A magnetic layer other than the above magnetic layer may be provided. Further, there are other layers such as a primer layer provided between the support and the magnetic layer or the back coat layer, and another magnetic layer provided for recording a servo signal or the like corresponding to a hard system using a long wavelength signal. May be provided. Also,
Instead of providing the back coat layer on the back surface of the support, another magnetic layer may be provided.

As the support used in the magnetic recording medium of the present invention, either a magnetic support or a non-magnetic support can be used, but a non-magnetic support is particularly preferably used. As the above-mentioned non-magnetic support, any conventionally known one can be used without any particular limitation. Specifically, a flexible film or disk made of a polymer resin; a non-magnetic support such as Cu, Al, or Zn. Films, disks, cards and the like made of magnetic metal, glass, ceramics such as porcelain and ceramics can be used.

Examples of the polymer resin forming the flexible film or the disk include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate, and polyethylene bisphenoxycarboxylate; , Polyolefins such as polypropylene, cellulose acetate butyrate,
Cellulose derivatives such as cellulose acetate propionate, polyvinyl chloride, vinyl resins such as polyvinylidene chloride, or polyamide, polyimide, polycarbonate, polysulfone, polyetheretherketone, polyurethane, etc. Two or more can be used in combination.

In the magnetic recording medium of the present invention, the magnetic layer provided on the support is a magnetic layer containing a ferromagnetic metal powder and a binder, and is formed by applying a magnetic paint on the support. . As the magnetic paint, a paint containing ferromagnetic metal powder, a binder, and a solvent as main components is preferably used.

The above-mentioned ferromagnetic metal powder is a ferromagnetic metal powder containing iron as a main component, specifically, 50 wt% or more of a metal component containing Fe atoms is contained in the total composition of the ferromagnetic metal powder. An example is one in which 60 wt% or more of the metal content is Fe atoms. Also, Sc, Y, La, Nd, Sm,
Contains lanthanoids such as Dy, Gd, Ce, Pr and Tb
A ferromagnetic metal powder containing 0.8 to 20 parts by weight of one or more Group IIIa elements with respect to 100 parts by weight of the Fe atoms can also be used. Furthermore, if necessary, a transition metal element, an alkaline earth metal element, another rare earth element, or the like can be contained. Specific examples of the ferromagnetic metal powder include, for example, Fe-Co, Fe-Ni, Fe-Al, Fe-Ni.
-Al, Fe-Co-Ni, Fe-Ni-Al-Zn,
Fe-Al-Si, Fe-Co-Y, Fe-Ni-Y,
Fe-Al-Y, Fe-Ni-Al-Y, Fe-Co-
Ni-Y, Fe-Ni-Al-Zn-Y, Fe-Al-
Si-Y, Fe-Co-La, Fe-Ni-La, Fe
-Al-La, Fe-Ni-Al-La, Fe-Co-
Ni-La, Fe-Ni-Al-Zn-La, Fe-A
l-Si-La, Fe-Co-Al-Y, Fe-Co-
Examples thereof include Al-La and Fe-Co-Al-Gd.

The ferromagnetic metal powder is preferably needle-shaped or spindle-shaped. The major axis diameter of the ferromagnetic metal powder is preferably 0.05 to 0.3 μm,
More preferably, it is 0.06 to 0.25 μm. If the major axis diameter is less than 0.05 μm, superparamagnetism develops,
The coercive force of the ferromagnetic metal powder may decrease, and
If it exceeds μm, the frequency characteristics of the magnetic recording medium may deteriorate. The crystallite size (X-ray particle size) of the ferromagnetic metal powder is preferably 140Å or more,
More preferably, it is 200Å. The crystallite size is 1
If it is less than 40Å, the saturation magnetization attenuation rate Δσs described later is obtained.
May not be within the range described below, and the storage stability of the magnetic recording medium may deteriorate. The axial ratio of the ferromagnetic metal powder is preferably 3-20, more preferably 4-8.

The coercive force of the ferromagnetic metal powder is 1500 O in order for the magnetic layer to achieve the above coercive force range.
e is preferably larger than 1580-2500 Oe
Is more preferable.

The saturation magnetization of the ferromagnetic metal powder is 120.
emu / g or less is preferable, and 100 to 120 emu / g
Is more preferable and 110 to 1 is particularly preferable.
It is 17 emu / g. If the saturation magnetization of the ferromagnetic metal powder exceeds 120 emu / g, it will be difficult to secure the storage stability of the magnetic recording medium, and the dispersibility of the magnetic coating material will decrease, resulting in a squareness ratio of 0. It becomes difficult to obtain a magnetic layer of 85 or more, and it becomes difficult to obtain a magnetic recording medium having excellent electromagnetic conversion characteristics such as frequency characteristics. The reason why the dispersibility of the magnetic paint is lowered as described above is not clear enough, but it is considered as follows. That is, when the saturation magnetization exceeds 120 emu / g, the formation of a sufficiently homogeneous oxide layer on the surface is insufficient, the binding with the binder is insufficient, and the dispersion stability of the ferromagnetic metal powder in the magnetic coating is weak. Become. On the other hand, the magnetic cohesive force increases as the saturation magnetization increases, and as a result, the balance between the dispersion stabilizing force and the magnetic cohesive force tends to shift to the magnetic cohesive force side. It should be noted that the saturation magnetization attenuation rate Δσs has been used so far by using a ferromagnetic metal powder having a saturation magnetization of 120 emu / g or less.
A magnetic recording medium with improved characteristics has not been proposed.

The saturation magnetization attenuation rate Δσs of the ferromagnetic metal powder is preferably 10% or less, more preferably 7% or less, and particularly preferably 5% or less. If the above Δσs exceeds 10%, the storage stability of the magnetic recording medium may decrease. Where Δσs is
The rate of change of the saturation magnetization σs ′ after standing for 7 days in an environment of a temperature of 60 ° C. and relative humidity of 90% with respect to the saturation magnetization σs of the ferromagnetic metal powder before standing, Δσs = (1−σs ′ /
σs) × 100, which is the value when the ferromagnetic metal powder immediately after production is left under the above conditions.

In the present invention, in particular, the ferromagnetic metal powder has a major axis diameter of 0.05 to 0.3 μm, a crystallite size of 140 Å or more, and a saturation magnetization of 120 emu / g.
It is preferably a ferromagnetic metal powder (hereinafter, referred to as "ferromagnetic metal powder A") having a saturation magnetization attenuation rate Δσs of 10% or less.

The ferromagnetic metal powder is produced by using iron oxide hydroxide powder or iron oxide powder as a raw material. Then, in order to control the shape, magnetic characteristics or dispersibility of the ferromagnetic metal powder, the raw material may be silicon, aluminum, barium, calcium, magnesium, zinc, tin, titanium, cobalt, nickel, if necessary. , Lanthanum, yttrium, and other transition metal elements, alkaline earth metal elements, rare earth elements, etc. are mixed by a conventional method in one or more kinds, and these elements are deposited on the surface of the above raw material and / or It can be contained in the above raw materials. here,
As the iron oxide hydroxide powder, for example, α-FeOO
H, β-FeOOH, γ-FeOOH, and the like. Examples of the iron oxide powder include α-Fe ₂ O ₃ ,
γ-Fe ₂ O ₃ , Fe ₃ O _{4 and the} like can be mentioned.

The ferromagnetic metal powder can be prepared, for example, as follows. That is, first, by adding 1 to 5 times the specified amount of alkali carbonate to a ferrous iron salt aqueous solution containing a metal salt to be contained, and performing air oxidation while maintaining the temperature at 30 to 60 ° C., a spindle shape containing different metals is formed. α-F
eOOH (Goethite) is synthesized. This is desalted by a conventional method and then dispersed to obtain a suspension water slurry. A fatty acid and aqueous ammonia in an equimolar amount to the fatty acid are added thereto at room temperature, and they are sufficiently stirred and mixed to obtain a slurry. The resulting slurry was 1.5 using a pressure type filter press.
Pressurized with a pressure of ~4kgf / cm ^2, water content 60 to 90
Get the cake in weight percent. Further, the cake was molded using a horizontal extrusion molding machine, and the obtained molded product was dried with a ventilated box dryer or the like, and then granulated into 4 mesh pass to 9 mesh on. The obtained granulated product was packed in a fixed bed reactor and was placed in a nitrogen stream (0.2 to 10 Nm ³ / hr per 1 kg of granulated product).
Aeration) to perform heat treatment at 350 to 700 ° C. for 0.5 to 3 hours. Then, in a steam flow (per 1 kg of granulated product,
Aeration at 1 to 15 Nm ³ / hr) at 350 to 600 ° C., 1
Reduction for 3 to 3 hours, and then 250 to 10 in nitrogen gas.
In a mixed gas containing 000 ppm of air (1 kg of granulated material
Per aeration of 1 to 15 Nm ³ / hr), 40 to 150
A ferromagnetic metal powder is obtained by performing a stabilizing treatment for forming a stable oxide film on the surface at ℃.

Examples of the binder used in the magnetic coating material for forming the magnetic layer include thermoplastic resins, thermosetting resins, and reactive resins, which may be used alone or as a mixture when used. Specific examples of the binder include a vinyl chloride resin, polyester,
Polyurethane, nitrocellulose, epoxy resin and the like. In addition, resins described in JP-A-57-162128, page 2, upper right column, line 19 to page 2, lower right column, line 19, etc. No. Further, the binder may contain a polar group for improving dispersibility and the like. The amount of the binder used is preferably 5 to 50 parts by weight with respect to 100 parts by weight of the ferromagnetic metal powder, and 5 to 3 parts by weight.
It is particularly preferred to use 0 parts by weight.

The solvent used in the magnetic coating material for forming the magnetic layer is a ketone solvent, an ester solvent, an ether solvent, an aromatic hydrocarbon solvent, or a chlorinated hydrocarbon solvent. And the like. Specifically, page 17, lower right column, line 17 of JP-A-57-162128
Solvents described on page 10, lower left column, line 10 and the like can be used. The solvent is preferably used in an amount of 80 to 500 parts by weight, more preferably 100 to 350 parts by weight, based on 100 parts by weight of the ferromagnetic metal powder.

In addition, additives commonly used in magnetic recording media such as dispersants, lubricants, abrasives, antistatic agents, rust inhibitors, antifungal agents, and hardeners are added to the magnetic paint. It can be added as needed. As the above additives,
Specifically, it is described in page 2, upper left column, line 6 to page 2, upper right column, line 10 and page 3, upper left column, line 6 to page 3, upper right column, line 18 of JP-A-57-162128. And various additives.

The above-mentioned magnetic coating material can be prepared according to the coating step in the method for producing a magnetic recording medium of the present invention described later.

The thickness of the magnetic layer is 0.02 to 3.0 μm.
It is preferably m, and more preferably 0.05 to 2.5 μm. Here, the thickness of the magnetic layer is 0.02.
When it is less than μm, it is difficult to apply the above-mentioned magnetic paint to form a magnetic layer, and when it exceeds 3.0 μm, it may be unsuitable for high density recording.

The saturation magnetic flux density of the magnetic layer is preferably 2900 to 4000 Gauss, more preferably 3000 to
It is 3600 gauss.

Thus, in the magnetic recording medium of the present invention,
The magnetic layer has a surface roughness (Ra) of 10 nm or less, preferably 1 to 8 nm, a coercive force of more than 1500 Oe, preferably 1580 to 2500 Oe, and a squareness ratio of 0.85 or more, preferably 0. 0.86 to 0.94 and the residual magnetic flux density is 2600 gauss or more, preferably 2
It is 700 to 3400 Gauss, and the saturation magnetic flux density attenuation rate ΔBs is 10% or less, preferably 7% or less.

Here, the surface roughness of the magnetic layer is 10 nm.
If it exceeds, high output cannot be obtained and the frequency characteristics of the magnetic recording medium deteriorate. The coercive force of the magnetic layer is 1500
If it is less than Oe, high output cannot be obtained and the frequency characteristics of the magnetic recording medium deteriorate. If the squareness ratio of the magnetic layer is less than 0.85, high output cannot be obtained and the frequency characteristics of the magnetic recording medium deteriorate. Further, if the residual magnetic flux density of the magnetic layer is less than 2600 Gauss, the high output in the low frequency region will decrease. In addition, the saturation magnetic flux density attenuation rate ΔB
When s exceeds 10%, the storage stability of the magnetic recording medium deteriorates. Here, ΔBs is a temperature of 60 ° C. and a relative humidity of 90
% Saturation magnetic flux density Bs' after being left in an environment of 30% for 30 days
Is a rate of change with respect to the saturation magnetic flux density Bs of the magnetic layer before being left, which is a value represented by ΔBs = (1−Bs ′ / Bs) × 100, and the magnetic recording medium immediately after manufacturing is left under the above conditions. It is the value when it is done.

The magnetic recording medium of the present invention is suitable as a magnetic recording tape such as an 8 mm video tape or a DAT tape, but can also be applied as another magnetic recording medium such as a floppy disk.

In the magnetic recording medium of the present invention, the surface roughness (Ra) of the magnetic layer is 10 nm or less, the coercive force of the magnetic layer is more than 1500 Oe, and the squareness ratio of the magnetic layer is 0.85 or more. And the residual magnetic flux density of the magnetic layer is 26
It is not less than 00 Gauss and the attenuation factor ΔBs of the saturation magnetic flux density of the magnetic layer is 10% or less, but the surface roughness, the coercive force, the squareness ratio, the residual magnetic flux density and the ΔBs can be easily adjusted within the above range by manufacturing a magnetic recording medium using the above-mentioned ferromagnetic metal powder A according to the manufacturing method of the present invention described later.

Particularly, in order to adjust each of the above physical properties in the magnetic recording medium of the present invention, the following may be performed. By doing so, it is possible to obtain the magnetic recording medium of the present invention having the above physical properties. The surface roughness of the magnetic layer is appropriately adjusted by selecting and adjusting the solvent composition, the drying conditions (air volume, temperature, etc.) of the coating film after coating, the calendering conditions (speed, pressure, roll temperature, etc.). Can be adjusted. Here, the solvent composition is preferably a composition containing at least one high-boiling solvent such as cyclohexane. In addition, the drying condition is that the temperature of hot air is 30 to
It is preferable that the temperature is 120 ° C., the wind speed is 10 to 35 m / sec, and the drying time is 1 to 60 seconds. The calender conditions are as follows: calender speed is 30 to 800 m / s, pressure is 100 to 500 kg / cm, and roll temperature is 60 to.
The temperature is preferably 140 ° C. The surface roughness (R
a) is a value indicated in accordance with the measurement method in Examples described later.

The coercive force of the magnetic layer can be appropriately adjusted by adjusting the type and amount of the ferromagnetic metal powder used, for example, the ferromagnetic metal powder having a coercive force of 1500 Oe or more. .

The squareness ratio of the magnetic layer can be adjusted by adjusting the dispersibility of the magnetic coating material by kneading conditions and the like, the drying condition of the coating film after coating, the magnetic field orientation conditions, and the like. Here, the kneading conditions of the magnetic paint are such that the shear rate is 300
It is preferable that the kneading time be ˜3000 S ⁻¹ and the kneading time be 1 minute to 1 hr. When the magnetic recording medium of the present invention is a magnetic tape, the magnetic field orientation conditions are about 500 Oe or more, preferably about 10 Oe in the direction parallel to the coated surface of the magnetic paint.
It is preferable to apply a magnetic field of 00 to 10000 Oe or to let the magnetic paint pass through a solenoid or the like of 1000 to 10000 Oe in a wet state.

The residual magnetic flux density of the magnetic layer can be adjusted by adjusting the dispersibility by the kneading conditions and the like of the magnetic coating, the amount of binder and other additives used, the calendering conditions and the like. The amount of the binder used is preferably 5 to 50 parts by weight with respect to 100 parts by weight of the ferromagnetic metal powder, and the amount of other additives used is 100 parts by weight of the ferromagnetic metal powder. , 1 to 40 parts by weight is preferable.

Further, the attenuation factor ΔBs of the saturation magnetic flux density of the magnetic layer is the metal element composition contained in the ferromagnetic metal powder used, and the surface oxide layer of the ferromagnetic metal powder when the surface oxide layer is provided. It can be appropriately adjusted by adjusting the thickness and denseness, the dispersibility of the magnetic coating material, and selecting the binder and the additive to be used. For example, by using a ferromagnetic metal powder manufactured by adding Co or the like as an additional element at the time of manufacturing the ferromagnetic metal powder,
Bs can be adjusted.

Next, the method for manufacturing the magnetic recording medium of the present invention will be described in detail. The manufacturing method of the present invention is a preferable manufacturing method of the above-described magnetic recording medium of the present invention. In the manufacturing method of the present invention, the magnetic recording medium is manufactured as follows.

That is, first, a coating composition is prepared using the ferromagnetic metal powder A and a binder so that the solid content is 70% by weight or more, preferably 75 to 90% by weight, and the coating composition is prepared. A kneading process is performed to obtain a magnetic paint. Then, the obtained magnetic coating material is applied onto the support so as to have a solid content in the range described above and a dry thickness of preferably the above-mentioned thickness to form a coating film of a magnetic layer. Further, after subjecting the coating film to magnetic field orientation treatment,
It is dried and wound up. Thereafter, after performing a calendering treatment, a back coat layer is further formed as necessary.
Then, if necessary, for example, when a magnetic tape is to be obtained, it is aged at 40 to 70 ° C. for 6 to 72 hours and slit into a desired width.

In the coating process, the solid content is 7%.
When the content is less than 0% by weight, when the coating composition is kneaded, the coating composition cannot be sufficiently sheared, the dispersibility of the magnetic coating becomes poor, and the squareness ratio and residual magnetic flux of the magnetic layer are reduced. The density cannot be set within the above range. Further, examples of the kneading machine used in the coating process include a twin-screw extruder and a pressure kneader. Also,
In the coating composition supplied to the kneader, the ferromagnetic metal powder A is preferably used within the range of the amount of the ferromagnetic metal powder used in the magnetic recording medium, and the binder is the magnetic recording medium. The binder is preferably used within the range of the kind and the amount of the binder used, and a solvent and other additives can be further added to the coating composition.
The kneading conditions of the above coating composition are such that the shear rate is 300.
To 3000 S ^-1 , preferably 500 to 2000
S ⁻¹ is more preferable, and the kneading time is from 1 minute to
It is preferably 1 hr, particularly preferably 2 to 30 minutes.

The magnetic field orientation treatment is carried out before the magnetic paint is dried. For example, when the magnetic recording medium of the present invention is a magnetic tape, the magnetic paint is applied in a direction parallel to the coated surface of the magnetic paint. About 500 Oe or more, preferably about 1000
It can be carried out by a method of applying a magnetic field of 〜１０10000 Oe, a method of passing the magnetic paint through a solenoid of 1000〜１０10000 Oe or the like in a wet state, or the like.

The above-mentioned drying treatment can be carried out, for example, by supplying a heated gas. At this time, the degree of drying of the coating film can be controlled by controlling the temperature of the gas and the supply amount thereof.

The calendering can be carried out by a super calendering method in which two rolls such as a metal roll and a cotton roll, a synthetic resin roll, a metal roll and a metal roll are passed.

The backcoat layer, which is provided if necessary, is provided on the back surface of the support (the surface on the side where the magnetic layer is not provided), and is usually used for forming the backcoat layer. It is obtained by applying the above-mentioned back coat paint on the above-mentioned support.

In the production of the magnetic recording medium of the present invention, finishing steps such as polishing and cleaning of the magnetic layer surface may be carried out if necessary.

[0045]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 A ferromagnetic metal powder was prepared according to the following <Preparation of ferromagnetic metal powder>. Then, using the ferromagnetic metal powder, a magnetic coating material was obtained according to the following <Preparation of magnetic coating material>. Using the obtained magnetic paint, and using a backcoat paint having the following composition as the backcoat paint,
A magnetic tape was manufactured according to the following <Method for manufacturing magnetic recording medium> to obtain a magnetic tape as a magnetic recording medium having a magnetic layer formed of a magnetic paint having the characteristics shown in [Table 1].

<Preparation of Ferromagnetic Metal Powder> A for Fe
Spindle-shaped α-FeOO containing 4 wt% of 1 and 6 wt% of Co
H <Goethite> (major axis length 0.25 μm, axial ratio 9) was dispersed in a reactor equipped with a stirrer to give a 4 wt% suspension water slurry. To this, 5% by weight of nonanoic acid with respect to the above-mentioned goethite and ammonia water in an equimolar amount with respect to the nonanoic acid were added at room temperature, and sufficiently stirred and mixed to deposit the nonanoic acid salt. Next, the obtained slurry was 2.0 kgf / cm using a pressure type filter press machine (manufactured by Kurita Machinery Co., Ltd.).
A pressure of ² was applied to carry out solid-liquid separation to obtain a cake (water content 80% by weight). Further, the cake was molded using a lateral extrusion molding machine [screen hole diameter: 5 mm, manufactured by Fuji Paudal Co., Ltd.], and the obtained molded product was then ventilated box dryer (manufactured by Fuji Paudal Co., Ltd.). ], The dried product was granulated with 4 mesh pass to 9 mesh on. Then, the obtained granulated product was filled in a fixed bed reactor and heat-treated at 500 ° C. for 1 hr in a nitrogen stream (aeration of 2.0 Nm ³ / hr per 1 kg of the granulated product). Next, reduction treatment is performed at 500 ° C. for 2 hours in a hydrogen gas flow (gas per 1 kg of granulation is 9.5 Nm ³ / hr), and further 500 ppm in nitrogen gas.
In a mixed gas containing air (2.0 kg / kg of granules)
(Aeration with Nm ³ / hr) and a stabilizing treatment for forming a stable oxide film on the surface were performed at 110 ° C. to obtain a ferromagnetic metal powder.

Here, the characteristics of the obtained ferromagnetic metal powder (major axis diameter, axial ratio, crystallite size, coercive force, saturation magnetization and Δσs) are shown in the following [Method for measuring characteristics of ferromagnetic metal powder].
When measured according to the above, it was as shown in [Table 1].

[Measurement Method of Properties of Ferromagnetic Metal Powder] ◎ Major axis diameter and axial ratio 300 powders were randomly extracted from the photograph of the powder photographed by a transmission electron microscope, and each major axis diameter and The axial ratio was measured, and the average value of them was used as the major axis diameter and the axial ratio. ◎ Crystallite size The half value width of the diffraction peak of Fe ₍₁₁₀₎ obtained with an X-ray diffractometer was obtained from the following formula from the 2θ value. D ₍₁₁₀₎ = Kλ / β cos θ [where K is the Scherrer constant (0.9), λ is the wavelength of the irradiation X-ray, β is the half-value width of the diffraction peak (corrected to the true value and used), θ: Diffraction angle] ◎ Coercive force and saturation magnetization A maximum applied magnetic field of 10 with a sample vibrating magnetometer (VSM)
It was measured in kOe. ◎ Saturation magnetization decay rate Δσs The obtained ferromagnetic metal powder was treated at a temperature of 60 ° C. and a relative humidity of 90.
%, The saturation magnetization σs ′ after standing for 7 days in an environment of 10% is measured by the above saturation magnetization measuring method, and the decay rate Δσ is calculated from the value of the saturation magnetization σs (initial value) of the above ferromagnetic metal powder before standing.
s = (1−σs ′ / σs) × 100 was calculated.

<Preparation of Magnetic Coating Material> 100 parts by weight of the obtained ferromagnetic metal powder, alumina (average particle size 0.3 μm)
10 parts by weight, carbon black (average primary particle size 48n
m) 1 part by weight, and the solid content of the previously obtained mixture is 80
A vinyl chloride-based copolymer resin containing a sulfonic acid group (trade name "MR10" in a solvent composed of an equal mixture of methyl ethyl ketone, toluene and cyclohexanone in an amount of 1% by weight).
4 ", 10 parts by weight of Nippon Zeon Co., Ltd.) was added to a Henschel mixer of Mitsui Miike Kakoki Co., Ltd., and the mixture was blended for 1 hour, and then the speed at the tip of the stirring blade was 30 m / The mixture was mixed for 2 minutes at sec to obtain a mixture having a solid content of 80% by weight. At this time, when a part of the mixture was taken out and observed, the surfaces of the ferromagnetic metal powder, alumina and carbon black were all thinly covered with the vinyl chloride copolymer resin. Thereafter, a sulfonic acid group-containing polyurethane resin (trade name "UR8300", Toyobo Co., Ltd.) was added to a solvent composed of an equal mixture of methyl ethyl ketone, toluene and cyclohexanone in an amount such that the solid content of the previously obtained mixture was 80% by weight.
5 parts by weight was added to the Henschel mixer, and the speed at the tip of the stirring blade was 10 m / se.
Mixing for 3 minutes at c gave a mixture with 80% solids by weight. Then, using a continuous twin-screw extruder (KEX-40) manufactured by Kurimoto Tekko Co., Ltd., the obtained mixture was subjected to a shear rate of 1500 S ^-1 and a residence time of 3 minutes in the kneading part was kept at 80% solid content. Kneaded. Then, while adding a solvent consisting of an equal mixture of methyl ethyl ketone, toluene and cyclohexanone, the mixture is disintegrated with a disper and further dispersed using a sand mill, and then palmitic acid (lubricant) 3
After adding 1 part by weight, the mixture was filtered, and 5 parts by weight of an isocyanate-based curing agent (trade name "Coronate HX", manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to give a magnetic coating (solid content: 3
5% by weight) was obtained.

(Blending of back coat paint) Carbon black (average primary particle size 0.028 μm) 32 parts by weight Carbon black (average primary particle size 0.062 μm) 8 parts by weight “Nipporan 2301” [trade name, Nippon Polyurethane Industry ( Polyurethane manufactured by Co., Ltd.] 50 parts by weight nitrocellulose (viscosity display made by Hercules Powder Co. of 1/2 second) 20 parts by weight polyisocyanate (Takeda Pharmaceutical Co., Ltd., trade name "D-250N") 4 parts by weight Copper phthalocyanine 5 parts by weight Stearic acid 1 part by weight Methyl ethyl ketone 120 parts by weight Toluene 120 parts by weight Cyclohexanone 120 parts by weight

<Production of magnetic recording medium> A solid content of 35 μm was obtained by coating the above magnetic coating on polyethylene terephthalate having a thickness of 6 μm.
In a state of weight%, a dry film thickness of 2.5 μm is applied, and while the coating film is in a wet state, it is passed through a solenoid of 5000 Oe to perform magnetic field orientation treatment, and the temperature is 60 to 10
After being dried for 40 seconds in a drying oven in which hot air of 0 ° C. was supplied at a wind speed of 15 m / sec, it was wound up. Then 85
Calendered under conditions of ℃ and 300kg / cm,
After forming the magnetic layer, the back coat coating composition was applied onto the back surface of the support so that the dry thickness was 0.6 μm, dried at 90 ° C., and then wound. After that, it is aged at 50 ° C. for 16 hours, and 3.8
It was slit to a width of 1 mm to obtain a magnetic tape having a width of 3.81.

Here, the characteristics (coercive force, squareness ratio, decay rate ΔBs of residual magnetic flux density and saturation magnetic flux density) of the magnetic layer formed by using the above-mentioned magnetic coating material are shown in the following [Method for measuring characteristics of magnetic layer]. According to the measurement, the results are shown in [Table 1]. [Measurement method of characteristics of magnetic layer] ◎ Coercive force, squareness ratio, and residual magnetic flux density The support and the magnetic layer were punched out to a predetermined size, and a maximum applied magnetic field of 10 kO was measured by a sample vibrating magnetometer (VSM).
e. Saturation magnetic flux density attenuation rate ΔBs The obtained magnetic tape was allowed to stand for 30 days in an environment of a temperature of 60 ° C. and a relative humidity of 90%, and the saturation magnetic flux density Bs ′ was measured by the above-mentioned method for measuring the coercive force of the magnetic layer. The same measurement was performed, and the attenuation rate ΔBs = (1−Bs ′ / Bs) × 100 was calculated from the value of the saturation magnetic flux density Bs (initial value) of the magnetic layer before storage.

With respect to the obtained magnetic tape, the surface roughness of the magnetic layer and the output (130
(kHz, 4.7 MHz) and frequency characteristics were evaluated.
The results are shown in [Table 2]. [Evaluation Method] ◎ Surface Roughness of Magnetic Recording Medium Surface Roughness Ra The obtained magnetic recording medium was manufactured by Zygo under the trade name "La.
ser Inter ferometric Microscope Maxim 3D Model 5700
, The measurement was performed under the conditions of Fizeau 40 and Filter off, and the surface roughness Ra was calculated from the following equation (Equation 1), with the sampling length being 180 μm and N being 260.

[0055]

(Equation 1)

Output (130 kHz and 4.7 MHz) The obtained 3.81 mm wide magnetic tape was loaded into a DAT cassette to obtain a DAT tape cassette for testing. The obtained DAT tape cassette for test and Media Logic,
Using the trade name "Tape Evaluator Model 4500", signals of 130 kHz and 4.7 MHz were recorded on the above magnetic tape, and the output (reproduction output) when reproducing this was measured. The recording wavelength of 130 kHz is 24 μm,
The recording wavelength of 4.7 MHz was 0.67 μm. The reference tape RSD1079 was used as a reference. ◎ Frequency characteristic The frequency characteristic was obtained by taking the difference between the 4.7 MHz output and the 130 kHz output obtained above.

[Example 2] The goethite used in <Preparation of ferromagnetic metal powder> in Example 1 was changed to A with respect to Fe.
Spindle-shaped α-FeOO containing 3% by weight of 1 and 3% by weight of La
H <Goethite> (major axis length 0.25 μm, axial ratio 8), the reduction treatment temperature was changed to 550 ° C., and the stabilization treatment temperature was changed to 90 ° C. Then, a magnetic tape was prepared, and the obtained magnetic tape was tested in the same manner as in Example 1. The results are shown in [Table 2].

[Example 3] The goethite used in <Preparation of ferromagnetic metal powder> in Example 1 was replaced with Fe to C.
Spindle-shaped α-FeOOH <goethite> containing 10% by weight of o, 3% by weight of Al and 1% by weight of Si (long axis length 0.23
μm, axial ratio 10), the same as in Example 1 except that the solid content at the time of kneading was changed to 83% by weight and the residence time in the kneading section was changed to 4 minutes in <Preparation of Magnetic Coating Material>. And then
A magnetic tape was prepared, and the obtained magnetic tape was tested in the same manner as in Example 1. The results are shown in [Table 2].

[Comparative Example 1] A magnetic tape was prepared in the same manner as in Example 1 except that the step of kneading with the biaxial extruder used in <Preparation of magnetic coating material> in Example 1 was not performed. The same test as in Example 1 was performed on the obtained magnetic tape. The results are shown in [Table 2].

Comparative Example 2 A magnetic tape was prepared in the same manner as in Example 1 except that the stabilizing temperature was changed to 70 ° C. in <Preparation of ferromagnetic metal powder> in Example 1. The same test as in Example 1 was performed on the obtained magnetic tape. The results are shown in [Table 2].

[Comparative Example 3] The goethite used in <Preparation of ferromagnetic metal powder> in Example 1 was replaced with A for Fe.
Spindle-shaped α-FeOO containing 3% by weight of 1 and 3% by weight of La
H <Goethite> (major axis length 0.25 μm, axial ratio 9), the reduction treatment temperature was changed to 500 ° C., and the stabilization treatment temperature was changed to 70 ° C. Then, a magnetic tape was prepared, and the obtained magnetic tape was tested in the same manner as in Example 1. The results are shown in [Table 2].

[Comparative Example 4] In <Production of magnetic recording medium> in Example 1, the hot air velocity was 45 m / sec,
Raise the final drying temperature up to 120 ° C, ie 60-1
A magnetic tape was prepared in the same manner as in Example 1 except that the magnetic tape was dried under the temperature condition of 20 ° C., and the obtained magnetic tape was tested in the same manner as in Example 1. The results are shown in [Table 2].

[0063]

[Table 1]

[0064]

[Table 2]

As is clear from the results shown in [Table 1] and [Table 2], the magnetic recording media of the present invention (Examples 1 to 3)
Indicates that the surface roughness, coercive force, squareness ratio, decay rate of residual magnetic flux density, and saturation magnetic flux density of the magnetic layer are within the above ranges, and thus is excellent in electromagnetic conversion characteristics such as frequency characteristics. . Further, the magnetic recording medium of the present invention (Examples 1 to 3)
All were excellent in storage stability.

[0066]

INDUSTRIAL APPLICABILITY The magnetic recording medium of the present invention is excellent in electromagnetic conversion characteristics such as frequency characteristics and storage stability and is capable of high density.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a magnetic recording medium of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic recording medium 2 Support 3 Magnetic layer 4 Back coat layer

Claims (3)

[Claims] 1. A magnetic recording medium comprising a support and a magnetic layer provided on the support, the magnetic layer containing a ferromagnetic metal powder and a binder, wherein the magnetic layer has a surface roughness. Of 10 nm or less, coercive force of more than 1500 Oe, squareness ratio of 0.85 or more, residual magnetic flux density of 2600 Gauss or more, and saturation magnetic flux density attenuation rate ΔBs (temperature 60 ° C., relative humidity 90
% Saturation magnetic flux density Bs' after being left in an environment of 30% for 30 days
Is a rate of change with respect to the saturation magnetic flux density Bs of the magnetic layer before being left, and ΔBs = (1−Bs ′ / Bs) × 100) is 10% or less. Medium. 2. The ferromagnetic metal powder has a major axis diameter of 0.0
5 to 0.3 μm, a crystallite size of 140 Å or more, a saturation magnetization of 120 emu / g or less, and a saturation magnetization attenuation rate Δσs (temperature 60 ° C, relative humidity 90%, left for 7 days. Is the rate of change of the saturation magnetization σs' of the ferromagnetic metal powder before standing with respect to the saturation magnetization σs,
Δσs = (1−σs ′ / σs) × 100)
Is 10% or less, the magnetic recording medium according to claim 1. 3. The method for producing a magnetic recording medium according to claim 1, wherein a coating composition is prepared using a ferromagnetic metal powder and a binder so that the solid content is 70% by weight or more,
The coating composition is obtained by kneading the coating composition to obtain a magnetic coating, and the ferromagnetic metal powder has a major axis diameter of 0.05 to
0.3 μm, a crystallite size of 140 Å or more, a saturation magnetization of 120 emu / g or less, and a saturation magnetization attenuation rate Δσs (after being left for 7 days in an environment of a temperature of 60 ° C. and a relative humidity of 90%). Is a change rate of the saturation magnetization σs ′ of the above with respect to the saturation magnetization σs before being left, and Δσs = (1−σs ′
/ Σs) × 100) is used, and a ferromagnetic metal powder having a content of 10% or less is used.