JPH1064044A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium excellent in durability and electromagnetic transducing characteristic. SOLUTION: In the magnetic recording medium with a magnetic recording layer containing a binder resin and a magnetic particle powder and formed on a non-magnetic base body, 1-30 pts.wt. hematite particle containing 10-30wt.% Mn and having 0.1-0.5μm average particle diameter per 100 pts.wt. magnetic particle powder is incorporated in the magnetic recording player. And in the magnetic recording medium with the magnetic recording layer containing the binder resin and the magnetic particle powder and formed on the non-magnetic base body, 1-30 pts.wt. hematite particle containing 10-30wt.% Mn, having a coating layer composed of one or more kinds selected from an Al oxide, an Al hydroxide, Si oxide and Si hydroxide and 0.1-0.5μm in average particle diameter per 100 pts.wt. magnetic particle powder is incorporated in the magnetic recording layer.

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 having excellent durability and good electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art In recent years, as the size and weight of video and audio magnetic recording / reproducing devices have been reduced and recording has been performed for a long time, the performance of magnetic recording media such as magnetic tapes and magnetic disks has been improved. Demands for high durability and good electromagnetic conversion characteristics are increasing.

In a magnetic recording medium such as a magnetic tape or a magnetic disk, recording and reproduction are performed while being in contact with a magnetic head, so that the magnetic recording layer is liable to be worn, thereby contaminating the magnetic head and deteriorating the recording and reproduction characteristics. To cause
There is a demand for a highly durable magnetic recording medium with less wear than before.

Conventionally, alumina (Al) has been used to improve the wear durability of the magnetic recording layer of a magnetic recording medium.
₂ O ₃ ), hematite (α-Fe ₂ O ₃ ) and trioxide 2
Attempts have been made to add various filler materials such as chromium (Cr ₂ O ₃ ) to the magnetic layer.

For example, in the case of using alumina (Al ₂ O ₃ ), a magnetic recording medium using α-Al ₂ O ₃ having an amorphous phase (Japanese Patent Laid-Open No. 5-36059) or a specific crystallinity can be obtained. And a magnetic recording medium using α-Al ₂ O ₃ (JP-A-7-244836). In the case of using hematite (α-Fe ₂ O ₃ ), a magnetic recording medium using granular α-Fe ₂ O ₃ (JP-A-61-1)
No. 94628) and liquid hydrocarbons and α-Fe ₂ O ₃
(Japanese Patent Laid-Open No. 54-70806). Also, 2 chromium trioxide (Cr ₂ O ₃ )
The one using a magnetic recording medium using the acicular Cr ₂ O ₃ (JP 62-112221 JP) and the like.

However, these filler materials include:
Each has its own problems. It is known that alumina has poor dispersibility in a binder resin, and the electromagnetic conversion characteristics are significantly reduced as the added amount increases. Hematite has a relatively good dispersibility in the binder resin, but it must be added in a large amount in order to obtain sufficient durability. Conversion characteristics will be degraded. 2 chromium trioxide is environmentally friendly.
Not preferred. It is known that when the amount of these filler materials is increased, the durability is improved, but the electromagnetic conversion characteristics are significantly reduced. Therefore, there is a demand for a magnetic recording medium using a filler material that suppresses the deterioration of the electromagnetic conversion characteristics even as an addition amount necessary for improving the durability.

Further, in a video tape system which is currently widely used, a mechanism for detecting the end of a magnetic recording medium includes:
This is done by detecting the transparent leader tape at the end with a sensor. Therefore, the magnetic recording portion needs to have a low light transmittance and a high blackness.

However, in recent years, high-density recording has been demanded, and the fine particles of magnetic particles used for that purpose increase the light transmittance of the magnetic recording layer. As a result, a malfunction may occur in the end detection. Have been. Therefore, as a method of improving the blackness of the magnetic tape, a method of decreasing the light transmittance by increasing the content of the carbon black particle powder in the magnetic layer has been performed. However, the dispersibility of the magnetic particle powder is reduced due to the poor dispersibility peculiar to the carbon black particle powder, and consequently, adverse effects such as a decrease in electromagnetic conversion characteristics and a decrease in durability are caused. This is shown in a comparative example described below in Japanese Patent Application Laid-Open No. 4-139819, in which "... a binder resin and a magnetic particle powder are kneaded to form a coating composition, and carbon black particle powder is added. As described above, there was a problem that the orientation and filling property of the magnetic particle powder were reduced, and the carbon black particle powder had a bulk density of about 0.1 g / cm ³ , which made handling difficult and difficult. In addition, safety and hygiene problems such as carcinogenicity have been pointed out .... ".

Therefore, filler materials as substitutes for carbon black have been demanded. The filler materials such as alumina, hematite and dichromium trioxide are described as white alumina, red hematite and green chromium trioxide. In each case, the contribution of the effect of reducing the light transmittance is lower than that of the black powder. As a material using black powder as a filler material, for example, a magnetic recording medium using black titanium (TiO) (Japanese Patent Publication No. 62-21185, Japanese Patent Publication No.
No. 22179) and a magnetic recording medium using fluorinated graphite (Japanese Patent Application Laid-Open No. 56-156930). However, black titanium is easily oxidized and has insufficient stability in air. Fluorinated graphite has poor dispersibility in a binder resin, and often causes deterioration of electromagnetic conversion characteristics.

Therefore, the dispersibility in the binder resin is good,
A magnetic recording medium having excellent durability and good electromagnetic conversion characteristics using a filler material having a higher degree of blackness is also demanded, even when the amount of addition necessary for improving durability is suppressed. I have.

On the other hand, there are several prior art documents on Mn-containing hematite particle powder.

For example, ferrous sulfate and Mn as a modifying element
By the heating and firing a homogeneous mixture of sulfuric acid salt, (JP-A-52-63199) method for obtaining a thermostable pigments, Fe ₂ O _3, FeOOH and Fe ₃ O ₄ 1 kind selected from or 2 A method of obtaining a dark red iron oxide pigment by heating and baking with a manganese compound and phosphoric acid, etc., using at least the seeds as starting materials (JP-A-54-37004), and producing spherical or granular magnetite particles by a wet method. Then, the surface of the magnetite particles is coated with a Mn compound or a Mn compound and an Fe compound, and then the coated magnetite particles are heated and fired to obtain hematite particles in which Mn is in a solid solution (particularly). JP-A-4-144924), mixed oxides of manganese and iron having a hematite structure (JP-A-5-221563).
JP-A-6-263449, a method of obtaining Mn-containing goethite particles in the presence of a Mn compound in advance to obtain goethite particles by wet oxidation, and obtaining Mn-containing hematite particles by heating and dehydration.
JP-A-7-66020).

The Mn-containing hematite particles described in the above publications are used as black pigments because of their blackness.

[0014]

A magnetic recording medium using a filler material for a magnetic recording medium such as alumina, hematite, trichromium oxide, etc., which has been conventionally used,
When the amount of the filler material added for obtaining the durability is increased, the electromagnetic conversion characteristics are greatly reduced, and a magnetic recording medium having sufficient durability and good electromagnetic conversion characteristics has not yet been obtained.

Accordingly, the present invention has excellent durability and good electromagnetic conversion characteristics by using a black filler material which can suppress the deterioration of the electromagnetic conversion characteristics even when the amount of addition is necessary for improving the durability. It is a technical object to provide a magnetic recording medium. The present inventor has performed numerous trial productions and experiments to achieve the above technical problem, and as a result, contains a specific amount of Mn, and a Mn-containing hematite particle powder having a specific average particle size as a black filler material. It has been found that by using the compound, a sufficient improvement in durability can be obtained, a decrease in electromagnetic conversion characteristics can be suppressed, and a reduction in light transmittance can be achieved.

[0016]

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

That is, according to the present invention, in a magnetic recording medium in which a magnetic recording layer containing a binder resin and magnetic particle powder is formed on a non-magnetic substrate, Mn is contained in the magnetic recording layer.
A magnetic material comprising 1 to 30 parts by weight of a black filler material composed of hematite particles having an average particle diameter of 0.1 to 0.5 μm and containing 0 to 30% by weight based on 100 parts by weight of the magnetic particle powder. In a recording medium and a magnetic recording medium in which a magnetic recording layer containing a binder resin and a magnetic particle powder is formed on a non-magnetic substrate, M
n in an amount of 10 to 30 wt.
Black, consisting of hematite particles having an average particle size of 0.1 to 0.5 μm having a coating layer of one or more selected from oxides of Al, hydroxides of Al, oxides of Si and hydroxides of Si A magnetic recording medium comprising a filler material in an amount of 1 to 30 parts by weight based on 100 parts by weight of the magnetic particle powder.

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

A magnetic recording medium according to the present invention is a magnetic recording medium in which a magnetic recording layer containing a binder resin and magnetic particle powder is formed on a non-magnetic substrate. 5 parts binder resin by weight
30 parts by weight, preferably 7 to 25 parts by weight, and Mn of 10
Average particle having a coating layer of at least one selected from the group consisting of Al oxide, Al hydroxide, Si oxide and Si hydroxide on the particle surface, if necessary. 1 to 30 parts by weight of a black filler material composed of hematite particles having a diameter of 0.1 to 0.5 μm (hereinafter, abbreviated as “specific Mn-containing hematite particles”), preferably 5 to 5 parts by weight
20 parts by weight.

The magnetic characteristics of the magnetic recording medium according to the present invention are as follows.
The saturation magnetic flux density is 1000 to 5000 Gauss, preferably 1500 to 5000 Gauss, and the residual magnetic flux density is 900 to 4500 Gauss, preferably 1000
~ 4500 Gauss and coercive force is 300 ~ 300
0 Oe, preferably 500 to 2500 Oe.

The electromagnetic conversion characteristic value of the magnetic recording medium according to the present invention is 0.5 dB or more at a recording frequency of 1 MHz, preferably 0.7 dB, as a relative value to a reference tape when Comparative Example 4 described later is used as a reference tape. That's it,
At a recording frequency of 4 MHz, it is 0.5 dB or more, preferably 0.7 dB or more.

The wavelength (λ) 9 of the magnetic recording medium according to the present invention
The linear absorption coefficient for light of 00 nm is 1.0 or more, preferably 1.2 or more.

The durability of the magnetic recording medium according to the present invention can be measured by a measuring method described later for 10 minutes or more, preferably 15 minutes or more.
Minutes or more, more preferably 20 minutes or more.

Next, a method for manufacturing the magnetic recording medium according to the present invention will be described.

The magnetic recording medium according to the present invention can be prepared by a conventional method on a non-magnetic substrate by adding 100 parts by weight of magnetic particle powder and 5 to 30 parts by weight, preferably 7 to 25 parts by weight, of a binder resin and a specific Mn-containing hematite. Black filler material 1 consisting of particles
It can be obtained by applying a coating composition containing 30 parts by weight, preferably 5 to 20 parts by weight, and other additives to be added as required, forming a coating film, and orienting in a magnetic field.

The magnetic particles in the present invention include maghemite particles (γ-Fe ₂ O ₃ ) and magnetite particles (Fe ²⁺ _x Fe ³⁺ _{(8-2x) / 3} O ₄ (0 <x ≦
1)) or other magnetic iron oxide particles, a particle powder in which the magnetic iron oxide particles contain other elements such as Co, Al, Ni, P, Zn, Si, and B other than Fe, or these magnetic iron oxide particles. Particle powder coated with Co or the like, metal magnetic particle powder containing iron as a main component, Co, Al, Ni, P other than iron,
Iron alloy magnetic particles containing Zn, Si, B, etc., plate-like Ba ferrite particles, and divalent metals (Co, Ni, Zn etc.) and covalent metals (Ti,
(Sn, Zr, etc.) can be used. The shape of the magnetic particle powder is needle-like, spindle-like, cubic, granular, spherical,
It may be any of a plate shape and the like. The size of the magnetic particle powder is 15 m ² / g or more in BET specific surface area.

In the present invention, the black filler material is a specific M
It is composed of n-containing hematite (α-Fe ₂ O ₃ ) particles. Its crystal structure is a corundum structure as shown in the X-ray diffraction pattern of FIG. The average particle size of the specific Mn-containing hematite particles is 0.1 to 0.5 μm, preferably 0.15 μm.
０．４0.4 μm. The particle shape may be any of a granular shape, a spherical shape, a needle shape, a plate shape, and the like, but a granular shape is particularly preferable in terms of dispersibility. BET specific surface area is 1 to 50 m ² /
g, preferably ² to 30 m ² / g.

The Mn content of the specific Mn-containing hematite particles is 10 to 30% by weight, preferably 15 to 25% by weight, based on the weight of the Mn-containing hematite particles. 10% by weight
If it is less than 1, sufficient blackness cannot be obtained. 30% by weight
In the case where it exceeds, blackness can be obtained, but it is industrially disadvantageous.

The specific Mn-containing hematite particles have an oxide of Al, an hydroxide of Al, an oxide of Si,
It is preferable to have one or two or more coating layers selected from the hydroxides of i. In that case, Si is S
The preferably iO ₂ terms 0.01-50 wt%, more preferably from 0.05 to 20% by weight. Further, Al is preferably 0.01 to 50% by weight, more preferably 0.05 to 20% by weight in terms of Al. In addition, when the specific Mn-containing hematite particle powder having the coating layer on the particle surface is used as a black filler material, the effect of improving durability can be further enhanced.

The colorimetric values of blackness of the specific Mn-containing hematite particles are as follows: L ^* value is 0 to 30.0, a ^* value is -1.0 to
6.0, b ^* value is -3.0 to 10.0. The blackness does not change even when the specific Mn-containing hematite particle powder having the coating layer on the particle surface is used as a black filler material.

There are several methods for producing the specific Mn-containing hematite particle powder, such as the methods described in the above publications.
Any of these methods may be used. For example,
A method of obtaining a Mn-containing hematite particle powder by heating and calcining a homogeneous mixture of ferrous sulfate and a sulfate of Mn as a modifying element (JP-A-52-63199), selected from goethite, hematite and magnetite 1
A method of obtaining a Mn-containing hematite particle powder by heating and sintering a seed or two or more kinds together with a manganese compound, phosphoric acid and sodium sulfate in a temperature range of 850 to 1000 ° C. (Japanese Patent Application Laid-Open No. 54-37004) ,
Spherical or granular magnetite particles are generated by a wet method or the like, and the surface of the magnetite particles is coated with a Mn compound or a Mn compound and an Fe compound. Then, the coated magnetite particles are heated at a temperature in the range of 750 to 1000 ° C. in method (Japanese Unexamined Patent Publication No. 4-144924) to obtain a Mn-containing hematite particles by firing, Fe _3-x Mn _x O spinel structure by precipitation the salt of iron and manganese are oxidized in the presence of an alkali ₄ (0
<X <3), which is heated and fired in an oxidizing atmosphere at a temperature in the range of 600 to 800 ° C. to obtain Mn-containing hematite particles (Japanese Patent Application Laid-Open No. 5-221563). In order to get
a method of obtaining Mn-containing hematite particle powder by obtaining Mn-containing goethite particles in the presence of an n-compound, and further heating and dehydrating (JP-A-6-263449,
JP-A-7-66020). Preferably, the method is mainly a method described in JP-A-4-144924.

Hereinafter, a preferred method for producing the specific Mn-containing hematite particle powder will be specifically described.

The suspension containing the ferrous hydroxide colloid obtained by reacting the aqueous ferrous salt solution and the aqueous alkali hydroxide solution is heated to a temperature range of 45 to 100 ° C. while passing an oxygen-containing gas through the suspension. To generate magnetite particles, and by adding a Mn salt or a Mn salt and a ferrous salt to the suspension of the magnetite particles, a Mn compound or a Mn compound and a Fe compound on the particle surface of the magnetite particles. The specific Mn-containing hematite particle powder can be obtained by coating and then firing the surface-coated magnetite particles in a temperature range of 750 to 1000 ° C.

As the aqueous ferrous salt solution, an aqueous ferrous sulfate solution and an aqueous ferrous chloride solution can be used.

As the aqueous alkali hydroxide solution, various aqueous solutions of sodium hydroxide, potassium hydroxide and the like can be used.

The amount of the aqueous alkali hydroxide solution to be added initially is 0.80 to 1.10 with respect to Fe ²⁺ in the aqueous ferrous salt solution.
3 equivalents. The reaction temperature ranges from 45 to 100 ° C. If the temperature is lower than 45 ° C, needle-like goethite particles may be mixed. If the temperature is higher than 100 ° C, equipment such as an autoclave is required, which is not economical.

As the aqueous solution of the Mn salt, various aqueous solutions of manganese sulfate, manganese chloride and the like can be used. The Mn
The amount of salt added is 10 to 45 with respect to the total of all Fe and Mn.
Atomic%, preferably 15 to 40 atomic%. If it is less than 10 atomic%, sufficient blackness cannot be obtained. When it exceeds 45 atomic%, blackness can be obtained, but it is industrially disadvantageous.

If necessary, a ferrous salt can be added together with the Mn salt. By simultaneously adding the ferrous salt, the particle surface can be easily coated with the Mn compound. The ferrous salt is preferably used in the form of an aqueous solution, and the above-mentioned aqueous ferrous salt solution can be used.
The addition amount of the ferrous salt is 75% or less as Fe ^{2+ based on} the total amount of all Fe and Mn in the suspension.

The temperature range for heating and sintering the magnetite particles having the particle surface coated with a Mn compound or a Mn compound and an Fe compound is 750 to 1000 ° C. 750 ° C
If it is less than 1,000, the degree of blackness is insufficient, and if it exceeds 1000 ° C, the particles become too large and the coloring power cannot be obtained. Note that the atmosphere for the heating and firing is an oxidizing atmosphere. Preferably in air. The heating and firing in an oxidizing atmosphere is for oxidizing magnetite and transforming it into hematite.

A compound containing one or more of Al and Si is added to the aqueous suspension containing Mn-containing hematite particles obtained by the above-mentioned production method at 20 to 95 ° C., and the pH is adjusted by adjusting the pH. The oxide of Al, the hydroxide of Al, the oxide of Si,
A coating layer composed of one or two or more selected from hydroxides of Si can be formed.

The addition of the compound containing Al and the compound containing Si can be carried out by dropping all at once, or divided into several times, or continuously. PH adjustment can be performed before, after, or before and after each of the compound containing Al and the compound containing Si. The pH range to be adjusted is between 5.0 and 9.0, preferably 6.0.
８8.0.

Examples of the compound containing Al include aluminum salts such as aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum acetate and aluminum oxalate; alkali aluminates such as sodium aluminate and potassium aluminate; and alumina sol. it can. The amount of the compound containing Al is preferably 0.01 to 0.01 wt.
-50% by weight, more preferably 0.05-20% by weight
It is.

As the compound containing Si, water glass, sodium silicate, potassium silicate, calcium silicate, colloidal silica, silicon dioxide and the like can be used. The amount of the compound containing Si is preferably 0.01 to 50% by weight, more preferably 0.05 to ₂ % by weight in terms of SiO2, based on the Mn-containing hematite particle powder.
0% by weight.

As the binder resin in the present invention, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, vinylidene chloride, Polyurethane resin, styrene-butadiene copolymer, butadiene-acrylonitrile copolymer, polyvinyl butyral, cellulose derivatives such as nitrocellulose, polyester resin, synthetic rubber resin such as polybutadiene, epoxy resin, polyamide resin, polyisocyanate polymer,
An electron beam-curable acrylic urethane resin or the like and a mixture thereof can be used.

As the non-magnetic base material in the present invention,
At present, polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, which are widely used in the production of magnetic recording media,
Synthetic resin films such as polyamide, polyamideimide, polyimide, and polysulfone, and metal foils and plates such as aluminum and stainless steel, and various papers can be used.

Other commonly used lubricants, abrasives,
You may add an antistatic agent, a coloring material, etc.

In kneading and dispersing the magnetic coating material of the present invention, for example, a kneading machine such as a twin-screw kneader, a twin-screw extruder, a pressure kneader, a two-roll mill, or a three-roll mill can be used. Ball mills, sand grinders, attritors, dispersers, homogenizers, ultrasonic dispersers and the like can be used.

In applying the magnetic paint of the present invention, a gravure coater, reverse roll coater, slit coater, die coater or the like can be used. The applied sheet can be oriented in a magnetic field by the orientation of a counter magnet, the orientation of a solenoid magnet, or the like.

[0049]

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

The average particle size of the filler material, the average major axis diameter, the average minor axis diameter, and the axial ratio of the filler material and the magnetic particles in the following embodiments, examples and comparative examples are all measured from electron micrographs. It was shown by the average value of the numerical values. The specific surface area was indicated by a value measured by the BET method.

The Mn content and the content of each element were measured using a “fluorescent X-ray analyzer 3063M” (manufactured by Rigaku Corporation) in accordance with JIS K0119 “General rules for fluorescent X-ray analysis”.

The colorimetry of the black filler material composed of the specific Mn-containing hematite particles was carried out by applying a dispersion paste of the black filler material obtained by using a Hoover type muller to a white paper, and then using a multi-source spectrophotometer MSC-IS-. Using a 2D (manufactured by Suga Test Instruments Co., Ltd.), colorimetric indices L ^* , a ^* , and b ^* as defined in JIS Z9729 were measured.

The surface gloss of the coating film was measured using a gloss meter UG.
It is a value measured at an incident angle of 45 ° with a V-5D (manufactured by Suga Test Instruments Co., Ltd.), and the value when the standard plate gloss is 86.3% is shown in%.

The surface roughness (Ra) is calculated as follows: “surfcom-
575A "(manufactured by Tokyo Seimitsu Co., Ltd.) as a center line average roughness value of a coating film after calendering.

The light transmittance was measured using a photoelectric spectrophotometer UV-210.
0 (manufactured by Shimadzu Corporation) was used to measure the light transmittance at λ = 900 nm with respect to a reference base film. The linear absorption coefficient is defined by the following equation, and the larger the value, the more difficult it is to transmit light. Linear absorption coefficient (μm ⁻¹ ) = ln (1 / t) / FT t: Light transmittance at λ = 900 nm FT: Thickness (μm) of coating composition layer of magnetic recording medium used for measurement

The coating viscosity was determined by measuring the apparent viscosity at 25 ° C. at a shear rate of 1.92 / sec using an E-type viscometer.

The durability was measured using a media durability tester MDT-3000 (Steinberg Assoc).
iates), relative speed 16 m / sec,
It is shown as a measured value at a load of 200 g.

The magnetic characteristics are described in "Vibrating sample magnetometer VSM-
3S-15 "(manufactured by Toei Kogyo Co., Ltd.) and measured at a maximum external magnetic field of 10 kOe.

The electromagnetic conversion characteristics of the drum tester BX-3
Relative speed 5.8m using 168 (manufactured by Verdex)
The electromagnetic conversion output values at recording frequencies of 1 MHz and 4 MHz in / sec are shown as relative values to the reference tape of Comparative Example 4 described later.

The surface electric resistance of the coating film was determined by exposing the coating film to be measured in an environment of a temperature of 25 ° C. and a relative humidity of 60% for 12 hours or more and then slitting the metal electrode having a width of 6.5 mm to a width of 6 mm. Place the coating film, attach 170 g of weight to each end, and make the coating film adhere to the electrodes.
The value was measured by applying a DC voltage of V.

<Production of Black Filler Material> Fe ²⁺ 1.40
300 l of an aqueous solution of ferrous sulfate containing 1 mol / l of water 21 previously prepared in a reactor equipped with a stirrer (900 l).
0 l and 60 l of 15.75N aqueous sodium hydroxide solution
In addition, an aqueous ferrous salt solution containing a ferrous hydroxide precipitate was produced at a pH of 13 or more and a temperature of 85 ° C.

At a temperature of 90 ° C., 250 liters of air per minute was added to the ferrous salt aqueous solution containing the ferrous hydroxide precipitate at a temperature of 90 ° C.
Vent for a minute to produce magnetite particles.

Next, the magnetite particles 32.4 k
g of an aqueous suspension containing 570 l of Fe ²⁺ 1.40 mol /
l of FeSO ₄ aqueous solution containing 100 l and Mn ²⁺ 1.40 m
ol / l of an aqueous solution of MnSO ₄ (100 liters, the amount of added Mn corresponds to 20 atom% based on the total of all Fe and Mn) and 50 liters of an aqueous solution of 11.2 N NaOH (added Fe ²⁺ , Mn And a pH of 13
At a temperature of 90 ° C., 700 liters of air per minute
Vent for a minute to produce magnetite particles having a particle surface coated with a Mn compound and an Fe compound.

The produced particles were separated by filtration, washed with water, dried, and pulverized to obtain black particles. Subsequently, the obtained black particle powder was placed in a porcelain crucible and fired in an electric furnace at 800 ° C. for 2 hours in air to obtain black particle powder.

The obtained black particle powder had an average particle size of 0.28 as shown in the electron micrograph (× 20000) of FIG.
μm, and the Mn content was 13.6% by weight as a result of a fluorescent X-ray analysis.
^{The *} value was 21.1, the a ^* value was 0.9, and the b ^* value was -1.2. Further, as shown in the X-ray diffraction pattern of FIG. 2, only a peak showing a hematite structure was observed.

The obtained specific Mn-containing hematite particle powder is used as a black filler material for magnetic recording media in the production of the following magnetic recording media.

<Manufacture of magnetic recording medium> Co-coated needle-like γ
-Fe ₂ O ₃ particle powder (major axis 0.25 μm, axial ratio (major axis diameter / minor axis diameter) 7.0, specific surface area 31.6 m ² / g, coercive force 682 Oe, saturation magnetization 79.6 emu / g, 100 parts by weight of Co content 2.69% by weight), 10.0 parts by weight of MR-110 (vinyl chloride resin) (manufactured by Zeon Corporation), 23.3 parts by weight of cyclohexanone, 10.0 parts by weight of methyl ethyl ketone, Carbon black particle powder (Mitsubishi Kasei Co., Ltd., particle size 26 nm, BET specific surface area 130 m)
² / g) After kneading 1.0 part by weight and 7.0 parts by weight of specific Mn-containing hematite particle powder using a kneader for 20 minutes, 79.6 parts by weight of toluene, 110.2 parts by weight of methyl ethyl ketone and Cyclohexanone 17.
The mixture was diluted by adding 8 parts by weight, and then mixed and dispersed by a sand grinder for 3 hours.

To the above mixed dispersion, 33.3 parts by weight of a 1/1 solution of methyl ethyl ketone / cyclohexanone containing 10.0 parts by weight of a solid content of a polyurethane resin (product name: TI-1075, manufactured by Sanyo Chemical Industries, Ltd.) was added. Add 3 more
After mixing and dispersing using a sand grinder for 0 minutes,
The filtrate obtained by filtration with a filter having an opening of 1 μm was added to 1.0 part by weight of myristic acid and butyl stearate.
12.1 parts by weight of a 5/3/2 solution of MEK / toluene / cyclohexanone containing 0 parts by weight and E-31 (trifunctional low molecular weight polyisocyanate, manufactured by Takeda Pharmaceutical Co., Ltd.)
15.2 parts by weight of a 5/3/2 solution of MEK / toluene / cyclohexanone containing 5.0 parts by weight were mixed with stirring to prepare a magnetic coating material. The paint viscosity at this time was 2270
cp.

After the magnetic paint was filtered through a filter having a mesh size of 1 μm, it was applied on a polyester base film having a thickness of 14 μm using a slit coater having a gap width of 45 μm, and then dried to obtain a film having a thickness of about 4 μm.
After the magnetic layer was formed, the surface was smoothed by calendering according to a conventional method, and then cut to a width of 1/2 inch. The obtained magnetic tape was allowed to stand in a curing furnace at 60 ° C. for 24 hours, and was sufficiently cured to obtain a magnetic recording medium composed of the magnetic tape.

The magnetic characteristics of the magnetic recording medium are as follows: coercive force is 721 Oe, residual magnetic flux density Br is 1420 Gauss,
The squareness ratio (Br / Bm) was 0.88, and the degree of orientation was 2.53. The glossiness is 172%, the surface roughness Ra is 6.8 nm,
The linear absorption coefficient is 1.21 μm ⁻¹ , the electromagnetic conversion characteristic at a recording wavelength of 1 MHz is +1.8 ^dB , the electromagnetic conversion characteristic at a recording wavelength of 4 MHz is +1.6 dB, the durability is 30 minutes or more, and the electric resistance is 5.0 × 10 ^9. Ω / cm ² .

The specific Mn used for the magnetic recording medium was
It is recognized from the values of the glossiness and the surface roughness Ra that the contained hematite particles are excellent in dispersibility.

[0072]

The magnetic recording medium according to the present invention has a sufficient linear absorption coefficient even if the amount of carbon black used is reduced, as described in the above-mentioned embodiment of the present invention. The surface roughness is good, the squareness ratio and orientation of the coating film are good, and sufficient durability is obtained. In addition, as described in the embodiment of the invention described above and Examples 13 and 14 described below, the amount of the specific Mn-containing hematite particles was increased from 7 parts by weight to 14 parts by weight, and further increased to 21 parts by weight. Even so, a decrease in electromagnetic conversion characteristics is suppressed.
The present inventor considers this fact as follows.

That is, since the magnetic recording medium according to the present invention uses a specific Mn-containing hematite particle powder having excellent blackness as a black filler material, a sufficient linear absorption coefficient can be obtained even when the amount of carbon black used in combination is reduced. I believe it was.

As described above, the dispersibility of the magnetic paint is improved due to the effect of reducing the carbon black having poor dispersibility and the effect of the specific Mn-containing hematite particles having good dispersibility. Coating film physical properties and squareness ratio,
It is considered that the magnetic properties such as the orientation were improved.

Further, since the specific Mn-containing hematite particles are excellent in dispersibility, the embodiment of the invention described above,
As described in Examples 13 and 14 below, specific Mn
Even if the added amount of the contained hematite particle powder is increased from 7 parts by weight to 14 parts by weight, and even 21 parts by weight, a decrease in electromagnetic conversion characteristics is suppressed, and sufficient durability equivalent to Al ₂ O ₃ is obtained. I believe it was.

[0076]

Next, examples and comparative examples will be described.

Examples 1 to 16, Comparative Examples 1 to 10 <Production of Black Filler Material> Examples 1 to 6, Comparative Examples 1 to 3 Amount of ferrous salt, amount of alkali hydroxide, type of Mn salt A black filler material composed of Mn-containing hematite particles was obtained in the same manner as in the embodiment of the present invention except that the addition amount, the heat treatment conditions, the presence or absence of the surface treatment, and the like were variously changed. Tables 1 to 3 show the production conditions of the Mn-containing hematite particle powder, and Table 4 shows its properties and the properties of other filler materials to be compared.

[0078]

[Table 1]

[0079]

[Table 2]

[0080]

[Table 3]

[0081]

[Table 4]

<Manufacture of Magnetic Recording Medium> Examples 7 to 16, Comparative Examples 4 to 10 The type of the magnetic particle powder, the amount of the binder resin, the type and amount of the black filler material or other filler material, and the amount of the solvent were determined. A magnetic recording medium was obtained in the same manner as in the embodiment of the present invention except for various changes. Table 5 shows the manufacturing conditions of the magnetic recording medium.
The properties are shown in Table 6.

[0083]

[Table 5]

[0084]

[Table 6]

[0085]

The magnetic recording medium according to the present invention can suppress the deterioration of the electromagnetic conversion characteristics even with the addition amount necessary for improving the durability, and has a sufficient blackness, so that the carbon black Uses a specific Mn-containing hematite particle powder having various characteristics that the amount used in combination can be reduced as a black filler material, so it has excellent durability and good electromagnetic conversion characteristics, and is used for high-density recording. Ideal for

[Brief description of the drawings]

FIG. 1 is an electron micrograph (× 20,000) showing the particle morphology of a specific Mn-containing hematite particle powder obtained in an embodiment of the present invention.

FIG. 2 is an X-ray diffraction pattern showing a particle structure of a specific Mn-containing hematite particle powder obtained in an embodiment of the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Tsunoda 4-1-2, Funariminami, Naka-ku, Hiroshima-shi, Hiroshima The inside of Toda Kogyo Co., Ltd.

Claims (2)

[Claims] 1. A magnetic recording medium in which a magnetic recording layer containing a binder resin and magnetic particle powder is formed on a non-magnetic substrate, wherein the magnetic recording layer contains an average of 10 to 30% by weight of Mn. A magnetic recording medium characterized in that a black filler material composed of hematite particles having a particle size of 0.1 to 0.5 μm is contained in an amount of 1 to 30 parts by weight based on 100 parts by weight of the magnetic particle powder. 2. A magnetic recording medium in which a magnetic recording layer containing a binder resin and magnetic particle powder is formed on a nonmagnetic substrate, wherein Mn is contained in the magnetic recording layer in an amount of 10 to 30% by weight.
An average particle diameter of 0.1 to 0.1 having a coating layer containing one or two or more selected from oxides of Al, hydroxides of Al, oxides of Si, and hydroxides of Si on the surface of the particles.
A magnetic recording medium characterized in that a black filler material comprising 0.5 μm hematite particles is contained in an amount of 1 to 30 parts by weight based on 100 parts by weight of the magnetic particle powder.