JPH0785459A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a high density recording medium by forming a magnetic layer of the two-layer structure including the upper and lower layers, using a particular magnetic powder for the lower magnetic layer and cobalt-covered iron oxide powder and barium ferrite powder for the upper magnetic layer. CONSTITUTION:The magnetic recording medium comprises a base material, a first magnetic layer which is formed on the base material and is composed of an iron oxide powder including cobalt and a binding agent, and a second magnetic layer consisting of a cobalt covered iron oxide powder having a coersive force of 1300 Oe or more and higher than that of iron oxide powder including cobalt and a mean axis length of 0.3mum or less, barium ferrite powder and a binding agent. The second magnetic layer is provided on the first magnetic layer and a weight ratio of the cobalt covered iron oxide powder and barium ferrite powder used for the second magnetic layer is set to 10:90 to 80:20. Thereby, the medium having the balanced electromagnetic conversion characteristics such as output, noise and the physical characteristics such as corrosion-proof and running characteristic can be obtained.

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 a two-layer magnetic layer structure, and more particularly to a magnetic recording medium excellent in electromagnetic conversion characteristics and durability.

[0002]

2. Description of the Related Art A coating type magnetic recording medium is obtained by coating a magnetic coating material obtained by dispersing magnetic powder in a binder and an organic solvent on a substrate such as polyester and drying it. There is an increasing demand for higher density recording such as high quality video tapes and large capacity floppy disks.

Ferromagnetic metal powders composed mainly of iron are most often used as magnetic powders for achieving this purpose. Ferromagnetic metal powder composed mainly of iron has high saturation magnetization and coercive force, and has excellent output characteristics. However, since it is chemically unstable and easily rusts (is easily oxidized), the saturation magnetization is lowered by oxidation, and the noise characteristic is not always sufficient, and generally the noise level is higher than that of the oxide magnetic powder. Further, the ferromagnetic metal powder mainly composed of iron has a high cost and has some drawbacks in practical use.

A perpendicular magnetic recording method has been proposed as a method for realizing high-density recording, and hexagonal plate-shaped barium ferrite is used as a magnetic powder particularly suitable for this method. However, since barium ferrite has a low saturation magnetization, when used as a magnetic tape or a magnetic disk, the residual magnetic flux density becomes low and the output in the low range becomes insufficient. Further, when barium ferrite is used, there is a problem that the surface roughness of the formed magnetic layer becomes large.

In order to solve such a problem, it has been attempted to improve the output characteristics by making the single-layer magnetic layer, which has been the mainstream in the past, a double-layer structure. For example, in JP-A-62-78718, an oxide having a coercive force equal to or higher than the coercive force of the metal magnetic powder in the lower layer is used by using a metal magnetic powder (iron, cobalt, nickel, etc. or an alloy thereof) in the lower layer. A magnetic recording medium has been disclosed in which magnetic powder (γ-Fe ₂ O ₃ , Fe ₃ O _4, etc.) is used as an upper layer and the magnetic layer has a two-layer structure. However, the magnetic recording medium described in this publication has an insufficient output in a high frequency region, and its S / N is low, so that the noise characteristic is also insufficient.

In addition to this, as a magnetic recording medium having a magnetic layer having a two-layer structure, Japanese Examined Patent Publication No. 63-56608, Japanese Examined Patent Publication No. 3-6575, Japanese Examined Patent Publication No. 3-53689, and Japanese Examined Publication No. 3-
No. 53690 and the like, but these are intended to improve either the magnetic properties or the corrosion resistance, and it has not been achieved to improve both of them.

[0007]

As described above, in a magnetic recording medium intended for high density recording, it is still insufficient to improve both magnetic characteristics and physical characteristics such as running property in a well-balanced manner. The problem to be solved by the present invention is to further improve the S / N, reduce the friction coefficient and improve the running property in a magnetic recording medium that enables high density recording, and a head using the same. It is to eliminate clogging and to reduce the decrease of the saturation magnetic flux density during storage more than the ferromagnetic metal powder mainly composed of iron.

[0008]

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have determined that the magnetic layer has a two-layer structure of upper and lower layers, a specific magnetic powder is used for the lower magnetic layer, and the coercive force is 1
By using cobalt-coated iron oxide powder having an average major axis length of 300 (Oe) or more and 0.3 μm or less and barium ferrite powder in the upper magnetic layer, it is possible to obtain a magnetic recording medium having excellent characteristics. Heading out, the present invention has been completed.

That is, according to the present invention, a base material, a first magnetic layer formed on the base material and comprising a cobalt-containing iron oxide powder and a binder, a coercive force of 1300 (Oe) or more, and the cobalt It comprises a cobalt-coated iron oxide powder having a coercive force greater than or equal to that of the contained iron oxide and an average major axis length of 0.3 μm or less, barium ferrite powder, and a binder.
The present invention provides a magnetic recording medium (hereinafter abbreviated as magnetic recording medium (I)) having a second magnetic layer formed on a magnetic layer.

In the present invention, a base material, a first magnetic layer formed on the base material, which is composed of a ferromagnetic metal powder mainly composed of iron and a binder, and a coercive force of 1300 (Oe) or more. And having a coercive force equal to or higher than that of the cobalt-containing iron oxide,
A magnetic recording medium comprising a cobalt-deposited iron oxide powder having an average major axis length of 0.3 μm or less, barium ferrite powder, and a second magnetic layer formed on the first magnetic layer, which comprises a binder ( Hereinafter, the magnetic recording medium (II) will be provided.

Further, the present invention comprises a base material, at least two kinds of magnetic powders selected from a ferromagnetic metal powder mainly composed of iron, a cobalt-containing iron oxide powder and a barium ferrite powder, and a binder. The first magnetic layer formed on the upper surface has a coercive force of 1300 (Oe) or more and a coercive force of not less than that of the cobalt-containing iron oxide, and an average major axis length of 0.3 μm or less. A magnetic recording medium (hereinafter abbreviated as magnetic recording medium (III)) having a second magnetic layer formed of iron oxide powder, barium ferrite powder, and a binder and formed on the first magnetic layer. Is provided.

The magnetic recording media (I) to (II of the present invention will be described below.
I) will be explained.

<Magnetic Recording Medium (I)> The magnetic recording medium (I) of the present invention has upper and lower two magnetic layers, and the lower magnetic layer is a cobalt-containing iron oxide powder (hereinafter abbreviated as Co—Fe). Do)
And the upper magnetic layer contains a cobalt-coated iron oxide powder having a coercive force of 1300 (Oe) or more and an average major axis length of 0.3 μm or less, and a ferromagnetic metal powder mainly containing iron.

First, the Co--Fe used in the first magnetic layer of the magnetic recording medium (I) will be described. In the present invention,
Cobalt-containing iron oxides include Co surface-forming cobalt-deposited iron oxides, as well as Co-doped iron oxides containing Co inside,
It contains an adsorption type cobalt-containing iron oxide, cobalt ferrite, or the like, and any of these can be used for the first magnetic layer. Especially in the first magnetic layer,
Co-deposited Fe ₃ O ₄ , Co-deposited Fe ₂ O ₃ , Co-deposited FeO _x (1.34
≦ x <1.50), or coated with cobalt ferrite
Fe ₃ O ₄ , Fe ₂ O ₃ and FeO _x are preferably used.

Further, the cobalt-containing iron oxide used in the first magnetic layer of the magnetic recording medium of the present invention is produced by a conventional method of depositing cobalt with the acicular iron oxide as a nucleus. The magnetic characteristics can be adjusted to predetermined values by controlling the amount of cobalt added and the amount of Fe ²⁺ in the manufacturing conditions. The amount of cobalt added is usually 1 to 20% by weight (based on the raw iron oxide),
It is preferably 2 to 15% by weight, and the amount of Fe ²⁺ is usually 0.1.
It is 5 to 30% by weight (ratio in the total cobalt-containing iron oxide), preferably 1 to 25% by weight.

The coercive force of Co--Fe used for the first magnetic layer is not particularly limited and may be appropriately determined according to the desired performance of the magnetic recording medium, but is generally about 700 to 1800 (Oe). is there.

The particle size of Co--Fe is not particularly limited, but the average major axis length is generally 0.1 to 1.0 .mu.m, and the average minor axis length is generally 0.01 to 0.1 .mu.m. The shape of the particles is not limited, but needle-like particles are preferable. Also Co
-Fe has a specific surface area of 20 to 60 m ² / g, especially 30 to 50 m ²
/ G is preferred.

The first magnetic layer of the magnetic recording medium (I) is Co--
It is formed by coating a magnetic coating material containing Fe and a binder as a main component on a substrate, and the thickness of the first magnetic layer is 1 to 5 μm, preferably 2 to 4 μm.

Next, the second magnetic layer of the magnetic recording medium (I) will be described. In the second magnetic layer of the magnetic recording medium (I) of the present invention, the coercive force is 1300 (Oe) or more, and the coercive force is larger than that of Co—Fe used for the first magnetic layer, and the average major axis length is Two types of magnetic powders are used: a cobalt-adhered iron oxide powder of 0.3 μm or less and a barium ferrite powder (hereinafter abbreviated as Ba).

The second magnetic layer of the magnetic recording medium (I) of the present invention has a coercive force of 1300 (Oe) or more, preferably 130.
Cobalt-coated iron oxide of 0-2000 (Oe) is used. As the cobalt-coated iron oxide powder of the second magnetic layer, one having a coercive force larger than that of Co—Fe used for the first magnetic layer is used. When the coercive force of the cobalt-adhered iron oxide used for the second magnetic layer is less than 1300 (Oe), high output cannot be achieved. Specifically, as cobalt-deposited iron oxide, Co-deposited Fe ₃ O ₄ , Co-deposited Fe ₂ O ₃ , Co-deposited Fe
O _x (1.34 ≦ x <1.50) is used, especially Co deposition
FeO _x is preferred. Cobalt-doped iron oxide is not preferable for the second magnetic layer because it has poor storage stability. The shape of the cobalt-coated iron oxide used in the second magnetic layer is not limited, but needle-shaped ones are preferably used. The average major axis length of the cobalt-coated iron oxide is 0.3 μm or less, and the axial ratio is preferably about 3-20.

The cobalt-adhered iron oxide used in the second magnetic layer of the magnetic recording medium of the present invention is also produced by the ordinary cobalt-adhesion method using acicular iron oxide as the nucleus, as described above.
The magnetic characteristics can be adjusted to predetermined values by controlling the amount of cobalt added and the amount of Fe ²⁺ in the manufacturing conditions. The amount of cobalt added is usually 1 to 20% by weight (based on iron oxide as a raw material), preferably 2 to 15% by weight, and the amount of Fe ²⁺ is usually 0.5 to 30% by weight (cobalt deposition oxidation). The proportion of iron as a whole), preferably 1 to 25% by weight.

The second aspect of the magnetic recording medium (I) of the present invention
As the Ba used in the magnetic layer, hexagonal plate-shaped particles are preferably used, and the particle size (diagonal length) is not particularly limited, but is generally 0.02 to 1.0 μm, The thickness is about 0.001 to 0.1 μm. Also,
The coercive force of Ba is not particularly limited and may be appropriately determined depending on the desired performance of the magnetic recording medium.
The degree of (Oe) is general.

The weight ratio of cobalt-coated iron oxide powder used in the second magnetic layer to Ba is preferably [cobalt-coated iron oxide powder]: [Ba] = 10: 90 to 80:20.

The second magnetic layer is formed by applying the above-described cobalt-adhered iron oxide powder, magnetic coating material containing Ba and a binder as the main components on the first magnetic layer. The layer thickness is preferably 0.1 to 3 .mu.m.

In the present invention, the method of forming (coating) the magnetic layers may be either a method of simultaneously forming the first magnetic layer and the second magnetic layer or a method of sequentially forming one layer at a time, and one layer at a time. In this case, calendar processing may be performed for each layer.

The magnetic coating material for forming the magnetic layer of the magnetic recording medium of the present invention uses the above-mentioned magnetic powder for the first and second magnetic layers, and other components such as binder and organic solvent are common. Can be used.

As the binder used in the present invention, urethane resin, particularly polyurethane containing polar groups such as sulfonic acid group, sulfonic acid metal base, sulfobetaine group, carbobetaine group, amino group, hydroxyl group, epoxy group and the like. Resins, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylonitrile copolymers, and other vinyl chloride-based copolymers, particularly sulfonic acid groups, sulfonic acid metal bases, amino Chloride copolymers containing polar groups such as groups, butadiene-acrylonitrile copolymers, polyamide resins, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer Coalesced, polyester resin, various synthetic rubber, Nol resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, low molecular weight glycol / Examples include high molecular weight diol / isocyanate mixtures, and mixtures thereof, and similar materials can be used for the first magnetic layer and the second magnetic layer. Usually, the binder is 3.0-
About 10.0% by weight is blended.

As the organic solvent, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, benzene, toluene, xylene, dimethyl sulfoxide, tetrahydrofuran, dioxane and the like are suitable solvents for dissolving the binder resin to be used. There is no particular limitation and they may be used alone or in combination of two or more. Usually, the organic solvent is 20 to 80% by weight in the magnetic paint.
The degree is mixed.

In the magnetic coating composition, various commonly used additives such as dispersants, abrasives and lubricants may be appropriately added and used. As the dispersant, lecithin,
Nonionic surfactants, anionic surfactants, cationic surfactants and the like can be used. As an abrasive, α-
Fine powders having an average particle size of 0.05 to 1 μm, such as alumina, fused alumina, chromium oxide (Cr ₂ O ₃ ), iron oxide, silicon carbide, corundum, and diamond can be used, and usually 100 parts by weight of the binder as described above. 0.5 to 100 parts by weight is added. Examples of lubricants include silicone oils such as various polysiloxanes, inorganic powders such as graphite and molybdenum disulfide, fine plastic powders such as polyethylene and polytetrafluoroethylene, higher fatty acids, higher alcohols, higher fatty acid esters, and fluorocarbons. Is 0.1 to 100 parts by weight of the above-mentioned binder.
It is added in a proportion of 50 parts by weight.

The substrate used in the magnetic recording medium of the present invention includes synthetic resins (for example, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyamides, polyolefins, cellulose derivatives), non-magnetic metals, glass, ceramics and papers. Etc., and the form thereof is used in films, tapes, sheets, cards, disks and the like.

<Magnetic Recording Medium (II)> The magnetic recording medium (II) of the present invention has upper and lower two magnetic layers, and the lower first magnetic layer is a ferromagnetic metal powder mainly composed of iron (hereinafter referred to as "ferromagnetic metal powder"). , Abbreviated as metal powder), and the upper second magnetic layer has a coercive force of 1
It contains Ba and a cobalt-adhered iron oxide powder having an average major axis length of 300 (Oe) or more and an average major axis length of 0.3 μm or less.

The metal powder used for the first magnetic layer in the magnetic recording medium (II) may be a conventionally known one mainly composed of iron, such as iron powder or an alloy powder of iron and cobalt, nickel, etc. And alloy powders containing transition metal elements such as aluminum, chromium, manganese, silicon, zinc, rare earth metal elements, lanthanoids and actinides. The remanent magnetization and coercive force of the metal powder are not limited,
For example, the coercive force is generally about 800 to 1900 (Oe). The particle size of the metal powder is also the same and is not particularly limited, but the average major axis length is generally 0.1 to 1.0 μm, and the average minor axis length is generally 0.01 to 0.1 μm. Also, the shape of the particles is not limited.

In the magnetic recording medium (II), the cobalt-coated iron oxide powder and Ba used in the second magnetic layer are the same as those described in the magnetic recording medium (I). The same applies to the magnetic recording medium (I).

Also, in the magnetic recording medium (II), the second
The weight ratio of cobalt-coated iron oxide powder used in the magnetic layer to Ba is [cobalt-coated iron oxide powder]: [Ba] = 10: 90.
The range of 80:20 is preferable.

<Magnetic Recording Medium (III)> The magnetic recording medium (III) of the present invention has two upper and lower magnetic layers, and the first lower magnetic layer is selected from metal powder, Co--Fe and Ba. At least two types of magnetic powders are contained, and the upper second magnetic layer contains cobalt-coated iron oxide powder having a coercive force of 1300 (Oe) or more and an average major axis length of 0.3 μm or less, and Ba.

The first part of the magnetic recording medium (III) of the present invention is described below.
The magnetic powder used in the magnetic layer will be described.

Metal Powder The metal powder used in the first magnetic layer of the magnetic recording medium (III) of the present invention is not particularly limited, and may be the magnetic recording medium (II) described above.
Conventionally known ones as described above can be used.

Co-Fe Used for the first magnetic layer of the magnetic recording medium (III) of the present invention.
Co-Fe is not particularly limited, and the conventionally known one as described in the magnetic recording medium (I) can be used. However,
It is necessary to use a material having a coercive force smaller than that of the cobalt-coated iron oxide used for the second magnetic layer.

Ba Used for the first magnetic layer of the magnetic recording medium (III) of the present invention.
Ba is not particularly limited, and conventionally known one as described in the magnetic recording medium (I) can be used.

The magnetic powder used in the first magnetic layer of the magnetic recording medium (III) may be selected in any combination,
It is possible to use all three types, and the weight ratio of the magnetic powders is arbitrary, but each magnetic powder used in the first magnetic layer is in the total amount of all magnetic powders used in the first magnetic layer. 1
It preferably accounts for 0% by weight or more.

When Co--Fe and metal powders are used among the above magnetic powders, the decrease in the saturation magnetic flux density during storage is less than when the metal powders are used alone. Further, since the surface properties of both the first and second magnetic layers are improved, one layer of metal powder or
S / N is improved as compared with the case where Ba alone is used. Further, the cost is reduced and the economical efficiency is improved. In this case, the weight ratio of Co-Fe and metal powder is Co-Fe: metal powder = 10: 90-9.
The range of 0:10 is preferable.

When Co--Fe and Ba are used, the surface property of the first magnetic layer is better than when Ba is used alone.
The surface property of the second magnetic layer is also improved, and the S / N is improved.
When Ba and Co-Fe are used, low-frequency output is improved by selecting Co-Fe having a larger saturation magnetization than Ba. In addition, since the decrease in the saturation magnetization amount is smaller than that when the metal powder is used alone, the low frequency output is stable for a long period of time. In this case, the weight ratio of Co-Fe and Ba is Co-Fe: Ba.
= 10: 90 to 90:10 is preferable, and the value (α) of [Co-Fe] / [Ba] in the first magnetic layer and the value of [Co-Fe] / [Ba] in the second magnetic layer It is desirable that (β) be α <β.

If metal powder and Ba are used, Ba
Since the surface property of the first magnetic layer is better than that in the case of using only, the surface property of the second magnetic layer is also improved and the S / N is improved. When using metal powder and Ba, by selecting a metal powder having a larger saturation magnetization than Ba,
The low range output is improved. Further, the corrosion resistance is improved as compared with the case where the metal powder is used alone. In this case, the metal powder and Ba
The weight ratio of is preferably in the range of metal powder: Ba = 10: 90 to 90:10.

It is also possible to use all three kinds of Ba, Co--Fe and metal powder, and in this case, a magnetic recording medium which is more excellent in output in addition to the above effects can be obtained. When all three types of magnetic powders are used, it is preferable to use each magnetic powder in an amount of at least 10% by weight based on the total amount of the magnetic powders. When the amount of each magnetic powder is less than 10% by weight, for example, the output is reduced when the metal powder is less than 10% by weight, and S / when the content of Co-Fe or Ba is less than 10% by weight.
N gets worse.

For the first magnetic layer, at least two kinds of magnetic powders are selected from metal powders, Co-Fe and Ba, and the respective magnetic powders are preferably blended in the above weight ratio, and these are combined with a binder. It is formed by coating a base material with a magnetic paint containing as a main component. The weight ratio of the magnetic powder is not limited. The thickness of the first magnetic layer is 1 to 5 μm, preferably 2 to 4 μm.

In the magnetic recording medium (III), the cobalt-coated iron oxide powder and Ba used in the second magnetic layer are those described in the magnetic recording medium (I). The same applies to the magnetic recording medium (I). Also in the magnetic recording medium (III), the weight ratio of the cobalt-coated iron oxide powder used in the second magnetic layer to Ba is in the range of [cobalt-coated iron oxide powder]: [Ba] = 10: 90 to 80:20. Is preferred.

[0047]

According to the present invention, high density recording is possible,
A magnetic recording medium having a well-balanced improvement in electromagnetic conversion characteristics and physical characteristics can be obtained. In particular, the magnetic recording medium of the present invention is
S / N is improved, friction coefficient is low, running property is good, and head clogging is small. In addition, the magnetic recording medium of the present invention has a smaller decrease in the saturation magnetic flux density and a lower manufacturing cost than the magnetic recording medium using only metal powder.

[0048]

The present invention will be further described in the following examples, but the present invention is not limited to these examples.

Examples 1 to 5 and Comparative Examples 1 to 4 The following components were dispersed in a sand mill to prepare a magnetic coating material for the first magnetic layer or a magnetic coating material for the second magnetic layer. In addition,
The magnetic powders shown in Table 1 are used, and the first magnetic layer and the second magnetic layer are used.
The magnetic powder used for the magnetic layer is shown in Table 2. <Magnetic paint components> Magnetic powder (A-E, see Table 1) 100 parts by weight Vinyl chloride resin (-SO ₃ Na group-containing) 10-F parts by weight Polyurethane resin (-SO ₃ Na group-containing) 5 - F part by weight ・ Coronate L 3 parts by weight [hardening agent manufactured by Nippon Polyurethane Industry Co., Ltd., added before coating] ・ Butyl stearate 2 parts by weight ・ Stearic acid 2 parts by weight ・ Carbon black (average particle size 0.02 μm) 3 parts by weight Alumina (average particle size 0.3 μm) 7 parts by weight Methyl ethyl ketone 80 parts by weight Toluene 80 parts by weight Cyclohexanone 120 parts by weight In the above formulation, “F” of the vinyl chloride resin and the polyurethane resin is It is a value calculated by the following formula.
However, the specific surface area shown in Table 1 and the weight ratio shown in Table 2 are used.

[0050]

[Equation 1]

[0051]

[Table 1]

Note) Co-Fe: FeO _x (1.34 ≦ x <1.
5) ... FeO _x is used as a raw material, and predetermined properties are obtained by controlling the amount of cobalt and the amount of Fe ²⁺ . Metal powder: Metal powder containing 95% by weight of iron and 5% by weight of nickel Ba: Hexagonal plate barium ferrite powder, plate ratio 6

[0053]

[Table 2]

The thickness after drying with a gravure roll is 2.5.
The magnetic coating material for the first magnetic layer was applied onto a polyethylene terephthalate (PET) film having a thickness of 7 μm so as to have a thickness of μm, magnetic field orientation (8000 G) was performed, and then the first coating was dried.
A magnetic layer was formed. Then, the magnetic coating material for the second magnetic layer is applied on the first magnetic layer so that the thickness after drying becomes 0.5 μm, the magnetic field is oriented (8000 G), and then dried to form the second magnetic layer. , After calendaring (80 ℃), 50
Aged at 24 ° C. for 24 hours.

Subsequently, the coating material for the back coat layer prepared by mixing the following components in a sand mill was applied to the surface of the film opposite to the surface provided with the magnetic layer so as to have a dry thickness of 0.5 μm, Then, it aged at 50 degreeC for 24 hours. <Backcoat layer coating composition> Carbon black (average particle size 0.02 μm) 32 parts by weight Carbon black (average particle size 0.06 μm) 8 parts by weight Polyurethane resin 20 parts by weight (Nippon Polyurethane Co., Ltd., Nipolan 2301) ・ Nitrocellulose 20 parts by weight (viscosity indication by Hercules Powder CO. Is 1/2 second) ・ Polyisocyanate 4 parts by weight [Coronate HX, a curing agent manufactured by Nippon Polyurethane Industry Co., Ltd.] ・ Stearic acid 1 Parts by weight: 320 parts by weight of solvent.

As described above, the film on which the magnetic layer and the back coat layer were formed was cut into a tape having a width of 8 mm, loaded into an 8 mm cassette case, and recorded for 8/60 minutes.
mm video tape was produced. The obtained 8 mm video tape was evaluated for friction coefficient, reduction rate of saturated magnetic flux density (ΔBs), S / N, and head clogging by the following methods. The results are shown in Table 3.

(1) Coefficient of Friction A tape running tester manufactured by Kyowa Tech Co., Ltd. was used, and the friction body was measured using a stainless guide pin for VTR having an outer diameter of 5 mm. (2) Saturation magnetic flux density reduction rate (ΔBs) 8mm video cassette 14 at 60 ° C, 90% RH
The decrease rate of the saturation magnetic flux density after storage for a day [ΔBs, the decrease amount is shown as a ratio (%) to the initial value. ] Was measured with a vibrating magnetometer. (3) The S / N 8 mm video cassette was set in a commercially available 8 mm VTR device to which a noise meter was connected, and the luminance S / N was measured by recording and reproducing a 50% white signal and measuring with a noise meter. The chroma S / N (AM, PM) was also measured according to this. Clogged head (4) Clogged head The 8mm video cassette was run for 120 minutes,
After repeated running tests, the magnetic head and the microscope were observed under a microscope to determine the stains attached to the head as follows. ◯: Almost no stain Δ: Slightly stain X: Severe stain (4) Head clogging The 8 mm video cassette was run for 120 minutes, and after running the test repeatedly 30 times, the magnetic head and the microscope were observed. Then, the dirt attached to the head was determined as follows. ◯: Almost no stain Δ: Slight stain x: Severe stain

[0058]

[Table 3]

Examples 6 to 9 and Comparative Examples 5 to 8 The following components were dispersed in a sand mill to prepare a magnetic coating material for the first magnetic layer or a magnetic coating material for the second magnetic layer. In addition,
Among the magnetic powders used in Examples 1 to 5, the magnetic powders A to
Table 4 shows the magnetic powder used for D and the first magnetic layer and the second magnetic layer. <Magnetic paint components> Magnetic powder (to D, see Table 1) 100 parts by weight Vinyl chloride resin (-SO ₃ Na group-containing) 10-F parts by weight Polyurethane resin (-SO ₃ Na group-containing) 5 - F part by weight ・ Coronate L 3 parts by weight [hardening agent manufactured by Nippon Polyurethane Industry Co., Ltd., added before coating] ・ Butyl stearate 2 parts by weight ・ Stearic acid 2 parts by weight ・ Carbon black (average particle size 0.02 μm) 3 parts by weight Alumina (average particle size 0.3 μm) 7 parts by weight Methyl ethyl ketone 80 parts by weight Toluene 80 parts by weight Cyclohexanone 120 parts by weight Here, “F” has the same meaning as above, but the weight ratio is Use those in Table 4.

[0060]

[Table 4]

Then, the first magnetic layer, the second magnetic layer and the back coat layer were formed in the same manner as in Examples 1 to 5 to prepare an 8 mm video tape. The same evaluation as described above was performed on the obtained 8 mm video tape. The results are shown in Table 5.

[0062]

[Table 5]

Examples 10 to 17 and Comparative Examples 9 to 13 The following components were dispersed in a sand mill to prepare a magnetic coating material for the first magnetic layer or a magnetic coating material for the second magnetic layer. In addition,
The magnetic powders shown in Table 6 are used, and the first magnetic layer and the second magnetic layer are used.
Table 7 shows the magnetic powder used in the magnetic layer. <Magnetic paint components> 100 parts by weight of magnetic powder (a to e, see Table 6) Vinyl chloride resin (containing -SO ₃ Na group) 10 parts by weight F Polyurethane resin (containing -SO ₃ Na group) 5 F part by weight ・ Coronate L 3 parts by weight [hardening agent manufactured by Nippon Polyurethane Industry Co., Ltd., added before coating] ・ Butyl stearate 2 parts by weight ・ Stearic acid 2 parts by weight ・ Carbon black (average particle size 0.02 μm) 3 parts by weight Alumina (average particle size 0.3 μm) 7 parts by weight Methyl ethyl ketone 80 parts by weight Toluene 80 parts by weight Cyclohexanone 120 parts by weight Here, “F” has the same meaning as above, but the specific surface area is The thing of Table 6 and the thing of Table 7 are used for a weight ratio.

[0064]

[Table 6]

Note) Co-Fe: FeO _x (1.34 ≦ x <1.
5) ... FeO _x is used as a raw material, and predetermined properties are obtained by controlling the amount of cobalt and the amount of Fe ²⁺ . Metal powder: Metal powder containing 95 wt% iron and 5 wt% nickel Ba: Hexagonal barium ferrite powder

[0066]

[Table 7]

Then, the first magnetic layer, the second magnetic layer and the back coat layer were formed in the same manner as in Examples 1 to 5 to prepare an 8 mm video tape. The same evaluation as described above was performed on the obtained 8 mm video tape. The results are shown in Table 8.

Table 8 also shows the magnetostatic characteristics (coercive force and residual magnetic flux density) of the first magnetic layer and the second magnetic layer, which are obtained by coating each of the magnetic paints alone on the PET film. (These are the dry film thickness of 2.5 μm), and the values are measured for the magnetic layer calendered after drying.

[0069]

[Table 8]

Claims (6)

[Claims] 1. A base material, a first magnetic layer formed on the base material, comprising a cobalt-containing iron oxide powder and a binder, a coercive force of 1300 (Oe) or more, and the cobalt-containing iron oxide. Has a coercive force equal to or greater than that of, and the average major axis length is 0.3.
A magnetic recording medium comprising a second magnetic layer formed on the first magnetic layer, which comprises a cobalt-deposited iron oxide powder having a particle size of not more than μm, barium ferrite powder, and a binder. 2. The weight ratio of the cobalt-coated iron oxide powder and the barium ferrite powder used in the second magnetic layer is [cobalt-coated iron oxide powder]: [barium ferrite powder] = 1.
The magnetic recording medium according to claim 1, which is 0:90 to 80:20. 3. A base material, a first magnetic layer formed on the base material, comprising a ferromagnetic metal powder mainly composed of iron and a binder, a coercive force of 1300 (Oe) or more, and an average length. A magnetic recording medium comprising: a cobalt-coated iron oxide powder having an axial length of 0.3 μm or less; barium ferrite powder; and a second magnetic layer formed on the first magnetic layer, which comprises a binder. 4. The weight ratio of the cobalt-coated iron oxide powder to the barium ferrite powder used in the second magnetic layer is [cobalt-coated iron oxide powder]: [barium ferrite powder] = 1.
The magnetic recording medium according to claim 3, wherein the magnetic recording medium has a thickness of 0:90 to 80:20. 5. A base material, a ferromagnetic metal powder containing iron as a main component, at least two kinds of magnetic powders selected from cobalt-containing iron oxide powder and barium ferrite powder, and a binder, and formed on the base material. And a first magnetic layer having a coercive force of 1300 (Oe) or more and a coercive force of at least the coercive force of the cobalt-containing iron oxide, and an average major axis length of 0.3 μm or less. A magnetic recording medium comprising a powder, a barium ferrite powder, and a binder, and a second magnetic layer formed on the first magnetic layer. 6. The weight ratio of the cobalt-coated iron oxide powder to the barium ferrite powder used in the second magnetic layer is [cobalt-coated iron oxide powder]: [barium ferrite powder] = 1.
The magnetic recording medium according to claim 5, which is 0:90 to 80:20.