JPH0773448A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium capable of high density recording and good in electromagnetic conversion characteristic, durability and traveling property by forming the magnetic layer consisting of a specified cobalt- coated iron oxide, barium ferrite powder and a binder on an intermediate layer. CONSTITUTION:The intermediate layer containing nonmagnetic particles is formed on a base material, and the magnetic layer consisting of the cobalt- coated iron oxide having >=1300(Oe) coercive force and <=0.3mum average long axis length, the barium ferrite powder and the binder is formed on the intermediate layer. The cobalt coated iron oxide is Co-coated FeOx (1.34<=x<=1.50), and the coercive force is 1300-2000(Oe) preferably. And, the wt. radio of the cobalt- coated iron oxide to the barium ferrite powder is (10:90)-(80:20) preferably.

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, and more particularly to a magnetic recording medium having excellent 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.

From the viewpoint of improving the durability of the magnetic recording medium and stably forming a thinner magnetic layer to improve the magnetic characteristics, a non-magnetic layer containing non-magnetic particles is formed on a substrate, A magnetic recording medium having a magnetic layer formed thereon has been proposed.

For example, Japanese Patent Application Laid-Open No. 62-214514 discloses a magnetic recording medium having a non-magnetic layer having a specific surface roughness and a magnetic layer formed on the non-magnetic layer. Further, Japanese Patent Laid-Open No. 62-231417 discloses a magnetic recording medium having a non-magnetic layer containing a lubricant and a magnetic layer containing a lubricant. However, although these magnetic recording media have relatively good running properties, it is necessary to further improve the electromagnetic conversion characteristics in order to achieve the high-density recording required today.

Further, JP-A-3-214422 and JP-A-3-214417 disclose a smooth non-magnetic layer formed on a relatively inexpensive non-magnetic support having a poor surface condition, and the non-magnetic layer. A magnetic recording medium having a good surface state, which has a magnetic layer formed on the layer, is disclosed. However, although these magnetic recording media have been improved in terms of reduction in production cost, it is still necessary to further improve electromagnetic conversion characteristics in order to achieve high density recording.

Further, in Japanese Patent Laid-Open No. 5-73883,
It is disclosed that by precisely defining the state of the interface between the non-magnetic layer and the magnetic layer, it is possible to obtain a magnetic recording medium with improved runnability and excellent output in the high frequency range. However, in this magnetic recording medium, in order to achieve high energy and high coercive force, it is necessary to use the above-mentioned ferromagnetic metal powder mainly composed of iron, and the saturation magnetic flux density during storage is lowered due to cost and oxidation. The problem has not been resolved.

[0009]

As described above, in order to further increase the recording density in the future, both magnetic properties and physical properties, especially durability are improved in a well-balanced manner, and they have been used conventionally. Although it is required to make up for the drawbacks of magnetic powders, such magnetic recording media have not yet been provided.

Therefore, the problem to be solved by the present invention is to further improve the S / N ratio in such a magnetic recording medium, specifically, a magnetic recording medium which enables high density recording. To reduce the decrease in the saturation magnetic flux density during storage more than to the ferromagnetic metal powder to improve the durability, lower the friction coefficient to improve the running property,
It is also necessary to eliminate the head clogging caused by it.

[0011]

Means for Solving the Problems As a result of earnest research by the present inventor, an intermediate layer containing non-magnetic particles was formed on a substrate, and an average coercive force of 1300 (Oe) or more was formed on the intermediate layer. It was found that a magnetic recording medium capable of solving the above problems can be obtained by forming a magnetic layer containing cobalt-coated iron oxide having a major axis length of 0.3 μm or less and barium ferrite powder, and completes the present invention. Came to.

That is, according to the present invention, a base material, an intermediate layer formed on the base material and comprising non-magnetic particles and a binder, and formed on the intermediate layer have a coercive force of 1300 (Oe) or more. It is intended to provide a magnetic recording medium having a magnetic layer comprising cobalt-coated iron oxide having an average major axis length of 0.3 μm or less, barium ferrite powder, and a binder.

The magnetic recording medium of the present invention has a coercive force of 1300 on the intermediate layer containing non-magnetic particles formed on the base.
A magnetic layer containing cobalt-coated iron oxide having an average major axis length of (Oe) or more and 0.3 μm or less and barium ferrite powder (hereinafter abbreviated as Ba) is formed.

Examples of the non-magnetic particles used in the intermediate layer of the magnetic recording medium of the present invention include carbon black and α-
Alumina, γ-alumina, α-γ-alumina, fused alumina, silicon carbide, chromium oxide, titanium oxide, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, emery (main components: corundum and magnetite), Examples thereof include garnet, silica stone, silicon nitride, boron nitride, tungsten carbide, titanium carbide, quartz, tripoly, diatomaceous earth and dolomite, which may be used alone or in combination. The average particle size of the non-magnetic particles is not particularly limited, but if the average particle size is too large, the surface property of the intermediate layer deteriorates, and if it is too small, the reinforcing effect of the intermediate layer deteriorates. A degree is preferable.

The intermediate layer is formed by coating a base material with a coating material containing non-magnetic particles and a binder as a main component. The thickness of the intermediate layer (when dried) is 0.5 to 5 μm, preferably 1-4 μm
Is preferred.

The cobalt-coated iron oxide used in the magnetic layer of the magnetic recording medium of the present invention has a coercive force of 1300 (Oe) or more, preferably 1300 to 2000 (Oe). If the coercive force of the cobalt-deposited iron oxide 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
Deposition FeO _x (1.34 ≦ x <1.50) is used, especially
Co-deposited FeO _x is preferred. Cobalt-doped iron oxide is not preferable because it has poor storage stability.

The cobalt-adhered iron oxide used in the present invention is produced by a usual cobalt-adhering method using acicular iron oxide as a nucleus. The magnetic characteristics are the amount of cobalt added, Fe
^The amount of ²⁺ can be adjusted to a predetermined value by controlling 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). Ratio of iron as a whole), preferably 1 to 25% by weight
Is.

The cobalt-coated iron oxide used in the present invention has an average major axis length of 0.3 μm or less, and the shape thereof is not limited, but needle-like ones are preferably used. If the average major axis length of the cobalt-deposited iron oxide exceeds 0.3 μm, the S / N becomes worse. Further, when very fine magnetic powder having an average major axis length of 0.3 μm or less is used, the durability of the magnetic recording medium tends to decrease, but in order to improve it, as described above in the present invention. An intermediate layer is provided.

Further, as the Ba used in the magnetic layer of the magnetic recording medium of the present invention, hexagonal plate-like particles are used, and the particle size (diagonal length) is not particularly limited.
Generally, the thickness is from 02 to 1.0 μm and the thickness is 0.00
It is about 1 to 0.1 μm. The coercive force of Ba 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 2000 (Oe).

In the magnetic recording medium of the present invention, the weight ratio of cobalt-deposited iron oxide powder used in the second magnetic layer to Ba is [B
a]: [Cobalt-deposited iron oxide powder] = 10: 90 to 8
The range of 0:20 is preferable.

The magnetic layer of the magnetic recording medium of the present invention is formed by coating the intermediate layer with a magnetic coating material containing the above cobalt-coated iron oxide, Ba and a binder as main components. The layer thickness is preferably 0.1 to 5 .mu.m. The total thickness of the intermediate layer and the magnetic layer of the magnetic recording medium of the present invention is 1 to 4 μm.
Is preferred.

In the present invention, the method of forming (coating) the intermediate layer and the magnetic layer may be either a method of simultaneously forming the intermediate layer and the magnetic layer or a method of sequentially forming one layer at a time. Calendar processing may be performed for each layer.

The coating material for forming the intermediate layer and the magnetic layer of the magnetic recording medium of the present invention uses non-magnetic particles in the intermediate layer, the above cobalt-coated iron oxide and Ba in the magnetic layer, and other binder, Common components such as organic solvents can be used.

The binder used in the present invention is a urethane resin, particularly a polyurethane containing polar groups such as sulfonic acid groups, metal sulfonate groups, sulfobetaine groups, carbobetaine groups, amino groups, hydroxyl groups and epoxy groups. 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-containing copolymers such as vinyl 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, and about 20 to 80% by weight in the paint for the intermediate layer.

As the organic solvent, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, benzene, toluene, xylene, dimethylsulfoxide, tetrahydrofuran, dioxane and the like are suitable solvents for dissolving the binder resin 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.
Approximately 20 to 80% by weight is blended in the paint for the intermediate layer.

In the magnetic coating composition, various commonly used additives such as a dispersant, an abrasive and a lubricant 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 base material 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.

[0028]

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 and durability is improved. Further, the magnetic recording medium of the present invention has a low coefficient of friction, good running properties, less head clogging, and less decrease in saturation magnetic flux density than a magnetic recording medium using only metal powder.

[0029]

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

Examples 1 to 4 and Comparative Examples 1 to 6 (A) Preparation of Magnetic Coating Material The following components were dispersed in a sand mill to prepare a magnetic coating material for the magnetic layer. As the magnetic powder, cobalt-coated iron oxide (hereinafter abbreviated as Co—Fe) shown in Table 1 and Ba were used in the ratio shown in Table 2. <Magnetic paint component> • Magnetic powder (A to D, see Table 1 and Table 2) 100 parts by weight • Vinyl chloride resin (containing -SO ₃ Na group) 10 · F parts by weight · Polyurethane resin (-SO ₃ Na 5 F parts by weight ・ Coronate L 4 parts by weight [Curing agent manufactured by Nippon Polyurethane Industry Co., Ltd., compounded just before coating] ・ Butyl stearate 1 part by weight ・ Myristic acid 4 parts by weight ・ α-alumina 7 parts by weight Carbon black 5 parts by weight Methyl ethyl ketone 75 parts by weight Toluene 75 parts by weight Cyclohexanone 100 parts by weight In the above formulation, "F" of the vinyl chloride resin and the polyurethane resin is calculated by the following formula. It is a value. F = (A / 55 × v / 100) + (B / 60 × w / 10
0) A: Specific surface area of Co—Fe shown in Table 1 (m ² / g) B: Specific surface area of Ba shown in Table 1 (m ² / g) v: Weight ratio of Co—Fe shown in Table 2 w: The weight ratio of Ba shown in Table 2 is v + w = 100.

[0031]

[Table 1]

Note) Co-Fe: acicular cobalt-coated FeO _x (1.33 ≦ x <1.50) ...
By using FeO _x as a raw material and manipulating the amount of cobalt and the amount of Fe ²⁺ , predetermined characteristics were obtained. Metal: Metal powder containing 94% of Fe, 2% of Al, 2% of Y, and 2% of Ni Ba: Hexagonal plate barium ferrite powder, plate ratio 5 Grain size: Co-Fe and metal have an average major axis length , Ba is the diagonal length

[0033]

[Table 2]

(B) Preparation of non-magnetic coating material (for intermediate layer) The following components were dispersed in a sand mill to prepare a non-magnetic coating material for the intermediate layer. (Containing -SO ₃ Na group) <nonmagnetic coating component> and non-magnetic particles (particulate TiO ₂₎ (containing -SO ₃ Na group) 100 parts by weight Vinyl chloride resin 10 parts Polyurethane resin 5 wt Parts-Coronate L 4 parts by weight [Curing agent manufactured by Nippon Polyurethane Industry Co., Ltd., compounded immediately before coating] -Carbon black (average particle size 0.02 μm) 3 parts by weight-Methyl ethyl ketone 150 parts by weight-Toluene 150 parts by weight-Cyclohexanone 100 parts by weight.

(C) Formation of intermediate layer and magnetic layer On a polyethylene terephthalate (PET) film having a thickness of 7 μm, the non-magnetic coating material prepared above was gravure-rolled to a thickness of 2.5 μm after drying. And apply
It was dried to form an intermediate layer. Then, a magnetic coating is applied on the intermediate layer so that the thickness after drying becomes 0.5 μm, and the magnetic field is oriented in a longitudinal magnetic field (8000 G), and then dried to form a magnetic layer, and further calendered (80 ° C.). Then, at 50 ℃ 24
Time aged.

However, in Comparative Example 6, the intermediate layer was not formed,
Only a magnetic layer having a thickness after drying of 3.0 μm was formed.

(D) Formation of Backcoat Layer Subsequently, a backcoat layer coating material prepared by mixing the following components in a sand mill was applied to the surface of the film opposite to the surface on which the magnetic layer was formed to a dry thickness of 0. Apply it to 5 μm,
Then, it aged at 50 degreeC for 24 hours. <Backcoat layer coating material> 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.) , Nipollan 2301) -Nitrocellulose 20 parts by weight (viscosity indication by Hercules Powder CO. Is 1/2 second) -Stearic acid 1 part by weight-Methyl ethyl ketone 160 parts by weight-Toluene 80 parts by weight-Cyclohexanone 80 parts by weight.

As described above, the film on which the intermediate layer, the magnetic layer and the back coat layer are formed is cut into a tape having a width of 8 mm and loaded into an 8 mm cassette case to record for 12 hours.
An 0 mm 8 mm video cassette was made. With respect to the obtained 8 mm video cassette, the friction coefficient, the saturation magnetic flux density decrease rate (ΔBs), the S / N ratio and the head clogging were evaluated 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 guide pin made of stainless steel for VTR and 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. (4) Clogged Head After running the 8 mm video cassette for 120 minutes and repeating the running test for 30 times, the magnetic head and the microscope were observed with a microscope to determine the dirt attached to the head as follows. ◯: Almost no stain Δ: Slightly stain X: Severe stain Note that Table 3 also shows the magnetostatic characteristics (coercive force and residual magnetic flux density) of the magnetic layer. PE
Apply on T film (all dry film thickness 2.5 μm),
It is the value measured for each magnetic layer that was calendered after drying.

[0040]

[Table 3]

Claims (2)

[Claims] 1. A base material, an intermediate layer formed on the base material and comprising non-magnetic particles and a binder, and an average major axis having a coercive force of 1300 (Oe) or more formed on the intermediate layer. Length is 0.
A magnetic recording medium having a magnetic layer comprising cobalt-coated iron oxide having a particle size of 3 μm or less, barium ferrite powder, and a binder. 2. The weight ratio of cobalt-coated iron oxide to barium ferrite powder used in the magnetic layer is [barium ferrite]: [cobalt-coated iron oxide] = 10: 90 to 8
The magnetic recording medium according to claim 1, which is 0:20.