JPH07182648A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which has an electromagnetic conversion characteristic and a physical property improved with a better balance by forming a magnetic layer containing a ferromagnetic metal powder mainly composed of a barium ferrite powder and ion on an intermediate layer. CONSTITUTION:A magnetic layer containing a ferromagnetic metal powder mainly composed of a barium ferrite powder and ion is formed on an intermediate layer comprising a non-magnetic particle and a binder formed on a substrate. A magnetic recording medium thus obtained make possible high-density recording and allows the improving of electromagnetic conversion characteristic and physical property with a better balance, especially the improving of the S/N and endurance. The ratio by weight between the barium ferrite powder used for the magnetic layer and the ferromagnetic powder mainly composed of the barium ferrite powder and ion is preferably in a range of 10:90-80:20 in [barium ferrite powder] : [ferromagnetic powder mainly composed of iron].

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,
More specifically, the present invention relates 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 base material such as polyester with a magnetic paint prepared by dispersing magnetic powder in a binder and an organic solvent and drying it. There is an increasing demand for higher density recording such as high-quality video tapes and large-capacity floppy disks. Ferromagnetic powders containing iron as the main component are most often used as the powder for achieving this effect. Ferromagnetic metal powders mainly composed of iron have high saturation magnetization and coercive force, and have 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 characteristics are not always sufficient, and the noise level is generally higher than that of oxide magnetic powder. In addition, the ferromagnetic metal powder mainly composed of iron is expensive and has some drawbacks in practical use.

Further, 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 magnetic powder particularly suitable for this method. However, the saturation saturation of barium ferrite is low, so when used as a magnetic tape or 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.

Further, 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 the 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, JP-A-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 this time. In addition, JP-A-3-214
No. 422 and Japanese Unexamined Patent Publication No. 3-214417, a smooth nonmagnetic layer formed on a relatively inexpensive nonmagnetic support having a poor surface state, and a magnetic layer formed on the nonmagnetic layer. A magnetic recording medium having a good surface condition is disclosed. However, although these magnetic recording media have been improved in terms of production cost reduction, it is still necessary to further improve electromagnetic conversion characteristics in order to achieve high density recording.

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

[0006]

As described above, in order to further increase the recording density in the future, both the magnetic characteristics and the physical characteristics, particularly the durability are improved in a well-balanced manner, and the conventional method has been used. Although it is required to make up for the drawbacks of magnetic powder, such a magnetic recording medium has not been proposed yet.

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. Reduction of saturation magnetic flux density during storage, improvement of durability, improvement of running performance by lowering friction coefficient, and elimination of head clogging due to it. Is.

[0008]

As a result of earnest research, the present inventor has formed an intermediate layer containing non-magnetic particles on a base material, and mainly contains barium ferrite powder and iron on the intermediate layer. The inventors have found that a magnetic recording medium having excellent characteristics can be obtained by using an upper magnetic layer of ferromagnetic metal powder, and have completed the present invention.

That is, according to the present invention, an intermediate layer formed on a base material and the base material, which is composed of non-magnetic particles and a binder, and formed and formed on the intermediate layer are mainly composed of barium ferrite powder and iron. The present invention provides a magnetic recording medium having a ferromagnetic metal powder and a magnetic layer made of a binder.

The magnetic recording medium of the present invention is a magnetic layer containing barium ferrite powder (hereinafter referred to as Ba) and a ferromagnetic metal powder mainly composed of iron on an intermediate layer containing non-magnetic particles formed on a base. Are 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, fused alumina, silicon carbide, chromium oxide, titanium oxide, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, emery, garnet, silica stone, silicon nitride, boron nitride, Tungsten carbide, titanium carbide ,. Examples thereof include quartz, tripoli, diatomaceous earth, dolomite, etc., which can 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 μm. ~ 4μ is preferred. Further, as 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 is not particularly limited, but is 0.02 to 1.0.
Generally, the thickness is about 0.001 to 0.
It is about 1 micron. Further, the coercive force of Ba is not particularly limited and may be appropriately determined depending on 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 the metal magnetic powder mainly composed of iron and Ba used in the magnetic layer is [Ba]: [ferromagnetic metal powder mainly composed of iron] = 10:
The range of 90 to 80:20 is preferable.

The magnetic layer of the magnetic recording medium of the present invention is formed by applying the above-described metallic magnetic powder mainly composed of iron and the magnetic paint mainly composed of Ba and the binder in the form of an intermediate layer. The thickness of the magnetic layer is preferably 0.1 to 5 μm. Further, the total thickness of the intermediate layer and the magnetic layer of the magnetic recording medium of the present invention is preferably 1 to 4 μm.

In the present invention, the method of forming 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-you may choose.

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-mentioned metallic magnetic powder mainly composed of iron and Ba in the magnetic layer, and other materials. Common components such as a binder and an organic solvent 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-based copolymers such as vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylonitrile copolymers, etc., particularly sulfonic acid groups, sulfonic acid metal bases, amino Chloride copolymers containing polar groups such as groups, butadiene-acrylonitrile copolymers, polyamide resins, polyvinyl butyra
Resin, cellulose derivative, styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenol resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction resin, high molecular weight Mixture of polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, low molecular weight glyco-
Examples thereof include a mixture of phenol / high molecular weight diol / isocyanate, and a mixture thereof, and similar materials can be used for the first magnetic layer and the second magnetic layer. Usually, the binder is mixed in the magnetic paint in an amount of about 3.0 to 10.0% by weight, and in the intermediate layer paint in an amount of about 20 to 80% by weight.

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. It is used alone or in combination of two or more kinds without particular limitation. 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 dispersants, abrasives and lubricants may be appropriately added and used. As the dispersant, lecithin,
Nonionic surfactants, anionic surfactants, cationic surfactants, etc. can be used. As the abrasive, α-
Average particle size of alumina, fused alumina, chromium oxide, iron oxide, silicon carbide, corundum, diamond, etc. 0.0
A fine powder of 5 to 1 micron can be used, and usually 0.5 to 100 parts by weight is added to 100 parts by weight of the binder as described above. As the lubricant, silicone oils such as various polysiloxanes, graphite, inorganic powders such as molybdenum disulfide, plastic fine powders such as polyethylene and polytrafluoroethylene, higher fatty acids, higher alcohols, higher fatty acid esters. , Fluorocarbons and the like are added at a ratio of 0.1 to 50 parts by weight to 100 parts by weight of the binder.

Examples of the base material used in the magnetic recording medium of the present invention include synthetic resin, non-magnetic metal, glass, ceramics, paper, and the like, and the forms thereof are film, tape, and
Used in sheets, cards, disks, etc.

[0021]

EXAMPLES The present invention will be further described below with reference to Examples.
The invention is not limited to these examples. (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, the magnetic powder shown in Table 1 was used at the ratio shown in Table 2. [Magnetic paint component] [Parts by weight] • Magnetic powder (A to D, Tables 1 and 2) 100 • Vinyl chloride resin (containing SO3Na group) 10 • F • Polyurethane resin (containing SO3Na group) 5 • F ・ Coronet L 4 (a curing agent manufactured by Nippon Polyurethane Industry Co., Ltd., compounded immediately before coating) ・ Butyl stearate 1 ・ Myristic acid 4 ・ α-alumina 7 ・ Carbon black 5 ・ Methyl ethyl ketone 75 ・ Toluene 75 ・Cyclohexanone 100 In the above formulation, “F” of vinyl chloride resin and polyurethane resin is a value calculated by the following formula. F = (A / 55 * V / 100) + (B / 60 * W / 10
0) A: Specific surface area of metal shown in Table 1 B; Specific surface area of Ba shown in Table 1 V: Weight ratio of metal shown in Table 2 W: Weight ratio of Ba shown in Table 2 where V + W = 100.

[Table 1]

[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. [Non-magnetic paint component] 100 parts by weight of non-magnetic particles (granular TiO2) Vinyl chloride resin (containing SO3Na group) 10 Polyurethane resin (containing SO3Na group) 5 Coronet L 4 [Nippon Polyurethane Industry] Hardener made by the manufacturer, compounded immediately after coating] ・ Carbon black (average particle size: 0.22 micron) 3 ・ Methyl ethyl ketone 150 ・ Toluene 150 ・ Cyclohexanone 100 Adjusted above on a polyethylene terephthalate film having a thickness of 7 micron The thickness after drying the non-magnetic paint is 2.
It was coated with a gravure roll so as to have a thickness of 5 microns and dried to form an intermediate layer.

Then, the thickness after drying is 0.5 on the intermediate layer.
Apply magnetic paint to make it micron, orient longitudinal magnetic field (8000 gauss), and dry to form magnetic layer.
After calendering, the sample was aged at 50 ° C. for 24 hours. However, in Comparative Example 3, the intermediate layer was not formed, and only the magnetic layer having a thickness after drying of 3.0 μm was formed.

(D) Formation of Backcoat Layer Subsequently, the coating material for the backcoat layer prepared by mixing the following components in a sand mill was dried on the surface opposite to the surface on which the magnetic layer was provided. The coating was carried out so as to have a thickness of 0.5 micron, and then aged at 50 ° C. for 24 hours. [Coating components for back coat layer] Carbon black (average particle size 0.02 micron) 32 parts by weight Carbon black (average particle size 0.06 micron) 8 Polyurethane resin 20 (Nippon Polyurethane, Niprolan 2301) ・ Nitrocellulose 20 ・ Stearic acid 1 ・ Methylethylketone 160 ・ Toluene 80 ・ Cyclohexanone 80 As described above, a film having an intermediate layer, a magnetic layer and a backcoat layer is formed into an 8 mm wide tape shape. Cut into 8
It was loaded into a milli-cassette case and an 8 millideca set with a recording time of 120 minutes was produced.

Regarding the obtained 8 mm video cassette,
The following methods are used to reduce the friction coefficient and saturation magnetic flux density (ΔB
s), S / N and head clogging were evaluated. The results are shown in Table 3. (1) Friction coefficient A tape running tester manufactured by Kyowa Tech was used, and the friction body was measured using a guide pin made of Tenless for VTR having an outer diameter of 5 mm. (2) Reduction rate of saturation magnetic flux density (ΔBs) Reduction rate of saturation magnetic flux density (ΔBs, after storing an 8 mm video cassette for 14 days at 60 ° C. and 90% RH)
The rate of decrease (indicated by the ratio (%) to the initial value) was measured by a vibrating magnetometer. (3) Set the S / N 8 mm video cassette to a commercially available 8 mm VTR device to which a noise meter is connected, and set the brightness S / N to 50
The% white signal was recorded and played back and measured with a noise meter. Chroma S / N (AM, PM) was also measured according to this. (4) Clogged head The 8 mm video cassette was run for 120 minutes,
After repeated running tests, the magnetic head was observed with a microscope and the dirt adhering to the head was judged as follows. ◯: Almost no stain Δ: Slight stain x: Severe stain

[Table 3]

Table 3 also shows the magnetostatic properties (coercive force and residual magnetic flux density) of the magnetic layer. Each magnetic paint was applied individually onto a PET film (both dry coating thickness 2. 5 μm), and the values were measured for the dried and calendered magnetic layer.

[0027]

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. Furthermore, 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.

Claims (2)

[Claims] 1. A base material, an intermediate layer formed on the base material and comprising non-magnetic particles and a binder, and a ferromagnetic powder mainly formed of barium ferrite powder and iron formed on the intermediate layer. And a magnetic recording medium having a magnetic layer comprising a binder. 2. The weight ratio of the barium ferrite powder used in the magnetic layer and the ferromagnetic powder mainly composed of iron is [barium ferrite powder]: [ferromagnetic metal powder mainly composed of iron] = 10: 90 to 80 The magnetic recording medium according to claim 1, wherein: 20.