JPH1186263A - Magnetic recording medium and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve recording density and output while restricting surface- oriented deterioration of a magnetic layer. SOLUTION: This recording medium has at least a magnetic layer as the outermost layer on a non-magnetic support body. In the magnetic recording layer, the thickness of the magnetic layer is 0.5 μm or less. A magnetic powder contained in the magnetic layer is a tabular magnetic powder with its easy to magnetize axis vertical to the surface of a plate thereof or a acicular magnetic powder with its easy to magnetize axis vertical to the long axis thereof. The easy to magnetize axis of the magnetic powder is oriented at an arbitrary angle in a range of 60±15 to a main surface of the non-magnetic support body.

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 a method for manufacturing the same, and more particularly, to a magnetic recording medium having improved magnetic recording density and output while suppressing deterioration in the surface properties of a magnetic layer, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium used for an audio tape recorder, a video tape recorder or the like, a magnetic recording medium in which needle-shaped magnetic powder is oriented in the longitudinal direction of a magnetic layer is widely used. This orientation treatment in the longitudinal direction is usually performed by using a permanent magnet, an electromagnet, or the like, and forcibly changing the orientation of the magnetic powder by applying a magnetic field larger than the coercive force of the magnetic powder in the longitudinal direction of the magnetic recording medium. It is performed so as to be directed in the longitudinal direction of the support.

However, such a magnetic recording medium in which the magnetic powder is oriented in the longitudinal direction cannot cope with the recent demand for higher density of the magnetic recording medium. In particular, it has been difficult to secure a high output and a high CN ratio in a short wavelength range.

As one method to cope with such a high density, a perpendicular magnetic recording system using residual magnetization in a direction perpendicular to the surface of a magnetic recording medium has been proposed (Japanese Patent Laid-Open Publication No. Hei 4-1992).
No. 182932, Japanese Patent Publication No. 6-14487).
Such a perpendicular magnetic recording medium has an easy axis of magnetization perpendicular to the surface of the recording medium. The perpendicular magnetic recording method using the residual magnetization perpendicular to the surface of the recording medium has a characteristic that the demagnetizing field in the recording medium is reduced at a high recording density, and is essentially a recording method suitable for high-density recording. It can be said that.

However, such a magnetic recording medium in which the magnetic powder is oriented in the vertical direction has a drawback that the output in the long wavelength region is smaller than that of the magnetic recording medium in which the magnetic powder is oriented in the longitudinal direction. Output cannot be realized.

In order to solve such a drawback, Japanese Patent Laid-Open Publication No. Hei 4-360020 discloses that the axis of easy magnetization is inclined obliquely from the longitudinal direction of the tape, preferably +
A magnetic tape inclined to 45 degrees is described.

[0007] However, when the easy axis is obliquely oriented as described above, a high output can be realized to a certain extent over a wide band, but there is a problem that the surface state of the magnetic layer surface is poor.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic recording medium having improved recording density and output while suppressing deterioration in the surface properties of a magnetic layer, and a method for manufacturing the same.

[0009]

Means for Solving the Problems As a result of earnest studies, the present inventors have used magnetic powder whose easy axis is perpendicular to the longitudinal direction of the magnetic recording medium, and forcibly set the easy axis of this magnetic powder. It has been found that a magnetic recording medium in which magnetic powder is obliquely oriented by orienting in the direction of a magnetic field can achieve the above object.

The present invention has been made on the basis of the above findings. In a magnetic recording medium having at least a magnetic layer as an outermost layer on a nonmagnetic support, the magnetic layer has a thickness of 0.5 μm or less. The magnetic powder contained in the magnetic layer is a plate-like magnetic powder having an easy axis of magnetization perpendicular to the plate surface or an acicular magnetic powder having an easy axis of magnetization perpendicular to the major axis, and the magnetization of the magnetic powder is It is an object of the present invention to provide a magnetic recording medium characterized in that the easy axis is oriented at an arbitrary angle within a range of 60 ± 15 ° with respect to the main surface of the nonmagnetic support.

The present invention also provides a method for producing a magnetic recording medium according to the present invention, wherein the magnetic recording medium is provided with at least a magnetic layer as an outermost layer by applying a magnetic paint on a nonmagnetic support. A magnetic powder contained in the magnetic paint, a plate-like magnetic powder having an easy axis of magnetization perpendicular to the plate surface or an acicular magnetic powder having an easy axis of magnetization perpendicular to the major axis; After being coated on the support, it is passed through a drying step before passing through the aligner, and a magnetic field is applied in the longitudinal direction before the drying step is completed, forcing the easy axis of the magnetic powder in the direction of the magnetic field. An object of the present invention is to provide a method for producing a magnetic recording medium, wherein the magnetic powder is obliquely oriented by orienting the magnetic powder.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic recording medium of the present invention will be described below in detail. FIG. 1 is a cross-sectional view of a magnetic recording medium of the present invention, in which 1 is a magnetic recording medium, 2 is a non-magnetic support, 3 is an intermediate layer, 4 is a magnetic layer, and 5 is a back coat layer. Show. The magnetic recording medium 1 of the present invention comprises at least a nonmagnetic support 2 and a magnetic layer 4 as an outermost layer provided on the nonmagnetic support 2.
Further, a magnetic or non-magnetic intermediate layer 3 may be provided between the non-magnetic support and the magnetic layer. Further, a backcoat layer 5 may be provided on the surface of the nonmagnetic support 2 opposite to the magnetic layer 4.

Incidentally, the magnetic recording medium of the present invention may further include another layer in addition to the above layers. Specifically, an adhesive layer (undercoat layer) is provided between the nonmagnetic support and the intermediate layer or between the nonmagnetic support and the backcoat layer, or between the support and the intermediate layer or between the nonmagnetic support and the intermediate layer. Another magnetic layer or a non-magnetic layer provided for recording a servo signal or the like corresponding to a hard system using a long wavelength signal may be provided between the magnetic layer and the magnetic layer.

The details of the support and each layer constituting the magnetic recording medium of the present invention will be described below. First, the non-magnetic support used in the present invention will be described. As the nonmagnetic support, a flexible film made of a generally known polymer resin can be used without any particular limitation.

Examples of the polymer synthetic resin forming the flexible film include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate and polyethylene bisphenoxycarboxylate; polyethylene, polypropylene and the like. Polyolefins; Cellulose derivatives such as cellulose acetate butyrate and cellulose acetate propionate; Vinyl resins such as polyvinyl chloride and polyvinylidene chloride; Aromatic polyamides; Polyimides; Polycarbonates; Polysulfones; And the like. Among these, aromatic polyamides,
Polyethylene terephthalate and polyethylene naphthalate are preferred. When using, select one of these
Species can be used alone or in combination of two or more.

The thickness of the non-magnetic support is 1 to 8 μm.
m is preferable and 3 to 5 μm is more preferable. The non-magnetic support preferably has a Young's modulus in the longitudinal direction of 5 GPa or more, particularly preferably 7 to 15 GPa, and more preferably a Young's modulus in the width direction of 7 GPa or more, particularly 10 to 20 GPa. When the non-magnetic support satisfies the above Young's modulus, the result is excellent film rigidity.

Next, the magnetic layer will be described. The magnetic layer is usually the uppermost layer of the magnetic recording medium, that is, a layer existing on the surface of the magnetic recording medium, and can be formed by using a magnetic paint containing magnetic powder, a binder and a solvent as main components.

In the magnetic recording medium of the present invention, the magnetic powder contained in the magnetic layer is a plate-like magnetic powder whose easy axis is perpendicular to the plate surface or a needle-like magnetic powder whose easy axis is perpendicular to the long axis. It is necessary to be. Unless such magnetic powder is used, a magnetic recording medium having excellent magnetic layer surface properties cannot be obtained.

As such a plate-like magnetic powder, a plate diameter of 0.3 is preferable.
Hexagonal ferrite having a tabular ratio of 3 to 6 or more and a long axis length of 0.1 μm or less as a needle-like magnetic powder, and a needle ratio of 3 to 6
And 10 needle barium ferrites.

The magnetic powder has a coercive force of 100 to 210.
kA / m, preferably 120 to 200 k
A / m is preferable. Within the above range, the RF output in all wavelength regions can be obtained without excess and deficiency, and the overwrite characteristics are also good. The saturation magnetization is 1.0
It is preferably from × 10 ^{−5 to} 2.5 × 10 ⁻⁵ Wb / g, and particularly preferably from 1.4 × 10 ^{−5 to} 2.0 × 10 ⁻⁵ Wb / g. Within the above range, a sufficient reproduction output can be obtained.

In the present invention, the axis of easy magnetization of the magnetic powder of the magnetic layer needs to be oriented at an arbitrary angle within a range of 60 ± 15 ° perpendicular to the main surface of the nonmagnetic support. is there. Here, the main surface is a surface on which the intermediate layer and the magnetic layer are provided. This will be described with reference to FIG. FIG. 2 is a partially enlarged cross-sectional view of the portion A in FIG. 1. In FIG. 2, reference numeral 10 denotes a magnetic powder, and θ denotes the angle of easy magnetization axis orientation of the magnetic powder with respect to the main surface of the nonmagnetic support. In the present invention, it is necessary that the angle indicated by θ is oriented at an arbitrary angle within a range of 60 ± 15 °. If the orientation of the magnetic powder is out of this range, the recording density of the magnetic recording medium cannot be improved.

Further, the magnetic powder contained in the magnetic paint used for forming the magnetic layer may contain a rare earth element or a transition metal element as required.

In the present invention, the magnetic powder may be subjected to a surface treatment in order to improve the dispersibility and the like of the magnetic powder. The above surface treatment is referred to as “Characterization of
Powder Surfaces ”(Academic Press), and the like. For example, a method of coating the surface of the magnetic powder with an inorganic oxide is described, and it is preferable to employ the method. it can. The inorganic oxide that can be used at this time is Al
₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , S
b ₂ O _3, ZnO and the like, may be used in combination of two or more even with these alone in use. In addition, the surface treatment is a silane coupling treatment other than the above method,
Organic treatment such as titanium coupling treatment and aluminum coupling treatment can also be performed.

The binder used in the magnetic paint for forming the magnetic layer includes a thermoplastic resin, a thermosetting resin,
And a reactive resin. When used, they can be used alone or in combination. Specific examples of the binder include vinyl chloride resins, polyesters, polyurethanes, nitrocellulose, epoxy resins, and the like. In addition, JP-A-57-162128, page 2, upper right column, line 19 to Resins and the like described on page 19, lower right column, line 19, and the like are included. Further, the binder may contain a polar group for improving dispersibility and the like. The mixing ratio of the binder is 5 to 20 with respect to 100 parts by weight of the magnetic powder.
0 parts by weight is preferable, and 5 to 70 parts by weight is more preferable.

Solvents contained in the magnetic paint used for the magnetic layer include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents and chlorinated hydrocarbon solvents. Specifically, the solvents described on page 3, lower right column, line 17 to page 4, lower left column, line 10 of JP-A-57-162128 can be used. The mixing ratio of the solvent is preferably 80 to 500 parts by weight based on 100 parts by weight of the magnetic powder,
100 to 350 parts by weight is more preferred.

The magnetic layer may contain an inorganic powder as an abrasive. As the inorganic powder, specifically, alumina, titanium oxide, calcium oxide, chromium oxide, silicon carbide, calcium carbonate, zinc oxide, α-Fe ₂ O ₃ ,
Talc, kaolin and the like. Among them, those having a Mohs hardness of 7 or more are preferably used from the viewpoint of durability. The average particle size d ₂ of the inorganic powder is from 0.1 to 0.
It is preferably 4 μm. This is because, as will be described later, the tape-shaped magnetic recording medium has a large effect of preventing transfer from the back coat layer when wound up in a roll shape.

The magnetic coating material used for forming the magnetic layer may contain a dispersing agent, a lubricant, an antistatic agent, a rust preventive, a fungicide, a fungicide and the like, which are used in ordinary magnetic recording media. Agents can be added as needed. Specific examples of the above-mentioned additives include the above-mentioned JP-A-57-162128, page 2, lower left column, line 6 to page 2, lower right column, line 10 and third line.
Various additives described on page 6, lower left column, line 6 to page 3, upper right column, line 18, etc. can be mentioned.

The thickness of the magnetic layer needs to be 0.5 μm or less, particularly preferably 0.10 to 0.5 μm. When the thickness of the magnetic layer is within the above range, the balance between durability and output stability is excellent, which is preferable.

Next, an intermediate layer appropriately provided below the magnetic layer will be described. The intermediate layer may be a magnetic layer or a non-magnetic layer. The purpose of providing the above-mentioned intermediate layer is to improve the surface smoothness and to easily make the outermost recording layer thinner. In the present invention, since the thickness of the magnetic layer as the outermost layer is as thin as 0.5 μm or less, the axis of easy magnetization is basically perpendicular to the nonmagnetic support due to the degree of freedom due to the shape factor in the non-oriented state. Use that thing.
When the intermediate layer is a layer having magnetism, the intermediate layer is a magnetic layer containing a magnetic powder (hereinafter, referred to as a magnetic intermediate layer), and has a magnetic powder containing a magnetic powder, a binder and a solvent as main components. It is formed using a paint (hereinafter, also referred to as an intermediate magnetic paint). On the other hand, when the intermediate layer is non-magnetic,
The intermediate layer is a layer containing a non-magnetic powder (hereinafter, referred to as a non-magnetic intermediate layer), and is a magnetic paint containing a non-magnetic powder, a binder, and a solvent as main components (hereinafter, also referred to as an intermediate non-magnetic paint).
It is formed by using.

As the magnetic powder contained in the magnetic paint used for forming the magnetic intermediate layer, a ferromagnetic powder is preferably used, and as the ferromagnetic powder, both a soft magnetic powder and a hard magnetic powder are preferably used. Can be The kind of the soft magnetic powder is not particularly limited, but is preferably used for a so-called weak electric device such as a magnetic head or an electronic circuit. (Shokabo, 1984) Soft magnetic materials (soft magnetic materials) described on pages 368 to 376, and specifically, oxide soft magnetic powder can be used.

The coercive force of the oxide soft magnetic powder is usually 0.01 to 12 kA / m, and the saturation magnetization thereof is usually 3.
It is 8 × 10 ^{−6 to} 1.2 × 10 ⁻⁵ Wb / g. The coercive force of the metal soft magnetic powder is usually 0.001 to 8 kA / m, and the saturation magnetization is usually 6.3 × 10 ^{−6 to} 6.3 × 10 ⁻⁵ W.
b / g.

The shape of the soft magnetic powder is not particularly limited, but may be spherical, plate-like, needle-like or the like, and the size is preferably 5 to 800 nm.

The hard magnetic powder includes γ-Fe
₂ O ₃ , Co-coated γ-Fe ₂ O _{3 and} other iron oxide based magnetic powders,
Examples include ferromagnetic metal powder mainly composed of iron, hexagonal ferrite powder and the like.

The ferromagnetic metal powder has a metal content of 7
0% by weight or more, and a ferromagnetic metal powder in which 60% by weight or more of the metal component is iron. Specific examples of the ferromagnetic metal powder include, for example, Fe, Fe-Co, Fe-N
i, Fe-Al, Fe-Ni-Al, Fe-Co-N
i, powders of alloys such as Fe-Ni-Al-Zn and Fe-Al-Si.

The ferromagnetic metal powder mainly composed of iron oxide and iron preferably has a needle-like or spindle-like shape. And the major axis length is preferably 0.05 to
It is 0.25 μm, more preferably 0.05 to 0.2 μm. The preferred needle ratio is 3 to 20, the preferred particle size is 130 to 250 ° as measured by an X-ray method, and the preferred specific surface area is 30 to 70 m ² / g.

The hexagonal ferrite includes:
Barium ferrite and strontium ferrite in the form of microplates and part of their Fe atoms are Ti, Co,
Examples include magnetic powders substituted with atoms such as Ni, Zn, and V. The hexagonal ferrite powder has a preferable plate diameter of 0.02 to 0.09 μm, a preferable plate ratio of 2 to 7, and a preferable specific surface area of 30 to 60 m ² / m.
g.

The coercive force of the hard magnetic powder is 100 to 21.
0 kA / m, preferably 120 to 200 kA / m.
It is preferably kA / m. Within the above range, the RF output in all wavelength regions can be obtained without excess and deficiency, and the overwrite characteristics are also good.

The above-mentioned iron oxide-based magnetic powder and ferromagnetic gold
The saturation magnetization of the genus powder is 1.0 × 10 ^-Five~ 2.5 × 10^-Five
Wb / g, particularly 1.4 × 10^-Five~
2.0 × 10^-FiveIt is preferably Wb / g. Also,
The saturation magnetization of the hexagonal ferrite powder is 3.8 × 1
0^-6~ 8.8 × 10^-6Wb / g,
Especially 5.7 × 10^-6~ 8.8 × 10^-6Wb / g
Is preferred. Within the above range, sufficient playback output can be obtained.
Can be

The magnetic powder contained in the intermediate magnetic paint may contain a rare earth element or a transition element, if necessary. Further, the same surface treatment as that of the magnetic layer may be performed on the magnetic powder.

The binder and the solvent contained in the above-mentioned intermediate magnetic paint are the same as the binder and the solvent contained in the magnetic paint used for forming the magnetic layer. The compounding ratio of the binder is preferably 5 to 200 parts by weight, more preferably 5 to 70 parts by weight, based on 100 parts by weight of the magnetic powder. The mixing ratio of the solvent is 10
80 to 500 parts by weight, preferably 1 part by weight,
More preferably, the amount is from 00 to 350 parts by weight.

The intermediate magnetic paint may optionally contain additives which are added to the magnetic paint used for forming the magnetic layer. Further, a non-magnetic powder contained in an intermediate non-magnetic paint used for forming a non-magnetic intermediate layer described later can be added to the above-mentioned intermediate magnetic paint.

The thickness of the magnetic intermediate layer is 0.2 to 5 μm
Is preferably 0.5 to 4 μm, and particularly preferably 0.5 to 3.5 μm. When it is within the above range, the magnetic recording medium can have sufficient bending rigidity.

Next, the non-magnetic intermediate layer will be described. As the non-magnetic powder contained in the intermediate non-magnetic paint used for forming the non-magnetic intermediate layer, for example, carbon black, graphite, titanium oxide, barium sulfate, zinc sulfide, magnesium carbonate, calcium carbonate, zinc oxide,
Calcium oxide, magnesium oxide, magnesium dioxide, tungsten disulfide, molybdenum disulfide, boron nitride, tin dioxide, silicon dioxide, non-magnetic chromium oxide, alumina, silicon carbide, cerium oxide, corundum, artificial diamond, non-magnetic iron oxide Garnet, garnet, silica stone, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, diatomaceous earth, dolomite, resinous powder and the like. Among them, nonmagnetic iron oxide, titanium oxide, carbon black, alumina, silicon oxide, silicon nitride, boron nitride and the like are preferably used.
These non-magnetic powders may be used alone or in combination of two or more.

The shape of the nonmagnetic powder may be spherical, plate-like, needle-like, or amorphous. The size of the non-magnetic powder is 5 to 200 nm in the case of spherical, plate-like, or amorphous. Preferably, the needle-shaped one has a major axis length of 20.
It is preferable that the needle ratio is 3 to 20 at ~ 300 nm.

In the present invention, in order to improve the dispersibility and the like of the non-magnetic powder, the non-magnetic powder is subjected to the same surface treatment as the magnetic powder contained in the magnetic paint used for forming the magnetic layer. be able to.

The binder and the solvent contained in the intermediate non-magnetic paint are the same as the binder and the solvent contained in the magnetic paint used for forming the magnetic layer.

The mixing ratio of the binder is preferably 5 to 200 parts by weight with respect to 100 parts by weight of the nonmagnetic powder.
5 to 70 parts by weight are more preferred. The mixing ratio of the solvent is 80 to 50 parts by weight per 100 parts by weight of the nonmagnetic powder.
0 parts by weight is preferable, and 100 to 350 parts by weight is more preferable.

The intermediate non-magnetic paint may optionally contain additives which are added to the magnetic paint used for forming the magnetic layer.

The thickness of the non-magnetic intermediate layer is 0.2 to 5 μm.
m, more preferably 0.5 to 4 μm, and particularly preferably 0.5 to 3.5 μm. When it is within the above range, the magnetic recording medium can have sufficient bending rigidity.

Further, in the magnetic recording medium of the present invention, the back coat layer provided on the back surface of the non-magnetic support as necessary can be formed using a known back coat paint without any particular limitation.

The magnetic recording medium of the present invention can be manufactured by the following method. First, a magnetic or non-magnetic intermediate paint for forming the intermediate layer and the magnetic paint for forming the magnetic layer are simultaneously coated on the non-magnetic support so that the dry thickness of the intermediate layer and the magnetic layer becomes a desired thickness. A coating film is formed by a multilayer coating method.

The simultaneous multi-layer coating method at this time is described in JP-A-5-73.
No. 883, column 42, line 31 to column 43, line 31.

Next, the formed coating film is once subjected to a drying step before passing through an aligner, and then subjected to a magnetic field alignment treatment in the longitudinal direction before the drying step is completed. This makes it possible to forcibly orient the axis of easy magnetization of the magnetic powder in the direction of the magnetic field and obliquely orient the magnetic powder.

In this case, since the thickness of the magnetic coating film is small, the movement in the direction perpendicular to the nonmagnetic support is restricted.
That is, the axis of easy magnetization of the magnetic powder is oriented perpendicular to the non-magnetic support. By performing drying in this state, curing of the coating film proceeds. However, by applying a magnetic field in the longitudinal direction before complete hardening, the axis of easy magnetization of the magnetic powder, that is, the plate surface, is forced to move in the direction of the magnetic field. As a result, it becomes possible to manufacture an obliquely oriented magnetic recording medium.

In this way, a magnetic recording medium is obtained in which the axis of easy magnetization of the magnetic powder is oriented at an arbitrary angle within a range of 60 ± 15 ° with respect to the main surface of the nonmagnetic support. This orientation angle can be controlled by the solid content of the coating before orientation.

Thereafter, after performing a calendering treatment, a back coat layer is further formed as necessary. Then, if necessary, for example, when obtaining a magnetic tape, 40 to
Aging treatment is performed at 70 ° C. for 6 to 72 hours, and slit into a desired width.

For example, when the magnetic recording medium of the present invention is a magnetic tape, the magnetic field orientation treatment is performed in a direction parallel to the coating surface of the magnetic layer coating material at about 40 kA / m or more, preferably about 80 to 800 kA. / M or a magnetic or non-magnetic coating material for forming the intermediate layer or a magnetic coating material for forming the magnetic layer in a wet state of 80 to 800 kA.
/ M through a solenoid or the like.

The drying treatment can be performed, for example, by supplying a heated gas. At this time, the degree of drying of the coating film can be controlled by controlling the temperature of the gas and the amount of the supplied gas. As the drying conditions, for example, a hot air temperature of 6
It is preferable that the temperature is 0 to 120 ° C., the wind speed is 5 to 35 m / sec, and the drying time is 1 to 60 seconds.

The calendering treatment can be performed by a super calendering method in which two rolls such as a metal roll and a cotton roll or a synthetic resin roll, a metal roll and a metal roll are passed. The calendar processing conditions are as follows: the calendar speed is 50 to 300 m / mi.
n, the pressure is preferably 50 to 450 kg / cm, and the roll temperature is preferably 60 to 120 ° C.

In the production of the magnetic recording medium of the present invention, a finishing step such as a polishing or cleaning step for the surface of the magnetic layer can be performed, if necessary. The coating for forming the intermediate layer and the coating for forming the magnetic layer can also be applied by a generally known sequential multilayer coating method.

[0061]

The present invention will be described more specifically with reference to the following examples. The “parts” described below are all based on weight.

(Example 1) [Blending of magnetic paint] 100 parts by weight of acicular barium ferrite (major axis length: 0.08 μm, axial ratio: 5.5, coercive force: 184.8 kA / m, saturation magnetization: 1.77 × 10 ⁻⁵ Wb / g) ・ 0.3 parts by weight of carbon black (average particle size 0.02 μm) ・ 7 parts by weight of alumina (average particle size 0.2 μm) ・ Vinyl chloride copolymer (molecular weight 2500) 10 parts by weight-5 parts by weight of polyurethane (molecular weight 2500)-2.0 parts by weight of myristic acid-1.0 part by weight of butyl stearate-150 parts by weight of methyl ethyl ketone-50 parts by weight of toluene-50 parts by weight of cyclohexanone

[Formulation of Intermediate Non-Magnetic Paint] 100 parts by weight of α-iron oxide powder (acicular, major axis length: 0.1 μm) 10 parts by weight of carbon black (average particle size 0.02 μm) (Diameter: 0.2 μm) 7 parts by weight-Vinyl chloride copolymer 10 parts by weight-Polyurethane 5 parts by weight-Myristic acid 2.0 parts by weight-Butyl stearate 2.0 parts by weight-Methyl ethyl ketone 150 parts by weight-Toluene 50 parts by weight・ 50 parts by weight of cyclohexanone

[Backcoat paint compounding] 40 parts by weight of carbon black (antistatic agent, average primary particle size 0.018 μm) 50 parts by weight of Nipporan 2301 (binder) [polyurethane manufactured by Nippon Polyurethane Industry Co., Ltd.] 4 parts by weight of polyisocyanate (curing agent) [trade name (D-250N) manufactured by Takeda Pharmaceutical Co., Ltd.] 20 parts by weight of nitrocellulose 1 part by weight of stearic acid 140 parts by weight of methyl ethyl ketone 140 parts by weight of toluene 140 parts by weight of cyclohexanone

[Production of Magnetic Recording Medium] The above-mentioned magnetic paint and intermediate non-magnetic paint were dispersed in a sand mill to obtain a paint. To these paints, 3 parts by weight of an isocyanate-based curing agent was added, and simultaneous multilayer coating was performed on an aramid film so that the dry thickness of the outermost magnetic layer was 0.2 μm. These paints once passed through a drying process before passing through an aligner, and a magnetic field was applied in the longitudinal direction before the drying was completed to orient the magnetic easy axis of the magnetic powder in the outermost layer in a predetermined direction. After the smoothing treatment, a back coat layer was applied and slit to a width of 3.81 mm.

Example 2 A magnetic recording medium was manufactured in the same manner as in Example 1 except that the following plate-like barium ferrite was used as the magnetic powder used in the magnetic paint. [Mixing of magnetic paint] 100 parts by weight of barium ferrite in plate form (plate diameter: 20 μm, plate diameter ratio: 5, coercive force: 170 kA / m, saturation magnetization: 7.50 × 10 ⁻⁶ Wb / g)

Comparative Example 1 A magnetic recording medium was manufactured in the same manner as in Example 1 except that the following orientation process was used in manufacturing the magnetic recording medium. (Manufacture of magnetic recording medium) The above magnetic paint and intermediate non-magnetic paint were dispersed in a sand mill to obtain a paint. To these paints, 3 parts by weight of an isocyanate-based curing agent was added, and simultaneous multilayer coating was performed on an aramid film so that the dry thickness of the outermost magnetic layer was 0.2 μm. These coatings went through a drying process while applying a magnetic field in the longitudinal direction, and after the drying was completed, the axis of easy magnetization of the outermost magnetic powder was oriented in the longitudinal direction. After the smoothing treatment, a back coat layer was applied and slit to a width of 3.81 mm.

(Comparative Example 2) As the magnetic powder used in the magnetic coating material, a needle-like ferromagnetic metal powder shown below was used.
A magnetic recording medium was manufactured in the same manner as in Example 1. [Mixing of magnetic coating material] 100 parts by weight of needle-shaped ferromagnetic metal powder mainly composed of iron (Fe: Co: Al: Y: Ba = 70: 25: 2: 2: 1 (weight ratio), major axis length: 0 0.07 μm, axial ratio: 4.2, coercive force: 189 kA / m, saturation magnetization: 1.83 × 10 ⁻⁵ Wb / g)

The magnetic recording media obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated for output and surface properties (surface average roughness: Ra) at 4.5 MHz and 9 MHz by the following methods. It is shown in Table 1.

[Output] A sample is mounted on a drum tester having a diameter of 160 mm, the drum is rotated at a peripheral speed of about 6 m / s, and recording / reproduction is performed with a magnetic head (SONY Hi8 video recorder head). The recording current at this time is 9 MH
The optimum recording current is used for z. The reproduction output was measured using a spectrum analyzer (3689A) manufactured by HP.

[Center line surface roughness (Ra)] Laser light interference type surface roughness meter [Zygo, Laser Interf
erometric Microscope Maxi
m 3D Model 5700] under the following conditions. Lens used: Fizeau 40x Remove: Cylinder Filter: off Sampling length: 180 nm Sampling number: 260

[0072]

[Table 1]

As shown in Table 1, Examples 1 and 2 have a high output in a wide band and the surface condition of the magnetic layer is good. On the other hand, in Comparative Example 1, the output in the long wavelength region was small, and in Comparative Example 2, the surface state of the magnetic layer was not good.

[0074]

As described above, the magnetic recording medium of the present invention can improve the recording density and the output while suppressing the deterioration of the surface properties of the magnetic layer. Further, the magnetic recording medium can be efficiently and stably manufactured on an industrial scale by the manufacturing method of the present invention.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a magnetic recording medium according to the present invention.

FIG. 2 is a partially enlarged sectional view of a portion A in FIG.

[Explanation of symbols]

1: magnetic recording medium, 2: non-magnetic support, 3: intermediate layer, 4: magnetic layer, 5: back coat layer, 10: magnetic powder, θ: easy axis orientation of magnetic powder relative to the main surface of the non-magnetic support angle.

Claims (9)

[Claims] 1. A magnetic recording medium having at least a magnetic layer as an outermost layer on a nonmagnetic support, wherein the thickness of the magnetic layer is 0.5 μm or less, and the magnetic powder contained in the magnetic layer is An easy axis of magnetization is a plate-like magnetic powder perpendicular to the plate surface or an acicular magnetic powder whose easy axis is perpendicular to the major axis, and the easy axis of the magnetic powder is in relation to the main surface of the nonmagnetic support. A magnetic recording medium oriented at an arbitrary angle within a range of 60 ± 15 °. 2. The method according to claim 1, wherein the plate-like magnetic powder has a plate diameter of 0.01 μm.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a hexagonal ferrite having a plate ratio of 3 to 6. 3. The method according to claim 1, wherein the acicular magnetic powder has a major axis length of 0.1 μm.
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a needle barium ferrite having a needle ratio of 3 to 10. 4. The method according to claim 1, wherein the non-magnetic support and the magnetic layer include:
4. The magnetic recording medium according to claim 1, further comprising a magnetic or non-magnetic intermediate layer. 5. A method for producing a magnetic recording medium in which at least a magnetic layer as an outermost layer is provided by applying a magnetic paint on a nonmagnetic support, wherein the magnetic powder contained in the magnetic paint has an axis of easy magnetization. After using the plate-shaped magnetic powder perpendicular to the plate surface or the needle-shaped magnetic powder whose easy axis is perpendicular to the long axis, the magnetic paint is applied on the non-magnetic support, and then once passed through the aligner. Through a drying step, a magnetic field is applied in the longitudinal direction before the drying step is completed, and the magnetic powder is obliquely oriented by forcibly orienting the axis of easy magnetization of the magnetic powder in the direction of the magnetic field. Of manufacturing a magnetic recording medium. 6. The method for manufacturing a recording medium according to claim 5, wherein the orientation angle of the axis of easy magnetization of the magnetic powder is in an arbitrary range of 60 ± 15 ° with respect to the main surface of the nonmagnetic support. 7. The plate-like magnetic powder has a plate diameter of 0.01 μm.
7. The method for producing a magnetic recording medium according to claim 5, wherein the ferrite is a hexagonal ferrite having a plate ratio of 3 to 6. 8. The method according to claim 1, wherein the acicular magnetic powder has a major axis length of 0.1 μm.
The method for producing a magnetic recording medium according to claim 5, wherein the magnetic recording medium is a needle barium ferrite having a needle ratio of 3 to 10. 9. Between the non-magnetic support and the magnetic layer,
9. The method for manufacturing a magnetic recording medium according to claim 6, further comprising a magnetic or non-magnetic intermediate layer.