JP2001344739A - Magnetic recording medium and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium excellent in stiffness, surface smoothness of a magnetic layer and electromagnetic conversion characteristics, and a method for manufacturing the magnetic recording medium. SOLUTION: This magnetic recording medium 1 consists of a nonmagnetic support 2, a nonmagnetic layer 3 formed by applying a nonmagnetic coating material containing nonmagnetic powder and a binder onto the support 2 and the magnetic layer 4 formed by applying a magnetic coating material containing magnetic powder and another binder onto the layer 3. The nonmagnetic powder is acicular and has >=0.2 μm to <=0.4 μm average length of the major axis. The binder contained in the layer 3 contains at least one resin having <=40 deg.C glass transition temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium such as an audio tape, a video tape, and a magnetic disk, and more particularly to a magnetic recording medium having a non-magnetic support, a non-magnetic layer, and a magnetic layer, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In the field of magnetic recording, a so-called coating type magnetic recording medium having a magnetic layer formed by applying a magnetic paint containing a magnetic powder and a binder is known.

In recent years, high-density recording has been required for a coating type magnetic recording medium. For example, by using a metal magnetic powder having a large saturation magnetization and a large coercive force as a magnetic powder, high-density recording is aimed at. ing. Magnetic recording media using metal magnetic powders as magnetic powders have extremely excellent magnetic properties, such as audio or video magnetic tapes, high-density floppy (registered trademark) disks, and data cartridges for backup. Are widely used as computer recording media and the like, and are currently the mainstream of magnetic recording media.

In order to realize high-density recording of a coating type magnetic recording medium, a metal magnetic powder is used as a magnetic powder, the surface of the medium is smoothed, spacing loss is minimized, and recording is reduced. It is important to improve electromagnetic conversion characteristics by reducing output loss due to magnetism. Techniques for achieving this object include (1) increasing the coercive force and saturation magnetization of the magnetic powder, (2) reducing the thickness of the magnetic layer, (3) smoothing the surface of the magnetic layer, and (4) improving the per head. And the like.

(1) Increasing the coercive force and saturation magnetization of a magnetic powder is a technique for directly improving the magnetic characteristics of a magnetic recording medium. Specifically, the coercive force and the saturation magnetization of the magnetic powder have been improved by examining the element composition and the like of the magnetic powder. The metal ferromagnetic powder having a coercive force exceeding 160 kA / m, Has also been developed which exceeds 140 Am ² / kg. The particle size distribution of the magnetic powder is reflected in the coercive force distribution, and the coercive force distribution is significantly improved by making the particle size uniform.

(2) The thinning of the magnetic layer is a technique for reducing the self-demagnetization loss of the magnetic recording medium, and is considered to be effective for improving the short-wavelength recording / reproducing characteristics. The thickness of the magnetic layer
For example, when the thickness is simply reduced to 0.5 μm or less, the surface shape of the nonmagnetic support tends to appear on the surface of the magnetic layer, and it is difficult to smooth the surface of the magnetic layer. In order to improve such a problem, a multilayer coating type structure in which a nonmagnetic layer is interposed between a nonmagnetic support and a magnetic layer is often adopted. That is, by interposing the non-magnetic layer, the thickness is increased between the surface of the non-magnetic support and the surface of the magnetic layer, and the surface shape of the non-magnetic support is less likely to appear on the surface of the magnetic layer. This makes it possible to form a thinned and smoothed magnetic layer.

(3) The surface of the magnetic layer is smoothed by using a film having excellent surface smoothness as a non-magnetic support, making the magnetic layer particles finer, improving the dispersibility of the magnetic layer paint, and roughening the surface during drying. And a mirror surface by calendar processing.

(4) Specifically, the improvement per head is to increase the bending stiffness (stiffness) of the magnetic recording medium and to improve the spacing loss between the head and the medium due to the tent shape. Flexural rigidity is generally proportional to the Young's modulus of the medium and the cube of its thickness. For this reason,
As a method for improving the bending rigidity of the magnetic recording medium, there is a method of increasing the thickness of the medium.

However, video tapes, data cartridges, and the like containing a tape-shaped magnetic recording medium are required to record a large amount of data. As a means for increasing the recording capacity per unit cassette, the recording medium itself is used. The thickness of a medium can be reduced to increase the amount of storable medium.

As described above, when the thickness of the medium itself is reduced, as a method of improving the bending rigidity of the magnetic recording medium, there is a method of increasing the elastic modulus of the medium itself. In order to increase the elastic modulus of the medium itself, the elastic modulus of each material constituting the medium may be increased. In particular, the rigidity of the non-magnetic support is important, and in recent years, in a thin magnetic recording medium, polyethylene naphthalate or aramid having a higher Young's modulus than polyethylene terephthalate, which has conventionally been mainly used, is used. It has become.

[0011]

Another method for improving the bending rigidity of a magnetic recording medium is to use a non-magnetic powder having a relatively large particle size in a non-magnetic layer in order to improve the head contact of the magnetic recording medium. Increasing the strength of the nonmagnetic layer against bending can be mentioned.

However, the non-magnetic powder having a relatively large particle size causes unevenness in the non-magnetic layer itself.
Therefore, the magnetic layer formed on the non-magnetic layer has a problem that the surface smoothness is deteriorated due to the influence of the unevenness of the non-magnetic layer. In particular, when the magnetic layer is thin, the non-magnetic powder may protrude from the surface of the magnetic layer, and the surface smoothness of the magnetic layer is extremely deteriorated.

In other words, in the magnetic recording medium, the bending rigidity of the medium itself cannot be improved, and at the same time, the surface smoothness of the magnetic layer cannot be maintained.

The present invention has been proposed in view of such a conventional situation, and has excellent rigidity, good surface smoothness of the magnetic layer, head contact characteristics and C / N ratio.
It is an object of the present invention to provide a magnetic recording medium having improved electromagnetic conversion characteristics such as characteristics, and a method for manufacturing the same.

[0015]

In order to achieve the above-mentioned object, a magnetic recording medium according to the present invention comprises a non-magnetic support,
A non-magnetic layer formed by applying a non-magnetic paint containing a non-magnetic powder and a binder on a non-magnetic support, and a magnetic layer formed by applying a magnetic paint containing a magnetic powder and a binder on a non-magnetic layer In the magnetic recording medium having the following, the shape of the nonmagnetic powder is acicular, and the average major axis length of the nonmagnetic powder is 0.2 μm.
As described above, the binder contained in the non-magnetic layer having a range of 0.4 μm or less contains at least one resin having a glass transition temperature of 40 ° C. or less.

In the magnetic recording medium according to the present invention having the above-mentioned structure, the non-magnetic layer has a needle-like shape and an average major axis length in the range of 0.2 μm to 0.4 μm. , So that it has excellent bending rigidity. In this magnetic recording medium, the binder has a glass transition temperature of 4
Since a non-magnetic layer containing at least one kind of resin having a temperature of 0 ° C. or less is provided, the non-magnetic layer contains a non-magnetic powder having a relatively large particle size, and even if the non-magnetic layer itself has irregularities. For example, when heat and pressure are applied by a calendering process, the nonmagnetic layer itself is deformed to absorb irregularities. Therefore, the magnetic recording medium includes the magnetic layer having excellent surface smoothness without being affected by the shape of the nonmagnetic powder contained in the nonmagnetic layer.

The method of manufacturing a magnetic recording medium according to the present invention is characterized in that the magnetic recording medium has a needle shape and an average major axis length of 0.2 μm or more;
A nonmagnetic paint prepared by dispersing a nonmagnetic powder having a range of 0.4 μm or less and a binder containing at least one resin having a glass transition temperature of 40 ° C. or less in a solvent is used as a nonmagnetic support. A non-magnetic layer is formed by coating on a non-magnetic layer, and a magnetic paint prepared by dispersing a magnetic powder and a binder in a solvent is coated on the non-magnetic layer to form a magnetic layer. After drying, a calendar process is performed.

In the method of manufacturing a magnetic recording medium according to the present invention, the nonmagnetic layer has a needle shape and an average major axis length of 0.2 μm or more and 0.4 μm or less. Since the non-magnetic powder is contained, a magnetic recording medium having excellent bending rigidity can be manufactured. In this magnetic recording medium, the glass transition temperature is 40 ° C. as a binder.
Since a nonmagnetic layer containing at least one or more of the following resins is provided, the nonmagnetic layer contains a nonmagnetic powder having a relatively large particle size, and even if the nonmagnetic layer itself has irregularities, By applying heat and pressure during the treatment, the nonmagnetic layer itself deforms and absorbs irregularities.
Therefore, it is possible to manufacture a magnetic recording medium having a magnetic layer having excellent surface smoothness without being affected by the shape of the nonmagnetic powder contained in the nonmagnetic layer.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetic recording medium according to the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, a magnetic recording medium 1 to which the present invention is applied is formed on a nonmagnetic support 2 and one main surface of the nonmagnetic support, and contains a nonmagnetic powder and a binder. A magnetic layer 3 and a magnetic layer 4 formed on a nonmagnetic layer and containing a magnetic powder and a binder are provided.

Examples of the nonmagnetic support 2 include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polyethylene and polypropylene, cellulose triacetate, and the like.
Cellulose diacetate, cellulose derivatives such as cellulose butyrate, polyvinyl chloride, vinyl resins such as polyvinylidene chloride, polycarbonate, polyimide,
In addition to plastics such as polyamide-imide, light metals such as aluminum alloys and titanium alloys, and ceramics such as alumina glass are exemplified. When a rigid substrate such as an Al alloy plate or a glass plate is used for the non-magnetic support 2, an oxide film such as alumite treatment or a Ni-P film is formed on the substrate surface so that the substrate surface is hardened. It may be.

The non-magnetic layer 3 is formed by applying a non-magnetic paint prepared by mixing at least a non-magnetic powder and a binder on one main surface of the non-magnetic support 2.

Examples of the non-magnetic powder include iron oxyhydroxide, hematite (α-Fe ₂ O ₃ ), titanium oxide and the like, and the particle size distribution is preferably relatively sharp.

The shape of the nonmagnetic powder is acicular. The needle-shaped non-magnetic powder forms a framework in the plane direction of the non-magnetic layer 3 and increases the strength of the non-magnetic layer 3 against bending. If the shape of the nonmagnetic powder is, for example, spherical, a desired strength against bending of the nonmagnetic layer 3 cannot be obtained.

Here, the acicular shape refers to one having an acicular ratio of 4 or more. If the needle ratio is 4 or more, a spindle shape,
It may be a rod-shaped or column-shaped one, or a particle having a flat shape. Further, the needle ratio is preferably in the range of 4 or more and 20 or less for the purpose of achieving bending rigidity.

The average major axis length of the nonmagnetic powder is 0.2
The range is not less than μm and not more than 0.4 μm. Here, the average major axis length is a photograph of a non-magnetic powder using an electron microscope,
This is the average value when the major axis length is measured for 200 or more nonmagnetic powder particles.

When the average major axis length of the nonmagnetic powder is less than 0.2 μm, the function of the nonmagnetic layer 3 as a skeleton is weak.
The strength against bending of the nonmagnetic layer 3 cannot be sufficiently increased. On the other hand, when the average major axis length of the nonmagnetic powder exceeds 0.4 μm, the probability that the nonmagnetic powder protrudes to the surface of the magnetic layer 4 increases, and the surface smoothness of the magnetic layer 4 deteriorates. Therefore, in the magnetic recording medium 1, the shape of the nonmagnetic powder contained in the nonmagnetic layer 3 is acicular, and the average major axis length of the nonmagnetic powder is in the range of 0.2 μm to 0.4 μm. Thereby, it has excellent bending rigidity.

The binder contained in the non-magnetic layer 3 includes
Known thermoplastic resins, thermosetting resins, reactive resins and the like conventionally used as binders for magnetic recording media can be used.

Examples of the thermoplastic resin include vinyl chloride, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer , Acrylate-vinyl chloride-
Vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylate-vinylidene chloride copolymer,
Methacrylate-vinyl chloride copolymer, methacrylate-ethylene copolymer, polyvinyl fluoride,
Vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene butadiene copolymer , Polyurethane resin, polyester resin, amino resin, synthetic rubber and the like.

As the thermosetting resin, for example, phenol resin, epoxy resin, polyurethane curable resin,
Examples include urea resin, melamine resin, alkyd resin, silicone resin, polyamine resin, urea formaldehyde resin and the like.

The binder contained in the nonmagnetic layer 3 contains at least one resin having a glass transition temperature of 40 ° C. or lower. As described above, the non-magnetic layer 3 has a needle shape and an average major axis length of 0.2 μm or more,
Since it contains nonmagnetic powder having a relatively large particle size of 0.4 μm or less, the nonmagnetic layer 3 itself may have irregularities. However, since the non-magnetic layer 3 contains at least one kind of resin having a glass transition temperature of 40 ° C. or lower as a binder, the non-magnetic layer 3 is easily deformed when heated and pressed by, for example, a calendering process. 3 Absorbs its own irregularities. As a binder contained in the non-magnetic layer 3,
When only a resin having a glass transition temperature exceeding 40 ° C. is used, the nonmagnetic layer 3 may not be deformed even if heated and pressed by, for example, a calendering process, and may not absorb irregularities of the nonmagnetic layer 3 itself. Therefore, the magnetic recording medium 1 includes the nonmagnetic layer 3 containing at least one kind of resin having a glass transition temperature of 40 ° C. or lower as a binder.
The magnetic layer 4 has a smooth surface without being affected by the shape of the nonmagnetic powder contained in the nonmagnetic layer 3.

The lower limit of the glass transition temperature of the resin contained in the nonmagnetic layer 3 as a binder is not particularly limited.
The nonmagnetic layer 3 is deformed and crushed by a calendering process or the like at any temperature as long as the temperature is lower than or equal to ° C. However, when a resin having a glass transition temperature of less than −20 ° C. is used as the binder contained in the nonmagnetic layer 3, the magnetic recording medium 1 becomes non-conductive when heated and pressed by, for example, a calendering process. The magnetic layer 3 may be excessively deformed, and the smoothness of the magnetic layer 4 may be excessively improved. As a result, during running of the magnetic recording medium 1, sticking to the magnetic head or the like may occur, and output fluctuation may occur. For this reason, it is preferable that the binder contained in the non-magnetic layer 3 contains at least one kind of resin having a glass transition temperature of −20 ° C. or higher.

It is also possible to use a resin having a glass transition temperature of 40 ° C. or lower and a resin having a glass transition temperature different from that of the resin. Specifically, a resin having a glass transition temperature of 40 ° C. or lower is used as a first binder, and a resin having a glass transition temperature exceeding 40 ° C. is used as a second binder.
When the binder is used in combination with the second binder, when the glass transition temperature of the second binder is more than 40 ° C. and less than 100 ° C., the weight ratio of the second binder is: It is preferable to be in the range of 10% or more and 50% or less. When the glass transition temperature of the second binder is 100 ° C. or higher, the weight ratio of the second binder is preferably in the range of 10% to 20%. In particular, when a resin having a low glass transition temperature of −20 ° C. is used as a binder,
As described above, it is preferable to use together with resins having different glass transition temperatures.

The glass transition temperature refers to a tan δ peak temperature obtained by dynamic viscoelasticity measurement. When adjusting the glass transition temperature of the resin, for example, as a method of adjusting the glass transition temperature of the polyester polyurethane, a synthetic raw material of the polyester polyurethane having a molecular weight of 200
Changing the type of polyester diol, which is a prepolymer of about 00, may be mentioned.

For example, when an aromatic polyester diol is used, a polyester polyurethane having a glass transition temperature of 70 ° C. or higher is synthesized. When an aliphatic polyester diol is used, the glass transition temperature is -3.
A polyester polyurethane having a temperature of about 0 ° C. is synthesized.

A polyester polyurethane having a glass transition temperature of about 40 ° C. is synthesized by using both an aromatic polyester diol and an aliphatic polyester diol as raw materials and appropriately adjusting the mixing ratio of the two. The adjustment of the glass transition temperature is performed by controlling the mixing ratio of the aromatic polyester diol and the aliphatic polyester diol.

Here, examples of the aromatic polyester diol include terephthalic acid and isophthalic acid. Examples of the aliphatic polyester diol include adipic acid, sebacic acid, and ethylene glycol.

The above-mentioned binders include —SO ₃ M, —OSO ₃ M, and —CO ₃ for the purpose of improving the dispersibility of the nonmagnetic pigment.
OM, P = O (OM) ₂ (where M represents a hydrogen atom or an alkali metal such as lithium, potassium, sodium, etc.), —NR ₁ R ₂ , —NR ₁ R ₂ R ₃ ⁺ X ⁻ A main chain amine represented by> NR ₁ R ₂ ⁺ X ⁻ (wherein R ₁ , R ₂ and R ₃ represent a hydrogen atom or a hydrocarbon group) represents, X ^- is fluorine, chlorine,
Represents halogen element ions such as bromine and iodine, inorganic ions, and organic ions. ), -OH, -SH,-
Polar functional groups such as CN and epoxy groups may be introduced. The introduction amount of these polar functional groups into the binder is 10 ^-1 to 10 ^-1 .
It is preferably 10 ⁻⁸ mol / g, and 10 ⁻² to 10 ^−6.
More preferably, it is mol / g.

The content of the binder is determined in consideration of the dispersibility of the non-magnetic powder and the like in preparing the non-magnetic paint, the adhesion, the tackiness, and the running durability between the non-magnetic support 2 and the non-magnetic paint. From
The amount is preferably 5 to 100 parts by weight, more preferably 10 to 30 parts by weight, per 100 parts by weight of the nonmagnetic powder. If the content of the binder is less than the above range,
There is a possibility that dispersibility, adhesiveness and running durability may be impaired. When the content of the binder exceeds the above range, tackiness,
Running durability may be impaired.

Generally, in a magnetic recording medium, sliding durability is ensured by using a resin having a high glass transition temperature as a binder to be contained in a magnetic layer. In the magnetic recording medium 1 to which the present invention is applied, a resin having a glass transition temperature of 40 ° C. or lower is used as a binder contained in the nonmagnetic layer 3. The non-magnetic layer 3 does not directly contact a sliding member such as a magnetic head, a drum, and a guide in the recording / reproducing apparatus of the magnetic recording medium. Therefore, even if the magnetic recording medium 1 includes the non-magnetic layer 3 containing a resin having a low glass transition temperature as a binder, that is, a resin having a glass transition temperature of 40 ° C. or lower, the impulse durability does not deteriorate.

Further, the non-magnetic layer 3 can contain conductive particles, a conductive resin and the like as an antistatic agent, and various conventionally known additives can be added.

In preparing a non-magnetic coating material, examples of solvents for mixing the above-mentioned various components to form a coating material include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone;
Ethanol, alcohol solvents such as propanol, methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, ester solvents such as ethylene glycol acetate, ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane, Examples thereof include aromatic hydrocarbon solvents such as benzene, toluene, and xylene, and halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene. These solvents are appropriately mixed and used.

The magnetic layer 4 is formed by applying a magnetic paint obtained by mixing at least a magnetic powder and a binder on the non-magnetic layer 3.

As the magnetic powder, VTR format,
Those having magnetic characteristics such as a coercive force and a magnetization amount suitable for recording and reproducing characteristics such as a drive format are used, and examples thereof include Fe-based or Fe-Co-based metal magnetic powder, barium ferrite, iron carbide, and iron oxide. . In addition, Co, Ni, Cr, Mn, Mg, C
a, Ba, Sr, Zn, Ti, Mo, Ag, Cu, N
a, K, Li, Al, Si, Ge, Ga, Y, Nd, L
Metal compounds such as a, Ce, and Zr may coexist.

As the binder contained in the magnetic layer 4, the same resin as the binder contained in the non-magnetic layer 3 described above can be used. However, the glass transition temperature of the resin used as the binder is not limited. Further, the magnetic layer 4 may contain various conventionally known additives.

The magnetic layer 4 can contain a lubricant. Examples of the lubricant include graphite, molybdenum disulfide, tungsten disulfide, silicone oil, fatty acids having 10 to 22 carbon atoms, fatty acid esters of these fatty acids and alcohols having 2 to 26 carbon atoms, terpene compounds. And their oligomers, fluorine-based lubricants and the like.

The lubricant may be contained only in the magnetic layer 4. However, in order to obtain a smoother lubricating effect, the lubricant may be contained in the magnetic layer 4.
And it is preferable to include it in both the nonmagnetic layer 3 and the nonmagnetic layer 3.

The magnetic layer 4 may be used together with a polyisocyanate for crosslinking and curing a binder as a curing agent. As the polyisocyanate, toluene diisocyanate and adducts thereof, alkylene diisocyanate and adducts thereof can be used. The addition amount of these polyisocyanates is preferably 5 to 80 parts by weight based on 100 parts by weight of the binder, and
More preferably, it is 50 parts by weight.

The curing agent may be used only in the magnetic layer 4.
It may be added to both the nonmagnetic layer 3 and the magnetic layer 4. When the hardener is added to both the non-magnetic layer 3 and the magnetic layer 4, the amount of the hardener may be the same for each layer, or may be different as an arbitrary ratio.

The magnetic layer 4 can contain conductive particles, conductive resin and the like as an antistatic agent. In addition, for the purpose of obtaining sliding durability, nonmagnetic reinforcing particles are added to the magnetic layer 4.
May be contained.

The non-magnetic reinforcing particles include aluminum oxide (α, β, γ), chromium oxide, silicon oxide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (rutile, Anatase) and the like. The non-magnetic reinforcing particles preferably have a Mohs hardness of 4 or more, more preferably 5 or more, and most preferably 6 or more. Further, the specific gravity is preferably 2 to 6, and 3
It is more preferable that the number is from 5 to 5. Further, the average primary particle size is preferably 1.0 μm or less, 0.5 μm
m or less, and most preferably 0.3 μm or less. The average primary particle size of the nonmagnetic reinforcing particles was randomly determined from a transmission electron micrograph.
It is obtained by selecting 0 pieces and performing statistical processing on them.

The amount of the non-magnetic reinforcing particles added was 10
It is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, most preferably 5 parts by weight or less with respect to 0 parts by weight. In addition, since the particle size of the nonmagnetic reinforcing particles strongly affects the surface roughness of the magnetic layer 4, it is preferable to use particles having an optimum particle size.

When preparing the magnetic paint, the same material as the solvent used when preparing the above-mentioned non-magnetic paint can be used as a solvent for mixing the above various components to form a paint. It is.

In the manufacturing method for manufacturing the magnetic recording medium 1 configured as described above, first, a nonmagnetic powder having a needle shape and an average major axis length in the range of 0.2 μm to 0.4 μm is used. A non-magnetic paint prepared by dispersing a binder having at least one resin having a glass transition temperature of 40 ° C. or lower in a solvent is applied to the non-magnetic support 2 to form the non-magnetic layer 3. I do. Next, a magnetic paint prepared by dispersing a magnetic powder and a binder in a solvent is applied on the non-magnetic layer 3 to form a magnetic layer 4. After the nonmagnetic layer 3 and the magnetic layer 4 are dried, a calendering process for smoothing the surface of the magnetic layer 4 is performed.

The magnetic paint and the non-magnetic paint are prepared through a kneading step and a dispersion step. Here, the kneading step is a step in which a mixture containing a pigment (a nonmagnetic powder, a magnetic powder, or the like) having a relatively high solid content and a resin is dispersed with a kneading device at high shear. As the kneading apparatus, a conventionally known kneading machine such as a continuous twin-screw kneader, a continuous twin-screw kneader capable of being diluted in multiple stages, a kneader, a pressure kneader, and a roll kneader can be used, and is not limited at all. The dispersing step is a step of dispersing a mixture containing a pigment having a relatively low solid content, a resin, and the like, using a dispersing device by the impact of beads or the like. As a dispersing device, a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill,
Examples include a pin mill, a tower mill, a double cylinder per mill, an agitator, a homogenizer, and an ultrasonic disperser.

In order to form the non-magnetic layer 3 and the magnetic layer 4, the non-magnetic paint and the magnetic paint prepared as described above are applied by coating the non-magnetic paint on the non-magnetic support 2. So-called wet-on-dry coating method in which a magnetic paint is applied on the dried non-magnetic coating film and dried. In addition, a so-called wet-on-wet coating method (wet multilayer coating method) in which a magnetic paint is applied over a non-magnetic coating film in a wet state is exemplified, but any other coating method may be used. Among these coating methods, particularly preferred is a wet-on-wet coating method.

After the non-magnetic paint and the magnetic paint are applied on the non-magnetic support 2 by the above-described coating method to form the non-magnetic layer 3 and the magnetic layer 4, a magnetic field orientation treatment is performed if necessary, and further drying is performed. Layer 3 and magnetic layer 4
Allow to dry. Thereafter, a calendar process is performed.

In the calendering process, usually, between a pair of rolls combining a resin elastic roll and a metal roll,
Alternatively, the heating is performed by passing the above-described raw material of the magnetic recording medium between a pair of rolls obtained by combining a metal roll and a metal roll, and applying heat and pressure.

In general, compared to the case where the calendering process is performed between metal rolls, the method for performing the calendering process between the elastic roll and the metal roll is such that the magnetic layer is in contact with the metal roll. When the magnetic layer is directly pressed by the metal roll, microslip occurs between the metal roll and the magnetic layer in contact with the metal roll. Therefore, it is possible to improve the surface properties of the magnetic recording medium and the packing density of the coating film.

As the elastic roll of the calender, a resin having heat resistance, for example, an epoxy type, a polyimide type, an aromatic polyamide type, a polyimide amide type or a urethane type is used. The metal roll is not particularly limited, but preferably has a hard chrome plating to increase the surface hardness. The temperature,
The pressure and speed can be set arbitrarily, but in terms of the balance between the crushing effect and the elasticity or damage to the steel roll, the processing temperature is in the range of 60 to 130 ° C, and the linear pressure is 200 to 450.
The processing speed is preferably in the range of 30 to 500 m / min in the range of kg / cm.

In this calendering process, the nonmagnetic layer 3 is heated and pressurized together with the magnetic layer 4. Non-magnetic layer 3
Contains at least one resin having a glass transition temperature of 40 ° C. or lower as a binder, so that the nonmagnetic layer 3 itself is deformed by heating and pressing, and the nonmagnetic layer 3 includes projections and the like made of nonmagnetic powder. Absorbs irregularities generated in the layer 3 itself.
Therefore, the magnetic recording medium 1 having the magnetic layer 4 having excellent surface smoothness can be manufactured without being affected by the shape of the nonmagnetic powder contained in the nonmagnetic layer 3.

As described above, an original magnetic recording medium in which the nonmagnetic layer 3 and the magnetic layer 4 are formed on one main surface of the nonmagnetic support 2 is obtained. Then, for example, when manufacturing the tape-shaped magnetic recording medium 1, this magnetic recording medium raw material is slit into a desired width and then housed in a tape cassette. The magnetic recording medium 1 may be provided with a back coat layer (not shown) on the other main surface of the non-magnetic support 2 opposite to the main surface on which the magnetic layer 4 is formed. By providing the back coat layer, the slidability between the other main surface of the magnetic recording medium 1 and various sliding members is improved.

In the case of producing a disk-shaped magnetic recording medium, although not shown, a non-magnetic layer and a magnetic layer are formed on both surfaces of a non-magnetic support, and the surface is smoothed if necessary. Punched into a disk shape and stored in a diskette.

In the magnetic recording medium 1 manufactured as described above, the nonmagnetic layer 3 has a needle shape and an average major axis length of 0.3.
Since it contains a nonmagnetic powder having a range of 2 μm or more and 0.4 μm or less, it has excellent bending rigidity. The magnetic recording medium 1 has a glass transition temperature of 40 ° C. as a binder.
Since the nonmagnetic layer 3 containing at least one or more of the following resins is provided, the nonmagnetic layer 3 is heated and pressed by, for example, a calendering process, so that the nonmagnetic layer 3 is deformed. Absorb the generated irregularities. Therefore, the magnetic recording medium 1 includes a magnetic layer having excellent surface smoothness without being affected by the shape of the nonmagnetic powder contained in the nonmagnetic layer. That is, in the magnetic recording medium 1, the improvement of the bending rigidity of the medium itself and the improvement of the surface smoothness of the magnetic layer are compatible, and the electromagnetic conversion characteristics such as head contact characteristics and C / N characteristics are improved.

The magnetic recording medium 1 has a non-magnetic layer 3
The needle ratio of the non-magnetic powder contained in the range of 4 or more, 20 or less, more flexural rigidity,
Electromagnetic conversion characteristics are further improved.

Further, the magnetic recording medium 1 has the non-magnetic layer 3
The glass transition temperature of the binder contained in -20 ℃ or more,
When the temperature is in the range of 40 ° C. or less, sticking is reliably prevented, and a stable output is exhibited.

[0066]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetic recording medium according to the present invention will be described.
This will be described in detail based on specific experimental results.

Sample 1 First, each component of the magnetic paint was weighed according to the following composition,
After kneading with an extruder, premixer mixing and sand mill mixing were performed, and the mixture was filtered to prepare a magnetic paint.

<Magnetic coating composition>-Magnetic powder: 100 parts by weight of Fe-Co magnetic powder-Binder: 10 parts by weight of vinyl chloride copolymer 10 parts by weight of polyester polyurethane-Additive: 1 part by weight of myristic acid heptyl stearate 2 parts by weight Lubricant: methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 80 parts by weight The major axis of the magnetic powder is 0.1 μm, and the specific surface area is 47.
m ² / g, saturation magnetization 150 Am ² / kg, coercive force 18
4 kA / m and Co / Fe were 30 atm%. The molecular weight of the vinyl chloride copolymer is 10000, the introduction amount of the functional group (-OSO ₃ K) is 0.07 mmol / g,
The glass transition temperature was 70 ° C. The polyester polyurethane has a molecular weight of 22,000 and a functional group (-OSO).
_The amount of 3Na) introduced was 0.07 mmol / g, and the glass transition temperature was 70 ° C.

Next, each component of the non-magnetic paint was weighed according to the following composition, kneaded by an extruder, mixed by premixer and sand mill, and filtered to prepare a non-magnetic paint.

<Non-magnetic paint composition> Non-magnetic powder: α-Fe ₂ O ₃ needle powder 100 parts by weight Binder: polyester polyurethane 20 parts by weight Additive: myristic acid 1 part by weight heptyl stearate 2 parts by weight Lubricant: 100 parts by weight methyl ethyl ketone 40 parts by weight toluene 60 parts by weight cyclohexanone The major axis of the nonmagnetic powder is 0.11 μm, the acicular ratio of the nonmagnetic powder is 5, and the specific surface area is 53 m ² / g. Also,
The molecular weight of the polyester polyurethane binder is 16
000, the introduction amount of the functional group (—OSO ₃ Na) is 0.07
mmol / g, glass transition temperature was 15 ° C.

Then, 4 parts by weight of a polyisocyanate (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added as a curing agent to the magnetic paint and the nonmagnetic paint prepared as described above. Thickness is 8.8
The thickness of the nonmagnetic layer is 1.3 μm and the thickness of the magnetic layer is 0.2 μm
After applying two layers at the same time, a magnetic field of 8 kG was passed through a solenoid coil magnet, and further dried with a drier, followed by calendering. As the calendering treatment, a 7-stage calendering device (6 nip method) combining a metal roll and an elastic roll was used, the treatment temperature was set to 100 ° C., and the linear pressure was set to 300.
kg / cm and the processing speed was 150 m / min.

Further, each component of the back coat paint was weighed and mixed according to the following composition. Then, on the other main surface opposite to the one main surface on which the magnetic layer of the non-magnetic support is formed, a back coat paint prepared and weighed according to the following composition is applied and dried, and the back coat is formed. A layer was formed.

<Backcoat paint> Carbon black (trade name: # 50, manufactured by Asahi) 100 parts by weight Polyester polyurethane (trade name: Nipporan N-2304) 100 parts by weight Methyl ethyl ketone 500 parts by weight Toluene 400 parts by weight 100 parts by weight cyclohexanone The raw magnetic recording medium thus formed was slit to produce a magnetic tape having a width of 1/2 inch (12.65 mm). Then, this magnetic tape is used as a cassette for digital video tape recorders (trade name: Digita
l Betacam, manufactured by Sony Corporation) to make a cassette tape.

Samples 2 to 6 The cassette was prepared in the same manner as in Sample 1 except that the non-magnetic powder contained in the non-magnetic layer had a major axis length and a needle ratio as shown in Table 1 below. A tape was made.

Samples 7 to 12 As the non-magnetic powder contained in the non-magnetic layer, those having a major axis length and a needle ratio as shown in Table 1 below are used, and
The binder contained in the non-magnetic layer has a molecular weight of 2000
0, and a cassette tape was prepared in the same manner as in Sample 1, except that a polyester polyurethane having a glass transition temperature of 25 ° C. was used.

Samples 13 to 19 As the non-magnetic powder contained in the non-magnetic layer, those having a major axis length and a needle ratio as shown in Table 1 below were used, and
The binder contained in the nonmagnetic layer has a molecular weight of 2200
A cassette tape was produced in the same manner as in Sample 1, except that a polyester polyurethane having a glass transition temperature of 40 ° C. was used.

Samples 20 to 26 As the nonmagnetic powder contained in the nonmagnetic layer, those having a major axis length and a needle ratio as shown in Table 1 below are used;
The binder contained in the nonmagnetic layer has a molecular weight of 2200
A cassette tape was prepared in the same manner as in Sample 1, except that polyester polyurethane having a glass transition temperature of 70 ° C. was used.

Various measurements were made on the cassette tapes of Samples 1 to 26 produced as described above to evaluate the characteristics.

<Surface smoothness> AFM (trade name: Nano
Using Scope 3), the center line average roughness (SRa) of the surface of the magnetic layer was measured. The measurement area is 50 × 5
It was set to 0 μm.

<Bending rigidity> 1/2 inch (12.65 m)
m) Cut a magnetic tape of width 6.35 mm x 12.65.
Two mm specimens were prepared, and the two specimens were bonded together such that the magnetic layer surface was on the outside. After setting the bonded sample pieces in the holder, the pieces were brought into contact with the detection section while being reciprocally oscillated, and the strain gage distortion at this time was measured. This strain gage distortion amount is the stiffness (arbitrary unit) in the tape width direction.

<Electromagnetic Conversion Characteristics> Simultaneous use of a reference signal having a recording wavelength of 0.65 μm using a digital video tape recorder (trade name: DVW-A500, manufactured by Sony Corporation) in an environment of an output of 20 ° C. and 50% RH. Recording and reproduction were performed. The output of the magnetic tape produced in Sample 20 was used as a reference, and the output of the other magnetic tapes was represented by the difference from the output of the magnetic tape of Sample 20. -C / N (Carrier to Noise Ratio) When the above-mentioned reproduction output was measured, frequency analysis was performed with a spectrum analyzer. -1M from carrier output
The output at a frequency separated by Hz is defined as noise, and the difference between the carrier output and the noise is defined as C / N. The difference between the C / N of the magnetic tape of Sample 20 and the C / N of the other magnetic tapes is described based on the C / N of the magnetic tape manufactured in Sample 20.

The above measurement results are shown in Table 1 together with the major axis length and needle ratio of the non-magnetic powder and the glass transition temperature of the binder contained in the non-magnetic layer.

[0083]

[Table 1]

As is clear from Table 1, a non-magnetic powder having a needle shape and an average major axis length in the range of 0.2 μm or more and 0.4 μm or less, and a resin having a glass transition temperature of 40 ° C. or less were used. The magnetic tapes of Samples 2 to 5, Samples 8 to 11, and Samples 14 to 17 each having a non-magnetic layer containing at least one or more binders have good surface smoothness and excellent bending. Because of the rigidity, it was found that the output and C / N were high.

On the other hand, a resin containing a resin having a glass transition temperature exceeding 40 ° C. as a binder and having an average major axis length of 0.2
The magnetic tape of Sample 20 having a non-magnetic layer containing a non-magnetic powder of less than μm has a low stiffness,
It was found that it did not have the desired bending stiffness.

Sample 2 having a nonmagnetic layer containing a resin having a glass transition temperature exceeding 40 ° C. as a binder and a nonmagnetic powder having an average major axis length exceeding 0.4 μm.
It was found that the magnetic tape of No. 6 had poor surface smoothness due to large surface roughness and could not obtain a desired output and C / N.

Further, Sample 1, Sample 7, and Sample 7 provided with a non-magnetic layer containing a non-magnetic powder containing a resin having a glass transition temperature of 40 ° C. or lower as a binder but having a major axis length of less than 0.2 μm. It was found that the magnetic tape of Sample 13 had low stiffness and did not have the desired bending rigidity.

Samples 6, 12 and 12 each containing a non-magnetic layer containing a non-magnetic powder containing a resin having a glass transition temperature of 40 ° C. or lower as a binder but having a major axis length exceeding 0.4 μm. It was found that the magnetic tape No. 18 had poor surface smoothness due to large surface roughness and could not obtain a desired output and C / N.

When the major axis length is 0.2 μm or more, 0.4
The magnetic tape of Samples 21 to 25, which contains a non-magnetic layer containing a resin having a non-magnetic powder in the range of μm or less but having a glass transition temperature exceeding 40 ° C. as a binder, has a large surface roughness. Poor surface smoothness from
It was found that the desired C / N could not be obtained.

Therefore, it is needle-shaped and has an average major axis length of 0.5.
A magnetic tape having a non-magnetic layer containing a non-magnetic powder having a range of 2 μm or more and 0.4 μm or less and a binder containing at least one or more resins having a glass transition temperature of 40 ° C. or less is an electromagnetic conversion material. It was found that the characteristics were improved.

Further, Sample 14 and Sample 19
In comparison, the magnetic tape of Sample 19, in which the nonmagnetic layer contains a nonmagnetic powder having a needle ratio of less than 4, has a low stiffness and the output per unit time is reduced because the head contact characteristics are not improved. all right. Therefore, it was found that when the acicular ratio of the nonmagnetic powder was 4 or more, the electromagnetic conversion characteristics were further improved.

In the magnetic tapes of Samples 1 to 26 manufactured as described above, the nonmagnetic layer contains only one kind of resin as a binder, but the nonmagnetic layer contains a plurality of resins. May be. Below, the glass transition temperature is 4
A first binder having a glass transition temperature of 40 ° C. or less;
The case where a second binder having a temperature exceeding ° C is used in combination will be described in detail based on specific experimental results.

Samples 27 to 29 Sample 1 was used as the first binder contained in the nonmagnetic layer.
7 having a molecular weight of 2200
0, a polyester polyurethane having a glass transition temperature of 40 ° C.), and having a molecular weight of 200 as a second binder.
00, using a polyester polyurethane having a glass transition temperature of 60 ° C., in the same manner as in Sample 17, except that the mixing ratio of the first binder and the second binder is as shown in Table 2 below. A cassette tape was produced.

Samples 30 to 32 Sample 1 was used as the first binder contained in the nonmagnetic layer.
7 having a molecular weight of 2200
0, a polyester polyurethane having a glass transition temperature of 40 ° C.), and having a molecular weight of 230 as a second binder.
00, using a polyester polyurethane having a glass transition temperature of 90 ° C., in the same manner as in Sample 17, except that the mixing ratio of the first binder and the second binder is as shown in Table 2 below. A cassette tape was produced.

Samples 33 to 35 Sample 1 was used as the first binder contained in the nonmagnetic layer.
7 having a molecular weight of 2200
0, a polyester polyurethane having a glass transition temperature of 40 ° C.), and having a molecular weight of 230 as a second binder.
00, using a polyester polyurethane having a glass transition temperature of 100 ° C., in the same manner as in Sample 17, except that the mixing ratio of the first binder and the second binder is as shown in Table 2 below. A cassette tape was produced.

Samples 27 to 27 produced as described above
Various measurements were performed on the cassette tape of Sample 35 in the same manner as the above-described measurement, and the characteristics were evaluated. Table 2 shows the results of the measurement together with the major axis length and needle ratio of the non-magnetic powder and the glass transition temperature of the binder contained in the non-magnetic layer.
Shown in

[0097]

[Table 2]

As can be seen from Table 2, samples 27 to
The magnetic tape of Sample 35 is a non-magnetic powder containing needle-like nonmagnetic powder having an average major axis length of 0.4 μm and a binder containing at least one resin having a glass transition temperature of 40 ° C. Since the magnetic layer was provided, it was found that it had desired surface smoothness and desired bending rigidity.

Here, comparing the magnetic tapes of Sample 28 and Sample 29, the magnetic tape of Sample 28, in which the blending ratio of the second binder having a glass transition temperature of 60 ° C. is 50%, is the second bonding tape, It was found that the C / N was improved as compared with the magnetic tape of Sample 29 in which the mixing ratio of the agent was 60%.

When comparing the magnetic tapes of Sample 31 and Sample 32, the magnetic tape of Sample 31 in which the mixing ratio of the second binder having a glass transition temperature of 90 ° C. is 50% is the same as that of the second binder. It was found that the C / N ratio was higher than that of the magnetic tape of Sample 32 in which the blending ratio was 60%.

Further, comparing the magnetic tapes of Sample 34 and Sample 35, the magnetic tape of Sample 34 in which the blending ratio of the second binder having a glass transition temperature of 100 ° C. is 20% is the same as that of the second binder. It was found that the C / N ratio was higher than that of the magnetic tape of Sample 32 in which the blending ratio was 60%.

Therefore, when the first binder having a glass transition temperature of 40 ° C. or lower is used in combination with the second binder having a glass transition temperature of more than 40 ° C., the glass transition temperature of the second binder is lowered. It has been found that when the temperature is higher than 40 ° C. and lower than 100 ° C., the compounding ratio with the second binder is preferably in the range of 10% or more and 50% or less. Also,
It has been found that when the glass transition temperature of the second binder is 100 ° C. or higher, the blending ratio of the second binder is preferably in the range of 10% to 20%.

The case where a resin having a glass transition temperature of −20 ° C. is used as a binder will be described in detail based on specific experimental results.

Sample 36 The binder contained in the nonmagnetic layer had a molecular weight of 2000
A cassette tape was produced in the same manner as in Sample 17, except that only polyester polyurethane having a glass transition temperature of -20 ° C was used.

Sample 37 As the first binder contained in the nonmagnetic layer, sample 3
No. 6 binder (molecular weight: 2000)
0, a polyester polyurethane having a glass transition temperature of −20 ° C.), and having a molecular weight of 20 as a second binder.
Sample 17, except that a polyester polyurethane having a glass transition temperature of 60 ° C. and a weight ratio of the first binder to the second binder of 90:10 was used.
In the same manner as in the above, a cassette tape was produced.

Sample 38 Sample 3 was used as the first binder contained in the nonmagnetic layer.
No. 6 binder (molecular weight: 2000)
0, a polyester polyurethane having a glass transition temperature of −20 ° C.), and having a molecular weight of 23 as a second binder.
Sample 1 was obtained by using a polyester polyurethane having a glass transition temperature of 100 ° C. and a weight ratio of the first binder to the second binder of 90:10.
In the same manner as in 7, a cassette tape was produced.

Samples 36 to 36 produced as described above
Various measurements were performed on the cassette tape of Sample 38 in the same manner as the measurement described above, and the characteristics were evaluated. Table 3 shows the results of the measurement together with the major axis length and needle ratio of the nonmagnetic powder and the glass transition temperature of the binder contained in the nonmagnetic layer.
Shown in

[0108]

[Table 3]

As is clear from Table 3, the magnetic tape of Sample 36 using only a resin having a glass transition temperature of -20 ° C. as a binder contained in the nonmagnetic layer was stuck during running of the magnetic tape. However, it was found that sticking was prevented and a stable output was obtained by using resins having different glass transition temperatures in combination, such as the magnetic tapes of Sample 37 and Sample 38.

[0110]

As is apparent from the above description, in the magnetic recording medium according to the present invention, the shape of the non-magnetic powder contained in the non-magnetic layer is acicular, and the average length of the non-magnetic powder is The axis length is in the range of 0.2 μm or more and 0.4 μm or less,
The binder contained in the nonmagnetic layer has a glass transition temperature of 40.
Since it contains at least one kind of resin having a temperature of not more than ℃, it has excellent bending rigidity and has a magnetic layer having excellent surface smoothness without being affected by the shape of the nonmagnetic powder contained in the nonmagnetic layer. . Therefore, this magnetic recording medium is excellent in electromagnetic conversion characteristics such as head contact characteristics and C / N characteristics.

The method of manufacturing a magnetic recording medium according to the present invention is characterized in that the magnetic recording medium is needle-shaped and has an average major axis length of 0.2 μm or more
A nonmagnetic paint prepared by dispersing a nonmagnetic powder having a range of 0.4 μm or less and a binder containing at least one resin having a glass transition temperature of 40 ° C. or less in a solvent is used as a nonmagnetic support. Apply on top to form a non-magnetic layer, apply magnetic paint on the non-magnetic layer to form a magnetic layer, dry the non-magnetic layer and the magnetic layer, and then perform a calendering process. A magnetic recording medium having rigidity, improved surface smoothness of the magnetic layer, and excellent electromagnetic conversion characteristics can be manufactured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration example of a magnetic recording medium.

[Explanation of symbols]

1 magnetic recording medium, 2 non-magnetic support, 3 non-magnetic layer,
4 Magnetic layer

Claims (4)

[Claims] 1. A non-magnetic layer formed by coating a non-magnetic support, a non-magnetic paint containing a non-magnetic powder and a binder on the non-magnetic support, and a magnetic paint containing a magnetic powder and a binder And a magnetic layer coated on the nonmagnetic layer, wherein the shape of the nonmagnetic powder is acicular, and the average long axis length of the nonmagnetic powder is 0.2 μm or more, and 0 A magnetic recording medium, wherein the binder contained in the non-magnetic layer contains at least one resin having a glass transition temperature of 40 ° C. or lower. 2. The needle ratio of the non-magnetic powder is 4 or more and 20 or more.
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium has the following range. 3. The magnetic recording medium according to claim 1, wherein the binder contained in the nonmagnetic layer has a glass transition temperature of −20 ° C. or higher. 4. An acicular shape having an average major axis length of 0.2 μm
A non-magnetic paint prepared by dispersing a non-magnetic powder having a range of 0.4 μm or less and a binder containing at least one resin having a glass transition temperature of 40 ° C. or less in a solvent is used as a non-magnetic paint. Forming a nonmagnetic layer by coating on a support to form a nonmagnetic layer; applying a magnetic paint prepared by dispersing a magnetic powder and a binder in a solvent onto the nonmagnetic layer to form a magnetic layer; And a method of manufacturing a magnetic recording medium, comprising performing a calendering process after drying the magnetic layer.