JP2002269727A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive high density recording and the enhancement of electromagnetic transducing characteristics in a magnetic recording medium. SOLUTION: A nonmagnetic substrate is specified to have a thickness of 2.5-4.0 [μm], Young's modulus (YMD) in the longitudinal direction of 700-1,500 [kg/mm<2> ] and the ratio (YMD)/(YTD) of the Young's modulus in the longitudinal direction to the Young's modulus in the lateral direction of 0.5-0.9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to various magnetic recording media such as a video tape, an audio tape, a floppy (registered trademark) disk, and a data storage.

[0002]

2. Description of the Related Art A so-called coating type magnetic recording medium, in which a magnetic layer is formed by applying a coating material containing a magnetic powder composed of metal fine particles and a binder, has been developed to meet the demand for high-density recording in recent years. It is used for digital recording of computer peripherals such as high-density floppy disks and data cartridges, as well as various analog recording formats for video and video. Especially for data cartridge applications, taking advantage of the removable property,
Demand for backup and long-term storage (so-called archive) applications is rapidly expanding.

In the digital magnetic recording medium as described above, technically important points include improvement of a recording capacity per cartridge and improvement of a data transfer speed.

[0004] In order to increase the recording capacity per cartridge, there are the following methods. A first method is to improve the recording density per unit area (area recording density) of a magnetic recording medium, that is, a magnetic tape,
A second method is to increase the amount of a magnetic recording medium to be incorporated in a cartridge, that is, the area of a magnetic tape.

In the method for improving the recording density per unit area of the magnetic tape according to the first method, the outermost surface of the magnetic tape on the side of the magnetic head contact surface is smoothed.
It is important to minimize output loss due to recording demagnetization while minimizing spacing loss. Practical methods include increasing the coercive force of the magnetic powder and making the coercive force distribution of the magnetic powder uniform. For example, the provision of perpendicular anisotropy, thinning of the magnetic layer, and the like have been studied.

In recent years, as a result of the improvement of the material of the magnetic powder, a material having a coercive force exceeding 160 [kA / m] has been developed. Is achieved.

[0007] In the case of a so-called coating type magnetic recording medium, the provision of perpendicular anisotropy largely depends on the magnetic orientation of magnetic particles. For needle-shaped particles, vertical or oblique orientation with respect to the coating film has been studied, but there are technical problems such as difficulty in controlling the alignment and disturbing the coating surface depending on the orientation. Therefore, it has not yet reached full-scale practical use.

[0008] The thinning of the magnetic layer is effective as a method for reducing the self-demagnetization loss. In recent years, various coating methods have been studied and put to practical use.

Next, as the second method, in order to increase the amount of the magnetic tape to be incorporated in the cartridge, there is a method of increasing the width of the magnetic tape or increasing the length of the magnetic tape. However, the width of the magnetic tape is specified in various formats, and even if a new tape format is developed in the future, it is expected that a magnetic tape extremely wide compared to the existing magnetic tape width will be put to practical use. hard. To increase the length of the magnetic tape, a method of increasing the number of turns of the magnetic tape is conceivable, but the capacity inside the cartridge is limited, and in order to store the magnetic tape in the cartridge, it is inevitable. The thickness of the magnetic tape must be made thinner than before, but there are limitations on the physical properties of the non-magnetic support, which is the base film for the magnetic tape.

[0010] In view of the above, as a material of the non-magnetic support constituting the magnetic tape, polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), which has been conventionally used, is replaced by a stronger material. Aramid (aromatic polyamide) films having excellent physical properties have been put into practical use, and the thickness of nonmagnetic supports has been reduced.

[0011]

However, as the thickness of the non-magnetic support decreases, the design of the head-media interface, specifically, the adjustment per magnetic head becomes difficult, and the output due to a defect per magnetic head becomes difficult. It is easy for the output to become unstable or to decrease the output, and when thinning the non-magnetic support, the strength of the non-magnetic support is improved,
It has become necessary to adjust the strength and other physical properties of a coating film formed on a nonmagnetic support.

For example, as a means for improving the contact with the magnetic head, the underlayer is improved in order to improve the contact with the magnetic head by paying attention to the flexibility of the underlayer formed as the lower layer of the magnetic layer (Japanese Patent Application Laid-Open No. HEI 9-163568). Japanese Patent Application Laid-Open No. 5-126650, Japanese Patent Application Laid-Open No. Hei 7-6346, and Japanese Patent Application Laid-Open No. Hei 5-6346 adjust the magnitude relationship of the Young's modulus of each layer constituting the magnetic recording medium.
298655), focusing on the fact that the pigment of the underlayer is related to the flexibility of the underlayer, adding a device to the non-magnetic pigment for forming the underlayer (JP-A-8-50718), and Various proposals have been made, such as a method of using a non-curable resin as a binder in the formation (Japanese Patent Application Laid-Open No. H8-50718), but none of these methods has provided a sufficient effect.

Many attempts have been made to improve the contact of the magnetic tape with the magnetic head by adjusting the physical properties of the non-magnetic support itself. A method of expressing the relationship by a predetermined formula (Japanese Patent Application Laid-Open No. 6-176345) and a method of restricting the thickness and Young's modulus of the nonmagnetic support (Japanese Patent Application Laid-Open No. 8-507)
No. 18, JP-A-11-273552), a method of restricting the ratio between the Young's modulus in the width direction and the Young's modulus in the longitudinal direction of the non-magnetic support (JP-A-8-329461, Japanese Patent Application No. 2000-123355). No., JP-A-10-69
634) have been proposed, but also in these, sufficient effects have not yet been obtained.

The inventors of the present invention have conducted intensive studies and, as a result, have realized a stable head-media interface with respect to a magnetic recording medium of high recording density, which has high electromagnetic conversion characteristics and excellent running durability. A recording medium has been provided.

[0015]

The magnetic recording medium of the present invention comprises a non-magnetic coating formed by applying a non-magnetic paint containing at least a non-magnetic powder and a binder on a long non-magnetic support. A magnetic recording medium having two or more coating layers comprising a magnetic layer and a magnetic layer formed by applying a magnetic paint containing at least a magnetic powder and a binder on the nonmagnetic layer The thickness of the nonmagnetic support is set to 2.5 to 4.0 [μm], and the Young's modulus (YMD) in the longitudinal direction of the nonmagnetic support is set to 700 to 1500 [k
g / mm ² ]. The ratio of the Young's modulus (YMD) in the longitudinal direction of the non-magnetic support 1 to the Young's modulus (YTD) in the width direction of the non-magnetic support, (YMD) / (Y
TD) is specified as in the following equation. 0.5 ≦ (YMD) / (YTD) ≦ 0.9

According to the magnetic recording medium of the present invention, a stable head-media interface can be realized, the electromagnetic conversion characteristics can be enhanced, and the running durability can be improved while achieving high-density recording.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the magnetic recording medium of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the examples shown below.

As shown in FIG. 1, the magnetic recording medium 10 of the present invention has a coating layer 4 in which a non-magnetic layer 2 and a magnetic layer 3 are formed on a long non-magnetic support 1. Things. Further, a back coat layer or a top coat layer may be formed on the magnetic layer 3 or on the main surface opposite to the magnetic layer forming surface side in order to improve durability.

As a material of the non-magnetic support 1 constituting the magnetic recording medium 10, an aromatic polyamide resin, that is, aramid is used.

The non-magnetic support 1 may be subjected to various surface treatments such as an easy adhesion treatment or decoration. For example, fine irregularities may be appropriately formed, heat treatment may be applied to correct deformation, or pretreatment such as corona discharge treatment or electron beam irradiation treatment may be performed on the surface. By arranging an inorganic filler such as kaolin or an organic filler on the surface of the non-magnetic support, the surface roughness can be controlled.

In the magnetic recording medium 10 of the present invention, the thickness (d ₁ ) of the nonmagnetic support ₁ is 2.5 to 4.0 [μm].
Further, the Young's modulus (YMD) in the longitudinal direction of the nonmagnetic support 1 is set to 700 to 1500 [kg / mm.
² ], the ratio of the Young's modulus in the longitudinal direction (YMD) to the Young's modulus in the width direction of the nonmagnetic support (YTD), (YMD)
/ (YTD), 0.5 ≦ (YMD) / (YT)
D) Specify ≦ 0.9.

As described above, when the non-magnetic support 1 having a thickness as thin as 2.5 to 4.0 [μm] is used, the rigidity is usually reduced, and the characteristics of the magnetic head contact are hindered. This may lead to a decrease in output, instability of output, a decrease in S / N, a decrease in error rate (bit error rate or block error rate), and a decrease in function as a digital magnetic recording medium. However, in the magnetic recording medium 10 of the present invention, the thickness is 2.5 to 4.0.
[Μm], the strength of the thin non-magnetic support 1 is determined by the Young's modulus (YMD) in the longitudinal direction, the Young's modulus (YMD) in the longitudinal direction, and the Young's modulus (YT) in the width direction of the non-magnetic support.
By specifying the ratio to (D) and the value of (YMD) / (YTD), the function of the magnetic recording medium is improved.

The Young's modulus of the non-magnetic support 1 can be adjusted and controlled within the above range, for example, by subjecting an aromatic polyamide film to stretching in a predetermined direction at a predetermined strength. The Young's modulus can be measured using a conventionally known commercially available tensile tester.

Non-magnetic layer 2 constituting magnetic recording medium 10
Is formed by applying a paint containing at least a non-magnetic powder and a binder. As the non-magnetic material, needle-like iron oxide can be mainly used, but in addition, carbon black, goethite, rutile-type titanium oxide, anatase-type titanium oxide, tin oxide, tungsten oxide, silicon oxide, zinc oxide, chromium oxide , Cerium oxide, titanium carbide, BN, α-alumina, β-alumina, γ-alumina, calcium sulfate, barium sulfate,
Molybdenum disulfide, magnesium carbonate, calcium carbonate, barium carbonate, strontium carbonate, barium titanate and the like may be used in combination.

When the above materials are used together for forming the non-magnetic layer 2, it is necessary to pay attention to the size of the particles used together.
That is, in order to ensure the smoothness of the surface after forming the coating film, the average particle size (for needle-like particles, the average major axis length)
Should be 0.3 [μm] or less, preferably 0.2 [μm] or less. The non-magnetic powder may be doped with an appropriate amount of impurities depending on the purpose.

The specific surface area of the nonmagnetic powder constituting the nonmagnetic layer 2 is 5 to 100 [m ² / g], more preferably 20 to 7 [m ² / g].
It is preferably 0 [m ² / g]. When the specific surface area is within the above range, accompanied by fine particles of non-magnetic powder,
The surface is smoothed.

The magnetic layer 3 is formed by applying a paint containing at least a magnetic powder and a binder.
The magnetic powder is, for example, a metal such as Fe, Co, or Ni, Fe
-Co, Fe-Ni, Fe-Al, Fe-Ni-Al,
Fe-Al-P, Fe-Ni-Si-Al, Fe-Ni
-Si-Al-Mn, Fe-Mn-Zn, Fe-Ni-
Zn, Co-Ni, Co-P, Fe-Co-Ni, Fe
-Co-Ni-Cr, Fe-Co-Ni-P, Fe-C
o-B, Fe-Co-Cr-B, Mn-Bi, Mn-A
1, alloys such as Fe-Co-V, iron nitride, iron carbide and the like. Further, a predetermined amount of a light metal element such as Al, Si, P, or B may be added for the purpose of preventing sintering during reduction or maintaining the shape.

For example, generally, Fe—Co or Fe—C
An alloy obtained by adding Al or Si to an o-Ni alloy for the purpose of preventing sintering is used. In these alloys,
The Co content is desirably 70% by weight or less in terms of Fe ratio. By alloying Co, the magnetic properties are improved as compared with Fe alone, and not only properties more suitable for high-density recording are obtained, but also weather resistance is improved and storage properties are improved. Further, two or more of the above magnetic powders can be used in combination.

The specific surface area of the applied magnetic powder is 20
90 [m ² / g], more preferably 25 to 70 [m
² / g]. When the specific surface area is set within the above range, the shape of the magnetic powder can be made finer, high density recording of the finally obtained magnetic recording medium can be realized, and noise characteristics can be improved.

However, in the case of metal magnetic powder,
The specific surface area does not directly reflect the particle size. That is, assuming that the metal magnetic powder has a substantially cylindrical shape in its microstructure, it has a three-layer structure of a pure metal center, an iron oxide layer, and a light metal layer from the innermost side. , The density (average density) of the entire metal magnetic powder changes. The specific surface area, which is the surface area per unit weight,
Since the value is affected by the density, the particle size of the metal magnetic powder cannot be specified merely by comparing the numerical values of the specific surface area. Furthermore, since the surface of the particles of the metal magnetic powder has fine irregularities after the gradual oxidation step, the surface area increases accordingly. Can not.

Therefore, in order to specify the particle size of the metal magnetic powder, a method of directly measuring the dimensions is desirable. The needle ratio is desirably small as long as the shape anisotropy is maintained, and is usually selected from 2 to 15 and desirably from 3 to less than 10. If the acicular ratio is less than 2, the orientation of the magnetic powder decreases, causing a decrease in the output of the finally obtained magnetic recording medium. If it exceeds 15, the short-wavelength signal output may decrease. .

Next, the binder used in the paint for forming each of the non-magnetic layer 2 and the magnetic layer 3 will be described.

Generally, when the non-magnetic powder or the magnetic powder is miniaturized, the voids between the powder particles are also miniaturized unless the geometrical arrangement changes. As a result, the gap between the fine particles is also reduced. As a result, in order to wet the fine space between particles and uniformly cover and disperse with the binder, use a binder that has high affinity for non-magnetic powder and magnetic powder and has excellent fluidity. It is necessary to knead the binder sufficiently so that the binder is sufficiently adsorbed to the nonmagnetic powder or the magnetic powder.

As the binder, any of known thermoplastic resins, thermosetting resins, reactive resins and the like conventionally used as binders for magnetic recording media can be used. Those having about 5000 to 100000 are preferable.

Examples of the thermoplastic resin include vinyl chloride,
Vinyl chloride copolymer, 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, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinyl chloride copolymer, methacrylic acid ester-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, nitro Cellulose), styrene-butadiene copolymer, polyurethane resin, polyester resin, amino resin, synthetic rubber, and the like.

Examples of the thermoplastic resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, polyamine resin, urea form resin and the like.

The above-mentioned binder contains -SO ₃ M, -OS in the molecule for the purpose of improving the dispersibility of the non-magnetic powder.
Polar functional groups such as O ₃ M, —COOM, and P ＝ O (OM) ₂ may be introduced. M in the functional group is a hydrogen atom,
Alternatively, it is an alkali metal such as lithium, potassium, and sodium. Further, as the polar functional group, -NR
_{1 R 2, -NR 1 R 2} R 3 + X - as the side chain type having an end group ^{_{of, NR 1 R 2 + X -}} - there is a main chain type.
Here, R ₁ , R ₂ and R ₃ are a hydrogen atom or a hydrocarbon group, and X− is a halogen element ion such as fluorine, chlorine, bromine or iodine or an inorganic or organic ion. There are also polar functional groups such as -OH, -SH, -CN, and epoxy resin. The amount of these polar functional groups is 10 ^-1 to 10 ^-8
[Mol / g], preferably 10 ^-2 to 10 ^-6 [mol / g]. These binders can be used alone, or a plurality of binders can be blended and used.

A polyisocyanate for crosslinking and curing the binder resin can be used in combination. Examples of the polyisocyanate include toluene diisocyanate and its adduct, alkylene diisocyanate and its adduct, and the like. The amount of the polyisocyanate to be added to the binder is 5 to 80 parts by weight, preferably 10 to 50 parts by weight, based on 100 parts by weight of the binder.
It is assumed that The polyisocyanate can be used for only one of the binder for forming the magnetic layer 3 and the binder for forming the non-magnetic layer 2, or can be applied to both layers. The blending amount can be appropriately adjusted in ratio.

As the organic solvent used for coating, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, methanol,
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 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. Can also be used.

As a device for mixing the above-mentioned magnetic paint for forming the magnetic layer 3 and a material for preparing the paint for forming the non-magnetic layer 2, a continuous paint used in a usual paint kneading process is used. Conventionally known kneaders such as a shaft kneader, a continuous twin-screw kneader capable of multistage dilution, a kneader, a pressure kneader, and a roll kneader can be used. In each of the above-mentioned paint production steps, in the dispersion step, a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill, a tower mill,
Any of an agitator, a homogenizer, an ultrasonic disperser and the like can be used.

The non-magnetic layer 2 and the magnetic layer 3 constituting the magnetic recording medium 10 can be formed by sequentially applying a coating material for forming each layer on the non-magnetic support 1. In the coating step, a die coater is mainly used. As the lip configuration of the die coater, a two-lip method, a three-lip method, a four-lip method, or the like is used. Generally, when the non-magnetic layer 2 and the magnetic layer 3 are formed on the non-magnetic support 1, a method in which coating and drying are performed one by one, that is, a so-called wet
An on-dry coating method and a method in which a magnetic layer 3 is overlaid on a non-dried lower layer in a wet state, in this case, a non-magnetic layer 2, so-called wet-on-wet coating method, that is, a wet multilayer coating method. However, it is desirable to perform simultaneous wet multilayer coating by a wet-on-wet multilayer coating method from the viewpoints of uniformity of the coating film, adhesion at the interface between the laminated films, and productivity.

FIG. 2 is a schematic view showing an example of a process for forming the non-magnetic layer 2 and the magnetic layer 3 on the non-magnetic support 1. In FIG. 2, first, the non-magnetic support 1 sequentially sent out from the supply roll is caused to travel in the direction of arrow A, and each of the coating materials 22 and 23 are simultaneously formed by the wet-on-wet method to form the coating films 12 and 13. In the simultaneous wet coating method in such a wet-on-wet method, the non-magnetic layer 2
Is formed in a wet state, so that the surface of the non-magnetic layer 2, that is, the interface between the non-magnetic layer 2 and the magnetic layer 3 is smoothed, thereby improving the surface properties of the magnetic layer 3. Also, the interlayer adhesion is improved. As a result, it is possible to satisfy the performance required for a magnetic recording medium which is required to have high output power and low noise particularly for high-density recording, to avoid delamination, and to improve mechanical strength. In addition, dropout is reduced, and the product reliability of the magnetic recording medium is improved.

On the other hand, the nonmagnetic layer 2 and the magnetic layer 3
Is formed by a so-called wet-on-dry method, it is necessary to select a nonmagnetic layer 2 having a sufficient solvent resistance to the paint of the upper magnetic layer 3.

The layers of the non-magnetic layer 2 and the magnetic layer 3 formed by the wet-on-wet coating method have a certain thickness except for a case where a clear boundary actually exists between the two layers. May be present in some cases, but the layers excluding such a boundary region are referred to as the nonmagnetic layer 2 and the magnetic layer 3, respectively.

After the formation of the non-magnetic layer coating film 12 and the magnetic layer coating film 13 as described above, the film is introduced into a dryer, and each coating film is dried. Thereafter, the film is calendered by a calender and wound around a take-up roll. take.

In the magnetic recording medium 10 of the present invention, the total thickness (d ₄ = d ₂ + d ₃ ) of the non-magnetic layer 2 after drying and the magnetic layer 3 after drying, that is, Coating layer 4
Has a thickness of 0.5 to 2.0 [μm].
This is because if the total value of the film thickness formed on the non-magnetic support 1 is less than 0.5 [μm], the surface property of the non-magnetic support 1 is changed to the magnetic head sliding surface of the magnetic recording medium 10. The surface property is deteriorated because it is reflected in the S / N, resulting in deterioration of S / N.
On the other hand, if the thickness exceeds 2.0 μm, the volume recording density of the entire magnetic recording medium 10 decreases when the nonmagnetic support 1 having a thickness of about 4 μm is used. This is because there is a disadvantage that the magnetic tape having a length of 230 [m] stored in a general magnetic tape cartridge cannot be stored in the cartridge.

The thickness (d ₃ ) of the magnetic layer 3 is 0.0
5 to 0.5 [μm]. This is because thin-wavelength recording is in progress to achieve high-density recording, and it is necessary to reduce the thickness of the magnetic layer.However, self-demagnetization loss during recording and thickness loss during reproduction are minimized. In order to keep the limit, the value is set in the range.

If the thickness of the magnetic layer 3 is larger than 0.5 [μm], the overwrite characteristics tend to deteriorate, while if the thickness is smaller than 0.05 [μm], a sufficient output can be obtained. I will not be able to. From this viewpoint as well, the thickness of the magnetic layer 3 is in the range of 0.05 to 0.5 [μm].

Subsequently, after forming the back coat layer 5 on the main surface opposite to the surface on which the magnetic layer 3 is formed, the magnetic tape is cut into a predetermined width to produce a magnetic tape, which is housed in a predetermined cartridge, and A tape cartridge is manufactured. The back coat layer 5 can be formed using a conventionally known material for forming a back coat layer of a magnetic recording medium.

A lubricant is usually applied to the surface on which the magnetic layer 3 is formed and the main surface opposite to the surface on which the magnetic layer is formed, and the lubricant is a conventionally known lubricant for magnetic tapes. Any of them can be applied. Examples thereof include silicone oils, fatty acids having 10 to 22 carbon atoms, fatty acid esters using alcohols having 2 to 26 carbon atoms, terpenes, terpene compounds, oligomers thereof, and fluorine-based lubricants.

In the magnetic recording medium 10 of the present invention, the coating film formed on the non-magnetic layer 1, that is, the non-magnetic layer 2
The laminated coating film of the magnetic layer 3 is not limited to the two-layer structure, and another layer having an additional function may be formed. For example, an undercoat layer may be formed between the non-magnetic layer 2 and the non-magnetic support 1 to enhance the adhesiveness, between the non-magnetic layer 2 and the non-magnetic support 1, or between the non-magnetic layer 2 and the non-magnetic support 1. A material layer having elastic properties may be formed between the layer 2 and the magnetic layer 3 to reduce the impact of the head-media interface. A plurality of layers made of a material having the various functions described above may be formed for a predetermined purpose.

Hereinafter, the magnetic recording medium 10 of the present invention will be specifically described with reference to Examples and Comparative Examples. However, the magnetic recording medium of the present invention is limited to the following examples. Not something.

Example 1 First, an aromatic polyamide film having a thickness of 3.8 μm was prepared as the nonmagnetic support 1. Young's modulus (YM) in the longitudinal direction of the non-magnetic support 1
D) was 1100 [kg / mm ² ], the Young's modulus (YTD) in the width direction was 1800 [kg / mm ² ], and their ratio (YMD) / (YTD) was 0.61.

Next, a paint used for forming the non-magnetic layer 2 and the magnetic layer 3 constituting the magnetic recording medium 10 was prepared. In the following, the particle length and needle ratio of the non-magnetic powder constituting the non-magnetic layer 2 and the magnetic powder constituting the magnetic layer 3 were randomly selected from photographs taken with a transmission electron microscope. Averaged from 200 samples.

[Composition of paint for preparing nonmagnetic layer] α-iron oxide: 100 parts by weight (needle ratio = 8, major axis length = 0.15 μm, Si = 3 atom% treatment) Polyvinyl chloride resin: 17 [Parts by weight] (degree of polymerization 150, containing 5 × 10 ⁻⁵ mol / g of sodium sulfonate as a polar functional group) Stearic acid: 1 [parts by weight] Heptyl stearate: 1 [parts by weight] Methyl ethyl ketone: 150 [Parts by weight] cyclohexanone: 150 [parts by weight] polyisocyanate: 6 [parts by weight]

[Composition of Coating Material for Producing Magnetic Layer] FeCo alloy-based metal ferromagnetic powder: 100 parts by weight (average major axis length = 0.12 μm, acicular ratio = 10.2, saturation magnetization = 145 Am ² / kg, coercive force = 191 kA / m) Polyvinyl chloride resin: 14 [parts by weight] (Polymerization degree: 150, containing 5 × 10 ⁻⁵ mol / g of sodium sulfonate in a polar functional group) Polyester polyurethane resin: 6 [parts by weight] (contains 1 × 10 ⁻⁴ mol / g of sodium sulfonate as a polar functional group) Additive (carbon): 2 [parts by weight] Additive: 5 [parts by weight] (primary particle size) 0.09 μm Al ₂ O ₃ , added as a slurry, center particle size 0.17 μm) Stearic acid: 1 [parts by weight] Heptyl stearate: 1 [parts by weight] Methyl ethyl ketone: 150 [parts by weight] ] Toluene: 100 [parts by weight] Cyclohexanone: 50 [parts by weight] Polyisocyanate: 8 [parts by weight]

The above magnetic properties were measured using a vibrating sample magnetometer (manufactured by Toei Kogyo KK) with an external magnetic field of 1.2 [MA /
m] (15 kOe).

In preparing the coating material for preparing the non-magnetic layer 2 and the coating material for preparing the magnetic layer 3, the non-magnetic powder (magnetic powder), binder, various additives, organic solvent Were mixed and kneaded with a continuous kneader, then subjected to a dispersion treatment with a sand mill, and filtered with a filter to prepare a coating material. The dispersion treatment was performed for 5 hours for the coating for forming the magnetic layer and for 3 hours for the coating for forming the non-magnetic layer.

Each of the paints prepared as described above was
The non-magnetic layer 2 and the magnetic layer 3 were sequentially formed on the non-magnetic support 1 as shown in FIG. The thickness of the nonmagnetic layer 2 is set to 0.7 μm, and the thickness of the magnetic layer 3 is set to 0.2 μm.
m]. Further, the back coat layer 5 is formed to a thickness of 0.6 [μm], a lubricant is applied to the surface,
The sample was cut into a predetermined width to produce a sample magnetic tape.

The thickness of the coating film was measured from a cross-sectional photograph (magnification: 50,000) of an electron microscope. The Young's modulus of the nonmagnetic support 1 was measured using a commercially available tensile tester.

Embodiment 2 to Embodiment 15 The thickness of the nonmagnetic support 1 and the Young's modulus in the longitudinal direction (YM
D), Young's modulus in the width direction (YTD), and their ratio (YM
D) / (YTD) was changed, and the other conditions were the same as in the above [Example 1] to prepare a sample magnetic tape.

Comparative Example 1 As the nonmagnetic support 1, an aromatic polyamide film having a thickness of 3.8 μm was used.
The Young's modulus (YMD) in the longitudinal direction is 1970 [kg / mm
² ], the Young's modulus (YTD) in the width direction is 3200 [kg /
mm ² ], and their ratio (YMD) / (YTD)
Was set to 0.62. Other conditions were the same as in the above [Example 1] to prepare a sample magnetic tape.

Comparative Example 2 As the nonmagnetic support 1, an aromatic polyamide film having a thickness of 3.8 μm was used.
The Young's modulus (YMD) in the longitudinal direction is 1100 kg / mm
² ], Young's modulus (YTD) in the width direction is 900 kg / m
m ² ], and their ratio (YMD) / (YTD) is
1.22. Other conditions were the same as in the above [Example 1] to prepare a sample magnetic tape.

Example 1 produced as described above
The surface roughness Ra, electromagnetic conversion characteristics (output), and output fluctuation were measured for the magnetic tapes of the samples of Examples 15 to 15, Comparative Example 1, and Comparative Example 2. Here, the surface roughness Ra was measured using a non-contact type surface roughness meter manufactured by ZYGO. The electromagnetic conversion characteristics (output) were measured using a Sony DDS4 drive “SDT-11000”, and the output of a 1T signal (wavelength 0.33 μm) was measured with an oscilloscope. The output was defined as a reference value of 0 [dB] obtained from the magnetic tape of the sample of [Example 1], and expressed as a relative value to this value. The output fluctuation was defined by the ratio between the maximum value and the minimum value of the envelope waveform.

The thickness of the non-magnetic support and the longitudinal Young's modulus (YMD) of the magnetic tapes of the samples of [Example 1] to [Example 15], [Comparative Example 1] and [Comparative Example 2] described above. , Young's modulus in the width direction (YTD), (YMD)
/ (YTD), surface roughness Ra, electromagnetic conversion characteristics (output),
The following Table 1 shows the output fluctuation.

[0066]

[Table 1]

As shown in [Table 1], [Example 1] to
In the magnetic tape of Example 15, the thickness of the nonmagnetic support 1 was set to 2.5 to 4.0 [μm], and the Young's modulus (YMD) in the longitudinal direction was set to 700 to 1500 [kg / mm ² ].
By specifying (YMD) / (YTD) in the range of 0.5 to 0.9, output fluctuations could be extremely reduced. That is, even when a thin nonmagnetic support is used, the Young's modulus in the longitudinal direction (YMD) and the ratio of the Young's modulus in the longitudinal direction to the Young's modulus in the width direction (YMD) /
By numerically specifying (YTD), high-density recording was achieved, and at the same time, the contact of the magnetic head was improved, and a magnetic tape having excellent electromagnetic conversion characteristics was obtained.

On the other hand, in [Comparative Example 1] in [Table 1], the Young's modulus of the non-magnetic support in the longitudinal direction is too large, so that the head contact of the magnetic tape is deteriorated and the output fluctuation is increased. A practically sufficient value could not be obtained.

In [Comparative Example 2] in [Table 1], the Young's modulus (YMD) in the longitudinal direction of the non-magnetic support and the ratio (YM) of the Young's modulus in the longitudinal direction to the Young's modulus in the width direction were determined.
D) / (YTD) is too large, and the balance of these Young's moduli is poor, so that the contact of the magnetic tape with the head is deteriorated, the output fluctuates, and a practically sufficient value cannot be obtained.

[0070]

According to the present invention, the non-magnetic support 1 constituting the magnetic recording medium, that is, the base film is formed in the range of 2.5 to
It is assumed to be thin with a thickness of 4.0 [μm], and its Young's modulus (YMD) in the longitudinal direction is 700 to 1500 [kg /
mm ² ], and the ratio (YMD) / (YTD) of the Young's modulus in the longitudinal direction to the Young's modulus in the width direction is numerically specified to be 0.5 to 0.9, whereby the overall thickness is reduced. As a result, a high density recording can be realized, and at the same time, the contact of the magnetic head is improved, and a magnetic recording medium having excellent electromagnetic conversion characteristics is obtained.

[Brief description of the drawings]

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

FIG. 2 shows a film forming process chart of the magnetic recording medium of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 nonmagnetic support, 2 nonmagnetic layer, 3 magnetic layer, 4 coating layer, 5 backcoat layer, 10 magnetic recording medium, 12
Non-magnetic layer coating, 13 Magnetic layer coating, 20 Extrusion coater, 22 Non-magnetic coating, 23 Magnetic coating

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yukiko Okumura 6-35 Kita Shinagawa, Shinagawa-ku, Tokyo Sony Corporation F-term (reference) 5D006 BA08 CB03 CB07 EA01 FA02 FA05 FA09

Claims (3)

[Claims] A non-magnetic layer formed by applying a non-magnetic paint containing at least a non-magnetic powder and a binder on a long non-magnetic support, and at least a magnetic layer on the non-magnetic layer. A magnetic recording medium having two or more coating layers composed of a magnetic layer formed by applying a magnetic paint containing a powder and a binder, wherein the thickness of the nonmagnetic support is , 2.5 to 4.0 [μm], and the Young's modulus (YMD) in the longitudinal direction of the nonmagnetic support is:
700 to 1500 [kg / mm ² ], the ratio of the Young's modulus in the longitudinal direction (YMD) to the Young's modulus in the width direction (YTD) of the nonmagnetic support, (YMD) /
A magnetic recording medium, wherein (YTD) satisfies the relationship of 0.5 ≦ (YMD) / (YTD) ≦ 0.9. 2. The total thickness of the coating layer is 0.5 to 2.0.
2. The magnetic recording medium according to claim 1, wherein the thickness is [μm]. 3. The magnetic recording medium according to claim 1, wherein the non-magnetic support is made of an aromatic polyamide resin.