JP2002312922A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating type magnetic recording medium with preferable traveling durability and electromagnetic transduction characteristics and containing hexagonal system ferromagnetic powder which can be easily dispersed and shows good dispersibility. SOLUTION: In the magnetic recording medium having structural layers containing at least a magnetic layer containing ferromagnetic powder on at least one surface of a supporting body, the magnetic layer contains ferromagnetic powder treated with at least one kind of anionic surfactant selected from carboxylic acid amine salts and phosphate amine salts having 1,000 to 80,000 molecular weight.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape, and more particularly, to a coating type magnetic recording in which a magnetic coating mainly composed of a ferromagnetic powder or a binder is coated on a support to form a magnetic layer. The present invention relates to a magnetic recording medium for high-density recording with a good degree of dispersion of a magnetic layer, which is particularly suitable for use in a system using an MR head utilizing the magnetoresistive effect for reproduction.

[0002]

2. Description of the Related Art A coating type magnetic recording medium is formed by applying a non-magnetic support such as polyethylene terephthalate and a magnetic coating material in which a ferromagnetic powder is uniformly dispersed in a resin binder solution. It is composed of layers. Conventionally, acicular ferromagnetic powders such as γ-Fe ₂ O ₃ have been used as the above magnetic powders. In recent years, magnetic powders using ultrafine magnetic particles of hexagonal ferrite have been developed with the aim of improving recording density. It has been partially commercialized.

In general, factors that govern the dispersion behavior of a magnetic powder in a resin binder liquid include the progress of agglomeration due to the magnetostatic interaction between the magnetic powder particles and the surface of the magnetic powder and the binder liquid. And the progress of dispersion caused by surface chemical interaction with the polymer.

[0004] It is believed that the surface chemical interaction between the binder liquid and the powder surface occurs in proportion to the surface area of the powder. In particular, it has become more difficult to disperse the ferromagnetic powder more and more due to the miniaturization of the ferromagnetic powder accompanying the recent high density.

In the case where hexagonal ferrite fine particles are used for magnetic powder, the magnetic interaction is large because the fine particles are plate-like, and each magnetic powder is single-crystal and polycrystalline. It has been pointed out that it is difficult to disperse due to the difficulty in obtaining a fine structure such as irregularities on the powder surface as compared with the conventional needle-like particles formed of the aggregate of the above, and the lack of dispersion stability. For this reason, the surface of the medium obtained by coating is often not finished to a surface accuracy sufficiently suitable for high-density recording.

[0006] In response to such an indication, a surface treatment with an organic material coat has been conventionally proposed, but no satisfactory effect has been found.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a coating type magnetic recording medium which is easy to disperse and has good running durability and electromagnetic conversion characteristics containing a ferromagnetic powder having a good degree of dispersion. It is in.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium comprising at least one surface of a support and a constituent layer containing at least a magnetic layer containing a ferromagnetic powder. This can be achieved by a magnetic recording medium characterized by comprising a ferromagnetic powder treated with at least one or more anionic surfactants selected from 1,000 to 80,000 carboxylic acid amine salts and phosphoric acid ester amine salts. Preferred embodiments of the present invention are as follows. 1. A magnetic recording medium, wherein the ferromagnetic powder treated with the anionic surfactant is a hexagonal ferrite powder. 2. The hexagonal ferrite powder has an average plate diameter of 10 to 10.
50 nm, average plate ratio is 2 to 5, and variation coefficient of plate diameter is 30%
A magnetic recording medium, which is a hexagonal ferrite powder that is one of the following:

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic recording medium of the present invention will be described below in detail. (Dispersant for the Present Invention) The ferromagnetic powder used in the present invention comprises at least one or more anionic surfactants selected from carboxylic acid amine salts and phosphoric acid ester amine salts having a molecular weight of 1,000 to 80,000 (hereinafter referred to as the present invention). (Also referred to as a dispersant). As the dispersant for the present invention, a compound represented by the following general formula (I) is preferable.

[0010]

Embedded image

The dispersant represented by the general formula (1) is a compound of a surfactant having a hydrophilic group, and it is presumed that these hydrophilic groups are adsorbed on the surface functional groups of the ferromagnetic powder by an acid-base interaction. Is done. R1, R2, R in the general formula (1)
3 and R4 are a polymer chain or a linear or branched alkyl group, preferably having 1 to 5000 carbon atoms. The polymer chains in R1, R2, R3 and R4 in the general formula (1) include polyether chains, polyester chains,
And polyether / ester chains. The molecular weight of these polymer chains is preferably in the range from 200 to 80,000.

The alkyl group or polymer chain may be substituted with a substituent, and the substituent may be an alkoxy group,
Examples include a hydroxy group, a sulfo group, and a carboxyl group. Further, the alkyl group or polymer chain may
The substituent may have a heterocyclic group, for example, a pyrrolidinyl group, a piperidino group, or the like. The general formula (1)
The molecular weight of the anionic surfactant of a carboxylic acid amine salt and a phosphoric acid ester amine salt represented by
000, preferably in the range of 2000 to 70000.

Among the compounds represented by the general formula (1), the amine value is 15 to 45 and / or the acid value is 10 to 30.
Are preferred. Here, the amine value and the acid value can be measured by a titration method using an indicator or an automatic potentiometric titrator. The unit of the amine value and the acid value is mg (KOH) / g.

Specific examples of the compound corresponding to the structure represented by the general formula (1) include, for example, trade names manufactured by Kusumoto Kasei Co., Ltd.
Dispalon DA-703-50, Dispalon DA-
705, Dispalon DA-725, Dispalon DA
-325 or the like, and these may be used alone or in combination.

The treatment of the ferromagnetic powder with the dispersant for use in the present invention is usually carried out when preparing a coating solution for forming a magnetic layer, but it is previously treated with the compound represented by the above general formula (I). The resulting solution can be used for preparing a coating solution. As the prior treatment method, a known dispersion treatment method is used, and for example, a method in which a ferromagnetic powder is treated with a solution of the dispersant for the present invention in an appropriate solvent is exemplified.

The amount of the dispersant for use in the present invention is as follows.
It is preferably 0.1 to 20 parts by mass with respect to 00 parts by mass. When the amount is within the above range, a good ferromagnetic powder dispersion effect can be obtained. If the amount is less than 0.1 parts by mass, the dispersing effect is small, which is not preferable. If the amount is more than 20 parts by mass, no remarkable improvement in the dispersing effect is observed. The layer in which the ferromagnetic powder is dispersed, that is, the solvent used in the manufacturing process of the magnetic layer can be water, an organic solvent, or a mixture thereof, but is not particularly limited. In a solvent containing the dispersant for the present invention, a ferromagnetic powder is subjected to dispersion treatment to prepare a dispersion coating of the ferromagnetic powder, which is applied, heated, and cured according to a conventional coating method to obtain a ferromagnetic powder. A layer in which the dispersion of the powder is good can be provided.

The ferromagnetic powder is well dispersed by mixing the ferromagnetic powder when the dispersant for the present invention and the binder are kneaded using an open kneader or the like, or when dispersed using a roll mill or a sand mill. You.

By treating the ferromagnetic powder with at least one or more dispersants of the present invention, the magnetic cohesion between the ferromagnetic powder particles can be reduced. By treating with the dispersant for the present invention, the affinity with the ferromagnetic powder and the binder and the acidity
-Improved base adsorption and reduced magnetic cohesion between ferromagnetic powder particles. As a result, not only ease of dispersion but also improvement of electromagnetic conversion characteristics such as degree of dispersion, orientation and S / N, and running durability Can be secured.

[Ferromagnetic powder]

The magnetic recording medium of the present invention has a magnetic layer containing at least a ferromagnetic powder treated with the dispersant of the present invention. Magnetite, such ferromagnetic powder,
Maghemite, bell hydride compound, barium ferrite compound, metal or ferromagnetic metal powder, and Fe or Fe
Co, FePt alloys and the like can be mentioned, but the present invention is suitable for hexagonal ferrite powder. The constituent layer containing the magnetic layer may include a magnetic layer containing ferromagnetic powder that has not been treated with the dispersant for the present invention, but at least the uppermost layer of the constituent layer (the layer farthest from the support) is included. It is preferred that a magnetic layer containing a ferromagnetic powder, preferably a hexagonal ferrite powder, treated with the dispersant for the present invention be present. Next, the hexagonal ferrite powder suitable for the present invention will be described in detail. [Hexagonal ferrite powder] As the hexagonal ferrite, the crystal structure or basic composition represented by M-type magnetoplumbite hexagonal iron represented by BaFe ₁₂ O _{19 in} which iron or a metal substituted for iron has an average valence of 3 is used. Crystal ferrite; 2
BaM ₂ Fe ₁₆ O _{27 in which} a valent metal (hereinafter referred to as M) is present
Crystal structure or basic composition represented by W-type magnetoplumbite hexagonal ferrite; represented by BaMFe ₆ O ₁₁ ; crystal structure or basic composition represented by Y-type magnetoplumbite hexagonal ferrite; Ba ₃ M ₂ Fe ₂₄ Z-type magnetoplumbite hexagonal ferrite having a crystal structure represented by O ₄₁ or a basic composition; and a so-called composite type hexagonal ferrite in which spinel ferrite is epitaxially compounded on the surface of these hexagonal ferrites Is used.

Here, M in the composition formula of hexagonal ferrite,
Examples of the divalent metal constituting the spinel ferrite include Co, Fe, Ni, Mn, Mg, Cu, and Zn.

In particular, in the case of W-type and composite-type hexagonal ferrite, the bulk composition or the composition of the powder surface is low in alkali metals and rich in transition metals and oxygen. -Interfacial chemical interaction due to the base is poor, and both systems have a large amount of magnetization and are rich in magnetic cohesion. The present invention
It also works effectively on such systems.

The average plate diameter of the hexagonal ferrite powder used in the present invention varies depending on the recording density.
m is preferable, and 10 to 40 nm is more preferable. If the average plate diameter is less than 10 nm, the amount of magnetization is remarkably reduced, so that it is not suitable for a recording medium. If it exceeds 50 nm, a noise component becomes large and is not suitable for high density recording. Here, the plate diameter means the maximum diameter of the hexagon on the bottom surface of the hexagonal columnar hexagonal ferrite powder, and the average plate diameter is its arithmetic mean.

On the other hand, the average plate ratio, which is the arithmetic average of the plate ratio expressed by the ratio of the plate diameter to the thickness of the hexagonal ferrite powder, is preferably 2 to 5. If the ratio is less than 2, it is difficult to produce a hexagonal ferrite powder, and if it exceeds 5, the magnetic cohesion becomes dominant as compared with the dispersing force, so that the dispersion becomes difficult. The coefficient of variation of the plate diameter is 30%
The following is preferred. This variation coefficient is obtained from 100 × σ / average plate diameter. Further, the coefficient of variation of the plate ratio is preferably 30% or less. This variation coefficient is obtained from 100 × σ / average plate ratio. σ indicates the standard deviation of the plate diameter or plate ratio.

In this specification, the size of various powders such as hexagonal ferrite powder and carbon black (hereinafter referred to as “powder size”) is determined by using a high-resolution transmission electron microscope photograph and an image analyzer. Desired. The size of the powder can be determined by tracing the contour of the powder in the high-resolution transmission electron micrograph with an image analyzer. That is, as for the powder size, the shape of the powder is needle-shaped, spindle-shaped, column-shaped (however,
In the case where the height is larger than the maximum major axis of the bottom surface, etc., the length is represented by the length of the major axis constituting the powder, that is, the major axis length, and the shape of the powder is plate-like or columnar (thickness or height). Is smaller than the maximum major axis of the plate surface or the bottom surface), it is represented by the maximum major axis of the plate surface or the bottom surface, that is, the plate diameter, and the shape of the powder is spherical, polyhedral, unspecified, or the like, and If the major axis of the powder cannot be specified from the shape, it is represented by a circle equivalent diameter.

The average powder size of the powder is an arithmetic average of the above powder sizes, and is obtained by measuring about 500 powders as described above. The average acicular ratio of the powder is obtained by measuring the length of the minor axis of the powder in the above measurement, that is, the minor axis length, and calculating the (major axis length / minor axis length) of each powder.
Means the arithmetic mean of the values of Here, the minor axis length is, in the case of the definition of the powder size, the length of the minor axis constituting the powder, in the same case, refers to the thickness to height, respectively, in the case of, Since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience. When the shape of the powder is specific, for example, in the case of the definition of the powder size, the average powder size is referred to as the average major axis length, and in the case of the same definition, the average powder size is referred to as the average plate diameter. , (Plate diameter / thickness to height) is referred to as an average plate ratio. In the case of the same definition, the average powder size is called the average particle diameter.

The method for producing the above hexagonal ferrite powder may be any method such as a glass crystallization method, a hydrothermal synthesis method, a coprecipitation method, and a flux method. In any of the methods, it is important to find a condition under which the shape distribution and the particle size distribution become sharp to achieve high density. Hexagonal ferrite powder has a saturation magnetization σs of 40 to 80 A · m ^2.
/ Kg, coercive force Hc is 135-440 kA / m, BET
The specific surface area (S _BET ) by the method is 40 to 80 g / m ² , and the pH of the magnetic powder is preferably optimized by a combination with a binder to be used, but is usually 4 to 12, preferably 5.5 to 10 It is.

[Magnetic Layer] In the magnetic recording medium of the present invention, a constituent layer including at least a magnetic layer having a ferromagnetic powder may be provided on only one side or both sides of the support. The magnetic layer provided on one side thereof may be a single layer or a multilayer having different compositions. Further, a nonmagnetic layer (also referred to as a lower layer) may be provided between the support and the magnetic layer. The present invention preferably has a configuration in which a magnetic layer is provided on a lower layer. The magnetic layer in this case is also referred to as an upper layer or an upper magnetic layer. The upper layer can be formed by applying the lower layer simultaneously or sequentially, and then forming the lower layer in a wet state by wet-on-wet (W / W) or by forming the lower layer after drying and then forming the wet-on-dry (W / D) . W / W is preferred in terms of production yield. In W / W, since the upper layer and the lower layer can be formed simultaneously, a surface treatment step such as a calendering step can be effectively utilized, and the surface roughness of the upper magnetic layer can be improved even in a thin layer.

[Lower Layer] Next, the details of the lower layer will be described. The lower layer is preferably composed mainly of a nonmagnetic inorganic powder and a binder. The nonmagnetic inorganic powder used for the lower layer can be selected from, for example, inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. Examples of the inorganic compound include α-alumina, β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, hematite, goethite, corundum, and silicon nitride having an α conversion of 90% or more. , Titanium carbide,
Titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide and the like are used alone or in combination. Particularly preferred is titanium dioxide, because of its small particle size distribution and many means for imparting functions.
Zinc oxide, iron oxide and barium sulfate are preferred, and titanium dioxide and α-iron oxide are more preferred. The average particle diameter of these nonmagnetic inorganic powders is preferably 0.005 to 2 μm,
If necessary, non-magnetic inorganic powders having different average particle diameters can be combined, or even a single non-magnetic inorganic powder can have the same effect by widening the particle size distribution. Particularly preferably, the average particle diameter of the nonmagnetic inorganic powder is 0.01 μm or more.
0.2 μm. In particular, when the nonmagnetic inorganic powder is a granular metal oxide, the average particle diameter is preferably 0.08 μm or less, and when the nonmagnetic inorganic powder is an acicular metal oxide, the average major axis length is preferably 0.3 μm or less. , 0.2 μm or less is more preferable. Tap density is usually 0.05-2 g / ml,
Preferably it is 0.2 to 1.5 g / ml. The water content of the nonmagnetic inorganic powder is usually 0.1 to 5% by mass, preferably 0.2 to 3% by mass, and more preferably 0.3 to 1.5% by mass. The pH of the nonmagnetic inorganic powder is usually from 2 to 11, but the pH is particularly preferably from 5.5 to 10. The S _{BET of the} nonmagnetic inorganic powder is usually 1 to 100 m ² / g, preferably 5 to 80 m ² / g, more preferably 10 to 70 m ² / g.
It is. Crystallite size of non-magnetic inorganic powder is 0.004μ
m to 1 μm is preferable, and 0.04 to 0.1 μm is more preferable. The oil absorption using DBP (dibutyl phthalate) is usually 5 to 100 ml / 100 g, preferably 1 to 100 ml / 100 g.
0 to 80 ml / 100 g, more preferably 20 to 60 m
1/100 g. The specific gravity is usually 1 to 12, preferably 3 to 6. The shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape. The Mohs' hardness is preferably 4 or more and 10 or less. The SA (stearic acid) adsorption amount of the nonmagnetic inorganic powder is 1 to 20 μmol / m ² , preferably ² to 15 μmol.
mol / m ² , more preferably 3 to 8 μmol / m ² . Preferably, the pH is between 3 and 6. Al ₂ O ₃ ,
SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , Zn
O and Y ₂ O ₃ are preferably present. Al ₂ O ₃ , SiO ₂ , TiO ₂ , and ZrO ₂ are particularly preferable for the dispersibility, and more preferable are Al ₂ O ₃ , SiO ₂ , and ZrO ₂ . These may be used in combination or may be used alone. Further, a co-precipitated surface treatment layer may be used according to the purpose, or a method in which alumina is first present and then silica is present in the surface layer, or vice versa, may be employed. Although the surface treatment layer may be a porous layer depending on the purpose, it is generally preferable that the surface treatment layer be homogeneous and dense. Specific examples of the non-magnetic inorganic powder used for the lower layer of the present invention and a production method thereof are described in WO98 / 3.
5345 is exemplified.

By mixing carbon black in the lower layer, it is possible to lower the surface electric resistance Rs, which is a known effect, to reduce the light transmittance, and to obtain a desired micro-Vickers hardness. In addition, it is possible to bring about the effect of storing the lubricant by including carbon black in the lower layer. As the type of carbon black, furnace for rubber, thermal for rubber, black for color, acetylene black, and the like can be used. The following characteristics of the carbon black in the lower layer should be optimized depending on the desired effect, and the combined effect may provide more effects.

The S _BET of the lower carbon black is usually
100 to 500 m ² / g, preferably 150 to 400 m ²
/ G, DBP oil absorption is 20 to 400 ml / 100 g, preferably 30 to 400 ml / 100 g. The average particle size of the carbon black is usually 5 nm to 80 nm, preferably 10 to 50 nm, and more preferably 10 to 40 n.
m. A small amount of carbon black having an average particle diameter of more than 80 nm may be included. The carbon black preferably has a pH of 2 to 10, a water content of 0.1 to 10%, and a tap density of 0.1 to 1 g / ml.

Specific examples of the carbon black used in the lower layer include those described in WO 98/35345. These carbon blacks are 50% by mass based on the above nonmagnetic inorganic powder (carbon black is not included).
And a range not exceeding 40% of the total mass of the nonmagnetic layer. These carbon blacks can be used alone or in combination. The carbon black that can be used in the present invention can be referred to, for example, “Carbon Black Handbook” (edited by Carbon Black Association).

In the lower layer, an organic powder is used according to the purpose.
It can also be added. For example, acrylic styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigments, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluoroethylene resin Can be used. The manufacturing method is disclosed in
No. 18,564, and those described in JP-A-60-255827 can be used.

The binder resin, lubricant, dispersant, additive, solvent, dispersing method and the like of the lower layer or the back layer described below can be applied to those of the magnetic layer described below. In particular, with respect to the amount and type of the binder resin, the amount of the additive and the type of the dispersant, and the type thereof, a known technique for the magnetic layer can be applied.

[Binder] As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of -100 to 150C and a number average molecular weight of 1,000 to 200,000, preferably 10,000.
It has a degree of polymerization of about 50 to 1,000. Examples of such vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether as a structural unit, polyurethane resins, and various rubber resins. Further, as thermosetting resins or reactive resins, phenol resins, epoxy resins, polyurethane curing resins, urea resins, melamine resins, alkyd resins, acrylic reaction resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, polyester resins And mixtures of isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, and mixtures of polyurethanes and polyisocyanates. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. In addition, a known electron beam-curable resin can be used for each layer. These examples and the production method thereof are described in JP-A-62-256219.
In more detail. The above resins can be used alone or in combination, but preferred are vinyl chloride resins, vinyl chloride vinyl acetate copolymers, vinyl chloride vinyl acetate vinyl alcohol copolymers, and vinyl chloride vinyl acetate maleic anhydride copolymers. At least one
Examples include a combination of a seed and a polyurethane resin, or a combination of these with a polyisocyanate.

As the structure of the polyurethane resin, known materials such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used. For all of the binders shown here, -COO is required to obtain better dispersibility and durability.
_{M, -SO 3 M, -OSO 3} M, -P = O (OM) 2, -
O-P = O (OM) 2, (M is a hydrogen atom or an alkali metal _{salt,), - NR 2, -N} + R 3 (R is a hydrocarbon group), epoxy group, -SH, -CN, It is preferable to use one obtained by introducing at least one or more polar groups selected from the group by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mol / g. In addition to these polar groups, it is preferable to have at least one OH group at each terminal of the polyurethane molecule, that is, a total of two or more OH groups. Since the OH group crosslinks with the polyisocyanate as a curing agent to form a three-dimensional network structure, it is preferable to include a large number of OH groups in the molecule.
In particular, it is preferable that the OH group be located at the molecular terminal because the reactivity with the curing agent is high. Polyurethane has three OH groups at the molecular terminals.
The number is preferably at least 4, more preferably at least 4. In the present invention, when polyurethane is used, the glass transition temperature is usually -50 to 150C, preferably 0C to 100C, particularly preferably 30 to 100C,
The elongation at break is 100-2000%, and the elongation at break is usually 0.
05-10 kg / mm ² (20.49-98 MPa),
The yield point is 0.05 to 10 kg / mm ² (≒ 0.49 to 9
8 MPa) is preferred. By having such physical properties, a coating film having good mechanical properties can be obtained.

Specific examples of these binders used in the present invention include VAGH, VYHH, VMCH and VAG manufactured by Union Carbide as vinyl chloride copolymers.
F, VAGD, VROH, VYES, VYNC, VMC
C, XYHL, XYSG, PKHH, PKHJ, PKH
C, PKFE, manufactured by Nissin Chemical Industries, MPR-TA, MP
R-TA5, MPR-TAL, MPR-TSN, MPR
-TMF, MPR-TS, MPR-TM, MPR-TA
O, 1000W, DX80, DX81, D manufactured by Denki Kagaku
X82, DX83, 100FD, MR-
104, MR-105, MR110, MR100, MR
555, 400X-110A, Nipporan N2301, N230 manufactured by Nippon Polyurethane Co., Ltd. as polyurethane resin
2, N2304, Pandex T-5 manufactured by Dainippon Ink and Chemicals, Inc.
105, T-R3080, T-5201, Burnock D
-400, D-210-80, Crisbon 6109,7
209, Toyobo Byron UR8200, UR830
0, UR-8700, RV530, RV280, polycarbonate polyurethane manufactured by Dainichi Seika, diferamine 4020, 5020, 5100, 5300, 9020,
9022, 7020, Mitsubishi Kasei polyurethane, MX
5004, Sanyo Kasei's polyurethane, Samprene SP
-150, Asahi Kasei's polyurethane, Saran F310,
F210 and the like.

The binder used in the nonmagnetic layer is based on the nonmagnetic inorganic powder, and the binder used in the magnetic layer is based on the ferromagnetic powder in an amount of 5 to 50% by mass, preferably 10 to 3% by mass.
It is used in the range of 0% by mass. It is preferable to use 5 to 30% by mass when using a vinyl chloride resin, 2 to 20% by mass when using a polyurethane resin, and 2 to 20% by mass of polyisocyanate in combination. If head corrosion occurs due to dechlorination of the polyurethane, it is also possible to use only polyurethane or only polyurethane and isocyanate.

When the magnetic recording medium of the present invention is composed of two or more layers, the amount of binder, the amount of vinyl chloride resin, polyurethane resin, polyisocyanate or other resin in the binder, It is, of course, possible to change the molecular weight of each resin to be formed, the amount of polar group, or the physical properties of the resin described above for each layer as necessary. Rather, it should be optimized for each layer. Technology can be applied. For example, when changing the amount of binder in each layer, it is effective to increase the amount of binder in the magnetic layer in order to reduce scratches on the surface of the magnetic layer. Can be made flexible by increasing the amount of binder.

Examples of the polyisocyanate used in the present invention include tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and naphthylene-isocyanate.
1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, isocyanates such as triphenylmethane triisocyanate,
The products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates, and the like are included. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Pharmaceutical Co., Ltd., Takenate D-10
2, Takenate D-110N, Takenate D-200,
Takenate D-202, manufactured by Sumitomo Bayer, Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, and the like. These may be used alone or in combination of two or more using the difference in curing reactivity. Each layer can be used.

[Carbon Black, Abrasive]
Carbon black used in the conductive layer
Heat, rubber thermal, color black, acetylene
A rack or the like can be used. S _BETIs 5 to 500
m^Two/ G, DBP oil absorption is 10-400 ml / 100
g, average particle size is 5 nm to 300 nm, pH is 2-1.
0, water content is 0.1-10%, tap density is 0.1-1
g / cc is preferred. Specifically, WO98 / 353
45.

Carbon black has functions such as preventing the magnetic layer from being charged, reducing the coefficient of friction, imparting light-shielding properties, and improving the film strength, and these differ depending on the carbon black used. Therefore, when the present invention has a multilayer structure, the type of each layer,
Change the amount and combination, particle size, oil absorption, conductivity, pH
It is, of course, possible to use differently according to the purpose based on the above-described various characteristics such as, for example, but rather to optimize each layer.

In the present invention, an abrasive can be used for a magnetic layer or the like. Examples of abrasives include α-alumina, β-alumina having an α conversion of 90% or more, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, and titanium oxide. Known materials having a Mohs hardness of 6 or more, such as silicon dioxide, boron nitride, and the like, are used alone or in combination. In addition, a composite of these abrasives (abrasive whose surface has been treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% or more. The average particle size of these abrasives is preferably from 0.01 to 2 μm, and in particular, in order to enhance the electromagnetic conversion characteristics, it is preferable that the particle size distribution is narrow. In order to improve durability, abrasives with different particle sizes may be combined as needed,
Even with a single abrasive, the same effect can be obtained by widening the particle size distribution. Tap density is 0.3-2g / m
1, the water content is preferably 0.1 to 5%, the pH is preferably ^{2 to} 11, and the S _BET is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but a shape having a part of a corner is preferable because of high abrasiveness. Specific examples include those described in WO 98/35345. Among them, the use of diamond as described above is effective in improving running durability and electromagnetic conversion characteristics. The particle size and amount of the abrasive added to the magnetic layer and the non-magnetic layer should of course be set to optimal values.

[Additives] As the additives used in the magnetic layer and the nonmagnetic layer of the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, and the like are used. Performance can be improved. As a material exhibiting a lubricating effect, a lubricant is used which exerts a remarkable effect on the adhesion which occurs during friction between the surfaces of the substances. There are two types of lubricants. It is not possible to determine whether a lubricant used in a magnetic recording medium is completely fluid lubrication or boundary lubrication, but if it is classified according to the general concept, higher fatty acid esters, liquid paraffin, silicone derivatives, etc. that indicate fluid lubrication and boundary lubrication. It is classified into lubricating long-chain fatty acids, fluorinated surfactants, fluorinated polymers and the like. In a coating type medium, the lubricant is dissolved in the binder or partially exists on the surface of the ferromagnetic powder, and the lubricant migrates to the surface of the magnetic layer. It depends on the compatibility of the lubricant with the lubricant. When the compatibility between the binder and the lubricant is high, the migration speed is low, and when the compatibility is low, the migration speed is high. One way of thinking about the compatibility is to compare the solubility parameters of the two. A non-polar lubricant is effective for fluid lubrication, and a polar lubricant is effective for boundary lubrication.

In the present invention, it is preferable to combine a higher fatty acid ester exhibiting fluid lubrication with different properties and a long-chain fatty acid exhibiting boundary lubrication, more preferably at least three kinds. Solid lubricants can also be used in combination with these. As the solid lubricant, for example, molybdenum disulfide, tungsten graphite disulfide, boron nitride, fluorinated graphite and the like are used.
As long-chain fatty acids that exhibit boundary lubrication, those having 10 to 24 carbon atoms
Monobasic fatty acids (which may contain unsaturated bonds or may be branched), and metal salts thereof (L
i, Na, K, Cu, etc.). Fluorinated surfactants, fluorine-containing silicones as fluorine-containing polymers
And fluorine-containing alcohols, fluorine-containing esters, fluorine-containing alkyl sulfates and alkali metal salts thereof. As higher fatty acid esters showing fluid lubrication, monobasic fatty acids having 10 to 24 carbon atoms (which may contain unsaturated bonds or may be branched) and monovalent or divalent carbon atoms having 2 to 12 carbon atoms, Mono-, di- or tri-fatty acid esters or tri-fatty acid esters comprising any one of trihydric, tetrahydric, pentahydric, and hexahydric alcohols (which may contain an unsaturated bond or may be branched) Examples include fatty acid esters of monoalkyl ethers of oxide polymers. In addition, liquid paraffin, and dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxy polysiloxane (alkoxy has 1 to 4 carbon atoms), and monoalkyl monoalkoxy polysiloxane (alkyl has 1 to 5 carbon atoms) as silicone derivatives 5, silicone oils such as phenylpolysiloxane and fluoroalkylpolysiloxane (alkyl has 1 to 5 carbon atoms), silicones having polar groups, and fatty acid-modified silicones. And fluorine-containing silicones.

As other lubricants, monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols having 12 to 22 carbon atoms (which may contain an unsaturated bond or may be branched),
Alkoxy alcohols having 12 to 22 carbon atoms (which may or may not contain unsaturated bonds), alcohols such as fluorine-containing alcohols, polyolefins such as polyethylene wax and polypropylene, and polyolefins such as ethylene glycol and polyethylene oxide wax Glycols, alkyl phosphates and alkali metal salts thereof, alkyl sulfates and alkali metal salts thereof, polyphenyl ethers, fatty acid amides having 8 to 22 carbon atoms, aliphatic amines having 8 to 22 carbon atoms and the like can be mentioned.

Phenylphosphonic acid such as α-naphthylphosphoric acid, phenylphosphoric acid, diphenylphosphoric acid, p-ethylbenzene and the like exhibiting an antistatic effect, a dispersing effect, a plasticizing effect, etc. Phosphonic acid, phenylphosphinic acid, aminoquinones, various silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof can be used.

The lubricant used in the present invention is particularly preferably a fatty acid or a fatty acid ester.
/ 35345. In addition to these, different lubricants and additives can be used in combination.

Nonionic surfactants such as alkylene oxides, glycerins, glycidols, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums and sulfoniums Surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfate groups, phosphate groups, etc., amino acids, aminosulfonic acids, sulfuric acid or phosphates of amino alcohols , An amphoteric surfactant such as an alkylbedine type or the like can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc.
Not pure, but isomers, unreacted materials,
Impurities such as by-products, decomposition products, and oxides may be included. These impurities are preferably 30% or less, more preferably 10% or less. In the present invention, it is also preferable to use a monoester and a diester in combination as described in WO 98/35345 as the fatty acid ester.

The C of the magnetic recording medium of the present invention, particularly the surface of the magnetic layer of the disk-shaped magnetic recording medium, is measured by Auger electron spectroscopy.
The / Fe peak ratio is preferably from 5 to 100, particularly preferably from 5 to 80. The measurement conditions of Auger electron spectroscopy are as follows. Apparatus: PHI-660 manufactured by Φ Company Measurement conditions: Primary electron beam acceleration voltage 3 KV Sample current 130 nA Magnification 250 times Tilt angle 30 ° Under the above conditions, kinetic energy (Kinetic Energy)
rgy) The range of 130 to 730 eV is integrated three times, the intensity of the KLL peak of carbon and the intensity of the LMM peak of iron are obtained in a differential form, and the ratio of C / Fe is obtained.

On the other hand, the amount of the lubricant contained in each of the upper and lower layers of the magnetic recording medium of the present invention is preferably 5 to 30 parts by mass with respect to 100 parts by mass of the ferromagnetic powder or the nonmagnetic inorganic powder.

Each of these lubricants and surfactants used in the present invention has a different physical action.
The type, amount, and combination ratio of the lubricant that produces a synergistic effect should be optimally determined according to the purpose.
To control leaching to the surface by using fatty acids with different melting points in the non-magnetic layer and magnetic layer, to control leaching to the surface by using esters with different boiling points, melting points and polarities, and to adjust the amount of surfactant It can be considered to improve the stability of coating and to improve the lubricating effect by increasing the amount of the lubricant added in the intermediate layer, and it is needless to say that the present invention is not limited to the examples shown here. Generally, the total amount of the lubricant is selected in the range of 0.1% by mass to 50% by mass, preferably 2% to 25% by mass based on the ferromagnetic powder or the nonmagnetic powder.

All or a part of the additives used in the present invention may be added in any step of producing a magnetic paint and a non-magnetic paint. For example, when the additives are mixed with a magnetic material before the kneading step, There are a case where it is added in a kneading step using a magnetic substance, a binder and a solvent, a case where it is added in a dispersion step, a case where it is added after dispersion, and a case where it is added just before coating.
In some cases, the purpose may be achieved by applying a part or all of the additive simultaneously or sequentially after applying the magnetic layer according to the purpose. Further, depending on the purpose, a lubricant can be applied to the surface of the magnetic layer after calendering or after the slit is completed.

[Layer Structure] In the thickness structure of the magnetic recording medium of the present invention, the support is usually 2 to 100 μm, preferably 2 to 8 μm.
0 μm. The support for the computer tape is:
Thicknesses in the range of 0 to 6.5 μm (preferably 3.0 to 6.0 μm, more preferably 4.0 to 5.5 μm) are used. An undercoat layer for improving adhesion may be provided between the support, preferably a nonmagnetic flexible support, and the nonmagnetic layer or magnetic layer. The thickness of the undercoat layer is 0.01
０．５0.5 μm, preferably 0.02 to 0.5 μm. A back layer may be provided on the support opposite to the side on which the magnetic layer is provided in order to provide effects such as antistatic and curl correction. This thickness is usually 0.1-4 μm,
Preferably it is 0.3 to 2.0 μm. Known undercoat layers and back layers can be used.

The thickness of the lower magnetic layer and the upper magnetic layer of the present invention is optimized by the saturation magnetization of the head used, the head gap length, and the band of the recording signal, but is generally 0.05 to 0.5 μm. And preferably 0.05 to
0.30 μm. The thickness of the lower layer is usually 0.2-5.
0 μm, preferably 0.3 to 3.0 μm, more preferably 1.0 to 2.5 μm. The lower layer exhibits its effect if it is substantially non-magnetic. For example, the lower layer exhibits the effect of the present invention even if it contains impurities or a small amount of magnetic powder intentionally. Needless to say, they can be regarded as identically configured. Substantially nonmagnetic layer has a lower residual magnetic flux density of 10 m.
T or less or coercive force of 100 Oersted ($ 8 kA /
m) or less, preferably showing no residual magnetic flux density and no coercive force. When the lower layer contains a magnetic powder, it is preferable that the lower layer contains less than 1/2 of the total inorganic powder. Further, as a lower layer, a soft magnetic layer containing a soft magnetic powder and a binder may be formed instead of the nonmagnetic layer. The thickness of the soft magnetic layer is the same as that of the lower layer.

In the case of a magnetic recording medium having two magnetic layers, a nonmagnetic layer or a soft magnetic layer may or may not be provided. For example, the magnetic layer farther from the support may be 0.2 to 2 μm.
m, preferably 0.2 to 1.5 μm, and the magnetic layer closer to the support can be 0.8 to 3 μm. In addition, when it has a magnetic layer alone, it is usually 0.2 to 5 μm.
m, preferably 0.5 to 3 μm, more preferably 0.1 μm.
5 to 1.5 μm.

[Back Layer] The magnetic recording medium of the present invention may have a back layer. Although a back layer can be provided on a magnetic disk, a magnetic tape for computer data recording is generally required to have a higher repeatability than a video tape and an audio tape. In order to maintain such high running durability, the back layer preferably contains carbon black and inorganic powder.

The carbon black is preferably used in combination of two kinds having different average particle diameters.
In this case, it is preferable to use a combination of fine-particle carbon black having an average particle diameter of 10 to 20 nm and coarse-particle carbon black having an average particle diameter of 230 to 300 nm. In general, the surface electric resistance of the back layer can be set low and the light transmittance can be set low by adding the fine carbon black particles as described above. Some magnetic recording devices use the light transmittance of the tape and use it as an operation signal. In such a case, the addition of fine carbon black is particularly effective. In addition, fine particle carbon black generally has excellent holding power for a liquid lubricant, and contributes to a reduction in friction coefficient when used in combination with a lubricant. On the other hand, coarse-grained carbon black having an average particle diameter of 230 to 300 nm has a function as a solid lubricant, and also forms minute projections on the surface of the back layer to reduce the contact area, thereby reducing the friction coefficient. Contributes to the reduction of

When commercial products are used as the fine-grained carbon black and the coarse-grained carbon black used in the present invention, specific products include WO 98/35.
345. When two types having different average particle diameters are used in the back layer, fine carbon black of 10 to 20 nm and 23
The content ratio (mass ratio) of the coarse particle carbon black of 0 to 300 nm is preferably in the range of the former: the latter = 98: 2 to 75:25, more preferably 95: 5 to 95: 5.
85:15. The content of carbon black (or the total amount thereof when two types are used) in the back layer is usually 30 to 80 parts by mass with respect to 100 parts by mass of the binder.
It is in the range of parts by mass, preferably in the range of 45 to 65 parts by mass.

It is preferable to use two kinds of inorganic powders having different hardnesses in combination. Specifically, Mohs hardness 3 ~
It is preferable to use a 4.5 soft inorganic powder and a 5 to 9 Mohs hardness hard inorganic powder. Mohs hardness is 3-4.
By adding the soft inorganic powder of No. 5, the friction coefficient can be stabilized by repeated running. Further, with the hardness in this range, the sliding guide pole is not cut off. The average particle diameter of the inorganic powder is 30 to 50 nm.
Is preferably within the range. Mohs hardness is 3-4.5
Examples of the soft inorganic powder include calcium sulfate, calcium carbonate, calcium silicate, barium sulfate, magnesium carbonate, zinc carbonate, and zinc oxide. These can be used alone or in combination of two or more. The content of the soft inorganic powder in the back layer was 1 to 100 parts by mass of carbon black.
It is preferably in the range of 0 to 140 parts by mass, more preferably 35 to 100 parts by mass.

The addition of the hard inorganic powder having a Mohs hardness of 5 to 9 enhances the strength of the back layer and improves running durability. When these inorganic powders are used together with carbon black or the above-mentioned soft inorganic powder, deterioration is small even in repeated sliding, and a strong back layer is obtained. In addition, the addition of the inorganic powder provides an appropriate polishing force, and reduces the adhesion of shavings to the tape guide pole and the like. In particular, when used in combination with a soft inorganic powder, the sliding characteristics with respect to a guide pole having a rough surface are improved, and the friction coefficient of the back layer can be stabilized. The average particle size of the hard inorganic powder is 80 to
It is preferably 250 nm, more preferably in the range of 100 to 210 nm. As the hard inorganic powder having a Mohs hardness of 5 to 9, for example, α-iron oxide, α-alumina,
And chromium oxide (Cr ₂ O ₃ ). These powders may be used alone or in combination. Among these, α-iron oxide or α
-Alumina is preferred. The content of the hard inorganic powder is usually 3 to 30 parts by mass, preferably 3 to 20 parts by mass with respect to 100 parts by mass of the carbon black.

When the soft inorganic powder and the hard inorganic powder are used in combination for the back layer, the difference in hardness between the soft inorganic powder and the hard inorganic powder is 2 or more (more preferably 2.5 or more, particularly 3 or more). As described above, it is preferable to select and use a soft inorganic powder and a hard inorganic powder. In the back layer,
It is preferable that two types of inorganic powders having different Mohs hardnesses each having a specific average particle size and two types of carbon black having different average particle sizes are contained.

The back layer can contain a lubricant. The lubricant can be appropriately selected from the above-mentioned lubricants that can be used for the nonmagnetic layer or the magnetic layer. In the back layer, the lubricant is usually added in the range of 1 to 5 parts by mass with respect to 100 parts by mass of the binder.

[Support] The support used in the present invention includes:
The support is preferably a non-magnetic flexible support, and has a heat shrinkage of 0.5 at 100 ° C. for 30 minutes in each in-plane direction of the support.
%, And the heat shrinkage at 80 ° C. for 30 minutes is preferably 0.5% or less, more preferably 0.2% or less. Further, it is preferable that the heat shrinkage of the support at 100 ° C. for 30 minutes and the heat shrinkage at 80 ° C. for 30 minutes are equal to each other in the in-plane direction of the support by a difference of 10% or less. The support is preferably non-magnetic. Polyesters such as polyethylene terephthalate, polyethylene naphthalate, etc., polyolefins, cellulose triacetate, polycarbonate, aromatic or aliphatic polyamide, polyimide, polyamide imide, polysulfone, polyaramide, polybenzoxazole, etc. Known films can be used. Polyethylene naphthalate,
It is preferable to use a high-strength support such as polyamide. If necessary, a laminated type support as disclosed in JP-A-3-224127 can be used to change the surface roughness of the magnetic surface and the base surface. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance. It is also possible to apply an aluminum or glass substrate as the support of the present invention.

In order to achieve the object of the present invention, the center surface average surface roughness Ra measured with a surface roughness meter TOPO-3D manufactured by WYKO as a support is 4.0 nm or less, preferably 2.0 nm or less. You need to use something. These supports preferably have not only a small center plane average surface roughness but also no coarse projections of 0.5 μm or more.
The surface roughness can be freely controlled by the size and amount of the filler added to the support as needed. Examples of these fillers include C
Examples thereof include oxides and carbonates of a, Si, Ti and the like, and organic powders of an acrylic system and the like. Maximum height of support Rma
x is 1 μm or less, ten-point average roughness Rz is 0.5 μm or less,
Center plane peak height Rp is 0.5 μm or less, center plane valley depth Rv
Is 0.5 μm or less, center plane area ratio Sr is 10% or more, 9
0% or less, and the average wavelength λa is preferably 5 μm or more and 300 μm or less. To obtain the desired electromagnetic conversion characteristics and durability,
The surface protrusion distribution of these supports can be arbitrarily controlled by a filler, and each of the supports having a size of 0.01 to 1 μm can be controlled in a range of 0 to 2000 per 0.1 mm ² .

The F-5 value of the support used in the present invention is preferably 5 to 50 kg / mm ² (≒ 49 to 490 MP
a) The heat shrinkage of the support at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, and 8% or less.
The heat shrinkage at 0 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less. Breaking strength is 5-100
Kg / mm ² (≒ 49-980 MPa), elastic modulus is 10
0 to 2000 kg / mm ² (≒ 0.98 to 19.6 GP
a) is preferred. The coefficient of thermal expansion is from 10 ^-4 to 10 ^-8 / ° C, preferably from 10 ^-5 to 10 ^-6 / ° C. The coefficient of humidity expansion is 10 ^-4 / RH% or less, preferably 10 ^-5 / RH
RH% or less. It is preferable that these thermal characteristics, dimensional characteristics, and mechanical strength characteristics are substantially equal to each other in the in-plane direction of the support with a difference of 10% or less.

[Production Method] The step of producing the magnetic coating material of the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. All the raw materials such as magnetic powder, non-magnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, and solvent used in the present invention may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and supplied in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, a conventionally known manufacturing technique can be used as a part of the steps. In the kneading step, it is preferable to use one having a strong kneading force, such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. When a kneader is used, all or a part of the magnetic powder or the non-magnetic powder and the binder (30% of the total binder) is used.
% Or more) and 15 parts per 100 parts of magnetic powder.
The kneading process is performed in a range of up to 500 parts. Details of these kneading processes are described in JP-A-1-106338 and JP-A-1-106338.
79274. Glass beads can be used to disperse the magnetic layer solution and the non-magnetic layer solution, but zirconia beads, titania beads, and steel beads, which are high-density dispersion media, are preferable. The particle size and the filling rate of these dispersion media are optimized and used. A well-known disperser can be used.

When applying a magnetic recording medium having a multilayer structure in the present invention, it is preferable to use the following method. First, the lower layer is first applied by a gravure coating, roll coating, blade coating, extrusion coating device or the like generally used in the application of a magnetic paint, and the lower layer is wet in a wet state. Showa 60-238
179, a method of applying an upper layer using a support-pressing-type extrusion coating apparatus disclosed in JP-A-2-265672. Second, JP-A-63-88080 and JP-A-2-
No. 17971, Japanese Patent Application Laid-Open No. 2-265672 discloses a method in which upper and lower layers are coated almost simultaneously by one coating head having two built-in coating liquid passage slits. A third method is to apply the upper and lower layers almost simultaneously using an extrusion coating apparatus with a backup roll disclosed in Japanese Patent Application Laid-Open No. 2-174965. Incidentally, in order to prevent the electromagnetic conversion characteristics of the magnetic recording medium from deteriorating due to agglomeration of the magnetic particles, Japanese Patent Application Laid-Open Nos.
It is desirable to apply shear to the coating liquid inside the coating head by a method as disclosed in US Pat. Further, the viscosity of the coating liquid must satisfy the numerical range disclosed in JP-A-3-8471. In order to realize the constitution of the present invention, it is of course possible to use a sequential multi-layer coating in which a lower layer is applied and dried, and then a magnetic layer is provided thereon, and the effect of the present invention is not lost. However, in order to reduce coating defects and improve quality such as dropout, it is preferable to use the above-described simultaneous multilayer coating.

In the case of a disc, a sufficient isotropic orientation may be obtained even without orientation, without using an orientation device. However, a cobalt magnet may be alternately arranged diagonally, or an alternating magnetic field may be applied by a solenoid. It is preferable to use a known random alignment device. Hexagonal ferrite generally tends to be three-dimensional random in the plane and in the vertical direction, but can be two-dimensional random in the plane. In addition, isotropic magnetic characteristics can be imparted in the circumferential direction by using a known method such as a different polarity opposed magnet and making the magnets vertically oriented. In particular, when performing high-density recording, vertical alignment is preferable. Alternatively, circumferential orientation may be performed by using spin coating.

In the case of a magnetic tape, it is oriented in the longitudinal direction using a cobalt magnet or a solenoid. It is preferable that the drying position of the coating film can be controlled by controlling the temperature of the drying air, the flow rate, and the coating speed, and the coating speed is from 20 m / min.
The drying air temperature is preferably 1000 m / min and the temperature of the drying air is 60 ° C. or higher. Also, an appropriate preliminary drying can be performed before entering the magnet zone. The calendering roll is treated with a heat-resistant plastic roll of epoxy, polyimide, polyamide, polyimide amide or the like or a metal roll. In particular, when a double-sided magnetic layer is formed, the treatment is preferably performed with the metal rolls. The processing temperature is preferably at least 50 ° C, more preferably at least 100 ° C. The linear pressure is preferably 200 kg / cm (ｃｍ196 kN / m) or more,
More preferably, 300 kg / cm (ｃｍ294 kN /
m) or more.

[Physical Characteristics] The thickness of the magnetic layer of the magnetic recording medium according to the present invention is preferably 0.01 to 0.5 μm, and the ratio of residual magnetic flux density × magnetic layer thickness is preferably 5 to 200 mT · μm. The coercive force Hc is preferably from 1800 to 5000 Oe (テ ッ ド 144 to 400 kA / m).
3000 Oersted ($ 144-240 kA / m) is more preferred. The distribution of coercive force is preferably narrow, and SF
D (switching field distribution) and SFDr are preferably 0.6 or less.

In the case of a magnetic disk, the squareness ratio is usually 0.55 to 0.67 in the case of two-dimensional random, preferably 0.58 to 0.64, and 0.45 in the case of three-dimensional random.
0.5 to 0.55, preferably 0.6 or more, preferably 0.7 or more in the vertical direction in the case of vertical orientation, and usually 0.7 or more, preferably 0.8 or more when demagnetizing field correction is performed. It is. The orientation ratio is preferably 0.8 or more for both two-dimensional random and three-dimensional random. In the case of two-dimensional randomness, the squareness ratio in the vertical direction, Br in the vertical direction, and Hc in the vertical direction are preferably within 0.1 to 0.5 times the in-plane direction. In the case of a magnetic tape, the squareness ratio is 0.7 or more, preferably 0.8 or more.

The friction of the magnetic recording medium of the present invention with respect to the head
Friction coefficient is in the range of temperature -10 to 40 ° C and humidity 0 to 95%
0.5 or less, preferably 0.3 or less,
The resistive is preferably a magnetic surface 10^Four-10¹²Ohm / s
q, the charge position is preferably -500V to + 500V. Magnetic
The elastic modulus at 0.5% elongation of the layer is preferably in each direction in the plane.
100-2000Kg / mm^Two(¥ 980 to 19600
N / mm^Two), The breaking strength is preferably 10 to 70 kg /
mm^Two(≒ 98-686N / mm^Two), Bullet on magnetic recording media
The modulus is preferably 100 to 1500 Kg / in each direction in the plane.
mm^Two($ 980 to 14700 N / mm^Two), Residual growth
Preferably 0.5% or less, any temperature of 100 ° C or less
Is preferably 1% or less, more preferably
0.5% or less, most preferably 0.1% or less
You. Glass transition temperature of magnetic layer (dynamics measured at 110 Hz)
(Maximum point of loss elastic modulus in dynamic viscoelasticity measurement) is 50 ° C or more and 12
0 ° C or lower is preferable, and that of the lower layer is preferably 0 ° C to 100 ° C.
Good. Loss modulus is 1 × 10 ^Three~ 1 × 10^FourN / cm^Two
It is preferable that the loss tangent is 0.2 or less.
Preferably, there is. Adhesion failure if loss tangent is too large
Is easy to occur. These thermal and mechanical properties are
In each direction, it is preferable to be substantially equal within 10%. Magnetic
The residual solvent contained in the functional layer is preferably 100 mg / m
^TwoOr less, more preferably 10 mg / m^TwoIt is as follows. Paint
The porosity of the lower and upper layers of the cloth layer is preferably 30 volumes.
%, More preferably 20% by volume or less. Sky
The porosity is preferably small to achieve high output,
Depending on the purpose, it may be better to secure a certain value.
For example, empty disk media for which repeated use is important
The larger the porosity, the better the running durability in many cases.

The center surface average surface roughness Ra of the surface of the magnetic layer measured by a surface roughness meter TOPO-3D manufactured by WYKO is preferably 5.0 nm or less, more preferably 4.0 nm or less, and particularly preferably 3.0 nm or less. 5 nm or less. The maximum height Rmax of the magnetic layer is 0.5 μm or less, the ten-point average roughness Rz is 0.3 μm or less, the center plane peak height Rp is 0.3 μm or less,
Center plane valley depth Rv is 0.3 μm or less, center plane area ratio Sr
Is preferably 20% or more and 80% or less, and the average wavelength λa is preferably 5 μm or more and 300 μm or less. The number of surface protrusions of the magnetic layer can be arbitrarily set in the range of 0 to 2,000 having a size of 0.01 to 1 μm, and it is preferable to optimize the electromagnetic conversion characteristics and the friction coefficient. These can be easily controlled by controlling the surface properties by the filler of the support, the particle size and amount of the powder added to the magnetic layer, the roll surface shape of the calendering treatment, and the like. The curl is preferably within ± 3 mm. It is easily presumed that the physical properties of the magnetic recording medium of the present invention can be changed between the lower layer and the upper layer according to the purpose. For example, the elastic modulus of the upper layer is made higher to improve running durability, and at the same time, the elastic modulus of the lower layer is made lower than that of the upper layer to improve the contact of the magnetic recording medium with the head.

[0075]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. In the examples, "parts" indicates "parts by weight". Magnetic liquid formulation 1 Barium ferrite powder (shown in Tables 1 and 2) 100 parts Binder resin Vinyl chloride copolymer 12 parts (contains 1 × 10 ^-4 eq / g of -SO ₃ K group, degree of polymerization: 300) Polyester Polyurethane resin 4 parts (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1, containing -SO ₃ Na group: 1 × 10 ⁻⁴ eq / g) Dispersant for the present invention (Table 2) 1 Part Phenylphosphonic acid 2 parts α-alumina (average particle diameter: 0.15 μm) 2 parts Carbon black (average particle diameter: 30 nm) 5 parts Butyl stearate 2 parts Stearic acid 3 parts Methyl ethyl ketone 125 parts Cyclohexanone 125 parts

Magnetic liquid formulation 2 Barium ferrite powder (shown in Tables 1 and 3) 100 parts Binder resin Vinyl chloride copolymer 15 parts (containing 1 × 10 ⁻⁴ eq / g of —SO ₃ K group, polymerization degree: 300) Polyester polyurethane resin 6 parts (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1, containing -SO ₃ Na group: 1 × 10 ^-4 eq / g) Dispersant for the present invention (Table 3) 2 parts Phenylphosphonic acid 1 part α-alumina (average particle diameter: 0.15 μm) 2 parts Carbon black (average particle diameter: 30 nm) 5 parts Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexa Decyl stearate 2 parts Stearic acid 3 parts Methyl ethyl ketone 125 parts Cyclohexanone 125 parts

Nonmagnetic Liquid Formulation 1 Acicular hematite 80 parts (S _BET : 55 m ² / g, average major axis length: 0.10 μm, average needle ratio: 7, pH: 8.8, aluminum treatment: Al ₂ O ₃ as 1 wt%) carbon black 20 parts (average particle diameter: 17 nm, DBP及油_{amount: 80ml / 100g, S BET:} 240m 2 /g,pH7.5) binder resin of vinyl chloride copolymer 12 parts (- 1 × 10 ⁻⁴ eq / g SO ₃ K group, degree of polymerization: 300) Polyester polyurethane resin 5 parts (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1, —SO ₃ Na group) 1 × 10 ^-4 eq / g) Phenylphosphonic acid 3 parts Butyl stearate 3 parts Stearic acid 3 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 280 parts

Non-magnetic liquid formulation 2 Acicular hematite 80 parts (S _BET : 55 m ² / g, average major axis length: 0.10 μm, average acicular ratio: 7, pH: 8.8, aluminum treatment: Al ₂ O ₃ as 1 wt%) carbon black 20 parts (average particle diameter: 17 nm, DBP及油_{amount: 80ml / 100g, S BET:} 240m 2 /g,pH7.5) binder resin of vinyl chloride copolymer 12 parts (- 1 × 10 ⁻⁴ eq / g SO ₃ K group, degree of polymerization: 300) Polyester polyurethane resin 5 parts (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1, —SO ₃ Na group) : 1 × 10 ^-4 eq / g containing) phenyl phosphonic acid 3 parts butyl stearate 10 parts butoxyethyl stearate 5 parts isohexadecyl stearate 2 parts stearic acid 3 Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 280 parts

The above-mentioned magnetic liquid formulations 1 and 2 and non-magnetic liquid formulations
For each of 1 and 2, powder, polyvinyl chloride, phenylphosphonic acid, and 50% by mass of the prescribed amount of each solvent were kneaded with a kneader, and then a polyurethane resin and the remaining components were added and dispersed with a sand grinder. Isocyanate is added to the resulting dispersion in an amount of 15 parts for the non-magnetic liquid and 14 parts for the magnetic liquid.
0 parts were added, and the mixture was filtered using a filter having an average pore diameter of 1 μm to prepare a coating solution for forming a nonmagnetic layer and a coating solution for forming a magnetic layer.

<Preparation of Tape; Example 1> The obtained coating solution 1 for the lower non-magnetic layer was applied on a polyethylene terephthalate support having a thickness of 7 μm so that the thickness after drying was 1.5 μm. Immediately thereafter, while the lower non-magnetic layer coating layer is still in a wet state, the wet simultaneous simultaneous multi-layer coating is performed so as to have a predetermined magnetic layer thickness by controlling the coating amount of the magnetic liquid formulation 1, While still wet, passed through an orienting device to longitudinally orient. At this time, the oriented magnet was passed through a rare-earth magnet (surface magnetic flux of 500 mT), then passed through a solenoid magnet (magnetic flux density of 500 mT), dried in the solenoid until the orientation did not return, dried the magnetic layer, and wound up. . Thereafter, calendering is performed at a roll temperature of 90 ° C. using a seven-stage calender composed of metal rolls to obtain a web-shaped magnetic recording medium, which is 8 mm thick.
An 8 mm videotape sample was prepared by slitting to width. Examples 2 to 4 and Comparative Examples 1 and 2 The same procedure as in Example 1 was carried out except that the hexagonal ferrite powder of the magnetic layer and / or the dispersant for the present invention were not changed or used in the types shown in Tables 1 and 2. To make a magnetic recording medium.
Using a vibrating sample magnetometer, the magnetic properties of the used hexagonal ferrite powder and the sample were measured. Further, the surface roughness and the electromagnetic conversion characteristics of the sample were measured and are shown in Table 2.

<Evaluation of Tape> The method of measuring the electromagnetic conversion characteristics was as follows. MI for 8mm deck for data recording
G head (head gap 0.2 μm, track width 17
μm, saturation magnetic flux density 1.5T, azimuth angle 20 °) and reproducing MR head (SAL bias, MR element is Fe-N
i, track width 6 μm, gap length 0.2 μm, azimuth angle 20 °). Using a MIG head, the relative speed between the tape and the head was set to 10.2 m / sec, and
The optimum recording current was determined from the input / output characteristics of b (λ = 0.5 μm), a signal was recorded with this current, and reproduced by the MR head.
C / N is from the peak of the reproduction carrier to the degaussing noise, and the resolution bandwidth of the spectrum analyzer is 100
kHz. It was represented by the characteristics of the tape of Comparative Example 1.

The surface roughness was measured on a 250 μm square sample area using an optical interference three-dimensional roughness meter “TOPO-3D” manufactured by WYKO (US, Arizona). In calculating the measured values, corrections such as tilt correction, spherical surface correction, and cylinder correction are performed in accordance with JIS-B601, and the center plane average roughness Ra is calculated.
Was taken as the value of the surface roughness.

The magnetic properties were measured using a vibrating sample magnetometer (manufactured by Toei Kogyo) and an external magnetic field of 10 kOe (ｋ800 kA / m).
It was measured in parallel with the orientation direction at [Oe = {1 / (4π)} kA / m].

<Preparation of Flexible Disk; Fifth Embodiment
> The obtained coating solution of Formulation 2 for the lower non-magnetic layer was
m on a polyethylene terephthalate support having a thickness of 1.5 μm after drying, and immediately thereafter, while the coating layer for the lower non-magnetic layer is still in a wet state, Wet simultaneous multi-layer coating is performed using a coating solution for the same, and while both layers are still in a wet state, they are passed through a same-pole opposed rare earth magnet having a central magnetic field strength of 398 kA / m,
After orientation in the longitudinal direction, a magnetic field strength of 24 at a frequency of 50 Hz
The sample was passed through two AC magnetic field generators having a magnetic field intensity of 12 kA / m at a frequency of 50 Hz and a random orientation treatment. The other support was similarly coated, oriented and dried, and then treated with a seven-stage calendar at a temperature of 90 ° C. and a linear pressure of 300 kg / cm (294 kN / m). A 3.5-inch blank was punched out, subjected to a thermo-treatment (70 ° C., 24 hours) to accelerate the curing treatment of the coating layer, burnished with a polishing tape, and subjected to a post-treatment of shaving surface projections. A 3.5 inch disk was punched out and subjected to a surface polishing treatment to obtain a disk medium. Examples 6 to 8, Comparative Example 3 The same procedure as in Example 1 was carried out except that the hexagonal ferrite powder of the magnetic layer and / or the dispersant for the present invention were not changed or used in the types shown in Tables 1 and 3. A recording medium was created.
The performance of each of the magnetic disks prepared above was evaluated by the following measurement methods, and the results are shown in Table 3. Measurement method (1) Magnetic properties (Hc, orientation ratio, σs): Hm10KOe [Oe, using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.)
= {1 / (4π)} kA / m]. The orientation ratio is determined by applying a magnetic field in the horizontal direction of the measurement sample, rotating the magnetic field from 0 ° to 360 ° every 10 ° to obtain a squareness ratio,
The value obtained by dividing the minimum value of the squareness ratio by the maximum value was calculated and defined as the orientation ratio. (2) Center surface average surface roughness Ra: same as tape. (3) Electromagnetic conversion characteristics Output: The reproduction output was measured using a disk tester manufactured by Kokusai Denshi Kogyo (former Tokyo Engineering) and a SK606B.
After recording with a recording wavelength of 90 KFCI at a radius of 24.6 mm using a metal in-gap head having a gap length of 0.3 μm using a mold evaluation device, the reproduction output of the head amplifier was measured with an oscilloscope type 7633 manufactured by Tektronix. S / N: After the disk whose reproduction output was measured was subjected to DC erasing, the reproduction output (noise) was measured with an advantest TR4171 spectroanalyzer. S / N: -20 log (noise / reproduction output), and S / N of Comparative Example 3 was shown as a relative value with 0 dB. (4) Durability: Floppy (registered trademark) disk drive (ZIP100 manufactured by Iomega Corporation in the United States: rotation number 296)
The head was fixed at a position with a radius of 38 mm using 8 rpm). Thereafter, the vehicle was run in a thermocycle environment in which the following flow was defined as one cycle. The time when the surface of the sample was visually scratched was regarded as NG. The durability time of Example 5 was set to 100%. (Thermocycle flow) 25 ° C, 50% RH 1 hour → (Temperature rise 2 hours) → 60
℃, 20% RH 7 hours → (Temperature drop 2 hours) → 25 ° C,
50% RH 1 hour → (Temperature drop 2 hours) → 5 ° C, 10%
RH 7 hours → (heating 2 hours) → <Repeat this>

[0085]

[Table 1]

Each value of the plate diameter and the plate ratio in Table 1 is 300 kV.
Was obtained by taking a 100,000-fold photograph with a transmission electron microscope photograph of No. 1, and tracing the electron microscope photograph with an image analyzer (IBASS-1 manufactured by Carl Zeiss) to read 500 particles.

[0087]

[Table 2]

[0088]

[Table 3]

[0089]

As is clear from the above examples, treatment with the dispersant of the present invention improves the dispersibility of ferromagnetic powders such as hexagonal ferrite powder, and is smooth and has a good orientation ratio. , A magnetic recording medium that is excellent in S / N and excellent in running durability.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01F 1/11 H01F 1/11 MF Term (Reference) 4J037 AA04 AA06 AA14 CB09 CB22 CC00 CC24 CC25 DD04 DD05 DD24 EE02 FF11 FF15 4J038 CA021 CB021 CC021 CD021 CD081 CE021 CE071 CF021 CG031 CG071 CG141 CG161 DA011 DA131 DA141 DB001 DD001 DG001 DH001 DL001 HA066 HA216 KA08 KA12 KA14 NA22 PB11 PC08 5D006 BA06 BA07 BA08 BA06 BA08

Claims (1)

[Claims] 1. A magnetic recording medium comprising, on at least one surface of a support, a constituent layer containing at least a magnetic layer containing ferromagnetic powder, said magnetic layer having a molecular weight of 1000 to 8
A magnetic recording medium comprising a ferromagnetic powder treated with at least one kind of anionic surfactant selected from 0000 carboxylic acid amine salts and phosphoric acid ester amine salts.