JP2566126B2 - Magnetic recording media - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a high density coating type magnetic recording medium.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, computer tapes, disks and the like. The density of magnetic recording media is increasing year by year,
Recording methods from analog to digital are being considered. To meet this demand for higher density, magnetic recording media using a metal thin film for the magnetic layer have been proposed. However, magnetic powder is dispersed in a binder in terms of productivity and practical reliability such as corrosion. A so-called coating type magnetic recording medium coated on a support is excellent. However, since the coating type medium has a low filling degree of the magnetic substance with respect to the metal thin film, the electromagnetic conversion characteristics are inferior. Various methods have been proposed for improving the electromagnetic conversion characteristics of the coating medium, such as improving the magnetic characteristics of the magnetic substance and smoothing the surface, but they are not sufficient for increasing the density.

In order to improve the performance of digital media, it is known to make the magnetic layer thinner. However, although effective in principle, there is a production problem in thinning the coating type medium. This is because coating defects such as pinholes and streaks tend to occur due to the thinning of the magnetic layer, and a sufficient yield cannot be obtained. In addition, since the molding effect of the calender becomes small, the surface properties are poor and the electromagnetic conversion characteristics are not good. In order to solve such a problem, it is considered that calendering is performed after simultaneously forming a thin magnetic layer of 1 μm or less on a non-magnetic layer having a certain thickness. As a means that can be used for such purposes, a non-magnetic granular abrasive,
Alternatively, it has been proposed to include a filler in the subbing layer. (JP-A-62-222427, JP-A-2-257)
However, as a problem of these techniques, when the magnetic layer and the non-magnetic layer are simultaneously coated and the magnetic material of the upper layer is oriented, the mixing at the interface between the upper and lower layers is caused by the rotational motion of the magnetic material due to the magnetic field. Occurs, and not only is it impossible to obtain sufficient surface properties,
Since the orientation is not performed sufficiently, sufficient electromagnetic conversion characteristics cannot be obtained.

Therefore, the present applicants tried to improve the orientation of the upper magnetic particles by forming the non-magnetic lower layer with non-magnetic scale-like particles. Regarding the provision of the nonmagnetic scale-like particle layer, a conductive intermediate layer using graphite has been proposed. (JP-A-55-55438)
However, with such a substance, although the orientation is improved, graphite itself does not have a reinforcing effect on the film, so that the durability is insufficient. For this problem, it has been proposed to mix an inorganic powder having a Mohs hardness of 5 or more. (JP-A-6
The present applicants have also tried to improve the orientation of the magnetic particles in the upper layer by forming the non-magnetic lower layer with non-magnetic acicular particles. Regarding the provision of the non-magnetic acicular particle layer, a reinforcing layer using acicular oxalate has been proposed.
(Japanese Patent Publication No. 58-51327). Although these proposals improve orientation and ensure durability, scale-like particles are prone to stacking at the stage of actually manufacturing the medium, and substances such as oxalate have poor dispersibility in the binder. Therefore, it was found that the smoothness of the magnetic surface was impaired.

[0005]

SUMMARY OF THE INVENTION A first object of the present invention is to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and excellent productivity. The second object of the present invention is to
It is an object of the present invention to provide a magnetic recording medium having a high RF output, excellent running durability, a small dropout, and a low block error rate (BER).

[0006]

That is, the above objects of the present invention can be achieved by the following inventions. In a magnetic recording medium in which a lower non-magnetic layer containing at least a non-magnetic powder and a binder is provided on a non-magnetic support, and an upper magnetic layer containing a ferromagnetic powder and a binder is provided thereon , the upper magnetic layer is dried. Magnetic recording having a thickness of 1 μm or less and a ratio r ₁ / r ₂ of the longest axial length r ₁ and the shortest axial length r ₂ of the nonmagnetic powder is 2.5 or more and less than 20. Medium. In a magnetic recording medium in which a lower non-magnetic layer containing at least non-magnetic powder and a binder is provided on a non-magnetic support, and an upper magnetic layer containing a ferromagnetic powder and a binder is provided thereon , the non-magnetic powder is a needle. The magnetic layer has a shape ratio of 2.5 or more and less than 20, a dry thickness of the upper magnetic layer of 1 μm or less, and an average diameter of the longest axial length of the ferromagnetic powder is 0.3 μm or less. Magnetic recording medium. Magnetic recording medium of the present invention
In the body, the preferred embodiments are as follows.
It (1) Mixed area between the lower non-magnetic layer and the upper magnetic layer
The magnetic recording medium according to the above 1 or 2, characterized in that there is no zone.
body. (2) The lower non-magnetic layer has the longest axial length of 3 μm or less
The magnetic properties of the above, characterized in that they include a non-magnetic powder.
recoding media. (3) The lower non-magnetic layer is made of Al ₂ O ₃ (α, γ), Cr
₂ O ₃ , αFe ₂ O ₃ , goethite, SiO ₂ , ZrO
Non-magnetism of ₂ , CeO ₂ , TiO ₂ (rutile, anatase)
Before containing at least one kind of powder
And a magnetic recording medium. (4) The ferromagnetic powder is mainly composed of Fe, Ni or Co
Before the needle-shaped ferromagnetic alloy powder
And a magnetic recording medium. (5) The magnetic recording medium is a recording tape or video tape.
Digital for tapes, computer tapes, discs, etc.
And a magnetic recording medium as described above.
body.

[0007] The present invention has been coated cloth upper magnetic layer on the lower non-magnetic layer, so-called wet - on - in which tried to improve the magnetic recording medium having a plurality of layers by wet coating. That is, in wet-on-wet coating, since the interface is soft, it is easily affected by other layers. For example, when oriented after coating, the ferromagnetic powder in the upper magnetic layer rotates, but the rotational movement causes the lower non-magnetic layer to move. Are affected by this, and mixing occurs at the interface. In the present invention, the lower non-magnetic layer is modified so that mixing does not occur at the interface. Therefore, this is the first time that a magnetic recording medium having no mixed region is obtained.

One invention for preventing a mixed region from occurring at the interface between the lower non-magnetic layer and the upper magnetic layer is to use acicular non-magnetic powder for the lower non-magnetic layer.
Compared with conventional granular non-magnetic powder, if needle-shaped non-magnetic powder is aligned and present, a strong coating film is formed even in an undried state,
Even if the ferromagnetic powder in the upper magnetic layer rotates, no mixing occurs at the interface.

As described above, the basic idea of the present invention is to provide a dispersion liquid in which a non-magnetic powder is dispersed in a binder as a coating liquid for the lower non-magnetic layer and a magnetic coating material for an upper magnetic layer in which a ferromagnetic powder is dispersed in the binder. use, by coating a lower layer non-magnetic layer coating liquid on a nonmagnetic support, which may be produced under conditions that multilayer coating magnetic paint for the upper magnetic layer thereon, particularly when the The upper magnetic layer can be made thin, for example, 1 μm or less with good yield.

In the present invention, the dry thickness of the upper magnetic layer is 1 μm.
A magnetic recording medium of m or less and having no mixed region between the lower non-magnetic layer and the upper magnetic layer is provided. Here, there is no mixed region between the lower non-magnetic layer and the upper magnetic layer, specifically, at the interface between the lower non-magnetic layer and the upper magnetic layer, the upper magnetic layer component and the lower non-magnetic layer component It means that there is no region where and are mixed, specifically, the ferromagnetic powder of the upper magnetic layer component and the nonmagnetic powder of the lower nonmagnetic layer component are not mixed at the interface. Therefore, the orientation of the ferromagnetic powder and the non-magnetic powder near the interface is less disturbed, and the surface property is improved and the orientation is improved.
(Block error rate), dropout and the like are effectively reduced. Further, by making the magnetic layer 1 μm or less, a magnetic recording medium suitable for short-wavelength recording can be stably obtained.

The specific method for producing the magnetic recording medium of the present invention is not particularly limited, but the means used in the inventions of to can be applied. That is, it can be produced by variously selecting the shape, size, etc. of the ferromagnetic powder and / or non-magnetic powder, selecting the type of binder, and the like. The feature of the present invention is that the dry thickness of the upper magnetic layer is 1 μm or less, and r ₁ / r ₂ is added to the lower non-magnetic layer.
(That is, the axial ratio) contains a non-magnetic powder having a prescribed value of 2.5 or more and less than 20. By defining the shape in this way, the non-magnetic powder is oriented in the longitudinal direction by the flow orientation at the time of coating, so that the rotational motion due to the magnetic field orientation of the upper magnetic layer to the ferromagnetic powder can be suppressed, and as a result, In addition, disturbance of the interface between the lower nonmagnetic layer and the upper magnetic layer can be suppressed, and the orientation of the ferromagnetic powder can be improved.

Here, r ₁ is the longest axial length and r ₂ is the shortest axial length, but the specific shape of the nonmagnetic powder is basically arbitrary, and may be needle-like or plate-like. Measured with an electron microscope. In addition, the axis does not mean a symmetric axis in a strict sense. In the case of needles, r ₁ is usually
That is, the so-called major axis length is in the range of 3 μm or less, preferably 1.5 μm or less (that is, r ₂ is uniaxial length or thickness), and the preferred axial ratio is 5 to 20. In the case of scale-like or plate-like, r ₁ refers to what is usually called a plate diameter, and its value is in the range of 0.01 to 3 μm, preferably 0.05 to 1.5 μm (that is, r ₂ Is a plate thickness), and a preferable plate ratio is 5 to 20.

The physical properties, shape, and size of the ferromagnetic powder in the upper magnetic layer are not particularly limited, but preferably, the acicular ferromagnetic powder and the plate-like ferromagnetic powder having the longest axial length having an average diameter of 0.3 μm or less. As a specific example, the acicular ferromagnetic powder is γ-Fe.
₂ O ₃ , Fe ₃ O ₄ , Co-γ-Fe ₂ O ₃ , Cr
O _2, Fe-Ni alloy, alloy ferromagnetic powder such as an Fe-Ni-Co alloy, plate-like ferromagnetic powder of barium ferrite, hexagonal ferrite such as strontium ferrite, and C
O alloy powder, particularly preferably an alloy containing Fe as a main component or hexagonal ferrite.

A feature of the present invention is that the dry thickness of the upper magnetic layer is 1 μm or less, and the lower nonmagnetic layer contains nonmagnetic powder having an acicular ratio of 2.5 or more, and the upper magnetic layer is magnetic. The layer contains a ferromagnetic powder having an average particle size of 0.3 μm or less, and is different from the above in that the shape of the non-magnetic powder in the lower non-magnetic layer is limited to a needle shape, and The average diameter of the longest axial length of ferromagnetic powder is 0.3 μm
It is limited to the following points, and it is possible to improve the filling degree and the output by making the particles fine. Here, the acicular ratio has the same meaning as the case where the shape of the non-magnetic powder in the case of being defined as r ₁ / r ₂ is limited to the acicular shape, but R ₁ / R _{2 is} used to distinguish it from the above. Is written. Here, R ₁ is the longest axial length, and R ₂ is the shortest axial length. R ₁ is in the range of 3 μm or less, preferably 1.5 μm or less, and the axial ratio is preferably 5 or more.

The acicular non-magnetic powder is preferably a non-magnetic metal (Cu, Cr, Ag, Al, Ti, W, etc.) or oxide, for example, Al ₂ O ₃ (α, γ), Cr ₂
O ₃ , α ferrite, goethite, SiO ₂ (including glass), ZrO ₂ , CeO ₂ , TiO ₂ (rutile, anatase) and the like can be mentioned. The thickness of the lower non-magnetic layer is preferably 0.5 μm or more, and particularly preferably 0.5 to 5.0 μm.
Although lower nonmagnetic layer is not easily calender moldability is obtained sufficient electromagnetic characteristics deteriorate with reduced thin and productivity than 0.5 [mu] m, practical in some applications even less
It can be used. The shape of the ferromagnetic powder is arbitrary, and may be, for example, a needle shape or a plate shape. The definition of the average particle size in this case is also the same as the definition of the axial ratio of the invention: r ₁ / r ₂ and it has the same meaning as r ₁ except for the difference in the material. Hereinafter, the axial ratio of the ferromagnetic powder is defined as φ ₁ / φ ₂ in accordance with r ₁ / r _2.
Write ₂ . If the ferromagnetic powder is acicular, phi ₁ is, 0.3 micron
m, preferably 0.25 μm or less, and φ ₁ / φ ₂ is 2.5 or more. In the case of a plate, φ ₁ / φ ₂
It is 2.5 or more, phi ₁ is 0.01 to 0.3 [mu] m, preferably in the range of 0.05 to 0.2 [mu] m.

When a resin containing an epoxy group is used as a binder used to disperse and bond these non-magnetic powders, the resin has a molecular weight of 30,000 or more.
The epoxy group is contained in an amount of 1 × 10 ^{−5 to} 20 × 10 ⁻⁴ eq / g, preferably 4 × 10 ^{−5 to} 16 × 10 ⁻⁴ eq / g.
Known techniques can be applied to the method of introducing the epoxy group. For example, it is possible to copolymerize a vinyl monomer having a glycidyl group with another monomer. In addition, the following description of the epoxy group-containing vinyl chloride resin can be applied to the method for producing the epoxy group-containing resin having a molecular weight of 30,000 or more. Further, in the present invention, the compounding ratio of the abrasive having a Mohs hardness of 5 or more to the lower non-magnetic layer is non-magnetic powder /
It is preferable to mix them so that the polishing agent is 95/5 to 60/40, which enhances the mechanical strength of the lower non-magnetic layer, and thus the magnetic recording medium, and prevents so-called powder drop, thereby increasing the BER. (Block error rate), dropout can be reduced and durability can be improved.

As an abrasive having a Mohs hardness of 5 or more, α-A
l ₂ O ₃ , Cr ₂ O ₃ , α-Fe ₂ O ₃ , ZrO ₂ , T
Examples thereof include iO ₂ , TiC, SiO ₂ , SiC, CeO ₂ . The particle size of the abrasive is preferably equal to or less than the thickness of the applied undercoat, and is about 0.1 to 5 μm, more preferably 0.1 to 2 μm. The shape of the particles may be either granular or acicular. The mixing ratio of the scaly nonmagnetic powder and the abrasive is 95/5 to 60/40. When the amount of the abrasive is small, sufficient durability cannot be obtained, and when the amount is too large, the effect of orienting the magnetic particles on the upper layer of the scale-like particles is impaired.

General items that can be selected in accordance with the present invention are listed below. In the present invention, the upper magnetic layer and the lower non-magnetic layer are usually each composed of a single layer, but each of them may have a single layer structure or a multi-layer structure as long as the above composition and prescribed conditions are satisfied. Hereinafter, the upper magnetic layer and the lower non-magnetic layer may be simply referred to as the upper layer and the lower layer. The above non-magnetic powder does not necessarily have to be 100% pure, and the surface may be treated with other compounds depending on the purpose. At that time, the purity is 70
If it is more than%, the effect is not reduced. For example, when using titanium oxide, it is generally used to treat the surface with alumina. The ignition loss is preferably 20% or less. The content of ferromagnetic powder in the upper layer is 7
0% or more is preferable. If the ferromagnetic powder content is less than 70%, the degree of filling is reduced, and the electromagnetic conversion characteristics are degraded. The ferromagnetic powder content here represents (% by weight) of (ferromagnetic powder) / (contained in the magnetic layer such as ferromagnetic powder + binder + additive).

The magnetic characteristic of the magnetic recording medium of the present invention is the magnetic field 5
When measured by KOe, the squareness ratio of each layer is 0.7 or more, preferably 0.8 or more, more preferably 0.9 or more. Σ _S of the ferromagnetic powder used in the present invention is 50e
mu / g or more, preferably 70 emu / g or more,
In the case of fine metal powder, 100 emu / g or more is preferable.
The water content is preferably 0.01 to 2%. It is preferable to optimize the water content of the ferromagnetic powder depending on the type of binder. When cobalt-modified iron oxide is used as the ferromagnetic powder of the present invention, the ratio of divalent iron to trivalent iron is preferably 0 to 33.3%, more preferably 5
-10%. The amount of cobalt atom to iron atom is 0 to 15%, preferably 3 to 8%.

The pH of the ferromagnetic powder is preferably optimized by the combination with the binder used. The range is 4-1
It is 2. The ferromagnetic powder may be subjected to surface treatment with Al, Si, P, or an oxide thereof. The amount is 0.1 to 10% based on the ferromagnetic powder. The ferromagnetic powder in the upper layer may contain soluble inorganic ions such as Na, Ca, Fe, Ni, and Sr, but if it is 500 ppm or less, it has no particular effect. Γ-FeOx as ferromagnetic powder
(X = 1.33 to 1.5), Co-modified γ-FeOx (x
= 1.33 to 1.5), and known ferromagnetic powders such as a ferromagnetic alloy fine powder containing Fe, Ni or Co as a main component (75% or more) can be used. These ferromagnetic powders include Al, Si, S, Sc, Ti, V, Cr,
Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, T
e, Ba, Ta, W, Re, Au, Hg, Pb, Bi,
La, Ce, Pr, Nd, P, Co, Mn, Zn, N
It may contain atoms such as i, Sr, and B.

These ferromagnetic fine powders may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent, etc., which will be described later, before the dispersion. Of the above-mentioned ferromagnetic powder, the ferromagnetic alloy fine powder may contain a small amount of hydroxide or oxide. What was obtained by the well-known manufacturing method of a ferromagnetic alloy fine powder can be used, and the following method can be mentioned. Method of reducing with complex organic acid salt (mainly oxalate) and reducing gas such as hydrogen,
A method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe-Co particles, a method of thermally decomposing a metal carbonyl compound, an aqueous solution of a ferromagnetic metal, sodium borohydride, hypophosphite or A method of adding a reducing agent such as hydrazine for reduction, a method of evaporating a metal in a low pressure inert gas to obtain a fine powder, and the like. The ferromagnetic alloy powder thus obtained is subjected to a known gradual oxidation treatment, that is, a method of immersing it in an organic solvent and then drying it. Any of the method of forming the oxide film on the surface by adjusting the partial pressure of oxygen gas and the inert gas without using an organic solvent can be used. The ferromagnetic powder used in the present invention preferably has a small number of vacancies, and the value is preferably 20% by volume or less, more preferably 5% by volume or less. The ferromagnetic powder used in the present invention can be manufactured according to a known method.

As the binder used in the lower non-magnetic layer and the upper magnetic layer of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used.
In the present invention, an epoxy group-containing resin can be used, and these epoxy group-containing resins can be used in combination. The glass transition temperature of the thermoplastic resin is −
100-150 ° C, number average molecular weight of 1000-2000
00, preferably 10,000 to 100,000, and the degree of polymerization is about 50 to 1,000. Such examples include 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 constituent unit, polyurethane resins, and various rubber resins.

Further, as the thermosetting resin or the reactive resin, a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reactive resin, a formaldehyde resin, a silicone resin, an epoxy-polyamide resin. , A mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, a mixture of polyurethane and polyisocyanate, and the like. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten.

It is also possible to use a known electron beam curable resin. These examples and the manufacturing method thereof are described in detail in JP-A-62-256219. The above resins can be used alone or in combination, but preferred are vinyl chloride resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol resin,
Vinyl chloride vinyl acetate maleic anhydride copolymer, a combination of at least one selected from the above and a polyurethane resin,
Alternatively, a combination of these with polyisocyanate can be used. Known polyurethane resin structures 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 listed here, in order to obtain better dispersibility and durability, C
OOM, SO ₃ M, OSO ₃ M, P = O (OM) ₂ , O
At least one selected from —P═O (OM) ₂ , (wherein M is a hydrogen atom or an alkali metal base), OH, NR ² , N ⁺ R ³ , and R is a hydrocarbon group), SH, CN, and the like. It is preferable to use one having one or more polar groups introduced by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 1
It is 0 ^-6 mol / g. As a vinyl chloride-based copolymer,
Preferably, an epoxy group-containing vinyl chloride copolymer can be mentioned a repeating unit having a vinyl chloride repeating unit, an epoxy group, -SO ₃ M, optionally, -OSO ₃ M,
Examples thereof include vinyl chloride-based copolymers containing a repeating unit having a polar group such as —COOM and —PO (OM) ₂ (wherein M is a hydrogen atom or an alkali metal base). In combination with a repeating unit having an epoxy group, -S
Epoxy group-containing vinyl chloride-based copolymers containing repeating units having O ₃ Na are preferred.

The content of the repeating unit having a polar group in the copolymer is usually 0.01 to 5.0 mol% (preferably 0.5 to 3.0 mol%). The content of the repeating unit having an epoxy group in the copolymer is usually in the range of 1.0 to 30 mol% (preferably 1 to 20 mol%). And the vinyl chloride polymer is
Usually 0.01 to 1 mol of vinyl chloride repeating unit
It contains a repeating unit having 0.5 mol (preferably 0.01 to 0.3 mol) of an epoxy group. Hydrochloric acid from a vinyl chloride copolymer when the content of the repeating unit having an epoxy group is lower than 1 mol% or when the amount of the repeating unit having an epoxy group is less than 0.01 mol per 1 mol of the vinyl chloride repeating unit. It may not be possible to effectively prevent the release of gas, while if it is higher than 30 mol% or the amount of the repeating unit having an epoxy group is more than 0.5 mol based on 1 mol of the vinyl chloride repeating unit, vinyl chloride is not present. The hardness of the copolymer may decrease, and when it is used, the running durability of the magnetic layer may decrease.

Further, if the content of the repeating unit having a specific polar group is less than 0.01 mol%, the dispersibility of the ferromagnetic powder may be insufficient, and if it is more than 5.0 mol%, the co-weight will increase. The coalescence becomes hygroscopic and the weather resistance may deteriorate. Usually, the number average molecular weight of such a vinyl chloride copolymer is in the range of 15,000 to 60,000. Such a vinyl chloride copolymer having an epoxy group and a specific polar group can be produced, for example, as follows.

For example, epoxy group and --SO as polar group.
_In the case of producing a vinyl chloride-based copolymer in which ₃ N is introduced, a reactive double bond and -SO ₃ as a polar group are used.
Sodium 2- (meth) acrylamido-2-methylpropanesulfonate having Na (a monomer having a reactive double bond and a polar group) and diglycidyl acrylate are mixed at low temperature, and this is mixed with vinyl chloride. 1 under pressure
It can be produced by polymerizing at a temperature of 00 ° C. or lower. Examples of the monomer having a reactive double bond and a polar group used for introducing the polar group by the above method include, in addition to the above-mentioned sodium 2- (meth) acrylamido-2-methylpropanesulfonate. 2- (meth) acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid and its sodium or potassium salt, ethyl (meth) acrylic acid-2-sulfonate and sodium or potassium salt, (anhydrous) maleic acid and (meth) Acrylic acid and (meth) acrylic acid-2-phosphate ester can be mentioned.

For introducing the epoxy group, glycidyl (meth) acrylate is generally used as a monomer having a reactive double bond and an epoxy group. In addition, in addition to the above-mentioned production method, for example, a vinyl chloride copolymer having polyfunctional OH is produced by a polymerization reaction of vinyl chloride and vinyl alcohol, and the copolymer and a polar solvent described below are produced. A method of reacting a compound containing a group and a chlorine atom (dehydrochlorination reaction) to introduce a polar group into the copolymer can be used. ClCH ₂ CH ₂ SO ₃ M, ClCH ₂ CH ₂ OSO ₃
M, ClCH ₂ COOM, ClCH ₂ PO (OM) ₂

Epichlorohydrin is usually used to introduce an epoxy group utilizing this dehydrochlorination reaction. The vinyl chloride-based copolymer may contain other monomers. Examples of other monomers include vinyl ether (eg, methyl vinyl ether, isobutyl vinyl ether, lauryl vinyl ether), α-monoolefin (eg, ethylene, propylene), acrylate ester (eg, methyl (meth) acrylate, hydroxy). (Meth) acrylic acid ester containing a functional group such as ethyl (meth) acrylate, unsaturated nitrile (eg, (meth) acrylonitrile), aromatic vinyl (eg, styrene, α-)
Methyl styrene), vinyl ester (eg vinyl acetate,
Vinyl propionate).

Specific examples of these binders used in the present invention are Union Carbide: VAGH, V
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Industries: MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, manufactured by Denki Kagaku: 1000W, DX80,
DX81, DX82, DX83, manufactured by Zeon Corporation: MR
110, MR100, 400X110A, manufactured by Nippon Polyurethane Co., Ltd .: Nipporan N2301, N2302, N23
04, manufactured by Dainippon Ink Co., Ltd .: Pandex T-5105,
T-R3080, T-5201, Burnock D-40
0, D-210-80, Crisbon 6109, 720
9. Toyobo: Byron UR8200, UR830
0, RV530, RV280, manufactured by Dainichi Seika Co., Ltd .: Daifu eramine 4020, 5020, 5100, 5300, 90
20,9022,7020, Mitsubishi Kasei: MX500
4. Sanyo Kasei Co., Ltd .: Samprene SP-150; Asahi Kasei Co., Ltd .: Saran F310, F210.

The binder used in the present invention is used in the upper layer in an amount of 5 to 50% by weight, preferably 10 to 35% by weight, based on the ferromagnetic powder. When vinyl chloride resin is used, 5 to 30% by weight, polyurethane resin is used in an amount of 2 to 20% by weight, and polyisocyanate is preferably used in a range of 2 to 20% by weight. The binder used in the present invention is used in the lower layer in a total amount of 5 to 50% by weight, preferably 10 to 35% by weight, based on the non-magnetic powder. When a vinyl chloride resin is used, it is 3 to
30% by weight, 3 to 30 when using polyurethane resin
It is preferable to use these in combination in the range of 0 to 20% by weight of polyisocyanate. Further, in the present invention, when an epoxy group-containing resin having a molecular weight of 30,000 or more is used, the resin can be used in an amount of 3 to 30% by weight based on the nonmagnetic powder, and a resin other than the epoxy group containing resin is nonmagnetic It can be used in an amount of 3 to 30% by weight based on the powder, 3 to 30% by weight when a polyurethane resin is used, and polyisocyanate is 0
Although the epoxy group can be used in an amount of 4 × 10 ^{−5 to} 16 × 10 ^{−4 based on the} total weight of the binder (including the curing agent).
It is preferable to be contained in the range of eq / g.

In the present invention, when a polyurethane resin is used, the glass transition temperature is -50 to 100 ° C., the breaking elongation is 100 to 2000%, and the breaking stress is 0.05 to 10 kg.
/ Cm ² , and the yield point is preferably 0.05 to 10 Kg / cm ² . Examples of the polyisocyanate used in the present invention include tolylene diisocyanate, 4-4′-diphenylmethane diisocyanate, hexamethylene diisocyanate,
Isocyanates such as xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidiisocyanate, isophorone diisocyanate and triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, and condensation of isocyanates The polyisocyanate produced by the above can be used. Commercially available trade names of these isocyanates include those manufactured by Nippon Polyurethane Co .: Coronate L, Coronate HL, Coronate 203
0, Coronate 2031, Millionate MR, Millionate MTL, Takeda Yakuhin: Takenate D-102, Takenate D-110N, Takenate D-200, Takenate D-202, Sumitomo Bayer: Death Module L, Death Module IL, Death There are a module N, a death module HL, and the like, and these can be used alone or in a combination of two or more by utilizing the difference in curing reactivity, for both the lower layer and the upper layer.

In the present invention, optional additives such as antistatic agents such as carbon black, abrasives, colorants, lubricants, dispersants and the like can be used in the upper layer and / or the lower layer, if necessary. As the carbon black, furnaces for rubber, thermal for rubber, black for color, acetylene black, etc. can be used. The carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be graphitized on a part of the surface. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint. These carbon blacks can be used alone or in combination.

The carbon black has the functions of preventing the upper magnetic layer from being charged, reducing the friction coefficient, imparting the light-shielding property, improving the film strength, etc. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention can be used in different types, amounts, and combinations depending on the purpose based on various characteristics such as particle size, oil absorption, electric conductivity, and pH shown above. Of course it is possible. 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).

As the abrasive used in the present invention, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, carbonized having an α conversion of 90% or more. Known materials having a Mohs hardness of 6 or more, such as silicon titanium carbide, titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. A composite of these abrasives (abrasive surface-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 particle size of these abrasives is preferably 0.01 to 2 μm, but if necessary, abrasives having different particle sizes may be combined, or a single abrasive may be used to broaden the particle size distribution to obtain the same effect. . 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 of the abrasive used in the present invention include: AKP-20, AKP-30, manufactured by Sumitomo Chemical Co., Ltd.
AKP-50, HIT-50, Nippon Kagaku Kogyo Co., Ltd .: G
5, G7, S-1, manufactured by Toda Kogyo: 100ED, 140
ED, etc. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint. In the present invention, the amount of the abrasive used is 20% by weight or less of the ferromagnetic powder in the upper magnetic layer and 20% by weight or less of the nonmagnetic powder in the lower nonmagnetic layer.

The following are listed as additives having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like. Solid lubricants such as molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride and carbon black. Silicone oils, polar group silicones, fatty acid-modified silicones, fluorine-containing silicones, fluorine-containing alcohols, fluorine-containing esters, polyolefins, polyglycols, alkyl phosphates and their alkali metal salts, alkyl sulfates and their alkali metal salts, polyphenyls Ethers, fluorine-containing alkyl sulfates and their alkali metal salts, carbon number 1
0 to 24 monobasic fatty acids (which may contain unsaturated bonds or may be branched), and metal salts of these (Li, Na, K, Cu, etc.) or C12 to C12
22 monohydric, dihydric, trihydric, tetrahydric, pentahydric, hexahydric alcohol (may contain unsaturated bonds or may be branched), alkoxy alcohol having 12 to 22 carbon atoms, 10 carbon atoms -24 monobasic fatty acids (which may contain unsaturated bonds or may be branched) and C2-C12
Mono-fatty acid ester or di-fatty acid consisting of any one of monohydric, dihydric, trihydric, tetrahydric, tetrahydric, pentahydric and hexahydric alcohols (which may contain unsaturated bonds or may be branched) Organic lubricants such as esters or tri-fatty acid esters, fatty acid esters of alkylene oxide polymer monoalkyl ethers, fatty acid amides having 8 to 22 carbon atoms, and aliphatic amines having 8 to 22 carbon atoms can be used.

Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, stearic acid. Examples thereof include isooctyl, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol and lauryl alcohol. Further, nonionic surfactants such as alkylene oxides, glycerin, glycidol, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums or sulfoniums, Cationic surfactants such as carboxylic acid, sulfonic acid,
Anionic surfactants containing acidic groups such as phosphoric acid, sulfuric acid ester groups, phosphoric acid ester groups, etc., amphoteric surface active agents such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, alkylbedine type, etc. Can be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.).

These lubricants, antistatic agents, etc. are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposition products, oxides, etc. in addition to the main component. I don't care. These impurities are preferably 30% or less, more preferably 10% or less. The types and amounts of these lubricants and surfactants used in the present invention can be properly used in the lower non-magnetic layer and the upper magnetic layer. For example, fatty acids with different melting points are used in the lower non-magnetic layer and upper magnetic layer to control bleeding to the surface, esters with different boiling points and polarities are used to control bleeding to the surface, and the amount of surfactant is adjusted. By doing so, it is considered that the stability of coating is improved, the amount of lubricant added is increased in the intermediate layer, and the lubrication effect is improved. Of course, the examples are not limited to those shown here. Further, all or part of the additives used in the present invention may be added in any step of the lower non-magnetic layer coating material and the upper magnetic coating material manufacturing process, for example, mixed with a ferromagnetic powder before the kneading step. If
When added in a kneading step with a ferromagnetic powder, a binder and a solvent, when added in a dispersion step, when added after dispersion,
There are cases where it is added immediately before application.

The organic solvent used in the present invention is any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol. , Alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol dimethyl ether, glycol monoethyl ether, dioxane, and other glycol ethers, benzene, etc. Aromatic hydrocarbons such as toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chlorine Chloroform, ethylene chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, N,
Those such as N-dimethylformamide and hexane can be used.

The thickness of the magnetic recording medium of the present invention is 1-100 μm, preferably 6-20 μm for the non-magnetic support, 1 μm or less for the upper magnetic layer, preferably 1-0.2 μm, and the lower non-magnetic layer is 0.1 μm. It is preferably 5 μm or more , and particularly preferably 0.5 to 5 μm. If the upper magnetic layer exceeds 1 μm, the effect of thinning the electromagnetic conversion characteristics is lost, and if the lower non-magnetic layer is thinner than 0.5 μm, the productivity decreases and the calender moldability deteriorates, and sufficient electromagnetic conversion characteristics cannot be obtained. . In addition, an undercoat layer may be provided between the non-magnetic support and the lower non-magnetic layer to improve adhesion. The thickness of these is 0.01 to 2 μm, preferably 0.05 to 0.5.
μm. Further, a back coat layer may be provided on the side opposite to the non-magnetic support side magnetic layer side. This thickness is 0.1 to 2 μm, preferably 0.3 to 1.0 μm. Known undercoat layers and back coat layers can be used.

The non-magnetic support used in the present invention is polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, polyaramid, polycarbonate, polyamide, polyimide, polyamideimide,
Known films such as polysulfone, aramid, and aromatic polyamide can be used. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance. The center line average surface roughness of the non-magnetic support is 0.1 μm or less, preferably 0.05 μm or less. Moreover, these non-magnetic supports are not only small in center line average surface roughness,
It is preferable that there are no large protrusions of μm or more. The surface roughness shape can be freely controlled by the size and amount of the filler added to the support, if necessary. Examples of these fillers are Ca and S.
In addition to oxides and carbonates such as i and Ti, organic fine powders such as acrylics can be used.

The F-5 value in the tape running direction of the non-magnetic support used in the present invention is preferably 5 to 50 kg / m.
m ² , F-5 value in the tape width direction is preferably 3 to 30 k
It is g / mm ² , and the F-5 value in the tape longitudinal direction is generally higher than the F-5 value in the tape width direction, but this is not the case especially when it is necessary to increase the strength in the width direction. . In addition, the support 10 in the tape running direction and the width direction is used.
The heat shrinkage at 0 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less. is there. Breaking strength is 5 to 100 kg / mm ^{2 in} both directions,
The elastic modulus is preferably 100 to 2000 kg / mm ² .

The process for producing the magnetic coating material and the non-magnetic coating material for 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, if necessary. Each step may be divided into two or more steps. Ferromagnetic powder, non-magnetic powder, binder, carbon black, abrasive used in the present invention,
All raw materials such as antistatic agents, lubricants and solvents may be added at the beginning or in the middle of 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 added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, it goes without saying that conventionally known manufacturing techniques can be used as a part of the steps, but those having a strong kneading force such as a continuous kneader or a pressure kneader in the kneading step. Can be used. When using a continuous kneader or a pressure kneader, each powder and all or a part of the binder (however, 30% or more of the total binder) and 100 parts of the powder are kneaded in a range of 15 to 500 parts. . For details of these kneading treatments, Japanese Patent Application Nos. 62-264722 and 62-236872.
No.

In the present invention, it is possible to more efficiently produce by using the simultaneous multi-layer coating method as disclosed in JP-A-62-212933. In order to obtain the medium of the present invention, it is necessary to perform strong orientation. 1000
It is preferable to use a G or more solenoid and a 2,000 G or more cobalt magnet in combination, and it is preferable to provide an appropriate drying step before orientation so that the orientation after drying is the highest. Further, a heat-resistant plastic roll made of epoxy, polyimide, polyamide, polyimideamide, etc. is used as the calendering roll. Also,
It can also be processed by metal rolls. The processing temperature is
It is preferably 70 ° C or higher, more preferably 80 ° C or higher. The linear pressure is preferably 200 kg / cm, more preferably 300 kg / cm or more.

The friction coefficient of the upper magnetic layer surface of the magnetic recording medium of the present invention and the opposite surface thereof to SUS420J is preferably 0.5 or less, more preferably 0.3 or less, and the surface resistivity is preferably 10 ^-5 to 10 ^-12 ohm. / Sq, the elastic modulus at 0.5% elongation of the magnetic layer is preferably 100 to 2000 kg / mm ^{2 in} the running direction and the width direction, the breaking strength is preferably 1 to 30 kg / cm ² , and the elastic modulus of the magnetic recording medium is Both running and longitudinal directions are preferably 100-1500 kg
/ Mm ² , residual spread is preferably 0.5% or less, 100
The thermal shrinkage at any temperature below ℃ is preferably 1% or less, more preferably 0.5% or less, most preferably 0.1% or less. The residual solvent contained in the upper magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less, and the residual solvent contained in the upper magnetic layer is less than that contained in the lower non-magnetic layer. preferable.

The porosity of the upper magnetic layer is preferably 3
0 vol% or less, more preferably 10 vol% or less. When the magnetic properties of the magnetic recording medium of the present invention are measured at a magnetic field of 5 KOe, the squareness ratio in the tape running direction is 0.70 or more, preferably 0.80 or more, and more preferably 0.10 or more.
90 or more. The squareness ratio in the two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction. The SFD of the upper magnetic layer is preferably 0.6 or less.

[0049]

EXAMPLES Next, the present invention will be described more specifically by showing Examples and Comparative Examples. In each example, “parts” means “parts by weight” unless otherwise specified. A magnetic coating liquid and a non-magnetic coating liquid were prepared according to the following formulations.

Example 1-1 Prescription of Magnetic Coating Liquid for Upper Magnetic Layer Ferromagnetic powder: Fe alloy powder (Fe—Ni—Co) 100 parts Composition: Fe: Ni: Co = 92: 6: 2 Hc1600Oe, σ _S 135 emu / G major axis length 0.18 μm, acicular ratio 9 vinyl chloride copolymer 10 parts —SO ₃ Na, epoxy group containing polyurethane resin 5 parts —SO ₃ Na containing, molecular weight 45000 α alumina (average particle size 0.2 μm) 5 parts cyclohexanone 150 parts methyl ethyl ketone 150 parts After mixing and dispersing the above composition in a sand mill for 6 hours,
Polyisocyanate (Coronate L), 5 parts of stearic acid, and 10 parts of butyl stearate were added to obtain a magnetic coating solution.

Coating liquid formulation for lower non-magnetic layer Needle-like α-Fe ₂ O ₃ 100 parts Long axis length 0.5 μm Needle-like ratio 10 Carbon black 5 parts Average particle size 20 mμ Vinyl chloride copolymer 8 parts —SO ₃ Na , Epoxy group-containing molecular weight 45000 Polyurethane resin 5 parts —SO ₃ Na-containing, molecular weight 45000 cyclohexane 100 parts Methyl ethyl ketone 100 parts After mixing and dispersing the above composition in a sand mill for 4 hours,
Polyisocyanate (Coronate L), 5 parts of stearic acid and 10 parts of butyl stearate were added to obtain a coating liquid for the lower non-magnetic layer.

The above coating solution was applied in a wet state by using two doctors having different gaps, and after orientation treatment with a permanent magnet, it was dried. After that, super calendar processing was performed. The coating thickness was 0.3 μm for the magnetic layer and 3.0 μm for the non-magnetic layer. The raw material thus obtained is cut into 3.81 mm wide digital audio tapes (D
AT). Other Examples and Comparative Examples are Example 1
On the other hand, tapes were prepared by changing the factors shown in Tables 1 and 2 . Also, physical properties of the Ba ferrite is as follows. Ferromagnetic powder: Ba ferrite Hc1100 Oe, σ _S 70 emu / g plate diameter 0.05 μm, plate ratio 5

These tapes were evaluated by the following methods, and the results are shown in Tables 1 and 2. Deck to be used: DTC-1000 manufactured by Sony Discrimination of presence or absence of mixed region: Preparation of sample Sample tape is sandwiched with epoxy resin, cooled with liquid nitrogen, and cut with a microtome in the longitudinal direction and width direction of the tape. Observation The cut surface was observed with a TEM (transmission electron microscope) at a magnification of 50,000 times, and the number of nonmagnetic particles contained in the magnetic layer near the interface between the magnetic layer and the nonmagnetic layer was measured.

Evaluation Ratio (%) of the number of non-magnetic particles to the number of magnetic particles
I asked. No mixed region: The above ratio is 0.5% or less There is a mixed region: The above ratio exceeds 0.5% i) When the particle shape is different For example, the ferromagnetic powder in the upper magnetic layer is needle-shaped When the non-magnetic powder of the lower non-magnetic layer is granular or scaly, or when the ferromagnetic powder of the upper magnetic layer is plate-shaped and the non-magnetic powder of the lower non-magnetic layer is granular or needle-shaped, The presence or absence of a mixed region was evaluated based on the degree of mixing. ii) When the particle shapes are the same, but the average diameters of the longest axial lengths are different. For example, when both the ferromagnetic powder of the upper magnetic layer and the nonmagnetic powder of the lower nonmagnetic layer are acicular, but the average diameters are different, or the upper layer is When the ferromagnetic powder in the magnetic layer is plate-like and the non-magnetic powder in the lower non-magnetic layer is scale-like, the presence or absence of the mixed region was evaluated depending on how much those having different average diameters were mixed.

Iii) When the particle shape and the average diameter are the same, the presence or absence of the mixed region is detected by detecting the peculiar element contained in each layer by the micro Auger electron spectroscopy in the vicinity of the interface between the upper magnetic layer and the lower nonmagnetic layer. Was evaluated. Reproduction output: A signal having a single frequency of 4.7 MHz was input, the reproduction signal was output to the spectrum analyzer, and the peak value of the signal was read. HP-3585A is the spectrum analyzer
OdB is the tape of the magnetic layer single layer of Comparative Example 1 BER (block error rate): A computer converted 24-25 random signals. The scrambled interleaved NRZ-I signal is used as a test signal, and the data obtained by PR demodulating the data obtained by recording / reproducing this test signal is compared with the test signal to detect an error, and the error ratio is calculated. BER. Dropout: 4.7MHz single frequency signal input, threshold (DO) level -10d
A 0.5 μSEC length dropout in B was measured with a dropout counter. In the present example, the dry thickness of the upper magnetic layer was measured from the cut surface observed by TEM by adjusting the sample in the same manner as in the method for determining the presence or absence of the mixed region.

[0056]

[Table 1]

[0057]

[Table 2]

As is clear from the results shown in Tables 1 and 2, the sample No. using the acicular non-magnetic powder of the present invention. Example 1
It was found that samples Nos. 1 to 1-7 have a low dropout and a low BER (block error rate) simultaneously with the improvement of the RF output. Sample N outside the scope of the invention
o. Comparative Examples 1-1 to 1-3 are BER, dropout,
Good results were not obtained for at least one of the RF outputs. The target level of the BER is 10 ⁻⁴ or less, the number of dropouts is 100 or less, and the RF output is 3.0 dB or more.

[0059]

EFFECT OF THE INVENTION In a magnetic recording medium having a plurality of layers formed by so-called wet-on-wet coating, in which a lower non-magnetic layer is wet, an upper magnetic layer is coated simultaneously or sequentially, and a mixed region is formed at the interface. Magnetic recording medium, specifically, by using needle-like or scale-like non-magnetic powder in the lower non-magnetic layer, good electromagnetic conversion characteristics and excellent productivity, specifically high RF output and running durability It is possible to obtain a magnetic recording medium that is excellent in magnetic field, has low dropout, and has a low block error rate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-12650 (JP, A) JP-A-5-298653 (JP, A) JP-A-5-182173 (JP, A) JP-A-5- 217149 (JP, A) JP 4-325917 (JP, A) JP 5-197946 (JP, A) JP 7-311932 (JP, A) JP 7-326038 (JP, A) JP 5-182177 (JP, A) JP 5-182178 (JP, A) JP 8-50718 (JP, A) JP 4-325915 (JP, A) JP 4-238111 (JP, A) JP-A-4-283416 (JP, A) JP-A-4-321924 (JP, A)

Claims (8)

(57) [Claims] 1. A magnetic recording medium in which a lower non-magnetic layer containing at least non-magnetic powder and a binder is provided on a non-magnetic support, and an upper magnetic layer containing ferromagnetic powder and a binder is provided thereon. The dry thickness of the upper magnetic layer is 1 μm or less,
A ratio r ₁ / r ₂ of the longest axial length r ₁ and the shortest axial length r ₂ of the non-magnetic powder is 2.5 or more and less than 20. 2. The average diameter of the longest axial length of the ferromagnetic powder
Is 0.3 μm or less, described in claim 1.
The magnetic recording medium mounted. 3. At least non-magnetic powder on a non-magnetic support.
And a lower non-magnetic layer containing a binder and a ferromagnetic powder
A magnetic recording medium provided with an upper magnetic layer containing powder and a binder.
The non-magnetic powder has an acicular ratio of 2.5 or more and less than 20.
And the dry thickness of the upper magnetic layer is 1 μm or less.
The average diameter of the longest axial length of the ferromagnetic powder is 0.3 μm.
A magnetic recording medium characterized by being m or less. 4. Between the lower non-magnetic layer and the upper magnetic layer
Claim 1 or Claim 1, characterized in that there is no mixed area in
3. The magnetic recording medium according to item 3. 5. The longest axial length of the lower non-magnetic layer is 3 μm.
2. A non-magnetic powder having a particle size of m or less is contained.
Is the magnetic recording medium according to claim 3. 6. The lower non-magnetic layer is Al ₂ O ₃ (Α,
γ), Cr ₂ O ₃ , ΑFe ₂ O ₃ , Goethite, SiO
₂ , ZrO ₂ , CeO ₂ , TiO ₂ (Rutile, Anata
Z)) containing at least one of the non-magnetic powders
The magnetic recording medium according to claim 1 or 3, which is a characteristic of the magnetic recording medium. 7. The ferromagnetic powder is Fe, Ni or Co.
It is a needle-shaped ferromagnetic alloy powder containing
The magnetic recording medium according to claim 1 or 3. 8. The magnetic recording medium is a recording tape or video
For tape, computer tape, disc, etc.
It is for digital, Claim 1 or Claim 3 characterized by the above-mentioned.
The magnetic recording medium according to 1.