JP2649943B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic sheet, and a magnetic disk.

B. 2. Description of the Related Art Recently, high-density magnetic recording media such as magnetic tapes,
With the N ratio, magnetic powder having a smaller particle diameter has been used.

Generally, it is said that the S / N ratio of a magnetic recording medium is proportional to the square root of the number of particles of magnetic powder in a recording material related to recording / reproducing.
The use of a magnetic powder having a smaller particle diameter is more advantageous for improving the S / N. Further, when the magnetic powder is made finer and its BET value is increased, the surface of the magnetic layer becomes smoother and the spacing loss is reduced, which is advantageous in obtaining high electromagnetic conversion characteristics. When metal magnetic powder is used, high-density recording is possible, and performance is further improved.

That is, such metal magnetic powder has high saturation magnetization and coercive force, and is excellent in properties as a high-density recording material. However, it has the following two main problems due to its high surface activity.

Oxidation resistance stability of metal magnetic powder in air If the metal magnetic powder is left in the air, the deterioration of magnetic properties gradually occurs due to the progress of oxidation.

Dispersibility in Binder When dispersing the metal magnetic powder in the binder, the surface activity is high and the dispersibility is poor and difficult to disperse. In extreme cases, the binder resin is gelled in the paint.

In particular, the use of video tapes in recent years has been diversified with the increase in portability, and their use conditions are various. Therefore, video tapes are required to have high corrosion resistance.

C. The object of the present invention is to enable high-density recording, excellent electromagnetic conversion characteristics such as S / N ratio, good dispersibility of magnetic powder, good corrosion resistance,
An object of the present invention is to provide a magnetic recording medium having excellent durability.

D. The present invention relates to a magnetic recording medium in which a binder and a metal magnetic powder are contained in a magnetic layer, wherein the metal magnetic powder has a specific surface area of 45 m ² / g or more. The metal magnetic powder contains Fe, Ni and Al, and the Ni (nickel atom) content in the metal magnetic powder is
0.1-9.9 atomic%, Al (aluminum atom) content is 0.1
-5 atomic%, Fe (iron atom) content is 90 atomic% or more, and ESCA (electron spectrosc
opy for chemical analysis), the abundance ratio Fe: Al: Ni corresponding to Fe of Al and Ni existing in the region (surface region) up to the analysis depth of 100Å (100: 40-140: 10-10 (atomic ratio)) The depth of analysis by ESCA from the surface of the metal magnetic powder is 100
The present invention relates to a magnetic recording medium, wherein the Al existing in the region up to Å is in a state of being bonded to oxygen.

According to the present invention, since a magnetic metal powder having a specific surface area of 45 m ² / g or more is used as the magnetic powder, it is possible to provide a medium capable of high-density recording and having an excellent S / N ratio and the like. More preferably, the specific surface area of the metal magnetic powder is 50 m ² / g or more and 70 m ² / g or less.

Further, since the content of iron atoms in the metal magnetic powder is set to 90 atomic% or more, a medium excellent in electric characteristics can be provided. Since the content of aluminum atoms is 0.1 to 5 atomic% (more preferably 1 to 5 atomic%), the corrosion resistance, which is the characteristic of aluminum, can be sufficiently exhibited. Dispersibility is improved.
Further, since the content of nickel atoms in the magnetic powder is 0.1 to 9.9 atomic% (more preferably, 1 to 8 atomic%), sintering of the magnetic powder can be sufficiently prevented.

Furthermore, since the aluminum atoms present in the surface area of the metal magnetic powder are in a state of being bonded to oxygen, the active points existing on the surface of each particle of the magnetic powder are further reduced, and the surface activity is suppressed. Therefore, corrosion resistance by aluminum atoms,
The effect of improving the dispersibility is more effectively exhibited, the corrosion resistance and dispersibility of the metal magnetic powder are further improved, and the durability of the medium is improved.

ESCA (electron spectroscopy) from the surface of metal magnetic powder
abundance ratio F corresponding to Fe in Al and Ni existing in the region (surface region) with an analysis depth of up to 100 mm by chemical analysis
Since e: Al: Ni is 100: 40 to 140: 10 to 10 (atomic ratio),
In other words, by increasing the abundance ratio of aluminum atoms present in the surface area of the metal magnetic powder and reducing the abundance ratio of iron atoms and nickel atoms, the corrosion resistance of aluminum atoms is more effectively exerted and oxidation of the magnetic powder is achieved. Can be suppressed. It is also effective for preventing aggregation of particles and improving the dispersibility of magnetic powder. In particular, reducing the abundance ratio of easily rustable nickel atoms in the surface area of the magnetic powder is effective for improving the oxidation resistance of the magnetic powder.

Examples of the metal magnetic powder include those obtained by a dry reduction method in which iron oxide is reduced with hydrogen or the like.

Usable metal magnetic powders include Fe-Al-Ni, Fe-
Ni-Al-Si-Zn system, Fe-Ni-Al-Si-Mn system, etc. are mentioned.

The above specific surface area is represented by a BET value and refers to the surface area per unit weight, which is a physical quantity completely different from the average particle diameter.For example, even if the average particle diameter is the same, the specific surface area is large. Some have small specific surface areas.
The measurement of the specific surface area, for example, first, the powder at around 250 ℃ 30
Was degassed with 60 minutes heating, to remove those adsorbed on the powder, then introduced into a measuring device, to set the initial pressure of nitrogen to 0.5 kg / m ^2, the liquid by nitrogen Perform adsorption measurement at nitrogen temperature (-195 ° C) (Method of measuring specific surface area generally called BET method. For details, see J. Ame. Chem. So
c. See 60 309 (1938)). As a device for measuring the specific surface area (BET value), a “granular material measuring device (canter soap)” jointly manufactured by Yuasa Battery Co., Ltd. and Yuasa Ionics Co., Ltd. can be used. For general description of specific surface area and its measurement method, see "Measurement of granules".
(Co-authored by JMDALLAVALLE, CLYDEORR Jr., translated by Benda et al .; published by Sangyo Toshosha), and is described in “Chemical Handbook” (Applied Edition, pages 1170-1171, edited by The Chemical Society of Japan, Maruzen Co., Ltd., Showa 41) (Issued on April 30) (in the aforementioned Chemical Handbook, the specific surface area is simply referred to as the surface area (m ² / g
Although described as r), it is the same as the specific surface area in the present specification. ).

Binders usable in the present invention have a nominal molecular weight of about
Among those of 10,000 to 200,000, for example, urethane resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer,
Butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various types Synthetic rubber, phenolic resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, A mixture of low molecular weight glycol / high molecular weight diol / isocyanate,
And mixtures thereof.

The resin _{is, -SO 3 M, -COOM, -PO} (OM ')
₂ (where M is hydrogen or an alkali metal such as lithium, potassium, sodium, etc., M ′ is hydrogen, lithium, potassium,
A resin containing a hydrophilic polar group such as an alkali metal such as sodium or a hydrocarbon residue) is preferable. In other words, such a resin has improved compatibility with the metal magnetic powder due to the polar group in the molecule, thereby further improving the dispersibility of the magnetic powder and preventing the aggregation of the metal magnetic powder, thereby further improving the stability of the coating liquid. This can improve the durability of the medium.

The binder used, especially the vinyl chloride copolymer, is obtained by copolymerizing a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid, and if necessary, other copolymerizable monomers. Can be. Since this copolymer is obtained by vinyl synthesis, it can be easily synthesized, and various copolymer components can be selected, so that the properties of the copolymer can be adjusted optimally.

The metal of the above-mentioned sulfonic acid or phosphoric acid salt is an alkali metal (particularly sodium, potassium, lithium), and potassium is particularly preferable in terms of solubility, reactivity, yield and the like.

Examples of the above copolymerizable monomer containing a sulfonate include CH ₂ CHCHSO ₃ M CH ₂ CHCHCH ₂ SO ₃ M CH ₂ ＣC (CH ₃ ) CH ₂ SO ₃ M CH ₂ CHCHCH ₂ OCOCH (CH _{2 COOR) SO 3 M CH 2} = CHCH 2 OCH 2 CH (OH) CH 2 SO 3 M CH 2 = C (CH 3) COOC 2 H 4 SO 3 M CH 2 = CHCOOC 4 H 8 SO 3 M CH 2 = _{CHCONHC (CH 3) 2 CH 2} SO 3 M and the like.

As the phosphate, CH ₂ CHCHCH ₂ OCH ₂ CH (OH) CH ₂ —O—PO ₃ MY ¹ CH ₂ 2CHCONHC (CH ₃ ) ₂ CH ₂ —O—PO ₃ MY ² CH ₂ CHCHCH ₂ O (CH ₂ CH ₂ O) mPO ₂ MX ^{2 In the} above, M is an alkali metal, and R is 1 to 1 carbon atoms.
20 alkyl group, Y ¹ is H, M or _{CH 2 = CHCH 2 OCH 2 CH} (OH) CH 2 -, Y 2 is H, M or _{CH 2 = CHCONHC (CH 3)} 2 CH 2 -, X 1 Is OH or OM, X ² is _{CH 2 = CHCH 2 O (CHCH} 2 O) m-, OH or OM. N is a positive number from 1 to 100, and m is a positive number from 11 to 100.

Further, as the copolymerizable monomer to be copolymerized as necessary, there are known polymerizable monomers, for example, various vinyl esters, vinylidene chloride, acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid,
Various acrylic acid esters, methacrylic acid esters, ethylene, propylene, isobutane, butadiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, maleic acid, maleic acid ester and the like are exemplified.

The binder used in the present invention is emulsion polymerization, solution polymerization,
It is polymerized by a polymerization method such as suspension polymerization or bulk polymerization. In any method, known techniques such as divisional addition or continuous addition of a molecular weight regulator, a polymerization initiator, and a monomer can be applied as necessary.

The amount of the acidic group salt-containing monomer in the binder used in the present invention is preferably 0.01 to 30 mol%. If the amount of the salt-containing monomer is too large, solubility in a solvent is poor and gelation is likely to occur. If the amount of the salt-containing monomer is too small, desired characteristics cannot be obtained.

The above vinyl chloride copolymer preferably further contains an epoxy group or a hydrogen group. By the way, a conventional PVC copolymer (for example, VAGH manufactured by UCC) was composed of the following copolymer components.

: Indicates a copolymer unit.

However, it is considered that the CH ₃ CO—O— group hardly contributes to a crosslinking reaction with a curing agent or the like. So CH ₃ C
Instead of O, It is preferable to contain an epoxy group such as For example, a copolymer having the following units may be mentioned.

(X: monomer unit portion containing an alkali metal salt of a sulfo or phospho group) In particular, it is preferable to use at least a urethane resin,
Further, a vinyl chloride copolymer, an epoxy resin (particularly, a phenoxy resin), a polyester resin, or a nitrocellulose resin (hereinafter, referred to as another resin) may be used in combination. In this case, as a compounding ratio of the urethane resin and the other resin, the other resin is 90 to 10 parts by weight, more preferably 80 to 20 parts by weight.
It is desirably in parts by weight. If the compounding ratio exceeds 90 parts by weight, the coating film becomes too brittle and the durability of the thin film is significantly deteriorated, and the adhesiveness to the support is also deteriorated. The above compounding ratio
If the amount is less than 10 parts by weight, the magnetic powder tends to fall off.

When carbon black is added to the magnetic layer, it is more advantageous in terms of improving running properties and electromagnetic conversion characteristics, slightly improving dispersibility, and reducing the amount of residual solvent in the magnetic layer.

If light-shielding carbon black is used as such carbon black, the degree of light shielding can be increased. Examples of the light-shielding carbon black include, for example, Raben 2000 (specific surface area 190 m ² / g, particle diameter 18 mμ), 2100, 1170, 1000 manufactured by Columbia Carbon Co., Ltd., # 1 manufactured by Mitsubishi Kasei Co., Ltd.
00, # 75, # 40, # 35, # 30, etc. can be used.

Examples of the conductive carbon black include Conductex 975 of Columbia Carbon.
(BET value (hereinafter abbreviated as BET) 250m ² / g, DBP oil absorption (hereinafter DBP
Abbreviated) 170ml / 100gr, particle size 24mμ), Conductex 90
0 (BET125m ² / g, particle size 27mμ), Conductex Tex 40-22
0 (particle size 20mμm), Conductex SC (BET220m ² / g
r, DBP115ml / 100gr, the particle size 20mμ), manufactured by Cabot Vulcan (Cabot Vulcan) XC-72 (specific surface area 254m ² / g, particle size 30mμ), Vulcan ^{P (BET143m 2 / gr, DBP118ml} / 100g
r, particle size 20 mμ), Raven 1040, 420, Black Pearls 2000 (particle size 15 μm), # 44 manufactured by Mitsubishi Kasei Corporation, and the like.

As another carbon blacks usable in the present invention, Columbian Carbon Co. Conductex tex ^{(Conductex) -SC. (BET220m 2} / g, DBP115ml / 100g, particle diameter 20Emumyu), Vulcan manufactured by Cabot Corporation (Vulcan) 9 (B
^{ET140m 2 / g, DBP114ml / 100g} , particle size 19mμ), manufactured by Asahi Carbon Co., Ltd. ^{# 80 (BET117m 2 / g,} DBP113ml / 100g, particle size 23m
μ), HS 100 (BET32m ² / g, DBP180ml / 1
00g, particle size 53mμ), # 22B manufactured by Mitsubishi Kasei (BET55m ² / g,
DBP131ml / 100g, particle size ^{40mμ), # 20B (BET56m 2} / g, DBP1
15ml / 100g, particle size ^{40mμ), # 3500 (BET47m 2} / g, DBP187m
l / 100g, particle size 40mμ), CF-9, # 4000, MA-600 manufactured by Mitsubishi Kasei, Black Pearls L manufactured by Cabot, Monarch (Monarc)
k) 800, Black Pearls 700, Black Pearls 1
000, Black Pearls 880, Black Pearls 90
0, Black Pearls 1300, Black Pearls 200
0, Sterling V, Raven 410, Raven 3200, Raven 420, Raven 450, Raven 825, Raven 1255, manufactured by Columbian Carbun.
Raven 1035, Raven 1000, Raven 5000, Ketjen Black FC and the like.

Furthermore, in the present invention, durability can be improved by further adding a polyisocyanate-based curing agent to the magnetic paint containing a binder. Examples of such a polyisocyanate-based curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate; Functional isocyanate,
Alternatively, any of those conventionally used as a curing agent, such as urethane prepolymers containing isocyanate groups at both ends, and any polyisocyanate usable as a curing agent can be used. The amount of the polyisocyanate-based curing agent is 5 to 80 parts by weight of the total amount of the binder.

The magnetic recording medium of the present invention has a magnetic layer 2 on a non-magnetic support 1 such as polyethylene terephthalate, for example, as shown in FIG. This is a configuration in which the layer 3 is provided. Further, as shown in FIG. 2, an overcoat layer (OC layer) 4 may be provided on the magnetic layer 2 of the magnetic recording medium of FIG.

1 and 2 may be provided with an undercoat layer (not shown) between the magnetic layer 2 and the support 1, or may be provided with no undercoat layer. You may. The support may be subjected to corona discharge treatment.

The magnetic layer 2 may contain a fatty acid and / or a fatty acid ester as a lubricant in addition to the metal magnetic powder and the binder described above. As a result, while exhibiting the respective features of the two, it is possible to cancel the defects that occur when used alone, to improve the lubrication effect, and to improve the still image durability, running stability, S / N ratio, and the like. In this case, the amount of the fatty acid added is preferably 0.2 to 10 parts by weight, more preferably 0.5 to 8.0 parts by weight, based on 100 parts by weight of the magnetic powder. When the amount of the fatty acid is less than the above range, the dispersibility of the magnetic powder is reduced, and the running property of the medium is also easily reduced. When the amount is too large, the fatty acid exudes and the output is liable to be reduced. The amount of the fatty acid ester is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 8.5 parts by weight, based on 100 parts by weight of the magnetic powder. When the amount of the ester is less than this range, the effect of improving the running property is poor when the amount of the ester is small.

In order to achieve the above effects more favorably, the weight ratio of fatty acid to fatty acid ester is preferably fatty acid / fatty acid ester = 10/90 to 90/10. Fatty acids also have a dispersing effect, and it is considered that the use of another fatty acid can reduce the amount of another low-molecular-weight dispersant used, thereby improving the Young's modulus of the magnetic recording medium.

Fatty acids may be monobasic or dibasic. Fatty acids having 6 to 30 carbon atoms, more preferably 12 to 22 carbon atoms, are preferred. Examples of fatty acids are as follows.

(1) caproic acid (2) caprylic acid (3) capric acid (4) lauric acid (5) myristic acid (6) palmitic acid (7) stearic acid (8) isostearic acid (9) linolenic acid (10) linoleic acid (11) Oleic acid (12) Elaidic acid (13) Behenic acid (14) Malonic acid (15) Succinic acid (16) Maleic acid (17) Glutaric acid (18) Adipic acid (19) Pimelic acid (20) Azelaic acid (21) Sebacic acid (22) 1,12-Dodecanedicarboxylic acid (23) Octanedicarboxylic acid Examples of the above fatty acid esters are as follows.

(1) Oleyl oleate (2) Oleyl stearate (3) Isocetyl stearate (4) Dioleyl maleate (5) Butyl stearate (6) Butyl palmitate (7) Butyl myristate (8) Octyl myristate ( 9) Octyl palmitate (10) Amyl stearate (11) Amyl palmitate (12) Isobutyl oleate (13) Stearyl stearate (14) Lauryl oleate (15) Octyl oleate (16) Isobutyl oleate (17) Ethyl oleate ( 18) isotridecyl oleate (19) 2-ethylhexyl stearate (20) 2-ethylhexyl myristate (21) ethyl stearate (22) 2-ethylhexyl palmitate (23) isopropyl palmitate (24) isopropyl myristate (25 ) Butyl laurate (2 6) Cetyl-2-ethylhexarate (27) Dioleyl adipate (28) Diethyl adipate (29) Diisobutyl adipate (30) Diisodecyl adipate In addition to the above fatty acids and fatty acid esters, other lubricants (for example, silicone oil) , Carboxylic acid modified,
Ester-modified), graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide, etc.) may be added to the magnetic layer.

Also, other non-magnetic abrasive particles can be added to the magnetic layer. For example, α-alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, silicon carbide, zirconium oxide, zinc oxide, cerium oxide, magnesium oxide, boron nitride, and the like are used. The average particle size of the abrasive is preferably 0.6 μm or less, more preferably 0.3 μm or less. The Mohs hardness is preferably 5 or more.

Further, an antistatic agent such as graphite and a dispersant such as powdered lecithin and a phosphate ester can be further added to the magnetic layer. Further, carbon black can also be used in combination.

Further, it is more preferable that the non-magnetic particles contained in the back coat layer have an average particle diameter in a range of 10 μm to 1000 μm. This is because, within the above range, the nonmagnetic particles do not become too fine, and the addition effect is good.

Non-magnetic particles include silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide, α-Fe ₂ O ₃ , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, and molybdenum dioxide. , Calcium carbide, barium sulfate and the like. In addition, an organic powder such as a benzoguanamine-based resin, a melamine-based resin, a phthalocyanine-based pigment, or the like can be used, and the organic powder and the inorganic powder can be used in combination.

Further, it is more preferable to use carbon black together with the above non-magnetic particles. This makes it possible to further stabilize the running property of the medium and further improve the durability of the medium in combination with the above-mentioned action of the non-magnetic particles.

E. Examples Hereinafter, examples of the present invention will be described.

The components, ratios, operation orders, and the like shown below can be variously changed without departing from the spirit of the present invention. In the following examples, "parts" are all parts by weight.

<Preparation of Video Tape> First, a magnetic layer was formed on a 10 μm-thick polyethylene terephthalate film as a support in the following manner.

That is, after using the predetermined metal magnetic powder and dispersing the respective components shown in FIG. 4, the magnetic coating material was filtered through a 1 μm filter, and 5 parts of a polyfunctional isocyanate was added thereto. Apply and super calendar, 4th
Magnetic layers having various compositions shown in the figure were obtained.

FIG. 4 also shows the content of iron, aluminum, and nickel atoms in the magnetic powder and the abundance ratio in the surface region. The above abundance ratio is determined by ESCA
The abundance ratio was measured at an analysis depth of less than about 100 mm from the surface to the inside. The above content ratio is measured by X-ray elemental analysis.

FIG. 3 is a graph showing the oxidation state of aluminum atoms in the magnetic powder surface area.

In FIG. 3, the vertical axis indicates the spectrum intensity detected by the counter, and the horizontal axis indicates the binding energy (eV). The binding energy corresponding to the peak is 76.8 eV, and the binding energy value (76.8 eV) for the aluminum oxide peak described in the handbook.
Matches. The binding energy of the peak of pure aluminum is 72.7 eV.

The metal magnetic powder of the embodiment of the present invention can be produced, for example, as follows.

As a method for producing the metal magnetic powder of the embodiment of the present invention, α-
FeOOH, iron hydrates such as γ-FeOOH, or α-Fe ₂ O ₃ , γ
-Fe ₂ O _3, Fe ₃ O iron oxide such as ₄ to a high temperature is reduced with H ₂ or the like. For example, after reacting an alkali component (eg, NaOH) with a ferrous salt compound (eg, FeSO ₄ , FeCl _2, etc.), α-Fe
OOH is generated, and the α-FeOOH is reduced at a high temperature (for example, H ₂
) Or by converting α-FeOOH to α-Fe ₂ O ₃ and then reducing (for example, with H ₂ ) at a high temperature to produce a magnetic metal powder. Thus, an Al compound and a Ni compound can be added. The same applies to compounds of other elements other than Fe.

In order to further oxidize aluminum in the surface area, the metal magnetic powder is subjected to oxygen or oxygen so that aluminum derived from the aluminum compound added at a later stage of the reaction is oxidized in the surface area during the production of the metal magnetic powder. There is a method in which a small amount of a compound having an OH group is present and only the surface area is oxidized.

Thereafter, a BC layer paint having a paired composition was applied to the opposite surface of the magnetic layer so as to have a dry thickness of 0.4 μm.

Carbon black (average particle diameter 50mμ) 40 parts Barium sulfate 10 parts Nitrocellulose 25 parts N-2301 (manufactured by Nippon Polyurethane) 25 parts Coronate L (〃) 10 parts Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts A wide magnetic film having a magnetic layer and a BC layer was obtained and wound up. This film was cut to a width of 8 mm to obtain each of the video tapes shown in FIG. 4 (corresponding to the numbers of the respective Examples and Comparative Examples). However, the numerical values in the second and subsequent columns in FIG. 4 represent parts by weight, "actual-" represents an example, and "ratio-" represents a comparative example.

<Measurement of Tape Performance> The results of measuring the performance of the tape obtained as described above are shown in FIG. However, the evaluation items are measured and displayed according to the following criteria.

Lumi S / N: Color video noise meter "Shibasoku 925 D / 1"
Was measured by The high-pass filter was operated at 10 kHz, and the low-pass filter was operated at 4.2 MHz. The VTR used an 8mm VCR.

Still Image Life: Indicates the time, in minutes, before a still image is reduced by 2 dB. The larger the value, the higher the durability and wear resistance of the magnetic recording medium.

Percentage of saturation magnetization remaining: The saturation magnetization measured after leaving the sample tape in an atmosphere of 60 ° C. and 80% RH for one week is what percentage of the saturation magnetization measured before standing.
Is shown.

Powder drop: clogging of the magnetic head: The sample tape was run on a VCR continuously at 40 ° C. and 80% for 200 hours, and powder drop and clogging of the magnetic head were measured.

非常 Very good ○ Good △ Somewhat good × Poor <Conclusion> From the results shown in FIG. 4, it can be seen that the tape performance is remarkably improved by configuring the magnetic tape based on the present invention. That is, using a metal magnetic powder having a BET value of 45 m ² / g or more, limiting the content of iron atoms, aluminum atoms and nickel atoms in the metal magnetic powder, and specifying the state of aluminum atoms in the surface area are not possible. is important.

[Brief description of the drawings]

1 and 2 are partially enlarged cross-sectional views showing an example of the magnetic recording medium of the present invention. FIG. 3 is a graph showing the presence of aluminum atoms in the surface area of the metal magnetic powder. 4 is a table showing a change in characteristics depending on the composition. In the reference numbers shown in the drawings, 1 is a non-magnetic support 2, a magnetic layer 3, a back coat layer (BC layer) 4, and an overcoat layer (OC layer).

Claims (1)

(57) [Claims] 1. A magnetic recording medium in which a binder and metal magnetic powder are contained in a magnetic layer, wherein the metal magnetic powder has a specific surface area of 45 m ² / g or more. , Containing Fe, Ni and Al, the Ni content in the metal magnetic powder is 0.1 to 9.9 atomic%,
The content is 0.1 to 5 atomic%, the Fe content is 90 atomic% or more, and the analysis depth by ESCA from the surface of the metal magnetic powder is 100Å.
Ratio of Al and Ni to Fe existing in the region up to Fe: Al: N
i is 100: 40 to 140: 10 to 10 (atomic ratio), and the depth of analysis by ESCA from the surface of the metal magnetic powder is 100Å
The magnetic recording medium, wherein the Al existing in the region up to the above is in a state of being bonded to oxygen.