JP2649941B2 - Magnetic recording media - Google Patents

Description

The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic sheet, and a magnetic disk.

B) Conventional technology Recently, the density of magnetic recording media such as magnetic tapes has been increased,
With N, magnetic powders having smaller particle diameters have 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, the metal magnetic powder has a large saturation magnetization and a large 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) Object of the invention The object of the present invention is to enable high-density storage, 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. Configuration of the invention and its operational effects The first invention is a magnetic recording medium in which a magnetic layer contains a metal magnetic powder containing Fe and Al and a binder, wherein the specific surface area of the metal magnetic powder is 45 m ² / g or more, Fe (iron atom) and Al contained in the metal magnetic powder
(Aluminum atom) content ratio Fe: Al is 100: 1 to 100: 20
(Atomic ratio) and the surface of the metal magnetic powder is ESCA (electron spe
ctroscopy for chemical analysis) analysis depth 100
The magnetism is characterized in that the abundance ratio of Fe to Al existing in the region up to Å (hereinafter also referred to as the surface region) is 30:70 to 70:30 (atomic ratio). It relates to a recording medium.

The second invention relates to the magnetic recording medium according to claim 1, wherein aluminum atoms present in the surface region of the metal magnetic powder are 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.

Further, iron atoms and aluminum atoms are contained in the metal magnetic powder in a specific range of content, and the abundance ratio of iron atoms and aluminum atoms present in the surface area of the metal magnetic powder is limited to a specific range. Is important.

That is, the abundance ratio of iron atoms to aluminum atoms is (100:
Since 1) to (100: 20), the content of iron atoms can be made sufficient, and an iron-based metal magnetic powder excellent in electric characteristics can be provided, and the content of aluminum atoms becomes sufficient,
Corrosion resistance, which is a characteristic of aluminum atoms, can be sufficiently exhibited. This range is further defined as (iron atom: aluminum atom) =
(100: 1) to (100: 8) are preferable.

However, when a large amount of iron atoms are present in the surface area of the metal magnetic powder, the oxidation of individual particles progresses in combination with the fact that the metal powder and the specific surface area are 45 m ² / g or more. It is likely that the particles are easily dispersed and easily aggregated with each other, so that the dispersibility is reduced and the durability of the medium is finally deteriorated.

In this regard, according to the present invention, the abundance ratio between iron atoms and aluminum atoms (iron atoms: aluminum atoms) existing in the surface area of the metal magnetic powder is in the atomic ratio (30:70) to (70:30). Therefore, the oxidation ratio of the magnetic powder can be suppressed by sufficiently increasing the abundance ratio of aluminum atoms in the surface area and sufficiently exhibiting the corrosion resistance of aluminum atoms. Further, the dispersibility of the particles is also improved. If the abundance ratio of iron atoms in the surface area of the magnetic powder is larger than the above range, the corrosion resistance and dispersibility of the magnetic powder become insufficient. Further, when the abundance ratio of iron atoms is smaller than the above range, the activity of the magnetic powder surface increases, and the adsorption of polar groups in fatty acids and binders increases,
The stagnation stability as a paint is deteriorated.

According to the second invention, 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 sites present on the surface of each particle of the magnetic powder are further reduced, and the surface activity is reduced. Is suppressed. Therefore, the corrosion resistance and dispersibility of the metal magnetic powder are further improved, and the durability of the medium is improved.

The metal magnetic powder refers to a powder obtained by a dry reduction method in which iron oxide is reduced with hydrogen or the like, and the metal powder obtained by wet reduction with borohydride or the like cannot obtain the high electric characteristics and high durability of the present invention.

As the metal magnetic powder used in the present invention, Fe-Al based, Fe
-Al-Zn-based, Fe-Al-Co-based metal magnetic powder and the like can be exemplified.

The iron-aluminum-based metal magnetic powder used for the magnetic recording medium of the present invention can be produced, for example, as follows. α-
FeOOH, iron hydrates such as γ-FeOOH, or α-Fe ₂ O ₃ ,
Iron oxides such as γ-Fe ₂ O ₃ and Fe ₃ O ₄ are reduced with H ₂ at high temperature.

For example, after reacting an alkali component (eg, NaOH) with a ferrous salt compound (eg, FeSO ₄ , FeCl ₂ ), α-
FeOOH is generated, and the α-FeOOH is reduced at a high temperature (for example,
Or H ₂ by) to, or the alpha-FeOOH to then converted to α-Fe ₂ O _3, may be made of metal magnetic powder by high temperature reduction (for example, as H _2), the various stages , An Al compound (such as sodium aluminate) can be added as necessary. The same applies when a compound of another element other than Fe is added in addition to Al.

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 about 250 ℃ 30 ~ 6
0 min heat treatment was degassed while 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, liquid nitrogen by nitrogen Adsorption measurement is performed at a temperature (−195 ° C.) (a method for measuring a specific surface area, which is generally called a BET method. For details, see J. Ame. Chem. Sco. 6
0 309 (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. ).

The binder usable in the present invention has an average 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 derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various kinds of synthesis 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, low A mixture of high 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, an alkali metal such as lithium, potassium, and sodium, and M 'is a resin containing a hydrophilic polar group such as hydrogen, an alkali metal such as lithium, potassium, and sodium or a hydrocarbon residue). Is good. 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. It is possible to 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. it can.
Since this copolymer is produced by vinyl synthesis, it is easy to synthesize, 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) _m PO 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 (CH} 2 CH 2 O) m -, OH or OM. N is a positive number from 1 to 100, and m is a positive number from 1 to 100.

Examples of the copolymerizable monomer to be copolymerized as needed include 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, isobutene, 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 of the methods, 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%. The amount of the salt-containing monomer is too large, the 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 vinyl chloride copolymer preferably further contains an epoxy group or a hydroxyl group. By the way, a conventional PVC-based copolymer (for example, VAGH manufactured by UCC) was composed of the following copolymer components.

However, it is considered that the CH ₃ CO—O— group hardly contributes to the crosslinking reaction with the 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 above mixing ratio exceeds 90 parts by weight, the coating film becomes too brittle and the durability of the coating film is remarkably deteriorated, and the adhesion to the support is also deteriorated. If the mixing ratio is less than 10 parts by weight, the magnetic powder tends to fall off.

The combined use of carbon black in the magnetic layer is further advantageous in terms of improving running properties and electromagnetic conversion characteristics in combination with the action of α-alumina having the above specific surface area.

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), manufactured by Denki Kagaku Co., Ltd. (BET32m ² / g, DBP180ml / 100
g, particle size 53mμ), # 22B manufactured by Mitsubishi Kasei (BET55m ² / g, DB
P131ml / 100g, particle size ^{40mμ), # 20B (BET56m 2} / g, DBP115
ml / 100 g, particle size ^{40mμ), # 3500 (BET47m 2} / g, DBP187ml /
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 900
0, Black Pearls 1300, Black Pearls 200
0, Sterling V, Raven 410, Raven 3200, Raven 430, Raven 450, Raven 825, Raven 1255, manufactured by Columbian Carbon Co.
Raven 1035, Raven 1000, Raven 5000, Ketjen Black FC and the like.

Further, 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, Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.), and Desmodur L (manufactured by Bayer). Conventionally used curing agents such as trifunctional isocyanates or 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 a 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.

In addition to the α-alumina, other non-magnetic abrasive particles can be added to the magnetic layer. For this, for example, 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 this abrasive is preferably 0.6 μm or less, and 0.3 μm or less.
μm or less is more preferable.

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 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 the 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, organic powders such as a benzoguanamine-based resin, a melamine-based resin, and a phthalocyanine-based pigment 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-mentioned nonmagnetic 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 base 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.

However, for the metal magnetic powder, the content ratio of iron atoms to aluminum atoms in the magnetic powder and the abundance ratio in the surface area are also shown in FIG. The above abundance ratio was measured by ESCA at an analysis depth of up to 100 ° from the surface toward 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 represents the spectrum intensity detected by the counter. The horizontal axis is the binding energy (e
V). And the peak value of the binding energy is 76.8 eV
The peak value of aluminum oxide is 76.8 eV from the handbook, and the peak value of the binding energy of pure aluminum not oxidized is 72.7 eV.

Thereafter, a BC layer paint having the following composition was applied to the opposite side 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 (Nippon Polyurethane) 25 parts Coronate L (Nippon Polyurethane) 10 parts Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts A wide magnetic film having a predetermined thickness of a magnetic layer and a BC layer was obtained and wound. 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.

When measuring the frequency of occurrence of scratches on the tape, a video tape having a width of 1/2 inch (12.65 mm) was used.

<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 ". 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: The time until the still image is reduced by 2dB,
Shown in minutes. The larger the value, the higher the durability and wear resistance of the magnetic recording medium.

Saturation magnetization residual ratio: The percentage of the saturation magnetization measured after the sample tape was left standing for one week in an atmosphere of 60 ° C. and 80% RH was shown.

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

◎ Very good ○ Good △ Somewhat good × Poor Magnetic head clogging: The sample tape was run on a video deck at 40 ° C. and 80% for 200 hours continuously, and the magnetic head clogging was 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 significantly 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, specifying the content ratio of iron atoms and aluminum atoms in the metal magnetic powder and the abundance in the magnetic powder surface area are extremely important. .

[Brief description of the drawings]

1 and 2 are partially enlarged 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 region of the metal magnetic powder. FIG. 4 is a table showing changes in characteristics depending on the composition of the magnetic layer. 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 (2)

(57) [Claims] 1. A magnetic recording medium comprising a magnetic layer containing a metal magnetic powder containing Fe and Al and a binder, wherein the specific surface area of the metal magnetic powder is 45 m ² / g or more, Content ratio F of Fe and Al contained in powder
e: Al is 100: 1 to 100: 20 (atomic ratio), and analysis depth by ESCA from the surface of the metal magnetic powder is 10
30: 7 Fe: Al abundance ratio of Fe and Al existing in the region up to 0 °
A magnetic recording medium characterized by having an atomic ratio of 0 to 70:30. 2. Depth of analysis from the surface of metal magnetic powder by ESCA
2. The magnetic recording medium according to claim 1, wherein aluminum atoms existing in a region up to 100 [deg.] Are bonded to oxygen.