JP3390062B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium,
Or abrasives in the upper and other lower layers of multiple magnetic layers
To a magnetic recording medium. [0002] BACKGROUND OF THE INVENTION Recently, Hi-eight (Hi-8) or Hi-Vision
For magnetic recording media such as magnetic tapes
The requirement for conformity is becoming more stringent. In order to support Hi-8 and Hi-Vision
Requires ultra-smoothness of the magnetic layer.
In addition, it is necessary to make the abrasive finer. JP
No. 63-74118 discloses an average of ferromagnetic powder as an abrasive.
Particles less than 1/2 the particle size and less than 0.1 μm
Α-Al of size₂O₃For adding 5 to 15 wt%
Is disclosed. However, the magnetic layer has a single-layer structure.
Therefore, when ferromagnetic metal powder is used, the lubricant is strong against magnetic powder.
It is easy to be absorbed and causes a problem in running durability. JP-A-2-110823 discloses a magnetic layer.
With two or more layers, and BET value 35 m in the lower layer²/ G or more
Technology to improve C / N by using baltic iron oxide
Techniques are disclosed. However, the α-Al
The amount of mina is relatively small, and
Racks are used for high-temperature, high-humidity and low-temperature
There was a problem in running durability. Further, JP-A-2-208822 discloses a magnetic layer.
And an abrasive with an average particle size of 0.3 μm or less
Is polished to a magnetic layer other than the top layer with an average grain size of 0.3 μm or more.
Using an agent to maintain sliding characteristics and
There is disclosed a technique for improving cloudiness of a pad. This technology
It is well adapted to an image quality system of about S-VHS.
Used for the lower layer as a tape for i-8 and HDTV
Abrasive is too large to obtain the desired electrical properties
Can not. In other words, the surface properties of the uppermost layer are
Is strongly influenced by the surface of
It is strongly dependent on the average particle size of the contained abrasive. Hi-
8 and Hi-Vision tape improve the surface properties of the top layer
To improve the surface properties of the layer adjacent to the top layer.
Need to be done. [0006] Japanese Patent Application Laid-Open No. 1-106331, 1-1
No. 06332, the abrasive is contained in the lower layer.
Powder from the tape edge is a problem.
And head clogs may occur. JP-A-3-4
In No. 0217, this point has been improved,
Both upper and lower layers use abrasives with an average particle size of 0.3 μm
Therefore, the electromagnetic conversion characteristics compatible with Hi-8 and Hi-Vision
In some cases, you couldn't get it. Further, any of the above magnetic recording media
The thickness of the uppermost layer is relatively thick, 0.5 μm or more, and magnetic
Since the thickness of the entire layer is relatively large, the film thickness loss is large.
Disadvantageously that satisfactory electromagnetic conversion characteristics cannot be obtained.
You. [0008] SUMMARY OF THE INVENTION The present invention is intended for Hi-8 and HDTV.
It has sufficient electromagnetic conversion characteristics even at high and low temperatures.
No running clogs and stable running even under high temperature and high humidity
To provide a magnetic recording medium with excellent running durability.
aimed to. [0009] The object of the present invention is to: For magnetic recording media with multiple magnetic layers on non-magnetic support
Of the magnetic layer located on the upper layer side of the magnetic layer.
The dry film thickness is 0.05-0.3 μm and the total magnetic layer
Having a dry film thickness of 0.5 to 2.5 μm, and the upper layer
The side magnetic layer has an atomic weight ratio (Fe: Al) of (100:
0.5) to (100: 20).
Α-Al with a uniform particle size of 0.05 to 0.30 μm_TwoO_ThreeOr Cr
_TwoO_ThreeA powdery magnetic layer other than the upper layer
Α-Al contained in the side magnetic layer_TwoO_ThreeOr Cr_TwoO_ThreeWith powder
Cr of the same or larger average particle size_TwoO_Three, Bengala or α-
Al_TwoO_ThreeAchieved by magnetic recording media containing powder
You. According to the structure of the present invention, the thickness of the uppermost layer
The electromagnetic conversion characteristics even if the overall thickness of the magnetic layer is reduced.
Instead, various running durability can be improved. Change
As an embodiment of the present invention, the use of the upper magnetic layer of the present invention
The abrasive used has a particle size of 0.05 μm or more and 0.30 μm or less
Lower, more preferably 0.05 μm or more and 0.25 μm or less
Α-Al_TwoO_ThreeIs preferred. Further, an upper magnetic layer (hereinafter referred to as an uppermost layer)
U. ) Is a ferromagnetic metal alloy powder having an average particle size of 35 to
80mμ, preferably 40-70mμ carbon black
Is 1% or less of the weight of the magnetic powder (hereinafter abbreviated as 1% wt).
Described), preferably containing 0.2-0.8% wt,
An abrasive having an average particle diameter of the above-mentioned particle diameter is 4% wt or more of the magnetic powder.
Magnetic layer containing Co, and a Co-containing acid
It is preferable to use iron fossil. The BET value of the carbon black is 80 m
²/ G or less, oil absorption 100ml / 100g or more
Is more preferable. In addition, strong magnetic layers used for magnetic layers other than the top layer
For iron oxide of magnetic powder, perform surface treatment with Si and / or Al
Core-shell (Co-coated) iron oxide with Co as shell
preferable. As an abrasive used for magnetic recording media
Conventionally, there are various kinds of organic powder and inorganic powder
However, as a result of studying various abrasives,
The magnetic layers other than the uppermost layer have a Mohs hardness (MS) of 6
A specific one of the above inorganic powders is used. That is,
As an abrasive having a hardness of 6 or more, α-Al₂O₃(M
S9), TiO₂(MS6.5), SiO₂(MS
7), SnO₂(MS6.5), Cr₂O₃(MS
9), SiC (MS9) and TiC (MS9)
In the present invention, chromium oxide,
Or α-Al₂O₃It is. And the top layer
Α-Al with a hardness of 9 or more₂O₃Or using chromium oxide
It is. In order to further obtain the effect of the present invention, the average
When used for the uppermost layer, the particle size should be 0.30 μm or less.
When using at least one layer other than the uppermost layer,
Must have a particle size equal to or larger than that of
In other words, the top layer is monodisperse
α-Al₂O₃(Corundum). This organic aluminum
The na method is based on the following reaction. [0015]   2 AlR₃  + 4H₂O → Al₂O₃・ H₂O +6 RH     (Alkyl alumina) (Boehmite)   Al₂O₃・ H₂O → Al₂O₃  + H₂O                   heat Α-Al by the above reaction₂O₃Means that the particles are fine and
The particles are narrow and well-sized. Α-Al produced by the organic alumina method
₂O₃Particles may be obtained by other manufacturing methods depending on the firing conditions.
No particulate α-Al₂O₃In addition to the
The rate of pregelatinization can be controlled. In-crystal alpha ratio
High α-Al₂O₃Is α-Al having a low α conversion rate.₂O₃
Polishing ability and abrasion resistance are higher than that. High quality video tape
Abrasives are required to have a head cleaning effect.
Α-Al with an α conversion rate of 50% or more₂O₃Has polishing effect
And high-quality video with head cleaning effect
Suitable as an abrasive for tapes. Α-Al used in the present invention₂O₃Particles
The magnetic powder is preferably at least 4% by weight, more preferably 5% by weight.
It is used in the range of １５15% wt. Less than 4% wt
Head wear, head adhesion, and head damage reduction
If it is more than 15% wt, the output may fluctuate and decrease.
There is. Strong magnetic field forming a plurality of magnetic layers according to the present invention
Fe-Al based magnetic powder in the uppermost magnetic layer
Ferromagnetic alloy powder is used, Fe-Al alloy powder,
Fe-Al-Ni alloy powder, Fe-Al-Ca alloy powder
Powder, Fe-Al-Ca-Ni alloy powder, Fe-Ni-C
o-Al-Si alloy powder, Fe-Ni-Si-Al alloy
Strong magnetism of powder, Fe-Ni-Si-Al-Mn alloy powder
Alloy powder and the like. Among these, those used in the present invention
Means that the atomic weight ratio (Fe: Al) is (100: 0.5)
(100: 20) alloy powder. The shape of the ferromagnetic alloy powder is crystallite size.
Less than 200 °, preferably less than 180 °, average major axis length
It is preferably less than 0.25 μm, more preferably 0.20 μm.
Less than μm is used. Specific surface area of the ferromagnetic powder (B
ET method) is usually 25m²/ G or more, preferably
Is 30-80m²/ G. Coercive force of the ferromagnetic powder
Is usually 500 to 2,000 Oersted, preferably
Is between 600 and 1.700 Oersteds. Next, a magnetic layer other than the uppermost layer is formed.
Co-deposited or Co-containing C
o-γ-Fe₂O₃Powder, Co-Fe₃O₄Powder, Co
-Magnetic properties of iron oxide such as FeOx (4/3 <x <3/2) powder
Powder. The magnetic layer has a crystallite size of 4
Fe less than 50 °, average major axis length less than 0.25 μm²⁺,
Fe³⁺Atomic ratio between Fe²⁺/ Fe³⁺Is 0.08 or less
The above Co-iron oxide is preferred. The magnetic properties of the present invention
The axial ratio of the powder is about 500 particles in the electron micrograph.
It is the ratio of the measured average major axis length to the average minor axis length. As the binder used in the present invention
Generally have an average molecular weight of about 10,000 to 200,0
Resins in the range of 00 can be used. Specifically, for example, urethane polymer, salt
Vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, chloride
Vinyl-vinylidene chloride copolymer, vinyl chloride-acrylic
Lonitrile copolymer, butadiene-acrylonitrile copolymer
Polymer, polyamide resin, polyvinyl butyral, cell
Loin derivatives (eg: cellulose acetate butyrate,
Cellulose diacetate, cellulose propionate
, Nitrocellulose, etc.), styrene butadiene copolymerization
Body, polyester resin, various synthetic rubber binders,
Enol resin, epoxy resin, urea resin, melamine tree
Fat, silicone resin, acrylic reaction resin, high molecular weight resin
Mixing of ester resin and isocyanate prepolymer
Product, polyester polyol and polyisocyanate
Mixture, urea formaldehyde resin, low molecular weight glyco
And high molecular weight diol compounds and their mixtures.
And mixtures thereof. In the present invention, these resins are used in combination,
Or preferably use a resin having a negative functional group alone
Can also. As a resin having this negative functional group, -SO₃M¹, -OSO₂M¹, -OSO₃M¹  as well as
− [(M²O-) PO (-OM³)] (However, in the formula, M¹Is a hydrogen atom, an alkali metal,
M²And M³Are hydrogen atom, alkali metal and
And an alkyl group. Also M²And M³When
Can be different from each other or the same
No. ). The resin having a negative functional group is, for example,
PVC resin, polyester resin, polyurethane resin
Resin, such as fat, to introduce the negative functional group.
And can be obtained by Tree having the negative functional group
The amount of the negative functional group in the fat is 0.005 to 1.0 mmol
It is preferably 1 / g. In a resin in which the amount of the negative functional group is regulated,
Good dispersion of magnetic powder, large output of magnetic recording medium
And running stability is improved. Conversely, if the amount is outside the above range,
These effects may not be sufficiently obtained. When the resin having the negative functional group is used,
In this case, the compounding amount is based on 100 (weight) of the ferromagnetic powder.
And usually 2 to 50% wt, preferably 5 to 40% w
t. When the blending ratio is less than 2% wt,
Should be performed when resin with negative functional group is blended
The desired effect may not be achieved sufficiently. 50% wt
If it is more, the sliding noise and the head opacity are deteriorated.
Sometimes. In the present invention, the compound has the above negative functional group.
Use a polyisocyanate-based curing agent together with the resin
This can improve the durability of the magnetic layer.
You. As the polyisocyanate-based curing agent, for example,
Tolylene diisocyanate, diphenylmethane diisocyanate
Bifunctional isocyanates such as anatate and hexane diisocyanate
Anato, Coronate L (trade name; Nippon Polyurethane Engineering)
Desmodur L (trade name; manufactured by Bayer AG)
Trifunctional isocyanate or isocyanate at both ends
Conventional urethane prepolymers containing
What is used as a curing agent, or as a curing agent
Any polyisocyanate that can be used
Can also be used. The amount of the curing agent used is generally
Usually, it is 5 to 80 parts by weight of the total binder amount. In the present invention, the above-mentioned various binders are provided outside.
Examples of the dispersant which is an active ingredient include lecithin and phosphate
Ter, fatty acid, amine compound, alkyl sulfate,
Fatty acid amide, higher alcohol, polyethylene oxide
, Sulfosuccinic acid, sulfosuccinate, known interface
Activators and their salts, negative organic groups (eg -CO
OH, -PO₃H) Use of salt of polymer dispersant
Can be. These may be used alone or in combination.
A combination of more than one species may be used. In the present invention,
Use of fatty acid esters as optional plasticizers
Can be. As this fatty acid ester, for example,
Iloleate, oleyl stearate, isocetyl stearate
Allate, Dioleyl maleate, butyl stearate
Butyl palmitate, butyl myristate, octi
Lumiristate, octyl palmitate, amil steer
Rate, amyl palmitate, stearyl stearate
G, lauryl oleate, octyl oleate, isobutyl
Oleate, ethyl oleate, isotridecyl oleate,
Butoxyethyl palmitate, butoxyethyl stearee
2-ethylhexyl stearate, 2-ethylhexyl
Xyl myristate, ethyl stearate, 2-ethyl
Hexyl palmitate, isopropyl palmitate, a
Sopropyl myristate, isooctyl palmitate,
Isooctyl myristate, butyl laurate, cetyl
-2-ethyl hexalate, dioleyl adipate, di
Ethyl adipate, diisobutyl adipate, diisode
And siladipate. Among them, special
Butyl stearate, butyl palmitate
, Butoxyethyl palmitate, butoxyethyl
Allate, isooctyl palmitate, isooctylmi
Restate. The above-mentioned various fatty acid esters are used alone.
May be used, or two or more kinds may be used in combination.
Dispersants such as lecithin and fatty acid esters
If the amount of plasticizer added is reduced, especially under high temperature and high humidity
The running durability of the magnetic recording medium can be improved. The magnetic layer in the magnetic recording medium of the present invention comprises:
A lubricant may be contained. As a lubricant, for example,
Fatty acids, silicone-based lubricants, fatty acid-modified silicones
Lubricants, fluorine-based lubricants, liquid paraffin, squalane,
Carbon black, graphite, carbon black
Raft polymer, molybdenum disulfide, tungste disulfide
And the like. These may be used alone
Alternatively, two or more kinds may be used in combination. In the present invention, among the above lubricants, fats
Fatty acids can be suitably used. As the fatty acid
Is, for example, caproic acid, caprylic acid, capric acid, lauric
Phosphoric acid, myristic acid, palmitic acid, stearic acid,
Isostearic acid, linolenic acid, linoleic acid, olein
Acid, elaidic acid, behenic acid, malonic acid, succinic acid,
Oleic acid, glutaric acid, adipic acid, pimelic acid, aze
Lineic acid, sebacic acid, 1,12-dodecanedicarboxylic
Acids, octanedicarboxylic acid and the like. these
Among them, particularly preferred are myristic acid, oleic acid,
Stearic acid. The mixing ratio of the lubricant is determined by the ferromagnetic powder
Usually, 20% wt or less for 100 (weight) is preferable.
Or less than 10% wt. This compounding ratio is 20% w
Beyond t, blooming and bleed-out are likely to occur
It may be. In the present invention, the magnetic layers other than the uppermost layer
Contains carbon black with an average particle size of 10-100mμ
May be. The magnetic layer preferably has an average particle size of 10 to 100 μm.
Or contain carbon black of 20 to 40 mμ.
With the above, the improved electromagnetic properties in the magnetic recording medium of the present invention
Driving durability is further improved without inducing conversion characteristics
Can be made. However, the average grain of carbon black
If the diameter is less than 10 mμ, running durability may be poor.
You. On the other hand, the average particle size of carbon black is 100 mμ.
If it exceeds, the electromagnetic conversion characteristics decrease when the additive amount is increased.
May be invited. Further, the effects expected in the present invention can be sufficiently achieved.
The mixing ratio of the carbon black to play in
0 to 1% wt is preferable for the ferromagnetic powder 100 (weight).
Good. The magnetic layer further includes, in addition to the various components described above,
A polishing agent and an antistatic agent outside the present invention may be contained.
In addition, the antistatic agent or the above-mentioned dispersant, etc. are used alone.
Does not only have the effect of, for example, one compound
Objects may act as lubricants and antistatic agents.
You. Therefore, the above-mentioned classification in the present invention has the main function.
The effect of the classified compound is classified into
It is not limited by the action shown. Further, in the present invention, a multi-layer having different characteristics is used.
By laminating a number of magnetic layers, the magnetic layer has a multilayer structure.
By doing so, the characteristics are adjusted. And the top layer magnetic
The dry film thickness of the layer is 0.05 to 0.3 μm or less, and
The dry film thickness of all the magnetic layers is preferably 0.5 to 2.5 μm or less.
More preferably, it is 0.5 to 2.3 μm or less. Material for forming non-magnetic support used in the present invention
As the material, for example, polyethylene terephthalate and
Polyester such as polyethylene-2,6-naphthalate
Classes; Polyolefins such as polypropylene; Cellulose
Triacetate and cellulose diacetate
Lulose derivatives; polycarbonate, aromatic polycarbonate
List plastics such as lamide and polyimide
Can be. In addition, metals such as Cu, Al, Zn, etc.
So-called new ceramics (eg, boron nitride, carbonized
Various ceramics such as silicon) can also be used.
You. The thickness of the support is usually 3 to 150 μm, preferably
Or 4 to 100 μm. In the present invention, on the back of the nonmagnetic support
Is to improve the runnability of the magnetic recording medium, prevent static electricity and transfer
A back coat layer may be provided for prevention and the like.
No. However, in the present invention, a back coat layer is provided.
Good electromagnetic conversion characteristics, running performance and durability
Can be The magnetic layer forming surface of the non-magnetic support
To improve the adhesion between the magnetic layer and the non-magnetic support
As an intermediate layer (for example, an adhesive layer)
You. Further, a protective layer can be provided on the uppermost layer. The non
On a magnetic support, either directly or via a suitable intermediate layer
The magnetic layer is formed by dispersing ferromagnetic powder in a binder.
Formed. The magnetic recording medium of the present invention is characterized in that the abrasive,
Ferromagnetic powder, vinyl chloride resin with negative functional groups
Which binder and other magnetic layer forming components
After kneading and dispersing to prepare a magnetic paint, this magnetic paint is
Coated on non-magnetic support and dried
Can be built. The solvent used for kneading and dispersing the components for forming the magnetic layer
As the medium, for example, acetone, methyl ethyl ketone (M
EK), methyl isobutyl ketone (MIBK) and
Ketones such as clohexanone; methanol, ethanol
Alcohols such as toluene, propanol and butanol;
Methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, vinegar
Propyl acid and ethylene glycol monoacetate
Esters of diethylene glycol dimethyl ether
, 2-ethoxyethanol, tetrahydrofuran, di
Ethers such as oxane; benzene, toluene and
Aromatic hydrocarbons such as silene; methylene chloride, ethyl
Len chloride, carbon tetrachloride, chloroform, ethylene
Halogenation of chlorohydrin and dichlorobenzene
Hydrocarbons and the like can be used. In kneading the composition of the components for forming the magnetic layer,
Simultaneously, the ferromagnetic powder and other magnetic paint components
Alternatively, they are individually put into a kneader. For example, first
The ferromagnetic powder is added to the solution containing the agent, and the mixture is kneaded for a predetermined time.
After mixing, add the remaining components and continue kneading
Paint. For kneading and dispersion, various kneading machines are used.
Can be used. For example, two kneaders
Roll mill, three roll mill, pressure kneader, continuous knee
Da, open kneader, ball mill, pebble mill, side
Grinder, Sqegvari attritor, high-speed impeller
La dispersing machine, high-speed stone mill, high-speed impact mill, disc
Parneader, high-speed mixer, homogenizer, ultrasonic dispersion machine
And the like. Coatings that can be used for applying magnetic coatings
As a cloth method, for example, gravure roll coating,
My bar coating, doctor blade coating
, Reverse roll coating, dip coating
, Air knife coating, calendar coating
, Skis coating, kiss coating, ex
Trusion coating and funtin coating
And the like. For multi-layer coating, wet-on-dry or
A wet-on-wet method is optionally used. This
After applying the magnetic layer forming component,
Then, if necessary, perform a magnetic field alignment treatment, and further, for example,
-Perform surface smoothing using a calender roll, etc.
U. Next, by cutting into a desired shape, the magnetic recording
Recording media can be obtained. The magnetic recording medium of the present invention is, for example,
Video tape, audio tape by cutting
Cut as a magnetic tape or disk
Can be used as a floppy disk, etc.
Wear. In addition, as with ordinary magnetic recording media, cards
Shapes, cylindrical shapes, and the like can also be used. [0050] Next, Examples and Comparative Examples of the present invention will be described.
The present invention will be described more specifically. In addition, below
In Examples and Comparative Examples described below, "parts"
Part ". [0051] Magnetic paint for top layer   100 parts of ferromagnetic metal powder     Hc: 17400c δs: 125 emu / g     Crystallite size: 150Å     Si content 1.4% by weight, Al content 2.1% by weight, Co content 3.8% by weight % (Based on metal powder)     Vinyl chloride resin containing sulfonic acid metal salt 10 parts           (MR-110 manufactured by Zeon Corporation)     5 parts polyurethane resin containing sulfonic acid metal salt           (UR-8700 manufactured by Toyobo Co., Ltd.) [0052] Abrasive   See Table 1 for abrasive types     Carbon black     1 part of stearic acid     1 part butyl stearate     Cyclohexanone 100 parts     100 parts of methyl ethyl ketone     100 parts of toluene [0053] Magnetic paint for lower layer     Co-γ-Fe₂O₃                                    100 copies           (Surface treatment with Si and Al compounds, Si content 0.1% by weight, Al content 0.8% by weight) (based on magnetic powder)     12 parts of vinyl chloride tree containing sulfonic acid metal salt           (MR-110 manufactured by Zeon Corporation)     Sulfonic acid metal salt-containing polyurethane resin 8 parts           (UR-8200 manufactured by Toyobo Co., Ltd.) [0054] Abrasive             See Table 1 for abrasive types     1 part of stearic acid     Myristic acid 1 part     1 part butyl stearate     Cyclohexanone 100 parts     100 parts of methyl ethyl ketone     100 parts of toluene The above magnetic paints for the uppermost layer and the lower layer are prepared according to the respective formulations.
Knead and disperse the composition with a kneader and sand mill to form a coating
Finished. Next, a polyisocyanate was added to the resulting paint, respectively.
(Coronate L; manufactured by Nippon Polyurethane Co.)
Wet-on-wet method with a thickness of 10 μm
After coating on the magnetic support polyethylene terephthalate,
Perform the magnetic field orientation treatment while the coating film is not dried, then dry
Thereafter, the surface was smoothed by a calendar to form a magnetic layer.
Calendar conditions: temperature 80 ° C, pressure 300Kg / cm²so
The upper layer thickness is 0.4 μm and the lower layer thickness is 2.0 μm.
there were. The web obtained as above is cut to 8
mm videotape was made. These videotape trials
Table 1 shows the composition of the materials and the results of the performance evaluation. [Head clog] High temperature (40 ° C.), low temperature
(0 ° C) Under each environment, S-550 (Sony
The tape runs for the full length using the
When the head has been continuously generated for more than 1 second
And the number of occurrences was counted. [RF output] Noise meter 9 made by Shibasoku
8C video movie V900 (Sony
(Manufactured by the company). [Running durability] Running durability at 40 ° C and 80% RH Under an environment of 40 ° C. and 80% RH, S-550 (Sony
50 passes over the entire length of the tape
The jitter value after the pass was measured. Meguroelek for measurement
Vron jitter meter “MK-61” manufactured by Toronix
24 "(measurement unit: μs). [0059] [Table 1]As can be seen at a glance from Table 1, the present invention
There is a clear difference between the example and the comparative example, and the effect of the present invention
Is evident. [0061] According to the present invention, Hi-8 and high vision
With sufficient electromagnetic conversion characteristics for high temperature and low temperature
No head clog, and stable even at low temperature and high humidity
Magnetic recording media with excellent running durability
It has become possible.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hisato Kato 1 Konica Corporation, Sakura-cho, Hino-shi, Tokyo (72) Inventor Takahiro Mori 1 Konica Corporation, Sakura-cho, Hino-shi, Tokyo (72 ) Inventor Takahiro Hayashi 1-13-1 Nihombashi, Chuo-ku, Tokyo Inside TDK Corporation (56) References JP-A-3-219424 (JP, A) JP-A 5-151557 (JP, A) JP Hei 5-166171 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5/70

Claims (1)

(57) [Claim 1] In a magnetic recording medium having a plurality of magnetic layers on a non-magnetic support, a dry thickness of a magnetic layer located on an upper layer side of the magnetic layer is not more than 0. And the dry film thickness of all the magnetic layers is 0.5 to 2.5 μm,
The upper magnetic layer contains magnetic powder having an atomic weight ratio (Fe: Al) of (100: 0.5) to (100: 20), and has an average particle diameter of 0.05 to 0.30 μm. Al ₂
Α-Al ₂ O ₃ or C containing O ₃ or Cr ₂ O ₃ powder, wherein the magnetic layer other than the upper magnetic layer is contained in the upper magnetic layer.
A magnetic recording medium containing Cr ₂ O ₃ , red iron oxide or α-Al ₂ O ₃ powder having an average particle size equal to or larger than that of r ₂ O ₃ powder.