JP2002183931A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having improved electromagnetic conversion characteristics with respect to a recording medium with durability and high recording density. SOLUTION: In the magnetic recording medium having a nonmagnetic base layer on a nonmagnetic supporting body and having at least one magnetic layer having ferromagnetic powder dispersed in a binder on the base layer, the magnetic layer contains diamond having 0.05 to 1 μm average particle size and the base layer contains at least one kind of compound expressed by general formula (1). In formula (1), each of R1, R2, R3 and R4 is an alkyl group having 2 to 7 carbon atoms.

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 for high-density recording containing a ferromagnetic fine powder as a magnetic layer, and more particularly to a high-density magnetic recording medium having good storage characteristics and markedly improved durability. It is about.

[0002]

2. Description of the Related Art As a magnetic recording medium for audio, video, computer and the like, a magnetic recording medium having a magnetic layer in which a ferromagnetic powder is dispersed in a binder on a non-magnetic support has been used. I have. In recent years, even in the field of home video tape recorders, the practical use of digital recording with less deterioration of recording has been progressing from conventional analog recording, but generally more signals are recorded in digital recording than in analog recording. In addition, the recording / reproducing apparatus and the recording medium to be used are required to have high image quality and high sound quality, and at the same time, to be downsized and space-saving.

[0003] In order to achieve high-density recording, it is necessary to shorten the wavelength of a recording signal and to narrow the track of the recording locus. At the same time, the writing speed and reading speed of the recording medium must be reduced, and the number of rotations of the cylinder and the transport speed of the magnetic tape have been improved. In a device using a magnetic recording medium, there is a problem that the magnetic head is stained because the medium and the magnetic head are in sliding contact with each other. In particular, in a device for high-density recording, the rotation speed of a magnetic head is increasing, and in a digital video tape recorder, the rotation speed of a magnetic head is 9600 rotations / minute, which is 1800 rotations / minute for an analog video tape recorder at home. 5000 for business
The rotation speed is much higher than the rotation speed / minute. As the sliding speed between the magnetic recording medium and the magnetic head increases, there is a demand for a magnetic recording medium having high durability and high scratch resistance that can withstand high-speed sliding.

[0004] In addition to the tape type magnetic recording medium, Zip type rotating at a higher speed than a conventional floppy (registered trademark) disk even in a disk type magnetic recording medium.
High-density magnetic recording media represented by (Iomega Co., Ltd.) are used, and a magnetic recording medium having high durability and scratch resistance is also required. In order to solve such problems, it is possible to disperse the ferromagnetic metal powder in the binder to a high degree, improve the durability even in high-density recording, and perform stable recording and reproduction. It has been proposed to use a magnetic recording medium containing various lubricants in the magnetic layer in order to provide a simple magnetic recording medium. It has been proposed that

For example, Japanese Patent Publication No. 63-21255 discloses trimethylolpropane, trimethylolethane,
Alternatively, it is described that a tri- or tetraester lubricant obtained from pentaerythritol is used, but it is insufficient for a high-density recording medium such as a digital recording tape, and its storage stability and scratch resistance are insufficient. Also,
Japanese Patent Application Laid-Open No. 59-65531 discloses a magnetic recording medium using a lubricant in which a triester of trimethylolpropane and another diester, a tetraester and a monoester are used in combination. Properties were insufficient, and the electromagnetic conversion characteristics in high-density recording were insufficient. JP-A-61-139921 describes a magnetic recording medium in which a fatty acid ester of a polyhydric alcohol and a phosphate ester of phenoxydiethylene glycol are used as lubricants, but their storage stability and scratch resistance are insufficient. At the same time, the electromagnetic conversion characteristics in high-density recording were insufficient.

Further, Japanese Patent Publication No. 7-15748 discloses that
Trimethylolpropane ester or pentaerythritol ester, and a magnetic recording medium using a monoester as a lubricant are described, but storage stability and scratch resistance are insufficient, and in terms of electromagnetic conversion characteristics in high density recording. It was not enough. Japanese Patent No. 2552958 discloses a magnetic recording medium in which a nonmagnetic lower layer and a thin upper magnetic layer are formed to improve electromagnetic conversion characteristics particularly in short wavelength recording. The preservability and scratch resistance were insufficient with the given formulation.

Further, Japanese Patent Application Laid-Open No. 6-52541 discloses that
Among magnetic recording media provided with a magnetic layer containing an abrasive having a Mohs hardness of 8 or more, a magnetic recording medium in which the average protrusion height of the abrasive is 15 nm or less has been proposed, but is insufficient in durability. Was. JP-A-11-86273 discloses a magnetic recording medium having a substantially non-magnetic lower layer and a magnetic layer formed by dispersing ferromagnetic powder in a binder on a support in this order. A magnetic recording medium having a magnetic force of 1800 Oe or more and a magnetic layer containing diamond fine particles having an average particle diameter of 0.1 to 1.0 μm has been proposed, but is insufficient in durability. .

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a medium for high-density magnetic recording in which electromagnetic conversion characteristics, high-density recording characteristics, and durability are significantly improved.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording apparatus comprising a non-magnetic support having at least one non-magnetic underlayer and a magnetic layer having a ferromagnetic powder dispersed in a binder. In the medium, the average particle size in the magnetic layer is 0.05 μm or more.
This problem can be solved by a magnetic recording medium containing 1 μm diamond and containing at least one compound represented by the following general formula (1) in an underlayer.

[0010]

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However, R ¹ , R ² , R ³ and R ^{4 each} have 2 to 2 carbon atoms.
The alkyl group of No. 7 has a thickness of 0.05 μm to 1
μm. Further, the above magnetic recording medium is a disk-type magnetic recording medium.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The invention of the present application shows that in a high-density magnetic recording medium, electromagnetic conversion characteristics, high-density recording characteristics, and durability can be greatly improved by using a lubricant having a specific tetraester structure. That is what I found. In particular, it has been found that when the tetraester compound of the present invention is added to an underlayer containing at least a nonmagnetic lower layer, a magnetic layer is coated thereon, dried and further calendered to form an extremely smooth magnetic layer. It has been found that a magnetic recording medium which is extremely excellent in durability and particularly excellent in high-speed durability at high temperatures can be obtained.

In the general formula (1) representing the tetraester compound of the present invention, an alkyl group, R ¹ , R ² ,
R ³ and R ⁴ may be the same or different from each other. Further, R ¹ , R ² , R ³ , and R ⁴ easily volatilize when the number of carbon atoms is less than 2, and when the magnetic recording medium becomes hot at the time of friction, the amount of the lubricant on the surface of the magnetic layer decreases. The durability decreases. On the other hand, as the number of carbon atoms increases, the viscosity increases, the liquid lubricity decreases, and the durability decreases. Further, the tetraalkyl compound of the present invention has excellent storage stability because it has an alkyl group as a hydrocarbon group. The alkyl group may be either a branched or straight-chain hydrocarbon group, but a straight-chain one can provide a magnetic recording medium having a lower viscosity and being more durable. As the lubricant used in the present invention, the following tetraester compounds are preferable.

[0014]

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Further, the tetraester compound of the present invention comprises
The amount is preferably 1 to 20 parts by weight, more preferably 1 to 13 parts by weight, based on 100 parts by weight of the nonmagnetic powder. Further, in the magnetic recording medium of the present invention, additives having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. are used in addition to the lubricant composed of the tetraester represented by the general formula (1). . For example, molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, polar group-containing silicone, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol
, A fluorine-containing ester, a polyolefin, a polyglycol, an alkyl phosphate and an alkali metal salt thereof, an alkyl sulfate and an alkali metal salt thereof,
Polyphenylether, phenylphosphonic acid, aminoquinones, various silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof, monobasic fatty acids having 10 to 24 carbon atoms (including unsaturated bonds) And may be branched), and their metal salts (Li, Na, K, Cu, etc.) or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent having 12 to 22 carbon atoms. Divalent alcohol (which may contain an unsaturated bond or may be branched), alkoxy alcohol having 12 to 22 carbon atoms, monobasic fatty acid having 10 to 24 carbon atoms (including an unsaturated bond, May be branched) and having 2 to 2 carbon atoms.
A monofatty acid ester comprising any one of 12 monovalent, divalent, trivalent, tetravalent, pentavalent, and hexavalent alcohols (which may contain an unsaturated bond or may be branched) or A difatty acid ester or a fatty acid ester of a monoalkyl ether of an alkylene oxide polymer, a fatty acid amide having 8 to 22 carbon atoms, or an aliphatic amine having 8 to 22 carbon atoms can be used. As the monoester compound, a saturated fatty acid monoester, an unsaturated fatty acid monoester, an ester of an alkylene oxide-added alcohol and a fatty acid, and the like are preferable.

Further, n-butyl stearate, sec-
Butyl stearate, n-butyl palmitate, n-butyl myristate, isoamyl stearate, isoamyl palmitate, isoamyl myristate, 2-ethylhexyl stearate, 2-ethylhexyl palmitate, 2-ethylhexyl myristate, oleyl oleate, Oleyl stearate, stearyl stearate
And butoxyethyl stearate, butoxydiethylene glycol stearate and the like are preferred. As fatty acids, palmitoleic acid, oleic acid, erucic acid,
Linoleic acid, stearic acid, palmitic acid, myristic acid and the like are preferred.

As a binder suitable for the magnetic layer and the non-magnetic layer, a thermoplastic resin, a thermosetting resin, a reactive resin, or a mixture thereof is used. As the thermoplastic resin, the glass transition temperature is −100 to 150 ° C., and the number average molecular weight is 100.
0 to 200,000, preferably 10,000 to 10,000
0, having a degree of polymerization of 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,
There are polymers or copolymers containing butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, and the like as constituent units, polyurethane resins, and various rubber resins. As the thermosetting resin or the reactive resin, phenol resin, epoxy resin, polyurethane curing resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin,
Epoxy-polyamide resin, mixture of polyester resin and isocyanate prepolymer, polyester polyol
And mixtures of polyurethane and polyisocyanate, and mixtures of polyurethane and polyisocyanate. These resins are described in detail in "Plastic Handbook" (published by Asakura Shoten). In addition, a known electron beam-curable resin can be used for each layer. These examples and the production method thereof are described in 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 copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate maleic anhydride copolymer, At least one selected from
Examples include a combination of a seed and a polyurethane resin, or a combination of these with a polyisocyanate.

Since the tetraester compound of the present invention has a high affinity for a vinyl chloride-based binder and a polyurethane-based binder, it is preferable to use these compounds as the binder. Particularly, the binder for the underlayer is particularly preferably a vinyl chloride-based binder and a polyurethane-based binder. Vinyl chloride binders include alkyl acrylates, acrylics such as alkyl methacrylates, methacrylic monomers, allyl ethers such as allyl alkyl ethers, vinyl acetate, fatty acid vinyl esters such as vinyl propionate, styrene,
A vinyl monomer such as ethylene and butadiene, and a monomer having a functional group such as a hydroxyl group and an epoxy group and a polar group described below may be copolymerized.

As the polyurethane, polyester urethane, polyether urethane, polycarbonate urethane, polyetherester urethane, acrylic polyurethane and the like can be used. A polyurethane having a glass transition temperature Tg of −50 ° C. to + 200 ° C. is used. Preferably it is 20 to 100 degreeC. If the glass transition temperature is too low, the durability will decrease. If it is too high, calender moldability decreases, and smoothness and electromagnetic conversion characteristics decrease.

The binder includes -COOM and -S as polar groups.
O_ThreeM, -SO_FourM, -PO (OM) _Two, -OPO (O
M)_Two, Amino group, quaternary ammonium base, etc.
0^-Fiveeq / g-2 x 10^-Foureq / g introduced
Is preferred. When the amount of these polar groups is 1 × 10^-Fiveeq / g
If less, the dispersibility decreases, and 2 × 10^-Foureq /
Even when the amount is larger than g, the dispersibility decreases. In addition,
OH group is introduced as a curable functional group with anate curing agent
Epoxy group, SH group, CN
Group, -NO_TwoGroups may be introduced. Of magnetic layer
Binder amount is 100 parts by weight of ferromagnetic fine powder including curing agent
On the other hand, it is preferably 10 to 25 parts by weight.

Specific examples of these binders used in the present invention include VAGH and VY manufactured by Union Carbide.
HH, VMCH, VAGF, VAGD, VROH, VY
ES, VYNC, VMCC, XYHL, XYSG, PK
HH, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Co., Ltd., MPR-TA, MPR-TA5, MPR-TAL,
MPR-TSN, MPR-TMF, MPR-TS, MP
R-TM, MPR-TAO, 1000W manufactured by Denki Kagaku,
100FD, MR-104, MR-10 manufactured by Zeon Corporation
5, MR110, MR100, MR555, 400X-
110A, Nipporan N230 manufactured by Nippon Polyurethane Co.
1, N2302, N2304, Pandex T-5105, T-R3080, T-5201 manufactured by Dainippon Ink and Chemicals, Inc.
Burnock D-400, D-210-80, Chris Bon 6109, 7209, Byron UR820 manufactured by Toyobo
0, UR8300, UR-8700, RV530, RV
280, manufactured by Dainichi Seika Co., Ltd., Diferamine 4020, 50
20, 5100, 5300, 9020, 9022, 70
20, MX5004, manufactured by Mitsubishi Chemical Corporation, Samplen SP-150, manufactured by Sanyo Kasei, Saran F310, F2 manufactured by Asahi Kasei
10 and the like.

The ferromagnetic powder used in the magnetic layer of the present invention is preferably a ferromagnetic alloy powder containing α-Fe as a main component. These ferromagnetic powders include Al, S
i, S, Sc, Ca, Ti, V, Cr, Cu, Y, M
o, Rh, Pd, Ag, Sn, Sb, Te, Ba, T
a, W, Re, Au, Hg, Pb, Bi, La, Ce,
It may contain atoms such as Pr, Nd, P, Co, Mn, Zn, Ni, Sr, and B. In particular, Al, Si, C
Preferably, at least one of a, Y, Ba, La, Nd, Co, Ni, and B is contained in addition to α-Fe.
More preferably, it contains at least one of Y and Al. The content of Co is preferably from 0 to 40 at%, more preferably from 15 to 35 at%, and still more preferably from 20 to 35 at%. The content of Y is preferably from 1.5 to 12 at%, more preferably from 3 to 10 at%, and still more preferably from 4 to 9 at%.
Al is preferably at least 5 at.% And at most 30 at.%, More preferably at least 5 at.% And at most 15 at.%, More preferably at least 7 at.% And at most 12 at. These ferromagnetic powders may be treated in advance with a dispersant, a lubricant, a surfactant, an antistatic agent or the like before dispersion. Specifically, Japanese Patent Publication No. 44-14090, Japanese Patent Publication No. 45-1
8372, JP-B-47-22062, JP-B-47-
No. 22513, JP-B-46-28466, JP-B-46
-38755, JP-B-47-4286, JP-B-47
-12422, JP-B-47-17284, JP-B-4
Nos. 7-18509, JP-B-47-18573, JP-B-39-10307, JP-B-46-39639, U.S. Pat. Nos. 3,026,215, 3,031,341 and 31,
No. 00194, No. 3242005, No. 3389014
No. etc.

The ferromagnetic alloy fine powder may contain a small amount of hydroxide or oxide. A ferromagnetic alloy fine powder obtained by a known production method can be used, and the following method can be used. A method of reducing a complex organic acid salt (mainly oxalate) with a 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, Thermal decomposition method, reduction method by adding reducing agent such as sodium borohydride, hypophosphite or hydrazine to aqueous solution of ferromagnetic metal, reduction of fine powder by evaporating metal in low pressure inert gas And how to get it. The ferromagnetic alloy powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing the powder in an organic solvent and then drying it.
A method of immersing in an organic solvent, sending an oxygen-containing gas to form an oxide film on the surface, and then drying. A method of adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent to form an oxide film on the surface. Any of these can be used.

The ferromagnetic powder of the magnetic layer of the present invention is applied to the BET method.
45-80m in terms of specific surface area ^Two/ G, preferred
Or 50-70m^Two/ G. 40m^Two/ G or less
Is noisy, 80m^Two/ G or more, surface properties
It is difficult to obtain and is not preferred. The ferromagnetic powder of the magnetic layer of the present invention
The crystallite size is 8-35 nm, preferably 10-35 nm.
It is 25 nm, more preferably 14 to 20 nm. Strong magnetism
The major axis diameter of the conductive powder is 0.02 μm or more and 0.25 μm or less.
Yes, preferably between 0.05 μm and 0.15 μm
Yes, more preferably 0.06 μm or more and 0.1 μm or less
Below.

The needle ratio of the ferromagnetic powder is preferably from 3 to 15, more preferably from 5 to 12. The sigma _s of the magnetic metal powder is 100~180Am ² / kg, preferably from 110Am ² / kg~170Am ² / kg, more preferably 125~160Am ² / kg. The coercive force of the metal powder is 111.4 kA / m or more and 278.5 kA / m.
Or less, more preferably 143.3 kA / m or more and 238.7 kA / m or less.

The ferromagnetic metal powder has a water content of 0.01 to 2%.
It is preferable to optimize the water content of the ferromagnetic powder depending on the type of the binder. Further, it is preferable that the pH of the ferromagnetic powder is optimized by a combination with the binder used. Its range is from 4 to 12, preferably from 6 to 10. The ferromagnetic powder can be made of Al,
Surface treatment may be performed with Si, P, or an oxide thereof. The amount thereof is 0.1 to 10% based on the ferromagnetic powder.
mg / m ² or less, which is preferable. The ferromagnetic powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr. It is preferable that these are essentially absent, but if they are 200 ppm or less, they do not particularly affect the characteristics. 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 shape may be any of needle-like, rice-grain-like, and spindle-like as long as the characteristics of the particle size described above are satisfied. The SFD of the ferromagnetic powder itself is preferably small, and is preferably 0.8 or less. It is necessary to reduce the distribution of Hc in the ferromagnetic powder.
When the SFD is 0.8 or less, the electromagnetic conversion characteristics are good, the output is high, and the magnetization reversal is sharp and the peak shift is small, which is suitable for high-density digital magnetic recording. In order to reduce the distribution of Hc, there are methods for improving the particle size distribution of goethite and preventing sintering in ferromagnetic metal powder.

As the ferromagnetic powder used in the magnetic layer of the present invention, fine hexagonal ferrite powder can also be used. Examples of hexagonal ferrite include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and Co-substitutes. Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite whose particle surface is coated with spinel, and magnetoplumbite-type barium ferrite and strontium ferrite further containing a part of spinel phase. , Other than predetermined atoms, Al, Si, S, Sc, Ti, V, Cr, Cu, Y,
Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, T
a, W, Re, Au, Hg, Pb, Bi, La, Ce,
Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B,
It may contain atoms such as Ge and Nb. Generally, Co-
Ti, Co-Ti-Zr, Co-Ti-Zn, Ni-T
i-Zn, Nb-Zn-Co, Sb-Zn-Co, Nb
A substance to which an element such as -Zn is added can be used.
Some raw materials and production methods contain specific impurities. The particle size is 10 to 200 nm, preferably 20 to 100 nm in hexagonal plate diameter.

When reproducing with a magnetoresistive head, it is necessary to reduce noise, and the plate diameter is preferably 40 nm or less, but if it is 10 nm or less, stable magnetization cannot be expected due to thermal fluctuation. Above 200 nm, noise is high and none of them is suitable for high-density magnetic recording. The plate ratio (plate diameter / plate thickness) is 1 to
15 is desirable. Preferably it is 2-7. When the plate ratio is small, the filling property in the magnetic layer is increased, which is preferable, but sufficient orientation cannot be obtained. If it is larger than 15, noise increases due to stacking between particles. The specific surface area by the BET method in this particle size range is from 10 to ²⁰⁰ m ² / g. The specific surface area generally corresponds to an arithmetic calculation value from the particle plate diameter and the plate thickness. The crystallite size is 5 to 45 nm, preferably 1
0 to 35 nm. The narrower the distribution of the particle plate diameter and plate thickness, the better. Although it is difficult to make a numerical value, comparison can be made by randomly measuring 500 particles from a transmission electron micrograph of the particles.

Although the distribution is often not a normal distribution, when calculated and expressed as a standard deviation with respect to the average size, σ / average size = 0.1 to 2.0. In order to sharpen the particle size distribution, the particle generation reaction system is made as uniform as possible, and the generated particles are subjected to a distribution improving treatment. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known. The coercive force Hc measured on the magnetic material can be made up to about 39.8 kA / m to 397.9 kA / m. A higher Hc is advantageous for high-density recording, but is limited by the capability of the recording head. Normal 63.7kA
/ M to 318 kA / m, preferably 119 kA / m.
A / m or more and 279 kA / m or less. When the saturation magnetization of the head exceeds 1.4 T, it is preferable to set it to 159 kA / m or more. Hc can be controlled by particle size (plate diameter / plate thickness), kind and amount of contained element, substitution site of element, particle generation reaction condition and the like. Saturation magnetization _s is 40A
m ² / kg to 80 Am ² / kg. σ _s is preferably higher, but tends to be smaller as the particles become finer. σs
For improvement, it is well known to combine spinel ferrite with magnetoplumbite ferrite, and to select the types and amounts of elements to be contained. It is also possible to use W-type hexagonal ferrite.

At the time of dispersing the magnetic substance, the surface of the magnetic substance particles is also treated with a substance matching the dispersion medium and the binder. As the surface treatment material, an inorganic compound or an organic compound is used. Typical examples of the main compound include oxides or hydroxides of Si, Al, P and the like, various silane coupling agents, and various titanium coupling agents. The compounding amount is 0.1 to 10% by weight based on the magnetic material. The pH of the magnetic material is also important for dispersion. Usually, the optimum value is about 4 to 12, depending on the dispersion medium and the polymer.
About 0 is selected. Water contained in the magnetic material also affects dispersion. There is an optimum value depending on the dispersion medium and the polymer, but usually 0.01 to 2.0% by weight is selected.

The method for producing hexagonal ferrite is as follows:
Barium oxide / iron oxide / metal oxide replacing iron and boron oxide etc. as a glass-forming substance were mixed to a desired ferrite composition, melted, quenched to form an amorphous body, and then re-heated. Thereafter, the glass crystallization method of obtaining barium ferrite crystal powder by washing and pulverizing. (2) A barium ferrite composition metal salt solution is neutralized with an alkali, a by-product is removed, and then a liquid phase heating is performed at 100 ° C. or higher, followed by washing, drying, and pulverization to obtain a barium ferrite crystal powder by a hydrothermal reaction method. . (3) The barium ferrite composition metal salt solution is neutralized with an alkali to remove by-products, and then dried and dried.
A material obtained by a coprecipitation method or the like which is treated at 0 ° C. or lower and pulverized to obtain a barium ferrite crystal powder can be used.

The fine diamond particles used in the present invention have an average particle diameter of 0.1 mm. 05 μm to 1.0 μm,
Preferably it is 0.05 to 0.8 μm. When the average particle size is less than 0.05 μm, the effect of improving the durability is reduced. On the other hand, when it is larger than 1.0 μm, the durability is excellent, but the surface properties of the magnetic layer are deteriorated, and the electromagnetic conversion characteristics are deteriorated. In the present invention, the maximum diameter of each diamond fine particle is defined as a particle diameter, and the average particle diameter indicates an average value of measured values of 500 particles randomly extracted from a particle diameter photographed by an electron microscope.

The addition amount of the diamond fine particles is set to 0.1 to the ferromagnetic powder. 01 to 5% by weight, preferably 0.0
It is in the range of 3 to 3.00% by weight. 0. If it is less than 01% by weight, it is difficult to ensure durability, and if it exceeds 5% by weight, the noise reduction effect due to the addition of diamond decreases. From the viewpoint of noise and durability, the addition amount and average particle size of the diamond fine particles are defined in the above range.From the viewpoint of noise, the addition amount of diamond is preferably as small as possible. It is preferable to appropriately select the amount of diamond added and the average particle diameter of the diamond suitable for the magnetic recording / reproducing apparatus from the above range.

The particle size distribution of the diamond fine particles is such that the number of particles having a particle diameter of 200% or more of the average particle diameter is 5% or less of the total number of diamonds, and the particle diameter is 50% or less of the average particle diameter. 20% of all diamonds
The following is preferred. The particle size distribution is measured by counting the number of particles based on the average particle size when measuring the particle size. The particle size distribution of diamond fine particles also affects durability and noise. If the particle size distribution is wider than the above range, the effect corresponding to the average particle size set in the present invention is shifted as described above. That is, if there are too many particles having too large a particle size, noise is increased or the head is damaged.
If there are many fine particles, the polishing effect becomes insufficient. Further, those having an extremely narrow particle size distribution increase the price of diamond fine particles, and setting the above range is advantageous in terms of cost. The use of diamond particles having high hardness and having a sharp particle size distribution and fine particles as in the present invention can be expected to have the same level of polishing effect as a conventional abrasive because the content is smaller than that of conventional abrasives. It is advantageous from a viewpoint.

Further, in the present invention, diamond fine particles are
Conventionally used abrasives, for example, alumina, SiC
And the like can be used in combination. The effect on durability and S / N ratio is better with only a small amount of diamond fine particles, but an abrasive other than diamond fine particles such as alumina or silicon carbide may be added for cost or other reasons. Also in this case, since alumina alone is used, the amount of alumina alone can be considerably reduced from the amount required for durability, which is preferable from the viewpoint of securing durability and reducing noise.

The inorganic powder used for the underlayer according to the present invention comprises:
Non-magnetic powder, for example, metal oxides, metal carbonates,
It can be selected from inorganic compounds such as metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. As the inorganic compound, for example, α-alumina having an α conversion of 90% or more, β-alumina
Alumina, γ-alumina, θ-alumina, silicon carbide,
Chromium oxide, cerium oxide, α-iron oxide, goethite,
Corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, etc., alone or in combination used. Particularly preferred are titanium dioxide, zinc oxide, iron oxide and barium sulfate because of their small particle size distribution and many means for imparting functions, and more preferred are titanium dioxide and α-
It is iron oxide.

The particle size of these nonmagnetic powders is 0.00
The thickness is preferably from 5 to 2 μm, but if necessary, non-magnetic powders having different particle sizes may be combined, or even a single non-magnetic powder may have the same effect by broadening the particle size distribution. Particularly preferably, the particle size of the non-magnetic powder is from 0.01 μm to 0.2 μm. In particular, when the nonmagnetic powder is a granular metal oxide, the average particle diameter is 0.08 μm.
Or less, and in the case of an acicular metal oxide, the major axis length is preferably 0.3 μm or less. Tap density is 0.05 ~
It is 2 g / ml, preferably 0.2 to 1.5 g / ml. The water content of the non-magnetic powder is 0.1 to 5% by weight, preferably 0.2 to 3% by weight, more preferably 0.3 to 1.5% by weight. The pH of the nonmagnetic powder is 2 to 11, but p
H is particularly preferably between 5.5 and 10. The specific surface area of the nonmagnetic powder 1 to 100 m ² / g, preferably 5~80m ² /
g, more preferably 10 to 70 m ² / g. The crystallite size of the non-magnetic powder is preferably from 0.004 μm to 1 μm, more preferably from 0.04 μm to 0.1 μm. DBP
Oil absorption using (dibutyl phthalate) is 5 to 100 m
1/100 g, preferably 10-80 ml / 100 g,
More preferably, it is 20 to 60 ml / 100 g. The specific gravity is 1 to 12, preferably 3 to 6. The shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape.

The ignition loss is preferably 20% by weight or less. The Mohs hardness of the nonmagnetic powder used in the present invention is preferably 4 or more and 10 or less. The roughness factor of the powder surface is preferably 0.8 to 1.5, and more preferably 0.9 to 1.2.
It is.

The amount of stearic acid adsorbed on the non-magnetic powder is 1-2.
0 μmol / m^Two, Preferably 2 to 15 μmol /
m^Two, More preferably 3 to 8 μmol / m^TwoIt is. Non
Heat of wetting of magnetic powder in water at 25 ° C. is 0.2 J / m^Two~
0.6J / m^TwoIs preferably within the range. Also,
Solvents in the range of the heat of wetting can be used. p
H is preferably between 3 and 6. Non-magnetic powder water
0-150ppm soluble sodium, water soluble calcium
Is 0 to 50 ppm. On the surface of these non-magnetic powders
Is Al_TwoO_Three, SiO_Two, TiO_Two, ZrO_Two, SnO_Two, S
b_TwoO_Three, ZnO, Y_TwoO_ThreeSurface treatment is preferred
No. Al is particularly preferable for dispersibility._TwoO_Three, SiO_Two, T
iO_Two, ZrO_TwoHowever, more preferred is Al_TwoO_Three,
SiO_Two, ZrO _TwoIt is. These are used in combination
Or may be used alone. Also co-precipitated
Surface treatment layer may be used, or first treated with alumina
And then treating the surface with silica, or
The reverse method can be used. The purpose of the surface treatment layer is
It may be a porous layer according to the conditions, but it is homogeneous and dense
Is generally preferred.

Specific examples of the non-magnetic powder used in the underlayer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, and α-hematite DPN-250, DPN- manufactured by Toda Kogyo. 250BX, DPN-2
45, DPN-270BX, DBN-SA1, DBN-
SA3, Titanium oxide TTO-51B, TTO manufactured by Ishihara Sangyo
-55A, TTO-55B, TTO-55C, TTO-
55S, TTO-55D, SN-100, α hematite E270, E271, E300, E303, titanium oxide STT-4D, STT-30D, STT-
30, STT-65C, α-hematite α-40, MT-100S, MT-100T, MT-150W manufactured by Teica,
MT-500B, MT-600B, MT-100F, M
T-500HD, Sakai Chemical FINEX-25, BF-
1, BF-10, BF-20, ST-M, Dowa Mining D
EFIC-Y, DEFIC-R, AS made by Nippon Aerosil
2BM, titanium oxide P25, Ube Industries 100A, 50
0A, and those obtained by baking it. Particularly preferred non-magnetic powders are titanium dioxide and α-iron oxide.

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

The specific surface area of the lower carbon black is 10
0~500m ² / g, preferably 150~400m ² /
g, DBP oil absorption is 20 to 400 ml / 100 g, preferably 30 to 200 ml / 100 g. The particle size of the carbon black is 5 nm to 80 nm, preferably 10 to 5 nm.
0 nm, more preferably 10 to 40 nm. Car
Bonblack has a pH of 2 to 10 and a water content of 0.1 to 10
% And the tap density are preferably 0.1 to 1 g / ml. Specific examples of the carbon black used in the present invention include BLACKPEARLS 2000, manufactured by Cabot Corporation.
1300, 1000, 900, 800, 880, 70
0, VULCAN XC-72, Mitsubishi Chemical # 305
0B, # 3150B, # 3250B, # 3750B, #
3950B, # 950, # 650B, # 970B, # 8
50B, MA-600, MA-230, # 4000, #
4010, CONDUCTE manufactured by Columbia Carbon
XSC, RAVEN 8800,8000,7000,
5750, 5250, 3500, 2100, 2000,
1800, 1500, 1255, 1250, Ketchen Black E manufactured by Ketchen Black International
C and the like. Carbon black may be surface-treated with a dispersing agent or the like, grafted with a resin, or used, or a part of the surface may be graphitized.
Further, the carbon black may be dispersed in a binder before adding it to the paint. These carbon blacks do not exceed 50% by weight based on the inorganic powder,
It can be used in a range not exceeding 40% of the total weight of the nonmagnetic layer.
These carbon blacks can be used alone or in combination. The carbon black that can be used in the present invention can be referred to, for example, “Carbon Black Handbook” (edited by Carbon Black Association).

Further, an organic powder can be added to the lower coating layer. For example, acrylic styrene resin powder,
Examples include benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment, but polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin powder, and polyfluoroethylene resin can also be used. The production method is disclosed in Japanese Patent Application Laid-Open No. 62-185.
No. 64 and JP-A-60-255827 can be used.

The binder resin, lubricant, dispersant, additive, solvent, dispersing method, etc. of the magnetic layer can be applied to the binder resin of the underlayer. In particular, with respect to the amount and type of the binder resin, the amount of the additive and the type of the dispersant, and the type thereof, a known technique for the magnetic layer can be applied. The amount of the binder in the underlayer is preferably 15 to 40 parts by weight with respect to 100 parts by weight of the nonmagnetic fine powder, and it is preferable to increase the amount of the binder in the lower layer.

The coating solution prepared from the above materials is coated on a non-magnetic support to form a lower non-magnetic layer. Non-magnetic supports that can be used in the present invention are biaxially stretched polyethylene naphthalate, polyethylene terephthalate, polyamide, polyimide, polyamide imide,
Aromatic polyamide, polybenzoxydazole and the like can be used. Preferred are polyethylene naphthalate and aromatic polyamide. These non-magnetic supports may be previously subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment, and the like. The non-magnetic support which can be used in the present invention has a center line average surface roughness of a cutoff value of 0.25 m.
0.1 to 20 nm in m, preferably 1 to 10 nm
It is preferable to have a surface having excellent smoothness in the range of. It is preferable that these non-magnetic supports have not only a small center line average surface roughness but also no coarse protrusions of 1 μ or more. The preferred thickness of the nonmagnetic support in the magnetic recording medium of the present invention is 4 μm to 100 μm.

The backcoat layer (backing layer) is formed on the surface of the non-magnetic support used in the present invention on which the magnetic paint is not applied.
May be provided. The back coat layer is provided by applying a back coat layer forming paint in which a particulate component such as an abrasive and an antistatic agent and a binder are dispersed in an organic solvent on a surface of the non-magnetic support on which the magnetic paint is not applied. Layer. Various inorganic pigments and carbon black can be used as the particulate component, and resins such as nitrocellulose, phenoxy resin, vinyl chloride resin, and polyurethane can be used alone or as a mixture of these as a binder. . An adhesive layer may be provided on the surface of the non-magnetic support of the present invention where the magnetic paint and the back coat layer forming paint are applied.

The method for producing a magnetic recording medium according to the present invention comprises, for example, applying an underlayer coating solution to the surface of a running nonmagnetic support.
And a magnetic coating liquid is applied so as to have a predetermined film thickness.
The underlayer coating solution and the magnetic layer coating solution may be sequentially or simultaneously multilayer-coated, or the underlayer coating solution and the magnetic layer coating solution may be sequentially or simultaneously multilayer-coated. Examples of the coating machine for applying the underlayer coating solution or the magnetic coating solution include air doctor coating, blade coating, rod coating,
Extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, spray coat, spin coat and the like can be used.

For these, reference can be made, for example, to “Latest Coating Technology” (May 31, 1983) issued by Sogo Gijutsu Center. When applied to the magnetic recording medium of the present invention, the following can be proposed as an example of a coating apparatus and method. (1) First, a lower layer is applied by a coating apparatus such as gravure, roll, blade, or extrusion which is generally applied in the application of a magnetic layer coating liquid, and the lower layer is dried while the lower layer is in an undried state. No., JP-A-60-23
The upper layer is applied by a support pressure type extrusion coating apparatus as disclosed in JP-A-8179, JP-A-2-265672 and the like. (2) JP-A-63-88080, JP-A-2-179
No. 71 and Japanese Patent Application Laid-Open No. 2-265672 disclose the upper and lower layers almost simultaneously by one coating head having two coating liquid passage slits. (3) The upper and lower layers are coated almost simultaneously by an extrusion coating device with a backup roll as disclosed in JP-A-2-174965. The coating layer of the magnetic layer coating solution is dried after subjecting the ferromagnetic powder contained in the coating layer of the magnetic layer coating solution to a magnetic field orientation treatment.

After drying as described above, the coating layer is subjected to a surface smoothing treatment. For the surface smoothing treatment, for example, a super calender roll or the like is used. By performing the surface smoothing treatment, voids generated by the removal of the solvent during drying disappear, and the filling rate of the ferromagnetic powder in the magnetic layer is improved, so that a magnetic recording medium having high electromagnetic conversion characteristics can be obtained. it can. As the calendering roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyamideimide is used. Moreover, it can also process with a metal roll.

As a method of this, for example, as described above, a magnetic layer formed by selecting a specific ferromagnetic powder and a binder is subjected to the above calender treatment. The calendering conditions were such that the temperature of the calender roll was 60 to 1
The temperature is in the range of 00 ° C, preferably in the range of 70 to 100 ° C, particularly preferably in the range of 80 to 100 ° C, and the pressure is 98.
0 to 490 kN / m, preferably 196 to 490 kN / m.
441 kN / m, and particularly preferably 294 to 294 kN / m.
It is preferably carried out by operating under conditions in the range of 392 kN / m. The obtained magnetic recording medium can be used after being cut into a desired size using a cutting machine or the like. In the magnetic recording medium of the present invention, the thickness of the magnetic layer is preferably 0.05 μm to 1 μm. In particular, since the thickness is extremely thin, 0.05 μm to 1 μm, a magnetic recording medium having high electromagnetic conversion characteristics can be obtained.

On the other hand, when a thin magnetic layer is provided directly on a non-magnetic support, the durability is insufficient even if a triester having excellent lubricity is added, and the magnetic layer has poor smoothness. Sufficient noise causes large electromagnetic conversion characteristics, and a sufficiently high value cannot be obtained. However, when the underlayer is formed as in the present invention and the triester compound is added to at least the underlayer, the magnetic layer is coated thereon and dried and calendered. 1.0 nm to 3.5 nm at 0.25 mm, preferably 1.0 to 3.0 nm.
A surface having an extremely excellent smoothness in the range of 0 nm is obtained. As described above, the magnetic recording medium of the present invention has a feature that an extremely smooth magnetic layer is formed and the durability is extremely excellent, and particularly, the high-speed durability at a high temperature is excellent.

In particular, the combination with the underlayer is important for improving the smoothness, and it cannot be expected with a conventional magnetic recording medium having a single magnetic layer. In addition, the durability is improved because the effect of improving the durability is because even if this tetraester compound is added only to the underlayer, the magnetic recording medium is formed and then gradually exudes to the surface of the magnetic layer.

[0054]

The present invention will be described below with reference to examples. However, in the examples, parts indicate parts by weight. Examples 1 to 12 and Comparative Examples 1 to 7 (Preparation of Upper Layer Magnetic Coating) 100 parts of ferromagnetic metal fine powder Composition: Fe: Co (atomic ratio of 70:30), Hc183 kA / m, specific surface area 55 m ² / g, σs 140 Am ² / Kg Crystal size 155 nm, major axis length 0.065 μm, needle ratio 5 Sintering inhibitor Aluminum compound (Al / Fe atomic ratio 8%) Y compound (Y / Fe atomic ratio 6%) Vinyl chloride copolymer ( ZEON MR110) 12 parts Sulfonic acid-containing polyurethane resin (UR8200 manufactured by Toyobo) (solid content) 3 parts α-alumina (described in Table 2) Carbon black (# 50 manufactured by Asahi Carbon) 5 parts Compound described in Table 1 (table 2) Stearic acid 2 parts Methyl ethyl ketone 180 parts Cyclohexanone 180 parts

(Preparation of Lower Nonmagnetic Paint) Nonmagnetic Powder Titanium Oxide Crystalline Rutile 80 Parts Average Primary Particle Size 0.035 μm Specific Surface Area by BET Method 40 m ² / g pH 7 TiO ₂ Content 90% or More DBP Oil Absorption 27 ３８38 g / 100 g Surface treatment agent Al ₂ O ₃ 4% by weight Carbon black 20 parts Conductex SC-U (manufactured by Columbian Carbon Co.) Vinyl chloride copolymer (MR110 manufactured by Zeon Corporation) 12 parts Sulfonic acid-containing polyurethane resin ( UR8200 manufactured by Toyobo (solid content) 5 parts Compound described in Table 1 (described in Table 2) Stearic acid 3 parts Methyl ethyl ketone / cyclohexanone (8/2 (weight ratio)) 250 parts For each of the above paints, each component is kneaded. After kneading, they were dispersed using a sand mill. In the obtained dispersion, 10 parts of a polyisocyanate was added to the coating solution for the non-magnetic layer,
To the coating solution for the magnetic layer, 10 parts were added, and 40 parts of butyl acetate was added to each, and the mixture was filtered using a filter having an average pore diameter of 1 μm. Prepared.

The obtained non-magnetic layer coating solution was dried to a thickness of 1.5 μm, and the magnetic layer was further coated thereon with a thickness of 62 μm to a thickness of 0.2 μm. Immediately after the application of the coating solution for the non-magnetic layer on the polyethylene terephthalate support having a center line surface roughness of 0.01 μm, the magnetic layer is coated simultaneously with the multi-layer coating. 2.5mT, frequency 50
After passing through an AC magnetic field generator having two magnetic field intensities of 1.2 Hz and 1.2 mT, a random orientation treatment was performed, followed by drying, followed by treatment at a temperature of 90 ° C. and a linear pressure of 294 kN / m using a seven-stage calender. After punching the surface of the mold and subjecting the surface to a polishing treatment, the mold was placed in a 3.7-type cartridge (Zip cartridge manufactured by Iomega Co.) provided with a liner inside to obtain a floppy disk.

Each sample of the prepared floppy disk was
It was measured by the following evaluation method. (Evaluation method) 1. Measurement of playback output S / N The playback output was measured using a disc evaluation device (R, manufactured by Guzik, USA).
AW1001 type) and a spin stand (LS-90 manufactured by Kyodo Electronic System Co., Ltd.) using a metal in-gap head with a gap length of 0.3 μm and reproducing output at a linear recording density of 90 kfci at a radius of 24.6 mm ( TAA) and the noise after DC demagnetization were measured to determine the S / N ratio. 2. Durable floppy disk drive (Zipped by Iomega)
100: the number of rotations was 2968 rpm), the head was fixed at a position with a radius of 38 mm, and recording was performed at a recording density of 34 kfci. Then, in a thermocycle environment where the following flow is one cycle, 100
It was run for 0 hours. Measure the output every 24 hours of running,
The time when the output became 70% or less of the initial value was defined as the life. Thermocycle flow test A. 25 ° C, 50% RH for 1 hour ↓ Temperature rise for 2 hours B. C. 20% RH for 7 hours ↓ Cooling for 2 hours C. D. 1 hour at 25 ° C, 50% RH ↓ 2 hours cooling 5 ° C, 10% RH, 7 hours ↓ Temperature rise, 2 hours Return to A, and repeat the cycle of A → B → C → D → A.

[0058]

Table 1 Structures of compounds R ¹ , R ² , R ³ , R ⁴ Compound A General formula (1) C ₂ H ₅ -Compound B General formula (1) C ₃ H ₇ -Compound C General formula (1) C ₄ H ₉ -Compound D General formula (1) C ₅ H ₁₁ -Compound E General formula (1) C ₆ H ₁₃ -Compound F General formula (1) C ₇ H ₁₅ -Compound G General formula (1) iC ₇ H ₁₅ -Compound H n-butyl stearate

[0059]

Table 2 Compound Diamond α-alumina S / N Durability Upper layer Non-magnetic Average particle size Addition amount Addition amount Addition amount Magnetic layer Lower layer (μm) (parts) (μm) (parts) (dB) (hr) Example 1A A 0.25 3 − − 5.2 1600 Example 2 BB 0.25 3 − − 5 1700 Example 3 C C 0.25 3 − − 5.6 1600 Example 4 DD 0.25 3 − − 6.2 1500 Example 5 EE 0.25 3 − − 5.8 1500 Example 6 FF 0.25 3 − − 5.4 1500 Example 7 GG 0.25 3 − − 5 1500 Example 8 HA 0.05 3 − − 5.2 1600 Example 9 A A 0.05 3 − − 5.6 1500 Example 10 A A 1 3 − − 5 1500 Example 11 A A 0.25 3 0.25 10 4 1700 Example 12 A A 1.5 3 − − 5 900 Comparative Example 1 A A − − 0.25 10 4.2 400 Comparative Example 2 A A − − 0.25 20 2 700 Comparative Example 3 A A − − 0.25 40 0 1300 Comparative Example 4 HH 0.25 3 − − 4 300 Comparative Example 5 H H − − 0.25 20 3 200 Comparative Example 6 A A − − 0.05 20 2.4 400 Comparative Example 7 A A − − 1 20 1.6 700

[0060]

According to the present invention, the electromagnetic conversion characteristics in a high-density recording medium can be improved by including at least the specific tetraester as a lubricant in the underlayer and the diamond particles in the magnetic layer. The durability was improved in a high recording density disk medium.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) G11B 5/82 G11B 5/82 (72) Inventor Jin Noguchi 2-12-1, Ogimachi, Odawara-shi, Kanagawa Wealth Wealth Photo Film Co., Ltd. (72) Inventor Shinji Saito 2-1-1, Ogimachi, Odawara-shi, Kanagawa F Photo Film Co., Ltd. F-term (reference) 4J038 CA001 CA021 CB021 CC021 CD031 CD081 CE021 CE051 CE071 CF031 CG031 CG141 CG161 DA011 DA111 DA161 DB001 DG001 DL001 HA026 HA066 JA57 MA13 MA14 NA22 NA26 PB11 PC02 PC08 5D006 BA10 BA19 CA04 DA02 FA02

Claims (3)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and at least one non-magnetic under layer on which a ferromagnetic powder is dispersed in a binder is provided. Containing diamond of 0.05 μm to 1 μm,
A magnetic recording medium characterized in that the underlayer contains at least one compound represented by the following general formula (1). Embedded image However, R ¹ , R ² , R ³ and R ⁴ are alkyl groups having 2 to 7 carbon atoms. 2. The method according to claim 1, wherein the thickness of the magnetic layer is 0.05 μm to 1 μm.
2. The magnetic recording medium according to claim 1, wherein m is m. 3. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a disk-type magnetic recording medium.