JP2001331929A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium for high density recording having high durability at high temperatures and enhanced electromagnetic transducing characteristics. SOLUTION: In the magnetic recording medium obtained by disposing an underlayer containing at least a nonmagnetic powder on a substrate and at least one magnetic layer containing a ferromagnetic powder dispersed in a binder on the underlayer, at least one compound of the formula R1COOR2 (where R1 is a 21-29C alkyl, R2 is a 22-36C alkyl and at least one of R1 and R2 is a branched alkyl) is contained at least in the underlayer.

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 has excellent durability, and particularly has high durability at high temperatures. 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 the field of magnetic disks, C
o 2MB MF when unformatted using denatured iron oxide
A 2HD type floppy (registered trademark) disk is standardly mounted on a personal computer.

Further, with the recent demand for higher data capacity and the improvement of thin layer coating technology, Iomega's 3.7-type floppy disk for Zip has been put into practical use at 100 Mb or 250 Mb. However, in today's rapidly increasing data capacity, the capacity cannot be said to be sufficient, and the surface recording density is 6.4.
High density recording of 0.2 Gb or more per 5 cm ² is being demanded. In addition, the demand for shortening the access time tends to increase the rotation speed of the disk.

[0004] Further, due to the high functionality and miniaturization of devices such as personal computers, the amount of heat generated during the operation of the devices has increased, and the inside of the devices has become hotter. However, there is a growing demand for high-temperature durability. 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. In order to provide a suitable magnetic recording medium, it has been proposed to use a magnetic recording medium containing various lubricants in a magnetic layer, and it has been proposed to use various esters as lubricants.

For example, Japanese Patent Publication No. 5-22970 discloses that a magnetic layer contains a fatty acid having a linear or branched saturated alkyl group having 8 to 28 carbon atoms and a 2-position branched alcohol having 24 to 28 carbon atoms. It has been proposed to use an ester, and specific examples of the compound include C8, C12,
14, 16, 18 or 22 fatty acids and 2 carbon atoms
An ester comprising alcohols of 4, 25 is described. However, such an ester compound has insufficient durability, has a poor electromagnetic conversion property for a medium for high-density recording, and has a poor magnetic property. Insufficient scratch resistance of the layer.

Further, Japanese Patent Publication Nos. 4-70689, 4-70690 and 4-70691 disclose a saturated or unsaturated carbon layer having a straight or branched chain having 8 to 30 carbon atoms in the magnetic layer. A fatty acid having an alkyl group,
It has been proposed to use an ester with a 2-branched alcohol having 24 to 36 carbon atoms.
12, 14, 16, 18, and 22 acids and 2 carbon atoms
Esters of alcohols of 4, 30, and 34 are described. Particularly, the preferred range of the fatty acid component is that the fatty acid component has 8 to 24 carbon atoms. The recording medium has insufficient electromagnetic conversion characteristics, and the magnetic layer has insufficient scratch resistance. Japanese Patent Application Laid-Open No. 11-339253 discloses that at least one of a nonmagnetic lower layer and a magnetic recording layer has a molecular weight of 7 or less.
A magnetic recording medium containing a fatty acid ester compound having at least one branched side chain of 0 or more is described, and as the ester compound, isostearyl stearate, isostearyl oleate, isocetyl stearate, trimethylolpropane tripandate Kanate is exemplified, but durability, electromagnetic conversion characteristics in a medium for high-density recording,
In addition, the scratch resistance of the magnetic layer is insufficient.

Further, Japanese Patent Publication No. 7-66519 discloses that
Although a magnetic recording medium having an ester of a fatty acid having a hydrocarbon group of 12 to 22 carbon atoms and a branched alcohol having 3 to 20 carbon atoms is described, the durability is insufficient and the magnetic recording medium is used for high-density recording. The medium has insufficient electromagnetic conversion characteristics and the magnetic layer has insufficient scratch resistance. Further, Japanese Patent No. 2649951 describes that an ester of a fatty acid having a linear alkyl or alkenyl group having 11 to 29 carbon atoms and a 2-position branched alcohol having 10 to 32 carbon atoms is used. Although a medium is described, durability, electromagnetic conversion characteristics in a medium for high-density recording, and scratch resistance of the magnetic layer are all insufficient. Also,
Japanese Patent No. 2662989 describes a magnetic recording medium having an ester of a linear fatty acid having 16 to 30 carbon atoms and a 2-position branched alcohol having 16 to 22 carbon atoms. Specifically, the fatty acid component is Although a straight-chain structure having 12 to 30 carbon atoms is mentioned, the durability is insufficient, the electromagnetic conversion properties are insufficient for a medium for high-density recording, and the scratch resistance of the magnetic layer is insufficient. Met.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having excellent durability, which has excellent electromagnetic conversion characteristics in high-density recording and can be used in a high-temperature environment. It is an object of the present invention to provide a magnetic recording medium having good durability and scratch resistance, and to provide a magnetic recording medium which is excellent in calender moldability and excellent in smoothness.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording apparatus comprising a support having at least one underlayer containing at least a nonmagnetic powder and at least one magnetic layer having a ferromagnetic powder dispersed in a binder. The problem can be solved by a magnetic recording medium in which at least the underlayer contains at least one compound represented by the general formula (1). General formula (1) R ¹ COOR ² where R ¹ is an alkyl group having 21 to 29 carbon atoms R ² is an alkyl group having 22 to 36 carbon atoms R ¹ and / or R ² is a branched alkyl group Further, R ¹ is a branched alkyl group having 23 to 27 carbon atoms, R ²
Is the above-mentioned magnetic recording medium, which is a branched alkyl group having 24 to 28 carbon atoms. When the thickness of the magnetic layer is 0.05 μm to 0.
The above magnetic recording medium having a thickness of 4 μm. The above magnetic recording medium which is a disk type magnetic recording medium. The magnetic recording medium according to the present invention is used for an apparatus for sliding a recording / reproducing head in a state where a disk rotates at 700 rotations or more per minute.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The invention of the present application achieves both high durability, scratch resistance and electromagnetic conversion characteristics in a high-density magnetic recording medium by using a lubricant having a specific chemical structure. In particular, when a fatty acid having a specific number of carbon atoms of the present invention and a branched ester compound composed of an alcohol having a specific number of carbon atoms are added to at least the nonmagnetic lower layer, the magnetic layer is coated thereon and dried, and further calendered. It has been found that a magnetic recording medium having excellent durability can be obtained, and in particular, a magnetic recording medium having excellent high-speed durability at high temperatures can be obtained.

The lubricant used in the present invention includes:
Esters represented by the following general formula (1) are exemplified. General formula (1) R ¹ COOR ² where R ¹ is an alkyl group having 21 to 29 carbon atoms R ² is an alkyl group having 22 to 36 carbon atoms R ¹ and / or R ² is a branched alkyl group More preferably, R ¹ is a branched alkyl group having 23 to 27 carbon atoms, and R ² is a branched alkyl group having 24 to 28 carbon atoms.

If the carbon number is too small, it is likely to volatilize, and if the temperature rises due to heat generation or friction inside the equipment used, the amount of the magnetic layer surface existing decreases and the durability decreases. In addition, when the hydrophilicity increases, the durability in a high humidity environment decreases. If it is too large, the viscosity will be high, and the fluid lubrication performance will decrease, and the durability will decrease.
The hydrocarbon is preferably a saturated hydrocarbon in terms of storage stability.

On the other hand, it is preferable that the alkyl group has a branch. Even if the branched structure has a large number of carbon atoms, it is preferable because it lowers the melting point, suppresses crystallization, and suppresses the surface roughening of the magnetic layer. It is necessary that at least a hydrocarbon group derived from an alcohol among the hydrocarbon groups derived from a fatty acid and an alcohol derived from an ester structure has a branched structure. When the carbon number of R ¹ is 30 or more and the carbon number of R ² is 37 or more, the viscosity increases due to an increase in molecular weight,
It is not preferable because solubility in a coating liquid for forming a magnetic recording medium is deteriorated and unevenness of a coating film is generated.

The general method for synthesizing a fatty acid ester of the present invention and the method for reacting a fatty acid or a fatty acid chloride with an alcohol can be used. For example, Koshobo
It is described in "New edition fatty acid chemistry". Examples of the ester compound that can be used in the present invention include behenic acid 2
-Butyloctadecyl, 2-decyltetradecyl behenate, 2-decylhexadecyl behenate, 2-decyloctadecyl behenate, 2-dodecyloctadecyl behenate, behenyl 2-decyltetradecanoate, 2-decyltetradecyltetradecanoate Decyl, hexacosyl 2-decyltetradecanoate, 2-decylhexadecyl 2-decyltetradecanoate, 2-decyloctadecyl 2-decyltetradecanoate, 2-dodecyloctadecyl 2-decyltetradecanoate, 2-hexadecyloctadecyl 2-decyltetradecanoate 2-octyldecyloctadecyl 2-decyltetradecanoate, behenyl 2-decylhexadecanoate, 2-decyltetradecyl 2-decylhexadecanoate, 2-decylhexadecyl 2-decylhexadecanoate, 2 Decyl hexadecanoic acid 2-decyl-octadecyl, 2-decyl hexadecanoic acid 2-dodecyl octadecyl, montanic acid 2-decyl tetradecyl, montanic acid 2-decyl hexadecyl, montanic acid 2-decyl-octadecyl, montanic acid 2-dodecyl tetradecyl,
2-dodecyl octadecyl montanate, montanic acid 2-
Hexadecyl octadecyl, 2-octadecyl octadecyl montanate, 2-decyl tetradecyl 2-decyl octadecanoate 2-decyl hexadecyl 2-decyl octadecanoate 2-decyl octadecyl 2-decyl octadecyl 2-decyl octadecyl 2-decyl octadecanoate 2- Dodecyl tetradecyl, 2-dodecyl octadecyl 2-decyl octadecanoate, 2-hexadecyl octadecyl 2-decyl octadecanoate, 2-octadecyl octadecyl 2-decyl octadecanoate, 2-butyl octadecyl melisinate, 2-decyl tetradecyl melisate, Melic acid 2
-Decylhexadecyl, 2-dodecylhexadecyl mericate, 2-hexadecyloctadecyl melicate, and 2-octadecyloctadecyl mericate.

Among these, 2-decyltetradecyl 2-decyltetradecanoate, 2-decylhexadecyl 2-decyltetradecanoate, 2-decyloctadecyl 2-decyltetradecanoate, 2-decyl 2-decylhexadecanoate are preferred. Tetradecyl, 2-decyl hexadecyl 2-decyl hexadecanoate, 2-decyl octadecyl 2-decyl hexadecanoate, 2-decyl tetradecyl 2-decyl octadecanoate, 2-decyl hexadecyl 2-decyl octadecanoate, 2-decyl octadecane Acid 2
-Decyl octadecyl 2-decyl octadecanoate 2-
Dodecyltetradecyl.

Further, more preferably, 2-decyltetradecyl 2-decyltetradecanoate, 2-decylhexadecyl 2-decyltetradecanoate, 2-decyloctadecyl 2-decyltetradecanoate, 2-decyltetradecyl-2-decyltetradecanoate Decyl, 2-decyl hexadecanoate 2-decyl hexadecanoate, 2-decyl hexadecanoate 2
-Decyloctadecyl.

It is necessary that these ester compounds are contained at least in the non-magnetic lower layer, and the addition amount is 0.1 to 25 parts per 100 parts by weight of the non-magnetic powder.
More preferably, it is 1 to 15 parts. When added to the magnetic layer, the addition amount is 0.1 to 25 parts, more preferably 1 to 15 parts, per 100 parts by weight of the magnetic material.

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 together with the ester compound 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,
Examples include polyphenyl ether, phenylphosphonic acid, aminoquinones, various silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof, ester compounds, and fatty acids.

Examples of the ester compound which can be used in combination include a monoester compound, such as a saturated fatty acid monoester, an unsaturated fatty acid monoester, and an ester of an alkylene oxide-added alcohol and a fatty acid. , 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. As fatty acids, palmitoleic acid, oleic acid,
Erucic acid, linoleic acid, stearic acid, palmitic acid,
Myristic acid and the like can be mentioned.

The thickness of the magnetic layer is 0.01 to 1 μm,
It is preferably 0.05 μm to 0.4 μm, and 0.01
If the thickness is smaller than μm, a uniform recording layer cannot be formed. On the other hand, if the thickness is more than 1 μm, the surface of the magnetic layer becomes rough, and the electromagnetic conversion characteristics deteriorate. The thickness of the nonmagnetic layer is 0.1 μm to 5 μm.
μm, and preferably 0.5 μm to 3 μm. If the thickness of the non-magnetic layer is less than 0.1 μm, the durability is reduced. If the thickness is more than 5 μm, the surface becomes rough and the electromagnetic conversion characteristics deteriorate.

Suitable binders for the magnetic layer and the non-magnetic layer include thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof. 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, acrylate, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylate, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal. , Vinyl ether, etc. as constituent units, such as polymers or copolymers, polyurethane resins, and various rubber resins. Also,
Phenolic resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic-based reactive resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, polyester resin as thermosetting resin or reactive resin And a mixture of a polyester polyol and a polyisocyanate, and a mixture of a polyurethane and a 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, and vinyl chloride vinyl acetate maleic anhydride copolymer. A combination of at least one selected member with a polyurethane resin, or a combination of these with a polyisocyanate is exemplified.

Since the ester compound of the present invention has a high affinity for a vinyl chloride binder and a polyurethane binder, it is preferable to use these compounds as the binder. Particularly, the binder in the non-magnetic lower layer is particularly preferably a vinyl chloride binder and a polyurethane binder. Vinyl chloride binders include acrylics such as alkyl acrylates and alkyl methacrylates, methacrylic monomers, allyl ethers such as allyl alkyl ethers, fatty acid vinyl esters such as vinyl acetate and vinyl propionate, and vinyls such as styrene, ethylene and butadiene. A monomer, a monomer having a functional group such as a hydroxyl group or an epoxy group, or a polar group described later may be copolymerized. As the polyurethane, polyester urethane, polyether urethane, polycarbonate urethane, polyetherester urethane, acrylic polyurethane, or the like can be used. The glass transition temperature Tg of polyurethane is from -50 ° C to
+ 200 ° C. is used. Preferably 20 ° C to 1
00 ° C. If the glass transition temperature is too low, the durability will decrease. If it is too high, calender moldability decreases and smoothness increases.
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 was introduced as a curable functional group with anate curing agent.
Preferably, epoxy group, SH group, CN
Group, -NO_TwoGroups may be introduced.

The amount of the binder in the magnetic layer is preferably 10 to 25 parts by weight based on 100 parts by weight of the ferromagnetic fine powder including the curing agent. The amount of the binder in the magnetic layer is 10 to 25 parts by weight per 100 parts by weight of the ferromagnetic fine powder including the curing agent, and the amount of the binder in the nonmagnetic lower layer is 15 to 40 parts by weight based on 100 parts by weight of the nonmagnetic fine powder. It is preferable to increase the amount of the binder.

As the ferromagnetic powder used in the magnetic layer of the present invention, a ferromagnetic alloy powder containing α-Fe as a main component is preferable. 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, Pb, Bi, La, Ce, Pr,
It may contain atoms such as Nd, P, Co, Mn, Zn, Ni, Sr, and B.

In particular, Al, Si, Ca, Y, Ba, L
a, Nd, Co, Ni, at least one of B and α-Fe
It is preferable to include at least one of Co, Y, and Al. The content of Co is
The amount is preferably 40 or less, more preferably 15 or more and 35 or less, more preferably 20 or more and 35 or less in terms of the atomic ratio of α-Fe to 100. The content of Y is 1.5 or more and 1
It is preferably 2 or less, more preferably 3 or more and 10 or less, more preferably 4 or more and 9 or less. Al is preferably 5 or more and 30 or less, more preferably 5 or more and 15 or less, more preferably 7 or more and 12 or less with respect to 100 of α-Fe in atomic ratio. These ferromagnetic powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent, or the like before dispersion before dispersion. Specifically, JP-B-44-14090, JP-B-45-18
No. 372, JP-B-47-22062, JP-B-47-22513, JP-B-46-28466, JP-B-46-38755, and JP-B-47-42.
No. 86, JP-B-47-12422, JP-B-4
7-17284, JP-B-47-18509, JP-B-47-18573, JP-B-39-10
No. 307, JP-B-46-39639, U.S. Pat. Nos. 3,026,215, 3,303,341 and 310.
No. 0194, No. 3242005, and No. 3389014.

The ferromagnetic alloy fine powder may contain a small amount of hydroxide or oxide. Ferromagnetic alloy fine powder, those obtained by a known manufacturing method can be used,
The following methods can be mentioned. 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, metal is evaporated in low-pressure inert gas atmosphere For example, a method of obtaining fine powder. The ferromagnetic alloy powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying, a method of immersing in an organic solvent and then forming an oxide film on the surface with an oxygen-containing gas and then drying. Alternatively, any of the methods of adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent to form an oxide film on the surface 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 high noise, 80m^Two/ G or more provides surface properties
It is not preferred. The ferromagnetic powder of the magnetic layer of the present invention
The crystallite size is 8-35 nm, preferably 10-2.
It is 5 nm, more preferably 14 to 20 nm. Ferromagnetic
The major axis diameter of the powder is not less than 0.02 μm and not more than 0.25 μm.
And preferably from 0.05 μm to 0.15 μm.
And more preferably 0.06 μm or more and 0.1 μm or less
It is. The needle ratio of the ferromagnetic powder is preferably 3 or more and 15 or less.
And more preferably 5 or more and 12 or less. Magnetic metal powder
Is 100 to 180 Am^Two/ Kg (emu / g)
Yes, preferably 110 Am^Two/ Kg (emu / g),
More preferably 125 to 160 Am^Two/ Kg (emu /
g). The coercive force of the metal powder is 111 kA / m (14
00 Oe) or more and 279 kA / m (3500 Oe) or less
And more preferably 143 kA / m (1800
Oe) or more and 238 kA / m (3000 Oe) or less
You. The water content of the ferromagnetic metal powder should be 0.01 to 2%.
Is preferred. Water content of ferromagnetic powder depending on the type of binder
Preferably, the rate is optimized.

The pH of the ferromagnetic powder is preferably adjusted by the combination with the binder used. The range is 4-1
2, but preferably 6 to 10. The ferromagnetic powder may be subjected to a surface treatment with Al, Si, P, or an oxide thereof. The amount thereof is 0.1 to 10% based on the ferromagnetic powder, and the surface treatment is preferable because the adsorption of a lubricant such as a fatty acid becomes 100 mg / m ² or less. Ferromagnetic powder contains soluble Na, Ca, Fe, Ni,
It may contain an inorganic ion such as 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 its value is 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 above-mentioned characteristics regarding the particle size are satisfied. The switching field distribution of the ferromagnetic powder itself (SF
D) is preferably smaller, more preferably 0.8 or less. It is necessary to reduce the distribution of Hc in the ferromagnetic powder. In addition,
When the SFD is 0.8 or less, the electromagnetic conversion characteristics are good,
The output is high, 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, a hexagonal ferrite fine 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, B
a, Ta, W, Re, Au, 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.

Generally, Co—Zn, Co—Ti, Co
-Ti-Zr, Co-Ti-Zn, Ni-Ti-Zn,
A substance to which an element such as Nb-Zn-Co, Sb-Zn-Co, or Nb-Zn is added can be used. In addition, those containing impurities that are inevitable depending on the raw materials and the production method can also be used.

The particle size is 10 to 200 n in hexagonal plate diameter.
m, preferably 20 to 100 nm. 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 are suitable for high-density magnetic recording. The plate ratio (plate diameter / plate thickness) is desirably 1 to 15. Preferably it is 2-7. If 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. Crystallite size is 5
４５45 nm, preferably 10-35 nm. The distribution of particle plate diameter and plate thickness is generally preferably as narrow as possible. Although difficult to quantify, comparison can be made by randomly measuring 500 particles taken by a transmission electron microscope (TEM) photograph. The distribution is often not a normal distribution, but when calculated and expressed as the standard deviation of the average size, σ / average size =
0.1 to 2.0. To sharpen the particle size distribution, make the particle generation reaction system as uniform as possible,
A distribution improvement treatment is also performed on the generated particles. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known.

The coercive force Hc of the magnetic material is 39.8 to 398 k
It can be manufactured up to about A / m (500 Oe to 5000 Oe). A higher Hc is advantageous for high-density recording, but is limited by the capability of the recording head. Usually 63 to 318 kA / m
(800 Oe to 4000 Oe), but preferably 119 kA / m (1500 Oe) or more and 279 kA
/ M (3500 Oe) or less. When the saturation magnetization of the head exceeds 1.4 Tesla, 159 kA / m (200
0 Oe) 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 σ
s is a ^{40Am 2 / kg ~80Am 2 / kg} . σs
Is preferably higher, but tends to be smaller as the particles become finer. It is well known to combine spinel ferrite with magnetoplumbite ferrite in order to improve σs, and to select the type of element contained and the amount to be added. It is also possible to use W-type hexagonal ferrite. When dispersing the magnetic material, the surface of the magnetic material particles is also treated with a substance suitable for the dispersion medium and the polymer. 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 amount is 0.1 to 10 parts by weight based on 100 parts by weight of the magnetic material.

The pH of the magnetic material is also important for dispersion.
Usually, about 4 to 12, there is an optimum value depending on the dispersion medium and the polymer, but about 6 to 10 is selected from the chemical stability and storage stability of the medium. 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 chosen. The method of producing hexagonal ferrite is as follows: (1) A metal oxide replacing barium oxide, iron oxide, and iron, and a glass-forming substance such as boron oxide are mixed so as to have a desired ferrite composition, and then melted and quenched. A glass crystallization method in which a barium ferrite crystal powder is obtained by forming an amorphous body, followed by reheating treatment, and then 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) Barium ferrite composition A coprecipitation method in which a metal salt solution is neutralized with an alkali to remove by-products, dried, treated at 1100 ° C. or lower, and pulverized to obtain barium ferrite crystal powder. Etc., but any method may be used.

Next, the lower layer of the magnetic recording medium of the present invention will be described. The inorganic powder used in the lower coating layer of the present invention is a non-magnetic powder, and is selected from, for example, inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. can do. Examples of the inorganic compound include α-alumina, β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, goethite, corundum, silicon nitride, titanium nitride having an α conversion of 90% or more. -Bites, titanium oxide, silicon dioxide, tin oxide, magnesium oxide,
Tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide and the like are used alone or in combination. 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-iron oxide. The particle size of these non-magnetic powders is preferably 0.005 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 a similar particle size distribution to achieve the same effect. You can also. Particularly preferably, the particle size of the non-magnetic powder is from 0.01 μm to 0.2 μm. In particular, when the non-magnetic powder is a granular metal oxide, the average particle diameter is not more than 0.1.
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 to 2 g / ml, preferably 0.2 to 1.5 g / ml.
ml. The water content of the nonmagnetic powder is 0.1 to 5% by weight,
Preferably 0.2 to 3% by weight, more preferably 0.3 to 3% by weight.
1.5% by weight.

The pH of the nonmagnetic powder is from 2 to 11, and the pH is particularly preferably from 5.5 to 10. The specific surface area of the nonmagnetic powder is 1 to 100 m ² / g, preferably 5 to 8 m ² / g.
0 m ² / g, more preferably from 10 to 70 m ² / g. The crystallite size of the non-magnetic powder is 0.004 μm to 1 μm
m is preferable, and 0.04 μm to 0.1 μm is more preferable. Oil absorption using DBP (dibutyl phthalate) is 5
~ 100ml / 100g, preferably 10-80ml /
100 g, more preferably 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.

It is preferable that the ignition loss is 20% by weight or less, and it is considered that it is most preferable that there is no ignition loss. 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 surface of these powders is preferably 0.8 to 1.5, and more preferably 0.9 to 1.2. The stearic acid adsorption amount of the non-magnetic powder is 1 to 20 μmol / m
² , preferably ² to 15 μmol / m ² , more preferably 3 to 8 μmol / m ² . The heat of wetting of the nonmagnetic powder in water at 25 ° C. is preferably in the range of 0.2 to 0.6 J / m ² . Further, a solvent having a range of the heat of wetting can be used. Preferably, the pH is between 3 and 6. The water-soluble sodium of the non-magnetic powder is 0 to 150
ppm, water-soluble calcium is 0 to 50 ppm.

Al ₂ O ₃ ,
SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , Zn
Surface treatment with O and Y ₂ O ₃ is preferred. Particularly preferable for dispersibility are Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂
More preferably, Al ₂ O ₃ , SiO ₂ , Zr
O ₂ . These may be used in combination,
It can be used alone. Further, a co-precipitated surface treatment layer may be used, or a method of treating the surface layer with silica after treating with alumina first, or vice versa, may be employed. Although the surface treatment layer may be a porous layer depending on the purpose, it is generally preferable that the surface treatment layer be homogeneous and dense.

Specific examples of the non-magnetic powder used in the lower coating layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, α-hematite DPN-250 manufactured by Toda Kogyo, and DPN. -250BX, DPN
-245, DPN-270BX, DBN-SA1, DB
N-SA3, Titanium oxide TTO-51B, T made by Ishihara Sangyo
TO-55A, TTO-55B, TTO-55C, TT
O-55S, TTO-55D, SN-100, α hematite E270, E271, E300, E303, Titanium oxide titanium oxide STT-4D, STT-30D, ST
T-30, STT-65C, α-hematite α-40, MT-100S, MT-100T, MT-150 manufactured by Teica
W, MT-500B, MT-600B, MT-100
F, MT-500HD, Sakai Chemical FINEX-25, B
F-1, BF-10, BF-20, ST-M, Dowa Mining Ltd. DEFIC-Y, DEFIC-R, manufactured by Japan Aerosil AS2BM, TiO ₂ P25, manufactured by Ube Industries, Ltd. 100A, 5
00A, and those obtained by firing the same. Particularly preferred non-magnetic powders are titanium dioxide and α-iron oxide.

By mixing carbon black in the lower coating layer, the surface electric resistance Rs, which is a known effect, can be reduced, the light transmittance can be reduced, and a desired micro Vickers hardness can be obtained. In addition, the effect of storing lubricant can be brought about by including carbon black in the lower layer. As the type of carbon black, furnace black for rubber, thermal black 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. The carbon black 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, manufactured by Mitsubishi Chemical Corporation # 30
50B, # 3150B, # 3250B, # 3750B,
# 3950B, # 950, # 650B, # 970B, #
850B, MA-600, MA-230, # 4000,
# 4010, CONDUC made by Konlon Via Carbon
TEX SC, RAVEN 8800, 8000, 70
00, 5750, 5250, 3500, 2100, 20
00, 1800, 1500, 1255, 1250, Ketjen Black EC manufactured by Ketjen Black International, 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 can be used in a range not exceeding 50% by weight based on the inorganic powder and in a range not exceeding 40% of the total weight of the nonmagnetic layer. These carbon blacks can be used alone or in combination. Cars that can be used in the present invention
Bon Black is described in, for example, "Carbon Black Handbook" (Car
Bon 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 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 lower coating layer can be the same as those of the magnetic layer described below. 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 coating solution prepared from the above materials is coated on a non-magnetic support to form a lower coating layer or a magnetic layer. As a nonmagnetic support that can be used in the present invention, biaxially stretched polyethylene naphthalate, polyethylene terephthalate, polyamide, polyimide, polyamide imide, aromatic polyamide, polybenzoxdazole, or the like can be used. Preferred are polyethylene naphthalate and aromatic polyamide. These non-magnetic supports are treated in advance by corona discharge, plasma treatment, easy adhesion treatment,
Heat treatment or the like may be performed. Further, the nonmagnetic support which can be used in the present invention has a surface having excellent smoothness such that the center line average surface roughness is in the range of 0.1 to 20 nm, preferably 1 to 10 nm at a cutoff value of 0.25 mm. Is preferred. Further, 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 μm or more. The preferable thickness of the nonmagnetic support in the magnetic recording medium of the present invention is 4 μm to 1 μm.
00 μm.

A back coat 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, for example, “Latest Coating Technology” (May 31, 1983) published by Sogo Gijutsu Center can be referred to. 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-2-17
No. 971 and Japanese Unexamined Patent Publication 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. Epoxy resin as calendering roll,
A heat-resistant plastic roll such as a polyimide resin, a polyamide resin, or a polyamide-imide resin is used. Moreover, it can also process with a metal roll.

As the method, for example, the magnetic layer formed by selecting a specific ferromagnetic powder and a binder as described above 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. The magnetic recording medium of the present invention has a magnetic layer thickness of 0.05 μm to 1 μm.
m, which is extremely thin, so that a magnetic recording medium having high electromagnetic conversion characteristics can be obtained. The magnetic recording medium of the present invention has a center line average roughness of 1.0 nm to 3.5 nm, preferably 1.0 to 3.0 nm at a cutoff value of 0.25 mm.
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 cannot be expected in a conventional magnetic recording medium having a single-layer magnetic layer. In addition, the effect of improving the durability is good because even if the tetraester compound is added only to the underlayer, it gradually exudes to the surface of the magnetic layer after the magnetic recording medium is manufactured.

With the above structure, the magnetic recording medium of the present invention achieves both extremely high durability and electromagnetic conversion characteristics as compared with the conventional one. DV in terms of tape
For tapes and discs for video systems with extremely high recording densities, such as C and DVC-PRO, excellent durability can be achieved with a high-speed recording system such as Zip, especially at a high rotation speed of 700 rpm or more. all right.

These magnetic recording media have extremely smooth surfaces to achieve their high electromagnetic conversion characteristics. If the recording head slides on this smooth surface at a high speed, it is extremely difficult to secure durability with the conventional technology. For example, conventionally used ester lubricants include butyl stearate, heptyl stearate, octyl stearate, isocetyl stearate, oleyl oleate, and the like.However, these lubricants do not provide sufficient durability. Impossible. In particular, it is considered that the durability in a high-temperature atmosphere is insufficient, and that extremely high frictional heat is generated by high-speed sliding between the head and the magnetic layer.

In order to solve these problems, the invention cited as a conventional example also discloses the use of relatively high molecular weight esters. However, when these high molecular weight esters are added to the magnetic layer, the surface of the magnetic layer becomes rough. However, since the electromagnetic conversion characteristics are reduced, it has been impossible to realize a magnetic recording medium having a smooth magnetic layer surface for high-density recording. In particular, in order to obtain a magnetic recording medium that has high electromagnetic conversion characteristics and realizes sufficient durability even when sliding with a recording / reproducing head that rotates at a high speed, the ester compound of the present invention is used as a magnetic layer. It is necessary that at least the non-magnetic lower layer of the magnetic recording medium having the non-magnetic lower layer includes the non-magnetic lower layer.

The ester compound of the present invention has a sufficiently high molecular weight to withstand high-speed sliding, and hardly volatilizes even at a high temperature.
In addition, since it has a branched structure, it has a relatively low melting point and is unlikely to be crystallized, so that the coating film is less likely to be roughened during coating and drying. Furthermore, it was found that when combined with a magnetic recording medium having a magnetic layer and a non-magnetic underlayer according to the present invention, the surface of the magnetic layer was not roughened and an extremely smooth magnetic recording medium was obtained.

Further, the thickness of the magnetic layer is set to 0.05 μm to 0.1 μm.
This effect is remarkable when the thickness is sufficiently reduced to 5 μm. This is because the ester lubricant having a high molecular weight of the invention of the present application has the effect of promoting the aggregation of the magnetic substance particularly during drying in the magnetic coating liquid,
It is considered that it is suppressed by the nonmagnetic lower layer. As described above, the combination with the non-magnetic lower layer is important for improving the smoothness, and this is an effect that cannot be expected with a conventional magnetic recording medium having a single magnetic layer. Further, even when the ester compound of the present invention is added only to the non-magnetic lower layer, the magnetic recording medium is gradually oozed out to the surface of the magnetic layer after the magnetic recording medium is manufactured, so that the durability is exhibited for a long time, so that the durability is improved. The effect is great.

[0057]

The present invention will be described below with reference to examples. However, in the examples, parts indicate parts by weight. Examples 1 to 7, Comparative Example 3 (Preparation of magnetic coating for upper layer) 100 parts of ferromagnetic alloy powder A Composition: Fe: Co: Al: Y = 100: 20: 9: 6 (atomic ratio) Hc 159 kA / m ( 2000 Oe), a crystallite size of 15 nm, a BET specific surface area of 59 m ² / g, a major axis diameter of 0.09 μm, a needle ratio of 7, and a s of 140 Am ² / kg were pulverized by an open kneader for 10 minutes, and then a vinyl chloride copolymer MR110 (Nihon Zeon) 7.5 parts Sulfonic acid-containing polyurethane resin (UR8200 manufactured by Toyobo) (solid content) 5 parts Cyclohexanone 60 parts is added and kneaded for 60 minutes, and then α-alumina HIT55 (Sumitomo Chemical) 10 parts carbon black # 50 ( 3 parts methyl ethyl ketone / toluene = 1: 1 (weight ratio) 200 parts were added and dispersed by a sand mill for 120 minutes. . To this was added 5 parts of polyisocyanate (Coronate 3041 manufactured by Nippon Polyurethane) (solid content) 4 parts of the compound of Table 1 1 part of stearic acid 1 part 1 part of oleic acid 50 parts of methyl ethyl ketone, and the mixture was further stirred and mixed for 20 minutes. The mixture was filtered using a filter having the same to prepare a magnetic paint.

(Preparation of Nonmagnetic Paint for Lower Layer) Titanium oxide 85 parts Average particle size 0.035 μm, crystalline rutile, TiO ₂ content 90% or more Surface treatment layer; alumina, S _BET 35 to 42 m ² / g, true Specific gravity 4.1 pH 6.5 to 8.0 15 parts of carbon black (Ketjen Black EC Ketjen Perak International) are pulverized for 10 minutes by an open kneader, and then 17 parts of vinyl chloride copolymer MR110 (Nippon Zeon) Sulfonic acid-containing polyurethane resin (10 parts of UR8200 (solid content) manufactured by Toyobo and 60 parts of cyclohexanone are added and kneaded for 60 minutes, and then 200 parts of methyl ethyl ketone / cyclohexanone = 6: 4 (weight ratio) is added and dispersed by a sand mill for 120 minutes. The lubricant and polyisocyanate shown in Table 1 (Nippon Poly Rethane coronate 3041) (solid content) 5 parts Stearic acid 1 part Oleic acid 1 part Methyl ethyl ketone 50 parts was added, and the mixture was further stirred and mixed for 20 minutes, and then filtered using a filter having an average pore diameter of 1 μm to remove the non-magnetic paint. Prepared.

(Preparation of Magnetic Recording Medium) A 62 μm thick polyethylene terephthalate support was applied so that the obtained non-magnetic paint had a thickness of 1.5 μm, and immediately thereafter the magnetic paint had a thickness of 0.2 μm after drying. Simultaneous overcoating was applied to the body surface. 50 Hz, 2.5 × 1 with both layers wet
After passing through an AC magnetic field generator having two magnetic field intensities of 0 ^-2 Tesla and a frequency of 50 Hz and 1.2 × 10 ^-2 Tesla, random orientation treatment is performed. min, linear pressure 2.94 × 10 ⁵
The test was performed under the conditions of N / m (300 kg / cm) and a temperature of 90 ° C. After punching into a 3.7-type disk shape and performing surface polishing treatment, Zip with a liner installed inside,
A magnetic recording medium composed of a floppy disk was prepared by mounting the cartridge on a cartridge (Iomega Co.) and evaluated by the following evaluation method.

Comparative Examples 1 and 2 Floppy disks were prepared in the same manner as in Example 1 except that the magnetic layer was directly coated on the support without coating the nonmagnetic lower layer.

(Evaluation method) 1. Electromagnetic conversion characteristics Disk evaluation device (RWA100 manufactured by GUZIK, USA)
Type 1) and spin stand (LS- made by Kyodo Electronic System)
At 90), using a metal-in-gap head with a gap length of 0.3 μm, the reproduction output (TAA) at a linear recording density of 60 kfci and the noise level after DC demagnetization were measured at a radius of 24.6 mm, and the S / N was measured. The value was determined. The relative S / N when the S / N of Comparative Example 1 was set to 0 dB was evaluated. 2. Durability 38 m radius using a floppy disk drive (ZIP100 (manufactured by Iomega Corporation: 2968 rpm))
After fixing the head at the m position and recording at a recording density of 34 kfci, the signal was reproduced and set to 100%. Then 55 ℃ 2
The vehicle was run for 1500 hours in two environments of 0% RH, 25 ° C. and 50% RH. The output was monitored every 24 hours of running, and when the output became 70% or less of the initial value, the life was defined as the life. 3. Calender-moldability The surface roughness of the magnetic layer before and after calendering was measured. The center line average roughness Ra was measured using a digital optical profilometer (manufactured by WYKO) under the condition of a cutoff of 0.25 mm by an optical interference method, and a decrease in roughness due to a calendar was determined.

[0062]

Table 1 Names of compounds Compound 1 2-butyloctadecyl behenate Compound 2 2-decyltetradecyl behenate Compound 3 2-decyltetradecyl 2-decyltetradecanoate Compound 4 2-decyloctadecyl 2-decyltetradecanoate Compound 5 2 2-decyltetradecyl decyl hexadecanoate compound 6 2-decyl octadecyl 2-decyl hexadecanoate compound 7 2-decyl tetradecyl 2-decyl octadecanoate compound 8 2-octadecyl octadecyl mericinate compound 9 isocetyl stearate

[0063]

[Table 2] Compound Electromagnetic durability (time) Calendar-formability Upper layer Non-magnetic conversion characteristics 25 ° C 55 ° C After coating After magnetic layer Lower layer S / N (dB) 50% RH 50% RH Ra Ra Example 1 Compound 1 Compound 1 1.5 1300 1100 11.5 2.7 Example 2 Compound 2 Compound 2 1.6 1300 1200 11.6 2.7 Example 3 Compound 3 Compound 3 1.6 1500 1500 11.4 2.6 Example 4 Compound 4 Compound 4 1.6 1500 1500 11.4 2.5 Example 5 Compound 5 Compound 5 1.6 1500 1500 11.8 2.7 Example 6 Compound 6 Compound 6 1.6 1500 1500 11.9 2.7 Example 7 Compound 7 Compound 7 1.5 1500 1500 12.0 2.8 Example 8 Compound 8 Compound 8 1.3 1500 1500 12.2 3.2 Example 9-Compound 3 1.6 1500 1500 11.9 2.8 Comparative Example 1 Compound 9-0.0 360 190 12.3 4.5 Comparative Example 2 Compound 2--1.8 300 180 17.5 5.6 Comparative Example 3 Compound 9 Compound 9 1.3 340 160 12.4 3.3

[0064]

According to the present invention, a magnetic recording medium containing at least a lower non-magnetic layer containing a tetraester having a hydrocarbon group of a specific chain length and having a carbon number can improve the electromagnetic conversion characteristics and provide a high recording density disk type. The durability of the magnetic recording medium was improved, especially at high temperatures, and a smooth magnetic layer with high calender moldability was realized.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J002 AA001 BD041 BF021 CC031 CD001 CK021 DE076 DE096 DE106 DE116 DE136 DE146 DE236 DG026 DG046 DG056 DJ006 DJ016 DK006 EH037 FA086 FD206 FD207 GS01 5D006 CA01 DA02 FA02

Claims (1)

[Claims] 1. A magnetic recording medium comprising a support and an underlayer containing at least a nonmagnetic powder and at least one magnetic layer in which a ferromagnetic powder is dispersed in a binder. A magnetic recording medium comprising at least one compound represented by 1). General formula (1) R ¹ COOR ² where R ¹ is an alkyl group having 21 to 29 carbon atoms R ² is an alkyl group having 22 to 36 carbon atoms R ¹ and / or R ² is a branched alkyl group