JPH1139643A - Magnetic recording medium and magnetic recording / reproducing apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recording medium excellent in continuous sliding, durability, low in tackiness and high in meniscus force by incorporating liquid crystal molecules having a specified monocyclic structure as a lubricant into the outermost layer. SOLUTION: The outermost layer of a magnetic recording medium having magnetic layers on a nonmagnetic supporting body contains a lubricant containing liquid crystal molecules having a monocyclic structure expressed by a general formula of L-X<1> -R or L-X<2> . In the formulae, X<1> , X<2> are atomic groups having cyclic structures, L, R are cyano groups, nitro groups, aldehyde groups, hydroxyl groups, amino groups, amide groups, ether groups, carbonyl groups, carboxyl groups, oxycarboxyl group, halogen groups, alkyl groups, allyl groups, hydroxyimino groups, or allyl groups, alkyl groups, oxycarboxyl groups, carboxyl groups, carbonyl groups, ether groups, amide groups and amino groups with substitution of groups above described. The lubricant is applied on the surface of a magnetic material or added in the magnetic layer.

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 and a magnetic recording / reproducing apparatus using the same.
In particular, it relates to improvement of lubricant.

[0002]

2. Description of the Related Art Magnetic recording media include audio tapes,
Video tape, backup data cartridge,
Widely used as floppy disks, hard disks, etc. As this magnetic recording medium, a so-called coating type magnetic recording medium in which a magnetic layer containing a very fine ferromagnetic powder and a binder containing a binder is coated on a non-magnetic support and dried to form a magnetic layer, Alternatively, a so-called metal thin film type magnetic recording medium in which a magnetic layer is formed by depositing a ferromagnetic metal material on a non-magnetic support by a method such as evaporation is used.

In these magnetic recording media, the surface of the magnetic layer is smoothed in order to minimize the spacing loss. In high-density recording, since the recording wavelength used is short, it is easily affected by the surface roughness, and control of the surface roughness is particularly important.

However, the better the smoothness of the surface of the magnetic layer, the larger the substantial contact area with a sliding member such as a magnetic head or a guide roller. Therefore, a magnetic recording medium having a good magnetic layer surface smoothness has a large friction coefficient, is likely to cause an adhesion phenomenon (so-called sticking) with a sliding member during running, and lacks running properties and durability. And more problems.

For example, in an 8 mm video deck,
If the coefficient of friction between the surface of the magnetic layer of the magnetic tape and the guide pins is large, the magnetic tape causes stick-slip, so-called tape squealing occurs, and the reproduced image is twitched. In addition, when the magnetic head slides at the same position on the tape at a high speed, such as in a pause state, if the coefficient of friction between the magnetic layer surface of the magnetic tape and the magnetic head is large, the magnetic layer wears and the resulting A problem arises in the reduction in reproduced output that occurs.

In a magnetic recording / reproducing apparatus typified by a hard disk or the like, a magnetic head is generally in contact with the disk when the disk is stopped. A flying method is used in which the head flies above the disk surface and recording and reproduction are performed in this state. In such a levitation method, at the time of startup, from the start of rotation of the disk to the floating of the magnetic head, and at the time of operation stop, from the contact of the magnetic head with the disk until the rotation of the disk stops. In the meantime, the magnetic head slides on the disk. At that time, friction between the magnetic head and the disk becomes a serious problem, and causes a reduction in wear of the magnetic recording medium and the magnetic head. When this wear damage reaches the magnetic layer,
A so-called head crash phenomenon occurs in which information recorded on the magnetic layer is destroyed.

Therefore, in order to improve these problems,
Attempts have been made to suppress the coefficient of friction by forming a lubricating film by internally adding a lubricant to the magnetic layer of the magnetic recording medium or by applying the lubricant to the surface of the magnetic layer. In addition, the magnetic layer is coated with a protective layer made of carbon, oxide, carbide, nitride, or the like, and a lubricant is applied on the protective film layer to form a lubricating film. Attempts have been made to improve the performance and prevent the head crash and the like.

[0008] Lubricants used in such magnetic recording media are required to have severe properties due to their properties, and generally the following properties are required.

(1) Excellent heat resistance and chemical stability.

(2) It has excellent low-temperature characteristics so that a predetermined lubricating effect is ensured even when used in a cold region.

(3) The thickness can be made extremely small because spacing with the magnetic head becomes a problem, and sufficient lubrication characteristics are exhibited even in such a case.

(4) To withstand long-term use and maintain the lubricating effect for a long time.

At present, various types of lubricants satisfying such characteristics have been studied. Among the lubricants most frequently used are higher fatty acids such as stearic acid and esters thereof, and perfluoroalkylpolyethylene. Ether compounds,
Alternatively, a fluorine-based lubricant such as a perfluoroalkyl-based compound may be used.

[0014]

However, in recent years, the density of magnetic recording / reproducing devices has been increasing at a rapid pace.
The flying height of the magnetic head also keeps decreasing. Further, as a limit of the flying height, a method of performing recording and reproduction while constantly contacting the magnetic head with the surface of the magnetic recording medium, that is, a so-called contact method has been proposed.

As described above, when the flying height decreases, the time required for the magnetic head and the surface of the magnetic recording medium to slide inevitably increases. It is necessary to reduce the coefficient and wear.

Further, as the flying height decreases, the surface roughness and waviness of the disk become smaller, so that a high maximum static frictional force (hereinafter referred to as "adhesion") tends to be generated between the magnetic head and the disk. . The sticking causes the disk to be unable to start or the head to be damaged. Therefore, it is necessary to reduce the adhesion of the lubricating film.

Further, in the contact method, the head slider and the magnetic disk are always in contact with each other. At this time, the head slider floats from the surface of the magnetic disk due to some vibration (particularly, vibration from the outside), and It may collide again and cause a head crash. In order to prevent this phenomenon, it is necessary to attract the head slider to the surface of the magnetic disk with a meniscus force acting between the lubricating film and the head slider to some extent.

Therefore, in the case of employing such an extremely low floating system or contact system, it is necessary to form the lubricating film with a lubricant which has both continuous sliding durability, low adhesion and high meniscus force. There is.

However, in general, continuous sliding durability,
The low tackiness and the high meniscus force are in a contradictory relationship, and there has been a limit to the compatibility of general lubricants.

For example, if the lubricating layer is made thick to provide continuous sliding durability, it is disadvantageous for low tackiness. Also, if the thickness of the lubricating film is reduced to avoid sticking,
The continuous sliding durability decreases, and the coverage of the lubricating film decreases.

Further, the following problems have arisen in the perfluoropolyether-based polymers which have been conventionally studied because of their excellent low surface energy, low tackiness, heat resistance and chemical stability. .

In a magnetic recording / reproducing apparatus employing an extremely low flying system or a contact system, a head slider (an oxide-based material such as Al ₂ O ₃ / TiC which is a main constituent material) comes into contact with a magnetic disk surface. It is known that the surface of the head slider wears out, exposing a very active new surface. Since the perfluoropolyether-based polymer is very easily decomposed on this active new surface, there is a problem that the continuous sliding durability is reduced and decomposition products adhere to the surfaces of the magnetic head and the head slider.

Further, since the perfluoropolyether polymer is a fluorine compound, when it is applied on a magnetic recording medium, its surface has low surface energy and water repellency. That is, the meniscus force generated between the lubricating film surface and the head slider surface is reduced. Therefore, in the magnetic recording / reproducing apparatus employing the extremely low flying system or the contact system, the head slider cannot be stably provided on the magnetic recording medium, and the magnetic head is liable to vibrate and the head crashes. Occurs.

As described above, the conventional lubricants have limitations in achieving continuous sliding durability, low tackiness, and high meniscus force.

Therefore, the present invention is intended to solve such problems, and a magnetic recording medium holding a lubricant satisfying all the characteristics of continuous sliding durability, low adhesiveness, and high meniscus force. And a magnetic recording / reproducing apparatus using the same.

[0026]

Means for Solving the Problems As a result of intensive studies by the present inventors, a liquid crystal having a monocyclic structure represented by the following general formula (A) or general formula (A ') By retaining molecules in the outermost layer of the magnetic recording medium as a lubricant, it was found that an excellent lubricating effect that satisfies all the lubricating properties of continuous sliding durability, low tackiness, and high meniscus force was obtained. The invention has been completed.

[0027]

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[0028]

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That is, the magnetic recording medium according to the present invention
In a magnetic recording medium in which at least a magnetic layer is formed on a non-magnetic support, the general formula (A) or the general formula (A ′)
Is characterized in that a lubricant containing monocyclic liquid crystal molecules represented by is held in the outermost layer.

The above lubricant may be applied to the surface of the magnetic layer or may be added internally to the magnetic layer.

When the magnetic layer is a metal magnetic thin film and a protective film is formed on the metal magnetic thin film, the lubricant may be applied to the surface of the protective film.

Further, when the back coat layer is formed on the surface of the non-magnetic support opposite to the surface on which the magnetic layer is formed, the above lubricant is applied to the surface of the back coat layer, or It may be internally added. When a non-magnetic layer is formed between the non-magnetic support and the magnetic layer,
The above lubricant may be internally added to the non-magnetic layer.

A magnetic recording / reproducing apparatus according to the present invention has a magnetic recording medium for recording information, and a magnetic head for recording and / or reproducing information on the magnetic recording medium. The minimum distance between the geometric mean planes of the surface is 50 nm or less. In the magnetic recording medium, a lubricant containing a monocyclic liquid crystal molecule represented by the general formula (A) of Chemical Formula 25 or the general formula (A ′) of Chemical Formula 26 in an outermost layer facing the magnetic head. Is held.

The lubricant used in the present invention contains liquid crystal molecules having a phase transition from solid to liquid and intermediate properties between liquid and solid. For this reason, the lubricant of the present invention can release the kinetic energy given by the sliding by the phase transition.

The lubricant containing the liquid crystal molecules is:
When the sliding energy is small (or there is no friction), it has low tackiness because it exists in a solid state, and once it receives the sliding energy by collision, it undergoes a phase transition to become a liquid state and wraps around the magnetic head. Generates a meniscus force. As described above, the lubricant containing liquid crystal molecules of the present invention undergoes a phase transition due to frictional energy obtained by sliding to become a liquid, and thus can satisfy both characteristics of low tackiness and high meniscus force.

The formula (A) or (A ')
Have a nematic phase or a smectic phase at room temperature (20 ° C.) or higher. Nematic / smectic phase liquid crystal molecules are likely to have their long axes aligned perpendicular to the substrate surface and form a thick film on the substrate. In many cases, it will be excellent in durability. In contrast, cholesteric liquid crystal molecules tend to have their major axes aligned parallel to the substrate surface.
When the lubricant molecules gradually wear due to repeated sliding, it is considered that the lubricant molecules are liable to wear (peel) and the durability is not sufficient.

Further, it is considered that the liquid crystal molecules exhibiting a nematic phase / smectic phase can obtain a high local viscosity by being oriented in a certain direction. On the other hand, in a liquid crystal exhibiting a cholesteric phase,
Since the layer is formed while the orientation surface is twisted, the intermolecular force is averaged, and a high local viscosity due to orientation cannot be obtained, which is disadvantageous in releasing frictional energy due to sliding.

As described above, the lubricant used in the present invention can release the kinetic energy given by the sliding by the phase transition and the phase transition to the liquid, so that the continuous sliding durability and low tackiness can be obtained. In addition, it is possible to satisfy all the lubricating properties of high meniscus force.

Since the magnetic recording medium and the magnetic recording / reproducing apparatus according to the present invention have such a lubricating layer as the outermost layer, excellent lubricating performance can be maintained under various use conditions, and the lubricating layer can be used for a long time. The lubrication effect is maintained, and the running performance, wear resistance, and durability are excellent.

Furthermore, the lubricant used in the present invention can be applied with a hydrocarbon solvent such as toluene and acetone, whereas the conventional fluorine-based lubricant can be applied only with a fluorine-based solvent. Also, the load on the environment can be reduced.

[0041]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetic recording medium according to the present invention will be described in detail.

The magnetic recording medium according to the present invention comprises at least a magnetic layer formed on a non-magnetic support.
A lubricant containing monocyclic liquid crystal molecules represented by the general formula (A) of formula (7) or (A ′) of formula (28) is held in the outermost layer.

[0043]

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[0044]

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In the general formula (A) of Chemical Formula 27, the atom group represented by X ¹ is represented by the general formulas (X ^1-
1) - it is preferably selected from the cyclic structure represented by the general formula (X ¹ -18).

[0046]

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[0047]

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[0048]

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[0049]

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[0050]

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[0051]

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[0052]

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[0053]

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[0054]

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[0055]

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[0056]

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[0057]

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[0058]

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[0059]

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[0060]

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[0061]

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[0062]

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[0063]

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Further, in the general formula (A ′) of Chemical formula 28,
The atom group represented by X ² is represented by the general formula (X ²
-1), preferably selected from the cyclic structure represented by (X ² -2).

[0065]

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[0066]

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The lubricant used in the present invention contains liquid crystal molecules having a phase transition from solid to liquid and intermediate properties between liquid and solid. For this reason, the lubricant of the present invention can release the kinetic energy given by the sliding by the phase transition.

The lubricant containing the liquid crystal molecules is:
When the sliding energy is small (or there is no friction), it has low tackiness because it exists in a solid state, and once it receives the sliding energy by collision, it undergoes a phase transition to become a liquid state and wraps around the magnetic head. Generates a meniscus force. As described above, the lubricant containing liquid crystal molecules of the present invention undergoes a phase transition due to frictional energy obtained by sliding to become a liquid, and thus can satisfy both characteristics of low tackiness and high meniscus force.

On the other hand, in the case of a solid lubricant, the kinetic energy given by the sliding is used to repel molecules, and as a result, the lubricant is decomposed.
The decomposition products adhere to the magnetic head and the magnetic recording medium and deteriorate the sliding characteristics. On the other hand, a lubricant containing liquid crystal molecules can release frictional energy given by sliding due to a change in state from a semi-solid to a liquid, so that decomposition of the lubricant is suppressed and sliding characteristics are deteriorated. Nothing.

In the case of a liquid lubricant, since the fluidity is high, the friction energy given by the sliding can be released without decomposing the lubricant. However, the liquid lubricant has a high fluidity and flows out of the surface by sliding, so that the coverage of the substrate is reduced and the lubricity is lost immediately. On the other hand, the lubricant containing liquid crystal molecules exists on the surface in a semi-solid / semi-liquid state, so that the sliding rate does not impair the coverage of the substrate surface unlike a liquid lubricant. Dynamic characteristics do not deteriorate.

Generally, there are three types of liquid crystal molecules, a nematic phase, a smectic phase, and a cholesteric phase, depending on the molecular arrangement.

The liquid crystal molecules used in the present invention are at room temperature (2
(0 ° C.) or more, having a nematic phase or a smectic phase. Nematic / smectic phase liquid crystal molecules are likely to have their long axes aligned perpendicular to the substrate surface and form a thick film on the substrate. In many cases, it will be excellent in durability. On the other hand, the liquid crystal molecules of the cholesteric phase tend to have their long axes aligned parallel to the substrate surface. Therefore, when the sliding is repeated and the lubricant molecules gradually decrease, the lubricant molecules become worn ( It is considered that the film is easily peeled off and the durability is not sufficient.

The liquid crystal exhibiting a nematic / smectic phase is considered to be able to obtain a high local viscosity because it is oriented in a certain direction. On the other hand, in a liquid crystal exhibiting a cholesteric phase, since the layers are formed while the alignment plane is twisted, it is considered that the intermolecular force is averaged. Therefore, a liquid crystal exhibiting a cholesteric phase cannot obtain a high local viscosity due to alignment, and is disadvantageous in releasing frictional energy due to sliding.

As described above, the lubricant used in the present invention can release the kinetic energy given by the sliding by the phase transition and the phase transition to the liquid. In addition, it is possible to satisfy all the lubricating properties of high meniscus force.

Incidentally, the magnetic recording medium according to the present invention comprises:
A so-called coating-type magnetic recording medium in which a magnetic layer containing a very fine ferromagnetic powder and a binder is coated on a non-magnetic support and dried to form a magnetic layer. A so-called metal thin film type magnetic recording medium in which a magnetic layer is formed by depositing a metal material on a non-magnetic support by a method such as vapor deposition may be used.

In the case of a coating type magnetic recording medium, a lubricant containing a monocyclic liquid crystal molecule represented by the general formula (A) or (A ′) is internally added to the magnetic paint in the magnetic layer. . Alternatively, after the magnetic layer is formed, the lubricant is applied by dipping or spin coating to form a lubricating film.

In the former case, the amount of the ferromagnetic powder 1
0.1 to 20 parts by weight is preferable with respect to 00 parts by weight,
0.5 to 10 parts by weight is more preferable. On the other hand, in the latter case,
The coating amount of the lubricant is preferably ^{0.5~100mg / m 2, 1~50mg / m} 2 is more preferable. In any case, when the amount of the lubricant in the outermost layer (magnetic layer surface) of the magnetic recording medium is small, the lubricating effect is insufficient. become. Therefore, the above-mentioned optimum amount is naturally determined. In the case of a recent ultra-fine particle high-packing medium, the latter can more efficiently hold the lubricant on the surface of the magnetic layer.

In the case of a magnetic recording medium of the metal magnetic thin film type, after a magnetic layer is formed by vapor deposition or the like, a single layer of the general formula (A) or (A ′) is formed on the magnetic layer. A lubricant containing cyclic liquid crystal molecules may be applied. Or
In order to provide continuous sliding durability, a protective film may be formed on a magnetic layer made of a metal magnetic thin film, and the lubricant may be applied to the surface of the protective film.

Examples of the method of applying the lubricant include an immersion method, a Langmuir-Blodgett (LB method), a spray method, a spin coating method, a casting method, a vacuum evaporation method, and a molecular beam evaporation method. Also in this case, the amount of the lubricant to be applied is preferably 0.5 to 100 mg / m ² ,
~50mg / m ² is more preferable. After the formation of the lubricating film, the coating amount may be adjusted by washing with a solvent. Whether or not cleaning with a solvent is performed after the formation of the lubricating film is determined from the viewpoint of film thickness adjustment.

Further, if necessary, a heat treatment or an ultraviolet irradiation treatment can be performed after the formation of the lubricating film. The heat treatment is performed at a temperature in the range of 70 to 200C, preferably in the range of 90 to 170C, depending on the lubricant used.

Further, in the present invention, a back coat layer is formed on the surface of the non-magnetic support opposite to the surface on which the magnetic layer is formed, and the lubricant containing the liquid crystal molecules is applied on the back coat layer. Alternatively, the lubricant may be internally added to the back coat layer.

In the present invention, a non-magnetic layer (lower layer) may be formed between the non-magnetic support and the magnetic layer for the purpose of obtaining the smoothness of the magnetic layer. This is generally called a multilayer coating type magnetic recording medium. Also in this case, it is preferable to internally add a lubricant containing liquid crystal molecules to the nonmagnetic layer.
The lubricant internally added to the non-magnetic layer seeps out to the magnetic layer side,
Eventually, it will be present in the outermost layer of the magnetic recording medium. The amount of the lubricant is preferably from 0.1 to 20 parts by weight, and more preferably from 0.5 to 1 part by weight based on 100 parts by weight of the nonmagnetic powder.
0 parts by weight is more preferred.

As described above, in the magnetic recording medium according to the present invention, since the lubricant containing the liquid crystal molecules described above is held in the outermost layer, excellent lubrication performance is maintained even under various use conditions. The lubrication effect is maintained over a long period of time, resulting in excellent running properties, wear resistance, and durability.

By the way, as the material constituting the nonmagnetic support and the magnetic layer in the magnetic recording medium to which the present invention is applied, any conventionally known materials can be used, and there is no particular limitation.

For example, as the non-magnetic support,
Polyethylene terephthalate, polyethylene-2,6-
Polyesters such as naphthalate, polyolefins such as polypropylene, celluloses such as cellulose triacetate and cellulose diacetate, vinyl resins, polyimides, polymer materials represented by polycarbonates, or metals, glass, ceramics, etc. The support to be formed is exemplified.

When the magnetic recording medium has a coating type magnetic layer, the magnetic layer is formed by applying a magnetic paint mainly composed of a magnetic powder and a binder. , Fe, Co, Ni, and other metals;
Co, Fe-Ni, Fe-Al, Fe-Ni-Al, F
e-Al-P, Fe-Ni-Si-Al, Fe-Ni-
Si-Al-Mn, Fe-Mn-Zn, Fe-Ni-Z
n, Co-Ni, Co-P, Fe-Co-Ni, Fe-
Co-Ni-Cr, Fe-Co-Ni-P, Fe-Co
-B, Fe-Co-Cr-B, Mn-Bi, Mn-A
1, alloys such as Fe-Co-V, iron nitride, iron carbide and the like. Of course, the effects of the present invention are not impeded even if an appropriate amount of a light metal element such as Al, Si, P, or B is added for the purpose of preventing sintering or maintaining the shape during reduction.

Further, as the ferromagnetic powder, γ-Fe ₂
O ₃ , Fe ₃ O ₄ , a beltride compound of γ-Fe ₂ O ₃ and Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃ , Co-containing Fe
₃ O _4, berthollide compound of containing Co γ-Fe ₂ O ₃ and Fe ₃ O _4, 1 or more metal elements CrO _2, for example, was included Te, Sb, Fe, and B, etc. Oxides and the like.

Further, hexagonal plate-like ferrites can also be used, and M-type, W-type, Y-type, and Z-type barium ferrites, strontium ferrites, calcium ferrites, lead ferrites, and those for controlling coercive force. For the purpose, Co-Ti, Co-Ti-Zn, Co-Ti-N
b, Co-Ti-Zn-Nb, Cu-Zr, Ni-Ti
And the like. These ferromagnetic powders
One type may be used for each type, but two or more types may be used in combination.

The specific surface area of the ferromagnetic powder used in the present invention is as follows:
30~80m ² / g are preferred, 40~70m ² / g is more preferable. When the specific surface area is within the above range, high-density recording becomes possible with finer particles of the shape of the ferromagnetic powder,
It is possible to obtain a magnetic recording medium having excellent noise characteristics.

Further, the ferromagnetic powder used in the present invention preferably has a major axis length of 0.05 to 0.50 μm and an axial ratio of 2 to 15. If the major axis length is less than 0.05 μm, dispersion in the magnetic paint becomes difficult, and the major axis length is 0.50 μm.
If it exceeds μm, the noise characteristics may deteriorate, which is not preferable. If the axial ratio is less than 5, the orientation of the ferromagnetic powder decreases and the output decreases. If the axial ratio exceeds 15, the short-wavelength signal output may decrease, which is not preferable. In the case of plate-like ferrite, the plate diameter is 0.01 to 0.5 μm, and the plate thickness is 0.
It is preferably about 001 to 0.2 μm. As the major axis length, the axial ratio, the plate diameter, and the plate thickness, an average value of 100 or more samples randomly selected from a transmission electron micrograph is adopted.

As the binder to be contained in the magnetic layer of the present invention, known thermoplastic resins, thermosetting resins, reactive resins and the like conventionally used as binders for magnetic recording media can be used. Those having an average molecular weight of 5,000 to 100,000 are preferred.

Examples of the thermoplastic resin include vinyl chloride,
Vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinyl chloride-vinylidene chloride copolymer, vinyl chloride Acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylate-vinylidene chloride copolymer, methacrylate-vinyl chloride copolymer, methacrylate-ethylene copolymer, Polyvinyl fluoride, vinylidene chloride-allylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulo Scan diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene-butadiene copolymer, polyurethane resin, polyester resin, amino resin, synthetic rubber, and the like. Examples of the thermosetting resin or the reactive resin include a phenol resin, an epoxy resin, a polyurethane curing resin, a urea resin, a melamine resin, an alkyd resin, a silicone resin, a polyamine resin, and a urea formaldehyde resin.

All of the above binders include -SO ₃ M, -OSO ₃ M, and -C for the purpose of improving the dispersibility of the pigment.
Polar functional groups such as OOM and P = O (OM) ₂ may be introduced. Here, M in the formula is a hydrogen atom or an alkali metal such as lithium, potassium, and sodium.
Further, the polar functional groups include -NR ¹ R ² , -NR ¹
R ² R ³⁺ X ⁻ side chain type having a terminal group,> NR ¹ R
²⁺ X ^- there is one of the main chain type. Where R ¹ , R ² ,
R ³ is a hydrogen atom or a hydrocarbon group, X ⁻ is fluorine,
It is a halogen element ion such as chlorine, bromine or iodine, or an inorganic or organic ion. Also, -OH, -SH, -C
There are also polar functional groups such as N and epoxy groups. The amount of these polar functional groups is preferably 10 ^-1 to 10 ^-8 mol / g, and
^-2 to 10 ^-6 mol / g is more preferred. These binders can be used alone or in combination of two or more.

These binders in the magnetic layer are added to the ferromagnetic powder or nonmagnetic powder in an amount of 1 to 2 parts by weight based on 100 parts by weight.
00 parts by weight is preferable, and 10 to 50 parts by weight is more preferable. If the amount of the binder is too large, the ratio of the ferromagnetic powder in the magnetic layer becomes relatively small, and the output is reduced. Further, plastic flow is likely to occur due to repeated sliding in a drive or the like, and the running durability of the magnetic recording medium is reduced. On the other hand, if the amount of the binder is too small, the magnetic layer becomes brittle, and the running durability of the magnetic recording medium decreases.

In the present invention, it is possible to use a polyisocyanate for crosslinking and curing the above binder. Examples of the polyisocyanate include tolylene diisocyanate and its adduct, alkylene diisocyanate and its adduct. The blending amount of these polyisocyanates with the binder is preferably 5 to 80 parts by weight, more preferably 10 to 50 parts by weight, based on 100 parts by weight of the binder.

The ferromagnetic powder and the binder as described above are dispersed in a solvent to form a magnetic paint. Solvents used for this coating include acetone, methyl ethyl ketone,
Ketone solvents such as methyl isobutyl ketone and cyclohexanone; alcohol solvents such as methanol, ethanol and propanol; ester solvents such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate and ethylene glycol acetate; diethylene glycol dimethyl ether; -Ether solvents such as ethoxyethanol, tetrahydrofuran, dioxane, benzene,
Examples include aromatic hydrocarbon solvents such as toluene and xylene, and halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene.

The magnetic paint may contain abrasive particles as needed. Examples of these are aluminum oxide (α, β, γ), chromium oxide,
Examples include silicon carbide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (rutile, anatase) and the like. These particles are used in an amount of 20 parts by weight or less, preferably 10 parts by weight or less based on 100 parts by weight of the ferromagnetic powder. The Mohs hardness of these particles is 4 or more, preferably 5 or more, the specific gravity is in the range of 2 to 6, preferably 3 to 5, and the average particle size is
It is 0.5 μm or less, preferably 0.3 μm or less.
The average particle size of the non-magnetic reinforcing particles is also measured from a transmission electron micrograph and processed statistically, as in the case of the ferromagnetic powder.

When preparing a magnetic coating material, the above-mentioned materials are formed into a coating material by kneading, mixing and dispersing steps. For dispersion and kneading, roll mill, ball mill,
Sand mill, agitator, kneader, extruder,
A homogenizer, an ultrasonic disperser or the like is used.

After the preparation of the magnetic paint, the magnetic paint is applied on the non-magnetic support by any method such as spraying or roll application and dried to form a magnetic layer. If necessary, it is guided to a calender and wound up on a take-up roll. Further, a back coat layer is applied to the surface of the non-magnetic support opposite to the surface on which the magnetic layer is formed.

When such a coating type magnetic layer is provided, a non-magnetic powder is dispersed in a binder between the magnetic layer and the non-magnetic support in order to smooth the magnetic layer. A formed non-magnetic layer (lower layer) may be formed.

When the multilayer coating is performed as described above, any of the binders exemplified for the magnetic layer can be used for the lower layer.

Examples of the nonmagnetic powder contained in the lower layer include nonmagnetic iron oxide such as α-Fe ₂ O ₃ , goethite, rutile type titanium oxide, anatase type titanium oxide, tin oxide, tungsten oxide, and silicon oxide. , Zinc oxide, chromium oxide, cerium oxide, titanium carbide, BN, α-alumina, β-alumina, γ-alumina, calcium sulfate, barium sulfate, molybdenum disulfide, magnesium carbonate, calcium carbonate, barium carbonate, strontium carbonate, Barium titanate and the like can be mentioned. These non-magnetic powders can be used alone or as a mixture of two or more.

The above non-magnetic powder can be doped with an appropriate amount of impurities according to the purpose. For the purpose of improving dispersibility, imparting conductivity, improving color tone, etc., Al, S
Surface treatment with compounds such as i, Ti, Sn, Sb, and Zr is also possible. The specific surface area of the nonmagnetic powder is 30 to 8
0 m ² / g are preferred, 40~70m ² / g is more preferable.

Further, in addition to the non-magnetic powder, if necessary, a furnace for rubber, pyrolytic carbon,
Carbon black such as color black and acetylene black may be contained. Carbon black has a specific surface area of 100 to 400 m ² / g, and a DBP oil absorption of 20 to 400 m ² / g.
It is preferably 200 ml / 100 g.

By setting the specific surface area of the non-magnetic powder and carbon black within the above range, the non-magnetic layer (lower layer) can be smoothed, and as a result, the magnetic layer (upper layer) can be smoothed. This makes it possible to obtain a magnetic recording medium that has excellent modulation noise characteristics and is less affected by spacing loss.

Further, when the magnetic recording medium of the present invention has a magnetic layer made of a metal magnetic thin film, the metal magnetic thin film is formed by coating a ferromagnetic metal material on a non-magnetic support by a technique such as plating, sputtering, or vacuum evaporation. Formed continuously.

As the non-magnetic support, the above-described non-magnetic support can be used. However, when a rigid substrate such as an aluminum alloy plate or a glass plate is used, the surface of the substrate may be oxidized by alumite treatment or the like. A film or a Ni-P coating may be formed to harden the surface.

As the metal magnetic thin film, Fe, Co, Ni
, A Co-Ni alloy, a Co-Pt alloy, C
o-Pt-Ni alloy, Fe-Co alloy, Fe-Ni
In-plane magnetization recording metal magnetic film or Co-Cr made of a base alloy, an Fe-Co-Ni-based alloy, an Fe-Ni-B-based alloy, an Fe-Co-B-based alloy, an Fe-Co-Ni-B-based alloy System alloy thin film.

In particular, in the case of an in-plane magnetization recording metal magnetic thin film,
Bi, Sb, Pb, Sn, Ga,
An underlayer of a low-melting nonmagnetic material such as In, Ge, Si, or Tl may be formed beforehand, and a metal magnetic thin film may be formed by vapor deposition or sputtering of a metal magnetic material from a vertical direction.
When a metal magnetic material is deposited on the underlayer, these low-melting non-magnetic materials diffuse into the metal magnetic thin film, canceling the orientation, ensuring in-plane isotropy, and improving antimagnetism.

Further, on the surface of the magnetic recording medium, before forming the lubricating film, a protective film of carbon or the like for the purpose of improving the coating film strength or rust prevention may be provided. As a method of forming the protective film, sputtering or chemical vapor deposition (C
VD) method is common and is not particularly limited.
Either method can be used. The thickness of the protective film is 2 to
It is preferably 100 nm, more preferably 5 to 30 nm.

Further, the above-mentioned lubricant may be used, if necessary,
A rust inhibitor may be used in combination. As the rust inhibitor, any one which is usually used as a rust inhibitor for this type of magnetic recording medium can be used, for example, phenols, naphthols, quinones, heterocyclic compounds containing a nitrogen atom, oxygen atoms And heterocyclic compounds containing a sulfur atom.

The rust preventive may be used in combination with the above-mentioned lubricant. However, after applying the rust preventive layer on the magnetic layer or the protective film such as carbon, the lubricant layer is applied. , 2
The effect is high if it is applied in layers or more.

The shape of the magnetic recording medium to which the present invention is applied is not particularly limited as long as the magnetic layer is formed on a nonmagnetic support.
It may be a magnetic tape slit to an m width, a magnetic disk obtained by punching into a 3.5-inch size disk, or a magnetic disk using a disk-shaped hard substrate (a so-called hard disk).

Next, the magnetic recording / reproducing apparatus of the present invention will be described.

This magnetic recording / reproducing apparatus comprises a magnetic disk and a magnetic head for recording and / or reproducing information on the magnetic disk while scanning the magnetic disk. The magnetic head may be a floating magnetic head that scans while floating at a minute interval with respect to the surface of the magnetic disk by the rotating wind force of the magnetic disk, or a contact record system that scans while contacting the surface of the magnetic disk. May be used. However, in the case of a floating magnetic head, the minimum distance from the geometric mean plane of the magnetic disk surface is set to 50 nm or less.

In this magnetic recording / reproducing apparatus, the lubricant containing the liquid crystal molecules represented by the general formula (A) or (A ') is held in the outermost layer as described above, particularly for the magnetic disk. Magnetic recording medium is used.

In such a magnetic recording / reproducing apparatus, when a magnetic recording medium in which the above liquid crystal molecules are held in the outermost layer is used, the liquid crystal molecules have low tackiness and a high meniscus force. Good sliding durability is obtained when the disk slides when stopping, when sliding the disk when recording and reproducing with a contact record type magnetic head, and excellent running performance, wear resistance and durability are obtained. Can be

[0118]

EXAMPLES Hereinafter, specific examples and comparative examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples.

<Preparation of Coated Magnetic Tape> Example 1 First, a ferromagnetic powder, a binder, an additive, a lubricant, and a solvent having the following composition were mixed and kneaded with an extruder. The mixture was dispersed in a sand mill for 6 hours to prepare a magnetic paint.

<Magnetic Paint Composition> 100 parts by weight of Fe-based metal ferromagnetic powder (coercive force = 160 kA / m, saturation magnetization = 145 Am ² / kg, specific surface area = 51 m ² / g, major axis length = 0.08 μm, Needle ratio = 3) Polyvinyl chloride resin (manufactured by Zeon Corporation; MR-110) 14 parts by weight Polyester polyurethane resin (manufactured by Toyobo; MG-130) 3 parts by weight Additive (Al ₂ O ₃ ) 5 parts by weight Lubricant (Liquid crystal molecule 1 represented by Chemical formula 49) 3 parts by weight Methyl ethyl ketone 150 parts by weight Cyclohexanone 150 parts by weight

[0121]

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Next, 3 parts by weight of polyisocyanate was added to the obtained magnetic paint. And this magnetic layer paint,
7 μm thick polyethylene terephthalate (hereinafter referred to as PE
Called T. ) A film was coated on the film so as to have a thickness of 6.5 μm, and subjected to an orientation treatment by a solenoid coil, followed by drying, calendering, and curing to form a magnetic layer. Further, a back coating having the following composition was applied to the surface of the PET film opposite to the surface on which the magnetic layer was formed. And
This PET film is cut into 8 mm width and taped,
A coating type magnetic tape was produced.

<Back Coating Composition> 100 parts by weight of carbon black (manufactured by Asahi Carbon Co .; # 50) 100 parts by weight of polyester polyurethane (trade name: Nipporan N-2304) 500 parts by weight of methyl ethyl ketone 500 parts by weight of toluene Examples 2 to 2 8 As a lubricant, instead of the liquid crystal molecules 1,
A coated magnetic tape was produced in the same manner as in Example 1 except that the liquid crystal molecules 2 to 8 represented by the following formulas were used.

[0124]

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[0125]

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[0126]

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[0127]

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[0128]

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[0129]

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[0130]

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Comparative Example 1 A coating type magnetic tape was produced in the same manner as in Example 1 except that stearic acid, which is a general lubricant, was used instead of the liquid crystal molecules 1 as a lubricant.

Comparative Example 2 A coating type magnetic tape was produced in the same manner as in Example 1 except that methyl stearate, which is a general lubricant, was used instead of the liquid crystal molecules 1 as a lubricant.

Evaluation of Characteristics The magnetic tapes of Examples 1 to 8 and Comparative Examples 1 and 2 obtained as described above were subjected to a temperature of 40 ° C. and a relative humidity of 60% at a temperature of 25 ° C. At 80%, the coefficient of friction and still durability at a temperature of -5 ° C were measured. Tables 1 and 2 show the results.

The friction coefficient was measured with a load of 20 g and a tape speed of 5 mm / sec using a general shuttle type friction meter. The value of the coefficient of friction was calculated from the change in tension using Euler's equation using the value after running 100 passes.

Still durability was evaluated by measuring the time required for the output in the pause state to attenuate to -3 dB. The longest measurement time was 150 minutes.

[0136]

[Table 1]

[0137]

[Table 2]

Tables 1 and 2 show that the liquid crystal molecules 1 were used as lubricants.
-The magnetic tape of the example using the liquid crystal molecules 8 has a reduced coefficient of friction compared to the comparative example using stearic acid or methyl stearate, which is a conventional lubricant, and has excellent still properties. You can see that there is. This indicates that excellent continuous sliding durability and low tackiness can be obtained by using liquid crystal molecules as a lubricant.

<Preparation of Metal Thin-Film Magnetic Tape> Example 9 First, a 10 nm thick PET film was coated with a Co—Ni alloy by oblique evaporation to form a 100 nm thick film.
Was formed. Next, a 10 nm-thick carbon protective film was formed on the surface of the ferromagnetic metal thin film by sputtering. Next, on this carbon protective film,
Liquid crystal molecule 1 represented by Chemical Formula 49 was applied as a lubricant.
The applied amount of the liquid crystal molecules 1 is 10 mg / m ² . Then, the PET film was cut into a width of 8 mm to form a tape, thereby producing a metal thin film magnetic tape.

Examples 10 to 16 In place of the liquid crystal molecule 1 as a lubricant,
In the same manner as in Example 9 except that the liquid crystal molecules 2 to 8 were used, a metal thin film magnetic tape was produced.

Comparative Example 3 A metal thin film magnetic tape was manufactured in the same manner as in Example 9 except that stearic acid, which is a general lubricant, was used instead of the liquid crystal molecules 1 as a lubricant.

Comparative Example 4 A metal thin film magnetic tape was produced in the same manner as in Example 9 except that methyl stearate, which is a general lubricant, was used instead of the liquid crystal molecules 1 as a lubricant.

Evaluation of Characteristics The magnetic tapes of Examples 9 to 16 and Comparative Examples 3 and 4 obtained as described above were subjected to a temperature of 25 ° C. and a relative humidity of 60% in the same manner as in Example 1. The friction coefficient and the still durability were measured at a temperature of -5 ° C and a temperature of 40 ° C and a relative humidity of 80%. The results are shown in Tables 3 and 4.

[0144]

[Table 3]

[0145]

[Table 4]

Tables 3 and 4 show that the liquid crystal molecule 1 was used as a lubricant.
-The magnetic tape of the example using the liquid crystal molecules 8 has a reduced coefficient of friction and excellent still characteristics as compared with a comparative example using stearic acid and methyl stearate as conventional lubricants. You can see that there is. This indicates that excellent continuous sliding durability and low tackiness can be obtained by using liquid crystal molecules as a lubricant.

Further, as can be seen from the above results, the lubricating effect is good in both the coating type magnetic tape and the metal thin film type magnetic tape. In addition, excellent characteristics can be obtained by any method of forming a lubricating film, whether it is an internal addition method as in the case of a coating type magnetic tape or a top coat method as in a metal thin film type magnetic tape.

<Preparation of Metal Thin-Film Magnetic Disk> Example 17 First, a NiP underlayer 10 μm and a Cr intermediate layer 0.1 mm were formed on a 3.5-inch aluminum alloy substrate whose surface was mirror-polished.
5 μm, a Co—Cr—Pt magnetic layer 60 nm, and a carbon protective film 20 nm were sequentially formed by sputtering. The surface roughness of the magnetic disk surface is determined by the center line average roughness (R
a) is 1.2 nm.

Next, a lubricant was prepared by dissolving the liquid crystal molecule 1 represented by Chemical formula 49 in chloroform at a concentration of 0.01% by weight. Then, the liquid crystal molecules 1 were coated on the magnetic disk by immersing the magnetic disk in the lubricant. The application conditions were such that the residence time in the lubricant was 180
Second, the lifting speed from the lubricant was 0.25 mm / sec. Further, the magnetic disk was immersed in pure chloroform to remove extra liquid crystal molecules 1 from the magnetic disk. As a result, a lubricating film having a total film thickness of 2.5 nm (as measured by an ellipsometer) and a coating amount of 10 mg / m ² was formed. Through the above steps, a metal magnetic thin film magnetic disk was manufactured.

Examples 18 to 24 In place of the liquid crystal molecule 1 as a lubricant,
In the same manner as in Example 17, except that the liquid crystal molecules 2 to 8 were used, a metal thin film magnetic disk was manufactured.

Comparative Example 5 A metal thin-film magnetic disk was manufactured in the same manner as in Example 17 except that a fluorine-based lubricant (molecular weight: 4000) represented by Chemical Formula 57 was used instead of the liquid crystal molecule 1 as a lubricant. .

[0152]

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Evaluation of Characteristics The magnetic disks of Examples 17 to 24 and Comparative Example 5 obtained as described above were mounted on a magnetic recording / reproducing apparatus.
The maximum static friction coefficient, the dynamic friction coefficient, and the number of turns before a head crash occurred were measured. Table 5 shows the results.

The maximum static friction coefficient was obtained by measuring the frictional force generated immediately after the magnetic disk was rotated at a low speed in a state where the head slider was in contact with the magnetic disk.
The measurement conditions were a head pressing load of 5 g and a disk rotation speed of 1 rpm.

The dynamic friction coefficient was measured by continuously sliding the head slider up to 200,000 times in contact with the magnetic disk, and measuring the maximum frictional force during the sliding. The measurement conditions were as follows: the head pressing load was 5 g, and the disk rotation speed was 150 rpm.
m. When a head crash occurred in 200,000 or less laps, the maximum frictional force until the head crash occurred was measured.

The head crash of the magnetic disk is a state in which the carbon protective film, which is the base of the lubricating film, is completely worn and the magnetic film is exposed. When this head crash occurs, a sliding mark that can be visually confirmed is generated. At that time, the experiment was stopped, and the number of laps to that point was recorded.
The maximum number of turns was 200,000.

[0157]

[Table 5]

As shown in Table 5, the magnetic disk of the example using liquid crystal molecules as the lubricant exhibited substantially the same maximum friction coefficient and dynamic friction coefficient as those of the magnetic disk of the comparative example, and showed a circumferential frictional coefficient up to head crash. The number of times has greatly improved. This indicates that when liquid crystal molecules are used as a lubricant, excellent continuous sliding durability, low tackiness, and high meniscus force can be obtained.

From the above Examples and Comparative Examples, it can be seen that the magnetic recording medium using liquid crystal molecules as the lubricant has a reduced friction coefficient and excellent durability under various conditions of use.

[0160]

As is clear from the above description, according to the present invention, since the liquid crystal material is used for the lubricant,
It is possible to provide a magnetic recording medium that maintains excellent lubricating performance under various use conditions, maintains a lubricating effect for a long time, and has excellent running properties, abrasion resistance, and durability.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G11B 5/71 G11B 5/71 // C09K 19/06 C09K 19/06 19/32 19/32 19/34 19/34 C10N 40 : 18 50:10 (72) Inventor Ken Takeshi Kobayashi 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Hiroshi Iwamoto 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony (72) Inventor Nobuyuki Matsuzawa 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation

Claims (8)

[Claims] 1. A magnetic recording medium comprising at least a magnetic layer formed on a non-magnetic support, wherein a lubricant containing a monocyclic liquid crystal molecule represented by the following formula (1) or (2) is used as an outermost layer: A magnetic recording medium characterized by being held in a magnetic recording medium. Embedded image Embedded image 2. X ¹ in the chemical formula ¹ represents the following chemical formulas 3 to 20:
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is selected from a cyclic structure represented by the following formula. Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image 3. The magnetic recording medium according to claim 1, wherein X ^{2 in} Chemical Formula ² is selected from the cyclic structures represented by Chemical Formula 21 or Chemical Formula 22 below. Embedded image Embedded image 4. The magnetic recording medium according to claim 1, wherein the lubricant is applied to the surface of the magnetic layer or is internally added to the magnetic layer. 5. The magnetic recording according to claim 1, wherein the magnetic layer is a metal magnetic thin film, a protective film is formed on the metal magnetic thin film, and the lubricant is applied to a surface of the protective film. Medium. 6. A backcoat layer is formed on the surface of the nonmagnetic support opposite to the surface on which the magnetic layer is formed, and the lubricant is applied to the surface of the backcoat layer, or the lubricant is applied to the inside of the backcoat layer. 2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is added. 7. The magnetic recording apparatus according to claim 1, wherein a nonmagnetic layer is formed between the nonmagnetic support and the magnetic layer, and the lubricant is internally added to the nonmagnetic layer. Medium. 8. A magnetic recording medium on which information is recorded, and a magnetic head for recording and / or reproducing information on and from the magnetic recording medium, wherein a geometric mean plane of each surface of the magnetic recording medium and the magnetic head is provided. In the magnetic recording / reproducing apparatus having a minimum distance of 50 nm or less, the magnetic recording medium includes a lubricating liquid containing a monocyclic liquid crystal molecule represented by the following formula (23) or (24) in the outermost layer facing the magnetic head. A magnetic recording / reproducing apparatus characterized by holding an agent. Embedded image Embedded image