JP2002170218A - Magnetic recording medium and method of manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium in which satisfactory electromagnetic transducing characteristics are realized and which is suitable for high density recording and to provide its manufacturing method. SOLUTION: In the magnetic recording medium wherein an upper layer formed by dispersing ferromagnetic powder in a bonding agent is formed on a non-magnetic substrate, the upper layer contains a complex of a metal with a 1,3-dicarbonyl derivative shown by the following formula 1 (wherein R1 and R3 are groups selected from an alkyl group and an alkoxy group; R2 is a group selected from hydrogen and an alkoxy group) as a dispersing agent for dispersing the ferromagnetic powder in the bonding agent.

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 having an upper layer formed by dispersing a ferromagnetic powder in a binder on a nonmagnetic support, and a method for producing the same.

[0002]

2. Description of the Related Art Magnetic recording media include audio tapes,
It is widely used as video tapes, backup data cartridges, flexible disks, and the like. In particular, recently, high-density recording such as shortening the recording wavelength or digital recording has been actively studied, and the development of a magnetic recording medium having excellent electromagnetic conversion characteristics has been demanded.

In a so-called coating type magnetic recording medium in which a magnetic layer is coated on a non-magnetic support, thinning of the magnetic layer is being studied in order to improve the electromagnetic conversion characteristics. By reducing the thickness of the magnetic layer, self-demagnetization loss during recording can be reduced, and electromagnetic conversion characteristics can be improved. However, when a single thin magnetic layer having a thickness of, for example, 0.5 μm or less is formed on the nonmagnetic support, the magnetic layer having a smooth surface is easily affected by the surface shape of the nonmagnetic support. A problem arises that it is difficult to obtain.

For this reason, a so-called multilayer magnetic recording medium having a structure in which a nonmagnetic undercoat layer is formed between a nonmagnetic support and a magnetic layer has been devised. This makes it possible to reduce the thickness of the magnetic layer and to smooth the surface of the magnetic layer.

A so-called simultaneous multilayer coating method has been proposed as a coating method for a magnetic recording medium having the above-mentioned multilayer structure. This simultaneous multilayer coating method, a coating material in which a ferromagnetic powder or a non-magnetic powder and a binder are dispersed in an organic solvent, is simultaneously applied to a non-magnetic support by an extrusion method, that is, a co-extrusion method, An upper magnetic layer and a lower undercoat layer are formed.

[0006] By manufacturing by the simultaneous multilayer coating method,
A uniform coating film having no coating defects or streaks is formed on the magnetic recording medium, so that electromagnetic conversion characteristics can be improved, noise can be reduced, and the like. In addition, by manufacturing using the simultaneous multi-layer coating method, it is possible to improve the adhesiveness of the interface between the upper layer and the lower layer in the magnetic recording medium. Because of the advantages described above, the simultaneous multilayer coating method is becoming a central coating method in recent years when manufacturing a magnetic recording medium having a multilayer structure.

Further, it is necessary to further smooth the surface of the magnetic layer in order to minimize spacing loss during recording and reproduction. Particularly in high-density recording, the recording wavelength used is short, and the surface roughness of the magnetic layer is easily affected. Therefore, it is important to smooth the surface of the magnetic layer, that is, control the surface roughness of the magnetic layer.

In recent years, a magneto-resistive effect type magnetic head (hereinafter, referred to as an MR head) using a magneto-resistive effect element (hereinafter, referred to as an MR element) based on the operation principle of the magneto-resistive effect has become a reproducing head. Has been proposed and adopted. This MR head has a higher reproduction sensitivity than that of an electromagnetic induction type magnetic head that operates on the principle of electromagnetic induction, and can obtain a reproduction output several times higher. In addition, since the MR head can obtain a sufficient SN ratio even when the area of the recording bit is small, the recording density of the magnetic recording medium can be significantly improved.

A helical scan magnetic recording / reproducing system using the above MR head as a reproducing head has been proposed. This helical scan magnetic recording / reproducing system has a rotating drum on which an MR head is mounted, and reproduces a magnetic signal by sliding the MR head on a magnetic recording medium according to the rotation of the rotating drum. . For this reason, in the helical scan magnetic recording / reproducing system, the magnetic recording medium and the head come into contact and slide more vigorously than the magnetic recording / reproducing system using the conventional fixed type head.

However, since the MR element is very fragile, it is easily damaged by uneven wear of the head. For this reason, the magnetic recording medium used for the helical scan magnetic recording / reproducing system needs to have a smoother magnetic layer surface than the magnetic recording medium used for the above-mentioned fixed type head.

[0011]

One of the techniques for improving the surface smoothness and electromagnetic conversion characteristics of a magnetic layer is to use finely divided ferromagnetic powder as a ferromagnetic powder contained in a magnetic layer. And dispersing the ferromagnetic powder uniformly in the magnetic layer. As such a finely divided ferromagnetic powder, for example, a ferromagnetic powder having a long axis length of 0.1 μm or less and excellent properties such as a coercive force exceeding 160 kA / m has been developed. It is also possible to make the particle size distribution reflecting the coercive force distribution extremely uniform.

However, the cohesive force tends to increase as the ferromagnetic powder becomes finer,
It becomes extremely difficult for the ferromagnetic powder to be uniformly dispersed in the binder in the magnetic layer. As a result, agglomerates of ferromagnetic powder are present in the magnetic layer, which may affect the electromagnetic conversion characteristics. In addition, since the surface smoothness of the magnetic layer becomes insufficient, the spacing loss increases, which hinders high density recording.

[0013] Therefore, as a technique for improving the dispersibility of the ferromagnetic powder, in a kneading step performed when preparing a coating material, a powder material such as a ferromagnetic powder or a non-magnetic powder and a mixture of a binder and the like are mixed. It is conceivable to increase the applied shearing force or to lengthen the processing time by a sand mill or the like in the subsequent dispersion step. However, when the dispersibility of the ferromagnetic powder is improved by using these techniques, inconveniences such as damaging the ferromagnetic powder and lowering the production efficiency occur.

[0014] The resin material serving as a binder is -SO₃
M, -OSO₃M, -COOM, -P = O (OM)₂,
-NR₁R₂, -NR₁R₂ ⁺R₃X⁻,> NR₁R₂
⁺X ⁻(Where M is a hydrogen atom or lithium)
Alkali metals such as potassium, potassium and sodium;
₁, R₂And R₃Represents a hydrogen atom, an inorganic ion or an organic ion.
Is on. ) To allow ferromagnetic powder and
Enhance interaction with resin material and improve dispersibility of ferromagnetic powder
Attempts have been made to improve it. Add the functional group as above
The binder having a binder having no functional group as described above
Shows higher dispersibility than. However, high density recording
Disperse finely divided ferromagnetic powder for
At present, it is still difficult.

Accordingly, the present invention has been proposed in view of such a conventional situation, and it is an object of the present invention to provide a magnetic recording medium which achieves good electromagnetic conversion characteristics and is suitable for high-density recording, and a method of manufacturing the same. Aim.

[0016]

In order to achieve the above-mentioned object, a magnetic recording medium according to the present invention has an upper layer formed by dispersing a ferromagnetic powder in a binder on a non-magnetic support. In the magnetic recording medium, the upper layer contains a metal and a complex of a 1,3-dicarbonyl derivative represented by the following chemical formula 3 as a dispersant.

[0017]

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In the magnetic recording medium constructed as described above, the complex of the metal and the 1,3-dicarbonyl derivative shown in Chemical formula 3 assists in stabilizing the dispersion of the ferromagnetic powder. Therefore, the ferromagnetic powder can be uniformly dispersed in the binder.

In particular, the complex of the metal and the 1,3-dicarbonyl derivative is preferably an acetylacetone complex.

By using an acetylacetone complex salt as the complex of the metal and the 1,3-dicarbonyl derivative, the dispersibility of the ferromagnetic powder in the binder can be further improved.

The method for producing a magnetic recording medium according to the present invention is characterized in that, when producing a magnetic recording medium having an upper layer formed by dispersing a ferromagnetic powder in a binder on a non-magnetic support, A coating preparation step of preparing a coating by dissolving a ferromagnetic powder, the binder, a metal as a dispersant and a complex of a 1,3-dicarbonyl derivative shown in Chemical Formula 4 below in a solvent, and preparing the coating; An upper layer forming step of forming the upper layer by coating on the non-magnetic support.

[0022]

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According to the method for manufacturing a magnetic recording medium as described above, a complex of a metal and a 1,3-dicarbonyl derivative represented by Chemical Formula 4 is contained in a paint as a dispersant together with a ferromagnetic powder and a binder. It becomes possible to prepare a paint having good dispersibility. For this reason, the ferromagnetic powder can be uniformly dispersed in the binder, and an upper layer having good surface smoothness can be formed.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of a magnetic recording medium to which the present invention is applied will be described in detail with reference to the drawings.

In the magnetic recording medium to which the present invention is applied, as shown in FIG. 1, a lower layer 2 in which a non-magnetic powder is dispersed in a binder is formed on one main surface of a non-magnetic support 1. On the lower layer 2, an upper layer 3 in which a ferromagnetic powder is dispersed in a binder is formed. A back coat layer 4 is formed on the other main surface of the non-magnetic support 1 for the purpose of improving the running properties of the magnetic recording medium, preventing charging, preventing transfer, and the like.

In addition, between the lower layer 2 and the nonmagnetic support 1,
For the purpose of improving their adhesiveness, an adhesive layer may be formed. Further, a protective film layer may be formed on the upper layer 3 for the purpose of protecting the upper layer 3 which is a magnetic recording layer.

The upper layer 3 comprises, together with a ferromagnetic powder and a binder,
As a dispersant for dispersing the ferromagnetic powder in the binder, a complex of a metal and a 1,3-dicarbonyl derivative represented by the following Chemical Formula 5 is contained.

[0028]

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The 1,3-dicarbonyl derivative exists as an equilibrium mixture of a keto form and an enol form as shown in the following chemical formula 6.

[0030]

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The 1,3-dicarbonyl derivative in the enol form forms a complex with a metal as a bidentate ligand by two oxygen atoms in the molecule to form a complex. Such a complex of a metal and a 1,3-dicarbonyl derivative can take various forms depending on the valence and coordination number of the metal, as described later.

The complex of the metal and the 1,3-dicarbonyl derivative interacts with a metal atom on the surface of the ferromagnetic powder to form a strong bond and is adsorbed on the surface of the ferromagnetic powder. Here, the complex of the metal and the 1,3-dicarbonyl derivative forms an adsorptive layer on the surface of the ferromagnetic powder, but is not a polymer but has a relatively low molecular weight. It does not lead to a repulsive force. Therefore, the dispersion of the ferromagnetic powder is actually stabilized by the adsorption of the binder, but the complex of the metal and the 1,3-dicarbonyl derivative plays an auxiliary role.

As a result, in the magnetic recording medium to which the present invention is applied, since the ferromagnetic powder is uniformly dispersed in the binder without forming an agglomerate, the characteristics of the ferromagnetic powder are sufficiently exhibited.
Has excellent electromagnetic conversion characteristics. In particular, even when a finely divided ferromagnetic powder is used for high-density recording, the ferromagnetic powder is uniformly dispersed in the binder, so that the magnetic recording medium achieves good electromagnetic conversion characteristics. Can be. Moreover, by using a complex of a metal and a 1,3-dicarbonyl derivative as a dispersant, even when a finely divided ferromagnetic powder is used, the ferromagnetic powder is uniformly dispersed in the binder, The surface smoothness of the upper layer 3 can be improved. As a result, the magnetic recording medium to which the present invention is applied has a small spacing loss and is suitable for high-density recording.

The content of the complex of the metal and the 1,3-dicarbonyl derivative in the upper layer 3 is preferably in the range of 0.5 to 8 parts by weight based on 100 parts by weight of the ferromagnetic powder. When the content of the complex of the metal and the 1,3-dicarbonyl derivative exceeds the above range, there is a concern that the adsorption of the binder may be suppressed to cause a problem such as a decrease in dispersibility. on the other hand,
If the content of the complex of the metal and the 1,3-dicarbonyl derivative is below the above range, it may be insufficient to improve the dispersibility of the ferromagnetic powder. So, metal and 1,3
When the content of the complex with the dicarbonyl derivative is within the above range, the dispersibility of the ferromagnetic powder is particularly improved.

As a specific complex of a metal and a 1,3-dicarbonyl derivative, it is particularly preferable to use an acetylacetone complex salt, which is a complex of a metal and acetylacetone. By using an acetylacetone complex salt as the complex of the metal and the 1,3-dicarbonyl derivative, the dispersibility of the ferromagnetic powder in the binder can be further improved. As a result, the magnetic recording medium realizes more favorable electromagnetic conversion characteristics and further improves the surface smoothness of the upper layer 3, which is extremely suitable for high-density recording.

The acetylacetone complex salt can take various forms depending on the valence and coordination number of the metal, as described below.

For example, an acetylacetonato complex salt in which one acetylacetone (hereinafter referred to as AA) is bonded to a metal is represented by the following chemical formula [M ^I (A
A)] and the like. However, ^{M I} will, Li, Na,
Indicates one element of K and Tl.

[0038]

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A bi-acetylacetone-bound metal
The subacetylacetonate complex has a chemical formula [M
^II(AA)₂]. Where M^II
Represents Cu, Be, Mg, Zn, Co, Ni, Pd, Pt
Represents one of the elements. Acetylacetone is gold
Other examples of bisacetylacetonato complex salts linked to two genus
Is represented by the chemical formula [M^II(AA)₂(OH)₂]
I can do it. Where M ^IIIs Ca, Sr, Ba
Represents one of the elements.

The trisacetylacetonato complex salt in which three acetylacetones are bonded to a metal includes a chemical formula [M ^III (AA) ₃ ] as shown in the following Chemical Formula 8.
Where M ^III is In, Se, Ce, Ta, Ti,
One element of Mn, Fe, Co, Ru, and Al is shown. Another example of the trisacetylacetonato complex salt in which three acetylacetones are bonded to a metal is a chemical formula [M ^III (AA) ₃ ] X. Where M
^III represents one element of Si and Ti. Also,
X represents a halogen element.

[0041]

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The tetraacetylacetonato complex salt in which four acetylacetones are bonded to a metal is represented by the chemical formula [M ^IV
(AA) ₄ ]. Where M ^IV is Ce,
One of Th and Zr is shown.

Among the above acetylacetone complex salts, it is particularly preferable to use a trisacetylacetonato complex salt. By using the trisacetylacetonato complex salt as the dispersant, the dispersibility of the ferromagnetic powder in the binder can be further improved. As a result, the magnetic recording medium realizes extremely good electromagnetic conversion characteristics, and the surface smoothness of the upper layer 3 is dramatically improved, so that the magnetic recording medium is very suitable for high-density recording.

As the dispersant, two or more kinds of the above-mentioned complexes of the metal and the 1,3-dicarbonyl derivative may be used as a mixture, or a mixture of the metal and the 1,3-dicarbonyl derivative may be used. Other dispersants may be used together with the complex.

In the magnetic recording medium to which the present invention is applied,
As the binder contained in the upper layer 3 and the lower layer 2, known thermoplastic resins, thermosetting resins, reactive resins, and the like, which are conventionally used as binders for magnetic recording media, can be used. It is preferable to use those having a molecular weight of 5,000 to 100,000.

Examples of the thermoplastic resin include vinyl chloride, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, and 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-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose Derivatives (cellulose acetate butyrate, cellulose 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. Can be

[0048] All of the above binders include pigment components.
-SO for the purpose of improving dispersibility₃M, -OSO₃M,
-COOM, P = O (OM)₂Polar functional groups such as
May be. Here, M is a hydrogen atom or lithium
Alkali metals such as potassium, potassium and sodium. Sa
Further, as the polar functional group, -NR₁R₂, -NR
₁R₂ ⁺R₃X⁻Side chain type having a terminal group of
R₁R₂ ⁺X⁻Main chain type. Where R₁,
R₂, R₃Is a hydrogen atom or a hydrocarbon group, and X⁻
Are halogen element ions such as fluorine, chlorine, bromine, iodine, etc.
Or inorganic or organic ions. Also, -OH, -S
There are also polar functional groups such as H, -CN and epoxy groups.

The amount of these polar functional groups can be used in a range of ^{10 -1 mol / g~10 -8 mol /} g of the ^{binder, 10 -2 mol / g~10 -6 mol} /
It is particularly preferable to use in the range of g. These binders can be used alone or in combination of two or more.

If the amount of the binder used is too large, the proportion of the ferromagnetic powder in the upper layer 3 is relatively reduced and the output is reduced, and plastic flow is caused by repeated sliding during driving. This tends to reduce the running durability of the magnetic recording medium. On the other hand, if the amount of the binder used is too small, both the upper layer 3 and the lower layer 2 become brittle, and the running durability of the medium may be reduced. Therefore, the amount of the binder used is preferably 1 part by weight to 200 parts by weight based on 100 parts by weight of the ferromagnetic powder or nonmagnetic powder, and is preferably 1 to 200 parts by weight.
It is particularly preferred that the amount is from 0 to 50 parts by weight.

In the magnetic recording medium to which the present invention is applied,
At least one of the upper layer 3 and the lower layer 2 can contain a crosslinking agent for crosslinking and curing the binder. As the crosslinking agent, a polyisocyanate, for example, toluene diisocyanate, an adduct thereof, an alkylene diisocyanate, an adduct thereof, and the like can be used.

The amount of the polyisocyanate used with respect to the binder is 5 parts by weight with respect to 100 parts by weight of the binder.
It is preferably from 10 to 80 parts by weight, particularly preferably from 10 to 50 parts by weight.

In the magnetic recording medium to which the present invention is applied,
The ferromagnetic powder used in the upper layer 3 includes Fe, Co,
Ni metal, Fe-Co, Fe-Ni, Fe-Al, F
e-Ni-Al, Fe-Al-P, Fe-Ni-Si-
Al, Fe-Ni-Si-Al-Mn, Fe-Mn-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. These may contain light metal elements such as Al, Si, P, and B added for the purpose of preventing sintering during reduction or maintaining the shape. Further, γ-Fe ₂ O ₃ , F
e 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 , a belt-ride compound of γ-Fe ₂ O ₃ and Fe ₃ O ₄ containing Co, an oxide containing CrO ₂ containing one or more metal elements, for example, Te, Sb, Fe, B, etc. And the like. Further, hexagonal plate-like ferrites can also be used. M-type, W-type, Y-type, and Z-type barium ferrites, strontium ferrites, calcium ferrites, lead ferrites, and for controlling the coercive force of these, -Ti, Co-Ti-Zn, Co
-Ti-Nb, Co-Ti-Zn-Nb, Cu-Zr,
One to which Ni-Ti or the like is added can also be mentioned. These ferromagnetic powders can be used alone or in combination of two or more.

The specific surface area of the ferromagnetic powder used for the magnetic recording medium to which the present invention is applied is 30 m ² / g to 80 m ^2.
It is preferably ^{/ g, 40m 2 / g~70m 2} /
g is particularly preferred. When the specific surface area is in the above-mentioned range, the shape of the ferromagnetic powder becomes finer, high-density recording becomes possible, and a magnetic recording medium having excellent noise characteristics can be obtained.

Further, if the long axis length of the ferromagnetic powder used in the magnetic recording medium to which the present invention is applied is too short, dispersion in the magnetic paint becomes difficult, and if it is too long, noise characteristics deteriorate. It is preferable to use those having a thickness of 0.05 μm to 0.50 μm. If the axial ratio is too small, the orientation of the ferromagnetic powder is reduced and the output is reduced. If the axial ratio is too large, the short-wavelength signal output may be reduced. Specifically, when the ferromagnetic powder is hexagonal plate-like ferrite, the plate diameter is 0.01 μm to 0.1 μm.
Preferably, the thickness is about 5 μm and the plate thickness is about 0.001 μm to 0.2 μm.

The above-described numerical ranges of the major axis length, the axial ratio, the plate diameter, and the plate thickness are obtained by the average value of 100 or more samples randomly selected from a transmission electron microscope photograph.

In the magnetic recording medium to which the present invention is applied,
When the lower layer 2 is a non-magnetic layer, the non-magnetic powder to be contained is, for example, a non-magnetic iron oxide such as α-Fe ₂ O ₃ ,
Goethite, rutile titanium oxide, anatase titanium oxide, tin oxide, tungsten oxide, silicon oxide, zinc oxide, chromium oxide, cerium oxide, titanium carbide, B
N, 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 powders can be used alone or in combination of two or more.

The non-magnetic powder can be doped with an appropriate amount of impurities according to the purpose. The nonmagnetic powder may be subjected to a surface treatment with a compound such as Al, Si, Ti, Sn, Sb, or Zr for the purpose of improving dispersibility, imparting conductivity, and improving color tone. .

The specific surface area of the non-magnetic powder is from 30 m ² / g to
It is preferably ^{80m 2 / g, 40m 2 /} g~7
It is particularly preferred that it is 0 m ² / g. Further, if necessary, carbon black such as furnace black for rubber, pyrolytic carbon, black for color, and acetylene black may be contained in the nonmagnetic powder. Here, the specific surface area of carbon black ^is preferably 100m ² / g~400m 2 / g. Further, the DBP oil absorption of carbon black is preferably from 20 ml / 100 g to 200 ml / 100 g.

Since nonmagnetic powder and carbon black do not have magnetic cohesion, they can be easily dispersed as compared with ferromagnetic powder. May be difficult to disperse uniformly. On the other hand, when the specific surface areas of the nonmagnetic powder and the carbon black are smaller than the above ranges, there is a possibility that surface smoothness that can withstand high-density recording cannot be secured. When the specific surface area of the nonmagnetic powder and carbon black is in the above range, the lower layer 2 is smoothed with the refinement of the shape, and as a result, the upper layer 3 can be smoothed. It is possible to obtain a magnetic recording medium less affected by pacing loss.

In the magnetic recording medium to which the present invention is applied, a lubricant can be contained in at least one of the upper layer 3 and the lower layer 2 as necessary. As the lubricant, graphite, molybdenum disulfide, tungsten disulfide, silicone oil, fatty acids having 10 to 22 carbon atoms, and fatty acid esters of alcohols having 2 to 26 carbon atoms, terpene compounds, and these And the like.

Further, in the magnetic recording medium to which the present invention is applied, the upper layer 3 can contain abrasive particles. Examples of the abrasive particles include alumina (α, β, γ), chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride, titanium carbide, titanium carbide, and titanium oxide (rutile, anatase). The use amount of these abrasive particles is preferably 20 parts by weight or less, particularly preferably 10 parts by weight or less, based on 100 parts by weight of the ferromagnetic powder. The Mohs hardness of the abrasive particles is preferably 4 or more, and particularly preferably 5 or more. The specific gravity of the abrasive particles is preferably from 2 to 6, particularly preferably from 3 to 5. The average particle size of the abrasive particles is preferably 0.5 μm or less, particularly preferably 0.3 μm or less.

The average particle size of the abrasive particles as described above is:
As in the case of the ferromagnetic powder, it is determined by measuring from a transmission electron micrograph and performing statistical processing.

The same non-magnetic support 1 as that used in known magnetic recording media can be used. For example, polyethylene terephthalate,
Polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, celluloses such as cellulose triacetate and cellulose diacetate, polymer materials represented by vinyl resins, polyimides and polycarbonates, or metals And films or sheets of inorganic materials such as glass and ceramics.

As described above, in the magnetic recording medium to which the present invention is applied, a complex of a metal and a 1,3-dicarbonyl derivative assists in stabilizing the dispersion of the ferromagnetic powder in the upper layer. Therefore, the magnetic recording medium to which the present invention is applied
In the upper layer, the ferromagnetic powder is uniformly dispersed in the binder, and achieves good electromagnetic conversion characteristics. In addition, even when a finely divided ferromagnetic powder is used for high density recording, the ferromagnetic powder is uniformly dispersed in the binder, so that the surface smoothness of the upper layer can be improved. Therefore, the magnetic recording medium to which the present invention is applied has a small spacing loss and is suitable for high-density recording.

Particularly, by using an acetylacetone complex salt as the complex of the metal and the 1,3-dicarbonyl derivative, the dispersibility of the ferromagnetic powder in the binder can be further improved. As a result, the magnetic recording medium realizes more excellent electromagnetic conversion characteristics and further improves the surface smoothness of the upper layer, so that it is very suitable for high-density recording.

The magnetic recording medium to which the present invention is applied is preferably used in a magnetic recording / reproducing system using a magneto-resistance effect type magnetic head (hereinafter, referred to as an MR head) as a reproducing head. Since the magnetic recording medium to which the present invention is applied has excellent electromagnetic conversion characteristics and surface smoothness, a magnetic recording / reproducing system which achieves unprecedented high-density recording by being combined with an MR head having good sensitivity to an external magnetic field. Can be built.

In particular, the magnetic recording medium to which the present invention is applied
It is preferably used in a helical scan magnetic recording / reproducing system using an MR head as a reproducing head. Since the magnetic recording medium to which the present invention is applied has good surface smoothness of the upper layer, even in a helical scan magnetic recording / reproducing system in which the contact / sliding conditions with the MR head are strict, the magnetic recording medium has a high recording density.
It is possible to suppress uneven wear of the R head.

In this helical scan magnetic recording / reproducing system, a shield type MR head having an MR element sandwiched between shields is used as a reproducing head, and the MR head is mounted on a rotating drum to constitute a magnetic recording / reproducing apparatus. You.

By combining a helical scan magnetic recording system using an MR head with a magnetic recording medium to which the present invention is applied, an unprecedented high-density recording system can be constructed.

FIGS. 2 and 3 show an example of the structure of a rotary drum device mounted on the magnetic recording / reproducing apparatus. Note that FIG.
FIG. 3 is a perspective view schematically showing the rotary drum device 11, and FIG.
FIG. 3 is a plan view schematically showing a magnetic tape feed mechanism 20 including the rotary drum device 11.

As shown in FIG. 2, the rotating drum device 11
Are cylindrical fixed drum 12 and cylindrical rotary drum 1
3, a motor 14 for rotating and driving the rotary drum 13, a pair of electromagnetic induction type magnetic heads 15a and 15b mounted on the rotary drum 13, and a pair of MR heads 16a and 16b mounted on the rotary drum 13. .

The fixed drum 12 is a drum that is held without rotating. On a side surface of the fixed drum 12, a lead guide portion 18 is formed along a running direction of a magnetic tape 17 obtained by slitting the magnetic recording medium having the above-described configuration to an appropriate width. As will be described later, the magnetic tape 17 runs along the read guide portion 18 during recording and reproduction. The rotating drum 13 is disposed so that the center axis of the fixed drum 12 coincides with that of the fixed drum 12.

The rotating drum 13 is a drum that is driven to rotate at a predetermined rotation speed by the motor 14 during recording and reproduction on the magnetic tape 17. This rotating drum 13
It is formed in a cylindrical shape having substantially the same diameter as the fixed drum 12, and is arranged so that the center axis of the fixed drum 12 coincides with the center axis.
A pair of electromagnetic induction type magnetic heads 15a, 15b is provided on a side of the rotary drum 13 facing the fixed drum 12.
And a pair of MR heads 16a and 16b.

The electromagnetic induction type magnetic heads 15a and 15b are
This is a recording magnetic head in which a pair of magnetic cores are joined through a magnetic gap and a coil is wound around the magnetic core, and is used when recording a signal on the magnetic tape 17. The electromagnetic induction type magnetic heads 15a and 15b are formed on the rotating drum 13 such that the angle formed therebetween with respect to the center of the rotating drum 13 is 180 °, and their magnetic gap portions protrude from the outer periphery of the rotating drum 13. It is installed. In addition, these electromagnetic induction type magnetic heads 15a and 15b are set so that the azimuth angles are opposite to each other.

On the other hand, the MR heads 16a and 16b are reproducing magnetic heads having an MR element as a magnetic sensing element for detecting a signal from the magnetic tape 17, and are used when reproducing a signal from the magnetic tape 17. . And these M
The R heads 16a and 16b are mounted on the rotating drum 13 so that the angle formed between them with respect to the center of the rotating drum 13 is 180 °, and the magnetic gap portion protrudes from the outer periphery of the rotating drum. Note that these MR heads 16
a and 16b are set such that the azimuth angles are opposite to each other.

The magnetic recording / reproducing apparatus records a signal on the magnetic tape 17 and reproduces a signal from the magnetic tape 17 by sliding the magnetic tape 17 on the rotating drum device 11.

That is, at the time of recording and reproduction,
As shown in FIG. 3, the recording medium is sent from a supply reel 21 via guide rollers 22 and 23 so as to be wound around a rotary drum device 11, and recording and reproduction are performed by the rotary drum device 11. The magnetic tape 17 recorded and reproduced by the rotating drum device 11 is sent to a take-up roll 28 via guide rollers 24 and 25, a capstan 26, and a guide roller 27. That is, the magnetic tape 17 is fed at a predetermined tension and speed by a capstan 26 rotated and driven by a capstan motor 29, and is wound on a winding roll 28 via a guide roller 27.

At this time, the rotating drum 13 is driven to rotate by a motor 14 as shown by an arrow A in FIG. On the other hand, the magnetic tape 17 is sent along the lead guide portion 18 of the fixed drum 12 so as to slide obliquely with respect to the fixed drum 12 and the rotating drum 13. That is, the magnetic tape 17 moves along the tape running direction as shown in FIG.
As shown by the middle arrow B, the fixed drum 12
And the lead guide portion 1 so as to be in sliding contact with the rotating drum 13.
8 and then to the tape exit side as shown by arrow C in FIG.

Next, the internal structure of the rotary drum device 11 will be described with reference to FIG.

As shown in FIG. 4, a rotating shaft 31 is inserted through the centers of the fixed drum 12 and the rotating drum 13. The fixed drum 12, the rotating drum 13, and the rotating shaft 31 are made of a conductive material, are electrically connected, and the fixed drum 12 is grounded.

Further, two bearings 32 and 33 are provided inside the sleeve of the fixed drum 12, whereby the rotating shaft 31 is rotatably supported on the fixed drum 12. That is, the rotating shaft 31 is
2, 33, it is rotatably supported with respect to the fixed drum 12. On the other hand, the rotating drum 13 has a flange 34 formed on the inner peripheral portion thereof, and the flange 34 is fixed to the upper end of the rotating shaft 31. Thus, the rotating drum 13 rotates with the rotation of the rotating shaft 31.

Further, a rotary transformer 35, which is a non-contact type signal transmission device, is disposed inside the rotary drum device 11 in order to transmit signals between the fixed drum 12 and the rotary drum 13. . This rotary transformer 35
The stator core 36 attached to the fixed drum 12
And a rotor core 37 attached to the rotating drum 13.

The stator core 36 and the rotor core 37 are
A magnetic material such as ferrite is formed in an annular shape around the rotation shaft 31. Also, the stator core 36
Includes a pair of signal transmission rings 36a and 36b corresponding to the pair of electromagnetic induction type magnetic heads 15a and 15b, a signal transmission ring 36c corresponding to the pair of MR heads 16a and 16b, and a pair of MR heads 16a and 16b. A power transmission ring 36d for supplying power required for driving the 16b is disposed concentrically. Similarly, rotor core 3
7, a pair of signal transmission rings 37a and 37b corresponding to the pair of electromagnetic induction type magnetic heads 15a and 15b, a signal transmission ring 37c corresponding to the pair of MR heads 16a and 16b, and a pair of MR heads 16a Transmission ring 37d for supplying electric power required for driving
Are concentrically arranged.

The rings 36a, 36b, 36c,
36d, 37a, 37b, 37c, and 37d are rotating shafts 3
1, each of the rings 36a, 36b, 36c, 3 of the stator core 36.
6d, each ring 37a, 37b, 3 of the rotor core 37.
7c and 37d are arranged to face each other. The rotary transformer 35 includes the rings 36a, 36b, 36c, 36d of the stator core 36,
Each ring 37a, 37b, 37c, 3 of the rotor core 37
Signals and electric power are transmitted in a non-contact manner with 7d.

A motor 14 for rotating the rotary drum 13 is mounted on the rotary drum device 11. The motor 14 includes a rotor 38 as a rotating part,
And a stator 39 which is a fixed portion. Rotor 3
8 is attached to the lower end of the rotating shaft 31 and includes a driving magnet 40. On the other hand, the stator 39
Is attached to the lower end of the fixed drum 12 and has a driving coil 41. And the driving coil 4
By supplying a current to the rotor 1, the rotor 38 is rotationally driven. Accordingly, the rotating shaft 31 attached to the rotor 38 rotates, and accordingly, the rotating drum 13 fixed to the rotating shaft 31 is driven to rotate.

Next, the rotary drum device 11 as described above
Will be described with reference to FIG. 5, which shows a schematic circuit configuration of the rotary drum device 11 and its peripheral circuits.

When recording a signal on the magnetic tape 17 using the rotary drum device 11, first, a current is supplied to the driving coil 41 of the motor 14, whereby the rotary drum 13 is driven to rotate. Then, while the rotating drum 13 is rotating, as shown in FIG.
Is supplied to the recording amplifier 51.

The recording amplifier 51 amplifies the recording signal from the external circuit 50, and amplifies the recording signal from the electromagnetic induction type magnetic head 15a.
At the time of recording the signal, the recording signal is supplied to the signal transmission ring 36a of the stator core 36 corresponding to the electromagnetic induction type magnetic head 15a, and the signal is recorded by the other electromagnetic induction type magnetic head 15b. At this time, the recording signal is supplied to the signal transmission ring 36b of the stator core 36 corresponding to the electromagnetic induction type magnetic head 15b.

Here, a pair of electromagnetic induction type magnetic heads 15
As described above, the electromagnetic induction type magnetic heads 15a, 1b are arranged so that the angle between them with respect to the center of the rotary drum 13 is 180 °, as described above.
5b is recorded alternately on the magnetic tape 17 with a phase difference of 180 °. That is, the recording amplifier 51 sets the timing of supplying a recording signal to one electromagnetic induction type magnetic head 15a and the timing of supplying a recording signal to the other electromagnetic induction type magnetic head 15b by 180.
Alternately with a phase difference of °.

The one electromagnetic induction type magnetic head 15
a signal transmission ring 36 of the stator core 36 corresponding to a
a is supplied to the rotor core 37 in a non-contact manner.
Is transmitted to the signal transmission ring 37a. Then, the recording signal transmitted to the signal transmission ring 37a of the rotor core 37 is supplied to the electromagnetic induction type magnetic head 15a, and the signal is recorded on the magnetic tape 17 by the electromagnetic induction type magnetic head 15a.

Similarly, the other electromagnetic induction type magnetic head 15
b signal transmission ring 36 of stator core 36 corresponding to b
b is supplied to the rotor core 37 in a non-contact manner.
Is transmitted to the signal transmission ring 37b. Then, the recording signal transmitted to the signal transmission ring 37b of the rotor core 37 is supplied to the electromagnetic induction type magnetic head 15b, and the signal is recorded on the magnetic tape 17 by the electromagnetic induction type magnetic head 15b.

When the signal from the magnetic tape 17 is reproduced using the rotary drum device 11, first, a current is supplied to the drive coil 41 of the motor 14, whereby the rotary drum 13 is driven to rotate. You. Then, while the rotating drum 13 is rotating, as shown in FIG.
High frequency current is supplied from the oscillator 52 to the power drive 53.
Supplied to

The high-frequency current from the oscillator 52 is converted into a predetermined alternating current by the power drive 53 and then supplied to the power transmission ring 36 d of the stator core 36. The alternating current supplied to the power transmission ring 36d of the stator core 36 is transmitted to the power transmission ring 37d of the rotor core 37 in a non-contact manner. The AC current transmitted to the power transmission ring 37d of the rotor core 37 is rectified by the rectifier 54 to become a DC current, which is supplied to the regulator 55. The DC current is set to a predetermined voltage by the regulator 55.

The current set to a predetermined voltage by the regulator 55 is applied to the pair of MR heads 16a, 1
6b is supplied as a sense current. Note that a pair of MRs
The heads 16a, 16b include the MR heads 16a, 1
A reproduction amplifier 56 for detecting a signal from 6b is connected, and a current from the regulator 55 is also supplied to the reproduction amplifier 56.

Here, each of the MR heads 16a and 16b has an MR element whose resistance value changes according to the magnitude of an external magnetic field. In the MR heads 16a and 16b, the resistance value of the MR element changes due to the signal magnetic field from the magnetic tape 17, whereby a voltage change appears in the sense current.

The reproducing amplifier 56 detects this voltage change and outputs a signal corresponding to the voltage change as a reproduced signal. The reproducing amplifier 56 outputs a reproduced signal detected by the MR head 16a at the timing of reproducing a signal by one MR head 16a, and outputs the reproduced signal by the other MR head 16b at the timing of reproducing the signal. And outputs a reproduction signal detected by the MR head 16b.

Here, a pair of MR heads 16a, 16b
Are arranged so that the angle between them with respect to the center of the rotating drum 13 is 180 °, as described above, these MR heads 16a and 16b are alternately provided with a phase difference of 180 °. Will be played. That is,
The reproduction amplifier 56 is configured to output a reproduction signal from one of the MR heads 16a,
The timing at which the reproduced signal from b is output is 180 °
Alternately with a phase difference of

The reproduced signal from the reproducing amplifier 56 is supplied to the signal transmission ring 37c of the rotor core 37, and the reproduced signal is transmitted to the signal transmission ring 36c of the stator core 36 without contact. Stator core 36
The reproduction signal transmitted to the signal transmission ring 36c is amplified by the reproduction amplifier 57 and then corrected by the correction circuit 58.
Supplied to Then, the reproduction signal is subjected to predetermined correction processing by the correction circuit 58, and then output to the external circuit 50.

In the circuit configuration shown in FIG. 5, the pair of electromagnetic induction type magnetic heads 15a and 15b, the pair of MR heads 16a and 16b, the rectifier 54, the regulator 55, and the reproducing amplifier 56 are rotated. It is mounted on the drum 13 and rotates together with the rotating drum 13. On the other hand, the recording amplifier 51, the oscillator 52, the power drive 53, the reproducing amplifier 57, and the correction circuit 58 may be disposed on a fixed portion of the rotary drum device 11, or may be an external device configured separately from the rotary drum device 11. Circuit.

Next, the MR heads 16a and 16b mounted on the rotary drum 13 will be described in detail with reference to FIG. The MR head 16a and the MR head 16b have the same configuration except that the azimuth angles are set to be opposite to each other. Therefore, in the following description, these MR heads 16a and 16b are collectively referred to as the MR head 16.

The MR head 16 is mounted on the rotating drum 13 and is a read-only magnetic head for detecting a signal from the magnetic tape 17 by a helical scan method using a magnetoresistance effect. As shown in FIG. 6, the MR head 16 includes a pair of magnetic shields 61 and 62 made of a soft magnetic material such as Ni—Zn polycrystalline ferrite and a pair of magnetic shields 61 and 62 with an insulator 63 interposed therebetween. And a substantially rectangular MR element portion 64 sandwiched between the MR element portions 64. In addition, a pair of terminals are led out from both ends of the MR element section 64, and a sense current can be supplied to the MR element section 64 via these terminals.

The MR element section 64 includes an MR element having a magnetoresistance effect, a SAL (Soft Adjacent Layer) film,
An insulator film disposed between the R element and the SAL film is laminated. MR element has anisotropic magnetoresistance effect (AMR)
, The resistance value of which varies with the magnitude of the external magnetic field
It is made of a soft magnetic material such as i-Fe. SAL membrane is
This is for applying a bias magnetic field to the MR element by a so-called SAL bias method, and is made of a magnetic material having a low coercive force and a high magnetic permeability such as permalloy. The insulator film is used to insulate the MR element and the SAL film from each other and to prevent electrical shunt loss, and is made of an insulating material such as Ta.

The MR element portion 64 is formed in a substantially rectangular shape, and the pair of magnetic shields 61 and 62 forms an insulator 6 so that one side surface is exposed to the magnetic tape sliding surface 65.
3. Specifically, the MR element portion 64 has a pair of magnetic shields such that the short axis direction is substantially perpendicular to the magnetic tape sliding surface 65 and the long axis direction is substantially orthogonal to the magnetic tape sliding direction. It is sandwiched between insulators 61 and 62 via an insulator 63.

The magnetic tape sliding surface 6 of the MR head 16
5 is cylindrically polished along the sliding direction of the magnetic tape 17 so that one side surface of the MR element portion 64 is exposed on the sliding surface 65 of the magnetic tape, and Cylindrically polished along the direction perpendicular to the direction. As a result, the MR head 16 is
4 or its vicinity is made to protrude most. In this way, by making the MR element portion 64 or the vicinity thereof most protrude, the contact characteristics of the MR element portion 64 with the magnetic tape 17 can be improved.

When reproducing signals from the magnetic tape 17 using the MR head 16 as described above, the magnetic tape 17 is slid on the MR element section 64 as shown in FIG. The arrows in FIG. 7 schematically show how the magnetic tape 17 is magnetized.

Then, the magnetic tape 17 is
While sliding on the element section 64, a sense current is supplied to the MR element section 64 via terminals 64a and 64b connected to both ends of the MR element section 64, and a voltage change of the sense current is detected. Specifically, a predetermined voltage Vc is applied from a terminal 64a connected to one end of the MR element section 64, and a terminal 64b connected to the other end of the MR element section 64.
Is connected to the rotating drum 13. Here, the rotating drum 13 is electrically connected to the fixed drum 12 via the rotating shaft 31, and the fixed drum 12 is grounded. Therefore, one terminal 64 b connected to the MR element section 64 is grounded via the rotating drum 13, the rotating shaft 31 and the fixed drum 12.

When a sense current is supplied to the MR element section 64 while the magnetic tape 17 is slid, the resistance value of the MR element formed on the MR element section 64 changes according to the magnetic field from the magnetic tape 17. Change, resulting in a voltage change in the sense current. Therefore, by detecting the voltage change of the sense current, the signal magnetic field from the magnetic tape 17 is detected, and the signal recorded on the magnetic tape 17 is reproduced.

In the MR head 16 used, M
The MR element formed in the R element section 64 may be any element exhibiting a magnetoresistance effect. For example, a so-called giant magnetoresistance in which a larger magnetoresistance effect is obtained by laminating a plurality of thin films. An effect element (GMR element) can also be used. Also, the method of applying a bias magnetic field to the MR element may not be the SAL bias method, for example, a permanent magnet bias method, a shunt current bias method, a self-bias method, an exchange bias method, a barber pole method, a split element method, Various methods such as a servo bias method can be applied. The giant magnetoresistive effect and various bias methods are described in detail in, for example, "Magnetoresistance Head-Basic and Application Translated by Kazuhiko Hayashi" published by Maruzen Co., Ltd.

As described above, the magnetic recording medium to which the present invention is applied is excellent in electromagnetic conversion characteristics and surface smoothness. Therefore, when combined with an MR head having a good sensitivity to an external magnetic field, it is unprecedented. A magnetic recording / reproducing system that achieves high-density recording can be constructed.

Particularly, the magnetic recording medium to which the present invention is applied
Since the upper layer has good surface smoothness, uneven wear of the MR head can be suppressed even in a helical scan magnetic recording / reproducing system in which contact and sliding conditions with the MR head are severe.

Hereinafter, a method of manufacturing the magnetic recording medium having the above configuration will be described.

In order to form the lower layer 2 and the upper layer 3 on the non-magnetic support 1, first, the lower layer material and the upper layer material are formed into a paint by using a solvent to prepare a lower layer paint and an upper layer paint. The lower layer paint and the upper layer paint are applied to the non-magnetic support 1 and dried to form the lower layer 2 and the upper layer 3.
To form

The preparation of the lower layer paint and the upper layer paint is carried out by a kneading step, a dispersing step and a mixing step provided before and after these steps as necessary. In the dispersion step and the kneading step, a roll mill, a ball mill, a sand mill,
Conventionally known devices such as an agitator, a kneader, an extruder, a homogenizer, and an ultrasonic disperser can be used.

Here, the coating material for the upper layer is prepared by simultaneously mixing a ferromagnetic powder, a binder, a complex of a metal and a 1,3-dicarbonyl derivative, various additives, and the like as a dispersant, and kneading the mixture with a solvent. It is made by dispersing.
Since a complex of a metal and a 1,3-dicarbonyl derivative is used as a dispersant, it is possible to prepare an upper layer coating material having good dispersibility of ferromagnetic powder. For this reason, the ferromagnetic powder can be uniformly dispersed in the binder, and the upper layer 3 having good surface smoothness can be formed. Therefore, a magnetic recording medium having good electromagnetic conversion characteristics and suitable for high-density recording can be manufactured.

The timing of adding the complex of the metal and the 1,3-dicarbonyl derivative may be after the kneading step, ie, at the beginning of the dispersion step, but is preferably before the kneading step, ie, at the mixing step. . Also, metals and 1,3
The complex with the dicarbonyl derivative may be added to the mixing step entirely, or may be added separately before and after the kneading step.

Further, all raw materials such as ferromagnetic powder, non-magnetic powder, carbon black, binder, lubricant, solvent and the like used in the present embodiment may be added at the beginning or during any step. . Further, each raw material may be added in two or more steps.

As a specific example of a complex of a metal and a 1,3-dicarbonyl derivative, an acetylacetone complex salt is preferably used. By using an acetylacetone complex salt as a dispersant, it becomes possible to prepare a coating material having good dispersibility even when a fine ferromagnetic powder is used.
For this reason, the ferromagnetic powder can be uniformly dispersed in the binder, and the upper layer 3 having good surface smoothness can be formed. Therefore, a magnetic recording medium having good electromagnetic conversion characteristics and suitable for high-density recording can be manufactured.

In particular, it is preferable to use a trisacetylacetonato complex salt as a dispersant. As a result, the upper layer 3 having better electromagnetic conversion characteristics and further improved surface smoothness can be formed, so that a magnetic recording medium very suitable for high-density recording can be manufactured.

The complex of the metal and the 1,3-dicarbonyl derivative is preferably contained in the range of 0.5 to 8 parts by weight based on 100 parts by weight of the ferromagnetic powder. When the content of the complex of the metal and the 1,3-dicarbonyl derivative exceeds the above range, there is a concern that the adsorption of the binder may be suppressed to cause a problem such as a decrease in dispersibility. Meanwhile, metal and 1,
If the content of the complex with the 3-dicarbonyl derivative is below the above range, it may be insufficient to improve the dispersibility of the ferromagnetic powder. Therefore, when the content of the complex of the metal and the 1,3-dicarbonyl derivative is within the above range, the dispersibility of the ferromagnetic powder can be particularly improved.

Examples of the solvent used for coating include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, and cyclohexanone; alcohol solvents such as methanol, ethanol, propanol, butanol, isopropanol, and isobutyl alcohol; Methyl, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, ester solvents such as ethylene glycol acetate, ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane, benzene,
Examples thereof 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 coating material thus prepared is applied to the non-magnetic support 1 by a conventionally known coating method, for example, various methods such as gravure coating, roll coating, blade coating, and die coating. Among them, a simultaneous multilayer coating method using a die coater is preferable. As the lip configuration of the die coater, a two-lip system, a three-lip system, a four-lip system, or the like is used.

For example, a so-called wet-on-wet multi-layer coating method using a three-lip type die coater will be described with reference to FIG. Extrusion coater 70 is provided with liquid pools 71 and 72 for storing lower layer paint 2a and upper layer paint 3a. First, the non-magnetic support 1 unwound from a supply roll (not shown)
The lower layer paint 2a and the upper layer paint 3a are supplied onto the non-magnetic support 1 through slits by an extrusion-type extrusion coater 70 while being fed in the direction of arrow D in the drawing, and the wet-on-wet method is used. Layer at the same time.

In such a wet-on-wet method, since the upper layer paint 3a is applied while the lower layer 2 is in a wet state, the surface of the lower layer 2, that is, the boundary surface between the lower layer 2 and the upper layer 3 becomes smooth. Thereby, the surface properties of the upper layer 3 are improved, and the adhesion between the lower layer 2 and the upper layer 3 is also improved. As a result, separation of the lower layer 2 and the upper layer 3 is prevented, the strength of the coating film is improved, the dropout can be reduced, and the reliability can be improved.
Therefore, it is possible to sufficiently cope with high-density recording in which high output and low noise are required, prevent film peeling, improve film strength, and reduce dropout, so that a magnetic recording medium having high reliability can be obtained. Can be manufactured.

The lower layer 2 and the upper layer 3 formed by the above-mentioned wet-on-wet method have a certain thickness except for a case where a clear boundary substantially exists. There may be a mixed boundary area. In the present embodiment, the upper layer side and the non-magnetic support 1 side excluding such a boundary region are referred to as an upper layer 3 and a lower layer 2, respectively. Also, in the present embodiment, when a clear boundary exists between the lower layer 2 and the upper layer 3, the lower layer 2 and the upper layer 3
May be any case where a boundary region exists between.

Incidentally, a magnetic recording medium may be manufactured by a so-called wet-on-dry method as disclosed in JP-A-6-236543, in contrast to the above-mentioned wet-on-wet method. When a magnetic recording medium is manufactured by a wet-on-dry method, it is necessary to select a material having sufficient solvent resistance to the upper layer paint as the lower layer.

Next, the nonmagnetic support 1 on which the upper layer 3 and the lower layer 2 are formed is introduced into a dryer, and the solvent is volatilized.

If necessary, the so-called calendering treatment may be performed on the non-magnetic support 1 on which the lower layer 2 and the upper layer 3 are formed, by passing the heated roll between pressurized rolls. Further, on the other main surface of the non-magnetic support 1,
The back coat layer 4 may be formed.

The magnetic recording medium thus obtained is
For example, it is slit into a width of 8 mm, and is housed in a cassette to form a cassette tape. In addition, the magnetic recording medium may be formed into a magnetic disk by coating the upper layer paint and the lower layer paint on both main surfaces of the non-magnetic support in a multi-layered form, punching out a disc shape, and storing in a shell. It is possible.

In the method for producing a magnetic recording medium as described above, a complex of a metal and a 1,3-dicarbonyl derivative is contained as a dispersant together with a ferromagnetic powder and a binder in the paint. Can be prepared. For this reason, the ferromagnetic powder is uniformly dispersed in the binder,
In addition, an upper layer having good surface smoothness can be formed.
Therefore, it is possible to manufacture a magnetic recording medium that exhibits good electromagnetic conversion characteristics and is suitable for high-density recording.

[0131]

EXAMPLES Specific examples to which the present invention is applied will be described below based on experimental results.

[Experiment 1] First, the effect of including a complex of a metal and a 1,3-dicarbonyl derivative as a dispersant in the upper layer of a multilayer coating type magnetic recording medium was examined.

Sample 1 An upper layer paint and a lower layer paint were prepared according to the following composition. Coating was performed according to a conventional method, and a ferromagnetic powder or a non-magnetic powder, a binder, an additive, a predetermined amount of a solvent, and an additive such as a dispersant were mixed, kneaded by an extruder, and dispersed by a sand mill for 6 hours. .

As the dispersant, a complex of a metal shown in Table 1 below and a 1,3-dicarbonyl derivative having a composition shown in Table 1 below in Chemical Formula 9 was used. In addition,
The dispersant used in sample 1 was acetylacetone with Fe
Is a trisacetylacetonato complex salt bonded to three.

[0135]

Embedded image

<Coating Composition for Upper Layer> 100 parts by weight of Fe-based metal ferromagnetic powder (coercive force = 160 kA / m, saturation magnetization = 130 Am ² / kg, specific surface area = 60 m ² / g, major axis length = 0 0.07 μm, needle ratio = 3) Polyvinyl chloride resin (manufactured by Zeon Corporation, trade name: MR110) 14 parts by weight Polyester polyurethane resin (manufactured by Toyobo Co., Ltd.) 3 parts by weight Additive (Al ₂ O ₃ ) 5 parts by weight Parts 2 parts by weight of dispersant (described in Table 1) 1 part by weight of stearic acid 1 part by weight of heptyl stearate 150 parts by weight of methyl ethyl ketone 150 parts by weight of cyclohexanone <Coating composition for lower layer> Acicular α-Fe ₂ O ₃ 100 parts by weight (specific surface area = 53 m ² / g, major axis length = 0.15 μm, needle ratio = 5) ・ Polyvinyl chloride resin (manufactured by Zeon Corporation, trade name MR110) 1 3 parts by weight ・ Polyester polyurethane resin (manufactured by Toyobo Co., Ltd.) 4 parts by weight ・ Additive (Al ₂ O ₃ ) 5 parts by weight ・ Dispersant (described in Table 1) 2 parts by weight ・ Stearic acid 1 part by weight ・ Heptyl stearate 1 105 parts by weight of methyl ethyl ketone 105 parts by weight of cyclohexanone To the upper layer paint and the lower layer paint prepared as described above, 3 parts by weight of polyisocyanate was added, and a 7 μm-thick non-magnetic support of polyethylene terephthalate was added. One main surface was coated simultaneously using a four-lip type die coater and then dried to produce a magnetic tape raw material. The upper layer had a coating thickness of 0.15 μm, and the lower layer had a coating thickness of 2.0 μm.

The original magnetic tape was subjected to an orientation treatment, a drying treatment, a calendar treatment, and a curing treatment by a solenoid coil in that order.

Next, a backcoat layer paint was prepared according to the following composition, and applied on the main surface opposite to the side on which the upper and lower layers of the nonmagnetic support were formed, to form a backcoat layer. .

<Backcoat layer coating composition> 100 parts by weight of carbon black (manufactured by Asahi Corporation, $ 80) 100 parts by weight of polyester polyurethane resin (Nipporan N-2304, manufactured by Nippon Polyurethane Industry Co., Ltd.) 500 parts by weight of methyl ethyl ketone 500 parts by weight The obtained raw magnetic tape was slit into a width of 8 mm,
mm video tape was produced.

Samples 2 to 11 were the same as the dispersants except that complexes of metals shown in Table 1 below and 1,3-dicarbonyl derivatives having the composition shown in Table 1 below were used. An 8 mm video tape was produced in the same manner as in Sample 1.

An 8 mm video tape was prepared in the same manner as in Sample 1, except that the upper layer of Sample 12 did not contain a dispersant.

Sample 13 An 8 mm video tape was prepared in the same manner as in Sample 1, except that acetylacetone not forming a complex was used as the dispersant.

With respect to the dispersants used in Samples 1 to 13, the composition and content of the 1,3-dicarbonyl derivative, the number of 1,3-dicarbonyl derivatives bonded to the metal, Table 1 below summarizes the metals to be used.

[0144]

[Table 1]

With respect to Samples 1 to 13 manufactured as described above, an electromagnetic conversion measuring machine having an electromagnetic induction type magnetic head as a reproducing head, and M as a reproducing head.
Each output (RF output) was measured using an electromagnetic conversion measuring device equipped with an R head.

A 10 MHz rectangular wave signal was recorded with an optimum recording current of each sample by an electromagnetic transducer having an electromagnetic induction type magnetic head as a reproducing head, and a 10 MHz output level was detected by a spectrum analyzer. The relative speed between the 8 mm video tape and the electromagnetic induction type magnetic head was 3.3 m / s.

As an electromagnetic conversion measuring instrument having an MR head as a reproducing head, a modified 8 mm VTR was used. The recording wavelength is 0.5 μm for each sample.
After recording the signal with, the shield type MR head
The reproduction output was measured. The MR element constituting the MR head is FeNi-AMR (anisotropic magnetoresistance effect element), the saturation magnetization is 800 emu / cc, the film thickness is 40 nm, the shield material is NiZn, and the shield material is NiZn. The distance between them is 0.17 μm. The track width is 18 μm and the azimuth angle is 25 ° C.

Table 2 below shows the reproduction output when using the electromagnetic conversion measuring device having the electromagnetic induction type magnetic head and the reproduction output when using the MR head. In Table 2, both the reproduction output when using the electromagnetic conversion measuring device having the electromagnetic induction type magnetic head and the reproduction output when using the electromagnetic conversion measuring device having the MR head are 0 dB. And expressed as a relative value.

In addition, Samples 1 to 1
The surface roughness of the upper layer of No. 3 was measured. Surface roughness is Zygo
A range of 0.14 mm × 0.1 mm was measured at a magnification of 50 times using a brand name New View 5000 manufactured by the company. Table 2 also shows the results of the surface roughness.

[0150]

[Table 2]

From the results shown in Table 2, it was found that metal and 1,1 were used as dispersants.
Sample 1 using complex with 3-dicarbonyl derivative
Sample 11 was Sample 1 in which no dispersant was used.
As compared with Sample No. 2 and Sample 13 using acetylacetone not forming a complex as a dispersant, it was found that excellent surface smoothness was exhibited and a high output was obtained.

Among them, it was found that Sample 1 using a trisacetylacetonate complex salt as a complex of a metal and a 1,3-dicarbonyl derivative exhibited particularly excellent surface smoothness and high output.

In addition, regardless of the number of 1,3-dicarbonyl derivatives bonded to the metal and the metal constituting the complex, the use of the complex of the metal and the 1,3-dicarbonyl derivative provides excellent surface smoothness. It showed that high output could be obtained.

The effect of improving the output by using a complex of a metal and a 1,3-dicarbonyl derivative as a dispersant is higher than that of a magnetic recording / reproducing system having an electromagnetic induction type magnetic head as a reproducing head. It has been found that this is more significant when used in a magnetic recording / reproducing system having an MR head.

[Experiment 2] Next, the effect of including a complex of a metal and a 1,3-dicarbonyl derivative as a dispersant in the upper layer of a so-called single-layer coating type magnetic recording medium was examined.

Sample 14 An 8 mm video tape was produced in the same manner as in Sample 1, except that the lower layer was not formed and the upper layer was formed directly on the nonmagnetic support by a single-layer die coater. Note that the thickness of the upper layer was 0.20 μm.

Sample 15 An 8 mm video tape was prepared in the same manner as in Sample 14, except that the upper layer did not contain a dispersant.

With respect to the samples 14 and 15 manufactured as described above, in the same manner as in Experiment 1 described above,
The output (RF output) was measured using an electromagnetic conversion measuring device having an electromagnetic induction type magnetic head as a reproducing head and an electromagnetic conversion measuring device having an MR head as a reproducing head. The results are shown in Table 3 below. In Table 3, both the reproduction output when using the electromagnetic conversion measuring device having the electromagnetic induction type magnetic head and the reproduction output when using the electromagnetic conversion measuring device having the MR head are 0 dB. And expressed as a relative value.

Further, the surface roughness of the upper layer was measured for the manufactured samples 14 and 15 in the same manner as in Experiment 1 described above. The results are shown in Table 3 below.

[0160]

[Table 3]

From the results shown in Table 3, it was found that metals as dispersants and 1,1
Sample 14 using complex with 3-dicarbonyl derivative
It was found that the sample exhibited excellent surface smoothness and obtained a high output as compared with Sample 15 in which the upper layer did not contain a dispersant.

Therefore, from the results of Experiment 2, it is apparent that the effect of using a complex of a metal and a 1,3-dicarbonyl derivative as a dispersant can be obtained even in a so-called single-layer coating type magnetic recording medium. became.

[Experiment 3] Next, the preferred content of a complex of a metal and a 1,3-dicarbonyl derivative was examined.

Samples 16 to 20 An 8 mm video tape was prepared in the same manner as in Sample 1 except that the content of the complex of the metal and the 1,3-dicarbonyl derivative was changed as shown in Table 4 below. Produced.

[0165]

[Table 4]

For samples 16 to 20 manufactured as described above, in the same manner as in Experiment 1 described above, an electromagnetic conversion measuring device having an electromagnetic induction type magnetic head as a reproducing head and an electromagnetic conversion measuring device having an MR head as a reproducing head. Each output (RF output) was measured using a measuring device. The results are shown in Table 5 below. In Table 5, both the reproduction output when using the electromagnetic conversion measuring device having the electromagnetic magnetic head and the reproduction output when using the electromagnetic conversion measuring device having the MR head are 0 dB.
And expressed as a relative value.

The surface roughness of the upper layer of each of Samples 16 to 20 was measured in the same manner as in Experiment 1 described above. The results are shown in Table 5 below.

[0168]

[Table 5]

From the results shown in Table 5, Samples 17 to 19 in which the content of the complex of the metal and the 1,3-dicarbonyl derivative was in the range of 0.5 to 8 parts by weight were excellent in surface smoothness. It showed that high output could be obtained.

On the other hand, Sample 1 containing less than 0.5 part by weight of a complex of a metal and a 1,3-dicarbonyl derivative
Sample 20 having a complex content of 6 and a metal with a 1,3-dicarbonyl derivative in excess of 8 parts by weight
-It was found that both the surface roughness and the output were slightly inferior to Sample 19.

Therefore, according to the result of Experiment 3, the content of the complex of the metal and the 1,3-dicarbonyl derivative was 0.1%.
It has been found that the content is preferably in the range of 5 to 8 parts by weight.

[0172]

As is clear from the above description, in the magnetic recording medium according to the present invention, the complex of the metal and the 1,3-dicarbonyl derivative assists in stabilizing the dispersion of the ferromagnetic powder. The ferromagnetic powder can be evenly dispersed in the binder. Therefore, according to the present invention, it is possible to provide a magnetic recording medium having excellent electromagnetic conversion characteristics, excellent surface smoothness, and suitable for high-density recording.

Further, in the method for producing a magnetic recording medium according to the present invention, a complex of a metal and a 1,3-dicarbonyl derivative is contained in a paint as a dispersant together with a ferromagnetic powder and a binder. It is possible to prepare a suitable paint. For this reason, the ferromagnetic powder can be uniformly dispersed in the binder, and an upper layer having good surface smoothness can be formed. Therefore, according to the present invention, it is possible to produce a magnetic recording medium that exhibits good electromagnetic conversion characteristics and is suitable for high-density recording.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration example of a magnetic recording medium to which the present invention is applied.

FIG. 2 shows a configuration example of a rotary drum device mounted on a magnetic recording / reproducing device of a helical scan magnetic recording system.
It is a perspective view showing the outline.

FIG. 3 is a plan view schematically showing a configuration example of a magnetic tape feeding mechanism including the rotary drum device.

FIG. 4 is a sectional view showing an internal structure of the rotary drum device.

FIG. 5 is a diagram schematically showing a circuit configuration of the rotary drum device and its peripheral circuits.

FIG. 6 is a perspective view, partially cut away, of an example of an MR head mounted on the rotary drum.

FIG. 7 is a diagram schematically showing how a signal from a magnetic tape is reproduced using an MR head.

FIG. 8 is a conceptual diagram for explaining a method for forming an upper layer and a lower layer on a nonmagnetic support by a die coater.

[Explanation of symbols]

1 Non-magnetic support, 2 Lower layer, 3 Upper layer, 4 Back coat layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J038 BA021 CA021 CD001 CF001 CG001 DA001 DB001 DD001 DG001 DH001 DL031 HA066 HA076 HA316 JC38 KA07 KA09 KA20 LA03 NA22 PA12 PB11 PC08 5D006 BA09 CA01 5D112 AA05 BB10 BB18

Claims (12)

[Claims] 1. A magnetic recording medium having an upper layer formed by dispersing a ferromagnetic powder in a binder on a nonmagnetic support, wherein the upper layer disperses the ferromagnetic powder in the binder. A magnetic recording medium comprising, as a dispersant, a complex of a metal and a 1,3-dicarbonyl derivative shown in Chemical Formula 1 below. Embedded image 2. The magnetic recording medium according to claim 1, wherein the complex of the metal and the 1,3-dicarbonyl derivative is an acetylacetone complex. 3. The complex according to claim 2, wherein the acetylacetone complex is a trisacetylacetonate complex.
The magnetic recording medium according to the above. 4. The content of the complex of the metal and the 1,3-dicarbonyl derivative in the upper layer is in the range of 0.5 to 8 parts by weight based on 100 parts by weight of the ferromagnetic powder. The magnetic recording medium according to claim 1, wherein: 5. A method according to claim 1, wherein said non-magnetic support and said upper layer are
2. The magnetic recording medium according to claim 1, wherein a lower layer in which the nonmagnetic powder is dispersed in a binder is formed. 6. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is used in a magnetic recording / reproducing system using a magnetoresistive read head. 7. The magnetic recording medium according to claim 6, wherein said magnetic recording / reproducing system is a helical scan magnetic recording / reproducing system. 8. When producing a magnetic recording medium having an upper layer formed by dispersing a ferromagnetic powder in a binder on a non-magnetic support, the ferromagnetic powder, the binder, and the binder As a dispersant for dispersing the ferromagnetic powder in the agent, a coating preparation step of preparing a coating by dissolving a metal and a complex of a 1,3-dicarbonyl derivative shown in Chemical Formula 2 below in a solvent, Forming an upper layer on the non-magnetic support by applying the compound onto the non-magnetic support. Embedded image 9. The method for producing a magnetic recording medium according to claim 8, wherein an acetylacetone complex salt is used as the complex of the metal and the 1,3-dicarbonyl derivative. 10. The method according to claim 9, wherein a trisacetylacetonato complex salt is used as the acetylacetone complex salt. 11. In the coating preparation step, a complex of the metal and a 1,3-dicarbonyl derivative is contained in an amount of 0.5 to 8 parts by weight based on 100 parts by weight of the ferromagnetic powder. 9. The method for manufacturing a magnetic recording medium according to claim 8, wherein: 12. A lower layer forming step of forming a lower layer in which a nonmagnetic powder is dispersed in a binder, between the nonmagnetic support and the upper layer, before the upper layer forming step. The method for manufacturing a magnetic recording medium according to claim 8, wherein