JPH10149532A - Magnetic recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having high electromagnetic conversion characteristics adequate for high-density recording and a process for producing the same. SOLUTION: A nonmagnetic base 1 is provided thereon with a lower layer 4a consisting of a nonmagnetic layer formed by dispersing nonmagnetic powder into a binder and an upper layer 2a consisting of a magnetic layer formed by dispersing magnetic powder into the binder. A dispersant consisting of ethylene glycol fatty acid ester is incorporated into the lower layer 4a. At the time of producing such magnetic recording medium, a nonmagnetic coating material for forming the lower layer 4a and a magnetic coating material for forming the upper layer 2a are simultaneously applied wet on wet on the nonmagnetic base 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-magnetic support comprising a lower layer composed of a non-magnetic layer in which non-magnetic powder is dispersed in a binder and an upper layer composed of a magnetic layer in which the magnetic powder is dispersed in a binder. The present invention relates to a magnetic recording medium provided on a body and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, magnetic recording media have been widely used as audio tapes, video tapes, backup data cartridges, floppy disks, and the like, and the demand for such media has been remarkably growing.

In particular, recently, studies on high-density recording, such as shortening the recording wavelength or digital recording, have been actively conducted, and the development of a magnetic recording medium having excellent electromagnetic conversion characteristics has been demanded. .

[0004] As such a magnetic recording medium, a powder magnetic material such as an oxide magnetic powder or an alloy magnetic powder is combined with a vinyl chloride-vinyl acetate copolymer, a polyester resin, a urethane resin, a polyurethane resin or the like organic binder (bonding). So-called coating-type magnetic recording media prepared by applying a magnetic coating material dispersed in a non-magnetic material) on a nonmagnetic support and drying the coating material are widely used.

In such a coated magnetic recording medium,
In order to improve the electromagnetic conversion characteristics, thinning of the magnetic layer has been studied.

This is to reduce the self-demagnetization loss at the time of recording by making the magnetic layer thinner, and to improve the electromagnetic conversion characteristics. In recent years, various coating methods have been studied.

When a thin magnetic layer having a thickness of 0.5 μm or less is provided as a single layer on a non-magnetic support, the influence of the surface shape of the non-magnetic support tends to appear, and it is difficult to obtain a smooth surface. Therefore, specifically, a non-magnetic undercoat layer is provided between the magnetic layer and the non-magnetic support, and the magnetic layer is thinned,
A structure for realizing the smoothness of the surface has been devised.

On the other hand, in a magnetic recording medium having two layers as described above on a non-magnetic support, there is no coating defect and no coating streak and uniform coating for the purpose of improving electromagnetic conversion characteristics and reducing noise. It is required to form each layer on the film. To achieve this, a magnetic coater (upper layer) and a non-magnetic layer (lower layer) are simultaneously coated on a non-magnetic support by a die coater (using an extrusion-type extrusion die), so-called simultaneous multi-layer coating. A scheme has been proposed.

This coating method is also effective as a method for improving the adhesiveness of the interface between the upper and lower layers, and is becoming the main coating method for recent multilayer coating type magnetic recording media.

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

In order for the magnetic recording medium to exhibit good electromagnetic conversion characteristics, it goes without saying that the ferromagnetic powder in the magnetic layer must be uniformly dispersed in the binder and oriented in the longitudinal direction. However, in addition to this, it is often necessary to make the upper layer made of a magnetic layer thinner and smoother.

Therefore, in order to achieve the objects such as thinning and smoothing, as described above, it is necessary to smooth the lower layer made of the non-magnetic layer which exerts a large effect.

In order to smooth the lower layer composed of the non-magnetic layer, the non-magnetic powder to be used may be finely divided to a specific surface area of 50 m ² / g or more, and may be uniformly dispersed in the binder.
As the powder becomes finer, dispersion of the powder in the binder tends to become more difficult.

As a method for solving such a problem, it is conceivable to lengthen the time required for kneading or dispersing when preparing the non-magnetic coating material in the lower layer. Problems such as reduction occur, which is not preferable.

On the other hand, -SO ₃ M, -OSO ₃
M, -COOM, -P = O ( OM) 2, -NR 1 R 2,
^{-NR 1 R 2 R 3+ X -} ,> NR 1 R 2+ X - by containing a functional group such as, strengthening the interaction with the non-magnetic powder and a binder, the dispersibility of the magnetic powder Attempts have been made to improve it.

However, although these binders having functional groups exhibit superior performance as compared with conventional binders, they still do not sufficiently disperse fine non-magnetic powders developed for high-density recording. At present, it is difficult.

[0017]

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional circumstances, and an object of the present invention is to provide a magnetic recording medium having high electromagnetic conversion characteristics suitable for high-density recording and a method of manufacturing the same. To provide.

[0018]

That is, the present invention provides a lower layer comprising a non-magnetic layer in which a non-magnetic powder is dispersed in a binder;
A magnetic recording medium in which an upper layer comprising a magnetic layer in which a magnetic powder is dispersed in a binder is provided on a non-magnetic support, and a dispersant comprising ethylene glycol fatty acid ester is contained in the lower layer (hereinafter, the present invention) (Hereinafter referred to as a magnetic recording medium).

According to the magnetic recording medium of the present invention, since the lower layer composed of the nonmagnetic layer in which the nonmagnetic powder is dispersed in the binder contains the dispersant composed of ethylene glycol fatty acid ester, the lower layer ( That is, the nonmagnetic powder in the nonmagnetic layer) can be uniformly dispersed in the binder and the solvent, and the average thickness (after calendering) of the upper layer (that is, the magnetic layer) is as thin as 0.5 μm or less. However, it is possible to provide a magnetic recording medium having a high electromagnetic conversion characteristic suitable for high-density recording by smoothing its surface.

In the magnetic recording medium of the present invention, as will be described in detail later, a portion such as a carboxyl group or a hydroxyl group of an ethylene glycol fatty acid ester is adsorbed on the surface of the nonmagnetic powder by hydrogen bonding, coordination bond, dehydration or the like. it is conceivable that. In addition, the ethylene glycol fatty acid ester has a good affinity for a binder, a solvent, and the like due to R ¹ , R ² , a hydrocarbon group, and a portion such as ethylene glycol (ethylene oxide), so that it functions as a dispersant. And improve the dispersibility of the non-magnetic powder.

Therefore, the characteristics of the finely divided non-magnetic powder are sufficiently exhibited, the surface of the non-magnetic layer is smoothed, and the surface of the magnetic layer is smoothed. It is considered that the characteristics are improved.

Further, the present invention provides a method for producing a magnetic recording medium comprising: a lower layer comprising a non-magnetic layer in which a non-magnetic powder is dispersed in a binder; and an upper layer comprising a magnetic layer in which the magnetic powder is dispersed in a binder. In producing a magnetic recording medium in which a dispersant composed of an ethylene glycol fatty acid ester is contained in the lower layer, a non-magnetic paint for forming the lower layer and a magnetic paint for forming the upper layer A method for producing a magnetic recording medium, in which a multi-layer coating is performed on the non-magnetic support
This is referred to as the production method of the present invention. ).

According to the manufacturing method of the present invention, in manufacturing the magnetic recording medium of the present invention, the non-magnetic coating for forming the lower layer and the magnetic coating for forming the upper layer are mixed with the non-magnetic support. Multi-layer coating on top (especially wet coating where magnetic coating is applied while the applied non-magnetic coating is not dried)
On-wet coating), the upper layer can be formed with good surface properties. In particular, in the case of a wet-on-wet coating method, the surface of the lower layer (that is, the boundary surface with the upper layer) tends to be smooth, the surface properties of the upper layer are further improved, and both upper and lower layers are used. Is also improved.

As a result, the performance of the magnetic recording medium required for high density recording, such as high output and low noise, is satisfied, film (layer) peeling is reduced, and film (layer) strength is improved. . In addition, dropout and the like can be reduced, and the reliability of the magnetic recording medium can be improved.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION In a magnetic recording medium of the present invention and a method of manufacturing the same (hereinafter, the magnetic recording medium of the present invention and a method of manufacturing the same may be simply referred to as “the present invention”), dispersion of non-magnetic powder is performed. The ethylene glycol fatty acid ester used as the agent is preferably a polyethylene glycol fatty acid ester represented by the following general formula (I).

Embedded image (However, in the above general formula, R ¹ and R ² are each an acyl group such as palmitic acid, stearic acid, oleic acid, linoleic acid or a hydrogen atom, at least one of which is the acyl group, and x is Indicates the degree of polymerization.)

In the polyethylene glycol fatty acid ester represented by the general formula (I), the degree of polymerization x can take any integer of 1 or more (preferably 2 or more). However, if the value of the degree of polymerization x is too large, the number of molecules of the polyethylene glycol fatty acid ester that can be adsorbed on the non-magnetic powder decreases, and the binding (affinity) with the non-magnetic powder in the polyethylene glycol fatty acid ester
Since the distribution density of the functional group becomes smaller, the dispersing effect tends to decrease. Therefore, there is an optimum value for exhibiting excellent dispersibility, and the degree of polymerization x is preferably in the range of 1 to 10, more preferably in the range of 2 to 5.

In the general formula (I), at least one of R ¹ and R ² is represented by the general formula (II): C _p H _{2p + 1} CO- (where p is 1 to 30) It is an integer.)
It is preferable that the polymer comprises a linear or branched acyl group represented by the formula: At this time, the acyl group represented by the general formula (II) may be linear or branched (that is, having a side chain). In the case, p is preferably set to about 11 to 19. It is thought that if p is too small, the affinity with a binder or a solvent decreases, and if p is too large, the relative amount of a functional group having an affinity for nonmagnetic powder contained in a certain amount of polyethylene glycol fatty acid ester is considered to decrease. Can be

Further, in the general formula (I), R ¹ and R
At least one of the ^two general formulas _{(III): C n H 2} (nm) +1 CO- ( where in the general formula, n 2 to 30, m is an integer of 1 to 10, in n> m ) And may contain one or more double bonds or triple bonds. However, when the number of double bonds or triple bonds increases, the viscosity of the nonmagnetic paint tends to increase. Therefore, it is preferable to set n <5.

In the general formula (I), R ¹ and R
^{Even if 2} is a mutually different acyl group or the same acyl group, there is almost no effect on characteristics such as electromagnetic conversion characteristics and surface properties.

The content of the ethylene glycol fatty acid ester contained in the nonmagnetic layer is preferably 0.5 to 10 parts by weight based on 100 parts by weight of the nonmagnetic powder.
When the content is more than 10 parts by weight, a large amount of the binder and the unreacted functional group remain in the nonmagnetic layer, and they interact with each other (for example, react with the polar group of the binder. And the viscosity increases.), So that the dispersibility tends to decrease. On the other hand, when the content of the ethylene glycol fatty acid ester is less than 0.5 part by weight, the function as a powder dispersant is hardly exhibited. Further, in order to sufficiently exert the function as a dispersant, it is more preferable that the amount added is in the range of 1.0 to 5.0 parts by weight.

When the ethylene glycol fatty acid ester is added to the non-magnetic layer, two or more kinds of ethylene glycol fatty acid esters may be added at the same time as long as the amount is within the above range. It may be used in combination with the agent.

Further, in the present invention, the specific surface area of the non-magnetic powder is 30 to 80 m ² / g, more preferably 40 to 70 m ² / g.
It is desirable to be within the range.

As will be described in detail later, by setting the specific surface area of the non-magnetic powder within the above range (ie, by making the non-magnetic powder finer), the surface of the non-magnetic layer can be smoothed due to the fineness of the non-magnetic powder. The non-magnetic powder is easily dispersed in the binder and the solvent in the non-magnetic layer by promoting the dispersing action of the ethylene glycol fatty acid ester.

When the specific surface area of the non-magnetic powder is smaller than 30 m ² / g (ie, the size of the non-magnetic powder is too large),
The influence of the shape of the non-magnetic powder appears on the surface of the non-magnetic layer,
The smoothing of the surface of the magnetic layer may be hindered. Also,
When the specific surface area of the nonmagnetic powder is larger than 80 m ² / g (that is, the size of the nonmagnetic powder is too small), even if the method of the present invention is used, that is, even if the ethylene glycol fatty acid ester is added, the ultrafine There is a tendency that it is difficult to disperse such a non-magnetic powder in a binder or the like. The specific surface area of the non-magnetic powder is more preferably 40 to 70 m ² / g.
Is within the range.

In the present invention, the average thickness of the upper layer made of the magnetic layer (actually, the average thickness after calendering: the average thickness per unit area) can be sufficiently reduced to 0.5 μm or less. Yes, if it is 0.5 μm or less,
The self-demagnetization loss (recording demagnetization) can be reduced, and the electromagnetic conversion characteristics can be improved, such as improvement in output at a short wavelength and improvement in overwrite characteristics.

In particular, in the case of a multilayer coating type magnetic recording medium as in the present invention, the average thickness of the upper layer comprising the magnetic layer is 0.5
When the average thickness of the magnetic layer is more than 0.5 μm, the influence of the upper layer (magnetic layer) on the lower layer (nonmagnetic layer: underlayer) is hardly remarkable. The effect of the present invention often appears remarkably, for example, by smoothing the surface of the magnetic layer even if the magnetic layer is thin, by smoothing it by the dispersing action of the ethylene glycol fatty acid ester.

In the production method of the present invention, it is preferable that a non-magnetic paint is applied on a non-magnetic support, and that the magnetic paint is applied in an undried state. As will be described in detail later, the non-magnetic layer is in an undried state (ie, in a wet state).
By applying the magnetic layer in the above, the surface of the lower layer becomes smooth, the surface properties of the upper layer are improved, and the adhesion between the upper and lower layers is improved.

As will be described in detail later, the lower layer (non-magnetic layer) and the upper layer (magnetic layer) are simultaneously coated on a non-magnetic support by using a die coater, so that the The magnetic layer can be applied while the layer is wet (ie, wet).

In the production method of the present invention, the non-magnetic paint used as a raw material for the lower layer composed of the non-magnetic layer is
A method for preparing a non-magnetic paint by kneading and dispersing an ethylene glycol fatty acid ester, a non-magnetic powder and a binder together with a solvent, or kneading and mixing a non-magnetic powder previously treated with an ethylene glycol fatty acid ester with a binder and a solvent. It can be prepared by a method of dispersing and producing a non-magnetic paint.

Here, the mechanism when the polyethylene glycol fatty acid ester functions as a dispersant in the present invention will be described with reference to FIG.

FIG. 5A shows an example of the structure of a polyethylene glycol fatty acid ester represented by the general formula (I) and usable in the present invention, wherein R ¹ and R ² represent the above-mentioned acyl group or A hydrogen atom can be used.

Next, as shown in FIG. 5 (B), a case where a polyethylene glycol fatty acid ester is added (added) to a non-magnetic powder (for example, an Fe-based non-magnetic powder represented by Fe—OH). Think.

[0043] In FIG. 5 the general formula (A) (I), R 1
Is a fatty acid, the carboxyl group forms a hydrogen bond with the hydrophilic surface of the nonmagnetic powder (for example, the hydroxyl group of Fe—OH) as shown in the general formula (IV) of FIG. As shown in the general formula (V) of FIG. 5 (B), the hydroxyl group portion binds to the hydrophilic surface of the non-magnetic powder (for example, the hydroxyl group portion of Fe—OH) as shown in the general formula (V) of FIG.
It is considered that a hydrogen bond is formed with the non-magnetic powder, or a dehydration reaction occurs to bond (adsorb) to the nonmagnetic powder. However, in the general formula (IV), R ′ is a hydrocarbon group.

Although only the R ¹ part is shown here, it is considered that the R ² part is bonded to the non-magnetic powder by the completely same mechanism. However, in the present invention, R ¹ and R ² are not both hydroxyl groups. That is, it is important that either of them is an ester.

The polyethylene glycol fatty acid ester has a binder (organic high molecular compound) due to its structure, in particular, that R ¹ and / or R ² is an acyl group and the action of a polar part such as an ether part in the molecule. And polyethylene glycol fatty acid ester, as a result, binds between the binder and the non-magnetic powder, and acts effectively as a dispersant. Can be

In the present invention, a back coat layer is formed on the surface of the non-magnetic support on which the magnetic layer is not provided (the back surface) for the purpose of improving the runnability of the magnetic recording medium, and preventing charge and transfer. May be provided. Further, an undercoat layer may be provided between the lower layer and the non-magnetic support for the purpose of enhancing the adhesion between the coating film and the support. Needless to say, this undercoat layer is different from the above-mentioned lower layer (nonmagnetic layer) in the present invention.

In the present invention, as the binder contained in the upper layer and the lower layer, known thermoplastic resins, thermosetting resins, and reactive resins conventionally used as binders for magnetic recording media can be used. Having a number average molecular weight of 5,000
Those having 0 to 100,000 are preferred.

Examples of the thermoplastic resin include polyvinyl chloride, polyvinyl 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, 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 derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene butadiene copolymer, polyurethane Resins, polyester resins, amino resins, synthetic rubbers, and the like.

Examples of the thermosetting resin or the reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, polyamine resin, urea formaldehyde resin and the like. Can be

In addition, all of the above-mentioned binders include -SO ₃ M, -OSO ₃ M, and-for the purpose of improving the dispersibility of the pigment.
A polar functional group represented by COOM, -P = O (OM) ₂ or the like may be introduced (here, M is a hydrogen atom or an alkali metal atom such as a lithium atom, a potassium atom, and a sodium atom). .

Further, as the polar functional group, -NR ¹
R ² , a side chain type having a terminal group represented by —NR ¹ R ² R ³⁺ X ⁻ , and a main chain type represented by> NR ¹ R ²⁺ X ⁻ (where, R ¹ , R ² and R ³ are a hydrogen atom or a hydrocarbon group, and X ⁻ is a halogen element ion such as fluorine, chlorine, bromine or iodine or an inorganic or organic ion. A polar functional group such as —CN or an epoxy group may be introduced).

The amount of these polar functional groups ranges from 10 ^-1 to 10
^-8 mol / g is preferred, more preferably 10 ^-2 to 10
^-6 mol / g.

One of the above binders can be used alone, or two or more can be used in combination.

The amount of these binders in the coating film is 1 to 2 parts per 100 parts by weight of the ferromagnetic powder or nonmagnetic powder.
The amount is preferably 00 parts by weight, more preferably 10 to 50 parts by weight.

If the amount of the binder used is too large, the ratio of the ferromagnetic powder in the magnetic layer in the upper layer is relatively reduced and the output is liable to decrease. Plastic flow tends to occur and the running durability of the medium tends to decrease. On the other hand, if the amount of the binder used is too small, the coating film becomes brittle in both the upper and lower layers, and the running durability of the medium tends to decrease.

In the present invention, it is possible to use a polyisocyanate for crosslinking and curing the above binder. Examples of the polyisocyanate include toluene diisocyanate or an adduct thereof, and alkylene diisocyanate or an adduct thereof.

The blending amount of these polyisocyanates with the binder is 5 to 100 parts by weight of the binder.
It is preferably 80 parts by weight, more preferably 10 to 50 parts by weight.

These polyisocyanates can be used in both the upper and lower layers, but they can also be used in only one layer. When used in both upper and lower layers, the amount of each compound can be added to each layer in equal amounts.
It is also possible to change at an arbitrary ratio.

In the present invention, examples of the ferromagnetic powder used in the upper layer include metals such as Fe, Co, and Ni;
o, Fe-Ni, Fe-Al, Fe-Ni-Al, Fe
-Al-P, Fe-Ni-Si-Al, Fe-Ni-S
i-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, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-
Belt compound of Fe ₂ O ₃ and Fe ₃ O ₄ , Co
Γ-Fe ₂ O ₃ , Co-containing Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃ and a belt-ride compound of Fe ₃ O ₄ , CrO ₂ contains one or more metal elements such as T
There are oxides containing e, Sb, Fe, B, 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
The addition of such as can also be used.

Each of these ferromagnetic powders can be used alone or in combination of two or more.

[0063] The specific surface area of the ferromagnetic powder used in the present invention is preferably 30~80m ² / g, more preferably 40~70m ² / g. When the specific surface area is in the above range, high-density recording becomes possible by making the shape of the ferromagnetic powder finer, and a magnetic recording medium having excellent noise characteristics can be obtained.

Further, the ferromagnetic powder used in the present invention is:
It is preferable that the major axis length is 0.05 to 0.50 μm and the axial ratio is 2 to 15. When the major axis length is less than 0.05 μm, dispersion in the magnetic paint becomes difficult, and the major axis length is not more than 0.1 μm.
If it exceeds 50 μm, noise characteristics may be degraded. When the axial ratio is less than 2, the orientation of the ferromagnetic powder is reduced, and the output is reduced. When the axial ratio exceeds 15, the short-wavelength signal output may be reduced. 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. However, the major axis length, the axial ratio, the plate diameter and the plate thickness are indicated by the average value of 100 or more sample particles randomly selected from a transmission electron micrograph.

In the present invention, the nonmagnetic powder used in the lower layer may be, for example, α-Fe ₂ O ₃
Such as non-magnetic iron oxide, goethite, rutile type titanium oxide,
Anatase type titanium oxide, tin oxide, tungsten oxide, silicon oxide, zinc oxide, chromium oxide, cerium oxide,
There are titanium carbide, boron nitride, 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. The powders can be used alone or in combination 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 non-magnetic powder is 30 to 80 m ^2.
/ G, more preferably 40 to 70 m ² / g.

If necessary, a furnace for rubber,
Carbon black such as pyrolytic carbon, black for color, and acetylene black may be contained.

The specific surface area of this carbon black is 100
~400m ² / g, a dibutyl phthalate (DBP) oil absorption is preferably 20 to 200/100 g.

When the specific surface area of the non-magnetic powder and carbon black is in the above range, the lower layer is smoothed by the fine particles, so that the upper layer can be smoothed.
It is possible to obtain a magnetic recording medium that has excellent modulation noise characteristics and is less affected by spacing loss. Since the non-magnetic powder has no magnetic cohesion, it is easier to disperse than the ferromagnetic powder, but when the specific surface area is larger than the above range, the method of the present invention can be used. In some cases, dispersion of the powder becomes difficult, and when the specific surface area is too small, surface smoothness that can withstand high-density recording may not be secured.

In the present invention, a lubricant can be contained in the magnetic layer and the non-magnetic layer as needed. As the lubricant, graphite, molybdenum disulfide,
Tungsten disulfide, silicone oil, 1 carbon atom
0 to 22 fatty acids, the fatty acids and 2 to 2 carbon atoms
There are fatty acid esters, terpene-based compounds, and oligomers of these with up to 6 alcohols. The lubricant can be added only to the upper layer,
It is also possible to add to both upper and lower layers.

In the present invention, the magnetic layer may contain abrasive particles. Examples of these are α-alumina, β-alumina, γ-alumina, chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (rutile, anatase) Etc.

The amount of these particles is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, based on 100 parts by weight of the ferromagnetic powder. The Mohs hardness is preferably 4 or more,
It is more preferably 5 or more, the specific gravity is preferably 2 to 6, more preferably 3 to 5, and the average particle size is preferably 0.5 μm or less, more preferably 0.3 μm or less.

However, the average particle size of these non-magnetic abrasive particles is also determined from a transmission electron micrograph and taken as an average value by statistical processing, as in the case of ferromagnetic powder.

In the present invention, as the non-magnetic support,
Known materials can be used, for example, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, celluloses such as cellulose triacetate and cellulose diacetate, vinyl resins, polyimides, polycarbonates And a support made of a metal material, glass, ceramics, or the like.

To form a coating film on the non-magnetic support, the above-mentioned upper and lower layer forming materials are applied as paints, respectively.
Although formed by drying, the solvent used for this coating is a ketone solvent such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, an alcohol solvent such as methanol, ethanol and propanol,
Methyl acetate, ethyl acetate, butyl acetate, propyl acetate,
Ester solvents such as ethyl lactate and ethylene glycol acetate, diethylene glycol dimethyl ether,
-Ether solvents such as ethoxyethanol, tetrahydrofuran and dioxane; aromatic hydrocarbon solvents such as benzene, toluene and xylene; and halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and chlorobenzene. All known solvents can be used.

The preparation of the paint is carried out in each of a kneading step, a mixing step and a dispersion step. For dispersing and kneading, a roll mill, a ball mill, a sand mill, an agitator, a kneader, an extruder, a homogenizer, an ultrasonic disperser and the like are used.

Further, in the production method of the present invention, it is preferable to apply the coating material thus formed on the non-magnetic support at the same time by multi-layer coating. Is used. As the lip configuration of the die coater, a two-lip method, a three-lip method, a four-lip method, or the like is used.

The above-mentioned die coating method is suitable for this multi-layer coating, but a method of multi-layer coating by a gravure method such as a direct gravure method, a reverse gravure method, and an offset gravure method can also be used.

FIG. 3A is a schematic sectional view of an example (for example, an 8 mm video tape) of the magnetic recording medium of the present invention, and FIG. 3 is a partially enlarged schematic cross-sectional view of FIG.

That is, to manufacture this magnetic recording medium,
Lower layer 4a made of the above-mentioned nonmagnetic layer on nonmagnetic support 1
And a method of applying the upper layer 2a composed of a magnetic layer while the lower layer 4a is not dried on the lower layer 4a (so-called wet-on-wet method = wet multilayer coating method: the same applies hereinafter). Therefore, the adhesive strength between the upper and lower layers is sufficient.

According to this method, the paint component in the magnetic layer 2a partially diffuses and mixes in the lower layer 4a, and the transition layer 5 mixed with the magnetic powder may be formed as shown by a broken line. This transition layer is not strictly an upper layer or a lower layer.

On the surface (rear surface) opposite to the upper layer 2a of the nonmagnetic support 1, the back coat layer 3
May be provided.

FIG. 3B shows a method of forming and coating the lower layer 4b and the magnetic layer 2b one by one (so-called wet-on-dry method). Also in this case, the back coat layer 3 may be provided on the surface opposite to the magnetic layer.

FIG. 4 shows three examples (A), (B) of multilayer coating using a wet-on-wet extrusion coating method (die coating) which can be used in the manufacturing method of the present invention.
(C) is shown.

FIG. 4A shows an example in which two coaters are used (4-lip system), and FIG. 4B shows a case in which one coater is used.
FIG. 4C shows an example in which paint is ejected from separate slits (three-lip method), and FIG. 4C shows an example in which each paint is ejected from a single slit by using one coater.

In the coating apparatus shown in FIG. 4, for example, FIG.
In manufacturing the magnetic recording medium of (A), the supplied nonmagnetic support 1 is fed toward the arrow D by an extrusion die coater 10, 11, or 10,
The lower layer paint 4a 'and the magnetic layer paint 2a' are discharged, and the lower layer 4a and the upper layer 2a are wet-on-wet.
It forms a layer.

The die coater is provided with liquid reservoirs 6 and 7, and the paints 2a 'and 4a' are simultaneously overlapped by a wet-on-wet method.

In general, when the lower layer 4a and the upper layer 2a are formed on a non-magnetic support, a method in which coating and drying are performed one by one (so-called wet-on-dry coating method) and a wet state in which the coating is not dried. There is a method in which an upper layer 2b made of a magnetic layer is applied on the lower layer 4a in a superimposed manner (so-called wet-on-wet coating method).

In the above-described wet-on-wet multi-layer coating, the upper magnetic layer 2a is applied while the lower layer 4a is in a wet (undried) state, so that the surface of the lower layer (that is, the boundary surface with the upper layer) is formed. And the surface properties of the upper layer are improved, there is no need to consider the solvent resistance of the lower layer with respect to the paint of the upper layer, and the adhesion between the upper and lower layers is improved.

As a result, in particular, the performance required for a magnetic recording medium which is required to have high output and low noise for high density recording is satisfied, and the film (layer) is not peeled off. Strength is improved. In addition, dropout can be reduced, and reliability is improved.

For example, in the case of a wet-on-dry coating method as disclosed in JP-A-6-236543, the lower layer 4a has a sufficient resistance to the paint of the upper layer 2a composed of a magnetic layer. It may be necessary to select a solvent-based material. However, as in the above-described wet-on-wet coating method, the coating components in the magnetic layer are partially diffused and mixed into the lower layer, and the transition layer containing the magnetic powder is not formed. .

Further, as described above, the upper and lower layers formed by the wet-on-wet multi-layer coating method are different from those shown in FIG.
As shown in FIG. 3 (A) and FIG. 3 (C), there may be a boundary region where the components of both layers are mixed with a certain thickness. It may be a magnetic layer or the above-mentioned non-magnetic layer. Either case is included in the scope of the present invention.

After the above-mentioned multi-layer coating, it is introduced into a drier and, if necessary, guided to a calender and wound up on a take-up roll. Further, after a back coat layer is applied to the opposite surface of the multilayer coating layer, a magnetic tape is formed by slitting the tape into, for example, an 8 mm width, and the magnetic tape is accommodated in a cassette to manufacture a tape cassette.

[0095]

EXAMPLES Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to the following examples.

With the following composition, paints for the upper layer (magnetic layer) and the lower layer (non-magnetic layer) were prepared. That is, according to the usual law,
The ferromagnetic powder or non-magnetic powder, binder, additive, solvent and polyethylene glycol fatty acid ester were mixed at a predetermined mixing ratio, kneaded with an extruder, and then mixed and dispersed with a sand mill for 6 hours. However, the composition and the amount of the polyethylene glycol fatty acid ester used in each of the following Examples and Comparative Examples are shown in Table 1 below.

[0097] The ferromagnetic metal powder (FE80-CO20) of Fe-based <upper magnetic coating composition for (a magnetic layer)> 100 parts by weight of (coercive force = 160 kA / m, saturation magnetization = 145Am ² / kg, specific surface area = 51 m ² / g, major axis length = 0.08 μm, needle ratio = 3) Polyvinyl chloride resin (containing -SO ₃ K) 14 parts by weight (MR-110 manufactured by Zeon Corporation) Polyester polyurethane resin (-SO ₃ parts by weight (UR8300 manufactured by Toyobo) 5 parts by weight of α-Al ₂ O ₃ 1 part by weight of stearic acid 1 part by weight of heptyl stearate 1 part by weight of methyl ethyl ketone 150 parts by weight of cyclohexanone 150 parts by weight

<Nonmagnetic coating composition for lower layer (nonmagnetic layer)> 100 parts by weight of acicular α-Fe ₂ O ₃ (specific surface area = 53 m ² / g, major axis length = 0.15 μm, acicular ratio = 5) ) polyvinyl chloride resin (-SO ₃ K content) 13 parts by weight (Nippon Zeon MR-110) polyester polyurethane resin (-SO ₃ Na content) 4 parts by weight (Toyobo Co., Ltd. UR8300) polyethylene glycol fatty acid ester ( The type and amount of addition are described in Table 1 below) Stearic acid 1 part by weight Heptyl stearate 1 part by weight Methyl ethyl ketone 105 parts by weight Cyclohexanone 105 parts by weight

To the magnetic paint for the upper layer and the non-magnetic paint for the lower layer obtained by the above composition, 3 parts by weight of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added as a curing agent. Using a four-lip type die coater as described above, a 7 μm-thick polyethylene terephthalate (PET) film as a non-magnetic support is simultaneously multi-layer coated, and then subjected to orientation treatment by a solenoid coil, followed by drying, calendering, and the like. A curing treatment was performed.
Here, the thickness of each layer is 0.2 μm for the upper layer composed of the magnetic layer.
m, the lower layer made of a nonmagnetic layer was 2.0 μm.

Further, a coating material for a back coat layer having the following composition was applied to the nonmagnetic support surface (back surface) opposite to the application surface, and then slit into 8 mm width to form a tape.

<Coating Composition of Backcoat Layer> 100 parts by weight of carbon black (Asahi # 50 manufactured by Asahi Carbon Co.) 100 parts by weight of polyester polyurethane (Nipporan N-2304 manufactured by Nippon Polyurethane Co.) 500 parts by weight of methyl ethyl ketone 500 parts by weight of toluene

Examples 1 to 25 Using a polyethylene glycol fatty acid ester having an addition amount (parts by weight) and a structure as shown in Table 1 below as a dispersant, a magnetic tape (Examples 1 to 2)
5) was obtained. Example 21 is an 8 mm Hi manufactured by Sony Corporation.
Eight tapes were used. The sample tape of Example 21 was a tape provided with a magnetic layer without a nonmagnetic layer (therefore, the magnetic layer did not contain a dispersant composed of polyethylene glycol fatty acid ester, of course).

The sample tape of Example 24 uses a titanate coupling agent conventionally used as a dispersant in the non-magnetic layer. The sample tape of Example 25 also has a dispersant in the non-magnetic layer. It uses a conventionally used silane coupling agent.

The sample tape of Example 20 has the same composition and film thickness as the sample tape of Example 4, but the coating for the non-magnetic layer (lower layer) of the sample tapes other than Example 20 is polyethylene glycol fatty acid ester. And a non-magnetic powder and a binder were kneaded and dispersed together with a solvent, whereas the coating for the non-magnetic layer (lower layer) of the sample tape of Example 4 was previously made of polyethylene glycol fatty acid ester. It is produced by kneading and dispersing the treated non-magnetic powder together with a binder and a solvent.

That is, the coating material for the non-magnetic layer (lower layer) of the sample tape of Example 20 was previously prepared using a non-magnetic powder (α-Fe ₂ O ₃ ).
And polyethylene glycol fatty acid ester are thoroughly mixed in a solution, and this mixed solution is kneaded and dispersed together with a binder such as polyvinyl chloride resin and polyester polyurethane resin, and a solvent such as methyl ethyl ketone and cyclohexanone and other additives. It was made.

Further, the sample tape of Example 23 has the same general formula (I) except that R ¹ and R ² are hydrogen atoms. That is, both ends of the general formula (I) are hydroxyl groups and do not contain an acyl group, and the compound contained in the sample tape of Example 23 is not a fatty acid ester.

Further, the polyethylene glycol fatty acid esters of the sample tapes other than Example 15 were all linear, and the sample tapes of Examples 16 to 19 were the same as those of the polyethylene glycol fatty acid ester represented by the general formula (I). Both ends are acyl groups.

The measurement of the electromagnetic conversion characteristics was performed using a fixed head type electromagnetic conversion characteristic measuring device (modified video deck manufactured by Sony Corporation). This measuring device comprises a rotating drum and a magnetic head in contact with the rotating drum, and the magnetic tape is wound around the drum. In the actual measurement, first, a 10 MHz rectangular wave signal was recorded at the optimum recording current of each sample tape, and the output level at 10 MHz (10 MHz reproduced output) was detected by a spectrum analyzer. The relative speed between the tape and the head was 3.33 m / s, and the reference (reproduction output 0 dB) of Example 26 was 8 mm manufactured by Sony Corporation.
Hi8 tape was used.

Further, the surface roughness Ra of each sample tape was measured by using a non-contact type surface roughness meter (a laser interference measurement microscope (Maximum manufactured by ZYGO) using a laser light interference method).
The center line average roughness Ra (nm) of the magnetic layer surface was measured using 3D Model 5700)).

The results are shown in Table 2 below. Also,
For each of the sample tapes of Examples 1 to 8 and Example 22, the amount of polyethylene glycol fatty acid ester added (parts by weight /
FIG. 1 is a graph showing changes in 10 MHz reproduction output (dB) and surface roughness Ra (nm) due to 100 parts by weight of nonmagnetic powder). FIG. 2 is a graph showing the changes in the 10 MHz reproduction output (dB) and the surface roughness Ra (nm) depending on the degree of polymerization x of the polyethylene glycol fatty acid ester for each of the sample tapes of Example 4 and Examples 9 to 11. .

Table 1

Embedded image (R ^1, R ^2: an acyl group or a hydrogen, x> 1) Example amount (parts by ^{weight) X R 1 R 2 1 0.2} 2 C 17 H 35 CO- -H 2 0.5 2 C 17 H 35 CO- -H 3 12 C ₁₇ H ₃₅ CO- -H 43 2 C ₁₇ H ₃₅ CO- -H 55 2 C ₁₇ H ₃₅ CO- -H 67 2 C ₁₇ H ₃₅ CO- -H 7 10 2 C ₁₇ H ₃₅ CO- -H 8 12 2 C ₁₇ H ₃₅ CO- -H 9 ₃₅ C ₁₇ H ₃₅ CO- -H 103 10 C ₁₇ H ₃₅ CO- -H 11 315 C ₁₇ H ₃₅ CO- -H 12 3 2 C ₁₇ H ₃₃ CO- -H 13 ₃₂ C ₁₇ H ₃₁ CO- -H 14 ₃₂ C ₁₅ H ₃₁ CO- -H 15 ₃₂ C ₈ H ₁₇ CH (C ₈ H ₁₇ ) CO- -H _{16 3 2 C 17 H 35 CO-} C 17 H 35 CO- 17 3 2 C 17 H 35 CO- C 17 H 33 CO- 18 3 2 C 17 H 35 CO- C 17 H 31 CO- 19 3 2 C 17 H ₃₅ CO- C ₁₅ H ₃₁ CO- 20 ₃₂ C ₁₇ H ₃₅ CO- -H 21--C ₁₇ H ₃₅ CO- -H 220-C ₁₇ H ₃₅ CO- -H 23 ₃₂ H-H 24 3---25 3---────────────────────────────────────

Table 2 Example 10 MHz Reproduction output (dB) Surface roughness Ra (nm) 1 +3.0 5.1 2 +4.0 4.4 3 +5.1 3.8 4 +5.3 3.55 +5.2 3.6 6 +5.0 3.97 +4.1 4.3 8 +2.5 5.5 9 +5.2 3.6 10 +5.1 3.8 11 +4.8 4.2 12 +5.2 3.6 13 +5.3 3.6 14 +5.2 3.6 15 +5.3 3.5 16 +5.5 3.4 17 +5.2 3.5 18 +5.3 3.5 19 +5.3 3.6 20 +5.4 3.5 210 0 8.3 22 +2.7 5.3 23 +2.8 5.1 24 +3.1 4.9 25 +3.1 4.9 ──────── ────────────────────────────

From the results shown in Table 2, it is found that the sample tape according to this example (Example 1 to Example 20: the same applies hereinafter) is the reference tape of Example 21 or Example 22 in which no dispersant is added to the lower layer made of nonmagnetic powder. It can be seen that the surface of the magnetic layer is smooth (that is, the surface roughness Ra is small) and the electromagnetic conversion characteristics are excellent (that is, the reproduction output is high at 10 MHz) as compared with the sample tape of No. 1. The output and surface properties of the tape of Example 22 in which the multilayer coating is performed are improved as compared with the reference tape of Example 21.

The sample tapes of Examples 24 and 25 are examples using a titanate coupling agent or a silane coupling agent instead of the polyethylene glycol fatty acid ester, but the adsorption to the non-magnetic powder proceeds as the polyethylene glycol fatty acid ester. Therefore, the dispersibility of the powder is not improved, and the output level, surface properties, and the like are not improved as much as the sample tape of this example.

Further, the sample tape of Example 23 has a structure in which R ¹ and R ² are hydrogen atoms in the general formula (I), but does not contain an acyl group, so that the surface smoothness is insufficient. , And the playback output is also low. That is,
In this example, it is understood that it is necessary to form a fatty acid and an ester.

FIG. 1 shows 10 MHz reproduction output (dB) of each of the sample tapes of Examples 1 to 8 and Example 22 depending on the added amount (parts by weight) of polyethylene glycol fatty acid ester.
And a change in surface roughness Ra (nm), particularly when the addition amount is in the range of 0.5 to 10 parts by weight,
The reproduction output and the surface roughness show very excellent values. Also, 5 parts by weight or less is excellent, and
It is understood that the range of the parts by weight is more excellent, and that the most effective is 3 to 5 parts by weight.

That is, when the addition amount is less than 0.5 part by weight, the effect of the dispersant is not sufficiently exhibited, and the surface of the magnetic layer is not smoother than the sample tape in the above range.
The reproduction output tends to be low. On the other hand, if the amount exceeds 10 parts by weight, the amount of the dispersant added becomes too large, and a large amount of the binder and the unreacted functional groups remain in the nonmagnetic layer, and these interact with each other to increase the dispersibility. Tends to decrease.

Further, there is almost no difference between the characteristics of the sample tapes of Example 4 and Example 20, and rather the sample tape of Example 20 seems to have improved performance. The coating may be prepared by kneading and dispersing a polyethylene glycol fatty acid ester, a non-magnetic powder and a binder together with a solvent, or a non-magnetic powder previously treated with a polyethylene glycol fatty acid ester, a binder and It can be seen that it may be produced by kneading and dispersing with a solvent, and that the latter may have better performance in some cases.

As in the case of the sample tapes of Example 4 and Examples 12 to 19, even if “R ¹ ” and “R ² ” in the general formula (I) change respectively, the electromagnetic conversion characteristics (reproduction output) It does not greatly affect the properties such as the surface roughness Ra and the like, and all have good results. However, as described above, in the sample tape in which “R ¹ ” and “R ² ” in the general formula (I) do not contain an acyl group (Example 23), both the surface smoothness and the reproduction output are low. .

Further, as in the sample tape of Example 16, the polyethylene glycol fatty acid ester represented by the general formula (I) in which both ends are acyl groups, only one end is an acyl group. It can be seen that the characteristics are slightly better than some.

Further, Example 4 is a sample tape in which the acyl group R ¹ of polyethylene glycol fatty acid ester is a saturated acyl group, Example 12 is a sample tape in which R ¹ has one double bond, and Example 13 is a sample tape in which R ¹ is a triple bond. However, since there is almost no difference in the properties of any of the sample tapes, the acyl group R ¹ of the polyethylene glycol fatty acid ester may be a saturated acyl group or an unsaturated acyl group. It can be seen that it may be a group.

Further, in the sample tapes of this example, high reproduction output values and good surface roughness Ra were obtained, but as shown in Table 2 and FIG.
From the sample tapes of Examples 9 to 11, the value of the degree of polymerization x of the polyethylene glycol fatty acid ester represented by the general formula (I) has an optimal value, and the degree of polymerization x is 1 to 1.
It can be seen that it is preferable to be within the range of 10. Also,
If the value of the degree of polymerization x is too large, the number of polyethylene glycol fatty acid esters that can be adsorbed on the non-magnetic powder decreases, and the distribution density of the bonding functional group with the non-magnetic powder in the polyethylene glycol fatty acid ester decreases. Therefore, the dispersion effect tends to decrease. Therefore, there is an optimum value for exhibiting excellent dispersibility, and the degree of polymerization x
Is more preferably in the range of 2 to 5.

[0123]

According to the magnetic recording medium of the present invention, since the lower layer composed of the non-magnetic layer in which the non-magnetic powder is dispersed in the binder contains the dispersant composed of ethylene glycol fatty acid ester, In particular, even if the average thickness (after calendering) of the magnetic layer (upper layer) is as thin as 0.5 μm or less, the non-magnetic powder in the lower layer (that is, the non-magnetic layer) is dissolved in a binder and a solvent by ethylene glycol fatty acid ester. The magnetic recording medium can be uniformly dispersed, and the surface of the upper layer (that is, the magnetic layer) can be smoothed to obtain a magnetic recording medium having high electromagnetic conversion characteristics suitable for high-density recording.

According to the production method of the present invention, when producing the magnetic recording medium of the present invention, the non-magnetic paint for forming the lower layer and the magnetic paint for forming the upper layer are mixed with the non-magnetic paint. Multi-layer coating on the support (particularly, wet-on-wet coating in which the applied non-magnetic paint is applied in a wet state while the magnetic paint is applied), so that the upper layer can be formed with good surface properties. . In particular, in the case of the wet-on-wet coating method, the surface of the lower layer (that is, the boundary surface with the upper layer) becomes smooth, the surface property of the upper layer becomes good, and the adhesion between the upper and lower layers is improved. I do. As a result, the performance required for a magnetic recording medium that requires high output and low noise, particularly for high-density recording, is satisfied, film (layer) peeling is reduced, and film (layer) strength is improved. In addition, dropout and the like can be reduced, and the reliability of the magnetic recording medium can be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing changes in 10 MHz reproduction output (dB) and surface roughness Ra (nm) depending on the amount (parts by weight) of polyethylene glycol fatty acid ester added.

FIG. 2 10 MHz reproduction output (dB) and surface roughness R depending on the degree of polymerization x of polyethylene glycol fatty acid ester
It is a graph which shows the change of a (nm).

3A is a schematic cross-sectional view of an example of the magnetic recording medium of the present invention, FIG. 3B is a schematic cross-sectional view of another example of the magnetic recording medium, and FIG. It is.

FIG. 4 shows a 4-lip type die coat coater (A), a 3-lip type die coat coater (B), and a 2-lip type die coat coater (C) which can be used in the method of manufacturing a magnetic recording medium. It is.

5A is a diagram showing the structure of an ethylene glycol fatty acid ester usable in the present invention, and FIG. 5B is a diagram showing a state when the ethylene glycol fatty acid ester and nonmagnetic powder are adsorbed (bonded). .

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic support, 2a, 2b ... Magnetic layer (upper layer), 2
a ', 4a': paint (coating), 3: back coat layer, 4
a, 4b: non-magnetic layer (lower layer), 5: transition layer, 10, 11
… Extrusion coater

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yuichi Sasaki 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation

Claims (24)

[Claims] A lower layer comprising a non-magnetic layer in which a non-magnetic powder is dispersed in a binder and an upper layer comprising a magnetic layer in which a magnetic powder is dispersed in a binder are provided on a non-magnetic support, A magnetic recording medium comprising a dispersant comprising an ethylene glycol fatty acid ester in the lower layer. 2. The method according to claim 1, wherein the ethylene glycol fatty acid ester is (Wherein, in the above general formula, R ¹ and R ² are each an acyl group or a hydrogen atom, at least one of which is the acyl group, and x indicates the degree of polymerization.) The magnetic recording medium according to claim 1, wherein 3. The magnetic recording medium according to claim 2, wherein the degree of polymerization x is in the range of 1 to 10 in the polyethylene glycol fatty acid ester represented by the general formula (I). 4. In the general formula (I), R ¹ and R
At least one of the ^two general formulas _{(II): C p H 2p} + 1 CO- ( where in the general formula, p is an integer of 1 to 30.)
3. The magnetic recording medium according to claim 2, comprising a linear or branched acyl group represented by the formula: 5. In the general formula (I), R ¹ and R
At least one of the ^two general formulas _{(III): C n H 2} (nm) +1 CO- ( where in the general formula, n 2 to 30, m is an integer of 1 to 10, in n> m 3. The magnetic recording medium according to claim 2, comprising a linear or branched acyl group represented by the formula (1), and containing at least one double bond or triple bond. 6. In the general formula (I), R ¹ and R
^{3. The} magnetic recording medium according to claim 2, wherein ² is different or the same acyl group. 7. The magnetic recording medium according to claim 2, wherein the lower layer contains at least one polyethylene glycol fatty acid ester represented by the general formula (I). 8. The magnetic recording medium according to claim 1, wherein the lower layer contains 0.5 to 10 parts by weight of the ethylene glycol fatty acid ester based on 100 parts by weight of the nonmagnetic powder. 9. The non-magnetic powder has a specific surface area of 30 to 80.
^{2. The} magnetic recording medium according to claim 1, which is in the range of m2 / g. 10. The magnetic recording medium according to claim 1, wherein the upper layer has an average thickness of 0.5 μm or less. 11. A non-magnetic support in which a lower layer composed of a non-magnetic layer in which a non-magnetic powder is dispersed in a binder and an upper layer composed of a magnetic layer in which a magnetic powder is dispersed in a binder are provided.
In producing a magnetic recording medium in which a dispersant comprising ethylene glycol fatty acid ester is contained in the lower layer, a non-magnetic coating for forming the lower layer and a magnetic coating for forming the upper layer are supported on the non-magnetic support. A method for producing a magnetic recording medium, wherein the magnetic recording medium is applied in layers on a body. 12. The method according to claim 11, wherein the non-magnetic paint is applied on the non-magnetic support, and the magnetic paint is applied in an undried state. 13. The production method according to claim 12, wherein the lower layer and the upper layer are simultaneously coated on the non-magnetic support using a die coater. 14. The method according to claim 11, wherein the non-magnetic paint is prepared by kneading and dispersing the ethylene glycol fatty acid ester, the non-magnetic powder, and the binder together with a solvent. 15. The non-magnetic powder, which has been previously treated with the ethylene glycol fatty acid ester, is kneaded and dispersed together with the binder and the solvent to prepare the non-magnetic paint.
The method according to claim 11. 16. As the ethylene glycol fatty acid ester, (Wherein, in the above general formula, R ¹ and R ² are each an acyl group or a hydrogen atom, at least one of which is the acyl group, and x represents the degree of polymerization.) 12. The method of claim 11, wherein
Production method described in 1. 17. The polyethylene glycol fatty acid ester represented by the general formula (I), wherein the degree of polymerization x
The manufacturing method according to claim 16, wherein is in the range of 1 to 10. 18. In the general formula (I), at least one of R ¹ and R ² is represented by the general formula (II): C _n H _{2n + 1} CO— (where n is 1 to 30) It is an integer.)
17. The method according to claim 16, wherein the acyl group is a linear or branched acyl group represented by the formula: 19. In the general formula (I), at least one of R ¹ and R ² is represented by the general formula (III): C _n H _{2 (nm) +1} CO— (where n is 2 To 30, m is an integer of 1 to 10, and n> m.), And contains one or more double bonds or triple bonds. The method according to claim 16. 20. In the general formula (I), R ¹ and R ² are different or the same acyl groups, respectively.
The method according to claim 16. 21. The method according to claim 16, wherein the lower layer contains at least one polyethylene glycol fatty acid ester represented by the general formula (I). 22. The method according to claim 11, wherein the lower layer contains 0.5 to 10 parts by weight of the ethylene glycol fatty acid ester based on 100 parts by weight of the nonmagnetic powder. 23. The non-magnetic powder has a specific surface area of 30 to 8
The method according to claim 11, wherein the amount is within a range of 0 m ² / g. 24. The method according to claim 11, wherein the average thickness of the upper layer is 0.5 μm or less.