JPH05217145A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To embody an excellent high-pass characteristic, an excellent overwrite characteristic and good weather resistance by allowing the upper most layer of a specific thickness to contain hexagonal system plate-shaped powder and its adjacent layers to contain a high magnetic permeability material. CONSTITUTION:Hexagonal system ferrite having an easy axis of magnetization in the vertical direction is provided on the uppermost layer while the thickness of the layer is specified to be 0.5mum and below. The lower layer is arranged to contain a high magnetic permeability material, thereby producing magnetic pass between inverse magnetization which magnetic flux adjoins and forming a horseshoe-shaped loop. As described above, each magnetization exists in a stabilized manner, which makes it possible to enhance the output. Even when a signal is overwritten, the lower layer, which contains the high magnetic permeability material does not affect this recording medium adversely. What is more, the hexagonal system ferrite powder is excellent in terms of weather resistance, which enhances the reliability.

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,
More specifically, the present invention relates to a magnetic recording medium having excellent high frequency characteristics, good signal overwriting characteristics, and good weather resistance (corrosion resistance).

[0002]

2. Description of the Related Art In a conventional magnetic recording medium, a magnetic layer containing magnetism containing ferromagnetic powder is formed on a non-magnetic support. It is said that a magnetic recording medium using a hexagonal ferrite-based ferromagnetic powder has high output on the high frequency side of short wavelength (Japanese Patent Laid-Open Nos. 57-195329 and 60-223018).
(See the official gazette). There is also a magnetic recording medium having a magnetic layer containing needle-like ferromagnetic powder in the lower layer and hexagonal ferromagnetic powder in the upper layer (Japanese Patent Laid-Open No. 63-128324). Further, there is also a proposal of a magnetic recording medium in which a layer containing a non-magnetic powder is provided in the lower layer and a ferromagnetic powder is contained in the upper layer (JP-A-63-1).
87418).

However, in a hexagonal ferrite magnetic recording medium, it is still difficult to sufficiently improve the characteristics in a high range, especially in high density recording (digital recording).
Further, even when a non-magnetic layer is provided as a lower layer, no improvement in characteristics in the high range is expected.

On the other hand, when a magnetic layer is provided in the lower layer, the residual signal of the lower layer causes distortion of the waveform of the reproduced signal during reproduction (interference between waveforms). As a result, the output peak value decreases and the peak position shifts, and the error rate and the like increase.

Furthermore, if there is residual magnetization in the lower layer, it becomes difficult to record a signal for re-recording, that is, so-called deterioration of overwrite characteristics occurs.

Vapor-deposited tapes and the like are promising for high-density recording (digital recording), but may have problems in practical use due to poor characteristics such as corrosion resistance.

An object of the present invention is to provide a magnetic recording medium which is excellent in high frequency characteristics, has good signal overwrite characteristics, and has good weather resistance (corrosion resistance).

[0008]

In order to solve the above-mentioned problems, the inventors of the present invention have studied and found that a plate-shaped hexagonal ferrite having an easy axis of magnetization in the vertical direction is provided in the uppermost layer and a high permeability as a lower layer. By providing a layer containing a magnetic susceptibility material, a magnetic path is created between adjacent magnetic fluxes in opposite directions, and by forming a horseshoe-shaped loop, each magnetization is stably present and the output is improved. In addition, it was found that the layer containing the high magnetic permeability material of the lower layer does not have any adverse effect even in the overwriting of signals, and furthermore, the plate-shaped hexagonal ferrite powder has excellent corrosion resistance. The present invention has been reached by finding that a highly reliable magnetic recording medium can be obtained.

That is, according to the first aspect of the invention for achieving the above object, in a magnetic recording medium having a plurality of layers on a non-magnetic support, the uppermost magnetic layer is a hexagonal plate as a main component. Containing magnetic powder and having a layer thickness of 0.
A magnetic recording medium having a thickness of 8 μm or less and containing a high magnetic permeability material in at least one layer other than the uppermost layer. The invention according to claim 2, wherein the high magnetic permeability material has a coercive force Hc of 0. <Hc ≦ 1.0 × 10 ⁴ [A / m] The magnetic recording medium according to claim 1, wherein the high magnetic permeability material is a metal soft magnetic material. The magnetic recording medium according to claim 1,
The invention according to claim 5 is the magnetic recording medium according to claim 1, wherein the high magnetic permeability material is an oxide soft magnetic material, and the invention according to claim 5 is a layer containing the high magnetic permeability material. Is the magnetic recording medium according to claim 1, which is adjacent to the uppermost magnetic layer, and the invention according to claim 6 is characterized in that the layer thickness of the uppermost layer is 0.5 μm or less. The magnetic recording medium according to claim 7, wherein the invention according to claim 7 is the magnetic recording medium according to claim 1, wherein the uppermost layer is provided when the lower layer is in a wet state.

The magnetic recording medium of the present invention will be described in detail below. —Nonmagnetic Support— Examples of materials for forming the nonmagnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, and cellulose derivatives such as cellulose triacetate and cellulose diacetate. ,polyamide,
Examples thereof include plastics such as polycarbonate. The form of the non-magnetic support is not particularly limited, and mainly includes tape, film, sheet, card, disk, drum and the like.

The thickness of the non-magnetic support is not particularly limited, but in the case of a film or sheet, it is usually 3 to 1.
00 μm, preferably 5 to 50 μm, about 30 μm to 10 mm in the case of a disk or card, and appropriately selected depending on the recorder etc. in the case of a drum. In addition,
This non-magnetic support may have a single-layer structure or a multi-layer structure. Further, the non-magnetic support may be subjected to surface treatment such as corona discharge treatment. A back coat layer is preferably provided on the surface (back surface) of the non-magnetic support, on which the magnetic layer is not provided, for the purpose of improving the running property of the magnetic recording medium, preventing electrification, and preventing transfer. Also, an undercoat layer may be provided between the magnetic layer and the non-magnetic support.

-Magnetic powder in the uppermost magnetic layer-The uppermost magnetic layer contains a hexagonal plate-like powder as magnetic powder, a binder described later, and other components described later. As a preferable hexagonal plate-like powder, Ba-ferrite powder having an average particle size (height of the diagonal of the plate surface of the hexagonal ferrite) of which a part of Fe is replaced by at least Co and Zn is 400 to 900Å, State ratio (value obtained by dividing the length of the diagonal line of the hexagonal ferrite plate surface by the plate thickness) 2.0 to 1
Ba-ferrite having a coercive force (Hc) of 450 to 1500 can be mentioned.

The Ba-ferrite powder has a coercive force controlled to an appropriate value by partially substituting Fe for Co, and further partially substituting for Zn, which cannot be obtained only by Co substitution. It is possible to obtain a magnetic recording medium that realizes saturation magnetization and has a high reproduction output and excellent electromagnetic conversion characteristics. Further, by substituting a part of Fe with Nb, it is possible to obtain a magnetic recording medium having a higher reproduction output and excellent in electromagnetic conversion characteristics. Further, in the Ba-ferrite used in the present invention, a part of Fe is T
It may be substituted with a transition metal such as i, In, Mn, Cu, Ge and Sn.

The Ba-ferrite used in the present invention is represented by the following general formula. _{BaO · n ((Fe 1-} m M m) 2 O 3) [ provided that, m> 0.36 (However, Co + Zn = 0.08
˜0.3, Co / Zn = 0.5 to 10), n is 5.4 to 11.0, preferably 5.4 to 6.0, and M represents a substituted metal, and the average. Magnetic particles that are a combination of two or more elements, the number of which is 3, are preferable. In the present invention, the reason why it is preferable that the average particle diameter, plate ratio and coercive force of Ba-ferrite are within the above ranges is as follows. That is, if the average particle size is less than 400Å, the reproduction output when used as a magnetic recording medium becomes insufficient, and conversely, if it exceeds 900Å, the surface smoothness when used as a magnetic recording medium deteriorates markedly, and the noise level increases. If the plate ratio is less than 2.0, the perpendicular orientation ratio suitable for high density recording cannot be obtained when the magnetic recording medium is used, and conversely the plate ratio becomes 6.0. If it exceeds, the surface smoothness of the magnetic recording medium is significantly deteriorated, the noise level becomes too high, and the coercive force of 350 O
If it is less than e, it becomes difficult to hold the recording signal, and
This is because if it exceeds 00 Oe, the head limit may decrease in saturation and recording may become difficult.

The barium ferrite magnetic powder used in the present invention usually has a saturation magnetization (σ _S ) which is a magnetic characteristic.
It is preferably 50 emu / g or more. This is because if the saturation magnetization is less than 50 emu / g, the electromagnetic conversion characteristics may deteriorate. Further, in the present invention, it is desirable to use Ba-ferrite magnetic powder having a specific surface area of 30 m ² / g or more by the BET method according to the higher recording density.

As the method for producing the hexagonal magnetic powder used in the present invention, for example, the oxides and carbonates of the respective elements necessary for forming the desired Ba-ferrite are prepared, for example, boric acid. Such a glass-forming substance is melted, the resulting melt is rapidly cooled to form a glass, and the glass is then heat-treated at a predetermined temperature to precipitate the desired Ba-ferrite crystal powder, and finally the glass component. In addition to the glass crystallization method of removing by heat treatment,
A coprecipitation-firing method, a hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method and the like can be applied.

In the present invention, the content of the hexagonal plate-like powder in the uppermost layer is usually 50 to 99% by weight, preferably 60 to 99% by weight.

-Magnetic Layer Adjacent to Uppermost Layer- In the present invention, a plurality of layers are formed on the non-magnetic support, and at least one layer other than the uppermost layer, preferably the layer adjacent to the uppermost layer. , High magnetic permeability material is contained.

As the high magnetic permeability material, its coercive force H
c is 0 <Hc ≦ 1.0 × 10 ⁴ [A / m], preferably 0 <Hc ≦ 5.0 × 10 ³ [A / m]. When the coercive force is within the above range, the effect of stabilizing the magnetization region of the uppermost layer is exhibited as the high magnetic permeability material. When the coercive force exceeds the above range, desired properties may not be obtained due to manifestation of properties as a magnetic material, which is not preferable.

In the present invention, it is preferable to appropriately select a material having a coercive force range as the high magnetic permeability material. Examples of such a high magnetic permeability material include a metal soft magnetic material and an oxide soft magnetic material.

As the metal soft magnetic material, Fe--S is used.
i alloy, Fe-Al alloy (Alperm, Alfeno
1, Alfer), permalloy (Ni-Fe binary alloy, and multi-component alloy in which Mo, Cu, Cr, etc. are added thereto), sendust (Fe-Si-Al [9.6 wt% Si, 5. 4% Al, the balance being Fe]], Fe—Co alloy, and the like. Among them, sendust is preferable as the preferable metal soft magnetic material. The metal soft magnetic material as the high magnetic permeability material is not limited to those exemplified above, and other metal soft magnetic materials can be used. The high permeability material can be used alone, or
Also, two or more of them can be used in combination.

As the soft oxide magnetic material, spinel type ferrites such as MnFe ₂ O ₄ , Fe ₃ O ₄ and C are used.
oFe ₂ O ₄ , NiFe ₂ O ₄ , MgFe ₂ O ₄ , Li
_0.5 Fe _2.5 O ₄ , Mn-Zn ferrite, Ni-
Zn-based ferrite, Ni-Cu-based ferrite, Cu-Z
n type ferrite, Mg-Zn type ferrite, Li-ZN
Examples include series ferrites. Among these, Mn-Zn type ferrite and Ni-Zn type ferrite are preferable. These soft oxide magnetic materials can be used alone or in combination of two or more.

This high-permeability material is made into a fine powder by using a ball mill or other crushing device, and its particle size is 1 mμ.
It is preferably 1,000 mμ, particularly preferably 1 mμ to 500 mμ. In order to obtain such a fine powder, the metal soft magnetic material can be obtained by spraying a molten alloy in a vacuum atmosphere. Further, the soft oxide magnetic material can be made into a fine powder by a glass crystallization method, a coprecipitation firing method, a hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method or the like.

In the layer containing the high magnetic permeability material, the content of the high magnetic permeability material is 10 to 100% by weight, preferably 50 to 100% by weight, more preferably 60 to 1%.
It is 00% by weight. When the content of the high magnetic permeability material is within the above range, the effect of stabilizing the magnetization of the uppermost layer can be sufficiently obtained. If the content of the high magnetic permeability material is less than 50% by weight, the effect of the high magnetic permeability layer may not be obtained, which is not preferable.

The layer containing the high magnetic permeability material may contain non-magnetic particles.

-Binder used in magnetic layer- As the binder used in the present invention, for example, vinyl chloride resins such as polyurethane, polyester, and vinyl chloride copolymer are typical, and these resins are used. _{-SO 3 M, -OSO 3 M,} -COOM and -PO is
It is preferable to include a repeating unit having at least one polar group selected from (OM ¹ ) ₂ .

However, in the above polar group, M represents a hydrogen atom or an alkali metal such as Na, K or Li,
M ¹ represents a hydrogen atom, an alkali atom such as Na, K or Li, or an alkyl group. The polar group has the function of improving the dispersibility of the ferromagnetic powder, and the content in each resin is 0.1 to 8.0 mol%, preferably 0.5 to 6.0 mol%. If this content is less than 0.1 mol%, the dispersibility of the ferromagnetic powder is reduced, and the content is 8.0 mol%.
If it exceeds, the magnetic coating material tends to gel. The weight average molecular weight of each resin is 15,000 to 50,000.
A range of 0 is preferred.

The content of the binder in the magnetic layer is usually 10 to 40 parts by weight, preferably 15 to 30 parts by weight, based on 100 parts by weight of the ferromagnetic powder. The binder is not limited to one kind alone, and two or more kinds can be used in combination. In this case, the ratio of the polyurethane and / or polyester to the vinyl chloride resin is usually 90: 1 by weight.
0 to 10:90, preferably 70:30 to 30:
The range is 70.

The polar group-containing vinyl chloride copolymer used as the binder in the present invention is a compound having a hydroxyl group and the following polar group and chlorine atom, such as a vinyl chloride-vinyl alcohol copolymer. It can be synthesized by addition reaction with. Cl-CH ₂ CH ₂ SO ₃ M, Cl-CH ₂ CH ₂ OSO ₃ M, Cl-CH ₂ COOM
, Cl-CH ₂ -P (= O) (OM ¹ ) _{2 From} these compounds, Cl-CH ₂ CH ₂ SO ₃ Na is taken as an example, and the above reaction is explained as follows. _{- (CH 2 C (OH)} H - + ClCH 2 CH 2 SO 3 Na → - CH 2 C (OCH 2 CH
₂ SO ₃ Na) H)-.

Further, in the polar group-containing vinyl chloride copolymer, a predetermined amount of a reactive monomer having an unsaturated bond into which a repeating unit containing a polar group is introduced is charged into a reaction vessel such as an autoclave to start a general polymerization. Agents, eg BPO
(Benzoyl peroxide), AIBN (azobisisobutyronitrile) and other radical polymerization initiators, redox polymerization initiators, cationic polymerization initiators and the like can be obtained by carrying out a polymerization reaction.

Specific examples of the reactive monomer for introducing the sulfonic acid or its salt include unsaturated hydrocarbon sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, p-styrene sulfonic acid, and the like. Mention may be made of salt. When introducing a carboxylic acid or a salt thereof, for example, (meth) acrylic acid or maleic acid is used, and when introducing a phosphoric acid or a salt thereof,
For example, (meth) acrylic acid-2-phosphate ester may be used.

It is preferable that an epoxy group is introduced into the vinyl chloride copolymer. This is because the thermal stability of the polymer is improved by doing so. When introducing an epoxy group, the content of the repeating unit having an epoxy group in the copolymer is preferably 1 to 30 mol%,
20 mol% is more preferable. For example, glycidyl acrylate is preferable as the monomer for introducing the epoxy group.

Regarding the technique for introducing a polar group into a vinyl chloride-based copolymer, JP-A-57-44227 and JP-A-5-44227 have been used.
8-108052, 59-8127, 60-1
No. 01161, No. 60-235814, No. 60-23
No. 8306, No. 60-238371, No. 62-121
No. 923, No. 62-146432, No. 62-1464.
No. 33 and the like are described, and these can be used in the present invention.

Next, the synthesis of polyester and polyurethane used in the present invention will be described. Generally, polyesters are obtained by reacting a polyol with a polybasic acid. By using this known method, a polyester (polyol) having a polar group can be synthesized from a polybasic acid partially having a polar group.

Examples of polybasic acids having polar groups include 5
-Sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-
Examples thereof include sulfoisophthalic acid, 3-sulfophthalic acid, dialkyl 5-sulfoisophthalate, dialkyl 2-sulfoisophthalate, dialkyl 4-sulfoisophthalate, dialkyl 3-sulfoisophthalate, and their sodium salts and potassium salts.

Examples of the polyol include trimethylolpropane, hexanetriol, glycerin, trimethylolethane, neopentyl glycol, pentaerythritol, ethylene glycol and propylene glycol.
1,3-butanediol, 1,4-butanediol
1,6-hexanediol, diethylene glycol
And cyclohexane dimethanol. Note that other polar group-introduced polyesters can also be synthesized by a known method.

Next, the polyurethane will be described. It results from the reaction of polyols with polyisocyanates. As the polyol, a polyester polyol obtained by reacting a polyol with a polybasic acid is generally used. Therefore, if a polyester polyol having a polar group is used as a raw material, a polyurethane having a polar group can be synthesized.

Examples of polyisocyanates include diphenylmethane-4-4'-diisocyanate (MDI),
Hexamethylene diisocyanate (HMDI), tolylene diisocyanate (TDI), 1,5-naphthalene diisocyanate (NDI), tolidine diisocyanate (TODI), lysine isocyanate methyl ester (LDI) and the like can be mentioned.

As another method for synthesizing a polyurethane having a polar group, an addition reaction between a polyurethane having a hydroxyl group and the following compound having a polar group and a chlorine atom is also effective. _{Cl-CH 2 CH 2 SO 3} M, Cl-CH 2 CH 2 OSO 2 M, Cl -CH 2 COOM, Cl
-CH ₂ -P (= O) (OM ¹ ) _{2 As} a technique for introducing a polar group into polyurethane, JP-B-58-41565 and JP-A-57-9242 are known.
No. 2, No. 57-92423, No. 59-8127, No. 59-5423, No. 59-5424, No. 62-12.
It is described in the publications such as 1923, and these can be used in the present invention.

In the present invention, the following resins can be used together as a binder in an amount of 20% by weight or less based on the total amount of the binder. The resin has a weight average molecular weight of 1
Vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose Derivatives (nitrocellulose etc.), styrene-butadiene copolymers, phenol resins, epoxy resins, urea resins, melamine resins, phenoxy resins, silicone resins, acrylic resins, urea formamide resins, various synthetic rubber resins, etc. ..

-Other Components- In the present invention, in order to improve the quality of the magnetic layer, additives such as a durability improver, a dispersant, an abrasive, an antistatic agent and a filler are contained as other components. You can
Examples of the durability improver include polyisocyanates. Examples of the polyisocyanates include aromatic polyisocyanates such as adducts of tolylene diisocyanate (TDI) and active hydrogen compounds, and hexamethylene diisocyanate (HMDI). And the like, and an aliphatic polyisocyanate such as an adduct thereof with an active hydrogen compound.
The weight average molecular weight of the polyisocyanate is 1
It is preferably in the range of 00 to 3,000.

As the dispersant, fatty acids having 12 to 18 carbon atoms such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid and oleic acid;
Salts of these alkali metals or salts of alkaline earth metals or their amides; polyalkylene oxide alkyl phosphates; lecithin; trialkyl polyolefinoxy quaternary ammonium salts; azo compounds having carboxyl groups and sulfonic acid groups, etc. Can be mentioned. These dispersants are usually used in the range of 0.5 to 5% by weight based on the ferromagnetic powder.

Specific examples of the polishing agent include α-aluminum, fused alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, tungsten carbide, molybdenum carbide, boron carbide, corundum, and oxidation. Examples thereof include zinc, cerium oxide, magnesium oxide, and boron nitride. The abrasive has an average particle size of 0.05 to 0.6.
Those having a thickness of μm are preferable, and those having a thickness of 0.1 to 0.3 μm are more preferable.

As the antistatic agent, carbon black,
Conductive powder such as graphite; cationic surfactant such as quaternary amine; anionic surfactant containing acid group such as sulfonic acid, sulfuric acid, phosphoric acid, phosphoric acid ester and carboxylic acid;
Examples thereof include amphoteric surfactants such as aminosulfonic acid; natural surfactants such as saponin. The above-mentioned antistatic agent is usually 0.01 to 40% by weight with respect to the binder.
It is added in the range of.

-Manufacture of Magnetic Recording Medium- In the magnetic recording medium of the present invention, the magnetic layer is preferably coated by a so-called wet-on-wet system in which the lower layer is in a wet state. As the wet-on-wet system, a known method used for manufacturing a multilayer structure type magnetic recording medium can be appropriately adopted. For example, generally ferromagnetic powders, binders, dispersants, lubricants,
A high-concentration magnetic coating is prepared by kneading an abrasive, an antistatic agent, etc. with a solvent, and then the high-concentration magnetic coating is diluted to prepare a magnetic coating, which is then applied to the surface of the non-magnetic support. Apply.

Examples of the solvent include ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK) and cyclohexanone; alcohols such as methanol, ethanol and propanol; esters such as methyl acetate, ethyl acetate and butyl acetate. Cyclic ethers such as tetrahydrofuran and the like; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and dichlorobenzene can be used.

When kneading and dispersing the components for forming the magnetic layer,
Various kneading dispersers can be used. Examples of this kneading disperser include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a cobol mill, a tron mill, a sand mill, a sand grinder, a Sqegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disper, and a high speed. Examples thereof include a mixer, a homogenizer, an ultrasonic disperser, an open kneader, a continuous kneader, and a pressure kneader. Among the above-mentioned kneading dispersers, kneading dispersers capable of providing a power consumption load of 0.05 to 0.5 KW (per 1 Kg of magnetic powder) include a pressure kneader, an open kneader, a continuous kneader, a two-roll mill, and a three-roll mill. This is a roll mill.

In order to coat the layer containing the high magnetic permeability material and the magnetic layer on the non-magnetic support, specifically, as shown in FIG. 1, first, as shown in FIG. 1, the coating materials of the magnetic layers 2 and 4 are multi-layered by the extrusion-type extrusion coaters 10 and 11 by the wet-on-wet method, and then passed through the orienting magnet or the vertically orienting magnet 33, and the drier. Then, hot air is blown from the nozzles arranged above and below to dry it. Next, the dried support 1 with each coating layer is guided to a super calender device 37 composed of a combination of calender rolls 38, where it is calendered and then wound on a winding roll 39. The magnetic film thus obtained is cut into a tape having a desired width, for example, 8 m.
Magnetic recording tapes for m-video cameras can be manufactured.

In the above method, each coating material is extruded through an in-line mixer (not shown), the coater 10,
11 may be supplied. In the figure, the arrow D indicates the transport direction of the non-magnetic base film. Extrusion coater 1
0 and 11 are provided with liquid reservoirs 13 and 14, respectively,
Wet-on-wet coating of paint from each coater. That is, the upper magnetic layer coating material is applied in multiple layers immediately after the lower magnetic layer coating material is applied (when it is in an undried state). The coater head shown in FIG. 2 (c) is preferable in the present invention.

As the solvent to be blended in the above paint or a diluent solvent when the paint is applied, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; alcohols such as methanol, ethanol, propanol, butanol; methyl acetate , Esters such as ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol cenoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, xylene; methylene chloride, Ethylene chloride, carbon tetrachloride, chloroform,
A halogenated hydrocarbon such as dichlorobenzene can be used. These various solvents may be used alone or in combination of two or more. The magnetic field in the orienting magnet or the vertically orienting magnet is about 20 to 5,000 gauss, the drying temperature by the dryer is about 30 to 120 ° C., and the drying time is about 0.
It is about 1 to 10 minutes.

In the wet-on-wet system, a combination of a reverse roll and an extrusion coater, a combination of a gravure roll and an extrusion coater, etc. can also be used. Furthermore, an air doctor coater, blade coater, air knife coater, squeeze coater, impregnation coater, transfer roll coater, kiss coater, cast coater, spray coater, etc. can be combined.

In this wet-on-wet multi-layer coating, since the upper magnetic layer is coated while the layer located under the uppermost layer is in a wet state, the surface of the lower layer (that is, the uppermost layer). The boundary surface) and the surface properties of the uppermost layer are improved, and the adhesiveness between the upper and lower layers is also improved. As a result, especially for high-density recording, the performance required for high output and low noise, such as a magnetic tape, is satisfied, and film durability is also required for film peeling. It is eliminated, the film strength is improved, and the durability is sufficient. Wet-on-
The wet multi-layer coating method can reduce dropout and improve reliability.

-Surface smoothing-In the present invention, it is also possible to carry out a surface smoothing process by calendering. After that, if necessary, burnishing or blade processing is performed for slitting. In the surface smoothing treatment, temperature, linear pressure, C / s (coating speed) and the like can be mentioned as calendar conditions. In the present invention, the temperature is usually 50 to 120 ° C., and the linear pressure is 50 to 4
It is preferable to maintain 00 kg / cm and the above C / s at 20 to 600 m / min.

The thickness of the uppermost layer obtained as a result of the above treatment is 0.8 μm or less, preferably 0.5 μm or less. When the layer thickness exceeds 0.8 μm, the high frequency characteristic and the overwrite characteristic are deteriorated, which is no different from a magnetic recording medium having a single layer structure, and the object of the present invention cannot be achieved.

[0055]

Embodiments of the present invention will be described below. The components, ratios, and operation sequences shown below can be variously modified without departing from the scope of the present invention. In the following examples, all "parts" are parts by weight.

A magnetic paint having the following composition was prepared.

[Magnetic Coating A for Top Layer] Co-Ti-substituted barium ferrite magnetic powder 100 parts (BET value = 40 m ² / g, Hc = 1200 Oe, average plate ratio 3.5, saturation magnetization 65 emu / g) Vinyl chloride Resin (MR110 manufactured by Nippon Zeon Co., Ltd.) 5 parts Polyurethane resin containing sulfonic acid metal salt 5 parts (Toyobo Co., Ltd., UR8700) Cr ₂ O ₃ 5 parts Carbon black (particle size 40 mμ) 0.5 parts Myristic acid 1 part Stearic acid 1 part Butyl stearate 1 part Methyl ethyl ketone 100 parts Toluene 100 parts Cyclohexanone 100 parts After kneading and dispersing the above composition, a polyisocyanate compound (Coronate L 5 parts) was added to prepare.

[Magnetic paint B for the uppermost layer] In the above magnetic paint A for the uppermost layer, 100 parts of Co-Ti-substituted barium ferrite magnetic powder was replaced with an Fe-Zn-Ni alloy (coercive force Hc = 1,200 Oe, A BET value of 50 m ² / g and an average major axis length of 0.2 μm) were used, and the same preparation as the magnetic coating material A for the uppermost layer was performed.

[Magnetic Coating C for Lower Layer] In the above magnetic coating A for uppermost layer, 100 parts of Co-Ti-substituted barium ferrite magnetic powder was replaced with Co-γ-Fe ₂ O ₃ powder [coercive force Hc = 900 Oe, A BET value of 40 m ² / g and an average major axis length of 0.3 μm) were used, and the same procedure as the preparation of the magnetic coating material A for the uppermost layer was used.

[Coating I for High Permeability Material-Containing Layer] Fe-Si-Al Sendust Alloy Powder 100 parts (Coercive force Hc = 40 A / m, μi = 200 H / m, particle size 0.1 μm) Vinyl chloride resin ( ZEON Corporation MR110) 1 part Sulfonic acid metal salt-containing polyurethane resin 4 parts (Toyobo Co., Ltd., UR8700) Methyl ethyl ketone 50 parts Toluene 50 parts Cyclohexanone 50 parts The above composition was kneaded and dispersed to prepare.

[High-Permeability Material-Containing Layer Coating II] In the above-mentioned high-permeability material-containing layer coating I, 100 parts by weight of Fe-Si-Al sendust alloy powder was replaced by Fe-Si-Al.
70 parts of Sendust alloy powder and TiO ₂ (particle size 0.0
3 μm) was used in the same manner as in the coating material I for a layer containing a high magnetic permeability material except that 30 parts was used.

[Coating for High Permeability Material-Containing Layer III] In the above-mentioned coating I for high magnetic permeability material-containing layer, Fe-Si-Al
Instead of 100 parts of Sendust alloy powder, Mn—Zn ferrite [composition of 18% by weight of MnO, 14% by weight of ZnO, and 68% by weight of Fe ₂ O ₃ and Hc = 700 (A /
m), μi = 80 (H / m), particle size 0.1 μm] 100
A high magnetic permeability material-containing layer coating material I was prepared in the same manner as the coating material I except for using parts.

[High-Permeability Material-Containing Layer Coating IV] In the high-permeability material-containing layer coating I, in place of 100 parts of Fe—Si—Al sendust alloy powder, Ni—Zn ferrite [NiO 19 wt%, ZnO 13 0.5 wt% and Fe ₂ O ₃ 67.5 wt% composition, Hc = 1,000
(A / m), μi = 50 (H / m), particle size 0.1 μm]
A high magnetic permeability material-containing layer coating material I was prepared in the same manner as the coating material I for the high magnetic permeability material-containing layer except that 100 parts was used.

[Coating V for High Permeability Material-Containing Layer] In the above coating composition I for high-permeability material-containing layer, TiO [particle size: 0.
03 μm] was used in the same manner as the preparation of the coating material I for a layer containing a high magnetic permeability material except that 100 parts was used.

The coercive force Hc of the high magnetic permeability material was measured by VSM with an external magnetic field of 1 T (Tesla).

Μi is expressed by the following equation 1 at the origin of the initial magnetization curve.

[0067]

[Equation 1]

(Examples 1 to 7) With a coating film composition having the composition shown in Table 1, a wet-on-wet system of 8 mm was used.
A wide magnetic recording medium was created. The following evaluation tests were conducted on this magnetic recording medium.

<CN characteristics> A single wave of 9 MHz was recorded,
The output level when the signal was reproduced was expressed by comparison with the reference sample (Comparative Example 1).

<Overwrite Characteristics> A residual output level of a 2 MHz signal was recorded when a 2 MHz signal was recorded at a saturation level and then a 9 MHz signal was (overwritten) recorded. The lower the residual output level, the better the overwrite characteristics.

<Weather resistance> The output level at 9 MHZ was measured in advance, and a magnetic recording medium as a sample
After being left for 7 days in an environment of 80 ° C. (humidity), the output level of 9 MHz was measured again, and the difference from the initial measured value was obtained.

(Comparative Examples 1 and 2) Magnetic recording media having a single magnetic layer were obtained by using the magnetic coating materials for the uppermost layer shown in Table 1, and the same evaluation tests as those in the above-mentioned Examples were conducted.

(Comparative Example 3) A magnetic recording medium having a two-layer structure was obtained by using the magnetic coating material for the uppermost layer and the magnetic coating material for the lower layer shown in Table 1, and the same evaluation test as in the above-mentioned example was conducted.

(Comparative Examples 4 to 5 and 7) Using the magnetic coating material for the uppermost layer and the coating material for the high magnetic permeability material-containing layer shown in Table 1, two-layer magnetic recording media were obtained, and the same procedure as in the above-mentioned Examples was performed. An evaluation test was conducted.

(Comparative Example 6) Co-Ni was coated on a non-magnetic support.
A vapor-deposited magnetic recording medium was prepared by vapor-depositing an alloy, and an evaluation test was conducted in the same manner as in the above example.

[0076]

[Table 1]

[0077]

According to the present invention, it is possible to provide a magnetic recording medium having excellent high frequency characteristics, good signal overwrite characteristics, and excellent weather resistance.

[Brief description of drawings]

FIG. 1 is a diagram for explaining simultaneous multi-layer coating of magnetic layers by a wet-on-wet coating method.

FIG. 2 is a diagram of a coater head for applying magnetic paint.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Goto Adult Konica Stock Company, Sakura Town, Hino City, Tokyo 1

Claims (7)

[Claims] 1. A magnetic recording medium having a plurality of layers on a non-magnetic support, wherein the uppermost magnetic layer contains hexagonal plate-like magnetic powder as a main component and has a layer thickness of 0.8 μm.
The following is a magnetic recording medium containing a high magnetic permeability material in at least one layer other than the uppermost layer. 2. The coercive force Hc of the high magnetic permeability material is 0 <H.
The magnetic recording medium according to claim 1, wherein c ≦ 1.0 × 10 ⁴ [A / m]. 3. The magnetic recording medium according to claim 1, wherein the high magnetic permeability material is a metal soft magnetic material. 4. The magnetic recording medium according to claim 1, wherein the high magnetic permeability material is an oxide soft magnetic material. 5. The magnetic recording medium according to claim 1, wherein the layer containing the high magnetic permeability material is adjacent to the uppermost magnetic layer. 6. The magnetic recording medium according to claim 1, wherein the thickness of the uppermost layer is 0.5 μm or less. 7. The magnetic recording medium according to claim 1, wherein the uppermost layer is provided when the lower layer is in a wet state.