JPH05225547A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the magnetic recording medium having an excellent high-frequency range characteristic and a good overwriting characteristic of signals and weatherability by laminating a nonmagnetic layer contg. specific nonmagnetic powder and a magnetic layer contg. specific magnetic powder on a nonmagnetic base. CONSTITUTION:A film-like base 1 formed with the nonmagnetic layer contg. at least one kind of the nonmagnetic powders selected from a group consisting of a nonmagnetic oxide, nonmagnetic nitride, nonmagnetic carbide and nonmagnetic sulfate is let off from a supply roll 32. The magnetic layer contg. the hexagonal ferrite magnetic powder is then applied thereon by extrusion coaters 10, 11. The base is thereafter passed between magnets 33 for orientation or perpendicular orientation and is dried 34. The base is subjected to calender treatments 37, 38 and are taken up on a take-up roll 39. As a result, the magnetic recording medium having the excellent high-frequency range characteristic and the good overwriting characteristic of signals and weatherability is obtd. The thickness of the magnetic layer is preferably <=1.5mum and the particle size of the hexagonal ferrite magnetic powder <=0.1mum.

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, it is still difficult to sufficiently improve the characteristics of a hexagonal ferrite-based magnetic recording medium in a high frequency band, particularly in high density recording (digital recording).

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 studied and found that a hexagonal ferrite having an easy axis of magnetization in the vertical direction was provided in the uppermost layer and a specific nonmagnetic layer was used as the lower layer. It was found that by providing a layer containing powder, a magnetic path is created between adjacent magnetic fluxes in opposite directions, each magnetization exists stably, and the output is improved, and hexagonal ferrite powder The present invention has reached the present invention by discovering that a magnetic recording medium having high corrosion resistance can be obtained.

That is, the invention according to claim 1 for achieving the above object is to provide at least one selected from the group consisting of nonmagnetic oxides, nitrides, carbides and sulfates on a nonmagnetic support. A magnetic recording medium comprising a non-magnetic layer containing a non-magnetic powder and a magnetic layer containing a hexagonal ferrite magnetic powder, which are laminated in this order. The invention according to claim 2, The magnetic recording medium according to claim 1, wherein the magnetic layer has a thickness of 1.5 μm or less. According to the invention of claim 3, the hexagonal ferrite magnetic powder has a particle diameter of 0.1 μm or less. The magnetic recording medium according to claim 1, and the invention according to claim 4 is the magnetic recording medium according to claim 1, wherein the particle diameter of the non-magnetic powder is 0.2 μm or less.

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 hexagonal ferrite magnetic powder as magnetic powder, a binder described later, and other components described later. As a preferable hexagonal ferrite magnetic powder,
The average particle size of the Ba-ferrite powder in which a part of Fe is replaced with at least Co and Zn is 0.1 μm or less, preferably 0.08 μm or less, and the coercive force (Hc) is 45.
There can be mentioned Ba-ferrite which is 0 to 1,500.

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 and coercive force of Ba-ferrite are within the above ranges is as follows. That is, if the average particle size exceeds 0.1 μm, the noise during reproduction is increased due to the influence of particle noise, which is not preferable, and if the coercive force is less than 350 Oe, it becomes difficult to hold the recording signal. Becomes 2,000 Oe
If the value exceeds the limit, the head limit may decrease in saturation and recording may be 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 a method for producing the hexagonal ferrite magnetic powder used in the present invention, for example, the desired Ba
An oxide of each element necessary to form ferrite, a carbonate, melted with a glass-forming substance such as boric acid, and the resulting melt quenched to form glass,
Then, this glass is heat treated at a predetermined temperature to obtain the desired B
In addition to the glass crystallization method of precipitating a-ferrite crystal powder and finally removing the glass component by heat treatment, coprecipitation-firing method, hydrothermal synthesis method, flux method, alkoxide method, plasma jet method, etc. Is applicable.

In the present invention, the content of the hexagonal ferrite magnetic powder in the magnetic layer is usually 50 to 99.
%, Preferably 60 to 99% by weight.

-Nonmagnetic Powder in Nonmagnetic Layer- The nonmagnetic layer contains at least one nonmagnetic powder selected from the group consisting of nonmagnetic oxides, nitrides, carbides and sulfates. Non-magnetic oxides include TiO ₂ , Zn
O, α-Fe ₂ O _{3 and the} like, nonmagnetic nitrides such as FeN, Si ₄ N and AlN, and nonmagnetic carbides such as SiC, Fe ₃ C and Ca.
C, B ₄ C and the like can be mentioned. As the non-magnetic sulfate, BaSO ₄ , FeSO ₄ , MnSO ₄ , MgSO ₄ ,
CaSO _{4 and the} like can be mentioned. These non-magnetic powders may be used alone or in combination of two or more.

The preferred particle size of the non-magnetic powder is usually 0.2.
It is less than or equal to μm, and particularly less than or equal to 0.1 μm. When the particle size of the non-magnetic powder is 0.2 μm or less, the surface of the non-magnetic layer after coating becomes smooth and there is an advantage that the upper layer surface is not adversely affected, which is preferable.

The content of the non-magnetic powder in the non-magnetic layer is 10
˜98% by weight, preferably 40 to 97% by weight, more preferably 50 to 96% by weight. When the content of the non-magnetic powder is within the above range, the dispersion of the non-magnetic layer can be improved, which is preferable.

-Binder used for 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-based copolymer used as the binder in the present invention is a compound having a hydroxyl group-containing copolymer 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 Taking ₂ SO ₃ Na as an example, 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-57-42727 are cited.
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, 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, 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.

Further, 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 Regarding the introduction of polar groups into polyurethane As the technology, Japanese Patent Publication No. 58-41565 and Japanese Patent Laid-Open No. 57-9242.
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 durability improvers, dispersants, lubricants, abrasives, antistatic agents and fillers are used as other components. Can be included. Examples of the durability improver include polyisocyanate, and examples of the polyisocyanate include aromatic polyisocyanates such as an adduct of tolylene diisocyanate (TDI) and the like and an active hydrogen compound,
There are aliphatic polyisocyanates such as adducts of hexamethylene diisocyanate (HMDI) and the like with active hydrogen compounds. The weight average molecular weight of the polyisocyanate is preferably in the range of 100 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.

Fatty acids and / or fatty acid esters can be used as the lubricant. In this case, the amount of the fatty acid added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the ferromagnetic powder. Addition amount is 0.
If it is less than 2% by weight, the running property tends to deteriorate,
When the content exceeds the weight%, the fatty acid tends to exude to the surface of the magnetic layer and the output tends to be reduced. The amount of fatty acid ester added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the ferromagnetic powder. If the addition amount is less than 0.2% by weight, the still durability is apt to deteriorate, and if it exceeds 10% by weight, the fatty acid ester is likely to seep out to the surface of the magnetic layer or the output tends to be lowered. When it is desired to use a fatty acid and a fatty acid ester together to further enhance the lubricating effect, the fatty acid and the fatty acid ester are in a weight ratio of 1
0:90 to 90:10 is preferable.

The fatty acid may be a monobasic acid or a dibasic acid and preferably has 6 to 30 carbon atoms.
The range of -22 is more preferable. Specific examples of fatty acids include caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, oleic acid, elaidic acid, behenic acid, malonic acid, succinic acid, maleic acid. Acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1,12-dodecanedicarboxylic acid, octanedicarboxylic acid and the like can be mentioned.

Specific examples of the fatty acid ester include oleyl oleate, isocetyl stearate, dioleyl malate, butyl stearate, butyl palmitate, butyl myristate, octyl myristate, octyl palmitate, pentyl stearate, pentyl palmiate. Tate, isobutyl oleate, stearyl stearate,
Lauryl oleate, octyl oleate, isobutyl oleate, ethyl oleate, isotridecyl oleate, 2-ethylhexyl stearate, 2-ethylhexyl palmitate, isopropyl palmitate, isopropyl myristate, butyl laurate, cetyl-2.
-Ethyl hexalate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate, oleyl stearate, 2-ethylhexyl myristate, isopentyl palmitate, isopentyl stearate, diethylene glycol-mono-butyl ether palmitate, diethylene glycol mono- Butyl ether palmitate and the like.

As the lubricant other than the above fatty acids and fatty acid esters, for example, silicone oil, graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide and the like can be used.

Specific examples of the polishing agent include α-alumina, fused alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, tungsten carbide, molybdenum carbide, boron carbide, corundum, and oxide. Examples thereof include zinc, cerium oxide, magnesium oxide, and boron nitride. The abrasive has an average particle size of 0.05 to 0.
It is preferably 6 μm, more preferably 0.1 to 0.3 μm.

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, it is preferable that the magnetic layer is coated by a so-called wet-on-wet system in which the non-magnetic 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, in general, a ferromagnetic powder, a binder, a dispersant, a lubricant, an abrasive, an antistatic agent, etc. and a solvent are kneaded to prepare a high-concentration magnetic paint, and then this high-concentration magnetic paint is diluted. After preparing the magnetic paint by applying the magnetic paint to the surface of the non-magnetic support.

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.

In 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 a layer containing a high magnetic permeability material and a magnetic layer on a non-magnetic support, specifically, as shown in FIG. 1, first, a film-like support fed from a supply roll 32. 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 was 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 added to the above paint or a diluent solvent for applying this paint, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; alcohols such as methanol, ethanol, propanol and 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 the multi-layer coating in the wet-on-wet system, the magnetic layer is coated while the non-magnetic layer is in a wet state, so that the surface of the non-magnetic layer becomes smooth and the surface property of the magnetic layer is improved. In addition, the adhesiveness between the upper and lower layers is 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-
The on-wet multi-layer coating method can also 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 calendering 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 keep the C / S at 00 kg / cm and 20 to 600 m / min.

A preferable layer thickness of the uppermost layer as a result of the above-mentioned treatment is usually 1.5 μm or less, particularly 0.1 to 0.8.
μm. When the layer thickness exceeds 1.5 μm, the output is lowered due to the effect of self-demagnetization, which is not preferable.

[0054]

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 material A for uppermost layer] Co-Ti-substituted barium ferrite magnetic powder 100 parts (BET value; 40 m ² / g, Hc; 1,200 Oe, average particle diameter; 0.05 μm, saturation magnetization amount; 65 emu) / g) vinyl chloride resin (manufactured by Nippon Zeon Co., Ltd. MR 110) 5 parts sulfonic acid metal salt-containing polyurethane resin 3 parts (Toyobo Co., Ltd., UR8700) Cr ₂ O ₃ 5 parts Ca - carbon black (particle size 40; m.mu. ) 0.5 part Butyl stearate 1 part Stearic acid 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 coating material B for the uppermost layer] In the magnetic coating material A for the uppermost layer, 100 parts of Co-Ti-substituted barium ferrite magnetic powder was replaced with Ni-Ti-substituted barium ferrite magnetic powder (coercive force Hc; 1,200). Oe, BET value 50 m ² / g, average particle diameter; 0.04 μm, saturation magnetization amount;
65 emu / g) was used, and was prepared in the same manner as the magnetic coating material A for the uppermost layer.

[Magnetic Coating C for Top Layer] In the above magnetic coating A for top layer, 100 parts of Co—Ti-substituted barium ferrite magnetic powder was replaced with Fe—Zn—Ni alloy (coercive force Hc; 1,200 Oe, A BET value of 50 m ² / g and an average axial length of 0.2 μm) were used, and the same procedure as the preparation of the magnetic coating material A for the uppermost layer was used.

[Magnetic Coating D 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.

[Paint I for Non-Magnetic Layer] TiO ₂ powder (particle size; 30 nm) 100 parts Vinyl chloride resin (MR110 manufactured by Zeon Corporation) 5 parts Polyurethane resin containing sulfonic acid metal salt 5 parts (Toyobo Co., Ltd.) , UR8700) Myristic acid 1 part Butyl stearate 1 part Methyl ethyl ketone 50 parts Toluene 50 parts Cyclohexanone 50 parts The above composition was kneaded and dispersed to prepare.

[Non-magnetic layer coating material II] In the non-magnetic layer coating material I, α-Fe was used in place of 100 parts of TiO ₂ powder.
_It was prepared in the same manner as the preparation of the non-magnetic layer coating material I except that 100 parts of ₂ O ₃ (average axial length; 0.1 μm) was used.

[Nonmagnetic Layer Coating III] In the above nonmagnetic layer coating I, ZnO was used instead of 100 parts of TiO ₂ powder.
(Average particle size: 0.2 μm) A coating material was prepared in the same manner as the coating material I for the non-magnetic layer except that 100 parts was used.

[Non-magnetic layer coating material IV] In the non-magnetic layer coating material I, 100 parts of TiO ₂ powder was used instead of BaSO 4.
₄ (average particle size; 50 nm) was used in the same manner as in the above non-magnetic layer coating material I except that 100 parts was used.

[Non-magnetic layer coating material V] In the non-magnetic layer coating material I, 100 parts of carbon black (XC-72 manufactured by Cabot Corporation) was used in place of 100 parts of TiO ₂ powder, except that the non-magnetic layer was formed. It was prepared in the same manner as the preparation of the coating material I.

(Examples 1 to 6) With the composition of the coating film having the composition shown in Table 1, the wet-on-wet system was 8 mm.
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 to 3) 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 Examples 4 to 5) Magnetic recording media having a two-layer magnetic layer were obtained using the uppermost layer magnetic coating material and the lower layer magnetic coating material shown in Table 1, and the same evaluation test as in the above Examples was performed. I went.

(Comparative Examples 6 and 8) A magnetic recording medium having a two-layer structure was obtained by using the magnetic coating material for the uppermost layer and the coating material for the non-magnetic layer shown in Table 1, and the same evaluation test as in the above-mentioned Examples was conducted. ..

(Comparative Example 7) Co-Ni was formed 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.

[0073]

[Table 1]

[0074]

According to the present invention, it is possible to provide a magnetic recording medium excellent in high frequency characteristics, excellent in signal overwriting characteristics, excellent in weather resistance and suitable for high density recording. ..

[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.

Claims (4)

[Claims] 1. A non-magnetic layer containing at least one non-magnetic powder selected from the group consisting of non-magnetic oxides, non-magnetic nitrides, non-magnetic carbides and non-magnetic sulfates on a non-magnetic support. And a magnetic layer containing hexagonal ferrite magnetic powder, which are laminated in this order. 2. The magnetic recording medium according to claim 1, wherein the magnetic layer has a thickness of 1.5 μm or less. 3. The magnetic recording medium according to claim 1, wherein the hexagonal ferrite magnetic powder has a particle diameter of 0.1 μm or less. 4. The magnetic recording medium according to claim 1, wherein the particle size of the non-magnetic powder is 0.2 μm or less.