JPH05242464A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium having excellent high-frequency characteristics, satisfactory signal overwriting characteristics and excellent weather resistance by specifying the thickness of a magnetic layer contg. fine hexagonal ferrite powder. CONSTITUTION:This magnetic recording medium has a thin film of a high permeability alloy formed on the nonmagnetic substrate and at least one magnetic layer contg. fine hexagonal ferrite powder and having <=1.0mum thickness formed on the thin film. When this medium is produced, a filmlike substrate 1 drawn out of a feed roll 32 is coated with coating materials forming the thin alloy film and the magnetic layer by means of extrusion coaters 10, 11 in a superposed state and the coated substrate is passed magnets 33 for orientation or perpendicular orientation, introduced into a drier 34, dried and introduced into a super-calendering device 37 composed of calendering rolls 38. In the device 37, the substrate 1 with dried coating layers is calendered and then wound around a winding roll 39. The resulting magnetic film is cut to a tape shape having a desired width.

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 which has excellent high frequency characteristics, is manufactured by digital recording, and has excellent signal overwriting characteristics.

[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, but a plate-like hexagonal ferrite-based ferromagnetic powder is used. It is said that the magnetic recording medium using the magnetic recording medium has a high output on the high frequency side of short wavelength (JP-A-57-195329 and JP-A-60-22).
See 3018). There is also a magnetic recording medium having a magnetic layer containing acicular 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 (see JP-A-63-187418).

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).
In addition, even if a non-magnetic layer is provided as the lower layer, sufficient improvement of characteristics in the high range cannot be 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 to be re-recorded, and so-called overwrite characteristics deteriorate.

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.

On the other hand, a plate-shaped hexagonal ferrite having an easy axis of magnetization in the vertical direction is provided in the uppermost layer, and a high magnetic permeability layer is provided as the lower layer, so that the magnetic head-
Magnetic recording layer-By forming a closed magnetic path (horseshoe-shaped loop) that passes through a high-permeability magnetic layer, each magnetization is stably present, output is improved, and a highly efficient magnetic recording medium is obtained. (JP-A-56-98718 and JP-A-54)
-59108, 56-34, 61-131233, 61-192032
issue).

However, 8mm video cassette, DA
Considering the recording wavelength, head current, etc., assuming a high-density recording medium such as a T or digital VTR, if the upper magnetic layer containing hexagonal ferrite fine powder has a certain thickness or more, the effect of the lower high-permeability layer Is significantly reduced, and the film thickness is severely restricted to thinner ones. Furthermore, the smoothness of the upper layer surface is required to be good, but the allowable range for the upper layer thickness remains unclear, and the technical method for smooth coating of the upper layer is not clear.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium which is excellent in high-frequency electromagnetic conversion characteristics, and has excellent digital characteristics, signal overwriting characteristics, and weather resistance.

[0010]

In a magnetic recording medium having a magnetic layer on a non-magnetic support, a high-permeability alloy thin film layer provided on the non-magnetic support, and at least one layer provided on the alloy thin film layer. Magnetic recording medium characterized by providing a magnetic recording layer having a magnetic layer having a thickness of 1.0 μm or less containing hexagonal ferrite fine powder as a constituent layer, and on the alloy thin film layer as still another constitutional aspect. The object of the present invention can be achieved by any one of the magnetic recording media in which the intermediate layer is provided and at least one magnetic layer is provided thereon.

In a further preferred embodiment, the constituent layers on the alloy thin film layer are extruded and applied by coating, particularly wet on.
A magnetic recording layer provided by wet simultaneous multilayer coating is preferred.

The magnetic recording medium of the present invention will be described in detail below.

-Nonmagnetic support-As the material for forming the nonmagnetic support, for example, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetate, cellulose diacetate, etc. Examples of the cellulose derivative include plastics such as polyamide and polycarbonate.

The form of the non-magnetic support is not particularly limited, and is mainly tape-like, film-like, sheet-like, card-like,
There are disc shape and drum shape.

The thickness of the non-magnetic support is not particularly limited, but in the case of a film or sheet, it is usually 3-10.
The thickness is 0 μm, preferably 5 to 50 μm, and is approximately 30 μm to 10 mm in the case of a disk or card, and is appropriately selected according to the recorder in the case of a drum.

The 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 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 charging and preventing transfer. It is preferable that an undercoat layer be provided between the magnetic layer and the non-magnetic support.

-Magnetic Powder Used in Magnetic Layer-The hexagonal ferrite fine powder contained in the magnetic layer is mainly composed of hexagonal Ba-ferrite, which easily adjusts the electromagnetic characteristics.

A preferable hexagonal Ba-ferrite fine powder is Ba-ferrite powder in which at least part of Fe is at least Co.
And average particle size of particles substituted with Zn (length of diagonal of hexagonal ferrite plate surface) 0.1 μm or less, more preferably 0.04 to 0.08 μm, plate-like ratio (diagonal line of hexagonal ferrite plate surface) The value obtained by dividing the length by the plate thickness) is 2.0 to 10.0, and the coercive force (Hc) is 450 to 2000 Oe.

The coercive force of Ba-ferrite powder is controlled to an appropriate value by partially substituting Fe with Co, and further by partially substituting with Zn, it is not possible to obtain it 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. Also, by substituting a part of Fe with Nb,
It is possible to obtain a magnetic recording medium having a higher reproduction output and excellent electromagnetic conversion characteristics. Also used in the present invention
In Ba-ferrite, part of Fe is Ti, In, Mn, Cu, G
It may be substituted with a transition metal such as e or Sn.

Ba-ferrite is represented by the following general formula.

BaO · n ((Fe _1-m M _m ) ₂ O ₃ ) where m> 0.36 (where Co + Zn = 0.08 to 0.3, Co / Zn
= 0.5-10) and n is 5.4-11.0, preferably
It is 5.4 to 6.0, M represents a substituted metal, and magnetic particles composed of a combination of two or more elements having an average number of 3 are preferable.

In the present invention, the reason why it is preferable that the average particle size, plate ratio and coercive force of Ba-ferrite are within the above ranges is as follows. That is, the average particle size is 0.
If it is less than 04 μm, the reproduction output when used as a magnetic recording medium will be insufficient, and conversely, if it exceeds 0.1 μm, the surface smoothness when used as a magnetic recording medium will significantly deteriorate and the noise level will become too high. If the plate ratio is less than 2.0, the perpendicular orientation ratio suitable for high density recording cannot be obtained when used as a magnetic recording medium, and conversely when the plate ratio exceeds 6.0 when used as a magnetic recording medium. Surface smoothness is significantly deteriorated, the noise level becomes too high, and when the coercive force is less than 350 Oe, it becomes difficult to hold the recording signal,
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 of 50.
Emu / g or more is desirable. This saturation magnetization is 50
If it is less than emu / g, the electromagnetic conversion characteristics may deteriorate.

Further, in the present invention, as the recording density becomes higher, the Ba- specific surface area by the BET method is 30 m ² / g or more.
It is desirable to use ferrite magnetic powder.

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 used, such as boric acid. It is melted together with a glass-forming substance, the obtained melt is rapidly cooled to form glass, and then this glass is heat-treated at a predetermined temperature to precipitate the desired Ba-ferrite crystal powder, and finally the glass component is heat-treated. In addition to the glass crystallization method of removing by means of co-precipitation, coprecipitation-firing method, hydrothermal synthesis method, flux method, alkoxide method, plasma jet method and the like can be applied.

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

-High permeability layer provided on the surface of the non-magnetic support-
In the magnetic recording layer of the aspect of the present invention, a plurality of constituent layers are formed on the non-magnetic support, and the constituent layer located on the support surface is lower than the magnetic layer provided at least one layer,
It is a high permeability alloy thin film layer.

As the high magnetic permeability alloy, 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 magnetized region of the magnetic layer is exhibited as a high magnetic permeability alloy. 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.

The film thickness is 0.01 to 1 μm, preferably 0.1 to 0.5 μm.

As the high-permeability alloy, an alloy having a coercive force within the above range is appropriately selected. A soft magnetic alloy can be mentioned as such a high magnetic permeability alloy.

As the soft magnetic alloy, Fe--Si alloy, F
e-Al alloys (Alperm, Alfenol, Alfer), Permalloy (Ni-F)
e-based binary alloys, multi-component alloys that include Mo, Cu, Cr, etc.), sendust (Fe-Si-Al: 9.6 wt% S)
i, 5.4% Al, the balance Fe)), Fe-Co alloy Fe-Si
-B-Cu-Nb alloy, Fe-Ru-Ga alloy, doving Si, doving Fe or amorphous Fe-Si-alloy, Co-Si-B alloy, Co-Nb-Zr alloy, doving Co, etc. be able to. Among these, permalloy is preferable as a preferable soft magnetic alloy. The soft magnetic alloy as the high-permeability alloy is not limited to those exemplified above, and other soft magnetic alloys can be used. The high-permeability alloys may be used alone or in combination of two or more.

This high-permeability layer is formed into a thin layer by a vacuum vapor deposition method, a magnetron sputtering method, a facing target sputtering method, an ion plating method or the like.

The content of the high-permeability alloy in this high-permeability alloy thin film layer is 10 to 100 wt%, preferably 50 to 100 wt%, and more preferably 60 to 100 wt%. When the content of the high magnetic permeability alloy is within the above range, the effect of stabilizing the magnetization of the magnetic layer can be sufficiently obtained. Further, if the content of the high magnetic permeability alloy is less than 50 wt%, the effect as the high magnetic permeability layer may not be obtained, which is not preferable.

As a result of earnest studies on the method of coating the magnetic recording layer of the present invention, the provision of the intermediate layer between the magnetic recording layer and the high-permeability alloy thin film layer also improves the smoothness of the surface after coating. It turned out to be good.

It is essential that the thickness of the intermediate layer after coating is sufficiently thin, but the intermediate layer can be coated by using an extremely dilute resin solution. Further, by coating the magnetic recording layer and the intermediate layer by simultaneous multi-layer coating by wet-on-wet extrusion coating, both coating layers can be further thinned, and the surface smoothness is also good. Become.

-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. Is -SO ₃
It preferably contains a repeating unit having at least one polar group selected from M, -OSO ₃ M, -COOM and -PO (OM ¹ ) ₂ .

However, in the above polar group, M represents a hydrogen atom or an alkali metal such as Na, K or Li, and M
¹ represents a hydrogen atom, an alkali atom such as Na, K and Li, or an alkyl group.

The above 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%,
It is preferably 0.5 to 6.0 mol%. When the content is less than 0.1 mol%, the dispersibility of the ferromagnetic powder is deteriorated, and when the content exceeds 8.0 mol%, the magnetic coating tends to gel. The weight average molecular weight of each resin is 15,000.
A range of up to 50,000 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 a single type, and two or more types can be used in combination. In this case, the ratio of polyurethane and / or polyester to vinyl chloride resin is usually 90:10 by weight. It is 10:90, preferably 70:30 to 30:70.

The polar group-containing vinyl chloride copolymer used as the binder is, for example, an addition reaction of a copolymer having a hydroxyl group with a compound having a polar group and a chlorine atom described below, such as a vinyl chloride-vinyl alcohol copolymer. Can be synthesized by.

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- Taking CH ₂ CH ₂ SO ₃ Na as an example, the above reaction will be explained based on the reaction structural unit 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 a salt thereof include unsaturated hydrocarbon sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, p-styrene sulfonic acid and the like, and these. Mention may be made of salt.

When the carboxylic acid or its salt is introduced, for example, (meth) acrylic acid or maleic acid is used,
When phosphoric acid or its salt is introduced, for example (meta)
Acrylic acid-2-phosphate ester may be used.

An epoxy group is preferably introduced into the vinyl chloride copolymer. This is because the thermal stability of the polymer is improved by doing so.

When an epoxy group is introduced, the content of the repeating unit having an epoxy group in the copolymer is 1 to
30 mol% is preferable, and 1 to 20 mol% is more preferable.

As the monomer for introducing the epoxy group, for example, glycidyl acrylate is preferable.

Regarding the technique for introducing a polar group into a vinyl chloride type copolymer, JP-A-57-44227 and JP-A-58-108052.
Issue 59-8127, Issue 60-101161, Issue 60-235814, Issue 6
0-238306, 60-238371, 62-121923, 62-146
It is described in the publications such as 432 and 62-146433, and these can also 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 polyol and a polybasic acid partially having a polar group.

Examples of the polybasic acid having a polar group include 5-
Sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-sulfoisophthalic acid, 3-sulfophthalic acid, dialkyl 5-sulfoisophthalate, dialkyl 2-sulfoisophthalate, dialkyl 4-sulfoisophthalate, dialkyl 3-sulfoisophthalate and these And sodium salts thereof.

Examples of polyols include trimethylolpropane, hexanetriol, glycerin, trimethylolethane, neopentyl glycol, pentaerythritol, ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1 Examples thereof include 6,6-hexanediol, diethylene glycol, cyclohexanedimethanol and the like.

Incidentally, other polar group-introduced polyesters can also be synthesized by a known method.

Next, the polyurethane will be described.

It is obtained 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, when 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 (TDI)
ODI), lysine isocyanate methyl ester (LD
I) and the like.

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 Polarity to polyurethane Techniques relating to the introduction of a group include Japanese Patent Publication No. 58-41565, JP-A Nos. 57-92422 and 57-92423.
Issue 59-8127, Issue 59-5423, Issue 59-5424, Issue 62-12
It is described in gazettes such as 1923, and these can also be used in this invention.

In the present invention, the following resins can be used together as a binder in an amount of 20 wt% or less of the total binder.

The resin has a weight average molecular weight of 10,0.
00 to 200,000, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (nitrocellulose Etc.), styrene-butadiene copolymer, phenol resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic resin, urea formamide resin, and various synthetic rubber resins.

-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 polyisocyanate, and examples of the polyisocyanate include:
For example, there are aromatic polyisocyanates such as adducts of tolylene diisocyanate (TDI) and active hydrogen compounds, and aliphatic polyisocyanates such as adducts of hexamethylene diisocyanate (HMDI) and active hydrogen compounds. The weight average molecular weight of the polyisocyanate is preferably in the range of 100 to 3,000.

Examples of the dispersant include 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 alkaline earth metals. Examples thereof include salts or amides thereof; polyalkylene oxide alkyl phosphates; lecithin; trialkyl polyolefinoxy quaternary ammonium salts; azo compounds having a carboxyl group and a sulfonic acid group. These dispersants are usually 0.
It is used in the range of 5 to 5 wt%.

Specific examples of the abrasive include α-aluminum, 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 preferably has an average particle size of 0.05 to 0.6 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, carboxylic acid; amphoteric surfactant such as aminosulfonic acid A natural surfactant such as saponin, etc .; The above-mentioned antistatic agent is usually added in the range of 0.01 to 40% by weight with respect to the binder.

—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 lower layer is in a wet state. As the wet-on-wet method, a method used for manufacturing a known multi-layer 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 and the like are kneaded with a solvent to prepare a high-concentration magnetic coating, and then this high-concentration magnetic coating is prepared. After diluting to prepare a magnetic paint, the magnetic paint is applied 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 / dispersing machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill,
Kobol Mill, Tron Mill, Sand Mill, Sand Grinder, Sqegvari Attritor, High Speed Impeller Disperser, High Speed Stone Mill, High Speed Impact Mill, Dispa, High Speed Mixer,
Examples thereof include a homogenizer, an ultrasonic disperser, an open kneader, a continuous kneader, and a pressure kneader. Among the above kneading dispersers, the kneading dispersers capable of providing a power consumption load of 0.05 to 0.5 KW (per 1 Kg of magnetic powder) are a pressure kneader, an open kneader, a continuous kneader, a two-roll mill and a three-roll mill. is there.

In order to coat the magnetic layer and the intermediate layer on the non-magnetic support, specifically, as shown in FIG. 1, first, the film-type support 1 fed from the supply roll 32 is applied to the film support 1. After coating each coating of the constituent layers by the wet-on-wet method by using the extrusion coaters 10 and 11, it is passed through the magnet for orientation or the magnet for vertical orientation 33 and introduced into the dryer 34, where it is vertically moved. Hot air is blown from the arranged nozzle to dry. 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 can be cut into a tape having a desired width to produce a magnetic recording tape for an 8 mm video camera, for example.

In the above method, each paint may be supplied to the extrusion coaters 10 and 11 through an in-line mixer (not shown). In the figure, the arrow D indicates the transport direction of the non-magnetic base film. Extrusion coaters 10 and 11 are provided with liquid pools 13 and 14, respectively, and the coating materials from the coaters are layered in a wet-on-wet system. That is, the upper layer coating material is applied in multiple layers immediately after the lower layer coating material is applied (when it is in an undried state).

The coater head is shown in FIG. 2 (c).
Heads are preferred 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 monoacetate; 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,
Halogenated hydrocarbons 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 oriented magnet or the magnet for vertical orientation 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 0.1 to 10 °.
It's about a minute.

In the multi-layer coating in the wet-on-wet system, the upper magnetic layer is coated while the layer located below the uppermost layer is in a wet state, so that the surface of the lower layer (that is, the uppermost layer The interface between the upper and lower layers is improved and the adhesiveness between the upper and lower layers is improved. As a result, high output, especially for high density recording,
Even if the performance required for low noise is satisfied, for example, as a magnetic tape and the performance with high durability is required, film peeling is eliminated, the film strength is improved, and the durability is sufficient. Become. In addition, the wet-on-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.

Thereafter, if necessary, burnishing or blade processing is performed for slitting.

In the surface smoothing treatment, the calender conditions are temperature, linear pressure, C / s (coating speed).
Etc. can be mentioned.

Usually, it is preferable to maintain the temperature at 50 to 120 ° C., the linear pressure at 50 to 400 kg / cm, and the C / s at 20 to 600 m / min.

The layer thickness of the uppermost layer obtained as a result of the above treatment is 0.8 μm or less, preferably 0.1 to 8 μm. Layer thickness
When it exceeds 0.8 μm, the high frequency characteristic and the overwrite characteristic are deteriorated, and the magnetic recording medium is the same as the single layer magnetic recording medium, and the object of the present invention cannot be achieved.

[0087]

Embodiments of the present invention will be described below.

The following components, ratios and operation sequences 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: Co-Ti-substituted barium ferrite magnetic powder 100 parts (BET value = 40 m ² / g, Hc = 1200 Oe, average plate ratio 3.5, average particle size 0.05 μm, 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 Stearic acid 1 Parts 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 L5 parts) was added to prepare.

: Magnetic paint B: In the above magnetic paint A,
Co-Ti substituted barium ferrite magnetic powder 100 parts instead of Ni
-Ti substituted barium ferrite magnetic powder alloy (coercive force Hc =
1,200 Oe, BET value 50m ² / g, average plate ratio 4.5, average particle size
The magnetic coating material A was prepared in the same manner as the magnetic coating material A except that 0.04 μm and a saturation magnetization of 65 emu / g) were used.

Magnetic coating C: In the above most magnetic coating A, 100 parts of Co-Ti-substituted barium ferrite magnetic powder was replaced with Fe-Zn-Ni alloy (coercive force Hc = 1200 Oe, BET value 50 m ²
/ G, average major axis length 0.2 μm) except that the magnetic coating material A was prepared.

: Resin paint E for intermediate layer: Polyurethane resin (Toyobo UR8700) 5 parts Cyclohexanone 100 parts Methyl ethyl ketone 50 parts Toluene 50 parts The above composition was dissolved by stirring.

Preparation of lower layer high permeability alloy thin film I: Fe-Ni alloy (Fe19wt%) was used as a target material and 5000Å Fe-Ni thin film (Hc50 Oe, μi700; μi is initial permeability) was used in the sputtering apparatus. Formed.

Note that μi is expressed by the following equation 1 at the origin of the initial magnetization curve.

[0095]

[Equation 1]

Examples 1 to 7 and Comparative Examples C _{1 to} C _{4 With} the coating composition of the composition shown in Table 1, wet-on
A magnetic recording medium having a width of 8 mm was prepared by the wet method. The following evaluation tests were conducted on this magnetic recording medium.

[0097]

[Table 1]

<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 C 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.

[0101]

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 multilayer coating of magnetic layers by wet-on-wet coating by an extrusion coating method.

FIG. 2 is a view of a coater head for applying paint.

[Explanation of symbols]

 1 Support 10 Coater 11 Coater 32 Supply Roll 33 Orientation Magnet 34 Dryer 37 Super Calendar Device 38 Calendar Roll 39 Winding Roll

Claims (4)

[Claims] 1. A magnetic recording medium having a magnetic layer on a non-magnetic support, wherein a high-permeability alloy thin film layer provided on the non-magnetic support and at least one layer further provided on the alloy thin film layer. A magnetic recording medium comprising a magnetic recording layer comprising a magnetic layer containing a hexagonal ferrite fine powder and having a film thickness of 1.0 μm or less. 2. A magnetic recording medium having a magnetic layer on a non-magnetic support, a high magnetic permeability alloy thin film layer provided on the surface of the non-magnetic support, and an intermediate layer further provided on the alloy thin film layer.
Further, a magnetic recording layer is provided on the intermediate layer, the magnetic recording layer comprising at least one magnetic layer containing hexagonal ferrite fine powder and having a film thickness of 1.0 μm or less. 3. The magnetic recording medium according to claim 1, wherein the constituent layer provided on the high magnetic permeability alloy thin film layer is provided by extrusion coating. 4. The magnetic recording medium according to claim 1, wherein the extrusion coating method is wet-on-wet simultaneous multilayer coating.