JPH05242463A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium having high frequency electromagnetic transducing characteristics fit for high density digital recording, satisfactory signal overwriting characteristics and excellent preservability by specifying the shape of ferromagnetic powder forming a magnetic layer. CONSTITUTION:At least one underlayer contg. nonmagnetic particles dispersed in a binder is formed on a nonmagnetic substrate and a magnetic layer contg. ferromagnetic powder dispersed in a binder is formed on the underlayer. The ferromagnetic powder in the upper layer is hexagonal platy magnetic powder and the thickness of the upper layer is 0.1-0.7mum. When the squareness ratios of magnetization curves obtd. at the time of applying an external magnetic field to the resulting tape in the longitudinal, transverse and perpendicular directions are expressed by SQ1, SQt and SQp, respectively, the relation of (SQ1<2>+SQp<2>)/SQt<2>>0.3 is established.

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, and more particularly to a magnetic recording medium for 8 mm video tape or the like.

[0002]

2. Description of the Related Art In recent years, there has been a demand for higher density and higher performance of magnetic recording media, and the magnetic layer has a single layer, or multiple layers or multiple layers.
Proposed.

As the prior art in the extrusion method mainly for the purpose of manufacturing a magnetic recording medium, those described in JP-A-57-8477, JP-A-58-104666 and JP-A-60-238179 are known. ing. As a conventional example of the multilayer and coating method using an extrusion coater, a sequential multilayer coating method described in JP-A-64-288364, and JP-A-2-251265 and JP-A-2-268862, simultaneous multilayering. There is a description of the coating method.

The multilayer structure of hexagonal magnetic powder and acicular magnetic powder is described in JP-A-1-128228.

As an example of providing a layer containing non-magnetic particles between a support and a magnetic layer, JP-A-60-125927 and JP-A-6-125927 can be used.
1-296525, 62-121927, Japanese Patent Publication No. 1-20488, etc., carbon black, in JP-A-59-142741, an example of SnO ₂ , in JP-A-63-187418, red iron oxide Examples are allowed.

However, the recording system is changing from the analog recording system to the digital recording system with the trend of increasing the density of magnetic recording. Although a digital recording system is about to be adopted for audio recording and video recording, the recording medium currently used is a diversion of an analog medium, and is not necessarily optimum as a digital recording medium.

That is, in the conventional medium structure, the thickness of the magnetic layer is relatively large, and in short wavelength recording, there is a decrease in output due to reproduction demagnetization due to thickness loss of the medium, or signal overwriting. There were drawbacks such as poor characteristics.

Further, as a high density recording digital recording medium, a metal thin film vapor deposition tape is regarded as promising.
Touch resistance and storage stability are not good.

[0009]

It is an object of the present invention to have a high-frequency electromagnetic conversion characteristic suitable for high-density digital recording, good signal overwriting characteristics, and excellent storage stability. Another object is to provide a magnetic recording medium.

[0010]

The above object of the present invention is to provide at least one lower layer having non-magnetic particles dispersed in a binder on a non-magnetic support, on which ferromagnetic powder is dispersed in the binder. In the magnetic recording medium provided with the magnetic layer, the upper ferromagnetic powder is hexagonal plate magnetic powder, and the upper layer film thickness is 0.
When the external magnetic field is applied in the longitudinal direction, width direction, and vertical direction of the tape, the squareness ratio of the obtained magnetization curve is SQ _l , SQ _t , and SQ _p , respectively. A magnetic recording medium characterized by the existence of the following relationship.

(SQ _l ² + SQ _p ² ) / SQ _t ² > 3.0 In a preferred embodiment, the magnetic recording medium comprises the lower layer and the magnetic layer provided by a wet-on-wet coating method.

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 in the case of a disc or card, it is about 30 μm to 10 mm, and in the case of a drum, it is appropriately selected according to the recorder and the like.

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 the magnetic layer of the present invention-The magnetic layer of the present invention contains hexagonal plate-shaped magnetic powder as magnetic powder, a binder described later, and other components described later.

The hexagonal plate-like magnetic powder is mainly composed of hexagonal Ba-ferrite whose electromagnetic characteristics can be easily adjusted.

As a preferable hexagonal Ba-ferrite magnetic powder, an average particle diameter of Ba-ferrite powder in which a part of Fe is replaced with at least Co and Zn (diagonal length of plate surface of hexagonal ferrite) 300 to 900Å, Plate ratio (Diagonal length of plate surface of hexagonal ferrite divided by plate thickness) 2.0 to 1
Ba-ferrite having a coercive force (Hc) of 450 to 1500 can be mentioned.

In the Ba-ferrite powder, the coercive force is controlled to an appropriate value by partially replacing Fe with Co, and by partially replacing it with Zn, it is not possible to obtain it only by Co replacement. 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, Ba-used in the present invention
In ferrite, a part of Fe is Ti, In, Mn, Cu, Ge,
It does not matter if it is substituted with a transition metal such as 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 ) [m> 0.36 (where Co + Zn = 0.08 to 0.3, Co / Z
n = 0.5 to 10), n is from 5 to 11.0, preferably from 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, average particle size 30
When it is less than 0 Å, the reproduction output when used as a magnetic recording medium becomes insufficient, and when it exceeds 900 Å, surface smoothness when used as a magnetic recording medium deteriorates significantly, and the noise level becomes too high. 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. If the coercive force is less than 350 Oe, it becomes difficult to hold the recording signal, and if it exceeds 2000 Oe, the head limit will decrease in saturation. This may be difficult to record.

The ba-ferrite magnetic powder used in the present invention normally has a saturation magnetization (σ _S ) which is a magnetic characteristic of 50 emu /
It is preferably g or more. This saturation magnetization is 50emu
This is because if it is less than / g, the electromagnetic conversion characteristics may deteriorate.

Furthermore, in the present invention, Ba having a specific surface area of 30 m ² / g or more as measured by the BET method is used in accordance with higher recording density.
-It is desirable to use ferrite magnetic powder.

As the method for producing the hexagonal magnetic powder used in the present invention, for example, oxides and carbonates of the respective elements necessary for forming the desired Ba-ferrite are used.
For example, it is melted with a glass-forming substance such as boric acid, the resulting melt is rapidly cooled to form a glass, and then this glass is heat-treated at a predetermined temperature to precipitate the target Ba-ferrite crystal powder, Finally, in addition to the glass crystallization method of removing the glass component 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 magnetic powder in the magnetic layer is usually 50 to 99% by weight, preferably 60 to 99% by weight.

The thickness of the magnetic layer of the present invention is 0.1 to 0.7 μm.
Is a preferred embodiment.

In the present invention, a plurality of layers are formed on the non-magnetic support, and the non-magnetic powder is contained in at least one layer other than the magnetic layer.

As the non-magnetic powder, those having the above-mentioned characteristics can be appropriately selected and used from various known non-magnetic powders used in this kind of magnetic recording medium.
Examples of the non-magnetic powder include carbon black,
Graphite, titanium oxide, barium sulfate, ZnS, MgC
O ₃ , CaCO ₃ , ZnO, CaO, γ-iron oxide, tungsten dioxide, molybdenum dioxide, boron nitride, MgO, SnO ₂ , Si
O ₂ , Cr ₂ O ₃ , α-Al ₂ O ₃ , SiC, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, garnet, silica stone, silicon nitride, boron nitride, silicon carbide,
Examples thereof include molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tribolite, diatomaceous earth, dolomite and the like.

Of these, preferred are inorganic powders such as carbon black, CaCO ₃ , titanium oxide, barium sulfate, γ-iron oxide, α-Al ₂ O ₃ and α-iron oxide, and organic polymer powders such as polyethylene. Etc.

The preferable particle size of the non-magnetic powder in the present invention is usually 1 to 100 nm, especially 1 to 50 nm. When the particle size of the non-magnetic powder is in the above range, a smooth lower layer can be formed, and the characteristics of the upper magnetic layer can be improved, which is preferable.

The binder used in the present invention
- As the binder used in the present invention, for example, polyurethane, polyester, vinyl chloride resins such as vinyl chloride copolymers are exemplary, these resins -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 and Li, and M ¹ represents a hydrogen atom, an alkali metal 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 one kind alone, and two or more kinds may be used in combination. In this case, the ratio of polyurethane and / or polyester to vinyl chloride resin is usually 90:10 by weight. ˜10: 90, preferably 70:30 to 30:70.

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 C
_{OOM, Cl-CH 2 -P (} = O) (OM 1) taken ₂ These compounds _{Cl-CH 2 CH 2 SO 3} Na Examples, describing the addition reaction, 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) -Also, the polar group-containing vinyl chloride copolymer is a predetermined amount of a reactive monomer having an unsaturated bond into which a repeating unit containing a polar group is introduced, such as an autoclave. Was charged into a reaction vessel of, and a general polymerization initiator, for example, a radical polymerization initiator such as BPO (benzoyl peroxide), AIBN (azobisisobutyronitrile), a redox polymerization initiator, a cationic polymerization initiator, etc. was used. It 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. Can be mentioned.

When introducing a carboxylic acid or a salt thereof, for example, (meth) acrylic acid or maleic acid is used,
When phosphoric acid or a salt thereof is introduced, 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 an epoxy group is introduced, the content of the repeating unit having an epoxy group in the copolymer is 1
-30 mol% is preferable, and 1-20 mol% is more preferable.
For example, glycidyl acrylate is preferable as the monomer for introducing the epoxy group.

The technique for introducing a polar group into a vinyl chloride copolymer is described in, for example, JP-A-57-44227 and 58-1.
08052, 59-8127, 60-101161, 60-235814
No. 60, No. 60-238306, No. 60-238371, No. 62-121923,
62-146432, 62-146433 and other publications,
These can also be used in the present invention.

Next, the synthesis of the polyester resin and polyurethane resin used in the present invention will be described.

Generally, the polyester resin is obtained by reacting a polyol with a polybasic acid.

By using the known method, a polyester (polyol) resin having a polar group can be synthesized from a polyol and a polybasic acid partially having a polar group.

Examples of polybasic acids having polar groups 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 and propylene glycol.
Examples thereof include 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, and cyclohexane dimethanol.

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

Next, the polyurethane resin 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 resin having a polar group can be synthesized.

Examples of polyisocyanates include, for example, diphenylmethane-4-4'-diisocyanate (MD
I), 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 resin having a polar group, an addition reaction of polyurethane having a hydroxyl group with 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 C
OOM, Cl-CH ₂ -P (= O) (OM ¹ ) ₂ Incidentally, as a technique for introducing a polar group into polyurethane, for example, JP-B-58-41565, JP-A-57-92422, 57
-92423, 59-8127, 59-5423, 59-5424,
It is described in Japanese Patent Publication No. 62-121923 and the like, 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, for example, a weight average molecular weight of
10,000 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,
Examples include 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 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 with respect to the ferromagnetic powder.

Next, specific examples of the polishing agent include, for example, α
-Aluminum, fused alumina, chromium oxide, titanium oxide, α-
Iron oxide, silicon oxide, silicon nitride, tungsten carbide,
Molybdenum carbide, boron carbide, corundum, zinc oxide,
Cerium oxide, magnesium oxide, boron nitride, etc. may be mentioned. As an abrasive, the average particle size is 0.05 ~ 0.6 μm
Those having a thickness of 0.1 to 0.3 μm are more preferable.

Examples of the antistatic agent include conductive powders such as carbon black and graphite; cationic surfactants such as quaternary amines; acid groups such as sulfonic acid, sulfuric acid, phosphoric acid, phosphoric acid ester and carboxylic acid. Examples thereof include anionic surfactants containing; 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 method, a known method used for manufacturing a multi-layer structure type magnetic recording medium can be appropriately adopted.

For example, ferromagnetic metal powder or hexagonal plate-like powder, binder, dispersant, lubricant, abrasive, antistatic agent, etc. and a solvent are generally kneaded to prepare a high-concentration magnetic coating. Then, the high-concentration magnetic coating is diluted to prepare a magnetic coating, and then the magnetic coating is applied to the surface of the non-magnetic support.

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

In kneading and dispersing the components for forming the magnetic layer,
Various kneading dispersers can be used.

Examples of the kneading and 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.

To coat, for example, a layer containing the high magnetic permeability material of the present invention and a magnetic layer on a non-magnetic support, specifically, as shown in FIG. 1, first, as shown in FIG. The coating materials of the magnetic layers 2 and 4 are applied to the magnetic support 1 by the extrusion-type extrusion coaters 10 and 11 by the wet-on-wet method and then passed through the orientation magnet or the vertical orientation magnet 33. Then, it is introduced into the dryer 34, and hot air is blown from the nozzles arranged above and below to dry it. Next, the dried support 1 with each coating layer is combined with a calendar roll 38 to form a super calendar device 37.
To the roll, and after calendering here, take-up roll 39
Roll it up. 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 coating material 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 magnetic 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.
Although (b) and (c) are shown, the head of (c) is preferable in the present invention.

Examples of the solvent to be added to the above paint or a diluent solvent for applying this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; alcohols such as methanol, ethanol, propanol and butanol; acetic acid. Esters such as methyl, 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 , Halogenated hydrocarbons such as ethylene chloride, carbon tetrachloride, chloroform and 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 0.1 to 10 °.
It's about a minute.

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 can also be used. Furthermore, an air doctor coater,
Blade coater, air knife coater, squeeze coater,
Impregnation coater, transfer roll coater, kiss coater,
It is also possible to combine a cast coater, a spray coater, and the like.

In the multi-layer coating by the wet-on-wet method, the upper magnetic layer is coated while the layer located under the uppermost layer is in a wet state, so that 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. In addition, the wet-on-wet multi-layer coating method can reduce dropout and improve reliability.

-Surface smoothing-In the present invention, a surface smoothing treatment is then performed by calendering.

After that, 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.

In the present invention, the above temperature is usually 50 to
120 ℃, above linear pressure 50 to 400kg / cm, above C / s 20 to
It is preferable to hold at 600 m / min.

The layer thickness of the upper layer as a result of the above treatment is preferably 0.1 to 0.7 μm. When the layer thickness exceeds 0.7 μm, high frequency characteristics and signal overwrite (overwrite)
The characteristics of the magnetic recording medium are deteriorated to be the same as those of the single-layer magnetic recording medium, and the object of the present invention cannot be achieved.

[0083]

EXAMPLES Examples 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.

Upper magnetic coating A CoTi-substituted Ba-ferrite magnetic powder 100 parts (particle size = 500Å, Hc = 1100 Oe, BET; 39 m ² / g) Vinyl sulfonate metal salt-containing copolymer (MR110 manufactured by Zeon Corporation) ) 5 parts Polyurethane resin containing sulfonic acid metal salt 5 parts (Toyobo Co., Ltd., UR8700) α-alumina (average particle size 0.2 μm) 4 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 (5 parts of Coronate L) was added to prepare.

Upper magnetic coating B In the above upper magnetic coating A, 100 parts of CoTi-substituted Ba-ferrite magnetic powder was replaced with NiTi-substituted Ba-ferrite magnetic powder (coercive force Hc = 1,200 Oe, BET value: 50 m ² / g, Particle size = 400
It was prepared in the same manner as in the preparation of the upper magnetic coating material A except that Å) was used.

Non-Magnetic Powder Coating I Titanium oxide (1) (TiO ₂ , particle size: 30 nm) 100 parts Vinyl sulfonic acid salt-containing vinyl copolymer (MR110 manufactured by Zeon Corporation) 10 parts Sulfonic acid metal salt-containing polyurethane resin 10 parts (manufactured by 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 Paint II The non-magnetic paint I was prepared in the same manner as the non-magnetic paint I except that 100 parts of αFe ₂ O ₃ was used in place of 100 parts of titanium oxide (1).

Non-Magnetic Paint III Instead of titanium oxide (TiO ₂ ) of the above non-magnetic paint I, ZnO
Other than 100 parts was prepared in the same manner as the above-mentioned non-magnetic paint I.

Lower magnetic coating IV Co Coated γFe ₂ O ₃ magnetic powder 100 parts (coercive force Hc: 780 0e, BET: 50 m ² / g) 12 parts vinyl sulfonic acid metal salt-containing copolymer (manufactured by Zeon Corporation) MR110) Polyurethane containing metal sulfonate 8 parts (Toyobo Co., Ltd., UR8700) α-alumina 4 parts (average particle size 0.2 μm) Stearic acid 1 part Myristic acid 1 part Butyl stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts Examples 1 to 6 Each sample was prepared by wet-on-wet multi-layer coating of the above paint, and slits were made to a width of 8 mm.
The following evaluation tests were conducted.

Comparative Examples 1 to 5 Samples were prepared using the upper layer coating material and the lower layer coating material shown in Table 1, and the same operation as in the above-mentioned example was carried out to carry out the same evaluation test.

(Measurement Method) Square Type Using a sample vibrating magnetometer VSM, the magnetization amount when a maximum magnetic field of 10 KOe is applied is the saturation magnetization Ms, and the magnetization amount when the magnetic field is returned to 0 Oe is the residual magnetization Mr. Then, the squareness ratio SQ is determined by SQ = Mr / Ms. The direction of the magnetic field applied is the length of the tape, the width of the tape,
The squareness ratios when vertical are SQ _l , SQ _t , and SQ _p , respectively. However, SQ _p shall be corrected by 4πMs.

[0094] · C / N remodeled Sony Corp. Hi8 video camera cCDV-900, a sine wave input of 9MH _Z to the recording head, using a spectrum analyzer the reproduced output, 9MH _Z output and 8MH _Z of the noise level C / N was defined as the difference between and, and the relative value to the reference sample was used.

[0095] - signal overwriting in (overwrite characteristic) 2 MH _Z signal saturation level of the recording and, thereafter overwriting the signals 9MH _Z, using a spectrum analyzer residual output of 2 MH _Z of the reproduced signal, It was measured. It is assumed that the residual output is low and light overwrite characteristics are good.

[0096] - recording and storing the sine wave stability 9MH _Z, its initial output level is measured in advance, after being left in an atmosphere of 60 ° 80% for 7 days, re-9
Measuring the output level of the MH _Z, and obtains the difference between the initial output.

The results are shown in Table 1.

[0098]

[Table 1]

As can be seen from the results shown in Table 1, the examples of the present invention are clearly superior to the comparative examples.

[0100]

INDUSTRIAL APPLICABILITY The magnetic recording medium of the present invention has a high frequency electromagnetic conversion characteristic suitable for high density digital recording, has a good signal overwriting characteristic, and is excellent in storage stability. Have the effect.

[Brief description of drawings]

FIG. 1 is a diagram for explaining simultaneous multilayer coating for producing a magnetic recording medium of the present invention by wet-on-wet coating by an extrusion coating method.

FIG. 2 is a view of a coater head for applying the coating material of the present invention.

[Explanation of symbols]

 1 Support 10 Extrusion coater 11 Extrusion coater 32 Supply roll 33 Orientation magnet 34 Dryer 37 Super calendar device 38 Calendar roll 39 Winding roll

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Ando Konica Stock Company, 1 Sakura-cho, Hino-shi, Tokyo In-house

Claims (2)

[Claims] 1. A magnetic device comprising a non-magnetic support having at least one lower layer having non-magnetic particles dispersed in a binder, and a magnetic layer having ferromagnetic powder dispersed in the binder thereon. In the recording medium, the ferromagnetic powder in the upper layer is hexagonal plate-shaped magnetic powder, and the upper layer film thickness is 0.1 to 0.7 μm,
Moreover, the squareness ratio of the magnetization curve obtained when an external magnetic field is applied in the longitudinal direction, width direction, and vertical direction of the tape is SQ, respectively.
A magnetic recording medium characterized in that the following relationships exist when _l , SQ _t , and SQ _p . (SQ _l ² + SQ _p ² ) / SQ _t ² > 3.0 2. The magnetic recording medium according to claim 1, wherein the lower layer and the magnetic layer are provided by a wet-on-wet coating method.