JPH08180381A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To obtain a magnetic recording medium having satisfactory surface smoothness and excellent in output (C/N) characteristics and overwriting characteristics. CONSTITUTION: In this magnetic recording medium 1 with a nonmagnetic substrate 2 and plural magnetic layers 3 disposed on the substrate 2 and including a 1st magnetic layer 3a as the top layer and a 2nd magnetic layer 3b adjacent to the 1st magnetic layer 3a, the 2nd magnetic layer 3b contains soft magnetic oxide powder adjusted to 200-300Å crystallite size.

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 excellent in output (C / N) characteristics and overwrite characteristics.

[0002]

2. Description of the Related Art Conventionally, magnetic recording media have been widely used in the form of tapes, disks, drums or sheets. Such a magnetic recording medium is usually manufactured by coating a nonmagnetic support such as a polyester film with a magnetic coating material containing magnetic powder and a binder as main components. In recent years, in particular, there has been a demand for miniaturization and high density recording of magnetic recording media. In order to meet such requirements, for example, the coercive force Hc of the magnetic layer and the residual magnetic flux density Br are
It has been proposed to improve the thickness of the magnetic layer and to reduce the thickness of the magnetic layer.
A so-called double coating method has been proposed in which a second layer is provided between a magnetic layer and a support, and the second layer and the magnetic layer are formed by multilayer coating. However, the above proposal has a problem that the overwrite characteristic is deteriorated. Further, in the above proposal, it is necessary to make the flow characteristics of the coating material forming the magnetic layer and the coating material forming the second layer uniform, but they are not yet sufficiently aligned, and the flow characteristics of the magnetic layer and There is a problem that the electromagnetic conversion characteristics are deteriorated due to the disturbance of the interface with the second layer and the deterioration of the surface smoothness of the magnetic layer.

Therefore, an object of the present invention is to provide a magnetic recording medium which has good surface smoothness and excellent output (C / N) characteristics and overwrite characteristics.

[0004]

As a result of intensive studies to solve the above problems, the present inventors have found that a specific crystallite size is provided adjacent to a magnetic layer provided as the uppermost layer of a magnetic recording medium. It was found that a magnetic recording medium provided with a magnetic layer containing a soft magnetic powder having the above can achieve the above object.

The present invention has been made based on the above findings, and has a non-magnetic support and a plurality of magnetic layers provided on the non-magnetic support, and the plurality of magnetic layers are the uppermost layers. In a magnetic recording medium including a first magnetic layer provided as a layer and a second magnetic layer provided adjacent to the first magnetic layer, the second magnetic layer is made of an oxide soft magnetic material. Powder, and the crystallite size of the oxide soft magnetic powder is 200 to
The present invention provides a magnetic recording medium characterized by being 300Å.

The magnetic recording medium of the present invention will be described in detail below. First, with reference to FIG. 1, a preferred configuration of the magnetic recording medium of the present invention will be illustrated and described.

The magnetic recording medium 1 of the present invention shown in FIG. 1 has a non-magnetic support 2 and a plurality of magnetic layers 3 provided on the non-magnetic support 2, and the plurality of magnetic layers 3 are provided. , The first magnetic layer 3a provided as the uppermost layer, and the first magnetic layer 3a
And a second magnetic layer 3b provided adjacent to. A back coat layer 4 is provided on the back surface of the non-magnetic support 2 as needed.

In addition to the non-magnetic support, the first magnetic layer, the second magnetic layer and the back coat layer, the magnetic recording medium of the present invention further comprises a non-magnetic support and a second magnetic layer. Other layers such as a primer layer provided between the magnetic layer or the back coat layer and a third magnetic layer provided for recording a servo signal corresponding to a hard system using a long wavelength signal. It may be provided.

As the non-magnetic support 1 used in the magnetic recording medium of the present invention, any known material can be used without any particular limitation. Specifically, it is made of a polymer resin and is flexible. Films and discs; Cu, Al,
Films, disks, cards and the like made of non-magnetic metal such as Zn, glass, ceramics such as porcelain and ceramics can be used.

Examples of the polymer resin forming the flexible film or the disc include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate, polyethylene bisphenoxycarboxylate, polyethylene and the like. , Polyolefins such as polypropylene, cellulose acetate butyrate,
Cellulose derivatives such as cellulose acetate propionate, polyvinyl resins such as polyvinyl chloride and polyvinylidene chloride, or polyamides, polyimides, polycarbonates, polysulfones, polyether ether ketones, polyurethanes, etc. may be used alone or Two or more kinds can be used in combination.

Further, in the magnetic recording medium of the present invention, the back coat layer, which is optionally provided on the back surface of the non-magnetic support, can be formed by using a known back coat paint without particular limitation.

In the magnetic recording medium of the present invention, the first magnetic layer provided on the non-magnetic support is an uppermost layer of the magnetic recording medium, that is, a layer provided on the surface of the magnetic recording medium. Yes, it is formed by applying the first magnetic paint on the second magnetic layer described later. As the above-mentioned first magnetic paint, a paint containing magnetic powder, a binder and a solvent as main components is preferably used.

Examples of the magnetic powder include a ferromagnetic metal powder mainly composed of iron or a hexagonal ferrite powder. The coercive force of the ferromagnetic metal powder is 1600 to 250.
It is preferably 0 Oe, more preferably 1700 to 2400 Oe. The coercive force of the hexagonal ferrite powder is preferably 1300 to 2300 Oe. When the coercive force of each of the ferromagnetic metal powder and the hexagonal ferrite is less than the above lower limit, demagnetization is likely to occur, so that short-wave RF output is lowered, and when the above upper limit is exceeded, the head magnetic field is increased. Is insufficient, the writing ability is insufficient, and the overwrite characteristic is further deteriorated. Therefore, it is preferable to set it within the above range. The saturation magnetization of the ferromagnetic metal powder is preferably 100 to 180 emu / g, more preferably 110 to 160 emu / g. The saturation magnetization of the hexagonal ferrite powder is preferably 30 to 70 emu / g, and is preferably 45 to 70.
More preferably, it is emu / g. When the saturation magnetization of the ferromagnetic metal powder and the hexagonal ferrite powder is less than the lower limit, respectively, the filling rate of the magnetic powder is lowered, the output is reduced, and when the upper limit is exceeded. ,
It is necessary to reduce the binder, the interaction between the magnetic powders becomes large, and as a result, the magnetic powders are in an agglomerated state and it becomes difficult to obtain a desired output. Is preferred. Therefore, the coercive force of the first magnetic layer containing the ferromagnetic metal powder is preferably 1800 to
2400 Oe, more preferably 1800-2300 Oe
And the coercive force of the first magnetic layer containing the hexagonal ferrite powder is preferably 1600 to 2200 Oe.
Is. The saturation magnetic flux density of the first magnetic layer containing the ferromagnetic metal powder is preferably 3000 to 4500.
Gauss, more preferably 3200 to 4000 Gauss, and the saturation magnetic flux density of the first magnetic layer containing the hexagonal ferrite powder is preferably 1500 to 2500 Gauss, more preferably 1600 to 2500 Gauss.

When the coercive force and the saturation magnetic flux density of the first magnetic layer containing the ferromagnetic metal powder or the hexagonal ferrite powder are within the above preferable ranges, the first magnetic layer described above is obtained. It is preferable that the first magnetic layer has a thickness of 0.05 to 1.0 μm and is applied and formed when the second magnetic layer described later is wet.

The ferromagnetic metal powder has a metal content of 7
0 wt% or more, and 80 wt% or more of the metal content is Fe
The ferromagnetic metal powder which is Specific examples of the ferromagnetic metal powder include, for example, Fe-Co, Fe-Ni,
Fe-Al, Fe-Ni-Al, Fe-Co-Ni, F
Examples thereof include e-Ni-Al-Zn and Fe-Al-Si. The shape of the ferromagnetic metal powder is needle-like or spindle-like, and its major axis length is preferably 0.05 to 0.25 μm.
More preferably, it is 0.05 to 0.2 μm, the preferable acicular ratio is 3 to 20, and the preferable crystallite size is 130.
It is desirable that it is ~ 250Å.

As the hexagonal ferrite powder, fine tabular barium ferrite and strontium ferrite, and some of their Fe atoms are Ti and C.
Examples thereof include magnetic powders substituted with atoms such as o, Ni, Zn and V. The hexagonal ferrite powder preferably has a plate diameter of 0.02 to 0.09 μm and a plate ratio of 2 to 7.

The magnetic powder may contain, if necessary,
A rare earth element or a transition metal element can be contained. In the present invention, the magnetic powder may be surface-treated in order to improve the dispersibility of the magnetic powder. The above surface treatment is "Characterization of Powder
Surfaces "; can be carried out by a method similar to the method described in Academic Press, for example, a method of coating the surface of the above magnetic powder with an inorganic oxide.
At this time, the inorganic oxides that can be used include Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , Sn.
O ₂ , Sb ₂ O ₃ , ZnO and the like can be mentioned, and when used, they can be used alone or in combination of two or more. The surface treatment may be performed by an organic treatment such as a silane coupling treatment, a titanium coupling treatment and an alumina coupling treatment other than the above method.

The binder may be a thermoplastic resin, a thermosetting resin, a reactive resin, or the like, which may be used alone or as a mixture.
Specific examples of the binder include vinyl chloride resin,
Examples thereof include polyester, polyurethane, nitrocellulose, and epoxy resin, and in addition, JP-A-57-16
No. 2128, page 2, upper right column, line 19 to page 2, lower right column 1,
Resins and the like described in line 9 and the like can be mentioned. further,
The binder may contain a polar group for improving dispersibility and the like. The amount of the binder used is the magnetic powder 10
It is preferably about 5 to 100 parts by weight, more preferably 5 to 70 parts by weight, based on 0 parts by weight.

Examples of the solvent include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, chlorinated hydrocarbon solvents, and the like. The solvents described in JP-A-57-162128, page 3, lower right column, line 17 to page 4, lower left column, line 10 and the like can be used. The amount of the solvent used is preferably 80 to 500 parts by weight, more preferably 100 to 350 parts by weight, based on 100 parts by weight of the magnetic powder.

The above-mentioned first magnetic coating material is usually used as a magnetic recording medium such as a dispersant, a lubricant, an abrasive, an antistatic agent, a rust preventive, a fungicide and a curing agent. Additives can be added as needed. Specific examples of the additive include page 2, upper left column, line 6 to page 2, upper right column, line 10 and page 3, upper left column, line 6 to page 3, upper right column 18 of JP-A-57-162128. There may be mentioned various additives described in the publications.

To prepare the above first magnetic coating material, for example, the above magnetic powder and the above binder together with a part of the solvent are put into a Nauter mixer or the like and premixed to obtain a mixture, and the obtained mixture is obtained. Are kneaded with a continuous pressure kneader, etc., then diluted with a part of the solvent and subjected to a dispersion treatment using a sand mill, etc., then additives such as a lubricant are mixed and filtered, and polyisocyanate and the like are further added. Examples thereof include a method of mixing a curing agent and the remaining solvent.

The thickness of the first magnetic layer is 0.05 to
It is preferably 1.0 μm, and 0.05 to 0.8 μm
Is more preferable. When it is less than 0.05 μm,
It may be difficult to apply evenly, and durability may decrease.
If it exceeds 1.0 μm, the thickness loss becomes large and the overwrite characteristics may be significantly deteriorated. Therefore, it is preferable that the thickness be within the above range.

In the magnetic recording medium of the present invention, the second magnetic layer provided adjacent to the first magnetic layer is a layer containing oxide soft magnetic powder and is provided on the non-magnetic support. This is a layer formed by applying a second magnetic paint. As the second magnetic paint, a paint containing oxide soft magnetic powder, a binder and a solvent as main components can be preferably used.

The above oxide soft magnetic powder is particularly magnetic.
Also used for so-called light electrical equipment such as heads and electronic circuits
Is preferred, for example, Satoshi Chikazumi, "Physics of Ferromagnetic Materials"
(Bottom) Magnetic properties and applications "(Sokabo, 1984) 368
To the soft magnetic oxide powders described on page 376.
Be done. Specific examples of the above oxide soft magnetic powder include spines.
Preferred is a ferrite ferrite powder, the spinel type
As the ferrite powder, MnFe₂O_Four, Fe
₃O _Four, CoFe₂O_Four, NiFe₂O_Four, MgFe₂
O_Four, Li_0.5Fe_2.5O_FourAnd Mn-Zn based ferrai
G, Ni-Zn ferrite, Ni-Cu ferrite
G, Cu-Zn ferrite, Mg-Zn ferrite
And Li-Zn based fate.
Among these, Mn-Zn ferrite and Ni-Z
N-type ferrite is preferable. When using it,
It is possible to use one type of
Can also be used together.

The coercive force of the above oxide soft magnetic powder is usually 0.1 to 150 Oe, and the saturation magnetization is usually 30 to 9 Oe.
It is 0 emu / g. The particle size of the soft magnetic powder is 1 m.
μm to 1,000 mμ is preferable, and 1 mμ to 50
It is more preferably 0 mμ.

Thus, in the magnetic recording medium of the present invention, the crystallite size of the above oxide soft magnetic powder contained in the above second magnetic layer is 200 to 300Å, preferably 220 to 300.
It is Å. If the crystallite size is less than 200Å, it is practically difficult to obtain, and if it exceeds 300Å, the particle size tends to be large, and the smoothness of the interface between the first magnetic layer and the second magnetic layer is likely to increase. Is deteriorated, and thus the surface smoothness of the first magnetic layer is deteriorated, which is not preferable.

The above oxide soft magnetic powder having a crystallite size in the above range is based on the basics of magnetic engineering II (Keizo Ohta, Kyoritsu Shuppan, 1986) P404 to 407 and Magnetic Handbook (Shinnobu Chikaku et al., Asakura Shoten). , 1990) Within the composition range based on the description of P601 to 706, Mn-Zn-Fe-O or Ni-Zn
By changing the composition of —Fe—O, it can be obtained by a glass crystallization method, a coprecipitation firing method, a calcination method, a hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method, or the like.

The binder and the solvent used in the second magnetic coating material may be the same as the binder and the solvent used in the first magnetic coating material. The blending ratio of the binder in the second magnetic coating material is 5 to 200 parts by weight with respect to 100 parts by weight of the total amount of the soft magnetic powder and a non-magnetic powder described later that is added as necessary. Is preferable, and 5 to 100
More preferably parts by weight. The blending ratio of the solvent in the second magnetic coating material is preferably 80 to 500 parts by weight, based on 100 parts by weight of the soft magnetic powder.
˜350 parts by weight is more preferred.

The second magnetic paint contains a dispersant,
Lubricants, abrasives, antistatic agents, rust preventives, antifungal agents, hardeners and other additives usually used in magnetic recording media,
It can be added if necessary. Specific examples of the additive include page 2, upper left column, line 6 to page 2, upper right column, line 10 and page 3, upper left column, line 6 to page 3, upper right column 18 of JP-A-57-162128. There may be mentioned various additives described in the publications.

Further, a non-magnetic powder can be added to the above-mentioned second magnetic paint. The non-magnetic powder is not particularly limited as long as it is non-magnetic, but carbon black, graphite, titanium oxide, barium sulfate, zinc sulfide, magnesium carbonate, calcium carbonate, zinc oxide,
Calcium oxide, magnesium oxide, tungsten disulfide, molybdenum disulfide, boron nitride, tin dioxide, silicon dioxide, non-magnetic chromium oxide, alumina, silicon carbide, cerium oxide, corundum, artificial diamond, non-magnetic iron oxide, garnet , Garnet, silica stone, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, diatomaceous earth, dolomite, resinous powder, and the like. Among them, carbon black, titanium oxide, barium sulfate, calcium carbonate, alumina. Non-magnetic iron oxide and the like are preferably used. Further, the nonmagnetic powder may be subjected to the same surface treatment as that of the magnetic powder used for the first magnetic layer in order to improve the dispersibility of the nonmagnetic powder. .

The thickness of the second magnetic layer is 0.
The thickness is preferably from 2 to 5 μm, more preferably from 0.5 to 4 μm, most preferably from 0.5 to 2.5 μm. If it is less than 0.2 μm, the strength of the obtained magnetic recording medium becomes weak, and if it exceeds 5 μm, the overwrite property is deteriorated. Therefore, it is preferably within the above range.

The magnetic recording medium of the present invention is suitable as a magnetic tape such as an 8 mm video tape or a DAT tape, but can also be applied as another magnetic recording medium such as a floppy disk.

Next, the outline of the method for producing the magnetic recording medium of the present invention will be described. First, the above-mentioned first magnetic paint and the above-mentioned second magnetic paint are wet-coated on the above-mentioned non-magnetic support so that the dry thicknesses of the first magnetic layer and the second magnetic layer become the above-mentioned thicknesses, respectively. Simultaneous multilayer coating is performed by an on-wet method to form coating films for the first and second magnetic layers. That is, it is preferable that the first magnetic layer is applied and formed when the second magnetic layer is wet. Next, the coating film is subjected to a magnetic field orientation treatment, followed by a drying treatment and winding. After that, calendering is performed if necessary, and then a back coat layer is further formed if necessary. Then, if necessary, for example, when a magnetic tape is to be obtained, it is aged at 40 to 70 ° C. for 6 to 72 hours and slit to a desired width.

The above-mentioned simultaneous multilayer coating method is disclosed in JP-A-5-73.
No. 42, line 31 to column 43, line 31 and the like of Japanese Patent No. 883 publication, the first magnetic layer is formed before the second magnetic coating material forming the second magnetic layer is dried. A method of applying the above-mentioned first magnetic coating material to be formed, wherein the interface between the above-mentioned first magnetic layer and the above-mentioned second magnetic layer is smoothed and the surface of the above-mentioned first magnetic layer is formed. Since the magnetic recording medium has good properties, it is possible to obtain a magnetic recording medium with less dropouts, high density recording, and excellent durability of the coating film (first magnetic layer and second magnetic layer).

The magnetic field orientation treatment is performed before the first and second magnetic paints are dried. For example, when the magnetic recording medium of the present invention is a magnetic tape, the first magnetic paint is used. 500 Oe or more in the direction parallel to the coated surface of
Preferably, it can be carried out by a method of applying a magnetic field of about 1000 to 10000 Oe, a method of passing a magnetic field of 1000 to 10000 Oe while the first and second magnetic paints are in a wet state.

The above drying treatment is carried out, for example, at 30 to 120 ° C.
The heating can be performed by supplying the gas heated to the above temperature. At this time, the drying degree of the coating film can be controlled by controlling the temperature of the gas and the supply amount thereof.

Further, the calendering treatment can be carried out by a super calendering method in which two rolls such as a metal roll and a cotton roll or a synthetic resin roll, a metal roll and a metal roll are passed. Also,
The conditions for the calendar treatment are 60 to 140 ° C. and 100
It can be up to 500 kg / cm.

The backcoat layer, which is provided if necessary, is provided on the back surface of the non-magnetic support (the surface on which the first and second magnetic layers are not provided), and is usually It is obtained by applying the backcoat paint used for forming the backcoat layer on the non-magnetic support.

When manufacturing the magnetic recording medium of the present invention, finishing steps such as polishing and cleaning of the surface of the magnetic layer may be carried out, if necessary. The first and second magnetic paints can also be applied by a generally known sequential multi-layer coating method.

[0040]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1 A first magnetic paint A having the following composition
And a second magnetic coating composition (a) having the following composition, and a back coating composition having the following composition as the back coating composition, to produce a magnetic tape according to the following [Method for producing magnetic recording medium]. A magnetic tape as a magnetic recording medium was obtained in which a first magnetic layer was formed by the first magnetic coating material A and a second magnetic layer was formed by the second magnetic coating material (a). When the coercive force and the saturation magnetic flux density of the first magnetic layer formed using the first magnetic coating material A were measured according to the [Measuring method] described below, the first magnetic coating material A was formed. The coercive force of the first magnetic layer was 1890 Oe, and the saturation magnetic flux density was 3570 gauss. The crystallite size was measured according to the [Measurement method] described later.

First magnetic coating material A : Needle-shaped ferromagnetic metal powder mainly composed of iron 100 parts by weight Fe: Al: Ba: Si: Ni: Co (weight ratio) = 88: 2: 1: 1: 3 : 5 coercive force; 1840 Oe, saturation magnetization; 134 emu / g average major axis length; 0.12 μm, specific surface area; 58 m ² / g crystallite size; 150Å, axial ratio; 10 ・ alumina (average particle size 0.3 μm) 8 Parts by weight carbon black (average primary particle size 20 nm) 2 parts by weight "MR-110" 10 parts by weight [trade name, manufactured by Nippon Zeon Co., Ltd., sulfonic acid group-containing vinyl chloride polymer]-"UR-8700" 7 parts by weight [trade name, manufactured by Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin] 2-ethylhexyl stearate 2 parts by weight palmitic acid 2 parts by weight "Coronate L" 3 parts by weight [trade name, Japan Poly Urethane Industry Co., Ltd., polyisocyanate compound] -Methyl ethyl ketone 120 parts by weight-Toluene 80 parts by weight-Cyclohexanone 40 parts by weight

Second magnetic paint (a) (parts by weight) Mn-Zn ferrite 100 (crystallite size 280Å, coercive force 61 Oe, saturation magnetization 62 emu / g, synthesized by hydrothermal synthesis) carbon black (Average primary particle diameter 20 nm) 2 “MR110” 10 [trade name, manufactured by Nippon Zeon Co., Ltd., vinyl chloride polymer containing sulfonic acid group] ・ “UR8700” 7 [trade name, manufactured by Toyobo Co., Ltd., Sulfonic acid group-containing polyurethane resin] ・ 2-Ethylhexyl stearate 2 ・ Palmitic acid 1 ・ "Coronate L" 3 (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd., polyisocyanate compound) ・ Methyl ethyl ketone 60 ・ Toluene 40 ・ Cyclohexanone 20

(Blending of back coat paint) Carbon black (average primary particle size 0.028 μm) 32 parts by weight Carbon black (average primary particle size 0.062 μm) 8 parts by weight “Nipporan 2301” [trade name, Nippon Polyurethane Industry ( Polyurethane manufactured by Co., Ltd.] 20 parts by weight nitrocellulose (viscosity display made by Hercules Powder Co. of 1/2 second) 20 parts by weight polyisocyanate (trade name “D-250N” manufactured by Takeda Pharmaceutical Co., Ltd.) 4 parts by weight Copper phthalocyanine 5 parts by weight Stearic acid 1 part by weight Methyl ethyl ketone 120 parts by weight Toluene 120 parts by weight Cyclohexanone 120 parts by weight

[Production of Magnetic Recording Medium] The above-mentioned first film was formed on the surface of a polyethylene terephthalate film having a thickness of 7 μm.
And the second magnetic coating material were applied so that the dry thickness was the value shown in [Table 1] to form coating films for the first and second magnetic layers. Then, while the coating film was in a wet state, the coating film was passed through a solenoid of 5000 Oe for magnetic field orientation treatment, dried at 80 ° C., and then wound. Then, 85 ℃, 3
After calendering under the conditions of 50 kg / cm to form the first and second magnetic layers, a back coat paint is applied on the back surface of the non-magnetic support so that the dry thickness becomes 0.5 μm. After performing a drying treatment at ℃, it was wound up.
Then, after aging treatment at 50 ° C for 16 hours, it was cut into a tape of 8 mm width, magnetic tape was obtained, and the obtained magnetic tape was loaded in an 8 mm cassette case and a recording time of 8 mm video cassette for 120 minutes. Was produced.

The magnetic tape as a magnetic recording medium thus obtained was evaluated for surface roughness, C / N characteristics and overwrite characteristics as follows. The results are shown in [Table 1].

[Measurement Method] ◎ Crystallite size It was determined from the half-value width of the analysis line peak of the (311) plane by a usual method from the X-ray analysis chart of the oxide soft magnetic powder. ◎ Coercive force and saturation magnetic flux density For the first magnetic layer coated on the non-magnetic support and the second magnetic layer, an adhesive tape is used to remove the non-magnetic support and the second magnetic layer from the first magnetic layer. Only one magnetic layer was peeled off, the first magnetic layer was punched into a predetermined size and shape, and a coercive force and a saturation magnetic flux density were measured with an applied magnetic field of 10 kOe using a vibrating magnetometer. ◎ Surface Roughness of Magnetic Recording Medium Surface Roughness Ra The magnetic recording medium obtained was manufactured by Tokyo Seimitsu Co., Ltd.
Using a surface roughness shape measuring instrument, trade name "Surfcom 553A", measurement was performed under the conditions of a needle radius of 2 µm, a load of 30 mg, a magnification of 200,000 and a cutoff of 0.08 mm. still,
Ra (center line average roughness) is obtained by extracting a portion of the measurement length L from the roughness curve in the direction of the center line, the center line of the extracted portion as the X axis, and the vertical magnification direction as the Y axis. Y
= F (x), the value obtained by the following equation is expressed in [nm].

[0048]

[Equation 1]

C / N characteristics (evaluation of 8 mm) Using a commercially available 8 mm video deck which is a modified Hi8 deck, a single wave of 9 MHz was recorded, and the reproduced output (C) was observed with a spectrum analyzer to measure the noise level. 8 MH
C / N was expressed as the z noise level (N). ◎ Overwrite characteristics Using an 8mm video deck that is a modification of a commercially available Hi8 deck, a signal of 2MHz is recorded at a saturation level, and then 9
The residual output level of the 2 MHz signal when the MHz signal was overwritten and recorded was measured. Also, the smaller the residual output level, the better the overwrite characteristic.

Example 2 A magnetic tape as a magnetic recording medium was manufactured in the same manner as in Example 1 except that the following first magnetic paint B was used as the first magnetic paint. The same test was performed. The results are shown in [Table 1]. The first magnetic paint B is used to form the first magnetic paint.
When the coercive force and the saturation magnetic flux density of the magnetic layer were measured in the same manner as in Example 1, the coercive force of the first magnetic layer formed using the first magnetic coating material B was 1820 Oe, and the saturation magnetic flux density was , 1910 Gauss.

First magnetic paint B. Hexagonal ferrite powder 100 parts by weight (Hexagonal plate-like Co-Ti substituted barium ferrite powder) Coercive force; 1670 Oe, Saturation magnetization; 56 emu / g Average plate diameter; 0.06 μm, plate State ratio; 4 ・ Alumina (average particle size 0.2 µm) 5 parts by weight ・ Carbon black (average primary particle size 20 nm) 2 parts by weight ・ "MR-110" 6 parts by weight [trade name, manufactured by Nippon Zeon Co., Ltd., Sulfonic acid group-containing vinyl chloride polymer] "UR-8700" 4 parts by weight [trade name, Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin] 2-Ethylhexyl stearate 1.5 parts by weight Palmitin Acid 1.5 parts by weight "Coronate L" 3 parts by weight (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd., polyisocyanate compound) -Methyl ethyl ketone 60 parts by weight Parts Toluene 60 parts Cyclohexanone 20 parts by weight

[Comparative Example 1] A magnetic tape as a magnetic recording medium was manufactured in the same manner as in Example 1 except that the following second magnetic coating material (b) was used as the second magnetic coating material.
The same test as in Example 1 was performed. The results are shown in [Table 1]. Second magnetic paint (b) As Mn-Zn ferrite, a crystallite size of 325Å,
Same as the above second magnetic paint (a) except that the one synthesized by hydrothermal synthesis with a coercive force of 76 Oe and a saturation magnetization of 59 emu / g was used.

[Comparative Example 2] A magnetic tape as a magnetic recording medium was manufactured in the same manner as in Example 1 except that the following second magnetic coating material (c) was used as the second magnetic coating material.
The same test as in Example 1 was performed. The results are shown in [Table 1]. Second magnetic paint (C) As Mn-Zn ferrite, crystallite size 320Å,
Same as the above second magnetic coating material (a) except that a Mn-Zn ferrite synthesized by a coprecipitation firing method with a coercive force of 25 Oe and a saturation magnetization of 78 emu / g was obtained by crushing with a ball mill.

Comparative Example 3 A magnetic tape was prepared in the same manner as in Example 1 except that the following non-magnetic paint was used in place of the above-mentioned second magnetic paint, and the obtained magnetic tape was used. The test was conducted and evaluated in the same manner as in Example 1. The results are shown in [Table 1]. Non-magnetic paint (d) Instead of Mn-Zn ferrite, TiO ₂ (manufactured by Ishihara Sangyo, trade name "TTO-55B", specific surface area 37 m ² /
Same as the above second magnetic paint (a) except that g) was used.

[Comparative Example 4] A magnetic tape was prepared in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 3 except that the second magnetic layer was not formed.
3 and Comparative Examples 1 to 3 were tested and evaluated. The results are shown in [Table 1].

[Comparative Example 5] A magnetic tape as a magnetic recording medium was manufactured in the same manner as in Example 2 except that the above-mentioned second magnetic coating material (b) was used as the second magnetic coating material.
The same test as in Example 1 was performed. The results are shown in [Table 1].

[0057]

[Table 1]

As is clear from the results shown in [Table 1],
The magnetic recording medium of the present invention has excellent overwrite characteristics because the second magnetic layer contains the soft magnetic powder, and since the soft magnetic powder is in the above crystallite size range, the surface roughness It can be seen that the hardness and the C / N characteristics are excellent.

[0059]

The magnetic recording medium of the present invention has good surface smoothness and excellent output (C / N) characteristics and overwrite characteristics.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a magnetic recording medium of the present invention.

Claims (6)

[Claims] 1. A non-magnetic support, and a plurality of magnetic layers provided on the non-magnetic support, wherein the plurality of magnetic layers include a first magnetic layer provided as an uppermost layer, and A magnetic recording medium including a second magnetic layer provided adjacent to the first magnetic layer, wherein the second magnetic layer contains an oxide soft magnetic powder, Powder crystallite size is 200-30
A magnetic recording medium characterized by being 0Å. 2. The first magnetic layer contains a ferromagnetic metal powder and has a coercive force of 1800 to 8000.
2400 Oe and saturation magnetic flux density of 3000 to 450
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is 0 gauss. 3. The first magnetic layer contains hexagonal ferrite powder, and the coercive force of the first magnetic layer is 1 or less.
It is 600-2200 Oe, and the saturation magnetic flux density is 1500.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a density of 2,500 Gauss. 4. The thickness of the first magnetic layer is 0.
4. The magnetic recording medium according to claim 2, wherein the first magnetic layer has a thickness of 05 to 1.0 [mu] m, and the first magnetic layer is applied and formed when the second magnetic layer is wet. 5. The magnetic recording medium according to claim 1, wherein the soft oxide magnetic powder is spinel ferrite powder. 6. The spinel-type ferrite powder is Mn.
The magnetic recording medium according to claim 5, wherein the magnetic recording medium is -Zn ferrite or Ni-Zn ferrite powder.