JPH0817044A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium capable of high density recording and having superior output characteristics over the region from a low frequency band to a high frequency band. CONSTITUTION:This magnetic recording medium consists essentially of a magnetic substrate 1, a nonmagnetic layer 2 formed on the substrate 1 and a magnetic layer 3 formed on the nonmagnetic layer 2. The coercive force Hc of the magnetic substrate 1 is 400-1,500Oe, the coercive force Hc' of the magnetic layer 3 is 700-2,500Oe and the ratio of Hc' to Hc (Hc'/Hc) is >=1.5.

Description

Detailed Description of the Invention

[0001]

The present invention enables high density recording,
In particular, the present invention relates to a magnetic recording medium having excellent output characteristics from a low frequency band to a high frequency band.

[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 of magnetic recording media and high density recording, and in order to meet such demands, for example, an attempt to improve coercive force or saturation magnetization or a magnetic layer Proposals have been made to reduce the thickness. In addition to the above requirements, there is a strong demand for magnetic recording media having excellent output characteristics, particularly in the low frequency band to the high frequency band, in order to meet the demands for high quality magnetic recording media. Therefore,
An object of the present invention is to provide a magnetic recording medium having excellent output characteristics, particularly in the low frequency band to the high frequency band.

[0003]

As a result of intensive studies, the present inventors have used a magnetic support instead of the conventionally used non-magnetic support, and have a coercive force Hc of the magnetic support of the magnetic layer. Is smaller than the coercive force Hc 'of
It has been found that a magnetic recording medium in which / Hc) is in a specific range can achieve the above object.

The present invention has been made based on the above findings, and comprises a magnetic support, at least a nonmagnetic layer provided on the magnetic support, and a magnetic layer provided on the nonmagnetic layer. In a magnetic recording medium, the ratio of the coercive force Hc of the magnetic support and the coercive force Hc 'of the magnetic layer (Hc' / H
c) is 1.5 or more, and the coercive force H of the magnetic support is
c is 400 to 1500 Oe, the coercive force H of the magnetic layer is
c ′ is 700 to 2500 Oe, and a magnetic recording medium is provided.

The magnetic recording medium of the present invention will be described in detail below. As shown in FIG. 1, the magnetic recording medium according to the present invention includes a magnetic support 1, a non-magnetic layer 2 provided on the magnetic support 1, and a magnetic layer 3 provided on the non-magnetic layer 2. And a back coat layer 4 is provided on the back surface of the magnetic support 1 as required.

The magnetic support 1 comprises at least a magnetic portion A (see FIGS. 2a to 2e) consisting of a matrix component made of a thermoplastic resin and a filler component made of magnetic powder.

Examples of the thermoplastic resin include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate and polyethylene bisphenoxycarboxylate, polyolefins such as polyethylene and polypropylene, and cellulose acetate butyrate. Cellulose derivatives such as cellulose acetate propionate, vinyl-based resins such as polyvinyl chloride and polyvinylidene chloride, or polyamides, polyimides, polycarbonates, polysulfones, polyether / etherketones, polyurethanes and the like are used. These resin components may be used alone or in combination.

As the magnetic powder, ferromagnetic powder such as metal magnetic powder or oxide-based magnetic powder can be used. Specific examples of the above oxide-based magnetic powder include the following. Iron oxide magnetic powder such as γ-iron oxide and magnetite; Cr, Mn,
Ferromagnetic powder containing a metal such as Co or Ni added thereto; chromium dioxide; a metal such as Na, K, Fe or Mn added to the chromium dioxide;
Ferromagnetic powder to which a non-metal element such as P or an oxide thereof is added; micro tabular barium ferrite; part of Fe atoms of the barium ferrite is Ti, Co, Zn, V
Ferromagnetic powder substituted with atoms such as. In addition, specific examples of the magnetic metal powder include Fe-Co, Fe-Ni, and Fe-A.
1, Fe-Ni-Al, Co-Ni, Fe-Co-N
i, Fe-Ni-Al-Zn, Fe-Al-Si, etc. are mentioned.

In the present invention, the magnetic powder may be subjected to surface treatment in order to improve the dispersibility of the magnetic powder. The above surface treatment is described in "Characterization o
f 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 , and Zr.
Examples thereof include O ₂ , SnO ₂ , Sb ₂ O ₃ , and ZnO, which may 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 magnetic support 1 may be composed of a single layer having only the magnetic portion A as shown in FIG. 2a, or as shown in FIGS. 2b to 2e, the magnetic portion A and the non-magnetic portion B may be multi-layered. It may be a structure. That is, the magnetic support 1 can have the following configurations a to e. a. As shown in FIG. 2 a, a structure consisting of a single layer of magnetic portion A only. b. As shown in FIG. 2B, the nonmagnetic portion B is provided on the surface of the magnetic portion A (the surface located on the magnetic layer 3 side in the magnetic recording medium). c. As shown in FIG. 2c, the magnetic part A is provided on the surface of the non-magnetic part B. d. As shown in FIG. 2D, a non-magnetic portion B is provided on each of the front surface and the back surface of the magnetic portion A. e. As shown in FIG. 2e, the nonmagnetic portion B is provided with magnetic portions A on the front surface and the back surface, respectively. Here, the preferable thickness of the entire magnetic support having the structure shown in FIGS. 2A to 2E is 1 to 300 μm. Also, FIGS.
The ratio of the thickness of the magnetic portion A to the thickness of the non-magnetic portion B in the magnetic support having the configuration shown in is 1:99 to 9
It is desirable that the ratio is 9: 1, preferably 2:98 to 98: 2, and more preferably 5:95 to 95: 5.

The material for forming the non-magnetic portion B is not particularly limited as long as it is a non-magnetic material, but the thermoplastic resin used as the matrix component of the magnetic portion A can be preferably used. Although the non-magnetic portion B can be formed only by itself, in order to control the surface property and running property of the outer surface of the non-magnetic portion B to be a predetermined value, the material for forming the non-magnetic portion B is It is preferable to use materials to which various fillers are added. Examples of the filler used in this case include the non-magnetic powder described below used for forming the non-magnetic layer, and the particle size thereof is preferably 0.8 μm or less, more preferably 0.0
2 to 0.2 μm, and its content (blending amount)
Is preferably 5% by weight or less in the non-magnetic portion, and more preferably 0.01 to 2% by weight.

The composition of the thermoplastic resin and the magnetic powder in the magnetic portion A can be appropriately changed according to the desired coercive force, saturation magnetization, etc., but in the magnetic support having the structure shown in FIGS. Is 0.1 to 1000 parts by weight of magnetic powder, preferably 0.1 to 100 parts by weight of the thermoplastic resin.
2 to 100 parts by weight, more preferably 0.3 to 80 parts by weight is desirable.

As another structure of the magnetic support, a non-magnetic film may be coated with a magnetic paint as shown in FIG. 2f. In this case, the non-magnetic portion is the non-magnetic film body B'and the magnetic portion is the magnetic film body A'formed by the magnetic paint containing the magnetic powder. Figure 2f
In the constitution of the film body A ′ shown in FIG.
10 to 1500 parts by weight of magnetic powder with respect to 00 parts by weight,
Preferably 200 to 1200 parts by weight, more preferably 5
It is desirable that the amount is from 0.00 to 1000 parts by weight.

Next, a preferred method for manufacturing the above magnetic support will be described separately for the magnetic support having the structure shown in FIG. 2a and the magnetic support having the structure shown in FIGS. A preferred method for producing a magnetic support having the structure shown in FIG. 2a;
After the thermoplastic resin and the magnetic powder are sufficiently dried, they are mixed in the above composition range and melt-mixed using an extruder to obtain a mixture of particles (raw material mixture for magnetic part). A method of molding using a molding machine capable of melt extrusion. The magnetic powder may be mixed at the same time as the reaction monomer is added during the polymerization of the thermoplastic resin, or may be added and mixed during the polymerization of the thermoplastic resin.

A preferred method for producing the magnetic support having the structure shown in FIGS. 2b to 2e; the raw material mixture for the magnetic portion and the raw material for the non-magnetic portion mainly composed of the thermoplastic resin are melt-extruded using a molding machine. A method of coextrusion to form a desired composition. In addition, as the above-mentioned "co-extrusion molding method", in addition to the method of simultaneously extrusion-molding the raw material mixture for the magnetic portion and the raw material for the non-magnetic portion to form a two-layer or multi-layer magnetic support, Either one of the raw material mixture for the magnetic portion and the raw material for the non-magnetic portion is extruded first to obtain a film-like material, and then the raw material mixture for the magnetic portion and / or the non-magnetic material is further formed on the film-like material. There is a method of forming a two-layer or multi-layer magnetic support by extrusion-molding a raw material for parts.

The magnetic support having the structure shown in FIG. 2f can be manufactured by the following method. In the process of extrusion molding using only the non-magnetic part raw material, the magnetic coating material is applied at any stage of the molding process to form the magnetic film body (magnetic part) A ′, A method for producing a magnetic support. However, in this case,
The above-mentioned magnetic film body A ′ in the configuration shown in FIG.
Is preferably one that does not swell or dissolve in the solvent used when forming the nonmagnetic layer and the magnetic layer provided on the film A ′.

When manufacturing the above magnetic support,
When forming the magnetic portion A or the magnetic film A ′, a magnetic field orientation treatment and a calender treatment can be performed, if necessary.

In the magnetic support used in the present invention, after the magnetic support having the structure shown in FIG. 2f is manufactured by the method described above, the magnetic support in the magnetic support having the structure shown in FIG. It may be manufactured by extruding the above-mentioned raw material for the non-magnetic portion or the like onto the film body A ′ or the like to form the non-magnetic portion B or the like.

The non-magnetic layer provided on the magnetic support is a layer formed by applying a non-magnetic coating material on the magnetic support. The non-magnetic coating material used when forming the non-magnetic layer is preferably a coating material composed of non-magnetic powder, a binder and a solvent, or a coating material composed of the binder and the solvent. 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,
Pomegranate, garnet, silica, 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. The non-magnetic powder may be subjected to the surface treatment described above in order to improve the dispersibility of the non-magnetic powder.

When the non-magnetic layer contains non-magnetic powder, the particle size of the non-magnetic powder is preferably 0.001.
˜3 μm, more preferably 0.005 to 1 μm, and most preferably 0.005 to 0.5 μm. The non-magnetic powder is preferably contained in the non-magnetic layer formed by applying the non-magnetic coating material in an amount of 5 to 99% by weight, more preferably 30 to 95% by weight, and most preferably 50 to 95% by weight. It is desirable to incorporate it in the above non-magnetic paint so that it is contained by weight.

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.
As the binder, specifically, vinyl chloride resin, polyester, polyurethane, nitrocellulose,
Epoxy resin and the like can be mentioned.
Resins and the like described in JP-A No. 162128, page 2, upper right column, line 19 to page 2, lower right column, line 19 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 preferably about 5 to 100 parts by weight, more preferably 10 to 30 parts by weight, based on 100 parts by weight of the non-magnetic powder.

Examples of the solvent include a ketone solvent, an ester solvent, an ether solvent, an aromatic hydrocarbon liquid solvent, and a chlorinated hydrocarbon solvent. 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.

In addition, the non-magnetic coating material contains additives generally used in magnetic recording media, such as a dispersant, a lubricant, an abrasive, an antistatic agent, a rust preventive, a fungicide, and a curing agent. , Can be added if necessary. As the above additives,
Specifically, it is described in JP-A-57-162128, page 2, upper left column, line 6 to page 2, upper right column, line 10 and page 3, upper left column, line 6 to third page upper right column, line 18 and the like. Various additives may be mentioned.

To prepare the above non-magnetic paint, for example,
The non-magnetic powder and the binder are charged together with a part of the solvent into a Nauter mixer or the like to be premixed to obtain a mixture, and the obtained mixture is kneaded by a continuous pressure kneader or the like, and then it is mixed with the solvent. Examples include a method of diluting a part of the mixture, carrying out a dispersion treatment using a sand mill or the like, mixing an additive such as a lubricant, filtering, and further mixing the remaining solvent and a curing agent.

The magnetic layer provided on the non-magnetic layer is a layer formed by applying a magnetic coating material on the non-magnetic layer. The magnetic paint used for forming the magnetic layer is preferably a paint containing magnetic powder, a binder, and a solvent as main components. Examples of the magnetic powder include ferromagnetic iron oxide, ferromagnetic chromium dioxide, and ferromagnetic metal powder.

The above-mentioned ferromagnetic iron oxide is FeOx (1.33).
A metal such as Cr, Mn, Co, or Ni added to ≦ x ≦ 1.5) can be used. Further, the ferromagnetic chromium dioxide is CrO ₂ or Na, K, F in the CrO _2.
Metals such as e and Mn, oxides of the metals, and nonmetal elements such as P may be used. Examples of the ferromagnetic metal powder include ferromagnetic metal powders having a metal content of 70% by weight or more, and 80% by weight or more of at least one type of ferromagnetic metal (eg, Fe, Co, Ni). . Specific examples of the ferromagnetic metal powder include, for example,
Fe-Co, Fe-Ni, Fe-Al, Fe-Ni-A
1, Co-Ni, Fe-Co-Ni, Fe-Ni-Al
-Zn, Fe-Al-Si, etc. are mentioned.

The magnetic powder may contain, if necessary,
A rare earth element or a transition metal element can be contained. In addition, as the magnetic powder, fine tabular barium ferrite and some of its Fe atoms are Ti, Co, Z.
Magnetic powders substituted with atoms such as n and V can also be used. The magnetic powder may be subjected to the above-mentioned surface treatment in order to improve the dispersibility of the magnetic powder.

As the binder and the solvent used for the magnetic paint, the same binder and the solvent used for the non-magnetic paint can be used. Also,
The amount of the binder used is preferably about 5 to 100 parts by weight with respect to 100 parts by weight of the magnetic powder.
It is particularly preferable to use 30 parts by weight. Further, the above-mentioned additives used in the above-mentioned non-magnetic paint can be added to the above-mentioned magnetic paint.

To prepare the above-mentioned magnetic coating material, for example, the above-mentioned magnetic powder and the above-mentioned binder are charged together with a part of the solvent into a Nauter mixer or the like to premix and obtain a mixture, and the obtained mixture is subjected to continuous addition. After kneading with a pressure kneader or the like, then diluting with a part of the solvent and dispersing treatment using a sand mill or the like, mixing additives such as a lubricant and filtering, and further curing agents such as polyisocyanate and the rest. And the like.

In the magnetic recording medium according to the present invention, the coercive force Hc of the magnetic support and the coercive force Hc 'of the magnetic layer.
The ratio (Hc ′ / Hc) with is preferably 1.5 or more, more preferably 1.6 or more (the lower limit in practice is 6.5 or less).
And the coercive force Hc of the magnetic support is preferably 4
00 to 1500 Oe, more preferably 600 to 1200
Oe, and the coercive force Hc ′ of the magnetic layer is preferably 700 to 2500 Oe, more preferably 1500 to 23.
It is 00 Oe. In order to perform high density recording, it is preferable that the coercive force is large, and the lower limits of Hc and Hc 'are set practically from this point. Further, there is a limit to the strength of the magnetic field generated from the magnetic head, and the upper limits of Hc and Hc 'are set practically.

In the magnetic recording medium according to the present invention, the magnetic layer is mainly involved in recording in the high frequency band, and in the low frequency band, the magnetic layer and the magnetic portion of the magnetic support (A or A'in FIG. 2). ) Is involved in the record. From this point, it is preferable that the distance t ₁ from the boundary between the magnetic layer and the nonmagnetic layer to the magnetic portion of the nonmagnetic support and the thickness t _{2 of the} magnetic layer satisfy the following relationship.
That is, λ _h / 5 ≦ t ₂ ≦ λ _h , t ₁ + t ₂ ≦ λ _l /
It is 3. When t ₂ <λ _h / 5 or less, since the recording layer is thin, the stiffness of the magnetic layer is weakened, the head contact cannot be sufficiently achieved, and the output is lowered. In addition, uniform coating is difficult in terms of manufacturing and dropout occurs. There are drawbacks such as rising.
On the other hand, when t ₂ > λ _h , the output in the high frequency band decreases due to the thickness loss. Furthermore, t ₁ + t ₂ > λ _l / 3
In the case of (1), the head magnetic field does not sufficiently reach the magnetic portion of the magnetic support in the low frequency band and cannot be used as the recording layer, so that the output in the low frequency band decreases. Here, the distance t ₁ is specifically the average value of the distance between the interface between the magnetic layer and the nonmagnetic layer and the interface between the magnetic portion of the magnetic support and the nonmagnetic layer. (The measuring method will be described in detail in Examples.)

In the present invention, the recording wavelength λ _{l in the} low frequency band is preferably 1.0 to 30 μm. Also,
The recording wavelength λ _{h in the} high frequency band is preferably 0.1 to
It is 1.0 μm.

The magnetic recording medium according to the present invention is mainly 8 m.
Although it is suitable as a magnetic tape such as m-video tape or DAT tape, it can also be used as another 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, wet-on the non-magnetic coating material and the magnetic coating material on the magnetic support so that the dry thicknesses of the non-magnetic layer and the magnetic layer are the above-mentioned thicknesses.
Simultaneous multi-layer coating is performed by a wet method to form coating films for the non-magnetic layer and the magnetic layer. 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, in the case of obtaining a magnetic tape, 40 to 70
Aging treatment is performed at a temperature of 6 to 72 hours for slitting 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, etc. of Japanese Patent No. 883, the above-mentioned magnetic coating material for forming the above-mentioned magnetic layer is applied before the above-mentioned non-magnetic coating material for forming the above-mentioned non-magnetic layer is dried. In this method, since the boundary surface between the non-magnetic layer and the magnetic layer is smooth and the surface property of the magnetic layer is good, dropout is small, high density recording is possible, and the coating film (magnetic layer Also, a magnetic recording medium having excellent durability of the (and non-magnetic layer) can be obtained.

The magnetic field orientation treatment is carried out before the magnetic paint is dried. For example, when the magnetic recording medium of the present invention is a magnetic tape, the magnetic paint is applied in a direction parallel to the coated surface of the magnetic paint. About 500 Oe or more, preferably about 1000
It can be performed by a method of applying a magnetic field of 10,000 to 10,000 Oe, a method of passing a magnetic paint through a solenoid or the like of 1,000 to 10,000 Oe in a wet state.

The 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.

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 magnetic support (the surface on which the nonmagnetic layer and the magnetic layer are not provided), and is usually a backcoat layer. It is obtained by applying the back coat paint used for forming the layer on the magnetic support.

The back coat paint is obtained by appropriately selecting and mixing the non-magnetic powder, the binder, the dispersant, the lubricant, the curing agent, the solvent and the like described in detail in the non-magnetic paint. . The above back coat paint can be prepared by a generally known back coat and paint manufacturing method.

In the production of the magnetic recording medium of the present invention, finishing steps such as polishing and cleaning of the magnetic layer surface may be carried out, if necessary. The non-magnetic coating material and the magnetic coating material can be applied by a generally known sequential multi-layer coating method.

[0042]

EXAMPLES Next, the magnetic recording medium according to the present invention will be described more specifically by the following examples. The present invention is not limited to this embodiment.

<Example 1> [Production of magnetic support] Granules of polyethylene terephthalate having an intrinsic viscosity of 0.60 and acicular Co-γ-FeO.
_X (1.33 <x <1.5, coercive force 890 Oe, saturation magnetization 82 emu / g, average major axis length 0.19 μm), Co−
γ-Fe ₂ O ₃ magnetic powder was prepared so that the magnetic powder would be 15 wt% and melt-mixed using an extruder to obtain a mixture of particles. Then, the above mixture was coextruded with a polyethylene terephthalate granular material containing no magnetic material to obtain a film having a magnetic portion in the upper portion and a non-magnetic portion in the lower portion. The film obtained has a longitudinal length of 3.3.
Double, stretched 3.3 times in the width direction, then heat treated,
The total thickness of the magnetic support of the structure shown in FIG. 2C is 7.5 μm.
A magnetic support having a magnetic portion thickness of 3 μm was obtained.

[Production of Nonmagnetic Support] A film having a thickness of 7.5 μm was obtained in the same manner as the above magnetic support except that only polyethylene terephthalate was used, and this film was used as a nonmagnetic support.

[Preparation of Magnetic Paint, Non-Magnetic Paint, and Backcoat Layer Paint] Each of the following paint compositions except for the polyisocyanate, fatty acid, and fatty acid ester was added to a Nauta mixer together with a part of the solvent. The mixture was charged and premixed to obtain a mixture, and the obtained mixture was kneaded by a continuous pressure kneader. Then, after diluting with a part of the solvent and dispersing with a sand mill, the fatty acid and the fatty acid ester are mixed, filtered, and the remaining solvent (and polyisocyanate) is further mixed to obtain a magnetic coating, A magnetic paint and a back coat layer paint were obtained.

(Composition of Magnetic Paint) Needle-like metallic magnetic powder mainly composed of iron (Fe: Al: Ba: Si: Ni: Co = 89: 2: 1: 1: 3: 4, coercive force 1620 Oe, saturation magnetization 128 emu / g, average major axis length 0.22 μm, specific surface area 51 m ² / g, X-ray particle size 165 Å, axial ratio 12, moisture 1.0% 100 parts by weight Alumina (average particle size 0.3 μm, specific surface area) 11 m ² / g) 9 parts by weight carbon black (average primary particle size 20 nm) 1 part by weight Sulfonic acid group- and epoxy group-containing vinyl chloride resin (sulfonic acid group content 1.5 × 10 ⁻⁴ eq / g, epoxy group content 6 × 10 ^-4 eq / g, average polymerization degree 250) 9 parts by weight of the sulfonic acid group-containing polyurethane (GPC number average molecular weight 25000, GPC weight average molecular weight 49000, acid content 1.9 × 1 ^-4 eq / g) 7 parts by weight 1.5 parts by weight of stearic acid, 2-ethylhexyl oleate 2 parts by weight Polyisocyanate [Nippon Polyurethane Industry Co., trade name "Coronate L"] 4 parts by weight Methyl ethyl ketone 100 parts Toluene 50 weight Part cyclohexanone 100 parts by weight

(Blending of non-magnetic paint) Needle-like α-Fe ₂ O ₃ (average major axis length 0.07 μm, axial ratio 6, surface treated with Al ₂ O ₃ ) 100 parts by weight carbon black (average primary particle size) 0.023 μm, specific surface area 125 m ² / g, D BP oil absorption 56 g / 100 g, pH 2.5 8 parts by weight Alumina (average particle size 0.2 μm, specific surface area 14 m ² / g) 3 parts by weight Sulfonic acid group and epoxy Group-containing vinyl chloride resin (sulfonic acid group content 1.5 × 10 ⁻⁴ eq / g, epoxy group content 6 × 10 ⁻⁴ eq / g, average degree of polymerization 250) 8 parts by weight Sulfonic acid group-containing polyurethane ( GPC number average molecular weight 25000, GPC weight average molecular weight 49000, sulfonic acid group content 1.9 × 10 ⁻⁴ eq / g) 6 parts by weight Polyisocyanate [Nippon Polyurethane Industry Co., Ltd., trade name “Coronate H” X ”] 3 parts by weight Oleyl oleate 1 part by weight Myristic acid 1 part by weight Methyl ethyl ketone 80 parts by weight Toluene 40 parts by weight Cyclohexanone 120 parts by weight

(Blending of coating material for back coat layer) Carbon black (average primary particle size 0.028 μm, specific surface area 65 m ² / g, DBP oil absorption 53 g / 100 g, pH 2.5) 32 parts by weight carbon black (average primary particle size Particle size 0.062 μm, specific surface area 35 m ² / g, DBP oil absorption 62 g / 100 g, pH 8.0 8 parts by weight Nippon Polyurethane Co., Ltd. trade name “Nipporan 2301” 20 parts by weight Nitrocellulose (Hercules Powder Co. Manufactured by Viscosity display for 1/2 second) 20 parts by weight Polyisocyanate [Takeda Pharmaceutical Co., Ltd. trade name "D-250N"] 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

[Manufacture of Magnetic Recording Medium] The nonmagnetic coating and the magnetic coating are provided on one surface of the magnetic support, and the distance from the boundary between the magnetic layer and the nonmagnetic layer to the magnetic portion of the magnetic support. Simultaneous multilayer coating was carried out by the wet-on-wet method so that t ₁ and the thickness t _{2 of the} magnetic layer were the values shown in Table 1 to form coating films of the non-magnetic layer and the magnetic layer. . Then, when the coating film is wet, 5000O
The magnetic field orientation processing is performed by passing through the solenoid of e.
After being dried at 0 ° C., it was wound up. Then 85
Calendered under the conditions of ℃ and 350kg / cm,
After forming the non-magnetic layer and the magnetic layer, a back coat layer coating material having a dry thickness of 0.5 μm is formed on the back surface of the magnetic support d.
And was dried at 90 ° C. and then wound up. Then, it was aged at 50 ° C. for 16 hours and slit into an 8 mm width to obtain a test 8 mm width magnetic tape. Magnetic characteristics of the magnetic support, magnetic characteristics and output of the magnetic tape (750 kHz for low frequency band, 7 MHz for high frequency band)
Were measured according to the following measuring methods. The results are shown in [Table 1].

[Measurement Method] ◎ Magnetic Properties As for the magnetic support, the magnetic support was punched into a predetermined shape, and the magnetic layer coated on the non-magnetic layer was coated with an adhesive tape. Only the magnetic layer was peeled from the body, punched into a predetermined size and shape like the above magnetic support, and each was measured with an applied magnetic field of 10 kOe using a vibrating magnetometer.

Output: The above magnetic tape was loaded into a test 8 mm VTR cassette to obtain a test 8 mm VTR tape cassette. This VT
The R tape cassette is loaded into a commercially available Hi8VTR modified device, and the magnetic tape is loaded with 750 kHz and 7 MHz.
Was recorded, and the output (reproduction output) when the signal was reproduced was measured. The recording wavelength of 750 kHz is 5.1 μm,
The recording wavelength at 7 MHz was 0.54 μm. 750k
Table 1 shows the results for Hz as output 1 and the results for 7 MHz as output 2.

The distance t ₁ from the boundary between the magnetic layer and the non-magnetic layer to the magnetic portion of the magnetic support and the thickness t _{2 of the} magnetic layer The distance t ₁ and the thickness t ₂ were measured by the following method. First, the obtained magnetic tape was cut into a thickness of about 0.1 micron with a diamond cutter in the longitudinal direction, and the magnification was 10,000 to 100,000 with a transmission electron microscope.
After observing at a magnification of 20,000 to 50,000, taking a picture of the observation, it was printed on a commercially available photographic paper. Then, paying attention to the difference in the shape of the magnetic powder and the nonmagnetic powder in the magnetic layer and the nonmagnetic layer, the interface between the magnetic layer and the nonmagnetic layer is visually determined on the photograph, and the interface is outlined in black. I drew a line. In addition, edging lines were similarly drawn at the interface between the magnetic portion of the magnetic support and the non-magnetic layer, and then the distance between these edging lines was measured by an image processing device. The distance between the edging lines is 100 cm for a 21 cm-long space.
It was segmented into 300 and its length was measured.

Example 2 A magnetic support, a magnetic layer and a magnetic tape obtained in the same manner as in Example 1 except that the above distance and the thickness of the magnetic layer were set to the values shown in Table 1, respectively. Evaluation was carried out according to the method of Example 1. The results are shown in [Table 1].

<Comparative Examples 1, 4, 5> A magnetic support, a magnetic layer, and a magnetic support obtained in the same manner as in Example 1 except that the distance and the thickness of the magnetic layer were set to the values shown in Table 1, respectively. The magnetic tapes were evaluated according to the method of Example 1. The results are shown in [Table 1].

Comparative Example 2 The above non-magnetic support (manufacturing method is described in the section of Example 1) is used in place of the magnetic support of Example 1, and the distance and the thickness of the magnetic layer are respectively set. The magnetic layer and the magnetic tape obtained in the same manner as in Example 1 except for the values shown in Table 1 were evaluated according to the method of Example 1, respectively. The results are shown in [Table 1].

Comparative Example 3 A hexagonal plate-shaped barium ferrite powder (coercive force 1810 Oe, saturation magnetization 59 emu) was used in place of Co-γ-FeO _x used in the magnetic support in Example 1.
/ G, average particle size 0.06 μm, plate ratio 5), and the magnetic support obtained in the same manner as in Example 1 except that the distance and the thickness of the magnetic layer were set to the values shown in Table 1, respectively. The body, the magnetic layer and the magnetic tape were evaluated according to the method of Example 1, respectively. The results are shown in [Table 1].

[0057]

[Table 1]

As shown in Table 1, the above magnetic support was used, and the ratio (Hc '/ Hc) of the coercive force Hc of the magnetic support and the coercive force Hc' of the magnetic layer was 1.5. Above, and the coercive force Hc of the magnetic support is 400 to 1500 Oe, and the coercive force Hc 'of the magnetic layer is 700 to 2500 Oe.
e, the thickness t _{2 of the} magnetic layer is 0.108 to 0..0 for a recording wavelength of 0.54 μm used in the high frequency band.
54 μm, and the sum of the distance t ₁ and the thickness t ₂ of the magnetic layer (t ₁ + t ₂ ) is (t ₁ + t ₂ ) ≦ for a recording wavelength of 5.1 μm used in the low frequency band. 1.7
The magnetic tape obtained by each of the above embodiments having
In addition to exhibiting excellent output characteristics from the low frequency band to the high frequency band, those using a conventionally used non-magnetic support, the above ratio (Hc '/ Hc), the above coercive force Hc', the above The magnetic tapes obtained by the respective comparative examples in which the coercive force Hc, the thickness t ₂ or the total of the thicknesses (t ₁ + t ₂ ) are out of the above ranges have output characteristics different from those of the above examples. It was confirmed to be inferior.

As described above, according to the magnetic recording medium of the present embodiment, excellent output characteristics can be obtained from the low frequency band to the high frequency band.

[0060]

According to the magnetic recording medium of the present invention, high density recording is possible and excellent output characteristics can be obtained from the low frequency band to the high frequency band.

[Brief description of drawings]

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

2A and 2B are schematic diagrams showing a structure of a magnetic support of the magnetic recording medium, FIG. 2A is a schematic view showing a structure in which only a magnetic portion is a single layer, and FIG. Schematic showing a structure in which a non-magnetic portion is provided on the surface of the portion to form two layers, (c)
Is a schematic diagram showing a configuration in which a magnetic portion is provided on the surface of a non-magnetic portion to form two layers, and (d) is a schematic diagram showing a configuration in which a non-magnetic portion is provided on each of the front surface and the back surface of the magnetic portion and forming three layers,
(E) is a schematic view showing a structure in which a magnetic portion is provided on each of the front surface and the back surface of the non-magnetic portion to form three layers, and (f) shows a configuration in which the magnetic portion is formed on the surface of the non-magnetic portion and formed into two layers. It is a schematic diagram.

Claims (2)

[Claims] 1. A magnetic recording medium comprising a magnetic support, at least a non-magnetic layer provided on the magnetic support, and a magnetic layer provided on the non-magnetic layer. Coercive force Hc of H and the coercive force H of the magnetic layer
the ratio (Hc ′ / Hc) to c ′ is 1.5 or more, and the coercive force Hc of the magnetic support is 400 to 1500 Oe,
A magnetic recording medium, wherein the magnetic layer has a coercive force Hc 'of 700 to 2500 Oe. 2. The thickness t _{2 of the} magnetic layer is λ _h / 5 ≦ t ₂ ≦ λ _{h with} respect to a recording wavelength λ _h used in a high frequency band.
And the sum (t ₁ + t ₂ ) of the distance t ₁ from the boundary surface between the magnetic layer and the non-magnetic layer to the magnetic portion of the magnetic support and the thickness t ₂ of the magnetic layer is in the low frequency band. (T ₁ + t ₂ ) ≦ λ _l / 3 for the recording wavelength λ _l used in
The magnetic recording medium according to claim 1, wherein