JPH09190624A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having improved dispersibility of magnetic powder, high output and high C/N. SOLUTION: The magnetic layer 3 of the magnetic recording medium 1 including a nonmagnetic base 2 and the magnetic layer 3 existing on the nomnagnetic base contains a ferromagnetic powder and a urethane binder. The urethane binder has 1 to 4 pieces of sulfonic acid (sulfonate) groups in one molecule and its number average mol.wt. is 10000 to 30000. The content of N therein is 0.1 to 1%.

Description

Detailed Description of the Invention TECHNICAL FIELD OF THE INVENTION

The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium having high output and high C / N.

2. Description of the Related Art

The magnetic layer of a magnetic recording medium is usually formed mainly of a binder and magnetic powder. With the recent increase in recording density of magnetic recording media, various attempts have been made to achieve high output and high C / N of magnetic recording media by using magnetic powder having a small particle size. However, as the particle size of the magnetic powder becomes smaller, the dispersibility of the magnetic powder in the binder tends to decrease,
In a magnetic recording medium using such magnetic powder,
It is not easy to improve output and surface smoothness.

Accordingly, an object of the present invention is to provide a magnetic recording medium having improved dispersibility of magnetic powder, high output and high C / N.

[0004]

Means for Solving the Problems As a result of intensive investigations by the present inventors, the magnetic layer contains a ferromagnetic powder and a urethane-based binder, and the molecular weight of the urethane-based binder, the number of sulfonic acid (salt) groups, It was found that a magnetic recording medium having a N content and a N content in a specific range can achieve the above object.

The present invention has been made based on the above findings, and in a magnetic recording medium comprising a non-magnetic support and a magnetic layer located on the non-magnetic support, the magnetic layer is a ferromagnetic powder. And a urethane-based binder, wherein the urethane-based binder has 1 to 4 sulfonic acid (salt) groups in one molecule and a number average molecular weight of 10,000 to 30,000.
The above object is achieved by providing a magnetic recording medium characterized by having an N content of 0.1 to 1%.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the magnetic recording medium of the present invention will be described below with reference to the drawings. Here, FIG. 1 is a schematic sectional view showing the structure of a preferred embodiment of the magnetic recording medium of the present invention.

The magnetic recording medium 1 of the embodiment shown in FIG.
It has a non-magnetic support 2 and a magnetic layer 3 provided on the non-magnetic support 2. In addition, the magnetic recording medium 1
Has a back coat layer 4 on the surface of the non-magnetic support 2 opposite to the surface on which the magnetic layer 3 is provided.

As the non-magnetic support 2 used in the magnetic recording medium 1, a generally known one can be used without particular limitation. Specifically, a flexible film or disk made of polymer resin; Cu, A
Films, disks, cards and the like made of non-magnetic metals such as l and Zn, ceramics such as glass, 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. Or two or more kinds can be used in combination.

The magnetic layer 3 provided on the non-magnetic support 2 contains a ferromagnetic powder and a urethane binder.
The magnetic layer 3 is generally formed of a magnetic paint containing the ferromagnetic powder, the urethane binder and a solvent as main components.

As the above-mentioned ferromagnetic powder, for example, needle-like ferromagnetic powder or plate-like ferromagnetic powder is preferably used. As the above-mentioned needle-like ferromagnetic powder, hard magnetic metal powder, hard magnetic oxide powder and the like can be used, but they are not limited to these. The hard magnetic metal powder has, for example, a metal content of 70% by weight or more and a metal content of 80.
A hard magnetic metal powder mainly composed of iron whose weight% is Fe is included. Specific examples of such hard magnetic metal powder include, for example, Fe-Co, Fe-Ni, Fe-Al,
Fe-Ni-Al, Fe-Co-Ni, Fe-Ni-A
1-Zn, Fe-Al-Si, etc. are mentioned. Further, as the above hard magnetic oxide powder, FeO _x (4/3 ≦ x ≦
3/2) iron oxide-based ferromagnetic powder, said FeO
Cr in _x, Mn, Co, divalent iron oxide powder metal is added, such as Ni, the FeO made by Co-deposited on the _x Co deposition FeO _x, chromium dioxide, or the chromium dioxide N
Examples thereof include metals such as a, K, Fe, and Mn, semiconductors such as P, and oxide powders to which an oxide of the metal is added. On the other hand, examples of the plate-like ferromagnetic powder include hexagonal ferromagnetic oxide, but the present invention is not limited to this. Examples of the hexagonal ferromagnetic oxide include hexagonal ferrite, for example, barium ferrite and strontium ferrite in the form of microplates, and some of Fe atoms thereof are replaced with atoms such as Ti, Co, Ni, Zn, and V. And the like.

When the acicular ferromagnetic powder is used as the ferromagnetic powder, the major axis length of the acicular ferromagnetic powder is 0.05 to
It is preferably 0.15 μm. Major axis length is 0.05
If it is less than 0.1 μm, dispersion becomes very difficult and sufficient characteristics may not be obtained in some cases, and if it exceeds 0.15 μm, sufficient C / N characteristics may not be obtained in a medium with high recording density. It is preferably within the above range. The more preferable major axis length of the needle-like ferromagnetic powder is 0.06 to 0.12 μ.
m, and the more preferable major axis length is 0.06 to 0.10 μ.
m.

The acicular ferromagnetic powder preferably has an acicular ratio of 3 to 10, an X-ray particle size of 150 to 210Å, and a BET specific surface area of 50 to 70 m. ² / g.

On the other hand, when the plate-shaped ferromagnetic powder is used as the ferromagnetic powder, the plate-shaped ferromagnetic powder has a plate diameter of 30 to 30.
It is preferably 50 nm. If the plate diameter is less than 30 nm, dispersion may be very difficult and sufficient characteristics may not be obtained, and if it exceeds 50 nm, sufficient C / N characteristics may not be obtained in a medium having a high recording density. Therefore, it is preferably within the above range. The plate diameter of the plate-like ferromagnetic powder is more preferably 35 to 50 nm, and further preferably the particle size is 40 to 45 nm.

The plate-like ferromagnetic powder preferably has a plate-like ratio of 2 to 7, and more preferably 3 to 5.

When the acicular ferromagnetic powder is used as the ferromagnetic powder, the coercive force of the acicular ferromagnetic powder is 1500.
To 2500 Oe, preferably 1700 to 23
More preferably, it is 00 Oe. On the other hand, when the plate-like ferromagnetic powder is used as the ferromagnetic powder, the coercive force of the plate-like ferromagnetic powder is preferably 700 to 2000 Oe, and more preferably 800 to 1600 Oe. When the coercive force of each of the needle-like ferromagnetic powder and the plate-like ferromagnetic powder is less than the above lower limit, demagnetization is likely to occur, so that the short wavelength RF output is lowered, and when the above upper limit is exceeded, the head is increased. The magnetic field is insufficient, the writing ability is insufficient, and the overwrite characteristic is deteriorated. Therefore, it is preferably within the above range.

When the acicular ferromagnetic powder is used as the ferromagnetic powder, the saturation magnetization of the acicular ferromagnetic powder is
70 to 145 emu / g is preferable, and 120
It is more preferably ˜145 emu / g. on the other hand,
When the plate-like ferromagnetic powder is used as the ferromagnetic powder, the saturation magnetization of the plate-like ferromagnetic powder is 50 to 70 emu.
/ G is preferable, and 60 to 70 emu / g is more preferable. When the saturation magnetization of the needle-like ferromagnetic powder and the plate-like ferromagnetic powder is less than the above lower limit, respectively, the packing ratio of the ferromagnetic powder becomes low, and the output decreases, and when the above upper limit is exceeded. , It becomes necessary to reduce the amount of binder compounded, the interaction between the ferromagnetic powders becomes large, and as a result, the ferromagnetic powders become in an agglomerated state,
Since it is difficult to obtain a desired output, it is preferable to set it within the above range.

The ferromagnetic powder may contain a rare earth element or a transition metal element, if necessary. Further, in order to improve the dispersibility of the ferromagnetic powder, the ferromagnetic powder may be surface-treated. Such surface treatment is described in "Characterization of Powder Surfaces"; Acad.
It can be carried out by a method similar to the method described in emic Press, and examples thereof include a method of coating the surface of the above ferromagnetic powder with an inorganic oxide. In this case, inorganic oxides that can be used include Al ₂ O ₃ and SiO.
₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , Zn
Examples thereof include O and the like, and when used, they can be used alone or in combination of two or more kinds. The surface treatment may be performed by an organic treatment such as a silane coupling treatment, a titanium coupling treatment and an aluminum coupling treatment other than the above method.

Next, the urethane binder will be described. The urethane-based binder has 1 to 4 sulfonic acid (salt) groups in one molecule (average value). If the number of sulfonic acid (salt) groups is less than one, the adsorption property to the ferromagnetic powder is poor and the dispersibility of the paint is deteriorated. On the other hand, when the number exceeds 4, the interaction force between the sulfonic acid (salt) groups increases, which adversely affects the adsorption property to the ferromagnetic powder. The number of sulfonic acid (salt) groups in the urethane binder is preferably 1.2 to 3.5, more preferably 1.5 to 3.0.

The number average molecular weight of the urethane binder is 10,000 to 30,000. When the number average molecular weight is less than 10,000, the crosslinkability of the binder is lowered to deteriorate the durability, and when it exceeds 30,000, the fluidity of the binder is lowered and the dispersibility of the magnetic coating composition is deteriorated. The number average molecular weight of the urethane-based binder is preferably 150.
It is 00 to 20000.

The urethane binder has an N (nitrogen) content of 0.1 to 1% (weight basis). When the N (nitrogen) content is less than 0.1%, the inherent properties (elasticity and dispersibility) of the urethane binder are lost, and when it exceeds 1%, the interaction force between sulfonic acid (salt) groups is high. Is increased, which adversely affects the adsorption characteristics of the ferromagnetic powder. The upper limit of the N content of the urethane binder is preferably 0.9%, more preferably 0.8%. On the other hand, the lower limit value is preferably 0.3%, more preferably 0.5%.

The method for measuring the N content in the urethane binder is as follows. That is, the urethane-based binder is diluted with a diluent solvent (for example, NEK) to an appropriate concentration (1 to 5 wt%), and N in the diluent is quantitatively determined using a Mitsubishi Kasei total nitrogen microanalyzer TN-10 type. By doing so, the N content in the urethane binder is determined.

The urethane binder having the above physical properties can be prepared, for example, by reacting a polyhydroxy compound having a sulfonic acid (salt) group with a polyisocyanate. In this case, as the polyhydroxy compound having a sulfonic acid (salt) group, for example, a polyester polyol having a sulfonic acid (salt) group is preferably used. Such polyester polyol is, for example,
It can be prepared from a carboxylic acid component having a sulfonic acid (salt) group, a carboxylic acid component having no sulfonic acid (salt) group, and an alcohol component. On the other hand, examples of the polyisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, and 3,3 ′. -Dimethoxy-4,4'-biphenylene diisocyanate, 2,4-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether , 1,5-naphthalene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,3-diisocyanate methylcyclohexane,
1,4-diisocyanate methylcyclohexane, 4,
4'-diisocyanate dicyclohexane, 4,4'-
Preferred examples thereof include diisocyanate dicyclohexylmethane and isophorone diisocyanate.

In the magnetic layer 3, in addition to the urethane-based binder, other binder may be contained if necessary. Examples of such a binder include vinyl chloride-based resins, polyesters, nitrocellulose, epoxy resins, and the like, and in addition, JP-A-57-162128, page 2, upper right column, line 19 to line 2. Resins and the like described in the lower right column, line 19 of the page and the like can be mentioned.

The above urethane binder is preferably mixed in the above magnetic coating material in an amount of 3 to 15 parts by weight, more preferably 5 to 1 part by weight, relative to 100 parts by weight of the ferromagnetic powder.
0 parts by weight are blended. When a binder other than the urethane-based binder is used in combination, the other binder is preferably mixed in the magnetic paint in an amount of 3 to 15 parts by weight based on 100 parts by weight of the ferromagnetic powder, More preferably, 5 to 10 parts by weight is blended.

When the magnetic layer 3 contains the acicular ferromagnetic powder as the ferromagnetic powder, its coercive force is
It is preferably 1500 to 2500 Oe, and more preferably 1700 to 2300 Oe. On the other hand, when the plate-like ferromagnetic powder is contained as the ferromagnetic powder, the coercive force thereof is preferably 700 to 2000 Oe,
More preferably, it is 800-1600 Oe. When the magnetic layer 3 contains the acicular ferromagnetic powder as the ferromagnetic powder, the saturation magnetic flux density thereof is preferably 1
500-4000 Gauss, more preferably 250
It is 0 to 4000 gauss. On the other hand, when the tabular ferromagnetic powder is contained as the ferromagnetic powder, the saturation magnetic flux density thereof is preferably 1500 to 2000 gauss, more preferably 1800 to 2000 gauss.

The magnetic layer 3 has a thickness of 0.1-3.
The thickness is preferably μm, more preferably 0.1 to 1.5 μm. The center line surface roughness (Ra) of the magnetic layer 3 is preferably 2 to 7 nm, more preferably 2 to 5 nm.

Next, the magnetic paint for forming the magnetic layer 3 will be described. As described above, the magnetic paint contains the ferromagnetic powder, the urethane binder and the solvent as main components. Examples of the solvent include ketone-based solvents, ester-based solvents, ether-based solvents, aromatic hydrocarbon-based solvents, chlorinated hydrocarbon-based solvents, and the like. The solvents described in JP-A-162128, page 3, lower right column, line 17 to page 4, lower left column, line 10 can be used. The solvent is preferably added in the magnetic paint in an amount of 200 to 350 parts by weight, more preferably 250 parts by weight, based on 100 parts by weight of the ferromagnetic powder.
~ 300 parts by weight are blended.

In addition, the above-mentioned magnetic paint contains additives usually 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. It 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.

In order to prepare the above magnetic coating material, for example, the ferromagnetic powder, the urethane type binder and, if necessary, other binder are charged together with a part of the solvent into a Nauter mixer or the like and premixed to prepare a mixture. The obtained mixture was kneaded with a continuous pressure kneader or the like, then diluted with a part of the solvent, and subjected to a dispersion treatment using a sand mill or the like,
Examples include a method of mixing additives such as a lubricant, filtering, and further mixing a curing agent such as polyisocyanate and the remaining solvent.

The magnetic layer 3 in the non-magnetic support 2
The back coat layer 4 provided on the surface side opposite to the surface provided with is provided to improve the durability and running property of the magnetic recording medium 1. The back coat layer 4 can be formed from a known back coat paint without particular limitation.

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.

The present invention has been described above based on its preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications can be made. For example, in the magnetic recording medium 1 of the embodiment shown in FIG. 1, one or more intermediate layers may be provided between the non-magnetic support 2 and the magnetic layer 3. As the intermediate layer, either a magnetic intermediate layer or a non-magnetic intermediate layer can be used.

Next, an outline of a preferred method for manufacturing the magnetic recording medium of the embodiment shown in FIG. 1 will be described. First, the magnetic paint for forming the magnetic layer 3 is applied on the non-magnetic support 2 so that the dry thickness of the magnetic layer becomes a predetermined thickness to form a coating film for the magnetic layer. Next, the coating film (wet state) is subjected to a predetermined magnetic field orientation treatment, followed by a drying treatment and winding. Then, after performing a calendar treatment, a back coat layer is formed from the above back coat paint. Next, if necessary, for example, when obtaining a magnetic tape, the magnetic tape is subjected to aging treatment at 40 to 70 ° C. for 6 to 72 hours, and slit into a desired width.

The magnetic field orientation treatment is performed before the coating film of the magnetic layer 3 is dried. For example, in the case of producing a magnetic tape as a magnetic recording medium, a method of applying a magnetic field of preferably about 500 Oe or more, more preferably about 1000 to 10000 Oe in a direction parallel to the coated surface of the magnetic paint, or 1000 to It can be performed by a method of passing through a 10000 Oe solenoid magnet or the like.

The above-mentioned drying treatment can be carried out, for example, by supplying heated gas. At this time, the degree of drying 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.

In manufacturing the above magnetic recording medium,
If necessary, finishing steps such as polishing and cleaning of the surface of the magnetic layer 3 may be performed.

[0039]

EXAMPLES Next, the magnetic recording medium of the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples.

Example 1 A magnetic tape was manufactured by using the magnetic coating material having the following composition and the back coating composition having the following composition according to the following [Method for manufacturing magnetic recording medium]. When the coercive force and the saturation magnetic flux density of the magnetic layer formed by using the above magnetic coating material were measured according to the [Measuring method] described later, the coercive force was 1590 Oe and the saturation magnetic flux density was 2900 Gauss.

<Blending of magnetic paint> 100% by weight of acicular ferromagnetic metal powder mainly composed of iron; average major axis length; 0.14 μm coercive force; 1600 Oe saturation magnetization; 120 emu / g acicular ratio; 8 BET ratio Surface area: 55 m ² / g X-ray particle size: 170Å ・ Binder “MR-110” (vinyl chloride binder) 12 parts by weight [trade name, manufactured by Nippon Zeon Co., Ltd., vinyl chloride binder containing sulfonate group, SO ₃ Na content: 1 / molecule, number average molecular weight: 20000] Sulfonate group-containing urethane binder 8 parts by weight [SO ₃ Na content: 1 / molecule, number average molecular weight: 30,000] -Alumina (abrasive, average Particle size 0.2 μm) 10 parts by weight Butyl stearate (lubricant) 2 parts by weight Myristic acid (lubricant) 2 parts by weight “Coronate L” (curing agent) 4 parts by weight [ Product name, Nippon Polyurethane Industry Co., Ltd., a polyisocyanate compound] Methyl ethyl ketone / toluene / cyclohexanone (1: 1: 1wt) 300 parts by weight

<Blending of backcoat paint> Carbon black (average primary particle size 20 μm) 97 parts by weight Carbon black (average primary particle size 300 μm) 3 parts by weight “Nipporan 2301” [trade name, Nippon Polyurethane Industry Co., Ltd. ) Polyurethane] 40 parts by weight-Nitrocellulose 60 parts by weight (viscosity indication made by Hercules Powder Co. of 1/2 second) -Polyisocyanate 20 parts by weight (Takeda Chemical Industries, Ltd., trade name "D" -250N ") Methyl ethyl ketone / toluene / cyclohexanone (1: 1: 1 wt) 1100 parts by weight

[Production of Magnetic Recording Medium] The magnetic coating material was coated on the surface of a polyethylene terephthalate film (nonmagnetic support) having a thickness of 7 μm so that the dry thickness of the magnetic coating material was 2.5 μm, and the magnetic coating A coating of layers was formed. Then, the magnetic field orientation treatment was performed while the coating film was in a wet state, and subsequently dried in a drying oven. Then, after calendering to form a magnetic layer, the back coat coating composition was applied onto the back surface of the non-magnetic support so that the dry thickness was 0.6 μm, dried, and then wound. Then, it was immediately cut into a width of 8 mm to obtain a magnetic tape. The obtained magnetic tape was loaded in an 8 mm cassette case to prepare an 8 mm cassette.

The output and C / N of the obtained magnetic tape as a magnetic recording medium were measured as follows. Table 1 shows the results.

[Measuring Method] <Coercive Force and Saturation Magnetic Flux Density> The obtained magnetic tape was punched into a predetermined size and shape, and a vibrating magnetometer (VSM) was used to apply a coercive force and a saturated magnetic flux at an applied magnetic field of 10 kOe. Each density was measured. <Output and C / N Characteristics> Using a commercially available 8 mm VTR modified evaluation device, a signal of 7.7 MHz was recorded on the magnetic tape of the obtained 8 mm cassette, and the output (reproduction output) and C when the signal was reproduced. / N was measured. Note that the noise level of C / N is a value of (7.7-1) = 6.7 MHz.

[Examples 2 to 6 and Comparative Examples 1 to 5] Instead of the urethane-based binder in Example 1, urethane-based binders having the molecular weight, the number of sulfonic acid groups, and the N content shown in Table 1 were used, respectively. A magnetic tape was obtained by the same operation as in Example 1. The same measurement as in Example 1 was performed on the obtained magnetic tape. Table 1 shows the results.

Example 7 A magnetic tape was obtained in the same manner as in Example 1 except that the plate-like ferromagnetic powder shown below was used instead of the needle-like ferromagnetic powder in Example 1. The same measurement as in Example 1 was performed on the obtained magnetic tape. Table 2 shows the results. The coercive force of the magnetic layer of the magnetic tape in this example was 1100 Oe, and the saturation magnetic flux density was 1800 gauss.・ Plate-like ferromagnetic powder Coercive force; 1100 Oe Saturation magnetization; 60 emu / g Plate diameter; 50 nm Plate-like ratio; 5 BET specific surface area; 40 m ² / g

[Examples 8 to 12 and Comparative Examples 6 to 10] Instead of the urethane-based binder in Example 7, urethane-based binders having the molecular weight, the number of sulfonic acid groups and the N content shown in Table 2 were used, respectively. In the same manner as in Example 7, a magnetic tape was obtained. The same measurement as in Example 1 was performed on the obtained magnetic tape. Table 2 shows the results.

[0049]

[Table 1]

[0050]

[Table 2]

As is clear from the results shown in Tables 1 and 2, in the magnetic tapes of the present invention (Examples 1 to 12), the molecular weight of the urethane binder, the number of sulfonate groups and the N content were specified. Therefore, the output power and C / value are higher than those of the magnetic tapes (Comparative Examples 1 to 10) having the magnetic layer containing the urethane binder outside of these ranges.
N has been achieved.

[0052]

As described above, according to the present invention,
By incorporating a ferromagnetic powder and a urethane-based binder in the magnetic layer, and by setting the molecular weight of the urethane-based binder, the number of sulfonate groups, and the N content in specific ranges,
The dispersibility of the ferromagnetic powder is improved, and a magnetic recording medium having high output and high C / N can be obtained.

[Brief description of the drawings]

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

[Explanation of symbols]

 1 magnetic recording medium 2 non-magnetic support 3 magnetic layer 4 back coat layer

Claims (3)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic layer located on the non-magnetic support, wherein the magnetic layer contains a ferromagnetic powder and a urethane binder, and the urethane binder is Having 1 to 4 sulfonic acid (salt) groups in one molecule and having a number average molecular weight of 10,000 to
A magnetic recording medium having a content of 30,000 and an N content of 0.1 to 1%. 2. The ferromagnetic powder has a major axis length of 0.05 to 0.
The magnetic recording medium according to claim 1, which is a 15 μm acicular ferromagnetic powder. 3. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is a plate-like ferromagnetic powder having a plate diameter of 30 to 50 nm.