JPH02260123A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics and traveling durability by selecting the axial ratio and specific surface area of the ferromagnetic powders used for first and second magnetic layers to satisfy the specified conditions. CONSTITUTION:The first and second magnetic layers each having ferromagnetic powder and a binder are laminated on a nonmagnetic supporting body. The axial ratio A<1> of the ferromagnetic powder of the first magnetic layer and the specific surface area B<1> by BET method, and the axial ratio A<2> of the second magnetic layer and the specific surface area B<2> are determined to satisfy the conditions expressed by formula I. By this method, the electromagnetic conversion characteristics and traveling durability of the magnetic layer are enhanced, so that the obtd. medium is suitable for high density recording.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium, and more specifically, a magnetic recording medium that has improved electromagnetic conversion characteristics and running durability and is suitable for high-density recording. Regarding.

[Prior art and problems to be solved by the invention] In recent years,
For example, in the audio field, DAT (digital audio tape recorder) has appeared, and in the VTR field, 8-inch
Due to circumstances such as the appearance and widespread use of mm width standards, there is an increasing demand for high-density recording in magnetic recording media. A magnetic recording medium with excellent properties is desired.

In order to meet this demand, various studies have been carried out. For example, with regard to ferromagnetic fine powder, by using powder with a large specific surface area, that is, particles with small particles, as determined by the BET method, the electromagnetic conversion characteristics of the magnetic recording medium can be improved. known to improve.

However, magnetic recording media using ferromagnetic fine powder with a large specific surface area produced by the BET method have a problem in that so-called edge folding and powder falling off easily occur, resulting in poor running durability.

On the other hand, when using a ferromagnetic fine powder with a small specific surface area obtained by the BET method, the running durability is good, but there is still room for improvement in the electromagnetic conversion characteristics.

There has also been an attempt to make the magnetic layer a two-layer structure, using ferromagnetic fine powder with a small axial ratio in the upper layer and using ferromagnetic fine powder with a large axial ratio in the lower layer (Japanese Patent Application Laid-Open No. 1987-1!
(See Publication No. 18135).

However, in a magnetic recording medium with such a structure, although the electromagnetic conversion characteristics are improved, the axial ratio of the ferromagnetic fine powder contained in the upper layer is too small, so the adhesiveness of the upper layer is insufficient, and the powder falls off. There are problems in that the running durability is significantly reduced due to the tendency of dropouts and dropouts. This problem cannot be compensated for by improving running durability by somewhat increasing the axial ratio contained in the lower layer.

In other words, it is difficult to improve both the electromagnetic conversion characteristics and running durability of a magnetic recording medium due to the characteristics of the ferromagnetic fine powder contained in the magnetic layer. At present, it has not been possible to sufficiently improve the running durability and the running durability in a well-balanced manner.

The present invention has been made in view of the above circumstances.

An object of the present invention is to provide a magnetic recording medium that has improved electromagnetic conversion characteristics and running durability and is suitable for high-density recording.

[Means for Solving the Problems] In order to solve the above problems, the present inventor has made extensive studies and found that the present inventor has at least two magnetic layers, and each magnetic layer has a specific axial ratio and ratio. The present invention was achieved by discovering that a magnetic recording medium containing a specific ferromagnetic fine powder having a surface area has improved electromagnetic conversion characteristics and running durability.

The structure of the present invention has a first magnetic layer and a second magnetic layer each containing a ferromagnetic fine powder and a binder in this order on a non-magnetic support, and The axial ratio of the ferromagnetic fine powder is At, the specific surface area by the BET method is B1, and the axial ratio of the ferromagnetic fine powder in the second magnetic layer is A2, and the specific surface area by the BET method is B2. Bl, A2 and B2 are each in the following range; 3≦A1≦8.40m2/g≦B1≦50+s2/
g8≦A2≦12.50m? /g≦B2 ≦70m2
/g.

The nonmagnetic support and magnetic layer constituting the magnetic recording medium of the present invention will be described in detail below.

Non-magnetic support Materials for forming the non-magnetic support include, for example, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and polycarbonate. Plastics such as Furthermore, metals such as Gu, An, and Zn, glass,
Various ceramics such as so-called new ceramics (for example, boron nitride, silicon carbide, etc.) can also be used.

There is no particular restriction on the form of the non-magnetic support, and it may be in the form of a tape, sheet, card, disk, drum, etc., and various materials may be used depending on the form and as necessary. It can be used selectively.

When the support is in the form of a tape or sheet, the thickness is usually 3 to 100 μm, preferably 3 to 50 μm.
It is Lm. In addition, in the case of disk-shaped or card-shaped,
Usually, it is 30-100 gm. Furthermore, in the case of a drum shape, it can be made into a cylindrical shape, etc., depending on the recorder used.

A back coat layer may be provided on the surface (back surface) of the nonmagnetic support on which the magnetic layer is not provided for the purpose of improving the running properties of the magnetic recording medium, preventing electrification, preventing transfer, and the like.

In addition, on the surface of the non-magnetic support on which the magnetic layer is provided, for the purpose of improving the adhesion between the magnetic layer and the non-magnetic support,
Intermediate layers (eg adhesive layers) may also be provided.

Magnetic Layer A magnetic layer consisting of at least a first magnetic layer and a second magnetic layer is provided in this order on the non-magnetic support.

(First Magnetic Layer) The first magnetic layer is a layer formed by dispersing fine ferromagnetic powder in a binder.

As the ferromagnetic fine powder, for example, CO-coated 7-F
e2O3 powder, CO-coated Fe3O4 powder, CO-coated Fe
d.

(4/3 < X < 3/2) powder or Fe-
AM metal powder, Fe-Ni metal powder, Fe-A, Q-
Ni metal powder, Fe-1j-P metal powder, Fe-N
i-5i-An metal powder, Fe-Xl-5i-A M-
Nn metal powder, N1-Go metal powder, Fe-Mn-Zn
Metal powder, Fe-Ni-Zn metal powder, FeCo-Ni
-0r metal powder, Fe-Go-N i-P metal powder, G
Examples include ferromagnetic metal powders such as o-Ni metal powder and Go-P metal powder.

Among these, CO-coated γFe2O3 powder is preferred.

In any case, the coercive force (He) of the ferromagnetic fine powder that can be suitably used for forming the magnetic layer in the present invention is usually 550 or more, preferably 600 or more.

By the way, as a result of repeated studies by the present inventor on the relationship between the specific surface area of ferromagnetic fine powder measured by the BET method, Young's modulus, and saturation magnetization (B-), the results shown in FIG. 1 were obtained.

From this result, in order to improve the running durability of a magnetic recording medium, it is generally necessary to increase the specific surface area (BET value) of ferromagnetic fine powder.
is preferably in the range of 40+*2/g to 50I12/g.

Further, as a result of repeated studies on the relationship between the axial ratio, Young's modulus, and saturation magnetization (Bm), the results shown in FIG. 2 were obtained.

From this result, in order to improve the running durability of the magnetic recording medium, it is generally desirable that the axial ratio of the ferromagnetic fine powder be in the range of 3 to 8.

In the present invention, the axial ratio (length/width) AI of the ferromagnetic fine powder contained in the first magnetic layer is in the range of 3≦A1×8, preferably 3.5≦A1×7. It is necessary.

If the axial ratio is less than 3, powder falling, edge bending, dropouts, etc. tend to occur, and running durability may not be sufficiently improved. On the other hand, if it exceeds 8, the improvement in running durability may deteriorate and the direction -L of the electromagnetic conversion characteristics may not be sufficient.

Further, B of the ferromagnetic fine powder contained in the first magnetic layer
The specific surface area 331 according to the ET method is 40 m2 /g≦B
+ (50m2/g, preferably 45m2/g≦Bl
It is necessary to be in the range <50+*2/g.

If the specific surface area is less than 40 m2/g, electromagnetic conversion characteristics may deteriorate and running durability may not be sufficiently improved. On the other hand, more than 50ffi2/g
If it is 2, it may lead to a decrease in running durability.

The shape of the ferromagnetic fine powder is not particularly limited as long as the axial ratio and specific surface area are within the above range, and for example, any shape such as needle, spherical or ellipsoid can be used. can.

As the binder, for example, thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, or mixtures thereof, which are conventionally used in magnetic recording media, can be used.

Examples of the thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, and acrylic ester. Acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-ethylene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile -butadiene copolymer, polyamide resin,
Polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate), cellulose diacetate,
Examples include cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymers, polyester resins, chlorovinyl ether acrylate copolymers, amine resins, and synthetic rubber-based thermoplastic resins.

These may be used alone or in combination of two or more.

Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reactive resin, high molecular weight polyester resin, and incyanate prepolymer. mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanates, and polyamine resins. .

These may be used alone or in combination of two or more.

Examples of the electron beam curable resin include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, epoxy acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, polyamide acrylic type; ether acrylic type; Examples include polyfunctional monomers such as urethane acrylic type, epoxy acrylic type, phosphoric acid ester acrylic type, aryl type, and hydrocarbon type.

These may be used alone or in combination of two or more.

In the present invention, the various resins mentioned above may be used as they are as a binder, but furthermore, a curing agent may be used together with the various resins mentioned above to serve as a binder.

Suitable examples of the curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, Coronate L (trade name: manufactured by Nippon Polyurethane Industries), and Desmodur L (trade name; manufactured by Bayer). trifunctional incyanates such as trifunctional incyanates, or urethane prepolymers containing incyanate groups at both ends, which are conventionally used as curing agents, and polyisocyanates that can be used as curing agents. Mention may be made of polyisocyanate compounds.

These may be used alone or in combination of two or more.

The amount of the curing agent used is usually 5 to 80 parts by weight based on the total amount of binder.

The blending ratio of the ferromagnetic fine powder and the binder (including the hardening agent when the hardening agent is used) in the first magnetic layer is usually based on 100 parts by weight of the ferromagnetic fine powder. The amount of binder is 10 to 50 parts by weight, preferably 15 to 30 parts by weight. If the amount of the binder is too large, the amount of ferromagnetic fine powder will be low and the recording density of the magnetic recording medium will be lowered. If it is too small, the strength of the first magnetic layer will be reduced. The running durability of the magnetic recording medium may deteriorate or the adhesiveness may deteriorate.

The first magnetic layer may further contain a lubricant, an abrasive, an antistatic agent, and the like.

Examples of the lubricant include solid lubricants such as carbon flakes, graphite, carbon black graft polymers, molybdenum disulfide, and tungsten disulfide; silicone oils, modified silicon compounds, fatty acid esters, and fatty acids having 12 to 2z carbon atoms; Examples include.

Among these, carbon blank, modified silicone compounds, fatty acids and fatty acid esters are preferred.

These may be used alone or in combination of two or more.

The amount of the lubricant used is usually 0.05 to 10 parts by weight per 100 parts by weight of the ferromagnetic fine powder.

Examples of the polishing agent include aluminum oxide, titanium oxide (TiO5TiO□), and silicon oxide (SiO1S).
iO2), inorganic powders of silicon nitride, chromium oxide, and boron carbide, and organic powders such as benzoguanamine resin powder, melamine resin powder, and phthalocyanine compound powder.

The average particle size of the abrasive is usually 0.1 to 1.0 lm.
is within the range of

Further, the blending amount of the abrasive is 100% of the ferromagnetic fine powder.
It is usually within the range of 0.5 to 20 parts by weight.

Examples of the antistatic agent include carbon black,
Conductive powders such as graphite, tin oxide-antimony oxide compounds, tin oxide-titanium oxide-antimony oxide compounds, and carbon black graft polymers; natural surfactants such as saponin; alkylene oxide-based, glycerin-based, glycidol-based, etc. Nonionic surfactants; higher alkylamines, quaternary pyridines, other heterocycles,
Cationic surfactants such as phosphonium and sulfoniums, anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfate ester groups, phosphoric ester groups, amino acids, aminosulfonic acids, and sulfuric and phosphoric acids of amino alcohols. Examples include amphoteric surfactants such as esters.

These may be used alone or in combination of two or more.

The amount of the antistatic agent added is usually 0.5 to 20 parts by weight per 100 parts by weight of the ferromagnetic fine powder.

Note that the lubricant, antistatic agent, etc. do not have a sole function; for example, a - compound may act as a lubricant and an antistatic agent.

The thickness of the first magnetic layer having the above structure is usually 4 gm.
It is preferably 2 gm or less.

If the thickness exceeds 4 m, the adhesion between the magnetic recording medium of the present invention and the magnetic head may deteriorate, resulting in a decrease in output.

A second magnetic layer, which will be described in detail below, is provided directly or indirectly on the first magnetic layer.

(Second Magnetic Layer) Like the first magnetic layer, the second magnetic layer is a layer formed by dispersing fine ferromagnetic powder in a binder.

Therefore, as for the ferromagnetic fine powder, binder, and other ingredients in the second magnetic layer, any of those that can be used in the first magnetic layer can be used in the same manner.

However, the second magnetic layer differs from the first magnetic layer in the following points.

That is, the inventor has calculated the specific surface area (BET) of the ferromagnetic fine powder.
As a result of repeated studies on the relationship between the squareness ratio (Sq), the squareness ratio (Sq), and the degree of powder shedding, the results shown in FIG. 3 were obtained.

From this result, in order to achieve good electromagnetic conversion characteristics without causing a decrease in the running durability of the magnetic recording medium, the specific surface area (BET value) of the ferromagnetic fine powder is generally 50 m2/g or more.
It is desirable that it be in the range of 70 m2/g.

Further, as a result of repeated studies on the relationship between the axial ratio and the squareness ratio (Sq), the results shown in FIG. 4 were obtained.

From this result, in order to improve the electromagnetic conversion characteristics of a magnetic recording medium, it is generally desirable that the axial ratio of the ferromagnetic fine powder be in the range of 8 to 12.

Therefore, in the present invention, the axial ratio A2 of the ferromagnetic fine powder contained in the second magnetic layer is 8≦A2≦12,
Preferably, it is necessary that the range is 8.5≦A2≦11.5.

If this axial ratio is less than 8, running durability may be lowered. On the other hand, if it exceeds 12, the electromagnetic conversion characteristics may deteriorate.

Further, B of the ferromagnetic fine powder contained in the second magnetic layer
The specific surface area B2 according to the ET method is 50 m2/g≦B2≦7
0m2/g, preferably 55m2/g≦B2≦65n2
/g.

If the specific surface area is less than 50 m2/g, the electromagnetic conversion characteristics may not be sufficiently improved. On the other hand, 70m2/
If it is more than g, it may lead to a decrease in running durability.

The thickness of the second magnetic layer having the above structure is usually 2 pm.
The thickness is preferably less than 1.5 μm. This thickness?2
If it exceeds m, there is a risk that the first magnetic layer will not exhibit the desired characteristics and will only exhibit characteristics that are equal to or worse than those of the single-layer second magnetic layer.

-Others- The thickness of the magnetic layer having the first magnetic layer and the second magnetic layer having the above structure is usually 6 pm or less, preferably 4 ILm or less.

Next, a method for manufacturing the magnetic recording medium of the present invention will be explained.

(Manufacturing method) The magnetic recording medium of the present invention is produced by cross-dispersing a first magnetic layer-forming component and a second magnetic layer-forming component each containing the ferromagnetic fine powder and a binder in a solvent. After preparing the paint and the second magnetic paint, the obtained first magnetic paint and second magnetic paint are placed on the non-magnetic support,
It can be manufactured by coating in this order.

Examples of the solvent used for kneading and dispersing the first magnetic layer forming component and the second magnetic layer forming component include acetone,
Ketones such as methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK) and cyclohexanone; alcohols such as methanol, ethanol, propatool and phthanol; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, propyl acetate and ethylene glycol mono Ester systems such as acetate, ether systems such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane; Aromatic hydrocarbons such as benzene, toluene, and xylene: methylene chlorite, ethylene chloride, carbon tetrachloride, chloroform, ethylene Halogenated hydrocarbons such as chlorohydrin and dichlorobenzene can be used.

Various types of kneading machines can be used for cross-mixing and dispersion. Examples of this kneading machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a side talinder, a Sqegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disper kneader-1 high-speed mixer, and a homogenizer. , ultrasonic disperser, etc.

Note that a dispersant may be used for cross-dispersion of the ferromagnetic fine powder.

Examples of the dispersant include lecithin, phosphate ester, amine compound, alkyl sulfate, fatty acid amide, higher alcohol, polyethylene oxide, sulfosuccinic acid, sulfosuccinate ester, known surfactants, salts thereof, negative organic groups ( For example -COOH,
-PO,H) salts of polymer dispersants, and the like.

These may be used alone or in combination of two or more.

The amount of the dispersant added is usually 1 to 20 parts by weight per 100 parts by weight of the ferromagnetic fine powder.

The first magnetic paint and the second magnetic paint thus prepared are each applied onto the non-magnetic support by a known method.

Application methods include, for example, Taravia roll coach ink, wire bar coating, doctor blade coating, reverse roll coach ink, dip coach ink, air knife coating, calendar coating, skies coach ink, kiss coating and fantine coating. Can be mentioned.

The thickness of the magnetic layer thus applied is usually 6 ILm or less in dry thickness.

After each of the first magnetic paint and the second magnetic paint is applied in this manner, a magnetic field orientation treatment is performed as necessary in an undried state, and a surface smoothing treatment is usually performed using a supercalent roll or the like. .

Next, by cutting into a desired shape, a magnetic recording medium can be obtained.

The magnetic recording medium of the present invention can be used, for example, as a magnetic tape such as a video tape or audio tape by cutting it into a long shape, or as a floppy disk or the like by cutting it into a disk shape. Furthermore, similar to ordinary magnetic recording media, cart-shaped, cylindrical, and other forms can also be used.

[Example] Next, Examples and Comparative Examples of the present invention will be shown to further specifically explain the present invention.

(Example 1) After sufficiently cross-dispersing each of the first magnetic layer composition and the second magnetic layer composition having the compositions shown below using a ball mill, 5 parts of a polyisocyanate compound was added to prepare a magnetic paint. did.

Primary Co-adhered - Fe203 ferromagnetic fine powder [specific surface area 40 2/g (BET value), axial ratio 3] α-A text, 03 100 parts 5 parts (average particle size 0.2 # Lm) Carbon black (average particle size 4omJL) Polyvinyl chloride copolymer (contains potassium sulfone) [manufactured by Nippon Zeon Co., Ltd.; Stearate cyclohexanone methyl ethyl ketone toluene 3 parts 13 parts 5 parts 1 part 1 part 2 parts 100 parts 100 parts 100 parts 2 - Go coated - Fe203 ferromagnetic fine powder [specific surface area 50 + 12/g (BET value), 100 parts Axial ratio: 8] The types and amounts of other components are the same as those for the first magnetic layer composition.

The obtained first magnetic paint was applied onto a polyethylene terephthalate nonmagnetic support having a thickness of 13 parts, and then a second magnetic paint was applied while the first magnetic paint was still wet. Next, a magnetic field orientation treatment was performed, and after drying, a supercalent treatment was performed to form a magnetic layer having a first magnetic layer and a second magnetic layer. Note that the dry thickness of the first magnetic layer is 2.51
The dry thickness of the second magnetic layer was 1.0 p, m.

Table 1 shows the specific surface area and axial ratio of the ferromagnetic fine powder in the first magnetic layer and the second magnetic layer.

Next, a back coat coating composition having the following composition was dispersed in a ball mill for 5 hours to prepare a back coat coating solution, and this coating solution was coated on the back side of the support having the above magnetic layer to a dry thickness of A back coat layer was formed by coating and drying to a thickness of .5 gm to produce a wide magnetic tape film.

Carbon black nitrocellulose polyurethane resin Methyl ethyl ketone Toluene 50 parts 20 parts 20 parts 200 parts The obtained wide magnetic tape film was made into a video tape.

For this video tape, Chroma-3/N, Lumi-3
/N, dropout, powder falling off, and edge bending were evaluated.

The results are shown in Table 1.

Note that each item was evaluated as follows.

Chroma S/N Using a noise meter (manufactured by Shihasoku), the difference in S/N of each sample in the chroma signal was determined using the tape of Comparative Example 1 as a reference (OdB).

In addition, the video deck is VH3 type. Video Deck [Japan Video Deck] rS-7000,] was used.

Lumi S/N: Using a noise meter (manufactured by Shibaku Co., Ltd.) and using the tape of Comparative Example 1 as a reference (OdB), the difference in S/N of each sample in a 100% white signal was determined.

Please note that the VH3 type video deck is Deodetsuki [manufactured by Victor Motors Japan; rS-7000,] was used.

Dropout: The dropout after running the tape 400 times at a temperature of 40° C. and a humidity of 80% was measured using a VTR dropout counter (manufactured by Shibaku Co., Ltd.).

Powder removal: After the tape was run 400 times under conditions of a temperature of 40°C and a humidity of 80%, stains were observed and evaluated on the following four levels.

◎: No stains are seen at all.

○ I can hardly see any dirt.

△: Dirt is visible.

×: Considerable dirt can be seen.

Edge folding: The tape was run 400 times under conditions of a temperature of 40° C. and a humidity of 80%, and then the presence or absence of edge folding was observed and evaluated in the following four grades.

A: None of the above B: Wakame occurrence on the edges C4 Edge creases occur in some parts D/Edge creases occur in the entire area (Examples 2 to 5, Comparative Examples 1 to 5) In Example 1, the first magnetic layer composition and A magnetic layer was formed in the same manner as in Example 1 except that the ferromagnetic fine powder in the second magnetic layer composition was replaced with those shown in Table 1.

Next, a video tape was prepared in the same manner as in Example 1, and the playback output of this video tape was measured. The results are shown in Table 1.

(Evaluation) As is clear from Table 1, the magnetic recording medium of the present invention:
Compared to the comparative magnetic recording media, the S/N ratio is better, the electromagnetic conversion characteristics are improved, and the running durability is improved because dropouts, powder dropouts, and edge breaks are less likely to occur. It was confirmed.

[Effects of the Invention] According to the present invention, (1) the magnetic layer consists of at least two layers, and
Since each magnetic layer contains a specific ferromagnetic fine powder having a specific specific surface area and axial ratio, it is possible to improve the electromagnetic conversion characteristics, and (2) to avoid deterioration of the improved electromagnetic conversion characteristics. Come true,
It is possible to provide an industrially useful magnetic recording medium which has the advantage that running durability can also be improved.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the specific surface area, Young's modulus, and saturation magnetization (Bm) of ferromagnetic fine powder measured by the BET method.
Fig. 2 is a graph showing the relationship between the axial ratio and Young's modulus of ferromagnetic fine powder, and Fig. 3 is a graph showing the relationship between the specific surface area, squareness ratio, and degree of powder falling off by the BET method of ferromagnetic fine powder.
FIG. 4 is a graph showing the relationship between the axial ratio and the squareness ratio of ferromagnetic fine powder. Figure 1 Figure 2 1; 'CC60n (BET/Ii-; m'/g
)---1-1 and Nio 0 stone bu nihi (Bm)---'7
＞Bu Cumshot Hi Figure 3 / Tachi Kosui 1111: Powder beam test: Box ratio (Sq) Figure 4 Car weight ζ

Claims (1)

[Claims] (1) A first magnetic layer and a second magnetic layer each containing a ferromagnetic fine powder and a binder are provided on a non-magnetic support in this order, and the ferromagnetic fine powder in the first magnetic layer The axial ratio of the powder is A^1, and the specific surface area by BET method is B^1.
and the axial ratio of the ferromagnetic fine powder in the second magnetic layer is A.
^2, When the specific surface area by BET method is B^2,
The above A^1, B^1, A^2 and B^2 are respectively in the following ranges; 3≦A^1<8, 40m^2/g≦B^1<50m^2
/g8≦A^2≦12, 50m^2/g≦B^2≦70
A magnetic recording medium characterized in that the magnetic recording medium is m^2/g.