JP3033983B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly, to a method for manufacturing a magnetic recording medium having excellent electromagnetic conversion characteristics and corrosion resistance.

[Problems to be Solved by the Prior Art and the Invention] In order to improve the characteristics of a magnetic recording medium, it is known that a magnetic layer is divided into a plurality of layers, and a ferromagnetic metal powder is contained in the uppermost layer (see, e.g. JP-A 64-19524, Japanese Patent Application No. 64-7
7450, Japanese Patent Application No. 64-79307, etc.).

However, in the technology disclosed in Japanese Patent Application Laid-Open No. 19524/1984, the electromagnetic conversion characteristics and corrosion resistance are not sufficiently improved,
Also, the techniques disclosed in Japanese Patent Application Nos. 64-77450 and 64-79307 did not sufficiently improve electromagnetic conversion characteristics such as chroma output.

The present invention has been made to improve the above situation.

That is, an object of the present invention is to provide a method for manufacturing a magnetic recording medium in which a plurality of magnetic layers are provided on a nonmagnetic support, the method for manufacturing a magnetic recording medium having both excellent electromagnetic conversion characteristics (especially, chroma output) and corrosion resistance. To provide.

The present invention for achieving the above object [Means for achieving the above object] is on a nonmagnetic _{support, -SO 3 M, -OSO 2 M} , -COOM, and -PO (OM ¹⁾ (O
M ² ) (provided that M is a hydrogen atom or an alkali metal, M ¹ and M ² are each a hydrogen atom, lithium, potassium, or sodium, and M ¹ and M ² are the same or different. ) Containing a modified resin that has been modified by introducing at least one functional group selected from the group consisting of: Formed, while the lower layer was in a wet state, on which the modified resin was contained, and the weight ratio between Fe atoms and Al atoms in the ferromagnetic metal powder was adjusted to 100: 0.5 to 100: 20. A method for manufacturing a magnetic recording medium, comprising: after forming an upper layer by applying a magnetic paint, drying the lower layer and the upper layer.

-Layer Configuration- According to the present invention, the magnetic recording medium basically includes a plurality of magnetic layers, that is, two or more magnetic layers laminated on the surface of a non-magnetic support.

For example, taking the case where the magnetic layer has a two-layer structure as an example, the magnetic recording medium according to the present invention has a magnetic layer comprising a lower layer 2 and an upper layer 3 on a non-magnetic support 1 as shown in FIG. The layers are stacked.

A back coat layer 1 'is provided on the surface of the non-magnetic support on which the magnetic layer is not provided (the back surface) for the purpose of improving the running properties of the magnetic recording medium, preventing charge and preventing transfer, and the like. Alternatively, an intermediate layer such as an adhesive layer may be provided between the magnetic layer and the nonmagnetic support.

-Ferromagnetic metal powder, ferromagnetic powder-Of the above magnetic layers, the upper layer is a ferromagnetic metal powder (Fe-Al
The magnetic layer other than the upper layer is formed by dispersing a known ferromagnetic powder in a binder.

In the present invention, the weight ratio of Fe atoms to Al atoms in the ferromagnetic metal powder contained in the upper layer is 100: 0.5 to 100: 20, and the coercive force (Hc) of the lower magnetic layer is 500 to 500. 1,200
It is important to be Oe.

By satisfying this condition, according to the present invention, the effect is obtained that the magnetic recording medium has excellent electromagnetic conversion characteristics and corrosion resistance.

If the weight ratio is out of the range, the effects of the present invention will not be sufficiently exhibited.

When the coercive force of the lower magnetic layer is less than 500 Oe, R
If the F output or Lumi S / N deteriorates and the coercive force exceeds 1,200 Oe, the chroma output will not be sufficiently improved.

The ferromagnetic metal powder contained in the upper layer is at least Fe
And an alloy powder containing Al and other components such as Ca, N
One or more of i, P, Si, Mn and the like may be contained.

When Al is contained in the upper layer at the above weight ratio, the dispersibility and dispersion stability of the magnetic paint are improved, and the corrosion resistance of the magnetic recording medium is improved.

Further, when Ca is contained in the upper layer in addition to Al, the dispersibility and dispersion stability of the magnetic paint are further improved, and the electromagnetic conversion characteristics of the magnetic recording medium can be kept high for a long period of time.

The preferred content of Ca is 100: 0.1 to 10 by weight of Fe: Ca.
0:10, more preferably 100: 1 to 100: 7.

In the present invention, the ferromagnetic metal powder used for the upper layer preferably satisfies the following conditions.

First, its coercivity is usually 800-5,000 Oe, preferably
1,000 to 2,000 Oe.

In this case, if the coercive force is less than 800 Oe, RF output and Lumi S / N may decrease, and if the coercive force exceeds 5,000 Oe, recording may not be possible with a normal head, which is not preferable. .

Next, when the specific surface area of the ferromagnetic metal powder is represented by a BET value, it is usually 30 m ² / g or more, preferably 50 m ² / g or more.

When the specific surface area is in this range, high density recording is possible and a medium excellent in S / N ratio and the like can be easily realized.

The ferromagnetic metal powder has a saturation magnetization (σ _s ), which is a magnetic property, of usually 100 emu / g or more, preferably 120 emu / g or more.
/ g or more.

If the saturation magnetization is less than 100 emu / g, the electromagnetic conversion characteristics may deteriorate.

On the other hand, as known ferromagnetic powders to be contained in the magnetic layers other than the upper layer, for example, Co-γ-FeO _x , Co-containing γ-Fe ₂ O
₃ powder, Co-containing Fe ₃ O ₄ powder, or Fe-Al metal powder, Fe
-Ni metal powder, Fe-Al-Ca metal powder, Fe-Al-Ni metal powder, Fe-Al-P metal powder, Fe-Ni-Si-Al metal powder, Fe
-Ni-Si-Al-Mn metal powder, Ni-Co metal powder, Fe-Mn-
Zn metal powder, Fe-Ni-Zn metal powder, Fe-Co-Ni-Cr metal powder, Fe-Co-Ni-P metal powder, Co-Ni metal powder and
Co-P metal powder and the like.

Among them, preferred is fine Co-γ-FeO.
_x (X is 1.33 to 1.5) powder.

These ferromagnetic powders can be used alone or in combination of two or more.

In the present invention, the ferromagnetic powder used for the magnetic layers other than the upper layer preferably satisfies the following conditions.

First, the coercive force is usually 500-1,200 Oe, preferably
It is between 650 and 1,000 Oe. In this case, if the coercive force is less than 500 Oe, the RF output and the Lumi / N may decrease, and if the coercive force exceeds 1,200 Oe, the chroma output may not be sufficiently improved, which is not preferable.

The specific surface area of the ferromagnetic powder, when expressed in BET value is usually 20~60m ² / g, preferably 30 to 50 m ² / g.

When the specific surface area is in this range, high density recording is possible and a medium excellent in S / N ratio and the like can be easily realized.

The ferromagnetic metal powder and the ferromagnetic powder are not particularly limited as long as they have a fine shape. For example, any of a needle shape, a spherical shape, and an ellipsoid shape can be used.

-Binder-In the present invention, as a binder to be contained in each magnetic layer (upper layer and other magnetic layers), a resin modified by introducing a functional group, particularly a modified vinyl chloride resin, a modified polyurethane resin (urethane elastomer) Is included in this category), and a modified polyester resin is used.

The functional group _{-SO 3 M, -OSO 2 M,} -COOM and (Where M is a hydrogen atom or an alkali metal such as lithium or sodium, M ¹ and M ² are each a hydrogen atom, lithium, potassium or sodium, and M ¹ and M ² are the same. Or may be different.)
At least one selected from the group consisting of:

When the modified resin contains such a functional group, the compatibility between the modified resin and the ferromagnetic metal powder and the ferromagnetic powder is improved, and the dispersibility of these magnetic powders is further improved, Since the aggregation is also prevented, the stability of the coating liquid is further improved, and the frequency characteristics from the high band to the low band are improved in a well-balanced manner, and the durability of the magnetic recording medium is improved in addition to the electromagnetic conversion characteristics.

The modified resin is a vinyl chloride resin, a polyurethane resin or a polyester resin and a compound having a negative functional group and chlorine in the molecule, for example, (Where M is a hydrogen atom or an alkali metal such as lithium or sodium, M ¹ and M ² are each a hydrogen atom, lithium, potassium or sodium, and M ¹ and M ² are the same. Or may be different.)
Can be produced by condensing the compound with a compound such as

In the present invention, thermoplastic resins, thermosetting resins, reactive resins, conventionally known in the field of magnetic recording media,
An electron beam irradiation curable resin or a mixture thereof can be used, or these can be used in combination with the modified resin.

Examples of the thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, and acrylate-vinylidene chloride copolymer. Polymer, methacrylate-vinylidene chloride copolymer, methacrylate-
Ethylene copolymer, polyvinyl fluoride, vinylidene chloride
Acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate), cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene butadiene copolymer, Examples include polyester resins, chlorovinyl ether acrylate copolymers, amino resins, and synthetic rubber-based thermoplastic resins.

As the thermosetting resin or the reactive resin, for example, a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, a silicone resin, an acrylic reaction resin, a high molecular weight polyester resin and an isocyanate prepolymer. , A mixture of a methacrylate copolymer and a diisocyanate prepolymer, a urea formaldehyde resin, and a polyamine resin.

Examples of the electron beam irradiation-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 And polyfunctional monomers such as urethane acrylic type, epoxy acrylic type, phosphoric acid ester acrylic type, aryl type and hydrocarbon type.

In the present invention, one of the above binders may be used alone, or two or more thereof may be used in combination.

The amount of the binder in each magnetic layer is usually 1 to 200 parts by weight, preferably 1 to 50 parts by weight, based on 100 parts by weight of the ferromagnetic metal powder or ferromagnetic powder.

If the amount of the binder is too large, as a result, the amount of the ferromagnetic metal powder or the ferromagnetic powder decreases, and the recording density of the magnetic recording medium may decrease. The strength of the magnetic layer may decrease, and the running durability of the magnetic recording medium may decrease.

In the present invention, an aromatic or aliphatic polyisocyanate can be used in combination with the binder as a curing agent.

Examples of the aromatic polyisocyanate include tolylene diisocyanate (TDI) and an adduct thereof with an active hydrogen compound, and those having an average molecular weight of 100 to 3,000 are preferable.

Examples of the aliphatic polyisocyanate include hexamethylene diisocyanate (HMDI) and an adduct thereof with an active hydrogen compound, and have an average molecular weight of 100 to 3,000.
And a non-alicyclic polyisocyanate and an adduct thereof with an active hydrogen compound are more preferable.

The amount of the aromatic or aliphatic polyisocyanate to be added is generally 1/20 to 7/10, preferably 1/10 to 1/2 by weight relative to the binder.

-Other components- In the method for producing a magnetic recording medium of the present invention, a lubricant, a non-magnetic abrasive particle, a conductive powder, a magnetic layer, as necessary, and as long as the object of the invention is not impaired.
Various additional components such as a surfactant can be contained.

Examples of the lubricant include silicone oil,
Graphite, molybdenum disulfide, 12-20 carbon atoms
Fatty acid esters composed of about monobasic fatty acids (for example, stearic acid) and monohydric alcohols having about 3 to 26 carbon atoms can be exemplified.

Examples of the non-magnetic abrasive particles include alumina [α-Al ₂ O ₃ (corundum) or the like], artificial corundum, fused alumina, silicon carbide, chromium oxide, diamond,
Examples include artificial diamond, garnet, and emery (main components: corundum and magnetite).

The content of the abrasive particles is preferably 20 parts by weight or less based on the ferromagnetic powder, and the average particle size is 0.5 μm.
m or less, more preferably 0.4 μm or less.

If the lubricant and the non-magnetic abrasive particles are particularly contained in the upper layer, the contact properties with the head (slip running property,
Wear resistance) can be significantly improved.

Examples of the conductive powder include carbon black, graphite, silver powder, and nickel powder, and examples of the surfactant include natural, nonionic, anionic, cationic, and amphoteric surfactants. .

The surface electric resistance can be effectively reduced by appropriately adding these conductive powders and surfactants, particularly in the upper layer, and the occurrence of noise due to the discharge of antistatic charges and the occurrence of dropout due to the adhesion of dust can be prevented. be able to.

In the present invention, the thickness of each magnetic layer is not particularly limited, but the total thickness of each magnetic layer is usually in the range of 0.1 to 5 μm.

-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. ,polyamide,
Plastics such as polycarbonate, metals such as Cu, Al, and Zn, glass, boron nitride, Si carbide, and ceramics can be used.

The form of the nonmagnetic support is not particularly limited, and is mainly a tape, a film, a sheet, a card, a disk,
There is a drum shape and the like.

The thickness of the nonmagnetic support is not particularly limited. For example, in the case of a film or sheet, the thickness is usually 3 to 100 μm,
It is preferably from 5 to 50 μm, and is appropriately selected according to a recorder or the like in the case of a disk or a card, in the order of 30 μm to 10 mm in the case of a disk or a card.

The non-magnetic support may have a single-layer structure or a multi-layer structure.

The non-magnetic support may be provided with, for example, a resin undercoat layer, or may be subjected to an easy-adhesion surface treatment such as a discharge treatment.

—Manufacture of Magnetic Recording Medium— The method for manufacturing a magnetic recording medium of the present invention can be manufactured according to a known wet-on-wet method applied to the manufacture of a magnetic recording medium having a multilayer structure.

For example, ferromagnetic metal powder or ferromagnetic powder,
After a magnetic layer-forming component such as a binder is kneaded and dispersed in a solvent to prepare a magnetic paint, the magnetic paint is applied to the surface of a nonmagnetic support.

Examples of the solvent include ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and cyclohexanone; alcohols such as methanol, ethanol, and propanol; methyl acetate, ethyl acetate, butyl acetate, propyl acetate, and ethyl lactate. , Ethylene glycol monoacetate, etc., ester system: diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane, etc. ether system: benzene, toluene, xylene, etc. aromatic hydrocarbon: methylene chloride, ethylene chloride carbon tetrachloride chloroform, ethylene chloride Halogenated hydrocarbons such as hydrin and dichlorobenzene can be used.

In preparing the magnetic paint, the components for forming the magnetic layer are simultaneously or individually charged into a kneader.

For example, the above-mentioned ferromagnetic metal powder or ferromagnetic powder is added to a solution containing a dispersant, and after kneading for a predetermined time, the remaining components are added, and further kneading is continued to obtain a magnetic paint.

In kneading and dispersing the components for forming the magnetic layer, various kneading machines can be used.

Examples of the kneading machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a side grinder, a Sqegvari attritor, a high-speed impeller disperser,
Examples include a high-speed stone mill, a high-speed impact mill, a disper kneader, a high-speed mixer, a homogenizer, and an ultrasonic disperser.

As a coating method, wet-on-wet (wet)
−on-wet) method.

According to this wet-on-wet method, the upper layer is applied thereon while the lower layer is in a wet state, so that the surface (interface) of the lower layer is smooth and the surface properties of the upper layer are improved, and furthermore, the upper layer is coated. Adhesion with the lower layer is also sufficient. Further, as compared with other coating methods, there are advantages that the productivity is excellent and that the upper layer can be easily thinned.

Examples of the method of applying the magnetic paint include gravure coating, knife coating, wire bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, skies coating, and the like. Examples include a kiss coating method, an extrusion method, and a funtin coating method.

After the magnetic paint is applied to the surface of the nonmagnetic support, the coating film in an undried state is generally subjected to a magnetic field orientation treatment, and further subjected to a surface smoothing treatment using a super calender roll or the like.

An example of the above process will be described with reference to FIG.
The film-shaped non-magnetic support 5 unwound from the supply roll 4 is provided with an extrusion-type extrusion coater 6,
7 (having liquid pool portions 6a and 7a, respectively), the lower layer paint and the upper layer paint are applied in a multi-layered manner by a wet-on-wet method, and then a drying zone in which a second-stage oriented magnet 9 is arranged via a first-stage oriented magnet 8 It is introduced into 10, where it is dried by blowing hot air from nozzles arranged above and below.

Non-magnetic support 5 having magnetic layer thus dried
Is led to a super calender device 12 composed of a combination of calendar rolls 11, where it is calendered, and then wound up by a winding roll 13.

By cutting the thus obtained material into a desired shape and dimensions, a magnetic recording medium can be obtained.

[Examples] Next, the present invention will be described more specifically with reference to examples and comparative examples.

 In the following, “parts” means “parts by weight”.

(Example 1) A coating material A was prepared by kneading and dispersing the following upper layer coating composition.

Upper layer coating composition Ferromagnetic metal powder 100 parts (weight ratio Fe: Al 100: 5, Hc: 1580Oe, σ _s : 120emμ / g,
BET value: 55.5m ² / g) Vinyl chloride-vinyl acetate resin containing potassium sulfonate: 10 parts Polyurethane resin containing sodium sulfonate: 5 parts (Toyobo Co., Ltd., trade name: UR-8300 parts) α-Al ₂ O ₃ (particle diameter 0.2 μm) 5 parts Carbon black 1 part Myristic acid 1 part Stearic acid 1 part Butyl stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene ... 100 parts Coronate L ... 5 parts (manufactured by Nippon Polyurethane Industry Co., Ltd.) Next, the ferromagnetic metal powder in the upper layer coating composition was mixed with a Co-containing magnetic oxide (Hc: 600 Oe, BET value 30 m ² / g). Was prepared by kneading and dispersing a lower layer coating composition having the same composition as the upper layer coating composition, except that the above composition was replaced.

Next, the paint A and the paint B were applied on a 10 μm-thick polyethylene terephthalate film by a wet-on-wet method and dried.
m was formed.

Subsequently, a paint C having the following composition was applied to the surface of the polyethylene terephthalate film opposite to the magnetic layer,
A back coat layer having a thickness of 0.8 μm after drying was formed.

Backcoat layer coating composition Carbon black (Raven 1035) ...... 40 parts Barium sulfate (average particle size 300 μm) ...... 10 parts Nitrocellulose ...... 25 parts Polyurethane ...... 25 parts (N-2301, manufactured by Nippon Polyurethane Co., Ltd.) Polyisocyanate compound: 10 parts (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) Cyclohexanone: 400 parts Methyl ethyl ketone: 250 parts Toluene: 250 parts The raw material thus obtained was cut into 8 m width, and the obtained 8 mm
Evaluation of the properties of the tape was performed in the following manner.

 Table 1 shows the results.

RF output and chroma output: Measured using an 8 mm video movie V900 (manufactured by Sony Corporation) using a noise meter 925C made by Shibasoku.

Lumi S / N; A 100% white signal is input on the sample tape at the reference level, and the reproduced video signal is input to the 921D / 1 (Shivasoku Co., Ltd. noise meter). Read / N.

Chroma S / N; S / N of the sample tape in the chroma signal was compared with the reference tape using a Shibasoku noise meter.
Was determined.

Corrosion resistance (environmental resistance): The measured value (Bm) of the sample tape after the environmental resistance test, relative to the measured value (Bm ') of the magnetic property before the test, expressed as a percentage.

The environmental resistance test was performed by leaving the sample tape at a temperature of 60 ° C. and a relative humidity of 80% for 7 days.

Example 2 The Co-containing magnetic oxide in the lower layer coating composition of Example 1 was
The same experiment as in Example 1 was performed, except that Hc800Oe and a BET value of 50 m ² / g were used.

(Example 3) The Co-containing magnetic oxide in the lower layer coating composition of Example 1 was used.
The same experiment as in Example 1 was performed except that Hc1000Oe and a BET value of 55 m ² / g were used.

(Example 4) The same experiment as in Example 1 was performed, except that the Fe: Al weight ratio of the ferromagnetic metal powder in the coating composition for the upper layer was changed to 100: 2 in Example 1.

(Example 5) The same experiment as in Example 1 was performed, except that the Fe: Al weight ratio of the ferromagnetic metal powder in the coating composition for the upper layer in Example 4 was changed to 100: 10.

(Example 6) The same experiment as in Example 1 was performed, except that the Fe: Al weight ratio of the ferromagnetic metal powder in the coating composition for the upper layer in Example 4 was changed to 100: 15.

Comparative Example 1 The Co-containing magnetic oxide in the lower layer coating composition of Example 1 was used.
The same experiment as in Example 1 was performed except that Hc405Oe and BET value of 30 m ² / g were used.

Comparative Example 2 The Co-containing magnetic oxide in the lower layer coating composition of Example 1 was used.
The same experiment as in Example 1 was performed, except that Hc1220Oe and BET value of 57 m ² / g were used.

(Comparative Example 3) Same as Example 1 except that the Co-containing magnetic oxide in the lower layer coating composition was changed to ferromagnetic metal powder (Hc: 1545 Oe, BET value 56 m ² / g). Was performed.

(Comparative Example 4) The same experiment as in Example 1 was performed, except that the weight ratio of Fe: Al in the ferromagnetic metal powder in the coating composition for the upper layer was changed to 100: 0.2.

(Comparative Example 5) The Fe: Al weight ratio in the ferromagnetic metal powder in Comparative Example 4 was set to 10
The same experiment as in Comparative Example 4 was performed except that the time was changed to 0:25.

(Comparative Example 6) The same experiment as in Example 1 was performed, except that Fe / Al of the ferromagnetic metal powder in the coating composition for the upper layer in Example 1 was changed to Fe / Ni.

(Examples 7 to 11) In the same manner as in Example 1 except that the composition of the upper ferromagnetic metal powder, the weight ratio of each element of the same metal powder, and the lower layer Hc were changed as shown in Table 1, respectively. An experiment was performed.

The characteristics of the obtained 8 m tape were evaluated in the same manner.

 Table 1 shows the results.

[Effects of the Invention] According to the present invention, it is possible to provide a method for manufacturing a magnetic recording medium having excellent electromagnetic conversion characteristics and corrosion resistance.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a magnetic recording medium manufactured according to the present invention, and FIG. 2 is a flowchart showing an example of a manufacturing process of the magnetic recording medium. 1 non-magnetic support, 2 lower layer, 3 upper layer, 4 layers
Supply roll, 5 ... Non-magnetic support, 6, 7 ... Coater, 8 ... Magnet for pre-stage non-orientation, 9 ... Magnet for post-stage non-orientation, 10 ... Dryer, 12 ... Super calender device ,
13 ... Rewind roll.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nobuyuki Sekiguchi 1 Konica Sakuracho, Hino-shi, Tokyo Inside Konica Corporation (56) References JP-A-53-16604 (JP, A) JP-A-63-171419 ( JP, A) JP-A-2-87319 (JP, A) JP-A-2-107701 (JP, A) JP-A-60-256917 (JP, A) JP-A-58-56231 (JP, A) JP JP-A-64-19524 (JP, A) JP-A-63-187418 (JP, A) JP-A-63-146211 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5 / 716 G11B 5/706 G11B 5/708 G11B 5/842

Claims (1)

(57) [Claims] 1. A method according to claim 1, wherein -SO ₃ M, -OSO ₂ M, -C
OOM, and ^{-PO (OM 1) (OM 2} ) ( however, M is a hydrogen atom or an alkali metal, M ¹ and M ² are each a hydrogen atom, lithium, potassium, and either sodium, and M ¹ M ² may be different even in the same as the.)
Contains a modified resin modified by introducing at least one functional group selected from the group consisting of, the coercive force is 500 to 120
A lower layer is formed by applying a magnetic paint prepared to 0 Oe, and while the lower layer is in a wet state, the modified resin is contained thereon, and the weight of Fe atoms and Al atoms in the ferromagnetic metal powder is contained. A method for producing a magnetic recording medium, comprising: applying a magnetic paint having a ratio of 100: 0.5 to 100: 20 to form an upper layer, and then drying the lower layer and the upper layer.